System and method of optical scanning with detection of return signals using a star coupler
A LIDAR system or the like uses a star coupler to distribute an input light beam over a steerable array. The input light beam is injected through an input signal waveguide on the input side of the star coupler. The light returning after reflecting from external objects is directed back through the star coupler to one or more waveguides on the input side. Return light is detected in one or more waveguides on the input side that are displaced from the input signal waveguide. In embodiments, the beam direction of the steerable array changes during the round-trip transit time of the returning light. This causes the returning light to arrive off-axis, which in turn causes it to couple into one or more of the displaced input-side waveguides instead of coupling back into the input signal waveguide.
1. A method of optical scanning of the kind in which a controllable phase shift is distributed across an array of output waveguides and used to steer a send beam of light, in which a return beam of light is detected after reflecting from external objects, and in which a star coupler is used to distribute an input beam of light into the array of output waveguides, comprising:
injecting the input beam of light into an input signal waveguide on an input side of the star coupler, wherein the input signal waveguide is part of an input waveguide array comprising the input signal waveguide and one or more additional input-side waveguides;
sweeping the send beam of light by controlling the controllable phase shift; and
detecting light from the return beam that has coupled into at least one of the additional input-side waveguides, wherein:
the return beam reenters the star coupler through the array of output waveguides.
2. The method of claim 1 , wherein the coupling of light from the return beam into at least one of the additional input-side waveguides is effectuated by the star coupler without additional optical beam-splitting elements.
3. The method of claim 2 , wherein the detecting of light from the return beam is performed concurrently with the sweeping of the send beam of light.
4. The method of claim 1 , wherein the send beam of light is transmitted by an array of antenna elements, and the return beam of light is received by the same array of antenna elements.
5. The method of claim 1 , wherein:
the input waveguide array comprises two additional input-side waveguides placed on opposite sides of the input signal waveguide;
the sweeping of the send beam comprises sweeping in a first direction and sweeping in a second direction opposite to the first direction;
the detecting of light from the return beam comprises detecting light from one of the additional input-side waveguides while the sweeping is in the first direction; and
the detecting of light from the return beam further comprises detecting light from the other of the additional input-side waveguides while the sweeping is in the second direction.
6. The method of claim 1 , wherein:
the input waveguide array comprises two or more additional input-side waveguides; and
the detecting of light from the return beam comprises detecting light from each of the two or more additional input-side waveguides while sweeping the send beam of light in one sweep direction.
7. Apparatus for optical scanning, comprising:
a star coupler in which an input waveguide array comprises an input signal waveguide and one or more additional input-side waveguides, and in which an output waveguide array comprises a plurality of output waveguides; and
an array of optical antenna elements adapted for transmitting send signals and receiving return signals, in which each optical antenna element is optically coupled to a respective output waveguide, wherein:
a respective phase shifter is conformed to controllably adjust a phase shift in each of the output waveguides, whereby a steerable send beam of transmitted light can be defined;
the input signal waveguide is adapted to receive an input beam of light from a light source in order for said input beam of light to be distributed by the star coupler into the array of output waveguides; and
a respective optical detector is optically coupled to each of the one or more additional input-side waveguides for detecting light from return signals that has reentered the star coupler through the output waveguides.
8. The apparatus of claim 7 , wherein each optical detector is optically coupled to a respective additional input-side waveguide without additional optical beam-splitting elements.
9. The apparatus of claim 7 , conformed for sweeping the steerable send beam of transmitted light, and conformed to perform said sweeping while concurrently detecting light from return signals.
10. The apparatus of claim 7 , conformed for sweeping the steerable send beam of transmitted light, and conformed to perform said sweeping while concurrently detecting light from return signals in two or more additional input-side waveguides.