EP-4738626-A1 - METHOD AND SYSTEM FOR LASER INJECTION LOCKING

EP4738626A1EP 4738626 A1EP4738626 A1EP 4738626A1EP-4738626-A1

Abstract

Provided is method for injection locking a first laser onto a second laser, the method comprising the steps of: a) providing at least part of light emitted by the first laser to the second laser; b) continuously changing an input parameter of the second laser until a value at which a signal of the second laser shifts is reached; c) adding the value at which the signal of the second laser shifts to a set of values; d) repeating steps b) and c) until the set of values converges to a convergence value; and e) setting the input parameter of the second laser based on the convergence value, thereby injection locking the first laser onto the second laser.

Inventors

GROSS, CHRISTIAN
de Martino, Alexandre
Auch, Jonas
Karpov, Kirill
Kiesel, Florian

Assignees

Eberhard Karls Universität Tübingen

Dates

Publication Date: 20260506
Application Date: 20241029

Claims (15)

A method for injection locking a first laser onto a second laser, the method comprising the steps of: a) providing at least part of light emitted by the first laser to the second laser; b) continuously changing an input parameter of the second laser until a value at which a signal of the second laser shifts is reached; c) adding the value at which the signal of the second laser shifts to a set of values; d) repeating steps b) and c) until the set of values converges to a convergence value; and e) setting the input parameter of the second laser based on the convergence value, thereby injection locking the first laser onto the second laser.
The method according to claim 1, further comprising receiving a trigger input to perform the injection locking synchronously to an external event.
The method according to claim 1, further comprising detecting that the second laser is not injection locked to the first laser, and performing the injection locking according to the detection.
The method according to any one of claims 1 to 3, wherein, in step b), the input parameter of the second laser is continuously decreased, or the input parameter of the second laser is continuously increased.
The method according to any one of claims 1 to 4, wherein, in step b), it is determined that the value at which the signal of the second laser shifts is reached by comparing subsequent values of the signal of the second laser.
The method according to claim 5, wherein comparing subsequent values of the signal of the second laser includes comparing two subsequent values and determining whether a difference between the two subsequent values exceeds a first predetermined threshold; and/or includes determining a slope of the signal and determining whether the slope of the signal exceeds a second predetermined threshold.
The method according to any one of claim 1 to 6, wherein, in step b), continuously changing an input parameter of the second laser is performed in discrete steps such that each value of the input parameter is held for a predetermined period of time.
The method according to any one of claims 1 to 7, wherein an output power of the second laser is greater than an output power of the first laser.
The method according to any one of claims 1 to 8, wherein the first and the second laser differ in at least one intrinsic property.
The method according to any one of claims 1 to 9, wherein the input parameter of the second laser is a current applied to the second laser, or a voltage controlling the current applied to the second laser.
The method according to claim 10, wherein the current applied to the second laser is modulated with a triangular waveform.
The method according to any one of claims 1 to 11, wherein the signal of the second laser is a signal of a photodiode integrated into the second laser, preferably a photocurrent of the photodiode or a voltage converted from the photocurrent.
A system for injection locking a first laser onto a second laser, the system comprising the first laser, the second laser, and a control unit, wherein the first laser is configured to provide at least part of light emitted by the first laser to the second laser, and the control unit is configured to perform the steps of: a) continuously changing an input parameter of the second laser until a value at which an signal of the second laser shifts is reached; b) adding the value at which the signal of the second laser shifts to a set of values; c) repeating steps a) and b) until the set of values converges to a convergence value; and d) setting the input parameter of the second laser based on the convergence value, thereby injection locking the first laser onto the second laser.
The system according to claim 13, wherein the control unit is further configured to receive a trigger input to perform the injection locking synchronously to an external event.
The system according to claim 13, wherein the control unit is further configured to detect that the second laser is not injection locked to the first laser, and perform the injection locking according to the detection.

Description

The present disclosure relates to a method for laser injection locking, specifically injection locking a first laser onto a second laser. Moreover, it relates to a system for injection locking. Background For many applications involving laser light, it is highly desirable to generate high output power at the same time as achieving narrow line single mode lasing. Unfortunately, these two characteristics are often mutually exclusive and/or technically demanding to achieve for available lasers/laser diodes such that efficient and scalable amplification of narrow line laser light remains a major driving point in current development of laser system designs. One approach to address this is injection locking (also referred to as "laser injection locking"). Injection locking relates to forcing the spectral characteristics of a first laser, sometimes referred to as seed laser or master laser, onto a second laser, sometimes referred to as slave laser, by optically injecting laser light from the first laser into the second laser. For this to work, the second laser's parameter, such as its temperature and its current, must be tuned to match its cavity with the laser light injected from the first laser. While injection locking, in particular of high-power semiconductor laser diodes, is able to address this problem in many scenarios it remains challenging to achieve (long-term) stable operation of the injection locked state due to the complex interplay of the non-linear effects as well as the thermal effects involved in injection locking. In view of these difficulties, conventional approaches of injection locking, no matter whether they are based on active or passive stabilization, typically require a large amount of optical and/or electrical equipment and can only applied to specific scenarios on a limited scale but are neither generally applicable nor scalable. Moreover, despite the amount of additional equipment employed in conventional approaches, long-term stability is often difficult to achieve. Hence, there is a need for an injection locking technique that allows for long-term stability of the system that at the same time is generally applicable as well as scalable. Summary The present disclosure has been made in view of the above technical limitations of the currently available solutions for injection locking and thus provides a method and a system for injection locking that overcomes these limitations. In particular, the present disclosure is based on understanding the thermalization characteristics of the laser to be injection locked and exploiting the same. Based on this, the present disclosure is able to provide long-term stable injection locking without the need of a large amount of optical and/or electrical equipment and without being tailored to the specifics of the setup such that the present disclosure allows generally applicable and scalable injection locking. According to an aspect of the present disclosure, a method for injection locking a first laser onto a second laser is provided, the method comprising the steps of: a) providing at least part of light emitted by the first laser to the second laser; b) continuously changing an input parameter of the second laser until a value at which a signal of the second laser shifts is reached; c) adding the value at which the signal of the second laser shifts to a set of values; d) repeating steps b) and c) until the set of values converges to a convergence value; and e) setting the input parameter of the second laser based on the convergence value, thereby injection locking the first laser onto the second laser. According to another aspect of the present disclosure, a system for injection locking a first laser onto a second laser is provided, the system comprising the first laser, the second laser, and a control unit, wherein the first laser is configured to provide at least part of light emitted by the first laser to the second laser, and the control unit is configured to perform the steps of: a) continuously changing an input parameter of the second laser until a value at which a signal of the second laser shifts is reached; b) adding the value at which the signal of the second laser shifts to a set of values; c) repeating steps a) and b) until the set of values converges to a convergence value; and d) setting the input parameter of the second laser based on the convergence value, thereby injection locking the first laser onto the second laser. In addition, preferred aspects of the present disclosure are defined in the dependent claims. According to the invention, an improved injection locking can be provided, in particular a long-term stable, generally applicable and scalable injection locking can be provided. Brief description of the drawings Embodiments of the present disclosure, which are presented for better understanding the inventive concepts, but which are not to be seen as limiting the disclosure, will be described with reference to the figures in w