WO2016090610A1 - 一种微环谐振器 - Google Patents

一种微环谐振器 Download PDF

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Publication number
WO2016090610A1
WO2016090610A1 PCT/CN2014/093612 CN2014093612W WO2016090610A1 WO 2016090610 A1 WO2016090610 A1 WO 2016090610A1 CN 2014093612 W CN2014093612 W CN 2014093612W WO 2016090610 A1 WO2016090610 A1 WO 2016090610A1
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Prior art keywords
waveguide
identify
microring resonator
polarization
neff
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PCT/CN2014/093612
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English (en)
French (fr)
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胡菁
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华为技术有限公司
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Priority to PCT/CN2014/093612 priority Critical patent/WO2016090610A1/zh
Priority to EP14907637.4A priority patent/EP3223048B1/en
Priority to CN201480011378.XA priority patent/CN106461869B/zh
Publication of WO2016090610A1 publication Critical patent/WO2016090610A1/zh
Priority to US15/618,356 priority patent/US10359568B2/en

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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
    • G02B6/10—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
    • G02B6/12007—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 forming wavelength selective elements, e.g. multiplexer, demultiplexer
    • 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
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/125—Bends, branchings or intersections
    • 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
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/1223—Basic optical elements, e.g. light-guiding paths high refractive index type, i.e. high-contrast waveguides
    • 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
    • G02B6/27—Optical coupling means with polarisation selective and adjusting means
    • 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
    • G02B6/27—Optical coupling means with polarisation selective and adjusting means
    • G02B6/2753—Optical coupling means with polarisation selective and adjusting means characterised by their function or use, i.e. of the complete device
    • G02B6/2773—Polarisation splitting or combining
    • 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
    • G02B6/29331—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 evanescent wave coupling
    • G02B6/29335—Evanescent coupling to a resonator cavity, i.e. between a waveguide mode and a resonant mode of the cavity
    • G02B6/29338—Loop resonators
    • 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
    • G02B6/29397—Polarisation insensitivity
    • 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
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12116—Polariser; Birefringent
    • 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
    • G02B6/27—Optical coupling means with polarisation selective and adjusting means
    • G02B6/2726—Optical coupling means with polarisation selective and adjusting means in or on light guides, e.g. polarisation means assembled in a light guide
    • G02B6/274—Optical coupling means with polarisation selective and adjusting means in or on light guides, e.g. polarisation means assembled in a light guide based on light guide birefringence, e.g. due to coupling between light guides

Definitions

  • the present invention relates to the field of optical communications, and in particular to a microring resonator.
  • the method of reducing the volume of the optical components mainly uses an integrated waveguide device having a high refractive index difference instead of the conventional discrete optical component.
  • commonly used high refractive index difference waveguide materials are silicon, silicon nitride, polymers (for example, SU8), and III-V compound semiconductor materials such as InP and the like.
  • Optical devices composed of these materials have a very strong polarization dependence, that is, Transverse Electric (TE) polarized light has different operating wavelengths as Transverse Magnetic (TM) polarized light.
  • TE Transverse Electric
  • TM Transverse Magnetic
  • the optical device on the receiving side is required to have polarization insensitivity characteristics, that is, the operating wavelengths of the two polarizations of TE and TM are required to be the same.
  • FIG. 1 shows a schematic structural view of a microring resonator provided by the prior art.
  • the input light of unknown polarization state is separated into TE and TM light by Polarization Splitter (PS), and processed by a microring resonator with the same working wavelength, respectively, and then polarized beam is used.
  • Polarization Combiner (PC) performs polarization combining. Since the operating wavelengths of the two microrings are required to be the same, and the constituent waveguides have a strong polarization dependence, since their radii are not the same, they are R and R', respectively. In order to make the two microrings not coupled to each other, the minimum distance between the microrings is set to Gap.
  • the spacing between devices is limited by the radius of the resonator, at least 2*R+2*R'+Gap, which cannot be further reduced.
  • the disadvantage of the solution in Figure 1 is that two sets of devices are required, and the control complexity and power consumption are doubled.
  • the polarization-dependent operating wavelength difference between TE and TM is limited by the current process level and the minimum distance between micro-rings, which cannot meet the requirements of Dense Wavelength Division Multiplexing (DWDM) applications. .
  • DWDM Dense Wavelength Division Multiplexing
  • embodiments of the present invention provide a microring resonator that solves the technical problem that the prior art microring resonator has a strong polarization dependence.
  • an embodiment of the present invention discloses a microring resonator including a first straight waveguide, a second waveguide, and a third waveguide, wherein the second waveguide and the third waveguide form a closed loop waveguide or form an unsealed a closed spiral, the annular waveguide being coupled to the first straight waveguide, the fourth waveguide, the fourth waveguide being arcuate, coupled to the third waveguide, a polarization beam splitter, wherein the polarization beam splitter One end of the device is connected to the fourth waveguide, and one end is connected to the second waveguide of the ring waveguide.
  • Neff is used to identify the effective refractive index
  • Neff(TE) is used for Identifies the effective refractive index of the transverse electric mode TE
  • L is used to identify the length of the waveguide
  • L (second waveguide) is used to identify the length of the second waveguide
  • m is used to identify the resonant level
  • ⁇ is used to identify the wavelength
  • ⁇ (TE ) is used to identify the wavelength of the transverse mode TE light.
  • the first straight waveguide is one, two or more.
  • one or both of the second waveguide, the third waveguide, and the fourth waveguide are curved waveguides .
  • the second waveguide, the third waveguide, and the fourth waveguide are One or a part or all of them are straight waveguides.
  • the microring resonator further includes a microelectrode coupled to the third waveguide Between the fourth waveguide and the fourth waveguide.
  • an absorbing layer is deposited on the second waveguide, the absorbing layer material being germanium, silicon, One or a combination of tin, or a III-V compound material.
  • the cross-sectional structure of the first waveguide, the second waveguide, the third waveguide, and the fourth waveguide is a strip Shape, or ridge type.
  • a microring resonator in a second aspect, includes a first straight waveguide, a second waveguide, and a third waveguide, wherein the second waveguide and the third waveguide form an arc shape, the arcuate waveguide and the first A waveguide coupler, a polarization combiner, the polarization combiner and the arcuate waveguide form a closed loop.
  • Neff is used to identify the effective refractive index
  • Neff (TE) is used to identify the effective refractive index of the transverse electric mode TE
  • L is used to identify the waveguide Length
  • L (closed loop perimeter) is used to identify the perimeter of the closed loop formed by the second waveguide, the third waveguide, and the polarization combiner
  • m is used to identify the resonant level
  • ⁇ is used to identify the wavelength
  • ⁇ (TE) is used to identify the wavelength of the transverse mode TE light.
  • the first straight waveguide is one, two or more.
  • one or both of the second waveguide and the third waveguide are curved waveguides.
  • one or both of the second waveguide and the third waveguide are straight waveguides.
  • an absorbing layer is deposited on the second waveguide, the absorbing layer material being germanium, silicon, tin One or a combination thereof, or a III-V compound material.
  • the cross-sectional structure of the first waveguide, the second waveguide, and the third waveguide is a strip shape, or a ridge shape .
  • FIG. 1 is a schematic structural view of a microring resonator provided by the prior art
  • FIG. 2 is a schematic structural diagram of a microring resonator according to Embodiment 1 of the present invention.
  • FIG. 3 is a schematic structural diagram of another microring resonator according to Embodiment 1 of the present invention.
  • FIG. 4 is a schematic structural diagram of another microring resonator according to Embodiment 1 of the present invention.
  • FIG. 5A is a schematic structural diagram of another microring resonator according to Embodiment 1 of the present invention.
  • FIG. 5B is a schematic structural diagram of another microring resonator according to Embodiment 1 of the present invention.
  • FIG. 6 is a schematic structural diagram of another microring resonator according to Embodiment 2 of the present invention.
  • FIG. 7 is a schematic structural diagram of another microring resonator according to Embodiment 2 of the present invention.
  • FIG. 8 is a schematic structural diagram of another microring resonator according to Embodiment 2 of the present invention.
  • FIG. 9A is a schematic structural diagram of another microring resonator according to Embodiment 2 of the present invention.
  • FIG. 9B is a schematic structural diagram of another microring resonator according to Embodiment 2 of the present invention.
  • FIG. 10 is a schematic structural diagram of another microring resonator according to Embodiment 3 of the present invention.
  • FIG. 11 is a schematic structural diagram of another microring resonator according to Embodiment 3 of the present invention.
  • FIG. 12 is a schematic structural diagram of another microring resonator according to Embodiment 3 of the present invention.
  • FIG. 13 is a schematic structural diagram of another microring resonator according to Embodiment 3 of the present invention.
  • Embodiment 1 of the present invention provides a novel microring resonator, in which the working wavelengths of the optical paths of TE and TM are made uniform through a common waveguide and two polarization beam splitters PS.
  • the spacing of the TE and TM optical paths exceeds the limitation of the radius of the microring, and the working wavelength difference caused by the process error can be better resisted.
  • a microring resonator according to Embodiment 1 of the present invention includes a first straight waveguide, a second waveguide, and a third waveguide, wherein the second waveguide and the third waveguide form a closed loop waveguide, and the ring waveguide and the first waveguide a straight waveguide coupled with a fourth waveguide having an arc shape coupled to the third waveguide, a polarization beam splitter, wherein one end of the polarization beam splitter is coupled to the fourth waveguide, one end of which The second waveguide of the ring waveguide is connected.
  • the structure of the microring resonator provided by the embodiment of the present invention is as shown in FIG. 2, and includes two perpendicular waveguides (the parallel lines in FIG. 2 are parallel straight waveguides, and the vertical lines are vertical straight waveguides). And a ring waveguide, two polarization beam splitters PS1 and PS2 coupled to the ring waveguide, and a curved waveguide (also referred to as a single polarization waveguide) connected to the two PSs.
  • the ring waveguide is marked with Arm3 and Arm2 in FIG. 2, wherein the semicircular arc near the bottom is Arm3 and the other half arc is Arm2.
  • the ring waveguide is a unitary body, labeled with Arm3 and Arm2 segments, for purposes of illustrating the principles of the present invention.
  • Figure The circular structure in 2 represents a circular waveguide. It should be noted that the appearance of the circular waveguide may be circular, elliptical, irregularly rounded, etc., and does not necessarily have to be a perfect circle, as long as the starting point and the ending point coincide. A closed annular shape is preferred.
  • the annular waveguide is coupled to two mutually perpendicular straight waveguides in a manner as shown in FIG. 2, the annular waveguide being located in a first quadrant composed of two straight waveguides.
  • two polarization beam splitters are respectively coupled to the ring waveguide, and the two polarization beam splitters are respectively located in a first coupling region of the ring waveguide to the vertical waveguide coupling, and a second coupling region in which the ring waveguide is coupled to the parallel waveguide.
  • the polarization state of the input light is unknown and is entered by the incident port Input on the right side of Figure 2.
  • the ring waveguide is coupled through a coupling region 1 (a coupling region of a ring waveguide and a parallel straight waveguide).
  • TE, TM polarized light is simultaneously present in the coupling region 1, Arm3, and the coupling region 2.
  • the path of the TE polarized light is the path shown by Arm2 in FIG. 2; after the TM polarized light passes through PS1, the polarization state is rotated to TE, and the path of the light is as shown by Arm1 in FIG. route.
  • the input light is transmitted through Arm1 and Arm2, respectively, all the light enters the second polarization beam splitter PS2.
  • the polarization state of the TE polarized light remains unchanged and enters the coupling region 1; the polarization of the original TM polarized light (the polarization state before entering the PS2 is TE) rotates and becomes the TM polarized light, entering the coupling region 1 . Since the light constantly resonates in the "ring", multi-beam interference occurs in the coupling region 1 and the coupling region 2, respectively.
  • the interference-enhanced light in the coupling region 1 is emitted at the exit port (Through exit in Fig. 2); the remaining interference-decomposed light in the coupling region 1 is interference-enhanced in the coupling region 2, and is emitted at the other exit port ( Drop outlet in Figure 2).
  • the optical path difference generated by the difference in length between Arm1 and Arm2 is used to compensate the optical path difference of TE and TM due to polarization in Arm3, thereby ensuring that the optical paths experienced by TE and TM polarized light are consistent, that is, their operation.
  • the same wavelength the purpose of the device polarization is not sensitive. Or to ensure that the single-pass phase changes of TE and TM are consistent, as shown in the following formula:
  • Neff is used to identify the effective refractive index (Neff)
  • neff (TE) is used to identify the effective refractive index of TE
  • L is used to identify the length of the waveguide
  • L (Arm3) is used to identify the length of the Arm3 waveguide
  • m is used to identify the resonant level
  • ⁇ is used to identify the wavelength
  • ⁇ (TE) is used to identify the wavelength of the TE light.
  • a straight waveguide can be used instead of the curved waveguides shown by Arm1 and Arm2 to minimize the polarization conversion phenomenon that may exist in the waveguide.
  • FIG. 3 is a structural schematic diagram of coupling of a plurality of straight waveguides and a ring waveguide.
  • the parallel waveguide in FIG. 3 is the first straight waveguide, the second straight waveguide is inclined to the Drop1 direction, and the Nth straight waveguide is inclined to the DropN direction; the coupling relationship between the circular waveguide and the curved waveguide and the polarization beam splitter Same as Figure 2.
  • the principle of coupling multiple straight waveguides and ring waveguides as shown in Figure 3 is described below:
  • the polarization of the input light is unknown and is entered by the Input port.
  • the microring resonator is coupled through the coupling region 1.
  • Arm3 and the coupling region 2 to the coupling region N+1 there are simultaneously TE, TM polarized light.
  • the path of the TE polarized light is the path shown by Arm2 in FIG. 3; after the TM polarized light passes through the PS1, the polarization state is rotated to TE, and the path is as shown by Arm2 in FIG. route.
  • All light enters the second polarization beam splitter PS2.
  • the polarization state of the TE polarized light remains unchanged into the coupling region 1; the polarization of the original TM polarized light (the TE before entering the PS2) is rotated, and then becomes the TM polarized light and enters the coupling region 1. Since the light constantly resonates in the "ring", multi-beam interference occurs in the coupling region 1 and the coupling region 2 to the coupling region N+1, respectively.
  • the interference-enhanced light in the coupling region 1 is output at the Trough port; the remaining interference-decomposed light in the coupling region 1 is interference-enhanced in the coupling region 2 to the coupling region N+1, and is equally divided by power from Drop1 to DropN. Output.
  • the optical path difference caused by the difference in length between Arm1 and Arm2 compensates for the optical path difference between TE and TM due to polarization in Arm3, thus ensuring that the light paths of TE and TM polarized light are consistent, that is, their working wavelengths are consistent.
  • the purpose of achieving polarization insensibility of the device is achieved; or, the one-way phase change of TE and TM is guaranteed to be consistent, as shown in the following formula:
  • Fig. 4 shows the structure of a microring resonator in which a single straight waveguide is coupled to a semi-annular waveguide.
  • the light whose polarization state is unknown is incident from the input port, and the optical paths passing through the coupling regions 1, PS1, Arm1, and Arm2 are consistent with the working principle of the above embodiment, and are not described herein again.
  • the difference is the working characteristics of PS2.
  • PS2 the polarization state of the TE polarized light is rotated to become the polarization of the TM and enters the coupling region 1; the polarization of the original TM (the polarization state before entering the PS2 is TE) remains unchanged and remains TE, entering the coupling region 1.
  • the average optical path of TE and TM is completely the same, and length compensation is not required in Arm1 and Arm2; Or, ensure that the single-pass phase changes of TE and TM are consistent, as shown in the following formula:
  • straight waveguides can be used instead of the curved waveguides shown by Arm1 and Arm2, and the polarization conversion phenomenon that may exist in the waveguide has been minimized.
  • a micro-electrode may be coupled between the waveguides Arm1 and Arm2, and the micro-electrodes are used to control the two waveguides.
  • the electrode is a yellow curved curve in Fig. 5A.
  • an absorbing layer can also be deposited on the waveguide Arm3, and the function of the polarization insensitive resonance detector can be realized.
  • the absorbing layer is the red curved portion of Figure 5B.
  • the material of the absorbing layer is one of yttrium, silicon, and tin, or a combination thereof, and a group III-V (such as InP, InGaAsP).
  • the absorbing layer material used in the embodiment of the present invention is halved, so that the noise is halved, so the receiving sensitivity can be higher.
  • the silicon germanium-based absorbing materials with high noise noise is the main factor limiting the receiving sensitivity at high temperatures, and the effect of reducing noise to improve the receiving sensitivity is better.
  • the material of the above waveguide may be one or a combination of germanium, silicon, tin, a group III-V material, or silicon nitride, or a polymer.
  • cross-sectional structure of the above waveguide may be a strip-shaped or shallow-Slab ridge waveguide, or different portions may use different waveguide cross-sectional structures.
  • the distance between the two waveguides separately transmitted by different polarizations exceeds the limitation of the radius of the resonator, thereby further reducing the distance between the TE and the TM path, thereby reducing the process error.
  • the resulting polarization-dependent operating wavelength difference of the resonator can meet the more stringent requirements for this indicator.
  • TE and TM to have the same operating wavelength, polarization crosstalk will not increase even if polarization conversion occurs.
  • the waveguide cross-sectional shape can be arbitrarily designed without using a special cross-sectional shape to suppress polarization conversion.
  • Embodiments of the present invention provide another microring resonator including a first straight waveguide, a second waveguide, and a third waveguide, wherein the second waveguide and the third waveguide form a closed loop waveguide or form an unclosed spiral.
  • a ring waveguide coupled to the first straight waveguide, a fourth waveguide, the fourth waveguide being an arc
  • a polarizing beam splitter coupled to the third waveguide, wherein one end of the polarizing beam splitter is coupled to the fourth waveguide, and one end is coupled to the second waveguide of the ring waveguide.
  • the structure of the microring resonator is as shown in FIG. 6, and includes two straight waveguides perpendicular to each other (the parallel lines and the vertical lines in FIG. 6 respectively represent two perpendicular straight waveguides), and an unclosed ring.
  • the waveguide (the two ring waveguides of Arm2 and Arm3 in Fig. 6) has a spiral structure without a closed "ring” shaped waveguide.
  • the appearance of the "ring” may be a circle, an ellipse, an irregular circle with similar edges. The shape or the like does not necessarily have to be a perfect circle), two polarization beam splitters PS1 and PS2 coupled to the ring waveguide, and an Arm1 waveguide connected to the two PSs.
  • the optical path with unknown polarization state from the input port through the coupling region 1, the coupling region 2, PS1, Arm1, and Arm2 is the same as that of the implementation, and will not be described here.
  • the difference is the working characteristics of PS2.
  • PS2 the polarization state of the TE polarized light is rotated into TE polarization and enters the coupling region 1; the polarization of the original TM polarization (the polarization state before entering the PS2 is TE) remains unchanged and remains TE, entering the coupling region 1.
  • the average optical paths of TE and TM are the same, and length compensation is not required in Arm1 and Arm2. Or, ensure that the single-pass phase changes of TE and TM are consistent, as shown in the following formula:
  • Neff is used to identify the effective refractive index (Neff)
  • neff (TE) is used to identify the effective refractive index of TE
  • L is used to identify the length of the waveguide
  • L (Arm3) is used to identify the length of the Arm3 waveguide
  • m is used to identify the resonant level
  • ⁇ is used to identify the wavelength
  • ⁇ (TE) is used to identify the wavelength of the TE light.
  • the interference-enhanced light in the coupling region 1 is outputted at the Through port; the rest interferes with the canceled light in the coupling region 1, and the interference-enhanced light occurs in the coupling region 2, and is outputted in the Drop segment.
  • a straight waveguide can be used instead of the curved waveguide shown by Arm1 and Arm2.
  • Fig. 7 shows a structure in which a straight waveguide and a so-called “ring” (i.e., an unclosed spiral waveguide formed of Arm1 and Arm2) are coupled. As shown in Figure 7, the principle is as follows:
  • the optical path with unknown polarization state passes through the coupling port 1, PS1, Arm1, and Arm2 from the input port.
  • the first principle works the same. The difference is the working characteristics of PS2.
  • PS2 the polarization state of the TE polarized light is rotated to become the polarization of the TM and enters the coupling region 1; the polarization of the original TM (the polarization state before entering the PS2 is TE) remains unchanged and remains TE, entering the coupling region 1.
  • the average optical path of TE and TM is completely the same, and length compensation is not required in Arm1 and Arm2.
  • the one-way phase change of the TE and the TM is consistent, that is, the embodiment of the present invention satisfies the following formula:
  • a straight waveguide can be used instead of the curved waveguide shown by Arm1 and Arm2.
  • Figure 8 shows a structure coupled by a plurality of straight waveguides and a so-called "ring".
  • the optical path of the light having unknown polarization state from the input port through the coupling region 1, the coupling region 2 to the coupling regions N+1, PS1, Arm1, and Arm2 is the same as that of the first embodiment. The difference is the working characteristics of PS2.
  • PS2 the polarization state of the TE polarized light is rotated to become the polarization of the TM and enters the coupling region 1; the polarization of the original TM (the polarization state before entering the PS2 is TE) remains unchanged and remains TE, entering the coupling region 1.
  • the average optical path of the TE and the TM is completely the same, and the length compensation is not required in the Arm1 and the Arm2, or the one-way phase change of the TE and the TM is consistent.
  • the embodiment of the present invention satisfies the following formula:
  • a straight waveguide can be used instead of the curved waveguide shown by Arm1 and Arm2.
  • Embodiments of the present invention provide a scheme in which a PS is built in a resonant loop.
  • TE/TM to have the same operating wavelength, polarization crosstalk is not increased even if polarization conversion occurs.
  • the waveguide cross-sectional shape can be arbitrarily designed without using a special cross-sectional shape to suppress polarization conversion.
  • a Micro Heater can be coupled between Arm1 and Arm2, and this microelectrode can be used to control two single polarizations through the waveguide to take advantage of the portion of the original that might be wasted.
  • the electrode is a yellow curved curve in Fig. 9A.
  • an absorbing layer can also be deposited on the waveguide Arm3, and the function of the polarization insensitive resonance detector can be realized.
  • the material of the absorbing layer is one or a combination of bismuth, silicon, tin, and a group III-V compound semiconductor material (such as InP, InGaAsP).
  • the material of the above waveguide may be one or a combination of germanium, silicon, tin, a group III-V (such as InP, InGaAsP) material, or silicon nitride, or a polymer (such as SU8).
  • germanium silicon, tin, a group III-V (such as InP, InGaAsP) material, or silicon nitride, or a polymer (such as SU8).
  • cross-sectional structure of the above waveguide may be a strip-shaped or shallow-Slab ridge waveguide, or different portions may use different waveguide cross-sectional structures.
  • the distance between the two waveguides separately transmitted by different polarizations exceeds the limitation of the radius of the resonator, thereby further reducing the distance between the TE and the TM path, thereby reducing the process error.
  • the resulting polarization-dependent operating wavelength difference of the resonator can meet the more stringent requirements for this indicator.
  • TE and TM to have the same operating wavelength, polarization crosstalk will not increase even if polarization conversion occurs.
  • the waveguide cross-sectional shape can be arbitrarily designed without using a special cross-sectional shape to suppress polarization conversion.
  • Embodiments of the present invention provide another microring resonator including a first straight waveguide, a second waveguide, and a third waveguide, wherein the second waveguide and the third waveguide form an arc shape, and the arcuate waveguide and the waveguide
  • the first waveguide is coupled to a polarization combiner, and the polarization combiner forms a closed loop with the arcuate waveguide.
  • the structure of the microring resonator is as shown in FIG. 10, and includes two straight waveguides perpendicular to each other (the parallel lines and the vertical lines in FIG. 10 respectively represent two mutually perpendicular straight waveguides) and one unclosed ring waveguide. (or an arc-shaped waveguide composed of Arm2 and Arm3), a polarization combiner PR coupled to the circular arc waveguide, wherein the circular arc waveguide and the PR are coupled to form a closed annular structure .
  • the appearance of the "ring” may be a circular shape, an elliptical shape, an irregular circular shape, or the like, and does not necessarily have to be a perfect circular shape.
  • the polarization of the input light is unknown and is incident by the Input port.
  • the microring resonator is coupled through the coupling region 1.
  • TE, TM polarized light is simultaneously present in the coupling region 1, Arm3, and the coupling region 2.
  • the polarization combiner PR After the polarization combiner PR, the TE polarized light is rotated into TM polarized light, and the TM polarized light is rotated into TE polarized light. Every two weeks The total optical path experienced by each of TE and TM is consistent, and the corresponding working wavelengths are consistent, thereby achieving polarization insensitivity. Among them, the following formula is satisfied:
  • Neff is used to identify the effective refractive index
  • Neff (TE) is used to identify the effective refractive index of the transverse electric mode TE
  • L is used to identify the length of the waveguide
  • L closed ring circumference
  • m is used to identify the resonant level
  • ⁇ is used to identify the wavelength
  • ⁇ (TE) is used to identify the wavelength of the transverse mode TE light.
  • the straight waveguides in the third embodiment may be one or more.
  • Fig. 11 shows a structure in which a straight waveguide and a so-called "ring" are coupled.
  • the polarization of the input light is unknown and is entered by the Input port.
  • the microring resonator is coupled through the coupling region 1.
  • Both TE and TM polarized light are present in the coupling region 1, Arm3.
  • the TE-polarized light is rotated into TM-polarized light
  • the TM-polarized light is rotated into TE-polarized light. Every two weeks, the total optical path experienced by TE and TM is consistent, and the corresponding working wavelengths are consistent, thereby achieving polarization insensitivity.
  • Neff is used to identify the effective refractive index
  • Neff (TE) is used to identify the effective refractive index of the transverse electric mode TE
  • L is used to identify the length of the waveguide
  • L closed ring circumference
  • m is used to identify the resonant level
  • ⁇ is used to identify the wavelength
  • ⁇ (TE) is used to identify the wavelength of the transverse mode TE light.
  • Figure 12 shows a structure coupled by a plurality of straight waveguides and a so-called "ring”.
  • the polarization of the input light is unknown and is entered by the Input port.
  • the microring resonator is coupled through the coupling region 1.
  • TE, TM polarized light is simultaneously present in the coupling region 1, Arm3, and the coupling region 2 to the coupling region N+1.
  • the TE-polarized light is rotated into TM-polarized light
  • the TM-polarized light is rotated into TE-polarized light. Every two weeks, TE and TM have the same total optical path, and the corresponding working wavelengths are consistent, thus achieving polarization insensitivity. sense.
  • the interference-enhanced light in the coupling region 1 is output at the Through port.
  • the remaining interference-destroying light in the coupling region 1 is interference-enhanced in the coupling region 2 to the coupling region N+1, and is equally divided by power from Drop1 to DropN.
  • an absorbing layer can also be deposited on the waveguide Arm3, and the function of the polarization insensitive resonance detector can be realized.
  • the material of the absorbing layer is one of yttrium, silicon, and tin, or a combination thereof, and a group III-V (such as InP, InGaAsP).
  • the absorbing layer material used in the embodiment of the present invention is halved, so that the noise is halved, so the receiving sensitivity can be higher.
  • the material of the above waveguide may be one or a combination of germanium, silicon, tin, a group III-V (such as InP, InGaAsP) material, or silicon nitride, or a polymer.
  • germanium silicon, tin, a group III-V (such as InP, InGaAsP) material, or silicon nitride, or a polymer.
  • cross-sectional structure of the above waveguide may be a strip-shaped or shallow-Slab ridge waveguide, or different portions may use different waveguide cross-sectional structures.
  • the distance between the two waveguides separately transmitted by different polarizations exceeds the limitation of the radius of the resonator, thereby further reducing the distance between the TE and the TM path, thereby reducing the process error.
  • the resulting polarization-dependent operating wavelength difference of the resonator can meet the more stringent requirements for this indicator.
  • TE and TM to have the same operating wavelength, polarization crosstalk will not increase even if polarization conversion occurs.
  • the waveguide cross-sectional shape can be arbitrarily designed without using a special cross-sectional shape to suppress polarization conversion.

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Abstract

一种微环谐振器，包括：至少一个第一直波导；第二波导（Arm3）以及第三波导（Arm2），第二波导（Arm3）和第三波导形（Arm2）成封闭环形波导，所述环形波导与第一波导耦合；第四波导（Arm1），所述第四波导（Arm1）与所述环形波导耦合；偏振分束器（PS），所述偏振分束器（PS）一端与所述第四波导（Arm1）连接，一端与所述环形波导的第二波导（Arm3）相连。该微环谐振器使不同偏振分开传输的两个波导距离突破谐振器半径的限制，进一步减小了TE、TM通路的距离，从而减小了工艺误差产生的谐振器偏振相关工作波长差异，可以满足对这一指标要求更为严格的场景。

Description

一种微环谐振器 技术领域
本发明涉及光通信领域，尤其涉及一种微环谐振器。
背景技术
随着网络的不断扩容升级，为了控制成本和功耗，光模块的小型化成了必不可少的演进方向。为了实现这一目的需要减小光模块中光组件和电路的体积，而减小光组件体积的方法主要是使用具有高折射率差的集成型波导器件代替传统的分立式光学组件。现有技术中，常用的高折射率差波导材料有硅、氮化硅、聚合物(例如SU8)以及Ⅲ-Ⅴ族化合物半导体材料例如InP等。这些材料组成的光器件具有非常强烈的偏振相关性，即横电模(Transverse Electric，TE)偏振光同横磁模(Transverse Magnetic，TM)偏振光具有不同的工作波长。但是在部分网络应用中，要求接收侧的光器件具有偏振不敏感的特性，即要求TE、TM两个偏振的工作波长相同。
图1示出了一种现有技术提供的微环谐振器的结构示意图。如图1所示，偏振态未知的输入光被偏振分束器(Polarization Splitter,PS)分开为TE、TM光，并分别采用具有相同工作波长的微环谐振器进行处理，然后使用偏振合束器(Polarization Combiner,PC)进行偏振合束。因为要求两个微环的工作波长相同，而且组成波导具有强偏振相关性，因为其半径不相同，分别为R和R’。为了使两个微环不相互耦合，设微环间的最小距离为Gap。采用图1中的方案，器件间的间距受谐振器半径的限制，至少为2*R+2*R’+Gap，无法进一步减少。图1中的方案缺点是需要使用两套器件，控制复杂度以及功耗都加倍。其次，使用该方案，TE、TM的偏振相关工作波长差异，受限于目前的工艺水平以及微环间的最小距离限制，无法满足密集波分复用(Dense Wavelength Division Multiplexing，DWDM)应用的需求。
发明内容
由鉴于此，本发明的实施例提供一种微环谐振器，解决了当前现有技术中的微环谐振器具有强烈偏振相关性的技术问题。
第一方面，本发明实施例公开一种微环谐振器，包括第一直波导，第二波导以及第三波导，其中，第二波导和第三波导形成封闭环形波导或者形成未封 闭的螺旋状，所述环形波导与第一直波导耦合，第四波导，所述第四波导呈圆弧状，与所述第三波导耦合，偏振分束器，其中，所述偏振分束器一端与所述第四波导相连，一端与所述环形波导的第二波导相连。
结合第一方面，在第一方面的第一种可能的实现方式中，所述微环谐振器满足以下公式：Neff(TE)×(L(第二波导)+L(第三波导))＝Neff(TM)×(L(第二波导)+L(第四波导))＝m×λ(TE)＝m×λ(TM)其中，Neff用于标识有效折射率，Neff(TE)用于标识横电模TE的有效折射率，L用于标识波导的长度，L(第二波导)用于标识第二波导的长度；m用于标识谐振级次；λ用于标识波长，λ(TE)用于标识横电模TE光的波长。
结合第一方面或第一方面的第一种可能的实现方式，在第一方面的第二种可能的实现方式中，所述第一直波导为一根、两根或多根。
结合第一方面的任意一种可能的实现方式，在第一方面的第三种可能的实现方式中，所述第二波导、第三波导、第四波导其中之一或者部分或者全部为弯曲波导。
结合第一方面以及第一方面的第一种至第二种可能的实现方式，在第一方面的第四种可能的实现方式中，所述第二波导、第三波导、第四波导其中之一或部分或全部为直波导。
结合第一方面的任意一种可能的实现方式中，在第一方面的第五种可能的实现方式中，所述微环谐振器还包括微型电极，所述微型电极耦合在所述第三波导和第四波导之间。
结合第一方面的任意一种可能的实现方式中，在第一方面的第六种可能的实现方式中，在所述第二波导上沉积有吸收层，所述吸收层材料为锗、硅、锡的一种或者其组合，或者是Ⅲ-Ⅴ族化合物材料。
结合第一方面的任意一种可能的实现方式中，在第一方面的第七种可能的实现方式中，所述第一波导、第二波导、第三波导以及第四波导的截面结构为条形，或者脊型。
第二方面，一种微环谐振器，包括第一直波导，第二波导和第三波导，其中，第二波导和第三波导形成圆弧状，所述圆弧状波导与所述第一波导耦合，偏振合束器，所述偏振合束器与所述圆弧状波导形成封闭环。
结合第二方面，在第二方面的第一种可能的实现方式中，所述微环谐振器满足以下公式：Neff(TE)×L(封闭环周长)+neff(TM)×L(封闭环周长)＝m×λ(TE)＝m×λ(TM)其中，Neff用于标识有效折射率，Neff(TE)用于标识横电模TE的有效折射率，L用于标识波导的长度，L(封闭环周长)用于标识由所述第二波导、第三波导和偏振合束器形成的封闭环的周长，m用于标识谐振级次，λ用于标识波长，λ(TE)用于标识横电模TE光的波长。
结合第二方面或第二方面的第一种可能的实现方式，在第二方面的第二种可能的实现方式中，所述第一直波导为一根、两根或多根。
结合第二方面的任意一种可能的实现方式，在第二方面的第三种可能的实现方式中，所述第二波导和第三波导其中之一或者全部为弯曲波导。
结合第二方面的任意一种可能的实现方式，在第二方面的第四种可能的实现方式中，所述第二波导和第三波导其中之一或者全部为直波导。
结合第二方面的任意一种可能的实现方式，在第二方的第五种可能的实现方式中，在所述第二波导上沉积有吸收层，所述吸收层材料为锗、硅、锡的一种或者其组合，或者是Ⅲ-Ⅴ族化合物材料。
结合第二方面的任意一种可能的实现方式，在第二方的第六种可能的实现方式中，所述第一波导、第二波导、第三波导的截面结构为条形，或者脊型。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为现有技术提供的一种微环谐振器的结构示意图；
图2为本发明实施例一提供的一种微环谐振器的结构示意图；
图3为本发明实施例一提供的另一种微环谐振器的结构示意图；
图4为本发明实施例一提供的另一种微环谐振器的结构示意图；
图5A为本发明实施例一提供的另一种微环谐振器的结构示意图；
图5B为本发明实施例一提供的另一种微环谐振器的结构示意图；
图6为本发明实施例二提供的另一种微环谐振器的结构示意图；
图7为本发明实施例二提供的另一种微环谐振器的结构示意图；
图8为本发明实施例二提供的另一种微环谐振器的结构示意图；
图9A为本发明实施例二提供的另一种微环谐振器的结构示意图；
图9B为本发明实施例二提供的另一种微环谐振器的结构示意图；
图10为本发明实施例三提供的另一种微环谐振器的结构示意图；
图11为本发明实施例三提供的另一种微环谐振器的结构示意图；
图12为本发明实施例三提供的另一种微环谐振器的结构示意图；
图13为本发明实施例三提供的另一种微环谐振器的结构示意图。
具体实施方式
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
实施例一
本发明实施例一提供了一种新型的微环谐振器，通过公共波导以及两个偏振分束器PS使得TE、TM的光路工作波长一致。在本发明实施例一公开的方案中，TE、TM光路的间距突破了微环半径的限制，能够更好的抵抗工艺误差带来的工作波长差异。
本发明的实施例一提供的微环谐振器，包括第一直波导，第二波导以及第三波导，其中，第二波导和第三波导形成封闭环形波导，所述环形波导与所述第一直波导耦合，第四波导，所述第四波导呈圆弧状，与所述第三波导耦合，偏振分束器，其中，所述偏振分束器一端与所述第四波导连接，一端与所述环形波导的第二波导相连。
具体地，本发明实施例提供的微环谐振器的结构如图2所示，包括两根互相垂直的直波导(图2中的平行线为平行的直波导，垂直线为垂直的直波导)、一个环形波导、两个耦合到所述环形波导的偏振分束器PS1和PS2、以及与两个PS连接的弯曲波导(也可称为单偏振波导)。其中，该环形波导在图2中采用Arm3和Arm2来标记，其中，靠近下方的半圆弧为Arm3，另一半圆弧为Arm2。环形波导为一个整体，采用Arm3和Arm2分段标记，为了后续说明本发明的原理。图 2中圆形结构代表环形波导，需要说明的是，该环形波导的外观可以是圆形、椭圆形、边缘不规则的类似圆形等，不一定必须是正圆形，只要是出发点和结束点重合的一个封闭环形形状即可，所述环形波导与两根互相垂直的直波导耦合，耦合方式为如图2所示的结构，所述环形波导位于由两根直波导组成的第一象限中。进一步地，分别有两个偏振分束器与环形波导耦合，两个偏振分束器分别位于环形波导至垂直波导耦合的第一耦合区，环形波导与平行波导耦合的第二耦合区。
本发明实施例提供的微环谐振器的工作原理如下：
输入光的偏振态未知，由图2中右侧的入射端口Input进入。通过耦合区1(环形波导与平行直波导的耦合区)耦合进入该环形波导。在耦合区1、Arm3以及耦合区2中同时存在TE、TM偏振的光。经过第一偏振分束器PS1，TE偏振的光的路径为图2中Arm2所示的路线；TM偏振的光经过PS1后，偏振态旋转为TE，其光的路径为图2中Arm1所示的路线。输入光分别通过Arm1和Arm2上的传输后，所有光进入第二偏振分束器PS2。经过PS2后，TE偏振的光偏振态保持不变，进入耦合区1；原TM偏振的光(进入PS2前偏振态为TE)偏振态发生旋转，重新变成TM偏振的光，进入耦合区1。由于光不断在“环”中谐振，从而在耦合区1和耦合区2分别发生多光束干涉现象。耦合区1中发生干涉加强的光，在出射端口射出(图2中的Through出口)；其余在耦合区1中干涉相消的光，在耦合区2发生干涉加强，在另一出射端口射出(图2中的Drop出口)。
本发明实施例采用Arm1和Arm2的长度差产生的光程差补偿在Arm3中TE、TM因偏振不同而存在的光程差，从而保证TE、TM偏振的光经历的光程一致，即其工作波长一致，也就达到了器件偏振不敏感的目的。或者说保证TE、TM的单程相位变化一致，如下方公式所示：
Neff(TE)×(L(Arm3)+L(Arm2))＝Neff(TM)×(L(Arm3)+L(Arm1))＝m×λ(TE)＝m×λ(TM)
其中，Neff用于标识有效折射率(Effective Refractive Index，Neff)，neff(TE)用于标识TE的有效折射率，L用于标识波导的长度，L(Arm3)用于标识Arm3波导的长度；m用于标识谐振级次；λ用于标识波长，λ(TE)用于标识TE光的波长。
进一步地，可以使用直波导代替Arm1和Arm2所示的弯曲波导，以尽可能减小波导中可能存在的偏振转换现象。
进一步地，图2中的直波导还可以是一根或多根。图3为多根直波导和一个环形波导耦合的结构示意图。图3中的平行波导为第一根直波导，与Drop1方向倾斜的为第二根直波导，与DropN方向倾斜的为第N根直波导；环形波导和弯曲波导以及偏振分束器的耦合关系同图2相同。以下介绍图3所示的多根直波导和环形波导耦合的原理：
输入光偏振态未知，由Input端口进入。通过耦合区1耦合进入微环谐振器。在耦合区1、Arm3以及耦合区2至耦合区N+1，同时存在TE、TM偏振的光。经过第一偏振分束器PS1，TE偏振的光的路径为图3中Arm2所示的路线；TM偏振的光经过PS1后，偏振态发生旋转为TE，其路径为图3中Arm2所示的路线。通过Arm1和Arm2的传输后，所有光进入第二偏振分束器PS2。经过PS2后，TE偏振的光偏振态保持不变进入耦合区1；原TM偏振的光(进入PS2前偏振态为TE)偏振态发生旋转，重新变成TM偏振的光，进入耦合区1。由于光不断在“环”中谐振，从而在耦合区1和耦合区2至耦合区N+1分别发生多光束干涉现象。耦合区1中发生干涉加强的光，在Trough端口输出；其余在耦合区1中干涉相消的光，在耦合区2至耦合区N+1中干涉加强，分别从Drop1至DropN按功率等分输出。
采用Arm1和Arm2的长度差产生的光程差补偿在Arm3中TE、TM因偏振不同而存在的光程差，从而保证TE、TM偏振的光经历的光程一致，即其工作波长一致，也就达到了器件偏振不敏感的目的；或者，保证TE、TM的单程相位变化一致，如下方公式所示：
Neff(TE)×(L(Arm3)+L(Arm2))＝Neff(TM)×(L(Arm3)+L(Arm1))＝m×λ(TE)＝m×λ(TM)
进一步地，图4示出了单根直波导与半环形波导耦合的微环谐振器的结构。如图4所示，偏振态未知的光从Input端口入射，经过耦合区1、PS1、Arm1以及Arm2的光路同上述实施例工作原理一致，这里不再赘述。不同点是PS2的工作特性。经过PS2后，TE偏振的光偏振态发生旋转变成TM偏振，进入耦合区1；原TM偏振的光(进入PS2前偏振态为TE)偏振态保持不变仍为TE，进入耦合区1。此时，TE、TM的平均光程完全一致，在Arm1、Arm2中不需要进行长度补偿； 或者，保证TE、TM的单程相位变化一致，如下方公式所示：
Neff(TE)×(L(Arm3)+L(Arm2))＝Neff(TM)×(L(Arm3)+L(Arm1))＝m×λ(TE)＝m×λ(TM)
其中，可以使用直波导代替Arm1和Arm2所示的弯曲波导，已尽可能减小波导中可能存在的偏振转换现象。
可选地，对于本发明实施例提供的微环谐振器，如图5A所示，可以将微型电极(Micro Heater，MH)耦合在波导Arm1和Arm2之间，并用这个微型电极控制该两个波导，从而充分利用原来可能被浪费掉的那部分能力。其中，电极为图5A中黄色弧形曲线。
进一步地，在本发明实施例提供的微环谐振器，还可以在波导Arm3上沉积吸收层，可实现偏振不敏感谐振型探测器的功能。吸收层为图5B中红色弧形部分。其中，吸收层材料为锗、硅、锡的一种或者其组合，Ⅲ-Ⅴ族(比如InP、InGaAsP)材料。本发明实施例与现有技术相比使用的吸收层材料减半，从而噪声减半，所以接收灵敏度可以更高。特别是对于噪声较大的硅锗系吸收材料，噪声是限制其高温时接收灵敏度的主要因素，降低噪声来提高接收灵敏度的效果会更好。
进一步地，上述波导的材料可以是锗、硅、锡的一种或者其组合，Ⅲ-Ⅴ族材料，或者氮化硅，或者聚合物。
进一步地，上述波导的截面结构可以是条形的也可以是浅Slab的脊形波导，或者是不同部分使用不同的波导截面结构。
本发明实施例通过采用将PS内置在谐振环路里的方案，不同偏振分开传输的两个波导距离突破谐振器半径的限制，进一步减小了TE、TM通路的距离，从而减小了工艺误差产生的谐振器偏振相关工作波长差异，可以满足对这一指标要求更为严格的场景。其次，通过设计使TE、TM具有相同的工作波长，即使发生偏振转换也不会增加偏振串扰。波导截面形状可以任意设计，而不会需要抑制偏振转换而使用特殊的截面形状。
实施例二
本发明的实施例提供另一种微环谐振器，包括第一直波导，第二波导以及第三波导，其中，第二波导和第三波导形成封闭环形波导或者形成未封闭的螺旋状，所述环形波导与所述第一直波导耦合，第四波导，所述第四波导呈圆弧 状，与所述第三波导耦合，偏振分束器，其中，所述偏振分束器一端与所述第四波导连接，一端与所述环形波导的第二波导相连。
具体地，该微环谐振器的结构如图6所示，包括两根互相垂直的直波导(图6中的平行线和垂直线分别代表2根互相垂直的直波导)、一个未封闭的环形波导(图6中Arm2和Arm3两段波导形成的呈螺旋结构没有封闭的“环”形波导，需要说明的是，该“环”的外观可以是圆形、椭圆形、边缘不规则的类似圆形等，不一定必须是正圆形)、两个耦合到所述环形波导的偏振分束器PS1和PS2、以及与两个PS连接的Arm1波导。
本发明实施例提供的微环谐振器的原理介绍如下：
偏振态未知的光从Input端口经过耦合区1、耦合区2、PS1、Arm1、Arm2的光路同实施一工作原理一样，这里不再赘述。不同点是PS2的工作特性。经过PS2后，TE偏振的光偏振态发生旋转变成TE偏振，进入耦合区1；原TM偏振的光(进入PS2前偏振态为TE)偏振态保持不变仍为TE，进入耦合区1。此时，TE、TM的平均光程一致，在Arm1、Arm2中不需要进行长度补偿。或者，保证TE、TM的单程相位变化一致，如下方公式所示：
Neff(TE)×(L(Arm3)+L(Arm2))＝Neff(TM)×(L(Arm3)+L(Arm1))＝m×λ(TE)＝m×λ(TM)
其中，Neff用于标识有效折射率(Effective Refractive Index，Neff)，neff(TE)用于标识TE的有效折射率，L用于标识波导的长度，L(Arm3)用于标识Arm3波导的长度；m用于标识谐振级次；λ用于标识波长，λ(TE)用于标识TE光的波长。
由于光不断在“环”中谐振，从而在耦合区1和耦合区2分别发生多光束干涉现象。耦合区1中发生干涉加强的光，在Through端口输出；其余在耦合区1中干涉相消的光，在耦合区2发生干涉加强的光，在Drop段输出。
进一步地，可以使用直波导代替Arm1和Arm2所示的弯曲波导。
同理地，实施例二中的的直波导可以为一根或多根。其中，图7示出了由一根直波导和所谓的“环”(即由Arm1和Arm2形成的未封闭的螺旋状的波导)耦合的结构。如图7所示，原理介绍如下：
偏振态未知的光从Input端口经过耦合区1、PS1、Arm1、Arm2的光路同实 施例一工作原理一样。不同点是PS2的工作特性。经过PS2后，TE偏振的光偏振态发生旋转变成TM偏振，进入耦合区1；原TM偏振的光(进入PS2前偏振态为TE)偏振态保持不变仍为TE，进入耦合区1。此时，TE、TM的平均光程完全一致，在Arm1、Arm2中不需要进行长度补偿。或者，保证TE、TM的单程相位变化一致，即本发明实施例满足如下方公式：
Neff(TE)×(L(Arm3)+L(Arm2))＝Neff(TM)×(L(Arm3)+L(Arm1))＝m×λ(TE)＝m×λ(TM)
由于光不断在“环”中谐振，从而在耦合区1和耦合区2分别发生多光束干涉现象。耦合区1中发生干涉加强的光，在Through端口输出。
其中，可以使用直波导代替Arm1、Arm2所示的弯曲波导。
图8示出了由多根直波导和所谓的“环”耦合的结构。如图8所示，偏振态未知的光从Input端口经过耦合区1、耦合区2至耦合区N+1、PS1、Arm1、Arm2的光路同实施例一工作原理一样。不同点是PS2的工作特性。经过PS2后，TE偏振的光偏振态发生旋转变成TM偏振，进入耦合区1；原TM偏振的光(进入PS2前偏振态为TE)偏振态保持不变仍为TE，进入耦合区1。此时，TE、TM的平均光程完全一致，在Arm1、Arm2中不需要进行长度补偿，或者，保证TE、TM的单程相位变化一致，本发明实施例满足如下公式：
Neff(TE)×(L(Arm3)+L(Arm2))＝Neff(TM)×(L(Arm3)+L(Arm1))＝m×λ(TE)＝m×λ(TM)
由于光不断在“环”中谐振，从而在耦合区1和耦合区2至耦合区N+1分别发生多光束干涉现象。耦合区1中发生干涉加强的光，在Through端输出；其余在耦合区1中干涉相消的光，在耦合区2至耦合区N+1中干涉加强，从Drop1至DropN按功率等分输出。
其中，可使用直波导代替Arm1、Arm2所示的弯曲波导。
本发明实施例提供采用PS内置在谐振环路里的方案，通过设计使TE/TM具有相同的工作波长，即使发生偏振转换也不会增加偏振串扰。波导截面形状可以任意设计，而不会需要抑制偏振转换而使用特殊的截面形状。
进一步，通常使用微型电极加热器件时，由于热是向四面八方扩散的，有很大一部分能量都被浪费了。对于本发明实施例提供的微环谐振器，如图5所示， 可以将微型电极(Micro Heater，MH)耦合在Arm1和Arm2之间，并用这个微型电极控制两个单偏振通过波导，从而充分利用原来可能被浪费掉的那部分能力。其中，电极为图9A中黄色弧形曲线。
进一步地，在本发明实施例提供的微环谐振器，还可以在波导Arm3上沉积吸收层，可实现偏振不敏感谐振型探测器的功能。其中，吸收层材料为锗、硅、锡的一种或者其组合，Ⅲ-Ⅴ族化合物半导体材料(比如InP、InGaAsP)。
进一步地，上述波导的材料可以是锗、硅、锡的一种或者其组合，Ⅲ-Ⅴ族(比如InP、InGaAsP)材料，或者氮化硅，或者聚合物(例如SU8)。
进一步地，上述波导的截面结构可以是条形的也可以是浅Slab的脊形波导，或者是不同部分使用不同的波导截面结构。
本发明实施例通过采用将PS内置在谐振环路里的方案，不同偏振分开传输的两个波导距离突破谐振器半径的限制，进一步减小了TE、TM通路的距离，从而减小了工艺误差产生的谐振器偏振相关工作波长差异，可以满足对这一指标要求更为严格的场景。其次，通过设计使TE、TM具有相同的工作波长，即使发生偏振转换也不会增加偏振串扰。波导截面形状可以任意设计，而不会需要抑制偏振转换而使用特殊的截面形状。
实施例三
本发明的实施例提供另一种微环谐振器，包括第一直波导，第二波导和第三波导，其中，第二波导和第三波导形成圆弧状，所述圆弧状波导与所述第一波导耦合，偏振合束器，所述偏振合束器与所述圆弧状波导形成封闭环。
具体地，该微环谐振器的结构如图10所示，包括两根互相垂直的直波导(图10中的平行线和垂直线分别代表2根互相垂直的直波导)、一个未封闭环形波导(或者是Arm2和Arm3组成的一个圆弧形波导)、一个耦合到所述圆弧形波导的偏振合束器PR，其中，所述圆弧形波导和所述PR耦合形成一个封闭的环形结构。需要说明的是，该“环”的外观可以是圆形、椭圆形、边缘不规则的类似圆形等，不一定必须是正圆形。
输入光偏振态未知，由Input端口入射。通过耦合区1耦合进入微环谐振器。在耦合区1、Arm3以及耦合区2中同时存在TE、TM偏振的光。经过偏振合束器PR，TE偏振的光旋转为TM偏振的光、TM偏振的光旋转为TE偏振的光。每两周 TE、TM的各自所经历的总光程一致，对应的工作波长一致，从而实现偏振不敏感。其中，满足以下公式：
neff(TE)×L(环周长)+neff(TM)×L(环周长)＝m×λ(TE)＝m×λ(TM)
其中，Neff用于标识有效折射率，Neff(TE)用于标识横电模TE的有效折射率，L用于标识波导的长度，L(封闭环周长)用于标识由所述第二波导、第三波导和偏振合束器形成的封闭环的周长，m用于标识谐振级次，λ用于标识波长，λ(TE)用于标识横电模TE光的波长。
由于光不断在“环”中谐振，从而在耦合区1和耦合区2分别发生多光束干涉现象。耦合区1中发生干涉加强的光，在Through端输出。其余在耦合区1中干涉相消的光，在耦合区2中干涉加强，从Drop端口输出。
同理地，实施例三中的的直波导可以为一根或多根。其中，图11示出了由一根直波导和所谓的“环”耦合的结构。原理介绍：
输入光偏振态未知，由Input端口进入。通过耦合区1耦合进入微环谐振器。在耦合区1、Arm3中同时存在TE、TM偏振的光。经过PR，TE偏振的光旋转为TM偏振的光、TM偏振的光旋转为TE偏振的光。每两周TE、TM的各自所经历的总光程一致，对应的工作波长一致，从而实现偏振不敏感。
其中，满足以下公式：
neff(TE)×L(环周长)+neff(TM)×L(环周长)＝m×λ(TE)＝m×λ(TM)
其中，Neff用于标识有效折射率，Neff(TE)用于标识横电模TE的有效折射率，L用于标识波导的长度，L(封闭环周长)用于标识由所述第二波导、第三波导和偏振合束器形成的封闭环的周长，m用于标识谐振级次，λ用于标识波长，λ(TE)用于标识横电模TE光的波长。
由于光不断在“环”中谐振，从而在耦合区1分别发生多光束干涉现象。耦合区1中发生干涉加强的光，在Through端输出。
图12示出了由多根直波导和所谓的“环”耦合的结构。原理介绍：
输入光偏振态未知，由Input端口进入。通过耦合区1耦合进入微环谐振器。在耦合区1、Arm3以及耦合区2至耦合区N+1中同时存在TE、TM偏振的光。经过PR，TE偏振的光旋转为TM偏振的光、TM偏振的光旋转为TE偏振的光。每两周TE、TM的各自所经历的总光程一致，对应的工作波长一致，从而实现偏振不敏 感。
由于光不断在“环”中谐振，从而在耦合区1和耦合区2至耦合区N+1分别发生多束干涉现象。耦合区1中发生干涉加强的光，在Through端口输出。其余在耦合区1中干涉相消的光，在耦合区2至耦合区N+1中干涉加强，从Drop1至DropN按功率等分输出。
进一步地，在本发明实施例提供的微环谐振器，还可以在波导Arm3上沉积吸收层，可实现偏振不敏感谐振型探测器的功能。其中，吸收层材料为锗、硅、锡的一种或者其组合，Ⅲ-Ⅴ族(比如InP、InGaAsP)材料。与现有技术相比，本发明实施例使用的吸收层材料减半，从而噪声减半，所以接收灵敏度可以更高。
进一步地，上述波导的材料可以是锗、硅、锡的一种或者其组合，Ⅲ-Ⅴ族(比如InP、InGaAsP)材料，或者氮化硅，或者聚合物。
进一步地，上述波导的截面结构可以是条形的也可以是浅Slab的脊形波导，或者是不同部分使用不同的波导截面结构。
本发明实施例通过采用将PR内置在谐振环路里的方案，不同偏振分开传输的两个波导距离突破谐振器半径的限制，进一步减小了TE、TM通路的距离，从而减小了工艺误差产生的谐振器偏振相关工作波长差异，可以满足对这一指标要求更为严格的场景。其次，通过设计使TE、TM具有相同的工作波长，即使发生偏振转换也不会增加偏振串扰。波导截面形状可以任意设计，而不会需要抑制偏振转换而使用特殊的截面形状。
以上所述，仅为本发明的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应所述以权利要求的保护范围为准。

Claims (15)

  1. 一种微环谐振器，其特征在于，包括：
    第一直波导，
    第二波导以及第三波导，其中，第二波导和第三波导形成封闭环形波导或者形成未封闭的螺旋状，所述环形波导与所述第一直波导耦合，
    第四波导，所述第四波导呈圆弧状，与所述第三波导耦合，
    偏振分束器，其中，所述偏振分束器一端与所述第四波导连接，一端与所述环形波导的第二波导相连。
  2. 根据权利要求2所述的微环谐振器，其特征在于，所述微环谐振器满足以下公式：
    Neff(TE)×(L(第二波导)+L(第三波导))＝Neff(TM)×(L(第二波导)+L(第四波导))＝m×λ(TE)＝m×λ(TM)
    其中，Neff用于标识有效折射率，Neff(TE)用于标识横电模TE的有效折射率，L用于标识波导的长度，L(第二波导)用于标识第二波导的长度；m用于标识谐振级次；λ用于标识波长，λ(TE)用于标识横电模TE光的波长。
  3. 根据权利要求1或2所述的微环谐振器，其特征在于，所述第一直波导为一根、两根或多根。
  4. 根据权利要求1～3任意一项所述的微环谐振器，其特征在于，所述第二波导、第三波导、第四波导其中之一或者部分或者全部为弯曲波导。
  5. 根据权利要求1～3任意一项所述的微环谐振器，其特征在于，所述第二波导、第三波导、第四波导其中之一或部分或全部为直波导。
  6. 根据权利要求1～5任意一项所述的微环谐振器，其特征在于，还包括微型电极，所述微型电极耦合在所述第三波导和第四波导之间。
  7. 根据权利要求1～6任意一项所述的微环谐振器，其特征在于，在所述第二波导上沉积有吸收层，所述吸收层材料为锗、硅、锡的一种或者其组合，或者是Ⅲ-Ⅴ族化合物材料。
  8. 根据权利要求1～6任意一项所述的微环谐振器，其特征在于，所述第一波导、第二波导、第三波导以及第四波导的截面结构为条形，或者脊型。
  9. 一种微环谐振器，其特征在于，包括：
    第一直波导，
    第二波导和第三波导，其中，第二波导和第三波导形成圆弧状，所述圆弧状波导与所述第一波导耦合，
    偏振合束器，所述偏振合束器与所述圆弧状波导形成封闭环。
  10. 根据权利要求9所述的微环谐振器，其特征在于，所述微环谐振器满足以下公式：
    Neff(TE)×L(封闭环周长)+neff(TM)×L(封闭环周长)＝m×λ(TE)＝m×λ(TM)
    其中，Neff用于标识有效折射率，Neff(TE)用于标识横电模TE的有效折射率，L用于标识波导的长度，L(封闭环周长)用于标识由所述第二波导、第三波导和偏振合束器形成的封闭环的周长，m用于标识谐振级次，λ用于标识波长，λ(TE)用于标识横电模TE光的波长。
  11. 根据权利要求9或10所述的微环谐振器，其特征在于，所述第一直波导为一根、两根或多根。
  12. 根据权利要求9～11任意一项所述的微环谐振器，其特征在于，所述第二波导和第三波导其中之一或者全部为弯曲波导。
  13. 根据权利要求9～11任意一项所述的微环谐振器，其特征在于，所述第二波导和第三波导其中之一或者全部为直波导。
  14. 根据权利要求9～13任意一项所述的微环谐振器，其特征在于，在所述第二波导上沉积有吸收层，所述吸收层材料为锗、硅、锡的一种或者其组合，或者是Ⅲ-Ⅴ族化合物材料。
  15. 根据权利要求9～14任意一项所述的微环谐振器，其特征在于，所述第一波导、第二波导、第三波导的截面结构为条形，或者脊型。
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Publication number Priority date Publication date Assignee Title
CN108873174B (zh) * 2017-05-11 2019-11-29 华为技术有限公司 一种偏振无关的光器件
WO2019005826A1 (en) * 2017-06-26 2019-01-03 The Trustees Of Columbia University In The City Of New York RECYCLING LIGHT WITHOUT RESONANCE IN WAVEGUIDES
CN108873178A (zh) * 2018-07-02 2018-11-23 浙江大学 基于微环谐振器和马赫-曾德尔调制器的波长切换无中断光学路由器
WO2021224240A1 (en) * 2020-05-04 2021-11-11 Danmarks Tekniske Universitet Polarization selective resonator
CN113050220A (zh) * 2021-03-15 2021-06-29 中国科学院微电子研究所 一种渐变弯曲波导器件
US11631431B2 (en) 2021-07-02 2023-04-18 Seagate Technology Llc Analog optical link for a moveable actuator in a data storage system
WO2023162181A1 (ja) * 2022-02-25 2023-08-31 日本電信電話株式会社 光リング変調器

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080123188A1 (en) * 2006-11-29 2008-05-29 Univsersiteit Twente Device Comprising a Polarization-Independent Micro-Resonator
CN101726801A (zh) * 2008-10-28 2010-06-09 华为技术有限公司 一种光开关装置的控制方法和光开关装置
CN101840028A (zh) * 2010-04-07 2010-09-22 中国科学院半导体研究所 基于微环谐振器的集成化可重构光插分复用器
CN101866066A (zh) * 2010-05-28 2010-10-20 浙江大学 一种相变材料辅助的基于微环的光波导开关
US20130039618A1 (en) * 2011-08-11 2013-02-14 Massachusetts Institute Of Technology Patterned non-reciprocal optical resonator

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0943558A (ja) * 1995-07-27 1997-02-14 Hitachi Cable Ltd 導波路型偏光コンペンセータ並びにそれを用いた導波路型リング共振器および導波路型マッハツェンダ干渉計
US8452185B2 (en) 2007-12-21 2013-05-28 Infinera Corporation Polarization insensitive optical circuit
WO2011098130A1 (en) * 2010-02-11 2011-08-18 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Apparatus and method for guiding optical waves
WO2015028086A1 (en) * 2013-08-30 2015-03-05 Telefonaktiebolaget L M Ericsson (Publ) Optical switch, optical switch apparatus and node, and communication network
CN103986671B (zh) * 2014-05-20 2017-02-15 上海交通大学 基于嵌套式硅基微环谐振腔的无阻塞2×2光交换节点

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080123188A1 (en) * 2006-11-29 2008-05-29 Univsersiteit Twente Device Comprising a Polarization-Independent Micro-Resonator
CN101726801A (zh) * 2008-10-28 2010-06-09 华为技术有限公司 一种光开关装置的控制方法和光开关装置
CN101840028A (zh) * 2010-04-07 2010-09-22 中国科学院半导体研究所 基于微环谐振器的集成化可重构光插分复用器
CN101866066A (zh) * 2010-05-28 2010-10-20 浙江大学 一种相变材料辅助的基于微环的光波导开关
US20130039618A1 (en) * 2011-08-11 2013-02-14 Massachusetts Institute Of Technology Patterned non-reciprocal optical resonator

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP3223048A4 *

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