Narrow bandwidth beam splitting device, optical module and beam splitting method for demultiplexing

Abstract

The present invention relates to a narrow bandwidth beam splitter device and an optical module for demultiplexing, and a light splitting method, wherein the narrow bandwidth beam splitter device comprises a substrate and at least two bandpass filters, and further comprises at least two filters, the number of the filters is the same as the number of the bandpass filters, and one filter and one bandpass filter constitute a combined filter, and the overall bandwidth of the combined filter is smaller than the bandwidth of the bandpass filter in the combined filter. The present invention uses a filter and a bandpass filter in combination, and uses the filter to perform a filtering operation once, so that the overall bandwidth of the combined filter is smaller than the bandwidth of the bandpass filter in the combined filter, and therefore, the bandwidth can be reduced compared to a single bandpass filter.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a narrow-bandwidth beam splitting device and an optical module for demultiplexing, and a light splitting method. Background Art

[0002] Optical modules are devices that realize the mutual conversion of photoelectric signals and are important equipment in the field of optical communications. In order to meet the needs of long-distance transmission, optical amplifiers are usually added to filters to amplify signals. Typical optical amplifiers, such as semiconductor optical amplifiers (SOAs), have spontaneous radiation in a wide range of spectral lines. These spontaneous radiation noises will cause signal degradation. Therefore, before the signal is received by the detector, a bandpass filter is needed to filter out the noise that does not belong to the detection channel. Assuming that the wavelength of the optical signal is between λc±δ, it is hoped that the central wavelength of the bandpass filter is λc and the passband is slightly larger than 2δ, so that the spontaneous radiation noise of the optical amplifier can be filtered out to the maximum extent. However, in the design and production of bandpass filters, temperature drift, angle offset and coating margin must be taken into account. The actual central wavelength will not be λc, and the bandwidth will be much larger than 2δ. A large amount of spontaneous radiation noise will not be cut off, which will lead to a decrease in the signal-to-noise ratio.

[0003] For example, the demultiplexer is an important component in the optical module to realize multi-channel optical signal transmission. Traditionally used four-channel demultiplexing devices such as Figure 1 As shown, 108 is a glass substrate, 104~107 are bandpass filters, 103 is an anti-reflection film coated on 108, and 102 is a high-reflection film coated on 108. The wide wavelength beam 101 is incident from 103. After reaching 104, the beam with a wavelength in the range of λ1±δ1 is directly transmitted, and the wavelength outside this range is reflected to 102, and after further reflection, it reaches 105. The beam with a wavelength in the range of λ2±δ2 is directly transmitted, and the beam outside this range is reflected to 102 again, and so on, until the wavelengths of λ3±δ3 and λ4±δ4 are decomposed. The bandwidth of each demultiplexed wavelength (±δx, x=1~4) depends on the performance of the bandpass filter. Due to process limitations, δx cannot be made very small. When the incident 101 beam spectrum is wide, δx will greatly affect the signal-to-noise ratio. Summary of the invention

[0004] The purpose of the present invention is to improve the above-mentioned problems existing in the prior art and to provide a narrow bandwidth beam splitting device and optical module for demultiplexing, and a beam splitting method.

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

[0006] A narrow bandwidth beam splitter device for demultiplexing comprises a substrate and at least two bandpass filters, and also comprises at least two filters, the number of the filters is the same as the number of the bandpass filters, and one filter and one bandpass filter constitute a combined filter, the overall bandwidth of the combined filter is smaller than the bandwidth of the bandpass filter in the combined filter.

[0007] In a preferred embodiment, the filter is a filter with an edge wavelength. In the same combined filter, the wavelength range of the bandpass filter is λ±δ, the edge wavelength of the filter is between λ-δ and λ+δ, and the incident light beam first passes through the filter and then through the bandpass filter; after passing through at least two combined filters in sequence, the wavelengths of at least two output light beams finally outputted increase or decrease in sequence.

[0008] In this solution, the filter uses a filter with an edge wavelength, and the edge wavelength of the filter is limited to between λ-δ and λ+δ, so that the combined filter can only allow a smaller range of optical signals to pass through, thereby achieving the purpose of reducing the bandwidth of the combined filter. This implementation method is simple, low-cost, and small in overall size.

[0009] In one embodiment, the at least two filters include a first filter and at least one second filter, the first filter is used to transmit the incident light beam to the bandpass filter, and the second filter is used to reflect the light beam reflected by the bandpass filter of the previous combined filter in the optical path to the bandpass filter belonging to the same combined filter, the first filter is a long-pass filter or a long-pass dichroic mirror, and the second filter is a long-reflective filter or a short-pass dichroic mirror.

[0010] In another embodiment, the at least two filters include a first filter and at least one second filter, the first filter is used to transmit the incident light beam to the bandpass filter, and the second filter is used to reflect the light beam reflected by the bandpass filter of the previous combined filter in the optical path to the bandpass filter belonging to the same combined filter, the first filter is a short-pass filter or a short-pass dichroic mirror, and the second filter is a short-reflective filter or a long-pass dichroic mirror.

[0011] On the other hand, the present invention further provides an optical module, comprising the narrow bandwidth beam splitter device for demultiplexing described in any embodiment of the present invention.

[0012] In another aspect, the present invention further provides a demultiplexing method, comprising the following steps:

[0013] preparing at least two bandpass filters and at least two filters, the number of the filters being the same as the number of the bandpass filters;

[0014] Based on the principle that a filter and a bandpass filter constitute a combined filter, all the bandpass filters and filters are grouped to obtain at least two combined filters, and the overall bandwidth of each combined filter is smaller than the bandwidth of the bandpass filter in the combined filter;

[0015] The incident light beam passes through each combined filter in sequence, and finally outputs at least two outgoing light beams.

[0016] Compared with the prior art, the present invention uses a filter and a bandpass filter in combination and uses the filter to perform a single filtering, so that the overall bandwidth of the combined filter is smaller than the bandwidth of the bandpass filter in the combined filter. Therefore, the bandwidth can be reduced compared to a single bandpass filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work, but they all fall within the scope of protection of the present invention.

[0018] Figure 1 The diagram is a structural diagram of a beam splitter device of a four-channel demultiplexer in the prior art.

[0019] Figure 2 Schematic diagram of the structure of a beam splitter device of a four-channel demultiplexer in an embodiment of the present invention.

[0020] Figure 3a This is a schematic diagram of the bandwidth of a conventional bandpass filter. Figure 3b Schematic diagram of bandwidth after the central wavelength is shifted; Figure 3c Schematic diagram of bandwidth change in the process of combining a filter with an edge wavelength and a bandpass filter. Figure 3d The bandwidth comparison chart of the combined filter and the bandpass filter is shown in Figure 2.

[0021] Figure 4a for Figure 2 Schematic diagram of the bandwidth of the four channels in the structure shown, Figure 4b The bandwidth comparison chart of the combined filter and the bandpass filter in the four channels. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0023] Before describing the narrow bandwidth beam splitting device for demultiplexing provided in this embodiment, the professional terms involved are briefly introduced.

[0024] Long pass filter: It belongs to edge pass filter. It transmits when the wavelength is longer than the edge wavelength, and cuts off when the wavelength is shorter than the edge wavelength.

[0025] Short pass filter: It belongs to edge pass filter. It cuts off when the wavelength is longer than the edge wavelength, and transmits when the wavelength is shorter than the edge wavelength.

[0026] Long reflection filter: It belongs to edge pass filter. It reflects when the wavelength is longer than the edge wavelength, and cuts off when the wavelength is shorter than the edge wavelength.

[0027] Short reflection filter: It belongs to edge pass filter. It cuts off when the wavelength is longer than the edge wavelength, and reflects when the wavelength is shorter than the edge wavelength.

[0028] Long-pass dichroic mirror: When the wavelength is longer than the edge wavelength, it transmits; when the wavelength is shorter than the edge wavelength, it reflects.

[0029] Short-pass dichroic mirror: When the wavelength is longer than the edge wavelength, it reflects; when the wavelength is shorter than the edge wavelength, it transmits.

[0030] Bandpass filter: transmits light within a certain wavelength range and reflects the rest.

[0031] See also Figure 2 , this embodiment provides a narrow bandwidth beam splitter 200 for demultiplexing, which can decompose an incident light beam (or incident light) into at least two outgoing light beams (or outgoing light), and the wavelength of the outgoing light beam increases or decreases with the optical path length. Through the combined design of an edge pass filter or a dichroic mirror and a bandpass filter, the outgoing light beam can achieve ultra-narrow bandwidth output. Different from the conventional demultiplexing beam splitter, the bandwidth of the bandpass filter in the beam splitter of the present invention does not need to be very narrow.

[0032] like Figure 2 As shown in the figure, 210 is the incident wide spectrum light beam, 211~214 are the outgoing light beams after demultiplexing, and 205~208 are bandpass filters. 201 is a first filter, which is used to transmit the incident light to the bandpass filter, and 202~204 are second filters, which are used to reflect the light reflected by the bandpass filter again.

[0033] If the central wavelengths of the outgoing light beams 211 - 214 increase sequentially, the first filter 201 is a long-pass filter or a long-pass dichroic mirror, and the second filters 202 - 204 are long-pass filters or short-pass dichroic mirrors.

[0034] If the central wavelengths of the outgoing light beams 211 - 214 decrease in sequence, the first filter 201 is a short-pass filter or a short-pass dichroic mirror, and the second filters 202 - 204 are short-pass filters or long-pass dichroic mirrors.

[0035] It should be noted that the core of the present invention is the combination of an edge pass filter or a dichroic mirror and a band pass filter to achieve narrow bandwidth output. Therefore, an edge pass filter or a dichroic mirror and a band pass filter constitute a combined filter, and the overall bandwidth of the combined filter is reduced relative to the bandwidth of a single band pass filter.

[0036] Figure 2 The structure shown is a narrow bandwidth beam splitter device suitable for a four-channel demultiplexer, so three second filters are required. Based on other multi-channel applications, the number of second filters can be set accordingly.

[0037] Conventional bandpass filters such as Figure 3a As shown, the central wavelength is λc, and the left and right 1dB bandwidths are represented as (δ_-1dB) and (δ_+1dB), respectively. Usually, the values ​​of the two are wider and not equal. Figure 3b As shown, keeping the bandwidth unchanged and shifting the center wavelength to λc1, the distance from the original center wavelength λc to the +1dB bandwidth is (δ_+1dB) – (δ_λc), that is, the 1dB bandwidth to the right of λc is reduced.

[0038] The edge wavelength λ_edge of the edge pass filter is δ_edge away from λc, and δ_edge < (δ_-1dB). When the light beam reaches the edge pass filter, the light beam with a wavelength less than δ_edge is cut off, that is, the 1dB bandwidth on the left side of λc is reduced.

[0039] The bandwidth of the filter after combining the edge pass filter and the band pass filter with the center wavelength shifted becomes: δ_edge + (δ_+1dB) - (δ_λc). The schematic diagram of the combination process is as follows Figure 3c shown.

[0040] Bandwidth of the combined filter: δ_edge + (δ_+1dB) - (δ_λc)

[0041] Original bandpass filter bandwidth: (δ_-1dB) + (δ_+1dB)

[0042] Since δ_edge < (δ_-1dB), (δ_λc) >0, the bandwidth of the combined filter < the bandwidth of the original filter, such as Figure 3d As shown in the figure, the solid line is the bandwidth of the combined filter, and the dotted line is the bandwidth of a single bandpass filter. Therefore, the present invention can reduce the overall bandwidth without reducing the bandwidth of the bandpass filter by combining the edgepass filter with the bandpass filter, thereby eliminating the spontaneous radiation noise in the optical amplifier. The desired bandwidth can be obtained by designing δ_edge and (δ_λc).

[0043] It should be understood that the descriptions such as narrow bandwidth or ultra-narrow bandwidth mentioned in this article are relative concepts, not absolute concepts, indicating that the overall bandwidth of the combined filter after the filter and the bandpass filter are combined is smaller than the bandwidth of a single bandpass filter. Therefore, the purpose of reducing the bandwidth can be achieved on the basis of existing processes, thereby meeting the signal-to-noise ratio requirements.

[0044] Please refer to Figure 2 Here, the principle of the present invention is further elaborated in detail by taking the case where the central wavelength of the outgoing light beam increases successively as an example.

[0045] 210 is an incident light beam with a wide spectrum. 211 to 214 are output light beams after demultiplexing, and the central wavelengths are λ1 to λ4, respectively, and the four central wavelengths increase in sequence.

[0046] In this example, the first filter 201 is a long-pass filter, the surface of which is connected to the substrate 209 is a functional surface, and the surface of the incident light beam 210 is coated with an anti-reflection film. The distance from its edge wavelength to the central wavelength λ1 is δ1_edge. The 1dB bandwidth of the bandpass filter 205 is expressed as (δ1_-1dB) + (δ1_+1dB), and the central wavelength of the bandpass filter 205 is shifted by (δ1_λ1) relative to λ1. The combination of the first filter 201 and the bandpass filter 205 is equivalent to: a narrowband filter with a central wavelength of λ1 and a bandwidth of (δ1_edge)+ [(δ1_+1dB) - (δ1_λ1)].

[0047] The second filters 202-204 are long reflection filters, and the surface in contact with the substrate 209 is a functional surface. Similarly, the combination of the second filter 202 and the bandpass filter 206 is equivalent to a narrowband filter with a central wavelength of λ2 and a bandwidth of (δ2_edge) + [(δ2_+1dB)- (δ2_λ2)].

[0048] The combination of the second filter 203 and the bandpass filter 207 is equivalent to a narrowband filter with a central wavelength of λ3 and a bandwidth of (δ3_edge) + [(δ3_+1dB) - (δ3_λ3)].

[0049] The combination of the second filter 204 and the bandpass filter 208 is equivalent to a narrowband filter with a central wavelength of λ4 and a bandwidth of (δ4_edge) + [(δ4_+1dB) - (δ4_λ4) ].

[0050] When the incident light beam 210 passes through the first filter 201 and the bandpass filter 205 in sequence, the following effects are achieved:

[0051] The light beam with a wavelength less than λ1- δ1_edge is cut off; the light beam with a wavelength in the range of (λ1- δ1_edge)<λ <λ1+ (δ1_+1dB)- (δ1_λ1) is transmitted and output, that is, the wavelength range of the output light beam 211 is (λ1- δ1_edge)<λ <λ1+ (δ1_+1dB) - (δ1_λ1), and the light with a wavelength greater than λ1+ (δ1_+1dB) - (δ1_λ1) is reflected to the second filter 202.

[0052] When the light beam passes through the second filter 202 and the bandpass filter 206 in sequence, the following effects are achieved:

[0053] The light beam with a wavelength less than λ2-δ2_edge is cut off; the light beam with a wavelength of (λ2- δ2_edge)<λ<λ2+(δ2_+1dB) - (δ2_λ2) is transmitted and output, that is, the wavelength range of the output light beam 212 is (λ2- δ2_edge)<λ<λ2+(δ2_+1dB) - (δ2_λ2), and the light with a wavelength greater than λ2+ (δ2_+1dB) - (δ2_λ2) is reflected to the second filter 203.

[0054] When the light beam passes through the second filter 203 and the bandpass filter 207 in sequence, the following effects are achieved:

[0055] The light beam with a wavelength less than λ3- δ3_edge is cut off; the light beam with a wavelength of (λ3- δ3_edge) < λ < λ3+ (δ3_+1dB) -(δ3_λ3) is transmitted and output, that is, the wavelength of the output light beam 213 is (λ3- δ3_edge) < λ < λ3+ (δ3_+1dB)- (δ3_λ3), and the light with a wavelength greater than λ3+ (δ3_+1dB) - (δ3_λ3) is reflected to the second filter 204.

[0056] When the light beam passes through the second filter 204 and the bandpass filter 208 in sequence, the following effects are achieved:

[0057] The light beam with wavelength less than λ4- δ4_edge is cut off; the light beam with wavelength (λ4- δ4_edge) < λ < λ4+ (δ4_+1dB) -(δ4_λ4) is transmitted and output, that is, the wavelength of the output light beam 214 is (λ4- δ4_edge) < λ < λ4+ (δ4_+1dB)- (δ4_λ4). At this point, the light beam demultiplexing is completed, and the spectrum is as follows: Figure 4a As shown, CH1-CH4 in the figure represent signal channels 1-4.

[0058] In an application example, assuming that the incident light beam 210 is a wide light beam of 1260nm~1300nm, and the wavelengths of 1295nm, 1300nm, 1304nm and 1309nm are to be demultiplexed, the four wavelengths of the light beam correspond to 211~214 respectively. The first filter 201 is a long pass filter, and its edge wavelength is 1294nm. The second filters 202~204 are short pass dichroic mirrors, and their edge wavelengths are 1299nm, 1303nm, and 1308nm respectively. The 1dB bandwidth of the bandpass filters 205~208 is ±2nm, and the center wavelengths are 1294nm, 1299nm, 1303nm, and 1308nm respectively.

[0059] After the incident light beam 210 is incident on the first filter 201, the light beam with a wavelength less than 1294nm is cut off, and the light beam with a wavelength greater than 1294nm continues to be incident on the bandpass filter 205. Then, the output light beam 211 of 1294nm~1296nm is output through the bandpass filter 205. The central wavelength of the output light beam 211 is 1295nm, and the bandwidth is ±1nm, which is 1 times smaller than the original bandwidth of the bandpass filter 205.

[0060] The light beam with a wavelength greater than 1296nm is reflected to the second filter 202, and the edge wavelength of the second filter 202 is 1299nm, so the light beam with a wavelength less than 1299nm is transmitted, and the light beam greater than 1299nm is further reflected to the bandpass filter 206. The central wavelength of the bandpass filter 206 is 1299nm, so the output light beam 212 of 1299nm~1301nm is transmitted through the bandpass filter 206 and outputted, and the central wavelength of this light beam is 1300 and the bandwidth is ±1nm.

[0061] After the light beam with a wavelength greater than 1301 nm is reflected by the second filter 203, the light beam less than 1303 nm is transmitted, and the light beam greater than 1303 nm is reflected to the bandpass filter 207. The outgoing light beam 213 with a wavelength of 1303-1305 nm is transmitted through the bandpass filter 207 and outputted, and the central wavelength of this light beam is 1304 nm, and the bandwidth is ±1 nm.

[0062] The light beam with a wavelength greater than 1305nm continues to be reflected to the second filter 204, and the light beam less than 1308nm is transmitted. After the light greater than 1308nm is reflected to the bandpass filter 208, the output light beam 214 of 1308nm~1310nm is transmitted through the diatribe filter 208 and outputted. The central wavelength of this light beam is 1309nm and the bandwidth is ±1nm.

[0063] The spectral curve of the combined filter is compared with the spectral curve of using only the bandpass filter. Figure 4b It can be seen that the present invention can greatly compress the bandwidth of the output light beam, reduce the crosstalk between channels, and reduce the noise energy.

[0064] In this embodiment, an edge pass filter or a dichroic mirror is combined with a band pass filter to achieve that the overall bandwidth of the combined filter is smaller than the bandwidth of the band pass filter in the combined filter. The edge pass filter or the dichroic mirror is a filter with an edge wavelength. In this embodiment, by limiting the edge wavelength of the filter to be between λ-δ and λ+δ (for the wavelength range of the band pass filter in the combined filter of the same group is λ±δ), the combined filter can only allow a smaller range of optical signals to pass through, thereby achieving the purpose of reducing the bandwidth of the combined filter. This implementation method is simple, low cost, and small overall size, but the present invention does not exclude other possible implementation methods.

[0065] Based on the same inventive concept, this embodiment also proposes a demultiplexing method, comprising the following steps:

[0066] preparing at least two bandpass filters and at least two filters, the number of the filters being the same as the number of the bandpass filters;

[0067] Based on the principle that a filter and a bandpass filter constitute a combined filter, all the bandpass filters and filters are grouped to obtain at least two combined filters, and the overall bandwidth of each combined filter is smaller than the bandwidth of the bandpass filter in the combined filter;

[0068] The incident light beam passes through each combined filter in sequence, and finally outputs at least two outgoing light beams.

[0069] The purpose of forming a combined filter with a filter plate and a bandpass filter plate is to filter with the filter plate on the basis of filtering with the bandpass filter plate so that the overall bandwidth of the combined filter is smaller than the bandwidth of the bandpass filter in the combined filter. Based on different implementations, the arrangement of the filter plate and a bandpass filter plate is different.

[0070] A preferred embodiment is that the filter uses a filter with an edge wavelength. In the same combined filter, the wavelength range of the bandpass filter is λ±δ, and the edge wavelength of the filter is between λ-δ and λ+δ. In this case, the filter and the bandpass filter are arranged in such a way that when the incident light beam passes through the combined filter, it first passes through the filter and then passes through the bandpass filter.

[0071] For example, you can refer to Figure 2 For the convenience of description, one of the at least two filters is defined as the first filter, and the rest are second filters. The first filter is arranged at the front end of the optical path, and is used to transmit the incident light beam to the bandpass filter. All the second filters are arranged in sequence along the optical path, and are used to reflect the light beam reflected by the bandpass filter of the previous combined filter in the optical path to the bandpass filter belonging to the same combined filter. In this way, the wavelength of the output light beam output from each bandpass filter increases or decreases in sequence.

[0072] If the first filter is a long-pass filter or a long-pass dichroic mirror, and the second filter is a long-pass filter or a short-pass dichroic mirror, the wavelength of the outgoing light beam output from each bandpass filter increases successively.

[0073] If the first filter is a short-pass filter or a short-pass dichroic mirror, and the second filter is a short-reflection filter or a long-pass dichroic mirror, the wavelength of the outgoing light beam output from each bandpass filter decreases in sequence.

[0074] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A narrow bandwidth beam splitter for demultiplexing, comprising a substrate and at least two bandpass filters, characterized in that: It also includes at least two filters, the number of the filters is the same as the number of the bandpass filters, and one filter and one bandpass filter form a combined filter, and the overall bandwidth of the combined filter is smaller than the bandwidth of the bandpass filter in the combined filter; The filter is a filter with an edge wavelength. In the same combined filter, the wavelength range of the bandpass filter is λ±δ, the edge wavelength of the filter is between λ-δ and λ+δ, and when the incident light beam passes through the combined filter, it first passes through the filter and then passes through the bandpass filter; after passing through at least two combined filters in sequence, the wavelengths of at least two output light beams are increased or decreased in sequence; The at least two filters include a first filter and at least one second filter, the first filter is used to transmit the incident light beam to the bandpass filter, and the second filter is used to reflect the light beam reflected by the bandpass filter of the previous combined filter in the optical path to the bandpass filter belonging to the same combined filter; wherein the first filter is a long-pass filter or a long-pass dichroic mirror, and the second filter is a long-reflective filter or a short-pass dichroic mirror, so as to achieve the wavelengths of at least two output light beams that are finally output to increase in sequence; the first filter is a short-pass filter or a short-pass dichroic mirror, and the second filter is a short-reflective filter or a long-pass dichroic mirror, so as to achieve the wavelengths of at least two output light beams that are finally output to decrease in sequence.

2. An optical module, characterized in that: The invention comprises the narrow bandwidth beam splitting device for demultiplexing as claimed in claim 1.

3. A method for splitting a narrow bandwidth beam splitter for demultiplexing according to claim 1, characterized in that: The following steps are involved: preparing at least two bandpass filters and at least two filters, the number of the filters being the same as the number of the bandpass filters; Based on the principle that a filter and a bandpass filter constitute a combined filter, all the bandpass filters and filters are grouped to obtain at least two combined filters, and the overall bandwidth of each combined filter is smaller than the bandwidth of the bandpass filter in the combined filter; The incident light beam passes through each combination filter in sequence, and finally outputs at least two outgoing light beams.

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