Hybrid waveguide amplifier based on co-doped erbium silicate film and preparation method thereof

Abstract

The invention discloses a hybrid waveguide amplifier based on a co-doped erbium silicate film and a preparation method of the hybrid waveguide amplifier. The hybrid waveguide amplifier based on the co-doped erbium silicate film comprises a substrate, a silicon nitride layer and a co-doped erbium silicate layer, the substrate is a thermal oxidation silicon wafer, and a silicon oxide layer is arranged on the surface of one side of the thermal oxidation silicon wafer; the silicon nitride layer is arranged on the silicon oxide layer and is etched into a waveguide structure; the co-doped erbium silicate layer is deposited on the silicon nitride layer and the silicon oxide layer, so that the silicon nitride layer is completely coated between the silicon oxide layer and the co-doped erbium silicate layer; co-doped elements in the co-doped erbium silicate layer comprise a first element and a second element, the first element is at least one of lithium, aluminum, sodium and magnesium, and the second element is ytterbium; the first element and the second element are co-doped within an erbium silicate lattice.

Description

Technical Field

[0001] The invention relates to the field of waveguide amplifiers, and in particular to a hybrid waveguide amplifier based on a co-doped erbium silicate film and a preparation method thereof. Background Art

[0002] With the rapid development of emerging technologies such as the Internet of Things and 5G, it is crucial to achieve high-capacity, high-speed, low-cost, and low-loss signal transmission and processing. Silicon-based optoelectronic integration realizes optical interconnection technology based on mature semiconductor process technology, which is expected to break through the problems of chip heating and signal crosstalk encountered by current integrated circuits and achieve higher-speed signal transmission. At present, this technology has been able to integrate optical devices such as optical switches, optical detectors, and optical modulators on the same silicon substrate. However, the most challenging problem is that due to the low luminous efficiency of silicon, it is difficult to directly realize on-chip silicon-based optical waveguide amplifiers and lasers. Silicon-based optoelectronic integration is difficult to avoid the loss caused by light during transmission. The realization of silicon-based optical waveguide amplifiers will provide compensation for the loss in the optical path, further improving the application prospects of silicon-based optoelectronic integration. The erbium-doped planar optical waveguide amplifier (EDWA), developed on the basis of the mature erbium-doped fiber amplifier (WDFA), is expected to provide a solution for the realization of high-performance waveguide amplifiers that can be integrated on chip.

[0003] Erbium-doped optical waveguide amplifiers are generally made by depositing erbium-doped thin films on silicon wafers and preparing them into planar optical waveguide amplifiers through micro-nano processing. Then, under the excitation of pump light, erbium ions can absorb pump light, transition erbium ions from the ground state to the excited state, achieve population inversion, and stimulate emission of 1.5μm light to amplify the signal light. EDWA makes full use of the advantages of erbium ions in the optical communication band: the 1.5μm transition wavelength from the first excited state to the ground state belongs to the minimum loss window of quartz optical fiber; the excited state fluorescence lifetime is long, up to the ms level; the luminescence is less affected by the surrounding environment, the luminescent waveguide is stable; the luminescence peak is sharp, etc., which has incomparable advantages in the field of optical amplification.

[0004] At present, there have been studies on the preparation of EDWA based on various erbium-doped matrix materials such as erbium-doped aluminum oxide, erbium-doped lithium niobate, erbium-doped zinc oxide, erbium-doped silicon nitride, etc. However, there are still some shortcomings that limit its use in the field of optoelectronic integration. The maximum gain of existing optical waveguide amplifiers is about 20dB / cm, which is still lower than the performance of erbium-doped fiber amplifiers. This leads to insufficient standards for use in the field of silicon-based optoelectronic integration and commercial-scale preparation. Due to the limitation of solid solubility, the erbium doping concentration of erbium-doped matrix materials is less than 10 20 cm -3 The order of magnitude of the erbium concentration is limited to a large extent, which greatly limits its ability to achieve higher gain. However, erbium compound materials such as erbium silicate have erbium ions as constituent cations, and their erbium concentration can reach 10 22 cm -3The order of magnitude has great potential to achieve high gain performance. However, erbium compounds face problems such as the obstruction of erbium ion 4f electron radiation transition, low pump absorption cross section, and difficulty in etching erbium silicate, so that the advantage of high erbium concentration has not been fully utilized. At present, the gain of optical waveguide amplifiers prepared based on erbium silicate films is only 3-7dB, and no net gain is obtained.

[0005] Therefore, how to develop high-concentration erbium-containing optical waveguide amplifiers, overcome the problems of limited luminescence and large transmission losses faced by erbium silicate materials, and realize the preparation of high-gain waveguide amplifiers has become a key and challenging issue in the current waveguide amplifier field. Summary of the invention

[0006] In view of the above technical problems and the deficiencies in the art, the present invention provides a hybrid waveguide amplifier based on co-doped erbium silicate film with higher optical amplification gain and a preparation method thereof.

[0007] The technical solution provided by the present invention overcomes the problems faced by erbium silicate that limit its luminescence, including limited radiation transition, poor pump absorption capacity, etc., and uses it as an optical amplification layer in a low-loss hybrid waveguide amplifier.

[0008] The specific technical solutions are as follows:

[0009] [1] A hybrid waveguide amplifier based on a co-doped erbium silicate film, comprising a substrate, a silicon nitride layer and a co-doped erbium silicate layer;

[0010] The substrate is a thermally oxidized silicon wafer, and one side surface of the thermally oxidized silicon wafer is a silicon oxide layer;

[0011] The silicon nitride layer is disposed on the silicon oxide layer and is etched into a waveguide structure;

[0012] The co-doped erbium silicate layer is deposited on the silicon nitride layer and the silicon oxide layer, so that the silicon nitride layer is completely covered between the silicon oxide layer and the co-doped erbium silicate layer;

[0013] The co-doped elements in the co-doped erbium silicate layer include a first element and a second element, wherein the first element is at least one of lithium, aluminum, sodium, and magnesium, and the second element is ytterbium; the first element and the second element are co-doped in the erbium silicate lattice.

[0014] The present invention uses a co-doped erbium silicate layer as a light amplification layer and a silicon nitride layer as a main light transmission layer, and the co-doped erbium silicate layer is light-confined by the silicon nitride layer.

[0015] In some embodiments, in the hybrid waveguide amplifier based on co-doped erbium silicate film, the thickness of the silicon oxide layer may be 2-10 microns, preferably 2 microns.

[0016] In some embodiments, in the hybrid waveguide amplifier based on co-doped erbium silicate film, the thickness of the silicon nitride layer may be 200-500 nanometers, preferably 300 nanometers.

[0017] In some embodiments, in the hybrid waveguide amplifier based on co-doped erbium silicate film, the silicon nitride layer can be etched into a strip waveguide structure, and the waveguide width can be 1-4 microns, preferably 2 microns.

[0018] In some embodiments, in the hybrid waveguide amplifier based on the co-doped erbium silicate film, the thickness of the co-doped erbium silicate layer may be 200-500 nanometers, preferably 400 nanometers.

[0019] In some embodiments, in the hybrid waveguide amplifier based on co-doped erbium silicate film, the atomic ratio of ytterbium to erbium in the co-doped erbium silicate layer may be (0.05:0.95) to (0.9:0.1).

[0020] In some embodiments, in the hybrid waveguide amplifier based on the co-doped erbium silicate film, in the co-doped erbium silicate layer, the ratio of the total number of ytterbium and erbium atoms to the number of silicon atoms may be 1:1.

[0021] In some embodiments, in the hybrid waveguide amplifier based on the co-doped erbium silicate film, in the co-doped erbium silicate layer, the ratio of the total number of atoms of the first element to the number of silicon atoms may be 0.05 to 1:1.

[0022] In some preferred examples, in the hybrid waveguide amplifier based on the co-doped erbium silicate film, in the co-doped erbium silicate layer, the atomic ratio of ytterbium to erbium is 1:1, the ratio of the total number of atoms of ytterbium and erbium to the number of silicon atoms is 1:1, and the ratio of the total number of atoms of the first element to the number of silicon atoms is 0.1:1. Under preferred conditions, the obtained co-doped erbium silicate layer has both good luminous intensity and suitable roughness, and the hybrid waveguide amplifier further manufactured has the highest gain performance. If the ratio of the total number of atoms of the first element to the number of silicon atoms is too small, the luminous intensity of the co-doped erbium silicate layer needs to be further improved. If the ratio of the total number of atoms of the first element to the number of silicon atoms is too large, such as 0.3:1, 0.5:1, etc., the roughness of the co-doped erbium silicate layer will be very large and even cracks will occur, and it cannot be further used in the hybrid waveguide amplifier or the manufactured hybrid waveguide amplifier has no gain.

[0023] In some preferred examples, in the hybrid waveguide amplifier based on the co-doped erbium silicate film, the co-doped erbium silicate layer is obtained by radio frequency magnetron sputtering and annealing. The radio frequency magnetron sputtering can adopt single target sputtering, and the target material used can be a mixed target material of ytterbium oxide, the first element oxide, silicon oxide, and erbium oxide.

[0024] The present invention provides a method for depositing a co-doped erbium silicate layer by radio frequency magnetron sputtering, comprising:

[0025] A single-target radio frequency magnetron sputtering system is used to install a mixed oxide target of ytterbium oxide, first element oxide, silicon oxide, and erbium oxide to deposit a co-doped erbium silicate layer;

[0026] The sample stage is heated, and the chamber is evacuated to the required vacuum level, and a sputtering atmosphere is introduced; subsequently, power is applied to the target material to start deposition, forming a co-doped erbium silicate layer.

[0027] In some embodiments, in the method of depositing the co-doped erbium silicate layer by radio frequency magnetron sputtering, the sample stage may be heated and maintained at a temperature above 200° C., such as 300° C.

[0028] In some embodiments, the method for depositing the co-doped erbium silicate layer by radio frequency magnetron sputtering can evacuate the chamber to a vacuum degree of no more than 2×10 -3 Pa, for example 1.5×10 -3 Pa et al.

[0029] In some embodiments, in the method of depositing the co-doped erbium silicate layer by radio frequency magnetron sputtering, the sputtering atmosphere may be argon.

[0030] In some embodiments, in the method of depositing the co-doped erbium silicate layer by radio frequency magnetron sputtering, a sputtering atmosphere may be introduced until the pressure in the chamber is 0.35-5 Pa.

[0031] In some embodiments, in the method of depositing the co-doped erbium silicate layer by radio frequency magnetron sputtering, the power applied to the target material may be 70-120W.

[0032] In some embodiments, in the method of depositing the co-doped erbium silicate layer by radio frequency magnetron sputtering, the deposition time can be adjusted according to the required thickness of the co-doped erbium silicate layer, for example, it can be 10 to 180 minutes.

[0033] The annealing operation after the radio frequency magnetron sputtering can activate the erbium ions and crystallize the erbium silicate. After the annealing is completed, the temperature can be naturally lowered to obtain the co-doped erbium silicate layer.

[0034] The annealing atmosphere is preferably an oxygen atmosphere, which can make the co-doped erbium silicate layer have high-efficiency luminescence performance.

[0035] Research has found that when the annealing temperature is above 900°C (e.g., 900°C, 950°C, 1000°C, 1200°C or higher), the co-doped erbium silicate layer has excessive roughness and may even crack, and cannot be further used in a hybrid waveguide amplifier, or the hybrid waveguide amplifier produced has no gain. Therefore, the annealing temperature of the present invention is preferably 850 to <900°C, which can take into account both the good luminous intensity and the appropriate roughness of the co-doped erbium silicate layer, and the hybrid waveguide amplifier produced further has excellent gain performance.

[0036] The annealing time is preferably 5 minutes to 1 hour, for example, 30 minutes.

[0037] [2] The method for preparing a hybrid waveguide amplifier based on a co-doped erbium silicate film according to [1] comprises:

[0038] depositing a silicon nitride layer on the silicon oxide layer of the substrate;

[0039] etching a waveguide structure on the deposited silicon nitride layer;

[0040] A co-doped erbium silicate layer is deposited on the silicon oxide layer and the silicon nitride layer having the waveguide structure.

[0041] In some preferred examples, the method for preparing a hybrid waveguide amplifier based on a co-doped erbium silicate film further performs an annealing operation after depositing the co-doped erbium silicate layer. The annealing operation can activate erbium ions and crystallize the erbium silicate. After the annealing is completed, the film can be taken out after natural cooling to obtain a hybrid waveguide amplifier.

[0042] The annealing atmosphere is an oxygen atmosphere, which can make the co-doped erbium silicate layer have high-efficiency luminescence performance.

[0043] Studies have shown that when the annealing temperature is above 900°C (e.g., 900°C, 950°C, 1000°C, 1200°C or higher), the resulting hybrid waveguide amplifier will fail and have no gain. Therefore, the annealing temperature of the present invention is preferably 850 to <900°C, and the resulting hybrid waveguide amplifier has excellent switching gain.

[0044] The annealing time is preferably 5 minutes to 1 hour, for example, 30 minutes.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The present invention improves the problems of limited 4f electron radiation transition and poor absorption capacity of erbium ions currently faced by erbium silicate by co-doping lithium and ytterbium in a relatively simple way. Lithium and other first elements and ytterbium occupy the interstitial and substitutional sites of erbium silicate respectively, and cooperate with each other to improve the 1.5μm luminescence performance of erbium silicate. The optimized co-doped erbium ytterbium silicate material is used in the optical amplification layer of the optical waveguide amplifier, achieving extremely high gain performance.

[0047] 2. Based on the regulation of lithium components and heat treatment process, the present invention prepares a co-doped erbium silicate film with good luminous intensity and low roughness. The hybrid waveguide amplifier further prepared has excellent gain performance.

[0048] 3. The optical waveguide amplifier based on the co-doped erbium silicate film in the present invention realizes light confinement by etching the passive waveguide silicon nitride, and deposits the co-doped erbium silicate layer directly on the passive waveguide, which not only avoids the problem that the co-doped erbium silicate is difficult to etch, but also reduces the overall loss of the waveguide by using silicon nitride as the main transmission layer, overcoming the problem of high loss of erbium silicate itself. The hybrid waveguide uses the co-doped erbium silicate film as the light amplification layer to provide excellent light amplification effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The present invention is a schematic diagram of the preparation process of a hybrid waveguide amplifier based on co-doped erbium silicate film.

[0050] Figure 2 It is a cross-sectional schematic diagram of a hybrid waveguide amplifier structure based on co-doped erbium silicate film of the present invention.

[0051] Figure 3 This is a diagram of the optical gain performance of a 2 mm long hybrid waveguide amplifier under 980 nm front-end pumping in an embodiment of the present invention.

[0052] Figure 4 Erbium silicate film and lithium ytterbium co-doped erbium silicate film are respectively 2 Photoluminescence (PL) image under 980nm excitation after annealing in atmosphere for 1h. DETAILED DESCRIPTION

[0053] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0054] The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturers.

[0055] In this embodiment, a hybrid optical waveguide amplifier based on a co-doped erbium silicate film and a preparation method thereof are provided. Specifically, Figure 1 As shown, the preparation method of the hybrid optical waveguide amplifier based on the co-doped erbium silicate film in this embodiment includes:

[0056] Step 1: Select a thermally oxidized silicon wafer with a 2 μm thick silicon oxide layer as a substrate, and deposit a silicon nitride film on the substrate by plasma enhanced chemical vapor deposition (PECVD) with a thickness of about 300 nm.

[0057] Step 2, the deposited silicon nitride film is etched to form a strip waveguide structure, and the waveguide width is about 2μm. Here, electron digital exposure (EBL), laser direct writing (LDWL) or ultraviolet (UV) lithography can be used as needed to expose the photoresist on the silicon nitride, and explore suitable exposure and development parameters; then the unnecessary silicon nitride part is removed by inductively coupled plasma etching (ICP) and other methods, thereby forming a strip passive silicon nitride waveguide structure.

[0058] Step 3: deposit a lithium ytterbium co-doped erbium silicate thin film on the passive silicon nitride waveguide structure using radio frequency (RF) magnetron sputtering, with a thickness of about 400 nm.

[0059] Finally, the prepared waveguide amplifier was placed in a tube furnace and heated at 850 °C in O 2 Thermal annealing was carried out in atmosphere for 30 minutes to obtain the final hybrid optical waveguide amplifier based on co-doped erbium silicate film.

[0060] The cross-sectional diagram of the prepared hybrid optical waveguide amplifier based on co-doped erbium silicate film is shown in Figure 2 shown.

[0061] The preparation of the lithium ytterbium co-doped erbium silicate optical amplification layer in step 3 above plays a key role in obtaining a high-performance waveguide amplifier. The specific preparation method is as follows:

[0062] Place the substrate into the RF magnetron sputtering chamber and heat the sample stage to 300°C and maintain it. 0.5 Yb 0.5 Li 0.1 SiO x target (x represents the number of O atoms, used to balance the charge), and the chamber is evacuated to 1.5×10 -3 Pa, reduce the impact of the environment on the sputtering process. Before starting sputtering, introduce Ar as the sputtering atmosphere, and adjust the pressure in the chamber to about 0.35Pa. After successful ignition, adjust the target power to 70W, and perform pre-sputtering for 15 minutes. Then start formal sputtering. By adjusting the time, the thickness of the lithium ytterbium co-doped erbium silicate film on the substrate silicon oxide layer is about 400nm.

[0063] The hybrid waveguide amplifier obtained based on the above embodiment was cut into 2 mm lengths to test its gain performance. Figure 3 As shown. Under 980nm front-end pumping, the maximum open-light gain of the waveguide amplifier at 1540nm reaches ~12.3dB, which is equivalent to a unit length gain coefficient of 6.15dB / mm. This should be the highest gain coefficient of silicon-based erbium planar waveguides in existing research. At the same time, the total loss of the tested waveguide was 3.3dB, and it was calculated that the waveguide finally achieved a net gain of 9dB, which was the first time that a net gain was obtained with a waveguide amplifier based on erbium silicate film. Therefore, based on the invention and the above examples, based on the application of co-doped erbium silicate film as the optical amplification layer, and the preferred waveguide preparation process, high-gain output can be achieved within a very short distance, which provides a new optical amplification solution for the increasingly compact silicon-based optoelectronic integration in the future.

[0064] Achieving high gain depends largely on optimizing the lithium-ytterbium co-doped erbium silicate film with excellent luminescence performance. To this end, we tested the photoluminescence performance of erbium silicate film and lithium-ytterbium co-doped erbium silicate film deposited under the same magnetron sputtering parameters. Under 980nm pump light excitation, the photoluminescence spectra of the two films are as follows: Figure 4 As shown in Figure 2, the lithium-ytterbium co-doped erbium silicate film has a more excellent luminescence performance, which is about 70 times stronger than the erbium silicate film.

[0065] In summary, the present invention does not require etching of the waveguide for the co-doped erbium silicate film, and reduces the overall loss of the waveguide by silicon nitride. The luminescence performance of the erbium silicate film at 1.5 μm is greatly optimized by co-doping, and as a light amplification layer, it provides excellent light gain performance.

[0066] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A hybrid waveguide amplifier based on co-doped erbium silicate film, characterized in that: It includes a substrate, a silicon nitride layer and a co-doped erbium silicate layer; The substrate is a thermally oxidized silicon wafer, and one side surface of the thermally oxidized silicon wafer is a silicon oxide layer; The silicon nitride layer is disposed on the silicon oxide layer and is etched into a waveguide structure; The co-doped erbium silicate layer is deposited on the silicon nitride layer and the silicon oxide layer, so that the silicon nitride layer is completely covered between the silicon oxide layer and the co-doped erbium silicate layer; The co-doped elements in the co-doped erbium silicate layer include a first element and a second element, wherein the first element is at least one of lithium, aluminum, sodium, and magnesium, and the second element is ytterbium; the first element and the second element are co-doped in the erbium silicate lattice.

2. The hybrid waveguide amplifier based on co-doped erbium silicate film according to claim 1, characterized in that: The thickness of the silicon oxide layer is 2-10 microns, preferably 2 microns.

3. The hybrid waveguide amplifier based on co-doped erbium silicate film according to claim 1, characterized in that: The thickness of the silicon nitride layer is 200-500 nanometers, preferably 300 nanometers.

4. The hybrid waveguide amplifier based on co-doped erbium silicate film according to claim 1, characterized in that: The silicon nitride layer is etched into a strip waveguide structure, and the waveguide width is 1-4 microns, preferably 2 microns.

5. The hybrid waveguide amplifier based on co-doped erbium silicate film according to claim 1, characterized in that: The thickness of the co-doped erbium silicate layer is 200-500 nanometers, preferably 400 nanometers.

6. The hybrid waveguide amplifier based on co-doped erbium silicate film according to claim 1, characterized in that: In the co-doped erbium silicate layer, the atomic ratio of ytterbium to erbium is (0.05:0.95) to (0.9:0.1), preferably 1:1, the ratio of the total number of ytterbium and erbium atoms to the number of silicon atoms is 1:1, and the ratio of the total number of atoms of the first element to the number of silicon atoms is 0.05 to 1:1, preferably 0.1:

1.

7. The hybrid waveguide amplifier based on co-doped erbium silicate film according to claim 1, characterized in that: The co-doped erbium silicate layer is obtained by radio frequency magnetron sputtering and annealing; The annealing atmosphere is an oxygen atmosphere; The annealing temperature is 850-<900°C; The annealing time is 5 minutes to 1 hour.

8. The method for preparing a hybrid waveguide amplifier based on co-doped erbium silicate thin film according to any one of claims 1 to 7, characterized in that: include: depositing a silicon nitride layer on the silicon oxide layer of the substrate; etching a waveguide structure on the deposited silicon nitride layer; A co-doped erbium silicate layer is deposited on the silicon oxide layer and the silicon nitride layer having the waveguide structure.

9. The method for preparing a hybrid waveguide amplifier based on co-doped erbium silicate film according to claim 8, characterized in that: The method for preparing the hybrid waveguide amplifier based on the co-doped erbium silicate film further performs an annealing operation after depositing the co-doped erbium silicate layer; The annealing atmosphere is an oxygen atmosphere; The annealing temperature is 850-<900°C; The annealing time is 5 minutes to 1 hour.

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