CN113296292A - Organic-inorganic hybrid integrated polymer variable optical attenuator and preparation method thereof - Google Patents

Organic-inorganic hybrid integrated polymer variable optical attenuator and preparation method thereof Download PDF

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CN113296292A
CN113296292A CN202110526977.7A CN202110526977A CN113296292A CN 113296292 A CN113296292 A CN 113296292A CN 202110526977 A CN202110526977 A CN 202110526977A CN 113296292 A CN113296292 A CN 113296292A
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polymer
silica
core layer
waveguide
silicon dioxide
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CN113296292B (en
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尹悦鑫
张大明
姚梦可
丁颖智
曹悦
陈长鸣
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Jilin University
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    • 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 
    • 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 
    • G02F1/011—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  in optical waveguides, not otherwise provided for in this subclass

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Abstract

A polymer variable optical attenuator of an organic-inorganic hybrid integrated vertical multimode interferometer structure and a preparation method thereof belong to the technical field of polymer optical waveguide variable optical attenuators. The light-emitting diode is composed of a silicon substrate, a silica lower cladding layer prepared on the substrate, a silica input waveguide unit, a polymer core layer waveguide unit and a silica output waveguide unit which are prepared on the silica lower cladding layer along the propagation direction of light, a silica upper cladding layer which is positioned on the silica lower cladding layer and covers the silica input waveguide unit and the silica output waveguide unit, a polymer cladding layer which is positioned on the silica upper cladding layer and the polymer core layer waveguide unit, and a metal modulation electrode which is positioned on the polymer cladding layer. The variable optical attenuator has the advantages of compact structure, low power consumption, high response speed, large extinction ratio and the like, can be used in a WDM system in optical communication, and plays a role in power balance.

Description

Organic-inorganic hybrid integrated polymer variable optical attenuator and preparation method thereof
Technical Field
The invention belongs to the technical field of polymer Optical waveguide Variable Optical attenuators, and particularly relates to a polymer Optical Attenuator (VOA) with a Multi-Mode Interference (MMI) structure for organic/inorganic hybrid integration and a preparation method thereof.
Background
In an optical network, there is a possibility that an optical signal added from a local node is multiplexed with other signals of different optical power transmitted at different distances and transmitted together; even if the optical signals are multiplexed and transmitted together, after a certain distance is transmitted, the power of the optical signals may be different because the response of devices such as an Erbium Doped Fiber Amplifier (EDFA), an optical filter, and an optical switch to each wavelength is slightly different. In addition, due to the reasons of add/drop, reconfiguration or network recovery of the optical network, the optical power of each wavelength channel entering the node also has a difference, and since the optical signal is going through a plurality of nodes and links, the optical power difference between each wavelength channel accumulates, resulting in inconsistent signal-to-noise ratio of each optical channel, affecting the service quality of the system, and even degrading some channels to an unacceptable level. In general, the channel power imbalance of a Wavelength Division Multiplexing (WDM) system causes the following three problems:
1. the received energy imbalance will eventually exceed the dynamic range allowed by the receiver;
2. an imbalance of the accumulated Signal-to-Noise ratio (SNR) results in an increase of Bit Error Rate (BER) for a certain wavelength, which may be lower than the required bit Error Rate;
3. due to insufficient gain, the signal strength of the minimum channel may be below the sensitivity of the receiver, such that the receiver cannot detect the signal.
Meanwhile, to put the optical network into practical use, the problem of power imbalance among wavelength channels needs to be solved. In Reconfigurable Optical Add-Drop multiplexers (ROADMs), in particular, in a system, since traffic and transmission distances of each channel are different, transmission (signal-to-noise ratio, power, bit error rate, and the like) of each channel must be equalized.
At present, a silicon dioxide-based flat optical waveguide device (PLC) has the advantages of low loss, high stability, easy integration with an optical fiber, and the like, and is widely used in the field of optical communication. However, the thermo-optic coefficient of silica PLC is only 1.19X 10-5K-1The application of the polymer PLC in the field of active devices is limited, and the thermo-optic coefficient of the polymer PLC is-1.86 multiplied by 10-4K-1And the method is one order of magnitude higher than that of silicon dioxide PLC, and is very suitable for manufacturing active photonic chips such as thermo-optical switches, tunable filters and the like. Based on the above reasons, the invention develops an organic-inorganic hybrid integration process method based on the traditional PLC preparation process by combining the advantages of two materials and utilizing the existing mature process for preparing the silica PLC to realize the advantages of a low-loss passive device and the low-power consumption active device of an organic polymer device, and finally realizes the low-loss, low-power consumption and high-performance organic-inorganic hybrid integrated photonic chip by mixing and integrating the silica PLC and the polymer PLC on one chip. The invention designs a VOA device with an MMI structure based on an organic-inorganic hybrid integration compatible process, and the device has the advantages of compact structure, low power consumption, high response speed and great application potential in the fields of optical communication, integrated optics and the like.
Disclosure of Invention
Aiming at the problem of large power consumption of silicon dioxide VOA, the invention provides an organic-inorganic hybrid integrated device by utilizing the advantages of fluidity and low-temperature treatment of a polymer on the basis of a silicon dioxide PLC (programmable logic controller) process and through the processes of Inductively Coupled Plasma (ICP) etching, spin coating, photoetching, developing and the like. Compared with the prior art, the method realizes the hybrid monolithic integration of the polymer PLC device and the silicon dioxide PLC device through a simple process on the premise of not influencing the silicon dioxide PLC process, and can greatly reduce the power consumption required by VOA modulation by utilizing the advantage that the thermo-optic coefficient of the polymer is one order of magnitude higher than that of the silicon dioxide.
An organic-inorganic hybrid integrated polymer variable optical attenuator based on a vertical multimode interferometer structure is composed of a silicon substrate, the light-emitting diode comprises a silicon dioxide lower cladding layer prepared on a silicon substrate, a silicon dioxide input waveguide unit, a polymer core layer waveguide unit and a silicon dioxide output waveguide unit which are prepared on the silicon dioxide lower cladding layer along the light propagation direction, a silicon dioxide upper cladding layer which is positioned on the upper surface and the lower surface of the silicon dioxide lower cladding layer, positioned on the same plane with the lower surfaces of the silicon dioxide input waveguide unit and the silicon dioxide output waveguide unit and wraps the silicon dioxide input waveguide unit and the silicon dioxide output waveguide unit, a polymer cladding layer which is positioned on the upper surface and the lower surface of the polymer core layer waveguide unit and wraps the polymer waveguide unit and is positioned on the same plane with the upper surface of the silicon dioxide upper cladding layer, and a metal modulation electrode positioned on the polymer cladding layer.
The bottoms of the silica input waveguide unit, the polymer core layer waveguide unit and the silica output waveguide unit are positioned on the same plane (namely the upper surface of the silica lower cladding), and the widths of the silica input waveguide unit, the polymer core layer waveguide unit and the silica output waveguide unit are the same (W is the width of the silica input waveguide unit, the polymer core layer waveguide unit and the silica output waveguide unit) in the light propagation directionwg) (ii) a The height of the input and output silica waveguides is the same (H)wg) The waveguide unit of polymer core layer extends into the polymer cladding layer and has a height (W)MMI) The height of the input waveguide unit is larger than that of the input waveguide unit and the output waveguide unit; the input light is coupled from the silica input waveguide unit and transmitted in the polymer core layer waveguide unit, the polymer core layer waveguide unit is of a vertical MMI structure, and the length L of the polymer core layer waveguide unit is optimizedMMICan be used forMore than 90% of input light is coupled into the silicon dioxide output waveguide unit; the modulation electrode is located the upper surface of polymer cladding directly over polymer core waveguide unit, and when applying voltage to the electrode, the electrode generates heat and can make the polymer core waveguide temperature of below change, and light can produce the phase difference when the polymer core waveguide that the temperature changes for the position from the image changes, and the coupling gets into the light intensity of silica output waveguide unit and changes, thereby constitutes polymer VOA device.
The refractive index difference between the silica upper cladding and the silica core layer is 0.36-2%, the calculation formula is shown as formula (1), and the refractive index of the core layer is n1Refractive index of cladding layer n2The refractive index of the core layer is greater than that of the cladding layer;
Figure BDA0003066001490000031
the polymer cladding material can be selected from polymethyl methacrylate (PMMA), Polyethylene (PE), Polyester (PET), Polystyrene (PS), EpoClad and the like;
the polymer core layer material is a polymer material with negative thermo-optic coefficient, and comprises SU-82002, SU-82005, EpoCore and the like.
The metal modulation electrode is made of one or more of gold, silver and aluminum.
The invention relates to a preparation method of an organic-inorganic hybrid integrated polymer variable optical attenuator, which comprises the following steps:
the method comprises the following steps: growing a compact silica lower cladding layer with the thickness of 12-18 mu m on a silicon wafer substrate by a thermal oxidation method;
step two: then depositing on the lower silicon dioxide cladding layer by a Plasma-Enhanced Chemical Vapor Deposition (PECVD) method to obtain a germanium-doped silicon dioxide core layer with the thickness of 3.5-6.5 mu m; the PECVD equipment comprises a PECVD device, a substrate, an upper electrode, a lower electrode, a gas source and a gas source, wherein the pressure of a cavity of the PECVD device is 300-800 mTorr, the temperature of the substrate is 300-350 ℃, the low-frequency radio frequency power of the upper electrode is 200-700W, the high-frequency radio frequency power of the upper electrode is 300-800W, the flow rate of silane gas is 15-30 sccm, the flow rate of nitric oxide gas is 1800-2000 sccm, the flow rate of germane gas is 1.3-2.4 sccm, and the deposition rate is 180-230 nm/min;
step three: spin-coating a photoresist layer I on a germanium-doped silicon dioxide core layer, naturally cooling and curing after prebaking treatment, transferring a pattern which is identical to or complementary with a strip-shaped waveguide structure to be prepared on a photoetching plate I (a photoresist layer I is positive photoresist) onto the photoresist layer I through ultraviolet photoetching, developing and postbaking, and preparing a silicon dioxide core layer waveguide with a strip-shaped structure on the germanium-doped silicon dioxide core layer through an ICP (inductively coupled plasma) etching method; then removing the photoresist layer I on the silicon dioxide core waveguide;
step IV: depositing on a silicon dioxide core layer waveguide with a strip structure by a PECVD method to obtain a silicon dioxide upper cladding layer which is doped with boron and phosphorus and has the thickness of 3-5 mu m, wherein the silicon dioxide upper cladding layer and the silicon dioxide lower cladding layer prepared in the first step are collectively called as a silicon dioxide cladding layer; the pressure of a chamber of the PECVD equipment is 2000-3000 mTorr, the temperature of a substrate is 335-365 ℃, the radio frequency power of a lower electrode is 1600-2000W, the flow of a mixed gas of borane and nitrogen is 100-140 sccm, and the mole fraction of the borane in the mixed gas is 5% -10%; the flow rate of the mixed gas of the phosphane and the nitrogen is 20-45 sccm, and the mole fraction of the phosphane in the mixed gas is 5% -10%;
step five: spin-coating on the silica cladding again to form a photoresist layer II, carrying out prebaking treatment, then naturally cooling and curing, then carrying out ultraviolet lithography, development and postbaking, transferring a pattern on the photoetching plate II, which has the same structure (the photoresist layer II is a positive photoresist) or is complementary (the photoresist layer II is a negative photoresist) with the polymer core layer waveguide structure to be prepared, onto the photoresist layer II, and etching a window with the same structure as the polymer core layer waveguide structure on the silica cladding by an ICP (inductively coupled plasma) etching method; along the transmission direction of light, the window is positioned at the middle position right above the silicon dioxide core layer waveguide of the strip-shaped structure; the bottom surface of the window and the bottom surface of the silica core waveguide are positioned on the same plane (namely the upper surface of the silica lower cladding); width and strip of windowThe width of the silicon dioxide core layer waveguide with the same structure is the same, and the length of the window is MMI which is the self-imaging length LMMISelf-image length LMMILess than the length of the silica core waveguide; then removing the photoresist layer II on the silicon dioxide cladding; along the transmission direction of light, the silicon dioxide core layer waveguide of the strip-shaped structure in front of the window is a silicon dioxide input waveguide unit, and the silicon dioxide core layer waveguide of the strip-shaped structure behind the window is a silicon dioxide output waveguide unit;
step (c): spin coating a polymer core layer material on the silica cladding layer, wherein the material has self-leveling property and does not need polishing treatment, except that the window in the fifth step is filled with the polymer core layer material, a polymer thin layer is formed on the silica cladding layer, and a polymer thin film with the thickness of 2-4 microns is formed by controlling the rotating speed and the spin coating time;
step (c): naturally cooling and curing the obtained polymer film after pre-baking treatment, transferring a pattern with the same structure (the polymer film is a positive photoresist) or complementary structure (the polymer film is a negative photoresist) on a photoetching plate III and a polymer core layer waveguide structure to be prepared onto the polymer film through ultraviolet photoetching, developing and post-baking, then putting the pattern into a developing solution corresponding to a polymer for developing, putting the pattern into a rinsing solution for rinsing to remove polymer materials except the polymer core layer waveguide structure, washing a reaction solution with deionized water, and finally hardening for 20-40 minutes to obtain the polymer core layer waveguide with a strip-shaped structure;
step (v): spin-coating a polymer cladding material on the polymer core layer waveguide, forming the polymer cladding material with the thickness of 5-7 microns by controlling the spin-coating rotation speed and the spin-coating time, putting the polymer cladding material into an oven, heating the polymer cladding material at 110-130 ℃ for 1.5-3.0 hours, and naturally cooling the polymer cladding material to room temperature to obtain a polymer cladding; the silicon dioxide cladding, the polymer core layer waveguide with the strip structure, the polymer cladding and the modulation electrode form a polymer VOA device;
step ninthly: a metal film with the thickness of 50-200 nm is vapor-plated on the polymer cladding, a photoresist layer IV is spin-coated on the metal film, the metal film is naturally cooled and solidified after prebaking treatment, then patterns which are the same as or complementary with the electrode structure to be prepared (the photoresist layer IV is a positive photoresist) on the photoresist plate IV (the photoresist layer IV is a negative photoresist) are transferred onto the photoresist layer IV through ultraviolet lithography, development and postbaking, the photoresist layer IV is hardened after development, and after natural cooling, the metal outside the electrode structure is corroded by using a corrosive liquid corresponding to the metal to obtain a modulation electrode; the modulation electrode is positioned right above the polymer core layer waveguide and aligned with the center of the polymer core layer waveguide, the left and right of the modulation electrode exceed the polymer core layer waveguide by more than 50 microns, and the width of the modulation electrode is 20-40 microns; and removing the residual photoresist to prepare the organic-inorganic hybrid integrated polymer variable optical attenuator based on the vertical MMI structure.
Compared with the prior art, the invention has the innovation points that:
1. monolithic integration of the organic and inorganic photonic devices is realized, the preparation process is compatible with the existing silicon dioxide PLC process, the device cost is easy to reduce, and large-scale production is realized;
2. the VOA device of the polymer PLC is used for replacing the VOA device of the silicon dioxide PLC, so that low-power-consumption tuning is realized, and the power consumption of the device is reduced;
3. the organic MMI device with the vertical structure has a compact structure, and the preparation of a three-dimensional photonic device is realized;
4. the process can realize the preparation of multilayer PLC devices and provides possibility for three-dimensional integrated devices.
In conclusion, the process developed by the invention can realize monolithic hybrid integration of organic and inorganic optical waveguide devices, the polymer VOA device of the vertical-structure MMI prepared based on the process has the advantages of compact structure, low power consumption, high response speed, large extinction ratio and the like, can be used in a WDM system in optical communication to play a role in power balance, and can be used for preparing three-dimensional integrated optical waveguide devices, thereby having important significance for photonic integration.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1: the cross-sectional structure of the polymer variable optical attenuator is shown in the figure;
FIG. 2: the invention discloses a schematic cross-sectional view of an inorganic waveguide part of a polymer variable optical attenuator;
FIG. 3: the invention discloses a schematic cross-sectional view of an organic waveguide part of a polymer variable optical attenuator;
FIG. 4: the invention relates to a preparation process flow chart of a polymer variable optical attenuator;
FIG. 5: the invention discloses a light field distribution schematic diagram of a polymer variable light attenuator under two working modes; wherein, the graph (a) is the light field distribution diagram under the first working mode, and the graph (b) is the light field distribution diagram under the second working mode;
FIG. 6: the invention relates to spectrograms of two working modes of a polymer variable optical attenuator.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and all other embodiments obtained by a person of ordinary skill in the art without any inventive work based on the embodiments of the present invention belong to the protection scope of the present invention.
Example 1
As shown in fig. 1, the organic-inorganic hybrid integrated VOA device based on a vertical MMI structure is provided. To show the device structure, the schematic diagram is partially cross-sectioned to expose the silica cladding, polymer core waveguide structure. The names of the parts are as follows: the silicon substrate 11, the silica cladding 12, the silica core waveguide with a strip structure as the silica input waveguide unit 131 and the silica output waveguide unit 132, the polymer cladding 14, the metal modulation electrode 15, and the polymer core waveguide 16, respectively.
The refractive index difference between the silica overclad and the silica core is 2%, and the calculation formula is shown as formula (1), wherein the silica core is a germanium-doped silica material, and the refractive index is n11.4739; the upper cladding is made of silicon dioxide material doped with boron and phosphorus and has a refractive index of n21.4450, the waveguide cross-section is as shown in FIG. 2, which is a schematic cross-sectional view of the inorganic waveguide portion of the polymer variable optical attenuator, the silica input waveguide unit 131 and the silica output waveguide unit 132 have the same dimensional parameters, and the silica input waveguide unit 131 is taken as an example for description, and the thickness H of the silica input waveguide unit 131wgAnd width WwgAll are 4 μm. Thickness H of silica upper cladding layer on silica input waveguide unit 131 for making the device compactgapAnd was 4 μm. The polymer clad 14 may be made of polymethyl methacrylate (PMMA), Polyethylene (PE), Polyester (PET), Polystyrene (PS), EpoClad, or the like, and in the present embodiment, PMMA is used as the polymer clad 14 and has a thickness Hclad_polyAnd 7 μm.
The polymer core waveguide 16 may be made of a polymer material with a negative thermo-optic coefficient, including SU-82002, SU-82005, EpoCore, etc., and in this embodiment, the polymer core waveguide 16 is made of SU-82002. As shown in FIG. 3, which is a schematic cross-sectional view of the organic waveguide portion of the polymer variable optical attenuator, the height W of the polymer core waveguide 16MMI12 μm, H was removedgapAnd Hwg(located in part of the silica overclad) still remaining 4 μm (i.e., H)wg_poly4 μm, located in the inner portion of the polymer cladding) for the purpose of improving the modulation efficiency of the electrode and preparing for the next three-dimensional integration.
Light enters the silica input waveguide unit 131 by coupling and then enters the polymer core waveguide 16. Due to the fabrication process, the polymer core waveguide 16 is fabricated to form an MMI structure, and light passes through a self-imaging length L using the self-imaging principle of MMIMMIA 3092 μm polymer core waveguide would again form a spot at the input of the silica output waveguide unit 132, coupling into the silica outputThe waveguide unit 132. The portion of the polymer core waveguide 16 extending into the polymer cladding is used for modulation, when voltage is applied to the electrodes, the heating of the electrodes changes the temperature of the polymer core waveguide below, and when light passes through the polymer core waveguide with the changed temperature, a phase difference is generated, so that the self-imaged position changes, the light intensity coupled into the silica output waveguide unit 132 changes, and thus a VOA device is formed.
As shown in fig. 4, the steps of preparing the organic-inorganic hybrid integrated VOA device based on the vertical MMI structure according to the present invention are as follows:
the method comprises the following steps: growing a compact 15-micron-thick silicon dioxide lower cladding layer on a silicon wafer substrate by a thermal oxidation method;
step two: then depositing a 4-micron germanium-doped silica core layer on the silica lower cladding layer by a PECVD method; the PECVD equipment comprises a PECVD chamber, a substrate, an upper electrode, a lower electrode and a lower electrode, wherein the chamber pressure of the PECVD apparatus is 500mTorr, the substrate temperature is 330 ℃, the low-frequency radio-frequency power of the upper electrode is 400W, the high-frequency radio-frequency power of the upper electrode is 600W, the silane gas flow is 25sccm, the nitric oxide gas flow is 1900sccm, the germane gas flow is 2.0sccm, and the deposition rate is 200 nm/min;
step three: the surface of a germanium-doped silicon dioxide core layer is coated with SU-82010 photoresist of MicroChem company in a spin mode, prebaking is carried out firstly at 65 ℃ for 10 minutes and 90 ℃ for 20 minutes, and the mixture is naturally cooled and solidified, and an SU-8 photoresist layer I with the thickness of 20 microns is formed by controlling the rotating speed to be 1000 rpm and the spin-coating time to be 20 s; under a 365nm ultraviolet photoetching machine, the optical power is 23mW/cm2Carrying out plate photoetching for 20s, carrying out postbaking at 65 ℃ for 10 min and at 95 ℃ for 20 min, cooling to room temperature, placing the plate into PGMEA (propylene glycol-monomethylether-acetate) developing solution for developing, placing the plate into isopropanol for rinsing to remove residual glue, washing the reaction solution by deionized water, erecting a film for 30 min and SU-82010 mask layer at 125 ℃, transferring a pattern with the same structure (the width is 4 mu m and the length is 10000 mu m) as a strip waveguide to be prepared on a photoetching plate onto a photoetching adhesive layer I, and preparing a strip junction on a germanium-doped silicon dioxide core layer by an ICP (inductively coupled plasma) etching methodA structured silica core waveguide; in order to ensure that the side wall of the waveguide is steep, the ICP is introduced with gas C4F8/SF8Mixing the gas; removing the photoresist layer I on the silicon dioxide core layer waveguide, wherein the width and the height of the silicon dioxide core layer waveguide with the strip-shaped structure are the same and are both 4 micrometers, and the length is 10000 micrometers for insensitivity of polarization;
step IV: an upper cladding layer of silica doped with boron and phosphorus, having a thickness of 4 μm, is deposited by PECVD on the silica core waveguide in a strip configuration, the upper and lower cladding layers collectively being referred to as cladding layer 12. The PECVD equipment comprises a PECVD device, a substrate, a bottom electrode, a mixed gas of borane and nitrogen, a molar fraction of borane in the mixed gas of 120sccm, a molar fraction of phosphine and nitrogen in the mixed gas of 30sccm, and a molar fraction of phosphine in the mixed gas of 8%, wherein the chamber pressure of the PECVD device is 2500mTorr, the substrate temperature is 355 ℃, the radio frequency power of the bottom electrode is 1800W; the difference between the refractive indexes of the core layer and the cladding layer of the finally obtained silica core layer waveguide is 2%;
step five: repeating the third step of spin coating again to form an SU-8 photoresist layer II on the silica cladding 12, carrying out pre-baking treatment, naturally cooling and curing, transferring the pattern with the same structure (the width is 4 microns and the length is 3092 microns) of the polymer core layer on the photoetching plate II and needing to be prepared onto the photoresist layer II through ultraviolet photoetching, developing and post-baking, and etching a window on the silica cladding 12 through an ICP (inductively coupled plasma) etching method, wherein the bottom surface of the window and the bottom surface of the silica core layer 13 are positioned on the same plane; in order to ensure that the side wall of the waveguide is steep, the ICP is introduced with gas C4F8/SF8Mixing the gas; the width of the window is the same as that of the silicon dioxide core layer 13, and the length of the window is 3092 mu m; the window is located at the middle position right above the silicon dioxide core layer 13 along the transmission direction of light; then removing the photoresist layer II of the silicon dioxide cladding layer 12;
step (c): SU-82005 photoresist of Micro Chem is spin-coated on the silicon dioxide cladding 12, the material has self-leveling property, polishing treatment is not needed, besides a window can be filled, an SU-8 thin layer can be formed on the silicon dioxide cladding 12, and an SU-8 thin film with the thickness of 4 microns is formed by controlling the rotating speed to be 4000 revolutions per minute and the spin-coating time to be 20 s;
step (c): pre-baking the obtained SU-8 polymer film, naturally cooling and curing, wherein the step firstly needs pre-baking at 65 ℃ for 10 minutes and 95 ℃ for 20 minutes, and under a 365nm ultraviolet photoetching machine, the light power is 23mW/cm2Performing plate photoetching for 8s, performing post-baking at 65 ℃ for 10 minutes and 95 ℃ for 20 minutes, cooling to room temperature, placing the materials into PGMEA developer for development, then placing the materials into isopropanol for rinsing to remove residual glue, washing reaction liquid by deionized water, and finally erecting the film for 30 minutes at 125 ℃ to obtain a polymer SU-8 core layer waveguide 16 with a strip-shaped structure; the width is the same as the width of the silica core layer, the length is 3092 μm, the overall height of the polymer core waveguide 16 is 12 μm, and the portion above the silica cladding 12 is 4 μm;
step (v): spin-coating polymethyl-methacrylate (PMMA) -C10 photoresist of Micro Chem company on the SU-8 polymer core layer waveguide 16, controlling the spin-coating rotation speed to be 1000r/min to ensure that the thickness of the photoresist outside the polymer core layer waveguide 16 is 7 microns (the thickness of the photoresist on the SU-8 polymer waveguide 16 is 3 microns), putting the photoresist in an oven, heating the photoresist at 120 ℃ for 2 hours, and naturally cooling the photoresist to room temperature to form a polymer cladding 14;
step ninthly: an Al film with the thickness of 100nm is vapor-plated on a polymer cladding 14, a spin coating process is adopted, 1.5 mu m of positive photoresist BP212 is spin-coated on the Al film, the Al film is baked for 20 minutes at 90 ℃, the Al film is in close contact with an electrode mask plate under an ultraviolet photoetching machine for plate alignment photoetching, the structure of the electrode mask plate is larger than that of the SU-8 core layer waveguide 16, the exposure is carried out for 8s, the waveguide mask plate is removed, the electrode mask plate is developed by BP212 developing solution and then baked for 15 minutes at 100 ℃, then the Al film which is not masked by the photoresist is removed by NaOH solution with the mass concentration of 6%, the residual BP212 is removed by exposure again, the Al electrode is exposed, the size of the Al electrode is 20 mu m wide, the length of the Al electrode is larger than that of the SU-8 core layer waveguide and is 4000 mu m, and the Al electrode is positioned above the SU-8 core layer waveguide 16.
FIG. 5 is a schematic diagram showing the optical field distribution of the polymer variable optical attenuator of the present invention in two operating modes; where plot (a) is a schematic diagram of the optical field distribution in the first mode of operation (i.e., light is mostly re-coupled into the silica output waveguide unit), at which time the temperature change in the modulation portion of polymer core waveguide 16 is 1.3K, and the loss is 0.58 dB; FIG. b is a schematic diagram of the optical field distribution in the second mode of operation (i.e., light is no longer coupled into the silica output waveguide unit), when the temperature change in the modulation portion of polymer core waveguide 16 is 7.0K, and the loss is 21.18 dB; the device can realize 20.6dB within the temperature change of 7K.
As shown in fig. 6, which is a simulated spectrum diagram of the polymer core layer 16 with a length of 3092 μm in both the on and off operating states, at a wavelength of 1316nm, even 41.89dB of extinction can be achieved, with a 1dB bandwidth of 27 nm. The device has the advantages of high extinction ratio, large bandwidth, low power consumption, compactness, easy preparation and suitability for large-scale production.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (7)

1. An organic-inorganic hybrid integrated polymer variable optical attenuator based on a vertical multimode interferometer structure, characterized in that: the light-emitting diode is composed of a silicon substrate, a silica lower cladding layer prepared on the silicon substrate, a silica input waveguide unit, a polymer core layer waveguide unit and a silica output waveguide unit which are prepared on the silica lower cladding layer along the light propagation direction, a silica upper cladding layer which is positioned on the upper surface and the lower surface of the silica lower cladding layer, positioned on the same plane with the lower surfaces of the silica input waveguide unit and the silica output waveguide unit and wraps the silica input waveguide unit and the silica output waveguide unit, a polymer cladding layer which is positioned on the polymer core layer waveguide unit and the silica upper cladding layer, positioned on the same plane with the upper surface of the silica upper cladding layer and wraps the polymer waveguide unit, and a metal modulation electrode positioned on the polymer cladding layer;
silica input waveguide unit, polymer core layer waveguide unit, and silica inputThe bottoms of the waveguide output units are positioned on the same plane, and the widths of the silica input waveguide unit, the polymer core layer waveguide unit and the silica output waveguide unit are the same in the light propagation direction; the height of the silica input waveguide unit is the same as that of the silica output waveguide unit, and the polymer core layer waveguide unit extends into the polymer cladding and is higher than that of the silica input waveguide unit and that of the silica output waveguide unit; the input light is coupled from the silica input waveguide unit and transmitted in the polymer core layer waveguide unit, the polymer core layer waveguide unit is of a vertical MMI structure, and the length L of the polymer core layer waveguide unit is optimizedMMIMore than 90% of input light is coupled into the silicon dioxide output waveguide unit; the modulating electrode is positioned on the upper surface of the polymer cladding layer right above the polymer core layer waveguide unit.
2. The organic-inorganic hybrid integrated polymer variable optical attenuator based on the vertical multimode interferometer structure of claim 1, wherein: the refractive index difference between the silica upper cladding layer and the silica core layer is 0.36-2%, the calculation formula is shown as formula (1), and the refractive index of the core layer is n1Refractive index of cladding layer n2The refractive index of the core layer is greater than that of the cladding layer;
Figure FDA0003066001480000011
3. the hybrid organic-inorganic integrated polymer variable optical attenuator based on the vertical multimode interferometer structure of claim 2, wherein: the silicon dioxide core layer is silicon dioxide doped with germanium, and the silicon dioxide upper cladding layer is silicon dioxide doped with boron and phosphorus.
4. The organic-inorganic hybrid integrated polymer variable optical attenuator based on the vertical multimode interferometer structure of claim 1, wherein: the polymer cladding material is polymethyl methacrylate, polyethylene, polyester, polystyrene or EpoClad.
5. The organic-inorganic hybrid integrated polymer variable optical attenuator based on the vertical multimode interferometer structure of claim 1, wherein: the polymer core layer is made of SU-82002, SU-82005 or EpoCore.
6. The organic-inorganic hybrid integrated polymer variable optical attenuator based on the vertical multimode interferometer structure of claim 1, wherein: the metal modulation electrode is made of one or more of gold, silver and aluminum.
7. The method for preparing an organic-inorganic hybrid integrated polymer variable optical attenuator based on a vertical multimode interferometer structure as claimed in claim 1, comprising the steps of:
the method comprises the following steps: growing a compact silica lower cladding layer with the thickness of 12-18 mu m on a silicon wafer substrate by a thermal oxidation method;
step two: then depositing on the silica lower cladding layer by a PECVD method to obtain a germanium-doped silica core layer with the thickness of 3.5-6.5 microns;
step three: spin-coating a photoresist layer I on the germanium-doped silica core layer, naturally cooling and curing after prebaking treatment, transferring a pattern which is on the photoetching plate I and has the same or complementary structure with the strip-shaped waveguide to be prepared onto the photoresist layer I through ultraviolet photoetching, developing and after-baking, and preparing the silica core layer waveguide with the strip-shaped structure on the germanium-doped silica core layer through an ICP (inductively coupled plasma) etching method; then removing the photoresist layer I on the silicon dioxide core waveguide;
step IV: depositing on a silicon dioxide core layer waveguide with a strip structure by a PECVD method to obtain a silicon dioxide upper cladding layer which is doped with boron and phosphorus and has the thickness of 3-5 mu m, wherein the silicon dioxide upper cladding layer and the silicon dioxide lower cladding layer prepared in the first step are collectively called as a silicon dioxide cladding layer;
step five: spin coating on the silicon dioxide cladding again to form a photoresist layer II, and naturally cooling after prebakingCuring, transferring a pattern which is the same as or complementary to the polymer core layer waveguide structure to be prepared on the photoetching plate II onto the photoresist layer II through ultraviolet photoetching, developing and post-baking, and etching a window which is the same as the polymer core layer waveguide structure on the silicon dioxide cladding layer through an ICP (inductively coupled plasma) etching method; along the transmission direction of light, the window is positioned at the middle position right above the silicon dioxide core layer waveguide of the strip-shaped structure; the bottom surface of the window and the bottom surface of the silicon dioxide core layer waveguide are positioned on the same plane; the width of the window is the same as that of the silicon dioxide core layer waveguide of the strip structure, and the length of the window is MMI which is the self-imaging length LMMISelf-image length LMMILess than the length of the silica core waveguide; then removing the photoresist layer II on the silicon dioxide cladding; along the transmission direction of light, the silicon dioxide core layer waveguide of the strip-shaped structure in front of the window is a silicon dioxide input waveguide unit, and the silicon dioxide core layer waveguide of the strip-shaped structure behind the window is a silicon dioxide output waveguide unit;
step (c): spin coating a polymer core layer material on the silica cladding layer, wherein the material has self-leveling property and does not need polishing treatment, except that the window in the fifth step is filled with the polymer core layer material, a polymer thin layer is formed on the silica cladding layer, and a polymer thin film with the thickness of 2-4 microns is formed by controlling the rotating speed and the spin coating time;
step (c): naturally cooling and curing the obtained polymer film after pre-baking treatment, transferring a graph with the same or complementary structure as that of the polymer core layer waveguide structure to be prepared on a photoetching plate onto the polymer film through ultraviolet photoetching, developing and post-baking, then placing the polymer film into a developing solution corresponding to a polymer for developing, then placing the polymer film into a rinsing solution for rinsing to remove polymer materials except the polymer core layer waveguide structure, washing the reaction solution with deionized water, and finally hardening for 20-40 minutes to obtain the polymer core layer waveguide with a strip-shaped structure;
step (v): spin-coating a polymer cladding material on the polymer core layer waveguide, forming the polymer cladding material with the thickness of 5-7 microns by controlling the spin-coating rotation speed and the spin-coating time, putting the polymer cladding material into an oven, heating the polymer cladding material at 110-130 ℃ for 1.5-3.0 hours, and naturally cooling the polymer cladding material to room temperature to obtain a polymer cladding; the silicon dioxide cladding, the polymer core layer waveguide with the strip structure, the polymer cladding and the modulation electrode form a polymer VOA device;
step ninthly: evaporating a metal film with the thickness of 50-200 nm on a polymer cladding, spinning a photoresist layer IV on the metal film, naturally cooling and curing after prebaking, transferring a pattern which is the same as or complementary to an electrode structure to be prepared on a photoetching plate IV onto the photoresist layer IV through ultraviolet photoetching, developing and postbaking, hardening the developed film, and corroding metal outside the electrode structure by using a corrosive liquid corresponding to the metal after naturally cooling to obtain a modulation electrode; the modulation electrode is positioned right above the polymer core layer waveguide and aligned with the center of the polymer core layer waveguide, the left and right of the modulation electrode exceed the polymer core layer waveguide by more than 50 microns, and the width of the modulation electrode is 20-40 microns; and removing the residual photoresist to prepare the polymer variable optical attenuator based on the organic-inorganic hybrid integration of the vertical MMI structure.
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