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Monolithic integrated optical time delay network for antenna beam steering
| Details |
Inventors: Yap, Daniel; Ng, Willie W.; Hayes, Robert R.;
Assignee: Hughes Aircraft Company (Los Angeles, CA)
Primary Examiner: Ullah; Akm E.
Assistant Examiner:
Attorney, Agent or Firm: Duraiswamy; V. D., Denson-Low; W. K.
A time delay network for phased array antenna beam steering employs a waveguide network as the delay element in a monolithic integration with other optical and electronic elements on a single substrate. A plurality of optical time delay stages are cascaded to form the delay network, with each stage having a selectable delay time. Each stage preferably has a reference or nominal time delay branch, and at least one other finite time delay branch. The lengths of the delay waveguides vary from stage to stage, permitting a high time delay resolution with a relatively small number of separate waveguides. The desired time delay is selected either by directing the modulated laser light into only one of the waveguide branches in each stage by means of waveguide switches or by splitting the light into all the waveguide branches of a stage and then activating only the detector connected to the desired delay waveguide. A variety of cascading schemes and waveguide layouts can be used to implement the time delay network. |
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DETAILED DESCRIPTION The present invention seeks to provide an optical time delay network for phased array antennas that is lighter and more compact than previous systems, does not suffer from beam squint or signal dispersion, achieves high resolution with only a limited number of delay lines, provides more uniform device characteristics and optical coupling, and offers improved ruggedness and greater ease of manufacturing.
In accordance with the invention, time delays are implemented with an optical delay network.
The various elements of the system are monolithically integrated on a semiconductor substrate.
The system includes a plurality of cascaded optical time delay stages that each have a plurality of different selectable delay times.
Each stage corresponds to one or more bits of resolution, with a maximum overall delay time for the network substantially equal to the sum of the maximum stage delays.
A switch mechanism selects delay times for each of the stages to produce a desired overall delay.
One or more lasers directs an electrically modulated optical beam into the optical waveguides of the delay stages, with one or more photodetectors detecting the delayed optical output and transducing it to an output electrical signal.
The time delay waveguides, switches, lasers, modulating mechanism and detectors are all monolithically integrated on the semiconductor substrate.
The electronics may also be integrated on the same substrate.
In general, each of the time delay stages is subdivided into a plurality of unequal length optical waveguide branches which include one or more waveguide delay segments that produce the specified delay times for that stage, and a reference segment that produces a reference delay time which is substantially less than the specified delay.
One branch of each stage is selected for inclusion in the overall delay network and provides the delay time for that stage.
The sum of the separate stage delay times is the desired overall time delay for the network.
For a base-p time delay system, the specified waveguide delay branches for the different stages vary in length in proportion to p
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Multiplexer-related 
