# US 10,119,857 B2 · Reflection-enhanced photo-detector

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- Number: US 10,119,857 B2
- Document ID: US10119857B2
- Status: Granted
- Kind: B2
- Application number: 13/588,248
- Filed: 2012-08-17
- Published: 2014-09-04
- Granted: 2018-11-06
- Earliest claimed: 2012-08-17
- Assignees: Oracle International Corporation
- Applicants: Guoliang Li; Xuezhe Zheng; Ying L. Luo; Ashok V. Krishnamoorthy
- Inventors: Guoliang Li; Xuezhe Zheng; Ying L. Luo; Ashok V. Krishnamoorthy
- Web page: https://patentgrep.com/patent/US10119857B2

## CPC

- G01J 1/0407: {Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings}
- G01J 1/0209: {Monolithic}
- G01J 1/0425: {using optical fibers}
- G01J 1/42: using electric radiation detectors (optical or mechanical part G01J1/04; by comparison with a reference light or electric value G01J1/10)
- G02B 6/12004: {Combinations of two or more optical elements}
- G02B 6/124: Geodesic lenses or integrated gratings
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

An integrated optical device includes a photo-detector (such as germanium) optically coupled to an optical waveguide. This photo-detector is deposited on the optical waveguide, and an optical signal propagating in the optical waveguide may be evanescently coupled to the photo-detector. In order to increase the absorption length of the photo-detector, a mirror (such as a distributed Bragg reflection grating) is included in the optical waveguide near the end of the photo-detector. This mirror reflects the optical signal back toward the photo-detector, thereby increasing the absorption of the optical signal by the photo-detector. In addition, absorption may be reduced by using electrical contacts that are electrically coupled to the photo-detector at locations where the optical mode of the optical signal is largely in the underlying optical waveguide, and by using a fingered metal layer to couple to the electrical contacts.

## Claims

### Claim 1

An optical device, comprising:
an optical waveguide configured to convey an optical signal having a wavelength;
a photo-detector having a first end and a second end on opposite sides of side surfaces of the photo-detector, wherein a bottom surface of the photo-detector is disposed on and optically coupled to a region of a top surface of the optical waveguide, wherein the photo-detector is configured to convert the optical signal to an electrical signal; and
a mirror after and proximate to the second end of the photo-detector, wherein the mirror is in a plane of the optical waveguide, and
wherein the mirror is coupled to an end of the optical waveguide on a side surface of the optical waveguide, wherein the end of the optical waveguide is aligned with the second end of the photo-detector wherein the mirror is configured to reflect the optical signal back toward the optical waveguide, wherein the mirror causes the optical signal to move in a reversed direction, thereby increasing an absorption length of the photo-detector, and wherein the optical signal is evanescently coupled between the optical waveguide and the photo-detector.

### Claim 2 (depends on 1)

The optical device of claim 1, wherein the mirror is included in the optical waveguide.

### Claim 3 (depends on 1)

The optical device of claim 1, wherein the mirror includes an element selected from the group consisting of: a distributed Bragg reflection grating and an etched vertical facet with a reflection coating.

### Claim 4 (depends on 1)

The optical device of claim 1, wherein the photo-detector includes periodic rows of electrical contacts along a length of the photo-detector.

### Claim 5 (depends on 4)

The optical device of claim 4, wherein the electrical contacts are positioned at locations along the length where the optical signal is substantially in the optical waveguide.

### Claim 6 (depends on 4)

The optical device of claim 4, wherein electrical contacts in a given row are electrically connected to each other via a metal layer.

### Claim 7 (depends on 6)

The optical device of claim 6, wherein the metal layer is fingered proximate to the electrical contacts.

### Claim 8 (depends on 1)

The optical device of claim 1, wherein the optical waveguide includes a taper that expands a width of the optical waveguide prior to the photo-detector.

### Claim 9 (depends on 1)

The optical device of claim 1, further comprising:
a substrate;
a buried-oxide layer disposed on the substrate; and
a semiconductor layer disposed on the buried-oxide layer, wherein the optical waveguide is included in the semiconductor layer.

### Claim 10 (depends on 9)

The optical device of claim 9, wherein the substrate includes a semiconductor.

### Claim 11 (depends on 1)

The optical device of claim 1, wherein the photo-detector includes germanium.

### Claim 12

A system, comprising:
a processor;
a memory storing a program module that is configured to be executed by the processor; and
an optical device, wherein the optical device includes:
an optical waveguide configured to convey an optical signal having a wavelength;
a photo-detector having a first end and a second end on opposite sides of side surfaces of the photo-detector, wherein a bottom surface of the photo-detector is disposed on and optically coupled to a region of a top surface of the optical waveguide, wherein the photo-detector is configured to convert the optical signal to an electrical signal; and
a mirror after and proximate to the second end of the photo-detector, wherein the mirror is in a plane of the optical waveguide, and
wherein the mirror is coupled to an end of the optical waveguide on a side surface of the optical waveguide, wherein the end of the optical waveguide is aligned with the second end of the photo-detector, wherein the mirror is configured to reflect the optical signal back toward the optical waveguide, wherein the mirror causes the optical signal to move in a reversed direction, thereby increasing an absorption length of the photo-detector, and wherein the optical signal is evanescently coupled between the optical waveguide and the photo-detector.

### Claim 13 (depends on 12)

The system of claim 12, wherein the mirror is included in the optical waveguide.

### Claim 14 (depends on 12)

The system of claim 12, wherein the photo-detector includes periodic rows of electrical contacts along a length of the photo-detector.

### Claim 15 (depends on 14)

The system of claim 14, wherein electrical contacts in a given row are electrically connected to each other via a metal layer.

### Claim 16 (depends on 15)

The system of claim 15, wherein the metal layer is fingered proximate to the electrical contacts.

### Claim 17 (depends on 14)

The system of claim 14, wherein the electrical contacts are positioned at locations along the length where the optical signal is substantially in the optical waveguide.

### Claim 18

A method for converting an optical signal into an electrical signal, wherein the method comprises:
conveying the optical signal in an optical waveguide in a first propagation direction;
evanescently coupling the optical signal into a photo-detector disposed on a surface of the optical waveguide;
converting a portion of the optical signal into an electrical signal in the photo-detector;
reflecting a remainder of the optical signal back toward the optical waveguide in a second propagation direction using a mirror proximate to an end of the photo-detector and in a plane of the optical waveguide, wherein the mirror causes the optical signal to move in a reversed direction, thereby increasing an absorption length of the photo-detector;
evanescently coupling the remainder of the optical signal into the photo-detector; and
converting a portion of the remainder of the optical signal into the electrical signal in the photo-detector,
wherein a bottom surface of the photo-detector is disposed on and optically coupled to a region of a top surface of the optical waveguide, wherein the mirror is coupled to an end of the optical waveguide on a side surface of the optical waveguide, wherein the end of the optical waveguide is aligned with the end of the photo-detector on a side surface of the photo-detector.