OPTOELECTRONIC MODULATOR, PHOTONIC INTEGRATED CIRCUIT, AND METHOD

• US 20200133034A1
• Filed: 10/29/2019
• Published: 04/30/2020
• Est. Priority Date: 10/30/2018
• Status: Active Grant

• Current Assignee: Rockley Photonics Limited
• Original Assignee: Rockley Photonics Limited
• Inventors: Schrans, Thomas Pierre, Oh, Dong Yoon, Zilkie, Aaron John
• Granted Patent: US 11,209,679 B2
• Time in Patent Office: Days
• CPC Class Codes: G02F 1/025 in an optical waveguide structure G02F1/017, G02F1/2257 take precedence
• CPC Class Codes: G02F 2203/06 Polarisation independent

Abstract

A photonic integrated circuit, an optoelectronic modulator, and a method of modulating light in a photonic integrated circuit are provided. The photonic integrated circuit comprises: an input waveguide which, in use, receives light in a superposition of two polarisation modes of the waveguide; a polarisation splitter, connected to the input waveguide, and configured to provide, at a first output, light in a first polarisation mode of the two polarisation modes of the waveguide and, at a second output, light in a second polarisation mode of the two polarisation modes of the waveguide; a first polarisation rotator, connected to the first output of the polarisation splitter, and configured to rotate light received therefrom from the first polarisation mode to the second polarisation mode; an optoelectronic modulator, having a first modulation waveguide connected to the first polarisation rotator and a second modulation waveguide connected to the second output of the polarisation splitter.

Claims

1. A photonic integrated circuit, comprising:

an input waveguide configured to guide light in a superposition of two polarisation modes of the waveguide;

a polarisation splitter, connected to the input waveguide, and configured to provide, at a first output, light in a first polarisation mode of the two polarisation modes and, at a second output, light in a second polarisation mode of the two polarisation modes;

a first polarisation rotator, connected to the first output of the polarisation splitter, and configured to rotate light received therefrom from the first polarisation mode to the second polarisation mode;

an optoelectronic modulator, having a first modulation waveguide connected to the first polarisation rotator and a second modulation waveguide connected to the second output of the polarisation splitter, and configured to modulate light in each waveguide according to a modulation scheme;

a first intermediate waveguide and a second intermediate waveguide, connected respectively to the first modulation waveguide and the second modulation waveguide; and

a polarisation combiner, connected to the first intermediate waveguide and the second intermediate waveguide, and configured to combine light received from each and provide the combined light to an output of the photonic integrated circuit as a modulated signal,

wherein one of the first intermediate waveguide and the second intermediate waveguide comprises a second polarisation rotator configured to rotate light received therein from one of the first and second polarisation modes to the other of the first and second polarisation modes.

2. The photonic integrated circuit of claim 1, wherein the first intermediate waveguide comprises the second polarisation rotator, and the second polarisation rotator is configured to rotate light received therein from the second polarisation mode to the first polarisation mode.

3. The photonic integrated circuit of claim 1, wherein the second intermediate waveguide comprises the second polarisation rotator, and the second polarisation rotator is configured to rotate light received therein from the first polarisation mode to the second polarisation mode.

4. The photonic integrated circuit of claim 1, wherein the optoelectronic modulator

a first waveguide, including a first modulation region;

a second waveguide, including a second modulation region; and

a driver, operable to modulate light in both the first waveguide and the second waveguide,

wherein the driver is configured to send the same modulation signal to each of the first modulation region and the second modulation region.

5. The photonic integrated circuit of claim 1, wherein either or both of the polarisation splitter and the polarisation splitter are provided as one or more multi-mode interference couplers.

6. The photonic integrated circuit of claim 1, wherein either or both of the first polarisation rotator and the second polarisation rotator is provided as a rib waveguide, the rib waveguide including:

a slab portion; and

a ridge portion, which is disposed along a surface of the slab portion;

wherein;

the slab portion has a first slab region whose width, as measured in a direction perpendicular to a guiding direction of the waveguide, increases from a first slab width to a second slab width along a first length, and

the ridge portion has a first ridge region whose width, as measured in the same direction as the slab widths, decreases from a first ridge width to a second ridge width along the same first length;

such that the rotator is configured to rotate the polarisation of light during its transmission through the rib waveguide.

7. The photonic integrated circuit of claim 1, wherein the polarisation splitter and first polarisation rotator, and/or the second polarisation rotator and polarisation splitter, are each provided as a single polarisation diverse grating coupler.

8. The photonic integrated circuit of claim 1, wherein the circuit is a passive polarisation diverse modulator circuit.

9. An optoelectronic modulator, comprising:

a first waveguide, including a first modulation region;

a second waveguide, including a second modulation region; and

a driver, operable to modulate light in both the first waveguide and the second waveguide,

wherein the driver is configured to send the same modulation signal to each of the first modulation region and the second modulation region.

10. The optoelectronic modulator of claim 9, wherein the first modulation region and the second modulation region each comprises a first doped region and a second doped region.

11. The optoelectronic modulator of claim 10, wherein the second doped region of each modulation region is contiguous with the other, and wherein a shared electrode is connected to the second doped regions of the modulation regions.

12. The optoelectronic modulator of claim 10, wherein the first doped region of the first modulation region is connected to a first electrode and the first doped region of the second modulation region is connected to a second electrode.

13. The optoelectronic modulator of claim 10, wherein the first doped region of each modulation region is connected to a second shared electrode.

14. The optoelectronic modulator of claim 9, wherein each waveguide is a ridge waveguide.

15. The optoelectronic modulator of claim 9, wherein the waveguides are formed from a III-V stack.

16. The optoelectronic modulator of claim 9, comprising electrodes formed from gold.

17. The optoelectronic modulator of claim 9, wherein the first waveguide and the second waveguide are counter-propagating waveguides.

18. The optoelectronic modulator of claim 9, wherein the first waveguide and the second waveguide are co-propagating waveguides.

19. A method of modulating light in a photonic integrated circuit, comprising the steps of:

providing light from an input waveguide, said light being in a superposition of two polarisation modes of the waveguide;

splitting the light into a first portion having a first polarisation mode of the two polarisation modes, and a second portion having a second polarisation mode of the two polarisation modes;

rotating the polarisation of the first portion, such that it has the second polarisation mode;

modulating the first portion and the second portion according to a modulation scheme;

rotating the polarisation of one of the first portion and the second portion, so as to provide one portion having the first polarisation mode and one portion having the second polarisation mode; and

combining the first portion and the second portion.

20. The method of claim 19, wherein the photonic integrated circuit comprises:

an input waveguide configured to guide light in a superposition of two polarisation modes of the waveguide;

a polarisation splitter, connected to the input waveguide, and configured to provide, at a first output, light in a first polarisation mode of the two polarisation modes and, at a second output, light in a second polarisation mode of the two polarisation modes;

a first polarisation rotator, connected to the first output of the polarisation splitter, and configured to rotate light received therefrom from the first polarisation mode to the second polarisation mode;

an optoelectronic modulator, having a first modulation waveguide connected to the first polarisation rotator and a second modulation waveguide connected to the second output of the polarisation splitter, and configured to modulate light in each waveguide according to a modulation scheme;

a first intermediate waveguide and a second intermediate waveguide, connected respectively to the first modulation waveguide and the second modulation waveguide; and

a polarisation combiner, connected to the first intermediate waveguide and the second intermediate waveguide, and configured to combine light received from each and provide the combined light to an output of the photonic integrated circuit as a modulated signal,

wherein one of the first intermediate waveguide and the second intermediate waveguide comprises a second polarisation rotator configured to rotate light received therein from one of the first and second polarisation modes to the other of the first and second polarisation modes.