LIDAR using on-chip optical phased arrays

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

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.

N: number of antennas

k: wave vector

w_i: complex weight for element I

r_i: position vector for antenna element i

LIDAR using on-chip waveguide antennas

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

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

• 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

FDTD

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

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

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

• 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.

Beam Steering

Detector design

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

Example: We look at Germanium detectors on Si

Ge on Si detector cross-section

Intensity profile in Ge using FDTD

• Electrical simulations using CHARGE can be used to calculate the photocurrent and the dark current for the detector
  

• Electrical simulations using CHARGE can be used to calculate the responsivity and gain

• Circuit simulations using INTERCONNECT can be used to simulate detector response to weak modulated signal