Lidar method and apparatus with improved signal-to-noise ratio

Lidar apparatus comprising:

• a light source having a source frequency;
• an electrical signal generator configured to generate a digitally-coded electrical signal;
• a modulator configured to impress the digitally-coded electrical signal onto a light beam emitted by the light source to generate a digitally-coded output beam, and to convert the digitally-coded output beam of the light source into a multi-dimensional modulated output beam;
• transmitter optics configured to propagate the multi-dimensional modulated output beam toward a target;
• receiver optics configured to receive the multi-dimensional modulated output beam as reflected by the target;
• an optical demodulator configured to demodulate the reflected multi-dimensional modulated output beam;
• electro-optical conversion circuitry configured to output an electrical signal representing the reflected multi-dimensional modulated output beam;
• and
• digital signal processing circuitry configured to compare the electrical signal representing the reflected multi-dimensional modulated output beam to the digitally-coded electrical signal to determine at least one of (a) range, and (b) velocity, of the target,
• wherein the electrical signal generator comprises phase-coded-modulation circuitry, and wherein the digital signal processing circuitry is configured to determine the velocity of the target by:
• forming a first complex-valued signal from a plurality of dimensions of the reflected multi-dimensional modulated output beam;
• raising the first complex-valued signal to the fourth power to yield a second complex-valued signal;
• generating a power spectrum of the second complex-valued signal;
• identifying a peak frequency of the power spectrum;
• and
• calculating the velocity from a difference between the source frequency and the peak frequency.

A light detection and ranging method comprising:

• generating a digitally-coded electrical signal and impressing the digitally-coded electrical signal onto a light beam emitted by a light source having a source frequency to generate a digitally-coded output beam;
• converting the digitally-coded output beam of the light source into a multi-dimensional modulated output beam;
• propagating the multi-dimensional modulated output beam toward a target;
• receiving the multi-dimensional modulated output beam as reflected by the target;
• demodulating the reflected multi-dimensional modulated output beam;
• electro-optically converting the reflected multi-dimensional modulated output beam and outputting an electrical signal representing the reflected multi-dimensional modulated output beam;
• and
• comparing the electrical signal representing the reflected multi-dimensional modulated output beam to the digitally-coded electrical signal to determine at least one of (a) range to, and (b) velocity of, the target,
• wherein, when the electrical signal comprises a plurality of respective portions, each respective portion representing a respective dimension of the reflected multi-dimensional modulated output beam;
• and
• comparing the electrical signal representing the reflected multi-dimensional modulated output beam to the digitally-coded electrical signal comprises respectively comparing each respective portion of the electrical signal to the digitally-coded electrical signal and outputting a respective comparison signal for each respective portion of the electrical signal.

A light detection and ranging method comprising:

• generating a digitally-coded electrical signal and impressing the digitally-coded electrical signal onto a light beam emitted by a light source having a source frequency to generate a digitally-coded output beam;
• converting the digitally-coded output beam of the light source into a multi-dimensional modulated output beam;
• propagating the multi-dimensional modulated output beam toward a target;
• receiving the multi-dimensional modulated output beam as reflected by the target;
• demodulating the reflected multi-dimensional modulated output beam;
• electro-optically converting the reflected multi-dimensional modulated output beam and outputting an electrical signal representing the reflected multi-dimensional modulated output beam;
• and
• comparing the electrical signal representing the reflected multi-dimensional modulated output beam to the digitally-coded electrical signal to determine at least one of (a) range to, and (b) velocity of, the target,
• wherein generating a digitally-coded electrical signal comprises generating a phase-code-modulated signal, and
• wherein determining the velocity of the target comprises:
• forming a first complex-valued signal from a plurality of dimensions of the reflected multi-dimensional modulated output beam;
• raising the first complex-valued signal to the fourth power to yield a second complex-valued signal;
• generating a power spectrum of the second complex-valued signal;
• identifying a peak frequency of the power spectrum;
• and calculating the velocity from a difference between the source frequency and the peak frequency.