FMCW Lidar Research Articles

Directly modulated FMCW tunable laser with highly linear frequency chirp and narrow linewidth

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.

Dynamic Measurement with High Precision Using Frequency Agile Spatial Encoding Integrated FMCW LiDAR

Dynamic Measurement with High Precision Using Frequency Agile Spatial Encoding Integrated FMCW LiDAR

Window size dependence of gain and bandwidth in avalanche photodiodes with multiple multiplication layers under near Geiger-mode operation.

We consider avalanche photodiodes (APDs) functioning under near Geiger-mode operation for extremely weak light (single or several photons) detection, such as in LiDAR receivers. To meet such demands, APDs which simultaneously have a large active window size, moderate bandwidth (∼GHz), and high internal gain (responsivity), are highly desired. However, it is difficult to design APDs capable of meeting the afore-mentioned performance requirements due to the intrinsic limitations of the gain-bandwidth product (GBP). In this work, we demonstrate that the GBP bottleneck in the APDs can be overcome by using multiple (3) In0.52Al0.48As based multiplication (M-) layers with a thick In0.53Ga0.47As absorber (2 µm). Moreover, the characteristic invariant 3-dB bandwidth in our APDs, from low to an extremely high operation gain, becomes more pronounced with an increase of its active window diameter (40 to 200 µm). This characteristic makes it very attractive for collecting weak light in free space as is required for LIDAR receiver applications. Comparison shows that the 200 µm APD exhibits a higher 0.9 Vbr responsivity (15 vs. 7 A/W), larger maximum gain (460 vs. 110), and higher GBP (468 vs. 131 GHz) than does the 40 µm reference sample and can sustain a constant 3-dB bandwidth (1.4 GHz) over a wide range of operation gains (10 to 460). The dependence of the APD performance on the window size can be attributed to the influence of the surface states on the edge of the etched mesa. Here, we further demonstrate a backside-illuminated structure with a flip-chip bonding package which minimizes this phenomenon in small APDs ensuring high-speed performance. Compared with the top-illuminated reference samples, the flip-chip bonding packaged device shows a further enhancement of the responsivity (10.7 vs. 7 A/W), 3-dB bandwidth (4.1 vs. 3.9 GHz), and saturation current (4.25 vs. 3.6 mA). The excellent static and dynamic performance of our flip-chip APD in turn leads to an unprecedented high velocity sensitivity (5 µm/sec) and superior quality 4-D FMCW LiDAR images compared to that obtainable with p-i-n-based or top-illuminated reference devices with the same small active window size (40 µm).

Silicon FMCW LiDAR chip integrated with SLG beam scanner and k-clock interferometer for operation with wavelength-swept laser source

We fabricated a frequency-modulated continuous-wave light detection and ranging (FMCW LiDAR) chip that integrates a slow-light grating (SLG) beam scanner and an optical interferometer for k-clock generation using silicon photonics. Beam scanning and FMCW light generation were performed simultaneously through a wavelength sweep, while the sweep nonlinearity was compensated by resampling the ranging signal using the k-clock. The interferometer incorporated a 24-cm-long Si waveguide delay line, facilitating ranging up to 7.1 m and the capture of point cloud images. The possibility of ranging longer distances by lengthening the waveguide and increasing the interpolation is discussed.

Linearization of wavelength sweeping lasers for the construction of 4-D FMCW LiDAR images of slow-moving objects using baseband beat note signals

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.

Photonic-electronic integrated circuit-based coherent LiDAR engine

Chip-scale integration is a key enabler for the deployment of photonic technologies. Coherent laser ranging or FMCW LiDAR, a perception technology that benefits from instantaneous velocity and distance detection, eye-safe operation, long-range, and immunity to interference. However, wafer-scale integration of these systems has been challenged by stringent requirements on laser coherence, frequency agility, and the necessity for optical amplifiers. Here, we demonstrate a photonic-electronic LiDAR source composed of a micro-electronic-based high-voltage arbitrary waveform generator, a hybrid photonic circuit-based tunable Vernier laser with piezoelectric actuators, and an erbium-doped waveguide amplifier. Importantly, all systems are realized in a wafer-scale manufacturing-compatible process comprising III-V semiconductors, silicon nitride photonic integrated circuits, and 130-nm SiGe bipolar complementary metal-oxide-semiconductor (CMOS) technology. We conducted ranging experiments at a 10-meter distance with a precision level of 10 cm and a 50 kHz acquisition rate. The laser source is turnkey and linearization-free, and it can be seamlessly integrated with existing focal plane and optical phased array LiDAR approaches.

High-Ranging-Precision FMCW LiDAR With Adaptive Pre-Distortion of Current Injection to a Semiconductor Laser

High-Ranging-Precision FMCW LiDAR With Adaptive Pre-Distortion of Current Injection to a Semiconductor Laser

A CMOS AFE Array With DC Input Current Cancellation for FMCW LiDAR

A CMOS AFE Array With DC Input Current Cancellation for FMCW LiDAR

Microcavity Raman Laser-Based FMCW LiDAR with Enhanced Echo Sensitivity

Microcavity Raman Laser-Based FMCW LiDAR with Enhanced Echo Sensitivity

Coherent heterodyne FMCW lidar based on combined single/double sideband modulation detection technology

The conventional coherent FMCW lidar system has the problem of frequency drift to meet the high accuracy range. When measuring the moving target, it cannot judge the target motion status in real-time. This paper proposes a high-stability coherent heterodyne FMCW lidar detection method to solve the above-proposed problems. The combined single/double sideband modulation method significantly suppresses the frequency drift and, combined with the spectrum refinement processing method, achieves high stability of laser ranging and speed measurement. The result shows that the target is located at an 8 m distance from the system, the range accuracy is 5 cm, the range error is less than 1.5 cm, and the root mean square(RMS) error is 6.6 × 10-3 m, which is an order of magnitude higher than that of the conventional FMCW laser detection system. We use the binomial fitting method to obtain a measurement speed error of fewer than 1.15 × 10-2 m/s.

Phase-noise-cancelled FMCW Lidar based on CS-DSB modulation and injection-locking technique

Phase-noise-cancelled FMCW Lidar based on CS-DSB modulation and injection-locking technique

Application of 632 nm FMCW lidar for simultaneous velocity and distance measurement in humid environment

Application of 632 nm FMCW lidar for simultaneous velocity and distance measurement in humid environment

Research progress of on-chip integrated FMCW LiDAR (cover paper·invited)

Research progress of on-chip integrated FMCW LiDAR (cover paper·invited)

Silicon Photonic FMCW LiDAR Calibration Engine with Optimized On-Chip Delay Lines

Silicon Photonic FMCW LiDAR Calibration Engine with Optimized On-Chip Delay Lines

A 4-D FMCW LiDAR With Ultra-High Velocity Sensitivity

A 4-D FMCW LiDAR With Ultra-High Velocity Sensitivity

Symmetrical dual-sideband oppositely chirped differential FMCW LiDAR.

A differential FMCW LiDAR for high-precision distance measurements of remote non-stationary targets is proposed and demonstrated experimentally. The required positive and negative symmetrically oppositely chirped laser beams are generated synchronously through a fixed-frequency laser by employing externally unified broadband optical phase modulation and symmetrical dual-sideband optical filtering. After coaxial transmission and reception, orthogonally polarized optical beat signals containing target distance and vector velocity data are de-chirped separately by optical in-phase and quadrature demodulations and then synchronously received by four-channel photoelectric balance detectors. After differential processing of the received beat signals and a fast Fourier transform, it is possible to implement real-time simultaneous range and vector velocity measurements. The inherent symmetrically oppositely chirped optical frequency make it possible to measure the target distance immune to the internal random phase noise introduced by the spectral linewidth of the frequency-swept laser and the external random phase noise introduced by atmospheric turbulence, speckle, and vibration. Meanwhile, the measurement of the target velocity is immune to the nonlinearity of the frequency-swept laser. These results encourage an approach to overcome the barriers of coherence length, nonlinearity, and external noise, and implement simultaneous real-time ranging and velocimetry of long-range, rapid-moving targets.

OFDR analysis of Si photonics FMCW LiDAR chip.

We experimentally analyzed the internal reflection and loss of each component in a Si photonics frequency-modulated continuous-wave light detection and ranging (FMCW LiDAR) device using optical frequency domain reflectometry (OFDR) with a spatial resolution of better than 2.5 µm. Sweeping the incident laser wavelength by 120 nm, the reflections and losses of wire waveguides, widened waveguides, and optical switches on the chip were individually revealed. The slow-light grating (SLG) beam scanner, which has a limited working wavelength range, was evaluated with a spatial resolution of >10 µm by narrowing the wavelength sweep range. Consequently, a strong reflection was observed at the transition between the wire waveguide and the SLG, which can be a noise source in the FMCW LiDAR. Additionally, this study showed that the OFDR can be an important analysis tool for Si photonics integrated circuits. To our knowledge, this is the first demonstration, showing that the OFDR can be an important analysis tool for Si photonic integrated circuits.

Long-range frequency-modulated continuous-wave LiDAR employing wavelength-swept optical frequency comb

We propose a FMCW LiDAR using a wavelength-swept optical frequency comb, which overcomes the ranging limitation caused by the receiver bandwidth. We have established the fundamental part of our proposal and conducted proof-of-concept ranging experiments. With optical fiber transmission for emulating long distance free-space propagation, we have succeeded in ranging corresponding to 1605-m free-space propagation with a 10-MHz FMCW receiver.

Laser Frequency Chirping With Silicon Photonic Circuit Comprising an IQ Modulator and a III-V/Si SOA

We report on the performance of a silicon photonic integrated circuit for laser frequency chirping, developed for FMCW LIDAR applications. An external laser source is fiber coupled to the photonic circuit and frequency chirping is achieved with a silicon IQ modulator and a monolithically integrated III-V/Si semiconductor optical amplifier to compensate for IQ modulator losses. A chirp distortion of 1.8% over 5% to 95% of the chirp ramp period was measured with a delayed self-heterodyne interferometric method. The high chirp linearity of our circuit is confirmed by FMCW ranging measurements using 2-18 m long fiber delay lines. The resulting beat frequency follows a linear dependency with the fiber delay line length (R²=0.999).

Si Photonics FMCW LiDAR Chip with Solid-State Beam Steering by Interleaved Coaxial Optical Phased Array.

LiDAR has attracted increasing attention because of its strong anti-interference ability and high resolution. Traditional LiDAR systems rely on discrete components and face the challenges of high cost, large volume, and complex construction. Photonic integration technology can solve these problems and achieve high integration, compact dimension, and low-cost on-chip LiDAR solutions. A solid-state frequency-modulated continuous-wave LiDAR based on a silicon photonic chip is proposed and demonstrated. Two sets of optical phased array antennas are integrated on an optical chip to form a transmitter-receiver interleaved coaxial all-solid-state coherent optical system which provides high power efficiency, in principle, compared with a coaxial optical system using a 2 × 2 beam splitter. The solid-state scanning on the chip is realized by optical phased array without a mechanical structure. A 32-channel transmitter-receiver interleaved coaxial all-solid-state FMCW LiDAR chip design is demonstrated. The measured beam width is 0.4° × 0.8°, and the grating lobe suppression ratio is 6 dB. Preliminary FMCW ranging of multiple targets scanned by OPA was performed. The photonic integrated chip is fabricated on a CMOS-compatible silicon photonics platform, providing a steady path to the commercialization of low-cost on-chip solid-state FMCW LiDAR.