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3.2.
Angular Deflection
DBSD deflects light at a specific wavelength over a total of field of view of 110° x 18° (horizontal x vertical).
A DBSD is used to perform the coarse light beam steering, and additional lenses can be used to further
increase the FoV.
DBSD deflects the transmitted and received laser source with the same angle. Therefore, a single DBSD
device may be conceptually sufficient for the purpose of specific LiDAR.
The number of angular deflection elements is as follows:
•
Five (5) stages to cover 110° horizontal field of view with 14 x approx. 7.5° tiles
•
Two (2) stages to cover 18° vertical field of view with 4 x approx. 6° tiles
Table 5: DBSD base parameters
Parameter
Value
FoV (horizontal x vertical)
110° x 18°
Number of controllable stages
7
Horizontal angular step
Approx. 7.5°
Vertical angular step
Approx. 6°
Number of tiles (horizontal x vertical)
56 (14 x 4)
3.3.
Quarter-Wave Plate
QWPs are used to create the required circular polarization needed for the DBSD. One is needed when the
laser source is linearly polarized. It can also be used to optimize light signal returns and to clean up potential
stray light.
Table 6: QWP base parameters
Parameter
Value
Number of QWPs
2
Number of controllable QWPs
1
3.4.
Voltage Waveform Control
At each stage, each specific liquid crystal cell is individually controlled with an AC square-wave voltage at a
frequency between 1 kHz and 5 kHz (typically 2 kHz) and a peak-to-peak amplitude between 2 V and 40 V.
Frequency is a trade-off between power consumption and cell stability during the cycle. Slower frequencies
consume less power but might cause a slight variation in light amplitude through the cycle.
We aim at controlling one DBSD with a maximum of 8
“stage
s.
” Each individual “stage” may have electrical
differences (capacitance and resistance change over the surface area); therefore, a characterization must
be considered by design.
The “positive” and “negative” sides of the waveform must cancel each other
sufficiently when integrated.
This means that, when subtracting them, the absolute residual must be lower than 20 mV. This measurement
can be done with a voltmeter in DC mode, measuring the average voltage of an AC square wave, and the
result should be close to zero.
The voltage control needs to be accurate. At low voltages (below a few volts), accuracy must be 10 mV or
better. On higher voltages (closer to 20 V), an accuracy of 200 mV is sufficient.
