Optical fiber filter with adjustable channel interval based on parallel Lyot filter merging MZI (Mach Zehnder Interval) and filtering method

Abstract

The invention discloses a channel interval adjustable optical fiber filter based on parallel Lyot filter combination MZI and a filtering method. The optical fiber filter is structurally characterized in that a 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, a first output port of the polarization beam splitter is sequentially connected with a second polarization controller and a polarization maintaining optical fiber. In the branch circuit II, an output port II of the polarization beam splitter is connected with a first optical coupler, an output port I and an output port II of the first optical coupler are respectively connected with an input port I and an input port II of a second optical coupler, and a single-mode optical fiber with length difference is connected between the two paths; and an output port of the polarization maintaining optical fiber and an output port of the second optical coupler are respectively connected with two input ports of the polarization beam combiner. According to the invention, by adjusting the first polarization controller and the second polarization controller, switching of three kinds of channel intervals, namely two kinds of channel intervals and channel intervals amplified by multiple times after superposition interference of the two kinds of channel intervals, can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communications, and in particular relates to an optical fiber filter with adjustable channel spacing based on a parallel Lyot filter combined with a Mach-Zehnder interferometer (MZI) and a filtering method. Background Art

[0002] A multi-wavelength fiber laser is a laser system capable of simultaneously outputting multiple discrete or continuous wavelengths. Its core feature is the use of optical fiber as both a gain medium and a transmission carrier, combined with optical filtering technology to achieve multi-wavelength selection. This type of laser has key application value in dense wavelength division multiplexing communications. Furthermore, multi-wavelength lasers are also finding widespread application in high-resolution spectral analysis, fiber-optic sensing, and lidar.

[0003] Periodic optical filters play a key role in dense wavelength division multiplexing systems. They precisely separate and multiplex optical signals of different wavelengths, ensuring isolation between channels and improving system transmission performance and stability. Fiber comb filters are widely used due to their low insertion loss, high tuning flexibility, good resistance to nonlinear effects, and high compatibility. These filters, such as traditional fiber-optic beam gap (FBG) filters, fiber-optic cavity filters, and their improved counterparts, however, suffer from slow tuning speeds, insufficient flexibility, and low integration when switching channel spacing. Summary of the Invention

[0004] In view of the above-mentioned shortcomings in the prior art, the present invention provides an optical fiber filter with adjustable channel spacing based on parallel Lyot filters combined with MZI and a filtering method.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0006] A fiber filter with adjustable channel spacing based on a parallel Lyot filter combined with an MZI, comprising a polarizer, a first polarization controller, a polarization beam splitter, a second polarization controller, a polarization-maintaining fiber, a first optical coupler, a single-mode optical fiber, a second optical coupler, and a polarization combiner; the Lyot filter is composed of a polarizer, a first polarization controller, a polarization beam splitter, a second polarization controller, a polarization-maintaining fiber, and a polarization combiner; the MZI is composed of a first optical coupler, a single-mode optical fiber, and a second optical coupler; wherein the polarizer, the first polarization controller, the polarization beam splitter, the second polarization controller, the polarization-maintaining fiber, and the polarization combiner are The beam splitters are connected in sequence; the polarization beam splitter branches out into branch one and branch two, wherein, in branch one, the output port one of the polarization beam splitter is connected to the second polarization controller and the polarization-maintaining optical fiber in sequence; in branch two, the output port two of the polarization beam splitter is connected to the first optical coupler, the output port one and the output port two of the first optical coupler are connected to the input port one and the input port two of the second optical coupler respectively, and a single-mode optical fiber with a length difference is connected between the two paths; the output port of the polarization-maintaining optical fiber and the output port of the second optical coupler are connected to the two input ports of the polarization combiner respectively.

[0007] As a preferred solution, in the first branch, the polarization-maintaining optical fiber can be replaced with different lengths and birefringence as needed; in the second branch, the single-mode optical fiber in the MZI structure can be replaced with different lengths as needed to adjust the length difference between the two arms.

[0008] As a preferred solution, the polarizer is connected to the broadband light source via an isolator.

[0009] As a preferred solution, the tail end of the polarization beam combiner is connected to a spectrometer.

[0010] As a preferred solution, the polarization beam splitter and the polarization beam combiner are the same optical device, and the different descriptions are intended to distinguish their working characteristics.

[0011] As a preferred solution, by controlling the length of the polarization-maintaining fiber in the Lyot filter and the length difference between the two arms of the MZI, branch one and branch two can have similar channel spacings, and at the output end, an output spectrum several times that of branch one and branch two can be obtained through interference superposition of periodic spectra.

[0012] As a preferred solution, the first polarization controller and the second polarization controller can change the input light intensity of the two input ports of the combiner by adjusting the polarization controllers as needed to achieve independent switching of any working branch.

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

[0014] The present invention also discloses a fiber optic filtering method with adjustable channel spacing based on a parallel Lyot filter combined with an MZI. Based on the above fiber optic filter, the fiber optic filtering method is as follows: the output light of the broadband light source is converted into polarized light with adjustable polarization state after passing through an isolator, a polarizer, and a first polarization controller, and then the polarized light is decomposed into two mutually orthogonal linear polarized lights by a polarization beam splitter, and respectively coupled into branch one and branch two; the linear polarized light of branch one enters the polarization-maintaining fiber through the second polarization controller, and the linear polarized light will be decomposed after entering the polarization-maintaining fiber. It is two orthogonal vector modes, which are transmitted along the fast and slow axes of the polarization-maintaining optical fiber respectively. Finally, the linearly polarized light passes through the polarization combiner, and the horizontally polarized light is selected for combined output; the linearly polarized light of branch two enters the first optical coupler, and the linearly polarized light entering the first optical coupler is decomposed into two beams of light with the same power. The linearly polarized light output from the output port 1 and the output port 2 of the first optical coupler respectively enters the input port 1 and the input port 2 of the second optical coupler through a single-mode optical fiber with a length difference. Finally, the linearly polarized light is combined by the combiner, and the vertically polarized light is selected for combined output.

[0015] The advantages of the present invention compared with the prior art are:

[0016] 1) The present invention realizes the single-branch switching output of branch 1 and branch 2 and the superposition interference output of the two branches by adjusting the first polarization controller and the second polarization controller.

[0017] 2) The present invention can generate a large free spectral range transmission spectrum based on the vernier effect at the output end by periodic interference through the similar free spectral range of branch one and branch two. On this basis, the optical fiber sensor can be designed to achieve sensitivity amplification compared to a single branch.

[0018] 3) The present invention has a simple structure, low cost, and good stability of the transmission spectrum. The multi-wavelength fiber laser designed on this basis can realize the switching of channel intervals, output more stable multi-wavelength lasers, and has a wider range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of a fiber filter with adjustable channel spacing based on parallel Lyot filters combined with MZI in a preferred embodiment of the present invention.

[0020] Figure 2 This is a transmission spectrum output diagram of a branch of an optical fiber filter with adjustable channel spacing based on a parallel Lyot filter combined with an MZI in a preferred embodiment of the present invention when it outputs separately.

[0021] Figure 3 This is a transmission spectrum output diagram of a preferred embodiment of the present invention, in which branch 2 of an optical fiber filter with adjustable channel spacing based on a parallel Lyot filter combined with an MZI is outputted separately.

[0022] Figure 4 This is a transmission spectrum output diagram of a fiber filter with adjustable channel spacing based on parallel Lyot filters combined with MZI in a preferred embodiment of the present invention when branch one and branch two superimpose interference output. DETAILED DESCRIPTION

[0023] To more clearly illustrate the embodiments of the present invention, specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other embodiments can be obtained based on these drawings without inventive efforts.

[0024] This embodiment is based on a parallel Lyot filter combined with an MZI with an adjustable channel spacing optical fiber filter, the structure of which is as follows: Figure 1 As shown, it includes a broadband light source 1, an isolator 2, a polarizer 3, a first polarization controller 4-1, a polarization beam splitter 5-1, a second polarization controller 4-2, a polarization-maintaining fiber 6, a first optical coupler 7-1, a single-mode optical fiber with a length difference 8, a second optical coupler 7-2, a polarization beam combiner 5-2, and an optical spectrum analyzer 9. The specific connection structure of each component is as follows:

[0025] The broadband light source 1, isolator 2, polarizer 3, first polarization controller 4-1, and port a of polarization beam splitter 5-1 are sequentially connected via optical fibers. The polarization beam splitter splits into branch 1 and branch 2. In branch 1, port b of the first polarization beam splitter 5-1, second polarization controller 4-2, polarization-maintaining fiber 6, and port b of polarization beam combiner 5-2 are sequentially connected via optical fibers. In branch 2, port c of polarization beam splitter 5-1 is connected to port a of first optical coupler 7-1 via optical fibers. Port b of the first optical coupler 7-1 is connected to port b of second optical coupler 7-2 via optical fibers. Port c of the first optical coupler 7-1 is connected to port c of second optical coupler 7-2 via optical fibers. A single-mode optical fiber 8 is connected between these two optical fibers. Port a of the second optical coupler 7-2 is connected to port c of polarization beam combiner 5-2 via optical fibers. Port a of polarization beam combiner 5-2 is connected to spectrometer 9 via optical fibers.

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

[0027] The output light of the broadband light source 1 passes through the isolator 2, polarizer 3, and first polarization controller 4-1, and is converted into polarized light with adjustable polarization state. The polarization beam splitter 5-1 then decomposes this polarized light into two mutually orthogonal linearly polarized beams, which are coupled into branch 1 and branch 2, respectively. Branch 1: The linearly polarized light passes through the second polarization controller 4-2 and enters the polarization-maintaining fiber 6. After entering the polarization-maintaining fiber 6, the linearly polarized light is decomposed into two orthogonal vector modes, which are transmitted along the fast and slow axes of the polarization-maintaining fiber 6. Due to the refractive index difference between the fast and slow axes, these two orthogonal vector modes produce a wavelength-dependent phase difference. The polarized light is ultimately combined and output by the beam combiner as horizontally polarized light. Branch 2: The linearly polarized light passes through the first optical coupler 7-1 and is split into two linearly polarized beams of equal power. These two linearly polarized beams then enter the second optical coupler 7-2 through single-mode optical fibers with different lengths. A wavelength-dependent phase difference occurs between the two linearly polarized beams upon entering the second optical coupler 7-2. After passing through the second optical coupler 7-2, the two linearly polarized beams are ultimately combined and output as perpendicularly polarized light by a beam combiner. The combined light output is observed by spectrometer 9 (AQ6370B).

[0028] The method of using this embodiment is as follows:

[0029] Turn on the broadband light source, adjust the light source power, select the appropriate polarization-maintaining fiber, adjust the first polarization controller to select the target working branch, and obtain the comb spectrum of the corresponding branch and the large-period output spectrum generated by the superposition interference of the two branches. The output spectrum of branch one is as follows: Figure 2 As shown, the output spectrum of branch 2 is Figure 3 As shown, the output spectrum of the superposition of branch 1 and branch 2 is as follows Figure 4 shown.

[0030] In summary, the present invention enables switching of wavelength intervals without replacing components by adjusting the first polarization controller to switch the active branch. In a preferred embodiment, by selecting a 7.15m polarization-maintaining fiber in branch one and an MZI with a 2.057mm difference in arm length between branches in branch two, channel spacings of 0.87nm and 0.80nm are achieved when branches one and two output independently, respectively, and an equivalent channel spacing of 9.50nm when branches one and two output together.

[0031] It should be noted that the above description is only a detailed description of the preferred embodiments and principles of the present invention. For ordinary technicians in this field, based on the ideas provided by the present invention, there will be changes in the specific implementation methods, and these changes should also be regarded as the scope of protection of the present invention.

Claims

1. A fiber filter with adjustable channel spacing based on parallel Lyot filters combined with MZI, characterized by: It includes a polarizer, a first polarization controller, a polarization beam splitter, a second polarization controller, a polarization-maintaining fiber, a first optical coupler, a single-mode optical fiber, a second optical coupler, and a polarization combiner; the polarizer, the first polarization controller and the polarization beam splitter are connected in sequence; the polarization beam splitter branches out into branch one and branch two, wherein, branch one: the output port one of the polarization beam splitter is connected to the second polarization controller and the polarization-maintaining optical fiber in sequence; branch two: the output port two of the polarization beam splitter is connected to the first optical coupler, the output port one and the output port two of the first optical coupler are connected to the input port one and the input port two of the second optical coupler respectively, and a single-mode optical fiber with a length difference is connected between the two paths; the output port of the polarization-maintaining optical fiber and the output port of the second optical coupler are connected to the two input ports of the polarization combiner respectively.

2. The optical fiber filter with adjustable channel spacing based on parallel Lyot filters combined with MZI as claimed in claim 1, characterized in that: The polarizer is connected to the broadband light source through an isolator.

3. The optical fiber filter with adjustable channel spacing based on parallel Lyot filters combined with MZI as claimed in claim 1, characterized in that: The output port of the polarization beam combiner is connected to a spectrum analyzer.

4. The optical fiber filter with adjustable channel spacing based on parallel Lyot filters combined with MZI as claimed in claim 1, characterized in that: By controlling the length of the polarization-maintaining fiber in the Lyot filter and the length difference between the two arms of the MZI, the channel spacing between branches one and two meets the set requirements. The polarization combiner obtains an output spectrum several times that of branches one and two through the interference superposition of periodic spectra.

5. The optical fiber filter with adjustable channel spacing based on parallel Lyot filters combined with MZI according to any one of claims 1 to 4, characterized in that: The output light intensities of the two output ports of the polarization beam splitter are changed by adjusting the first polarization controller and the second polarization controller, thereby realizing the switching of the working branches.

6. The optical fiber filter with adjustable channel spacing based on parallel Lyot filters combined with MZI according to any one of claims 1 to 3, characterized in that: All components are connected using optical fiber.

7. A fiber filtering method with adjustable channel spacing based on parallel Lyot filters combined with MZI, based on the fiber filter according to claim 2, characterized in that: The optical fiber filtering method is specifically as follows: The output light of the broadband light source is converted into polarized light with adjustable polarization state after passing through an isolator, a polarizer, and a first polarization controller. The polarized light is decomposed into two mutually orthogonal linear polarized lights by a polarization beam splitter, and coupled into branch one and branch two respectively; the linear polarized light of branch one enters the polarization-maintaining fiber through the second polarization controller. After entering the polarization-maintaining fiber, the linear polarized light is decomposed into two orthogonal vector modes, which are transmitted along the fast and slow axes of the polarization-maintaining fiber respectively. Finally, the linear polarized light passes through a polarization combiner, and horizontal polarized light is selected for combined output; the linear polarized light of branch two enters the first optical coupler, and the linear polarized light entering the first optical coupler is decomposed into two linear polarized lights with equal power. The linear polarized light output from output port one and output port two of the first optical coupler enters input port one and input port two of the second optical coupler respectively through single-mode optical fibers with a length difference. Finally, the linear polarized light passes through a combiner, and vertical polarized light is selected for combined output.

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