Wavelength selective optical add/drop multiplexer and method of manufacture

• US 20020039470A1
• Filed: 08/02/2001
• Published: 04/04/2002
• Est. Priority Date: 09/29/2000
• Status: Active Grant

• Current Assignee: Sarnoff Corporation (SRI International, Inc.)
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Braun, Alan Michael, Abeles, Joseph Hy, Amantea, Robert
• Granted Patent: US 6,665,476 B2
• Time in Patent Office: Days
• US Class Current: 385/50
• CPC Class Codes: G02B 6/12002 Three-dimensional structures
• CPC Class Codes: G02B 6/12007 forming wavelength selective elements, e.g. multiplexer, demultiplexer
• CPC Class Codes: G02B 6/29341 Loop resonators operating in a whispering gallery mode evanescently coupled to a light guide, e.g. sphere or disk or cylinder evanescent coupling for sensing fluorescence G01N21/648
• CPC Class Codes: G02B 6/29383 Adding and dropping
• CPC Class Codes: G02B 6/3508 Lateral or transverse displacement of the whole waveguides, e.g. by varying the distance between opposed waveguide ends, or by mutual lateral displacement of opposed waveguide ends
• CPC Class Codes: G02B 6/3536 involving evanescent coupling variation, e.g. by a moving element such as a membrane which changes the effective refractive index mode converters G02B6/14; adjustable lateral coupling between waveguides G02B6/283; electro- optical refractive index variations G02F1/0118
• CPC Class Codes: G02B 6/3544 2D constellations, i.e. with switching elements and switched beams located in a plane
• CPC Class Codes: G02B 6/3566 involving bending a beam, e.g. with cantilever
• CPC Class Codes: G02B 6/3576 Temperature or heat actuation thermal forces controlling reflecting elements in general G02B26/0866; thermo-optic devices G02F1/0147
• CPC Class Codes: G02B 6/3578 Piezoelectric force piezoelectric forces controlling reflecting elements in general G02B26/0858; piezo-optic devices G02F1/0131
• CPC Class Codes: G02B 6/3584 constructional details of an associated actuator having a MEMS construction, i.e. constructed using semiconductor technology such as etching MEMS per se B81B, B81C
• CPC Class Codes: G02B 6/3596 With planar waveguide arrangement, i.e. in a substrate, regardless if actuating mechanism is outside the substrate
• CPC Class Codes: G02B 6/42 Coupling light guides with opto-electronic elements

Abstract

One embodiment of the present invention is an exemplary wavelength selective optical coupling device. This exemplary device includes two waveguides, a ring or disc resonator, and resonator coupling means. The waveguides are disposed on top of a substrate, not in contact with each other. The waveguides may transmit multiple wavelengths of light. The ring or disc resonator includes a dielectric member which extends parallel to the top of the substrate and overlaps, without contacting, the waveguides. The resonator is sized to resonate at a subset of resonant wavelengths. The resonator coupling means couple the resonator to the substrate. The resonator coupling means may include a bridge coupled to the top surface of the substrate and electrically coupled to control circuitry within the substrate. A waveguide coupling signal from the control circuitry causes the bridge to deform, translating the resonator up and down, thereby intermittently coupling and decoupling the waveguides.

Claims

1. A wavelength selective optical coupling device comprising:

a substrate including a top surface and a bottom surface;

a primary waveguide disposed on the top surface of the substrate, the primary waveguide including a first coupling portion and adapted to transmit a plurality of wavelengths of light;

a secondary waveguide disposed on the top surface of the substrate and separate from the primary waveguide, the secondary waveguide including a second coupling portion and adapted to transmit the plurality of wavelengths of light;

a resonator including a dielectric member which extends parallel to the top surface of the substrate and overlaps, without contacting, the first coupling portion of the primary waveguide and the second coupling portion of the secondary waveguide, the dielectric member including an upper surface and a lower surface; and

resonator coupling means for coupling the resonator to the top surface of the substrate;

wherein the resonator is sized to resonate at a subset of resonant wavelengths of the plurality of wavelengths of light.

2. A wavelength selective waveguide coupling device according to claim 1, wherein the substrate includes a CMOS control circuit layer and a passivation layer forming the top surface of the substrate.

3. A wavelength selective waveguide coupling device according to claim 2, wherein the CMOS control circuit layer includes at least one of:

silicon;

germanium;

InP;

GaAs;

InGaAs; and

InGaAsP.

4. A wavelength selective waveguide coupling device according to claim 2, wherein the passivation layer includes at least one of:

silicon dioxide;

silicon carbide; and

alumina.

5. A wavelength selective waveguide coupling device according to claim 1, wherein:

the primary waveguide includes at least one of;

alumina;

hydrogenated amorphous silicon carbide;

silicon nitride; and

silicon oxynitride;

the secondary waveguide includes at least one of;

alumina;

hydrogenated amorphous silicon carbide;

silicon nitride; and

silicon oxynitride; and

the dielectric member includes at least one of;

alumina;

hydrogenated amorphous silicon carbide;

silicon nitride; and

silicon oxynitride.

6. A wavelength selective waveguide according to claim 1, wherein the dielectric member comprises a disc-shaped element formed from an amorphous material.

7. A wavelength selective waveguide coupling device according to claim 1, wherein the resonator further includes a ring waveguide disposed on the lower surface of the dielectric member.

8. A wavelength selective waveguide coupling device according to claim 1, wherein the resonator further includes:

an electrical heating element disposed on the upper surface of the dielectric member; and

means for applying an electric current to the electrical heating element;

whereby the subset of resonant wavelengths of the resonator is tuned by a level of the current applied to the heating element.

9. A wavelength selective waveguide coupling device according to claim 8, wherein the heating element includes at least one of:

titanium;

tungsten;

titanium-tungsten; and

polysilicon.

10. A wavelength selective waveguide coupling device according to claim 8, wherein the substrate further includes wavelength control circuitry electrically coupled to the means for applying the electric current to the electrical heating element.

11. A wavelength selective waveguide coupling device according to claim 10, wherein the substrate further includes optical sensing means optically coupled to the secondary waveguide and electrically coupled to the wavelength control circuitry.

12. A wavelength selective waveguide coupling device according to claim 11, wherein optical sensing means includes an amorphous germanium optical detector.

13. A wavelength selective waveguide coupling device according to claim 8, wherein:

the means for applying the electric current to the electrical heating element includes a radio frequency (RF) signal generator providing an RF signal having a frequency selected to induce an electric current in the electrical heating element.

14. A wavelength selective waveguide coupling device according to claim 1, wherein the substrate further includes a laser optical signal source optically coupled to at least one of the primary waveguide and the secondary waveguide.

15. A wavelength selective waveguide coupling device according to claim 1, wherein the substrate further includes an optical amplifier optically coupled to at least one of the primary waveguide and the secondary waveguide.

16. A wavelength selective waveguide coupling device according to claim 1, wherein:

the substrate includes coupling control circuitry adapted to provide a waveguide coupling signal; and

the resonator coupling means includes a bridge coupled to the top surface of the substrate and electrically coupled to the coupling control circuitry, the bridge adapted to deform and translate the resonator between a waveguide decoupled position and a waveguide coupled position responsive to the waveguide coupling signal;

whereby the resonator is optically coupled to the primary waveguide and the secondary waveguide in the waveguide coupled position and substantially decoupled from at least one of the primary waveguides and the secondary waveguide in the waveguide decoupled position.

17. A wavelength selective waveguide coupling device according to claim 16, wherein the bridge includes:

a first layer including a conductive portion and exhibiting a first coefficient of thermal expansion; and

a second layer which exhibits a second coefficient of thermal expansion;

the first coefficient of thermal expansion and the second coefficient of thermal expansion selected such that the bridge deforms in response to heat generated when the waveguide coupling signal is applied to the conductive portion of the first layer due to unequal expansion of the first layer as compared to the second layer.

18. A wavelength selective waveguide coupling device according to claim 16, wherein:

the substrate includes a substrate electrode electrically coupled to the coupling control circuitry; and

the bridge includes a bridge electrode electrically coupled to the coupling control circuitry;

whereby the waveguide coupling signal deforms the bridge based on an electrostatic attraction between the bridge electrode and the substrate electrode.

19. A wavelength selective waveguide coupling device according to claim 16, wherein the bridge includes:

a flexible portion;

a piezoelectric portion including a first end and a second end;

a first electrode coupled to the first end of the piezoelectric portion and electrically coupled to the coupling control circuitry of the substrate; and

a second electrode coupled to the second end of the piezoelectric portion and electrically coupled to the coupling control circuitry of the substrate;

the piezoelectric portion deforming in response to the waveguide coupling signal and being sized and arranged such that the flexible portion of the bridge deforms in response to the deformation of the piezoelectric portion.

20. A wavelength selective waveguide coupling device according to claim 16, wherein the bridge includes:

a strained portion;

an electrostrictive portion including a first end and a second end, connected to the strained portion in elastic opposition;

a first electrode coupled to the first end of the electrostrictive portion and electrically coupled to the coupling control circuitry of the substrate; and

a second electrode coupled to the second end of the electrostrictive portion and electrically coupled to the coupling control circuitry of the substrate;

the electrostrictive portion deforming in response to the waveguide coupling signal and being sized and arranged such that strained portion of the bridge deforms in response to the deformation of the electrostrictive portion.

21. A wavelength selective waveguide coupling device according to claim 1, wherein:

the substrate includes coupling control circuitry adapted to provide a waveguide coupling signal;

the resonator coupling means includes;

a bridge coupled to the resonator and electrically coupled to the coupling control circuitry, the bridge adapted to deform and translate the resonator between a waveguide decoupled position and a waveguide coupled position based on the waveguide coupling signal; and

a spacing column including a first end coupled to the bridge and a second end coupled to the resonator;

whereby the resonator is optically coupled to the primary waveguide and the secondary waveguide in the waveguide coupled position.

22. A wavelength selective waveguide according to claim 21 further comprising:

an electrical heating element disposed on the upper surface of the dielectric member; and

means for applying an electric current to the electrical heating element whereby the subset of resonant wavelengths of the resonator is tuned responsive to a level of the current applied to the heating element.

23. A wavelength selective waveguide according to claim 22 wherein the means for applying the electric current to the electrical heating element includes a radio frequency (RF) signal generator providing an RF signal having a frequency selected to induce an electric current in the electrical heating element.

24. A wavelength selective waveguide according to claim 22 wherein the means for applying the electric current to the electrical heating element includes at least first and second conductors connecting the electrical heating element to the control circuitry via the bridge and the spacing column.

25. A wavelength selective waveguide coupling device according to claim 1, wherein the dielectric member includes at least one of a dielectric disc and a ring waveguide.

26. A wavelength selective waveguide coupling device according to claim 1, wherein the resonator coupling means are sized and arranged such that the resonator coupling means does not interfere with the primary waveguide, the secondary waveguide, or the resonator.

27. A wavelength selective waveguide coupling device according to claim 1, wherein:

the substrate includes coupling control circuitry adapted to provide a waveguide coupling signal;

the resonator coupling means includes;

a bridge coupled to the resonator and electrically coupled to the coupling control circuitry, the bridge adapted to deform and translate the resonator between a waveguide decoupled position and a waveguide coupled position based on the waveguide coupling signal; and

a spacing column including a first end coupled to the bridge and a second end coupled to the substrate;

whereby the resonator is optically coupled to the primary waveguide and the secondary waveguide in the waveguide coupled position.

28. A wavelength selective waveguide coupling device according to claim 1, wherein:

the substrate includes coupling control circuitry adapted to provide a waveguide coupling signal;

the resonator coupling means includes a bridge coupled to the top surface of the substrate and electrically coupled to the coupling control circuitry, the bridge adapted to deform and translate the resonator to a plurality of positions responsive to the waveguide coupling signal, the plurality of positions including at least one signal splitting position;

whereby the resonator is partially optically coupled to the primary waveguide and the secondary waveguide in the at least one signal splitting position.

30. A multi-wavelength optical multiplexer according to claim 29, wherein the plurality of waveguides includes a main waveguide and a plurality of branch waveguides, wherein a portion of each of the branch waveguides is positioned proximate to the main waveguide and to a respective one of the plurality of switchable wavelength selective optical couplers, whereby when one of the resonators is optically coupled to the main waveguide and a respective one of the branch waveguides, optical signals are transferred between the main waveguide and the one branch waveguide.

31. A multi-wavelength optical multiplexer according to claim 30, wherein a group of the plurality of resonators are tuned to respectively different subsets of the resonant wavelengths, whereby, when one resonator of the group of resonators is optically coupled to the main waveguide and to a respective one of the plurality of branch waveguides, optical signals having the subset of resonant wavelengths to which the one

resonator is tuned is transferred between the main waveguide and the one of the branch waveguides to the relative exclusion of optical signals having wavelengths outside of the subset of resonant wavelengths to which the one resonator is tuned.

29. A multi-wavelength optical multiplexer comprising:

a substrate including a top surface and a bottom surface, and coupling control circuitry adapted to provide a plurality of waveguide coupling signals;

a plurality of waveguides disposed on the top surface of the substrate, each waveguide separated from the remaining waveguides, and adapted to transmit the plurality of wavelengths of light; and

a plurality of switchable wavelength selective optical couplers coupled to the top surface of the substrate and adapted to resonate at a subset of resonant wavelengths of the plurality of wavelengths of light, each switchable wavelength selective optical coupler including;

a resonator including a dielectric member which extends parallel to the top surface of the substrate and overlaps, without contacting, at least two of the plurality of waveguides, the dielectric member including an upper surface and a lower surface; and

a bridge coupled to the resonator and electrically coupled to the coupling control circuitry, the bridge adapted to deform and translate the resonator between a waveguide decoupled position and a waveguide coupled position responsive to one of the plurality of waveguide coupling signals;

whereby the resonator is optically coupled to the at least two of the plurality of waveguides in the waveguide coupled position.

32. A method of manufacturing a wavelength selective waveguide coupling device which includes a substrate;

a primary waveguide transmitting a plurality of optical signals having a plurality of wavelengths;

a secondary waveguide;

a resonator which extends over the primary waveguide and the secondary waveguide; and

a pedestal to couple the resonator to the substrate, the method comprising the steps of;

a) planarizing the substrate;

b) depositing a passivation layer on the substrate, the passivation layer including an electrically insulating and optically transmissive material characterized by a first index of refraction;

c) depositing a waveguide layer on the passivation layer, the waveguide layer including an optically transmissive material characterized by a second index of refraction and a waveguide thickness, the second index of refraction being greater than the first index of refraction;

d) defining and etching the waveguide layer to form the primary waveguide and the secondary waveguide;

e) depositing a release layer over the passivation layer, the primary waveguide, and the secondary waveguide, the release layer having a first thickness on top of the passivation layer, the first thickness being greater than the waveguide thickness;

f) planarizing the release layer, the planarized release layer having a second thickness on top of the passivation layer, the second thickness being greater than the waveguide thickness;

g) depositing a resonator layer on the release layer, the resonator layer including an optically transmissive material with a third index of refraction, the third index of refraction being substantially the same as the second index of refraction;

h) defining and etching the resonator layer to form the resonator; and

i) etching the release layer to form the pedestal and to uncover the primary waveguide and the secondary waveguide.

33. A method of manufacturing a wavelength selective waveguide coupling device according to claim 32, wherein:

step a) includes the step of chemical-mechanical planarizing the substrate;

step f) includes the step of chemical-mechanical planarizing the release layer.

35. A method of manufacturing a wavelength selective waveguide coupling device according to claim 34, wherein step r) includes the step of dry etching the release layer to uncover the primary waveguide and the secondary waveguide and substantially remove the release layer.

34. A method of manufacturing a wavelength selective waveguide coupling device which includes a CMOS control circuit substrate having a top surface;

a primary waveguide;

a secondary waveguide;

a resonator which extends over the primary waveguide and the secondary waveguide;

a heating means to tune a resonant wavelength of the resonator; and

a coupling means to couple the resonator to the substrate, the method comprising the steps of;

a) planarizing the top surface of the CMOS control circuit substrate;

b) depositing a passivation layer on the top surface of the CMOS control circuit substrate, the passivation layer including an electrically insulating and optically transmissive material characterized by a first index of refraction;

c) depositing a waveguide layer on the passivation layer, the waveguide layer including an optically transmissive material characterized by a second index of refraction and a waveguide thickness, the second index of refraction being greater than the first index of refraction;

d) defining and etching the waveguide layer to form the primary waveguide and the secondary waveguide;

e) defining and etching the passivation layer to form a first plurality of vias exposing a plurality of electrical contacts on the top surface of the CMOS control circuit substrate;

f) depositing a first plurality of metal plugs in the first plurality of vias, the first plurality of metal plugs electrically coupled to the electrical contacts;

g) depositing a release layer over the passivation layer, the first plurality of metal plugs, the primary waveguide, and the secondary waveguide, the release layer having a first thickness on top of the passivation layer, the first thickness being greater than the waveguide thickness;

h) defining and etching the release layer to form a second plurality of vias exposing the first plurality of metal plugs;

i) depositing a second plurality of metal plugs in the second plurality of vias, the second plurality of metal plugs electrically coupled to the first plurality of metal plugs and forming at least a portion of the coupling means;

j) planarizing the release layer and the second plurality of metal plugs, the planarized release layer having a second thickness on top of the passivation layer, the second thickness being greater than the waveguide thickness;

k) depositing a resonator layer on the release layer and the second plurality of metal plugs, the resonator layer including an optically transmissive material characterized by a third index of refraction, the third index of refraction being substantially the same as the second index of refraction;

l) depositing a resonator cover layer on the resonator layer, the resonator cover layer including an electrically insulating and optically transmissive material characterized by a fourth index of refraction, the fourth index of refraction being less than the third index of refraction;

m) defining and etching the resonator cover layer to form a resonator cover and a third plurality of vias;

n) defining and etching the resonator layer to form the resonator and a fourth plurality of vias extending from the third plurality of vias to the second plurality of metal plugs;

o) depositing a third plurality of metal plugs in the fourth plurality of vias and the third plurality of vias, the third plurality of metal plugs being electrically coupled to the second plurality of metal plugs;

p) depositing a heating layer on the resonator cover, the heating layer including an electrically conductive material and being electrically coupled to the third plurality of metal plugs;

q) defining and etching the heating layer to form the heating means; and

r) etching the release layer to uncover the primary waveguide and the secondary waveguide and substantially remove the release layer.

36. A method of manufacturing a wavelength selective waveguide coupling device which includes a CMOS control circuit substrate having a top surface;

a primary waveguide;

a secondary waveguide;

a resonator which extends over the primary waveguide and the secondary waveguide;

a heating means to tune a resonant wavelength of the resonator;

a coupling means to couple the resonator to the substrate; and

at least one deformable bridge adapted to translate the resonator between a coupled position and a decoupled position, the method comprising the steps of;

a) depositing a CMOS cap layer on the top surface of the CMOS control circuit substrate, the CMOS cap layer including an electrically insulating material;

b) depositing a passivation layer on the top surface of the CMOS cap layer, the passivation layer including an optically transmissive material exhibiting a first index of refraction;

c) defining and etching the passivation layer to form a first plurality of vias and openings to allow release of the at least one deformable bridge;

d) defining and etching the CMOS cap layer to form a second plurality of vias extending from the first plurality of vias to a plurality of electrical contacts on the top surface of the CMOS control circuit substrate;

e) depositing a first plurality of metal plugs in the second plurality of vias and the first plurality of vias, the first plurality of metal plugs electrically coupled to the electrical contacts;

f) depositing a first release layer to fill in the openings in the passivation layer;

g) planarizing the passivation layer, the release layer, and the first plurality of metal plugs;

h) depositing a waveguide and bridge layer on the passivation layer, the release layer, and the first plurality of metal plugs, the waveguide and bridge layer including an optically transmissive material characterized by a second index of refraction and a waveguide thickness, the second index of refraction being greater than the first index of refraction;

i) defining and etching the waveguide layer to form the primary waveguide, the secondary waveguide, and the at least one deformable bridge, the at least one deformable bridge including a third plurality of vias exposing the first plurality of metal plugs;

j) depositing a second plurality of metal plugs in the third plurality of vias, the second plurality of metal plugs electrically coupled to the first plurality of metal plugs;

k) depositing a plurality of bridge electrodes on the at least one deformable bridge, the plurality of bridge electrodes including an electrically conductive material and being electrically coupled to the second plurality of metal plugs;

l) depositing a second release layer over the passivation layer, the first release layer, the primary waveguide, the secondary waveguide, the at least one deformable bridge and the plurality of bridge electrodes, the second release layer having a first thickness on top of the passivation layer, the first thickness being greater than the waveguide thickness;

m) defining and etching the release layer to form a forth plurality of vias exposing a contact portion of the plurality of bridge electrodes;

n) depositing a third plurality of metal plugs in the forth plurality of vias, the third plurality of metal plugs electrically coupled to the plurality of bridge electrodes and forming at least a portion of the coupling means;

o) planarizing the second release layer and the third plurality of metal plugs, the planarized second release layer having a second thickness on top of the passivation layer, the second thickness being greater than the waveguide thickness;

p) depositing a resonator layer on the second release layer and the third plurality of metal plugs, the resonator layer including an optically transmissive material characterized by a third index of refraction, the third index of refraction being substantially the same as the second index of refraction;

q) depositing a resonator cover layer on the resonator layer, the resonator cover layer including an electrically insulating and optically transmissive material characterized by a fourth index of refraction, the fourth index of refraction being less than the third index of refraction;

r) defining and etching the resonator cover layer to form a resonator cover and a fifth plurality of vias;

s) defining and etching the resonator layer to form the resonator and a sixth plurality of vias extending from the fifth plurality of vias to the third plurality of metal plugs;

t) depositing a fourth plurality of metal plugs in the sixth plurality of vias and the fourth plurality of vias, the fourth plurality of metal plugs electrically coupled to the third plurality of metal plugs;

u) depositing a heating layer on the resonator cover, the heating layer including an electrically conductive material and being electrically coupled to the fourth plurality of metal plugs;

v) defining and etching the heating layer to form the heating means; and

w) etching the second release layer and the first release layer to uncover the primary waveguide and the secondary waveguide, release the at least one deformable bridge, and substantially remove the release layer.

37. A method encoding information as a narrow wavelength band digital optical signal using an integrated optical component including an optical source optically coupled to a first waveguide;

a second waveguide;

a resonator sized to resonate in a narrow resonator wavelength band;

a resonator translating means adapted to translate the resonator between a coupled position in which the resonator optically couples the first waveguide to the second waveguide and a decoupled position in which the resonator does not optically couples the first waveguide to the second waveguide; and

control circuitry electrically coupled to the resonator coupling means and adapted to form a digital electric signal in response to the information, the method comprising the steps of;

a) operating the optical source to provide optical radiation to the first waveguide, the optical radiation exhibiting a substantially constant amplitude and a source wavelength band which includes the narrow resonator wavelength band;

b) providing the information to the control circuitry to form the digital electric signal;

c) providing the digital electric signal to the resonator translating means to translate the resonator between the coupled position and the decoupled position; and

d) transferring optical radiation in the narrow resonator wavelength band from the first waveguide to the second waveguide when the resonator is in the coupled position and not transferring optical radiation from the first waveguide to the second waveguide when the resonator is in the decoupled position to form the narrow wavelength band digital optical signal in the second waveguide.