Apparatus and method for generating frequency-locked optical comb sources
View Patent ↗Frequency-locked optical comb sources are provided that utilize recirculating frequency shifting based on frequency conversion in a modulator, together with a filter. The filter may be a wavelength notch filter and include a plurality of notches. An example apparatus includes a coupler, an I/Q modulator, and a filter. A first input of the coupler receives a first input optical carrier having a first frequency, and a second input of the coupler re receives a set of frequency-shifted carriers from the filter. The input optical carrier may have a plurality of frequencies. The I/Q modulator shifts the frequency of a first output of the coupler. The filter filters modulated output from the I/Q modulator thereby limiting the frequency-shifted carriers to be within an optical bandwidth. A second output of the coupler provides a plurality of frequency-locked carriers containing the first input optical carrier and the set of frequency-shifted carriers.
1. An apparatus comprising:
a coupler;
an I/Q modulator; and
a wavelength notch filter that has at least one narrow wavelength blocking band;
wherein a first input of the coupler is configured to receive at least a first input optical carrier having a first frequency, and wherein a second input of the coupler is configured to receive a set of frequency-shifted carriers from the filter;
wherein the I/Q modulator is configured to shift the frequency of a first output of the coupler;
wherein the filter is configured to filter shifted output from the I/Q modulator to limit the optical bandwidth of the set of frequency-shifted carriers;
wherein a second output of the coupler is configured to provide a plurality of frequency-locked carriers containing the first input carrier and the set of frequency-shifted carriers, and
wherein a 3-dB bandwidth of the at least one narrow wavelength blocking band is about equal to the spacing between the frequency-shifted carriers.
2. The apparatus of claim 1 wherein the wavelength notch filter is an asymmetric wavelength interleaver or a fiber Bragg grating (FBG) array.
3. The apparatus of claim 1 wherein the optical filter is a notch filter and the coupler is configured to receive a plurality of input optical carriers, the plurality of input optical carriers spaced by at least one blocking band of the optical filter.
4. The apparatus of claim 1 further comprising:
a multi-carrier generator, the second output of the coupler provided to the multi-carrier generator.
5. The apparatus of claim 4 wherein the multi-carrier generator is a 2-carrier generator.
6. The apparatus of claim 1 wherein the coupler, the I/Q modulator, and the filter are polarization-maintaining components.
7. The apparatus of claim 1 wherein the I/Q modulator and the filter are photonic integrated circuits.
8. The apparatus of claim 1 further comprising:
an optical amplifier configured to amplify the shifted output from the I/Q modulator.
9. The apparatus of claim 1 further comprising:
a modulator array, wherein the modulator array is configured to generate multi-carrier signal under the optical OFDM condition based on the plurality of frequency-locked carriers.
10. The apparatus of claim 1 wherein the coupler, the I/Q modulator and the filter form a recirculating frequency shifter (RFS), and wherein dispersion per round trip (D RT ) of the RFS is controllable.
11. The apparatus of claim 10 wherein the dispersion per round trip D RT is about λ/(8cΔλ), where c is the speed of light, λ is the wavelength of the first input optical carrier, and λ is the wavelength spacing of the frequency-locked carriers.
12. The apparatus of claim 1 wherein the coupler, the I/Q modulator and the filter form a recirculating frequency shifter (RFS), and wherein phase delay per round trip (φ RT ) of the RFS is stabilized.
13. The apparatus of claim 12 wherein the phase delay per round trip φ RT of the RFS is stabilized to approximately zero.
14. A method comprising:
at a frequency-locked optical comb source:
coupling at least a first input optical carrier having a first frequency and a set of frequency-shifted carriers to generate a first coupled output and a second coupled output;
frequency-shifting the first coupled output; and
filtering the first coupled output that has been frequency-shifted to limit its optical bandwidth to generate the set of frequency-shifted carriers, the filtering being performed by a wavelength notch filter that has at least one narrow wavelength blocking band,
wherein the second coupled output provides a plurality of frequency-locked carriers containing the first input optical carrier and the set of frequency-shifted carriers; and
wherein the 3-dB bandwidth of the narrow wavelength blocking band is about the spacing between the frequency-shifted carriers.
15. The method of claim 14 further comprising:
multiplying the plurality of frequency-locked carriers using a multi-carrier generator.
16. The method of claim 14 wherein dispersion per round trip (D RT ) is controlled.
17. The method of claim 14 wherein phase delay per round trip (φ RT ) is stabilized.
18. The method of claim 14 wherein the at least a first input optical carrier comprises a plurality of input optical carriers spaced by the at least one narrow wavelength blocking band.
19. An apparatus comprising:
a coupler;
an I/Q modulator; and
a filter,
wherein a first input of the coupler is configured to receive at least a first input optical carrier having a first frequency, and wherein a second input of the coupler is configured to receive a set of frequency-shifted carriers from the filter;
wherein the I/Q modulator is configured to shift the frequency of a first output of the coupler;
wherein the filter is configured to filter shifted output from the I/Q modulator to limit the optical bandwidth of the set of frequency-shifted carriers;
wherein a second output of the coupler is configured to provide a plurality of frequency-locked carriers containing the first input carrier and the set of frequency-shifted carriers; and
wherein the coupler, the I/Q modulator and the filter form a recirculating frequency shifter (RFS), and wherein dispersion per round trip (D RT ) of the RFS is controllable.
20. An apparatus comprising:
a coupler;
an I/Q modulator; and
a filter,
wherein a first input of the coupler is configured to receive at least a first input optical carrier having a first frequency, and wherein a second input of the coupler is configured to receive a set of frequency-shifted carriers from the filter,
wherein the I/Q modulator is configured to shift the frequency of a first output of the coupler,
wherein the filter is configured to filter shifted output from the I/Q modulator to limit the optical bandwidth of the set of frequency-shifted carriers,
wherein a second output of the coupler is configured to provide a plurality of frequency-locked carriers containing the first input carrier and the set of frequency-shifted carriers, and
wherein the coupler, the I/Q modulator and the filter form a recirculating frequency shifter (RFS), and wherein phase delay per round trip (φ RT ) of the RFS is stabilized to approximately zero.
21. A method comprising:
at a frequency-locked optical comb source:
coupling at least a first input optical carrier having a first frequency and a set of frequency-shifted carriers to generate a first coupled output and a second coupled output;
frequency-shifting the first coupled output;
filtering the first coupled output that has been frequency-shifted to limit its optical bandwidth to generate the set of frequency-shifted carriers,
wherein the second coupled output provides a plurality of frequency-locked carriers containing the first input optical carrier and the set of frequency-shifted carriers; and
wherein the coupling, frequency-shifting and filtering provide a recirculating frequency shifter (RFS), and wherein dispersion per round trip (D RT ) of the RFS is controllable.