阅读说明：本技术 一种聚合物少模波导及其制备方法 (Polymer few-mode waveguide and preparation method thereof ) 是由 胡贵军 于成 于 2021-10-11 设计创作，主要内容包括：本发明公开了一种聚合物少模波导及其制备方法,属于平面光子器件技术领域,从下到上,依次由二氧化硅衬底、在二氧化硅衬底上旋涂的少模波导芯层、在少模波导芯层上旋涂的上包层组成,所述少模波导芯层采用稀土掺杂有源聚合物材料,所述上包层采用无掺杂的聚合物材料；所述稀土掺杂有源聚合物材料是将稀土纳米粒子通过物理方法均匀掺杂到SU-8聚合物材料中制备的芯层增益介质,所述稀土纳米粒子为NaYF-(4)：Yb,Er纳米粒子,本发明的一种少模聚合物波导克服了传统光波导放大器仅能对单一模式放大的局限,实现多个信号模式同时放大的功能。有效补偿模分复用系统中由于模式间转换、耦合以及传输过程中所产生的损耗,从而改善系统的传输性能。(The invention discloses a polymer few-mode waveguide and a preparation method thereof, belonging to the technical field of planar photonic devices, and sequentially consisting of a silicon dioxide substrate, a few-mode waveguide core layer spin-coated on the silicon dioxide substrate and an upper cladding layer spin-coated on the few-mode waveguide core layer from bottom to top, wherein the few-mode waveguide core layer is made of a rare earth doped active polymer material, and the upper cladding layer is made of an undoped polymer material; the rare earth doped active polymer material is a core layer gain medium prepared by uniformly doping rare earth nanoparticles into SU-8 polymer material by a physical method, wherein the rare earth nanoparticles are NaYF 4 : yb and Er nano particles, the few-mode polymer waveguide overcomes the limitation that the traditional optical waveguide amplifier can only amplify a single mode, and realizes the function of simultaneously amplifying a plurality of signal modes. Effectively compensate for losses due to mode-to-mode conversion, coupling and transmission in a mode division multiplexing system, thereby improvingTransmission performance of the system.)

1. The polymer few-mode waveguide is characterized by sequentially comprising a silicon dioxide substrate, a few-mode waveguide core layer and an upper cladding layer from bottom to top, wherein the few-mode waveguide core layer is formed by spin coating on the silicon dioxide substrate, the few-mode waveguide core layer is made of a rare earth doped active polymer material, and the upper cladding layer is made of an undoped polymer material.

2. The polymer few-mode waveguide of claim 1, wherein the rare earth doped active polymer material is a core gain medium prepared by uniformly doping rare earth nanoparticles into SU-8 polymer material by a physical method, wherein the rare earth nanoparticles are NaYF₄: yb and Er nano particles, wherein Er ions are luminescence center ions, and Yb is doped sensitizer ions.

3. The polymeric few-mode waveguide of claim 1, wherein the rare earth nanoparticles are NaYF₄:10％Er³⁺，18％Yb³⁺Wherein the concentration of the doped sensitizer ions is 18%, and the concentration of the luminescence center ions is 10%.

4. The polymer few-mode waveguide of claim 1, wherein the rare earth nanoparticles have erbium ion doping concentration of 0.4 x 10²⁰～0.8×10²⁰cm^-3The doping concentration of ytterbium ion is 0.4X 10²¹～0.8×10²¹cm^-3。

5. The polymeric few-mode waveguide of claim 1, wherein the upper cladding is undoped Polymethylmethacrylate (PMMA) material.

6. The polymer few-mode waveguide of claim 1, wherein the polymer few-mode waveguide adopts a square central symmetric structure, and the size of a few-mode waveguide core layer is 5 μm x 5 μm; the thickness range of the silicon dioxide substrate is as follows: 2-3 μm; the upper cladding thickness range is: 3-5 μm; the refractive indexes of the few-mode waveguide core layer and the upper cladding layer at the wavelength of 1550nm are 1.576 and 1.485 respectively.

7. The method of claim 1, wherein the steps are performed in the same order asThe method comprises the following steps: firstly, cleaning a silicon dioxide substrate by sequentially adopting acetone, ethanol and deionized water; then, NaYF₄:10％Er³⁺，18％Yb³⁺Dissolving the nano particles in toluene, physically doping the solution into SU-8 negative photoresist of a polymer, and preparing a core layer polymer material; coating a core layer polymer material on a silicon dioxide substrate by adopting a spin-coating method, and curing to form a few-mode waveguide core layer; carrying out ultraviolet photoetching on the photoresist, and transferring the pattern on the photoetching plate to the core layer photoresist; developing with SU-8 special developer, removing negative photoresist of the exposed part, baking to obtain few-mode square waveguide, and coating PMMA upper cladding.

Technical Field

The invention belongs to the technical field of planar photonic devices, and particularly relates to a polymer few-mode waveguide and a preparation method thereof.

Background

In recent years, services such as mobile internet and cloud computing have been rapidly developed, and demands for communication speed and capacity have been increased, and optical communication technology has been developed vigorously due to its advantages such as high speed, large capacity, and low power consumption. However, limited by the nonlinear effect, the communication transmission capacity of the standard single-mode fiber is already close to its theoretical limit (shannon limit), and the bandwidth expansion based on the wavelength division multiplexing technology in the conventional optical communication system cannot meet the continuous increase of the network bandwidth in the future, so that the transmission capability of the fiber needs to be developed and improved by using different optical dimensions. The mode division multiplexing is used as a transmission mode of space division multiplexing, mode dimensions which are orthogonal to each other in few-mode optical fibers are used as multiplexing channels, and the method is compatible with technologies such as dense wavelength division multiplexing and time division multiplexing, and can greatly improve communication capacity.

The construction of a mode division multiplexing system with ultra-large capacity and high spectral efficiency requires the support of core mode devices such as an optical modulator, a mode converter, a multiplexer/demultiplexer and the like. However, the transmission performance of the mode division multiplexing system is seriously affected by the conversion between modes, coupling and loss generated in the transmission process, and if the mode division multiplexing system is not compensated, the error rate of a transmission signal is inevitably greatly increased and the transmission distance of the signal is limited. The optical amplifier can directly amplify optical signals without conversion of the optical signals, and is an indispensable device for compensating the reduction of the optical transmission power of the signals. Therefore, it is urgently required to develop an optical amplifier capable of simultaneously amplifying a plurality of signal modes to solve the problem, thereby improving the mode signal transmission quality and improving the transmission performance of the mode division multiplexing communication system.

An erbium-doped optical waveguide amplifier (EDWA) is an optical amplifier with great prospect, which not only inherits the advantages of polarization crosstalk independence, low noise index and the like of an erbium-doped optical fiber amplifier, but also can realize high signal gain of a unit length waveguide near an operating wavelength (1550nm) by doping erbium ions with higher concentration in the waveguide by using an optical waveguide structure, and has the important advantages of miniaturization and compact structure. The erbium-doped optical waveguide amplifier taking the polymer as the matrix material has the outstanding advantages of low manufacturing cost, simple process, easy photonic integration and the like, becomes a research hotspot in recent years, and is applied to access networks.

The research on erbium-doped polymer optical waveguide amplifiers at home and abroad is remarkably advanced, but the devices are always on the aspect of single signal mode amplification, cannot amplify a plurality of signal modes and cannot meet the practical requirements of a mode division multiplexing communication system.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention provides a polymer few-mode waveguide amplifier which can realize the amplification function of a plurality of signal modes.

The invention is realized by the following technical scheme:

a polymer few-mode waveguide sequentially comprises a silicon dioxide substrate, a few-mode waveguide core layer and an upper cladding layer, wherein the few-mode waveguide core layer is in spin coating on the silicon dioxide substrate, the few-mode waveguide core layer is made of a rare earth doped active polymer material, and the upper cladding layer is made of an undoped polymer material.

Furthermore, the rare earth doped active polymer material is a core layer gain medium prepared by uniformly doping rare earth nanoparticles into SU-8 polymer material by a physical method, wherein the rare earth nanoparticles are NaYF₄: yb and Er nano particles, wherein Er ions are luminescence center ions, and Yb is doped sensitizer ions.

Further, the rare earth nanoparticles are NaYF₄:10％Er³⁺，18％Yb³⁺Wherein the concentration of the doped sensitizer ions is 18%, and the concentration of the luminescence center ions is 10%.

Furthermore, the doping concentration of erbium ions in the rare earth nanoparticles is 0.4 multiplied by 10²⁰～0.8×10²⁰cm^-3The doping concentration of ytterbium ion is 0.4X 10²¹～0.8×10²¹cm^-3。

Further, the upper cladding layer is an undoped polymethyl methacrylate (PMMA) material.

Further, the polymer few-mode waveguide adopts a square central symmetry structure, and the size of a few-mode waveguide core layer is 5 micrometers multiplied by 5 micrometers; the thickness range of the silicon dioxide substrate is as follows: 2-3 μm; the upper cladding thickness range is: 3-5 μm; the refractive indexes of the few-mode waveguide core layer and the upper cladding layer at the wavelength of 1550nm are 1.576 and 1.485 respectively.

Another object of the present invention is to provideA preparation method of a polymer few-mode waveguide comprises the following specific steps: firstly, cleaning a silicon dioxide substrate by sequentially adopting acetone, ethanol and deionized water; then, NaYF₄:10％Er³⁺，18％Yb³⁺Dissolving the nano particles in toluene, physically doping the solution into SU-8 negative photoresist of a polymer, and preparing a core layer polymer material; coating a core layer polymer material on a silicon dioxide substrate by adopting a spin-coating method, and curing to form a few-mode waveguide core layer; carrying out ultraviolet photoetching on the photoresist, and transferring the pattern on the photoetching plate to the core layer photoresist; developing with SU-8 special developer, removing negative photoresist of the exposed part, baking to obtain few-mode square waveguide, and coating PMMA upper cladding.

Compared with the prior art, the invention has the following advantages:

(1) the polymer few-mode waveguide amplifier combines the advantages of erbium-ytterbium co-doped organic polymer such as high doping concentration, low cost, simple process, easy integration and the like, has the important advantages of miniaturization and compact structure compared with the traditional few-mode optical fiber amplifier, and can be integrated with other optical waveguide devices (such as an optical modulator, a mode division multiplexer/demultiplexer, a wavelength division multiplexer and the like) in a planar and three-dimensional manner to form a high-efficiency integrated optical system;

(2) the few-mode polymer waveguide overcomes the limitation that the traditional optical waveguide amplifier can only amplify a single mode, and realizes the function of simultaneously amplifying a plurality of signal modes. The loss generated in the mode division multiplexing system due to the mode conversion, the coupling and the transmission process is effectively compensated, and therefore the transmission performance of the system is improved.

Drawings

In order to more clearly illustrate the detailed description of the invention or the technical solutions in the prior art, the drawings that are needed in the detailed description of the invention or the prior art will be briefly described below. Throughout the drawings, like elements or portions are generally identified by like reference numerals. In the drawings, elements or portions are not necessarily drawn to scale.

FIG. 1 is a schematic structural diagram of a few-mode polymer waveguide according to the present invention;

FIG. 2 is a schematic flow chart of a method for fabricating a few-mode polymer waveguide according to the present invention;

FIG. 3 is a view of the LP mode group of the few-mode polymer waveguide of the present invention capable of stable transmission;

wherein (a) is LP₀₁Mode (b) is LP₁₁A mode;

FIG. 4 is a schematic diagram of an exemplary test system for few-mode polymer waveguides in accordance with the present invention;

FIG. 5 is a photograph of a few-mode polymer optical waveguide embodiment of the present invention.

Detailed Description

The following embodiments are only used for illustrating the technical solutions of the present invention more clearly, and therefore, the following embodiments are only used as examples, and the protection scope of the present invention is not limited thereby.

It is to be noted that, unless otherwise specified, technical or scientific terms used herein shall have the ordinary meaning as understood by those skilled in the art to which the invention pertains.

Example 1

As shown in fig. 1, the present embodiment provides a polymer few-mode waveguide, which sequentially comprises, from bottom to top, a silica substrate, a few-mode waveguide core layer spin-coated on the silica substrate, and an upper cladding layer spin-coated on the few-mode waveguide core layer, where the few-mode waveguide core layer is made of a rare earth doped active polymer material, and the upper cladding layer is made of an undoped polymer material.

The rare earth doped active polymer material is a core layer gain medium prepared by uniformly doping rare earth nanoparticles into SU-8 polymer material by a physical method, wherein the rare earth nanoparticles are NaYF₄:10％Er³⁺，18％Yb³⁺Er ion is luminescence center ion, Yb is doped sensitizer ion, wherein the concentration of the doped sensitizer ion is 18% (defined as the molar amount of sensitizer ion/(the molar amount of sensitizer ion + the molar amount of luminescence center ion + the molar amount of rare earth ion in rare earth nanoparticle), and the concentration of luminescence center ion is 10%(the concentration of the luminescence center ion is defined as the molar amount of the luminescence center ion/(the molar amount of the sensitizer ion + the molar amount of the luminescence center ion + the molar amount of the rare earth ion in the rare earth nanoparticle).

The rare earth doped active polymer material is doped NaYF₄：10％Er³⁺、18％Yb³⁺SU-8 polymer material of nanoparticles with erbium ion doping concentration of 0.4 × 10²⁰～0.8×10²⁰cm^-3The doping concentration of ytterbium ion is 0.4X 10²¹～0.8×10²¹cm^-3. The upper cladding layer is made of undoped polymethyl methacrylate (PMMA) material. The refractive indexes of the few-mode waveguide core layer and the upper cladding layer at the wavelength of 1550nm are 1.576 and 1.485 respectively. The waveguide core region is of a square central symmetrical structure, and the size of the core region is 5 micrometers multiplied by 5 micrometers.

The few-mode polymer optical waveguide can transmit and amplify LP modes.

The few-mode polymer optical waveguide supports 2 stable transmission modes at a wavelength of 1550 nm.

Example 2

As shown in fig. 2, this embodiment provides a method for preparing a polymer few-mode waveguide, which includes the following specific steps:

(1) firstly, preparing NaYF with surface modified unsaturated double bonds by a high-temperature thermal decomposition method: yb, Er nanoparticles: the substrate of the rare earth nano particle is fluoride NaYF₄The sensitizer ion is Yb³⁺The luminous central ion is Er³⁺(ii) a The surface of the nano particle is modified with an oleic acid group with polymerization activity unsaturated double bonds, and the specific synthetic steps are as follows: mixing 1.44mmo1 YC1₃·6H₂O、0.36mmo1 YbC1₃·6H₂O、0.2mmo1ErC1₃·6H₂O, 30mL of octadecene, and 12mL of oleic acid were charged into a four-necked flask having a volume of 100 mL. Stirring was continued under an argon atmosphere and the solvent was heated to 100 ℃ for 10 minutes, then raised to 150 ℃ for 30 minutes, the heating was turned off and cooled to room temperature. Then 8mmol of NH₄F and 5mmol NaOH were dissolved in 20mL of methanol, and the solution was slowly dropped into a four-necked flask usingThe stirrer was stirred at low speed for 1 hour. The mixture was then heated to 50 ℃ for 1 hour in argon-purged swordsman to evaporate all the methanol in the reaction mixture. After the methanol had been removed, the solvent was heated to 290 ℃ under a blanket of hydrogen and held for 1 hour. And (3) after the reaction system is naturally cooled to room temperature, taking out the solution, and centrifuging by using ethanol for repeated washing. Keeping the centrifuged powder and drying the powder by using an oven to obtain the NaYF with the surface modified with unsaturated double bonds₄: yb, Er nanoparticles;

(2) a polymeric core material is prepared. Adding 0.5mmol NaYF₄：Er³⁺，Yb³⁺The nanocrystals were dissolved in 2mL of cyclohexane and sonicated for 2 hours to give a clear and homogeneous solution. 0.5g of the solution and 2.0g of SU-82005 type ultraviolet curing glue (the mass ratio is 1: 4) are respectively taken out and mixed, and the mixture is continuously subjected to ultrasonic treatment for 1 hour under the dark condition to obtain a uniformly doped polymer which is used as a core layer material of the polymer optical waveguide.

(3) Preparing few-mode polymer waveguide:

s1, cleaning the substrate;

growing SiO on the surface by acetone and ethanol respectively₂Cleaning the surface of the substrate, washing the residual ethanol on the surface by using deionized water, and drying the water on the surface;

s2, preparing a core layer;

the synthesized NaYF4 Er3+, Yb3+ nanocrystalline-doped SU-82005 polymer is spin-coated (3000rpm, 20s) with SiO growing on the surface₂On the Si substrate of the layer, the thickness of the core layer is in the range of 4-5 μm, the Si substrate is placed in an oven for constant temperature heating (85 ℃), the temperature is reduced for 20 minutes, and the Si substrate is naturally cooled;

s3, patterning the core layer;

placing the negative photoetching plate with the waveguide structure on a photoetching machine, and exposing SU-8 negative photoresist (365nm,350mW) for 10 seconds;

s4, developing;

configuration 1 g: 200mL of NaOH deionized water solution as a developing solution; removing the photoresist exposed by ultraviolet light, washing off the residual developing solution on the surface by using deionized water, and curing and hardening (100 ℃) in an oven for 5 minutes;

s5, preparing an upper cladding;

a PMMA over cladding layer 3 μm thick was spin coated (3500rpm, 20s) onto the coupon, placed in an oven and heated (120 ℃ C.) for 120 minutes to room temperature to complete the device fabrication.

As shown in FIG. 3, the waveguide that is simulated by the actual parameters of the few-mode waveguide prepared in this embodiment can transmit LP mode, and the polymer few-mode waveguide of the present application can transmit and amplify the LP mode of the signal mode group₀₁And LP₁₁As shown in fig. 3(a) and 3(b), respectively. Compared with a single-mode polymer waveguide, the few-mode waveguide utilizes mutually orthogonal mode dimensions as a multiplexing channel, can greatly improve communication capacity, realizes high fidelity and low crosstalk of multi-signal mode transmission, and provides technical support for the realization of an on-chip mode division multiplexing system.

The polymer few-mode waveguide prepared in example 2 was applied to a waveguide amplifier. The structural schematic diagram of the amplifier test system is shown in fig. 4, and the amplification characteristic of the few-mode waveguide amplifier is measured by adopting a forward pumping mode. The pump light wavelength and the signal light wavelength are respectively selected to be 980nm and 1550 nm. The signal light source provides signal light with 1550nm wavelength, the pump light source provides pump light with 980nm wavelength, the signal light with 1550nm wavelength and the pump light with 980nm wavelength are combined by a wavelength division multiplexer (WDM: 1550nm/980nm), a high-order mode is excited by a mode coupler, and then the light is coupled into the optical waveguide amplifier by an optical fiber.

In a waveguide amplifier, in the ground state level²F_7/2The energy of the absorbed pump light is transferred to the energy level upwards under the excitation of 980nm pump light²F_5/2. Due to Yb³⁺Ion energy level²F_5/2And²F_7/2with erbium ion energy level⁴I_11/2And⁴I_15/2the erbium and ytterbium atoms are closely spaced, Yb³⁺Ions can rapidly transfer energy to Er on the ground state energy level in a cross relaxation mode³⁺Ions, let it pass through⁴I_15/2Transition of energy level to excited state energy level⁴I_11/2Due to this energy levelInstability of (2) Er³⁺The ions are quickly transferred to metastable energy levels through a non-radiative relaxation process⁴I_13/2Form population inversion and go to the ground state energy level⁴I_15/2The transition forms stimulated emission, photons with the same frequency as the signal light are emitted, and the amplification function of the signal light is realized. The amplified signal light is coupled and output to the mode demultiplexer through the optical fiber, and then data analysis is carried out on the output signal light through the spectrometer.

FIG. 5 shows NaYF₄：10％Er³⁺、18％Yb³⁺The nano-particle doped polymer is used as a gain medium to prepare a physical photo of the optical waveguide amplifier. The length of the waveguide amplifier is only 1.2cm, compared with the traditional optical fiber amplifier, the volume of the device is greatly reduced, and a feasible scheme is provided for miniaturization and integration of optoelectronic devices while optical transmission loss in the device is effectively compensated.

The preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.