External cavity laser tuning device and method

Abstract

The present invention provides an external cavity laser tuning device and method. A gain chip, a collimating lens, a wedge lens, and a diffraction grating are sequentially installed along an optical axis. 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. The device has a simple structure. The cavity length is tuned by longitudinally translating the wedge lens installed between the collimating lens and the diffraction grating. At the same time, the rotation pivot point is located at the center of the diffraction grating. Rotating the diffraction grating only affects frequency selection but not longitudinal modes. This greatly reduces the effects 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.

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] A wavelength-tunable external-cavity semiconductor laser consists of an internal cavity composed of an active chip and an external cavity composed of passive feedback elements such as a diffraction grating. The semiconductor laser gain chip is capable of outputting a broadband spectrum, and the feedback element has a frequency-selective function. By tuning the position and angle of the external cavity feedback element, light of a specific wavelength within the broadband spectrum can be reflected back to the active region. This gives the external-cavity laser excellent properties 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, and high-resolution spectral analysis.

[0003] The Littrow structure is a typical structure for wavelength-tunable external-cavity semiconductor lasers, offering advantages such as high power output and a simple structure. Its basic structure consists of a gain chip, a collimating lens, and a plane grating, all placed sequentially along the optical axis. The gain chip outputs divergent laser light, which is collimated by the collimating lens and then irradiated onto the diffraction grating, where it diffracts. The zero-order diffracted light is coupled out, and the first-order diffraction angle of a specific wavelength satisfies the grating's Littrow condition and is reflected back along the original path into the active region of the gain chip, resulting in a high gain resonance at that wavelength in the mode competition, thus achieving single longitudinal mode output.

[0004] However, the current tuning method of Littrow external cavity lasers 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 mode-hop-free tuning characteristics. Summary of the Invention

[0005] To address the problems of the prior art, at least one embodiment of the present invention provides an external cavity laser tuning device with a simple structure. This device significantly reduces the impact of mechanical instability and thermal sensitivity on cavity length during rotation, thereby improving wavelength tuning stability and optimizing wide-range mode-hop-free wavelength tuning. 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 in the middle 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] Adjusting the positions of the wedge lens and the diffraction grating, and when the longitudinal mode wavelength and the resonant wavelength are both the central wavelength, taking the positions of the wedge lens and the diffraction grating as the initial positions, obtaining 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 center 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 Equation 1;

[0017] Among them, 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 gain chip emitting surface 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] Where 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 moving the wedge lens relative to the initial positions of the wedge lens and the diffraction grating and rotating the diffraction grating to perform continuous mode-hop-free tuning includes:

[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 of the wedge lens by the following formula 3:

[0024]

[0025] Where 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 of the diffraction grating, λ' is the tuned wavelength, θ0 is the initial incident angle, and d is the grating constant of the diffraction grating.

[0029] It can be seen that the external cavity laser tuning device and method of the embodiment of the present invention have a simple device structure. The cavity length is tuned by longitudinally translating a wedge lens installed between a collimating lens and a diffraction grating. At the same time, the rotation pivot point is set at the center position of the diffraction grating. The rotating 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 the rotation process, 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 following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. 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 any creative work.

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

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

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

[0034] The reference numerals in the accompanying drawings 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] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying 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 making creative efforts shall fall within the scope of protection of the present invention.

[0037] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this document, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes 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 presence of other identical elements in the process, method, article or device that includes the element.

[0038] The inventors of this solution have found that in the prior art, the Littrow structure is a typical structure of a wavelength tunable external cavity semiconductor laser, and the resonant wavelength λ g It is related to the incident angle θ and can be expressed as follows:

[0039] λ g =2dsinθ

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

[0045]

[0046] The Littrow external cavity laser tuning method primarily ensures synchronous tuning of the cavity length longitudinal mode and the selected frequency by rotating the diffraction grating around a specific pivot point. However, accurate positioning of the pivot point is difficult, and factors such as mechanical structure instability and thermal sensitivity during rotation around the pivot point can cause cavity length fluctuations, degrading the wavelength mode-hop-free tuning characteristics. The present invention provides the following solutions:

[0047] [Example 1]

[0048] like Figures 1 to 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 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 the rotation process, and the axial error of the wedge lens 3 can be ignored, thereby improving the stability of the wavelength tuning.

[0050] In some embodiments, the rotation pivot point 5 is located in 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, the method comprising:

[0054] Adjust the positions of the wedge lens 3 and the diffraction grating 4. When the longitudinal mode wavelength and the resonant wavelength are both the center 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, continuous mode-hop-free tuning is performed by longitudinally moving the wedge lens 3 and rotating the diffraction grating 4 relative to their initial positions.

[0057] It should be noted that the side of the gain chip 1 closest to the collimating lens 2 is the output surface, and the side of the diffraction grating 4 closest to the wedge lens 3 is the diffraction surface. Laser light emitted from the gain chip 1 passes through the collimating lens 2, becoming parallel light parallel to the optical axis I. This light then passes through the wedge lens 3 and is diffracted by the diffraction grating 4. The zeroth-order diffraction is coupled out, while the first-order diffraction of a specific wavelength returns to the gain chip 1 along the same path through the diffraction grating 4.

[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 center wavelength. At this time, the positions of the wedge lens 3 and the diffraction grating 4 are at the initial positions, and the longitudinal mode wavelength λ of the external cavity laser is 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 shifted 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 Equation 1;

[0066] Among them, L0 is the initial optical path introduced by the wedge lens 3, L ld is the thickness of the 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 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 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 with a simple device structure. The cavity length is tuned by longitudinally translating a wedge-shaped lens installed between a collimating lens and a diffraction grating. At the same time, the rotation pivot point is set at the center of the diffraction grating. Rotating the diffraction grating only affects the frequency selection but not the longitudinal mode, thereby greatly reducing the effects of mechanical structure instability and thermal sensitivity on the cavity length during the rotation process, thereby improving the stability of wavelength tuning and optimizing wavelength tuning without mode hopping over a large range.

[0079] The above content is only a specific embodiment 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 should all be within the protection scope of the present application.

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

[0081] Although the embodiments of the present invention have been described with reference to 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 optical system 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 set 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 located 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 external cavity laser tuning device according to any one of claims 1 to 3, wherein the method comprises: Adjusting the positions of the wedge lens and the diffraction grating, and when the longitudinal mode wavelength and the resonant wavelength are both the center wavelength, taking the positions of the wedge lens and the diffraction grating as initial positions, obtaining an initial optical path introduced by the wedge lens; Obtaining the longitudinal mode number by the initial wavelength of the output and the initial optical path introduced by the wedge 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 method further 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 lens relative to initial positions of the wedge 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: Wherein, 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.

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