CN114690313A - Based on thick Si3N4Low insertion loss, large bandwidth compact multimode interference coupler of material - Google Patents

Based on thick Si3N4Low insertion loss, large bandwidth compact multimode interference coupler of material Download PDF

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Publication number
CN114690313A
CN114690313A CN202210440234.2A CN202210440234A CN114690313A CN 114690313 A CN114690313 A CN 114690313A CN 202210440234 A CN202210440234 A CN 202210440234A CN 114690313 A CN114690313 A CN 114690313A
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multimode interference
tapered
waveguide
thick
insertion loss
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CN202210440234.2A
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林曈
胡国华
喻杭
崔一平
恽斌峰
张若虎
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Southeast University
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Southeast University
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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
    • 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
    • G02B6/1228—Tapered waveguides, e.g. integrated spot-size transformers
    • 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
    • G02B2006/12035—Materials
    • G02B2006/12061—Silicon
    • 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
    • G02B2006/12133—Functions
    • G02B2006/12147—Coupler
    • 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
    • G02B2006/12133—Functions
    • G02B2006/12159—Interferometer

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Power Engineering (AREA)
  • Optical Integrated Circuits (AREA)

Abstract

The invention discloses a method based on thick Si3N4Low insertion loss, large bandwidth compact multimode interference couplers of materials, including thick Si based3N4A single tapered input waveguide, a multimode interference region, a tapered output waveguide of material. The invention can realize that incident light is distributed to two output waveguides by one port to form a one-in-two power divider or a two-in-one coupler, is suitable for a silicon nitride integrated optical path optical device system such as microwave photon filtering and shaping, a double optical comb technology, an optical coherence tomography technology, an optical communication transceiving module, optical calculation and the like, and has the advantages of compact size, high coupling efficiency, large bandwidth, low insertion loss and the like.

Description

Based on thick Si3N4Low insertion loss, large bandwidth compact multimode interference coupler of material
Technical Field
The invention belongs to the technical field of optical communication technology, and particularly relates to a novel optical fiberBased on thick Si3N4A compact multi-mode interference coupler with low insertion loss and large bandwidth.
Background
With the rapid development of optical fiber communication technology, the requirements for information transmission and processing are also higher and higher. High integration, low loss, and functional diversity have been the pursuit of optical communication device developers. The selected material type is designed and manufactured to form the optical device, which not only relates to the performance parameters of the system, but also determines the problems of manufacturing cost, processing feasibility, compatibility with the existing system and the like.
Si3N4(Silicon Nitride) benefits from its large refractive index contrast with Silicon dioxide so that optical signals can be well confined to transmission in Silicon Nitride waveguides. The silicon nitride film waveguide deposited by low pressure chemical evaporation (LPCVD) has the advantages of small transmission loss, small bending loss and the like, the silicon nitride has higher third-order nonlinear coefficient, the thick silicon nitride waveguide (the thickness of the waveguide is more than 600nm) further improves the mode binding capability, and is favorable for dispersion engineering, not only can realize positive dispersion, but also can realize anomalous dispersion, is a core enabler of Kerr micro optical comb and supercontinuum, and simultaneously has the advantages of being compatible with a microelectronic CMOS process and the like, thereby being favorable for the miniaturization and large-scale integration of waveguide devices and greatly reducing the cost. At present, silicon nitride photonic integrated circuits show wide prospects in the aspects of manufacturing advanced photonic functional devices such as dense spiral waveguides, nonlinear frequency conversion, frequency comb generation and the like.
Aiming at practical application, realizing 3dB beam combination and beam splitting of on-chip light beams is the basis for constructing various functions. To date, the insertion loss of a typical thick silicon nitride 2 × 2MMI is usually about 0.37dB, the size is usually 0.35mm × 0.06mm, and the larger size means that a plurality of MMIs are cascaded to form a structure such as a multilevel optical switch array, which requires further size reduction in order to further improve the integration level. The MMI which has better compactness, lower insertion loss and bandwidth covering C + L wave band has great practical significance.
Disclosure of Invention
To solve the above problems, the inventionThe invention discloses a method based on thick Si3N4The MMI realizes the functions of splitting beams into two parts and two halves and combining the two parts into one and two beams. Compared with the existing MMI, the optical fiber has larger working bandwidth and more compact size, and is suitable for optical time division multiplexing chips, microwave photon filtering and time delay, double optical comb sensing chips, optical coherence tomography imaging and other miniaturized optical devices.
In order to achieve the purpose, the technical scheme of the invention is as follows:
based on thick Si3N4A low insertion loss, large bandwidth, multimode interference coupler of material comprises a Si substrate, and a waveguide layer and SiO on the surface of the Si substrate2And (3) a layer. Wherein the waveguide layer is embedded in SiO2Si in the layer3N4A waveguide;
said Si3N4The waveguide comprises two tapered gradient input waveguides, a multimode interference area for intermode interference and two tapered gradient output waveguides; the two tapered gradual change input waveguides are connected with one end face of the multimode interference area, and the two tapered gradual change output waveguides are connected with the other end face of the multimode interference area;
the modes of each order in the multimode waveguide are subjected to coherent superposition again to form a double image; the input TE light sequentially passes through the two conical gradient input waveguides, the multimode interference area and the two conical gradient output waveguides and then is connected with other devices; the end face of the multimode interference region is matched with the effective refractive indexes of TE modes of the end faces of the tapered gradual change input waveguide and the tapered gradual change output waveguide, and coupling can be achieved with extremely low loss.
As a preferred technical scheme of the invention: the tapered input waveguide and the tapered output waveguide have the same structure and are symmetrically arranged about the multimode interference region.
As a preferred technical scheme of the invention: the cross-sectional width of the tapered, tapered input waveguide widens linearly along the direction of transmission.
As a preferred technical scheme of the invention: the cross-sectional width of the tapered input waveguide is gradually widened at a rate of change of 50nm/um, the cross-section of the tapered input waveguide being a cross-section through the axis.
As a preferred technical scheme of the invention: the cross-sectional width of the tapered output waveguide narrows linearly along the transmission direction.
As a preferred technical scheme of the invention: the width of the cross section of the tapered gradual change output waveguide is gradually reduced at a change rate of-50 nm/um, and the cross section of the tapered gradual change output waveguide is a cross section passing through an axis.
As a preferred technical scheme of the invention: the length and the width of the multimode interference area ensure that the high-order mode changes the phase of integral multiple of 2 pi.
As a preferred technical scheme of the invention: the end face width of the tapered gradual change input waveguide and/or the tapered gradual change output waveguide is designed to be matched with the mode effective refractive index of the waveguide in the multimode interference region, so that the coupling loss at the joint is reduced, and the processing tolerance is large.
As a preferred technical scheme of the invention: the light field enters a multimode interference region, each order mode is subjected to coherence superposition propagation again to form a double image, and the imaging point is the central point of the connecting surface of the two conical gradual change output waveguides and the multimode interference region. By designing the size of the multimode interference waveguide region, high-order modes propagating in the multimode interference waveguide region are coherently superposed to form a double image, and the processing tolerance is large.
The invention has the beneficial effects that:
the invention provides a thick Si-based alloy3N4The compact multi-mode interference coupler with low insertion loss, large bandwidth and high material bandwidth is formed by two pairs of inverted cone structures and multi-mode interference coupling waveguides, fully utilizes the advantages of high mode field binding degree and low transmission loss of the thick silicon nitride waveguide, and realizes the purpose of combining Si with a waveguide3N4The light in the strip waveguide has the functions of splitting and combining beams and has high coupling efficiency.
Compared with common thick Si3N4The platform 2 x 2MMI has the main advantages that the total size is reduced by 89% on the basis of keeping excellent performance, and the set is greatly improvedThe advantages of compactness are more obvious, especially N +1 MMIs are needed in an N-level Mach Zehnder interferometer structure adopted in microwave photon filters, optical calculation and other applications.
The invention can be used as a compact multi-mode interference coupler with low loss and large bandwidth and applied to thick Si3N4The cascade Mach-Zehnder interferometer is used for beam splitting and beam combining on the platform, and the constructed cascade Mach-Zehnder interferometer is a core component of a photoelectric modulation chip, an optical time division multiplexing chip, a microwave photon reconfigurable filter, an adjustable light delay line, a double-optical comb distance measurement and sensing system, an optical computing matrix network and other structures. Moreover, the manufacturing process of the invention is compatible with CMOS, can realize large-scale mass production, and greatly saves the chip cost.
Drawings
Fig. 1 is a schematic top view of the waveguide of the present invention.
Fig. 2 is a schematic cross-sectional view of a waveguide of the present invention.
FIG. 3 is a diagram illustrating an optical field transmission distribution pattern according to the present invention.
Fig. 4 is a diagram of an output light transmission spectrum according to the present invention.
Wherein, 1, a tapered gradual change input waveguide; 2. a multimode interference region; 3. a tapered graded output waveguide.
Detailed Description
The invention is further elucidated with reference to the drawings and the detailed description. It should be understood that the following detailed description is illustrative of the invention only and is not intended to limit the scope of the invention.
As shown in figures 1 and 2, the invention designs a thick Si-based material3N4The waveguide layer of the compact multi-mode interference coupler with low insertion loss and large bandwidth is embedded in SiO2Si in the form of stripes3N4Waveguide, said Si3N4The waveguide comprises two tapered input waveguides 1, a multimode interference region 2 and two tapered output waveguides 3. The effective refractive index of the TE mode at the emergent end of the tapered gradual change input waveguide 1 is basically consistent with that of the incident end of the multimode interference region, and the insertion loss can be obviously reduced. When light is input in TE mode, light energy passes throughAfter the tapered graded waveguide and the multimode interference area, light is converted from a single mode into multimode and then into two single modes, and the light is coupled out through the two tapered linear graded waveguides to be connected with a subsequent device. The low-loss and compact multi-mode interference coupling function is realized.
The working principle of the structure of the invention is as follows:
when light in a TE mode is input, the light in the TE mode is polarized along the Y direction in the graph 2, the cross section width of the input waveguide is widened to 3um by the conical gradually-changed input waveguide 1 through adiabatic evolution, so that the mode mismatch of the input waveguide mode and a multi-mode area can be reduced, the insertion loss is reduced, and the processing fault tolerance can be improved; after the light field enters the multimode interference region 2, in the propagation direction of the X direction, coherent superposition of each order mode obtains different transverse mode field distributions, each order mode in the multimode interference region 2 is subjected to coherent superposition again, when all the modes propagate in the X direction, a double image is formed, and an imaging point is the central point of the connecting surface of the tapered gradually-changed output waveguide 3 and the multimode interference region 2. Finally, the light enters the tapered output waveguide 3 and is connected with a subsequent device through reducing the section width of the tapered output waveguide 3 through adiabatic evolution. Therefore, the functions of low insertion loss light splitting and beam combining are realized.
In order to verify that the present invention can realize the function, a verification example will be specifically described.
The time domain finite difference method adopted in the verification example is used for calculation and analysis, wherein the used main parameters comprise: the thickness of all waveguides is 800nm, the width of the cross section of the input end of the tapered gradual change input waveguide 1 is 1.5um, the length of the tapered gradual change waveguide is 30um, the tapered gradual change waveguide is linearly widened to 3um, and the change rate of the width of the cross section of the tapered gradual change input waveguide 1 is 50 nm/um; the section of the multimode interference area 2 is rectangular, the width is 12.6um, the length is 130um, the section width of one end of the tapered gradual change output waveguide 3 is 3um, linear reduction is carried out, the section width of the other end of the tapered gradual change output waveguide is 1.5um, the change rate of the tapered gradual change output waveguide 3 is-50 nm/um, and the length of the gradual change waveguide is 30 um; the input/output waveguide ports are centered at the multimode interference zone 2 widths 1/3 and 2/3, respectively. The thickness of the silica upper cladding layer is 3.3um, and the thickness of the lower cladding layer is 4 um.
When light is input from the upper waveguide in the TE mode, the optical field transmission is calculated as shown in fig. 3. It can be seen that the optical power is input from the tapered graded input waveguide 1, and is transmitted through the graded waveguide adiabatic transformation, the multimode interference region and the graded output waveguide, and the optical energy is not greatly leaked. As shown in fig. 4, in the wavelength range from 1500nm to 1600nm, the variation range of the port transmittance of the two tapered output waveguides 3 is 47% -49.8%, the corresponding insertion loss is 0.287dB to 0.026dB, the device insertion loss corresponding to the 1550nm communication band is about 0.025dB to 0.06dB, and the insertion loss in the 200nm bandwidth range (1450nm to 1650nm) is less than 0.7 dB. The size of the MMI is compared with other MMIs of the same bench: the width is reduced by 80%, the length is reduced by 41%, and the total size is reduced by 89%.
In conclusion, the thick Si-based material provided by the invention3N4The integrated photon platform realizes one-to-two and two-to-two light beam splitting and two-in-one and two-in-two light beam combining. Device insertion loss is small within 200nm operating bandwidth as based on thick Si3N4Compared with the existing solution, the size of the device of the material of the multimode interference coupler is reduced by 89%, the multimode interference coupler can be used for combining a multi-stage Mach Zehnder interferometer and other core optical devices, and has an important role in an integrated optical system on optical communication, microwave photon, imaging and sensing chips.
The technical means disclosed in the invention are not limited to the technical means disclosed in the above embodiments, but also include technical means formed by any combination of the above technical features.

Claims (7)

1. Based on thick Si3N4The multimode interference coupler with low insertion loss and large bandwidth of the material is characterized in that: si3N4Waveguide embedded in SiO2In the layer of Si3N4The waveguide comprises two tapered graded input waveguides (1), a multimode interference region (2) for intermode interference and two tapered graded output waveguides (3); the two tapered gradual change input waveguides (1) are connected with one end face of the multimode interference area (2), and the two tapered gradual change output waveguides (3) are connected with the other end face of the multimode interference area (2);
the input TE light sequentially passes through two conical gradual change input waveguides (1), a multimode interference region (2) and two conical gradual change output waveguides (3); two connecting end faces of the multimode interference region (2) are respectively matched with the effective refractive indexes of the TE modes of the end faces of the tapered gradual change input waveguide (1) and the tapered gradual change output waveguide (3).
2. A thick Si based alloy according to claim 13N4The compact multimode interference coupler with low insertion loss and large bandwidth made of the material is characterized in that: : the cross-sectional width of the tapered input waveguide (1) widens linearly in the transmission direction.
3. A thick Si based alloy according to claim 23N4The compact multimode interference coupler with low insertion loss and large bandwidth made of the material is characterized in that: the cross-sectional width of the tapered input waveguide (1) is gradually widened at a rate of change of 50 nm/um.
4. A thick Si based alloy according to claim 13N4The compact multimode interference coupler with low insertion loss and large bandwidth made of the material is characterized in that: the cross-sectional width of the tapered output waveguide (3) narrows linearly along the transmission direction.
5. A thick Si based alloy according to claim 43N4The compact multimode interference coupler with low insertion loss and large bandwidth made of the material is characterized in that: the cross-sectional width of the tapered output waveguide (3) is gradually reduced at a rate of change of-50 nm/um.
6. A thick Si based alloy according to claim 13N4The compact multimode interference coupler with low insertion loss and large bandwidth made of the material is characterized in that: the length and the width of the multimode interference region (2) meet the condition that the phase of the high-order mode changes by integral multiple of 2 pi.
7. The method of claim 1Based on thick Si3N4The compact multimode interference coupler with low insertion loss and large bandwidth made of the material is characterized in that: the light field enters a multimode interference region (2), each order mode is subjected to re-coherent superposition propagation to form a double image, and the imaging point is the central point of the connecting surface of the two conical gradual change output waveguides (3) and the multimode interference region (2).
CN202210440234.2A 2022-04-25 2022-04-25 Based on thick Si3N4Low insertion loss, large bandwidth compact multimode interference coupler of material Withdrawn CN114690313A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115032743A (en) * 2022-07-26 2022-09-09 上海安湃芯研科技有限公司 Multi-mode interference coupler type polarizer based on thin-film lithium niobate

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115032743A (en) * 2022-07-26 2022-09-09 上海安湃芯研科技有限公司 Multi-mode interference coupler type polarizer based on thin-film lithium niobate

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