Photonic technique for generating arbitrary waveforms
View Patent ↗In a radio frequency (RF)-photonic arbitrary waveform generator (AWG), an optical carrier signal is phase-modulated using an arbitrary waveform optical phase generator (AWPOG), which may include, e.g., sequential optical phase modulators. The phase-modulated optical signal is combined with a version of the optical carrier signal to yield an optical waveform, whose amplitude varies with a phase shift introduced by the AWPOG to the optical carrier signal. By manipulating electrical inputs to the AWPOG which control the phase shift, the optical waveform can be arbitrary shaped. The optical waveform may then be converted to an electrical waveform having a radio frequency.
1. An apparatus, comprising:
a phase-modulation device for phase-modulating a first optical carrier signal having a given phase, resulting in a phase-modulated optical signal whose phase differs from the first phase by a phase value which is controllable by one or more inputs to the device, the phase-modulation device comprising a plurality of electrodes configured to produce a plurality of discrete phase shifts on the first optical carrier signal based on the inputs, such that the phase value is based on a sum of the plurality of discrete phase shifts; and
a combiner element for combining a second optical carrier signal having the given phase with the phase-modulated optical signal to provide a waveform whose amplitude varies with the phase value;
wherein the phase-modulation device comprises a plurality of optical phase modulators arranged sequentially over an optical path configured to propagate the first optical carrier signal; and
wherein at least one of the optical phase modulators comprise at least one of the electrodes.
2. The apparatus of claim 1 wherein the waveform is optical, further comprising an optical detector for converting the waveform to an electrical waveform.
3. The apparatus of claim 1 wherein a first of the plurality of electrodes is configured to produce a first phase shift and a second of the plurality of electrodes is configured to produce a second phase shift that is about twice said first phase shift.
4. The apparatus of claim 1 wherein the plurality of electrodes are configured such that the sum has a maximum value less than about 2π radians.
5. The apparatus of claim 1 wherein each of the electrodes is associated with a respective one of a plurality of portions of the optical path, each optical path portion having a different length.
6. The apparatus of claim 5 wherein each optical path portion has a length that is about twice as long as a path length of a next shorter optical path portion.
7. The apparatus of claim 1 wherein the plurality of electrodes include n electrodes configured to shift the first phase by any of 2 n different phase shift values.
8. The apparatus of claim 7 wherein an incremental phase shift between any two subsequent phase shift values is about π/2 n-1 radians.