Bitstream Photon Counting Chirped AM Lidar with a Digital Logic Local Oscillator

Concept, Various Configurations, Theory, Simulations and Proof-of-Concept Experiment

Abstract

This paper introduces the bitstream Photon Counting Chirped Amplitude Modulation (AM) Lidar (PC-CAML) with a Digital Logic Local Oscillator (DLLO) concept in various configurations.

Rather than using a radio-frequency (RF) analog local oscillator (LO) applied electronically either in post-detection mixing or via opto-electronic mixing (OEM) at the detector, or applied via pre-detection mixing using an optical intensity modulator, as in previous PC-CAML systems, the new method mixes the single-bit binary counts from the photon counting detector with a single-bit binary LO using a digital logic gate. This type of LO is called the Digital Logic Local Oscillator (DLLO), and the resulting system is called bitstream PC-CAML.

The key advantage of the DLLO is that it replaces bulky, power-hungry, and expensive wideband RF analog electronics with single-bit digital logic components that can be implemented in inexpensive silicon complementary metal-oxide-semiconductor (CMOS) read-out integrated circuits (ROICs) to make the bitstream PC-CAML with a DLLO more suitable for compact lidar-on-a-chip systems and lidar array receivers than previous PC-CAML systems.

This paper presents the DLLO for bitstream PC-CAML concept along with an initial signal-to-noise ratio (SNR) theory with comparisons to Monte Carlo simulation results and initial proof-of-concept experimental results. Using the simulation results, the improvements in SNR provided by using a bipolar DLLO and digital I/Q demodulation configuration compared to the original single channel unipolar DLLO without digital I/Q demodulation configuration, and provided by using the new concept of a dual unipolar (DU) transmitted signal to yield a bipolar signal in the receiver are demonstrated.