Gain medium for low-differential-mode-gain few-mode optical amplifier, and preparation method therefor and application thereof

Abstract

A gain medium for a low-differential-mode-gain few-mode optical amplifier, a preparation method therefor and the application thereof, and a low-differential-mode-gain few-mode optical amplifier comprising same. The gain medium sequentially comprises, from bottom to top, a silicon substrate (1), a silicon oxide layer (2), a passive transmission waveguide layer (3), rare-earth-doped gain layers (4-7) and an upper waveguide cladding layer (8), wherein the rare-earth doping concentrations in the rare-earth-doped gain layers (4-7) gradually increase from bottom to top. The present invention can improve the mode gain; and by means of regulating a matching mode between a doping concentration and a light field distribution, the effect of reducing the gain difference between modes is also achieved.

Description

A gain medium for low differential mode gain few-mode optical amplifier and its preparation method and application Technical Field

[0001] The present invention relates to the field of optical communication technology, and more particularly to a gain medium for a low differential mode gain few-mode optical amplifier, a preparation method thereof, and applications thereof. Background Art

[0002] Optical amplifiers are widely used in optical communication networks, primarily for amplifying and compensating optical signals in fiber-optic transmission systems and on-chip integrated optical interconnect systems. With the advancement of micro-nanofabrication technologies, on-chip integrated optical communication systems have become a research hotspot. Attempts are underway to implement few-mode signal transmission in on-chip systems to further increase communication transmission capacity. However, the inherently high losses inherent in on-chip systems have a significant impact on signal transmission rate, capacity, and signal-to-noise ratio.

[0003] Optical waveguide amplifiers can amplify optical signals without requiring optoelectronic conversion, thus addressing the problem of on-chip signal compensation. However, most current on-chip integrated system optical waveguide amplifiers are designed for single-mode signals and fail to effectively compensate for few-mode signals. To compensate for the loss issues of on-chip integrated few-mode systems, one effective solution is to design an on-chip integrated few-mode optical waveguide amplifier, modeled after few-mode rare-earth-doped fiber amplifiers used for signal compensation in long-haul fiber transmission systems. However, unlike fiber transmission systems, the rectangular structure of the optical waveguide cannot guarantee identical light field distribution for each mode, thus affecting amplification and resulting in greater differential-mode gain.

[0004] Patent CN113866877A discloses a polymer few-mode waveguide and its fabrication method. The structure consists, from bottom to top, of a silica substrate, a few-mode waveguide core layer spin-coated on the silica substrate, and an upper cladding layer spin-coated on the core layer. The few-mode waveguide core layer utilizes a rare-earth-doped active polymer material, a core gain medium prepared by physically doping rare-earth nanoparticles uniformly into a SU-8 polymer material. This overcomes the limitation of conventional optical waveguide amplifiers, which can only amplify a single mode, by enabling simultaneous amplification of multiple signal modes. However, the modal gain and differential mode gain of each mode require further improvement.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects and shortcomings of existing optical waveguide amplifiers, such as low modal gain and large differential mode gain, and to provide a gain medium for a low differential mode gain few-mode optical amplifier.

[0007] Another object of the present invention is to provide a method for preparing the gain medium for the low differential mode gain few-mode optical amplifier.

[0008] Another object of the present invention is to provide an application of a gain medium for a low differential mode gain few-mode optical amplifier in the preparation of a low differential mode gain few-mode optical amplifier.

[0009] Another object of the present invention is to provide a low differential mode gain few-mode optical amplifier, in which the center of the optical field can achieve gain amplification effect by leaking part of the energy to the gain medium cladding while transmitting in a low-loss passive waveguide, and has excellent optical field confinement effect and excellent gain amplification characteristics.

[0010] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0011] The present invention protects a gain medium for a low differential mode gain few-mode optical amplifier, which comprises, from bottom to top, a silicon substrate, a silicon oxide layer, a passive transmission waveguide layer, a rare earth doped gain layer, and a waveguide upper cladding layer;

[0012] The rare earth doping concentration in the rare earth doped gain layer increases gradually from bottom to top.

[0013] The gain medium of the present invention utilizes a rare-earth-doped gain layer with a gradually increasing rare-earth dopant concentration from bottom to top. This not only improves mode gain but also reduces the gain difference between modes by adjusting the matching pattern of the dopant concentration and the light field distribution. Since the primary process by which rare-earth ions amplify signal light is based on the interaction between the light field and the rare-earth ions, the optical gain effect generated at different locations can be roughly viewed as a positive correlation with the product of the light field intensity and the rare-earth dopant concentration at each point. The present invention achieves low differential mode gain between different modes by optimizing the rare-earth ion dopant concentration at different light field locations to match the light field distribution.

[0014] In some embodiments, the refractive index of the silicon oxide layer is 1.44-1.46, the refractive index of the passive transmission waveguide layer is 1.977-1.985, the refractive index of the rare earth doped gain layer is 1.658-1.668, and the refractive index of the waveguide upper cladding is 1.44-1.46.

[0015] In some embodiments, the rare earth-doped gain layer is composed of a plurality of rare earth-doped unit layers with different rare earth doping concentrations, and the rare earth doping concentration ratio between adjacent rare earth-doped unit layers is 1:(1.1-2).

[0016] Preferably, the rare earth doping concentration ratio between adjacent rare earth doping unit layers is 1:(1.3-1.6).

[0017] In some embodiments, the main material of the rare earth-doped gain layer is at least one of aluminum oxide, tellurium oxide, and tantalum oxide; preferably, the main material is aluminum oxide (Al2O3). Aluminum oxide has better rare earth ion solubility and excellent emission cross-section, making it easier to achieve a larger gain coefficient.

[0018] In some embodiments, the doped rare earth element is at least one of erbium, ytterbium, thulium, dysprosium, or holmium. Preferably, the doped rare earth element is erbium. The present invention allows selection of appropriate rare earth elements based on gain characteristics at different wavelengths. Erbium is primarily designed for amplifying light at wavelengths near 1550 nm, compatible with the C-band of current optical communication systems.

[0019] In some embodiments, the rare earth-doped gain layer is composed of a plurality of rare earth-doped unit layers stacked by atomic layer deposition technology; in each rare earth-doped unit layer, a rare earth film and a main material film are sequentially atomically layer deposited in a single cycle, and a rare earth-doped unit layer is formed after periodic cyclic deposition, and the thickness ratio of the rare earth film and the main material film deposited in a single cycle between adjacent rare earth-doped unit layers increases, forming a rare earth-doped gain layer with a gradually increasing rare earth doping concentration.

[0020] In some embodiments, the total thickness of the rare earth doped gain layer is in the range of 300-1000 nm, and the thickness of each rare earth doped unit layer is in the range of 100-300 nm, which is conducive to improving the modal gain and reducing the differential mode gain.

[0021] In some embodiments, the method for preparing the rare earth-doped gain layer comprises the following steps:

[0022] 1) performing atomic layer deposition on the surface of the silicon oxide layer, wherein the number of rare earth thin film deposition times in a single cycle is 1-5 times, and the number of main material thin film deposition times is N1 times, and the cyclic deposition is performed until a first rare earth doped unit layer with a thickness of 100-300 nm is formed;

[0023] 2) performing atomic layer deposition on the surface of the rare earth doped unit layer A1 in step 1), wherein the number of rare earth thin film deposition times in a single cycle is 1-5 times, and the number of main material thin film deposition times is N2 times, and the deposition is repeated until a second rare earth doped unit layer with a thickness of 100-300 nm is formed;

[0024] 3) Repeating atomic layer deposition sequentially until the i-th rare earth doped unit layer, thus obtaining a rare earth doped gain layer composed of multiple layers of rare earth doped unit layers;

[0025] In the i-th rare earth doped unit layer, the number of rare earth film deposition times in a single cycle is 1-5 times, and the number of main material film deposition times is N. itimes, and cyclically depositing until a rare earth doped unit layer with a thickness of 100-300 nm is formed;

[0026] Among them, N1>N2>...>N i , and N 1、 N2...N i and i are both natural numbers; 3<N1≤20, N i ≥2, i≥3.

[0027] The above method is based on atomic layer deposition technology to prepare rare earth doped gain layers, which has great uniformity and is easy to control the doping concentration. The obtained rare earth doped gain layer with increasing doping concentration can effectively improve the mode gain. At the same time, by adjusting the matching mode between the doping concentration and the light field distribution, the differential mode gain can be reduced.

[0028] In some embodiments, the rare earth doping unit layer A1 to the rare earth doping unit layer A i The present invention can achieve a more balanced amplification effect and reduce the gain difference between modes by adjusting the thickness distribution to correct the optical gain.

[0029] In some embodiments, the method for preparing the rare earth-doped gain layer comprises the following steps:

[0030] 1) performing atomic layer deposition on the surface of the silicon oxide layer, wherein the number of rare earth thin film deposition times in a single cycle is 1-4 times, the number of main material thin film deposition times is 10-14 times, and the cycle is repeated 150-240 times to obtain a first rare earth doped unit layer;

[0031] 2) performing atomic layer deposition on the surface of the first rare earth-doped unit layer, wherein the number of rare earth thin film depositions in a single cycle is 1-4 times, the number of host material thin film depositions is 6-9 times, and the cycle is repeated 220-310 times to obtain a second rare earth-doped unit layer;

[0032] 3) performing atomic layer deposition on the surface of the second rare earth doped unit layer, wherein the number of rare earth thin film depositions in a single cycle is 1-4 times, the number of host material thin film depositions is 4-5 times, and the cycle is repeated 300-350 times to obtain a third rare earth doped unit layer;

[0033] 4) Performing atomic layer deposition on the surface of the third rare earth doped unit layer, wherein the rare earth thin film is deposited 1-4 times in a single cycle, and the main material thin film is deposited 2-3 times, and the cycle is repeated 360-500 times to obtain a fourth rare earth doped unit layer.

[0034] In some embodiments, in the method for preparing the rare earth-doped gain layer, the number of rare earth thin film depositions in each single cycle is the same.

[0035] In some embodiments, the material of the passive transmission waveguide layer is at least one of silicon nitride, lithium niobate, tellurium oxide, chalcogenide inorganic material or silicon.

[0036] The present invention can select different shapes according to different mode transmission requirements; preferably, the passive transmission waveguide layer is rectangular or circular. By designing passive transmission waveguide layers of different shapes, it can be suitable for different mode transmissions.

[0037] In some embodiments, the material of the waveguide upper cladding layer is at least one of silicon oxide, HSQ or PMMA.

[0038] The present invention provides a method for preparing a gain medium for a low differential mode gain few-mode optical amplifier, comprising the following steps:

[0039] S1, superimposing a silicon oxide layer on the surface of a silicon substrate, and then depositing and growing a passive material on the surface of the silicon oxide layer to obtain a passive material film;

[0040] S2, etching the passive material film into a waveguide structure to form a passive transmission waveguide layer capable of transmitting light fields;

[0041] S3, depositing a rare earth doped gain layer on the surface of the passive transmission waveguide layer, wherein the rare earth doping concentration gradually increases from bottom to top;

[0042] S4, performing annealing treatment on the sample obtained in step S3;

[0043] S5, depositing a waveguide upper cladding layer on the surface of the sample after annealing in step S4, thereby obtaining the gain medium for the low differential mode gain few-mode optical amplifier.

[0044] The present invention has no special requirements for the etching technology, and conventional etching methods in the art can be selected; illustratively, the etching adopts electron beam exposure technology or dry etching technology.

[0045] The present invention protects the use of a gain medium for a low differential mode gain few-mode optical amplifier in preparing a low differential mode gain few-mode optical amplifier.

[0046] The present invention protects a low differential mode gain few-mode optical amplifier, comprising an excitation light source, a coupling structure and a gain medium, wherein the gain medium is the gain medium for the low differential mode gain few-mode optical amplifier.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The present invention discloses a gain medium for a low differential mode gain few-mode optical amplifier. The gain medium adopts a rare earth doped gain layer with a rare earth doping concentration gradually increasing from bottom to top to improve the mode gain. At the same time, by regulating the matching mode of the doping concentration and the light field distribution, the gain difference between the modes is reduced.

[0049] Experiments show that the gain medium of the present invention has a high 00 、E 01 、E 10 and E 20 ) mode gains are all greater than 17dB, and the differential mode gain between each mode is effectively controlled within 2dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG1 is a schematic structural diagram of a gain medium for a low differential mode gain few-mode optical amplifier according to Example 1.

[0051] FIG2 is a flow chart of a method for preparing a gain medium for a low differential mode gain few-mode optical amplifier according to Example 1.

[0052] FIG3 is a simulation diagram of the optical field distribution of a gain medium for a low differential mode gain few-mode optical amplifier according to Example 1. FIG.

[0053] FIG4 is a comparison diagram of the signal light gain intensities of a gain medium for a low differential mode gain few-mode optical amplifier in different modes according to Example 1. FIG.

[0054] FIG5 is a comparison diagram of the signal light gain intensity in different modes of a gain medium for a low differential mode gain few-mode optical amplifier in Comparative Example 1. FIG. DETAILED DESCRIPTION

[0055] The present invention will be further described below in conjunction with specific embodiments, but the examples do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the examples of the present invention are conventionally purchased raw materials and reagents.

[0056] In the present invention, terms such as "upper," "lower," "left," "right," "front," "back," "top," "bottom," "inner," "outer," "center," "vertical," "horizontal," "transverse," and "longitudinal" indicate positions or locations based on the positions or locations shown in the accompanying drawings. These terms are primarily intended to better describe the present application and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.

[0057] Furthermore, the terms "first," "second," etc., are primarily used to distinguish between different devices, elements, or components (which may or may not be of the same type and configuration), and are not intended to indicate or imply the relative importance or quantity of the devices, elements, or components indicated. Unless otherwise specified, "plurality" means two or more.

[0058] Example 1

[0059] A gain medium for a low differential mode gain few-mode optical amplifier, as shown in FIG1 , comprises, from bottom to top, a silicon substrate 1, a silicon oxide layer 2, a passive transmission waveguide layer 3, a rare earth doped gain layer, and a waveguide upper cladding layer 8.

[0060] Among them, the refractive indices of the silicon oxide layer 2, the passive transmission waveguide layer 3, the rare earth doped gain layer and the waveguide upper cladding 8 are respectively recorded as n1, n2, n3 and n4, and the specific measured values ​​are: n1 = 1.45, n2 = 1.978, n3 = 1.663, n4 = 1.45.

[0061] The passive transmission waveguide layer 3 is made of silicon nitride and is rectangular in shape with a size of approximately 1.72 μm in width and 675 nm in height.

[0062] The main material of the rare earth doped gain layer is aluminum oxide (Al2O3), the doping element is erbium (Er), and the total thickness is 432.6nm; it consists of a first rare earth doped unit layer 4, a second rare earth doped unit layer 5, a third rare earth doped unit layer 6, and a fourth rare earth doped unit layer 7, with the rare earth doping concentration gradually increasing from bottom to top.

[0063] The material of the waveguide upper cladding layer 8 is silicon dioxide, and the cladding thickness is 1.5 μm.

[0064] The method for preparing the gain medium for the low differential mode gain few-mode optical amplifier, as shown in FIG2 , comprises the following steps:

[0065] S1, preparation of passive transmission waveguide layer;

[0066] 1.1. A silicon substrate with a silicon dioxide layer deposited on its surface was used to grow a silicon nitride thin film layer at 300°C using atmospheric pressure chemical vapor deposition (APC). The deposition time was 50 minutes at a deposition rate of approximately 14 nm / min. The thickness of the silicon nitride thin film layer was approximately 687 nm as determined by SEM.

[0067] 1.2. The passive transmission medium is etched using electron beam exposure etching technology to prepare a silicon nitride rectangular transmission waveguide. The size of the obtained passive transmission waveguide layer is about 1.72 μm wide and 675 nm high under SEM detection.

[0068] S2, depositing a gain medium thin film (rare earth doped gain layer) with gradually increasing rare earth doping concentration using atomic layer deposition technology;

[0069] 2.1. Er(thd)3 and ozone were selected as precursors for the preparation of Er2O3 thin films; trimethylaluminum (TMA) and water were selected as precursors for the preparation of Al2O3 thin films, and nitrogen was selected as the transport and purge gas;

[0070] 2.2. Preheat the deposition reaction chamber and the sample obtained in step S1 above to maintain a constant temperature of 300°C;

[0071] 2.3. Adjust the pulse duration of each precursor and the nitrogen purge duration in step 2.1 so that each precursor is uniformly and efficiently deposited on the silicon dioxide substrate and the byproducts generated by the reaction are completely removed;

[0072] 2.4. The number of deposition times and cycle periods of the Er2O3 film and Al2O3 film in a single cycle are set to obtain an erbium-doped aluminum oxide gain medium film with a gradually increasing erbium doping concentration. Specifically, the atomic layer deposition process parameters are as follows:

[0073] (1-1) A single cycle is performed, in which the Er2O3 film is deposited once and the Al2O3 film is deposited 12 times;

[0074] (1-2) performing the cycle described in step (1-1) 200 times;

[0075] (2-1) A single cycle is performed, in which the Er2O3 film is deposited once and the Al2O3 film is deposited eight times;

[0076] (2-2) performing the cycle described in step (2-1) 240 times in total;

[0077] (3-1) A single cycle is performed, in which the Er2O3 film is deposited once and the Al2O3 film is deposited five times;

[0078] (3-2) performing the cycle described in step (3-1) 300 times;

[0079] (4-1) A single cycle is performed, wherein the Er2O3 film is deposited once and the Al2O3 film is deposited three times;

[0080] (4-2) performing the cycle described in step (4-1) 360 times in total;

[0081] The thickness of the prepared erbium-doped aluminum oxide gain medium film was observed to be 432.6 nm under SEM, and a rare earth-doped gain layer was obtained.

[0082] S3, annealing the sample obtained in step S2;

[0083] 3.1. Place the sample obtained in step S2 in a tubular annealing furnace, perform vacuuming and argon filling operations in the tube, repeat this three times, and finally fill the tube with argon;

[0084] 3.2. Set the sample to heat up to 750℃ at a rate of 10℃ / min and maintain the temperature at 750℃ for 30min;

[0085] 3.3. Turn off the heat source and allow the sample temperature to cool naturally to room temperature before taking out the sample.

[0086] S4, preparing the waveguide upper cladding;

[0087] A silicon dioxide cladding layer was deposited on the surface of the sample after annealing in step S3 by chemical vapor deposition, which served as the waveguide upper cladding layer. SEM testing showed that the thickness of the silicon dioxide cladding layer on the silicon nitride waveguide was 1.5 μm. At this point, the gain medium for the low differential mode gain few-mode optical amplifier was prepared.

[0088] Example 2

[0089] A gain medium for a low differential mode gain few-mode optical amplifier, which differs from Example 1 in that: a rare earth doped aluminum oxide gain film is composed of Er2O3-Yb2O3-Al2O3; and in its preparation method,

[0090] Er(thd)3 and ozone were selected as precursors for preparing Er2O3 thin films; Yb(thd)3 and ozone were selected as precursors for preparing Yb2O3 thin films; trimethylaluminum (TMA) and water were selected as precursors for preparing Al2O3 thin films, and nitrogen was selected as the transport and purge gas.

[0091] The atomic layer deposition process parameters are as follows:

[0092] (1-1) A single cycle is performed, in which the Er2O3 film is deposited once, the Yb2O3 film is deposited three times, and the Al2O3 film is deposited 12 times;

[0093] (1-2) performing the cycle described in step (1-1) 200 times;

[0094] (2-1) A single cycle is performed, in which the Er2O3 thin film is deposited once, the Yb2O3 thin film is deposited three times, and the Al2O3 thin film is deposited eight times;

[0095] (2-2) performing the cycle described in step (2-1) 240 times in total;

[0096] (3-1) A single cycle is performed, in which the Er2O3 thin film is deposited once, the Yb2O3 thin film is deposited three times, and the Al2O3 thin film is deposited five times;

[0097] (3-2) performing the cycle described in step (3-1) 300 times;

[0098] (4-1) A single cycle is performed, in which the Er2O3 thin film is deposited once, the Yb2O3 thin film is deposited three times, and the Al2O3 thin film is deposited three times;

[0099] (4-2) The cycle described in step (4-1) was performed 360 times in total.

[0100] Example 3

[0101] A gain medium for a low differential mode gain few-mode optical amplifier, which differs from Example 1 in that: in the preparation method of the gain medium of this embodiment, the atomic layer deposition process parameters of the prepared erbium-doped aluminum oxide gain medium film are as follows:

[0102] (1-1) A single cycle is performed, in which the Er2O3 film is deposited once and the Al2O3 film is deposited 12 times;

[0103] (1-2) performing the cycle described in step (1-1) 155 times in total;

[0104] (2-1) A single cycle is performed, in which the Er2O3 film is deposited once and the Al2O3 film is deposited eight times;

[0105] (2-2) performing the cycle described in step (2-1) 225 times in total;

[0106] (3-1) A single cycle is performed, in which the Er2O3 film is deposited once and the Al2O3 film is deposited five times;

[0107] (3-2) performing the cycle described in step (3-1) 335 times in total;

[0108] (4-1) A single cycle is performed, wherein the Er2O3 film is deposited once and the Al2O3 film is deposited three times;

[0109] (4-2) Perform the cycle described in step (4-1) 500 times in total.

[0110] Example 4

[0111] A gain medium for a low differential mode gain few-mode optical amplifier, which differs from Example 1 in that: in the preparation method of the gain medium of this embodiment, the atomic layer deposition process parameters of the prepared erbium-doped aluminum oxide gain medium film are as follows:

[0112] (1-1) A single cycle was performed, in which the Er2O3 film was deposited once and the Al2O3 film was deposited 10 times;

[0113] (1-2) performing the cycle described in step (1-1) 240 times in total;

[0114] (2-1) A single cycle is performed, in which the Er2O3 film is deposited once and the Al2O3 film is deposited six times;

[0115] (2-2) performing the cycle described in step (2-1) 310 times in total;

[0116] (3-1) A single cycle is performed, in which the Er2O3 film is deposited once and the Al2O3 film is deposited four times;

[0117] (3-2) performing the cycle described in step (3-1) 350 times in total;

[0118] (4-1) A single cycle is performed, wherein the Er2O3 film is deposited once and the Al2O3 film is deposited twice;

[0119] (4-2) The cycle described in step (4-1) was performed 480 times in total.

[0120] Example 5

[0121] A gain medium for a low differential mode gain few-mode optical amplifier, which differs from Example 1 in that: the main material of the rare earth doped gain layer is tellurium oxide, the doping element is erbium (Er), and the refractive index is 2.05;

[0122] The preparation method is basically the same as that of Example 1.

[0123] Example 6

[0124] A gain medium for a low differential mode gain few-mode optical amplifier, which differs from Example 1 in that: the main material of the rare earth doped gain layer is tantalum oxide, the doping element is erbium (Er), and the refractive index is 2.07;

[0125] The preparation method is basically the same as that of Example 1.

[0126] Example 7

[0127] A gain medium for a low differential mode gain few-mode optical amplifier, which differs from Example 1 in that: the material of the passive transmission waveguide layer is aluminum oxide; the refractive index is 1.65; and the preparation method is basically the same as that of Example 1.

[0128] Example 8

[0129] A gain medium for a low differential mode gain few-mode optical amplifier, which differs from Example 1 in that: the passive transmission waveguide layer is circular with a diameter of 3 μm; the silicon nitride circular waveguide is suitable for OAM mode transmission.

[0130] Example 9

[0131] A low differential mode gain few-mode optical amplifier comprises 1480nm few-mode pump light, a coupling structure and the gain medium obtained in Example 1; the few-mode pump light and signal light are connected to the gain medium via the coupling structure, and the signal light is amplified by the gain medium.

[0132] Comparative Example 1

[0133] A gain medium for an optical amplifier, which differs from Example 1 in that the rare earth doped gain layer of this comparative example comprises the following steps:

[0134] 1. Er(thd)3 and ozone were selected as precursors for preparing Er2O3 thin films; trimethylaluminum (TMA) and water were selected as precursors for preparing Al2O3 thin films, and nitrogen was selected as the transport and purge gas;

[0135] 2. Preheat the deposition reaction chamber and the sample obtained in step S1 above to maintain a constant temperature of 300°C;

[0136] 3. Adjust the pulse duration of each precursor and the nitrogen purge duration in step 1 so that each precursor is evenly and efficiently deposited on the silicon dioxide substrate and the by-products generated by the reaction are completely removed;

[0137] 4. Set the number of deposition times and cycle period of Er2O3 thin films and Al2O3 thin films in a single cycle to obtain an erbium-doped aluminum oxide gain medium thin film. Specifically, the parameter conditions are as follows:

[0138] (1) A single cycle was performed, wherein the Er2O3 film was deposited once and the Al2O3 film was deposited eight times;

[0139] (2) Perform the cycle described in step (1) 889 times in total to obtain a rare earth doped gain layer.

[0140] Performance Testing

[0141] 1. Light field simulation experiment

[0142] The gain medium for the low differential mode gain few-mode optical amplifier obtained in Example 1 was used to simulate the light field distribution at a wavelength of 1533 nm. The result is shown in FIG3 .

[0143] As can be seen from Figure 3, the light field is well confined in the waveguide area and can effectively transmit E 00 、E 01 、E 10 and E 20 model.

[0144] 2. Signal light gain intensity experiment

[0145] The gain medium for the low differential mode gain few-mode optical amplifier obtained in Example 1 and Comparative Example 1 is taken, and the overall length of the waveguide is 1.5 cm. 1533 nm few-mode signal light and 1480 nm few-mode pump light are injected, and the front-end multiplexer is used to perform E multiplication of the signal light and the pump light. 00 、E 01 、E 10 and E 20 After mode multiplexing, the multiplexed optical path is coupled into the waveguide structure through a focusing lens system. At the output end of the waveguide, the amplified signal light is filtered using a lens system and an optical isolator, and a multi-mode demultiplexer is used to separate the signal light intensities of different modes and detect them. The results are shown in Figure 4-5.

[0146] As can be seen from FIG4, the gain medium of Example 1 has 00 、E 01 、E 10 and E 20 )'s mode gain is greater than 17dB, and the differential-mode gain between each mode is efficiently controlled within 2dB; it has the characteristics of large mode gain and small differential-mode gain, which provides a guarantee for on-chip few-mode optical amplification.

[0147] As can be seen from FIG5 , the gain medium of Comparative Example 1 has 00 、E 01 、E 10 and E 20 ) between 3-16dB, and the maximum differential mode gain reaches 10dB.

[0148] The aforementioned signal light gain intensity experiments demonstrate that the present invention's devices, utilizing the gain medium of a low-differential-mode gain few-mode optical amplifier, offer advantages in controlling the gain difference between different modes. All embodiments of the present invention utilize a gradually increasing rare-earth dopant concentration in the rare-earth-doped gain layer, with varying doping concentrations at different heights. This allows the doping concentration profile to be aligned with the optical field distribution between different modes, effectively compensating for the significant differential-mode gain caused by differences in optical field confinement factors between different modes.

[0149] The above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications may be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the claims of the present invention.

Claims

1. A gain medium for a low differential mode gain few-mode optical amplifier, characterized in that: From bottom to top, it includes silicon substrate, silicon oxide layer, passive transmission waveguide layer, rare earth doped gain layer, and waveguide upper cladding layer; The rare earth doping concentration in the rare earth doped gain layer increases gradually from bottom to top.

2. The gain medium for a low differential mode gain few-mode optical amplifier according to claim 1, wherein: The rare earth doping gain layer is composed of a plurality of rare earth doping unit layers with different rare earth doping concentrations, and the rare earth doping concentration ratio between adjacent rare earth doping unit layers is 1:(1.1-2).

3. The gain medium for a low differential mode gain few-mode optical amplifier according to claim 1, wherein: The main material of the rare earth doped gain layer is at least one of aluminum oxide, tellurium oxide, and tantalum oxide; the doped rare earth element is at least one of erbium, ytterbium, thulium, dysprosium, or holmium.

4. The gain medium for a low differential mode gain few-mode optical amplifier according to claim 1, wherein: The rare earth doped gain layer is composed of a plurality of stacked rare earth doped unit layers manufactured by atomic layer deposition technology. In each rare earth doped unit layer, a rare earth thin film and a main material thin film are sequentially atomically layer deposited in a single cycle, and a rare earth doped unit layer is formed after periodic cyclic deposition. The thickness ratio of the rare earth thin film and the main material thin film deposited in a single cycle between adjacent rare earth doped unit layers increases, thereby forming a rare earth doped gain layer with a gradually increasing rare earth doping concentration.

5. The gain medium for a low differential mode gain few-mode optical amplifier according to any one of claims 1 to 4, characterized in that: The method for preparing the rare earth doped gain layer comprises the following steps: 1) performing atomic layer deposition on the surface of the silicon oxide layer, wherein the number of rare earth thin film deposition times in a single cycle is 1-5 times, and the number of main material thin film deposition times is N1 times, and the cyclic deposition is performed until a first rare earth doped unit layer with a thickness of 100-300 nm is formed; 2) performing atomic layer deposition on the surface of the rare earth doped unit layer A1 in step 1), wherein the number of rare earth thin film deposition times in a single cycle is 1-5 times, and the number of main material thin film deposition times is N2 times, and the deposition is repeated until a second rare earth doped unit layer with a thickness of 100-300 nm is formed; 3) Repeating atomic layer deposition sequentially until the i-th rare earth doped unit layer, thus obtaining a rare earth doped gain layer composed of multiple layers of rare earth doped unit layers; In the i-th rare earth doped unit layer, the number of rare earth film deposition times in a single cycle is 1-5 times, and the number of main material film deposition times is N. i times, and cyclically depositing until a rare earth doped unit layer with a thickness of 100-300 nm is formed; Among them, N1>N2>...>N i , and N1, N2...N i and i are both natural numbers; 3<N1≤20, N i ≥2, i≥3。 6. The gain medium for a low differential mode gain few-mode optical amplifier according to claim 5, characterized in that: The method for preparing the rare earth doped gain layer comprises the following steps: 1) performing atomic layer deposition on the surface of the silicon oxide layer, wherein the number of rare earth thin film deposition times in a single cycle is 1-4 times, the number of main material thin film deposition times is 10-14 times, and the cycle is repeated 150-240 times to obtain a first rare earth doped unit layer; 2) performing atomic layer deposition on the surface of the first rare earth-doped unit layer, wherein the number of rare earth thin film depositions in a single cycle is 1-4 times, the number of host material thin film depositions is 6-9 times, and the cycle is repeated 220-310 times to obtain a second rare earth-doped unit layer; 3) performing atomic layer deposition on the surface of the second rare earth doped unit layer, wherein the number of rare earth thin film depositions in a single cycle is 1-4 times, the number of host material thin film depositions is 4-5 times, and the cycle is repeated 300-350 times to obtain a third rare earth doped unit layer; 4) Performing atomic layer deposition on the surface of the third rare earth doped unit layer, wherein the rare earth thin film is deposited 1-4 times in a single cycle, and the main material thin film is deposited 2-3 times, and the cycle is repeated 360-500 times to obtain a fourth rare earth doped unit layer.

7. The gain medium for a low differential mode gain few-mode optical amplifier according to claim 1, wherein: The material of the passive transmission waveguide layer is at least one of silicon nitride, lithium niobate, tellurium oxide, chalcogenide inorganic material or silicon; The material of the waveguide upper cladding layer is at least one of silicon oxide, HSQ or PMMA.

8. A method for preparing a gain medium for a low differential mode gain few-mode optical amplifier according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1, superimposing a silicon oxide layer on the surface of a silicon substrate, and then depositing and growing a passive material on the surface of the silicon oxide layer to obtain a passive material film; S2, etching the passive material film into a waveguide structure to form a passive transmission waveguide layer capable of transmitting light fields; S3, depositing a rare earth doped gain layer on the surface of the passive transmission waveguide layer, wherein the rare earth doping concentration gradually increases from bottom to top; S4, performing annealing treatment on the sample obtained in step S3; S5, depositing a waveguide upper cladding layer on the surface of the sample after annealing in step S4, thereby obtaining the gain medium for the low differential mode gain few-mode optical amplifier.

9. Use of the gain medium for a low differential mode gain few-mode optical amplifier according to any one of claims 1 to 7 in preparing a low differential mode gain few-mode optical amplifier.

10. A low differential mode gain few-mode optical amplifier, comprising an excitation light source, a coupling structure and a gain medium, characterized in that: The gain medium is as described in any one of claims 1 to 7 as the gain medium for a low differential mode gain few-mode optical amplifier.

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