Optical waveguide, preparation method thereof and optical waveguide amplifier

Abstract

The invention discloses an optical waveguide, a preparation method thereof and an optical waveguide amplifier, and relates to the technical field of optical waveguides. An active overlying layer having a second refractive index, the first refractive index being greater than the second refractive index; wherein the active overlying layer comprises a substrate and a quantum dot structure uniformly mixed in the substrate, the quantum dot structure at least comprises a first size and a second size, and the first size is not equal to the second size. According to the optical waveguide doped with the quantum dot structures, higher luminous efficiency can be achieved through the quantum effect of the quantum dot structures, and the bandwidth and luminous efficiency of the waveguide amplifier can be improved through the quantum effect of the quantum dot structures of different sizes by doping at least two kinds of quantum dot structures of different sizes in the active upper covering layer.

Description

Technical Field

[0001] This application relates to the technical field of optical waveguides, and particularly to an optical waveguide, a preparation method thereof, and an optical waveguide amplifier. Background Art

[0002] With the rapid development of mobile Internet, Internet of Things, cloud computing, and 5G networks, the demand for the capacity of the next-generation optical communication is increasing. Under the action of pump light, based on the principle of stimulated emission, an optical waveguide amplifier can directly amplify the signal light, making up for the attenuation caused by loss during the transmission of the optical signal. It is a key component in the optical communication system. The continuous improvement of its performance and the continuous reduction of cost have promoted the all-optical network into a new era.

[0003] An optical waveguide is one of the key components in an optical waveguide amplifier. However, the existing rare-earth ion optical waveguide amplifier has a small bandwidth and low luminous efficiency, which will affect the performance improvement of the optical waveguide amplifier. At the same time, the flexibility of the rare-earth ion pump spectrum is low, and it can only adapt to a specific wavelength pump. Summary of the Invention

[0004] In view of the above problems, this application provides an optical waveguide, a preparation method thereof, and an optical waveguide amplifier to achieve the purpose of improving the bandwidth and luminous efficiency of the optical waveguide. At the same time, this optical waveguide amplifier has high pump spectrum flexibility.

[0005] The specific solutions are as follows:

[0006] The first aspect of this application provides an optical waveguide, including:

[0007] A passive core layer with a first refractive index;

[0008] An active upper cladding layer with a second refractive index, and the first refractive index is greater than the second refractive index;

[0009] Wherein, the active upper cladding layer includes a matrix and quantum dot structures uniformly mixed in the matrix. The quantum dot structures include at least a first size and a second size, and the first size is not equal to the second size.

[0010] Optionally, in the above optical waveguide, the quantum dot structure includes: a quantum dot core and a shell layer coating the quantum dot core.

[0011] Optionally, in the above optical waveguide, the material of the quantum dot core is PbS;

[0012] The material of the shell layer is CdS.

[0013] Optionally, in the above optical waveguide, the quantum dot structure further includes:

[0014] An oleic acid coating covering the shell layer.

[0015] Optionally, in the above optical waveguide, the value range of the first dimension is 2.5 nm to 4.0 nm, and the value range of the second dimension is 4.5 nm to 7.0 nm.

[0016] Optionally, in the above optical waveguide, the optical waveguide further includes a substrate;

[0017] wherein,

[0018] the passive core layer includes at least one convex structure located on the surface of the substrate; the active overcoat covers the side wall and the top surface of the convex structure;

[0019] or, at least one ion exchange region is provided in one side surface of the substrate, the passive core layer includes the ion exchange region; the active overcoat covers the ion exchange region.

[0020] The second aspect of the present application provides an optical waveguide amplifier, including:

[0021] the above optical waveguide;

[0022] a first light source, the first light source provides signal light for the passive core layer from one end of the passive core layer;

[0023] a second light source, the second light source provides pump light for the passive core layer from the top of the passive core layer;

[0024] a photodetector, the photodetector collects the excited light output by the passive core layer from the other end of the passive core layer.

[0025] Optionally, in the above optical waveguide amplifier, the second light source is any one of an LED emitting ultraviolet light, an LED emitting visible light, an LED emitting broadband white light, and a natural light source.

[0026] The third aspect of the present application provides a preparation method of the above optical waveguide, including:

[0027] Preparing a quantum dot broadband hybrid colloid;

[0028] Using the quantum dot broadband hybrid colloid, an active overcoat with a second refractive index is formed on the surface of the passive core layer with a first refractive index;

[0029] wherein, the first refractive index is greater than the second refractive index; the active overcoat includes a matrix and quantum dot structures uniformly mixed in the matrix, and the quantum dot structures include at least a first dimension and a second dimension, and the first dimension is not equal to the second dimension.

[0030] Optionally, in the above preparation method, the method for preparing the quantum dot broadband hybrid colloid includes:

[0031] Respectively preparing an organic solution mixed with quantum dot structures of a first dimension and an organic solution mixed with quantum dot structures of a second dimension;

[0032] Two organic solutions are uniformly mixed in a matrix to form a quantum dot broadband hybrid colloid.

[0033] Optionally, in the above preparation method, it further includes:

[0034] Forming a core layer film on the surface of a substrate;

[0035] Patternizing the core layer film to form a plurality of convex structures; an active overcoat covers the sidewalls and the top surface of the convex structures;

[0036] Or, forming an ion exchange region within the surface of the substrate, the passive core layer includes the ion exchange region; the active overcoat covers the ion exchange region.

[0037] By means of the above technical solutions, in the optical waveguide, the preparation method thereof, and the optical waveguide amplifier provided by the present application, the active overcoat of the optical waveguide includes at least a quantum dot structure of a first size and a second quantum dot structure. Compared with a conventional rare earth doped optical waveguide, the optical waveguide doped with a quantum dot structure can achieve a higher luminous efficiency by utilizing the quantum effect of the quantum dot structure, and can also improve the bandwidth and luminous efficiency of the waveguide amplifier by doping at least two different sizes of quantum dot structures in the active overcoat and utilizing the quantum effects of the quantum dot structures of different sizes. Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0039] The structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions under which the present application can be implemented. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present application can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present application.

[0040] Figure 1 It is a top view of an optical waveguide provided by an embodiment of the present application;

[0041] Figure 2 It is Figure 1 A sectional view of the shown optical waveguide in the A - A' direction;

[0042] Figure 3 It is a sectional view of a quantum dot structure provided by an embodiment of the present application;

[0043] Figure 4 Cross-sectional view of another quantum dot structure provided by an embodiment of the present application;

[0044] Figure 5 Top view of another optical waveguide provided by an embodiment of the present application;

[0045] Figure 6 is Figure 5 Cross-sectional view of the shown optical waveguide in the B-B' direction;

[0046] Figure 7 Transmission electron microscope (TEM) image of the active overcladding layer when two sizes of quantum dot structures are co-doped;

[0047] Figure 8 Photoluminescence (PL) spectrum diagram of the active overcladding layer when two sizes of quantum dot structures are co-doped;

[0048] Figure 9 Schematic structural diagram of an optical waveguide amplifier provided by an embodiment of the present application;

[0049] Figure 10 Photoluminescence spectrum curve diagram of an ultra-wide spectrum quantum dot PMMA thin film provided by an embodiment of the present application;

[0050] Figure 11 Absorption spectrum curve diagram of an ultra-wide spectrum quantum dot PMMA thin film provided by an embodiment of the present application;

[0051] Figure 12 Schematic flow chart of a method for preparing an optical waveguide provided by an embodiment of the present application;

[0052] Figure 13 Flow chart of a method for preparing a quantum dot wide-spectrum hybrid colloid provided by an embodiment of the present application.

[0053] Reference numerals:

[0054] 11 - Passive core layer; 12 - Active overcladding layer; 13 - Substrate; 14 - Lower cladding; 15 - Quantum dot core; 16 - Shell layer; 17 - Oleic acid coating; 18 - Optical waveguide; 19 - First light source; 20 - Second light source; 21 - Photodetector; 22 - Uniform rectangular spot lens; 23 - Signal light; 24 - Pump light. Detailed implementation manners

[0055] Next, the embodiments in the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Those of ordinary skill in the art can know that with the development of technology and the emergence of new scenarios, the technical solutions provided by the embodiments of the present application are also applicable to similar technical problems.

[0056] Currently, there has been much research on organic polymer optical waveguides, but there are also some problems. This is because organic polymer optical waveguides need to achieve broadband amplification / multi-wavelength amplification by doping rare earth ions. However, the complex energy level structure and f-f transition limitations of rare earth ions bring some disadvantages, including large gain ripple (>5 dB) and narrow bandwidth (<100 nm). The amplification band is only limited to the S+C+L or S+C band, thus reducing the transmission capacity and easily causing signal distortion. In addition, the pump spectral flexibility of rare earth ions is relatively low, and it can only adapt to specific wavelength pumping (such as 980 nm / 1480 nm). At the same time, the upconversion luminescence of rare earth ions will compete for energy with the emission of the target light, and may reduce the emission intensity of the target light under high doping concentration or high-power pumping conditions. Moreover, the co-doping of multiple rare earth ions has been proven to enhance the thermal effect of the material, especially under high-power laser pumping conditions. This enhanced thermal effect will reduce the optical properties of the material and cause thermal damage to centimeter-long, highly doped RDWAs. In addition, achieving broadband amplification usually requires precise control of the doping concentration and distribution of different rare earth ions. Methods such as layered doping or core-shell structures have been proven to improve performance. However, these methods have high manufacturing complexity and high costs.

[0057] With the rapid development of artificial nanomaterials, theoretical research and experimental exploration have shown that using nanomaterials with quantum dot structures to fabricate optical waveguides can effectively solve the above problems of organic polymer optical waveguides. First, the doping amount of the quantum dot structure can be adjusted according to needs, so high-concentration doping can be achieved. Second, the quantum effect of the nanomaterials with quantum dot structures is its unique advantage. Its excitation spectrum is relatively wide, with high pump spectral flexibility, its emission spectrum is relatively narrow, the quantum efficiency is significantly improved, and the fluorescence lifetime is also longer. This can enable the optical waveguide to have a larger bandwidth and higher luminous efficiency, with higher flexibility in the selection of pump light sources, making the optical waveguide have a more tolerant pump scenario, thereby improving its adaptability and versatility in different application scenarios.

[0058] In optical waveguides doped with conventional quantum dot structures, generally a single-size quantum dot structure is used, resulting in a narrow bandwidth of the optical waveguide.

[0059] In addition, the surface of the conventional quantum dot structure has a large number of defects such as dangling bonds, which will aggravate the non-radiative recombination effect, resulting in the ineffective consumption of pump energy and failure to effectively act on optical amplification. Moreover, the amplification bandwidth is very narrow, and it only has an amplification effect in the C band. The most core reason for the above problems is the poor material stability of the quantum dot structure, and the potential of the quantum dot material for ultra-wideband amplification cannot be explored.

[0060] To solve the above problems, an embodiment of the present application provides an optical waveguide, including:

[0061] A passive core layer having a first refractive index;

[0062] An active overcladding layer having a second refractive index, the first refractive index being greater than the second refractive index;

[0063] Wherein, the active overcladding layer includes a matrix and quantum dot structures uniformly mixed in the matrix, and the quantum dot structures include at least a first size and a second size, and the first size is not equal to the second size.

[0064] In the embodiments of the present application, the active overcladding layer of the optical waveguide includes at least quantum dot structures of a first size and a second quantum dot structure. Compared with a conventional rare-earth doped optical waveguide, an optical waveguide doped with quantum dot structures can achieve higher luminous efficiency by utilizing the quantum effect of the quantum dot structures. Moreover, by doping at least two different sizes of quantum dot structures in the active overcladding layer, the bandwidth and luminous efficiency of the waveguide amplifier can be improved by utilizing the quantum effects of the quantum dot structures of different sizes.

[0065] The optical waveguide is at least used for optical communication in the O+C band. Among them, the O band is an important band in optical fiber communication, and its wavelength range is from 1260nm to 1360nm. The O band has low dispersion characteristics and can maintain low signal distortion during signal transmission, making it very suitable for 5G fronthaul solutions. The C band in optical communication refers to the wavelength range from 1530nm to 1565nm. The C band has low fiber loss and is therefore widely used in metropolitan area networks, long-distance, ultra-long-distance, and submarine optical cable systems. The C band is also one of the commonly used bands in WDM (wavelength division multiplexing) systems. With the development of technology, the concept of the C band is also expanding, such as the CE band (extended C band) and the C+L band (combination of the C band and the L band), etc., to meet greater data transmission requirements.

[0066] Furthermore, the quantum dot structure can also be a core-shell structure based on a shell coating the quantum dot core, which can improve the material stability of the quantum dot structure, effectively block the energy transfer between multi-size quantum dots, improve its flat-top amplification property, reduce the amplifier gain fluctuation, can make more full use of the ultra-wide spectrum amplification ability of the quantum dot material, can suppress the non-radiative recombination effect caused by surface defects of the quantum dot core, can improve the utilization rate of the pump light, enable more pump light to be used for optical amplification, improve the amplification bandwidth, can greatly improve the luminescent quantum efficiency, and can achieve a higher relative gain.

[0067] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0068] Refer to Figure 1 and Figure 2 , Figure 1 is a top view of an optical waveguide provided by an embodiment of the present application, Figure 2 isFigure 1 Cross-sectional view of the optical waveguide shown in the A-A' direction. The optical waveguide includes:

[0069] A passive core layer 11 with a first refractive index;

[0070] An active overcladding layer 12 with a second refractive index, where the first refractive index is greater than the second refractive index;

[0071] Wherein, the active overcladding layer 12 includes a matrix and quantum dot structures uniformly mixed in the matrix. The quantum dot structures include at least a first size and a second size, and the first size is not equal to the second size.

[0072] In the optical waveguide, the film layer doped with quantum dot structures is the active film layer, and the film layer without quantum dot structure doping is the passive film layer. The optical waveguide provided by the embodiments of the present application is an evanescent wave type optical waveguide, that is, the high refractive index light guiding core layer (passive core layer 11) in the optical waveguide is a passive waveguide, and the low refractive index active material is used as the active overcladding layer 12 to cover the passive core layer 11. This optical waveguide can be used to construct an evanescent wave type optical waveguide amplifier.

[0073] When the optical waveguide is used for signal light amplification, the signal light coupled into the passive core layer 11 can penetrate into the active overcladding layer 12 through the evanescent field. In the active overcladding layer 12, the signal light can simultaneously excite the quantum dot structures with the pump light irradiating the active overcladding layer 12, so that the quantum dot structures are stimulated to emit to form amplified signal light. The amplified signal light can penetrate into the passive core layer 11 based on the evanescent field, and the amplified signal light can be transmitted to the photodetector through the passive core layer 11 to realize the acquisition and detection of the amplified signal light.

[0074] Optionally, the matrix in the active overcladding layer 12 can be PMMA or other light-transmitting organic materials.

[0075] In the embodiments of the present application, the active overcladding layer 12 includes at least quantum dot structures of a first size and second quantum dot structures. Compared with the conventional rare earth doped optical waveguide, the optical waveguide doped with quantum dot structures can utilize the quantum effect of the quantum dot structures to achieve higher luminous efficiency. It is also possible to dope at least two different sizes of quantum dot structures in the active overcladding layer 12 to improve the bandwidth and luminous efficiency of the waveguide amplifier by using the quantum effects of different sizes of quantum dot structures.

[0076] In the embodiments of the present application, the quantum dot structures are uniformly distributed in the matrix of the active overcladding layer 12. Based on the uniform distribution characteristics of different sizes of quantum dot structures in the active overcladding layer 12, the quantum dot structures as the gain medium can exhibit an ultra-wide emission spectrum, and the emission spectrum can cover the entire optical communication band (O+E+S+C+L+U).

[0077] Optionally, for an optical waveguide with a quantum dot structure as the gain medium, the active overcladding layer 12 doped with quantum dot structures of at least two sizes can be prepared by a simple spin coating process, with a simple preparation process and low production cost. Moreover, the optical waveguide can also optically amplify the signal light by utilizing the principle of evanescent wave type light waves, provide gain for optical waveguides of different substrates 13, and the active material for preparing the active overcladding layer 12 (i.e., the quantum dot broadband hybrid colloid in the following text) can be commonly used for optical waveguides employing substrates 13 such as polymer-based, glass-based, and silicon nitride-based substrates.

[0078] Among them, the material of the active overcladding layer 12 is different from that of the substrate 13, so the optical waveguide is a heterogeneous integrated optical waveguide and can be used to prepare a heterogeneous integrated optical waveguide amplifier. As described above, the active overcladding layer 12 can be formed on the surface of the substrate 13 by a spin coating process, and can provide effective gain for optical waveguides employing substrates 13 made of materials such as glass-based or silicon nitride-based substrates.

[0079] Reference Figure 3 , Figure 3 is a cross-sectional view of a quantum dot structure provided by an embodiment of the present application. The shown quantum dot structure includes: a quantum dot core 15 and a shell layer 16 coating the quantum dot core 15.

[0080] Quantum dot structures of different sizes can emit excitation light of different wavelength bands. The shell layer 16 can prevent energy transfer between quantum dot structures of different sizes and prevent interference problems between the excitation lights emitted by quantum dot structures of different sizes.

[0081] In addition, based on the core-shell structure with the shell layer 16 coating the quantum dot core 15, the core-shell structure can improve the material stability of the quantum dot structure, effectively block energy transfer between multi-size quantum dots, improve its flat-top amplification property, reduce the gain fluctuation of the amplifier, can make more full use of the ultra-wideband amplification ability of the quantum dot material, can suppress the non-radiative recombination effect caused by surface defects of the quantum dot core, can improve the utilization rate of the pump light, enable more pump light to be used for optical amplification, improve the amplification bandwidth, can greatly improve the luminescence quantum efficiency, and can achieve a relatively high gain. <{}

[0082] Optionally, the material of the quantum dot core 15 is PbS; the material of the shell layer 16 is CdS. The CdS material shell layer 16 has a protective shielding effect on the PbS material quantum dot core 15. In the case of co-doping of multiple sizes, PbS coated with a CdS shell will reduce many surface defect states, block the energy transfer path between quantum dot cores 15 of different sizes made of PbS material, ensure uniform amplification performance in multiple wavelength bands, reduce gain fluctuation. At the same time, the presence of the shell layer avoids the process of non-radiative recombination, greatly improves the luminescence quantum efficiency, and can achieve a relatively high gain.

[0083] With PbS as the quantum dot core 15 and CdS as the shell 16, the strong absorption of PbS itself in the ultraviolet can be utilized to achieve ultra-wide spectrum optical amplification by pumping with a 365 nm LED. In the case of co-doping of multiple sizes, the CdS shell can suppress many surface defect states, shielding and protecting the PbS quantum dot core, blocking the energy transfer path from small-sized to large-sized quantum dots, ensuring uniform amplification performance in multiple bands, reducing gain fluctuations. At the same time, the presence of the shell avoids the process of non-radiative recombination, greatly improving the luminescence quantum efficiency and enabling a relatively high gain to be achieved.

[0084] Reference Figure 4 , Figure 4 is a cross-sectional view of another quantum dot structure provided by an embodiment of the present application. On the basis of the manner shown in Figure 3 , Figure 4 the quantum dot structure shown further includes: an oleic acid coating film 17 covering the shell.

[0085] In Figure 4 the manner shown, the oleic acid coating film 17 enables the quantum dot structure to be better dispersed in the organic solution, avoiding precipitation and clustering problems of the quantum dot structure in the matrix, so as to improve the distribution uniformity of the quantum dot structure in the active overcoat layer 12 and improve the performance of the optical waveguide.

[0086] For the quantum dot structure based on the PbS / CdS shell structure, its working principle is mainly based on the stimulated emission of the quantum dot core 15. The quantum dot core 15 has a wide and strong absorption band in the ultraviolet band. When excited by light of 365 nm, it emits light at 1.3 μm and 1.5 μm according to different particle sizes. The shell 16 is coated outside the quantum dot core 15. The shell 16 can reduce the defect states on the surface of the quantum dot core 15, effectively increasing the photoluminescence efficiency, reducing non-radiative recombination. At the same time, due to the protection of the shell 16, there is almost no energy transfer influence between co-doped quantum dot structures of different sizes, enabling a consistent amplification effect from short wavelengths to long wavelengths and reducing the amplifier gain fluctuation. Further, through the outermost oleic acid coating film 17, the quantum dot structure can be well integrated and dispersed with organic substances.

[0087] In an embodiment of the present application, the quantum dot structure is a semiconductor particle at the nanoscale, and the size range can be 1 nm to 10 nm. The specific size of the quantum dot structure enables it to have a quantum confinement effect, and different emission wavelengths can be achieved by adjusting the size. Optionally, the thickness of the shell 16 is about 0.5 nm. Optionally, for the core-shell structure quantum dot, the value range of the first size is 2.5 nm to 4.0 nm, and the value range of the second size is 4.5 nm to 7.0 nm. Further, the first size can be 3 nm and the second size can be 5 nm.

[0088] When the first dimension is equal to or approximately equal to 3 nm and the second dimension is equal to or approximately equal to 5 nm, the operating wavelength of the optical waveguide can cover both the O + C bands, and optical amplification gain can be obtained in the wavelength band of 1260 nm to 1580 nm, and the gain is relatively flat. Moreover, under the pumping mode of the LED top light source converged by a uniform rectangular spot lens, the relative gain that can be obtained simultaneously in the 1310 nm and 1550 nm bands can reach 8 dB / cm - 10 dB / cm. Therefore, the optical waveguide amplifier prepared based on the optical waveguide provided in the embodiments of the present application can greatly improve the bandwidth utilization rate of the optical chip.

[0089] In the embodiments of the present application, the first dimension can also be other dimensions, such as 3.5 nm, and the second dimension can also be other dimensions, such as 5.5 nm. The embodiments of the present application do not limit the specific values of the first dimension and the second dimension.

[0090] A conventional optical waveguide is an embedded optical waveguide. This type of optical waveguide needs to form a groove in a passive layer with a low refractive index through an etching process and prepare a high-refractive-index active waveguide core layer in the groove. This not only makes the manufacturing process complex but also brings relatively large transmission losses, with the transmission loss up to 5 dB / cm. Another conventional optical waveguide needs to be prepared by optical bleaching. Based on the high temperature after exposure, a high-refractive-index active waveguide core layer is generated. The sidewalls of the active waveguide core layer have a low-refractive-index thin film. This solution requires ultraviolet exposure and heating in the preparation process, resulting in the material being prone to change during pumping and heating. Generally, a 980 nm laser diode (LD) is used for end pumping, which cannot utilize the strongest absorption cross-section of the material, and the pumping efficiency is low. Moreover, in the case of LD end pumping, the pumping optical power gradually decreases as the pumping light propagates in the waveguide, and gain saturation occurs, which cannot effectively utilize the energy of the pumping light and the active substance in the waveguide. In addition, excessive instantaneous power at the input end is likely to cause problems such as device burnout. The LD itself is expensive and bulky, which is not suitable for the development trend of integration and miniaturization. The method of doping the core layer causes a large amount of additional optical loss due to the large absorption and refraction of the signal light by the active substance, and the gain brought may be difficult to compensate for the loss of the waveguide itself.

[0091] To address the above problems, in one implementation of the embodiments of the present application, the structure of the optical waveguide can be as Figure 2 shown, and further includes a substrate 13; wherein, the passive core layer 11 includes at least one convex structure located on the surface of the substrate 13; the active overlying layer 12 covers the sidewalls and the top surface of the convex structure. In this way, the relative two sidewalls and the top surface of the passive core layer 11 can be covered by the evanescent wave type active overlying layer, which is convenient for obtaining greater gain.

[0092] Optionally, when the passive core layer 11 includes at least one convex structure located on the surface of the substrate 13, the optical waveguide further includes a lower cladding layer 14 located on the surface of the substrate 13, and the passive core layer 11 is located on the surface of the lower cladding layer 14 facing away from the substrate 13.

[0093] In Figure 2 the shown manner, on the surface of the convex structure serving as the waveguide, a thin film of the active material can be directly formed by a spin coating process. The thin film of the active material serves as the active upper cladding layer 12 covering the convex structure. The preparation process is simple and the preparation cost is relatively low. Since the core layer serving as the waveguide is the undoped passive core layer 11, it has a relatively small transmission loss. Compared with the passive waveguide, the increase in the transmission loss is less than 0.5 dB / cm. Moreover, since the upper cladding layer is actively doped, the doping concentration can be greatly increased without affecting the transmission effect of the signal light in the core layer. In addition, the quantum dot structure of the core-shell structure can achieve a relatively high excitation effect in the ultraviolet waveband, and the excitation effect is much higher than the conventional excitation schemes in the near-infrared wavebands such as 808 nm or 980 nm. The active upper cladding layer 12 is an evanescent wave type active upper cladding layer, which can avoid the defect of excessive scattering loss of the passive core layer 11 and is applicable to various pumping modes in optical wavebands such as ultraviolet LEDs. The waveguide properties are stable and not easily changed.

[0094] In the embodiment of the present application, the substrate 13 can be any one of a polymer-based, glass-based, and silicon nitride-based manner. The active upper cladding layer 12 can be prepared by a spin coating process and is applicable to substrates of various materials. Compared with the conventional inorganic optical waveguide preparation process, the preparation process of the optical waveguide provided in the embodiment of the present application is more convenient and simple.

[0095] Reference Figure 5 and Figure 6 , Figure 5 is a top view of another optical waveguide provided in the embodiment of the present application. Figure 6 is Figure 5 a sectional view of the shown optical waveguide in the B-B' direction. On the basis of the above-described embodiment, the optical waveguide includes a substrate 13, and at least one ion exchange region is provided in one surface of the substrate 13. The passive core layer 11 includes the ion exchange region; the active upper cladding layer 12 covers the ion exchange region.

[0096] In a conventional optical waveguide, active doping is generally performed on the core layer serving as the waveguide. However, due to the large absorption and refraction of the signal light by the active material in the core layer doping method, a large amount of additional optical loss will be caused, and the gain brought may be difficult to compensate for the loss of the waveguide itself. In the embodiment of the present application, active doping is performed on the upper cladding layer of the optical waveguide, and there is no need to perform active doping on the core layer serving as the waveguide, thereby avoiding the above problems caused by core layer doping.

[0097] Reference Figure 7 and Figure 8 ,Figure 7 Transmission electron microscope (TEM) image of the active overcladding layer when two-size quantum dot structures are co-doped Figure 8 Photoluminescence (PL) spectrum of the active overcladding layer when two-size quantum dot structures are co-doped. In Figure 7 and Figure 8 The following manner is taken as an example for illustration, where the active overcladding layer 12 uniformly mixes 3-nm quantum dot structures and 5-nm quantum dot structures at the same time

[0098] The 3-nm quantum dot structures and 5-nm quantum dot structures are uniformly mixed in the matrix at a ratio of 1:1. Based on Figure 7 it can be known that two different-size quantum dot structures are uniformly dispersed together, which can effectively reduce the cluster quenching problem of the quantum dot structures

[0099] The quantum dot structures and 5-nm quantum dot structures are uniformly doped at a ratio of 1:1, and can cover the ultra-wide photoluminescence spectrum in bands such as O+C. Based on Figure 8 it can be known that under the excitation of a 365-nm pump light, the excitation spectrum line covers the entire region from 1100 nm to 1600 nm, and the ultra-wide full width at half maximum > 500 nm

[0100] From the above description, it can be seen that the optical waveguide provided by the embodiment of the present application can achieve an ultra-wide spectrum (ultra-wide bandwidth > 500 nm) covering the entire core communication region of O+E+S+C+L+U bands through the active overcladding layer 12 formed by co-doping at least two different-size quantum dot structures. The optical waveguide can simultaneously achieve a high gain of 8 dB / cm - 10 dB / cm at the 1.3-μm optical communication window and the 1.5-μm optical communication window. Moreover, the optical waveguide of this structure can be applied to various substrates, such as glass substrates and silicon nitride substrates, can provide higher gain at lower loss, has a simple preparation method and a low preparation cost, can be used in an evanescent wave type quantum dot polymer / hybrid-based optical waveguide amplifier, can be combined with a top-pumping method of an ultraviolet / visible light band LED, and can be combined with the use of a uniform rectangular spot lens for focusing to achieve a higher chip pumping efficiency

[0101] The optical waveguide provided by the embodiment of the present application is an evanescent wave type optical waveguide. Not only is the preparation process method simple, but the active overcladding layer 12 used is suitable for integration with various optical platforms, such as glass-based / silicon nitride-based, can provide higher gain at lower loss, has a simple and inexpensive preparation method, and is adapted to the trend of integration and miniaturization of integrated optical systems

[0102] Since the optical waveguide uses core-shell structure quantum dots as the gain material, and the ultra-wide excitation spectrum of the gain material has a high overlap with the white light source spectrum, the optical waveguide is pumped by cold light sources such as white light, greatly reducing the possibility of thermal damage in the pump, and can be applied to most indoor light source application scenarios. Moreover, since the ultra-wide excitation spectrum of the gain material has a high overlap with the solar spectrum, the optical waveguide can also be driven by sunlight and can absorb the energy of sunlight to convert it into the amplification driving energy of the signal light.

[0103] Based on the optical waveguide provided in the above embodiments, another embodiment of the present application further provides an optical waveguide amplifier, and the structure of the optical waveguide amplifier can be as Figure 9 shown.

[0104] Referring to Figure 9 , Figure 9 which is a schematic structural diagram of an optical waveguide amplifier provided by an embodiment of the present application. The shown optical waveguide amplifier includes: the optical waveguide 18 provided by any one of the above embodiments; a first light source 19, and the first light source 19 provides a signal light 23 for the passive core layer 11 from one end of the passive core layer; a second light source 20, and the second light source 20 provides a pump light 24 for the passive core layer 11 from the top of the passive core layer 11; a photodetector 21, and the photodetector 21 collects the excitation light output from the passive core layer 11 from the other end of the passive core layer 11.

[0105] Optionally, since the gain material in the optical waveguide has an ultra-wide excitation spectrum, the pump light can be any one of white light, ultraviolet light, visible light, and natural light, and the second light source 20 can be any one of an LED emitting ultraviolet light, an LED emitting visible light, an LED emitting broadband white light, and a natural light source. Specifically, since the optical waveguide amplifier provided by the embodiment of the present application uses the optical waveguide provided by the above embodiments, as described above, the optical waveguide can be pumped by cold light sources such as white light (such as a white light LED), which can greatly reduce the possibility of thermal damage in the pump. Or, the optical waveguide amplifier can be driven by natural light, such as directly driven by sunlight, and can absorb the energy of sunlight to convert it into the amplification driving energy of the signal light.

[0106] Experimental data shows that when a white light LED is used as the pump light, a gain of 7 - 8 db / cm can be achieved.

[0107] An optical waveguide amplifier is a device integrated in optical and communication systems for enhancing optical signals. It combines optical waveguide technology and optical amplification effects. Its working principle is to excite particles (such as quantum dot structures in the active overclad layer 12) in the optical amplification medium through the pump light 24 and the signal light 23, so that they transition to high energy levels, thereby generating an optical amplification effect.

[0108] Quantum dot structures are also excellent materials for fabricating optical waveguide amplifiers and have important application prospects in the field of optical communication. The size effect of quantum dot structures has a significant impact on their optoelectronic properties. In the preparation process of quantum dot structures, by controlling the growth or reaction time of quantum dot structures and the preparation conditions, the size of quantum dot structures can be adjusted, thereby changing the absorption and emission spectra of quantum dot structures and realizing the regulation of the peak wavelengths of absorption peaks and radiation peaks. Quantum dot fiber amplifiers can amplify signal light through the interaction between quantum dot structures and fiber structures.

[0109] As described above, in this application, the optical waveguide adopts a core-shell structure quantum dot structure. When different-sized quantum dot structures are doped in the active overcladding 12 through the shell layer 16, the interference of the emitted bands of different-sized quantum dot structures can be effectively reduced, enabling the optical waveguide amplifier to cover both the O band and the S band simultaneously.

[0110] In the embodiments of this application, based on the dependence of the optical properties of quantum dot structures on their size, by precisely controlling the size of quantum dot structures, fine adjustment of the emission spectrum of quantum dot structures can be achieved, thereby realizing coverage of a wide spectral range.

[0111] Combined with Figure 9 As shown in the optical waveguide amplifier and the optical waveguide drawings in the above embodiments, the signal light 23 is coupled into the passive core layer 11 from the left end of the passive core layer 11. The signal light 23 coupled into the passive core layer 11 can penetrate into the active overcladding 12 covering the passive core layer 11 through the evanescent field. In the active overcladding 12, the signal light 23 and the pump light 24 irradiating the active overcladding 12 can simultaneously excite the quantum dot structures in the active overcladding 12, causing the quantum dot structures to emit stimulated emission to form amplified signal light. The amplified signal light can penetrate into the passive core layer 11 based on the evanescent field, and the amplified signal light can be transmitted through the passive core layer 11 and collected and detected by the photodetector 21 at the left end of the passive core layer 11.

[0112] In the optical waveguide 18, the passive core layer 11 includes at least one waveguide for transmitting optical signals. The waveguide can be a raised structure on the surface of the substrate 13 or an ion exchange region in the substrate 13.

[0113] In the embodiments of this application, the second light source 20 providing the pump light 24 is arranged above the optical waveguide 18, such that the transmission direction of the pump light 24 is orthogonal to the transmission direction of the signal light 23, which can enable the signal light 23 and the pump light 24 to have a large overlapping region in the waveguide length direction and can enable the optical waveguide to have a large gain.

[0114] Optionally, as Figure 9As shown, the pump light 24 emitted by the second light source 20 irradiates the active upper cladding 12 through the uniform rectangular spot lens 22.

[0115] In a conventional optical waveguide amplifier, the method of using only the top pumping of an LED lamp bead generally causes a large amount of pump light to be dissipated outside the optical waveguide, resulting in a low pump efficiency. In the embodiment of the present application, the optical waveguide amplifier uses the uniform rectangular spot lens 22 to converge the pump light 24 emitted by the second light source 20, and the rectangular spot emitted by the uniform rectangular spot lens 22 is used to pump and excite the optical waveguide from the top. The pump light 24 with a rectangular spot can be evenly irradiated on the waveguide region of the optical waveguide 18, effectively utilizing the pump light energy of the second light source 20, reducing energy loss, and improving the pump efficiency, so that the pump efficiency can be increased by 20%. Optionally, the second light source 20 can be an LED lamp bead. In addition, the method of focusing the LED top pumping by the uniform rectangular spot lens 22 is cheaper than the traditional LD, the shape of the pump region is easy to control, can be changed according to requirements, and is more flexible and convenient to use.

[0116] The top structure of the optical waveguide is as Figure 5 shown, which is a rectangular structure. The conventional pump method with a circular spot will cause a large proportion of energy waste. In the embodiment of the present application, the pump light 24 can be converted into a rectangular uniform converging spot through the uniform rectangular spot lens 22. By adjusting the position of the uniform rectangular spot lens 22, a rectangular uniform converging spot matching the size and shape of the optical waveguide can be adjusted, and the utilization rate of the pump light 24 can be increased to 100%. Optionally, the wavelength of the pump light 24 can be 365 nm; the distance between the second light source 20 emitting the pump light 24 and the optical waveguide 18 is 1 cm or approximately 1 cm.

[0117] As described above, in a conventional quantum dot structure-doped optical waveguide, the waveguide is generally fabricated by the optical bleaching method and optically pumped by the end-pumping method using a 980 nm laser. However, the pumping efficiency is low. The core reason for this problem is that the ultraviolet and thermal stability of the waveguide is poor, and the pumping wavelength with the largest absorption cross-section cannot be selected according to the best absorption cross-section of the material. Moreover, in the case of LD end-pumping, the pumping optical power gradually decreases as the pumping light propagates in the waveguide, and the gain saturation phenomenon will occur. The energy of the pumping light and the active substance in the waveguide cannot be effectively utilized, and the instantaneous power at the input end is too large, which is likely to cause problems such as device burnout. The LD itself is expensive and bulky, which is not suitable for the development trend of integration and miniaturization. When using the single LED bead top-pumping method, a large amount of pumping light will be dissipated outside the optical waveguide chip, resulting in low pumping efficiency. At present, some studies have shown that when using a 405 nm blue LED to directly pump an erbium ion-doped organic optical waveguide from the top, an internal net gain of 4.5 dB / cm can be obtained, and the gain range only covers the C band and part of the L band. The most core reason for these problems is that the LED bead emits divergent light, and directly using the bead for pumping will inevitably cause the problem of energy loss and waste of the pumping light due to dissipation.

[0118] As Figure 10 shown, the optical waveguide amplifier prepared based on the optical waveguide provided in the embodiment of the present application can emit an ultra-wide photoluminescence spectrum under the excitation of a pumping light with a wavelength of 365 nm.

[0119] Referring Figure 10 , Figure 10 is a graph of the photoluminescence spectrum of an ultra-wide spectrum quantum dot PMMA thin film provided in the embodiment of the present application. The ultra-wide spectrum quantum dot PMMA thin film is the active upper cladding layer 12 of the optical waveguide in the embodiment of the present application. The ultra-wide spectrum quantum dot PMMA thin film includes a PMMA matrix and quantum dot structures with a size of 3 nm and quantum dot structures with a size of 5 nm uniformly mixed in the PMMA matrix.

[0120] Based Figure 10 on the spectrum shown, the ultra-wide spectrum quantum dot PMMA thin film can emit excitation light with a width greater than 500 nm and covering the O+E+S+C+L+U bands under the excitation of a pumping light with a wavelength of 365 nm. The operating wavelengths of the broadband optical waveguide amplifier prepared based on the ultra-wide spectrum quantum dot PMMA thin film simultaneously cover the O and C bands, which are the two communication windows with the lowest fiber attenuation. Optical amplification gain can be obtained in the 1260 nm - 1580 nm band, and the gain is relatively flat. Under the same fixed ultraviolet LED light source pumping method, relative gains of 8 dB / cm - 10 dB / cm can be obtained simultaneously in the 1310 nm and 1550 nm bands. Moreover, based on the core-shell structure quantum dot structure, it can have a very wide excitation spectrum and a very large absorption cross-section in the visible light band, which is 10 times the absorption intensity of rare earth ions.4 times. By adopting a suitable ultraviolet pumping method, high fluorescence emission can be achieved. Therefore, the optical waveguide amplifier prepared based on the optical waveguide provided in the embodiments of the present application can meet the optical chip with high bandwidth capacity requirements and can be combined with a mature silicon optical chip network.

[0121] In the conventional wide-spectrum amplification scheme with active doping based on rare-earth ions and perovskite, although the absorption cross-section of perovskite is large, its absorption of ultraviolet light energy still depends on the energy transfer between rare-earth ions and perovskite to achieve the amplification effect. Due to the second problem of energy level mismatch, the energy transfer efficiency between perovskite and rare-earth ions is not high, directly resulting in a low pumping efficiency. Since the wide-spectrum emission achieved by multi-rare-earth ion doping is often accompanied by complex cluster and up-conversion problems, the pumping light is difficult to effectively act on the optical amplification of the target signal, and the pumping efficiency is extremely low. Moreover, the perovskite itself has unstable properties, resulting in a short service life of the device.

[0122] Reference Figure 11 , Figure 11 is the absorption spectrum curve diagram of an ultra-wide-spectrum quantum dot PMMA thin film provided by the embodiments of the present application. In the optical waveguide amplifier provided by the embodiments of the present application, the second light source 20 of the outgoing pumping light 24 can be an ultraviolet LED, and the quantum dot structure with a core-shell structure can be directly excited by the ultraviolet pumping light 24. Since the quantum dot structure with a core-shell structure provided by the embodiments of the present application has a strong absorption ability for ultraviolet light and visible light, it can directly absorb ultraviolet light to achieve the photoluminescence process, with a higher pumping efficiency. Moreover, the quantum dot structure has relatively stable properties at room temperature and a long service life. The gain properties remain unchanged during indoor dry storage for half a year. And in the embodiments of the present application, a semiconductor material is used to prepare the quantum dot structure, and there is no up-conversion problem in luminescence. Therefore, a higher gain effect can be achieved under the irradiation of pumping light with the same power.

[0123] As described above, in the embodiments of the present application, the quantum dot structure includes a quantum dot core 15 made of PbS and a shell layer 16 made of CdS that coats the quantum dot core. Compared with a core-shell-free quantum dot structure made only of PbS material, the quantum dot structure in the embodiments of the present application can absorb more pump light in the short wavelength band through the shell layer 16 made of CdS. The shell layer 16 made of CdS has an energy transfer effect on the quantum dot core 15 made of PbS, improving the excitation effect when top-pumping with ultraviolet light or visible light. Moreover, the active shell layer 16 can also suppress the surface defect states of the quantum dot core 15, avoid the non-radiative recombination process, and greatly improve the luminescence quantum efficiency. Experiments show that when the quantum dot core 15 is made of PbS and the shell layer 16 is made of CdS, the quantum efficiency is higher than that of the PbS quantum dot core without shell coating. Therefore, the quantum dot structure provided by the embodiments of the present application can achieve a higher relative gain. When quantum dot structures of different sizes are doped simultaneously, due to the protection of the shell layer 16, the cluster quenching problem of the quantum dot structure can be effectively reduced, the energy transfer problem between quantum dot structures of different sizes can be avoided, the amplification flat top of the wide spectrum can be ensured, and the 3dB bandwidth can be increased.

[0124] Based on the optical waveguide and the optical waveguide amplifier provided in the above embodiments, another embodiment of the present application further provides a method for manufacturing an optical waveguide. The manufacturing method can be as Figure 12 shown.

[0125] Referring to Figure 12 , Figure 12 which is a schematic flowchart of a method for manufacturing an optical waveguide provided by an embodiment of the present application. The manufacturing method includes:

[0126] Step S11: Prepare a quantum dot wide-spectrum hybrid colloid;

[0127] Step S12: Use the quantum dot wide-spectrum hybrid colloid to form an active overcoat layer with a second refractive index on the surface of a passive core layer with a first refractive index; wherein, the first refractive index is greater than the second refractive index; the active overcoat layer includes a matrix and quantum dot structures uniformly mixed in the matrix. The quantum dot structures include at least a first size and a second size, and the first size is not equal to the second size.

[0128] In the embodiments of the present application, by using the quantum dot wide-spectrum hybrid colloid to prepare the active overcoat layer with a low refractive index, the active overcoat layer can be formed by a spin coating process, and the manufacturing process is simple.

[0129] Referring to Figure 13 , Figure 13 which is a flowchart of a method for preparing a quantum dot wide-spectrum hybrid colloid provided by an embodiment of the present application. The method includes:

[0130] Step S21: Prepare an organic solution mixed with quantum dot structures of a first size and an organic solution mixed with quantum dot structures of a second size respectively.

[0131] Step S22: Uniformly mix the two organic solutions in a matrix to form a quantum dot broadband hybrid colloid.

[0132] In Figure 13 the shown manner, the first size can be 3 nm and the second size can be 5 nm. The quantum dot structure is generally spherical, and its size can be the particle diameter.

[0133] In the preparation method provided by the embodiment of the present application, it also includes preparing a passive core layer as a waveguide on a substrate.

[0134] In one way, the method for preparing the passive core layer includes: First, form a core layer thin film on the surface of the substrate; then, pattern the core layer thin film to form a plurality of convex structures. Among them, the active overcoat covers the side walls and the top surface of the convex structures. The optical waveguide structure prepared by this method can be as Figure 1 and Figure 2 shown.

[0135] In another way, the method for preparing the passive core layer includes: forming an ion exchange region in the surface of the substrate, and the passive core layer includes the ion exchange region; the active overcoat covers the ion exchange region. The optical waveguide structure prepared by this method can be as Figure 5 and Figure 6 shown.

[0136] In the embodiment of the present application, the passive core layer can be prepared with passive SU-8; a doping medium with discrete particle sizes of ~3 nm and ~5 nm doped in a 1:1 ratio can be used as the doping medium, and the doping medium is uniformly dispersed in PMMA to be used as the active overcoat of the optical waveguide. The quantum dot structure is a PbS / CdS core-shell structure. Optionally, the thickness of the CdS shell layer is about 0.5 nm, which is easily soluble in organic solvents (such as toluene and n-hexane), and its stability in organic solvents is higher. Therefore, the PbS / CdS core-shell structure is dissolved in toluene and n-hexane to improve its stability. At the same time, the PbS / CdS core-shell structure is very sensitive to temperature and is prone to failure in a high-temperature environment. Therefore, the process flow is changed. By using the spin coating and low-temperature hard baking processes, the PbS / CdS core-shell structure does not need to go through the development or high-temperature process, but only forms a low-temperature active doping in the doped PMMA. The signal light is amplified by the principle of evanescent wave, and the refractive index difference between the low-loss waveguide region (passive core layer) and the non-waveguide region (active overcoat) realizes the light guiding channel, so that the temperature of the PbS / CdS core-shell structure can be controlled within an adjustable range, the doping concentration can be reasonably increased, and at the same time, the passive core layer can realize a low-loss optical waveguide amplifier.

[0137] In one embodiment, a method for preparing a quantum dot broadband hybrid colloid includes:

[0138] First, take equal amounts of organic solutions of quantum dot structures of the first size and the second size with the same concentration, and mix the two organic solutions to form a quantum dot broadband hybrid solution. Optionally, the first size can be 3 nm to 4 nm, such as 3 nm, and the second size can be 5 nm to 7 nm, such as 5 nm. The quantum dot structure is dispersed in an organic solvent to form an organic solution, and the organic solvent includes at least one of toluene and n-hexane. Then, add the quantum dot broadband hybrid solution to PMMA and place it in an ultrasonic machine for uniform mixing to form a quantum dot broadband hybrid colloid, which is used as the active material for preparing the active overcoat. The concentration of the quantum dot structure in the quantum dot broadband hybrid colloid can be 0.1 wt%.

[0139] In one embodiment, the substrate can be a cut silica wafer. The silica wafer can be cleaned with acetone, ethanol, and deionized water respectively to remove surface stains. In this method, the method for forming the passive core layer includes:

[0140] First, the SU-8 material can be spin-coated onto the surface of the cleaned silica wafer by spin coating. The SU-8 material is a negative photoresist based on epoxy resin. After spin coating, a pre-baking treatment can be carried out at 95 °C for 2 minutes, and then cooled to room temperature to form a core layer film.

[0141] Then, the core layer film is etched by ultraviolet lithography to form a passive core layer with the required graphic structure. In this step, a negative photomask with a waveguide shape can be selected for ultraviolet lithography. The negative photomask is placed face-to-face on the prepared core layer film. The area outside the strip waveguide is exposed to ultraviolet light, and the strip waveguide area is blocked. The ultraviolet exposure time is 22 s - 26 s. The photolithographed sample can be subjected to post-baking treatment. The sample can be placed on a hot plate, first heated to 65 °C, and after maintaining at 65 °C for 1 minute, the temperature is then raised to 95 °C and maintained at 95 °C for 1.5 minutes. After the post-baking treatment is completed, the sample is placed in the developer for 1.5 minutes, then put into isopropyl alcohol to wash the residual developer for 1 minute, and then put into an oven for a 2-hour hardening treatment at 100 °C to form a passive core layer with the required graphic structure.

[0142] After forming the passive core layer on the surface of the silica wafer, after spin-coating the pre-prepared quantum dot broadband hybrid colloid on the surface of the silica wafer, the sample is placed in an oven and cured at 100 °C for 2 h to form an active overcoat covering the passive core layer. Optionally, the spin coating speed can be 3000 rpm and the spin coating time can be 30 s. At this time, the prepared optical waveguide is as Figure 1 and Figure 2As shown, the passive core layer 11 is a raised structure located on the surface of the substrate 13. The active overlying layer 12 is PMMA doped with quantum dot structures, and the substrate is a silica wafer. The two are a heterostructure, and this method can form an evanescent wave-type polymer-based / hetero-integrated quantum dot optical waveguide.

[0143] In the embodiments of the present application, it is not limited to preparing the passive core layer through SU-8 material. A silicon nitride thin film can also be used to prepare the passive core layer to form a polymer / silicon nitride-based evanescent wave-type quantum dot optical waveguide. In this method, after cleaning the silica substrate, a silicon nitride thin film with a thickness of 500 nm can be grown on its surface. The silicon nitride thin film is etched using the above-mentioned strip-shaped SU-8 after photolithography etching as a mask layer, and the silicon nitride thin film is etched into a strip-shaped raised structure. The etching gas can be CF4. Optionally, in this method, there is also a lower cladding with a thickness of 3 μm on the surface of the substrate. The lower cladding can be a silica thin film, and the substrate can be silicon. The passive core layer is located on the surface of the lower cladding facing away from the substrate.

[0144] In the embodiments of the present application, a polymer / silicon nitride-based evanescent wave-type quantum dot optical waveguide can also be prepared using a silicon nitride substrate. At this time, a silicon nitride wafer is used as the optical waveguide substrate. The method for preparing an optical waveguide using a silicon nitride wafer as the substrate can refer to the method for preparing an optical waveguide using a silica wafer as the substrate described above, and this embodiment will not be elaborated. In this method, the

[0145] In the embodiments of the present application, a polymer / glass-based hybrid integrated evanescent wave-type quantum dot optical waveguide can also be prepared using a glass substrate. At this time, a glass substrate is used as the optical waveguide substrate. An ion exchange region serving as a waveguide can be formed inside the surface of the glass substrate through an ion exchange process to form a passive core layer inside the surface of the glass substrate. After cleaning the glass substrate that has completed the ion exchange, an active overlying layer is formed on its surface. At this time, the structure of the optical waveguide can be as Figure and ​ shown.

[0146] When using a glass substrate, it can also be cleaned respectively with acetone, ethanol, and deionized water. When preparing an active core layer on the surface of the glass substrate, a pre-prepared quantum dot broadband hybrid colloid can be spin-coated on the entire surface of the surface with the ion exchange region, or a peelable mask tape can be used to cover the four peripheries of the surface and both end faces of the waveguide, exposing the central region of the surface, and a pre-prepared quantum dot broadband hybrid colloid is spin-coated in the central region. After spin-coating the quantum dot broadband hybrid colloid, the sample is cured at 100 °C for 2 h to form an active overlying layer covering the passive core layer. Optionally, the spin-coating speed can be 3000 rpm, and the spin-coating time can be 30 s; the peelable mask tape can be a pressure-sensitive adhesive tape.

[0147] The descriptions of the various embodiments in the specification of this application are presented in a progressive, or parallel, or a combination of progressive and parallel manners. Each embodiment focuses on the differences from other embodiments, and the same or similar parts among the embodiments can be referred to each other. The embodiments provided in the embodiments of this application can be combined with each other without conflict.

[0148] It should be noted that in the description of this application, it should be understood that the descriptions of the drawings and embodiments are illustrative rather than restrictive. The same reference numerals throughout the embodiments of the specification identify the same structures. Additionally, for the sake of understanding and easy description, some layers, films, panels, regions, etc. may be exaggerated in thickness in the drawings. At the same time, it can be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element can be directly on the other element or there may be intermediate elements. Additionally, "on..." means positioning the element on or below another element, but essentially does not mean positioning on the upper side of another element according to the direction of gravity.

[0149] The orientation or positional relationship indicated by terms such as "upper", "lower", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be intermediate components present at the same time.

[0150] It also should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprising", "including", or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the presence of additional identical elements in the article or device including the above elements.

[0151] The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An optical waveguide, characterized in that, Comprising: A passive core layer having a first refractive index; An active overcladding layer having a second refractive index, the first refractive index being greater than the second refractive index; Wherein, the active overcladding layer comprises a matrix and quantum dot structures uniformly mixed in the matrix, the quantum dot structures at least comprising a first size and a second size, the first size being not equal to the second size.

2. The optical waveguide according to claim 1, wherein The quantum dot structure comprises: a quantum dot core and a shell layer coating the quantum dot core.

3. The optical waveguide according to claim 2, wherein, The material of the quantum dot core is PbS; Or, the material of the shell layer is CdS; Or, the quantum dot structure further comprises: an oleic acid coating film coating the shell layer.

4. The optical waveguide according to claim 1, wherein The value range of the first size is 2.5 nm to 4.0 nm, and the value range of the second size is 4.5 nm to 7.0 nm.

5. The optical waveguide according to any one of claims 1-4, characterized in that, The optical waveguide further comprises a substrate; Wherein, The passive core layer comprises at least one convex structure located on the surface of the substrate; the active overcladding layer covers the side wall and the top surface of the convex structure; Or, at least one ion exchange region is formed in one side surface of the substrate, the passive core layer comprises the ion exchange region; the active overcladding layer covers the ion exchange region.

6. An optical waveguide amplifier, characterized in that, Comprising: The optical waveguide according to any one of claims 1-5; A first light source, the first light source providing signal light for the passive core layer from one end of the passive core layer; A second light source, the second light source providing pump light for the passive core layer from the top of the passive core layer; A photodetector, the photodetector collecting the excitation light output by the passive core layer from the other end of the passive core layer.

7. The optical waveguide amplifier according to claim 6, characterized in that, The second light source is any one of an LED emitting ultraviolet light, an LED emitting visible light, an LED emitting broadband white light, and a natural light source.

8. A method for preparing an optical waveguide according to any one of claims 1-5, characterized in that, Comprising: Preparing a quantum dot broadband mixed colloid; Using the quantum dot broadband mixed colloid to form an active overcladding layer having a second refractive index on the surface of a passive core layer having a first refractive index; Wherein, the first refractive index is greater than the second refractive index; the active overcladding layer comprises a matrix and quantum dot structures uniformly mixed in the matrix, the quantum dot structures at least comprising a first size and a second size, the first size being not equal to the second size.

9. The preparation method according to claim 8, wherein The method for preparing the quantum dot broadband mixed colloid comprises: Respectively preparing an organic solution mixed with the quantum dot structures of the first size and an organic solution mixed with the quantum dot structures of the second size; Uniformly mixing the two organic solutions in the matrix to form the quantum dot broadband mixed colloid.

10. The preparation method according to claim 8, wherein, Further comprising: Forming a core layer film on the surface of the substrate; Patternizing the core layer film to form a plurality of convex structures; The active overcladding layer covers the side wall and the top surface of the convex structure; Or, forming an ion exchange region in the surface of the substrate, the passive core layer comprises the ion exchange region; the active overcladding layer covers the ion exchange region.

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