HITLESS TUNING AND SWITCHING OF OPTICAL RESONATOR AMPLITUDE AND PHASE RESPONSES

• US 20100209038A1
• Filed: 03/26/2008
• Published: 08/19/2010
• Est. Priority Date: 03/26/2007
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Popovic, Milos, Watts, Michael R.
• Granted Patent: US 8,655,114 B2
• Time in Patent Office: Days
• US Class Current: 385/1
• CPC Class Codes: G02B 2006/12145 Switch
• CPC Class Codes: G02B 6/12007 forming wavelength selective elements, e.g. multiplexer, demultiplexer
• CPC Class Codes: G02F 1/0147 based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: G02F 1/212 Mach-Zehnder type
• CPC Class Codes: G02F 1/3132 of directional coupler type
• CPC Class Codes: G02F 1/3133 the optical waveguides being made of semiconducting materials
• CPC Class Codes: G02F 2202/103 a-Si
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: G02F 2203/15 involving resonance effects, e.g. resonantly enhanced interaction
• CPC Class Codes: G02F 2203/585 Add/drop devices
• CPC Class Codes: H04J 14/021 Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]

Abstract

A hitless tunable filter may include a ring resonator, a Mach-Zehnder coupler, and first and second phase shifters. The Mach-Zehnder coupler may include a switching arm that is coupled to the ring resonator at first and second coupling points. The first phase shifter may be used to introduce a first phase shift to light propagating through the ring resonator, while the second phase shifter may be used to introduce a second phase shift to light propagating through the Mach-Zehnder coupler. The Mach-Zehnder coupler may have a free spectral range substantially equal to a free spectral range of the ring resonator divided by a non-negative integer.

Claims

1. A hitless tunable filter, comprising:

a ring resonator;

a first phase shifter for introducing a first phase shift to light propagating through the ring resonator;

a Mach-Zehnder coupler comprising a switching arm coupled to the ring resonator at first and second coupling points; and

a second phase shifter for introducing a second phase shift to light propagating through the Mach-Zehnder coupler,

wherein the Mach-Zehnder coupler has a free spectral range substantially equal to a free spectral range of the ring resonator divided by a non-negative integer.

2. The filter of claim 1, wherein the free spectral range of the Mach-Zehnder coupler is substantially equal to the free spectral range of the ring resonator.

3. The filter of claim 1, wherein the free spectral range of the Mach-Zehnder coupler is infinite.

4. The filter of claim 1 further comprising a drop waveguide coupled to the ring resonator.

5. The filter of claim 1, wherein the Mach-Zehnder coupler is configured to introduce a phase shift of approximately 180°

to the light propagating therethrough in addition to the second phase shift introduced by the second phase shifter.

6. The filter of claim 1, wherein the ring resonator and the Mach-Zehnder coupler share a waveguide section between the first and second coupling points.

7. The filter of claim 6, wherein the first phase shifter is located at a point proximate to the ring resonator and away from the shared waveguide section.

8. The filter of claim 6, wherein the second phase shifter is located at a point proximate to the Mach-Zehnder switching arm and away from the shared waveguide section.

9. The filter of claim 6 further comprising a third phase shifter located at a point proximate to the shared waveguide section.

10. The filter of claim 9 further comprising a fourth phase shifter located at a point proximate to the Mach-Zehnder switching arm and away from the shared waveguide section.

11. The filter of claim 6, wherein the first and second phase shifters each comprise a heater element.

12. The filter of claim 11, wherein the first phase shifter is thermooptically coupled to a portion of the ring resonator other than the shared waveguide section and the second phase shifter is thermooptically coupled to the Mach-Zehnder switching arm.

13. The filter of claim 11, wherein the first phase shifter is thermooptically coupled to the entire ring resonator and to a portion of the Mach-Zehnder switching arm located proximate to the shared waveguide section and the second phase shifter is thermooptically coupled to the Mach-Zehnder switching arm.

14. The filter of claim 11, wherein the first phase shifter is thermooptically coupled to a portion of the ring resonator other than the shared waveguide section and to the Mach-Zehnder switching arm and the second phase shifter is thermooptically coupled to the Mach-Zehnder switching arm.

15. The filter of claim 11, wherein the first phase shifter is thermooptically coupled to the entire ring resonator and to the entire Mach-Zehnder switching arm and the second phase shifter is thermooptically coupled to the Mach-Zehnder switching arm.

16. A hitless tunable higher-order filter, comprising:

a plurality of ring resonators, each ring resonator being coupled to another ring resonator;

a first variable Mach-Zehnder coupler, for providing an input mechanism, coupled to a first ring resonator;

a second variable Mach-Zehnder coupler, for providing a loss mechanism, coupled to a second ring resonator; and

a drop waveguide coupled to at least one of the plurality of ring resonators.

17. The filter of claim 16, wherein the first ring resonator and the second ring resonator are the same ring resonator.

18. The filter of claim 16, wherein the drop waveguide comprises a third variable Mach-Zehnder coupler.

19. The filter of claim 18, wherein at least one of the first variable Mach-Zehnder coupler and the third variable Mach-Zehnder coupler is configured to introduce a phase shift of approximately 180°

to light propagating therethrough.

20. A method for switching a hitless tunable filter from a first state to a second state, the method comprising:

a) providing a hitless tunable filter, comprising;

i) a ring resonator;

ii) a first heater element for heating at least the ring resonator;

iii) a Mach-Zehnder coupler comprising a switching arm coupled to the ring resonator at first and second coupling points; and

iv) a second heater element for heating at least the Mach-Zehnder switching arm;

b) actuating the first heater element and the second heater element substantially simultaneously to tune the filter to a desired target channel wavelength; and

c) switching the filter on at the desired target channel wavelength by further actuating the second heater element.

23. The method of claim 20 further comprising switching the filter off at the desired target channel wavelength prior to performing step b).

24. The method of claim 23, wherein the filter is switched off by actuating the second heater to decrease its temperature output and thereby subtract a phase shift of approximately 180°

from light propagating through the Mach-Zehnder coupler if the filter is less than one-half the free spectral range of the ring resonator away from the filter'"'"'s wavelength when both the first and second heater elements are shut off.

25. The method of claim 23, wherein the filter is switched off by actuating the second heater to increase its temperature output and thereby add a phase shift of approximately 180°

to light propagating through the Mach-Zehnder coupler if the filter is more than one-half the free spectral range of the ring resonator away from the filter'"'"'s wavelength when both the first and second heater elements are shut off.

21. The method of 20, wherein the second heater element is actuated in step c) to increase its temperature output and thereby add a phase shift of approximately 180°

to light propagating through the Mach-Zehnder coupler if the filter was tuned in step b) to a desired target channel wavelength that was less than one-half the free spectral range of the ring resonator away from the filter'"'"'s wavelength when both the first and second heater elements are shut off.

22. The method of 20, wherein the second heater element is actuated in step c) to decrease its temperature output and thereby subtract a phase shift of approximately 180°

from light propagating through the Mach-Zehnder coupler if the filter was tuned in step b) to a desired target channel wavelength that was more than one-half the free spectral range of the ring resonator away from the filter'"'"'s wavelength when both the first and second heater elements are shut off.

26. A method for switching a hitless tunable filter from a first state to a second state, the method comprising:

a) providing a hitless tunable filter, comprising;

i) a ring resonator;

ii) a Mach-Zehnder coupler comprising a switching arm coupled to the ring resonator at first and second coupling points;

iii) a first heater element for heating at least the ring resonator and the Mach-Zehnder switching arm; and

iv) a second heater element for heating the Mach-Zehnder switching arm;

b) actuating the first heater element to tune the filter to a desired target channel wavelength; and

c) switching the filter on at the desired target channel wavelength by actuating the second heater element.