Apparatus, systems, and methods for on-chip spectroscopy using optical switches

Patent metadata

Field	Value
Publication number	US-10006809-B2
Application number	US-201715429321-A
Country	US
Kind code	B2
Filing date	Feb 10, 2017
Priority date	Feb 10, 2016
Publication date	Jun 26, 2018
Grant date	Jun 26, 2018

Abstract

A spectrometer includes an interferometer having a first interference arm and a second interference arm to produce interference patterns from incident light. At least one of the interference arms includes a series of cascaded optical switches connected by two (or more) waveguides of different lengths. Each optical switch directs the incident light into one waveguide or another, thereby changing the optical path length difference between the first interference arm and the second interference arm. This approach can be extended to multi-mode incident light by placing parallel interferometers together, each of which performs spectroscopy of one single mode in the multi-mode incident light. To maintain the compactness of the spectrometer, adjacent interferometers can share one interference arm.

First claim

The invention claimed is:

1. A spectrometer, comprising:
a beam splitter to split incident light into a first portion and a second portion;
a first interference arm, in optical communication with the beam splitter, to receive the first portion of the incident light, the first interference arm comprising:
a first optical switch switchable between a first state and a second state;
a first reference waveguide having a first waveguide length to produce a first optical path length L 1 to receive the first portion of the incident light when the first optical switch is in the first state; and
a first variable waveguide having a second waveguide length to produce a second optical path length L 2 , different than the first optical path length L 1 , to receive the first portion of the incident light when the first optical switch is in the second state;

a second interference arm, in optical communication with the beam splitter, to receive the second portion of the incident light; and
a detector, in optical communication with the first interference arm and the second interference arm, to detect interference of the first portion of the incident light from the first interference arm and the second portion of the incident light from the second interference arm.

2. The spectrometer of claim 1 , wherein the second interference arm comprises:
a second optical switch switchable between the first state and the second state;
a second reference waveguide having a third waveguide length to produce a third optical path length L 3 to receive the second portion of the incident light when the first optical switch is in the first state; and
a second variable waveguide having a fourth waveguide length to produce a fourth optical path length L 4 , different than the third optical path length L 3 , to receive the second portion of the incident light when the first optical switch is in the second state.

3. The spectrometer of claim 2 , wherein the first optical path length L 1 is substantially equal to the third optical path length L 3 , the second optical path length L 2 is greater than the first optical path length L 1 , and the fourth optical path length L 4 is less than the third optical path length L 3 .

4. The spectrometer of claim 2 , wherein the first optical path length L 1 is substantially equal to the third optical path length L 3 , L 2 =L 1 +ΔL, and L 4 =L 3 −ΔL, where ΔL is a length difference.

5. The spectrometer of claim 1 , wherein:
the first interference arm comprises:
j/2 optical switches, where j is a positive even integer greater than 4, each optical switch in the j/2 optical switches switchable between the first state and the second state;
j/2 reference waveguides, an nth reference waveguide in the j/2 reference waveguides receiving the first portion of the incident light when an nth optical switch in the j/2 optical switches is in the first state, where n=1, 2, . . . , j/2; and
j/2 variable waveguides, an nth variable waveguide in the j/2 variable waveguides receiving the first portion of the incident light when the nth optical switch in the j/2 optical switches is in the second state;

the second interference arm comprises:
j/2 optical switches, each optical switch in the j/2 optical switches switchable between the first state and the second state;
j/2 reference waveguides, an mth reference waveguide in the j/2 reference waveguides receiving the second portion of the incident light when an mth optical switch in the j/2 optical switches is in the first state, where m=1, 2, . . . , j/2; and
j/2 variable waveguides, an mth variable waveguide in the j/2 variable waveguides receiving the second portion of the incident light when the mth optical switch in the j/2 optical switches is in the second state.

6. The spectrometer of claim 5 , wherein the nth variable waveguide in the first interference arm has an nth variable optical path length greater than an nth reference optical path length of the nth reference waveguide, and wherein the mth variable waveguide in the second interference arm has an mth variable optical path length less than an mth reference optical path length of the mth reference waveguide.

7. The spectrometer of claim 5 , wherein each of the j/2 reference waveguides in the first interference arm and the j/2 reference waveguides in the second interference arm has an optical path length L, wherein the nth variable waveguide in the first interference arm has an nth variable optical path length L+2 2(n−1) ΔL, wherein the mth variable waveguide in the second interference arm has an mth variable optical path length L−2 2m−1 ΔL, where ΔL is a length difference.

8. The spectrometer of claim 7 , wherein ΔL/L is about 0.01 to about 0.3.

9. The spectrometer of claim 7 , wherein ΔL is about 2 μm to about 1 mm.

10. The spectrometer of claim 5 , wherein a first total optical path length of the j/2 reference waveguides in the first interference arm is substantially equal to a second total optical path length of the j/2 reference waveguides in the second interference arm.

11. The spectrometer of claim 1 , wherein the first optical switch comprises at least one of a Mach-Zehnder interferometer, a multi-mode interferometer (MMI), a micro-resonator, a directional coupler, or a hybrid plasmonic switch.

12. The spectrometer of claim 1 , wherein the detector is a first detector and the spectrometer further comprises:
a second detector; and
a beam combiner comprising:
a first input in optical communication with the first interference arm to receive the first portion of the incident light;
a second input in optical communication with the second interference arm to receive the second portion of the incident light;
a first output in optical communication with the first detector; and
a second output in optical communication with the second output.

13. A method of spectroscopy, the method comprising:
splitting incident light into a first portion and a second portion;
coupling the first portion of the incident light into a first interference arm including a first optical switch, a first reference waveguide having a first waveguide length to produce a first optical path length L 1 , and a first variable waveguide having a second waveguide length to produce a second optical path length L 2 different than the first optical path length L 1 ;
coupling the second portion of the incident light into a second interference arm;
actuating the first optical switch to couple the first portion of the incident light through the first reference waveguide so as to generate a first optical path difference between the first interference arm and the second interference arm;
detecting first interference between the first portion of the incident light and the second portion of the incident light when the first portion of the incident light is guided through the first reference waveguide;
actuating the first optical switch to couple the first portion of the incident light through the first variable waveguide so as to generate a second optical path difference between the first interference arm and the second interference arm; and
detecting second interference between the first portion of the incident light and the second portion of the incident light when the first portion of the incident light is guided through the first variable waveguide.

14. The method of claim 13 , wherein coupling the second portion of the incident light comprises:
coupling the second portion through a second optical switch;
actuating the second optical switch to couple the second portion of the incident light through a second reference waveguide having a third wavegui

Assignees

• Massachusetts Inst Technology

Inventors

• Hu Juejun
• Gu Tian
• Lin Hongtao
• Kita Derek Matthew
• Agarwal Anuradha M

Classifications

• G01J3/4531 Primary

  Devices without moving parts · CPC title

• G02F1/313

  in an optical waveguide structure · CPC title

• G02F1/3136

  of interferometric switch type · CPC title

• G01J3/0218

  using optical fibers · CPC title

• G02F2001/311

  Physics · mapped topic