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

Abstract

This paper introduces a new concept for the local oscillator (LO) for the Photon Counting Chirped Amplitude Modulation Lidar (PC-CAML). Rather than using a radio-frequency (RF) analog 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 systems, the new method mixes the single-bit binary counts from the photon counting detector with a single-bit binary LO using an AND binary digital logic gate. This type of LO is called the Digital Logic Local Oscillator (DLLO), and the resulting PC-CAML system is a type of bitstream lidar called bitstream PC-CAML (patent pending).The key advantage of the DLLO in the bitstream PC-CAML 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 PCCAML systems.This paper introduces the DLLO for bitstream PC-CAML concept, presents the initial signal-to-noise-ratio (SNR) theory with comparisons to Monte Carlo simulation results, and makes suggestions for future work on this concept.

Bitstream Photon Counting Chirped AM Lidar with a Dual Unipolar Signal

“…The bitstream PC-CAML with a dual unipolar signal and bipolar DLLO with digital I/Q demodulation architecture discussed in this paper adds complexity to the transmitter and receiver compared to the architectures presented in the previous papers [ref [15][16][17]. With wavelength tagging of the two channels, two sources, or one source and a wavelength shifter are required in the transmitter.…”

“…(The use of CDMA code tagging would require only one source in the transmitter, and one optical filter, one Gm-APD, and one edge-triggered pulse detector in the receiver, but it has other complexities that require investigation in future work.) Whether or not the additional complexity, which may translate to increased size, weight, power, and cost compared to the previous bitstream PC-CAML architectures [ref [15][16][17], is worth the improved SNR will have to be decided by system trade studies for particular systems and applications.…”

“…For the fully modulated unipolar chirped sinusoidal signal there is some signal everywhere except at the exact nulls of the waveform so that the speckle induced amplitude fluctuations cause photon arrival rate fluctuations at almost all points on the signal, and these fluctuations are higher for lower M causing the SNR to be lower for lower M just as seen in the Monte Carlo simulation results and theory predictions for the unipolar chirped sinusoidal signal. [ref [15][16][17] For the sake of brevity, this paper discusses only the dual unipolar chirped sinusoidal signal, whereas reference 15 discussed both the unipolar chirped sinusoidal signal and the unipolar chirped square wave signal. However, the dual unipolar signal may be either a chirped sinusoidal signal or a chirped square wave signal.…”

“…This paper is a follow-up to three previous papers: the first introducing the new Bitstream Photon Counting Chirped Amplitude Modulation (AM) Lidar (PC-CAML) with the unipolar Digital Logic Local Oscillator (DLLO) concept [ref 15], the second introducing the improvement thereof using the bipolar DLLO [ref 16], and the third introducing the improvement of digital Inphase and Quadrature-phase (I/Q) demodulation [ref 17]. Reading the previous papers [ref [15][16][17] before proceeding to read this paper is recommended.…”

“…However, the new architecure still retains the key advantages of the previous bitstream PC-CAML architectures [ref [15][16][17] since it still replaces bulky, power-hungry, and expensive wideband RF analog electronics in the receiver with digital 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 lidaron-a-chip systems and lidar array receivers than previous PC-CAML systems. This paper introduces the dual unipolar signal and bipolar DLLOs with digital I/Q demodulation transceiver architecture for bitstream PC-CAML, and presents the initial SNR theory with comparisons to Monte Carlo simulation results.…”