# US 2014/0233593 A1 · Multi-wavelength laser

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- Number: US 2014/0233593 A1
- Document ID: US20140233593A1
- Status: Published application
- Kind: A1
- Application number: 13/771,054
- Filed: 2013-02-19
- Published: 2014-08-21
- Earliest claimed: 2013-02-19
- Assignees: King Fahd University of Petroleum and Minerals
- Applicants: King Fahd University of Petroleum and Minerals
- Inventors: KHURRAM KARIM QURESHI
- Web page: https://patentgrep.com/patent/US20140233593A1

## CPC

- H01S 5/142: {which comprises an additional resonator}
- H01S 3/083: Ring lasers {(fibre ring lasers H01S3/06791)}
- H01S 3/08022: Longitudinal modes (mode suppression using a plurality of resonators H01S3/082)
- H01S 3/08054: {Passive cavity elements acting on the polarization, e.g. a polarizer for branching or walk-off compensation (quarter-wave plates in a Q-switch laser H01S3/1124, H01S3/115)}
- H01S 3/1062: {using a controlled passive interferometer, e.g. a Fabry-Perot etalon}
- H01S 5/0653: {Mode suppression, e.g. specific multimode}
- H01S 5/5072: {Gain clamping, i.e. stabilisation by saturation using a further mode or frequency}
- 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 multi-wavelength laser is a ring laser source working at room temperature. The laser has an inner cavity disposed in an outer cavity. A pair of circulators disposed in the inner cavity is configured to assure counter-propagation of light between the inner cavity and the outer cavity. A gain-clamped semiconductor optical amplifier (GC-SOA) is formed by combining a SOA and a Fiber Fabry-Perot Tunable Filter (FFP-TF) with the circulator pair. This configuration in the laser cavity results in an improvement in terms of transient gain excursions by applying an optical feedback. This attribute of the GC-SOA enables realizing a stable multi-wavelength laser source.

## Claims

### Claim 1

A multi-wavelength laser, comprising:
a ring multi-wavelength laser having an outer long cavity and an inner short cavity disposed within the outer long cavity;
a pair of circulators disposed inside the inner short cavity;
a Fiber Fabry-Perot Tunable Filter (FFP-TF) and a semiconductor optical amplifier (SOA) operably connected to the circulator pair within the inner short cavity, the filter providing a feedback path and forming a gain-clamped semiconductor optical amplifier (GC-SOA) having an optical output directing first optical signals to the outer long cavity and an optical input accepting second optical signals from the outer long cavity;
a variable optical attenuator (VOA) disposed in the outer long cavity, the variable optical attenuator variably attenuating the first optical signals;
a polarization controller disposed in the outer long cavity and operably connected to the variable optical attenuator, thereby controlling polarization of the variably attenuated first optical signals;
an optical coupler disposed in the outer long cavity, the optical coupler having an input and a split output; and
a filter disposed in the outer long cavity and operably connected to the polarization controller, the filter being configured for filtering the variably attenuated, polarization controlled first optical signals, the filter having an output connected to the optical coupler; and
wherein a first portion of the split output from the optical coupler provides a multi-wavelength coherent beam emitted from the multi-wavelength laser, and a second portion of the split output comprises optical signals retained in the cavities.

### Claim 2 (depends on 1)

The multi-wavelength laser according to claim 1, wherein said circulator pair is configured for causing light flowing inside said inner short cavity to flow in a counterclockwise direction and for causing light flowing inside said outer long cavity to flow in a clockwise direction.

### Claim 3 (depends on 2)

The multi-wavelength laser according to claim 2, wherein said filter disposed in said outer long cavity is a thin film etalon comb filter.

### Claim 4 (depends on 3)

The multi-wavelength laser according to claim 3, wherein said thin film etalon comb filter has a Free Spectral Range (FSR) of about 0.8 nm (100 GHz) and exhibits an absolute wavelength accuracy of approximately 71.25 GHz over a temperature range from about 0° C. to about 70° C.

### Claim 5 (depends on 4)

The multi-wavelength laser according to claim 4, wherein the multi-wavelength coherent beam emitted from said multi-wavelength laser comprises more than 50 lasing lines generated with an average peak power of approximately −30 dBm when said VOA is set to zero attenuation.

### Claim 6 (depends on 2)

The multi-wavelength laser according to claim 2, wherein said optical coupler disposed in said outer long cavity is a 10% fused fiber coupler, the coupler retaining 90% of the light in said outer long cavity.

### Claim 7 (depends on 2)

The multi-wavelength laser according to claim 2, wherein said SOA is biased at between about 180 mA and about 185 mA.

### Claim 8 (depends on 2)

The multi-wavelength laser according to claim 2, wherein said inner short cavity has a length of about 4 m.

### Claim 9 (depends on 2)

The multi-wavelength laser according to claim 2, wherein said outer long cavity has a length of about 7 m.

### Claim 10 (depends on 2)

The multi-wavelength laser according to claim 2, wherein said FFP-TF is tuned at about 1530 nm to provide optical feedback in said inner short cavity.