CN113541799A - Digital-analog combined cascade adjustable silicon-based dispersion compensation device - Google Patents
Digital-analog combined cascade adjustable silicon-based dispersion compensation device Download PDFInfo
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- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2513—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion
- H04B10/2519—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion using Bragg gratings
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- 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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- G02B6/29394—Compensating wavelength dispersion
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- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/0147—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on thermo-optic effects
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Abstract
The invention discloses a digital-analog combined cascade adjustable silicon-based dispersion compensation device. Performing on-chip dispersion compensation on an optical signal by using the dispersion compensation characteristic of a chirped Bragg grating device with gradually changed width, connecting multiple stages of chirped Bragg gratings in series through an optical switch, and separating input and output signals of the gratings in a mode regulation and control mode; the chirped Bragg grating of the heating metal is distributed above the last stage, and the width of the heating metal is gradually changed to realize that the temperature is distributed along the grating in a gradient manner so as to achieve the purpose of precisely regulating and controlling the dispersion compensation value of a single grating through a thermo-optic effect. The invention combines the digital and analog cascade compensation grating layout, and simultaneously realizes the large-range and high-precision optical signal dispersion regulation and control, thereby reducing the error rate of the optical signal in a communication system and improving the quality of the optical signal.
Description
Technical Field
The invention relates to a silicon-based dispersion compensation device, in particular to a digital-analog combined cascade type adjustable silicon-based Bragg grating dispersion compensation device.
Background
Silicon-based optoelectronic integration technology compatible with CMOS standard process is the focus of research in the field of optical communication in recent years. The high refractive index of silicon enables a silicon-based chip to have very strong light beam-binding capacity, the size of the chip is greatly reduced, and the silicon optical chip can integrate active devices including a laser, an amplifier, a detector and a sensor, and passive devices including a coupler, a beam splitter, an optical switch and the like on a single silicon-based chip. All-optical integrated systems are implemented on a single chip. The method has the advantages of high integration level, low energy consumption, low cost and the like, so that the method has excellent application prospect. The important application field of the silicon optical chip is an optical communication system, the optical communication system is a mature basic component module in the communication field, the optical communication technology realizes high-speed, low-loss, large-bandwidth and stable information transmission, and generally, an optical communication device is low in price and plays an important role in daily life of people. The silicon-on-chip device has important application value in the field of optical communication, and the communication transceiver module can realize high-density integration on a silicon-on-chip.
Dispersion is an important factor affecting signal quality in optical communications, which is caused by differences in the propagation speed of light at different frequencies. The dispersion causes distortion of pulse broadening and greatly increases the bit error rate of the signal. With the increase of the signal error rate, the transmission rate and the transmission bandwidth both decrease to different degrees, and finally, the signal is greatly distorted. In order to obtain higher quality signals and longer transmission distances, it is necessary to compensate for the dispersion. The existing widely used compensation device is a fiber Bragg grating dispersion compensation device, the defects of large size and non-adjustability limit the high integration of an optical communication system, and a smaller device is urgently needed to replace the dispersion compensation device to play an important role in the communication system. The dispersion in the communication system has great randomness, and the adjustable dispersion compensation device can greatly improve the convenience of the communication system and ensure the signal quality.
Disclosure of Invention
Aiming at the problems in the background art, the invention aims to provide a digital and analog combined adjustable silicon-based dispersion compensation device, thereby realizing large-range and high-precision optical signal dispersion compensation on a highly integrated silicon-based chip and having important application value.
The invention utilizes the dispersion compensation characteristic of the chirp Bragg grating device with gradually changing width to carry out on-chip large-range dispersion compensation on the optical signal, and the temperature of the heating metal with the same gradually changing width is distributed in a gradient manner along the grating to carry out on-chip small-range dispersion compensation on the optical signal, thereby realizing two-stage dispersion compensation and being more accurate and effective.
The digital grating layout with 2 power numbers of each level and the analog compensation layout for fine adjustment by using the heating electrode can simultaneously achieve the compensation effect with large range and high precision.
The technical scheme adopted by the invention is as follows:
the optical signal dispersion compensation device comprises an input waveguide used for receiving an optical signal input needing dispersion compensation, wherein the input waveguide inputs the received optical signal to a first-stage optical switch;
the method comprises selecting each stage of optical switch for performing current stage compensation on input optical signals, wherein other stages of optical switches except a first stage of optical switch receive the input optical signals which are compensated or not compensated and are received by a previous stage of optical switch;
the method comprises directly inputting optical signals selected by the optical switch without current stage compensation into each stage of connecting waveguide of the next stage of optical switch;
the grating reflection component is used for carrying out dispersion compensation processing on the optical signal which is selected by the optical switch and is subjected to the current-stage compensation;
the optical switch comprises an output waveguide for outputting a complete output optical signal after final compensation, and the output waveguide receives the compensated or uncompensated output optical signal from the last stage of optical switch.
An output end of the nth stage optical switch is connected with 2n-1The grating reflection assembly is connected with one input end of the (n + 1) th-level optical switch, and the other output end of the (n) th-level optical switch is directly connected with the other input end of the (n + 1) th-level optical switch through the connecting waveguide.
One output end of the last stage of optical switch is connected with one output waveguide through a grating reflection assembly, the other output end of the last stage of optical switch is connected with the other output waveguide through a connecting waveguide, and heating metal used for dispersion regulation and control of a thermo-optic effect is arranged on the grating reflection assembly.
Each grating reflection assembly specifically comprises:
the optical signal which is compensated at the current stage is input into a grating input waveguide of the chirped Bragg grating, the input end of the grating input waveguide is used as the input end of a grating reflection component, and the output end of the grating input waveguide is connected to one end of the chirped Bragg grating;
the optical signal which is subjected to the primary compensation is subjected to dispersion compensation and then is reflected back to the chirped Bragg grating of the grating input waveguide;
the optical signal reflected back to the grating input waveguide through the chirp Bragg grating dispersion compensation is separated and received by utilizing mode regulation and control so as to be output, the download waveguide is arranged beside the grating input waveguide and coupled with the grating input waveguide, and the output end of the download waveguide is used as the output end of the grating reflection component.
The mode regulation and control is to utilize the chirped Bragg grating to carry out mode conversion on an input optical signal, convert the optical signal input by the grating input waveguide in one conduction mode into the optical signal in another conduction mode, further reflect the optical signal back to the grating input waveguide, and finally utilize a download waveguide designed for another conduction mode to download and separate to obtain the optical signal reflected back to the grating input waveguide in another conduction mode.
The chirped Bragg grating is a Bragg grating with gradually changed grating section width, so that signal parts with different wavelengths in an input optical signal are reflected in different grating sections, different time delays are generated for the signal parts corresponding to the different wavelengths, and further, time delay differences among the signals corresponding to the different wavelengths are generated, and dispersion compensation is performed.
The widths of all the grating sections of the chirped Bragg grating along the transmission direction of the optical signal are gradually increased or decreased, and the widths of the grating sections are gradually increased along the input direction of the optical signal to realize positive dispersion compensation; the width of the grating section is gradually reduced along the input direction of the optical signal to realize negative dispersion compensation.
The chirped Bragg grating removes time delay spectrum fluctuation caused by sudden change of a connecting part of the straight waveguide and the grating in an apodization mode, and achieves smooth transition from the straight waveguide to grating teeth through the apodized grating side wall.
The heating metal is arranged right above the chirped Bragg grating in the grating reflection assembly connected with the output end of the last stage of optical switch, the heating metal is a whole heating metal structure with nonuniform width along the width change direction of the chirped Bragg grating section, two ends of the heating metal are respectively connected to two ends of a voltage source, so that the heating power generated by heating the metal at different grating sections of the chirped Bragg grating is different, the temperature applied to the chirped Bragg grating is in gradient distribution along the optical signal transmission direction, the waveguide equivalent refractive index of the chirped Bragg grating is also in gradient distribution by utilizing the thermo-optic effect, and the fine adjustment of different wavelength delays and the fine adjustment of a dispersion compensation value are realized.
The input waveguide, the optical switch, the grating input waveguide, the downloading waveguide, the connecting waveguide, the chirped Bragg grating and the output waveguide are all arranged on the substrate silicon and are manufactured by adopting monolithic integration, and the core layer materials are also all silicon.
The invention inputs the signal which needs dispersion compensation into the device through the input waveguide, selects whether the compensation is needed through each stage of optical switch, inputs the signal which needs the compensation of the stage through each stage of grating input waveguide, separates the signal which inputs and outputs the grating by using mode regulation, downloads by using each stage of download waveguide, and inputs the optical signal which does not need the compensation of the stage into the next stage of optical switch through the connecting waveguide. Each stage of chirped Bragg grating is used for realizing dispersion compensation, a thermal field generated by heating metal is used for generating a temperature gradient, precise dispersion regulation and control are carried out according to waveguide refractive index change generated by a thermo-optical effect, and finally a complete optical signal after compensation is output through an output waveguide.
The existing silicon-based Bragg grating dispersion compensator mostly adopts a single grating structure with gradually changed width, and the input and the output need to be separated through a circulator, so that the number of devices in the system is increased, and the use is inconvenient. The adjustable delay amount of the device which only adopts heating metal and uniform Bragg grating for dispersion compensation is very small, and the actual requirement is difficult to meet. The digital-analog combined type adjustable Bragg grating dispersion compensator can obtain a large-range dispersion compensation value by using a cascaded structure, and can be combined with a heating electrode for fine adjustment, thereby meeting the requirements of the large-range dispersion compensation value and high precision.
The invention uses the chirped Bragg grating as a dispersion compensation device, and in the chirped Bragg grating with gradually changed width, optical signals with different wavelengths are reflected in different grating sections to generate delay difference among the signals with different wavelengths, thereby carrying out dispersion compensation.
The invention has the beneficial effects that:
the invention has the advantages of high integration, low loss performance and the like of optical devices on a silicon substrate, realizes the dispersion adjustment function with large range and high precision, and is particularly suitable for a transceiver module in an optical communication system.
The present invention utilizes both digital and analog compensation modes. The digital cascade chirped Bragg grating is used for greatly improving the dispersion compensation value and can be digitally adjusted in a large range. The dispersion compensation effect is greatly improved by using the same grating device. The specially designed heating electrode is used to obtain the analog chirped Bragg grating distributed with the heating electrode to accurately adjust the dispersion compensation value, and the continuous adjustment is realized in a small range. The device structure combining the digital compensation area and the analog compensation area can simultaneously achieve the purpose of large-range and high-precision compensation.
The invention uses the principle of mode regulation to realize the effective separation of the input and the output of the chirped Bragg grating, simultaneously ensures the quality of low loss of signals, avoids the redundancy of an external circulator and improves the integration level of the whole system.
Drawings
FIG. 1 is a schematic diagram of the structure of a digital-analog combined cascaded tunable silicon-based dispersion compensation device under positive dispersion compensation.
FIG. 2 is a schematic diagram of the digital-analog combined cascaded tunable silicon-based dispersion compensation device structure under negative dispersion compensation.
Figure 3 is a schematic diagram of an embodiment of a chirped bragg grating according to the present invention.
Fig. 4 is a schematic diagram of an embodiment of mode conversion in the present invention.
FIG. 5 is an embodiment of the present invention: and (3) a temperature field change diagram of the heating electrode.
In the figure: the optical fiber grating loading device comprises an input waveguide (1), an optical switch (2), a grating input waveguide (3), a download waveguide (4), a connection waveguide (5), a chirped Bragg grating (6), a heating metal (7) and an output waveguide (8). A is an asymmetric Bragg grating structure, and B is a symmetric Bragg grating structure.
Detailed Description
The invention is further illustrated by the following figures and examples.
The specific implementation is shown in fig. 1 and comprises the following components:
the optical signal dispersion compensation device comprises an input waveguide 1 for receiving an optical signal input needing dispersion compensation, wherein the input waveguide 1 inputs the received optical signal to a first-stage optical switch 2;
the optical switch 2 of each stage is used for selecting whether to perform the current stage compensation on the input optical signal, and the optical switches 2 of other stages except the first stage optical switch 2 receive the input optical signal which is subjected to compensation or not subjected to compensation and is received by the previous stage optical switch 2;
the method comprises the steps that optical signals which are selected by an optical switch 2 and not subjected to current-stage compensation are directly input into each stage of connecting waveguide 5 of a next-stage optical switch 2, and the current-stage connecting waveguide 5 receives the optical signals which are selected by the current-stage optical switch 2 and not subjected to the current-stage compensation and directly inputs the optical signals into the next-stage optical switch 2;
the grating reflection assembly receives the optical signal which is selected by the optical switch 2 to carry out the local-level compensation, carries out the dispersion compensation and then inputs the optical signal to the next-level optical switch 2;
the optical switch comprises an output waveguide 8 for outputting a complete output optical signal after final compensation, and the output waveguide 8 receives the compensated or uncompensated output optical signal from the last stage optical switch 2.
The optical switch 2 selectively switches the optical signal input to any one of the two input ends of the optical switch to be output from any one of the two output ends of the optical switch, so that the optical switch 2 at each stage controls the optical signal input to the optical switch to enter the compensation grating at the stage for dispersion compensation or directly enter the optical switch 2 at the next stage through the connecting waveguide 5.
Two input ends of the first-stage optical switch 2 are respectively connected with two input waveguides 1.
An output terminal of the nth stage optical switch 2 is connected to the second stage optical switch 2 via 2n-1The grating reflection assembly is connected with one input end of the (n + 1) th-level optical switch 2, and the other output end of the (n) th-level optical switch 2 is directly connected with the other input end of the (n + 1) th-level optical switch 2 through a connecting waveguide 5. 2n-1The input end and the output end of each grating reflection assembly are sequentially connected end to form a sequential series connection relationship.
All grating reflection assemblies in the device form a digital compensation area, all grating reflection assemblies between every two adjacent stages of optical switches 2 are used as a first-stage grating compensation area, all stages of grating compensation areas jointly form the digital compensation area, the total number of the grating reflection assemblies in all stages of grating compensation areas is increased by 2 times when the total number of the grating reflection assemblies is increased by stages, and the total number of the grating reflection assemblies in the first-stage grating compensation area is 1, so that the purpose of adjusting a large-range dispersion compensation value is achieved.
An output end of the last stage optical switch 2 is connected with an output waveguide 8 through a grating reflection assembly, specifically, an output end of the last stage optical switch 2 is connected with an input end of the grating reflection assembly, an output end of the grating reflection assembly is connected with an output waveguide 8, another output end of the last stage optical switch 2 is connected with another output waveguide 8 through a connecting waveguide 5, and a heating metal 7 for performing precise dispersion micro-regulation and control on a thermo-optic effect is arranged on the grating reflection assembly.
Each grating reflection assembly specifically comprises:
the optical signal selected by the optical switch 2 to be compensated at the current stage is input into the grating input waveguide 3 of the chirped Bragg grating 6, the optical signal selected by the optical switch 2 to be compensated at the current stage is received by the grating input waveguide 3 at the current stage and is directly input into the chirped Bragg grating 6, the input end of the grating input waveguide 3 is used as the input end of the grating reflection component, and the output end of the grating input waveguide 3 is connected to one end of the chirped Bragg grating 6;
the optical signal selected by the optical switch 2 to be compensated at the current stage is subjected to dispersion compensation and then reflected back to the chirped Bragg grating 6 of the grating input waveguide 3, and the other end of the chirped Bragg grating 6 is suspended and vacant;
the optical fiber grating loading device comprises a loading waveguide 4 which separates and receives an optical signal which is reflected to a grating input waveguide 3 through dispersion compensation of a chirped Bragg grating 6 by utilizing mode regulation and control so as to output the optical signal, wherein the loading waveguide 4 is arranged beside the grating input waveguide 3 and coupled with the grating input waveguide 3, and the output end of the loading waveguide 4 is used as the output end of a grating reflection component. The optical signal output by the down-loading waveguide 4 of this stage is sent to the next stage optical switch 2 or the next grating reflection assembly of this stage.
When adjacent grating reflection assemblies are connected, the output end of the down-loading waveguide 4 of the previous grating reflection assembly is connected with the input end of the grating input waveguide 3 of the next grating reflection assembly.
The mode regulation is to perform mode conversion on an input optical signal by using a chirped bragg grating 6, convert an optical signal of one conduction mode input by the grating input waveguide 3 into an optical signal of another conduction mode and further reflect the optical signal back to the grating input waveguide 3, and finally download and separate the optical signal of the other conduction mode reflected back to the grating input waveguide 3 by using a download waveguide 4 designed for the other conduction mode.
As shown in fig. 3, in each stage of chirped bragg grating, the compensated reflection signal is converted into other modes by designing a special grating structure through mode regulation, so that the downloading and separation are facilitated. As shown in fig. 3A, the conversion mode from the even-order mode including the fundamental mode to the odd-order mode requires that the grating teeth have an asymmetric structure and the teeth on both sides are in a staggered layout. As shown in fig. 3B, the conversion mode from the even-order mode including the fundamental mode to the even-order mode or from the odd-order mode to the odd-order mode requires that the grating teeth are symmetrically arranged, i.e., the teeth on both sides of the grating are completely symmetrically arranged.
As shown in fig. 4, a specific structure is designed to separate input and output optical signals by using mode modulation in each stage of chirped bragg grating. Inputting the optical signal with the guided wave mode of mode 1, returning the optical signal which is compensated and converted into the mode 2 through the chirped Bragg grating, downloading the optical signal separation of the mode 2 through the download waveguide, and converting the optical signal separation into the mode 1 again for outputting. By the mode conversion of the input and output optical signals, the band-pass optical signals reflected by the optical signals input by the grating input waveguides at all levels are converted into the reflected signals of different conduction modes, so that the effect of efficiently separating the input and output signals is achieved, and the reflected signals are downloaded by the download waveguides designed for the specific converted modes and output by the download waveguides at all levels.
More specifically, as shown in FIG. 4, in the grating reflective element, the fundamental mode TE0The optical signal of the mode is input into the grating input waveguide 3, is conducted into the chirped Bragg grating 6 through the grating input waveguide 3, is subjected to dispersion compensation and then is changed into a first-order mode TE1The optical signal of the mode, reflected back into the grating input waveguide 3, passes through the structure as a first-order mode TE1Mode-coupled download waveguide 4 converts the first order mode TE1The optical signal of the mode is coupled and separated from the grating input waveguide 3 and then output. TE passing through fundamental mode in each grating reflection assembly0And first order mode TE1The mode separation coupling realizes mode regulation and control, and further realizes dispersion compensation and output of signals. The download waveguide 4 is preset to pass through a first-order mode TE1To the basic mode TE0The switched mode structure of (1).
The chirped bragg grating 6 is a bragg grating with gradually changed grating section width, so that signal parts with different wavelengths in the input optical signal are reflected in different grating sections, different time delays are generated for the signal parts corresponding to the different wavelengths, and further, time delay differences among the signals corresponding to the different wavelengths are generated, thereby performing dispersion compensation.
The chirped bragg grating 6 gradually increases or decreases in width along the optical signal transmission direction, that is, the length direction, and as shown in fig. 1 and shown in the drawing, the width of the grating segment gradually increases along the optical signal input direction along with the length to realize positive dispersion compensation; as shown in fig. 2, the width of the grating segment gradually decreases with length along the input direction of the optical signal to realize negative dispersion compensation, and thus positive dispersion compensation or negative dispersion compensation of dispersion is realized by adjusting the increase or decrease of the width of each grating segment with length.
The chirped bragg grating 6 is specifically implemented as shown in fig. 2, wherein two ends of the chirped bragg grating have different widths, one end of the chirped bragg grating is a narrow end, the other end of the chirped bragg grating is a wide end, the narrow end and the wide end are connected through a middle section with gradually changed widths, the middle section is divided into a plurality of grating sections along a connecting line direction between the narrow end and the wide end, two side surfaces of each grating section are in a convex triangular shape, and the widths of the grating sections are gradually increased or decreased.
When the narrow end is connected to the grating input waveguide 3, positive dispersion compensation is achieved, as shown in fig. 1; when the wide end is connected to the grating input waveguide 3, negative dispersion compensation is achieved, as shown in fig. 2.
The chirped Bragg grating 6 removes time delay spectrum fluctuation caused by sudden change of a connecting part of the straight waveguide and the grating in an apodization mode, and achieves smooth transition from the straight waveguide to grating teeth through the apodized grating side wall.
The chirped bragg grating 6 is implemented as shown in fig. 3, the chirped bragg grating 6 is connected with the input waveguide 3, and the apodization method is that a structure that the tooth depth is gradually changed from zero to a fixed tooth depth is adopted at the front end part of the connection of the grating and the input waveguide, and the tooth depth of the rest part of the grating is kept unchanged.
The heating metal 7 is arranged right above the chirped Bragg grating 6 in the grating reflection assembly connected with the output end of the last stage of optical switch 2, the heating metal 7 is a monolithic heating metal structure with nonuniform width along the grating section width variation direction of the chirped Bragg grating 6, two ends of the widest end and the narrowest end of the heating metal 7 are respectively connected to two ends of a voltage source, the monolithic heating metal 7 applies the same voltage, so that the heating power generated by the heating metal 7 at different grating sections of the chirped Bragg grating 6 is different, the temperature applied to the chirped Bragg grating 6 is in gradient distribution along the optical signal transmission direction, the waveguide equivalent refractive index of the chirped Bragg grating 6 is also in gradient distribution by utilizing the thermo-optical effect, and the fine adjustment of different wavelength delays and the fine adjustment of the dispersion compensation value are realized. In specific implementation, the narrow end of the chirped bragg grating 6 is also arranged at the narrow end of the heating metal 7, the wide end of the chirped bragg grating 6 is also arranged at the wide end of the heating metal 7, and the width gradient direction of the heating metal 7 is the same as that of the chirped bragg grating 6. The narrow heating metal generates a higher heat amount than the wide heating metal at the same current, and the temperature tends to decrease gradually along the light input direction. Specific examples temperature changes are shown in fig. 5.
Therefore, large-range coarse adjustment of dispersion compensation is realized through each grating reflection assembly of each stage of grating compensation area, and small-range fine adjustment of dispersion compensation is realized through the heating metal 7 on the grating reflection assembly connected with the output end of the last stage of optical switch 2.
The input waveguide 1, the optical switch 2, the grating input waveguide 3, the download waveguide 4, the connection waveguide 5, the chirped Bragg grating 6 and the output waveguide 8 are all arranged on the substrate silicon and are manufactured by adopting monolithic integration, and the core layer materials are also all silicon.
Examples of the invention are as follows:
the silicon nanowire optical waveguide, the chirped Bragg grating and the optical switch based on the silicon material are selected, the core layer is made of silicon, the refractive index is 3.4744, the working waveband is a communication waveband near 1550nm, the thickness is 220nm, and the upper cladding layer is made of silicon dioxide. A single mode waveguide with a width of 450nm was chosen as the input output and connecting waveguide. The heating electrode is made of titanium nitride material, the thickness of the heating electrode is 100nm, the sheet resistance of the heating electrode is 12 omega, and a lead part connected out of the heating electrode is made of copper-aluminum alloy.
TE is designed for a single dispersion compensation device for a communication band around 1550nm0The mode is input optical signal, which is reflected by Bragg grating and converted into TE1The mode is reflected and output, and the purpose of mode conversion is achieved by adopting a staggered tooth structure. The chirped Bragg grating with the period of 302nm, the length of 4mm, the center width of 1 mu m and the width variation value of 100nm is selected by calculation. And considering the machining precision, selecting a triangular tooth shape with lower precision requirement as the chirped Bragg grating tooth. Aiming at the time delay spectrum fluctuation caused by the sudden change between the straight waveguide and the grating tooth, a gentle transition area is obtained by adopting an apodization mode, specifically, a cos type window function is used for apodization in the 1/3 part before the length of the grating input end, and the smooth time delay spectrum can be generated while the bandwidth is ensured.
The optical switch part adopts an optical switch composed of two multimode interference regions as a selection device of each stage, and adjusts the phase by a way of thermal modulation to match, thereby achieving the effect of path selection. The heating arm uses a wide waveguide to avoid the effect of random signal errors on the phase. The optical switch determines whether to use the cascaded dispersion compensation device of the stage, and is an important component for carrying out digital dispersion selection.
The width of the heating metal part is gradually changed from 2 mu m to 3 mu m along the input direction of the waveguide by using a titanium nitride electrode with gradually changed width as a heat source, and the temperature of the thermal field is changed from high to low, as shown in figure 4. According to the thermo-optic effect, the equivalent refractive index change value of the chirped Bragg grating changes from large to small along the waveguide input direction, the reflection positions of different wavelengths in the chirped Bragg grating change, and further the time delay spectrum changes, so that the dispersion is precisely regulated and controlled. The temperature is changed by controlling the voltage at the two ends of the heating metal, and the precise regulation and control of the dispersion compensation value are realized.
All the connected heating metals of the heating metal and the thermal dimming switch are adjusted by using the integrated electric control system, so that the function of quickly and conveniently adjusting and controlling the dispersion compensation value is achieved.
Therefore, the implementation of the invention combines the digital and analog cascade compensation grating layout, and realizes the large-range and high-precision optical signal dispersion regulation and control, thereby reducing the error rate of the optical signal in a communication system and improving the quality of the optical signal.
The above-described embodiments are intended to illustrate rather than to limit the invention, and any modifications and variations of the present invention are within the spirit of the invention and the scope of the appended claims.
Claims (10)
1. A digital-analog combined cascade adjustable silicon-based dispersion compensation device is characterized in that:
the optical signal dispersion compensation device comprises an input waveguide (1) used for receiving an optical signal input needing dispersion compensation, wherein the input waveguide (1) inputs the received optical signal to a first-stage optical switch (2);
the optical switch comprises optical switches (2) of different levels for selecting whether to perform current-level compensation on input optical signals, wherein the optical switches (2) of the other levels except the first-level optical switch (2) receive the input optical signals which are subjected to compensation or not subjected to compensation and are received by the previous-level optical switch (2);
comprises connecting waveguides (5) for each stage, which directly input the optical signal selected by the optical switch (2) without the compensation of the current stage into the optical switch (2) of the next stage;
comprises a grating reflection component for carrying out dispersion compensation processing on the optical signal which is selected by the optical switch (2) to carry out the current-stage compensation;
the optical switch comprises an output waveguide (8) used for outputting a complete output optical signal after final compensation, wherein the output waveguide (8) receives the compensated or uncompensated output optical signal from the last stage of optical switch (2).
2. The digital-analog combined cascaded tunable silicon-based dispersion compensation device of claim 1, wherein: an output terminal of the nth stage optical switch (2) is connected via 2n-1The grating reflection assembly is connected with one input end of the (n + 1) th-order optical switch (2), and the other output end of the (n) th-order optical switch (2) is directly connected with the other input end of the (n + 1) th-order optical switch (2) through a connecting waveguide (5).
3. The digital-analog combined cascaded tunable silicon-based dispersion compensation device of claim 1, wherein: one output end of the last stage of optical switch (2) is connected with one output waveguide (8) through one grating reflection assembly, the other output end of the last stage of optical switch (2) is connected with the other output waveguide (8) through a connecting waveguide (5), and the grating reflection assembly is provided with heating metal (7) for dispersion regulation and control through a thermo-optic effect.
4. The digital-analog combined cascaded tunable silicon-based dispersion compensation device of claim 1, wherein: each grating reflection assembly specifically comprises:
the optical signal which is compensated at the current stage is input into a grating input waveguide (3) of a chirped Bragg grating (6), the input end of the grating input waveguide (3) is used as the input end of a grating reflection component, and the output end of the grating input waveguide (3) is connected to one end of the chirped Bragg grating (6);
the optical fiber grating coupler comprises a chirped Bragg grating (6) which is used for reflecting an optical signal subjected to the primary compensation back to a grating input waveguide (3) after carrying out dispersion compensation;
the optical fiber grating loading device comprises a loading waveguide (4) which separates and receives an optical signal which is reflected back to a grating input waveguide (3) through dispersion compensation of a chirped Bragg grating (6) by utilizing mode regulation and control so as to output the optical signal, wherein the loading waveguide (4) is arranged beside the side of the grating input waveguide (3) and is coupled with the grating input waveguide (3), and the output end of the loading waveguide (4) is used as the output end of a grating reflection component.
5. The digital-analog combined cascaded tunable silicon-based dispersion compensation device of claim 4, wherein: the mode regulation and control is to convert the input optical signal into a mode by using a chirped Bragg grating (6), convert the optical signal of one conduction mode input by a grating input waveguide (3) into the optical signal of another conduction mode and further reflect the optical signal back to the grating input waveguide (3), and finally download and separate the optical signal of another conduction mode reflected back to the grating input waveguide (3) by using a download waveguide (4) designed for another conduction mode.
6. The digital-analog combined cascaded tunable silicon-based dispersion compensation device of claim 4, wherein: the chirped Bragg grating (6) is a Bragg grating with gradually-changed grating section width, so that signal parts with different wavelengths in an input optical signal are reflected in different grating sections, different time delays are generated for the signal parts corresponding to the different wavelengths, and further, time delay differences among the signals corresponding to the different wavelengths are generated, and dispersion compensation is performed.
7. The digital-analog combined cascaded tunable silicon-based dispersion compensation device of claim 4, wherein: the widths of all grating sections of the chirped Bragg grating (6) along the transmission direction of the optical signal are gradually increased or decreased, and the widths of the grating sections are gradually increased along the input direction of the optical signal to realize positive dispersion compensation; the width of the grating section is gradually reduced along the input direction of the optical signal to realize negative dispersion compensation.
8. The digital-analog combined cascaded tunable silicon-based dispersion compensation device of claim 4, wherein:
the chirped Bragg grating (6) removes time delay spectrum fluctuation caused by sudden change of a connecting part of the straight waveguide and the grating in an apodization mode, and achieves smooth transition from the straight waveguide to grating teeth through the apodized grating side wall.
9. The digital-analog combined cascaded tunable silicon-based dispersion compensation device of claim 4, wherein: the heating metal (7) is arranged right above the chirped Bragg grating (6) in the grating reflection assembly connected with the output end of the last stage of optical switch (2), the heating metal (7) is a monolithic heating metal structure with non-uniform width along the grating section width change direction of the chirped Bragg grating (6), two ends of the heating metal (7) are respectively connected to two ends of a voltage source, so that heating power generated by heating the metal (7) at different grating sections of the chirped Bragg grating (6) is different, the temperature applied to the chirped Bragg grating (6) is in gradient distribution along the optical signal transmission direction, the waveguide equivalent refractive index of the chirped Bragg grating (6) is also in gradient distribution by utilizing the thermo-optical effect, and fine adjustment of different wavelength delays is realized so as to finely adjust a dispersion compensation value.
10. The digital-analog combined cascaded tunable silicon-based dispersion compensation device of claim 1, wherein: the input waveguide (1), the optical switch (2), the grating input waveguide (3), the download waveguide (4), the connection waveguide (5), the chirped Bragg grating (6) and the output waveguide (8) are all arranged on the substrate silicon and are manufactured by adopting single-chip integration, and core layer materials of the input waveguide, the optical switch and the output waveguide are also all silicon.
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