Technology integration of liquid crystal cells for electro-optic modulation has been implemented on the commercial TriPleX photonic platform. Design and fabrication procedure have been optimized for fulfilling the low insertion loss criterion for applications such as space communication and enabling the implementation of compact liquid crystal tuning elements for achieving high integration density. First performance testing of this concept has confirmed low-power consumption switching with 2π phase tuning being obtained within a voltage range of 2.5 V.
An overview is given of the output of two main pixels based on a Current Assistant Photonic Demodulator (CAPD) and
their usability in a ranging camera based on the Time-Of-Flight (TOF) principle. The first structure is based on an active
pixel with an integrating capacitor, while the second structure is based on a transimpedance amplifier. A measurement
system capable of interfacing with a one-dimensional array of CAPD pixels has been designed and is briefly discussed.
The linearity of both CAPD pixels is measured, compared to each other and discussed. Several sources of non-idealities
present in the CAPD output have been investigated, including differences between rise and fall time and duty cycle
imperfections of the high frequency binary correlating signal, as well as CAPD bandwidth. The possible influences of
such non-idealities of the correlating wave on the measurements as well as on the calculated distance are discussed.
Resulting non-idealities in the raw CAPD output values include clipping and non-linearity, yielding offsets and non-linearities
in the calculated phase difference between the original and the reflected signal. Theoretic values are shown
and compared against measurements.
Finally, inter-pixel properties of a one-dimensional array of CAPD structures are presented, as well as a sample range
image acquired by scanning.
An in depth view is given of time-of-flight distance sensor and read-out circuit implementations. The sensor
is a current assisted photonic demodulator, using majority currents to accelerate generated minority carriers
towards the detecting junctions, and combines an efficient mixer with a sensitive detector. Single ended and
differential configurations of the structure are illustrated. Measurements show a quantum efficiency of 58%, a
DC demodulation contrast of nearly 100% and a contrast of over 40% maintained up till 60 MHz. An improved
embodiment, having an extra drain tap to tune sensitivity, is also presented. With this structure automatic gain
control and improved dynamic range can be achieved. Measurements demonstrate a controllable sensitivity from
maximal to below 1% by changing a sensor control voltage. Secondly design aspects of the read-out circuit are
discussed. A circuit with improved background light suppression and dynamic range is explained, called variable
transimpedance amplifier. Special low pass filters for in-pixel averaging are presented, having a tuneable cut-off
frequency of 10 Hz to 10 kHz and using only 100 μm2. Circuit simulations show a dynamic range of 87 dB, as
well as a background light tolerance up to 10 μA. Combining the circuit with a drain tap sensor yields a dynamic
range of 127 dB. A standard CMOS 0.35 μm proof of principle prototype pixel, measuring 50 μm x 50 μm and
having a 60% fill factor, is presented. Properties, as well as an example image, of a 32x32 CAPD imager are