External cavity laser tuning device and method

Abstract

According to the external cavity laser tuning device and method, the gain chip, the collimating lens, the wedge-shaped lens and the diffraction grating are sequentially installed along the optical axis, the rotating pivot point of the diffraction grating is arranged at the intersection point of the optical axis and the diffraction surface of the diffraction grating, and the device is simple in structure and low in cost. The cavity length is tuned by longitudinally translating a wedge-shaped lens mounted between a collimating lens and a diffraction grating, meanwhile, a rotating pivot point is arranged at the central position of the diffraction grating, and the rotation of the diffraction grating only affects frequency selection and does not affect a longitudinal mode, so that the influence of unstable mechanical structure and heat sensitivity on the cavity length in the rotation process is reduced to a great extent, and the cavity length is tuned. Therefore, the stability of wavelength tuning is improved, and wide-range mode-hopping-free wavelength tuning is optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of laser tuning, and in particular to an external cavity laser tuning device; in addition, the present invention also relates to an external cavity laser tuning method. Background Art

[0002] The wavelength tunable external cavity semiconductor laser is composed of an inner cavity composed of an active chip and an external cavity composed of passive feedback elements such as a diffraction grating. Among them, the semiconductor laser gain chip can output a broadband spectrum, and the feedback element has a frequency selection function. By tuning the position and angle of the external cavity feedback element, the light of a specific wavelength in the broadband spectrum can be reflected back to the active area, so that the external cavity laser has excellent performance such as tunable output wavelength, single longitudinal mode output, and high side mode suppression ratio. It has been widely used in optical communications, wavelength division multiplexing systems, interferometry, high-resolution spectral analysis and other fields.

[0003] The Littrow structure is a typical structure of a wavelength tunable external cavity semiconductor laser, which has the advantages of high power output and simple structure. Its basic structure includes a gain chip, a collimating lens and a plane grating placed in sequence along the optical axis. The gain chip outputs divergent laser, which is collimated by the collimating lens and then irradiated onto the diffraction grating for diffraction, where the zero-order diffraction light is coupled out, and the first-order diffraction angle of a specific wavelength satisfies the Littrow condition of the grating and is reflected back to the active area of ​​the gain chip, so that the wavelength obtains a larger gain resonance in the mode competition, thereby achieving single longitudinal mode output.

[0004] However, the current tuning method of Littrow external cavity laser mainly ensures the synchronous tuning of the cavity length longitudinal mode and the selected frequency by selecting a specific pivot point to rotate the diffraction grating. However, it is difficult to accurately locate the pivot point, and factors such as the instability and thermal sensitivity of the mechanical structure during rotation around the pivot point will cause the cavity length to fluctuate, degrading the wavelength non-mode hopping tuning characteristics. Summary of the invention

[0005] In order to solve the problems existing in the prior art, at least one embodiment of the present invention provides an external cavity laser tuning device, which has a simple structure and greatly reduces the influence of mechanical structure instability and thermal sensitivity on cavity length during rotation, thereby improving the stability of wavelength tuning and optimizing wavelength tuning without mode hopping over a large range. To this end, at least one embodiment of the present invention also provides an external cavity laser tuning method.

[0006] In a first aspect, an embodiment of the present invention proposes an external cavity laser tuning device, comprising a gain chip, a collimating lens, a wedge lens and a diffraction grating, wherein the gain chip, the collimating lens, the wedge lens and the diffraction grating are installed in sequence along the optical axis, and the rotation pivot point of the diffraction grating is located at the intersection of the optical axis and the diffraction surface of the diffraction grating.

[0007] In some embodiments, the external cavity laser tuning device provided by the present invention has a rotation pivot point located at the middle position of the diffraction surface.

[0008] In some embodiments, in the external cavity laser tuning device provided by the present invention, the diffraction grating is driven to rotate by a motor, and the motor shaft of the motor is connected to the middle position of one side of the diffraction grating.

[0009] In a second aspect, an embodiment of the present invention further provides an external cavity laser tuning method, including the external cavity laser tuning device of the first aspect, the method comprising:

[0010] Adjust the positions of the wedge lens and the diffraction grating, and when the longitudinal mode wavelength and the resonance wavelength are both the central wavelength, take the positions of the wedge lens and the diffraction grating as the initial positions to obtain the initial optical path introduced by the wedge lens;

[0011] The longitudinal mode number is obtained by the initial wavelength of the output and the initial optical path introduced by the wedge lens;

[0012] When the longitudinal mode number is constant and the longitudinal mode wavelength is the same as the resonance wavelength, the wedge lens is longitudinally moved relative to the initial positions of the wedge lens and the diffraction grating and the diffraction grating is rotated to perform continuous mode-hop-free tuning.

[0013] In some embodiments, the external cavity laser tuning method provided by the present invention, when the longitudinal mode wavelength and the resonant wavelength are both the central wavelength, further comprises:

[0014] The initial incident angle and the initial longitudinal distance from the bottom of the wedge lens to the optical axis are measured.

[0015] In some embodiments, the external cavity laser tuning method provided by the present invention obtains the initial optical path introduced by the wedge lens by the following formula 1:

[0016] L0=L ld +L ld,g +(n-1)(h-y0)tanα Formula 1;

[0017] Where L0 is the initial optical path introduced by the wedge lens, L ld is the thickness of the gain chip, L ld,g is the distance from the emitting surface of the gain chip to the rotation pivot point, y0 is the longitudinal initial distance from the bottom of the wedge lens to the optical axis, h is the height of the wedge lens, α is the angle of the wedge lens, and n is the refractive index of the wedge lens.

[0018] In some embodiments, the external cavity laser tuning method provided by the present invention obtains the longitudinal mode number by the following formula 2:

[0019] q=2L0 / λ0 Equation 2;

[0020] Among them, q is the longitudinal mode number, L0 is the initial optical path introduced by the wedge lens, and λ0 is the initial wavelength of the output.

[0021] In some embodiments, the external cavity laser tuning method provided by the present invention longitudinally moves the wedge lens relative to the initial positions of the wedge lens and the diffraction grating and rotates the diffraction grating to perform continuous mode-hop-free tuning, including:

[0022] When tuning to a certain wavelength is required, the longitudinal translation of the wedge lens and the rotation of the diffraction grating are calculated.

[0023] In some embodiments, the external cavity laser tuning method provided by the present invention obtains the longitudinal translation amount of the wedge lens by the following formula 3:

[0024]

[0025] Among them, Δy is the longitudinal translation of the wedge lens, L0 is the initial optical path introduced by the wedge lens, λ' is a tuned wavelength, λ0 is the initial output wavelength, α is the angle of the wedge lens, and n is the refractive index of the wedge lens.

[0026] In some embodiments, the external cavity laser tuning method provided by the present invention obtains the rotation amount of the diffraction grating by the following formula 4:

[0027]

[0028] Where Δθ is the rotation amount of the diffraction grating, λ' is a certain wavelength to be tuned, θ0 is the initial incident angle, and d is the grating constant of the diffraction grating.

[0029] It can be seen that an external cavity laser tuning device and method according to an embodiment of the present invention has a simple device structure, and the cavity length is tuned by longitudinally translating a wedge-shaped lens installed between a collimating lens and a diffraction grating. Meanwhile, a rotation pivot point is set at the center of the diffraction grating, and the rotation of the diffraction grating only affects the frequency selection but not the longitudinal mode, thereby greatly reducing the influence of mechanical structure instability and thermal sensitivity on the cavity length during rotation, thereby improving the stability of wavelength tuning and optimizing wavelength tuning without mode hopping over a large range. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0031] Figure 1 Shown is a schematic diagram of the initial structure of an external cavity laser tuning device in an embodiment of the present invention;

[0032] Figure 2 Shown is a schematic diagram of the structure of an external cavity laser tuning device after tuning in an embodiment of the present invention;

[0033] Figure 3 Shown is a flow chart of an external cavity laser tuning method in an embodiment of the present invention.

[0034] The reference numerals in the accompanying drawings of the specification are as follows:

[0035] Gain chip 1, collimating lens 2, wedge lens 3, diffraction grating 4, rotation pivot point 5, optical axis I, Specific implementation plan

[0036] 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this article, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0038] The inventor of the present invention has found that in the prior art, the Littrow structure is a typical structure of a wavelength tunable external cavity semiconductor laser, and the resonance wavelength λ g It is related to the incident angle θ and can be expressed by the following formula:

[0039] λ g =2dsinθ

[0040] Where d is the grating constant. Rotating the grating around the pivot point can change the θ tuning resonant wavelength. When the pivot point is not at the center of the grating, the rotating grating will also modulate the cavity length. Ignoring the dispersion of the gain chip and the collimating lens, the laser cavity length L is shown in the following formula:

[0041] L=L ld +L ld,g

[0042] Among them, L ld is the thickness of the gain chip, L ld,g is the distance from the gain chip emission surface to the rotation pivot point. The longitudinal mode wavelength λ caused by the change in cavity length q The modulation is shown in the formula:

[0043] λ q =2L / q

[0044] Where q (q = 1, 2, 3...) is the longitudinal mode number. When the diffraction grating rotates around the pivot point, the cavity length and the incident angle will be tuned simultaneously. g and the longitudinal mode wavelength λ q The wavelength interval is less than half of the laser longitudinal mode interval Δλ, which can achieve continuous tuning of the wavelength, as shown in the following formula:

[0045]

[0046] The tuning method of Littrow external cavity laser mainly ensures synchronous tuning of cavity length longitudinal mode and selected frequency by selecting a specific pivot point to rotate the diffraction grating. However, it is difficult to accurately locate the pivot point, and factors such as instability and thermal sensitivity of the mechanical structure during the rotation around the pivot point will cause cavity length fluctuations and degrade the wavelength non-mode hopping tuning characteristics. The embodiment of the present invention provides the following solution:

[0047] [Example 1]

[0048] like Figure 1 to Figure 2 As shown, an embodiment of the present invention provides an external cavity laser tuning device, including a gain chip 1, a collimating lens 2, a wedge lens 3 and a diffraction grating 4. The gain chip 1, the collimating lens 2, the wedge lens 3 and the diffraction grating 4 are installed in sequence along the optical axis I, and the rotation pivot point 5 of the diffraction grating 4 is set at the intersection of the optical axis I and the diffraction surface of the diffraction grating 4.

[0049] It should be noted that the cavity length can be tuned by longitudinally translating the wedge-shaped lens 3, and the resonant wavelength can be tuned by rotating the diffraction grating 4, thereby reducing the influence of mechanical structure instability and thermal sensitivity on the cavity length during rotation, and the axial error of the wedge-shaped lens 3 can be ignored, thereby improving the stability of wavelength tuning.

[0050] In some embodiments, the rotation pivot point 5 is disposed at the middle of the diffraction surface, thereby increasing the stability of the diffraction grating 4 during rotation.

[0051] In some embodiments, the diffraction grating 4 is driven to rotate by a motor, and the motor shaft of the motor is connected to the middle position of one side of the diffraction grating. It should be noted that when the motor rotates, the motor shaft drives the diffraction grating 4 to rotate around the optical axis I, thereby achieving the purpose of precise tuning.

[0052] [Example 2]

[0053] like Figures 1 to 3 As shown, an embodiment of the present invention further provides an external cavity laser tuning method, including the external cavity laser tuning device in embodiment 1, and the method comprises:

[0054] Adjust the positions of the wedge lens 3 and the diffraction grating 4. When the longitudinal mode wavelength and the resonance wavelength are both the central wavelength, the positions of the wedge lens 3 and the diffraction grating 4 are taken as the initial positions to obtain the initial optical path L0 introduced by the wedge lens.

[0055] The longitudinal mode number q is obtained by the initial wavelength of the output and the initial optical path L0 introduced by the wedge lens;

[0056] When the longitudinal mode number q is constant and the longitudinal mode wavelength is the same as the resonance wavelength, the wedge lens 3 is longitudinally moved relative to the initial positions of the wedge lens 3 and the diffraction grating 4 and the diffraction grating 4 is rotated to perform continuous mode-hop-free tuning.

[0057] It should be noted that the side of the gain chip 1 close to the collimating lens 2 is the exit surface, and the side of the diffraction grating 4 close to the wedge lens 3 is the diffraction surface. The laser emitted from the gain chip 1 passes through the collimating lens 2, becomes parallel light parallel to the optical axis I, passes through the wedge lens 3 and irradiates the diffraction grating 4 to be diffracted, wherein the zero-order diffraction is coupled out, and the first-order diffraction of a specific wavelength passes through the diffraction grating 4 and returns to the gain chip 1 along the original path.

[0058] Specifically, in Figure 1 In the process, the wedge lens 3 is longitudinally translated, and the diffraction grating 4 is rotated around the rotation pivot point 5, so that the initial wavelength λ0 of the output is the central wavelength. At this time, the positions of the wedge lens 3 and the diffraction grating 4 are the initial positions, and the longitudinal mode wavelength λ q and the resonant wavelength λ g The thickness of the intracavity gain chip is recorded as L. ld , the distance from the emitting surface of the gain chip 1 to the rotation pivot point 5 is L ld,g The initial longitudinal distance from the bottom of the wedge lens 3 to the optical axis I is y0, and the initial incident angle is θ0, that is, θ0 is the angle between the normal A of the diffraction surface of the diffraction grating 4 and the optical axis I.

[0059] exist Figure 2 In the embodiment, based on the initial positions of the wedge-shaped lens 3 and the diffraction grating 4, the wedge-shaped lens 3 is longitudinally translated by Δy to y':

[0060] y′=y0+Δy;

[0061] The diffraction grating 4 rotates by Δθ to θ':

[0062] θ′=θ0+Δθ;

[0063] To continuously tune the laser wavelength to a certain wavelength λ', it is necessary to ensure that the longitudinal mode wavelength λ is constant under the premise that the longitudinal mode number q remains unchanged. q and the resonant wavelength λ g At the same time, the wavelength λ' is tuned to a certain wavelength, and the longitudinal translation amount Δy of the wedge lens 3 and the rotation amount Δθ of the diffraction grating 4 at this time are calculated.

[0064] In some embodiments, the initial optical path introduced by the wedge lens is obtained by the following formula 1:

[0065] L0=L ld +L ld,g +(n-1)(h-y0)tanα Formula 1;

[0066] Wherein, L0 is the initial optical path introduced by the wedge lens 3, L ld is the thickness of gain chip 1, L ld,g is the distance from the gain chip emitting surface to the rotation pivot point 5, y0 is the longitudinal initial distance from the bottom of the wedge lens 3 to the optical axis I, h is the height of the wedge lens 3, α is the angle of the wedge lens 3, and n is the refractive index of the wedge lens 3.

[0067] The longitudinal mode number is obtained by the following formula 2:

[0068] q=2L0 / λ0 Equation 2;

[0069] Wherein, q is the longitudinal mode number, L0 is the initial optical path introduced by the wedge lens 3, and λ0 is the initial wavelength of the output.

[0070] In some embodiments, longitudinally moving the wedge lens 3 relative to the initial positions of the wedge lens 3 and the diffraction grating 4 and rotating the diffraction grating 4 to perform continuous mode-hop-free tuning comprises:

[0071] When tuning to a certain wavelength is required, the longitudinal translation amount of the wedge lens 3 and the rotation amount of the diffraction grating 4 are calculated.

[0072] The longitudinal translation of the wedge lens 3 is obtained by the following formula 3:

[0073]

[0074] Wherein, Δy is the longitudinal translation of the wedge lens 3 , L0 is the initial optical path introduced by the wedge lens 3 , λ′ is a tuned wavelength, λ0 is the initial output wavelength, α is the angle of the wedge lens 3 , and n is the refractive index of the wedge lens 3 .

[0075] The rotation amount of the diffraction grating 4 is obtained by the following formula 4:

[0076]

[0077] Wherein, Δθ is the rotation amount of the diffraction grating 4 , λ′ is a certain tuned wavelength, θ0 is the initial incident angle, and d is the grating constant of the diffraction grating 4 .

[0078] In summary, embodiments 1-2 of the present invention provide an external cavity laser tuning device and method, the device has a simple structure, and the cavity length is tuned by longitudinally translating a wedge lens installed between a collimating lens and a diffraction grating. At the same time, a rotation pivot point is set at the center of the diffraction grating, and the rotation of the diffraction grating only affects the frequency selection but not the longitudinal mode, thereby greatly reducing the influence of mechanical structure instability and thermal sensitivity on the cavity length during rotation, thereby improving the stability of wavelength tuning and optimizing wavelength tuning without mode hopping over a large range.

[0079] The above contents are only specific implementation methods of the present application, and the protection scope of the present application is not limited thereto. Those skilled in the art may make changes or substitutions within the technical scope disclosed in the present application, and these changes or substitutions shall be within the protection scope of the present application.

[0080] Those skilled in the art will appreciate that although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features from different embodiments is meant to be within the scope of the present invention and to form different embodiments.

[0081] 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 appended claims.

Claims

1. An external cavity laser tuning device, characterized in that: The invention comprises a gain chip, a collimating lens, a wedge lens and a diffraction grating, wherein the gain chip, the collimating lens, the wedge lens and the diffraction grating are sequentially installed along the optical axis, and the rotation pivot point of the diffraction grating is arranged at the intersection of the optical axis and the diffraction surface of the diffraction grating.

2. The external cavity laser tuning device according to claim 1, characterized in that: The rotation pivot point is arranged at the middle position of the diffraction surface.

3. The external cavity laser tuning device according to claim 2, characterized in that: The diffraction grating is driven to rotate by a motor, and a motor shaft of the motor is connected to a middle position of one side of the diffraction grating.

4. A method for tuning an external cavity laser, characterized in that: The method comprises the external cavity laser tuning device according to any one of claims 1 to 3, wherein: Adjusting the positions of the wedge-shaped lens and the diffraction grating, when the longitudinal mode wavelength and the resonance wavelength are both the central wavelength, taking the positions of the wedge-shaped lens and the diffraction grating as the initial positions, obtaining the initial optical path introduced by the wedge-shaped lens; Obtaining the longitudinal mode number by the initial wavelength output and the initial optical path introduced by the wedge-shaped lens; When the longitudinal mode number is constant and the longitudinal mode wavelength is the same as the resonance wavelength, the wedge lens is longitudinally moved relative to the initial positions of the wedge lens and the diffraction grating and the diffraction grating is rotated to perform continuous mode-hop-free tuning.

5. The external cavity laser tuning method according to claim 4, characterized in that: When the longitudinal mode wavelength and the resonant wavelength are both the central wavelength, the following also includes: The initial incident angle and the initial longitudinal distance from the bottom of the wedge lens to the optical axis are measured.

6. The external cavity laser tuning method according to claim 5, characterized in that: The initial optical path introduced by the wedge lens is obtained by the following formula 1: L0 = L ld + L ld,g +(n - 1)(h - y0)tanα Equation 1; Wherein, L0 is the initial optical path introduced by the wedge lens, L ld is the thickness of the gain chip, L ld,g is the distance from the emitting surface of the gain chip to the rotation pivot point, y0 is the longitudinal initial distance from the bottom of the wedge lens to the optical axis, h is the height of the wedge lens, α is the angle of the wedge lens, and n is the refractive index of the wedge lens.

7. The external cavity laser tuning method according to claim 6, characterized in that: The longitudinal mode number is obtained by the following formula 2: q=2L0 / λ0 Equation 2; Wherein, q is the longitudinal mode number, L0 is the initial optical path introduced by the wedge lens, and λ0 is the initial wavelength of the output.

8. The external cavity laser tuning method according to claim 7, characterized in that: The step of longitudinally moving the wedge-shaped lens relative to initial positions of the wedge-shaped lens and the diffraction grating and rotating the diffraction grating to perform continuous mode-hop-free tuning comprises: When tuning to a certain wavelength is required, the longitudinal translation amount of the wedge lens and the rotation amount of the diffraction grating are calculated.

9. The external cavity laser tuning method according to claim 8, characterized in that: The longitudinal translation of the wedge lens is obtained by the following formula 3: Among them, Δy is the longitudinal translation of the wedge lens, L0 is the initial optical path introduced by the wedge lens, λ' is a tuned wavelength, λ0 is the initial output wavelength, α is the angle of the wedge lens, and n is the refractive index of the wedge lens.

10. The external cavity laser tuning method according to claim 8, characterized in that: The rotation amount of the diffraction grating is obtained by the following formula 4: Wherein, Δθ is the rotation amount of the diffraction grating, λ' is a tuned wavelength, θ0 is the initial incident angle, and d is the grating constant of the diffraction grating.

Images