# US 10,502,547 B2 · Laser sensor for self-mixing interferometry having a vertical external cavity surface emission laser (VECSEL) as the light source

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- Number: US 10,502,547 B2
- Document ID: US10502547B2
- Status: Granted
- Kind: B2
- Application number: 15/177,753
- Filed: 2016-06-09
- Published: 2016-10-06
- Granted: 2019-12-10
- Earliest claimed: 2007-05-07
- Assignees: Philips Photonics GmbH
- Applicants: Philips Photonics GmbH
- Inventors: Johannes Baier; Holger Moench
- Web page: https://patentgrep.com/patent/US10502547B2

## CPC

- G01B 9/02092: {Self-mixing interferometers, i.e. feedback of light from object into laser cavity}
- H01S 5/0028: {Laser diodes used as detectors}
- H01S 3/1062: {using a controlled passive interferometer, e.g. a Fabry-Perot etalon}
- H01S 5/0264: {for monitoring the laser-output}
- H01S 5/0427: {for applying modulation to the laser}
- H01S 5/0607: {by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature}
- H01S 5/141: {using a wavelength selective device, e.g. a grating or etalon (H01S5/146 takes precedence)}
- H01S 5/183: having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
- H01S 5/187: using Bragg reflection
- H01S 5/0262: {Photo-diodes, e.g. transceiver devices, bidirectional devices (H01S5/0265 takes precedence)}
- H01S 5/142: {which comprises an additional resonator}
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL

## Abstract

The present invention relates to a laser sensor for self-mixing interferometry. The laser sensor comprises at least one semiconductor laser light source emitting laser radiation and at least one photodetector (6) monitoring the laser radiation of the laser light source. The laser light source is a VECSEL having a gain medium (3) arranged in a layer structure (15) on a front side of a first end mirror (4), said first end mirror (4) forming an external cavity with an external second end mirror (5). The proposed laser sensor provides an increased detection range and can be manufactured in a low-cost production process.

## Claims

### Claim 1

A self-mixing interferometric laser sensor comprising:
at least one semiconductor laser light source emitting laser radiation, the laser light source being a vertical external cavity surface emission laser, the at least one semiconductor laser light source comprising:
a first end mirror having a front side and a back side,
a gain medium arranged in a layer structure on the front side of the first end mirror, wherein the front side of the first end mirror forms an external cavity with an external second end mirror;
at least one photodetector located on the back side of the front end mirror for measuring changes in properties of subsequent emitted laser radiation; and
at least one Fabry-Perot interferometer situated within the external cavity, between the external second end mirror and the gain medium,
wherein the external second end mirror comprises a coupling mirror for deflecting a portion of the laser radiation resonating in the external cavity so as to cause the portion of the laser radiation to pass through the gain medium of at least one adjacent vertical external cavity surface emission laser.

### Claim 2 (depends on 1)

The laser sensor according to claim 1,
wherein the gain medium is sandwiched between two distributed Bragg reflectors in the layer structure,
wherein an outer one of the distributed Bragg reflectors has a higher reflectance for a lasing wavelength than an inner distributed Bragg reflector,
wherein the outer one of the distributed Bragg reflectors forms the first end mirror of the external cavity.

### Claim 3 (depends on 2)

The laser sensor according to claim 2, wherein the layer structure is formed on an optically transparent substrate inside the external cavity.

### Claim 4 (depends on 2)

The laser sensor according to claim 2, wherein the layer structure is formed on a substrate outside the external cavity.

### Claim 5 (depends on 1)

The laser sensor according to claim 1, the laser sensor further comprising a control circuit that modulates in time an operating current of the vertical external cavity surface emission laser,
wherein the operating current comprises a sawtooth operating current.

### Claim 6 (depends on 1)

The laser sensor according to claim 1, the laser sensor further comprising a control circuit that modulates in time an operating current of the vertical external cavity surface emission laser,
wherein the operating current comprises a triangular operating current.

### Claim 7 (depends on 1)

The laser sensor according to claim 1, wherein either:
the external second end mirror is mounted on a displacement mechanism, the displacement mechanism being controlled by the control circuit so as to move the external second end mirror to modulate an optical cavity length of the external cavity in time, or
the layer structure including the first end mirror is mounted on a displacement mechanism.

### Claim 8 (depends on 1)

The laser sensor according to claim 1, wherein either:
the external second end mirror is mounted on a displacement mechanism, or
the layer structure including the first end mirror is mounted on a displacement mechanism, the displacement mechanism being controlled by the control circuit so as to move the first end mirror to modulate an optical cavity length of the external cavity in time.

### Claim 9 (depends on 1)

The laser sensor according to claim 1,
wherein a width of the Farby Perot interferometer is controlled by a control circuit so as to modulate in time a central wavelength of the laser radiation emitted by the vertical external cavity surface emission laser,
wherein the Fabry-Perot interferometer is driven by an actuator, and
wherein the control circuit operates the actuator.

### Claim 10

A self-mixing interferometric laser sensor comprising:
at least one semiconductor laser light source emitting laser radiation, the laser light source being a vertical external cavity surface emission laser comprising a first end mirror having a front side and a back side, a gain medium arranged in a layer structure on the front side of the first end mirror, the front side of the first end mirror forming an external cavity with an external second end mirror; and
at least one photodetector, located on the back side of the front end mirror, for measuring affected subsequent radiation wherein the photodetector is connected to an evaluation circuit, the evaluation circuit being designed to calculate at least one of a velocity and a distance associated with a target from measurement signals of the photodetector;
wherein several vertical external cavity surface emission lasers with corresponding photodetectors are arranged side by side and form a one dimensional array, the vertical external cavity surface emission lasers being coherently coupled.

### Claim 11 (depends on 10)

The self-mixing interferometric laser sensor according to claim 10, wherein the corresponding photodetectors are arranged side by side and form a two dimensional array.