A wavelength-locked semiconductor laser

Abstract

The invention relates to the technical field of semiconductor lasers, and discloses a wavelength-locked semiconductor laser. The semiconductor laser comprises a semiconductor laser unit, a fast axis collimator, a polarization beam splitter, a quarter wave plate and a reflective Bragg grating lens. The polarization beam splitter is used for polarization splitting of a first polarized light after being collimated to obtain polarized light in a target polarization direction. The quarter wave plate is used for converting the polarized light in the target polarization direction into a second polarized light. The reflective Bragg grating lens is used for mode selection of the second polarized light and reflecting the second polarized light of the target wavelength to the quarter wave plate. The quarter wave plate is also used for adjusting the proportion of polarized light in a target polarization direction of the target wavelength. The polarization beam splitter is also used for fully transmitting or fully reflecting the polarized light in the target polarization direction of the target wavelength, so that the polarized light in the target polarization direction of the target wavelength returns to the semiconductor laser unit. The invention can equivalently realize adjustable diffraction efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor lasers, and in particular to a wavelength-locked semiconductor laser. Background Art

[0002] Wavelength-locked semiconductor lasers are semiconductor lasers that can stabilize the wavelength of the output laser at a specific value or within a narrow band. They have the advantages of stable output wavelength, narrow spectral linewidth, and high pumping efficiency, and are widely used in fiber-optic communications, laser spectroscopy, and precision measurement. In order to meet complex and changing scenarios, semiconductor lasers are required to achieve a side mode suppression ratio of more than 30dB at different temperatures and currents.

[0003] The wavelength-locked semiconductor laser includes a semiconductor laser unit, a collimator and a reflective Volume Bragg Grating (VBG) lens. The laser emitted by the semiconductor laser unit is collimated by the collimator and then selected in the external cavity through the VBG lens, so that the laser of a specific wavelength is reflected and injected into the FP resonant cavity formed by the front and rear cavity surfaces of the semiconductor laser unit. The longitudinal modes that meet the oscillation and threshold conditions form oscillation amplification, while other longitudinal modes are suppressed, thereby realizing the selection and locking of the output wavelength of the semiconductor laser source.

[0004] Since the wavelength of the laser output by the semiconductor laser is different at different temperatures and currents, in order to prevent the wavelength locking range from changing with temperature or current and affecting the high side mode suppression ratio, the diffraction efficiency of the VBG lens needs to be flexibly adjusted according to the temperature or current. However, the diffraction efficiency of the VBG lens in the semiconductor laser is fixed and difficult to adjust flexibly. Summary of the invention

[0005] In view of this, the present invention provides a wavelength-locked semiconductor laser to solve the problem that it is difficult for a semiconductor laser to achieve a side mode suppression ratio exceeding 30 dB at different temperatures or currents.

[0006] The invention provides a wavelength-locked semiconductor laser, which comprises a semiconductor laser unit, a fast-axis collimator, a polarization beam splitter, a quarter-wave plate and a reflective Bragg grating lens, wherein the angle of the optical axis of the quarter-wave plate is adjustable; the semiconductor laser unit is used to emit a first polarized light, the fast-axis collimator is used to collimate the divergence angle of the first polarized light in the fast-axis direction, the polarization beam splitter is used to polarize the collimated first polarized light to obtain polarized light in a target polarization direction, the quarter-wave plate is used to convert the polarized light in the target polarization direction into a second polarized light, and the reflective Bragg grating lens is used to transmit the ..., and the polarization beam splitter is used to polarize the collimated first polarized light to obtain polarized light in a target polarization direction. The Ragu grating lens is used to select the second polarized light and reflect the second polarized light of the target wavelength to the 1 / 4 wave plate, wherein the target polarization direction is the horizontal polarization direction or the vertical polarization direction, and the second polarized light is the superposition state of the polarized light in the horizontal polarization direction and the polarized light in the vertical polarization direction; the 1 / 4 wave plate is also used to adjust the ratio of the polarized light in the target polarization direction of the target wavelength, and the polarization beam splitter is also used to make the polarized light in the target polarization direction of the target wavelength fully transmitted or fully reflected, so that the polarized light in the target polarization direction of the target wavelength returns to the semiconductor laser unit through the fast axis collimator.

[0007] In an optional implementation, when the target polarization direction is the horizontal polarization direction, the fast axis collimator, the polarization beam splitter, the quarter wave plate and the reflective Bragg grating lens are sequentially arranged along the optical path of the semiconductor laser unit.

[0008] In an optional embodiment, when the target polarization direction is a vertical polarization direction, a fast axis collimator and a polarization beam splitter are sequentially arranged along the optical path of the semiconductor laser unit, and a quarter wave plate and a reflective Bragg grating lens are sequentially arranged on the reflective optical path of the polarization beam splitter.

[0009] In an optional embodiment, the proportion of polarized light in the target polarization direction of the target wavelength is greater than 5%.

[0010] In an optional embodiment, when the target polarization direction is a horizontal polarization direction, the angle between the 1 / 4 wave plate optical axis and the horizontal polarization direction ranges from 0° to 37°, or the angle between the 1 / 4 wave plate optical axis and the horizontal polarization direction ranges from 53° to 90°.

[0011] In an optional implementation, when the target polarization direction is a vertical polarization direction, the angle between the optical axis of the 1 / 4 wave plate and the target polarization direction ranges from 10° to 80°.

[0012] In an optional embodiment, the diffraction efficiency of the reflective Bragg grating lens is greater than or equal to 99.7%.

[0013] In an optional implementation, the light-transmitting surface of the polarizing beam splitter is provided with an anti-reflection film, and the transmittance of the anti-reflection film is greater than or equal to 99%.

[0014] In an optional implementation, the semiconductor laser further includes a slow axis collimator, and the slow axis collimator is located between the fast axis collimator and the polarization beam splitter.

[0015] In an optional implementation, the light-transmitting surfaces of the fast-axis collimator and the slow-axis collimator are both provided with anti-reflection films, and the transmittance of the anti-reflection films is greater than or equal to 99%.

[0016] The wavelength-locked semiconductor laser provided in this embodiment can flexibly adjust the wavelength-locking power injected into the semiconductor laser unit according to the wavelength locking requirements by setting a polarization beam splitter and a quarter wave plate between the fast axis collimator and the reflective Bragg grating lens, and equivalently achieve adjustable diffraction efficiency, so that the semiconductor laser can achieve a side mode suppression ratio of more than 30dB at different temperatures or currents. Moreover, this embodiment can arbitrarily adjust the energy of the injected chip wavelength-locking mode according to the locking side mode suppression ratio requirements without additional laser power loss to meet the wavelength locking requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the related technologies, the drawings required for use in the specific embodiments or the related technical descriptions will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 is a schematic diagram of a semiconductor laser in the form of multiple single-tube fiber coupling according to an embodiment of the present invention;

[0019] Figure 2 is a schematic diagram of a semiconductor laser in a bar packaging structure according to an embodiment of the present invention;

[0020] Figure 3 is a schematic structural diagram of a first wavelength-locked semiconductor laser according to an embodiment of the present invention;

[0021] Figure 4 is a schematic diagram of an optical path of a wavelength-locked semiconductor laser according to an embodiment of the present invention;

[0022] Figure 5 is a schematic structural diagram of a second wavelength-locked semiconductor laser according to an embodiment of the present invention;

[0023] Figure 6 is a schematic structural diagram of a third wavelength-locked semiconductor laser according to an embodiment of the present invention;

[0024] Figure 7is a schematic structural diagram of a fourth wavelength-locked semiconductor laser according to an embodiment of the present invention;

[0025] Figure 8 is a schematic diagram of a curve showing the relationship between the intensity ratio of S-polarized light / P-polarized light entering a semiconductor laser unit and the angle according to an embodiment of the present invention;

[0026] Fig. 9 is a schematic diagram of a curve showing the relationship between the intensity ratio of P polarized light output by a half wave plate and the angle according to an embodiment of the present invention;

[0027] Fig.10 is a schematic diagram of a relationship curve between the intensity ratio of the P-polarized light / S-polarized light entering the semiconductor laser unit and the intensity ratio of the output P-polarized light according to an embodiment of the present invention;

[0028] Fig.11 is a schematic diagram of the relationship between the wavelength range and intensity of laser light output by a semiconductor laser unit according to an embodiment of the present invention;

[0029] Fig.12 is a schematic structural diagram of a fifth wavelength-locked semiconductor laser according to an embodiment of the present invention;

[0030] Fig.13 is a schematic diagram of a curve showing the relationship between the intensity of P-polarized light entering a semiconductor laser unit and the angle according to an embodiment of the present invention;

[0031] Fig.14 is a schematic diagram of a curve showing the relationship between the intensity of S-polarized light entering a semiconductor laser unit and the angle according to an embodiment of the present invention;

[0032] Fig.15 is a schematic diagram of the relationship between the intensity of P-polarized light entering a semiconductor laser unit and the intensity of S-polarized light output according to an embodiment of the present invention;

[0033] Fig.16 is a schematic structural diagram of a sixth wavelength-locked semiconductor laser according to an embodiment of the present invention;

[0034] Fig.17 is a schematic diagram of a relationship curve between the intensity ratio of S-polarized light / P-polarized light entering a semiconductor laser unit and the intensity ratio of the output P-polarized light according to an embodiment of the present invention;

[0035] Fig.18 is a schematic diagram of a curve showing the relationship between the intensity of P polarized light passing through a quarter wave plate for the first time and the angle according to an embodiment of the present invention;

[0036] Fig.19is another schematic diagram of a curve showing the relationship between the intensity of P-polarized light entering a semiconductor laser unit and the angle according to an embodiment of the present invention;

[0037] Fig. 20 is another schematic diagram of a curve showing the relationship between the intensity of S-polarized light entering a semiconductor laser unit and the angle according to an embodiment of the present invention;

[0038] Fig.21 is a schematic diagram of another relationship between the intensity of P-polarized light entering a semiconductor laser unit and the intensity of S-polarized light output according to an embodiment of the present invention;

[0039] Fig. 22 FIG. 4 is a schematic diagram showing the relationship between the wavelength range and intensity of laser light outputted by another semiconductor laser unit according to an embodiment of the present invention.

[0040] Figure numerals: 110, fast axis collimator; 120, slow axis collimator; 130, reflective Bragg grating lens; 140, bar; 150, step reflector; 160, semiconductor laser unit; 161, P polarized light; 170, polarization beam splitter; 180, 1 / 4 wave plate; 200, power meter; 310, 1 / 2 wave plate. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0042] For example, whether Figure 1 The semiconductor laser of the multi-single-tube fiber-coupled form shown in FIG. Figure 2 The semiconductor laser of the Bar package structure shown in the figure generally uses a VBG lens 130 as an external cavity for mode selection after the semiconductor laser unit is collimated by a Fast Axis Collimation (FAC) mirror 110 and a Slow Axis Collimation (SAC) mirror 120, so that the laser of a specific wavelength is reflected and injected into the FP resonant cavity formed by the front cavity surface and the back cavity surface of the semiconductor laser unit, thereby realizing the selection and locking of the output wavelength of the semiconductor laser unit. Among them, the semiconductor laser unit can be arranged on the Bar 140, and a step reflector 150 is arranged on the light-emitting side of the SAC mirror 120, and the step reflector 150 is used to reflect the light emitted from the SAC mirror 120 to the VBG lens 130.

[0043] Since the wavelength of the laser output by the semiconductor laser is different at different temperatures and currents, in order to avoid the wavelength locking range changing with temperature or current and affecting the high side mode suppression ratio, the diffraction efficiency of the VBG lens needs to be flexibly adjusted according to the temperature or current. However, after the working conditions (temperature and current) are determined, the diffraction efficiency of the VBG lens in the semiconductor laser is fixed and difficult to adjust flexibly.

[0044] Specifically, the wavelength locking range is related to the light intensity (power) reflected by the VBG lens and injected into the semiconductor laser unit, and the light intensity reflected by the VBG lens and injected into the semiconductor laser unit is related to the diffraction efficiency of the VBG lens. Therefore, by adjusting the diffraction efficiency of the VBG lens, the wavelength locking range can be flexibly adjusted, so that the semiconductor laser can achieve a side mode suppression ratio of more than 30dB at different temperatures or currents.

[0045] In view of this, the present invention provides a wavelength-locked semiconductor laser. By arranging a polarization beam splitter and a quarter wave plate between the FAC mirror and the VBG lens, the wavelength-locked power injected into the semiconductor laser unit can be flexibly adjusted according to the wavelength locking requirements, thereby equivalently achieving adjustable VBG diffraction efficiency, so that the semiconductor laser can achieve a side mode suppression ratio of more than 30 dB at different temperatures or currents.

[0046] The structure of the wavelength-locked semiconductor laser provided by the present invention is described in detail below in conjunction with the accompanying drawings.

[0047] like Figures 3 to 5 As shown, the wavelength-locked semiconductor laser includes a semiconductor laser unit 160 , a fast axis collimator 110 , a polarization beam splitter 170 , a quarter wave plate 180 and a reflective Bragg grating lens 130 .

[0048] Specifically, the semiconductor laser unit 160 is used to emit laser light that is approximately linearly polarized light. The linearly polarized light may be transverse electric (TE) mode, that is, horizontal (P) polarized light; the linearly polarized light may also be transverse magnetic (TM) mode, that is, vertical (S) polarized light.

[0049] The laser emitted by the semiconductor laser unit may include P polarized light and S polarized light. For example, the TE mode accounts for 98% of the laser emitted by the semiconductor laser unit, that is, the power occupied by the P polarized light in the semiconductor laser unit is 98%, and the power occupied by the S polarized light is 2%. For another example, the TM mode accounts for 98% of the laser emitted by the semiconductor laser unit, that is, the power occupied by the S polarized light in the semiconductor laser unit is 98%, and the power occupied by the P polarized light is 2%.

[0050] P polarized light indicates that the polarization direction (vibration direction) of the linear polarized light is horizontal, and S polarized light indicates that the polarization direction of the linear polarized light is vertical. For the convenience of subsequent description, the laser light emitted by the semiconductor laser unit 160 is recorded as the first polarized light.

[0051] It should be understood that linearly polarized light can be light in which the light vector always vibrates in a fixed direction in the direction of light propagation. The vibration of linearly polarized light has a clear directionality, and its electric field vector or light vector only vibrates in a specific direction in a plane perpendicular to the direction of light propagation. The TE mode refers to an electromagnetic wave mode in which the electric field vector is perpendicular to the propagation direction and in the transverse plane (a plane perpendicular to the propagation direction), and the magnetic field vector has components in both the propagation direction and the transverse plane. The TM mode refers to an electromagnetic wave mode in which the magnetic field vector is perpendicular to the propagation direction and in the transverse plane, and the electric field vector has components in both the propagation direction and the transverse plane.

[0052] Specifically, the fast axis collimator 110 is used to collimate the divergence angle of the first polarized light in the fast axis direction, and the divergence angle can be collimated to milliradian (mrad). The fast axis direction refers to the direction of the short side of the light-emitting surface of the semiconductor laser unit 160. The active region of the semiconductor laser unit 160 is very thin, and the light field is less restricted in this direction, which makes the light beam easy to diverge quickly. The fast axis collimator 110 can collimate and shape the light beam in the fast axis direction, thereby improving the quality of the first polarized light.

[0053] The polarization beam splitter 170 is used to perform polarization beam splitting on the collimated first polarized light to obtain polarized light in a target polarization direction, where the target polarization direction is horizontal polarized light (ie, P polarized light) or vertical polarized light (ie, S polarized light).

[0054] Specifically, the target polarization direction is determined based on the proportions of P-polarized light and S-polarized light in the first polarized light. If the proportion of P-polarized light in the first polarized light is 100% (i.e., the semiconductor laser unit 160 emits P-polarized light), the target polarization direction is a horizontal polarization direction; if the proportion of P-polarized light in the first polarized light is less than 100%, but the proportion of P-polarized light is greater than the proportion of S-polarized light, the target polarization direction is still a horizontal polarization direction; if the proportion of S-polarized light in the first polarized light is 100% (i.e., the semiconductor laser unit 160 emits S-polarized light), the target polarization direction is a vertical polarization direction; if the proportion of S-polarized light in the first polarized light is less than 100%, but the proportion of S-polarized light is greater than the proportion of P-polarized light, the target polarization direction is still a vertical polarization direction.

[0055] Exemplarily, the polarization beam splitter 170 is used to transmit polarized light in a horizontal polarization direction and to reflect polarized light in a vertical polarization direction.

[0056] At this time, when the target polarization direction is horizontal, such as Figure 3 and Figure 4 As shown in FIG. 1 , the fast axis collimator 110, the polarization beam splitter 170, the quarter wave plate 180 and the reflective Bragg grating lens 130 are sequentially arranged along the optical path of the semiconductor laser unit 160. Figure 3 As shown, the semiconductor laser unit 160, the fast axis collimator 110, the polarization beam splitter 170, the quarter wave plate 180 and the reflective Bragg grating lens 130 are arranged in sequence from left to right.

[0057] When the target polarization direction is the vertical polarization direction, the fast axis collimator 110 and the polarization beam splitter 170 are sequentially arranged along the optical path of the semiconductor laser unit 160, and the 1 / 4 wave plate 180 and the reflective Bragg grating lens 130 are sequentially arranged on the reflection optical path of the polarization beam splitter.

[0058] For example, Figure 5 As shown, the reflection light path of the polarization beam splitter 170 is located above the polarization beam splitter 170 , and the quarter wave plate 180 and the reflection type Bragg grating lens 130 are also sequentially arranged above the polarization beam splitter 170 .

[0059] Specifically, the polarization beam splitter 170 can be formed by gluing two right-angle prisms, with a polarization beam splitter film coated on the gluing surface (diagonal position), and the polarization beam splitter film is used to increase the transmittance of polarized light in the horizontal polarization direction and to highly reflect polarized light in the vertical polarization direction.

[0060] The 1 / 4 wave plate 180 is used to convert polarized light in the target polarization direction into a second polarized light, and the reflective Bragg grating lens 130 is used to select the second polarized light and reflect the second polarized light of the target wavelength to the 1 / 4 wave plate 180. The second polarized light is a superposition state of polarized light in the horizontal polarization direction and polarized light in the vertical polarization direction.

[0061] Specifically, based on the Bragg reflection principle and the dispersion characteristics of light, the reflective Bragg grating lens 130 can selectively reflect light of a specific wavelength (i.e., the target wavelength) to filter and separate the wavelength of light. The target wavelength can be determined by the designer according to the requirements of the semiconductor laser wavelength locking, and the designer can select a suitable reflective Bragg grating lens 130 based on the target wavelength.

[0062] The 1 / 4 wave plate 180 is also used to adjust the ratio of polarized light in the target polarization direction of the target wavelength, and the polarization beam splitter 170 is also used to make the polarized light in the target polarization direction of the target wavelength fully transmitted or fully reflected, so that the polarized light in the target polarization direction of the target wavelength returns to the semiconductor laser unit 160 through the fast axis collimator 110. The polarized light injected into the semiconductor laser unit 160 participates in mode competition to achieve wavelength locking. The polarization beam splitter 170 is also used to make the polarized light in the vertical polarization direction of the target wavelength fully reflected, and the fully reflected polarized light can be used as laser output to enter the power meter or subsequent optical processing elements (such as coupling into optical fiber, etc.).

[0063] Specifically, when the target polarization direction is horizontal, the polarization beam splitter 170 is also used to fully transmit polarized light of the target wavelength and the target polarization direction; when the target polarization direction is vertical, the polarization beam splitter 170 is also used to fully reflect polarized light of the target wavelength and the target polarization direction.

[0064] Among them, the angle of the optical axis of the 1 / 4 wave plate 180 is adjustable, that is, the angle between the optical axis of the 1 / 4 wave plate 180 and the target polarization direction is adjustable. By adjusting the angle of the optical axis of the 1 / 4 wave plate 180, the proportion of polarized light of the target polarization direction of the target wavelength can be adjusted, that is, the proportion of the intensity of the polarized light of the horizontal component to the intensity of the polarized light of the vertical component in the linear polarized light can be adjusted.

[0065] Specifically, the angle between the optical axis of the 1 / 4 wave plate 180 and the target polarization direction is determined according to the wavelength locking range, so that the intensity of the polarized light in the target polarization direction injected into the semiconductor laser unit 160 is greater than or equal to a preset value (for example, 5%), so as to lock the wavelength within the preset range. The value range of the angle can be 0° to 90°, that is, the adjustment range of the angle can be any value between 0° and 90°, for example, the angle can be 0°, 30°, 45°, 60° or 90°, etc.

[0066] It should be noted that the laser energy injected into the semiconductor laser unit 160 to participate in the mode competition is consistent with the intrinsic polarization state of the semiconductor laser unit 160 to achieve oscillation amplification.

[0067] The following is combined with Figure 3 and attached Figure 4 , taking the semiconductor laser unit 160 emitting P-polarized light (ie, the laser emitted by the semiconductor laser unit 160 is 100% P-polarized light) as an example, the optical path of the P-polarized light is described in detail.

[0068] Specifically, if Figure 4 As shown, the P polarized light 161 emitted by the semiconductor laser unit 160 is first incident on the fast axis collimator 110 for collimation, and the collimated P polarized light ( Figure 4Then, the collimated P polarized light is incident on the polarization beam splitter film of the polarization beam splitter 170, and the polarization beam splitter film increases the transmittance of the collimated P polarized light, so that all the collimated P polarized light is emitted from the polarization beam splitter 170. At this time, the target polarization direction is the horizontal polarization direction.

[0069] Afterwards, the polarized light in the target polarization direction is incident on the 1 / 4 wave plate 180, and the 1 / 4 wave plate 180 changes the polarization characteristics of the polarized light in the target polarization direction, converting the polarized light in the target polarization direction into a superposition state of P polarized light and S polarized light (i.e., the second polarized light mentioned above, such as Figure 4 ), and then the second polarized light is transmitted forward into the reflective Bragg grating lens 130, which selects the mode of the second polarized light and reflects the second polarized light of the target wavelength to the 1 / 4 wave plate 180. The 1 / 4 wave plate 180 is also used to change the ratio of the P polarized light of the target wavelength in the second polarized light of the target wavelength, so that the ratio of the P polarized light of the target wavelength is a preset ratio (this value is determined based on the requirement of wavelength locking). After that, the second polarized light of the target wavelength enters the polarization beam splitter film of the polarization beam splitter 170, and the polarization beam splitter film fully transmits the P polarized light of the target wavelength of the preset ratio, and returns to the resonant cavity of the semiconductor laser unit 160 through the fast axis collimator 110, participates in mode competition, and realizes wavelength locking. The polarization beam splitter film also makes the S polarized light ( Figure 4 The totally reflected polarized light can be output as laser light and enter the power meter 200 or subsequent optical processing elements (such as coupling into an optical fiber, etc.).

[0070] Optionally, in the case where the polarization beam splitter 170 transmits P polarized light and reflects S polarized light, if the laser emitted by the semiconductor laser unit 160 is 100% S polarized light, the target polarization direction is the vertical polarization direction, and the optical path of the 100% S polarized light can be as follows: Figure 5 shown.

[0071] Among them, the solid arrow still represents P polarized light, the dotted arrow still represents S polarized light, and the dot-dash arrow still represents the superposition state of P polarized light and S polarized light.

[0072] The wavelength-locked semiconductor laser provided in this embodiment can flexibly adjust the wavelength-locking power injected into the semiconductor laser unit according to the wavelength locking requirements by setting a polarization beam splitter 170 and a quarter wave plate 180 between the fast axis collimator 110 and the reflective Bragg grating lens 130, and equivalently realize adjustable diffraction efficiency, so that the semiconductor laser can achieve a side mode suppression ratio of more than 30 dB at different temperatures or currents. Moreover, this embodiment can arbitrarily adjust the energy of the injected chip wavelength-locking mode according to the locking side mode suppression ratio requirements without additional laser power loss to meet the wavelength locking requirements.

[0073] Specifically, to ensure VBG locking, the proportion of polarized light in the target polarization direction of the target wavelength is greater than 5%.

[0074] Furthermore, in some optional embodiments, the target polarization direction can be a horizontal polarization direction. In this case, the angle between the optical axis of the 1 / 4 wave plate 180 and the horizontal polarization direction ranges from 0° to 37°, or the angle between the optical axis of the 1 / 4 wave plate and the horizontal polarization direction ranges from 53° to 90°, so as to ensure that the proportion of polarized light in the target polarization direction of the target wavelength is greater than 5%.

[0075] Specifically, the angle between the optical axis of the 1 / 4 wave plate 180 and the horizontal polarization direction can be any value between 0° and 37°, or can be any value between 53° and 90°. For example, the angle between the optical axis of the 1 / 4 wave plate 180 and the horizontal polarization direction can be 0°, 15°, 20°, 35°, 37°, 53°, 60°, 80° or 90°, etc.

[0076] In some other optional embodiments, the target polarization direction may be a vertical polarization direction. In this case, the angle between the optical axis of the quarter wave plate 180 and the vertical polarization direction ranges from 10° to 80° to ensure that the proportion of polarized light in the target polarization direction of the target wavelength is greater than 5%.

[0077] Specifically, the angle between the optical axis of the 1 / 4 wave plate 180 and the vertical polarization direction can be any value between 10° and 80°. For example, the angle between the optical axis of the 1 / 4 wave plate 180 and the vertical polarization direction can be 10°, 20°, 35°, 45°, 60° or 80°.

[0078] Exemplarily, the diffraction efficiency of the reflective Bragg grating lens is greater than or equal to 99.7%.

[0079] Specifically, the diffraction efficiency of the reflective Bragg grating lens is controlled to be above 99.7%, so that most of the light of a specific wavelength can be accurately reflected to the 1 / 4 wave plate 180, and the laser output by the semiconductor laser unit 160 is selectively reflected back to the original laser generating resonant cavity, and the free-running spectrum is locked at the reflection wavelength of the Bragg grating, and wavelength selection is performed to realize spectrum compression and wavelength locking of the semiconductor laser unit 160, thereby achieving a wavelength locking effect.

[0080] In one example, in order to reduce the loss of emitted laser light, improve the utilization rate of laser light and enhance the stability of wavelength locking, the light-transmitting surface of the polarization beam splitter is provided with an anti-reflection film, and the transmittance of the anti-reflection film is greater than or equal to 99%.

[0081] For example, Figure 6As shown, the semiconductor laser further includes a slow axis collimator 120 , which is located between the fast axis collimator 110 and the polarization beam splitter 170 .

[0082] Specifically, in order to further reduce the loss of emitted laser light, improve the utilization rate of laser light and enhance the stability of wavelength locking, the light-transmitting surfaces of the fast-axis collimator 110 and the slow-axis collimator 120 are also provided with anti-reflection films, and the transmittance of the anti-reflection films is greater than or equal to 99%.

[0083] The above embodiment is further described below in conjunction with specific comparative examples.

[0084] Comparative Example 1

[0085] Another schematic diagram of a wavelength-locked semiconductor laser can be shown as Figure 7 As shown, the semiconductor laser unit 160 , the fast axis collimator 110 , the half wave plate 310 , and the polarization beam splitter 170 are arranged in sequence along the horizontal direction, and the reflective Bragg grating lens 130 is arranged at the upper end of the polarization beam splitter 170 .

[0086] In this embodiment, if the semiconductor laser unit 160 emits P polarized light, the relationship curve between the intensity ratio of the S polarized light entering the semiconductor laser unit 160 and the angle obtained by simulation can be as follows: Figure 8 As shown by the solid line in FIG. 1 , the relationship curve between the intensity ratio of the P polarized light entering the semiconductor laser unit 160 and the angle can be shown as follows: Figure 8 As shown by the dotted line in FIG. 1 , the relationship curve between the intensity ratio of the P polarized light output by the half wave plate 310 and the angle obtained by simulation can be shown as follows: Fig. 9 As shown, the relationship curve between the intensity ratio of the P-polarized light entering the semiconductor laser unit 160 and the intensity ratio of the output P-polarized light obtained by simulation can be shown as follows: Fig.10 As shown by the dotted line in FIG, the relationship curve between the intensity of the S polarized light entering the semiconductor laser unit and the intensity of the P polarized light output can be shown as Fig.10 As shown by the solid line in .

[0087] In this embodiment, the angle refers to the angle between the optical axis of the 1 / 2 wave plate 310 and the horizontal polarization direction.

[0088] from Figures 8 to 10 It can be seen that when the semiconductor laser unit 160 emits P polarized light, except for the cases where the angles are 0°, 45° and 90°, a certain proportion of S polarized light always enters the semiconductor laser unit 160 and is lost. Except for the cases where the angles are 0°, 45° and 90°, when the intensity of the P polarized light entering the semiconductor laser unit 160 is limited to between 5% and 20% in order to ensure the wavelength locking range, more than 15% of the S polarized light enters the semiconductor laser unit 160 and is lost.

[0089] In this embodiment, if the semiconductor laser unit 160 emits P polarized light, the angle is 15°, the P polarized light power and efficiency output by the 1 / 2 wave plate 310 under different currents and different emission powers determined by actual tests are shown in Table 1, and the relationship between the wavelength range and intensity of the laser output by the semiconductor laser unit 160 is shown in Fig.11 shown.

[0090] Table 1

[0091]

[0092] It can be seen from Table 1 that the power of the P polarized light output by the 1 / 2 wave plate 310 is about 77%, which is consistent with the theoretically calculated 75%. At this time, the VBG lock has a side peak and the locking effect is poor. In other words, 25% of the laser power returns to the semiconductor laser unit 160, but the proportion of P polarized light that helps the locking effect is low, so the locking effect is poor.

[0093] Comparative Example 2

[0094] Another schematic diagram of a wavelength-locked semiconductor laser can be shown as follows: Fig.12 As shown, the semiconductor laser unit 160, the fast axis collimator 110, the polarization beam splitter 170, the 1 / 2 wave plate 310 and the reflective Bragg grating lens 130 are arranged in sequence along the horizontal direction.

[0095] In this embodiment, if the semiconductor laser unit 160 emits P-polarized light, the relationship curve between the intensity of the P-polarized light entering the semiconductor laser unit 160 and the angle obtained by simulation can be as follows: Fig.13 As shown, the relationship curve between the output S polarization light intensity and the angle obtained by simulation can be shown as Fig.14 As shown, the relationship between the intensity of the P polarized light entering the semiconductor laser unit and the intensity of the S polarized light outputted can be expressed as Fig.15 shown.

[0096] In this embodiment, the angle refers to the angle between the optical axis of the 1 / 2 wave plate 310 and the horizontal polarization direction.

[0097] from Figures 13 to 15 It can be seen that no matter how the 1 / 2 wave plate 310 is rotated, the ratio of the light intensity entering the chip cannot be changed (which is also confirmed by actual experiments). Almost 100% of the emitted P-polarized light returns to the semiconductor laser unit 160, and the light intensity reflected by the VBG lens and injected into the semiconductor laser unit cannot be adjusted.

[0098] Moreover, almost 100% of the emitted P-polarized light returns to the semiconductor laser unit 160 , which may cause the internal temperature of the semiconductor laser unit 160 to rise, affect the stability of the laser output, and increase the risk of catastrophic optical damage (COD).

[0099] Comparative Example 3

[0100] Another schematic diagram of a wavelength-locked semiconductor laser can be shown as follows: Fig.16 As shown, the semiconductor laser unit 160 , the fast axis collimator 110 , the quarter wave plate 180 , and the polarization beam splitter 170 are arranged in sequence along the horizontal direction, and the reflective Bragg grating lens 130 is arranged at the upper end of the polarization beam splitter 170 .

[0101] In this embodiment, if the semiconductor laser unit 160 emits P polarized light, the relationship curve between the intensity ratio of the S polarized light entering the semiconductor laser unit 160 and the intensity ratio of the output P polarized light obtained by simulation can be as follows: Fig.16 As shown by the solid line in FIG. 1 , the relationship curve between the intensity ratio of the P-polarized light entering the semiconductor laser unit 160 and the intensity ratio of the output P-polarized light can be shown as follows: Fig.17 As shown by the dotted line in FIG. 1 , the relationship curve between the intensity of the P polarized light and the angle obtained by simulation for the first time passing through the 1 / 4 wave plate 180 can be shown as follows: Fig.18 shown.

[0102] In this embodiment, the angle refers to the angle between the optical axis of the 1 / 4 wave plate 180 and the horizontal polarization direction.

[0103] from Fig.17 and Fig.18 It can be seen that, in order to ensure VBG locking, when the intensity of the P polarized light injected into the semiconductor laser unit 160 is limited to a range greater than 5%, and the angle is limited to 20°, the P polarized light output from the 1 / 4 wave plate 180 is about 77.5%, the P polarized light intensity entering the semiconductor laser unit 160 is about 5%, and the S polarized light intensity entering the semiconductor laser unit 160 is about 17.5%. Specifically, the S polarized light returning to the semiconductor laser unit 160 cannot become the injected light of the VBG locking wavelength, and this part of the light is consumed as heat, which is easy to cause COD damage.

[0104] Example 1

[0105] The schematic diagram of a semiconductor laser is shown in Figure 4 As shown, the semiconductor laser unit 160, the fast axis collimator 110, the polarization beam splitter 170, the quarter wave plate 180 and the reflective Bragg grating lens 130 are arranged in sequence along the horizontal direction.

[0106] Specifically, in the above Figure 4 In the example shown, the relationship curve between the intensity ratio of the P polarized light entering the semiconductor laser unit and the angle obtained by simulation can be shown as Fig.19 As shown, the relationship curve between the output S polarization light intensity ratio and the angle obtained by simulation can be shown as Fig. 20 As shown, the relationship between the intensity ratio of the P polarized light entering the semiconductor laser unit and the intensity ratio of the S polarized light output obtained by simulation can be expressed as Fig.21 shown.

[0107] In this embodiment, the angle refers to the angle between the optical axis of the 1 / 4 wave plate 180 and the horizontal polarization direction.

[0108] from Figures 19 to 21 It can be seen that the ratio of the intensity of the P polarized light entering the semiconductor laser unit can be accurately controlled by the quarter wave plate 180, and no S polarized light will enter the semiconductor laser unit 160 to cause COD interference. Moreover, the S polarized light can be completely output as laser, reducing laser loss.

[0109] In this embodiment, if the semiconductor laser unit 160 emits P polarized light, the ratio of the S polarized light power output at different angles to the P polarized light entering the semiconductor laser unit under different currents and different emission powers determined by actual tests is shown in Table 2. The relationship between the wavelength range and intensity of the laser output by the semiconductor laser unit is shown in Table 2. Fig. 22 shown.

[0110] From Table 2, we can see that Figure 4 The arrangement shown can accurately control the light intensity ratio entering the semiconductor laser unit 160, and the light intensity ratio can vary between 1% and 99%. Taking the angle of 32° as an example, the light intensity of the P-polarized light entering the semiconductor laser unit 160 is about 20%, which is similar to the simulation result, and the locking effect is good. Moreover, the S-polarized light can be completely output as laser light with less loss. Among them, the chip in Table 2 refers to the semiconductor laser unit 160 mentioned above.

[0111] Table 2

[0112]

[0113] In summary, compared with the arrangement of the fast axis collimator 110, the polarization beam splitter 170, the wave plate and the reflective Bragg grating lens 130 in Comparative Examples 1 to 3, the present embodiment sequentially arranges the fast axis collimator 110, the polarization beam splitter 170, the quarter wave plate 180 and the reflective Bragg grating lens 130 along the optical path of the semiconductor laser unit, which can not only achieve the adjustable diffraction efficiency and the adjustable locking wavelength entering the semiconductor laser unit, but also can arbitrarily adjust the injected chip locking wavelength mode energy according to the locking side mode suppression ratio requirement without additional laser power loss.

[0114] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0115] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0116] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiment, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0117] In the description of this specification, the description with reference to the terms "this embodiment", "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0118] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0119] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the present invention.

Claims

1. A wavelength-locked semiconductor laser, characterized in that: The semiconductor laser comprises a semiconductor laser unit, a fast axis collimator, a polarization beam splitter, a quarter wave plate and a reflective Bragg grating lens, wherein the angle of the optical axis of the quarter wave plate is adjustable; The semiconductor laser unit is used to emit a first polarized light, the fast axis collimator is used to collimate the divergence angle of the first polarized light in the fast axis direction, the polarization beam splitter is used to polarize the collimated first polarized light to obtain polarized light in a target polarization direction, the 1 / 4 wave plate is used to convert the polarized light in the target polarization direction into a second polarized light, the reflective Bragg grating lens is used to select the second polarized light, and reflect the second polarized light of the target wavelength to the 1 / 4 wave plate, wherein the first polarized light includes vertical polarized light and / or horizontal polarized light, when the proportion of the horizontal polarized light is greater than the proportion of the vertical polarized light, the target polarization direction is the horizontal polarization direction, when the proportion of the vertical polarized light is greater than the proportion of the horizontal polarized light, the target polarization direction is the vertical polarization direction, and the second polarized light is a superposition state of the polarized light in the horizontal polarization direction and the polarized light in the vertical polarization direction; The 1 / 4 wave plate is also used to adjust the ratio of polarized light of the target wavelength in the target polarization direction, and the polarization beam splitter is also used to make the polarized light of the target wavelength in the target polarization direction fully transmitted or fully reflected, so that the polarized light of the target wavelength in the target polarization direction returns to the semiconductor laser unit through the fast axis collimator; When the target polarization direction is a horizontal polarization direction, the fast axis collimator, the polarization beam splitter, the quarter wave plate and the reflective Bragg grating lens are sequentially arranged along the optical path of the semiconductor laser unit; when the target polarization direction is a vertical polarization direction, the fast axis collimator and the polarization beam splitter are sequentially arranged along the optical path of the semiconductor laser unit, and the quarter wave plate and the reflective Bragg grating lens are sequentially arranged on the reflected optical path of the polarization beam splitter.

2. The wavelength-locked semiconductor laser according to claim 1, characterized in that: The proportion of polarized light of the target wavelength in the target polarization direction is greater than 5%.

3. The wavelength-locked semiconductor laser according to claim 2, characterized in that: When the target polarization direction is a horizontal polarization direction, the angle between the 1 / 4 wave plate optical axis and the target polarization direction ranges from 0° to 37°, or the angle between the 1 / 4 wave plate optical axis and the target polarization direction ranges from 53° to 90°.

4. The wavelength-locked semiconductor laser according to claim 2, characterized in that: When the target polarization direction is a vertical polarization direction, the angle between the optical axis of the 1 / 4 wave plate and the target polarization direction ranges from 10° to 80°.

5. The wavelength-locked semiconductor laser according to any one of claims 1 to 4, characterized in that: The diffraction efficiency of the reflective Bragg grating lens is greater than or equal to 99.7%.

6. The wavelength-locked semiconductor laser according to any one of claims 1 to 4, characterized in that: The light-transmitting surface of the polarizing beam splitter is provided with an anti-reflection film, and the transmittance of the anti-reflection film is greater than or equal to 99%.

7. The wavelength-locked semiconductor laser according to any one of claims 1 to 4, characterized in that: The semiconductor laser further comprises a slow axis collimator, and the slow axis collimator is located between the fast axis collimator and the polarization beam splitter.

8. The wavelength-locked semiconductor laser according to claim 7, characterized in that: The light-transmitting surfaces of the fast-axis collimator and the slow-axis collimator are both provided with anti-reflection films, and the transmittance of the anti-reflection films is greater than or equal to 99%.

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