# US 10,120,132 B2 · Photonic integrated circuit

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- Number: US 10,120,132 B2
- Document ID: US10120132B2
- Status: Granted
- Kind: B2
- Application number: 15/473,752
- Filed: 2017-03-30
- Published: 2018-10-04
- Granted: 2018-11-06
- Earliest claimed: 2017-03-30
- Assignees: Mitsubishi Electric Research Laboratories, Inc.; Mitsubishi Electric Corporation
- Applicants: Mitsubishi Electric Research Laboratories, Inc.
- Inventors: Keisuke Kojima; Satoshi Nishikawa; Toshiaki Koike-Akino; Bingnan Wang; Eiji Yagyu
- Web page: https://patentgrep.com/patent/US10120132B2

## CPC

- G02B 6/125: Bends, branchings or intersections
- G02B 6/12004: {Combinations of two or more optical elements}
- G02B 6/293: with wavelength selective means
- G02B 6/2935: {Mach-Zehnder configuration, i.e. comprising separate splitting and combining means}
- G02B 6/30: for use between fibre and thin-film device
- G02B 6/4257: {having a supporting carrier or a mounting substrate or a mounting plate (G02B6/3648 takes precedence)}
- G02B 6/4269: {with heat sinks or radiation fins}
- H10W 40/226: {characterised by projecting parts, e.g. fins to increase surface area (leadframes for cooling H10W70/461)}
- H10W 40/28: comprising Peltier coolers
- G02B 2006/12135: {Temperature control}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10

## Abstract

A photonic integrated circuit having discrete optical components arranged on a top side of a substrate includes a first and second optical sources respectively configured to emit light beams, a first interferometer having a first and second input ports respectively coupled to the first and second optical sources via first waveguides, a second interferometer configured to receive signals from the first interferometer via second waveguides and combine the signals to transmit a combined signal via a third waveguide, and a submount configured to contact a back side of the substrate, wherein the submount includes a first thermal conductor having a first thermal conductivity and a second conductor having a second thermal conductivity, wherein the first thermal conductivity is greater than the second thermal conductivity, and the first and second optical sources are more proximity to the first thermal conductor than the second thermal conductor.

## Claims

### Claim 1

A photonic integrated circuit disposed on a substrate, comprising:
first and second light sources to transmit a first light beam and a second light beam via first and second waveguides;
an interferometer to combine the first and second light beams from the first and second waveguides and transmit a combined signal light beam from an output port of a combined waveguide, wherein the interferometer includes a first coupler, a second coupler and first and second signal waveguides connecting between the first and second couplers;
a contact layer formed on a backside of the substrate; and
a submount to contact the contact layer, wherein the submount includes a first thermal conductor corresponding to regions of the first and second light sources, a second thermal conductor corresponding to a region of the interferometer and a third thermal conductor corresponding to a part of the combined waveguide, wherein a temperature gradient of the substrate is defined by a heat flow from a region of the first and second light sources to the third thermal conductor, wherein the first signal waveguide and the second signal waveguide are substantially aligned along the temperature gradient.

### Claim 2 (depends on 1)

The photonic integrated circuit of claim 1, further comprising:
a heatsink including a thermoelectric cooling device to contact the submount.

### Claim 3 (depends on 1)

The photonic integrated circuit of claim 1, wherein the contact layer is formed to partly cover the backside of the substrate and arranged to substantially overlap the regions of the first and second light sources.

### Claim 4 (depends on 1)

The photonic integrated circuit of claim 1, wherein the first and second couplers are disposed at substantially equal distances from the first and second light sources and the first and second waveguides have different lengths, wherein intermediate curved regions of the first and second signal waveguides are separated by at least more than 500 μm.

### Claim 5 (depends on 1)

The photonic integrated circuit of claim 1, wherein the submount has a groove region.

### Claim 6 (depends on 1)

The photonic integrated circuit of claim 1, wherein the first thermal conductor has a first thermal conductivity, the second thermal conductor has a second thermal conductivity, and the third thermal conductor has a third thermal conductivity, wherein each of the first and third thermal conductivities is greater than the second thermal conductivity.

### Claim 7 (depends on 6)

The photonic integrated circuit of claim 6, wherein the third thermal conductivity is at least one order of magnitude greater than the second thermal conductivity.

### Claim 8 (depends on 1)

The photonic integrated circuit of claim 1, wherein a material of the third thermal conductor is the same as a material of the first thermal conductor.

### Claim 9 (depends on 1)

The photonic integrated circuit of claim 1, wherein materials of the first and third thermal conductors are gold.

### Claim 10 (depends on 1)

The photonic integrated circuit of claim 1, wherein the second thermal conductor is an air.

### Claim 11 (depends on 1)

The photonic integrated circuit of claim 1, wherein the first thermal conductor substantially overlaps the regions of the first and second light sources.

### Claim 12 (depends on 1)

The photonic integrated circuit of claim 1, wherein an area of the first thermal conductor is greater than an area of the third thermal conductor.

### Claim 13 (depends on 1)

The photonic integrated circuit of claim 1, wherein the interferometer is a Mach-Zehnder interferometer.

### Claim 14 (depends on 1)

The photonic integrated circuit of claim 1, wherein the first and second light sources are laser diodes.

### Claim 15 (depends on 1)

The photonic integrated circuit of claim 1, wherein the first thermal conductor is gold or gold composite alloy and the second thermal conductor is indium phosphide.

### Claim 16 (depends on 1)

The photonic integrated circuit of claim 1, wherein a material of the substrate is different from those of the first, second light sources and interferometer.

### Claim 17 (depends on 1)

The photonic integrated circuit of claim 1, wherein the first and second light sources and the interferometer are formed on an indium phosphide substrate.