Methods and systems for delaying optical waves
Coupled-resonator optical waveguides (CROW) can be used to control a speed of an optical signal. In particular, the coupling distance between the resonators can be adjusted to precisely control a group delay of an optical wave. Systems and methods are described to control such coupling distance in a CROW.
1. A system for delaying an optical signal, the system comprising:
a first optical signal path, the first optical signal path being both an input portion for the optical signal and an output portion for the optical signal; and
a second optical signal path, the second optical signal path being coupled resonator optical waveguides (CROW), the CROW comprising a plurality of resonators, wherein each resonator of the plurality of resonators is optically coupled with one or more adjacent resonators at a set coupling distance, and
wherein the first optical signal path is optically coupled with a first resonator of the plurality of resonators at a set coupling distance,
wherein the set coupling distance changes a group velocity of the optical signal in the second optical signal path and the output portion of the first optical signal path,
wherein the plurality of resonators comprises at least three resonators,
wherein each of the set coupling distances match coupling coefficients according to a desired transfer function, the transfer function describing an output optical signal of the system and wherein the coupling coefficients decrease monotonically from the input portion towards the output portion for the optical signal.
2. The system of claim 1 , wherein each set coupling distance is different from each other.
3. The system of claim 1 , wherein the CROW is selected from the group consisting of: ring shaped resonators, spherical resonators, defects in periodic structures, and cavities with partially transmitting mirrors.
4. The system of claim 1 , wherein the CROW is made with silicon, silica, nitride or polymer.
5. The system of claim 1 , wherein the plurality of resonators of the CROW are arranged in a chain or array configuration.
6. The system of claim 1 , further comprising an optical amplifier adapted to amplify the optical signal.
7. The system of claim 1 , wherein the group velocity at the output portion of the first optical signal path is substantially constant along an entire frequency spectrum.
8. A system comprising a plurality of the system according to claim 1 arranged in series such that the delayed optical signal outputted from a first system is adapted to be inputted into a second system.
9. The system of claim 1 , wherein the transfer function is for a Butterworth filter or a Bessel filter.
10. The system of claim 1 , wherein the coupling distances give a constant amplitude and flat group delay for the output optical signal within a desired bandwidth.
11. The system of claim 1 , wherein the coupling coefficients multiplied by a bandwidth parameter results in a constant group delay between a maximum and minimum frequency that are functions of the bandwidth parameter.
12. The system of claim 1 , wherein the plurality of resonators of the CROW are arranged in such a way as to compensate a group velocity dispersion due to different light propagating distances within the CROW as a function of a light frequency in such a way to obtain a constant group delay.
13. The system of claim 9 , wherein the Bessel filter is an all-pass Bessel filter.