A WDM demultiplexer based on a thin-film interference filter

Abstract

The present invention discloses a WDM demultiplexer based on a thin-film interference filter, which includes a pre-stage demultiplexer and a post-stage demultiplexer. The pre-stage demultiplexer is arranged in front of the light beam incident port of the post-stage demultiplexer. The pre-stage demultiplexer divides the incident light beam into two beams, the upper beam and the lower beam, each carrying the first half of each wavelength and the second half of each wavelength of light waves. When the upper and lower light waves are emitted in parallel, there is a vertical distance between them. The post-stage demultiplexer further demultiplexes the incident upper and lower light waves, making full use of the extensibility in all directions of the three-dimensional space. The optical demultiplexer (DeMUX) can be made more compact, and at the same time, the optical path of some channels is relatively shortened, making the device easy to couple, which is beneficial to the production of an optical demultiplexer (DeMUX) with more wavelength channels.

Description

Technical Field

[0001] The present invention relates to the technical fields of physical optics and fiber optic communication passive devices, and particularly relates to a WDM demultiplexer based on a thin film interference filter. Background Art

[0002] Wavelength Division Multiplexing (WDM) technology has been widely applied in fiber optic transmission systems and optical network systems. This technology uses a single optical fiber to transmit multiple optical carriers of different wavelengths, making full use of the optical fiber bandwidth, doubling the amount of information transmitted by the optical fiber, and thus greatly reducing the cost of optical fiber transmission. The key devices used in this WDM technology are optical wavelength multiplexers and demultiplexers. As for optical wavelength demultiplexers, the most mature ones currently are demultiplexers based on Thin Film Interference Filters (TFFs). Figure 1 FIG. 10 is a schematic diagram of the typical structure of an existing four-wave WDM demultiplexer (DeMUX) based on a thin film interference filter and the optical path when the incident light is collimated light. Figure 2 FIG. 11 is a schematic diagram of the typical structure of an existing eight-wave WDM demultiplexer (DeMUX) based on a thin film interference filter and the optical path when the incident light is collimated light. The entire structure of this optical demultiplexer consists of a quartz prism in the shape of a parallelogram with an acute angle of 82°. The incident port of the multi-wave (λ1, λ2, λ3, λ4, etc.) light beam on its front-end plane is coated with an anti-reflection (AR) film area, and the rest is coated with a high-reflection (HR) film area. Multiple narrowband thin film interference filters (TFFs) are attached at the output ports of each optical wave on its rear-end plane. It can be seen from the schematic diagram that the optical path of the existing thin film interference filter WDM demultiplexer (DeMUX) is unfolded on a plane. Therefore, in terms of the linear dimension of the device, the width of the device is much larger than its height. For a typical four-wave device, the width is 3.5 mm, the length is 3.92 mm, and the height of the device is 1 mm. Compared with the width and length of the device, its height is very small. If the width of the device is limited during use, for example, it must be less than 2 mm, then the existing four-wave thin film interference filter WDM demultiplexer (DeMUX) cannot be used. In addition, the optical path that the fourth optical wave λ4 travels is much longer than the optical path that the first optical wave λ1 travels. Before the fourth optical wave λ4 reaches its output port, it has to accompany the first three optical waves to complete all their optical paths. Therefore, compared with the first and second optical waves, the coupling of the third and fourth optical waves is much more difficult. If the existing thin film interference filter WDM demultiplexer (DeMUX) is made into an eight-wave one, its width will reach 7 mm, and the optical paths of the seventh and eighth optical waves will be even longer. It is very difficult for a general collimator to have such a long collimation distance. Summary of the Invention

[0003] Objective of the present invention: To overcome the defects that the lateral dimension occupied by the device is much larger than the longitudinal dimension, the 3D space cannot be fully utilized, and the optical path traveled by the finally emitted light wave is too long, making it difficult for the collimator to achieve such a long collimation distance, etc., the present invention proposes a novel WDM demultiplexer based on a thin-film interference filter.

[0004] Technical solution: A WDM demultiplexer based on a thin-film interference filter includes a pre-stage demultiplexer and a post-stage demultiplexer arranged in front of the light beam incident port of the post-stage demultiplexer. The upper beam of light includes the light beams of each wavelength in the latter half of the incident light beam, and the lower beam of light includes the light beams of each wavelength in the former half of the incident light beam. There is an upper and lower spacing when the upper and lower parallel light beams are emitted. The post-stage demultiplexer demultiplexes the incident upper and lower parallel light beams again.

[0005] Further, the pre-stage demultiplexer includes a pre-stage prism and a band-pass thin-film interference filter arranged at the lower output port of the rear end plane of the pre-stage prism. The band-pass thin-film interference filter fully transmits the light beams of each wavelength in the former half of the input light beam and totally reflects the light beams of each wavelength in the latter half.

[0006] Further, the post-stage demultiplexer includes a post-stage prism and narrow-band thin-film interference filters arranged corresponding to the output ports of each light beam at the rear end plane of the post-stage prism.

[0007] Further, both the pre-stage prism and the post-stage prism are of a parallelogram structure.

[0008] Further, the upper and lower spacing required when the upper and lower parallel light beams are emitted is obtained by adjusting the acute angle and length of the pre-stage prism.

[0009] Further, the post-stage prism is composed of two sub-prisms with the same structure and stacked vertically.

[0010] Further, an anti-reflection film coating area is provided at the light beam incident port of the front end plane of the pre-stage prism and the post-stage prism, and the rest is a high-reflection film coating area. Further, the bottom surfaces of the pre-stage prism and the post-stage prism are on the same horizontal plane, and the side surface of the post-stage prism is parallel to the side surface of the pre-stage prism.

[0011] Further, an anti-reflection film coating area is provided at the upper output port of the rear end plane of the pre-stage prism of the pre-stage demultiplexer, and the part between its upper output port and lower output port is a high-reflection film coating area.

[0012] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0013] 1. In the WDM demultiplexer (DeMUX) of the present invention, the optical path traveled by the light wave with the longest optical path among the demultiplexed light beams is shorter than that of the corresponding light wave in the existing demultiplexer, and the linear dimension in the width direction is also smaller than that of the existing demultiplexer;

[0014] 2. When the WDM demultiplexer (DeMUX) of the present invention is used for demultiplexing more than four waves (such as six waves, eight waves or more waves) of light waves, its characteristics of short optical path and compact structure can be more prominent;

[0015] 3. The pre-stage prism of the present invention and the thin-film interference filter attached thereto serve as a pre-stage demultiplexer, which divides the light waves of various wavelengths of the incident collimated light beam into two parallel light beams, each carrying the first half and the second half of the wavelengths, respectively. The vertical spatial distance between the two parallel light beams can be achieved by appropriately designing the acute angle and the length of the pre-stage prism. Compared with the existing thin-film interference filter demultiplexer, the optical path of the longest optical path is shorter, so that the coupling of the device light beam becomes convenient;

[0016] 4. By using the pre-demultiplexing of the pre-stage prism and the stacking of the post-stage prism, the demultiplexer of the present invention can be made more compact in terms of the device width than the existing thin-film interference filter demultiplexer;

[0017] 5. By making full use of the extensibility in all directions of the three-dimensional space, the optical demultiplexer (DeMUX) can be made more compact, and at the same time, the optical path of the long optical path channel is relatively shortened, making the device easy to couple, which is beneficial to the manufacture of an optical demultiplexer (DeMUX) with more wavelength channels. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of the typical optical path and structure of an existing four-wave WDM demultiplexer (DeMUX) based on a narrowband thin-film interference filter;

[0019] Figure 2 is a schematic diagram of the typical optical path and structure of an existing eight-wave WDM demultiplexer (DeMUX) based on a narrowband thin-film interference filter;

[0020] Figure 3 is a schematic diagram of the structure and geometric configuration of a four-wave WDM demultiplexer based on a thin-film interference filter of the present invention;

[0021] Figure 4 is a detailed engineering drawing of the third prism of the present invention;

[0022] Figure 5 is a schematic diagram of the optical path of a four-wave WDM demultiplexer based on a thin-film interference filter of the present invention;

[0023] Figure 6Top view of the four-wave WDM demultiplexer based on thin-film interference filter of the present invention;

[0024] Figure 7 Schematic structural diagram of the eight-wave WDM demultiplexer based on thin-film interference filter of the present invention. Detailed implementation manners

[0025] The technical solution of the present invention will be further elaborated in combination with the accompanying drawings and embodiments.

[0026] Embodiment 1:

[0027] Figure 3 Schematic diagram of the structure and geometric configuration of the four-wave WDM demultiplexer based on thin-film interference filter of the present invention, which is composed of three prisms, namely the first prism 1, the second prism 2 and the third prism 3. The widths of the first prism 1 and the second prism 2 are Figure 1 half of those of the prisms used in the existing four-wave WDM demultiplexer, and the lengths and heights are the same as Figure 1 . Anti-reflection coating regions AR are provided at the light incident ports of the front end planes of the first prism 1, the second prism 2 and the third prism 3, and the remaining parts are high-reflection coating regions HR. An anti-reflection coating region is provided at the upper output port of the rear end plane of the third prism 3, and the part between its upper output port and the lower output port is a high-reflection coating region. Two narrow-band thin-film interference filters TFF are attached to the output ports of the rear end planes of the first prism 1 and the second prism 2 respectively. The first prism 1 and the second prism 2 are stacked on top of each other. Specifically, the first prism 1 is arranged below the second prism 2. A narrow-band thin-film interference filter TFF for demultiplexing the first light wave λ1 and the second light wave λ2 is attached to the output port of the first prism 1, and a narrow-band thin-film interference filter TFF for demultiplexing the third light wave λ3 and the fourth light wave λ4 is attached to the output port of the second prism 2. The third prism 3 is arranged in front of the light incident ports of the first prism 1 and the second prism 2. The bottom surfaces of the third prism and the first prism are on the same horizontal plane, and the side surface of the third prism 3 is parallel to the side surfaces of the first prism 1 and the second prism 2. Under the allowable geometric configuration space, the third prism 3 should be as close as possible to the first prism 1 and the second prism 2. The third prism 3 is a prism in the shape of a parallelogram with an acute angle. If the paper surface is the X-Y plane, with the horizontal right direction on the paper surface as the X direction and the vertical upward direction perpendicular to the paper surface as the Z direction, then the orientation of the third prism 3 is similar to rotating the Figure 1 prism counterclockwise by 90° around the X axis.

[0028] A band-pass thin-film interference filter is attached to the lower output port on the rear plane of the third prism 3. This band-pass thin-film interference filter TFF can fully transmit the light waves of the first half of each wavelength in the input light beam but fully reflect the light waves of the second half of each wavelength. The acute angle value of the parallelogram and the length L value of the third prism 3 are appropriately set so that the optical path of the light beam of the second half of each wavelength after total reflection is lifted by 1 mm in the Z direction. In this way, after passing through the third prism 3, the input light beam is split into parallel light beams with a vertical spacing of 1 mm in the Z direction, and each carries half of the wavelengths of all the wavelengths carried by the input light beam. These two parallel light beams are respectively incident on the first prism 1 and the second prism 2 stacked together, and the required light beams of different wavelengths are spatially separated by the corresponding narrow-band thin-film interference filters TFF attached to the output ports of the first prism 1 and the second prism 2 after refraction and reflection.

[0029] As a design scheme of the prism in Embodiment 1, Figure 4 The detailed engineering drawing of the third prism 3 is shown. The width of the third prism 3 is 1 mm, the height is 2 mm, the acute angle of the parallelogram of the third prism 3 is designed to be 82°, and quartz is used as the prism material. The length L of the prism is 2.64 mm.

[0030] Specifically, when the four-wave (λ1, λ2, λ3, λ4) incident collimated light beam enters the third prism 3 horizontally and parallel to the side surfaces of the three prisms, after refraction, it encounters a band-pass thin-film interference filter at its bottom output port. This band-pass thin-film interference filter TFF is designed to fully transmit the first light wave λ1 and the second light wave λ2, and fully reflect the third light wave λ3 and the fourth light wave λ4, that is, the light beam λ1, λ2, λ3, λ4 is split into two parallel light beams λ1, λ2 and λ3, λ4 by the third prism 3. The light beam emerging from the output port at the bottom of the third prism 3 contains the light waves λ1 and λ2. Appropriately adjusting the height of the four-wave (λ1, λ2, λ3, λ4) incident collimated light beam in the Z-axis direction makes the height of the light beam containing λ1 and λ2 from the bottom surface of the first prism in the Z-axis direction exactly half of the thickness of the first prism. After it enters the first prism, it is split in the horizontal direction inside the first prism and two independent parallel light beams λ1 and λ2 are emitted. The light beam containing λ3 and λ4 is reflected internally several times inside the third prism 3, and when it emerges from the upper output port of the third prism 3, it is lifted by 1 mm in the Z-axis direction, exactly making its height from the bottom surface of the second prism in the Z-axis direction half of the thickness of the second prism. This light beam enters the second prism 2 horizontally and is spatially split in the horizontal direction after refraction and reflection inside the second prism 2, and two independent parallel light beams λ3 and λ4 are emitted.

[0031] By appropriately adjusting the acute angle and the length L of the parallelogram of the third prism 3, it is always possible to make the beams containing λ3 and λ4 exit from the third prism 3 1 mm higher in the Z-axis direction than the beams containing λ1 and λ2 exiting from the third prism 3 in the Z-axis direction, so that each beam can be respectively incident on the first prism 1 and the second prism 2 according to the designed optical path and be split by wavelength again.

[0032] In the four-wave WDM demultiplexer (DeMUX) based on the thin-film interference filter of this embodiment, the optical paths of λ3 and λ4 are shorter than Figure 1 the optical paths of the corresponding λ3 and λ4 in the existing four-wave WDM demultiplexer (DeMUX) of the thin-film interference filter. And the linear dimension in the Y direction is only Figure 1 half of that of the four-wave WDM demultiplexer (DeMUX) of the thin-film interference filter.

[0033] Embodiment 2:

[0034] In this embodiment, the first prism 1 and the second prism 2 can be combined into a prism with a thickness of 2 mm, and the corresponding narrow-band thin-film interference filter TFF is appropriately pasted at its output port. This 2-mm-thick prism can perform the same functions as the first prism 1 and the second prism 2, but the assembly is more convenient.

[0035] If the first prism 1 and the second prism 2 are for two waves, the demultiplexer of the present invention is a four-wave demultiplexer. If the first prism 1 and the second prism 2 are for four waves, the demultiplexer of the present invention can be an eight-wave demultiplexer. From Figure 7 it can be seen that the four-wave WDM demultiplexer (DeMUX) based on the thin-film interference filter of the present invention can be conveniently extended to eight waves. The demultiplexer (DeMUX) of the present invention is much more compact than the existing demultiplexer (DeMUX), and the optical path lengths of λ5, λ6, λ7 and λ8 are also shorter. By using a similar method, the demultiplexer of the present invention can also be made into a demultiplexer with more waves.

[0036] The third prism 3 of the present invention and the band-pass thin film interference filter attached thereto serve as a pre-demultiplexer, which divides the light waves of various wavelengths of the incident light beam into two upper and lower beams, each carrying the light waves of the first half and the second half of the wavelengths. The spatial distance between the upper and lower beams can be achieved by appropriately designing the acute angle of the third prism and the prism length. By using the pre-demultiplexing of the third prism 3 and the stack of the first prism 1 and the second prism 2, the demultiplexer of the present invention can be made more compact in terms of device width than the existing thin film interference filter demultiplexer. By using the pre-demultiplexing of the third prism 3 to divide the light waves of various wavelengths of the incident light beam into two upper and lower beams, each carrying the light waves of the first half and the second half of the wavelengths, the light waves of the second half of the wavelengths can have a shorter optical path when completing the spatial separation of the light waves of each final wavelength compared to the optical path that the corresponding light waves have to travel in the existing thin film interference filter demultiplexer, so that the coupling of the device light beam becomes convenient.

Claims

1. A WDM demultiplexer based on a thin-film interference filter, characterized in that: It includes a pre-stage demultiplexer and a post-stage demultiplexer arranged in front of the light beam incident port of the post-stage demultiplexer. The pre-stage demultiplexer divides the incident light beam into two parallel light beams, the upper light beam includes the light beams of the latter half of each wavelength in the incident light beam, and the lower light beam includes the light beams of the former half of each wavelength in the incident light beam. There is a vertical distance when the two parallel light beams are emitted. The post-stage demultiplexer demultiplexes the incident two parallel light beams again; The pre-stage demultiplexer includes a pre-stage prism and a band-pass thin film interference filter arranged at the lower output port of the rear end plane of the pre-stage prism. The band-pass thin film interference filter fully transmits the light beams of the former half of each wavelength in the input light beam and fully reflects the light beams of the latter half of each wavelength; The post-stage demultiplexer includes a post-stage prism and a narrow-band thin film interference filter arranged corresponding to each light beam output port on the rear end plane of the post-stage prism; Both the pre-stage prism and the post-stage prism are in a parallelogram structure; The required vertical distance when the two parallel light beams are emitted is obtained by adjusting the acute angle and length of the pre-stage prism; An anti-reflection film coating area is provided at the light beam incident port of the front end plane of the pre-stage prism and the post-stage prism, and the rest is a high-reflection film coating area; an anti-reflection film coating area is provided at the upper output port of the rear end plane of the pre-stage prism of the pre-stage demultiplexer, and the part between its upper output port and the lower output port is a high-reflection film coating area; The bottom surfaces of the pre-stage prism and the post-stage prism are on the same horizontal plane, and the side surface of the post-stage prism is parallel to the side surface of the pre-stage prism.

2. The WDM demultiplexer based on a thin film interference filter according to claim 1, wherein: The post-stage prism can be composed of two sub-prisms with the same structure and stacked vertically.

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