LIDAR BASICS

  • LIDAR is based on well known principles of RADAR
  • Radar is well known technology existing since the beginning of the 20th century
  • LIDAR uses optical frequencies instead of radio waves

LidarSpeosRadar

Lidar and Radar

 

LIDAR using phased arrays improves directionality using interference

  • Output profile of a LIDAR is the product of the array factor and the single antenna far field.

 

phased array schematic

Phased array results

Phased Array equation

N: number of antennas

k: wave vector

w_i: complex weight for element I

r_i: position vector for antenna element i

Phased Array equation 2

LIDAR using on-chip waveguide antennas

  • Corrugated waveguides are used as antennas
    corrugated waveguid
  • Pitch corrugation is chosen so that Bragg reflected light is scattered to free space
    Bragg reflection equations
  • Multiple such antennas are used in an array to for beam forming
    Array of waveguides

Lidar modeling in Lumerical

  • MODE analysis of waveguide to calculate n_eff
  • Choosing optimum antenna separation so that there is minimum coupling between adjacent antennas
  • 3d FDTD simulation to calculate bandgap region
  • Far field analysis to calculate far-field profile of a single antenna
  • Array factor multiplication to see beam steering

Mode

Calculate effective refractive index for thinner and thicker cross-sections

Lidar Mode picture

Model results

  • Optimizing separation to minimize cross-coupling
  • We perform simulations with 2 waveguides and calculate after how much length can 10% of light from waveguide 1 couple to waveguide 2

Mode optimization

Mode optimization results

FDTD

  • Calculate the band-gap region
  • Observe wavelength dependent single antenna scattering

FDTD graph

fdtd phased array results

  • 2d beam-steering(θ,ϕ) using results from FDTD

11 beam steering

System level simulations using INTERCONNECT

  • Integrate multiple components
  • Simulate an actual experiment
  • Extensive library of standard components
  • Custom components can be created
  • Allows integration of optical, electrical and thermal elements
12 interconnect

  • We see the effect of applying a optical delay using a voltage ramp on an optical modulator
  • For a given range of voltage values we can monitor θ,ϕ of the steered beam and beam properties.

13 phased array steering

Beam Steering

 

Detector design

  • Detector design using Lumerical
  • Optical simulations to study light absorption in detectors

Example: We look at Germanium detectors on Si

15 GE on SI detector

Ge on Si detector cross-section

15 fdtd detector

Intensity profile in Ge using FDTD

  • Electrical simulations using CHARGE can be used to calculate the photocurrent and the dark current for the detector
    16 10um current vias
  • Electrical simulations using CHARGE can be used to calculate the responsivity and gain
17 responsivity
  • Circuit simulations using INTERCONNECT can be used to simulate detector response to weak modulated signal
18 Gain

 

Sachin
Post by Sachin
May 16, 2022

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