An optical waveguide amplifier based on an erbium-ytterbium co-doped polymer composite structure core layer and a preparation method thereof

Abstract

An erbium-ytterbium co-doped polymer composite structure core layer optical waveguide amplifier belongs to the technical field of polymer optical waveguide amplifiers. It is composed of a silicon substrate, a silica lower cladding layer, a low-loss polymer core layer, an erbium-ytterbium co-doped polymer gain layer, and a polymethyl methacrylate upper cladding layer in sequence; the low-loss polymer core layer, the erbium-ytterbium co-doped polymer gain layer, and the polymethyl methacrylate upper cladding layer are all located above the silica lower cladding layer, the low-loss polymer core layer is coated in the erbium-ytterbium co-doped polymer gain layer, and the erbium-ytterbium co-doped polymer gain layer is coated in the polymethyl methacrylate upper cladding layer; the low-loss polymer core layer and the erbium-ytterbium co-doped polymer gain layer form a composite structure core layer. The composite structure core layer optical waveguide amplifier designed by the present invention can obtain a greater gain than traditional rectangular waveguide and inverted ridge optical waveguide amplifiers under the conditions of the same waveguide size and waveguide length, further improving the application prospect of the polymer optical waveguide amplifier.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer optical waveguide amplifiers, and particularly relates to an erbium-ytterbium co-doped polymer composite structure core layer optical waveguide amplifier and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of silicon-based integrated photonics, the integration degree of various silicon optical devices has been increasing day by day. With the increase in the number of devices, the losses brought by silicon optical devices cannot be ignored. External losses introduced by reasons such as the inherent insertion loss of the device and the roughness of the waveguide sidewall will limit the performance of the on-chip optical interconnection optical path. Therefore, compensating for optical signals is particularly important in optical chips. For this reason, people have tried various ways to amplify optical signals. Among them, rare-earth doped optical waveguide amplifiers have received more and more attention due to their advantages such as linear gain response, temperature insensitivity, and low noise.

[0003] An erbium-doped optical waveguide amplifier (EDWA) mainly uses the transition within the 4f energy level of erbium ions to amplify the signal light in the communication wavelength range of 1550 nm. According to the properties of the matrix material, erbium-doped optical waveguide amplifiers can be divided into two categories: inorganic erbium-doped optical waveguide amplifiers and organic erbium-doped optical waveguide amplifiers. Compared with inorganic erbium-doped optical waveguide amplifiers, preparing an organic erbium-doped optical waveguide amplifier by incorporating an erbium-doped nanocrystal into a low-loss photosensitive polymer has the advantages of simple process, low cost, and easy silicon-based integration, and has become a very promising technical solution in recent years.

[0004] Optical waveguide amplifiers for on-chip applications require high signal gain and low transmission loss. However, it is difficult to simultaneously achieve this goal for a rectangular structure erbium-doped nanocrystal polymer optical waveguide amplifier due to the absorption and scattering of nanocrystals in the waveguide. Therefore, it is urgent to design an optical waveguide amplifier structure to meet the requirements of high gain and low loss. Summary of the Invention

[0005] The purpose of the present invention is to provide an erbium-ytterbium co-doped polymer composite structure core layer optical waveguide amplifier and a preparation method thereof.

[0006] An erbium-ytterbium co-doped polymer composite structure core layer optical waveguide amplifier described in the present invention, such as Figure 1As shown in Figure 2, it is composed of a silicon substrate 1, a silica lower cladding 2, a low-loss polymer core layer 3, an erbium-ytterbium co-doped polymer gain layer 4, and a polymethyl methacrylate (PMMA) upper cladding 5 from bottom to top in sequence; the low-loss polymer core layer 3 and the erbium-ytterbium co-doped polymer gain layer 4 are in a strip structure, and the low-loss polymer core layer 3, the erbium-ytterbium co-doped polymer gain layer 4, and the polymethyl methacrylate upper cladding 5 are all located on the silica lower cladding 2. The low-loss polymer core layer 3 is coated in the erbium-ytterbium co-doped polymer gain layer 4, and the erbium-ytterbium co-doped polymer gain layer 4 is coated in the polymethyl methacrylate upper cladding 5; the low-loss polymer core layer 3 and the erbium-ytterbium co-doped polymer gain layer 4 form a composite structure core layer. After the signal light and the pump light are respectively emitted by a laser, they are coupled through a wavelength division multiplexer. The coupled optical signal is docked with the optical waveguide amplifier through an optical fiber and finally input into the composite structure core layer.

[0007] The present invention designs an optical waveguide amplifier with a silica as the lower cladding, and a composite structure core layer composed of a low-loss polymer and an erbium-ytterbium nanocrystal co-doped polymer. The absorption loss of the low-loss polymer core layer 3 in the 1550 nm communication band is very small, so the transmission loss of the signal light can be effectively reduced; the erbium-ytterbium nanocrystal co-doped polymer is used as the gain layer 4 to amplify the signal light. The refractive index of the erbium-ytterbium co-doped polymer gain layer 4 (about 1.57) is slightly greater than that of the low-loss polymer core layer 3 (about 1.55), and the erbium-ytterbium nanocrystal co-doped polymer can obtain a strip waveguide structure through a simple photolithography and development technology. After coating the low-loss polymer core layer 3, a composite waveguide core layer structure is formed. By optimizing the waveguide structure size, most of the optical field of the signal light can be distributed in the erbium-ytterbium co-doped polymer gain layer 4 when the signal light is transmitted in the waveguide, so as to achieve the purpose of reducing the transmission loss; almost all of the optical field of the pump light is distributed in the erbium-ytterbium co-doped polymer gain layer 4, providing sufficient pump energy for realizing the population inversion between the ground state and the excited state energy levels of erbium ions (amplification of the signal light). The signal light and the pump light in the erbium-ytterbium co-doped polymer gain layer 4 have a high overlap factor, so as to achieve the purpose of increasing the gain. Through the comparison of the simulation results, the composite structure core layer optical waveguide amplifier designed by the present invention can obtain a greater gain than the traditional rectangular waveguide and inverted ridge optical waveguide amplifier under the conditions of the same waveguide size and waveguide length, further improving the application prospect of the polymer optical waveguide amplifier.

[0008] The photoresist material of the low-loss polymer core layer described in the present invention is fluorinated epoxy resin (F-SU8,

J.Polym.Sci., Part A: Polym.Chem. 45, 5923 (2007)

[0009]

[0010] The absorption loss of SU-8 waveguide material for optical signals is mainly due to the vibrational absorption of carbon-hydrogen bonds in the near-infrared band. This absorption loss can be reduced by replacing hydrogen atoms with atoms of relatively large atomic mass, such as fluorine atoms. After replacing hydrogen atoms with fluorine atoms in F-SU8, the molecular mass is increased and the harmonic frequency is reduced, resulting in a red shift of the low-loss band, thereby reducing the inherent optical absorption loss of this waveguide material in the 1310nm - 1550nm near-infrared wavelength region. Therefore, F-SU8 (or ZPU) polymer materials can significantly reduce the absorption loss of the waveguide in the near-infrared band.

[0011] The erbium-ytterbium co-doped polymer gain layer 4 material is an ultraviolet negative photoresist material doped with erbium-ytterbium nanocrystals. The ultraviolet negative photoresist is SU-8 2002, SU-8 2005, EpoCore, EpoClad, etc. This ultraviolet negative photoresist will undergo a cross-linking reaction and solidify under ultraviolet light exposure conditions, while the unexposed area of the ultraviolet negative photoresist will be removed under the action of a special developer during the subsequent development process. By simple ultraviolet exposure and development techniques, an erbium-ytterbium co-doped polymer gain layer 4 coating the low-loss polymer core layer 3 can be obtained, thus forming a composite structure core layer. In this invention, 2 mmol of erbium-ytterbium nanocrystals (0.5 g, where the molar concentration ratio of erbium ions to ytterbium ions is 1:9) prepared by a high-temperature thermal decomposition method are dissolved in 1 mL of toluene to obtain a toluene solution of erbium-ytterbium nanocrystals; then the obtained toluene solution is mixed with the ultraviolet negative photoresist in a mass ratio of 1:4 and stirred in an ultrasonic machine to fully mix the toluene solution and the ultraviolet negative photoresist, so that the erbium-ytterbium nanocrystals are evenly distributed in the ultraviolet negative photoresist, thereby obtaining the erbium-ytterbium co-doped polymer gain layer material.

[0012] In the embodiment of this invention, the erbium-ytterbium nanocrystals synthesized by the high-temperature thermal decomposition method are NaYF4:Er 3+ ,Yb 3+ nanocrystals. The erbium-ytterbium nanocrystals are not limited to NaYF4:Er 3+ ,Yb 3+ nanocrystals (it can also be BaYF4:Er 3+ ,Yb 3+ , NaYF4:Er 3+ ,Yb 3+ ,Ce 3+ etc.). For the erbium-ytterbium nanocrystals of this invention, ytterbium ions are used as sensitizers, which can inhibit the agglomeration of erbium ions caused by too high concentration and the phenomenon of concentration quenching; at the same time, ytterbium ions have a larger absorption cross-section for 980nm pump light, and the energy of the absorbed pump light can be transferred to erbium ions through energy transfer between erbium and ytterbium ions, thereby improving the utilization rate of the pump light and greatly reducing the threshold power of the pump light.

[0013] The optical field distribution of the composite structure core layer composed of the low-loss polymer core layer 3 and the erbium-ytterbium co-doped polymer gain layer 4 is shown in Figure 2. Almost all of the pump light is confined in the gain layer 4, providing sufficient pump energy for achieving population inversion of erbium ions; the signal light is distributed in both the low-loss polymer core layer 3 and the erbium-ytterbium co-doped polymer gain layer, but mainly concentrated in the gain layer 4, so that the signal light in the gain layer has a large enough optical power density to achieve stimulated emission of erbium ions for the signal light.

[0014] In the embodiment of the present invention, a fluorinated polymer is used to fabricate the low-loss polymer core layer, and an erbium-ytterbium co-doped polymer is used to fabricate a gain layer matching the core layer waveguide. The low absorption characteristics of the fluorinated polymer in the near-infrared band reduce the transmission loss of the waveguide. The erbium-ytterbium co-doped polymer can fabricate a strip waveguide structure through photolithography and development technology. The formed composite structure core layer confines almost all of the pump light in the gain layer and most of the signal light in the gain layer, ensuring the overlap of the optical field modes of the pump light and the signal light to the greatest extent and providing high gain for the signal light. After calculation, under the conditions of the same waveguide size and waveguide length, the gain obtained by the composite structure core layer optical waveguide amplifier designed by the present invention is 1.75 dB larger than that of the rectangular waveguide and 4 dB larger than that of the ridge waveguide, as Figure 5 shown. The results show that the composite structure core layer designed by the present invention can effectively amplify the signal light, and the gain performance of the device is significantly improved compared with the traditional rectangular waveguide [J. Nanosci. Nanotechnol. 10, 1947 (2010)] and inverted ridge waveguide [Microw. Opt. Technol. Lett. 53, 2157 (2011)], and it is expected to play a greater role in the application of polymer optical waveguide amplifiers.

[0015] A preparation method of a composite structure core layer optical waveguide amplifier based on an erbium-ytterbium co-doped polymer according to the present invention comprises the following steps:

[0016] (1) Grow 5 - 10 μm thick silicon dioxide on the silicon substrate 1 to serve as the lower cladding 2; then wipe the surface of the silicon dioxide with acetone to remove impurities such as grease on the surface of the silicon dioxide, then use ethanol to remove the acetone on the surface of the silicon dioxide, and finally rinse and dry with deionized water;

[0017] (2) Spin-coat the low-loss polymer core layer photoresist material on the silicon dioxide lower cladding 2 with a spin coater at a speed of 2500 - 4000 revolutions per second to obtain a 2 - 4 μm thick photoresist film; then perform pre-baking at 55 - 65 °C for 10 - 15 minutes and at 85 - 95 °C for 20 - 25 minutes, and finally cool naturally to room temperature;

[0018] (3) Cover a mask plate with a strip-shaped structure in the hollow area and a strip width of 2 - 4 μm on the low-loss polymer photoresist film, and make the two closely fit; perform ultraviolet exposure on the photoresist film for 5 - 10 seconds in a nitrogen atmosphere, so that the cross-linking reaction occurs in the exposed part of the photoresist, and cure to form a strip-shaped photoresist pattern with a width of 2 - 4 μm;

[0019] (4) Keep the ultraviolet-exposed photoresist film at 60 - 70 °C for 10 - 15 minutes and at 90 - 100 °C for 20 - 25 minutes for post-baking, and finally cool it naturally to room temperature;

[0020] (5) Place the post-baked photoresist film in the developer for 5 - 10 seconds to fully dissolve the photoresist that has not undergone cross-linking reaction, then use isopropyl alcohol solution to remove the residual developer and the dissolved photoresist residue, then rinse with deionized water to remove the residual isopropyl alcohol, and finally heat the obtained device to 120 - 150 °C for 30 - 60 minutes to make the waveguide structure more solid and the surface topography more flat, so as to prepare a strip-shaped low-loss polymer core layer 3 on the lower cladding 2, with a width of 2 - 4 μm and a thickness of 2 - 4 μm;

[0021] (6) Spin-coat a UV-negative photoresist material doped with erbium ytterbium nanocrystals on the low-loss polymer core layer 3 and the lower cladding 2 at a rotation speed of 2500 - 4000 revolutions per second, cover a UV-negative photoresist film doped with erbium ytterbium nanocrystals with a thickness of 2 - 4 μm on the low-loss polymer core layer 3, then perform pre-baking at 55 - 65 °C for 10 - 15 minutes and at 85 - 95 °C for 20 - 25 minutes, and finally cool it naturally to room temperature;

[0022] (7) Cover a mask plate with a strip-shaped structure in the hollow area and a strip width of 4 - 6 μm on the UV-negative photoresist film, and adjust the position of the silicon substrate 1 so that the low-loss polymer core layer 3 is in the center of the strip-shaped hollow area with a width of 4 - 6 μm, then make the mask plate closely fit with the UV-negative photoresist film; perform ultraviolet exposure on the UV-negative photoresist film for 5 - 10 seconds in a nitrogen atmosphere, so that the cross-linking reaction occurs in the exposed part of the photoresist, and cure to form a strip-shaped UV-negative photoresist pattern with a width of 4 - 6 μm;

[0023] (8) Keep the ultraviolet-exposed UV-negative photoresist film at 60 - 70 °C for 10 - 15 minutes and at 90 - 100 °C for 20 - 25 minutes for post-baking, and finally cool it naturally to room temperature;

[0024] (9) Place the post-baked ultraviolet negative photoresist film in the developer for 5 - 10 seconds to fully dissolve the photoresist that has not undergone cross-linking reaction. Then, use isopropyl alcohol solution to remove the residual developer and the dissolved ultraviolet negative photoresist residues. Next, rinse with deionized water to remove the residual isopropyl alcohol. Finally, heat the obtained device to 120 - 150 °C and hold for 30 - 60 minutes to make the waveguide structure more robust and the surface topography more flat. Thus, a strip-shaped erbium-ytterbium co-doped polymer gain layer 4 is prepared on the lower cladding 2 and the low-loss polymer core layer 3. The low-loss polymer core layer 3 is coated within the erbium-ytterbium co-doped polymer gain layer 4. The width of the gain layer 4 is 4 - 6 μm, and the thickness is 4 - 6 μm.

[0025] (10) Use a spin coater to spin-coat a cyclopentanone solution of polymethyl methacrylate on the erbium-ytterbium co-doped polymer gain layer 4 and the lower cladding 2 at a rotational speed of 3000 - 5000 revolutions per second. Then, heat to 120 - 150 °C and hold for 120 - 150 minutes to cure it, obtaining a 7 - 10 μm thick polymethyl methacrylate upper cladding 5 on the lower cladding 2. Thus, the composite structure core layer optical waveguide amplifier based on erbium-ytterbium co-doped polymer described in the present invention is prepared.

[0026] The composite structure core layer optical waveguide amplifier designed by the present invention can effectively achieve the amplification of signal light, and has the characteristics of simple process, low cost, high integration with silicon-based optical devices, and large gain per unit length. Compared with traditional rectangular waveguides and inverted ridge waveguides, the gain performance of the device has a relatively obvious improvement. This composite structure core layer optical waveguide amplifier is expected to play a greater role in the application of polymer optical waveguide amplifiers. Description of the Drawings

[0027] Figure 1 : Schematic structural diagram of the composite structure core layer optical waveguide amplifier based on erbium-ytterbium co-doped polymer described in the present invention;

[0028] The names of each part are: silicon substrate 1, silica lower cladding 2, low-loss polymer core layer 3, erbium-ytterbium co-doped polymer gain layer 4, polymethyl methacrylate upper cladding 5;

[0029] Figure 2(a): Simulation image of the optical field distribution of the signal light with a wavelength of 1550 nm in the composite structure core layer designed by the present invention;

[0030] The right side of the optical field distribution simulation diagram is provided with a gray scale coordinate, and the optical field intensity in each region of the waveguide is characterized by the gray scale of that region. Analyzing Figure 2(a), it can be seen that 80% of the signal light intensity is distributed in the erbium-ytterbium co-doped polymer gain layer 4, and 14.8% of the signal light intensity is distributed in the low-loss fluorinated polymer core layer 3;

[0031] Figure 2(b): Optical field distribution diagram of the pump light with a wavelength of 980 nm in the composite structure core layer designed in the present invention;

[0032] It can be analyzed from Figure 2(b) that 92.4% of the pump light intensity is concentrated in the erbium-ytterbium co-doped polymer gain layer (4), which can provide sufficient pump energy for the amplification of the signal light;

[0033] Figure 3 : Schematic cross-sectional view of the rectangular structure optical waveguide amplifier described in the background technology along the direction perpendicular to the light transmission direction;

[0034] The names of each part are: silicon substrate 31, silica lower cladding 32, erbium-ytterbium co-doped polymer gain layer 33, and polymethyl methacrylate upper cladding 34;

[0035] Figure 4 : Schematic cross-sectional view of the inverted ridge structure optical waveguide amplifier described in the background technology along the direction perpendicular to the light transmission direction;

[0036] The names of each part are: silicon substrate 41, silica lower cladding 42, erbium-ytterbium co-doped polymer gain layer 43 with an inverted ridge structure, and polymethyl methacrylate upper cladding 44;

[0037] Figure 5 : Curve showing the relationship between the gain and the pump power of the composite structure core layer, rectangular structure, and inverted ridge structure optical waveguide amplifiers obtained by programming and simulating with Matlab software;

[0038] From Figure 5 It can be seen that the gain of the composite structure core layer optical waveguide amplifier is significantly greater than that of the rectangular structure and the inverted ridge structure. Specific implementation manner

[0039] Example 1

[0040] The specific implementation steps of the composite structure core layer optical waveguide amplifier based on erbium-ytterbium co-doped polymer of the present invention are as follows:

[0041] (1) Grow 5 μm thick silica on the silicon substrate 1 to be used as the lower cladding 2, then wipe the surface of the silica with a cotton ball dipped in acetone solution to remove impurities such as grease on the silica surface, then use ethanol to remove the acetone on the silica surface, and finally rinse with deionized water and dry;

[0042] (2) Spin-coat and pre-bake the F-SU8 negative ultraviolet photoresist. Spin-coat the F-SU8 negative ultraviolet photoresist on the lower cladding 2 with a spin coater at a speed of 3000 revolutions per second for 30 seconds to obtain a 2 μm thick F-SU8 photoresist film, and then perform a pre-baking operation on it, keep it at 60 °C for 10 minutes, then heat it to 90 °C and keep it for 20 minutes, and finally cool it naturally to room temperature;

[0043] (3) Perform photolithography to fabricate the F-SU8 core layer waveguide. Cover the silica lower cladding 2 coated with F-SU8 negative ultraviolet photoresist with a mask plate having a strip-shaped structure in the hollowed-out area and a strip width of 2 μm, and make the two fit tightly; perform ultraviolet exposure on the F-SU8 photoresist for 5.2 seconds in a nitrogen atmosphere to cause the cross-linking reaction of the exposed part of the photoresist and cure it to form a strip-shaped photoresist pattern with a width of 2 μm.

[0044] (4) Place the silica lower cladding 2 after ultraviolet exposure on a hot plate for post-baking, keep it at 65 °C for 10 minutes, then heat it to 95 °C and keep it for 20 minutes, and finally cool it naturally to room temperature.

[0045] (5) Develop the waveguide after post-baking. Use developer, isopropyl alcohol, and deionized water. Place the silica lower cladding 2 in the developer for 6 seconds to fully dissolve the uncross-linked photoresist, then use an isopropyl alcohol solution to remove the residual developer and the dissolved photoresist residues, and finally rinse the silica lower cladding 2 with deionized water to remove the residual isopropyl alcohol to obtain the F-SU8 core layer 3 with a size of 2 μm × 2 μm. Heat the developed silica lower cladding 2 to 120 °C and keep it for 30 minutes to make the waveguide structure more solid and the surface topography more flat, thereby preparing a strip-shaped low-loss polymer core layer 3 on the lower cladding 2, with both the height and width being 2 μm.

[0046] (6) Spin-coat SU-8 2005 negative ultraviolet photoresist doped with NaYF4:Er 3+ ,Yb 3+ nanocrystals on the silica lower cladding 2 with the F-SU8 core layer 3 fabricated thereon. First, dissolve 2 mmol of NaYF4:Er 3+ ,Yb 3+ nanocrystals (about 0.5 g) prepared by a fully automatic nanosynthesizer in 2 mL of toluene, then mix the mixed solution with SU-8 2005 negative ultraviolet photoresist at a mass ratio of 1:4. Drop the photoresist doped with nanocrystals on the silica lower cladding 2 with the F-SU8 core layer 3 fabricated thereon. The rotation speed of the spin coater is 3000 revolutions per second, and spin coat for 30 seconds to cover a 2-μm-thick photoresist film doped with nanocrystals on the F-SU8 core layer 3 (the thickness of the erbium ytterbium nanocrystal-doped polymer photoresist film on the silica lower cladding 2 is 4 μm), and then perform pre-baking. Heat the silica lower cladding 2 to 60 °C and keep it for 10 minutes, then heat it to 90 °C and keep it for 20 minutes, and finally cool it naturally to room temperature.

[0047] (7) Cover the silica lower cladding 2 coated with doped NaYF4:Er with a mask plate having a strip-shaped structure in the hollowed-out area and a strip width of 4 μm3+ , Yb 3+ On the silica undercladding 2 of the nanocrystalline SU-8 2005 negative ultraviolet photoresist, the position of the silicon substrate 1 was adjusted under a microscope so that the F-SU8 core layer 3 was at the center of the strip-shaped structure hollowed-out area with a width of 4 μm, and then the mask plate was closely attached to the negative ultraviolet photoresist film; the photoresist was exposed to ultraviolet light for 6 seconds in a nitrogen atmosphere, causing the cross-linking reaction of the exposed part of the photoresist and curing to form a strip-shaped structure negative ultraviolet photoresist pattern with a width of 4 μm.

[0048] (8) The silica undercladding 2 after ultraviolet exposure was placed on a hot plate for post-baking, maintained at 65 °C for 10 minutes, then heated to 95 °C and maintained for 20 minutes, and finally naturally cooled to room temperature.

[0049] (9) The silica undercladding 2 after post-baking was developed using a photoresist developer, isopropyl alcohol, and deionized water. The silica undercladding 2 was placed in the developer for 6 seconds to fully dissolve the uncross-linked photoresist, then the residual developer and the dissolved photoresist residue were removed with an isopropyl alcohol solution, and finally the silica undercladding 2 was rinsed with deionized water to remove the residual isopropyl alcohol. The developed silica undercladding 2 was heated to 120 °C and maintained for 30 minutes to make the waveguide structure more robust and the surface morphology more flat, thereby preparing a strip-shaped erbium-ytterbium co-doped polymer gain layer 4 (both the height and width are 4 μm) on the undercladding 2 and the low-loss polymer core layer 3, and the low-loss polymer core layer 3 was coated in the erbium-ytterbium co-doped polymer gain layer 4.

[0050] (10) 3 g of polymethyl methacrylate was dissolved in 27 g of cyclopentanone to prepare the PMMA upper cladding material. The PMMA upper cladding material was spin-coated on the erbium-ytterbium co-doped polymer gain layer 4 and the silica undercladding 2 at a rotational speed of 3500 revolutions per second using a spin coater, and then heated to 120 °C and maintained for 150 minutes to cure it. The thickness of the PMMA on the silica undercladding 2 was 7 μm (the thickness of the PMMA on the erbium-ytterbium co-doped polymer gain layer was 3 μm), and finally the composite structure core layer optical waveguide amplifier based on the erbium-ytterbium co-doped polymer of the present invention was prepared.

Claims

1. An optical waveguide amplifier based on an erbium-ytterbium co-doped polymer composite structure core layer, characterized in that: It is composed of a silicon substrate (1), a silica lower cladding (2), a low-loss polymer core layer (3), an erbium-ytterbium co-doped polymer gain layer (4), and a polymethyl methacrylate upper cladding (5) from bottom to top in sequence; the low-loss polymer core layer (3) and the erbium-ytterbium co-doped polymer gain layer (4) are in a strip structure, and the low-loss polymer core layer (3), the erbium-ytterbium co-doped polymer gain layer (4), and the polymethyl methacrylate upper cladding (5) are jointly located above the silica lower cladding (2). The low-loss polymer core layer (3) is coated in the erbium-ytterbium co-doped polymer gain layer (4), and the erbium-ytterbium co-doped polymer gain layer (4) is coated in the polymethyl methacrylate upper cladding (5); the low-loss polymer core layer (3) and the erbium-ytterbium co-doped polymer gain layer (4) form a composite structure core layer.

2. An optical waveguide amplifier based on an erbium-ytterbium co-doped polymer composite structure core layer as described in claim 1, characterized in that: The material of the low-loss polymer core layer (3) is fluorinated epoxy resin or ZPU.

3. An optical waveguide amplifier based on an erbium-ytterbium co-doped polymer composite structure core layer as claimed in claim 1, characterized in that: The material of the erbium-ytterbium co-doped polymer gain layer (4) is an ultraviolet negative photoresist doped with erbium-ytterbium nanocrystals, and the ultraviolet negative photoresist is SU-8 2002, SU-8 2005, EpoCore or EpoClad.

4. The optical waveguide amplifier based on an erbium and ytterbium co-doped polymer composite structure core layer as claimed in claim 3, wherein: 2 mmol of erbium-ytterbium nanocrystals with a molar concentration ratio of erbium ions to ytterbium ions of 1:9 are dissolved in 1 mL of toluene, and then the obtained toluene solution is mixed with the ultraviolet negative photoresist at a mass ratio of 1:4, and stirred in an ultrasonic machine to fully mix the toluene solution and the ultraviolet negative photoresist, so that the erbium-ytterbium nanocrystals are evenly distributed in the ultraviolet negative photoresist, thereby obtaining the material of the erbium-ytterbium co-doped polymer gain layer (4).

5. An optical waveguide amplifier based on an erbium-ytterbium co-doped polymer composite structure core layer according to claim 4, characterized in that: The erbium ytterbium nanocrystals are NaYF4:Er 3+ ,Yb 3+ nanocrystals, BaYF4:Er 3+ ,Yb 3+ nanocrystals or NaYF4:Er 3+ ,Yb 3+ ,Ce 3+ nanocrystals.

6. An optical waveguide amplifier based on an erbium-ytterbium co-doped polymer composite structure core layer as claimed in claim 4, wherein: The thickness of the silica lower cladding (2) is 5 - 10 μm, the width of the low-loss polymer core layer (3) is 2 - 4 μm, and the thickness is 2 - 4 μm; the width of the erbium-ytterbium co-doped polymer gain layer (4) is 4 - 6 μm, and the thickness is 4 - 6 μm; the thickness of the polymethyl methacrylate upper cladding (5) above the silica lower cladding (2) is 7 - 10 μm.

7. The preparation method of an optical waveguide amplifier based on an erbium-ytterbium co-doped polymer composite structure core layer according to claim 6, the steps are as follows: (1) Grow 5 - 10 μm thick silica on the silicon substrate (1) to be used as the lower cladding (2); then wipe the surface of the silica with acetone to remove impurities on the surface of the silica, then use ethanol to remove the acetone on the surface of the silica, and finally rinse with deionized water and dry. (2) Use a spin coater to spin-coat the low-loss polymer core layer photoresist material on the silica lower cladding (2) at a rotation speed of 2500 - 4000 revolutions per second to obtain a photoresist film with a thickness of 2 - 4 μm; then keep it at 55 - 65 °C for 10 - 15 minutes and at 85 - 95 °C for 20 - 25 minutes for pre-baking, and finally naturally cool to room temperature. (3) Cover a mask plate with a hollowed-out area in a strip structure and a strip structure width of 2-4 μm on the low-loss polymer photoresist film, and make the two fit tightly; Ultraviolet expose the photoresist film for 5 - 10 seconds in a nitrogen atmosphere to cause the cross-linking reaction of the exposed part of the photoresist and solidify to form a strip-shaped photoresist pattern with a width of 2 - 4 μm. (4) Keep the ultraviolet-exposed photoresist film at 60 - 70 °C for 10 - 15 minutes and at 90 - 100 °C for 20 - 25 minutes for post-baking, and finally naturally cool to room temperature. (5) Place the post-baked photoresist film in the developer for 5 - 10 seconds to fully dissolve the photoresist that has not undergone cross-linking reaction. Then, use isopropyl alcohol solution to remove the residual developer and the dissolved photoresist residues, and then rinse with deionized water to remove the residual isopropyl alcohol. Finally, heat the obtained device to 120 - 150 °C and hold for 30 - 60 minutes to make the waveguide structure more robust and the surface topography more flat, thereby preparing a strip-shaped low-loss polymer core layer (3) on the silica lower cladding (2), with a width of 2 - 4 μm and a thickness of 2 - 4 μm. (6) Spin-coat a UV negative photoresist material doped with erbium and ytterbium nanocrystals on the low-loss polymer core layer (3) and the lower cladding (2) at a rotational speed of 2500 - 4000 revolutions per second to cover a 2 - 4 μm thick UV negative photoresist film doped with erbium and ytterbium nanocrystals on the low-loss polymer core layer (3). Then, perform pre-baking at 55 - 65 °C for 10 - 15 minutes and at 85 - 95 °C for 20 - 25 minutes, and finally cool naturally to room temperature. (7) Cover a mask plate with a strip-shaped structure in the hollowed area and a strip width of 4 - 6 μm on the UV negative photoresist film, and adjust the position of the silicon substrate (1) so that the low-loss polymer core layer (3) is at the center of the strip-shaped hollowed area with a width of 4 - 6 μm. Then, closely attach the mask plate to the UV negative photoresist film. Perform UV exposure on the UV negative photoresist film in a nitrogen atmosphere for 5 - 10 seconds to cause the cross-linking reaction of the exposed part of the photoresist and cure it to form a strip-shaped UV negative photoresist pattern with a width of 4 - 6 μm. (8) Perform post-baking on the UV negative photoresist film after UV exposure at 60 - 70 °C for 10 - 15 minutes and at 90 - 100 °C for 20 - 25 minutes, and finally cool naturally to room temperature. (9) Place the post-baked UV negative photoresist film in the developer for 5 - 10 seconds to fully dissolve the photoresist that has not undergone cross-linking reaction. Then, use isopropyl alcohol solution to remove the residual developer and the dissolved UV negative photoresist residues, and then rinse with deionized water to remove the residual isopropyl alcohol. Finally, heat the obtained device to 120 - 150 °C and hold for 30 - 60 minutes to make the waveguide structure more robust and the surface topography more flat, thereby preparing a strip-shaped erbium and ytterbium co-doped polymer gain layer (4) on the silica lower cladding (2) and the low-loss polymer core layer (3). The low-loss polymer core layer (3) is coated in the erbium and ytterbium co-doped polymer gain layer (4), and the width of the gain layer (4) is 4 - 6 μm and the thickness is 4 - 6 μm. (10) Using a spin coater at a rotational speed of 3000 - 5000 revolutions per second, spin coat a cyclopentanone solution of polymethyl methacrylate on the erbium-ytterbium co-doped polymer gain layer (4) and the silica lower cladding layer (2), and then heat it to 120 - 150 °C and hold for 120 - 150 minutes to cure it, obtaining a polymethyl methacrylate upper cladding layer (5) with a thickness of 7 - 10 μm on the silica lower cladding layer (2), thereby fabricating a composite structure core layer optical waveguide amplifier based on erbium-ytterbium co-doped polymer.

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