Phase-wrapping method for beam steering in optical phased arrays
View Patent ↗A method and apparatus are provided for controlling the phase shifts produced in a binary corporate tree network of the kind, e.g., that can drive a phased array for steering an optical beam. The method employs a novel phase-wrapping technique in which an entire layer of the binary tree is disabled when the phase added in that layer reaches 2π. With that technique, it is possible to economize on electrical control lines and on the use of electric power, while still maintaining the ability to produce arbitrary phases at the output of the tree network.
1. A method, comprising:
injecting an input optical signal into a binary tree network conformed to split the input optical signal into output optical signals distributed over a plurality of output waveguides, wherein the network has a plurality of levels and one or more nodes at each level;
at each of the nodes, splitting incoming light between a phase-shifting path and a non-phase-shifting path, wherein each of the phase-shifting paths passes through a primary phase shifter at the level to which the node belongs; and
applying control signals to at least some of the primary phase shifters so as to produce controlled phase shifts;
wherein all primary phase shifters at each level receive the same control signal, thereby to produce a level-specific phase shift that is the same for all primary phase shifters at that level; and
wherein the control signals are applied subject to a condition that when a level-specific phase shift increases to 2π, it must be reset to zero.
2. The method of claim 1 , wherein:
the plurality of output waveguides drives an antenna array having a beam direction; and
the control signals are varied so as to sweep the beam direction.
3. The method of claim 2 , wherein any level-specific phase shift that is reset to zero while sweeping the beam direction is maintained at zero until the sweeping terminates or changes direction.
4. The method of claim 1 , wherein:
the binary tree network has a first level, a last level, and at least one intermediate level between the first and last levels; and
unless it has been reset to zero, the level-specific phase shift at the first and each intermediate level is double the level-specific phase shift at the level that next follows it.
5. The method of claim 1 , further comprising: operating a plurality of active corrective phase shifters that are arranged to correct phase errors in the output optical signals.
6. The method of claim 5 , wherein the active corrective phase shifters are situated in non-phase-shifting paths of the binary tree network.
7. The method of claim 1 , wherein passive corrective phase shifters are used to correct phase errors in the output optical signals.
8. Apparatus, comprising:
an optical binary tree network conformed to split an input optical signal into output optical signals distributed over a plurality of output waveguides; and
a control circuit arranged for applying control signals to primary phase shifters in the optical binary tree network, thereby to produce respective controlled phase shifts, wherein:
the network has a plurality of levels and one or more nodes at each level;
incoming light is split at each of the nodes between a phase-shifting path and a non-phase-shifting path;
each of the phase-shifting paths passes through a primary phase shifter at the level to which the node belongs;
the control circuit is arranged to deliver the same control signal to all primary phase shifters at each level, thereby to produce a level-specific phase shift that is the same for all primary phase shifters at that level; and
the control circuit comprises a tangible medium in which is embodied a condition that when a level-specific phase shift increases to 2π, it must be reset to zero.
9. The apparatus of claim 8 , wherein:
the plurality of output waveguides drives an antenna array having a beam direction;
the control signals are variable in a manner that can sweep the beam direction; and
the tangible medium further embodies a condition that any level-specific phase shift that is reset to zero while sweeping the beam direction must be maintained at zero until the sweeping terminates or changes direction.
10. The apparatus of claim 8 , wherein:
the binary tree network has a first level, a last level, and at least one intermediate level between the first and last levels; and
the tangible medium further embodies a condition that unless it has been reset to zero, the level-specific phase shift at the first and each intermediate level must be double the level-specific phase shift at the level that next follows it.
11. The apparatus of claim 8 , further comprising a plurality of corrective phase shifters arranged to correct phase errors in the output optical signals.
12. The apparatus of claim 8 , wherein the plurality of corrective phase shifters comprises active phase shifters.
13. The apparatus of claim 8 , wherein the plurality of corrective phase shifters comprises passive phase shifters.
14. The method of claim 8 , wherein the corrective phase shifters are situated in non-phase-shifting paths of the binary tree network.