Fig. 1. Schematic diagrams of LiDAR. (a) Direct time-of-flight (dToF); (b) indirect time-of-flight (iToF); (c) frequency-modulated continuous wave (FMCW)

Fig. 2. Autocorrelation calculation results of the output signal of the LFM DW-DFB laser. (a) Calculated autocorrelation result; (b) zoom-in view of the autocorrelation peak (red line curve is the fitted envelope). Reprinted with permission from Ref. [6]. The copyright is owned by American Chemical Society

Fig. 3. Performance of the remote ranging system built in the experiment. (a) Spectra of the detected electrical signal with different target distances; (b) measured distances versus actual target distances; (c) measurement errors under different target distances. Reprinted with permission from Ref. [6]. The copyright is owned by American Chemical Society

Fig. 4. Side mode suppression ratio (SMSR) of coarse tuning spectrum with a tuning range of 110 nm and corresponding wavelength tuning graph. (a) Coarse tuning spectra showing the tuning range of 110 nm; (b) two-dimensional wavelength tuning map of the triple-ring mirror laser, where the color indicates the lasing wavelength in units of nm; (c) SMSR of the corresponding wavelength tuning map, showing SMSR >40 dB on most of the operation points. Reprinted with permission from Ref. [9]. The copyright is owned by the original authors: Tran M A, Huang D, Guo J, et al.

Fig. 5. Characterization of laser properties of colloidal quantum dot integrated DFB laser. (a) Spectra measured from an unpatterned waveguide (black) and DFB lasers with different grating periods (colored); (b) light (in)‒light (out) curve on a double linear scale, with indication of the lasing threshold around 270 μJ/cm², which has an equivalent CW power density of 39 kW/cm²; (c) light (in)‒light (out) curve on a double log-scale with rate equation fit (black solid). A spontaneous emission factor (β) of 0.009 is extracted. Reprinted with permission from Ref. [12]. The copyright is owned by American Chemical Society

Fig. 6. Output wavelength of each DFB laser of this four-wavelength laser array at 60 mA injection current and 50 mA SOA forward bias. (a) PIC chip optical spectra with four DFB sections simultaneously turned on, where I_DFB1=I_DFB2=I_DFB3=I_DFB4=60 mA, and I_SOA=50 mA; (b) wavelength tuning characteristics of the four DFB sections as a function of the DFB injection current. Reprinted with permission from Ref. [13]. The copyright is owned by IEEE

Fig. 7. Emission spectra and single-mode peak output power of six DFB lasers with different spacings between silicon gratings. Reprinted with permission from Ref. [14]. The copyright is owned by Optica

Fig. 8. Emission spectrum of a tunable VCSEL measured by OSA at the repetition rate of 50 Hz and pulse width of 12 μs. (a) Pump current of i_B=1 mA and i_P=28 mA; (b) pump current of i_B=1 mA and i_P=20 mA. Reprinted with permission from Ref. [20]. The copyright is owned by the original authors: R. Kruglov, G. Saur, and R. Engelbrecht

Fig. 9. Spectral characteristics of the BH-DFB laser as a function of temperature and current input. (a) BH-DFB laser exhibits spectra with an interval of 25 mA at room temperature and injection currents ranging from 25 mA to 125 mA; (b) temperature dependence of peak wavelength and SMSR at injection current of 100 mA, where the blue inverted triangle represents SMSR and the red triangle represents peak wavelength. Reprinted with permission from Ref. [25]. The copyright is owned by Optica

Fig. 10. Performance of assembled vertical and inverted chip VCSEL arrays. (a)(b) L-I-V curves of assembled vertical and inverted chip VCSEL arrays at 300 K and 360 K, where the insets show the optical microscopy images of vertical and inverted chip VCSEL arrays respectively, and the arrows distinguish the groups of I-V and L-I curves; (c) simulated modulation response of vertical and flip-chip VCSEL arrays at 300 K; (d) measured modulation response of vertical and flip-chip VCSEL arrays at 300 K. Reprinted with permission from Ref. [29]. The copyright is owned by MDPI

Fig. 11. Schematic diagram and output laser characteristics of 6-junction anti reflection AR-VCSEL structure. (a) Schematic of AR-VCSEL structure consisting of top and bottom DBRs, an active region, an antireflective mirror, and a light reservoir; (b) array far-field pattern 50 mm away; (c) refractive index profile and electric field intensity distribution with the output level normalized to unity (the epitaxial direction is from left to right); (d) a standard VCSEL structure with a bottom mirror next to the active region; (e) an AR-VCSEL structure with a π/2 (or quarter wavelength) phase shift between the antireflective mirror and the active region; (f) reflectance spectrum of the as-grown AR-VCSEL structure showing several FP longitudinal modes within the stopband (solid black line), as well as a measured PL spectrum aligned with the center FP dip (blue dashed line); (g) measured temperature-dependent lasing spectra from 25 ℃ to 125 ℃, showing single-longitudinal-mode lasing. Reprinted with permission from Ref. [32]. The copyright is owned by Springer Nature

Fig. 12. Linearity and depth accuracy for different target reflectivity under indoor lighting and actual distances over 1000 mm. (a) Linearity; (b) depth accuracy. Reprinted with permission from Ref. [34]. The copyright is owned by MDPI

Fig. 13. Laser structure. Reprinted with permission from Ref.[39]. The copyright is owned by Chinese Laser Press

Fig. 14. Waveguide schematic of the modulator, where the phase tuning section is composed of a hybrid waveguide (shown in red). Reprinted with permission from Ref.[41], under a Creative Commons Attribution 4.0 International License

Fig. 15. Laser emitter. AFG: arbitrary function generator; WGR: whispering gallery resonator. Reprinted with permission from Ref. [42], under a Creative Commons Attribution 4.0 International License

Fig. 16. Schematic diagram of waveguide section. Reprinted with permission from Ref. [43]. The copyright is owned by IEEE

Fig. 17. Schematic diagram of waveguide cross-section. Reprinted with permission from Ref. [44], under a Creative Commons Attribution 4.0 International License

Fig. 18. Schematic diagram of AOM. Reprinted with permission from Ref. [46], under a Creative Commons Attribution 4.0 International License

Fig. 19. PZT actuators in combination with micro heaters. Reprinted with permission from Ref. [47], under a Creative Commons Attribution 4.0 International License

Fig. 20. Spatial modulation using multiple laser beams to form vertical line and 1D MEMS mirror for horizontal scanning. Reprinted with permission from Ref. [51], under a Creative Commons Attribution 4.0 International License

Fig. 21. Hierarchical schematic diagram of the OPA structure. (a) A 3D view of the OPA on a MEMS cantilever; (b) top-view image of the fabricated device; (c) simplified schematic of the layer stack; (d) scanning electron microscopy image of thermal phase modulator (TPM) cross section showing adjacent waveguides (WGs) separated by air-filled voids; (e) 200 mm wafer containing fabricated devices. Reprinted with permission from Ref. [53], under a Creative Commons CC BY License

Fig. 22. Schematic diagram of a single resonator structure on a metasurface. Reprinted with permission from Ref. [56], under a Creative Commons Attribution 4.0 International License

Fig. 23. LiDAR imaging. (a) Schematic diagram of the LiDAR system; (b) spectrum of the receiver as the scanned beam passes through the FOV; (c) imaging of the object; (d) raw signal of a representative pixel; (e) raw signal of another representative pixel. Reprinted with permission from Ref. [60]. The copyright is owned by Springer Nature

Fig. 24. Different working regions of Lm-APD and Gm-APD. Reprinted with permission from Ref.[62]. The copyright is owned by IEEE Journal of Quantum Electronics

Fig. 25. Principle of SNSPD based on hotspot modeling. Reprinted with permission from Ref. [69]. The copyright is owned by Applied Physics Letters

Fig. 26. Responsivity of backside illuminated Ge-on-Si diodes and Ge_xSn_1-x-on-Si diodes with a Sn doping concentration of up to 4%. The solar spectrum is also plotted. Reprinted with permission from Ref. [72]

Fig. 27. Top view SEM image of GeSi APD with outer and inner metal rings attached to the n-contact and p-contact doped regions, respectively. Reprinted with permission from Ref. [74]. The copyright is owned by IEEE

Fig. 28. Characteristic curves under different conditions. (a) Current-voltage curves measured under light-on and light-off conditions; (b) gain curves derived from photocurrent and dark current data. Reprinted with permission from Ref. [74]. The copyright is owned by IEEE

Fig. 29. Schematic of 1×7 Ge-on-Si APD device structure. Reprinted with permission from Ref. [75]. The copyright is owned by IEEE Electron Device Letters

Fig. 30. Ge-on-Si APD array. (a) Ge-on-Si APD array (2×7) layout, where labels (1) and (2) are used to show two different rows of APDs; (b) dark current of Ge-on-Si APD array; (c) encapsulated Ge-on-Si APD array chip; (d) photocurrent of Ge-on-Si APD array. Reprinted with permission from Ref. [75]. The copyright is owned by IEEE Electron Device Letters

Fig. 31. SACM APD epitaxial cross section with 1 μm random alloy InGaAs absorber layer and 1 μm digital alloy AlInAsSb multiplier layer. Reprinted with permission from Ref. [81]. The copyright is owned by IEEE

Fig. 32. Different characteristics of InGaAs/AlInAsSb APD. (a) Dark current, photocurrent and gain of InGaAs/AlInAsSb SACM APD with 150 μm diameter under 1550 nm irradiation at room temperature; (b) excess noise characteristics of InGaAs/AlInAsSb APD under 1550 nm irradiation; (c) temperature-dependent dark current characteristics of InGaAs/AlInAsSb SACM APD with a diameter of 150 μm from 200 K to 320 K in steps of 20 K. Reprinted with permission from Ref. [81]. The copyright is owned by IEEE

Fig. 33. A cross-sectional view of an APD using a three-multiplier layer design, with the inset indicating an effective window diameter of 200 μm. Reprinted with permission from Ref. [85]. The copyright is owned by IEEE

Fig. 34. LiDAR images captured based on the amplitude and distance information of each pixel from Device A. (a) “OK” image presented in the planar pixel map; (b) 3D image containing distance depth information. Reprinted with permission from Ref. [85]. The copyright is owned by IEEE

Fig. 35. LiDAR experimental setup using free-running InGaAs/InP single-photon detectors. Reprinted with permission from Ref. [93]. The copyright is owned by Optica Publishing Group

Fig. 36. Schematic of InGaAs/InP SPAD in quasi-free-running mode. GHz SG: GHz signal generator; HPF: high-pass filter; TCSPC: time-correlated single-photon counter; HV: high voltage; LPF: low-pass filter; AMP: amplifier. Reprinted with permission from Ref. [94]. The copyright is owned by IEEE Journal of Quantum Electronics

Fig. 37. Detection performance of InGaAs/InP SPAD in quasi-continuous mode with sinusoidal gating at different repetition frequencies. (a) Timing jitter and PDE; (b) effective window width and duty cycle; (c) post-pulse probability and dark count rate. Reprinted with permission from Ref. [94]. The copyright is owned by IEEE Journal of Quantum Electronics

Fig. 38. System detection efficiency (SDE) versus voltage bias applied at maximum input polarization (max_pol) and minimum input polarization (min_pol), as measured for four 50 µm diameter devices (labeled A, B, C, and D) from the same wafer. These devices had a 450 Ω resistor in series as well as a 50 Ω coaxial line when reading pulses. Reprinted with permission from Ref. [99]. The copyright is owned by Optica Publishing Group

Fig. 39. Structure and performance of meandering nanowire detectors on SiO₂/Au film. (a) The upper panel shows the device structure of meandering nanowires on SiO₂/Au film, and the lower panel presents optical images of meandering nanowires on SiO₂ film before/after (left/right) gold deposition; (b) simulated light absorption of the device with an air gap of 0‒10 μm (Cutline 1 shows that only one SDE peak appears near 1350 nm when the air gap is about 2.2 μm, while Cutline 2 shows that two SDE peaks appear when the air gap is 4.1 μm); (c) measurement and simulation of detector #1 showing SDE peak over 99% at 1350 nm; (d) measurement and simulation of detector #2 exhibiting dual peaks exceeding 94% SDE peak at both 1280 nm and 1500 nm. Reprinted with permission from Ref. [98]. The copyright is owned by APL Photonics

Fig. 40. Principle of lens-based beam-steering device. Reprinted with permission from Ref. [125]

Fig. 41. Experimental setup of target detection with the beam-steering device. The insets show output spectra and waveforms of pulsed laser (i), pulse picker (ii), and spectral filter (iii). Reprinted with permission from Ref. [129]

Fig. 42. Schematic illustration of a 2D dispersor. The light source is a frequency swept laser. The different colors of light spots represent the different wavelengths. CL: cylindrical lens; VIPA: virtually imaged phased array. Reprinted with permission from Ref. [130]. The copyright is owned by the Optical Society of America