Electro optical device with parallel sections for orthogonal polarization modes

• US 20040184699A1
• Filed: 01/29/2004
• Published: 09/23/2004
• Est. Priority Date: 08/01/2001
• Status: Abandoned Application

• Current Assignee: DigiLens Inc
• Original Assignee: DigiLens Inc
• Inventors: Yeralan, Serdar
• Application Number:
  US10/767,923
• Publication Number:
  US 20040184699A1
• Time in Patent Office: Days
• US Class Current: 385/11
• CPC Class Codes: G02B 6/105 having optical polarisation effects
• CPC Class Codes: G02B 6/2706 as bulk elements, i.e. free space arrangements external to a light guide, e.g. polarising beam splitters
• CPC Class Codes: G02B 6/29302 based on birefringence or polarisation, e.g. wavelength dependent birefringence, polarisation interferometers
• 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: G02F 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G02F 2201/307 Reflective grating, i.e. Bragg grating
• CPC Class Codes: G02F 2203/06 Polarisation independent

Abstract

An improved solution to achieving low PDL and low PDM in wavelength selective filter devices for use in fiber optic communications systems is disclosed. In one embodiment, an optical input signal is divided into orthogonal polarization components by a polarizing beam splitter. The two polarization components are provided to an Electrically Switchable Bragg Grating (ESBG) device. The polarization of one of the two components is rotated ninety degrees such that the two components enter the ESBG device having the same polarization orientation. At the output of the ESBG device, one of the two components is rotated ninety degrees, such that the polarization of the component so rotated is orthogonal to the polarization of the other component. The two components are then combined, using a polarizing beam combiner, and the combined signal is provided as an optical output signal.

Claims

1. An electro optical device having approximately parallel sections for orthogonal polarization modes, comprising:

a beam splitter configured to receive an input light signal and to separate said input light signal into physically separated first and second component light signals, said first component light signal having a polarization that is approximately orthogonal to that of said second component light signal;

a first polarization rotator configured to receive said first component light signal and rotate the polarization of said first component light signal, such that the polarization of said first component light signal is approximately parallel to that of said second component light signal; and

an electrically switchable Bragg grating (ESBG) device comprising approximately parallel waveguides configured to receive said rotated first component light signal and said second component light signal.

2. An electro optical device as recited in claim 1, further comprising:

a second polarization rotator configured to receive said second component light signal from the output of said planar optical circuit and rotate the polarization of said second component light signal, such that the polarization of said second component light signal is approximately orthogonal to that of said rotated first component light signal; and

a beam combiner configured to combine said rotated first component light signal and said rotated second component light signal to provide a combined output signal.

3. An electro optical device as recited in claim 1, further comprising:

a second polarization rotator configured to receive said rotated first component light signal from the output of said planar optical circuit and rotate the polarization of said rotated first component light signal, such that the polarization of said rotated first component light signal is approximately orthogonal to that of said second component light signal; and

a beam combiner configured to combine said rotated first component light signal and said second component light signal to provide a combined output signal.

4. An electro optical device as recited in claim 1, wherein the beam splitter comprises a polarizing beam splitter.

5. An electro optical device as recited in claim 1, wherein the beam splitter comprises a self imaging waveguide polarization splitter.

6. An electro optical device as recited in claim 1, wherein the beam splitter comprises a Y branch polarization splitter.

7. An electro optical device as recited in claim 1, wherein the first polarization rotator comprises a half wave retardation plate.

8. An electro optical device as recited in claim 1, wherein the first polarization rotator comprises a Faraday rotator.

9. An electro optical device as recited in claim 1, wherein the first polarization rotator comprises a polarization converter based on the principle of alternating waveguide sections.

10. An electro optical device as recited in claim 1, wherein the first polarization rotator comprises a polarization converter based on poled electro optic polymers.

11. An electro optical device as recited in claim 1, further comprising a polarization preserving fiber optic link configured to carry said first component light signal from said beam splitter to said first polarization rotator.

12. An electro optical device as recited in claim 1, further comprising a polarization preserving fiber optic link configured to carry said rotated first component light signal from said polarization rotator to said ESBG device.

13. An electro optical device as recited in claim 1, wherein said ESBG device comprises:

a substrate;

a planar optical circuit formed on said substrate;

a cover glass layer; and

a holographic polymer dispersed liquid crystal layer sandwiched between said planar optical circuit and said cover glass layer.

14. An electro optical device as recited in claim 1, wherein said ESBG device comprises one or more electrodes configured to generate an electrical field sufficient to alter the state of the Bragg grating of said ESBG device.

15. An electro optical device as recited in claim 1, wherein said first polarization rotator is integrated onto the same substrate as said ESBG device.

16. An electro optical device as recited in claim 1, wherein said beam splitter is integrated onto the same substrate as said ESBG device.

17. An electro optical device as recited in claim 1, wherein said beam splitter, said first polarization rotators, said second polarization rotator, and said beam combiner are integrated onto the same substrate as said ESBG device, whereby said electro optical device comprises a fully integrated device and does not require the use of optical fiber links to conduct light signals between its components.

18. An electro optical device having approximately parallel sections for orthogonal polarization modes, comprising:

a beam splitter configured to receive an input light signal and to separate said input light signal into physically separated first and second component light signals, said first component light signal having a polarization that is approximately orthogonal to that of said second component light signal;

a first polarization rotator configured to receive said first component light signal and rotate the polarization of said first component light signal, such that the polarization of said first component light signal is approximately parallel to that of said second component light signal;

a planar optical circuit comprising;

a first waveguide configured to receive said rotated first component light signal;

a second waveguide, approximately parallel to said first waveguide, the second waveguide being configured to receive said second component light signal; and

a plurality of electrically switchable Bragg gratings, each of said plurality of electrically switchable Bragg gratings having a first state in which light passing through the grating is substantially unmodified by the grating and a second state in which light passing through the grating is modified by the grating;

wherein said planar optical circuit is configured such that light traveling through said first waveguide passes through one or more of said plurality of electrically switchable Bragg gratings and light traveling through said second waveguide passes through one or more of said plurality of electrically switchable Bragg gratings;

a second polarization rotator configured to receive said second component light signal from the output of said planar optical circuit and rotate the polarization of said second component light signal, such that the polarization of said second component light signal is approximately orthogonal to that of said rotated first component light signal; and

a beam combiner configured to combine said rotated first component light signal and said rotated second component light signal to provide a combined output signal.

19. An electro optical device having approximately parallel sections for orthogonal polarization modes, comprising:

a beam splitter configured to receive an input light signal and to separate said input light signal into physically separated first and second component light signals, said first component light signal having a polarization that is approximately orthogonal to that of said second component light signal;

an electrically switchable Bragg grating (ESBG) device comprising approximately parallel waveguides configured to receive said first component light signal and said second component light signal;

a first polarization preserving optical fiber configured to receive said first component light signal from said beam splitter and deliver said first component light signal to said ESBG device, such that said first component light signal enters said ESBG device having approximately the same polarization state as it had when it emerged from said beam splitter;

a second polarization preserving optical fiber configured to receive said second component light signal from said beam splitter and deliver said second component light signal to said ESBG device, said second polarization preserving optical fiber being rotated about its own axis prior to alignment and bonding to said ESBG device, such that the polarization of said second component light signal as it enters said ESBG device is approximately parallel to that of said first component light signal;

a beam combiner configured to receive said first component light signal via a third polarization preserving optical fiber and said rotated second component light signal via a fourth polarization preserving optical fiber, said fourth polarization preserving optical fiber being configured and aligned so as to deliver said rotated second component light signal to said beam combiner at approximately the same polarization state as it had when it emerged from said ESBG device and said third polarization preserving optical fiber being rotated about its own axis between said ESBG device and said beam combiner, such that said first component light signal is delivered to said beam combiner having a polarization that is approximately orthogonal to the polarization at which said rotated second component light signal is received at said beam combiner;

whereby said rotated first component light signal and said rotated second component light signal are combined to provide a combined output signal.

20. An electro optical device having approximately parallel sections for orthogonal polarization modes, comprising:

means for receiving the input light signal;

means for splitting the input light signal into a first component light signal and a second component light signal, wherein the first component light signal has a polarization state that is approximately orthogonal to that of the second component light signal;

means for rotating the polarization of the first component light signal, such that polarization of the rotated first component light signal is approximately parallel to that of the second component light signal;

means for providing said rotated first component light signal as input to a first waveguide of said ESBG device and for providing said second component light signal as input to a second waveguide of said ESBG device, said first and second waveguides being approximately parallel to each other, whereby said rotated first component light signal and said second component light signal interact with said ESBG device in parallel and emerge as a first component output light signal and a second component output light signal;

means for rotating the polarization of said second component output light signal, such that the polarization of said second component output light signal is approximately orthogonal to that of said first component output light signal; and

means for combining said rotated second component output light signal with said first component output light signal to create a combined output light signal.

21. A method for providing for the interaction of an input light signal with an electrically switchable Bragg grating (ESBG) device in a manner largely independent of the polarization state of the input light signal, comprising:

receiving the input light signal;

splitting the input light signal into a first component light signal and a second component light signal, wherein the first component light signal has a polarization state that is approximately orthogonal to that of the second component light signal;

rotating the polarization of the first component light signal, such that the polarization of the rotated first component light signal is approximately parallel to that of the second component light signal;

providing said rotated first component light signal as input to a first waveguide of said ESBG device and providing said second component light signal as input to a second waveguide of said ESBG device, said first and second waveguides being approximately parallel to each other, whereby said rotated first component light signal and said second component light signal interact with said ESBG device in parallel and emerge as a first component output light signal and a second component output light signal;

rotating the polarization of said second component output light signal, such that the polarization of said second component output light signal is approximately orthogonal to that of said first component output light signal; and

combining said rotated second component output light signal with said first component output light signal to create a combined output light signal.