LIDARs

LIght Detection And Ranging

OVERVIEW

Main Variants	Alternatives

Sources of differences

A combination of all options leads to (~8k) LiDaRs:

• beam steering (9)
• Time of flight measurement (3)
• Optics (288)

Notes: beam steering (9): - Solid state (3) : none , DMD in TX, DMD in RX path - Rotating Mirrors (3) : polygon, galvano,

• Time of flight measurement (3): PMCW, FMCW, AMCW
• Optics (288):
  • wavelength (4) : 850, 905, 940, 1550 nm
  • Front-End dimensions (3) : (respectively #RX, #TX): 1x1, few x few, few x many
  • Laser diode technology (2): edge emiting or VCSEL
    • LD bias circuitry (2)
  • Photo diode technology (3) : MPPC/SiPM, APD, Pin
    • PD bias circuitry (2)

beam steering

• Non-mechanical (aka static or solid-state)
• Mechanical

Non-mechanical beam steering

• DMD (Digital Micro Mirror), a MEMS technology for controlling micro-mirrors
  • can be on the TX side
  • can be on the RX side
• Flash LiDaR - a very powerful Laser illuminates the entire scene and an array of photodetectors senses the return light.
• OPA - (Optical phase array) - In an OPA system, an optical phase modulator controls the speed of light passing through the lens.

Mecanical

• polygon-beam-scanners
• galvano scanner (polygon vs galvano)
• motorized with encoders

ToF measurement:

• PB-ToF (or PMCW): pulse based or pseudo-random sequences
• FMCW-ToF: Frequency Modulated Continuous Wave
• AMCW-ToF: Amplitude Modulated Contiuous Wave

PB-ToF (pulse based time of flight) or PMCW

• Simple version: simple pulse
• dual-slope or dual gate as in 1 - doi: 10.3390/s18061679 or 2 - doi=10.1.1.579.1245
• Advanced version - pseudorandom modulation continuous-wave (PMCW): with multiple pulse sent with a pseudo-random sequence.

FMCW-ToF

FMCW: Frequency Modulated Continuous Wave for Time of flight measurement

AMCW-ToF

Amplitude Modulated Continuous Wave Time of Flight

Notes:

• error analysis

Optics

• Wavelengthts
• Front-End dimensions
• Opto-electronics

Wavelengths

905nm and 1550nm are the dominant wavelength

more

Front-End dimensions

• 1x1: single pixel TX, single pixel RX
• few x few : often multiple discrete LD and discrete LD
• few x many : eitehr 1x or few discrete LD and an integrated array of photos sensors

Laser diode

• Opto-electronic Technology
• Electronic bias circuitry (2)

Notes: p-i-n silicon detectors vs avalanche photodiodes or silicon photomultipliers CWFM-ToF can use coherent detection can be used with pin diodes which are significantly cheaper than APD often used in PB-ToF.

Atmospheric considerations

test: \(x_{1,2} = {-b\pm\sqrt{b^2 - 4ac} \over 2a}.\) some fundamentals \(P=P_0 * rho * A0/(pi*R2) *eta * exp(-2*gamma*R)\) Where:

• η0 is the detection optics’ spectral transmission,
• γ is the atmospheric extinction coefficient.

Back-up slides

Sources

1. slashgear on lidar
2. Forbes
   • claims 468 variants of LiDaRs