A multi-channel micro-nano coupled fiber filter and a method for multi-channel selective filtering

Abstract

The present invention discloses a multi-channel micro-nano coupled fiber optic filter and a method for multi-channel selective filtering, which includes a light source, a detector, a multi-channel micro-nano fiber coupling structure, a first and a second 2×2 fiber optic switch, an optical fiber loop, and an optical fiber polarization controller. The multi-channel micro-nano fiber coupling structure is composed of n input optical fibers and n output optical fibers, where n≥3. The light source and the detector are connected to any two input optical fibers in the multi-channel micro-nano fiber coupling structure through the first 2×2 fiber optic switch. Two output optical fibers corresponding to the two input optical fibers are selected as output ports and are respectively connected to the two input ports of the second 2×2 fiber optic switch. The two output ports of the second 2×2 fiber optic switch are connected to an optical fiber loop with a fixed length, and an optical fiber polarization controller is connected inside the optical fiber loop. As a multi-channel micro-nano coupled filtering device, the present invention can achieve the tuning of different filtering characteristics by switching different input-output optical fiber pairs.

Description

Technical Field

[0001] The present invention belongs to the field of photoelectric detection technology, and more specifically, relates to a multi-channel micro-nano coupled optical fiber filter and a multi-channel selective filtering method. Background Art

[0002] As one of the optical passive devices, the coupler plays an important role in optical passive devices. In 1975, Kuwahara et al. made the first optical fiber coupler by winding two optical fibers and placing them in a refractive index solution. Since then, polished optical fiber couplers made by physical grinding methods and fused-taper optical fiber couplers made by fused-taper technology have appeared one after another. Couplers are widely used and are also indispensable devices in optical fiber sensors, wavelength division multiplexers, semiconductor lasers and optical fiber amplifiers.

[0003] The existing micro-nano coupler obtained by the melt cone process has an uneven spectrum. Figure 1 It was found that it could not be used as a comb filter. At present, micro-nano couplers are mainly used in sensors to detect refractive index, temperature, biology, chemistry, magnetic field, current, etc. There are few studies on multi-channel comb filters obtained by simple taper method, and flexible wavelength switching cannot be achieved. Summary of the invention

[0004] The present invention is committed to realizing flexible switching of multiple wavelengths to meet the wavelength filtering requirements under different conditions, and proposes a multi-channel micro-nano coupled optical fiber filter and a multi-channel selective filtering method, which has a reasonable design, overcomes the shortcomings of the prior art, and has good effects.

[0005] In order to achieve the above purpose 1, the present invention adopts the following technical solution:

[0006] A multi-channel switchable combined micro-nano optical fiber coupling filter comprises a light source, a detector, a multi-channel micro-nano optical fiber coupling structure, a first and a second 2×2 optical fiber switch, an optical fiber loop and an optical fiber polarization controller, wherein the multi-channel micro-nano optical fiber coupling structure is composed of n input optical fibers and n output optical fibers, wherein n≥3;

[0007] The light source and the detector are connected to two input ports of the first 2×2 optical fiber switch, the two output ports of the first 2×2 optical fiber switch are connected to any two input optical fibers in the multi-channel micro-nano optical fiber coupling structure, two output optical fibers corresponding to the two input optical fibers are selected as output ports, and are respectively connected to the two input ports of the second 2×2 optical fiber switch, and the two output ports of the second 2×2 optical fiber switch are connected to an optical fiber loop of fixed length, and an optical fiber polarization controller is connected in the optical fiber loop;

[0008] The light source and the detector constitute a photoelectric detection device for recording the output spectrum information;

[0009] The first 2×2 fiber optic switch and the multi-channel micro-nano fiber coupling structure form a fiber optic loop filter switching device, which is used to realize the switching of the optical coupling loop, and further realize the switching of the wavelength, bandwidth and transmission / reflection rate of the coupling filter;

[0010] The fiber optic polarization controller and the fiber optic loop form a filtering transmission / reflection rate tuning device, which is used to realize the adjustable spectral extinction ratio of each fiber optic filter.

[0011] In order to achieve the above object 2, the present invention adopts the following technical solutions:

[0012] A multi-channel selective filtering method, the second 2×2 fiber optic switch realizes the tuning of different filtering characteristics by switching different input and output fiber pairs.

[0013] Furthermore, the light emitted by the light source is divided into two paths through the multi-channel micro-nano fiber coupling structure. One path of the optical signal passes through the fiber optic polarization controller in the clockwise direction, and the other path of the optical signal passes through the fiber optic polarization controller in the counterclockwise direction. The fiber optic polarization controller changes the spectral amplitude of the two paths of optical signals. The two paths of optical signals return to the multi-channel micro-nano fiber coupling structure for coupling, and finally output to the detector.

[0014] Furthermore, by tuning the polarization angle of the fiber optic polarization controller in the fiber optic loop, the continuous adjustable extinction ratio of the filter is realized. When the polarization angle of the polarization controller reaches 90°, the extinction ratios of the transmission spectrum and the reflection spectrum are the largest.

[0015] The beneficial technical effects brought by the present invention:

[0016] As a multi-channel micro-nano coupled filtering device, the present invention can realize the tuning of different filtering characteristics by switching different input and output fiber pairs. Moreover, for the same filter, by adjusting the polarization controller, the extinction ratio tuning of the filter can also be realized. The linear tuning effect of the inventive device is good, and the flexible switching of the wavelength and bandwidth can be realized. It can be used as a wavelength control element in a laser to achieve different wavelength outputs, used for power equalization in an amplifier, and used for sensing various physical quantities and eliminating cross-sensitivity in sensing, etc. Description of the Drawings

[0017] Figure 1 is the output transmission spectrum of the micro-nano fiber coupler in the prior art;

[0018] Figure 2 is the structural schematic diagram of the multi-channel micro-nano coupled fiber optic filter in the present invention;

[0019] Among them, 1 - light source; 2 - detector; 3 - first 2×2 fiber optic switch; 4 - multi-channel micro-nano fiber coupling structure; 5 - second 2×2 fiber optic switch; 6 - fiber optic loop; 7 - fiber optic polarization controller;

[0020] Figure 3 is the output spectrogram of the transmission spectrum and reflection spectrum of the micro-nano coupled fiber optic filter in the present invention;

[0021] Among them, (a) is the output spectrogram of the transmission spectrum of the micro-nano coupled fiber optic filter when the polarization controller angle is -45° to 0;

[0022] (b) is the output spectrogram of the transmission spectrum of the micro-nano coupled fiber optic filter when the polarization controller angle is 0 to 45°;

[0023] (c) is the curve graph of the extinction ratio of the transmission spectrum of the micro-nano coupled fiber optic filter changing with the rotation angle of the polarization controller;

[0024] (d) is the output spectrogram of the reflection spectrum of the micro-nano coupled fiber optic filter when the polarization controller angle is -45° to 0;

[0025] (e) is the curve graph of the extinction ratio of the reflection spectrum of the micro-nano coupled fiber optic filter changing with the rotation angle of the polarization controller; Detailed implementation manners

[0026] The following further describes the detailed implementation manners of the present invention in conjunction with the accompanying drawings and specific embodiments:

[0027] A multi-channel micro-nano coupled fiber optic filter, as Figure 2 shown, includes a light source 1, a detector 2, a first 2×2 fiber optic switch 3, a multi-channel micro-nano fiber coupling structure 4, a second 2×2 fiber optic switch 5, a fiber optic loop 6, and a fiber optic polarization controller 7; the multi-channel micro-nano fiber coupling structure is composed of n input optical fibers and n output optical fibers, where n ≥ 3;

[0028] The light source 1 and the detector 2 are connected to two input ports of the first 2×2 fiber optic switch 3. Two output ports of the first 2×2 fiber optic switch 3 are connected to any two input optical fibers in the multi-channel micro-nano fiber coupling structure 4. Two output optical fibers corresponding to the two input optical fibers are selected as output ports and are respectively connected to two input ports of the second 2×2 fiber optic switch 5. Two output ports of the second 2×2 fiber optic switch 5 are connected to a fiber optic loop 5 with a fixed length, and a fiber optic polarization controller 6 is connected inside the fiber optic loop 5;

[0029] Specifically, the light source 1 and the detector 2 form an optoelectronic detection device for recording the output spectral information;

[0030] Specifically, the first 2×2 fiber optic switch 3 and the multi-channel micro-nano fiber coupling structure 4 form a fiber optic loop filter switching device, which is used to realize the switching of the optical coupling loop, and further realize the switching of the wavelength, bandwidth, and transmission / reflection rate of the coupling filter;

[0031] Specifically, the fiber polarization controller 7 and the fiber optic loop 8 form a filtering transmission / reflection rate tuning device, which is used to realize the adjustable spectral extinction ratio of each fiber optic filter.

[0032] Specifically, the light emitted by the light source 1 is divided into two paths by the multi-channel micro-nano fiber coupling structure 4 and enters the fiber optic loop 6. These two beams of light respectively pass through the fiber polarization controller 7 and then return to the micro-nano fiber coupling mechanism 4 for coupling, and finally output to the detector 2.

[0033] The preparation method of the multi-channel micro-nano coupled fiber optic filter includes the following steps:

[0034] S1. Strip the coating layer of the optical fiber and mark the input end and output end of the optical fiber;

[0035] S2. Wind the optical fiber and fix it on the displacement platform. Set the taper length of the fiber taper machine to 18000 um, the hydrogen flow rate to 140 scm, and the speed of the displacement platform to 150 um / s;

[0036] S3. Package the multi-channel micro-nano fiber coupling structure 4 with a quartz glass tube;

[0037] S4. The input end of the multi-channel micro-nano fiber coupling structure 4 is respectively connected to the light source 1 and the detector 2 through the first 2×2 fiber optic switch 3. The input end of the second 2×2 fiber optic switch 5 is connected to the output end of the multi-channel micro-nano fiber coupling structure 4. The output end of the second 2×2 fiber optic switch 5 is connected to the fiber optic loop 6 with a fixed length. The fiber polarization controller 7 is connected inside the fiber optic loop 6.

[0038] Specifically, the head diameter of the fiber taper machine is 6 mm.

[0039] A multi-channel selection filtering method. The second 2×2 fiber optic switch 4 switches different pairs of input and output optical fibers, so that the multi-channel micro-nano fiber coupling structure 4 and the fiber polarization controller 7 form different loops x and loop y to meet the requirements of different wavelength filtering. The fiber polarization controller 7 is connected inside the loop to obtain its transmission spectrum filtering characteristics.

[0040] Based on the filtering characteristics of the filter proposed through theoretical research, the light source transmits in the loop in the clockwise and counterclockwise directions respectively through the micro-nano fiber coupler 3. The transmission matrix equation of the polarization regulator 5 is as follows:

[0041]

[0042]

[0043]

[0044] Counterclockwise direction:

[0045]

[0046] Clockwise direction:

[0047]

[0048] Wherein,

[0049] A = cos²(θ1 - θ2) + cos²(θ3 - θ2)

[0050] B = cos²θ2 - cos²(θ3 + θ1 - θ2)

[0051] C = sin²(θ1 - θ2) - sin²(θ3 - θ2)

[0052] D = sin²θ2 - sin²(θ3 + θ1 - θ2)

[0053] Then the output functions of the transmission spectrum and the reflection spectrum are:

[0054]

[0055]

[0056] Wherein, β = 2arctan(D / C), β is the induced phase shift, is the phase, and Δn, L, and λ are the effective refractive index difference, the fiber length, and the operating wavelength, respectively. In order to make its spectrum only affected by the polarization angle, the induced phase shift must be constant, that is, β is 0 or π. At this time, one of the solutions obtained is θ1 = θ3 = 0. Multiply both sides of the formula by the coupler matrix to obtain its output function as:

[0057]

[0058]

[0059] Wherein, k is the coupling coefficient.

[0060] It can be seen from the above formula that the extinction ratio of the filter is related to the coupling coefficient of the micro-nano fiber coupler and the rotation angle of the polarization controller. When the coupling coefficient of the micro-nano coupler is determined, it is only related to the rotation angle of the polarization controller.

[0061] Further study the filtering performance of the filter through experiments. Connect the light source 1 and the detector 2 to both ends of the circulator respectively, and connect the other end of the circulator to the input port of the multi-channel micro-nano fiber coupling structure 4 to explore the filtering characteristics of the reflection spectrum; as Figure 3 shown, according to the actually measured transmission spectrum diagram, reflection spectrum diagram, and the relationship diagram between the polarization angle and the extinction ratio, adjust the angle of the fiber polarization controller 7. The transmission spectrum shape of the filter only changes in the extinction ratio, and the wavelength and transmission intensity basically do not change. The change in the transmission intensity and the extinction ratio of the reflection spectrum shape is basically consistent. The extinction ratios of both the transmission spectrum and the reflection spectrum reach the maximum value at 90°, verifying the feasibility and accuracy in actual measurement.

[0062] The above is the complete implementation process of this embodiment.

[0063] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those skilled in the art within the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A multi-channel switching combined micro-nano fiber coupling filter, characterized in that, It includes a light source, a detector, a multi-channel micro-nano fiber coupling structure, a first and a second 2×2 fiber optic switch, an optical fiber loop, and an optical fiber polarization controller. The multi-channel micro-nano fiber coupling structure is composed of n input optical fibers and n output optical fibers, where n≥3; The light source and the detector are connected to two input ports of the first 2×2 fiber optic switch. Two output ports of the first 2×2 fiber optic switch are connected to any two input optical fibers in the multi-channel micro-nano fiber coupling structure. Two output optical fibers corresponding to the two input optical fibers are selected as output ports and are respectively connected to two input ports of the second 2×2 fiber optic switch. Two output ports of the second 2×2 fiber optic switch are connected to an optical fiber loop with a fixed length, and an optical fiber polarization controller is connected inside the optical fiber loop; The light source and the detector form an optoelectronic detection device for recording the output spectral information; The first 2×2 fiber optic switch and the multi-channel micro-nano fiber coupling structure form an optical fiber loop filter switching device for realizing the switching of the optical coupling loop, and further realizing the switching of the wavelength, bandwidth, and transmittance / reflection rate of the coupling filter; The optical fiber polarization controller and the optical fiber loop form a filtering transmittance / reflection rate tuning device for realizing the adjustable spectral extinction ratio of each optical fiber filter.

2. A method for multi-channel selective filtering, characterized in that, Adopting a filter as described in claim 1, the second 2×2 fiber optic switch realizes the tuning of different filtering characteristics by switching different input and output fiber pairs.

3. A method for multi-channel selection filtering according to claim 2, characterized in that, The light emitted by the light source is divided into two paths by the multi-channel micro-nano fiber coupling structure. One optical signal passes through the optical fiber polarization controller in the clockwise direction, and the other optical signal passes through the optical fiber polarization controller in the counterclockwise direction. The optical fiber polarization controller changes the spectral amplitude of the two optical signals. The two optical signals return to the multi-channel micro-nano fiber coupling structure for coupling and are finally output to the detector.

4. A method for multi-channel selection filtering according to claim 2, characterized in that, By tuning the polarization angle of the optical fiber polarization controller in the optical fiber loop, the continuous adjustment of the extinction ratio of the filter is realized. When the polarization angle of the polarization controller reaches 90°, the extinction ratios of the transmission spectrum and the reflection spectrum are the largest.

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