CN111175903B - Ultra-wide band adjustable optical filter based on MEMS - Google Patents
Ultra-wide band adjustable optical filter based on MEMS Download PDFInfo
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
- G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/35—Optical coupling means having switching means
- G02B6/351—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements
- G02B6/3512—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements the optical element being reflective, e.g. mirror
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/35—Optical coupling means having switching means
- G02B6/354—Switching arrangements, i.e. number of input/output ports and interconnection types
- G02B6/3544—2D constellations, i.e. with switching elements and switched beams located in a plane
- G02B6/3548—1xN switch, i.e. one input and a selectable single output of N possible outputs
Abstract
The invention belongs to the technical field of optical communication, and particularly discloses an ultra-wide band adjustable optical filter based on MEMS, which comprises: the optical switch comprises a 1 XN port optical switch group, an optical fiber array, an array optical waveguide, a collimating lens, a diffraction grating, a light beam compression unit and an MEMS micro-mirror; the optical switch group is connected with the optical fiber array, one side of the array optical waveguide is in butt coupling with the optical fiber array, the other side of the array optical waveguide is arranged on the front focal plane of the collimating lens, the diffraction grating is arranged on the rear focal plane of the collimating lens, and the diffraction grating and the MEMS micro-mirror are respectively arranged on the front focal plane and the rear focal plane of the light beam compression unit; the working waveband is divided into N sub-wavebands through the combination of the 1 XN port optical switch group and the array optical waveguide, and the extension of the tuning range is realized. The invention can solve the problem of narrow tuning range caused by the limitation of MEMS manufacturing process in the prior art, and particularly, the tuning range of the filter can be expanded to N times by the band segmentation technology.
Description
Technical Field
The invention belongs to the technical field of optical communication, and particularly relates to an ultra-wide band adjustable optical filter based on an MEMS.
Background
Dense Wavelength Division Multiplexing (DWDM) technology is currently the mainstream technology in the field of optical fiber communication. In DWDM optical networks, Tunable Optical Filters (TOF) are one of the important dynamic optical devices used to implement functions such as channel selection, optical performance monitoring, optical channel monitoring, etc. in the wavelength domain. The TOF requirements of optical networks include low loss, narrow bandwidth, sufficient tuning range, and good filtering characteristics, while minimizing device size and reducing manufacturing costs.
Currently, the TOF used in the optical fiber communication System is based on a free-space optical structure, and the wavelength tuning is performed by a Micro-Electro-Mechanical System (MEMS) Micro-mirror. In order to obtain narrow-band filtering characteristics, the size of a light spot incident on a grating needs to be enlarged; the size of the MEMS micro-mirror is limited by the process conditions, and the dispersed light beams from the grating need to be compressed by a lens system before being incident on the MEMS micro-mirror; the compressed dispersed beam has a larger angular dispersion, and the deflection angle of the MEMS micromirror is also subject to process limitations, thereby limiting the wavelength tuning range of TOF.
Therefore, the operating band of the conventional TOF is usually limited to the C band 40nm (i.e. the wavelength range is 1530nm to 1570nm), but as the optical fiber network is upgraded and expanded, the operating band of the TOF also needs to be expanded, and users put forward the requirements of the C + L band 80nm (i.e. the wavelength range is 1530nm to 1610nm), even the S + C + L band 120nm (i.e. the wavelength range is 1490nm to 1610 nm).
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide an ultra-wide band adjustable optical filter based on MEMS (micro electro mechanical systems), and aims to solve the problem of narrow tuning range caused by the limitation of MEMS manufacturing process in the prior art.
The invention provides an ultra-wide band adjustable optical filter based on MEMS, comprising: the optical switch comprises a 1 XN port optical switch group, an optical fiber array, an array optical waveguide, a collimating lens, a diffraction grating, a light beam compression unit and an MEMS micro-mirror; the 1 xN port optical switch group is connected with the optical fiber array through an optical fiber, one side of the array optical waveguide is in butt coupling with the optical fiber array, the other side of the array optical waveguide is arranged on the front focal plane of the collimating lens, the diffraction grating is arranged on the rear focal plane of the collimating lens, and the diffraction grating and the MEMS micro-mirror are respectively arranged on the front focal plane and the rear focal plane of the light beam compression unit; when the MEMS micro-mirror is in work, the working waveband is divided into N sub-wavebands through the combination of the 1 XN port optical switch group and the array optical waveguide, the sub-wavebands where the wavelengths to be filtered out are located control optical signals to enter from the corresponding input ports in the array optical waveguide, the diffraction angle range of the sub-waveband light beams is covered by the tuning range of the MEMS micro-mirror, and therefore the light beams with the target wavelengths in the sub-wavebands are reflected to the output ports, and the tuning range is expanded; wherein N is an integer of 1 or more.
Further, the ultra-wide band tunable optical filter further includes: and the plane reflector is used for reflecting the light collimated by the collimating lens to the diffraction grating.
As a further preference, a plane mirror may be disposed before or after the diffraction grating, the plane mirror being parallel to the diffraction grating for folding the optical path to facilitate downsizing of the module.
Further, the 1 × N port optical switch group includes: a first optical switch and a second optical switch; the first optical switch and the second optical switch are both optical switches with 1 multiplied by N ports; the first optical switch is used for switching the input optical signals of the whole wave band to corresponding ports in the N ports of the array optical waveguide; the second optical switch is used for receiving signals from the N ports of the array optical waveguide.
When the MEMS micro-mirror is in work, the first optical switch exchanges input optical signals from the input port to the ith input port in the optical fiber array, the optical signals are transmitted to the collimating lens from the ith input port of the array optical waveguide, and collimated light beams are diffracted by the diffraction grating and are compressed by the light beam compression unit and then are incident on the MEMS micro-mirror.
Furthermore, the array optical waveguide is provided with N input ports and N output ports; the N input ports enable the emitted light beams to be collimated by the collimating lens and then to be incident on the diffraction grating at different angles due to different positions of the N input ports.
The distribution range of the diffraction angles of the light beams from each input port on the array optical waveguide is different according to the diffraction characteristics of the grating, wherein the diffraction angles of the light beams of only a certain sub-waveband are distributed in the tuning range of the MEMS micro-mirror.
Furthermore, the array optical waveguide is arranged in a single row, and all the waveguides in the array optical waveguide are arranged at unequal intervals; specifically, the mutual spacing of the individual waveguides on one side of the arrayed optical waveguide (the side opposite to the optical fiber array) is the same as the mutual spacing of the optical fibers in the optical fiber array (equal-spacing arrangement), and the mutual spacing of the individual waveguides on the other side of the arrayed optical waveguide (the side opposite to the collimator lens) (non-equal-spacing arrangement) is determined according to the sub-band division condition and the optical system parameters.
As an embodiment of the present invention, in an S + C + L band ultra-wide band tunable optical filter, the entire operating band is divided into three sub-bands: s wave band (1490-1530nm), C wave band (1530-1570nm) and L wave band (1570-1610nm), in order to filter out S, C or some wavelength of L wave band, the optical signal is controlled to be input from the waveguide 32, 34 or 36 on the array optical waveguide 3 through the optical switch of one 1X 3 port, the MEMS micro-mirror 8 reflects the light beam of some selected wavelength of S, C or L wave band to the waveguide 31, 33 or 35 on the array optical waveguide 3, and finally the light beam is switched to the output port 13 through the optical switch of the second 1X 3 port.
Furthermore, the collimating lens is used for collimating the input signal into parallel light, and the collimating lens is a single spherical lens, an aspheric lens or a double-cemented lens.
Furthermore, the main function of the beam compression unit is embodied in two aspects, namely, the mirror surface size of the MEMS micro-mirror is small, so that the beam diffracted by the diffraction grating can be incident on the MEMS micro-mirror after being compressed by the beam compression unit; and the angular dispersion (namely, the diffraction angles of the light beams with different wavelengths) of the optical signals are increased after passing through the compression unit.
The light beam compression unit comprises a first lens and a second lens, the first lens is used for compressing light beams, the second lens is used for collimating the light beams, and the distance between the two lenses is the sum of focal lengths of one time of the two lenses.
Further, a diffraction grating for realizing dispersion splitting is provided between the collimator lens and the beam compressing unit at one focal length of the first lens in the collimator lens and the beam compressing unit.
As a further preference, the diffraction grating may be a transmission grating.
Furthermore, the MEMS micromirror is located at one focal length of the second lens, and the rotation of the MEMS micromirror changes the angle of the reflected light, thereby realizing wavelength selection. Specifically, the MEMS micro-mirror can be controlled to rotate by changing voltage, current and the like through a driving circuit.
Compared with the prior art, the technical scheme of the invention has the advantages that due to the combination of the 1 XN port optical switch and the array optical waveguide, optical signals of different wave bands are incident on the diffraction grating from the optical waveguides at different positions, so that the incidence angles of the diffraction grating are different, the diffraction angles are the same, and the multiplexing of the compression unit MEMS micro-mirror is realized; under the condition that the size and deflection angle of the MEMS micro-mirror are limited, an operating waveband of more than or equal to 120nm can be obtained.
Drawings
Fig. 1 is a schematic diagram of an ultra-wide band tunable optical filtering structure based on MEMS according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a tunable optical filter with a tuning range covering an S + C + L band and dividing three sub-bands according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an input/output structure based on a 1 XN port optical switch group and an array optical waveguide;
fig. 4 is a schematic diagram of S, C, L time division multiplexing of optical signals in three sub-bands by an input/output structure, where fig. 4(a) shows a configuration state of an optical switch group when operating in an S-band, fig. 4(b) shows a configuration state of an optical switch group when operating in a C-band, and fig. 4(C) shows a configuration state of an optical switch group when operating in an L-band;
fig. 5 is an input/output schematic diagram of S, C, L optical signals of three sub-bands passing through different optical waveguide ports, and fig. 5(a) shows an input/output port and an optical path of an S-band optical signal; FIG. 5(b) shows the input/output ports and optical paths of the C-band optical signals; FIG. 5(c) shows the input/output ports and optical paths of L-band optical signals;
FIG. 6 is a schematic diagram of space division multiplexing on a grating of S, C, L central wavelengths 1510nm, 1550nm and 1590nm of three sub-bands;
FIG. 7 shows dispersion of S, C, L when three sub-bands of light are incident at different angles, the diffraction angle ranges are substantially the same, FIG. 7(a) shows the incident angle and dispersion of the S-band light, FIG. 7(b) shows the incident angle and dispersion of the C-band light, and FIG. 7(C) shows the incident angle and dispersion of the L-band light;
fig. 8 shows the structure of the beam compression unit and the change of the dispersion angle of the front and rear beams.
Wherein like reference numerals refer to like physical meanings and the physical meanings represented by the respective reference numerals are as follows:
the optical switch comprises a 1 XN port optical switch group, an optical fiber array 2, an array optical waveguide 3, a collimating lens 4, a plane mirror 5, a diffraction grating 6, a light beam compression unit 7 and an MEMS micro-mirror 8.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention discloses an ultra-wide band adjustable optical filter based on MEMS, which is based on a combined structure of a 1 XN port optical switch and an array optical waveguide and divides a working band into N sub-bands; and controlling an optical signal to enter the optical system from a corresponding input port in the array optical waveguide according to the condition of a sub-waveband where the wavelength to be filtered out is located, wherein the diffraction angle range of the sub-waveband light beam can be covered by the tuning range of the MEMS micro-mirror, so that the light beam with the target wavelength in the sub-waveband is reflected to an output port. The structure reserves the narrow-band filtering characteristic of the traditional TOF through a wave band segmentation technology, and simultaneously expands the tuning range of the TOF to N times.
The invention provides an ultra-wide waveband adjustable optical filter based on an MEMS, which can be used in an optical performance monitor with a wider working waveband range.
Fig. 1 is a structure of an ultra-wide band tunable optical filter based on MEMS according to an embodiment of the present invention, which only shows a part related to the embodiment of the present invention for convenience of description, and the following detailed description is provided with reference to the accompanying drawings:
the ultra-wide band tunable optical filter based on MEMS comprises: the optical switch set comprises a 1 XN port optical switch set 1, an optical fiber array 2, an array optical waveguide 3, a collimating lens 4, a diffraction grating 6, a light beam compression unit 7 and an MEMS micromirror 81 XN port optical switch set 1, wherein the optical fiber array 2 is connected with the optical fiber array 1 through an optical fiber, the left side of the array optical waveguide 3 is in butt coupling with the optical fiber array 2, the right end face of the array optical waveguide is arranged at the front focal plane of the collimating lens 4, the diffraction grating 6 is arranged on the rear focal plane of the collimating lens 4, and the diffraction grating 6 and the MEMS micromirror 8 are respectively arranged on the front focal plane and the rear.
The optical switch group 1 includes a first optical switch 10 and a second optical switch 11 (both the first optical switch 10 and the second optical switch 11 are optical switches with 1 × N ports); the first optical switch 10 is used for switching the input optical signals of the whole wave band to a proper port in 101-10N on the array optical waveguide 3 as an input; the second optical switch 11 is used for receiving and outputting signals from ports 111-11N on the array optical waveguide 3.
The working process of the adjustable optical filter is as follows: the first optical switch 10 switches an input optical signal from the input port 12 to the ith input port (port number i is between 1 and N) in the optical fiber array 2, the optical signal is transmitted from the ith input port of the array optical waveguide 3 to the collimating lens 4, and the collimated light beam is diffracted by the diffraction grating 6, compressed by the light beam compression unit 7 and then incident on the MEMS micromirror 8. The incident angle of the collimated light beam on the diffraction grating 6 depends on the position of the ith port in the arrayed waveguide 3, and only the light beam of the ith waveband has the diffraction angle within the tuning range of the MEMS micro-mirror 8 according to the diffraction characteristic of the grating. The deflection angle of the MEMS micro-mirror 8 is adjusted, the light beam with a certain wavelength in the ith waveband is reflected to the ith output port of the array optical waveguide 3, and then is switched to the output port 13 by the second optical switch 11 through the optical fiber array 2. The plane mirror 5 is used to fold the optical path to facilitate downsizing of the module.
In order to obtain a narrow linewidth filter characteristic, a large spot of light incident on the diffraction grating 6 is required, and can be realized by the long-focus collimator lens 4. Due to the limitation of the manufacturing process, the mirror surface size of the MEMS micro-mirror 8 is small, so that the light beam diffracted by the diffraction grating 6 can be incident on the MEMS micro-mirror 8 after being compressed by the light beam compression unit 7. The diffraction grating 6 generates angular dispersion to the wide-spectrum light beam, and the angular dispersion of the light beam is larger after being compressed by the light beam compression unit 7. Due to the limitation of the manufacturing process, the deflection angle of the MEMS micro-mirror 8 is also limited, so that only light beams within a limited wavelength range can be reflected to the corresponding output port on the array optical waveguide 3.
The array optical waveguide 3 is provided with N input ports and N output ports, and the emitted light beams are collimated by the collimating lens 4 and then incident on the diffraction grating 6 at different angles due to different positions of the input ports. The diffraction angle distribution range of the light beams from each input port on the array optical waveguide 3 is different according to the diffraction characteristics of the grating, wherein the diffraction angle distribution of the light beams of only a certain sub-waveband is within the tuning range of the MEMS micro-mirror 8. Specifically, after the wide-spectrum light beam from the ith input port on the array optical waveguide 3 is collimated and diffracted, only the light beam of the ith sub-band is distributed in the tuning range of the MEMS micro-mirror 8, and can be reflected by the micro-mirror to the ith output port on the array optical waveguide 3, and further switched to the output port 13 through the 1 × N port optical switch 11.
In summary, the system divides the operating band of the tunable optical filter into N sub-bands and performs time-sharing processing, and the process is briefly described as follows: the input optical signal of the whole waveband is switched to the ith input port on the array optical waveguide 3 through the 1 xN port optical switch 10, after being collimated by the lens 4, the input optical signal is incident on the diffraction grating 6 at an angle corresponding to the ith port, and according to the diffraction characteristics of the grating, only the light beam of the ith waveband with the diffraction angle within the tuning range of the MEMS micro-mirror 8 can be reflected to the ith output port on the array optical waveguide 3, and then is switched to the output port 13 through the 1 xN port optical switch 11. The selection of the sub-bands by the optical switch is time-shared, and at a certain moment, if the passband to be filtered out is located at the jth sub-band, the input port 12 is connected to the jth input port on the optical fiber array 2 by the optical switch 10, and the jth output port on the optical fiber array 2 is connected to the output port 13 by the optical switch 11.
The array optical waveguide 3 can be arranged in a single row, the left side waveguide spacing is the same as the optical fiber spacing in the optical fiber array 2, and the right side waveguide spacing is determined according to the sub-waveband division condition and the optical system parameters. For example, an ultra-wide band tunable optical filter with a tuning range covering an S + C + L band is designed to divide the entire operating band into three sub-bands: an S band (1490 nm-1530 nm), a C band (1530 nm-1570 nm) and an L band (1570 nm-1610 nm). In order to filter out S, C or a certain wavelength of the L-band, the optical signal is controlled to be input from the waveguide 32, 34 or 36 on the arrayed optical waveguide 3 through the optical switch of one 1 × 3 port, the MEMS micro-mirror 8 reflects the light beam of a certain selected wavelength of the S, C or L-band to the waveguide 31, 33 or 35 on the arrayed optical waveguide 3, and finally the light beam is switched to the output port 13 through the optical switch of the second 1 × 3 port.
Preferably, the cross-sectional shape of the optical waveguide in the arrayed optical waveguide 3 can be rectangular, square, circular or elliptical, and is selected according to the requirements of the package design.
Preferably, the collimating lens 4 may adopt a single spherical lens, an aspherical lens or a double cemented lens to collimate the input light beam. The lens with longer focal length is adopted, the collimated light beam with large light spots can be directly obtained, and therefore the narrow-band filtering characteristic is achieved.
Preferably, the right end face of the array optical waveguide 3 is located on the front focal plane of the collimator lens 4.
As an embodiment of the present invention, the ultra-wide band tunable optical filter further includes: and the plane reflector 5 is used for reflecting the light collimated by the collimating lens to the diffraction grating.
As a further preference, the plane mirror 5 may be disposed before or after the diffraction grating, and the plane mirror is parallel to the diffraction grating and is used for folding the optical path, so as to reduce the size of the module; making the system more compact.
In the embodiment of the present invention, the diffraction grating 6 may be a transmissive phase grating, and is disposed between the collimating lens 4 and the beam compressing unit 7, and is located on the back focal plane of the collimating lens 4 and the front focal plane of the first lens 71, and is used for dispersing and splitting light.
The light beam compression unit 7 is located between the diffraction grating 6 and the MEMS micro-mirror 8, and after the large-spot light beam incident on the diffraction grating 6 is compressed, the large-spot light beam can be completely reflected by the MEMS micro-mirror 8 with a smaller area.
Preferably, the first lens 71 and the second lens 72 in the compression unit are selected from a double cemented achromatic lens or an aspherical lens so that the compression unit has a minimum of aberration.
The MEMS micromirror 8 is located on the back focal plane of the second lens 72, and can be controlled to rotate by changing voltage, current and other methods through the driving circuit board, so that the angle of reflected light is changed and the reflected light is directed to an output port, and the purpose of wavelength selection is achieved.
To further illustrate the MEMS-based ultra-wide band tunable optical filter according to the embodiments of the present invention, reference is now made to the following descriptions, taken in conjunction with the accompanying drawings, where N-3 is taken as an example:
the embodiment of the application provides an ultra-wide band adjustable optical filter based on MEMS, which comprises a 1 x 3 port optical switch group 1, an optical fiber array 2, an array optical waveguide 3, a collimating lens 4, a plane mirror 5, a diffraction grating 6, a light beam compression unit 7 and an MEMS micro-mirror 8; the 1 x 3 port optical switch group 1 is connected with the optical fiber array 2 through an optical fiber, the left side of the array optical waveguide 3 is in butt coupling with the optical fiber array 2, the right end face is arranged at the front focal plane of the collimating lens 4, the diffraction grating 6 is arranged on the rear focal plane of the collimating lens 4, the plane reflector 5 is arranged at the front and the rear of the diffraction grating 6, and the diffraction grating 6 and the MEMS micro-mirror 8 are respectively arranged on the front and the rear focal planes of the compression unit 7 according to the width of a designed system.
The optical switch group 1 includes a first optical switch 10 and a second optical switch 11 (both the first optical switch 10 and the second optical switch 11 are optical switches with 1 × 3 ports); the first optical switch 10 is used for switching the input optical signals of the whole wave band to the proper ports in 101-103 on the array optical waveguide 3 as input; the second optical switch 11 is used for receiving and outputting signals from the ports 111-113 on the array optical waveguide 3.
An input optical signal is switched from an input port 12 to an ith input port (port number i is between 1 and 3) in the optical fiber array 2 by the first optical switch 10, the optical signal is transmitted from the ith input port of the array optical waveguide 3 to the collimating lens 4, and the collimated light beam is diffracted by the diffraction grating 6, compressed by the light beam compression unit 7 and then incident on the MEMS micro-mirror 8. The angle of incidence of the collimated beam on the diffraction grating 6 depends on the position of the ith port in the arrayed waveguide 3, whereby the entire operating band is divided into N sub-bands, with only the ith sub-band beam having a diffraction angle within the tuning range of the MEMS micro-mirror 8, depending on the diffraction characteristics of the grating. The deflection angle of the MEMS micro-mirror 8 is adjusted, the light beam with a certain wavelength in the ith sub-waveband is reflected to the ith output port of the array optical waveguide 3, and then the light beam is switched to the output port 13 by the second optical switch 11 through the optical fiber array 2.
For the convenience of describing the present invention, an ultra-wide band tunable optical filter with a tuning range covering S + C + L bands (1490nm to 1530nm, 1530nm to 1570nm, 1570nm to 1610nm) is designed to divide the whole operating band into three sub-bands, i.e., N ═ 3. Fig. 2 is a schematic structural diagram of an ultra-wide band tunable optical filter with a tuning range of 1490 nm-1610 nm and divided into S, C, L three sub-bands.
The input/output structure of the tunable optical filter is designed based on the 1 × 3 port optical switch group 1 and the arrayed optical waveguide 3, as shown in fig. 3. For facilitating the optical fiber connection, the left side of the array optical waveguide 3 is coupled and butted with the optical fiber array 2, so that the left side optical waveguide spacing is the same as that of the optical fiber array 2, and the right side optical waveguide spacing is determined according to the sub-band splitting condition and the optical system parameters. Optical signals input from the port 12 enter the optical system from 3 input ends (respectively marked as 101, 102, 103) of the input port 12 of the first optical switch 10 in a time-sharing manner under the control of the first optical switch 10, and the optical signals selected to be filtered out are output from 3 output ends (respectively marked as 111, 112, 113) of the output port 13 according to the sub-band to which the optical signals belong, and are switched to the output port 13 by the second optical switch 11.
Fig. 4 is a schematic diagram of S, C, L time division multiplexing of optical signals in three sub-bands by an input/output structure. Fig. 4(a) shows the configuration state of the optical switch group when the system operates in the S-band, and when the connection state of the optical switch 10 is ports 12 to 103, the connection state of the second optical switch 11 is ports 111 to 13; fig. 4(b) shows the configuration state of the optical switch set when the system operates in the C-band, and when the connection state of the optical switch 10 is ports 12-102, the connection state of the second optical switch 11 is ports 112-13; fig. 4(c) shows the configuration state of the optical switch group when the system operates in the L-band, and when the connection state of the first optical switch 10 is ports 12 to 101, the connection state of the second optical switch 11 is ports 113 to 13.
Fig. 5 is a schematic diagram of S, C, L input/output of optical signals in three sub-bands through different optical waveguide ports, and fig. 5(a) shows an input/output port and an optical path of an S-band optical signal, which is input from port 32 of the array optical waveguide and output from port 31; fig. 5(b) shows an input/output port and an optical path of a C-band optical signal, which is input from the port 34 of the array optical waveguide and output from the port 33; fig. 5(c) shows an input/output port and an optical path of an L-band optical signal, and the signal is input from the port 36 of the array optical waveguide and output from the port 35.
When the wavelength to be selectively filtered is in the S band, the 1 × 3 port optical switch 10 switches the input optical signal of the entire band to the input port 32 on the array optical waveguide 3, and after the tuning of the MEMS micro-mirror 8 and the subsequent optical path, the optical signal of the selected wavelength in the S band is guided to the output port 31 on the array optical waveguide 3, and after passing through the optical fiber array 2, is switched to the output port 13 through the 1 × 3 port optical switch 11. When the wavelength to be selectively filtered is in the C band, the 1 × 3 port optical switch 10 switches the input optical signal of the entire band to the input port 34 on the array optical waveguide 3, and after the tuning of the MEMS micro-mirror 8 and the subsequent optical path, the optical signal of the selected wavelength in the C band is guided to the output port 33 on the array optical waveguide 3, and after passing through the optical fiber array 2, is switched to the output port 13 through the 1 × 3 port optical switch 11. When the wavelength to be selectively filtered is in the L band, the 1 × 3 port optical switch 10 switches the input optical signal of the entire band to the input port 36 on the array optical waveguide 3, and after the tuning of the MEMS micro-mirror 8 and the subsequent optical path, the optical signal of the selected wavelength in the L band is guided to the output port 35 on the array optical waveguide 3, and after passing through the optical fiber array 2, is switched to the output port 13 through the 1 × 3 port optical switch 11.
The array optical waveguide is located on the front focal plane of the collimating lens, optical signals are input from different ports of the array optical waveguide in a time-sharing manner, after being collimated by the lens 4, the optical signals are incident on the diffraction grating 6 at different angles, and the space division multiplexing condition of the optical beams of each sub-waveband on the diffraction grating 6 is shown in fig. 6. The angle of incidence of the light beam depends on the position of each port on the array optical waveguide 3,the right side waveguide spacing on the array optical waveguide 3 is properly designed, the central wavelength of each sub-band is 1510nm, 1550nm and 1590nm, and the angles i are different1、i2、i3Incident on the diffraction grating 6, while the diffraction angle θ thereof is the same. The diffraction grating is usually a transmission phase grating, which uses the +1 st order diffraction light, and uses the central wavelength λ of each sub-band according to the grating equation (1) under the condition that the diffraction angle θ is the same1＝1510nm、λ2＝1550nm、λ31590nm, the incident angle i corresponding to the ports 32, 34 and 36 on the array optical waveguide 3 is obtained1、i2、i3Then, the position r of each optical waveguide port is calculated according to the formula (2)m. Wherein d is the period of the diffraction grating and f is the focal length of the collimating lens.
d(sinim+sinθ)＝λm(m＝1，2，3)……(1)
rm＝f·im(m＝1,2,3)……(2)
Fig. 7 shows dispersion of S, C, L when three sub-bands of light are incident on the diffraction grating 6 at different angles. When an optical signal is input from the port 32 of the array optical waveguide 3, the optical signal is collimated by the collimating lens 4 and then is at an angle i1An incident diffraction grating 6, in which only the optical signal of the S band has a diffraction angle distribution within a range of Δ θ that can be tuned by the subsequent MEMS micro-mirror 8, according to the diffraction characteristics of the grating, as shown in fig. 7 (a); when an optical signal is input from port 34, at an angle i2An incident grating 6 in which only the optical signal of the C band has a diffraction angle distribution within Δ θ, as shown in fig. 7 (b); when an optical signal is input from port 36, at an angle i3The diffraction angle distribution of the incident grating 6, in which only the optical signal of the L band is present, is within Δ θ, as shown in fig. 7 (c).
The filtering line width of the adjustable optical filter is related to the size of a light spot incident on the grating, in order to obtain the filtering characteristic with a narrow line width, the light spot incident on the diffraction grating 6 is required to be large, and a collimating lens 4 with a long focal length is adopted, so that a collimated light beam with a large light spot can be obtained and is incident on the diffraction grating 6.
Limited by practical manufacturing process, the mirror size of the MEMS micro-mirror 8 is small and the MEMS micro-mirror is very smallThe large light spot light beam on the light emitting grating 6 needs to pass through the light beam compression unit 7 before entering the MEMS micro-mirror 8, and the light spot is compressed and then enters the MEMS micro-mirror 8. The beam compression unit is constructed as shown in FIG. 8 and comprises a first lens 71 with long focal length and a second lens 72 with short focal length, wherein the rear focal plane of the first lens coincides with the front focal plane of the second lens, and the beam compression ratio f1/f2Focal length f dependent on both1、f2。
The light beam is dispersed and expanded by the diffraction grating 6, and the diffraction angle distribution range is delta theta. As can be seen from fig. 8, after the spot size is compressed, the diffraction angle distribution range of the dispersed beam changes, expanding from Δ θ to Δ θ'. The angularly expanded dispersed light beams are incident on the MEMS micro-mirrors 8, the deflection angles of the micro-mirrors are adjusted, and light beams with a certain wavelength are reflected to output ports corresponding to the input ports (the input ports 32, 34, 36 correspond to the output ports 31, 33, 35, respectively) on the array optical waveguide 3, and after passing through the optical fiber array 2, are switched to the output port 13 by the second optical switch 11.
Limited by the practical manufacturing process, the deflection angle of the MEMS micro-mirror 8 is limited in magnitude, and only a limited angular range (corresponding to a limited wavelength range) of the dispersed light beam can be reflected to the output port. The invention realizes the wavelength division by time division and space division multiplexing of the diffraction grating 6, optical signals enter an optical system from different input ports on the array optical waveguide 3 in a time-sharing manner and are incident on the diffraction grating 6 at different angles, and the tuning range of the MEMS micro-mirror 8 only needs to cover a single sub-wave band of which the diffraction angle range is within delta theta; in other words, the optical signals of the respective sub-bands enter the tuning range of the MEMS micro-mirror 8 in a time-sharing manner.
Therefore, the present invention can extend the wavelength tuning range of the tunable optical filter to N times.
Those skilled in the art will readily appreciate that the foregoing is illustrative of the present invention in further detail in connection with the specific embodiments, and that the invention is not to be construed as limited to such specific embodiments. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all such alterations and substitutions are considered to be included in the scope of the invention.
Claims (10)
1. A MEMS-based ultra-wide band tunable optical filter, comprising: the optical switch comprises a 1 XN port optical switch group (1), an optical fiber array (2), an array optical waveguide (3), a collimating lens (4), a diffraction grating (6), a light beam compression unit (7) and an MEMS micro-mirror (8);
the 1 xN port optical switch group (1) is connected with the optical fiber array (2), one side of the array optical waveguide (3) is in butt coupling with the optical fiber array (2), the other side of the array optical waveguide (3) is arranged on the front focal plane of the collimating lens (4), the diffraction grating (6) is arranged on the rear focal plane of the collimating lens (4), and the diffraction grating (6) and the MEMS micro-mirror (8) are respectively arranged on the front focal plane and the rear focal plane of the beam compression unit (7);
when the MEMS micro-mirror is in work, the working waveband is divided into N sub-wavebands through the combination of the 1 XN port optical switch group and the array optical waveguide, the sub-wavebands where the wavelengths to be filtered out are located control optical signals to enter from the corresponding input ports in the array optical waveguide, the diffraction angle range of the sub-waveband light beams is covered by the tuning range of the MEMS micro-mirror, and therefore the light beams with the target wavelengths in the sub-wavebands are reflected to the output ports, and the tuning range is expanded;
wherein N is an integer of 1 or more.
2. The ultra-wide band tunable optical filter of claim 1, wherein said ultra-wide band tunable optical filter further comprises: a plane mirror (5);
the plane mirror (5) is used for reflecting the light collimated by the collimating lens (4) to the diffraction grating (6).
3. The ultra-wide band tunable optical filter of claim 1, wherein said 1 x N port optical switch bank (1) comprises: a first optical switch (10) and a second optical switch (11);
the first optical switch (10) and the second optical switch (11) are both optical switches with 1 xN ports; the first optical switch (10) is used for switching the input optical signals of the whole waveband to the corresponding port in the N ports of the array optical waveguide (3); the second optical switch (11) is used for receiving signals transmitted from N ports of the array optical waveguide (3).
4. The ultra-wide band tunable optical filter according to claim 3, wherein in operation, the first optical switch (10) switches an input optical signal from the input port (12) to the i-th input port of the optical fiber array (2), the optical signal is transmitted from the i-th input port of the array optical waveguide (3) to the collimating lens (4), and the collimated beam is diffracted by the diffraction grating (6), compressed by the beam compression unit (7), and then incident on the MEMS micro-mirrors (8).
5. The ultra-wide band tunable optical filter of any one of claims 1-4, wherein the arrayed optical waveguide (3) has N input ports and N output ports;
the N input ports enable emitted light beams to be collimated by the collimating lens (4) and then to be incident on the diffraction grating (6) at different angles due to different positions of the N input ports.
6. The ultra-wide band tunable optical filter of any one of claims 1-4, wherein the arrayed optical waveguides (3) are arranged in a single row, and the individual waveguides of the arrayed optical waveguides (3) are disposed at non-equal distances from each other.
7. The ultra-wide band tunable optical filter of any one of claims 1-4, wherein said collimating lens (4) is configured to collimate an input signal into parallel light, and said collimating lens (4) is a single spherical lens, an aspheric lens, or a double cemented lens.
8. The ultra-wide band tunable optical filter according to any one of claims 1-4, wherein the beam compression unit (7) comprises a first lens (71) and a second lens (72);
the first lens (71) is used for compressing light beams, the second lens (72) is used for collimating the light beams, and the distance between the two lenses is the sum of focal lengths of one time of the two lenses.
9. The ultra-wide band tunable optical filter according to claim 8, wherein the diffraction grating (6) is arranged between the collimator lens (4) and the beam compression unit (7) at a focal length of one of the collimator lens (4) and the first lens (71) for achieving dispersive splitting.
10. The ultra-wide band tunable optical filter of claim 8, wherein said MEMS micro-mirror (8) is located at one focal length of said second lens (72), and the rotation of said MEMS micro-mirror (8) changes the angle of the reflected light, thereby achieving wavelength selection.
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