External cavity tunable laser tuning apparatus and method

Abstract

This application provides a tuning device and method for an external cavity tunable laser. The device includes: a blazed grating for diffracting a parallel beam to generate a resonant beam; a first adjustment module for carrying and rotating the blazed grating to adjust its rotation angle; a second adjustment module for carrying the first adjustment module and adjusting the longitudinal position of the blazed grating to adjust the cavity length of the external cavity tunable laser; a first control module for controlling the first adjustment module to rotate at a first speed according to an input first signal to adjust the rotation angle of the blazed grating; a second control module for controlling the second adjustment module to longitudinally translate at a second speed according to an input second signal to change the longitudinal position of the blazed grating; and an information processing module for setting the first speed and calculating the second speed according to the current rotation angle information output by the first adjustment module and the current actual position information output by the second adjustment module, and outputting the first signal and the second signal.

Description

Technical Field

[0001] This application relates to the field of laser technology, and in particular to a tuning device and method for an external cavity tunable laser. Background Technology

[0002] Tunable lasers are key devices in modern optical technology. In the biomedical field, these lasers are central to optical coherence tomography (OCT), enabling non-invasive, high-resolution three-dimensional imaging of the human retina or skin tissue through high-speed wavelength scanning, which is crucial for early disease diagnosis. In lidar systems, their wavelength tuning characteristics help improve the angular resolution of long-range detection. Based on their high-precision wavelength selectivity, they can achieve rapid and sensitive spectral detection of multi-component gases in environmental monitoring.

[0003] External cavity diode lasers (ECDLs) based on blazed gratings have become a mature technology due to their wide tuning range and narrow linewidth. These lasers use a blazed grating as the beam-splitting element. Broadband light emitted from the source is collimated and then diffracts on the blazed grating. Different wavelengths of light are reflected at different angles on the blazed grating surface. By adjusting the rotation angle of the blazed grating, light of a specific wavelength can be returned to the source to form resonance, thus generating laser lasing at that wavelength. This structure is called a Littrow structure. Furthermore, if the beam diffracted by the blazed grating is reflected by a mirror and then returns along the original optical path, this structure is called a Littman structure. Regardless of the specific structure, the frequency selection mechanism of these lasers relies on the combined effect of the blazed grating diffraction spectrum and the external cavity spectrum: the former is controlled by the grating angle, and the latter is determined by the external cavity optical length. Changing the rotation angle of either the blazed grating or the mirror alone will cause a shift in the blazed grating diffraction spectrum, resulting in a mismatch with the external cavity spectrum and leading to mode hopping. Summary of the Invention

[0004] In view of this, this application provides a tuning device and method for an external cavity tunable laser, which at least partially solves the above-mentioned technical problems.

[0005] One embodiment of this application provides a tuning device for an external cavity tunable laser, comprising: a blazed grating for diffracting a parallel beam to generate a resonant beam; a first adjustment module for carrying and rotating the blazed grating to adjust its rotation angle; a second adjustment module for carrying the first adjustment module and adjusting the longitudinal position of the blazed grating to adjust the cavity length of the external cavity tunable laser; a first control module for controlling the first adjustment module to rotate at a first speed according to an input first signal to adjust the rotation angle of the blazed grating; a second control module for controlling the second adjustment module to translate longitudinally at a second speed according to an input second signal to change the longitudinal position of the blazed grating and adjust the cavity length of the external cavity tunable laser; and an information processing module for setting a first speed and calculating a second speed based on the current rotation angle information output by the first adjustment module and the current actual position information output by the second adjustment module, and outputting a first signal and a second signal based on the first speed and the second speed, respectively.

[0006] According to the embodiments of this application, the rate of change of the cavity length of the external cavity tunable laser is positively correlated with the longitudinal mode number of the external cavity tunable laser and the grating constant of the blazed grating, and negatively correlated with the rotation angle of the blazed grating.

[0007] According to an embodiment of this application, the first speed remains constant during tuning; the first control module is used to control the input first signal and output a first control signal to control the first adjustment module to rotate independently at the first speed; the second control module is used to control the input second signal and output a second control signal to control the second adjustment module to translate longitudinally at the second speed.

[0008] According to an embodiment of this application, the device further includes: a gain chip for generating a broadband beam; a collimating lens disposed between one end of the gain chip having a waveguide and a blazed grating for converting the broadband beam into a parallel beam; and a coupling output component disposed at the other end of the gain chip having a waveguide for coupling the resonant beam to output laser light.

[0009] According to an embodiment of this application, the gain chip generates amplified spontaneous radiation by injecting current. The front end of the waveguide of the gain chip is partially transparent, and the rear end is nearly completely transparent.

[0010] According to embodiments of this application, the collimating lens is an aspherical lens or a lens group.

[0011] According to embodiments of this application, the coupling output component is a spatial optical coupling output component or an optical fiber coupling output component.

[0012] Another aspect of this application provides a method for tuning an external cavity tunable laser based on an external cavity tunable laser tuning device, comprising: starting the external cavity tunable laser, causing the temperature and driving current of the external cavity tunable laser to reach preset values, adjusting a first adjustment module to an initial rotation angle, and adjusting a second adjustment module to an initial position; using an information processing module to set a first speed and calculate a second speed, and outputting a first signal and a second signal based on the first speed and the second speed respectively; a first control module using the input first signal to control the first adjustment module to rotate at the first speed to adjust the rotation angle of the blazed grating; a second control module using the input second signal to control the second adjustment module to longitudinally translate at the second speed to change the longitudinal position of the blazed grating and adjust the cavity length of the external cavity tunable laser; after waiting for a preset time, using the information processing module to calculate the deviation between the current actual cavity length and the current desired cavity length based on the current rotation angle of the first adjustment module and the current actual position of the second adjustment module; determining whether the absolute value of the deviation is greater than or equal to a preset deviation threshold; if so, the information processing module recalculates the second speed, outputs a second signal, and resets the second speed of the second adjustment module.

[0013] According to an embodiment of this application, the information processing module calculates the deviation between the current actual cavity length and the current desired cavity length based on the current rotation angle of the first adjustment module and the current actual position of the second adjustment module. This includes: calculating the current desired cavity length of the external cavity tunable laser based on the current rotation angle of the first adjustment module; calculating the current actual cavity length of the external cavity tunable laser based on the current actual position of the second adjustment module; and calculating the deviation between the current actual cavity length and the current desired cavity length.

[0014] According to an embodiment of this application, resetting the second speed of the second adjustment module includes: calculating the current desired speed of the second adjustment module based on the current rotation angle of the first adjustment module; and setting the second speed to the difference between twice the current desired speed and the current second speed.

[0015] The external cavity tunable laser tuning device and method provided in this application have at least the following technical effects:

[0016] The two control modules of the external cavity tunable laser tuning device regulate two adjustment modules respectively, achieving the goal of simultaneously rotating and longitudinally moving the blazed grating. By setting the movement speed of the two modules, the rotation angle and cavity length are synchronously tuned, thereby avoiding mode skipping within a large tuning range.

[0017] The tuning device of the external cavity tunable laser can be set independently and the motion state of the two adjustment modules can be adjusted at any time, providing greater freedom, avoiding interference caused by the coupling of rotation and translation, and reducing the lateral dimension of the external cavity structure. Attached Figure Description

[0018] The above-mentioned contents, other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0019] Figure 1 This schematic diagram illustrates the structure of a tuning device for an external cavity tunable laser according to an embodiment of this application.

[0020] Figure 2 A flowchart illustrating a tuning method for an external cavity tunable laser according to an embodiment of this application is shown schematically.

[0021] Explanation of reference numerals in the attached diagram: 1. Gain chip; 2. Collimating lens; 3. Blazed grating; 4. First adjustment module; 5. Second adjustment module; 6. Coupled output component; 7. First control module; 8. Second control module; 9. Information processing module. Detailed Implementation

[0022] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0023] Figure 1 The diagram schematically illustrates a structural diagram of an external cavity tunable laser tuning device according to an embodiment of this application.

[0024] like Figure 1 As shown, the external cavity tunable laser tuning device of this embodiment may include a blazed grating 3, a first adjustment module 4, a second adjustment module 5, a first control module 7, a second control module 8, and an information processing module 9.

[0025] Blazed grating 3 is used to diffract a parallel beam to produce a resonant beam.

[0026] The first adjustment module 4 is used to carry and rotate the blazed grating 3 to adjust the rotation angle of the blazed grating 3.

[0027] The second adjustment module 5 is used to support the first adjustment module 4 and adjust the longitudinal position of the blazed grating 3 to adjust the cavity length of the external cavity tunable laser.

[0028] The first control module 7 is used to control the first adjustment module 4 to rotate at a first speed according to the input first signal, so as to adjust the rotation angle of the blazed grating 3.

[0029] The second control module 8 controls the second adjustment module 5 to move longitudinally at a second speed according to the input second signal, so as to change the longitudinal position of the blazed grating 3 and adjust the cavity length of the external cavity tunable laser.

[0030] The information processing module 9 sets a first speed and calculates a second speed based on the current rotation angle information output by the first adjustment module 4 and the current actual position information output by the second adjustment module 5, and outputs a first signal and a second signal based on the first speed and the second speed, respectively.

[0031] Furthermore, the external cavity tunable laser tuning device may also include: a gain chip 1, a collimating lens 2, and a coupling output component 6.

[0032] Gain chip 1 is used to generate a broadband beam.

[0033] Collimating lens 2 is positioned between the waveguide end of the gain chip and the blazed grating to convert a broadband beam into a parallel beam.

[0034] The coupling output component 3 is located at the other end of the gain chip with a waveguide and is used to couple the resonant beam to output laser light.

[0035] In one embodiment of this application, the gain chip 1 generates amplified spontaneous emission by injecting current. The two end faces of the waveguide are controlled by coating technology to achieve transmittance. The front end face is partially transmissive, and the rear end face is nearly completely transmissive.

[0036] In one embodiment of this application, the collimating lens 2 is an aspherical lens or a lens group.

[0037] In one embodiment of this application, the coupling output component 6 is a spatial optical coupling output component or an optical fiber coupling output component.

[0038] According to an embodiment of this application, the broadband beam emitted by the gain chip 1 is converted into a parallel beam after passing through the collimating lens 2, and then diffracts on the blazed grating 3. Different wavelengths of light are reflected at different angles on the surface of the blazed grating 3. The blazed grating 3 is located on a dual adjustment mechanism consisting of the first adjustment module 4 and the second adjustment module 5, and its grating lines are perpendicular to the horizontal plane. The diffracted beam of a specific wavelength will return along the incident light path, pass through the collimating lens 2 again, and be focused into the waveguide of the gain chip 1 to form a resonance. The final laser generated is output through the coupling output component 6.

[0039] In one embodiment of this application, the rate of change of the cavity length of the external cavity tunable laser is positively correlated with the longitudinal mode number of the external cavity tunable laser and the grating constant of the blazed grating, and negatively correlated with the rotation angle of the blazed grating.

[0040] It should be noted that the rate of change of the laser cavity length is the same as and equivalent to the second speed of the second adjustment module, and the rotation speed of the blazed grating is the same as and equivalent to the first speed of the first adjustment module. The angle between the parallel beam and the normal to the blazed grating surface is the same as and equivalent to the rotation angle of the blazed grating, and the rotation angle of the blazed grating is the same as and equivalent to the rotation angle of the first adjustment module.

[0041] For example, the relationship between the cavity length of the laser, the rotation angle of the blazed grating, and the wavelength of the output light satisfies L = q·d·sinθ, 2·L = q·λ, and λ = 2·d·sinθ. Here, L is the cavity length of the laser, θ is the angle between the parallel beam and the normal to the blazed grating surface, λ is the wavelength of the output light, q is the longitudinal mode number, and d is the grating constant of the blazed grating. Therefore, the relationship between the rate of change of the laser cavity length and the rotation speed of the blazed grating satisfies v L / v θ =d L / d θ =q·d·cosθ. Where, v L v is the rate of change of the laser cavity length. θ The rotational speed of the blazing grating.

[0042] In one embodiment of this application, the first speed remains constant during tuning. A first control module processes the input first signal and outputs a first control signal to independently control the rotation of the first adjustment module at the first speed. A second control module processes the input second signal and outputs a second control signal to control the longitudinal translation of the second adjustment module at the second speed. The second control module calculates the second speed based on the current rotation angle information output by the first adjustment module and the current actual position information output by the second adjustment module, and outputs a second signal. Processing the second signal input to the second control module and outputting the second control signal enables independent control of the longitudinal translation of the second adjustment module at the second speed.

[0043] Based on the above-described external cavity tunable laser tuning device, this application also provides an external cavity tunable laser tuning method in its embodiments.

[0044] The method may include: activating an external cavity tunable laser, causing the temperature and drive current of the external cavity tunable laser to reach preset values, adjusting a first adjustment module to an initial rotation angle, and adjusting a second adjustment module to an initial position; using an information processing module to set a first speed and calculate a second speed, and outputting a first signal and a second signal based on the first speed and the second speed, respectively; a first control module using the input first signal to control the first adjustment module to rotate at the first speed to adjust the rotation angle of the blazed grating; a second control module using the input second signal to control the second adjustment module to longitudinally translate at the second speed to change the longitudinal position of the blazed grating and adjust the cavity length of the external cavity tunable laser; after waiting for a preset time, using the information processing module to calculate the deviation between the current actual cavity length and the current desired cavity length based on the current rotation angle of the first adjustment module and the current actual position of the second adjustment module; determining whether the absolute value of the deviation is greater than or equal to a preset deviation threshold; if so, the information processing module recalculates the second speed, outputs the second signal, and resets the second speed of the second adjustment module.

[0045] Figure 2 A flowchart illustrating a tuning method for an external cavity tunable laser according to an embodiment of this application is shown schematically.

[0046] like Figure 2 As shown, the tuning method may include steps S101 to S105.

[0047] In step S101, the external cavity tunable laser is started, and its temperature and drive current reach preset values. The first adjustment module is adjusted to the initial rotation angle, and the second adjustment module is adjusted to the initial position. Then, step S102 is executed.

[0048] In step S102, the information processing module sets the first speed, calculates the second speed, outputs the first signal and the second signal, and finally sets the first speed of the first adjustment module and the second speed of the second adjustment module; then step S103 is executed.

[0049] According to an embodiment of this application, the second velocity v in step S102 is calculated. L =q·d·cosθ start ·v θ Among them, v θ The first velocity θ is set in step S102. start The initial rotation angle of the first adjustment module in step S101 is q; the calculation method for q is q=2·L start / λ start , where L start λ is the cavity length of the external cavity tunable laser corresponding to the initial position of the second adjustment module in step S101; start The calculation method is λ start=2·d·sinθ start .

[0050] In step S103, after waiting for a preset time, the information processing module calculates the deviation between the current actual cavity length and the current expected cavity length based on the current rotation angle of the first adjustment module and the current actual position of the second adjustment module; then, step S104 is executed.

[0051] In step S104, it is determined whether the absolute value of the deviation calculated in step S103 is greater than or equal to the preset deviation threshold: if yes, proceed to step S105; if no, proceed to step S103.

[0052] In step S105, the information processing module recalculates the second speed, outputs the second signal, and finally resets the second speed of the second adjustment module; then step S103 is executed.

[0053] According to an embodiment of this application, the current desired cavity length of the external cavity tunable laser is calculated based on the current rotation angle of the first adjustment module; the current actual cavity length of the external cavity tunable laser is calculated based on the current actual position of the second adjustment module; the deviation between the current actual cavity length and the current desired cavity length is calculated, and when the absolute value of the deviation is greater than or equal to a preset deviation threshold, the second speed of the second adjustment module is reset.

[0054] In one exemplary embodiment, it is assumed that the preset deviation threshold is ΔL. _threshold Calculate the current desired cavity length L of an external cavity tunable laser. _expected =q·d·sinθ; Calculate the current actual cavity length L of the external cavity tunable laser; Calculate the current desired speed v of the second adjustment module. L_expected =q·d·cosθ·v θ ; Calculate the cavity length deviation ΔL=LL _expected When |ΔL|≥ΔL _threshold At that time, the second speed of the second adjustment module is reset to v. L_new =2·v L_expected -v L .

[0055] The embodiments of this application have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of this application. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this application is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this application, and all such substitutions and modifications should fall within the scope of this application.

Claims

1. A tuning device for an external cavity tunable laser, characterized in that, include: Blazed gratings are used to diffract parallel beams to produce resonant beams; The first adjustment module is used to carry and rotate the blazed grating to adjust the rotation angle of the blazed grating; The second adjustment module is used to support the first adjustment module and adjust the longitudinal position of the blazed grating to adjust the cavity length of the external cavity tunable laser. The first control module is used to control the first adjustment module to rotate at a first speed according to the input first signal, so as to adjust the rotation angle of the blazed grating; The second control module controls the second adjustment module to move longitudinally at a second speed according to the input second signal, so as to change the longitudinal position of the blazed grating and adjust the cavity length of the external cavity tunable laser. The information processing module sets the first speed and calculates the second speed based on the current rotation angle information output by the first adjustment module and the current actual position information output by the second adjustment module, and outputs the first signal and the second signal based on the first speed and the second speed, respectively.

2. The tuning device for an external cavity tunable laser according to claim 1, characterized in that, The rate of change of the cavity length of the external cavity tunable laser is positively correlated with the longitudinal mode number of the external cavity tunable laser and the grating constant of the blazed grating, and negatively correlated with the rotation angle of the blazed grating.

3. The tuning device for an external cavity tunable laser according to claim 1, characterized in that, The first speed remains constant during tuning; the first control module is used to control the input first signal and output a first control signal to independently control the rotation of the first adjustment module at the first speed. The second control module is used to control and process the input second signal, and output a second control signal to control the second adjustment module to perform longitudinal translation at a second speed.

4. The tuning device for an external cavity tunable laser according to any one of claims 1 to 3, characterized in that, Also includes: Gain chip, used to generate broadband beams; A collimating lens is disposed between the waveguide end of the gain chip and the blazed grating to convert the broadband beam into the parallel beam. A coupling output component, disposed at the other end of the gain chip having a waveguide, is used to couple the resonant beam to output laser light.

5. The tuning device for an external cavity tunable laser according to claim 4, characterized in that, The gain chip generates amplified spontaneous radiation by injecting current. The front end of the waveguide of the gain chip is partially transparent, while the rear end is nearly completely transparent.

6. The tuning device for an external cavity tunable laser according to claim 4, characterized in that, The collimating lens is an aspherical lens or a lens group.

7. The tuning device for an external cavity tunable laser according to claim 4, characterized in that, The coupling output component is a spatial optical coupling output component or an optical fiber coupling output component.

8. A method for tuning an external cavity tunable laser based on the external cavity tunable laser tuning device according to any one of claims 1 to 7, characterized in that, include: Start the external cavity tunable laser, so that the temperature and drive current of the external cavity tunable laser reach the preset values, adjust the first adjustment module to the initial rotation angle, and adjust the second adjustment module to the initial position; The information processing module is used to set a first speed and calculate a second speed, and a first signal and a second signal are output based on the first speed and the second speed, respectively. The first control module uses the input first signal to control the first adjustment module to rotate at a first speed in order to adjust the rotation angle of the blazed grating; The second control module uses the input second signal to control the second adjustment module to perform longitudinal translation at the second speed, so as to change the longitudinal position of the blazed grating and adjust the cavity length of the external cavity tunable laser. After waiting for a preset period of time, the information processing module calculates the deviation between the current actual cavity length and the current expected cavity length based on the current rotation angle of the first adjustment module and the current actual position of the second adjustment module. Determine whether the absolute value of the deviation is greater than or equal to a preset deviation threshold; if so, the information processing module recalculates the second speed, outputs the second signal, and resets the second speed of the second adjustment module.

9. The tuning method for an external cavity tunable laser according to claim 8, characterized in that, The information processing module calculates the deviation between the current actual cavity length and the current desired cavity length based on the current rotation angle of the first adjustment module and the current actual position of the second adjustment module, including: The current desired cavity length of the external cavity tunable laser is calculated based on the current rotation angle of the first adjustment module; The current actual cavity length of the external cavity tunable laser is calculated based on the current actual position of the second adjustment module; Calculate the deviation between the current actual cavity length and the current expected cavity length.

10. The tuning method for an external cavity tunable laser according to claim 8, characterized in that, The resetting of the second speed of the second adjustment module includes: The current desired speed of the second adjustment module is calculated based on the current rotation angle of the first adjustment module; The second speed is set to the difference between twice the current desired speed and the current second speed.

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