On-chip integrated laser source and preparation method thereof

Abstract

The invention discloses an on-chip integrated laser source and a preparation method thereof. According to the on-chip erbium-doped laser source, tantalum oxide doped with rare earth ions serves as a gain dielectric layer, tantalum oxide not doped with rare earth ions serves as a waveguide layer to be deposited on the gain dielectric layer to form a double-layer thin film structure, and then an Euler bent micro-ring resonant cavity structure is designed and prepared on the undoped layer. Compared with a conventional micro-ring resonant cavity prepared on a rare earth doped film, the Euler micro-ring designed in the invention not only can reduce scattering loss and high-order mode crosstalk in a wide waveguide, but also can avoid roughness caused by conventional direct etching of a rare earth ion doped film layer.

Description

Technical Field

[0001] The present invention particularly relates to an on-chip integrated laser source and a preparation method thereof, belonging to the technical field of laser sources. Background Art

[0002] Society is in the era of rapid development of information. Under the impact of emerging industries such as big data, 5G networks, artificial intelligence, the Internet of Things and cloud computing, the signal processing speed, system power consumption and signal transmission bandwidth of current integrated optoelectronic devices are facing unprecedented challenges. Compared with traditional telecommunications systems, all-optical signal processing with fast transmission speed, large bandwidth, no electromagnetic interference, low power consumption and high confidentiality is highly favored in today's high-speed optical communication era. Therefore, it is urgent to develop a new generation of photonic integrated chips with high integration, low power consumption and efficient all-optical operation. In recent years, silicon-based optoelectronics based on all-optical manipulation has flourished. At present, passive devices such as optical waveguides, filters and multiplexers in silicon-based optical components and active devices such as high-speed optical modulators, optical switches and photodetectors have attracted widespread attention in the new generation of optical communication technology. However, the slow development of silicon-based on-chip light sources has hindered the large-scale on-chip system integration of silicon-based photonic devices, which has always been a major challenge for silicon-based on-chip integrated photonic devices in communication systems. Since silicon is an indirect bandgap semiconductor material, electron-hole recombination must be emitted or absorbed by phonons to maintain momentum, making radiative carrier recombination much less likely than non-radiative carrier recombination, and thus the luminescence efficiency is low. In addition, the bandgap of silicon is 1.1eV, and the light emitted by carrier recombination is also limited to a wavelength of <1.1μm, which is lower than the wavelength compatible with low-loss silicon photonic microsystems. Obviously, there are great limitations in the direct development of on-chip light sources based on silicon materials.

[0003] On-chip laser sources based on erbium-doped optical microcavities show great application prospects in expanding silicon-based light sources. The main working principle is: erbium elements are doped in thin film materials, and the erbium ion population inversion is achieved when an external pump laser is connected. The stimulated radiation emits light with a wavelength of about 1.53μm. After microcavity resonance enhancement, laser performance can be finally generated. The generated laser wavelength corresponds to the minimum absorption value of quartz glass in optical fiber communication, and the energy of this wavelength is not affected by the excitation power and the ambient temperature. It is the standard wavelength in silicon-based photonics, with the advantages of high thermal stability and narrow intrinsic linewidth, which can meet the requirements of efficient signal processing of silicon photonic chips in the communication band. In addition, the preparation method of erbium ion thin film is compatible with the silicon photonic manufacturing process, and its low cost and versatility are very attractive in device and system design. Therefore, the development of an erbium-doped on-chip light source that can be integrated with a silicon-based photonic chip system based on a new material platform is an excellent solution to increase the application scope of silicon-based optoelectronic technology in the field of optical communications, which is of great significance to the development of silicon-based photonics technology.

[0004] At present, the material platforms for realizing on-chip laser based on rare earth ion doping mainly include aluminum oxide, tellurium oxide and lithium niobate. However, the existing on-chip laser sources still have shortcomings: 1) the rare earth ion doping concentration is low, which is not conducive to obtaining high-gain waveguide devices; 2) the waveguide transmission loss is still relatively high; 3) the pump power consumption of the laser is high and the output power is low. Summary of the invention

[0005] The object of the present invention is to provide an on-chip integrated laser source and a method for preparing the same, thereby overcoming the deficiencies in the prior art.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0007] A first aspect of an embodiment of the present invention provides an on-chip integrated laser source, comprising: a gain medium layer and an optical field limiting layer arranged on the gain medium layer, the optical field limiting layer comprising a resonator, a coupling waveguide, a pump light input structure and an on-chip laser output structure, the coupling waveguide extends along a first direction, the pump light input structure and the on-chip laser output structure are respectively arranged at two ends of the coupling waveguide along the first direction and connected to the coupling waveguide, the coupling waveguide is arranged at intervals on one side of the resonator along a second direction, wherein the material of the gain medium layer is tantalum oxide doped with rare earth ions, the material of the optical field limiting layer is undoped tantalum oxide, and the first direction and the second direction intersect.

[0008] A second aspect of an embodiment of the present invention provides a method for preparing the on-chip integrated laser source, which comprises:

[0009] Providing a tantalum oxide film doped with rare earth ions as a gain medium layer;

[0010] An undoped tantalum oxide film is formed on the tantalum oxide film doped with rare earth ions, and the tantalum oxide film is processed to form the resonator and the coupling waveguide.

[0011] Compared with the prior art, the advantages of the present invention include:

[0012] 1) The present invention uses Ta2O5 as the matrix material for erbium ion doping. With its low film defects and intrinsic losses, and Ta atoms with larger diameters, it helps to reduce the clustering of erbium ions and improve the luminous efficiency. Moreover, the material itself has a thermo-optical coefficient that is two orders of magnitude lower than that of silicon, which is conducive to obtaining a high-gain on-chip integrated light source while improving its stability.

[0013] 2) The present invention develops a micro-ring resonant cavity structure based on the principle of Euler bending, which not only solves the problem of high direct etching loss of rare earth-doped thin films, but also can suppress crosstalk between high-order modes in a wide waveguide and obtain a micro-ring resonator with efficient single-mode transmission, which is helpful to obtain an on-chip integrated laser source with a low pumping threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic structural diagram of an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity in an embodiment of the present invention;

[0015] Figure 2 A waveguide cross-sectional view of an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity in an embodiment of the present invention;

[0016] Figure 3 A top view of an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity in an embodiment of the present invention;

[0017] Figure 4a , Figure 4b They are respectively electric field distribution diagrams corresponding to the TE fundamental mode at wavelengths of 980nm and 1550nm of a double-layer waveguide structure of an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity in an embodiment of the present invention;

[0018] Figure 5 The relationship between the length of the tapered region of the inverted tapered coupling straight waveguide and the coupling efficiency of an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity in an embodiment of the present invention;

[0019] Figure 6 The relationship between the crosstalk between TE high-order modes and the waveguide width in an Euler microring resonator of an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity in an embodiment of the present invention;

[0020] Figure 7 The relationship between crosstalk and maximum curvature of TE high-order modes in an Euler microring resonator of an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity in an embodiment of the present invention;

[0021] Figure 8 The relationship between the crosstalk between TE high-order modes and the minimum radius of curvature in an Euler microring resonator of an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity in an embodiment of the present invention;

[0022] Figure 9a , Figure 9b A diagram showing TE high-order mode crosstalk and electric field distribution in an Euler microring resonator of an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity in an embodiment of the present invention;

[0023] Fig.10 The present invention is a flow chart of the preparation of an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0025] A first aspect of an embodiment of the present invention provides an on-chip integrated laser source, comprising: a gain medium layer and an optical field limiting layer arranged on the gain medium layer, the optical field limiting layer comprising a resonator, a coupling waveguide, a pump light input structure and an on-chip laser output structure, the coupling waveguide extends along a first direction, the pump light input structure and the on-chip laser output structure are respectively arranged at two ends of the coupling waveguide along the first direction and connected to the coupling waveguide, the coupling waveguide is arranged at intervals on one side of the resonator along a second direction, wherein the material of the gain medium layer is tantalum oxide doped with rare earth ions, the material of the optical field limiting layer is undoped tantalum oxide, and the first direction and the second direction intersect.

[0026] Furthermore, the doping concentration of the rare earth ions in the tantalum oxide material doped with rare earth ions is (2-6)×10 20 ions / cm 3 If the doping concentration of rare earth ions exceeds this range, rare earth ion quenching will occur.

[0027] Furthermore, the rare earth ions include one or a combination of two or more of erbium ions, ytterbium ions and thulium ions.

[0028] Further, the coupling spacing W3 between the coupling waveguide and the resonator in the second direction satisfies |t 2 |+|k c 2 |=1, where t represents the transmission coefficient in the coupled waveguide, and kc represents the coupling coefficient between the coupled waveguide and the resonator. As the coupling spacing W3 increases, the coupling coefficient decreases. In the process of modulating the coupling spacing, the coupling coefficient will also gradually change.

[0029] Furthermore, a coupling spacing W3 between the coupling waveguide and the resonator in the second direction is 500 nm to 900 nm.

[0030] Further, the resonator includes an Euler microring waveguide and a resonant cavity enclosed by the Euler microring waveguide, the coupled waveguide is a coupled straight waveguide, in the first direction, the middle part of the Euler microring waveguide is a straight waveguide, the middle part is parallel to the coupled waveguide, the two side parts are curved waveguides, and the maximum curvature radius R of the Euler microring waveguide is max and the minimum radius of curvature Rmin satisfy:

[0031]

[0032]

[0033] Where A is a constant, L total is the length of the single-side bent waveguide of the Euler microring waveguide.

[0034] Furthermore, the curved waveguides on both sides of the Euler microring waveguide are arranged in mirror symmetry, that is, the structures and structural parameters of the curved waveguides on both sides are completely the same.

[0035] Furthermore, the maximum curvature radius R of the Euler microring waveguide is max 500μm~1000μm, minimum curvature radius R min It is 20μm~100μm.

[0036] Furthermore, the width W1 of the coupled straight waveguide is 2 μm to 4 μm, and the width W2 of the Euler microring waveguide is 2 μm to 4 μm.

[0037] Furthermore, the effective refractive indexes of the coupled straight waveguide and the Euler microring waveguide are equal.

[0038] Furthermore, the pump light input structure and the on-chip laser output structure are both tapered waveguide structures.

[0039] Furthermore, the tapered waveguide structure includes a tapered waveguide section and a straight waveguide section connected in sequence, the tapered waveguide section is directly connected to the coupling waveguide, the maximum width of the tapered waveguide section is equal to the width of the coupling waveguide, and the minimum width is equal to the width of the straight waveguide section, wherein the width W4 of the straight waveguide section is 50nm~150mm, and the length L of the tapered waveguide section is 50μm~300μm.

[0040] Furthermore, the coupling waveguide, the pump light input structure and the on-chip laser output structure are integrated.

[0041] Furthermore, the thickness of the gain medium layer is 0.5 μm to 1 μm.

[0042] Furthermore, the resonator and the coupling waveguide are formed by integrally processing an undoped tantalum oxide thin film.

[0043] Furthermore, the thickness of the optical confinement layer is 100-300 nm.

[0044] A second aspect of an embodiment of the present invention provides a method for preparing the on-chip integrated laser source, which comprises:

[0045] Providing a tantalum oxide film doped with rare earth ions as a gain medium layer;

[0046] An undoped tantalum oxide film is formed on the tantalum oxide film doped with rare earth ions, and the tantalum oxide film is processed to form the resonator and the coupling waveguide.

[0047] The technical solution, its implementation process and principles, etc. will be further explained below in conjunction with the accompanying drawings and specific implementation cases. Unless otherwise specified, the thin film preparation process and equipment, etching process and equipment, etc. used in the embodiments of the present invention are all known in the art and are not specifically limited here.

[0048] An embodiment of the present invention provides an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity. The on-chip integrated laser source uses a tantalum oxide film doped with rare earth ions as a gain medium layer, and uses a tantalum oxide film not doped with rare earth ions to form a light field confinement layer with a resonator and a coupled waveguide. The resonator uses a microring resonator designed based on the Euler bending principle. It should be noted that the rare earth ions used here are not limited to erbium ions, but can also be one or more of other rare earth ions such as ytterbium ions and thulium ions. The microring resonator can also be other types of resonators, such as microdisks and microrings designed based on other bending principles.

[0049] The on-chip erbium-doped laser source uses tantalum oxide doped with rare earth ions as a gain medium layer, and after depositing tantalum oxide undoped with rare earth ions as a waveguide layer on the gain medium layer to form a double-layer film structure, an Euler curved resonator is designed and prepared on the undoped layer. Compared with the conventional resonator prepared on a rare earth-doped film, the Euler microring resonator designed in the invention can reduce scattering loss and high-order mode crosstalk in a wide waveguide, and can avoid the roughness introduced by conventional direct etching of the thin film layer doped with rare earth ions. Therefore, by using the rare earth ion-doped thin film layer to provide high gain and using the tantalum oxide film doped with rare earth ions as a microring waveguide layer to provide a resonant cavity, the interaction between light and the active medium can be maximized in this double-layer structure, and at the same time, combined with the Euler microring resonant cavity structure that can achieve a high quality factor, the demand for high-performance on-chip integrable laser source devices can be met.

[0050] Example

[0051] See also Figure 1, an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity, comprising an optical substrate substrate 1, a silicon dioxide layer 2, a gain medium layer 3 providing optical gain and a light field limiting layer, the gain medium layer 3 and the light field limiting layer, the material of the gain medium layer 3 is erbium-doped tantalum oxide, the material of the light field limiting layer is undoped tantalum oxide, the light field limiting layer comprises an Euler microring resonator (i.e., Euler microring waveguide, the same below) 41, a coupled straight waveguide 42, a pump light input structure 6 and an on-chip laser output structure 7, the pump light input structure 6 and the on-chip laser output structure 7 are respectively arranged at two ends of the coupled straight waveguide 42 along a first direction, and a coupling spacing 5 is provided between the Euler microring resonator 41 and the coupled straight waveguide 42.

[0052] In this embodiment, the thickness of the optical substrate substrate 1 is 0.5 mm-1 mm, the thickness of the silicon dioxide layer is 2 μm-10 μm, the thickness of the gain medium layer 3 is 0.5 μm-1 μm, and the thickness of the light field confinement layer is 100 nm-300 nm.

[0053] Specifically, the optical substrate substrate 1 is a silicon wafer, a silicon dioxide layer 2 is deposited on the optical substrate substrate 1 to form a low refractive index lower cladding, an erbium-doped tantalum oxide film (Ta2O5: Er) is directly deposited on the silicon dioxide layer 2 to form a gain medium layer 3, an undoped tantalum oxide film is deposited on the erbium-doped gain medium layer 3, and the undoped tantalum oxide film is integrally processed to form an Euler microring resonator 41 and a coupled straight waveguide 42 to form a light field confinement layer, and the coupling spacing 5 between the microring resonator 41 and the coupled straight waveguide 42 is designed to obtain an optimal coupling coefficient, and the pump light input structure 6 of the coupled straight waveguide 42 and the on-chip laser output structure 7 are tapered waveguide structures to improve the coupling efficiency with the output light in the lens optical fiber, thereby further improving the input and output of the laser power.

[0054] The working principle of the on-chip integrated laser source in this embodiment is: under the action of an excitation source with a wavelength corresponding to a specific energy level of erbium ions, erbium ions between different energy levels in erbium-doped tantalum oxide undergo transitions, achieving a population inversion, and emitting light with a wavelength of about 1.5 μm by stimulated radiation. At the same time, under the repeated resonance of the Euler microring resonator, laser output with a certain repetition frequency is finally achieved.

[0055] Tantalum oxide is selected in the embodiment of the present invention mainly because it has a high solubility of rare earth ions, and the radius of the Ta atom is larger than the radius of the Al atom in aluminum oxide, which helps to disperse the distance between rare earth ions and reduce the probability of clustering and quenching of rare earth ions, thereby greatly increasing the luminous efficiency of rare earth ions. Specifically, the refractive index of tantalum oxide (~2.1) is greater than the refractive index of aluminum oxide (~1.7), so that the waveguide can better confine the light field, which is conducive to further reducing the size of the on-chip integrated laser source and increasing the integration of the on-chip integrated laser source. At the same time, tantalum oxide material has a high laser loss threshold and a low thermo-optical coefficient (two orders of magnitude smaller than silicon), which is more helpful to improve the stability of the on-chip integrated laser source. The tantalum oxide film prepared by the same film-forming method has low internal defects and low stress (carbon oxide stress is 100MPa, silicon nitride stress is 800MPa), which is more conducive to obtaining tantalum oxide films with low intrinsic losses. In addition, the film-forming method of amorphous tantalum oxide films is simple and can be prepared on any substrate by sputtering or evaporation, which reduces costs and is compatible with current COMS processes. It can achieve heterogeneous integration with silicon-based optical chips.

[0056] The embodiment of the present invention adopts the Euler microring resonator, mainly because the structure can produce a waveguide device with efficient single-mode transmission under wide waveguide size. With the design advantage of the Euler bending principle, first, the interaction between the light field and the waveguide sidewall can be greatly reduced in the wide waveguide, reducing the scattering loss, which is helpful to obtain a microring resonator with a high quality factor and reducing the pump power consumption of the entire device; second, the crosstalk between high-order modes in the wide waveguide is greatly reduced, reducing the loss of mode mismatch. In the microring of the same width and conventional bending size, there will be multiple modes of transmission, which greatly reduces the transmission efficiency. In addition, the embodiment of the invention prepares the Euler microring resonator based on tantalum oxide thin film without rare earth ion doping, avoiding the roughness introduced by direct etching of the rare earth doping layer, which can greatly improve the optical performance of the entire on-chip integrated laser source.

[0057] See also Figure 3 , Figure 3 The top view of the on-chip integrated laser source device of the erbium-doped tantalum oxide microcavity provided in this embodiment. The Euler microring resonator made of tantalum oxide thin film without rare earth ion doping in this embodiment is based on the principle of Euler bending curve, which makes the curvature radius of the curved waveguide gradually change, wherein the maximum curvature radius constituting the Euler microring resonator 41 is defined as R max , R max 500μm-1000μm, suitable R max The size can effectively reduce the mode mismatch rate at the connection between the multimode waveguide and the curved waveguide. The minimum radius of curvature is defined as R min , which mainly affects the footprint of the entire device and the strength of the mode crosstalk, R min 20μm-100μm.

[0058] In this embodiment, the width W1 of the coupled straight waveguide 42 is 2μm-4μm. The width of the coupled straight waveguide 42 is controlled mainly to ensure that only single-mode light fields can be transmitted, thereby reducing the transmission of high-order modes. The width W2 of the Euler microring resonator 41 is 2-4μm. Increasing the width of the Euler microring resonator 41 can effectively reduce the scattering loss caused by the interaction between the light field and the side of the waveguide. The coupling spacing W3 between the coupled straight waveguide 42 and the Euler microring resonator 41 is 500-900nm. The coupling coefficient optimized by the FDTD software can control the extinction ratio and Q value of the Euler microring resonator, further reducing the pump power consumption of the on-chip light source.

[0059] In this embodiment, the pump light input structure 6 and the on-chip laser output structure 6 are both tapered waveguide structures. Specifically, the tapered waveguide structure includes a tapered waveguide section and a straight waveguide section connected in sequence. The tapered waveguide section is directly connected to the coupled straight waveguide 42. The maximum width of the tapered waveguide section is equal to the width of the coupled straight waveguide 42, and the minimum width is equal to the width of the straight waveguide section. The width W4 of the straight waveguide section is 50nm to 150mm, and the length L of the tapered waveguide section is 50μm to 300μm. Preferably, the coupled straight waveguide 42, the pump light input structure 6 and the on-chip laser output structure 7 are integrated.

[0060] In this embodiment, the coupling spacing between the coupled straight waveguide 42 and the Euler microring resonator 41 should satisfy the condition that |t 2 |+|k c 2 |=1, t represents the transmission coefficient of the coupled straight waveguide 42, kc represents the coupling coefficient between the coupled straight waveguide 42 and the Euler microring resonator 41, and only a suitable coupling spacing can make the two coupled, and the light in the coupled straight waveguide 42 will be coupled into the Euler microring resonator 41 to resonate.

[0061] It should be noted that both sides of the conventional microring waveguide will interact with light. Under the conditions determined by the process, the roughness on both sides will increase the scattering of the light field, thus increasing the device loss and reducing the Q value of the microring. Of course, the scattering of light by the roughness on both sides can be weakened by increasing the width of the microring waveguide. However, such a design is easy to excite the high-order mode in the wide waveguide, so there is mode crosstalk. Especially in the process of realizing the on-chip laser source in combination with the gain material proposed in the present invention, it is difficult to ensure only single-mode transmission, which reduces the transmission efficiency of the waveguide and also reduces the conversion efficiency of the on-chip light source. On the contrary, the Euler microring resonator used in the present invention can take into account the disadvantages of the conventional microring. Through the Euler bending, adiabatic coupling and transmission can be achieved while increasing the waveguide width, ensuring the single-mode transmission efficiency of the light field. In particular, in the present invention, increasing the waveguide width further reduces the transmission loss of the waveguide, improves the Q value of the resonator, and helps to reduce the pumping threshold of the on-chip laser source. On the other hand, the interaction between the single-mode light field and the gain film will further increase the conversion efficiency of the on-chip laser.

[0062] See also Figure 4a , Figure 4b , Figure 4a , Figure 4b They are the light field distribution diagrams corresponding to the TE fundamental mode at the pump wavelength of 980nm and the laser generation wavelength of 1550nm in the on-chip integrated laser source of the erbium-doped tantalum oxide microcavity of this embodiment, which are simulated by the MODE Solutions software. The reference standard of the simulation results is to optimize the overlap integral of light in the rare earth-doped and undoped rare earth layers to obtain the maximum proportion of light in the rare earth ion-doped thin film layer that can simultaneously ensure the efficient transmission of the TE fundamental mode, which can best improve the activity and luminous efficiency of the rare earth ions and obtain a higher gain output. Of course, according to actual needs, the wavelengths of the pump light and signal light here can be changed to wavelengths such as 1480nm and 1530nm, and the corresponding wavelength light source can also be selected according to the different energy levels of the rare earth ions.

[0063] See also Figure 5 , Figure 5 This is the relationship between the length of the inverted tapered waveguide segment and the coupling efficiency of an on-chip integrated laser source designed for an erbium-doped tantalum oxide microcavity in this embodiment. It can be seen that after fixing the waveguide thickness, when the width of the tapered waveguide is below 100nm and the length of the tapered region is above 100μm, the coupling efficiency can reach more than 80%.

[0064] The design principle of the coupled straight waveguide with an inverted tapered waveguide structure in the present invention is: the inverted tapered waveguide structure used by the pump light input structure 6 and the on-chip laser output structure 7 is mainly to match the effective area of ​​the light field restricted by the cross section of the coupled straight waveguide with the effective mode field area of ​​the lens optical fiber used for coupling light, thereby improving the coupling efficiency between the optical fiber and the waveguide end face. The condition that needs to be satisfied between the two is n eff =n eff , n eff represents the effective refractive index of the pump light input structure 6, n eff Represents the effective refractive index in the lensed fiber.

[0065] See also Figure 6 , Figure 6 This is the relationship between the high-order mode crosstalk and the waveguide width in the Euler microring resonator 41 of the on-chip integrated laser source design of the erbium-doped tantalum oxide microcavity in this embodiment. It can be seen that when the width of the Euler microring resonator 41 changes from 2μm to 4μm, the corresponding TE first-order mode extinction ratio is above -20dB, among which the extinction ratio of the second-order mode is less than -30dB when the waveguide width is less than 3μm; when it is greater than 3μm, the extinction ratio is greater than -20dB, and the extinction ratio of the third-order mode is basically maintained at less than -40dB, indicating that when the waveguide width is between 2-3μm, the crosstalk of other high-order modes except the TE fundamental mode can be ignored, and more efficient single-mode transmission can be obtained.

[0066] See also Figure 7 , Figure 7 This is the relationship between the high-order mode crosstalk and the maximum curvature radius in the Euler microring resonator 41 of the on-chip integrated laser source design of the erbium-doped tantalum oxide microcavity in this embodiment. It can be seen that when the maximum curvature radius Rmax changes from 500-1000μm, the extinction ratio of the TE first-order mode at 800μm reaches the maximum, which is less than -40dB, and when the maximum curvature radius changes, the extinction ratios of the second-order and third-order modes are maintained at -50dB, achieving a good suppression effect.

[0067] See also Figure 8 , Figure 8 This is the relationship between the high-order mode crosstalk and the minimum radius of curvature in the Euler microring resonator 41 of the on-chip integrated laser source design of the erbium-doped tantalum oxide microcavity in Example 1. It can be seen that when the minimum radius of curvature is between 30-90μm, the mode crosstalk greater than the second order is less than -40dB, and when Rmin is between 40μm and 90μm, the extinction ratio of the first-order mode is also around -30dB, indicating that it can have lower crosstalk between high-order modes.

[0068] See also Figure 9a , Figure 9b , Figure 9a , Figure 9bIt is a diagram of high-order mode crosstalk and the corresponding fundamental mode electric field distribution in the Euler microring resonator 41 of the on-chip integrated laser source design of the erbium-doped tantalum oxide microcavity in this embodiment. Figure 9a The optimal parameters of the Euler microring resonator are given: the maximum curvature radius Rmax is 800μm, the minimum curvature radius Rmin is 100μm, the width of the Euler microring resonator is 2.5μm, and the height is 200nm, corresponding to the transmittance distribution between the TE fundamental mode and the high-order mode in the communication band. It can be seen that except for the TE fundamental mode, the light field transmittance of other high-order modes is below -30dB and is well suppressed, which is conducive to the efficient transmission of TE single mode. It also helps to obtain a high-Q Euler microring resonator, which can greatly reduce the pumping threshold of the on-chip laser source, and at the same time Figure 9b It can also be seen that only the TE fundamental mode is transmitted in the Euler microring resonator corresponding to this parameter, and the electric field intensity is evenly distributed.

[0069] See also Fig.10 A method for preparing an on-chip integrated laser source of an erbium-doped tantalum oxide microcavity comprises the following steps:

[0070] Step 1: Deposit rare earth erbium ions Er on an optical substrate by magnetron sputtering or ion beam evaporation. 3+ Tantalum oxide film (Ta2O5:Er);

[0071] Step 2, depositing a tantalum oxide thin film layer not doped with rare earth ions on the deposited tantalum oxide thin film (Ta2O5:Er) by ion beam evaporation;

[0072] Step 3, depositing a layer of chromium (Cr, thickness of 50-100 nm) on the deposited double-layer tantalum oxide film by magnetron sputtering, mainly serving as a hard mask;

[0073] Step 4, spin-coating a layer of PMMA photoresist on the Cr film with a thickness of 200-400 nm;

[0074] Step 5, firstly exposing PMMA photoresist by electron beam lithography, and then developing, so that the patterns of the Euler microring resonator and the coupled straight waveguide are transferred to PMMA;

[0075] Step 6, using an inductively coupled plasma etching device (Cl2 and O2 mixed gas) to etch the Cr film, and transferring the patterns of the Euler microring resonator and the coupled straight waveguide on the PMMA to the Cr film;

[0076] Step 7, again using dry etching (a combination of CF4, O2 and Ar gases) to etch the tantalum oxide film not doped with rare earth ions, and finally successfully transferring the patterns of the Euler microring resonator and coupled straight waveguide on the Cr film to the target material, forming an on-chip microring resonant structure, which improves the resonant cavity effect for generating on-chip lasers;

[0077] Step 8. Finally, use N-methylpyrrolidone and plasma degumming equipment to remove the residual glue of the entire device to obtain a complete erbium-doped on-chip microcavity laser source device. During the entire waveguide preparation process, the side wall roughness of the tantalum oxide waveguide can be optimized by combining processes such as photoresist thermal reflow and waveguide annealing.

[0078] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An on-chip integrated laser source, characterized in that: include: A gain medium layer and an optical field limiting layer arranged on the gain medium layer, the optical field limiting layer comprising a resonator, a coupling waveguide, a pump light input structure and an on-chip laser output structure, the coupling waveguide extends along a first direction, the pump light input structure and the on-chip laser output structure are respectively arranged at two ends of the coupling waveguide and connected to the coupling waveguide, the coupling waveguide is arranged at one side of the resonator at intervals along a second direction, wherein the material of the gain medium layer is tantalum oxide doped with rare earth ions, the material of the optical field limiting layer is undoped tantalum oxide, and the first direction and the second direction intersect.

2. The on-chip integrated laser source according to claim 1, characterized in that: The doping concentration of the rare earth ions in the tantalum oxide material doped with rare earth ions is (2-6)×10 20 ions / cm 3 ; Preferably, the rare earth ions include one or a combination of two or more of erbium ions, ytterbium ions and thulium ions.

3. The on-chip integrated laser source according to claim 1, characterized in that: The coupling spacing W3 between the coupling waveguide and the resonator in the second direction satisfies |t 2 |+|k c 2 |=1, where t represents the transmission coefficient in the coupled waveguide and kc represents the coupling coefficient between the coupled waveguide and the resonator.

4. The on-chip integrated laser source according to claim 3, characterized in that: A coupling spacing W3 between the coupling waveguide and the resonator in the second direction is 500 nm to 900 nm.

5. The on-chip integrated laser source according to claim 3, characterized in that: The resonator comprises an Euler microring waveguide and a resonant cavity enclosed by the Euler microring waveguide, the coupled waveguide is a coupled straight waveguide, in the first direction, the middle part of the Euler microring waveguide is a straight waveguide, the middle part is parallel to the coupled waveguide, the two side parts are curved waveguides, and the maximum curvature radius R of the Euler microring waveguide is max and the minimum radius of curvature R min satisfy: Where A is a constant, L total is the length of the single-side curved waveguide of the Euler microring waveguide; Preferably, the curved waveguides on both sides of the Euler microring waveguide are arranged in mirror symmetry.

6. The on-chip integrated laser source according to claim 5, characterized in that: The maximum curvature radius R of the Euler microring waveguide max 500μm~1000μm, minimum curvature radius R min It is 20μm~100μm.

7. The on-chip integrated laser source according to claim 5, characterized in that: The width W1 of the coupled waveguide is 2 μm to 4 μm, and the width W2 of the Euler microring waveguide is 2 μm to 4 μm; And / or, the effective refractive index of the coupled straight waveguide and the Euler microring waveguide is equal.

8. The on-chip integrated laser source according to claim 1, characterized in that: The pump light input structure and the on-chip laser output structure are both tapered waveguide structures; Preferably, the tapered waveguide structure comprises a tapered waveguide section and a straight waveguide section connected in sequence, the tapered waveguide section is directly connected to the coupling waveguide, the maximum width of the tapered waveguide section is equal to the width of the coupling waveguide, and the minimum width is equal to the width of the straight waveguide section, wherein the width W4 of the straight waveguide section is 50nm to 150mm, and the length L of the tapered waveguide section is 50μm to 300μm; Preferably, the coupling waveguide, the pump light input structure and the on-chip laser output structure are integrated.

9. The on-chip integrated laser source according to claim 1, characterized in that: The thickness of the gain medium layer is 0.5 μm to 1 μm; And / or, the resonator and the coupling waveguide are formed by integrally processing an undoped tantalum oxide thin film; Preferably, the optical confinement layer has a thickness of 100-300 nm.

10. The method for preparing an on-chip integrated laser source according to any one of claims 1 to 9, characterized in that: Providing a tantalum oxide film doped with rare earth ions as a gain medium layer; An undoped tantalum oxide film is formed on the tantalum oxide film doped with rare earth ions, and the tantalum oxide film is processed to form the resonator and the coupling waveguide.

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