Improved parallel Lyot filter based on secondary interference

Abstract

The improved parallel Lyot filter based on secondary interference comprises a polarizer and the like, and the polarizer, a first polarization controller and a polarization beam splitter are connected in sequence; the polarization beam splitter is divided into a first branch and a second branch. According to the first branch, one output port of the polarization beam splitter is connected with one input port of the beam combiner through a first polarization maintaining optical fiber and a second polarization controller in sequence. According to the second branch, the other output port of the polarization beam splitter is connected with a first port of a first circulator, a second port of the first circulator is connected with a second port of a second circulator through a second polarization maintaining optical fiber, and a third polarization controller is connected between the first port and a third port of the second circulator; and a third port of the first circulator is connected with the other input port of the beam combiner. By adjusting the first polarization controller, the second polarization controller and the third polarization controller, switching of three channel intervals can be achieved under the condition that devices are not replaced.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communication, and particularly relates to an improved parallel Lyot filter based on double interference. Background Art

[0002] Multi-wavelength fiber lasers are a new type of laser technology that has emerged with the development of fiber optic communication technology. Their main characteristics include multi-wavelength output, wide bandwidth, tunability, high power, and stable output. These characteristics make them ideal light sources for dense wavelength division multiplexing systems, capable of meeting the requirements of high-capacity information transmission in fiber optic communication. In addition, multi-wavelength fiber lasers also have the advantages of compact structure, low cost, and reliable heat dissipation, thus having broad application prospects in fiber optic sensing, microwave photonics, and spectroscopy.

[0003] However, despite the many advantages of multi-wavelength fiber lasers, in practical applications, they still face some challenges. Existing multi-wavelength fiber lasers are easily affected by environmental disturbances, resulting in poor stability. In addition, the flexibility of the system is not strong, and the working threshold power is relatively large, which limits their performance in practical applications. To overcome the above deficiencies and improve the performance of multi-wavelength fiber lasers, those skilled in the art are researching comb filters with multi-wavelength switching functions. These new filters aim to improve the flexibility and practicality of operation, reduce sensitivity to environmental disturbances, and lower the working threshold power. Especially in terms of wavelength interval switching and wavelength tuning, although traditional filter designs such as Mach-Zehnder interferometers, Sagnac loops, and Lyot filters have made certain technological progress after improvement, they still have deficiencies in terms of structure, cost, and stability, and their flexibility is not high. Summary of the Invention

[0004] In view of the above-mentioned drawbacks and deficiencies in the prior art, the present invention provides an improved parallel Lyot filter based on double interference.

[0005] To achieve the above object of the invention, the present invention adopts the following technical solutions:

[0006] An improved parallel Lyot filter based on quadratic interference, comprising a polarizer, a first polarization controller, a polarization beam splitter, a first polarization-maintaining fiber, a second polarization controller, a first circulator, a second polarization-maintaining fiber, a second circulator, a third polarization controller, and a beam combiner; the polarizer, the first polarization controller, and the first polarization beam splitter are connected in sequence; the polarization beam splitter divides into branch one and branch two, wherein the structure of branch one is as follows: an output port of the polarization beam splitter is connected to an input port of the beam combiner through the first polarization-maintaining fiber and the second polarization controller in sequence; the structure of branch two is as follows: another output port of the polarization beam splitter is connected to the first port of the first circulator, the second port of the first circulator is connected to the second port of the second circulator through the second polarization-maintaining fiber, and a third polarization controller is connected between the first port and the third port of the second circulator; the third port of the first circulator is connected to another input port of the beam combiner.

[0007] As a preferred solution, the first polarization-maintaining fiber and the second polarization-maintaining fiber have different lengths or birefringences.

[0008] As a preferred solution, the first polarization-maintaining fiber and the second polarization-maintaining fiber can be replaced with different lengths and birefringences according to needs.

[0009] As a preferred solution, the polarization beam splitter and the polarization beam combiner are the same kind of optical device, and different expressions are intended to distinguish their working characteristics.

[0010] As a preferred solution, the polarizer is also connected to a broadband light source through an isolator.

[0011] As a preferred solution, the tail end of the polarization beam combiner is also connected to a spectrometer.

[0012] As a preferred solution, the combination of the first polarization controller and the first polarization beam splitter can change the output light intensities of the two output ports of the polarization beam splitter by adjusting the polarization controller, so as to realize the switching of the working branch.

[0013] As a preferred solution, the above-mentioned connections are all fiber connections.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1) The present invention can realize the switching of two optical paths by adjusting the first polarization controller.

[0016] 2) The present invention can realize the switching of the channel interval, and can realize various switchable wavelength interval combinations by replacing the polarization-maintaining fiber.

[0017] 3) The structure of the present invention is simple, with low cost and good stability of the transmission spectrum. Based on this, the multi-wavelength fiber laser designed can achieve the switching of channel intervals and has high power stability and wavelength stability. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of an improved parallel Lyot filter based on second-order interference according to a preferred embodiment of the present invention.

[0019] Figure 2 It is an output diagram of the transmission spectrum of a channel interval (branch one) of an improved parallel Lyot filter based on second-order interference according to a preferred embodiment of the present invention.

[0020] Figure 3 It is an output diagram of the transmission spectrum of a first channel interval (branch two) of an improved parallel Lyot filter based on second-order interference according to a preferred embodiment of the present invention.

[0021] Figure 4 It is an output diagram of the transmission spectrum of a second channel interval (branch two) of an improved parallel Lyot filter based on second-order interference according to a preferred embodiment of the present invention. Detailed Embodiment

[0022] To more clearly illustrate the embodiments of the present invention, the following will describe the specific embodiments of the present invention with reference to the accompanying drawings. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings, and other embodiments can also be obtained.

[0023] An improved parallel Lyot filter based on second-order interference in this embodiment has a structure as Figure 1 shown, including a broad-spectrum light source 1, an isolator 2, a polarizer 3, a first polarization controller 4-1, a first polarization beam splitter 5-1, a first polarization-maintaining fiber 6-1, a second polarization controller 4-2, a first circulator 7-1, a second polarization-maintaining fiber 6-2, a second circulator 7-2, a third polarization controller 4-3, a first beam combiner 5-2, and a spectrum analyzer 8. The specific structure is as follows:

[0024] A broadband light source 1, an isolator 2, a polarizer 3, a first polarization controller 4-1 and port a of a polarization beam splitter 5-1 are sequentially connected by optical fibers; port c of the first polarization beam splitter 5-1, a first polarization maintaining fiber 6-1, a second polarization controller 4-2 and port b of a beam combiner 5-2 are sequentially connected by optical fibers; port b of the first polarization beam splitter 5-1 and port a of a first circulator 7-1 are connected by an optical fiber; port b of the first circulator 7-1, a second polarization maintaining fiber 6-2 and port b of a second circulator 7-2 are sequentially connected by optical fibers; port c of the second circulator 7-2, a third polarization controller 4-3 and port b of the second circulator 7-2 are sequentially connected by optical fibers; port c of the second circulator 7-2 and port c of the beam combiner 5-2 are connected by an optical fiber; port a of the first beam combiner 5-2 and a spectrum analyzer 8 are connected by an optical fiber.

[0025] In this embodiment, the first polarization maintaining fiber and the second polarization maintaining fiber have different lengths or birefringences.

[0026] The principle of the present invention will be further described below in conjunction with the above structure:

[0027] The light output by the broadband light source 1 is converted into linearly polarized light with a controlled polarization state after passing through the isolator 2, the polarizer 3 and the first polarization controller 4-1. Due to the polarization beam splitting characteristics of the first polarization beam splitter 5-1, the polarized light is split into two mutually orthogonal linearly polarized light beams with horizontal polarization and vertical polarization. Among them, the linearly polarized light polarized in the horizontal direction enters the lower branch, is guided into port a by the first circulator 7-1, and is output at port b; after converting the coordinate system, it enters the second polarization maintaining fiber 6-2 for the first time, and is decomposed into two orthogonal vector modes, which propagate on the fast and slow axes of the second polarization maintaining fiber 6-2 respectively. Due to the effective refractive index difference between the fast and slow axes, these two orthogonal vector modes will generate a wavelength-related phase difference, generating a wavelength phase difference. Subsequently, it enters the loop formed by port c and port a from port b of the second circulator 7-2, and the third polarization controller 4-3 in this loop is used to control the polarization state of the polarized light. After circulation, it is output from port b of the second circulator 7-2, and enters the second polarization maintaining fiber 6-2 for the second time, generating a wavelength-related phase difference again. The light beam passing through the second polarization maintaining fiber 6-2 for the second time is output from port c of the first circulator 7-1, and the vertically polarized light is combined and output by the beam combiner 5-2. And the linearly polarized light polarized in the vertical direction, after entering the upper branch, only passes through the first polarization maintaining fiber 6-1 once to generate a wavelength-related phase difference, and under the control of the second polarization controller 4-2 of the polarization state, the horizontally polarized light is combined and output by the beam combiner 5-2. The combined light output is observed by a spectrometer 8 (AQ6370B).

[0028] The filter designed by the present invention can generate three wavelength phase differences. Among them, two wavelength phase differences are respectively generated by polarized light passing through the polarization-maintaining fiber once, and the third wavelength phase difference is generated by polarized light passing through the polarization-maintaining fiber twice. The three wavelength phase differences correspond to three channel intervals. By adjusting the second polarization controller 4-2, the polarization state of the upper-branch light beam can be made parallel to one of the main axes of the first beam combiner 5-2, so that the phase information generated by the first polarization-maintaining fiber 6-1 in the output light disappears. Similarly, the third polarization controller 4-3 is equivalent to being placed in the middle of two identical polarization-maintaining fibers. Therefore, by adjusting the third polarization controller 4-3, one of the two phase information generated by the second polarization-maintaining fiber 6-2 can be made to disappear. Therefore, by adjusting the second polarization controller 4-2 and the third polarization controller 4-3, the switching of the three channel intervals can be realized. In addition, by adjusting the first polarization controller 4-1, the switching of the channel interval can also be realized, and this method is more effective. Adjusting the first polarization controller 4-1 can make the polarization state of the input light parallel to one of the main axes of the first polarization beam splitter 5-1, so that only one optical path in both the upper and lower branches has light beams passing through. For example, if the first polarization controller 4-1 is adjusted to make the incident light a vertically polarized light, at this time only the upper branch has light beams passing through, and the output light only contains the phase information item generated by the first polarization-maintaining fiber 6-1, corresponding to one channel interval. The same applies to the lower branch.

[0029] The usage method of this embodiment is as follows:

[0030] Turn on the broadband light source, adjust the light source power, select a suitable polarization-maintaining fiber, adjust the first polarization controller to select the target working branch, and adjust the polarization controller (the second or third polarization controller) of the corresponding branch to obtain a comb spectrum. The output spectrum of branch one is as Figure 2 shown, and the output spectrum of branch two is as Figure 3 shown. By adjusting the third polarization controller, the output spectrum of branch two can also be made as Figure 4 shown.

[0031] In summary, the present invention can switch the working branch by adjusting the first polarization controller, the second polarization controller, and the third polarization controller, thereby realizing the switching of the wavelength interval without replacing the device, and can obtain more switchable combinations of wavelength intervals by replacing the polarization-maintaining fiber.

[0032] It should be noted that the above is only a detailed description of the preferred embodiment and principle of the present invention. For those of ordinary skill in the art, according to the idea provided by the present invention, there will be changes in the specific implementation manners, and these changes should also be regarded as the protection scope of the present invention.

Claims

1. An improved parallel Lyot filter based on quadratic interference, characterized in that: It includes a polarizer, a first polarization controller, a polarization beam splitter, a first polarization maintaining fiber, a second polarization controller, a first circulator, a second polarization maintaining fiber, a second circulator, a third polarization controller, and a beam combiner; the polarizer, the first polarization controller, and the polarization beam splitter are connected in sequence; the polarization beam splitter branches into branch one and branch two. Among them, for branch one: one output port of the polarization beam splitter is connected to one input port of the beam combiner through the first polarization maintaining fiber and the second polarization controller in sequence; for branch two: the other output port of the polarization beam splitter is connected to the first port of the first circulator, the second port of the first circulator is connected to the second port of the second circulator through the second polarization maintaining fiber, and a third polarization controller is connected between the first port and the third port of the second circulator; the third port of the first circulator is connected to the other input port of the beam combiner.

2. The improved parallel Lyot filter based on secondary interference according to claim 1, wherein, The polarizer is connected to a broadband light source through an isolator.

3. An improved parallel Lyot filter based on double interference as claimed in claim 1, wherein, The beam combiner is connected to a spectrometer.

4. The improved parallel Lyot filter based on double interference as claimed in claim 1, wherein, The first polarization maintaining fiber and the second polarization maintaining fiber have different lengths or birefringences.

5. An improved parallel Lyot filter based on secondary interference according to any one of claims 1-3, characterized in that, The so-called "connected" and "connected to" are all fiber optic connections.

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