A tunable wavelength filter

Abstract

The application belongs to the technical field of filters and provides a wavelength-adjustable filter.The filter comprises at least a radiation grating module, a first light collection module, a mask module, a second light collection module, a multimode fiber module and a wavelength detection module.The wavelength-adjustable filter based on the radiation grating is used to realize light splitting by one-to-one correspondence between the wavelength and the diffraction angle through the radiation grating, thereby reducing the volume of the adjustable filter and the cost of the light splitting device;and the wavelength detection speed of the existing detector is significantly improved through the mode dispersion scheme, thereby realizing high-speed detection.The filter has simple overall structure, is easy to construct, has a large adjustable optical wavelength range, can adjust the bandwidth at will, has high system stability, is low in cost and is more conducive to promotion and popularization.

Description

Technical Field

[0001] This invention belongs to the field of filter technology, and in particular relates to a filter with adjustable wavelength. Background Technology

[0002] A tunable wavelength fiber optic filter is a device used to adjust the wavelength of an optical signal. It can selectively transmit or block optical signals of specific wavelengths, thereby achieving wavelength modulation and control. Such filters are typically composed of optical fibers and specialized optical components. Their main principle is based on gratings, interference, or optical modulation effects within the fiber. By adjusting the filter's operating parameters, such as grating period, optical path difference, or electric field strength, the filter's response to different wavelengths of optical signals can be altered, thus achieving selective wavelength modulation.

[0003] These filters have wide applications in optical communication, optical sensing, and spectral analysis. For example, in optical communication systems, tunable wavelength fiber filters can be used for wavelength division multiplexing and demultiplexing in multi-wavelength fiber optic transmission systems to achieve simultaneous transmission of optical signals of multiple wavelengths. In spectral analysis, tunable wavelength fiber filters can be used to selectively extract or filter optical signals of specific wavelengths for accurate spectral measurements and analysis.

[0004] Currently, common tunable wavelength fiber optic filters mainly include the following types: Fabry-Perot filters: These utilize two flat-surface reflective glass plates to form an air gap, creating a resonant cavity. Wavelength modulation is achieved by changing the cavity length. Michelson interferometer filters: These use the principle of a Michelson interferometer to split a beam of light into two paths of different lengths, which are then combined. Wavelength modulation is achieved by adjusting the path length of one of the paths. Modulated fiber optic gratings: These incorporate a grating structure into the optical fiber, and wavelength modulation is achieved by changing the grating period.

[0005] However, the existing mainstream filters often suffer from problems such as complex optical paths, limited tunable wavelength range, and high overall manufacturing and usage costs. Therefore, it is necessary to improve the existing filters. Summary of the Invention

[0006] The purpose of this application is to provide a tunable wavelength filter, which aims to solve the problems that existing mainstream filters often have complex optical paths, small tunable wavelength ranges, and high overall manufacturing and usage costs.

[0007] This application provides an embodiment of a tunable wavelength filter, the filter comprising at least:

[0008] Radiation grating module, first focusing module, mask module, second focusing module, multimode fiber module, and wavelength detection module;

[0009] The radiation grating module is used to provide a light source containing light of several different wavelengths;

[0010] The first focusing module is used to focus the light emitted by the radiation grating module into a point light source and illuminate the mask module;

[0011] The mask module controls the wavelength of light passing through the mask based on the mechanical structure of adjusting its own mask;

[0012] The second focusing module is used to focus the light after wavelength selection by the mask module into a point light source and incident it into the fiber core of the multi-module fiber optic module;

[0013] The multi-mode fiber optic module is used to generate mode dispersion of incident light of different wavelengths, so that the time taken for light of different wavelengths to pass through the multimode fiber optic module is different.

[0014] The wavelength detection module performs spectral identification by detecting the time it takes for light of different wavelengths to arrive at the wavelength detection module.

[0015] Preferably, the radiation grating module is a fiber grating with a tilt angle set to 45°.

[0016] Preferably, the first focusing module includes at least a first cylindrical lens and a first convex lens; the first cylindrical lens is used to convert the emitted light from the radiation grating module into parallel light; the first convex lens is used to converge the parallel light emitted from the first cylindrical lens into a point light source.

[0017] Preferably, the wavelengths of light passing through the radiation grating module at different wavelengths have a one-to-one correspondence with their diffraction angles, specifically as follows:

[0018]

[0019] Wherein, the diffraction angle is α, n is the refractive index of the fiber core in the radiation grating module, θ is the tilt angle of the radiation grating, Λ is the period of the radiation grating, and λ is the wavelength of the optical signal transmitted through the radiation grating.

[0020] Preferably, the mask module is located on the focal plane of the converged light formed by the first focusing module. Based on the adjustable mask structure, it blocks part or all of the converged light from passing through, thereby filtering out light of different wavelengths that pass through different spatial positions of the mask, and realizing the filtering of optical fibers of different wavelengths.

[0021] Preferably, the incident light in the radiation grating module is a coupled light source with wavelengths set in the infrared band.

[0022] Preferably, the wavelength detection module is a photodetector with a detection time on the order of nanoseconds.

[0023] Preferably, the radiation grating module is one of a multimode fiber that generates mode dispersion, a dispersion-compensating fiber, or a chirped grating.

[0024] This application provides a tunable wavelength filter that uses a radiation grating to establish a one-to-one correspondence between wavelength and diffraction angle, achieving beam splitting. This reduces the size of the tunable filter and the cost of the beam splitter. Furthermore, by employing a modal dispersion scheme, it significantly improves the wavelength detection speed of existing detectors, enabling high-speed detection. The filter provided in this application has a simple overall structure, is easy to construct, has a wide tunable wavelength range, allows for arbitrary bandwidth adjustment, and offers high system stability and low cost, making it more suitable for widespread adoption and promotion. Attached Figure Description

[0025] Figure 1 A schematic diagram of the module connection of a tunable wavelength filter provided in an embodiment of this application;

[0026] Figure 2 A side view of the internal structure of a radiation grating and a schematic diagram of the diffraction and transmission of light signals after entering the radiation grating, provided for embodiments of this application;

[0027] Figure 3 A simplified optical path diagram of light entering a multimode fiber is provided in an embodiment of this application;

[0028] Figure 4 This is a schematic diagram of the structure of a mask provided in an embodiment of this application;

[0029] Figure 5 This is a graph showing the wavelength changes of optical signals of different wavelengths before and after entering an adjustable wavelength filter, as provided in an embodiment of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] The directional terms mentioned in the embodiments of this application, such as "upper", "lower", "side", "top", "bottom", etc., are only for reference to the direction of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of this application, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0032] The term "and / or" describes a relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The terms "first," "second," etc., are used for descriptive purposes only and should not be construed as implying relative importance or specifying the number of indicated technical features. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0033] Figure 1 A schematic diagram of the module connection of a tunable wavelength filter provided in an embodiment of this application is shown below. Figure 1 As shown, the filter includes at least: a radiation grating module, a first focusing module, a mask module, a second focusing module, a multimode fiber module, and a wavelength detection module.

[0034] The radiation grating module provides a light source containing several different wavelengths of light. The first focusing module focuses the light emitted by the radiation grating module into a point light source and illuminates the mask module. The mask module controls the wavelength of the light passing through the mask by adjusting its mechanical structure. The second focusing module focuses the light filtered by the mask module into a point light source and incident it into the fiber core of the multi-module fiber optic module. The multi-module fiber optic module causes modal dispersion of incident light of different wavelengths, so that the time taken for light of different wavelengths to pass through the multimode fiber optic module is different. The wavelength detection module performs spectral identification by detecting the time it takes for light of different wavelengths to arrive at the wavelength detection module.

[0035] like Figure 2 The diagram shows a schematic of filtering based on this device. This embodiment uses a radiation grating to establish a one-to-one correspondence between wavelength and diffraction angle, achieving beam splitting, reducing the size of the tunable filter, and simultaneously reducing the cost of the beam splitter. Figure 2 In the process, the filtered divergent light signal passes through convex lens 2, is focused, and then enters the multimode fiber. Different wavelengths of light entering the multimode fiber produce different modes, resulting in modal dispersion, such as... Figure 3As shown, when the end face of the multimode fiber is placed on the focal plane behind the convex lens module 2, light signals of different wavelengths will travel through the multimode fiber along different paths. Since these paths differ, the distances and transit times within the multimode fiber also differ. A high-speed photodetector is placed at the rear end of the multimode fiber. By detecting the arrival times of different wavelengths at the high-speed photodetector, the wavelength of the light signal can be quickly detected. In this system, all modules have fixed positions, ensuring consistency in the paths taken by different wavelengths of light signals through the multimode fiber. After pre-calibrating the arrival times of different wavelengths at the high-speed photodetector, this system can be used for wavelength filtering and detection. After traveling a certain distance through the multimode fiber, the arrival times of different wavelengths of light at the end of the multimode fiber are different. By detecting the order of arrival times of the light signals at the high-speed photodetector, different wavelength signals can be distinguished.

[0036] This solution significantly improves the wavelength detection speed of existing detectors by employing a modal dispersion scheme, achieving high-speed detection. The filter provided in this application has a simple overall structure, is easy to construct, has a wide tunable wavelength range, and its bandwidth can be arbitrarily adjusted. Simultaneously, the system boasts high stability, low cost, and is more conducive to promotion and widespread adoption. The modal dispersion scheme adopted in this application can creatively improve the wavelength detection speed, transforming traditional millisecond-level detection into nanosecond-level detection, achieving high-speed detection.

[0037] In one embodiment, the radiation grating module is a fiber grating with a tilt angle set to 45°.

[0038] In this embodiment, the tilt angle of the radiation grating refers to the degree of tilt of the grating's ridges relative to the vertical direction. A grating is an optical element with a regular periodic structure, consisting of a series of parallel and equidistant grooves or protrusions. When incident light shines on the grating, diffraction occurs on its surface. The tilt angle determines the angle between the direction of the grating ridges and the vertical direction. This angle has a significant impact on the diffraction effect and application of the grating. Different tilt angles result in the deflection and angular changes of the diffracted beam. By adjusting the tilt angle, the direction, intensity, and phase difference of the diffracted beam can be controlled. The divergence of the radiation grating's tilt angle with wavelength can be represented by angular dispersion D.

[0039]

[0040] From the above equation, we can deduce that when D is at its maximum, sin(2θ) = 1, that is, θ = 45°. At this point, the radiation grating has the maximum angular dispersion value. Therefore, preferably, the tilt angle is set to 45°.

[0041] The radiation grating based on a 45° tilted fiber Bragg grating used in this embodiment serves two main purposes: firstly, as a spatial light emitter (fiber Bragg gratings are a special type of high-efficiency side-emitting light emitter); and secondly, as a spatial light diffracting device, enabling a one-to-one correspondence between wavelength and angle, thus achieving beam splitting. The application of the radiation grating significantly reduces the size of the tunable filter and lowers the cost of the beam splitting device.

[0042] In one embodiment, the first focusing module includes at least a first cylindrical lens and a first convex lens; the first cylindrical lens is used to convert the emitted light from the radiation grating module into parallel light; the first convex lens is used to converge the parallel light emitted from the first cylindrical lens into a point light source.

[0043] In this embodiment, the multi-wavelength light signal diffracted into free space enters the cylindrical lens and becomes horizontally parallel light. Then, after passing through the first convex lens, the parallel light becomes focused light. By placing a mask on the focal plane of the convex lens, the adjustable mask can block some or all of the focused light from passing through. The spatial diffraction angle of the parallel light passing through the radiation grating is wavelength-dependent; that is, parallel light of different wavelengths passes through the mask at different spatial positions. By adjusting the structure of the mask, the passage of different wavelengths through the mask can be controlled, thus achieving the function of wavelength filtering.

[0044] In this embodiment, the first cylindrical lens module can be a short focal length cylindrical lens; the first convex lens module can be a short focal length convex lens. The cylindrical lens and convex lens are combined to converge the light emitted by the radiation grating module into a point light source, which then illuminates the mask module. Those skilled in the art will understand that similar functionality can be achieved using more or fewer lenses, and this is also within the scope of this application. Preferably, a combination of a cylindrical lens and a convex lens is used.

[0045] In one embodiment, light rays of different wavelengths passing through the radiation grating module have a one-to-one correspondence between their wavelengths and their diffraction angles, specifically as follows:

[0046]

[0047] Wherein, the diffraction angle is α, n is the refractive index of the fiber core in the radiation grating module, θ is the tilt angle of the radiation grating, Λ is the period of the radiation grating, and λ is the wavelength of the optical signal transmitted through the radiation grating.

[0048] In this embodiment, the radiation grating serves two main functions. First, as a special type of side-emitting light device, it can emit multi-wavelength light transmitted inside the fiber core into free space via the cladding side, acting as a spatial light emitter with a spatial light emission efficiency exceeding 93%. Second, as a spatial light diffraction device, it achieves wavelength-dependent angle adjustment because the multi-wavelength light passing through the radiation grating generates a one-to-one correspondence between wavelength and angle. Let the spatial light diffraction angle α be:

[0049]

[0050] Where n is the refractive index of the fiber core, θ is the tilt angle of the radiation grating, Λ is the period of the radiation grating, and λ is the wavelength of the optical signal transmitted through the radiation grating.

[0051] In one embodiment, the mask module is located on the focal plane of the converged light formed by the first focusing module. Based on the adjustable mask structure, it blocks part or all of the converged light from passing through, thereby filtering out light of different wavelengths that pass through different spatial positions of the mask, and realizing the filtering of optical fibers of different wavelengths.

[0052] like Figure 4 The diagram illustrates a mask structure. In this embodiment, the mask comprises two layers, A and B. By changing the relative positions of layers A and B, light of different wavelengths passing through different spatial positions of the mask can be filtered out. Those skilled in the art will understand that mask structures achieving the above function are not limited to this one.

[0053] In one embodiment, the incident light in the radiation grating module is a coupled light source with wavelengths set in the infrared band.

[0054] In one embodiment, the wavelength detection module is a photodetector with a detection time on the order of nanoseconds.

[0055] In this embodiment, a high-speed photodetector is required to achieve higher precision time detection.

[0056] In one embodiment, the radiation grating module is one of a multimode fiber, a dispersion-compensating fiber, or a chirped grating.

[0057] In this embodiment, multimode fiber is used as an example. The multimode fiber that generates modal dispersion can be replaced by dispersion-compensating fiber or a chirped grating, both of which can produce a one-to-one correspondence between wavelength and time. In one embodiment, such as... Figure 5 As shown, this illustrates the changes in wavelength signals before and after optical signals of different wavelengths enter the tunable wavelength filter. Figure 5'a' is the original optical signal input to the tunable wavelength filter, i.e., the optical signal that has not passed through the tunable wavelength filter. Figure 5 b is the optical signal after being filtered by the tunable wavelength filter. It can be seen that after the filter is applied, some wavelength information is filtered out, and the optical signal shows a steep negative peak, that is, the optical signal of this wavelength is filtered out by the tunable filter.

[0058] Those skilled in the art will understand that Figure 1 and Figure 2 The structure shown in the figure is only a partial structure related to the solution of this application and does not constitute a limitation on the device on which the solution of this application is applied. The specific device may include more or fewer components than shown in the figure, or combine certain components, or have different component arrangements.

[0059] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A filter with adjustable wavelength, characterized in that, The filter includes at least: Radiation grating module, first focusing module, mask module, second focusing module, multimode fiber module, and wavelength detection module; The radiation grating module is used to provide a light source containing light of several different wavelengths; The first focusing module is used to focus the light emitted by the radiation grating module into a point light source and illuminate the mask module; The mask module controls the wavelength of light passing through the mask based on the mechanical structure of adjusting its own mask; The second focusing module is used to focus the light after wavelength selection by the mask module into a point light source and incident it into the fiber core of the multimode fiber module. The multimode fiber module is used to generate mode dispersion of incident light of different wavelengths, so that the time taken for light of different wavelengths to pass through the multimode fiber module is different. The wavelength detection module performs spectral identification by detecting the time it takes for light of different wavelengths to arrive at the wavelength detection module. The wavelength detection module detects the wavelength of the light signal based on the time it takes for different wavelength light signals to arrive at the photodetector, which is pre-calibrated. The first focusing module includes at least a first cylindrical lens and a first convex lens; The first cylindrical lens is used to convert the emitted light from the radiation grating module into parallel light; The first convex lens is used to converge the parallel light emitted from the first cylindrical lens into a point light source; The mask module is located on the focal plane of the focused light formed by the first focusing module. The adjustable mask structure includes an A layer mask and a B layer mask arranged in sequence. The A layer mask and the B layer mask each include a strip-shaped connecting portion and a plurality of light-shielding portions connected to the strip-shaped connecting portion and extending to the same side. The plurality of light-shielding portions are spaced apart along the length direction of the strip-shaped connecting portion, and a light-transmitting gap is formed between two adjacent light-shielding portions. In the A-layer mask, at least two of the multiple light-shielding portions have different widths, and at least two of the multiple light-transmitting gaps have different widths; in the B-layer mask, at least two of the multiple light-shielding portions have different widths, and at least two of the multiple light-transmitting gaps have different widths. By changing the relative positions of the A-layer mask and the B-layer mask, the overlap position of the light transmission gaps of the A-layer mask and the B-layer mask in the light incident direction is changed, so that the converging light passes through the A-layer mask and the B-layer mask in sequence, thereby blocking part or all of the converging light from passing through, and thus filtering out light of different wavelengths that pass through different spatial positions of the mask, achieving filtering of light of different wavelengths.

2. The tunable wavelength filter according to claim 1, characterized in that, The radiation grating module is a fiber grating with a tilt angle set at 45°.

3. The tunable wavelength filter according to claim 1, characterized in that, The wavelengths of light passing through the radiation grating module have a one-to-one correspondence with their diffraction angles. Specifically, the correspondence is as follows: Wherein, the diffraction angle is α, n is the refractive index of the fiber core in the radiation grating module, θ is the tilt angle of the radiation grating, Λ is the period of the radiation grating, and λ is the wavelength of the optical signal transmitted through the radiation grating.

4. A tunable wavelength filter according to claim 1, characterized in that, The incident light in the radiation grating module is a coupled light source with wavelengths set in the infrared band.

5. A tunable wavelength filter according to claim 1, characterized in that, The wavelength detection module is a photodetector with a detection time in the nanosecond range.

6. A tunable wavelength filter according to claim 1, characterized in that, The radiation grating module is one of a multimode fiber that generates mode dispersion, a dispersion-compensating fiber, or a chirped grating.

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