# US 10,312,387 B2 · Single photon detection using a resonator with an absorber

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- Number: US 10,312,387 B2
- Document ID: US10312387B2
- Status: Granted
- Kind: B2
- Application number: 15/436,372
- Filed: 2017-02-17
- Published: 2018-01-11
- Granted: 2019-06-04
- Earliest claimed: 2016-02-18
- Assignees: Massachusetts Institute of Technology
- Applicants: Massachusetts Institute of Technology
- Inventors: Dirk Robert Englund
- Web page: https://patentgrep.com/patent/US10312387B2

## CPC

- H10F 77/413: {directly associated or integrated with the devices, e.g. back reflectors (directly associated or integrated with photovoltaic cells H10F77/42)}
- G01J 1/44: Electric circuits {(for command of an exposure part G03B7/02)}
- G02F 1/3515: {All-optical modulation, gating, switching, e.g. control of a light beam by another light beam (G02F1/353, G02F1/37, G02F1/39 take precedence)}
- G02F 1/353: {Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams}
- H04B 10/70: Photonic quantum communication
- H10F 77/1246: {III-V nitrides, e.g. GaN}
- H10F 77/12485: {comprising nitride compounds, e.g. InGaN}
- H10F 77/407: {indirectly associated with the devices}
- G01J 2001/442: {Single-photon detection or photon counting}
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- 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)
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- H04B: TRANSMISSION

## Abstract

A single photon detector (SPD) includes a resonator to store probe photons at a probe wavelength and an absorber disposed in the resonator to absorb a signal photon at a signal wavelength. The absorber is also substantially transparent to the probe photons. In the absence of the signal photon, the resonator is on resonance with the probe photons, thereby confining the probe photons within the resonator. Absorption of the signal photon by the absorber disturbs the resonant condition of the resonator, causing the resonator to release multiple probe photons. A photodetector (PD) then detects these multiple probe photons to determine the presence of the signal photon.

## Claims

### Claim 1

An apparatus for detecting a signal photon at a first wavelength, the apparatus comprising:
a resonator to store a plurality of probe photons at a second wavelength different from the first wavelength;
an absorber, disposed at least partially in the resonator and substantially transparent to the plurality of probe photons, to absorb the signal photon, absorption of the signal photon causing a change of a resonant wavelength of the resonator, the change of the resonant wavelength causing release of at least some of the plurality of probe photons from the resonator; and
a detector, in optical communication with the resonator, to generate an electrical signal in response to detection of the at least some of the plurality of probe photons, the electrical signal indicating a presence of the signal photon.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the resonant wavelength of the resonator is substantially equal to or greater than 1.5 μm.

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein the resonator has a quality factor greater than 104.

### Claim 4 (depends on 1)

The apparatus of claim 1, wherein the resonator comprises a first distributed Bragg reflector (DBR) and a second DBR disposed opposite the first DBR.

### Claim 5 (depends on 4)

The apparatus of claim 4, wherein the absorber comprises a semiconductor heterostructure disposed between the first DBR and the second DBR.

### Claim 6 (depends on 4)

The apparatus of claim 4, wherein the absorber is disposed between the first DBR and the second DBR, the absorber comprising:
a first semiconductor layer having a first bandgap;
a second semiconductor layer disposed on a first side of the first semiconductor layer; and
a third semiconductor layer disposed on a second side, opposite the first side, of the first semiconductor layer, the second semiconductor layer and the third semiconductor layer having a second bandgap greater than the first bandgap of the first semiconductor layer.

### Claim 7 (depends on 6)

The apparatus of claim 6, wherein the first semiconductor layer comprises InGaN and the second semiconductor layer and the third semiconductor layer comprise GaN.

### Claim 8 (depends on 1)

The apparatus of claim 1, wherein the resonator comprises:
a photonic crystal, the photonic crystal including:
a first line defect to receive the plurality of probe photons;
a first point defect to define a first cavity having a first resonant frequency ω1;
a second point defect to define a second cavity having a second resonant frequency ω2 and a linewidth Γ2, a difference between the first resonant frequency and the second resonant frequency |ω1-ω2| being substantially equal to the linewidth Γ2, the first cavity and the second cavity defining a photonic waveguide to store the plurality of probe photons; and
a second line defect to output the at least some of the plurality of probe photons.

### Claim 9 (depends on 1)

The apparatus of claim 1, wherein the resonator comprises:
an input waveguide; and
a micro-ring resonator, evanescently coupled to the input waveguide, to receive the plurality of probe photons via the input waveguide.

### Claim 10 (depends on 9)

The apparatus of claim 9, wherein the input waveguide comprises:
a first section, evanescently coupled to a first location of the micro-ring resonator, to couple out a first portion of the plurality of probe photons; and
a second section, evanescently coupled to a second location of the micro-ring resonator, to couple out a second portion of the plurality of probe photons, the second portion destructively interfering with the first portion.

### Claim 11 (depends on 1)

The apparatus of claim 1, wherein the absorber comprises a III-N semiconductor.

### Claim 12 (depends on 1)

The apparatus of claim 1, wherein the absorber comprises a semiconductor having a bandgap energy at least two times greater than a photon energy of the probe photons in the plurality of probe photons.

### Claim 13 (depends on 1)

The apparatus of claim 1, wherein the resonator comprises:
a first reflector having a first reflectance greater than 99.9% at the second wavelength; and
a second reflector disposed opposite the first reflector and having a second reflectance less than 99.5% at the second wavelength.

### Claim 14

A method of detecting a signal photon at a first wavelength, the method comprising:
coupling a plurality of probe photons at a second wavelength, different from the first wavelength, into a resonator, the resonator including an absorber disposed at least partially in the resonator and substantially transparent to the plurality of probe photons;
absorbing the signal photon with the absorber, the absorber changing a resonant wavelength of the resonator in response to absorption of the signal photon, thereby releasing at least some of the plurality of probe photons from the resonator; and
detecting the at least some of the plurality of probe photons; and
determining a presence of the signal photon based on detection of the at least some of the plurality of probe photons.

### Claim 15 (depends on 14)

The method of claim 14, wherein coupling the plurality of probe photons into the resonator comprises transmitting the plurality of probe photons through a first DBR disposed opposite a second DBR and wherein absorbing the signal photon comprises coupling the signal photon into a semiconductor heterostructure disposed between the first DBR and the second DBR.

### Claim 16 (depends on 15)

The method of claim 15, wherein absorbing the signal photon comprises transmitting the signal photon through a first semiconductor layer having a first bandgap disposed between two second semiconductor layers having a second bandgap greater than the first bandgap.

### Claim 17 (depends on 14)

The method of claim 14, wherein coupling the plurality of probe photons comprises transmitting the plurality of probe photons through a first line defect in a photonic crystal to a photonic waveguide defined by a first point defect and a second point defect, and wherein detecting the at least some of the plurality of probe photons comprises transmitting the at least some of the plurality of probe photons through a second line defect in the photonic crystal to a detector.

### Claim 18 (depends on 14)

The method of claim 14, wherein coupling the plurality of probe photons comprises:
transmitting the plurality of probe photons through a first section of an input waveguide evanescently coupled to a first location of a ring resonator so as to couple out a first portion of the plurality of probe photons; and
transmitting the plurality of probe photons through a second section of the input waveguide evanescently coupled to a second location of the ring resonator so as to couple out a second portion of the plurality of probe photons, the second portion destructively interfering with the first portion.

### Claim 19 (depends on 14)

The method of claim 14, wherein absorbing the signal photon comprises absorbing the signal photon with a III-N semiconductor having a bandgap energy at least two times greater than a photon energy of the plurality of probe photons.

### Claim 20 (depends on 14)

The method of claim 14, wherein coupling the plurality of probe photons comprises transmitting the plurality of photons through a first reflector having a first reflectance less than 99.5% at the second wavelength and disposed opposite a second reflector and having a second reflectance greater than 99.9% at the second wavelength.

### Claim 21

A single-photon detector to detect a signal photon at a signal wavelength, the single-photon detector comprising:
an input waveguide to receive a plurality of probe photons at a probe wavelength less than half of the signal wavelength;
a micro-ring resonator, evanescently coupled to the input waveguide, to receive the plurality of probe photons, the input waveguide comprising:
a first section, evanescently coupled to a first location of the micro-ring resonator, to couple out a first portion of the plurality of probe photons; and
a second section, evanescently coupled to a second location of the micro-ring resonator, to couple out a second portion of the probe photons, the second portion destructively interfering with the first portion;
an absorber, disposed at least partially in the micro-ring resonator and substantially transparent at the probe wavelength, to absorb the signal photon, absorption of the signal photon causing a change of a resonant wavelength of the micro-ring resonator releasing at least some of the plurality of probe photons from the micro-ring resonator, the absorber comprising a III-N semiconductor having a bandgap energy at least two times greater than a photon energy of the probe photons in the plurality of probe photons; and
a detector, in optical communication with the resonator, to detect the at least some of the plurality of probe photons.