# US 11,444,435 B2 · Method and device for combining laser beams

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- Number: US 11,444,435 B2
- Document ID: US11444435B2
- Status: Granted
- Kind: B2
- Application number: 16/321,969
- Filed: 2016-10-05
- Published: 2019-06-13
- Granted: 2022-09-13
- Earliest claimed: 2016-08-05
- Assignees: Obshchestvo S Ogranichennoj Otvetstvennostyu "Femtovizhn"
- Applicants: Obshchestvo S Ogranichennoj Otvetstvennostyu “Femtovizhn”
- Inventors: Sergej Petrovich Nikitin; Matvej Sergeevich Pochechuev; Aleksej Mihajlovich Zheltikov
- Web page: https://patentgrep.com/patent/US11444435B2

## CPC

- G02B 27/1006: {for splitting or combining different wavelengths (G02B27/1086, G02B27/141 take precedence)}
- H01S 5/4012: {Beam combining, e.g. by the use of fibres, gratings, polarisers, prisms}
- G02B 27/14: operating by reflection only
- G02B 27/146: {with a tree or branched structure}
- G02B 27/283: {used for beam splitting or combining}
- H01S 3/005: {Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping (shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B)}
- H01S 5/06236: {controlling the polarisation, e.g. TM/TE polarisation switching}
- H01S 5/4087: {emitting more than one wavelength}
- G02B 5/3083: {Birefringent or phase retarding elements (G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001)}
- G02B 27/288: {Filters employing polarising elements, e.g. Lyot or Solc filters (G02B5/3016 takes precedence)}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- 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 invention relates to the field of laser technology and can be used for more efficient optical pumping of laser media in laser generators and amplifiers. The invention can be used for the efficient optical pumping of practically all types of lasers, provided that the absorption profile of the pumped medium is sufficiently broadband. The invention discloses a method and device for combining at least two laser beams of different wavelengths, the polarization states of which are substantially orthogonal, into an exit beam by using a polarizing beamsplitter which spatially combines two beams in mutually orthogonal polarization states, and then changing the polarization state of one of the beams relative to the other using a spectrally selective polarization filter such that the polarization state of the exit beam becomes substantially identical for all of the wavelengths of the exit beam, thus permitting the subsequent combining thereof with another beam.

## Claims

### Claim 1

A method of combining at least a first input laser beam and a second input laser beam, of different wavelengths, polarization states of which are predominantly orthogonal to an output beam, comprising:
using a polarization beam splitter for spatially combining the at least first and second input laser beams in mutually orthogonal polarization states,
directing the spatially combined at least first and second input laser beams to a set of birefringent plates, and
changing a state of polarization of the first input laser beam relative to the second input laser beam by tilting the set of birefringent plates in such a way that a state of polarization of the output beam becomes predominantly the same for all wavelengths of the output beam, wherein the set of birefringent plates maintains a beam quality parameter M2.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the mutually orthogonal polarization states are mutually perpendicular linear polarizations, which are combined by a polarization beam splitter for linear polarizations.

### Claim 3 (depends on 2)

The method according to claim 2, wherein a S̆olc filter comprises the set of birefringent plates.

### Claim 4

A method of combining a plurality of input laser beams, of different wavelengths, polarization states of which are predominantly orthogonal to an output beam, comprising:
using a polarization beam splitter for spatially combining at least two input laser beams of the plurality of input laser beams in mutually orthogonal polarization states, and
directing the spatially combined at least two input laser beams to a set of birefringent plates, and
changing a state of polarization of one of the at least two input laser beams relative to the other input laser beam by tilting the set of birefringent plates in such a way that a state of polarization of the output beam becomes predominantly the same for all wavelengths of the output beam, wherein the set of birefringent plates maintains a beam quality parameter M2,
directing the output beam to a next polarization beam splitter to combine the output beam with a third input laser beam, directing the combined output beam with the third input laser beam to a next set of birefringent plates to perform a spectrally-selective change of light polarization of the third input laser beam relative to the output beam, and repeating for any additional input laser beams.

### Claim 5 (depends on 4)

The method according to claim 4, wherein the mutually orthogonal polarization states are mutually perpendicular linear polarizations, which are combined by a polarization beam splitter for linear polarizations.

### Claim 6 (depends on 4)

The method according to claim 4, wherein the mutually orthogonal polarization states are mutually perpendicular linear polarizations, which are combined by a polarization beam splitter for linear polarizations.

### Claim 7

A device for combining at least a first input laser beam and a second input laser beam with different wavelengths, polarization states of which are predominantly orthogonal, into one output beam, a polarization state of which is predominantly the same for all wavelengths of the output beam, comprising at least one combination of:
a polarization beam splitter that spatially combines the two input laser beams with different wavelengths whose polarization states are predominantly orthogonal, and
a successively placed set of birefringent plates mutually oriented at an angle,
wherein a thickness, a mutual orientation, and a material of the set of birefringent plates provides a change of the polarization of the first input laser beam relative to the second input laser beam in such a way that a state of polarization becomes predominantly the same for all wavelengths of the output beam,
wherein the set of birefringent plates preserves a beam quality parameter M2.

### Claim 8 (depends on 7)

The device according to claim 7, wherein a polarization cube or a polarization prism is used as the polarization beam splitter.

### Claim 9 (depends on 8)

The device according to claim 8, wherein a S̆olc filter comprises the set of birefringent plates.

### Claim 10 (depends on 9)

The device according to claim 9, wherein the set of birefringent plates are equipped with a spectral polarization adjustment using an applied external control voltage.

### Claim 11 (depends on 8)

The device according to claim 8, wherein the birefringent plates have different thicknesses.

### Claim 12 (depends on 11)

The device according to claim 11, wherein the set of birefringent plates are equipped with a spectral polarization adjustment using an applied external control voltage.

### Claim 13 (depends on 8)

The device according to claim 8, wherein the birefringent plates are made of different materials.

### Claim 14 (depends on 13)

The device according to claim 13, wherein the set of birefringent plates are equipped with a spectral polarization adjustment using an applied external control voltage.

### Claim 15 (depends on 8)

The device according to claim 8, wherein the set of birefringent plates are equipped with a spectral polarization adjustment using an applied external control voltage.

### Claim 16 (depends on 7)

The device according to claim 7, wherein the set of birefringent plates are equipped with a spectral polarization adjustment using an applied external control voltage.

### Claim 17 (depends on 7)

A system for spatial combining of K laser beams with different wavelengths, polarization states of which are predominantly orthogonal, into at least one output beam, comprising: two or more devices according to claim 7 being sequentially arranged; and on each output beam of those two or more devices the rest of K-1 beams are combined; wherein a design of the set of birefringent plates is such that the state of polarization of the output beam becomes predominantly the same for all wavelengths of the output beam.

### Claim 18 (depends on 17)

The system of claim 17, wherein the beam splitter is used as a final stage which provides simplification of the optical system for spatial combining of laser beams when the state of polarization of the output beam is not important.