Method and system for high-precision real-time detection of wavelength drift of semiconductor laser

Abstract

The invention discloses a semiconductor laser wavelength drift high-precision real-time detection method and system, and the method comprises the steps: enabling light emitted by a laser to pass through a collimating mirror to form a collimated laser beam, and enabling the collimated laser beam to pass through a reflector, a spectroscope and a to-be-detected optical mirror; through the transmission of the spectroscope, the transmission grating forms a Talbot image; a telecentric lens and a camera are used for collecting stripe images of the Talbot image; the grating moves along the optical axis direction of the telecentric lens to acquire multiple frames of stripe images; and performing two-dimensional Fourier transform on the acquired fringe image, extracting a spatial frequency or a spatial phase, calculating a phase shift, and calculating laser wavelength drift according to the phase shift. Multiple frames of fringe images are collected by precisely moving the grating in the optical axis direction, and spatial frequency and phase information are extracted through two-dimensional Fourier transform, so that the tiny drift distance of the laser wavelength is inverted, non-contact, high-sensitivity and real-time online detection of the laser wavelength is realized, and the detection precision is improved. And the stability and the reliability of a complex system under extreme performance requirements are obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical test analysis, in particular to a method and system for high-precision real-time detection of wavelength drift of a semiconductor laser. BACKGROUND

[0002] Traditionally, the wavelength of a laser is set at the factory and is assumed to be stable during use. However, with the development of technology, many advanced applications have found that a small drift or uncertainty in the wavelength of a laser can become a performance bottleneck or even a failure point of the entire system. For example:

[0003] In order to increase the information transmission capacity of an optical fiber, a dense wavelength division multiplexing (DWDM) optical fiber communication system simultaneously transmits dozens or even hundreds of different wavelength laser signals in one optical fiber. The wavelength interval between each channel is very narrow (as low as 50GHz, about 0.4nm). If the wavelength of a certain laser drifts due to temperature changes or aging, it will invade the adjacent channel, causing serious crosstalk, leading to a sharp increase in communication error rate, and even interrupting communication. Therefore, the wavelength of each laser must be locked and monitored in real time and with high precision.

[0004] Quantum measurement: Many quantum phenomena (such as hyperfine energy level transitions of atoms) have extremely stringent requirements for the wavelength of a laser. The laser needs to be accurately locked on a specific absorption line of an atom (such as the D line of cesium atoms or rubidium atoms). The natural linewidth of these lines is very narrow (possibly less than 1MHz). Even a small drift in the wavelength of the laser (corresponding to a frequency drift) will greatly reduce the efficiency of interaction with the atom, making the atomic clock inaccurate, the cold atom experiment a failure, and the quantum logic gate operation fidelity low.

[0005] In order to ensure the stability and reliability of a complex system under extreme performance indicators, the wavelength of a laser must be changed from a "factory-set" static parameter to a "full-range controllable" dynamic variable. The key to achieving this change is to invent a technology that can integrate, quickly and accurately "read" this variable - a high-precision real-time wavelength detection technology. This application greatly promotes the transformation of semiconductor lasers from a "rough" light source to a "precise" instrument-level tool. SUMMARY

[0006] The present application provides a method and system for high-precision real-time detection of wavelength drift of a semiconductor laser, which solves the technical problem of being unable to accurately detect the wavelength drift of a laser in the prior art.

[0007] The present application provides a method for high-precision real-time detection of wavelength drift of a semiconductor laser, which comprises:

[0008] Step 1: the light emitted by the laser forms a collimated laser beam after passing through the collimating mirror; the collimated laser beam is completely reflected by the reflecting mirror and is incident on the beam splitter; the collimated laser beam is reflected by the beam splitter and irradiates the optical mirror to be tested; the optical mirror to be tested reflects the collimated laser beam back to the beam splitter, which is transmitted through the beam splitter, the grating, and the Talbot image is formed at the Talbot position;

[0009] Step 2: use a telecentric lens and a camera to capture the fringe image of the Talbot image;

[0010] Step 3: move the grating along the optical axis direction of the telecentric lens, and capture multiple frames of the fringe image;

[0011] Step 4: perform two-dimensional Fourier transform on the captured fringe image to extract the spatial frequency or spatial phase, calculate the phase shift, and calculate the laser wavelength drift according to the phase shift.

[0012] In some embodiments, the grating is a fringe grating, and the grating pitch of the grating is 20-50 μm.

[0013] In some embodiments, the step length of the grating is 1-5 μm.

[0014] In some embodiments, in step 4,

[0015] performing two-dimensional Fourier transform on the captured fringe image to obtain an amplitude-frequency characteristic;

[0016] extracting the spatial frequency or spatial phase from the amplitude-frequency characteristic;

[0017] calculating the phase shift based on the spatial frequency or spatial phase;

[0018] calculating the laser wavelength drift according to the phase shift.

[0019] In some embodiments, the calculation of the phase shift based on the spatial frequency or spatial phase comprises:

[0020] phase unwrapping the spatial phase to obtain an unwrapped phase.

[0021] In some embodiments, the unwrapped phase is calculated by the following formula:

[0022]

[0023] In the above formula, Ψ 12(n) is the unwrapped phase of Λ 120 represents the initial phase at the spatial coordinate origin (0, 0) coordinate, is the initial phase difference of

[0024] In some embodiments, the phase shift is calculated based on the spatial frequency or spatial phase, comprising:

[0025] The phase shift is calculated based on the spatial frequency by using the linear relationship between the spatial frequency and the phase shift.

[0026] In some embodiments, the multi-frame fringe image is described as:

[0027] Λ 12(x,y) = Λ 120 + ΔΛ 12x · (x-1) + ΔΛ 12y · (y-1)

[0028] In the formula, Λ 12(x,y) represents the spatial coordinates (x, y), Λ 120 represents the initial phase at the spatial coordinate origin (0, 0), ΔΛ 12x and ΔΛ 12y are the change rates of the pixels of each point of the image along the x and y directions, respectively.

[0029] In some embodiments, the two-dimensional Fourier transform is performed on the collected fringe image, specifically as follows:

[0030]

[0031] Ψ 12(n) = 2Λ 120 · k (n) + φ 120

[0032] I1 and I2 represent the DC size, respectively; wherein Ω u and Ωv are the spatial frequency two-dimensional coordinates in the x and y directions, respectively, and δ[u, v] is a 2D increment function.

[0033] The application also provides a system for high-precision real-time detection of wavelength drift of a semiconductor laser, comprising:

[0034] A light source module is configured to emit a light source and form a light path.

[0035] The light path module is sequentially provided with a collimating mirror configured to form a collimated laser beam, a reflecting mirror configured to reflect the collimated laser beam, and a beam splitter configured to reflect the light beam to a to-be-measured optical mirror and receive the reflected light of the to-be-measured optical mirror.

[0036] The measurement module comprises a grating arranged on the light path after the transmission of the beam splitter, configured to form a Talbot image at a Talbot position; and an image acquisition unit configured to acquire a fringe image of the Talbot image, wherein the image acquisition unit comprises a telecentric lens and a camera.

[0037] A mobile control module is configured to drive the grating to move along the optical axis of the telecentric lens.

[0038] A controller is in communication connection with the camera and the mobile control module, configured to perform two-dimensional Fourier transform on the collected multiple frames of the fringe images, extract spatial frequency or spatial phase, calculate phase shift, and calculate laser wavelength shift according to the phase shift.

[0039] The present application has the following advantages:

[0040] The method for high-precision real-time detection of semiconductor laser wavelength shift provided by the present application utilizes the Talbot effect to construct a high-stability interference system, combines a telecentric lens with a camera to realize distortion-free imaging of Talbot images, and collects multiple frames of fringe images by precisely moving the grating along the optical axis, and then extracts spatial frequency and phase information through two-dimensional Fourier transform, thereby inverting the tiny shift amount of the laser wavelength, realizing non-contact, high-sensitivity, real-time online detection of the laser wavelength, significantly improving the stability and reliability of complex systems under extreme performance requirements, and promoting the leap-forward development of semiconductor lasers from traditional "extensive" light sources to "precision optical tools" with instrument-level precision and controllability. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application.

[0042] Figure 1 A structural schematic diagram of a semiconductor laser wavelength shift high-precision real-time detection system provided by the present application;

[0043] Figure 2a A Talbot imaging diagram of the grating;

[0044] Figure 2b A two-dimensional Fourier transform amplitude-frequency diagram;

[0045] Figure 3a A wrapped phase diagram;

[0046] Figure 3b An unwrapped phase diagram;

[0047] Figure 4 A real-time detection diagram of laser wavelength shift;

[0048] Figure 5 A real-time detection diagram of laser wavelength phase shift.

[0049] Wherein, 1, light source module; 2, collimating mirror; 3, reflecting mirror; 4, beam splitter; 5, optical mirror to be measured; 6, grating; 7, telecentric lens; 8, camera; 9, movement control module; 10, controller. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0051] It should be noted that all directionality indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present application are only used to explain the relative positional relationship, movement condition, etc. between components in a certain posture (as shown in the drawings), and if the certain posture changes, the directionality indications also change accordingly.

[0052] In addition, the description of "first", "second" and the like in the present application is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the scope of protection claimed by the present application.

[0053] The embodiments of the present application provide a method and system for high-precision real-time detection of wavelength drift of a semiconductor laser, which solves the technical problem that the wavelength drift of a laser cannot be accurately detected in the prior art.

[0054] The technical solutions in the embodiments of the present application are as follows to solve the above technical problems:

[0055] As shown in Figure 1 The present application provides a method for high-precision real-time detection of wavelength drift of a semiconductor laser, which comprises the following steps:

[0056] Step 1: The light emitted by the laser forms a collimated laser beam after passing through the collimating mirror; the collimated laser beam is completely reflected by the reflecting mirror and is incident on the beam splitter; the collimated laser beam is reflected by the beam splitter and is incident on the optical mirror to be measured; the optical mirror to be measured reflects the collimated laser beam back to the beam splitter, and the collimated laser beam is transmitted through the beam splitter, the grating and the Talbot position to form a Talbot image;

[0057] Step 2: Collecting the Talbot image using a telecentric lens and a camera;

[0058] Step 3: Moving the grating along the optical axis of the telecentric lens, and collecting multiple frames of the fringe images;

[0059] Step 4: Performing two-dimensional Fourier transform on the collected fringe images, extracting spatial frequency or spatial phase, calculating phase shift, and calculating the laser wavelength drift according to the phase shift.

[0060] The present application constructs a high-stability interference system using the Talbot effect, realizes the distortionless imaging of the Talbot image by combining a telecentric lens with a camera, collects multiple frames of fringe images by precisely moving the grating along the optical axis, and inversely calculates the small drift of the laser wavelength by extracting the spatial frequency and phase information through two-dimensional Fourier transform, thereby realizing the non-contact, high-sensitivity, and real-time online detection of the laser wavelength, significantly improving the stability and reliability of complex systems under extreme performance requirements, and promoting the leapfrog development of semiconductor lasers from traditional "extensive" light sources to "precision optical tools" with instrument-level precision and controllability.

[0061] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the drawings in the specification and specific embodiments.

[0062] Preferably, the grating is a fringe grating, the grating pitch of the grating is 20-50 microns, and the step length of the grating is 1-5 microns.

[0063] Specifically, the experimental system is a grating Talbot self-imaging measurement system, as shown in Figure 1 The light emitted by the semiconductor fiber laser forms a collimated laser beam after the collimating mirror, is completely reflected by the reflecting mirror, is incident on the beam splitter, is reflected by the beam splitter, is irradiated on the to-be-measured optical mirror, is reflected by the to-be-measured reflecting mirror back to the beam splitter, is transmitted through the beam splitter, transmits through the grating G2, forms a Talbot image at the Talbot position, and the fringe image is collected by a telecentric lens and a camera, as shown in Figure 2a In this embodiment, the voice coil motor moves the fringe grating with a grating pitch of 50 microns in the horizontal direction, the step length is 3 microns, and the total number of steps is 1585.

[0064] During the specific test, the Talbot image of the grating is clear at the Talbot distance behind the grating, as shown in Figure 2a

[0065] The grating Talbot fringe image can be described as:

[0066] Λ 12(x,y) =Λ 120 +ΔΛ 12x ·(x-1)+ΔΛ 12y ·(y-1)​

[0067] In the formula, Λ 12(x,y) Represents spatial coordinates (x, y), Λ 120 ΔΛ represents the initial phase at the origin (0, 0) in spatial coordinates. 12x and ΔΛ 12y These are the rates of change of each pixel in the image along the x and y directions, respectively.

[0068] like Figure 2b As shown, the two-dimensional Fourier transform of the interference fringe image yields:

[0069]

[0070] Ψ 12(n) =2Λ 120 ·k(n)+φ 120

[0071] I1 and I2 represent the magnitude of DC; where Ω u Let Ω and Ωv be the two-dimensional spatial frequency coordinates in the x and y directions, respectively, and δ[u,v] be the 2D increment function. Since the grating fringes are all straight, Ω... 12u and Ω 12v The amplitudes are two increment functions symmetric about the origin. A two-dimensional Fourier transform is performed on one frame of the fringe image captured by the camera, yielding the amplitude-frequency response as follows: Figure 2b As shown, peaks ① and ③ correspond to the spatial frequency Ω. 12u Ω 12v and spatial phase Ψ 12 Furthermore, since it is symmetrical about the origin, we can analyze one of them; peak ② is the DC component of the two-dimensional Fourier transform of the interference fringe image.

[0072] Phase shift can be calculated from the spatial frequency or spatial phase of the fringe image. Λ 120 Given a known initial phase difference and a linear relationship between spatial frequency and phase shift, the phase shift can be easily calculated using spatial frequency. When the acquired image satisfies the sampling theorem, the phase shift can be calculated by unwrapping the spatial phase extracted after the two-dimensional Fourier transform of the image.

[0073]

[0074] In the above formula, Ψ 12(n) for The unwrapping phase; Yes, it's the initial phase difference. When the laser wavenumber has no mode hopping, the spatial phase is extracted by performing a two-dimensional Fourier transform on 500 images captured by the camera, such as... Figure 3a , Figure 3b As shown.

[0075] In the specific detection process, the wrapped phase distribution of the fundamental frequency, the real-time detection of the laser wavelength drift, the Talbot self-imaging focal length and the profile measurement system, the coordinates: (150, 1), as shown in Figure 4 Fig. 1 is the Talbot self-imaging, Fig. 2 is the light intensity distribution of the camera field of view, Fig. 3 is the average light intensity distribution of the camera field of view, and Fig. 4 is the full-field wrapped phase of the Fourier transform of the 1585-step image sequence.

[0076] As shown in Figure 5 , the real-time detection result of the laser wavelength drift, the total step length of the grating 6: 1585 steps, the total distance traveled: 4.755 mm, the drift phase movement of the fundamental frequency grating 6: 597.4658884 rad, the average movement per step: 0.3769500 rad, the average error of the step length: 0.04573036 rad, and the RMS error: 0.08684550 rad.

[0077] The application also provides a system for high-precision real-time detection of semiconductor laser wavelength drift, which comprises:

[0078] A light source module 1, which is a semiconductor laser, is used to emit a light source and form a light path;

[0079] A light path module, which is sequentially provided with a collimating mirror 2 for forming a collimated laser beam, a reflecting mirror 3 for reflecting the collimated laser beam, and a beam splitter 4 for reflecting the light beam to a to-be-measured optical mirror 5 and receiving the reflected light;

[0080] A measurement module, which comprises a grating 6 provided on the light path after the transmission of the beam splitter 4, the grating 6 having a grating pitch of 20 μm to 50 μm and being used to form a Talbot image at a Talbot position; and an image acquisition unit for acquiring a fringe image of the Talbot image, the image acquisition unit comprising a telecentric lens 7 and a camera 8;

[0081] A movement control module 9 for driving the grating 6 to move along the optical axis direction of the telecentric lens 7, the movement control module 9 being configured to drive the grating 6 to move at a step length of 1 μm to 5 μm, and the movement control module 9 comprising a voice coil motor;

[0082] A controller 10, which is in communication connection with the camera 8 and the movement control module 9, is used to perform two-dimensional Fourier transform on the acquired multiple frames of the fringe image, extract spatial frequency or spatial phase, calculate phase shift, and calculate laser wavelength drift according to the phase shift.

[0083] The controller 10 is further configured to:

[0084] perform two-dimensional Fourier transform on the acquired fringe image to obtain the amplitude-frequency characteristic;

[0085] extracting a spatial frequency or a spatial phase from the amplitude-frequency characteristic;

[0086] calculating a phase shift based on the spatial frequency or the spatial phase, configured to unwrap the spatial phase to obtain an unwrapped phase;

[0087] calculating a laser wavelength shift according to the phase shift.

[0088] By integrating the light source module, the optical path module, the measurement module, the movement control module and the controller, a stable and precise Talbot interference detection platform is constructed. The system uses a grating with a grating pitch of 20 to 50 μm to form a high-contrast Talbot image at the Talbot position, and realizes non-distortion and high-fidelity fringe image acquisition through a telecentric lens and a camera; combined with the voice coil motor to drive the grating to move along the optical axis direction of the telecentric lens with a small step of 1 to 5 μm, the stable acquisition of multiple phase shift images is realized; the controller extracts the spatial frequency and phase information in the amplitude-frequency characteristic by two-dimensional Fourier transform of the image, further performs phase unwrapping and calculates the phase shift, and finally realizes high-sensitivity, non-contact and real-time dynamic detection of the laser wavelength shift. The system changes the laser wavelength from a static parameter to a controllable dynamic variable throughout the process, significantly improves the stability and reliability of the semiconductor laser under complex environment and extreme performance requirements, promotes its transformation from a traditional light source to an instrument-level precision measurement tool, and has high precision, high repeatability and good engineering application prospect.

[0089] While the preferred embodiments of the application have been described, additional modifications and changes can occur to persons skilled in the art upon reading the preceding description. It is therefore desired that the appended claims shall be construed to include all such modifications and changes as fall within the true spirit and scope of the present application.

[0090] Obviously, various modifications and changes can be made to the present application by those skilled in the art without departing from the spirit and scope of the present application. Thus, it is intended that the present application embrace all such modifications and changes that fall within the scope of the appended claims and their equivalents.

Claims

1. A method for high-precision real-time detection of wavelength drift of a semiconductor laser, characterized in that, The method comprises: Step 1: the light emitted by the laser forms a collimated laser beam after passing through the collimating mirror; the collimated laser beam is fully reflected by the reflecting mirror and is incident on the beam splitter; after being reflected by the beam splitter, the collimated laser beam irradiates the optical mirror to be measured; the optical mirror to be measured reflects the collimated laser beam back to the beam splitter, and the collimated laser beam is transmitted through the beam splitter, the grating and the Talbot position to form a Talbot image; Step 2: use the telecentric lens and the camera to collect the fringe image of the Talbot image; Step 3: move the grating along the optical axis direction of the telecentric lens, and collect multiple frames of the fringe image; Step 4: perform two-dimensional Fourier transform on the collected fringe image, extract the spatial frequency or spatial phase, calculate the phase shift, and calculate the laser wavelength drift according to the phase shift.

2. The method for detecting wavelength shift of semiconductor laser with high precision in real time according to claim 1, wherein, The step length of the grating is 1-5 microns.

3. The method for detecting the wavelength shift of the semiconductor laser with high precision in real time according to claim 1, wherein, In step 4, perform two-dimensional Fourier transform on the collected fringe image to obtain the amplitude-frequency characteristic; extract the spatial frequency or spatial phase from the amplitude-frequency characteristic; calculate the phase shift based on the spatial frequency or spatial phase; calculate the laser wavelength drift according to the phase shift.

4. The method for detecting wavelength shift of semiconductor laser with high precision in real time according to claim 3, wherein, The calculation of the phase shift based on the spatial frequency or spatial phase comprises: phase unwrapping of the spatial phase to obtain an unwrapped phase.

5. The method for high-precision real-time detection of wavelength drift of a semiconductor laser according to claim 4, wherein, The unwrapped phase is calculated by the following formula: Ψ 12(n) is the unwrapped phase of Λ 120 represents the initial phase at the spatial coordinate origin (0, 0) coordinate, is the initial phase difference of 6. The method for detecting wavelength shift of semiconductor laser with high precision in real time according to claim 3, wherein, The calculation of the phase shift based on the spatial frequency or spatial phase comprises: based on the spatial frequency, the phase shift is calculated by using the linear relationship between the spatial frequency and the phase shift.

7. The method for detecting the wavelength shift of the semiconductor laser with high precision in real time according to claim 1, wherein, The multiple frames of the fringe image are described as: Λ 12(x,y) = Λ 120 + ΔΛ 12x • (x - 1) + ΔΛ 12y • (y - 1) where Λ 12(x,y) represents spatial coordinates (x, y), Λ 120 denotes the initial phase at the spatial coordinate origin (0, 0), ΔΛ 12x and ΔΛ 12y are the rates of change of the pixels of each point of the image in the x and y directions, respectively.

8. The method for detecting high-precision real-time wavelength shift of semiconductor laser according to claim 3, wherein, The two-dimensional Fourier transform on the collected fringe image is specifically as follows: Ψ 12(n) = 2Λ 120 · k(n) + φ 120 I1and I2represent DC magnitudes, respectively; where Ω u and Ωvare spatial frequency two-dimensional coordinates in x and y directions, respectively, and δ[u, v] is a 2D delta function.

9. A system for high-precision real-time detection of wavelength drift of a semiconductor laser, characterized in that it comprises: The system comprises: a light source module for emitting a light source and forming a light path; a light path module, which is sequentially provided with a collimating mirror for forming a collimated laser beam, a reflecting mirror for reflecting the collimated laser beam, and a beam splitter for reflecting the light beam to an optical mirror to be measured and receiving the reflected light; a measurement module, which comprises a grating provided on the light path after being transmitted through the beam splitter, for forming a Talbot image at the Talbot position; and an image acquisition unit for collecting the fringe image of the Talbot image, the image acquisition unit comprising a telecentric lens and a camera; a movement control module for driving the grating to move along the optical axis direction of the telecentric lens; a controller, which is in communication connection with the camera and the movement control module, is used for performing two-dimensional Fourier transform on the collected multiple frames of the fringe image, extracting the spatial frequency or spatial phase, calculating the phase shift, and calculating the laser wavelength drift according to the phase shift.

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