External cavity tunable laser and cavity mode locking method thereof

Patent metadata

Field	Value
Publication number	US-10050406-B2
Application number	US-201715460956-A
Country	US
Kind code	B2
Filing date	Mar 16, 2017
Priority date	Sep 18, 2014
Publication date	Aug 14, 2018
Grant date	Aug 14, 2018

Abstract

The present invention relates to an external cavity tunable laser and a cavity mode locking method thereof. In an embodiment, an external cavity tunable laser comprises a semiconductor amplifier having a partial reflective film provided on one end and an anti-reflective film provided on the other end, a cavity mirror provided at the anti-reflective end to define an external cavity therebetween, a large-range phasing assembly and a quick phasing assembly provided to adjust the optical length of the external cavity independently, an optical power detector provided to detect the optical power of the light output from the semiconductor amplifier, and a control unit in communication with the optical power detector, the large-range phasing assembly, and the quick phasing assembly.

First claim

The invention claimed is:

1. An external cavity tunable laser comprising:
a semiconductor amplifier having a partial reflective film provided on one end and an anti-reflective film provided on the other end;
a cavity mirror provided at the anti-reflective end of the semiconductor amplifier to define an external cavity therebetween;
a large-range phasing assembly and a quick phasing assembly provided to adjust the optical length of the external cavity independently, wherein the large-range phasing assembly comprises at least one temperature adjustable thermo-optic assembly having a silicon plate with light-passing surfaces and anti-reflective films provided on both light-passing surfaces, a heating resistor attached to a non-light region of one of the light-passing surfaces, and a temperature sensor attached to a non-light region of the other of the light-passing surfaces, wherein the large-range phasing assembly further comprises a substrate having the cavity mirror and the quick phasing assembly disposed thereon, the temperature sensor being disposed on the substrate, and a semiconductor cooler disposed below the substrate;
an optical power detector provided at the partial reflective end of the semiconductor amplifier to detect the optical power of the light output from the semiconductor amplifier; and
a control unit in communication with the optical power detector, the large-range phasing assembly, and the quick phasing assembly, the control unit also in communication with the heating resistor and the temperature sensor to control the temperature of the silicon plate, the control unit also in communication with the temperature sensor and the semiconductor cooler and configured to adjust the optical length of the external cavity by controlling the temperature of the substrate, the control unit being configured to perform the following steps:
monitoring whether a difference between the output optical power value received from the optical power detector and a previous maximum output optical power value (P 1 Max ) in a cavity mode locking state is higher than a threshold;
if yes, changing the driving input (D f ) of the quick phasing assembly to obtain a present maximum output optical power value (P 2 Max );
converting the driving input change (D f −CD f ) of the quick phasing assembly to a driving input change (ΔD L ) of the large-range phasing assembly; and
adjusting the driving input of the large-range phasing assembly according to the converted driving input change and resetting the quick phasing assembly to the original driving input, so as to realize cavity mode locking.

2. The external cavity tunable laser of claim 1 , wherein the quick phasing assembly comprises a displacement control element fixed to the cavity mirror to move the cavity mirror in a direction perpendicular to the mirror surface.

3. The external cavity tunable laser of claim 2 , wherein the quick phasing assembly comprises PZT.

4. The external cavity tunable laser of claim 1 , wherein the large-range phasing assembly comprises one or more controlled optical assemblies disposed between the semiconductor amplifier and the cavity mirror controlled by the control unit to change refractive indexes or thicknesses so as to adjust the optical length of the external cavity.

5. The external cavity tunable laser of claim 4 , wherein the controlled optical assembly comprises a driving-voltage or driving-current adjustable electro-optic assembly based on the electro-optic effect.

6. The external cavity tunable laser of claim 5 , wherein the driving-voltage or driving-current adjustable electro-optic assembly comprises a phase adjustable liquid crystal sheet having anti-reflective films provided on both light-passing surfaces, and the control unit is configured to rotate the optical axis of the liquid crystal sheet by controlling its driving voltage or current, thereby adjusting the refractive index of the liquid crystal sheet and thus the optical length of the external cavity.

7. The external cavity tunable laser of claim 1 , wherein the control unit is further configured to receive an instruction to switch the optical channel wavelength of the laser and, in response to the instruction, adjust the driving input of the large-range phasing assembly within a predetermined range to achieve a maximum optical output power.

8. The external cavity tunable laser of claim 7 , wherein the large-range phasing assembly comprises a first large-range phasing assembly and a second large-range phasing assembly, the control unit adjusts the first large-range phasing assembly in response to the instruction to switch the optical channel wavelength of the laser and performs the converting and adjusting steps on the second large-range phasing assembly.

9. The external cavity tunable laser of claim 1 , further comprising a beam splitter to split the output beam from the semiconductor amplifier into two sub-beams, one of which is directed to an output optical fiber and the other is directed to the optical power detector.

10. The external cavity tunable laser of claim 9 , further comprising:
a beam expanding and collimation lens disposed between the semiconductor amplifier and the cavity mirror; and
a plurality of filters disposed between the beam expanding and collimation lens and the cavity mirror.

11. The external cavity tunable laser of claim 10 , further comprising:
a first output beam collimation lens disposed between the semiconductor amplifier and the beam splitter;
an optical isolator disposed downstream the beam splitter; and
a second output beam collimation lens disposed downstream the optical isolator to direct the output beam to the output optical fiber.

12. A cavity mode locking method for an external cavity tunable laser including a semiconductor amplifier having a partial reflective end and an anti-reflective end, a cavity mirror provided at the anti-reflective end of the semiconductor amplifier to define an external cavity therebetween, a large-range phasing assembly and a quick phasing assembly ( 7 ) provided to adjust the optical length of the external cavity independently, the large-range phasing assembly comprising at least one temperature adjustable thermo-optic assembly having a silicon plate with light-passing surfaces and anti-reflective films provided on both light-passing surfaces, a heating resistor attached to a non-light region of one of the light-passing surfaces, and a temperature sensor attached to a non-light region of the other of the light-passing surfaces, the large-range phasing assembly further comprising a substrate having the cavity mirror and the quick phasing assembly disposed thereon, the temperature sensor being disposed on the substrate, and a semiconductor cooler disposed below the substrate an optical power detector to detect the optical power of the light output from the semiconductor amplifier, and a control unit in communication with the optical power detector, the large-range phasing assembly, and the quick phasing assembly, the control unit also in communication with the heating resistor and the temperature sensor to control the temperature of the silicon plate, the control unit also in communication with the temperature sensor and the semiconductor cooler and configured to adjust the optical length of the external cavity by controlling the temperature of the substrate, the method comprising:
the control unit monitoring whether a difference between the output optical power value received from the optical power detector and a previous maximum output optical power value (P 1 Max ) in a cavity mode locking state is higher than a threshold;
if yes, the control unit changing the driving

Assignees

• Accelink Tech Co Ltd

Inventors

• Tang Xuesheng
• Fu Yanfeng
• Qian Kun
• Luo Yong
• Chen Yizong
• Zhang Di
• Hu Qianggao
• Tang Yi
• Luo Chao

Classifications

• H01S3/1067

  using pressure or deformation · CPC title

• H01S5/028

  Coatings {; Treatment of the laser facets, e.g. etching, passivation layers or reflecting layers} · CPC title

• H01S5/0687

  Stabilising the frequency of the laser · CPC title

• H01S3/1307

  Stabilisation of the phase · CPC title

• H01S5/02438

  Characterized by cooling of elements other than the laser chip, e.g. an optical element being part of an external cavity or a collimating lens · CPC title