WO2015089844A1 - 起偏器及偏振调制系统 - Google Patents

起偏器及偏振调制系统 Download PDF

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Publication number
WO2015089844A1
WO2015089844A1 PCT/CN2013/090151 CN2013090151W WO2015089844A1 WO 2015089844 A1 WO2015089844 A1 WO 2015089844A1 CN 2013090151 W CN2013090151 W CN 2013090151W WO 2015089844 A1 WO2015089844 A1 WO 2015089844A1
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Prior art keywords
polarizer
waveguide
adjustable part
controller
polarization
Prior art date
Application number
PCT/CN2013/090151
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English (en)
French (fr)
Inventor
涂鑫
付红岩
刘万元
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华为技术有限公司
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Application filed by 华为技术有限公司 filed Critical 华为技术有限公司
Priority to PCT/CN2013/090151 priority Critical patent/WO2015089844A1/zh
Priority to JP2016541480A priority patent/JP6226496B2/ja
Priority to CN201380081689.9A priority patent/CN105829935A/zh
Priority to EP13899938.8A priority patent/EP3073302B1/en
Publication of WO2015089844A1 publication Critical patent/WO2015089844A1/zh
Priority to US15/187,328 priority patent/US10067363B2/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • 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 
    • G02F1/0136—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  for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation
    • 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
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/126—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind using polarisation effects
    • 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
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2808—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs
    • G02B6/2813—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using a mixing element which evenly distributes an input signal over a number of outputs based on multimode interference effect, i.e. self-imaging
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • 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
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • 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 
    • G02F1/015—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 semiconductor elements having potential barriers, e.g. having a PN or PIN junction
    • G02F1/025—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 semiconductor elements having potential barriers, e.g. having a PN or PIN junction in an optical waveguide structure
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • 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 
    • G02F1/09—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 magneto-optical elements, e.g. exhibiting Faraday effect
    • G02F1/095—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 magneto-optical elements, e.g. exhibiting Faraday effect in an optical waveguide structure
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
    • G02F2201/05—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 multimode
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
    • G02F2201/58—Arrangements comprising a monitoring photodetector
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2202/00—Materials and properties
    • G02F2202/10—Materials and properties semiconductor
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2202/00—Materials and properties
    • G02F2202/10—Materials and properties semiconductor
    • G02F2202/105—Materials and properties semiconductor single crystal Si
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/07—Polarisation dependent

Definitions

  • the present invention relates to communication technologies, and in particular, to a polarizer and a polarization modulation system. Background technique
  • the Photonic Integrated Circuit (PIC) chip is an important optical switching module. Since the fiber cross section is not strictly circular and is affected by other factors such as stress, the polarization state of the optical signal entering the PIC chip from the optical fiber is uncertain. When these optical signals with uncertain polarization states pass directly through the PIC chip, they will be generated. Non-negligible polarization dependent loss (Polarization Dependent Loss, PDL) and Polarization Mode Dispersion (PMD), which reduces the signal-to-noise ratio of the system.
  • PDL Non-negligible polarization dependent loss
  • PMD Polarization Mode Dispersion
  • the PIC chip needs to separately process the optical signals of different polarization states, and use a polarizer or the like to convert the transverse electric wave (Transverse Electric Wave, referred to as TE) and the horizontal in the chip.
  • TE Transverse Electric Wave
  • TM Transverse Magnetic Wave
  • the waveguide polarizer is an indispensable component in the PIC chip. It is based on the different propagation constants of TE and TM modes, different cutoff wavelengths or different coupling lengths. Only one polarization state (TE mode or TM mode) is allowed.
  • the optical signal passes through, while blocking or absorbing the propagation of the optical signal of another polarization state.
  • current waveguide polarizers usually only produce polarized light with a fixed direction. That is, once the waveguide polarizer is designed and processed, only the polarization function of the TE mode or the TM mode can be realized. If optical signals of different polarization states are required, the original optical signals can only be split first, and then polarizers of the desired polarization state are respectively installed on the respective optical paths to realize a complicated system.
  • the present invention provides a polarizer and a polarization modulation system, the purpose of which is to achieve polarization adjustment and a simple structure.
  • a polarizer comprising: at least one MMI multimode waveguide, each One side of the MMI multimode waveguide is connected to the input waveguide, and the other side is connected to the output waveguide; at an end of the MMI multimode waveguide on the side of the output waveguide, an adjustable portion is provided, the adjustable portion Connected to the output waveguide;
  • the polarizer further includes: a controller coupled to the adjustable portion, the controller configured to change a material property of the adjustable portion by control such that the output waveguide outputs optical signals of different polarization states.
  • the material characteristics of the adjustable portion include one or more of the following: a refractive index of the adjustable portion, the adjustable portion Magnetic permeability, light transmittance of the adjustable portion.
  • the material characteristics of the adjustable portion include: an absorption rate of the adjustable portion.
  • the adjustable portion includes an electrode and a p-i-n junction
  • the controller is configured to change a refractive index, a magnetic permeability, and/or a light transmittance of a p-i-n junction region of the adjustable portion by applying an electric field to the electrode.
  • the adjustable portion includes an electrode and a p-i-n junction
  • the controller is configured to change an absorption rate of a p-i-n junction region of the adjustable portion by applying an electric field to the electrode.
  • the pin junction comprises a SiGe alloy, the SiGe alloy having a length ranging from 25 to 35 microns. The width ranges from 5-7 microns.
  • the SiGe alloy has a length of 29 microns and a width of 6.5 microns.
  • the adjustable portion includes a thermo-optic material
  • the controller is configured to change a refractive index, a magnetic permeability, and/or a light transmittance of the thermo-optic material by applying a temperature field to the thermo-optic material;
  • the adjustable portion includes a magneto-optical material;
  • the controller is configured to change a refractive index, a magnetic permeability, and/or a light transmittance of the magneto-optical material by applying a magnetic field to the magneto-optical material.
  • the adjustable portion includes a thermo-optic material
  • the controller is configured to change an absorption rate of the thermo-optic material by applying a temperature field to the thermo-optic material;
  • the adjustable portion includes a magneto-optical material
  • the controller is configured to change an absorption rate of the magneto-optical material by applying a magnetic field to the magneto-optical material.
  • the polarizer when the polarizer includes at least two MMI multimode waveguides, the polarizer includes at least two sub-polarizers Each of the sub-polarizers includes one of the MMI multimode waveguides, one of the input waveguides, and one of the output waveguides; the at least two sub-polarizers are cascaded.
  • a polarization modulation system comprising the polarizer of any one of the inventions, further comprising: an encoder, a polarization beam splitter, a differentiator and a photodetector; the encoder, a polarizer, The polarization beam splitter, the differentiator and the photodetector are connected in sequence.
  • FIG. 1 is a schematic structural view of an embodiment of a polarizer according to the present invention.
  • FIG. 2 is a schematic structural view of another embodiment of a polarizer of the present invention.
  • FIG. 3 is a schematic structural view of still another embodiment of a polarizer of the present invention.
  • Figure 4 is a cross-sectional view taken along line A-A of Figure 3;
  • Figure 5 is a cross-sectional view taken along line BB of Figure 3; 6 is a schematic diagram 1 of a simulation result of a light field in still another embodiment of the polarizer of the present invention;
  • FIG. 7 is a schematic diagram 2 of a simulation result of a light field in still another embodiment of the polarizer of the present invention;
  • FIG. 8 is a polarizer of the present invention;
  • FIG. 9 is a schematic structural view of still another embodiment of a polarizer of the present invention.
  • Figure 10 is a cross-sectional view taken along line C-C of Figure 9;
  • Figure 11 is a cross-sectional view taken along line D-D of Figure 9;
  • FIG. 12 is a schematic structural view of still another embodiment of a polarizer of the present invention.
  • Figure 13 is a cross-sectional view taken along line E-E of Figure 12;
  • Figure 14 is a cross-sectional view taken along line F-F of Figure 12;
  • 15 is a schematic structural view of an embodiment of a polarization modulation system of the present invention. detailed description
  • Fig. 1 is a schematic structural view of an embodiment of a polarizer according to the present invention, and the structure of the lower polarizer is schematically illustrated by Fig. 1.
  • the polarizer comprises: at least one multi-mode interference (MMI) multimode waveguide, and a waveguide, which is a device for transmitting electromagnetic waves in a microwave or optical band, for radio communication, radar, Navigation and other radio fields.
  • MMI multi-mode interference
  • the aforementioned MMI waveguide is a wide waveguide device in which a plurality of propagating light wave modes have an interference effect therein, thereby outputting at different end positions.
  • 1 is a schematic diagram showing a structure including only one MMI multimode waveguide, one side of each MMI multimode waveguide 11 is connected to an input waveguide 12, and the input waveguide 12 is an optical signal input for an arbitrary polarization state; MMI multimode waveguide 11 The other side is connected to the output waveguide 13, which is for outputting an optical signal.
  • an adjustable portion 14 is provided at an end of the MMI multimode waveguide 11 on the side of the output waveguide 13; and, as can be seen from FIG. 1, the adjustable portion 14 is in contact with the output waveguide 13. , see junction A.
  • the MMI multimode waveguide 11, the input waveguide 12, the output waveguide 13, and the tunable portion 14 are fabricated on a semiconductor wafer (eg, silicon on an insulator) by a standard Complementary Metal Oxide Semiconductor (CMOS) process. They are in close contact with each other on the same plane waveguide.
  • the polarizer further includes: The controllers 15 to which the adjustable portion 14 are connected, as shown by the arrows in Fig. 1, are connected to each other by metal wires or metal pins on the chip.
  • the controller 15 can apply a control signal to the adjustable portion 14 (the embodiment of the present invention does not limit the connection manner of the controller 15 and the adjustable portion 14 as long as a control signal can be applied), and controls the material properties of the adjustable portion 14.
  • the output waveguide 13 is caused to output optical signals of different polarization states.
  • the material property of the adjustable portion 14 can be, for example, the refractive index or the absorptivity of the adjustable portion, that is, the change in the refractive index or the absorptivity can change the polarization state of the output optical signal; It is also possible to change other properties (such as magnetic permeability and light transmittance) other than the refractive index or the absorptivity of the adjustable portion, as long as the polarization state of the optical signal output from the output waveguide can be changed.
  • Commonly used tunable materials include alloys of silicon, tri-five compounds, and highly optical nonlinear compounds.
  • An optional example is as follows: When the controller does not apply a control signal, the output waveguide 13 outputs an optical signal of the TE polarization state; when the controller applies a control signal to the adjustable portion 14, the refractive index of the adjustable portion 14 changes. In turn, the output waveguide 13 outputs an optical signal of the TM polarization state, thus achieving polarization tunability of the polarizer.
  • the polarizer may include: at least one MMI multimode waveguide; for example, may include two, three, four or even more MMI multimode waveguides; however, it should be noted that when at least two are included In the case of MMI multimode waveguides, unlike the prior art, the adjustable portions of each MMI multimode waveguide are connected to the controller.
  • FIG. 2 is a schematic structural view of another embodiment of a polarizer of the present invention, and FIG. 2 illustrates an alternative structure when two MMI multimode waveguides are included.
  • the polarizer at this time may include two sub-polarizers, each of which includes an MMI multimode waveguide, an input waveguide, and an output waveguide, and the structure of each sub-polarizer is as shown in FIG. The structure is the same.
  • the two sub-polarizers are cascaded, that is, referring to FIG. 2, the input waveguide of the sub-polarizer on the right side is connected to the output waveguide of the left sub-polarizer, so that the output from the left sub-polarizer is output.
  • the optical signal can be used as the input optical signal of the right sub-polarizer.
  • the sub-polarizers in which the two MMI multimode waveguides are respectively can share a controller, and the controller can apply a first control signal to one of the sub-polarizers and apply to the other sub-polarizer. a second control signal, the first control signal and the second control signal being the same.
  • the controller can go to A sub-polarizer applies a first control signal such that it outputs an optical signal of the TE polarization state, and applies the same second control signal to the other sub-polarizer such that it outputs a polarization-extinction ratio of a better TE polarization state.
  • Optical signal may be a well-known connection method, which is described in detail in this embodiment.
  • the polarizer of the embodiment of the invention provides an output waveguide by setting an adjustable portion in the MMI multimode waveguide and changing a refractive index and an absorptivity, a permeability, a transmittance, and the like of the adjustable portion by using a controller. Outputting optical signals of different polarization states, realizing that the same polarizer can output optical signals of different polarization states.
  • the polarizer can output both the TE polarization state and the TM polarization state optical signal, as opposed to The prior art realizes polarization adjustment; and the polarizer of the present invention can only provide one MMI multimode waveguide between the input waveguide and the output waveguide, and has a simple structure and low cost.
  • the material or the setting method is various.
  • the following are the structures of several optional adjustable parts, and all of them include only one MMI multimode waveguide in the polarizer. For example, the description will be made, but it should be understood that the specific implementation is not limited thereto.
  • Fig. 3 is a cross-sectional view showing a further embodiment of the polarizer of the present invention
  • Fig. 4 is a cross-sectional view taken along line A-A of Fig. 3
  • Fig. 5 is a cross-sectional view taken along line B-B of Fig. 3.
  • the adjustable portion of the present embodiment is provided with an electrode, and the controller can change the absorptance of the adjustable portion by applying an electric field to the electrode; and this embodiment sets the adjustable portion to a structure of a semiconductor p-i-n junction.
  • the controller can be a programmable current source, such as a programmable power module of the NI PXI model or an iC-NZP series chip.
  • the input waveguide, the input waveguide, and the multimode waveguide are each a 3 micrometer thick silicon layer (ie, crystalline silicon c-Si), and below the silicon layer is 2 A micron thick silicon dioxide layer and a few millimeters thick silicon substrate.
  • the input waveguide and the output waveguide of the present embodiment respectively comprise a straight waveguide having a length of 50 micrometers, a height of 3 micrometers, a width of 1 micrometer, a length of 50 micrometers, a height of 3 micrometers, and a width.
  • the multimode waveguide has a length of 602 microns, a height of 3 microns, and a width of 8 microns.
  • the adjustable portion of this embodiment is a rectangular SiGe alloy having a length ranging from 25 micrometers to 35 micrometers and a width ranging from 5 micrometers to 7 micrometers.
  • the SiGe alloy has a length of 29 microns and a width of 6.5 microns.
  • a SiGe alloy as an example, and in other embodiments, it may be other A semiconductor material having an electroabsorption effect, and said length of 25-35 micrometers and width of 5-7 micrometers may also be varied, such as a length of 19-30 micrometers and a width of 4.5-7 micrometers, except that the length is 29 microns and a width of 6.5 microns make the polarizer achieve better extinction ratios.
  • the electrode is located on the top layer of the pin junction.
  • the adjustable portion is an Al/Cu electrode, an n+ doped Si layer, a SiGe alloy, and a p+ doped Si layer from top to bottom, forming a pin of the above semiconductor material.
  • the absorption rate of the SiGe alloy can vary with the applied electric field.
  • the controller applies an applied electric field to the Al/Cu electrode, the absorption coefficient of the SiGe alloy to the incident light, that is, the absorption rate, varies with the applied electric field, thereby changing the polarization.
  • the propagation path of the optical signal in the multimode waveguide realizes the selection function of the polarization state of the output optical signal.
  • FIG. 6 is a schematic diagram 1 of a simulation result of a light field in still another embodiment of the polarizer of the present invention.
  • FIG. 6 is an optical signal of a TE and a TM polarization state of a 1550 nm passing through an MMI type polarizer when an applied electric field is not applied to the controller. Simulation results of the 3D-BPM light field. It can be seen from Fig. 6 that the TE mode is reflected before the output port of the output waveguide, so that the output waveguide is staggered to leak into the cover layer; the self-image point of the TM mode is located at the output port of the output waveguide, so the output waveguide Output. At this time, the polarizer was used as a TM mode polarizer with a polarization extinction ratio of 12 dB.
  • FIG. 7 is a second schematic diagram of a light field simulation result in another embodiment of the polarizer of the present invention.
  • FIG. 7 is a 3D of a light signal of a TE50 and a TM polarization state of a 1550 nm passing through an MMI type polarizer when an applied electric field is applied by the controller.
  • the polarizer acts as a TE mode polarizer with a polarization extinction ratio of 7 dB.
  • FIG. 8 is a schematic diagram of polarization extinction ratio in another embodiment of the polarizer of the present invention, showing a polarization extinction ratio in a state in which an applied electric field is applied on a communication band and an applied electric field is not applied, as can be seen from FIG.
  • the polarization extinction ratio of the TM mode is near l ldB, and the polarization extinction ratio of the TE mode is around 7 dB.
  • Fig. 9 is a cross-sectional view showing a further embodiment of the polarizer of the present invention
  • Fig. 10 is a cross-sectional view taken along line CC in Fig. 9
  • Fig. 11 is a cross-sectional view taken along line DD in Fig. 9.
  • Polarizer and embodiment of the present embodiment the adjustable portion of the MMI multimode waveguide replaces the semiconductor material with variable absorbance in the first embodiment with a material having a variable refractive index of the electric field, so that the adjustable portion becomes a controller. An area where an electric field is applied to the electrode to change the refractive index.
  • the input waveguide and the output waveguide of this embodiment may each be a straight waveguide, a curved waveguide, a strip waveguide, a ridge waveguide, a tapered waveguide, a slit waveguide, or the like.
  • the input waveguide and the output waveguide shown in Fig. 9 are structures of a straight waveguide.
  • the adjustable portion in the polarizer of the present embodiment may also be a structure designed as a p-i-n junction, and may of course not be a p-i-n junction but other structures.
  • the input waveguide, the input waveguide, and the multimode waveguide (MMI multimode waveguide) are crystalline silicon (c-Si), which is still a silicon dioxide layer and a few millimeters thick silicon substrate under the silicon layer.
  • the electrode is located on the top layer, and below the electrode is a semiconductor material whose refractive index can change according to an applied electric field, such as Si or a tri-five compound, etc., these materials can form a refractive index variable region, and the controller changes by applying An applied electric field can change the refractive index of the region.
  • the refractive index variable region under the electrode may include an n+ doped Si layer, a semiconductor material (a material having a variable electric field refractive index), and a p+ doped Si layer.
  • the refractive index of the semiconductor material in the variable refractive index region may vary according to an applied electric field.
  • the controller applies an applied electric field to the electrode
  • the refractive index of the semiconductor material to the incident light is The refractive index changes with the applied electric field, thereby changing the propagation path of the optical signals of different polarization states in the multimode waveguide, and realizing the selection function of the polarization state of the output optical signal.
  • the MMI multimode waveguide, the input waveguide, and the output waveguide of the present embodiment may be made of a material such as a semiconductor, a polymer, a silicon dioxide, or a nitride.
  • the size design of the adjustable portion such as the length and the width of the semiconductor material design, may be specifically set according to the use of the material, which is not limited by the embodiment of the present invention.
  • the controller adjusts the absorptivity or the refractive index of the adjustable portion by applying an electric field.
  • the adjustable portion of the MMI multimode waveguide may include a thermo-optic material (for example, a polymer or the like) or a magneto-optical material (such as yttrium iron garnet), such that the controller can change the thermo-optic material or the magneto-optical material by applying a temperature field to the thermo-optic material or by applying a magnetic field to the magneto-optical material.
  • Refractive index change the absorptivity of the thermo-optic material or magneto-optical material, or change the magnetic permeability of the thermo-optic material or magneto-optical material, or The light transmittance of a thermo-optic material or a magneto-optical material.
  • Fig. 12 is a cross-sectional view showing a further embodiment of the polarizer of the present invention
  • Fig. 13 is a cross-sectional view taken along the line E-E in Fig. 12
  • Fig. 14 is a cross-sectional view taken along the line F-F in Fig. 12.
  • the polarizer of this embodiment is different from the second embodiment in that the electro-refracting index in the second embodiment is replaced by the thermo-optic material having a variable refractive index of the external heating field in the adjustable portion of the MMI multimode waveguide.
  • the variable semiconductor material replaces the ordinary electrode of the second embodiment with a hot electrode such that the adjustable portion becomes a region in which the controller can change the refractive index by controlling the temperature of the hot electrode.
  • thermo-optic material in the present embodiment with a magneto-optical material so that the adjustable portion becomes a region in which the controller can change the refractive index by controlling the magnetic field of the magnetic pole.
  • FIG. 15 is a schematic structural diagram of an embodiment of a polarization modulation system according to the present invention.
  • the system may include sequential connections.
  • the polarization beam splitter 1502, the differentiator 1503, the photodetector 1504, and the encoder 1505 in this embodiment can refer to various existing devices, which will not be described in detail in this embodiment.
  • the encoder 1505, the polarizer 1501, the polarization beam splitter 1502, the differentiator 1503, and the radio and television detection 1504 are sequentially connected, and the connection manner thereof is not limited herein.
  • the signal flow direction of the polarization modulation system can be seen in FIG. 15.
  • the encoder 1505 applies a preset coded signal to the controller, and the controller applies a control signal.
  • the output port of the polarizer outputs two complementary signals of different polarization states (actually, the whole of the polarizer and the controller in FIG. 15 is a polarizer, and the embodiment is for convenience of description and the display in FIG. 15 is performed.
  • the box labeled by the polarizer in Fig. 15 actually includes the MMI multimode waveguide, the input waveguide, and the output waveguide), that is, the TE mode is 101010... and the TM mode 010101....
  • two channels are entered through the polarization beam splitter 1502, and a differential signal having a light intensity of 202020... is generated in the differentiator 1503, and finally detected by the photodetector 1504.
  • the polarization modulation system of this embodiment transmits the same data through two optical signals with different polarization states, and finally uses a differentiator to improve the signal-to-noise ratio of the entire transmission system, and thus tolerates in the PMD.
  • the optical signal noise ratio (OSNR) can be improved by 3dB o.
  • the aforementioned program can be stored in a computer readable storage medium.
  • the program when executed, performs the steps including the above-described method embodiments; and the foregoing storage medium includes: a medium that can store program codes, such as a ROM, a RAM, a magnetic disk, or an optical disk.

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Abstract

　本发明提供一种起偏器及偏振调制系统，其中起偏器，包括：至少一个MMI多模波导，每个所述MMI多模波导的一侧连接输入波导，另一侧连接输出波导；在所述MMI多模波导的位于所述输出波导一侧的端部，设置有可调部，所述可调部与所述输出波导连接；所述起偏器还包括：与所述可调部连接的控制器，所述控制器用于通过控制改变所述可调部的材料特性，使得所述输出波导输出不同偏振态的光信号。本发明实现了偏振可调，结构简单。

Description

起偏器及偏振调制系统
技术领域 本发明涉及通信技术， 尤其涉及一种起偏器及偏振调制系统。 背景技术
电信网干线传输容量的不断扩大及速率的不断提高使得光纤通信成为现 代信息网络的主要传输手段， 光子集成回路 （Photonic Integrated Circuit, 简 称： PIC)芯片是一种重要的光交换模块。 由于光纤截面不是严格的圆形以及 受到应力等其他因素的影响， 从光纤进入到 PIC芯片的光信号偏振态是不确 定的， 当这些偏振态不确定的光信号直接通过 PIC芯片时， 将产生不可忽略 的偏振相关损耗（Polarization Dependent Loss, 简称： PDL)和偏振模态色散 (Polarization Mode Dispersion, 简称： PMD ) ， 从而降低系统的信噪比。 目 前， 为了保证信号的传输质量， 消除偏振的影响， PIC 芯片需要分别处理不 同偏振态的光信号，利用起偏器等技术将芯片中的横电波（Transverse Electric Wave, 简称： TE) 模和横磁波 （ Transverse Magnetic Wave， 简称： TM) 模 分离到两条光路分别处理。 波导起偏器是 PIC芯片中不可或缺的组成元件， 其基于 TE模和 TM模的不同传播常数、 不同截止波长或者不同耦合长度等 原理， 只允许一种偏振态 (TE模或者 TM模)的光信号通过， 而阻断或吸收另 一种偏振态的光信号的传播。
简言之， 目前的波导起偏器通常仅能产生方向固定的偏振光， 即一旦波 导起偏器设计和加工完毕， 就只能实现 TE模或者 TM模的起偏功能。 如果 需要不同偏振态的光信号， 只能将原来的光信号先分束， 然后在各条光路上 分别安装所需偏振态的起偏器， 实现系统复杂。 发明内容 本发明提供一种起偏器及偏振调制系统， 目的是实现偏振可调， 结构 简单。
第一方面， 提供一种起偏器， 包括： 至少一个 MMI多模波导， 每个 所述 MMI多模波导的一侧连接输入波导， 另一侧连接输出波导； 在所述 MMI多模波导的位于所述输出波导一侧的端部， 设置有可调 部， 所述可调部与所述输出波导连接；
所述起偏器还包括： 与所述可调部连接的控制器， 所述控制器用于通 过控制改变所述可调部的材料特性， 使得所述输出波导输出不同偏振态的 光信号。
结合第一方面，在第一种可选的实现方式中，所述可调部的材料特性， 包括下述的一种或多种： 所述可调部的折射率、 所述可调部的磁导率、 所 述可调部的透光率。
结合第一方面，在第二种可选的实现方式中，所述可调部的材料特性， 包括： 所述可调部的吸收率。
结合第一方面及第一种可选的实现方式， 在第三种可选的实现方式 中， 所述可调部包括电极和 p-i-n结；
所述控制器， 用于通过向所述电极施加电场， 改变所述可调部的 p-i-n 结区域的折射率、 磁导率和 /或透光率。
结合第一方面及第二种可选的实现方式， 在第四种可选的实现方式 中， 所述可调部包括电极和 p-i-n结；
所述控制器， 用于通过向所述电极施加电场， 改变所述可调部的 p-i-n 结区域的吸收率。
结合第一方面及第三种、 第四种可选的实现方式， 在第五种可选的实 现方式中，所述 p-i-n结包括 SiGe合金，所述 SiGe合金的长度范围为 25-35 微米， 宽度范围为 5-7微米。
结合第一方面及第五种可选的实现方式， 在第六种可选的实现方式 中， 所述 SiGe合金的长度是 29微米， 宽度是 6.5微米。
结合第一方面及第一种可选的实现方式， 在第七种可选的实现方式 中， 所述可调部包括热光材料；
所述控制器， 用于通过向所述热光材料施加温度场， 改变所述热光材 料的折射率、 磁导率和 /或透光率；
或者，
所述可调部包括磁光材料； 所述控制器， 用于通过向所述磁光材料施加磁场， 改变所述磁光材料 的折射率、 磁导率和 /或透光率。
结合第一方面及第二种可选的实现方式， 在第八种可选的实现方式 中， 所述可调部包括热光材料；
所述控制器， 用于通过向所述热光材料施加温度场， 改变所述热光材 料的吸收率；
或者，
所述可调部包括磁光材料；
所述控制器， 用于通过向所述磁光材料施加磁场， 改变所述磁光材料 的吸收率。
结合第一方面及上述可能的实现方式， 在第九种可选的实现方式中， 当所述起偏器包括至少两个 MMI多模波导时， 所述起偏器包括至少两个 子起偏器， 每个所述子起偏器包括一个所述 MMI多模波导、 一个所述输 入波导以及一个所述输出波导； 所述至少两个子起偏器进行级联。
第二方面， 提供一种偏振调制系统， 包括本发明任一所述的起偏器， 还包括： 编码器、 偏振分束器、 差分器和光电探测器； 所述编码器、 起偏 器、 偏振分束器、 差分器和光电探测器依次连接。
本发明提供的起偏器及偏振调制系统的技术效果是： 通过在 MMI多 模波导中设置可调部， 并通过采用控制器改变可调部的材料特性使得输出 波导输出不同偏振态的光信号， 实现了同一个起偏器能够输出不同偏振态 的光信号， 比如该起偏器既可以输出 TE偏振态的光信号也可以输出 TM 偏振态的光信号， 相对于现有技术实现了偏振可调； 并且， 本发明的起偏 器在输入波导和输出波导之间只设置一个 MMI多模波导即可， 结构简单。 附图说明 图 1为本发明起偏器一实施例的结构示意图；
图 2为本发明起偏器另一实施例的结构示意图；
图 3为本发明起偏器又一实施例的结构示意图；
图 4为图 3中的 A-A向剖视图；
图 5为图 3中的 B-B向剖视图； 图 6为本发明起偏器又一实施例中的光场仿真结果示意图一； 图 7为本发明起偏器又一实施例中的光场仿真结果示意图二； 图 8为本发明起偏器又一实施例中的偏振消光比示意图；
图 9为本发明起偏器又一实施例的结构示意图；
图 10为图 9中的 C-C向剖视图；
图 11为图 9中的 D-D向剖视图；
图 12为本发明起偏器又一实施例的结构示意图；
图 13为图 12中的 E-E向剖视图；
图 14为图 12中的 F-F向剖视图；
图 15为本发明偏振调制系统实施例的结构示意图。 具体实施方式
本发明实施例对起偏器的结构进行了改进， 设计了一种起偏器， 以实 现同一个起偏器能够输出不同偏振态的光信号。 可以参见图 1， 图 1为本 发明起偏器一实施例的结构示意图， 通过该图 1示意性的简单说明下起偏 器的结构。
其中， 该起偏器包括： 至少一个多模干涉 （Multi-Mode Interference, 简称： MMI) 多模波导， 波导， 指一种在微波或光波段中传输电磁波的装 置， 用于无线电通讯、 雷达、 导航等无线电领域。 前述的 MMI波导是一 种宽波导器件， 可以使多个传播的光波模式在其中发生干涉效应， 从而在 不同的末端位置输出。 图 1先示意仅包括一个 MMI多模波导时的结构， 每个 MMI多模波导 11的一侧连接输入波导 12， 输入波导 12是用于任意 偏振态的光信号输入的； MMI多模波导 11的另一侧连接输出波导 13， 输 出波导 13是用于输出光信号的。
本实施例中， 在 MMI多模波导 11的位于输出波导 13—侧的端部， 设置有可调部 14; 并且， 从图 1中可以看到， 可调部 14是与输出波导 13 接触连接的， 参见连接部位 A。 MMI多模波导 11、 输入波导 12、 输出波 导 13和可调部 14是通过标准的互补金属氧化物 （Complementary Metal Oxide Semiconductor, 简称 CMOS ) 工艺制备在半导体晶圆 （例如绝缘体 上的硅） 上， 彼此位于同一层平面波导上相互紧贴。 该起偏器还包括： 与 可调部 14连接的控制器 15， 参见图 1中的箭头所示， 彼此通过金属导线 或者芯片上的金属引脚连接。控制器 15可以向可调部 14施加控制信号（本 发明实施例不限制控制器 15与可调部 14的连接方式， 只要能施加控制信 号即可） ， 控制改变可调部 14的材料特性， 使得输出波导 13输出不同偏 振态的光信号。
具体的， 上述的可调部 14的材料特性， 例如可以是可调部的折射率 或者吸收率， 也就是说， 折射率或者吸收率的变化能够改变输出的光信号 的偏振态； 具体实施中， 也可以是改变可调部的折射率或者吸收率之外的 其他性质 （例如磁导率和透光率等） ， 只要能改变输出波导输出的光信号 的偏振态即可。 常用的可调部材料包括硅的合金、 三五族化合物以及高光 学非线性化合物等。
一个可选的例子如下： 当控制器不施加控制信号时， 输出波导 13输 出 TE偏振态的光信号； 当控制器向可调部 14施加控制信号时， 使得可调 部 14的折射率发生变化，进而使得输出波导 13输出 TM偏振态的光信号， 这样就实现了该起偏器的偏振可调性。
本发明实施例中， 该起偏器可以包括： 至少一个 MMI多模波导； 比 如可以包括两个、 三个、 四个甚至更多的 MMI多模波导； 但是需要说明 的是， 当包括至少两个 MMI多模波导时， 与现有技术不同的是， 每一个 MMI多模波导中的可调部都和控制器连接。
图 2为本发明起偏器另一实施例的结构示意图， 该图 2示意了一种可 选的当包括两个 MMI多模波导时的结构。 具体的， 此时的起偏器可以包 括两个子起偏器， 每个子起偏器均包括一个 MMI多模波导、 一个输入波 导以及一个输出波导， 每个子起偏器的结构与图 1所示的结构是相同的。 这两个子起偏器进行级联， 也就是说， 参见图 2， 右侧的子起偏器的输入 波导连接左侧的子起偏器的输出波导， 这样从左侧子起偏器输出的光信号 就可以作为右侧子起偏器的输入光信号。 设置这种多个子起偏器级联结构 的起偏器， 可以使得该起偏器的偏振消光比效果更好。 如图 2所示， 两个 MMI多模波导分别所在的子起偏器可以共用一个控制器，该控制器可以向 其中一个子起偏器施加第一控制信号， 向另一个子起偏器施加第二控制信 号， 该第一控制信号和第二控制信号是相同的。 例如， 控制器可以向其中 一个子起偏器施加第一控制信号， 使得其输出 TE偏振态的光信号， 而向 另一个子起偏器施加相同的第二控制信号， 使得其输出偏振消光比更好的 TE偏振态的光信号。 应理解， 多个子起偏器的连接方式可为公知的连接 方式， 本实施例本对其进行详细说明。
本发明实施例的起偏器， 通过在 MMI多模波导中设置可调部， 并通 过采用控制器改变可调部的折射率和吸收率、 磁导率、 透光率等材料特性 使得输出波导输出不同偏振态的光信号， 实现了同一个起偏器能够输出不 同偏振态的光信号， 比如该起偏器既可以输出 TE偏振态的光信号也可以 输出 TM偏振态的光信号， 相对于现有技术实现了偏振可调； 并且， 本发 明的起偏器在输入波导和输出波导之间只设置一个 MMI多模波导即可， 结构简单， 成本低。
对于起偏器中的可调部， 其设置材料或者说设置方式是多种多样的， 下面列举几种可选的可调部的结构， 并且均以起偏器中仅包括一个 MMI 多模波导为例进行说明， 但是应该理解的是， 具体实施中并不局限于此。
实施例一
图 3为本发明起偏器又一实施例的结构示意图， 图 4为图 3中的 A-A 向剖视图， 图 5为图 3中的 B-B向剖视图。本实施例的可调部中设置了电 极， 控制器可以通过向电极施加电场改变可调部的吸收率； 并且本实施例 将可调部设置成半导体 p-i-n结的结构。 其中控制器可以是可编程电流源， 例如 NI PXI型号的可编程电源模块或者 iC-NZP系列芯片等。
结合图 3-图 5所示， 具体的， 输入波导、 输入波导和多模波导 （MMI 多模波导） 均是 3微米厚的硅层 （即晶体硅 c-Si) ， 在硅层下面是 2微米 厚的二氧化硅层和几毫米厚的硅衬底。 为了降低模式失配造成的插入损 耗， 本实施例的输入波导和输出波导分别包含长度为 50微米， 高度为 3 微米， 宽度为 1微米的直波导以及长度为 50微米， 高度为 3微米， 宽度 从 1微米线性增长到 1.5微米的锥形波导。 多模波导的长度是 602微米， 高度是 3微米， 宽度是 8微米。
本实施例的可调部， 是长度范围为 25微米至 35微米， 宽度范围为 5 微米至 7微米的矩形 SiGe合金。 可选地， SiGe合金的长度是 29微米， 宽 度是 6.5微米。 当然此处是以 SiGe合金为例， 具体实施中也可以是其他具 有电吸收效应的半导体材料， 并且所述的长度为 25-35微米和宽度为 5-7 微米也是可以改变的， 比如长度是 19-30微米， 宽度是 4.5-7微米， 只是 上述的长度为 29微米和宽度为 6.5微米能够使得该起偏器实现的消光比效 果更好。 本实施例中， 电极位于 p-i-n结的顶层， 具体的， 可调部从上到 下依次是 Al/Cu电极， n+掺杂 Si层， SiGe合金和 p+掺杂 Si层，形成 p-i-n 上述的半导体材料 SiGe合金的吸收率可以随外加电场的不同而变化， 当控制器给 Al/Cu电极施加外加电场时， SiGe合金对入射光的吸收系数即 吸收率随外加电场的不同而变化， 从而改变不同偏振态的光信号在多模波 导中的传播路径， 实现了输出光信号的偏振态的选择功能。
图 6为本发明起偏器又一实施例中的光场仿真结果示意图一， 该图 6 是控制器未施加外加电场时， 1550nm的 TE和 TM偏振态的光信号通过 MMI型起偏器的 3D-BPM的光场的仿真结果。 从图 6中可以看到， TE模 在输出波导的输出端口前发生反射， 因此错开了输出波导从而泄露到覆盖 层中； TM模的自成像点正好位于输出波导的输出端口， 因此从输出波导 输出。 此时该起偏器作为一个 TM模偏振器， 偏振消光比为 12dB。
图 7为本发明起偏器又一实施例中的光场仿真结果示意图二， 该图 7 是控制器施加外加电场时， 1550nm的 TE和 TM偏振态的光信号通过 MMI 型起偏器的 3D-BPM的光场的仿真结果。 从图 7中可以看到， 由于外加电 场下 SiGe合金的强吸收特性， 反射的 TE模光的部分能量被吸收， 剩余的 能量从输出端口输出； TM模在传输过程中被 SiGe合金几乎全部吸收， 因 此无法从输出波导输出。 此时该起偏器作为一个 TE模偏振器， 偏振消光 比为 7dB。
图 8为本发明起偏器又一实施例中的偏振消光比示意图， 示出了通信 波段上施加外加电场和未施加外加电场两种状态下的偏振消光比， 从图 8 中可以看出， TM模的偏振消光比为 l ldB附近， TE模的偏振消光比为 7dB 附近。
实施例二
图 9为本发明起偏器又一实施例的结构示意图，图 10为图 9中的 C-C 向剖视图， 图 11为图 9中的 D-D向剖视图。 本实施例的起偏器与实施例 一相比，不同点在于， MMI多模波导的可调部中用外加电场折射率可变的 材料替换了实施例一中的吸收率可变的半导体材料， 使得可调部成为控制 器可以通过向电极施加电场改变折射率的区域。 此外， 本实施例的输入波 导和输出波导均可为直波导、 弯曲波导、 条形波导、 脊型波导、 锥形波导 和狭缝波导等。 图 9中示出的输入波导和输出波导为直波导的结构。
结合图 9-图 11所示， 具体的， 本实施例的起偏器中的可调部也可以 是设计为 p-i-n结的结构， 当然也可以不是 p-i-n结而是其他结构。 输入波 导、 输入波导和多模波导 （MMI多模波导） 是晶体硅 （c-Si) ， 在硅层下 面仍然是二氧化硅层和几毫米厚的硅衬底。 本实施例中， 电极位于顶层， 电极下方是折射率可以随外加电场变化的半导体材料，例如是 Si或者是三 五族化合物等， 这些材料可以形成折射率可变区， 控制器通过施加变化的 外加电场可以改变该区域的折射率。 可选的， 该位于电极下方的折射率可 变区可以包括 n+掺杂 Si层， 半导体材料 （外加电场折射率可变的材料） 和 p+掺杂 Si层。
本实施例的起偏器， 所述折射率可变区中的半导体材料的折射率可以 随外加电场的不同而变化， 当控制器给电极施加外加电场时， 半导体材料 对入射光的折射系数即折射率随外加电场的不同而变化， 从而改变不同偏 振态的光信号在多模波导中的传播路径， 实现输出光信号的偏振态的选择 功能。
此外， 本实施例的 MMI多模波导、 输入波导和输出波导， 可以采用 半导体、 聚合物、 二氧化硅和氮化物等材料。 本实施例中， 可调部的尺寸 设计， 比如半导体材料设计的长度、 宽度等， 可以随着材料使用的不同而 具体设定， 本发明实施例不做限制。
实施例三
上述的实施例一和实施例二是以控制器通过施加电场的作用来改变 可调部的吸收率或者折射率； 本实施例中， MMI多模波导中的可调部可以 包括热光材料 (例如聚合物等)或者磁光材料 （例如钇铁石榴石等） ， 这样 控制器就可以通过向热光材料施加温度场， 或者通过向磁光材料施加磁 场， 来改变热光材料或者磁光材料的折射率， 或者， 改变热光材料或者磁 光材料的吸收率， 或者， 改变热光材料或者磁光材料的磁导率， 或者， 改 变热光材料或者磁光材料的透光率。
图 12为本发明起偏器又一实施例的结构示意图， 图 13为图 12中的 E-E向剖视图， 图 14为图 12中的 F-F向剖视图。 本实施例的起偏器与实 施例二相比，不同点在于， MMI多模波导的可调部中用外加热场折射率可 变的热光材料替换了实施例二中的电致折射率可变的半导体材料， 用热电 极替换了实施例二中的普通电极， 使得可调部成为控制器可以通过控制热 电极的温度改变折射率的区域。
此外， 还可以用一对磁极替换本实施例中的热电极， 用磁光材料替换 本实施例中的热光材料， 使得可调部成为控制器可以通过控制磁极的磁场 改变折射率的区域。
实施例四
基于本发明实施例所述的起偏器， 本实施例提供了一种偏振调制系 统， 图 15为本发明偏振调制系统实施例的结构示意图， 如图 15所示， 该 系统可以包括依次连接的起偏器 1501、 偏振分束器 1502、 差分器 1503、 光电探测器 1504和编码器 1505 ; 其中， 起偏器 1501可以是本发明任意实 施例所述的起偏器。
本实施例中的偏振分束器 1502、 差分器 1503、 光电探测器 1504和编 码器 1505可参照现有的各种器件， 本实施例不对其进行详细说明。 此外， 上述编码器 1505、 起偏器 1501、 偏振分束器 1502、 差分器 1503、 和广电 探测其 1504依次连接， 其连接方式在此不做限定。
具体的， 偏振调制系统的信号流向可参见图 15， 当 45°线偏光从起偏 器的输入端口进入起偏器， 编码器 1505施加预先设定的编码信号给控制 器， 控制器施加控制信号使起偏器的输出端口输出两路不同偏振态的互补 信号 （实际上图 15中的起偏器和控制器组成的整体是起偏器， 本实施例 是为了描述方便进行图 15中的显示， 图 15中的起偏器标示的方框实际上 包括 MMI多模波导、 输入波导和输出波导） ， 即 TE模是 101010...和 TM 模式 010101...。然后通过偏振分束器 1502进入两个信道，并在差分器 1503 中产生光强为 202020...的差分信号， 最后被光电探测器 1504检测。
本实施例的偏振调制系统， 通过两路偏振态不同的光信号传输同一路 数据， 最后采用差分器提高了整个传输系统的信噪比， 因此在 PMD容忍 范围内， 可以改善光信噪比 （Optical Signal Noise Ratio, 简称： OSNR) 3dB o
本领域普通技术人员可以理解： 实现上述各方法实施例的全部或部分 步骤可以通过程序指令相关的硬件来完成。 前述的程序可以存储于一计算 机可读取存储介质中。 该程序在执行时， 执行包括上述各方法实施例的步 骤； 而前述的存储介质包括： ROM、 RAM, 磁碟或者光盘等各种可以存 储程序代码的介质。 最后应说明的是： 以上各实施例仅用以说明本发明的技术方案， 而非 对其限制； 尽管参照前述各实施例对本发明进行了详细的说明， 本领域的 普通技术人员应当理解： 其依然可以对前述各实施例所记载的技术方案进 行修改， 或者对其中部分或者全部技术特征进行等同替换； 而这些修改或 者替换， 并不使相应技术方案的本质脱离本发明各实施例技术方案的范 围。

Claims

权 利 要 求 书
1、 一种起偏器， 其特征在于， 包括： 至少一个 MMI多模波导， 每个 所述 MMI多模波导的一侧连接输入波导， 另一侧连接输出波导；
在所述 MMI多模波导的位于所述输出波导一侧的端部， 设置有可调 部， 所述可调部与所述输出波导连接；
所述起偏器还包括： 与所述可调部连接的控制器， 所述控制器用于通 过控制改变所述可调部的材料特性， 使得所述输出波导输出不同偏振态的 光信号。
2、 根据权利要求 1所述的起偏器， 其特征在于， 所述可调部的材料 特性， 包括下述的一种或多种： 所述可调部的折射率、 所述可调部的磁导 率、 所述可调部的透光率。
3、 根据权利要求 1所述的起偏器， 其特征在于， 所述可调部的材料 特性， 包括： 所述可调部的吸收率。
4、 根据权利要求 2所述的起偏器， 其特征在于，
所述可调部包括电极和 p-i-n结；
所述控制器， 用于通过向所述电极施加电场， 改变所述可调部的 p-i-n 结区域的折射率、 磁导率和 /或透光率。
5、 根据权利要求 3所述的可调部起偏器， 其特征在于，
所述可调部包括电极和 p-i-n结；
所述控制器， 用于通过向所述电极施加电场， 改变所述可调部的 p-i-n 结区域的吸收率。
6、 根据权利要求 4或 5所述的起偏器， 其特征在于， 所述 p-i-n结包 括 SiGe合金， 所述 SiGe合金的长度范围为 25-35微米， 宽度范围为 5-7 微米。
7、 根据权利要求 6所述的起偏器， 其特征在于， 所述 SiGe合金的长 度是 29微米， 宽度是 6.5微米。
8、 根据权利要求 2所述的起偏器， 其特征在于，
所述可调部包括热光材料；
所述控制器， 用于通过向所述热光材料施加温度场， 改变所述热光材 料的折射率、 磁导率和 /或透光率； 或者，
所述可调部包括磁光材料；
所述控制器， 用于通过向所述磁光材料施加磁场， 改变所述磁光材料 的折射率、 磁导率和 /或透光率。
9、 根据权利要求 3所述的起偏器， 其特征在于，
所述可调部包括热光材料；
所述控制器， 用于通过向所述热光材料施加温度场， 改变所述热光材 料的吸收率；
或者，
所述可调部包括磁光材料；
所述控制器， 用于通过向所述磁光材料施加磁场， 改变所述磁光材料 的吸收率。
10、 根据权利要求 1-9任一所述的起偏器， 其特征在于，
当所述起偏器包括至少两个 MMI多模波导时， 所述起偏器包括至少 两个子起偏器， 每个所述子起偏器包括一个所述 MMI多模波导、 一个所 述输入波导以及一个所述输出波导； 所述至少两个子起偏器进行级联。
11、一种偏振调制系统， 其特征在于， 包括权利要求 1-10任一所述的 起偏器， 还包括： 编码器、 偏振分束器、 差分器和光电探测器；
所述编码器、 起偏器、 偏振分束器、 差分器和光电探测器依次连接。
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