# US 9,203,214 B2 · Laser system

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- Number: US 9,203,214 B2
- Document ID: US9203214B2
- Status: Granted
- Kind: B2
- Application number: 14/107,269
- Filed: 2013-12-16
- Published: 2014-09-04
- Granted: 2015-12-01
- Earliest claimed: 2012-12-18
- Assignees: Laser Quantum Limited
- Applicants: Laser Quantum Inc.
- Inventors: Alan Cox
- Web page: https://patentgrep.com/patent/US9203214B2

## CPC

- H01S 5/06817: {Noise reduction}
- H01S 5/0683: by monitoring the optical output parameters
- H01S 3/09415: {the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping}
- H01S 3/1312: {by controlling the optical pumping}
- H01S 5/042: Electrical excitation {; Circuits therefor (monolithically integrated laser drive components H01S5/0261)}
- 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

A laser system comprising a laser configured to generate a laser beam, a power supply arranged to provide a drive power to the laser, a photodetector arranged to detect the power of the laser beam and provide a detection signal from the power of the laser beam and a feedback loop arranged to form a feedback signal by subtracting a target signal from the detection signal wherein the feedback signal has a high bandwidth, amplify the feedback signal and adjust the drive power according to the amplified feedback signal, thereby reducing noise in the laser beam.

## Claims

### Claim 1

A laser system comprising:
a laser configured to generate a laser beam;
a power supply arranged to provide a drive power to the laser;
a photodetector arranged to detect the power of the laser beam and provide a detection signal from the power of the laser beam, wherein the detection signal corresponds to the power of the laser beam; and
a feedback loop arranged to:
form a feedback signal by subtracting a target signal from the detection signal, wherein the feedback signal has a high bandwidth which extends continuously from a DC frequency to a high frequency;
amplify the feedback signal; and
adjust the drive power according to the amplified feedback signal, thereby reducing noise in the laser beam.

### Claim 2 (depends on 1)

The laser system of claim 1, wherein the target signal has a lower bandwidth than the feedback signal.

### Claim 3 (depends on 1)

The laser system of claim 1, wherein the feedback signal has a bandwidth greater than 10 times the bandwidth of the target signal.

### Claim 4 (depends on 3)

The laser system of claim 3, wherein the feedback signal has a bandwidth greater than 1000 times the bandwidth of the target signal.

### Claim 5 (depends on 1)

The laser system of claim 1, wherein the target signal has a low bandwidth.

### Claim 6 (depends on 1)

The laser system of claim 1, wherein the feedback signal has a bandwidth which is greater than or equal to 10 kHz.

### Claim 7 (depends on 6)

The laser system of claim 6, wherein the feedback signal has a bandwidth which is greater than or equal to 100 kHz.

### Claim 8 (depends on 1)

The laser system of claim 1, further comprising a low-pass filter configured to low-pass filter the target signal before the subtraction of the target signal from the detection signal.

### Claim 9 (depends on 1)

The laser system of claim 1, wherein the target signal has an amplitude of greater than two times the amplitude of the feedback signal.

### Claim 10 (depends on 1)

The laser system of claim 1, wherein the drive power comprises a first power having a low bandwidth from which a second power having a high bandwidth is subtracted.

### Claim 11 (depends on 1)

The laser system of claim 1, wherein the drive power comprises a first power having a low bandwidth summed with a second power having a high bandwidth.

### Claim 12 (depends on 10)

The laser system of claim 10, wherein adjusting the drive power according to the amplified feedback signal comprises adjusting the second power according to the amplified feedback signal.

### Claim 13 (depends on 10)

The laser system of any of claim 10, further comprising a controller arranged to control the first power and/or the target signal such that an average over time of the feedback signal is substantially equal to zero or a predetermined constant.

### Claim 14 (depends on 1)

The laser system of claim 1, wherein the feedback loop further comprises a variable gain amplifier.

### Claim 15 (depends on 13)

The laser system of claim 13, wherein the feedback loop further comprises a variable gain amplifier and wherein the controller is further arranged to control the gain of the variable gain amplifier such that it reduces noise in the laser beam over a predetermined bandwidth.

### Claim 16 (depends on 1)

The laser system of any of claim 1, wherein the feedback loop further comprises one or more phase lead compensator circuits, wherein the one or more phase lead compensator circuits are configured to advance the phase of the amplified feedback signal.

### Claim 17 (depends on 15)

The laser system of claim 15, wherein the feedback loop further comprises one or more phase lead compensator circuits, wherein the one or more phase lead compensator circuits are configured to advance the phase of the amplified feedback signal, and wherein the controller is further arranged to adjust the phase lead compensation of the one or more phase lead compensator circuits such that it reduces noise in the laser beam over a predetermined bandwidth.

### Claim 18 (depends on 1)

The laser system of claim 1, further comprising an input configured to receive an error signal and add the error signal to the feedback signal.

### Claim 19 (depends on 18)

The laser system of claim 18, wherein the input is further configured to:
add a first portion of the error signal to the feedback signal before amplification; and
add a second portion of the error signal to the feedback signal after amplification.

### Claim 20 (depends on 1)

The laser system of claim 1, wherein the laser comprises a pump configured to transfer power to a gain medium, the gain medium being configured to generate a laser beam.

### Claim 21 (depends on 20)

The laser system of claim 20, wherein the pump comprises a laser diode system, comprising:
a laser diode configured to generate a laser diode beam;
a second photodetector arranged to detect the power of the laser diode beam and form a laser diode detection signal from the power of the laser diode beam; and
a laser diode feedback loop arranged to form a high bandwidth laser diode feedback signal by subtracting a low bandwidth laser diode target signal from the laser diode detection signal, amplify the high bandwidth laser diode feedback signal and adjust, according to the amplified high bandwidth laser diode feedback signal, the drive power, thereby reducing fluctuations of the power of the laser diode beam.

### Claim 22 (depends on 21)

The laser system of claim 21, wherein a portion of the feedback signal is added to the high bandwidth laser diode feedback signal.

### Claim 23 (depends on 22)

The laser system of claim 22, wherein a first portion of the feedback signal is added to the high bandwidth laser diode feedback signal before amplification and a second portion of the feedback signal is added to the high bandwidth laser diode feedback signal after amplification.

### Claim 24 (depends on 1)

The laser system of claim 1, wherein the power supply is positioned within a control box, and wherein the laser, the photodetector and the feedback loop are positioned within a laser head.

### Claim 25

A method of reducing noise in a laser beam generated by a laser, the method comprising:
detecting the power of the laser beam to form a detection signal, wherein the detection signal corresponds to the power of the laser beam;
forming a feedback signal by subtracting a target signal from the detection signal, wherein the feedback signal has a high bandwidth which extends continuously from a DC frequency to a high frequency;
amplifying the feedback signal; and
adjusting, according to the amplified feedback signal, a drive power which drives the laser, thereby reducing noise in the laser beam.

### Claim 26 (depends on 25)

The method of claim 25, wherein the target signal has a lower bandwidth than the feedback signal.

### Claim 27 (depends on 25)

The method of claim 25, wherein the feedback signal has a bandwidth greater than 10 times the bandwidth of the target signal.

### Claim 28 (depends on 27)

The method of claim 27, wherein the feedback signal has a bandwidth greater than 1000 times the bandwidth of the target signal.

### Claim 29 (depends on 25)

The method of claim 25, wherein the target signal has a low bandwidth.

### Claim 30 (depends on 25)

The method of claim 25, wherein the feedback signal has a bandwidth which is greater than or equal to 10 kHz.

### Claim 31 (depends on 30)

The method of claim 30, wherein the feedback signal has a bandwidth which is greater than or equal to 100 kHz.

### Claim 32 (depends on 25)

The method of claim 25, wherein forming the feedback signal by subtracting the target signal from the detection signal, further comprises low-pass filtering the target signal before the subtraction of the target signal from the detection signal.

### Claim 33 (depends on 25)

The method of claim 25, wherein the target signal has an amplitude of greater than two times the amplitude of the feedback signal.

### Claim 34 (depends on 25)

The method of claim 25, wherein the drive power comprises a first power having a low bandwidth from which a second power having a high bandwidth is subtracted.

### Claim 35 (depends on 25)

The method of claim 25, wherein the drive power comprises a first power having a low bandwidth summed with a second power having a high bandwidth.

### Claim 36 (depends on 34, 35)

The method of claim 34 or 35, wherein adjusting the drive power according to the amplified feedback signal comprises adjusting the second power, according to the amplified feedback signal.

### Claim 37 (depends on 34)

The method of claim 34, further comprising controlling the first power and/or the target signal such that an average over time of the feedback signal is substantially equal to zero or a predetermined constant.

### Claim 38 (depends on 25)

The method of claim 25, further comprising adding an error signal to the feedback signal.

### Claim 39 (depends on 38)

The method of claim 38, wherein a first portion of the error signal is added to the feedback signal before amplification and a second portion of the error signal is added to the feedback signal after amplification.

### Claim 40 (depends on 31)

The method of claim 31, wherein the feedback signal has a bandwidth which is greater than or equal to 1 MHz.

### Claim 41 (depends on 40)

The method of claim 40, wherein the feedback signal has a bandwidth which is greater than or equal to 10 MHz.

### Claim 42 (depends on 7)

The laser system of claim 7, wherein the feedback signal has a bandwidth which is greater than or equal to 1 MHz.

### Claim 43 (depends on 42)

The laser system of claim 42, wherein the feedback signal has a bandwidth which is greater than or equal to 10 MHz.