FMCW激光雷达对于外腔激光器的要求

A light source with well-rounded performance including the narrow linewidth, wide frequency tuning range, high repetition rate and good linearity, is highly sought-after for frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR). In this work, we report a directly frequency modulated external cavity laser with the linewidth of 5.06 kHz. The frequency tuning range of 1.1 GHz, 445.5 MHz, 228.9 MHz are demonstrated at the repetition rate of 1 kHz, 10 kHz and 100 kHz, respectively. The frequency sweep linearization is achieved by iterative learning pre-distortion. The ranging performance with the repetition rate up to 100 kHz is investigated. The signal-to-noise ratio is still higher than 35 dB while the length of delay fiber is 156 m, corresponding to a target 110 m away in free space. These results indicate that the proposed swept-frequency laser has great potential for autonomous driving applications.

In this paper we discuss how different feedback gratings affect the tuning range and the output power of external feedback diode laser systems. A tunable high-power narrow-spectrum external-cavity diode laser system around 455 nm is investigated. The laser system is based on a high-power GaN diode laser in a Littrow external-cavity. Both a holographic diffraction grating and a ruled diffraction grating are used as feedback elements in the external cavity. The output power, spectral bandwidth, and tunable range of the external cavity diode laser system are measured and compared with the two gratings at different injected currents. When the holographic grating is used, the laser system can be tuned over a range of 1.4 nm with an output power around 530 mW. When the ruled grating is used, the laser system can be tuned over a range of 6.0 nm with an output power around 80 mW. The results can be used as a guide for selecting gratings for external-cavity diode lasers for different requirements.

In this study, the simultaneous distance and vibration mapping of frequency-modulated continuous-wave light detection and ranging (FMCW-LiDAR) is performed using an electro-optical external cavity diode laser (ECDL). Owing to the akinetic operation regime of the ECDL, a uniform (R2 = 1.0000) interference signal can be generated over a bandwidth of 1 GHz at an optical frequency sweep rate of 10 kHz without any postprocessing or system for linearization. Furthermore, the proposed ECDL exhibits a high optical frequency sweep rate of 200 kHz with a considerable linearity of R2 = 0.99975. Based on a point sensing experiment using the FMCW-LiDAR system, three measurands, namely, distance, vibration frequency, and vibration velocity change, are demonstrated with a highly linear relationship between the beat frequency and amplitude of each individual parameter. Furthermore, temporal variations in multiple targets with rapidly frequency-varying vibrations, such as those occurring in music or voice sounds, can be successfully acquired by tracking the temporal change in the beat frequency of each target. Moreover, three-dimensional (3D) mapping of distance, vibration frequency, and vibration velocity change is simultaneously implemented in the same 3D space. The results show that the proposed FMCW-LiDAR system can be used for the 3D visualized display of various measurands within the same space frame.

Abstract Possessing a long coherent length, high repetition rate, and fast frequency‐sweeping laser sources with narrow linewidth is crucial components in coherent frequency‐modulated continuous‐wave (FMCW) light detection and ranging (LiDAR) systems. While these attributes are realized individually in standalone devices, the integration of these features into a single laser represents a significant advancement in the field. In this study, a hybrid integrated laser that achieves a linewidth of 9 kHz, a wide frequency‐modulation response extending up to 68 MHz, and a low chirp nonlinearity of 4.3 × 10 −6 at a repetition rate of 100 kHz is presented. The achievement of this performance is made possible through self‐injection locking of a DFB laser diode to a low‐loss Si 3 N 4 micro‐ring resonator on the dual‐layer Si 3 N 4 ‐Si platform. Through the application of a fast‐converging pre‐distortion algorithm and a driving signal with 150 mV amplitude, a linear FMCW signal with 1.05 GHz frequency excursion is generated. Exploiting the wideband FM response of the PIN phase shifter, a frequency‐agile FMCW light source engine capable of generating linear FMCW signals at repetition rates of up to 2 MHz is successfully developed. Leveraging these cutting‐edge capabilities, an FMCW LiDAR ranging system for target detection across varying distances, achieving a high ranging precision of 0.4 cm for targets at 6.2 m, is implemented. This innovative work not only demonstrates the feasibility of integrating multiple advanced functionalities into a single laser but also demonstrates the potential for enhancing the resolution and precision of FMCW LiDAR systems for a wide range of applications.

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Si-photonic Hybrid Ring-filter External Cavity (SHREC) wavelength tunable lasers by passive alignment techniques with over 100-mW fiber-coupled power and linewidth narrower than 15 kHz along the whole C-band are demonstrated. Obtained results show excellent features of Si-photonics towards commercial products.

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A closed form solution for the transmission and reflection coefficients of a double cavity Fabry-Perot resonator is given. The explicit expressions for these coefficients are used in a formula to give the output power of diode lasers coupled to multiple external cavities. Analysis of a cleaved or etched coupled-cavity laser shows that stable operation depends on proper choice of the phase length of both the gap and the control section. A study of a diode laser coupled to an external waveguide containing a Bragg reflector shows that for correct choice of grating reflectivity only modestly effective antireflection coatings (5 percent on laser facet and 2 percent on waveguide face) are required to allow the grating to dominate the operating wavelength of the laser diode. A single external cavity with loss coupled to a laser diode is also considered. In this case the theory indicates the necessity of proper control of loss or coupling fraction between diode and cavity for there to be effective control of wavelength.

Frequency-modulated continuous-wave light detection and ranging (FMCW LiDAR) is a promising technology for long-range, high-accuracy, stray-light-immune distance and velocimetry sensing. To achieve this, a precisely chirped and highly coherent laser source is required. In this work, we propose to generate a highly linear frequency chirp by utilizing an intracavity phase modulator with high linearity and demonstrate a proof-of-concept fully integrated monolithic FMCW laser source based on an InP generic platform. By electrically modulating the intracavity phase modulator at a repetition rate of 100 kHz, a 1.85 GHz chirp range with root mean square (RMS) frequency nonlinearity down to 1.8 MHz is achieved without the need of external feedback loop or predistortion. Meanwhile, the laser shows a 51 nm tuning range with a linewidth down to 16 kHz. By taking advantage of the high-speed electro-optical effects, fast frequency modulation with repetition rate of up to 1 MHz is realized with a frequency chirp range of ∼1.65 GHz and RMS frequency nonlinearity of ∼12 MHz. We demonstrate its feasibility for LiDAR through in-fiber ranging at a distance of 50 m, where a 51 cm resolution is directly achieved.

Asymmetry in optical power versus external-cavity length characteristics has been observed in a short-external-cavity laser-diode configuration. It is shown that this phenomenon can be explained only by introducing a complex coupling coefficient, representing the coupled field amplitude into the laser diode at each reflection. This supports the open resonator model description of the short-external-cavity laser diode. Such an asymmetry effect should be recognized and properly dealt with in any laser-diode sensor.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

We report the design and performance of a Littrow-type 671-nm external cavity diode laser (ECDL) that delivers output power greater than 150 mW and features enhanced passive stability. The main body of the ECDL is constructed using titanium to minimize temperature related frequency drifts. The laser diode is mounted in a cylindrical mount that allows vertical adjustments while maintaining thermal contact with the temperature stabilized baseplate. The wavelength tuning is achieved by horizontal displacement of the diffraction grating about an optimal pivot point. The compact design increases the robustness and passive stability of the ECDL and the stiff but lightweight diffraction grating-arm reduces the susceptibility to low-frequency mechanical vibrations. The linewidth of the ECDL is ∼360 kHz. We use the 671-nm ECDL, without any additional power amplification, for laser cooling and trapping of lithium atoms in a magneto-optical trap. This simple, low-cost ECDL design using off-the-shelf laser diodes without anti-reflection coating can also be adapted to other wavelengths.

A diode-pumped single-frequency piezoelectrically tuned fiber laser with narrow spectral linewidth has been used as a light source in applications for long-range coherent frequency-domain reflectometry. Frequency-modulated continuous-wave (FMCW) measurements of Rayleigh back-scattering and Fresnel reflection from a 95-km-long fiber have been demonstrated without the use of an optical amplifier. This is, to our knowledge, the longest distance measurement with FMCW. The high sensitivity and dynamic range of the long-range backscattering measurements benefit from the extremely long coherence length of the narrow linewidth fiber laser, which has been estimated to be 210 km in air.

We demonstrate a semiconductor external-cavity laser comprising a slab-coupled optical waveguide amplifier (SCOWA) and a fiber Bragg grating. The laser exhibits a Lorentzian linewidth of 1.75 kHz and a sidemode suppression ratio &gt; 80 dB.

The performance of a frequency-modulated continuous-wave (FMCW) semiconductor laser radar has been examined. Frequency modulation (linear chirp) has been studied experimentally in detail. To create a linear frequency sweep, we modified the modulating function according to the measured frequency response of the laser, using an arbitrary function generator. The measurements indicate the possibility of achieving a spectral width of the signal peak that is transform limited rather than limited by the frequency modulation response of the laser, which permits the use of a narrow detection bandwidth. The narrow width results in a relatively high signal-to-noise ratio for low output power and thus also in relatively long-range and high-range accuracy. We have performed measurements of a diffuse target to determine the performance of a test laser radar system. The maximum range, range accuracy, and speed accuracy for a semiconductor laser with an output power of 10 mW and a linewidth of 400 kHz are presented. The influence of the laser's output power and coherence length on the performance of a semiconductor-laser-based FMCW laser radar is discussed.

We demonstrate a hybrid-integrated self-injection-locked laser on the Si 3 N 4 -on-SOI platform to generate FMCW signal with 9 kHz linewidth, 2 MHz repetition rate, and high linearity, supporting FMCW-LiDAR with refresh rate up to megapixels per second.

We report a novel hybrid laser based on a silicon-wire external cavity filter. We characterize the hybrid silicon laser from the viewpoint of high output extraction efficiency and temperature control free operation with a silicon microring resonator. First, it is experimentally verified that output extraction efficiency of the laser is significantly improved by locating an optical coupler within the laser cavity. As a result, we show mW-order output power and wall-plug efficiency of ∼0.9%. In addition, we demonstrate that the operating window of the silicon microring modulator is adaptable to the oscillation wavelength of the hybrid silicon laser in regard to temperature change of a silicon substrate from 25 to 55 °C.

In this paper, the design methodology and main experimental results of an External Cavity Laser (ECL) with narrow linewidth (<; 100 kHz) is presented. The ECL is based on a wavelength-selective mirror controlled by voltage. Among other features, the device presents high optical output power (> 16 dBm) and potential to achieve 40 nm tunability in C-band. System performance of 16-Quadrature Amplitude Modulation (QAM) transmission is better than commercial reference Integrated Tunable Laser Assembly (ITLA). The device is compact, suitable for small-form factor transceivers and modules.

Frequency-modulated continuous wave (FMCW) laser ranging is one of the most interesting techniques for precision distance metrology. In order to ensure the theoretical measurement range and precision, a narrow linewidth external cavity tunable laser with large tuning range is chosen. In practical situations, the tuning nonlinearity of the laser reduces the measurement precision, hence an auxiliary interferometer is used to measure the laser tuning rate and linearize the frequency ramp. Then, fast Fourier transform algorithm is applied to the resampled signal of the main interferometer, and the full-width at half maximum of the frequency spectrum is narrowed. In the end, the experiments are carried out using the FMCW laser ranging system and demonstrate 50-μm range resolution at 8.7 m.

Abstract Frequency‐sweeping laser sources play a critical role in the accurate 3D mapping of frequency‐modulated continuous‐wave (FMCW) LiDAR systems, whose chirp linearity greatly impacts the measurement precision. Although various pre‐distortion algorithms have been proposed to reduce chirp nonlinearity, these open‐loop methods can rapidly suppress the chirp nonlinearity but they are susceptible to environmental variations and often exhibit subpar performance in long‐range detection scenarios. In contrast, the electro–optical phase‐locked loop (EO‐PLL) serves as a real‐time linearizing solution for FMCW LiDAR, enabling high‐precision, high‐resolution, and long‐distance measurement capabilities. In this study, a III/V‐Si 3 N 4 hybrid‐integrated external cavity laser (ECL) is used to generate an FMCW signal over a large wavelength tuning range of 68 nm. The maximum output optical power is 15.8 mW, and the intrinsic linewidth is 0.9 kHz. By modulating the phase shifter, an FMCW signal with a chirp bandwidth of 0.7 GHz is generated at a repetition rate of 1 kHz. The pre‐distortion algorithm is combined with the gain‐tunable EO‐PLL system to suppress the chirp nonlinearity and frequency noise across multiple wavelengths, leading to a remarkable improvement in range precision from 202 to 4.2 cm when targeting a distance of 200 m.

We report a wavelength widely-tunable hybrid integrated external cavity laser (ECL) with synchronous tuning to achieve a large frequency chirp bandwidth and high chirp linearity. Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Vernier microring resonators (MRRs) in the ECL function as an optical bandpass filter to offer strong wavelength selectivity and fast frequency tunability. The wavelength tuning range is 56 nm, the maximum output optical power is 22.5 mW, the minimum intrinsic linewidth is 2.9 kHz, and the static frequency sweep bandwidth is 56 GHz. A frequency-modulated continuous-wave (FMCW) signal is generated under synchronous modulation with a chirp bandwidth of 7.68 GHz at a 1 kHz repetition rate, much larger than that produced by modulating the phase shifter or the Vernier filter alone. A chirp linearization method based on a non-uniform sampling algorithm and an iterative learning algorithm is employed to reduce the chirp nonlinearity to 1.02×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> , allowing for a detection resolution of 2.47 cm.

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This paper reports on the experimental demonstration of a fully integrated frequency-modulated continuous-wave (FMCW) LiDAR sensing system, operating at 2.0 µm. It makes use of a widely tunable hybrid external cavity laser based on the combination of GaSb gain chip and silicon waveguide circuits. The single-frequency laser operation over the full spectral bandwidth of the gain chip is secured using a frequency-selective filter, consisting of two sequential microring resonators in a Vernier configuration. To increase the mode-hop free wavelength tuning range while preserving the linewidth of the laser, the heater of the phase section placed along the bus waveguide is synchronously controlled with two independent heaters placed on each microring resonator. This laser is then implemented for the development of an FMCW LiDAR, consisting of all-optical fiber-based two independent unbalanced Mach-Zehnder interferometers: k-space interferometer for the linearization of continuously swept laser frequency and main interferometer for the measurement of the distributed back-reflection over the distance. The optical frequency of the laser is continuously swept over a ∼100 GHz range (or Δλ=1.47 nm at the operating wavelength) at a modulation speed of 100 Hz. Using this wavelength tunable laser, a light detection and ranging system (LiDAR) is experimentally demonstrated, showing a very high axial resolution of 1.36 mm in air with an extremely high precision of ∼9 µm at a 100 Hz measurement rate.

Piezoelectric fast steering mirror (PZT FSM) is the core component of the fine tracking system for space laser communication, and its actuator is a piezoelectric ceramic. Consequently, there is a hysteretic nonlinear disturbance throughout the entire range of the FSM’s steering. To enhance the fine tracking system’s performance, this paper innovatively analyzes and verifies the effect of the PZT FSM hysteresis characteristics on the error suppression bandwidth of the fine tracking system. Firstly, the rate-dependent hysteresis model is established by serially connecting the Prandtl–Ishlinskii (P-I) model with the dynamic linear mode. The inverse model is designed as a feedforward controller, followed by the conduction of open-loop feedforward compensation experiments. Subsequently, we propose a compound control method based on the rate-dependent hysteresis mode and conduct a simulation analysis. Finally, the experimental platform for the fine tracking system is set up, and the optimization effect of compensating for hysteresis nonlinearity on the fine tracking system is verified. The experimental results show that the nonlinearity of the PZT FSM is improved by 30% in the middle- and high-frequency ranges, and the error suppression bandwidth of the fine tracking system is improved by 41.7%. This effectively enhances the fine tracking system’s error suppression capability.

We demonstrate electrical wavelength tuning by mode locking of an external cavity laser (ECL) with linearly chirped fiber Bragg grating (LCFBG). The configuration consists of a laser chip providing the gain coupled to an LCFBG with a large chip rate of 10 or 55 nm/cm providing the counter-reaction for laser oscillation. The laser chirp is electrically modulated by a sinusoidal signal in such a way that the ECL is mode locked. By changing the modulation frequency, a wavelength tuning range of 27 nm is achieved with the 10 nm/cm LCFBG, and a partial tuning range over 41 nm is demonstrated with the 55-nm/cm LCFBG. The output pulse stream at a specific mode-locking frequency and a corresponding wavelength is obtained for both positively and negatively chirped grating. A time bandwidth product reduction is measured in the case of negatively chirp grating when compared with positively chirp grating. A simple general law between the laser parameters is given (locking frequency, tuning range, and FBG chirp value). The parameters for a 40-nm tunable source modulated at 10 GHz are given. This simple tuning mechanism is very well adapted for a structure that requires accurate wavelength monitoring.

A homemade PQ:PMMA VBG was fabricated and characterized with a diffraction efficiency of about 8%. Mounting on an annular piezo-transducer, this VBG served as a narrow band feedback mirror of a 1060 nm external cavity diode laser (ECDL), which achieved a single longitudinal mode and frequency-tunable operation. With the laser source, an FMCW LiDAR system was demonstrated and successfully measuring target distance within 8.5 m.

Recent advancements in Distributed Feedback (DFB) lasers have improved output power levels, offering benefits for automotive FMCW LiDAR. However, these high-power DFB lasers often show increased phase noise and broader linewidths. External Cavity Diode Lasers (ECDLs) offer an alternative, enabling high output power with narrow linewidths&mdash;especially when incorporating high-Q resonators within the external cavity. For optimal LiDAR performance, the laser must support a mode-hop-free (MHF) chirp excursion &gt; 3 GHz, chirp rates on the order of several hundred kHz, and maintain optical output power above 500 mW with less than 1 dB variation. In photonic integrated circuit (PIC) implementations, linewidths as low as 1 kHz are achievable using high-Q resonators. However, the narrowband nature of these resonators limit the MHF tuning range to &lt; 1 GHz and results in significant power fluctuations (3–6 dB) across the chirp range. This work presents a laser design targeting an MHF tuning range of approximately 10 GHz, with stable output power, chirp rates around 100 kHz, a linewidth below 10 kHz, and output power exceeding 500 mW—making it suitable for next-generation FMCW LiDAR in automotive applications.

The authors report the detailed characterisation of a widely tunable laser and module that offers the elusive combination of very fast (nanosecond) tuning and narrow linewidth. The laser is fabricated on an active-passive InP-based platform and packaged into a 14-pin butterfly module. Electro-optic tuning is used with reversevoltage bias of tuning sections allowing mA-order dark currents and facilitating nanosecond switching speeds with low power dissipation. The device is suitable for integration into fiber coupled modules such as the nanoiTLA or can be monolithically integrated with other components in a III-V PIC. It is a promising new laser for applications that require fast and wide tuning with low linewidth, such as FMCW (Frequency-Modulated Continuous-Wave) LiDAR and coherent optical packet or burst switching.

Frequency-modulated continuous wave (FMCW) light detection and ranging (LiDAR) is a technology that measures the distance and velocity of objects using coherent detection. Conventional LiDAR using mechanical scanning systems suffer from low stability, large size, easy to wear, and high installation costs. We proposed a solid-state FMCW LiDAR system using wavelength division multiplexing (WDM) with a wideband external cavity tunable laser. The sample light, divided into N x M channels by WDM with 100 GHz (0.8 nm) channel spacing, is arranged through a fiber array in a N x M configuration. The proposed FMCW LiDAR system performs sequential solid-state scanning. We acquired 3D images without mechanical scanning, ensuring greater stability compared to conventional scanning systems.

Early works¹ and recent advances in thin-film lithium niobate (LiNbO₃) on insulator have enabled low-loss photonic integrated circuits^2,3, modulators with improved half-wave voltage^4,5, electro-optic frequency combs⁶ and on-chip electro-optic devices, with applications ranging from microwave photonics to microwave-to-optical quantum interfaces⁷. Although recent advances have demonstrated tunable integrated lasers based on LiNbO₃ (refs. ^8,9), the full potential of this platform to demonstrate frequency-agile, narrow-linewidth integrated lasers has not been achieved. Here we report such a laser with a fast tuning rate based on a hybrid silicon nitride (Si₃N₄)-LiNbO₃ photonic platform and demonstrate its use for coherent laser ranging. Our platform is based on heterogeneous integration of ultralow-loss Si₃N₄ photonic integrated circuits with thin-film LiNbO₃ through direct bonding at the wafer level, in contrast to previously demonstrated chiplet-level integration¹⁰, featuring low propagation loss of 8.5 decibels per metre, enabling narrow-linewidth lasing (intrinsic linewidth of 3 kilohertz) by self-injection locking to a laser diode. The hybrid mode of the resonator allows electro-optic laser frequency tuning at a speed of 12 × 10¹⁵ hertz per second with high linearity and low hysteresis while retaining the narrow linewidth. Using a hybrid integrated laser, we perform a proof-of-concept coherent optical ranging (FMCW LiDAR) experiment. Endowing Si₃N₄ photonic integrated circuits with LiNbO₃ creates a platform that combines the individual advantages of thin-film LiNbO₃ with those of Si₃N₄, which show precise lithographic control, mature manufacturing and ultralow loss^11,12.

We develop a novel gas sensing system based on a widely-swept (150 GHz), narrow-linewidth (180 kHz) laser utilizing silicon photonics integrated technology. Compared with traditional mechanical scanning lasers, it achieves rapid multi-point detection within 0.5 ms through micro-ring resonators and the Vernier effect. When applied in a frequency-modulated continuous-wave (FMCW) system, it realizes a spatial resolution of 30 cm at a distance of 30 m, with a minimum detectable concentration (MDC) of 6.14 ppm for methane gas. The detection sensitivity is further improved through software post-processing. This technology is particularly suitable for rapid gas leakage monitoring in hazardous environments such as natural gas and coal mine pipelines, and holds significant application value in emergency safety scenarios.

A narrow-linewidth semiconductor laser chip with highly linear frequency modulation response is presented and validated in two coherent sensing test experiments. This distributed feedback laser monolithic chip has an intrinsic linewidth of less than 10 kHz and an output power over 60 mW. When its injection current is modulated by a triangular function, the laser optical frequency can be modulated by more than 7 GHz at rates up to 100 kHz. The laser frequency modulation response is extremely flat up to 100 MHz, which allows correcting the residual sweep nonlinearities by a proper pre-distortion of the modulation signal. In a first test experiment, the laser was used into a monostatic FMCW lidar system. A point cloud was acquired with a field of view of 20&deg;(H) &times; 10&deg;(V) and an angular resolution of 0.05&deg; along both axes. The acquisition was performed without averaging using a 7 mm diameter output beam of 100 mW. A high-quality point cloud including several objects of varying reflectivity was measured. In a second test experiment, the laser was used into an OFDR system for a distributed acoustic sensing (DAS) experiment. A short portion of a 50 m long SMF-28 fiber was exposed to a 2 kHz acoustic signal. Processed data clearly shows a strong 2 kHz tone at the location of the acoustic perturbation. In both test experiments, the laser was successfully linearized using modulation signal pre-distortion based on interferograms obtained with a Mach-Zehnder interferometer.

A FMCW LiDAR system of both the distributed feedback laser and external cavity laser is established in baseband beat notes, rather than up-conversion to an intermediate frequency to exclude flicker noise. Meanwhile, utilizing fast-scanning MEMS mirrors, high-quality real-time (1 fps) 4-D images of the slow-moving object (10 mm/s) can be directly constructed at the baseband with a central frequency as low as 100 kHz and a small Doppler shift. The proposed LiDAR architecture based on such a low-frequency baseband significantly improves the optical power budget on the transmitter side and eliminates the costly high-speed sampling circuits on the receiver side.

Frequency modulated continuous wave laser ranging (FMCW LiDAR) enables distance mapping with simultaneous position and velocity information, is immune to stray light, can achieve long range, operate in the eye-safe region of 1550 nm and achieve high sensitivity. Despite its advantages, it is compounded by the simultaneous requirement of both narrow linewidth low noise lasers that can be precisely chirped. While integrated silicon-based lasers, compatible with wafer scale manufacturing in large volumes at low cost, have experienced major advances and are now employed on a commercial scale in data centers, and impressive progress has led to integrated lasers with (ultra) narrow sub-100 Hz-level intrinsic linewidth based on optical feedback from photonic circuits, these lasers presently lack fast nonthermal tuning, i.e. frequency agility as required for coherent ranging. Here, we demonstrate a hybrid photonic integrated laser that exhibits very narrow intrinsic linewidth of 25 Hz while offering linear, hysteresis-free, and mode-hop-free-tuning beyond 1 GHz with up to megahertz actuation bandwidth constituting 1.6 × 10¹⁵ Hz/s tuning speed. Our approach uses foundry-based technologies - ultralow-loss (1 dB/m) Si₃N₄ photonic microresonators, combined with aluminium nitride (AlN) or lead zirconium titanate (PZT) microelectromechanical systems (MEMS) based stress-optic actuation. Electrically driven low-phase-noise lasing is attained by self-injection locking of an Indium Phosphide (InP) laser chip and only limited by fundamental thermo-refractive noise at mid-range offsets. By utilizing difference-drive and apodization of the photonic chip to suppress mechanical vibrations of the chip, a flat actuation response up to 10 MHz is achieved. We leverage this capability to demonstrate a compact coherent LiDAR engine that can generate up to 800 kHz FMCW triangular optical chirp signals, requiring neither any active linearization nor predistortion compensation, and perform a 10 m optical ranging experiment, with a resolution of 12.5 cm. Our results constitute a photonic integrated laser system for scenarios where high compactness, fast frequency actuation, and high spectral purity are required.

We demonstrate a monolithic FMCW laser based on InP generic platform. The laser shows 51-nm tuning range with the linewidth down to 16 kHz. By electronically modulating an intra-cavity phase section, a frequency modulation signal with 99.99% linearity and 1.8-GHz chirp range is directly achieved.

A laser source that is both narrow-linewidth and frequency-agile is essential for FMCW applications, such as LIDAR or distributed optical fiber sensing (DOFS). In this work, we present the design and characterization of a laser architecture based on the heterogeneous integration of III-V gain material on a SiN photonic circuit that meets these specifications. By incorporating a dual-ring resonator mirror in the cavity, we achieved a linewidth of 2.4 kHz and a large frequency excursion. We obtained chirps with an amplitude of 20 GHz, with residual nonlinearities of less than 1%. A preliminary DOFS measurement was carried out, demonstrating the excellent performance of the laser.

A FMCW LiDAR system of extended cavity distributed Bragg grating (DBR) lasers, on an InP generic foundry platform, is established with a narrow linewidth of ≈ 25 kHz. Meanwhile, utilizing the coupled phase modulator in the reverse-bias configuration, highly linear wavelength sweeping is demonstrated without the need for laser driving with a pre-distorted waveform. Real-time 4-D images (up to 1 fps) of the slow-moving object (10 mm/sec) can be directly constructed at the baseband with a central frequency as low as 100 kHz and a small Doppler shift, rather than up-conversion to an intermediate frequency to exclude flicker noise. The proposed LiDAR architecture based on the InP generic foundry shows the potential in a monolithically integrated photonic platform for compact 4-D FMCW systems.

We propose a frequency-modulated continuous-wave (FMCW) laser based on misaligned grating waveguide external cavity coupled with a reflective semiconductor optical amplifier (RSOA). Compared with waveguide external cavity lasers using two cascading microring resonators, which adopt vernier effect for frequency modulation, the proposed laser has a much simpler frequency modulation scheme. The proposed laser can realize linear frequency tuning through one electric control circuit, compared to that the waveguide external cavity lasers using two cascading microring resonators need more than three electric control circuits. Moreover, the proposed laser has a linewidth less than 1 kHz with the misaligned grating structure, while the linear chirp bandwidth is about 2.2GHz with non-linearity of ~10^-3. This laser has been used in a laser ranging application, demonstrating a ranging accuracy of ~6.5cm. These results show that the proposed laser can be a potential solution for LiDAR, long-range optical fiber sensing, optical interferometry and coherent optical communication, etc.

We report a long-distance detection experiment based on our proposed ultra-narrow linewidth frequency-modulated continuous wave laser. The laser is a hybrid integrated laser working under self-injection locked state by coupling semiconductor laser to an external high-Q cavity. The laser operates at 1 kHz chirped frequency with 6.6 GHz modulated frequency range. The intrinsic linewidth is less than 20 Hz and the modulated linearity 1 − r <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is optimized to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−6</sup> . In the 2.2 km ranging experiment, we get the signal-to-noise ratio of the detected signal higher than 5 dB with a amplified output power of 100 mW and expanded beam diameter of 15 mm. The mean value of the demodulated distance is 2209 m, and the standard deviation is 0.67 m. This is the first demonstration of the application of hybrid integrated lasers for long-range detection, verifying the application of narrow linewidth FMCW laser in LiDAR is system.

We demonstrate an architecture for massively parallel frequency-modulated continuous wave (FMCW) laser ranging (LiDAR) by transferring linear chirps of a single narrow linewidth laser onto all soliton comb teeth though generation of a dissipative Kerr soliton in an integrated Si 3 N 4 microresonator.

LIDARs are considered a key enabling technology for an array of applications in space, including celestial body approach, landing, rendezvous and docking, space debris identification and CubeSat constellations. Reliability, low cost and low size, weight and power (SWaP) are critical factors for these applications. Current spaceborne LIDAR systems are based on discrete optical components. These systems consume a lot of power and are bulky. In this work, a hybrid integrated (FMCW) LIDAR system operating at 1550 nm and based on an indium phosphide (InP) and silicon nitride (Si₃N₄) platform along with an external erbium-doped fiber amplifier (EDFA) compact module is proposed. By using a telecom-wavelength laser with an ultra-narrow linewidth of 1 kHz, and a 1D optical phased array (OPA) using lead zirconate titanate (PZT) phase shifters, the proposed PIC microlidar can operate up to 100 km. In order to realize small beam divergence, a 1x100 linear array consisting of 4 mm Si₃N₄ dual-layer grating antennas with a coupling efficiency of up to 80% of the incident power is utilized.

Narrow line-width fiber grating 1535 nm erbium laser was demonstrated by introducing fiber grating F-P cavity. It was composed by high Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> doped fiber, 980/1550 nm WDM and fiber grating F-P cavity. Linear and ring cavity experiments were demonstrated respectively. In the experiment, pumped by 976 nm diode laser, the associated fiber lasers with frequency selecting by fiber grating F-P cavity exhibited about 11 mW threshold. 15% and 30% slope efficiency were obtained respectively in the experiments. The 3 dB line-width of fiber lasers were both less than 0.01 nm, and SNR were both about 50 dB. Narrow linewidth fiber laser can be used to build distributed fiber optical sensor systems. Frequency modulated continuous wave (FMCW) technique and Brillouin optical fiber time domain reflectometry (BOTDR) technique were described in this paper

Frequency-modulated continuous-wave (FMCW) narrow linewidth lasers have served as the cornerstone behind applications such as autonomous driving, wearable technology, virtual reality, and remote sensing mapping. Strongly coherent lasers are typically used for these studies, with a clear demand for linear fast response and wide frequency tuning range. In this paper, profiting from the ultrahigh-quality factor of the crystalline whispering-gallery-mode resonator, by using a self-injection locking mechanism to suppress spontaneous emission noise and improve coherence, sub-kHz linewidth at 450 nm is obtained. Furthermore, based on the dispersive response principle, fast electrical tuning is realized by using the strain-influenced resonator, and the experimental test result reaches 81 pm/V. More importantly, we demonstrate the comprehensive performance of this type of FMCW laser in underwater detection, with a sensitivity of 319 MHz/m at a chirp frequency of 1 kHz.

We propose and demonstrate a Frequency Modulated Continuous Wave (FMCW) laser source realized through sideband modulation and four-wave mixing (FWM). A silicon waveguide, featuring a reverse-biased P-i-N junction, is designed to excite FWM process. With the increase of the applied bias voltage, the efficiency of the FWM effect in the silicon waveguide is improved due to more effective removal of free-carriers. The silicon integrated waveguide enables a high conversion efficiency of −12 dB. In the experiment, the radio frequency (RF) signal swept over a range of 9 GHz to 11 GHz. A laser was modulated by a Mach-Zehnder modulator to generate a first-order sideband. Meanwhile, the FWM process in silicon waveguide expand threefold frequency sweeping span to 6 GHz, thereby enhancing spatial resolution to 2.5 cm. The original tuning range of 2 GHz and tuning rate of 0.2 GHz/s is multiplied by 3 times to 6 GHz and 0.6 GHz/μs respectively. The results show that FMCW laser source has a wider frequency bandwidth of 6 GHz, a high linearity of 11.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> , and a fast chirp rate of 0.6 GHz/μs. The frequency-modulated light source exhibits excellent linearity, low noise, narrow linewidth, and fast tuning rates, which are critical attributes for modern electrical systems such as FMCW light detection and ranging (LiDAR) system. Additionally, the system obviates the need for intricate linearization algorithms, offering the advantages of simplicity in structure, high precision and easy to integrate.

Integrated external cavity lasers (ECLs) are emerging as a promising chip-scale implementation of tunable lasers, promoting system miniaturization and functionality expansion with the booming of silicon photonics. In spite of the extensive exploration and great progresses on ECLs, challenge remains in the combination of wide tunability and frequency agility. Here we address this problem by proposing a hybrid III-V/Si<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula>N<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{4}$</tex-math></inline-formula> dual external cavity laser (DECL) with complementary tuning. The hybrid DECL consists of two Si<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula>N<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{4}$</tex-math></inline-formula> -based external cavities butt-coupled with a semiconductor optical amplifier at each side. On the two external cavities, complementary high-efficiency thermal-optic tuning and fast photoelastic tuning are employed, respectively. The experimentally demonstrated hybrid DECL leverages a combination of a tuning range of 27.4 nm in the C-band, a linear frequency modulation at a speed of 200 kHz, a wavelength-switching time below 900 ns, and an ultra-low intrinsic linewidth down to 33.1 Hz. With the unification of wide tunability, frequency agility and ultra-low linewidth, this hybrid DECL holds promise for many applications in telecommunications, interconnects and light detection and ranging.

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Semiconductor optical amplifier (SOA) has drawn much attention due to its critical need in coherent detection scheme such as FMCW (frequency-modulated continuous-wave) in automotive LiDAR (Light Detection and Ranging). Coherent detection provides more features than ToF (Time of Flight) such as speed and direction for autonomous vehicles. Instead of a bulky and expensive fiber laser, a coherent laser source with high gain SOA can achieve small form factor with Si PIC (Photonic Integrated Circuit). Here we present a proprietary SOA structure based on AlInGaAs material system with multiple quantum wells on InP substrate. The SOAs with curved and tilted straight waveguides were developed and tested. The saturated output power of such SOA at 1550nm and 1310nm can reach higher than 350mW and 450mW with high wallplug efficiency. The small signal gain exceeds 40dB for both 1310nm and 1550nm. The low anti-reflection (AR) coating can achieve 0.01% reflectivity, and the noise figure and near-field mode fields of various SOA configurations are presented and compared. An array of four SOA waveguides at 127m or 500m pitch can deliver total output power over 2 Watts with proper heat sinking. SOA arrays can also be processed as individually addressable with electrical and optical isolations. Such high-performance SOA array offers the design freedom to LiDAR systems with various scanning strategies such that long range detection can be realized. Gain chip, RSOA (Reflective SOA) based on the curved waveguide for external cavity laser configurations is tested and discussed. Self-alignment features can be built onto the SOA chipset to achieve integration of Si PIC for minimal footprint and low-cost mass production.

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An overview of the most recent developments and improvements to the low-loss TriPleX Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> waveguide technology is presented in this paper. The TriPleX platform provides a suite of waveguide geometries (box, double stripe, symmetric single stripe, and asymmetric double stripe) that can be combined to design complex functional circuits, but more important are manufactured in a single monolithic process flow to create a compact photonic integrated circuit. All functionalities of the integrated circuit are constructed using standard basic building blocks, namely straight and bent waveguides, splitters/combiners and couplers, spot size converters, and phase tuning elements. The basic functionalities that have been realized are: ring resonators and Mach-Zehnder interferometer filters, tunable delay elements, and waveguide switches. Combination of these basic functionalities evolves into more complex functions such as higher order filters, beamforming networks, and fully programmable architectures. Introduction of the active InP chip platform in a combination with the TriPleX will introduce light generation, modulation, and detection to the low-loss platform. This hybrid integration strategy enables fabrication of tunable lasers, fully integrated filters, and optical beamforming networks.

We present a photonic integrated circuit (PIC) transceiver for frequency modulated continuous wave (FMCW) LiDAR applications. The transmitter consists of a widely tunable sampled grating distributed Bragg reflector laser (SGDBR) and a frequency discriminator which combines multimode interference couplers, a tunable asymmetric Mach-Zehnder Interferometer (a-MZI), and balanced photodiodes. The frequency discriminator converts frequency fluctuations of the laser to amplitude fluctuations of the photodiode currents. This provides an error signal for feedback into the laser cavity for frequency stabilization. Frequency modulation is obtained by a phase shifter in the a-MZI which tunes the quadrature point of the filter and the frequency where the error is zero. An on-chip receiver couples power from the transmitter to self-heterodyne with the time-delayed echo of a distant object. The generated beat frequency of the self-heterodyne measurement gives the echo signals time-of-flight to obtain the distance and velocity of the reflecting object. The theory of the components is described, and characterization of the transmitter and receiver is presented.

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Photonic crystal slow-light gratings fabricated using Si photonics enable high-speed, high-resolution, and wide field-of-view two-dimensional beam scanning via the thermo-optic effect. In this paper, we built a frequency-modulated continuous-wave light detection and ranging system on a chip by combining a beam scanner with Ge photodiodes for delay homodyne coherent detection. Emitting and scanning frequency-swept laser beam, point cloud images of 154 × 32 = 4928 points were obtained. The real-time operation and velocity imaging were also demonstrated. This device is expected to detect Lambertian targets over long distances in the 100-m class by reasonably reducing chip and optics losses and suppressing internal noise components.

In the last 25 years, optical coherence tomography (OCT) has advanced to be one of the most innovative and most successful translational optical imaging techniques, achieving substantial economic impact as well as clinical acceptance. This is largely owing to the resolution improvements by a factor of 10 to the submicron regime and to the imaging speed increase by more than half a million times to more than 5 million A-scans per second, with the latter one accomplished by the state-of-the-art swept source laser technologies that are reviewed in this article. In addition, parallelization of OCT detection, such as line-field and full-field OCT, has shortened the acquisition time even further by establishing quasi-akinetic scanning. Besides the technical improvements, several functional and contrast-enhancing OCT applications have been investigated, among which the label-free angiography shows great potential for future studies. Finally, various multimodal imaging modalities with OCT incorporated are reviewed, in that these multimodal implementations can synergistically compensate for the fundamental limitations of OCT when it is used alone.

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This paper describes the design, fabrication, and record performance of a new class of ultra-wideband wavelength tuning, ultra-low noise semiconductor laser, the Integrated Coherent Tunable Laser (ICTL). The ICTL device is designed for, and fabricated in, a CMOS foundry based Silicon Photonics platform, utilizing heterogeneous integration of III-V material to create the integrated gain section of the laser&#x2013;enabling high-volume mass-market manufacturing at low cost and with high reliability. The ICTL incorporates three or more ultra-low loss micro-ring resonators, with large ring size, in a Sagnac loop reflector geometry, creating exceptional laser reflector performance, plus an extended laser cavity length that enables highly-coherent output; ultra-low linewidth and phase noise. This paper describes record integrated laser performance; 118 nm wavelength tuning, covering S-, C- and L-bands, with Lorentzian linewidth &lt;100 Hz, and with excellent relative intensity noise (RIN) of &#x2264; &#x2212;155 dBc&#x002F;Hz. The remarkable performance of the ICTL device, coupled with the high volume&#x002F;low cost capability of the Silicon Photonics platform enables next-generation applications including ultra-wideband WDM transmission systems, fiber-optic and medical-wearable sensing systems, and automotive FMCW LiDAR systems utilizing wavelength scanning.

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Fiber-optic distributed acoustic sensing (DAS) has proven to be a revolutionary technology for the detection of seismic and acoustic waves with ultralarge scale and ultrahigh sensitivity, and is widely used in oil/gas industry and intrusion monitoring. Nowadays, the single-frequency laser source in DAS becomes one of the bottlenecks limiting its advance. Here, we report a dual-comb-based coherently parallel DAS concept, enabling linear superposition of sensing signals scaling with the comb-line number to result in unprecedented sensitivity enhancement, straightforward fading suppression, and high-power Brillouin-free transmission that can extend the detection distance considerably. Leveraging 10-line comb pairs, a world-class detection limit of 560 fε/√Hz@1 kHz with 5 m spatial resolution is achieved. Such a combination of dual-comb metrology and DAS technology may open an era of extremely sensitive DAS at the fε/√Hz level, leading to the creation of next-generation distributed geophones and sonars.

We present a simple iterative pre-distortion algorithm for achieving a rapid linear frequency sweep of semiconductor lasers. The algorithm achieves the desired frequency swept linearity with only four iterations. We derive a general formula for iterative pre-distortion by establishing the relationship between the laser output frequency and the drive current. The linear frequency-swept laser source obtained by this algorithm can be used in FMCW LiDAR systems. Experimentally, we investigated the algorithm using a 1550 nm distributed feedback (DFB) laser, achieving frequency swept excursion of 30.26 GHz, and frequency swept slope of 504 THz/s. We analyzed the linearity of the frequency swept results for the fourth iteration, achieving less than 5 MHz root mean square (RMS) value of frequency swept nonlinearity.

The frequency-modulated continuous-wave (FMCW) technology combined with optical phased array (OPA) is promising for the all-solid-state light detection and ranging (LiDAR). We propose and experimentally demonstrate a silicon integrated OPA combined with an optical frequency microcomb for parallel LiDAR system. For realizing the parallel wavelengths emission consistent with Rayleigh criterion, the wide waveguide beyond single mode region combined with the bound state in the continuum (BIC) effect is harnessed to obtain an ultra-long optical grating antenna array. The single soliton comb, generating about multiple distinct wavelength channels and combined with the high performance integrated OPA, is also demonstrated for coherent three-dimensional (3D) imaging by utilizing FMCW method. The modulation bandwidth of parallel modulation of the microcomb is beyond the modulation region of single soliton microcomb. The result paves the way for developing all-solid-state and ultrahigh-frame-rate coherent LiDAR systems.

Abstract External cavity tunable lasers have been around for many years and now constitute a large group of semiconductor lasers featuring very unique properties. The present review has been restricted to the systems based on the edge emitting diode lasers set-up in a hybrid configuration. The aim was to make the paper as concise as possible without sacrificing, however, most important details. We start with short description of the fundamentals essential for operation of the external cavity lasers to set the stage for explanation of their properties and some typical designs. Then, semiconductor optical amplifiers used in the external cavity lasers are highlighted more in detail as well as diffraction gratings and other types of wavelength-selective reflectors used to provide optical feedback in these lasers. This is followed by a survey of designs and properties of various external cavity lasers both with mobile bulk gratings and with fixed wavelength selective mirrors. The paper closes with description of some recent developments in the field to show prospects for further progress directed towards miniaturization and integration of the external cavity laser components used so far to set-up hybrid systems.

本文介绍了一种以未泵浦的掺铒光纤作为可饱和吸收体，通过3 dB耦合器及环形器，构成一个由驻波效应形成动态光栅的一种窄线宽光纤激光器。测得在中心波长在1559.54 nm处得到输出的激光器，在泵浦功率为150 mW以下时可以保持长时间的稳定工作，泵浦功率为70 mW，输出光功率为17.03 mW，斜率效率为30.73%，光学信噪比为39 dB，波长分辨率的不稳定性小于0.03 nm，光学信噪比的波动小于0.16 dB，从0到1 MHz的37.5 kHz信号频谱中的弛豫振荡频率峰值为−89.6 dB/Hz。通过延时自外差法测量线宽为1.99 kHz。

可调谐外腔半导体激光器具有调谐范围宽、线宽窄、输出功率高、单模输出等优良特性，在白光干涉测量技术、波分复用系统、相干光通信、光纤传感等领域有着广泛的应用。本文首先介绍了可调谐外腔半导体激光器的基本原理, 对衍射光栅结构、光纤布拉格光栅结构、波导结构三种主要的TECDL结构进行了详细的综述和比较。阐述了各种可调谐外腔半导体激光器的国内外发展状况，分析了不同外腔结构的优缺点，最后总结可调谐外腔半导体激光器的不足，展望了可调谐外腔半导体激光器的发展前景。

介绍了一种泵浦振荡器腔长调谐的光纤参量振荡器，研究了改变泵浦振荡器的腔长时，光纤参量振荡器输出的波长调谐特性。泵浦振荡器经放大和选频后，为光纤参量振荡器提供泵浦光。当选频比为10、泵浦振荡器的中心波长为1030 nm时，泵浦振荡器的腔长改变0.8 mm，等效于光纤参量振荡器的腔长改变8 mm，在色散滤波的作用下，光纤参量振荡器的波长在748.3~754.9 mm范围内可调谐。当在1030~1040 nm范围内改变泵浦振荡器的中心波长时，采用上述方式，光纤参量振荡器的输出波长在748.3~789.2 nm内可调谐。该方法仅通过改变泵浦振荡器的腔长，就能实现光纤参量振荡器的波长调谐。相比传统改变光纤参量振荡器腔长的方案，泵浦振荡器的腔长改变量仅为原来的选频比分之一，有望用于快速调谐的光纤参量振荡器上。

本文设计了一种基于声光移频器(AOFS)的光学锁相环系统，实现了DFB半导体激光器与窄线宽光纤激光器的频率锁定。系统采用高速数据采集卡获取主从激光器的相位与频率误差信号，并结合PID控制策略调节本振激光器。同时引入AOFS作为快速精密调谐元件，提升了系统的环路带宽和相位噪声抑制能力。本文首先从理论上分析了系统的工作原理，建立了包含噪声因素的仿真模型，并对锁相性能进行模拟验证。实验结果进一步证实了系统的有效性，显示出良好的频率稳定性和抗干扰能力。

窄线宽532 nm在高反金属材料加工、荧光检测、紫外波段和中红外波段激光的产生等领域均有广泛的应用。近红外波段1064 nm光纤激光腔外倍频产生的532 nm具有噪声低、效率高，光束质量好和功率稳定性好等优点。本文从常见的腔外倍频结构和晶体出发，对四种常见倍频晶体的有效非线性系数、激光损伤阈值进行分析对比；重点总结了窄线宽光纤激光单通双折射晶体、周期性极化晶体产生绿光；角度匹配、温度匹配下外腔谐振倍频产生532 nm激光的研究进展。讨论了腔外倍频中两种结构的特性和应用场景。

We present a 10GHz passively mode-locked vertical external-cavity surface-emitting semiconductor laser (VECSEL) with 1.4W average output power in 6.1ps pulses. The output features a very good pulse quality with a time–bandwidth product of 0.42 in a nearly diffraction-limited beam. This demonstrates that passively mode-locked VECSELs are suitable for generating high powers in high-repetition-rate pulse trains.

Monolithic distributed feedback semiconductor lasers (1550 nm) for FMCW LiDAR applications have been designed, fabricated and tested. The strong optical frequency modulation distortion observed when a standard DFB laser is modulated with a triangular current waveform is significantly mitigated in our laser. A 100 kHz frequency modulation with amplitude of 0.9 GHz and nonlinear distortion of 0.3%, calculated as the standard deviation of the optical frequency after removal of a linear fit, was measured through an unbalanced fiber interferometer. This was achieved without electronic pre-distortion of the triangular waveform. The 60 kHz intrinsic linewidth of the laser was unaffected by the modulation. Two lasers were co-packaged in a 2.6 cm³ multi-layer ceramic package and coupled to fiber pigtails with micro-lenses. The pins of the ceramic package were soldered to a printed circuit board containing the current sources driving the lasers. This optical source was used in a two-channel LiDAR demonstrator built from off-the-shelf fiber optic components and a twodimensional gimbal scanning mirror. This demonstrator enabled detecting a target with 10 % Lambertian reflectivity up to a distance of &gt;120 m and recording point clouds of different scenes. This shows that FMCW LiDAR in combination with highly coherent and linear DFB laser sources is a very promising technology for long range sensing. A version under development will include a silicon photonics chip for further integration and functionality including I/Q detection.

Vertical-external-cavity surface-emitting lasers (VECSELs) are the most versatile laser sources, combining unique features such as wide spectral coverage, ultrashort pulse operation, low noise properties, high output power, high brightness and compact form-factor. This paper reviews the recent technological developments of VECSELs in connection with the new milestones that continue to pave the way towards their use in numerous applications. Significant attention is devoted to the fabrication of VECSEL gain mirrors in challenging wavelength regions, especially at the yellow and red wavelengths. The reviewed fabrication approaches address wafer-bonded VECSEL structures as well as the use of hybrid mirror structures. Moreover, a comprehensive summary of VECSEL characterization methods is presented; the discussion covers different stages of VECSEL development and different operation regimes, pointing out specific characterization techniques for each of them. Finally, several emerging applications are discussed, with emphasis on the unique application objectives that VECSELs render possible, for example in atom and molecular physics, dermatology and spectroscopy.

We demonstrated a high output power distributed-Bragg-reflector (DBR) laser integrated with semiconductor optical amplifier (SOA) for the frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) system. In order to acquire higher output power, different from the conventional SG-DBR laser, the front mirror in this work is a section of uniform grating to get higher transmissivity. Therefore, the output power of the laser reaches 96 mW when the gain current and SOA current are 200 mA and 400 mA, respectively. Besides, we fabricated a spot size converter (SSC) at the laser output port to enhance the fiber coupling efficiency, which reached 64% coupled into the lensed fiber whose beam waist diameter is 2.5 μm. A tuning range of 2.8 nm with free spectral range (FSR) of 0.29 nm and narrow Lorentzian linewidth of 313 kHz is achieved. To realize distance and velocity measurement, we use the iterative learning pre-distortion method to linearize the frequency sweep, which is an important part of the FMCW LiDAR technology.

Lidar imaging systems are one of the hottest topics in the optronics industry. The need to sense the surroundings of every autonomous vehicle has pushed forward a race dedicated to deciding the final solution to be implemented. However, the diversity of state-of-the-art approaches to the solution brings a large uncertainty on the decision of the dominant final solution. Furthermore, the performance data of each approach often arise from different manufacturers and developers, which usually have some interest in the dispute. Within this paper, we intend to overcome the situation by providing an introductory, neutral overview of the technology linked to lidar imaging systems for autonomous vehicles, and its current state of development. We start with the main single-point measurement principles utilized, which then are combined with different imaging strategies, also described in the paper. An overview of the features of the light sources and photodetectors specific to lidar imaging systems most frequently used in practice is also presented. Finally, a brief section on pending issues for lidar development in autonomous vehicles has been included, in order to present some of the problems which still need to be solved before implementation may be considered as final. The reader is provided with a detailed bibliography containing both relevant books and state-of-the-art papers for further progress in the subject.

Phase noise (PN) of a laser source is a limitation on the measurement range for a frequency-modulated continuous-wave (FMCW) laser ranging system. A narrow-linewidth laser is required to achieve long-range ranging. We proposed a FMCW laser ranging system which is able to break the limitation of coherence length via pilot-assisted PN cancellation. The system adds an acousto-optic modulator (AOM) to generate a frequency known pilot signal, from which the PN can be extracted. PN-cancellated signal can be obtained by removing the extracted PN term. The experimental results show the proposed system can recover the coherent peak beyond the 8-times of coherence length and achieve 0.88-cm precision at 861.39 m. This method can be used to achieve long-range of FMCW laser ranging using a wide linewidth laser.

Abstract The rising demand for high scanning accuracy and resolution in sensors for self-driving vehicles has led to the rapid development of parallelization in light detection and ranging (LiDAR) technologies. However, for the two major existing LiDAR categories—time-of-flight and frequency-modulated continuous wave—the light sources and measurement principles currently used for parallel detection face severe limitations from time- and frequency-domain congestion, leading to degraded measurement performance and increased system complexity. In this work we introduce a light source—the chaotic microcomb—to overcome this problem. This physical entropy light source exhibits naturally orthogonalized light channels that are immune to any congestion problem. Based on this microcomb state, we demonstrate a new type of LiDAR—parallel chaotic LiDAR—that is interference-free and has a greatly simplified system architecture. Our approach also enables the state-of-the-art ranging performance among parallel LiDARs: millimetre-level ranging accuracy and millimetre-per-second-level velocity resolution. Combining all of these desirable properties, this technology has the potential to reshape the entire LiDAR ecosystem.

Light detection and ranging (LiDAR) sensors bring remarkable features to the automotive industry, enabling the development of autonomous vehicles. More concretely, frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) sensors offer several advantages over their time-of-flight (ToF) counterparts in terms of maximum achievable distance, interference immunity, and velocity detection. Nonetheless, FMCW LiDAR systems are inevitably affected by phase noise, limiting the sensor performance. One evident solution consists in using narrow linewidth lasers, at the expense of overall sensor cost. Therefore, in this work, a thorough analysis of the phase noise is conducted for FMCW LiDAR sensors. Moreover, a novel and low-complex phase noise compensation algorithm based on pre-estimation and feedforward correction (PNC-PEFC) is proposed. The PNC-PEFC algorithm is extensively evaluated in an experimental setup under different target distances and additive white Gaussian noise (AWGN) conditions. The experimental results show excellent performance when applying the proposed PNC-PEFC algorithm, proving its robustness across all evaluated conditions.

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This paper presents a C-band DFB laser with low threshold current and high optical power, featuring a low RIN (-151.63 dB/Hz) and narrow linewidth (43.23 kHz), present the suitability for FMCW LiDAR applications. © 2024 The Author(s)

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From an industry perspective, the past decade has been a whirlwind of innovation in automotive light detection and ranging (LiDAR). Numerous laser technologies and system solutions have been fiercely competing for market share. However, recent trends suggest a growing convergence on vertical-cavity surface-emitting laser (VCSEL) and antireflective VCSEL (AR-VCSEL) based solutions. This commentary, rooted in the practical realities of the industry, examines the historical trajectory of industrial laser technology for commercial automotive LiDAR. It specifically focuses on the recent applications of VCSEL/AR-VCSEL technologies and their future prospects. Liang et al. present an industrial perspective on the evolving landscape of laser technology used in advanced LiDAR systems. The authors discuss recent trends, practical considerations within the industry, current challenges, and potential solutions, explicitly focusing on VCSEL/AR-VCSEL-based technologies and their strong potential for commercial LiDAR applications.

As LiDAR technology progressively advances, the capability of radar in detecting targets has become increasingly vital across diverse domains, including industrial, military, and automotive sectors. Frequency-modulated continuous-wave (FMCW) LiDAR in particular has garnered substantial interest due to its efficient direct velocity measurement and excellent anti-interference characteristics. It is widely recognized for its significant potential within radar technology. This study begins by elucidating the operational mechanism of FMCW LiDAR and delves into its basic principles. It discuss, in depth, the influence of various parameters on FMCW LiDAR’s performance and reviews the latest progress in the field. This paper proposes that future studies should focus on the synergistic optimization of key parameters to promote the miniaturization, weight reduction, cost-effectiveness, and longevity of FMCW LiDAR systems. This approach aims at the comprehensive development of FMCW LiDAR, striving for significant improvements in system performance. By optimizing these key parameters, the goal is to promote FMCW LiDAR technology, ensuring more reliable and accurate applications in automated driving and environmental sensing.