Case Study CS-TC02 Rev. A

Page 2

© 2020 • Sales & Technical Support: (406) 587-4910 • email: sales@teamWavelength.com • web: www.teamWavelength.com

The laser engine in both systems utilizes Bridger Photonics'

patented

Frequency

Modulated

Continuous

Wave

(FMCW) LiDAR (Light Detection and Ranging) technology.

The laser's output is chirped (the frequency is ramped with

time). This frequency is swept over a given bandwidth (B),

seen in

Figure 3. The light from the chirped laser is split

into two portions: transmitted (Tx) and a reference (local

oscillator or LO). The transmitted light is incident on the

optic under test and reflects back to the detection system.

The returned (Rx) frequencies are compared with the

reference frequencies. The setup is shown in

Figure 4.

Because the return signal has covered the distance to the

object and returned, it will be shifted in time compared

to the reference waveform as seen in

Figure 3. The

two signals are combined, and a detector measures the

beat created from the frequency difference. The beat is

dependent on the chirp rate (κ) and the time delay (τ

D). The

signal is then converted with a fast Fourier transform to

give the full-waveform range profile (seen in

Figure 5). The

peaks show the location of each surface of the given object.

The widths of the peaks (ΔR) are dependent upon the

chirp bandwidth. From the peaks the thickness of the optic

can be realized. This method allows for measurements of

diffusely scattering surfaces which challenge the accuracy

and resolution of other non-contact techniques.

Figure 2. Bridger Photonics' SLM-IM Length

Metrology System2

Figure 1. Bridger Photonics' Thickness Metrology

Station2

LO

Rx

f

beat = κτ

D

B

Time

τD

Figure 3. Frequency Ramp with Local Oscillator (LO)

and Return Signal (Rx) showing time delay (τ

D)

1

Figure 4. (FMCW) LiDAR measurement technique1