Arbitrary optical waveform generation utilizing optical phase-locked loops
AssigneesTelaris Inc., California Institute of Technology
InventorsGeorge Rakuljic, Naresh Satyan, Arseny Vasilyev, Ammon Yariv
Life of this patent
Estimating the term…
Abstract
This invention relates to opto-electronic systems using semiconductor lasers driven by optical phase-locked loops that control the laser's optical phase and frequency. Feedback control provides a means for precise, wideband control of optical frequency and phase, augmented further by four wave mixing stages and digitally stitched independent optical waveforms for enhanced tunability.
Claims22
An opto-electronic swept-frequency laser system having a wide frequency range and precise control of the frequency of optical emission within the range, the system comprising:
- a semiconductor laser emitting in the optical spectrum, said laser including an injection current input and providing an output of controllable frequency in response thereto;
- an optical feedback circuit coupled to control the output of the semiconductor laser by varying the injection current input thereto;
- the feedback circuit including a signal divider receiving the laser output and providing a major power output signal and a fractional feedback signal therefrom;
- an interferometer receiving the feedback signal from the divider and providing an optical beat signal that varies in accordance with the laser output frequency;
- an optical mixer responsive to the optical beat signal for generating an RF beat signal in response to the optical beat signal;
- a reference oscillator providing an electronic reference signal;
- an electronic mixer receiving as one input the RF beat signal output from the optical mixer and the electronic reference signal as another input, to provide a mixed RF output signal;
- a circuit responsive to the electronic reference signal for providing a time-varying offset signal for optical frequency predistortion of the injection current to the laser in synchronism with the electronic reference signal, and
- an integrator circuit receiving both the RF output from the electronic mixer and the time varying offset signal, and having an output coupled to the injection current input of the semiconductor laser to provide precise control of the optical frequency thereof.
A method of generating a swept frequency signal using an optical laser having an injection current input to provide an inherently nonlinear response comprising the steps of:
- generating a coherent optical laser beam subject to optical frequency nonlinearity;
- dividing the laser beam into a power beam comprising a substantial majority of the laser output and a feedback beam comprising the remainder of the laser output;
- generating an optical beat signal by interferometrically establishing the signal differential between delayed and undelayed portions of the feedback beam;
- converting the optical beat signal into a responsive RF signal variation
- generating a variable frequency RF reference signal changing in frequency in repetitive cycles at a selected repetition rate;
- mixing the optical beat signal with the variable frequency RF reference signal to generate an output error signal;
- generating an offset signal varying at a repetition rate that varies concurrently with the RF reference signal rate;
- integrating the offset signal and output error signal from the mixing step to provide an injection current signal;
- modifying the laser optical frequency with the injection current to correct optical phase and frequency nonlinearities, and
- resetting the integration in synchronism with the frequency sweep cycle.
A laser system providing an agile, high coherence, swept frequency optical output at a high repetition rate with precise control over a wide frequency range, comprising:
- a semiconductor laser controllable by varying an injection current at its input;
- a reference signal source enabling an optical swept frequency output at a high repetition rate and varying between wide frequency limits;
- an opto-electronic feedback loop including an interferometer receiving a portion of the laser output and providing an optical beat signal, said loop further including an electronic mixer receiving both the reference signal and the optical beat signals, and providing an electronic beat signal,
- the opto-electronic feedback loop further including an optical phase/frequency pre-distortion signal circuit including a cyclic offset source synchronized to the reference signal and an integrator circuit receiving the electronic beat signal and the cyclic offset signal and providing the current injection signal to the semiconductor laser.
Dependencies are inferred from the claim text.