WO2025231947A1 - External cavity tunable semiconductor laser - Google Patents

Abstract

An external cavity tunable semiconductor laser, comprising, successively and optically connected to each other, a semiconductor laser (10), a collimating lens (20), a cylindrical lens (30), a diffraction grating (40), and a partially reflecting mirror (50). The collimating lens (20) is close to the position at one focal length from a side of the cylindrical lens (30). The center of the diffraction grating (40) coincides with the position at one focal length from the other side of the cylindrical lens (30). The ruling direction of the diffraction grating (40) is the same as the polarization direction of a light beam transmitted to the partially reflecting mirror (50) via the diffraction grating (40). The normal to the diffraction grating (40) and the transmission direction of the light beam transmitted to the partially reflecting mirror (50) form a littrow angle. The transmission direction of the light beam via the partially reflecting mirror (50) is perpendicular to the partially reflecting mirror (50). The cylindrical lens (30) is used to move in a direction perpendicular to the transmission direction of the light beam transmitted to the cylindrical lens (30) so as to tune the wavelength of an output light beam.

Description

External cavity tunable semiconductor laser

Related applications

This application claims priority to Chinese patent application No. 202410553266.2, filed on May 7, 2024, the entire contents of which are incorporated herein by reference.

Technical Field

This application relates to the field of fiber laser technology, and specifically to a method for an external cavity tunable semiconductor laser.

Background Technology

An external cavity tunable semiconductor laser is an effective structure for achieving tunable output of a semiconductor laser. It mainly consists of three parts: a semiconductor laser chip, a collimating lens, and an optical feedback element. The optical feedback element acts as a frequency selection element, selecting and feeding back the laser output from the semiconductor laser chip. Adjusting the optical feedback element achieves wavelength tuning of the output laser.

To achieve wide tuning of optical power in semiconductor lasers, the external cavity tunable structure provided in related technologies mainly adjusts the lasing wavelength of the resonant cavity by changing the grating angle, thereby realizing the wavelength tuning function. However, the beam output direction also changes with the rotation of the grating.

Therefore, there is an urgent need for an external cavity tunable semiconductor laser that can achieve wavelength tuning while ensuring that the direction of the beam output remains unchanged.

Summary of the Invention

This application provides an external cavity tunable semiconductor laser to solve the technical problem in related technologies that external cavity tunable semiconductor lasers cannot simultaneously guarantee wavelength tuning function and beam output direction.

To address the aforementioned technical problems, this application provides an external cavity tunable semiconductor laser, comprising a semiconductor laser, a collimating lens, a cylindrical lens, a diffraction grating, and a partial reflector connected in sequence.

The collimating lens is located at one focal length from the cylindrical lens, and the center of the diffraction grating coincides with the positions at one focal length on both sides of the cylindrical lens, respectively. Furthermore, the grating direction of the diffraction grating is the same as the polarization direction of the light beam transmitted to the partial mirror via the diffraction grating.

The normal of the diffraction grating forms a littrow angle with the transmission direction of the light beam transmitted to the partial mirror, and the transmission direction of the light beam through the partial mirror is perpendicular to the partial mirror.

The cylindrical lens is used to move in a direction perpendicular to the transmission direction of the light beam transmitted to the cylindrical lens in order to tune the wavelength of the output light beam.

In this embodiment of the application, the moving distance of the cylindrical lens in the direction perpendicular to the transmission direction of the light beam transmitted to the cylindrical lens satisfies a first preset relationship with the first incident angle and the second incident angle. The first incident angle is the incident angle of the light beam transmitted to the diffraction grating before the cylindrical lens moves, and the second incident angle is the incident angle of the light beam transmitted to the diffraction grating after the cylindrical lens moves.

The first preset relationship is:

Where θ’ is the second incident angle, θ is the first incident angle, Δx is the moving distance, and f is the focal length of the cylindrical lens.

In this embodiment of the application, the wavelength of the tuned beam satisfies a second preset relationship with the first incident angle and the second incident angle;

The second preset relationship is:

Wherein, λ is the wavelength, and d is the spacing between adjacent grooves on the surface of the diffraction grating. In this embodiment, the semiconductor laser is a blue semiconductor laser.

In this embodiment, the collimating lens includes a fast-axis collimating lens and a slow-axis collimating lens, with the fast-axis collimating lens disposed between the semiconductor laser and the slow-axis collimating lens.

In this embodiment, the fast-axis collimating lens is an aspherical cylindrical lens, and the slow-axis collimating lens is a spherical cylindrical lens.

In this embodiment, the focal length of the aspherical cylindrical lens is 300 micrometers, and the focal length of the spherical cylindrical lens is 12 millimeters.

In this embodiment, the cylindrical lens is a plano-convex cylindrical lens, and the convex direction of the plano-convex cylindrical lens is close to the diffraction grating.

In this embodiment of the application, the diffraction grating is a planar grating.

In this embodiment, the planar grating is a transmissive grating.

This application provides an external cavity tunable semiconductor laser. By placing a collimating lens at one focal length from the cylindrical lens side and the center of a diffraction grating at one focal length from both sides of the cylindrical lens, and keeping the grating's scribe line direction the same as the beam polarization direction, and the normal of the diffraction grating forming a littrow angle with the beam propagation direction transmitted to the partial mirror, and the beam propagation direction via the partial mirror being perpendicular to the partial mirror, the wavelength of the output beam can be tuned by moving the cylindrical lens perpendicular to the beam propagation direction transmitted to the cylindrical lens, while ensuring that the beam output direction remains unchanged.

Attached Figure Description

To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

Figure 1 is a schematic diagram of a structure of an external cavity tunable semiconductor laser provided in an embodiment of this application;

Figure 2 is a schematic diagram of another structure of the external cavity tunable semiconductor laser provided in the embodiments of this application.

The reference numerals in the attached figures are as follows:

10. Semiconductor laser; 20. Collimating lens; 21. Fast-axis collimating lens; 22. Slow-axis collimating lens; 30. Cylindrical lens; 40. Diffraction grating; 50. Partial reflector.

Detailed Implementation

The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

In the description of this application, it should be understood that the terms "longitudinal," "lateral," "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," and "horizontal," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified. In this application, "/" means "or."

Reference numbers and/or reference letters may be repeated in different examples in this application. Such repetition is for the purpose of simplification and clarity and does not in itself indicate the relationship between the various implementations and/or settings discussed.

In this embodiment, the external cavity tunable semiconductor laser is an effective structure for achieving tunable output of a semiconductor laser, mainly composed of three parts: a semiconductor laser chip, a collimating lens, and an optical feedback element. The optical feedback element, acting as a frequency selection element, selects and feeds back the laser output from the semiconductor laser chip. Adjustment of the optical feedback element achieves wavelength tuning of the output laser.

To achieve wide power tuning in semiconductor lasers, the external cavity tunable structures provided in related technologies mainly adjust the lasing wavelength of the resonant cavity by changing the grating angle, thereby achieving wavelength tuning. Yes, but the beam output direction will change as the grating rotates.

Therefore, there is an urgent need for an external cavity tunable semiconductor laser that can achieve wavelength tuning while ensuring that the direction of the beam output remains unchanged.

To address the aforementioned technical problems, this application provides an external cavity tunable semiconductor laser. Specifically, please refer to Figure 1, which is a structural schematic diagram of an external cavity tunable semiconductor laser provided in this application. As shown in Figure 1, the external cavity tunable semiconductor laser provided in this application includes a semiconductor laser 10, a collimating lens 20, a cylindrical lens 30, a diffraction grating 40, and a partial reflector 50, which are sequentially connected optically.

The collimating lens 20 is located at one focal length from the cylindrical lens 30, and the center of the diffraction grating 40 is located at one focal length from both sides of the cylindrical lens 30, respectively. The grating direction of the diffraction grating 40 is the same as the polarization direction of the light beam transmitted to the partial mirror via the diffraction grating 40.

The normal of the diffraction grating 40 forms a littrow angle with the transmission direction of the light beam transmitted to the partial reflector, and the transmission direction of the light beam via the partial reflector 50 is perpendicular to the partial reflector.

The cylindrical lens 30 is used to move in a direction perpendicular to the transmission direction of the light beam transmitted to the cylindrical lens 30 in order to tune the wavelength of the output light beam.

The littrow angle is an important concept in optics, particularly in grating diffraction and spectroscopy. It refers to the diffraction angle when the diffracted light from the grating coincides with the incident light in a littrow configuration. A littrow configuration is a specific geometry in which light of a specific wavelength diffracted from the grating to a given diffraction order propagates back along the direction of the incident light. In a littrow configuration, the incident angle and the diffraction angle are equal, i.e., α = β. In this case, the grating equation can be simplified to mλ = 2dsinα, where m is the diffraction order, λ is the wavelength, and d is the spacing between adjacent grooves on the grating surface. The littrow angle is the angle formed by the diffracted light and the grating normal in this configuration.

Using the external cavity tunable semiconductor laser provided in this application embodiment, the collimating lens 20 is positioned at one focal length from the cylindrical lens 30, and the center of the diffraction grating 40 is positioned at one focal length from both sides of the cylindrical lens 30, while maintaining the grating direction of the diffraction grating 40 in the same direction as the polarization direction of the beam. The normal of the diffraction grating 40 forms a littrow angle with the transmission direction of the light beam transmitted to the partial mirror. The transmission direction of the light beam via the partial mirror 50 is perpendicular to the partial mirror. This allows the wavelength of the output light beam to be tuned by moving the cylindrical lens 30 in a direction perpendicular to the transmission direction of the light beam transmitted to the cylindrical lens 30, while ensuring that the direction of the output light beam remains unchanged.

In some embodiments, please refer to Figures 1 and 2 simultaneously. Figure 2 is a schematic diagram of another structure of the external cavity tunable semiconductor laser provided in this application embodiment, and Figure 2 is a schematic diagram of the cylindrical lens 30 in Figure 1 after it has been moved. As shown in Figures 1 and 2, in this application embodiment, the wavelength of the output beam can be tuned by moving the cylindrical lens 30 in a direction perpendicular to the beam transmission direction to the cylindrical lens 30, while ensuring that the direction of the beam output remains unchanged.

Specifically, the moving distance of the cylindrical lens 30 in the transmission direction perpendicular to the beam transmitted to the cylindrical lens 30 provided in this application embodiment satisfies a first preset relationship with the first incident angle and the second incident angle. The first incident angle is the incident angle of the beam transmitted to the diffraction grating 40 before the cylindrical lens 30 moves, and the second incident angle is the incident angle of the beam transmitted to the diffraction grating 40 after the cylindrical lens 30 moves.

The first preset relationship provided in this application embodiment is:

Wherein, θ’ is the second incident angle, θ is the first incident angle, Δx is the moving distance, and f is the focal length of the cylindrical lens 30.

In this embodiment, the wavelength of the tuned beam provided in this application embodiment satisfies a second preset relationship with the first incident angle and the second incident angle;

The second preset relationship provided in this application embodiment is as follows:

Wherein, λ is the wavelength, and d is the spacing between adjacent grooves on the surface of the diffraction grating 40.

In some embodiments, the semiconductor laser 10 provided in this application is a blue semiconductor. The bulk laser, specifically the blue semiconductor laser, can directly emit blue light and has advantages such as simple structure, ease of use, and high electro-optical conversion efficiency. Furthermore, the semiconductor laser 10 provided in this embodiment can also be other types of semiconductor lasers, and no specific limitations are made here.

In some embodiments, the collimating lens 20 provided in this application may include a fast-axis collimating lens 21 and a slow-axis collimating lens 22. The fast-axis collimating lens 21 is disposed between the semiconductor laser 10 and the slow-axis collimating lens 22. The fast-axis collimating lens 21 performs fast-axis collimation on the beam emitted by the semiconductor laser 10, and the slow-axis collimating lens 22 performs slow-axis collimation on the beam transmitted from the fast-axis collimating lens 21 to the slow-axis collimating lens 22. In this embodiment, the position of the slow-axis collimating lens 22 near the cylindrical lens 30 at one focal length coincides with the position of the cylindrical lens 30 near the slow-axis collimating lens 22 at one focal length.

In some embodiments, the fast-axis collimating lens 21 provided in this application can be an aspherical cylindrical lens, and the slow-axis collimating lens 22 can be a spherical cylindrical lens. In one embodiment, the focal length of the aspherical cylindrical lens provided in this application can be 300 micrometers, and the focal length of the spherical cylindrical lens can be 12 millimeters.

It should be noted that the focal lengths of the aspherical cylindrical lens and the spherical cylindrical lens provided in this embodiment are not limited to the values provided in the above embodiment, and can be customized and adjusted according to specific application scenarios, without specific limitations here.

In some embodiments, the cylindrical lens 30 provided in this application can be a plano-convex cylindrical lens 30, wherein the convex direction of the plano-convex cylindrical lens 30 is close to the diffraction grating 40.

In one embodiment, the diffraction grating 40 provided in this application can be a planar grating. In another embodiment, the planar grating can be a transmissive grating. The main characteristics of a transmissive grating are high transmittance, high resolution, and high stability. Because the grating's scribe line spacing is extremely small, typically only a few hundred nanometers to a few micrometers, a transmissive grating can achieve high-precision modulation of light waves. Furthermore, the transmissive grating also has very high transmittance, effectively reducing light energy loss.

In summary, this application provides an external cavity tunable semiconductor laser, comprising a semiconductor laser, a collimating lens, a cylindrical lens, a diffraction grating, and a partial reflector connected in sequence. The collimating lens, located at one focal length near the cylindrical lens, and the center of the diffraction grating, respectively, coincide with the positions at one focal length on both sides of the cylindrical lens. The grating's scribe line direction is the same as the polarization direction of the beam transmitted to the partial mirror via the diffraction grating. The normal to the diffraction grating forms a littrow angle with the transmission direction of the beam transmitted to the partial mirror. The transmission direction of the beam transmitted through the partial mirror is perpendicular to the partial mirror. The cylindrical lens is used to move in a direction perpendicular to the transmission direction of the beam transmitted to the cylindrical lens to tune the output beam's wavelength. Using the external cavity tunable semiconductor laser provided in this application embodiment, the following effects can be achieved:

By placing the collimating lens at one focal length from the cylindrical lens side and the center of the diffraction grating at one focal length from both sides of the cylindrical lens, while keeping the grating's scribe line direction the same as the beam polarization direction, and the normal of the diffraction grating forming a littrow angle with the beam propagation direction to the partial mirror, and the beam propagation direction via the partial mirror perpendicular to the partial mirror, it is possible to tune the output beam wavelength by moving the cylindrical lens perpendicular to the beam propagation direction to the cylindrical lens, while ensuring the beam output direction remains unchanged.

Some embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

The above are merely specific embodiments of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims (10)

An external cavity tunable semiconductor laser, wherein the external cavity tunable semiconductor laser comprises a semiconductor laser, a collimating lens, a cylindrical lens, a diffraction grating, and a partially reflecting mirror connected in sequence. The collimating lens is located at one focal length from the cylindrical lens, and the center of the diffraction grating coincides with the positions at one focal length on both sides of the cylindrical lens, respectively. Furthermore, the grating direction of the diffraction grating is the same as the polarization direction of the light beam transmitted to the partial mirror via the diffraction grating. The normal of the diffraction grating forms a littrow angle with the transmission direction of the light beam transmitted to the partial mirror, and the transmission direction of the light beam through the partial mirror is perpendicular to the partial mirror. The cylindrical lens is used to move in a direction perpendicular to the transmission direction of the light beam transmitted to the cylindrical lens in order to tune the wavelength of the output light beam. According to claim 1, in the external cavity tunable semiconductor laser, the moving distance of the cylindrical lens in the direction perpendicular to the transmission direction of the light beam transmitted to the cylindrical lens satisfies a first preset relationship with the first incident angle and the second incident angle, wherein the first incident angle is the incident angle of the light beam transmitted to the diffraction grating before the cylindrical lens moves, and the second incident angle is the incident angle of the light beam transmitted to the diffraction grating after the cylindrical lens moves; The first preset relationship is:
Where θ’ is the second incident angle, θ is the first incident angle, Δx is the moving distance, and f is the focal length of the cylindrical lens. The external cavity tunable semiconductor laser according to claim 2, wherein the beam is tuned The harmonic wavelength satisfies a second preset relationship with the first incident angle and the second incident angle; The second preset relationship is:
Wherein, λ is the wavelength, and d is the spacing between adjacent grooves on the surface of the diffraction grating. The external cavity tunable semiconductor laser according to claim 1, wherein the semiconductor laser is a blue semiconductor laser. According to claim 1, the external cavity tunable semiconductor laser comprises a fast-axis collimating lens and a slow-axis collimating lens, wherein the fast-axis collimating lens is disposed between the semiconductor laser and the slow-axis collimating lens. According to claim 5, the external cavity tunable semiconductor laser is wherein the fast-axis collimating lens is an aspherical cylindrical lens and the slow-axis collimating lens is a spherical cylindrical lens. According to claim 6, the external cavity tunable semiconductor laser has a focal length of 300 micrometers and a focal length of 12 millimeters for the aspherical cylindrical lens. According to claim 1, the external cavity tunable semiconductor laser is wherein the cylindrical lens is a plano-convex cylindrical lens, and the convex direction of the plano-convex cylindrical lens is close to the diffraction grating. The external cavity tunable semiconductor laser according to claim 1, wherein the diffraction grating is a planar grating. The external cavity tunable semiconductor laser according to claim 9, wherein the planar grating is a transmission grating.