Silicon-based tunable single passband optical filter

• US 20040033003A1
• Filed: 08/16/2002
• Published: 02/19/2004
• Est. Priority Date: 08/16/2002
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Liu, Ansheng
• Granted Patent: US 7,245,792 B2
• Time in Patent Office: Days
• US Class Current: 385/14
• CPC Class Codes: G02B 6/124 Geodesic lenses or integrated gratings
• CPC Class Codes: G02B 6/29317 Light guides of the optical fibre type
• CPC Class Codes: G02B 6/29322 Diffractive elements of the tunable type G02B6/02195 takes precedence; optical modulation devices based on a change of the optical properties of the medium G02F1/00
• CPC Class Codes: G02B 6/29359 Cavity formed by light guide ends, e.g. fibre Fabry Pérot [FFP]
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35

Abstract

A tunable optical filter includes a tunable Fabry-Perot (FP) filter, two tunable waveguide Bragg gratings (WBGs) and a 2×2 3-dB coupler. In one embodiment, the WBGs are implemented in a silicon substrate using polysilicon filled trenches. The FP filter is implemented with two silicon nitride trench WBGs with a gap region between them. The FP filter and the WBGs are respectively tuned to transmit and reflect a selected wavelength. A broadband optical signal is propagated into a first port of the coupler. The coupler propagates half of the beam to one WBG and the other half to the other WBG. The WBGs reflect these portions back to the coupler, which then propagates the reflected portions to the FP filter.

Claims

1. An apparatus, comprising:

a semiconductor substrate;

a waveguide disposed in the semiconductor substrate, the waveguide having a core;

a first reflector and a second reflector disposed in the waveguide defining a resonator region between the first and second reflector, the first and second reflectors including a plurality of regions formed in the core of a material having a refractive index different from that of the core, wherein any resonant wavelengths of an optical signal propagated in the waveguide to the first and second reflectors propagates through the first and second reflectors with substantially no loss.

2. The apparatus of claim 1 wherein the core comprises silicon and the material of the plurality of regions comprises silicon nitride.

3. The apparatus of claim 1 further comprising a heating element disposed proximate the resonator region.

4. The apparatus of claim 1 wherein the semiconductor substrate is part of a silicon-on-insulator (SOI) wafer, the waveguide having a cladding layer formed from the insulator of the SOI wafer.

5. The apparatus of claim 3 further comprising another cladding layer formed on the semiconductor substrate.

6. The apparatus of claim 2 wherein the resonator region has a length of approximately one hundred microns.

7. The apparatus of claim 2 wherein the first and second reflectors have a length along the waveguide of approximately 20 microns.

8. The apparatus of claim 1 wherein each region of the plurality of regions has a width of approximately one micron.

9. An integrated circuit Fabry-Perot (FP) filter, comprising:

a semiconductor layer having a first region; and

a first reflector and a second reflector formed in the semiconductor layer at opposite ends of the first region, the first and second reflectors including trenches formed in the semiconductor layer and filled with a material having a refractive index different from that of the semiconductor layer.

10. The integrated circuit FP filter of claim 9 wherein the semiconductor layer comprises crystalline silicon disposed above an insulator layer of a silicon-on-insulator (SOI) wafer, and the material of the trenches comprises silicon nitride.

11. The integrated circuit FP filter of claim 10 wherein the semiconductor layer is a core layer of a rib waveguide.

12. An integrated circuit interferometer, comprising:

a first waveguide formed in a semiconductor substrate;

a first grating formed in the semiconductor substrate;

a second grating formed in the semiconductor substrate; and

a coupler having a first port, a second port and a third port, the first, second and third ports formed in the semiconductor substrate, wherein the first, second and third ports are operatively coupled to the first waveguide, the first grating and the second grating, respectively, the coupler to cause first and second portions of an optical signal propagated to the coupler via the first waveguide to propagate to the first and second gratings, respectively.

13. The integrated circuit interferometer of claim 12 further comprising an optical filter device operatively coupled to a fourth port of the coupler.

14. The integrated circuit interferometer of claim 13 wherein the coupler comprises a multimode interference (MMI) device.

15. The integrated circuit interferometer of claim 13 wherein the coupler is a resonant waveguide coupler.

16. The integrated circuit interferometer of claim 13 wherein the optical filter device comprises a Fabry-Perot filter.

17. The integrated circuit interferometer of claim 16 wherein the Fabry-Perot filter includes:

a first region formed in the semiconductor substrate; and

a first reflector and a second reflector formed in the semiconductor substrate at opposite sides of the first region, the first and second reflectors including regions formed in the semiconductor substrate, the regions being of a material having a refractive index different from that of the semiconductor substrate.

18. A wavelength division multiplexed (WDM) system comprising:

an optical signal source; and

a tunable optical filter to receive an optical signal from the optical signal source, the optical filter comprising;

a coupler disposed on a semiconductor substrate, the coupler having a first port, a second port, a third port and a fourth port, the coupler to receive the optical signal at the first port and propagate first and second portions of the optical signal to the second and third ports, respectively, the first and second portions having substantially equal power,

a first tunable grating disposed on the semiconductor substrate to receive the first portion from the second port of the coupler and reflect a third portion of the first portion having a selected wavelength back to the coupler,

a second tunable grating disposed on the semiconductor substrate to receive the second portion from the third port of the coupler and reflect a fourth portion of the second portion having the selected wavelength back to the coupler, and

a tunable Fabry-Perot filter disposed on the semiconductor substrate to receive reflected signals from the fourth port of the coupler, the Fabry-Perot filter having a resonant wavelength equal to the selected wavelength.

19. The WDM system of claim 18 wherein the tunable Fabry-Perot filter includes:

a first region formed in the semiconductor substrate; and

a first reflector and a second reflector formed in the semiconductor substrate at opposite sides of the first region, the first and second reflectors including regions formed in the semiconductor substrate and filled with a material having a refractive index different from that of the semiconductor substrate.

20. The WDM system of claim 19 wherein the tunable Fabry-Perot filter includes a structure disposed proximate to the first region to selectively alter a refractive index of the first region.

21. The WDM system of claim 20 wherein the structure includes a heating element.

22. The WDM system of claim 18, wherein the tunable Fabry-Perot filter and the first and second tunable gratings are each part of a single mode silicon rib waveguide.

23. A method of fabricating a Fabry-Perot filter, comprising:

forming a planar waveguide in a semiconductor substrate having a core layer;

forming a pair of reflectors in the planar waveguide with a resonant region between the pair of reflectors.

24. The method of claim 23 wherein forming a pair of reflectors further comprises forming a plurality of regions in the core layer of a material having a refractive index different from that of the core layer.

25. The method of claim 24, wherein the core comprises silicon and the plurality of regions comprise silicon nitride.

26. The method of claim 23 further comprising disposing a heating element proximate the resonant region.

27. A method, comprising:

propagating a multiple wavelength optical signal into a waveguide formed in a semiconductor substrate;

splitting the optical signal into first and second substantially equal portions to respectively propagate in second and third planar waveguides formed in the semiconductor substrate;

reflecting a selected wavelength of the first portion to propagate in the second planar waveguide and the selected wavelength of the second portion to propagate in the propagate in the third planar waveguide;

combining the reflected wavelengths from the first and second portions to propagate in a fourth planar waveguide formed in the semiconductor substrate; and

filtering the combined reflected wavelengths to transmit the selected wavelength.

28. The method of claim 27 wherein reflecting a selected wavelength comprises introducing a ½

π

phase shift between the first and second portions with a three-dB coupler.

29. The method of claim 28 wherein a silicon-based Fabry-Perot filter is used to filter the combined reflected wavelengths.

30. The method of claim 28 wherein silicon-based Bragg gratings are used to reflect the selected wavelength from the first and second portions.