Method for manufacturing a rare-earth doped optical waveguide and a rare-earth doped optical waveguide

Abstract

The present invention relates to a method for manufacturing an aluminum oxide optical waveguide doped with rare earth ions. The present invention further relates to an aluminum oxide optical waveguide doped with rare earth ions, preferably manufactured by the method described above. According to the present invention, the method includes the steps of preparing a substrate, laminating an aluminum oxide waveguide core layer doped with rare earth metal ions onto the substrate, and arranging a cladding layer on the laminated waveguide core, wherein the arranging step includes at least one processing step in which the laminated waveguide core is exposed to a predetermined maximum temperature. The method is characterized in that the step of laminating the waveguide core includes the step of forming nanocrystallites within the waveguide core. The minimum temperature at which the extinction rate of the laminated waveguide core increases significantly exceeds the predetermined maximum temperature, where the predetermined maximum temperature is about 400°C or higher.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a rare-earth ion-doped aluminum oxide optical waveguide. Preferably, the present invention further relates to a rare-earth ion-doped aluminum oxide optical waveguide manufactured by the above method. [Background technology]

[0002] Integrated photonics is gaining widespread adoption as it opens up possibilities for performance improvements in application areas beyond highly advanced microelectronics. In particular, with the realization of ultra-low-loss waveguides, it is becoming possible to explore various applications of photonic integrated circuits, such as quantum computers, microwave photonics, biosensing, and nonlinear sources. Rare-earth doped media, in particular, are emerging as a competitive light source platform for diverse applications in areas such as communications, LiDAR (light detection and ranging), and environmental and biosensing.

[0003] In the prior art, optical waveguides can be manufactured by preparing a substrate, laminating aluminum oxide waveguide cores doped with rare earth metal ions onto the substrate, and then placing a cladding layer on the laminated aluminum oxide waveguide cores. It should be noted that the step of placing the cladding layer includes at least one processing step in which the laminated aluminum oxide waveguide cores are exposed to the highest temperature. Such optical waveguides can be used, for example, as part of an optical amplifier.

[0004] An optical signal consists of one, several, or a continuous stream of signal photons of a specific wavelength. Optical amplifiers can amplify such signals by providing an environment that can induce stimulated emission of these signal photons. Stimulated emission is the process by which a signal photon interacts with an excited ion, causing the ion to emit the same photon and return to a relaxed state. Specifically, such an environment can be provided by doping a medium, such as a fiber or waveguide, with rare-earth ions, such as rare-earth metal ions, and then exciting the rare-earth ions by injecting excitation energy into the medium. This excitation energy can be supplied by an excitation laser, although alternative means are also known.

[0005] Those skilled in the art recognize that desirable stimulated emission processes have more undesirable counterparts in energy transfer and energy transfer upconversion. In energy transfer, a signal photon, whether the original photon or a photon resulting from stimulated emission, is excited by absorption by a "relaxed" rare-earth ion. In energy transfer upconversion, a signal photon, whether the original photon or a photon resulting from stimulated emission, is absorbed and further excited by an already excited rare-earth ion. These processes are sometimes referred to as quenching. The degree of quenching can be indicated by any of several properties, including extinction rate, extinction coefficient, and extinction velocity.

[0006] In this invention, we refer to the extinction rate. [Overview of the project] [Problems that the invention aims to solve]

[0007] In this technical field, optical waveguides having rare-earth doped waveguide cores are known. For integrated photonics, aluminum oxide (Al2O3) has emerged as a promising platform material due to its large transparent window, low propagation loss, and high rare-earth solubility. Specifically, waveguide core optical waveguides made from amorphous aluminum oxide are known. These tend to exhibit high optical performance and / or low loss. However, after deposition, when the doped waveguide core is exposed to high temperatures, the extinction rate increases significantly, making it unsuitable for use in optical amplifiers.

[0008] Those skilled in the art recognize that optical loss in an optical waveguide is determined not only by the loss in the waveguide core but also by the loss in the cladding layer.

[0009] The optical loss in a cladding layer can vary depending on the material. For example, tetraethyl orthosilicate (TEOS) is known to exhibit relatively low optical loss. However, the manufacturing of TEOS cladding layers typically requires a high-temperature annealing step. When the TEOS cladding layer is combined with an amorphous aluminum oxide waveguide core doped with rare earth metal ions, the high temperature generated when using the TEOS cladding layer with the amorphous aluminum oxide waveguide core significantly increases the extinction rate of the amorphous aluminum oxide waveguide core, resulting in a problem where the optical quality advantages of the TEOS cladding layer are compromised.

[0010] Other types of cladding layers may also exist that are placed on the stacked aluminum oxide waveguide cores, requiring a processing step in which the aluminum oxide waveguide cores are exposed to high temperatures, resulting in the aforementioned increase in the extinction rate of the aluminum oxide waveguide cores. Hereinafter, cladding layers that require a high-temperature step of 400°C or higher during or after deposition will be referred to as high-temperature cladding layers.

[0011] Therefore, when combining an aluminum oxide waveguide core doped with known rare earth metal ions and a high-temperature cladding layer, problems occur. Due to this problem, further reduction of the optical loss of the aluminum oxide waveguide core is hindered. As a result, even though both are considered to exhibit high optical performance and / or low loss and are advantageous for combined use, it has not been possible to combine a high-temperature cladding layer with a known amorphous aluminum oxide waveguide core doped with rare earth metal ions.

[0012] This problem occurs, for example, in the paper "Characteristics of Erbium-Doped Al2O3 Thin Films Deposited by Reactive Co-Sputtering Method" (IEEE journal of quantum electronics, 2000, 36.9: 1089 - 1097) by MUSA, S et al. This paper discusses an Al2O3 thin film doped with erbium deposited by the reactive co-sputtering method on a silicon wafer subjected to thermal oxidation treatment. The thin film is deposited at a substrate temperature of 400 °C, and these are amorphous, and the waveguide is not annealed. A wide emission band having a FWHM of 55 nm around a wavelength of 1533 nm has been measured. From the gain-versus-excitation power curve, an upconversion coefficient of less than 20x10 -25 m 3 / s has been derived.

[0013] The authors point out that ion-implanted materials are clustered by high-temperature annealing, and energy transfer at the center of the waveguide core increases. As a result, the authors limited the production of Er:Al2O3 thin films to low-temperature reactive co-sputtering to avoid clustering of Er ions.

[0014] In this technical field, optical waveguides including waveguide cores manufactured as single crystals are also known. These exhibit a low extinction ratio, but are more expensive, more difficult to manufacture, and not easy to commercialize.

[0015] The object of the present invention is to provide a method for manufacturing an optical waveguide including an aluminum oxide waveguide core and a cladding layer that solves at least one of the above-mentioned problems at least partially.

Means for Solving the Problems

[0016] According to the present invention, the object is achieved by the method defined in claim 1. The step of laminating the aluminum oxide waveguide core includes a step of forming nanocrystallites in the aluminum oxide waveguide core. Here, the lowest temperature at which the extinction coefficient of the laminated waveguide core significantly increases exceeds the predetermined maximum temperature. Here, the predetermined maximum temperature is about 400 °C or higher.

[0017] The applicant has found that by allowing the formation of nanocrystallites during deposition, an aluminum oxide waveguide core having a lower extinction coefficient than that manufactured from an amorphous material can be manufactured, and further, the extinction coefficient can be maintained until a higher temperature in subsequent processing steps.

[0018] When depositing at a relatively low temperature, significant crystallization does not occur, an amorphous layer doped with rare earth ions is formed, and a certain amount of ion clusters are formed. However, when such an amorphous aluminum oxide layer is then exposed to a high temperature of, for example, 400 °C or higher, clearly, more clustering occurs. In the amorphous material, rare earth ions move towards each other, and the extinction coefficient significantly increases.

[0019] When depositing at a relatively high temperature, crystallization occurs and spreads so that substantially the entire deposited layer is filled with nanocrystallites.

[0020] Without being bound by theory, the applicant points out that in the above-mentioned aluminum oxide layer having a large number of relatively small crystallites during the processing step necessary for arranging the cladding layer, rare earth ions move and the energy required to form clusters is too high.

[0021] The achievement of such a waveguide core can be confirmed by exposing it to the predetermined maximum temperature. Since only very slight clustering occurs within the layer, a significant increase in extinction rate does not occur.

[0022] By allowing the formation of nanocrystallites, amorphous material is eliminated or reduced to a very small amount. This means that the mobility of the rare earth ions is very low, and cluster formation is unlikely. In this way, the applicant has overcome the technical prejudice that rare earth ion-doped aluminum oxide waveguide cores must be manufactured from amorphous aluminum oxide and / or that such cores cannot be annealed.

[0023] The applicant has found that a favorable extinction rate of the optical waveguide can be obtained by forming the nanocrystallites such that the predetermined maximum temperature is in the range of about 400 to about 1400°C. If the maximum temperature is less than 400°C, a relatively large amount of amorphous aluminum oxide will be present after the lamination of the waveguide core, resulting in a relatively high mobility of the rare earth ions when the cladding layer is placed. On the other hand, if the maximum temperature exceeds 1400°C, there is a risk of degradation of the aluminum oxide waveguide core. Those skilled in the art will understand that since the glass transition temperature of aluminum oxide begins at about 1400°C, exposing the aluminum oxide waveguide core to this temperature may cause reflow of the structure.

[0024] It should be noted that the predetermined maximum temperature is preferably in the range of about 400 to about 1400°C, preferably in the range of about 500 to about 800°C, and more preferably about 550°C.

[0025] In the context of the present invention, an increase in extinction rate may be considered significant if it is about 20 percentage points or more, preferably in the range of about 5% to about 20%.

[0026] Based on the specific clad layer used, the step of disposing the clad layer may include a step of laminating the clad layer on the laminated waveguide core. The at least one processing step at which the predetermined maximum temperature is achieved includes a step of annealing the combination of the substrate, the laminated waveguide core, and the laminated clad layer at the predetermined maximum temperature. In such an embodiment, the extinction ratio of the aluminum oxide waveguide core after the lamination of the clad layer and before the annealing treatment may range between about 5% and about 35%. Further, or alternatively, the extinction ratio of the waveguide core after the annealing treatment ranges between about 0% and about 35%, preferably between about 0% and about 5%.

[0027] In some clad layers, the at least one processing step includes a step of laminating the clad layer on the aluminum oxide waveguide core at the predetermined maximum temperature. In such an embodiment, the extinction ratio of the aluminum oxide waveguide core after the lamination of the clad layer may range between about 0% and about 35%, preferably between about 0% and about 5%.

[0028] In the specific implementation of the rare earth ions, various materials can be used. The rare earth metal may be a lanthanoid such as erbium (Er 3+ ), ytterbium (Yb 3+ ), thulium (Tm 3+ ), and / or neodymium (Nd 3+ ).

[0029] In a preferred embodiment, the aluminum oxide is stoichiometric. Those skilled in the art will understand that this is based on practical implementation and is not always achievable. Thus, in some embodiments, it can be said that the waveguide core contains Al x O y , where 1.5 < x < 2.5 and 2.5 < y < 3.5, for example, x = 1.6 and y = 3.4, and preferably, x = 2 and y = 3.

[0030] Those skilled in the art will understand that the waveguide core may be grown using a variety of methods, such as reactive sputtering, atomic layer deposition, vapor deposition, or pulsed laser deposition.

[0031] Various types of cladding layers may be used, such as TEOS layers, silicon oxynitride layers, or polymer layers. Based on the desired cladding layer, one of several application methods may be used. This may involve deploying the cladding layer using one of the following methods: plasma-excited deposition, low-pressure chemical deposition, evaporation, sputtering, or atomic layer deposition.

[0032] Various types of substrates may be used, such as silicon substrates, silicon thermooxide substrates, or quartz substrates.

[0033] The optical waveguide may be any one of various forms, such as a slab waveguide or a channel waveguide.

[0034] In some embodiments, the loss in the waveguide produced by the manufacturing method may be further reduced by including a step between the step of laminating the aluminum oxide waveguide core and the step of arranging the cladding layer, for example, by using chemical mechanical polishing to reduce the surface roughness of the aluminum oxide waveguide core.

[0035] In some embodiments, the method further includes defining the shape and / or size of the aluminum oxide waveguide core using, for example, lithography and etching, before placing the cladding layer.

[0036] Those skilled in the art will understand that the precise settings for manufacturing an optical waveguide always depend on the specific machine used, the lot of resources / materials used, etc. To understand the ideal precise settings for preparing an optical waveguide according to the present invention, in some embodiments, the method is - A process of depositing aluminum oxide layers doped with rare earth ions onto each substrate while varying the substrate temperature and / or substrate bias voltage during the deposition rate of aluminum oxide, - A step of measuring the extinction rate for each layered aluminum oxide layer, - Select the deposition rate, the substrate temperature on which the aluminum oxide layer was manufactured, and the substrate bias voltage as the optimal settings, and perform the process that has the lowest extinction rate. -Further comprising the step of using the optimal setting when stacking the aluminum oxide waveguide cores in order to manufacture the optical waveguide described in any of the claims.

[0037] According to a further aspect of the present invention, an optical waveguide core is provided, comprising a substrate, an aluminum oxide waveguide core, and a cladding layer. The aluminum oxide waveguide core is doped with rare earth metal ions and disposed on the substrate. The cladding layer is disposed on the waveguide core. The aluminum oxide waveguide core contains nanocrystallites and has an extinction rate of 5% or less of the optical waveguide. The cladding layer comprises a high-temperature cladding layer.

[0038] The overall morphology of the waveguide core can be considered as nanocrystallites or polycrystallites, depending on the size of the crystallites and the proportion of this morphology in the waveguide core. In certain embodiments, the size of the nanocrystallites is in the range of about 1 nm to about 30 nm, preferably in the range of about 1 nm to about 10 nm. In certain embodiments, the nanocrystallites account for at least 50% by weight of the aluminum oxide waveguide core, preferably at least 75%, and more preferably at least 99%.

[0039] Various cladding layers can be used. For example, the high-temperature cladding layer may include at least one TEOS layer or silicon oxynitride layer.

[0040] The optical waveguide can take any one of various forms, including a slab waveguide or a channel waveguide.

[0041] The optical waveguide described above is preferably manufactured by one of the methods described above. [Brief explanation of the drawing]

[0042] Next, the present invention will be described with reference to the attached drawings. Here, the same reference numerals indicate the same or similar components. [Figure 1] This is a flowchart showing the method for manufacturing an optical waveguide according to the present invention. [Figure 2] This is a cross-sectional view showing a slab waveguide according to the present invention. [Figure 3] Figure 1 is a flowchart showing a preferred embodiment of the method described above. [Figure 4] This is an example of a reactive simultaneous sputtering system that can be configured to deposit an aluminum oxide waveguide core according to the present invention. [Figure 5] TEM images of stacked aluminum oxide waveguide cores at various substrate temperatures are shown. [Figure 6a] AFM images of stacked aluminum oxide waveguide cores at various substrate temperatures are shown. [Figure 6b] AFM images of stacked aluminum oxide waveguide cores at various substrate temperatures are shown. [Figure 7] The graph shows the deposition temperature of the aluminum oxide waveguide core on the X axis and the measured refractive index on the Y axis. For multiple deposition temperatures, the graph shows the wavelength of light propagating through the aluminum oxide waveguide core deposited at the said temperature on the X axis and the measured propagation loss on the Y axis. [Figure 8a] The graph shows the temperature at which the waveguide core is deposited on the X axis, and the size of the crystallites formed within the aluminum oxide waveguide core on the Y axis. [Figure 8b] The graph shows the temperature at which the waveguide core is deposited on the X axis, and the weight percentage of the waveguide core in a specific phase, specifically amorphous (A) or crystalline (C), on the Y axis. [Figure 8c]The graph shows the temperature at which the waveguide core is deposited on the X axis, and the optical loss achieved within the waveguide core on the Y axis. [Figure 9a] The graph shows the distance light travels through the waveguide core on the X-axis, and the intensity of the light on the Y-axis. [Figure 9b] The graph shows the distance light travels through the waveguide core on the X-axis, and the intensity of the light on the Y-axis. [Figure 10] This shows a test apparatus for measuring the gain in an optical waveguide. [Figure 11] It shows spirals of different lengths. [Modes for carrying out the invention]

[0043] In the context of the present invention, the extinction rate is used as an index to describe the amount of extinction that occurs in an optical waveguide, more specifically, the amount of extinction that occurs when the waveguide is used for optical amplification and / or incorporated into an optical amplifier. Those skilled in the art will recognize that this can be derived in several ways.

[0044] In any case, according to one definition in the context of this invention, the extinction rate may refer to the proportion of rare earth ions that the signal photons cannot reach. This may be because the decay rate constant is too fast.

[0045] This ratio can be derived by exciting a doped waveguide core in a steady state, for example, by supplying excitation energy to the waveguide core until saturation, and then measuring non-radioactive decay after the supply of excitation energy has stopped. Based on the assumed excited state distribution, assumptions recognized by the engineer and dependent on the said rare earth ions, and the total amount of measured non-radioactive decay, the quenched or unquenched proportion or portion of the said rare earth ions can be derived.

[0046] FIG. 1 shows a flowchart including steps S1 to S3 according to an embodiment of a method for manufacturing an optical waveguide of the present invention. FIG. 2 shows a schematic cross-section of the optical waveguide, for example, which can be manufactured by the method according to the present invention. FIG. 3 shows a flowchart according to a preferred embodiment of the method.

[0047] In step S1, a substrate 10 is prepared. In the next step S2, an aluminum oxide waveguide core 11 doped with rare earth metal ions is deposited on the substrate. Specifically, the aluminum oxide core 11 is deposited such that nanocrystals are formed. In the next step S3, a cladding layer 12 is disposed on the aluminum oxide waveguide core 11. In at least one processing step required for the step of disposing the cladding layer 12, the aluminum oxide waveguide core 11 is exposed to a predetermined maximum temperature in a range of about 400° C. or higher, preferably between about 400° C. and about 1400° C. The minimum temperature at which the extinction ratio of the stacked waveguide core significantly increases exceeds the predetermined maximum temperature.

[0048] When the maximum temperature rises until it exceeds about 1400° C., there is a risk of deterioration of the aluminum oxide waveguide core 11. Those skilled in the art understand that the glass transition temperature of aluminum oxide starts at about 1400° C., and exposing the waveguide core to this temperature may cause reflow of the structure. Further, such a maximum temperature may reduce the performance of other members of the waveguide depending on the materials used. The substrate 10 may be made of silicon and may start to melt at about 1400° C. The substrate 10 may contain silicon dioxide, and when exposed to such a temperature, local density fluctuations may be formed, scattering may occur, and the performance may be reduced.

[0049] In a specific embodiment, the substrate is made of thermal SiO2 and has a thickness of about 6.0 μm. The waveguide core is made of Al2O3:Er 3+ and has a width of about 1.6 μm and a thickness of 0.78 μm. The cladding layer is made of CVD SiO2 and has a thickness of about 8.0 μm.

[0050] The applicant has found that, in addition to the aluminum oxide described above, other matrix materials that allow the formation of nanocrystallites and have sufficiently high rare-earth solubility can also be used. One such alternative matrix material is aluminum nitride. Those skilled in the art will recognize how the following specifications for the manufacturing process of aluminum oxide waveguide cores can and / or should be applied to the manufacture of other matrix materials such as aluminum nitride waveguide cores.

[0051] Other rare earth metals can also be used. The ions may be, for example, lanthanides. Some specific examples include erbium (Er 3+ ), Ytterbium (Yb 3+ ), Thulium (Tm 3+ ), and / or neodymium (Nd 3+ Those skilled in the art will recognize how the specifications of the following manufacturing processes for known erbium are applicable and / or should be applied to the manufacture of waveguide cores doped with other rare earth ions.

[0052] The concentration of rare earth ions is approximately 0.25 × 10⁻⁶. 20 Ions / cm 3 ~Approx. 1×10 21 Ions / cm 3 It may be in the range between, preferably about 0.25 × 10 20 Ions / cm 3 ~Approx. 4×10 20 Ions / cm 3 It is within the range of [the specified period].

[0053] The method according to the present invention guarantees that no clusters will form, or at least only a very small number of clusters will form. In corresponding positive terms, the method according to the present invention provides a waveguide core in which the rare earth metal ions are uniformly and / or evenly distributed. Those skilled in the art will understand that the positions of the rare earth ions will not be perfectly uniform or even. However, this is not required. In the context of the present invention, uniform or even distribution is understood to mean that, if the distribution of the ions throughout the waveguide core is described as a stochastic process, the process exhibits a substantially uniform distribution.

[0054] Referring to Figure 3, step S3 for arranging the cladding layer may include step S31 for laminating the cladding layer 12 onto the aluminum oxide waveguide core 11. Step 31 may also be the processing step in which the aluminum oxide waveguide core 11 is exposed to the predetermined maximum temperature. This can be applied, for example, to embodiments in which a polymer-based cladding layer is laminated.

[0055] Alternatively, the high-temperature step may be part of a subsequent heating step, rather than part of the process of laminating the cladding layers. Figure 3 shows step S32 as an example of such a subsequent step, in which the combination of the substrate 10, the laminated aluminum oxide waveguide core 11, and the arranged cladding layers 12 is annealed, and the aluminum oxide waveguide core 11 is exposed to the predetermined maximum temperature. This applies, for example, to embodiments in which TEOS cladding layers are laminated.

[0056] Incidentally, various other steps can be performed between the step of stacking the aluminum oxide waveguide core 11 and the step of arranging the cladding layer 12. For example, chemical mechanical polishing can be performed on the stacked aluminum oxide layers to reduce surface roughness, and channel waveguides or other types of waveguides can be defined by electron beam lithography and reactive etching steps.

[0057] Referring to Figures 4 to 7, a first possible embodiment for stacking the aluminum oxide waveguide cores 11 so that nanocrystallites are formed is described below. A conceptual description of the nanocrystallites formed is shown in relation to Figures 8a to 8c.

[0058] Al2O3:Er used in this embodiment 3+ The thin film is deposited on a silicon wafer having an 8 μm oxide buffer layer by reactive sputtering. The advantage of the reactive sputtering method used here lies in the energy available per adsorbed atom on the substrate. The adsorbed atoms that land on the substrate have high mobility, and a high-density layer morphology can be obtained at a relatively low substrate temperature and a high deposition rate. In this way, a high-density Al2O3:Er layer can be formed at a CMOS-compatible wafer temperature. 3+ Layers can be stacked, and the propagation loss of the slab waveguide is less than 0.1 dB / cm at 1550 nm.

[0059] Al2O3:Er has low quenching properties. 3+ While several methods for achieving optical waveguides have been discussed, their relevance to the morphology of aluminum oxide has not been demonstrated in the prior art. The applicant recognized that, given the complexity of reproducibility in reactive sputter deposition processes, understanding the morphology of aluminum oxide could improve reproducibility and layer quality.

[0060] Al2O3:Er deposited by reactive sputtering method 3+ The morphology of the layer is primarily determined by the energy available per adsorbed atom, the EPA, and the material properties of the deposited layer. The material properties determining the morphology are the activation energy and diffusion constant, which determine the diffusion length of the adsorbed atoms given the available kinetic energy per adsorbed atom, and the critical nucleation dimension, which determines the critical diffusion length required for stable nucleation. Al2O3:Er 3+ The material properties of the layer are predetermined, but the energy per adsorbed atom is the ratio of the deposition rate and the total energy contribution during the deposition process.

[0061] In reactive sputtering, the total energy flux is a linear combination of different contributions. The contribution of the sputtering process to the energy flux directed toward the substrate can be classified into at least four groups.

[0062] First, it is necessary to consider the contributions of atoms and molecules adhering to the substrate necessary for the formation of the Al2O3 layer. Adsorbed atoms accelerated from the target contribute their kinetic energy when they are adsorbed onto the substrate. Furthermore, when oxygen molecules are adsorbed, their kinetic energy also contributes. Even if atoms or molecules are not adsorbed, some of their kinetic energy may be transferred when they collide with the substrate. In particular, when gas molecules are excited by collisions with high-speed ions, this contribution can become significant. Other forms of kinetic energy are related to the temperature of the substrate. Furthermore, in addition to the contribution of kinetic energy to the formation of the layer, Al2O3:Er 3+ The potential energy released by the exothermic chemical reactions during the formation of the material is also an important contribution.

[0063] The other three groups contributing to energy are radiation from the plasma, electrons incident on the substrate, and ions accelerated toward the substrate. Incidentally, a substrate bias can be applied. By increasing and / or decreasing the bias, the impact of the electrons and ions on the substrate can be increased or decreased.

[0064] All energy contributions are added to the energy available to each adsorbed atom, which affects the morphology of the layer and the resulting propagation loss.

[0065] In one embodiment, the Al2O3:Er 3+ The layer can be deposited on a 10 cm silicon wafer having an 8 μm thick thermal oxide buffer layer using the AJA ATC 1500 RF reactive simultaneous sputtering system 100.

[0066] The system 100 schematicly shown in Figure 4 comprises a target 101 made of 99.9995% pure aluminum, positioned on the cathode 102. The system 100 further comprises a second target 101B (not shown) containing the aforementioned rare earth metals, such as 99.95% pure erbium or 99.9% pure ytterbium. The second target can be positioned on the same cathode or on another cathode adjacent to cathode 102. The substrate 10 is positioned on the anode 103 and electrically connected to the chamber 103A, facing targets 101 and 101B. RF power is applied between the anode 103 and the cathode 102. The two targets 101 and 101B have independent bias voltages, powered by their respective RF power supplies. This generates plasma 104, in which supplied argon atoms 105 are ionized into argon ions 106 and electrons 107. Argon ions 106 are accelerated toward target 101 under the influence of a self-generated DC bias. At target 101, they collide with aluminum atoms, generating a flow of aluminum atoms 108 toward substrate 10. At substrate 10, the aluminum atoms 108 deposited on substrate 10 react with oxygen molecules 109 to form aluminum oxide. At target 101B, the argon ions 106 collide with erbium atoms, generating a flow of erbium atoms, particularly Er 3+ Ions flow toward the substrate 10.

[0067] The hydroxide ions that cause absorption loss at approximately 750 nm, 970 nm, and 1400 nm are the Al2O3:Er 3+ To prevent incorporation into the layer, the main deposition chamber is evacuated via inlet 110 until the base pressure reaches 0.1 μTorr.

[0068] To sustain the magnetron discharge, it is necessary to maintain equilibrium between the secondary electron emission from target 101 under ion bombardment and the velocity of electrons 107 escaping from plasma 104. The RF power supply does not directly apply a DC potential difference between cathode 102 and anode 103, and electrons 107 in plasma 104 absorb RF energy far more efficiently than heavy argon ions 106. Due to their high electron mobility, electrons 107 are collected on the electrodes. A self-generated DC bias voltage is produced as a result of the asymmetry between target 101 and chamber 103A of the sputtering system 100.

[0069] By applying a magnetic field using a permanent magnet below the target, the electron density in the plasma 104 increases, which in turn increases the ionization rate of argon and reduces the required discharge voltage. In addition, the magnetic field significantly increases the sputtering yield by increasing the impact rate of the target as ionization increases.

[0070] The sputtering system 100 further includes heating means such as an infrared heater 111 for directly heating the substrate 10 or heating it via the anode 103 on which the substrate 10 is located.

[0071] The following table lists exemplary process conditions for stacking the aforementioned aluminum oxide waveguide cores. [Table 1]

[0072] Given that the layer morphology depends on the energy available per adsorbed atom, it is possible to change the substrate temperature to alter the energy available per adsorbed atom, which is substantially independent of other process parameters. This allows for detailed examination of the changes in layer morphology with respect to substrate temperature and the corresponding optical propagation losses within the layer.

[0073] The substrate temperature is the set temperature measured on the substrate holder and is therefore not the exact temperature of the substrate. Calibration of the substrate temperature can be provided as a function of the set temperature.

[0074] Figure 5 shows TEM images of stacked aluminum oxide waveguide layers at various substrate temperatures. At the lowest select temperature of 420°C, the morphology of the layers is amorphous. As the substrate temperature rises to 460°C, nanocrystallite formation begins, and the density increases significantly in the range of 500°C to 540°C.

[0075] As the temperature rises from 500 to 580°C, the surface roughness increases and the ripples become larger. At 580°C, ripples are still present on the surface of the deposited layer, and a clear transition occurs from a nearly amorphous layer with nanocrystallites to a nearly polycrystalline morphology. The ripples disappear at temperatures above 620°C, and a polycrystalline morphology with slight columnar growth contours is gradually observed. No clear change in morphology is observed even when the temperature rises to 700°C.

[0076] Figures 6a and 6b show AFM measurements of stacked aluminum oxide waveguide layers at various substrate temperatures. The AFM measurements show that the ripple appears at 500°C (shown in the lower left of Figure 6a), its amplitude increases at 540°C (shown in the lower right of Figure 6a), and decreases and disappears at 620°C (shown in the upper right of Figure 6b). In addition to the ripple, the uniformity of refractive index and thickness is reduced in the layers grown at temperatures from 500°C (shown in the lower left of Figure 6a) to 580°C (shown in the upper left of Figure 6b).

[0077] In the lower part of Figure 7, the refractive index of the aluminum oxide layer, measured by polarization analysis, is shown in particular at 1550 nm, depending on the change in deposition temperature.

[0078] The optical propagation loss in each aluminum oxide layer was examined using a Metricon 2010 / M41 equipped with a fiber loss module. These losses are shown in the figure above. Clearly, the loss of the layer grown at a substrate temperature of 700°C decreased, and with increasing deposition temperature, it decreased to 1.57 dB / cm for 377 nm and to 0.84 dB / cm for 403 nm.

[0079] In another embodiment, when aluminum nitride waveguide cores are laminated, the exact deposition temperature may differ from that described in relation to Figures 5 and 6, but the applicant has found that similar behavior occurs. Even when deposited at different temperatures, similar changes in morphology and / or similar trends in refractive index and thickness uniformity were observed in the aluminum nitride waveguide cores. The teachings derived from Figures 4 to 7 are explained based on the embodiment of the aluminum oxide waveguide core, but are also applicable to the embodiment of the aluminum nitride waveguide core.

[0080] Figures 8a to 8c show graphs relating to the deposition temperature at which an aluminum oxide waveguide core 11 is deposited, and various characteristics of the core 11, respectively. The X-axis of each of these graphs represents the deposition temperature. Those skilled in the art will understand that the precise temperature at which a particular waveguide core is deposited is highly dependent on the apparatus, and for example, a predetermined value for the "deposition temperature" of the apparatus may deviate from the actual, and particularly difficult-to-determine, temperature of the waveguide core. However, given a specific machine and an achievable deposition rate, temperature sweeps can be performed to determine the precise temperature values ​​of the behavior revealed in the graphs shown in Figures 8a to 8c.

[0081] In this technical field, the fabrication of amorphous Al2O3 waveguide cores doped with rare earth ions is clearly preferred because these cores exhibit low optical loss. In Figures 8a to 8c, the deposition temperature at which the waveguide is achieved is called temperature P1. Starting from P1, as the deposition temperature decreases, the density of the deposited layer decreases, and gaps are created in the amorphous aluminum oxide. These gaps act as scatterers and can cause losses. Starting from P1, as the deposition temperature increases, nanocrystallites are formed in the amorphous material. These nanocrystallites act as scatterers and can cause losses.

[0082] As shown in Figures 8a to 8c, P1 is a minimum value that balances the reduction of the gap amount with the prevention of nanocrystallite formation. Relatively low losses can be achieved at P1. Known aluminum oxide optical waveguides are based on aluminum oxide layers deposited at a temperature corresponding to P1. However, such layers have the aforementioned drawback of being vulnerable to high-temperature processing steps after the process of laminating the aluminum oxide layers.

[0083] The applicant has found that the greatest loss in aluminum oxide optical waveguides deposited at deposition temperatures near P1 is caused by local differences in dielectric properties. Both the gaps and crystallites have different dielectric properties than amorphous aluminum oxide. As the number of gaps and / or crystallites increases, local differences occur more frequently, and optical loss increases.

[0084] The applicant has further found that such local differences occur most frequently, and the resulting losses are greatest, when the aluminum oxide layer contains amorphous material and nanocrystallites in roughly equal amounts. For example, as shown in Figure 8b, line A represents the proportion of aluminum oxide in the amorphous phase in the layer in weight percent, and line C represents the proportion of aluminum oxide in the crystalline phase in weight percent. Those skilled in the art will understand that the amount of amorphous material and / or the number of nanocrystallites can be expressed using other units and / or indices.

[0085] The applicant has further found that as the deposition temperature increases, at a certain temperature, the nanocrystallites outnumber the amorphous material and become the dominant material in the deposited layer. As the amount of amorphous aluminum oxide decreases, the discontinuity between amorphous and crystalline aluminum oxide decreases, and above temperature P2, a decrease in optical loss can be observed. In Figure 8b, for illustrative purposes, temperature P2 is selected as the temperature at which the content of amorphous and crystalline aluminum oxide is equal.

[0086] The reduction in optical loss continues until the deposition temperature is reached at which substantially all of the aluminum oxide in the waveguide core takes on the form of nanocrystallites, and the amorphous phase becomes minimal or nonexistent. This point can be called P3. Figure 8c further shows a rectangle R indicating the temperature range corresponding to the temperature change in the upper part of Figure 7.

[0087] To be precise, at the deposition temperature between P2 and P3, the volume of amorphous material scattered among the nanocrystalline aluminum oxide is considered to be the cause of scattering. Therefore, as the deposition temperature increases further, a decrease and / or reduction in the volume of amorphous material occurs, the frequency of local differences decreases, and losses decrease.

[0088] The applicant further found that in the range of P1 and P3, more aluminum oxide takes the shape of nanocrystallites, but the size of the independent nanocrystallites does not increase significantly. This is conceptually reflected in Figure 8a. Only when deposition temperatures above P3 is it possible for the size of the independent crystallites to increase significantly while the proportion of aluminum oxide contained in the crystallites themselves is maintained. It should be noted that at deposition temperatures below P1, nanocrystallites are virtually nonexistent, and therefore the size is not shown. As the temperature rises above P3, the nanocrystallites bind to larger crystallites. These relatively large crystallites increase light scattering, thereby increasing the light loss in the layer. As a result, a minimum value in loss can be observed at temperature P3, which is equivalent to the minimum value at temperature P1. However, unlike the laminated aluminum oxide layer deposited at temperature P1, the aluminum oxide layer deposited at temperature P3 is far less susceptible to the effects of subsequent heating steps, such as the annealing step for processing the deposited cladding layer.

[0089] The morphology obtained at deposition temperature P3 can also be described as polycrystalline aluminum oxide saturated with nanocrystallites. Here, nanocrystallites refer to crystallites that are relatively small in size compared to the waveguide of light propagating through the optical waveguide. The advantages of this morphology are as follows: a) The nanocrystallites are extremely small, and due to their size, they do not cause significant Rayleigh scattering. b) The saturation of nanocrystallites within the core ensures that the dielectric properties of the entire core are hardly or never altered, thereby limiting Rayleigh scattering. c) Saturation of nanocrystallites within the core means that there is little to no amorphous material around the existing nanocrystallites to absorb and grow together. d) Growth that occurs when nanocrystallites align with each other to form one large crystallite only occurs at much higher temperatures.

[0090] The graphs in Figures 8a to 8c schematically illustrate the process of laminating aluminum oxide layers at various substrate temperatures. Points P1, P2, and P3 are shown in each graph, but the behaviors related to each characteristic described in Figures 8a to 8c do not necessarily occur at exactly the same temperature. Furthermore, although Figure 8c suggests that the minimum values ​​of P1 and P3 achieve similarly low losses, in the embodiments of the method according to the present invention, for many reasons, different degrees of loss may be achieved at the minimum values ​​P1 and P3.

[0091] The applicant has found that it is advantageous to expose the aluminum oxide waveguide core 11, on which nanocrystallites are formed, to a temperature of 550°C or higher, such as 800°C or higher, and / or that losses can be reduced. The latter is shown, for example, in Figures 9a and 9b.

[0092] When the aluminum oxide waveguide core 11 is exposed to such temperatures, the growth of the nanocrystallites is severely limited, but the growth still consumes all, or at least most, of the amorphous aluminum oxide that may have been formed during the stacking process of the aluminum oxide waveguide core 11. As the amount of amorphous aluminum oxide decreases after exposure to such temperatures, the frequency of local differences in dielectric properties also decreases, as does scattering.

[0093] Those skilled in the art will understand that by stacking the cores without the rare earth ions and exposing them to a temperature of about 800°C or higher, preferably in the range of about 800 to about 1400°C, an aluminum oxide waveguide core having nanocrystallites can be obtained. In the undoped layer, only very slight crystal growth occurs, so no significant change in optical performance occurs. The aforementioned increase in crystallite size may be considered significant in the range of about 100% or more, preferably in the range of about 100% to about 50%. This is because the rare earth ions cause clustering in the amorphous material at temperatures below 800°C, such as 400°C, which degrades the optical performance; therefore, testing must be performed without the rare earth ions.

[0094] As shown in Figure 9a, the aluminum oxide waveguide core in question is deposited in the aluminum oxide so that nanocrystallites are formed within it. No further processing steps are performed that expose the deposited aluminum oxide waveguide core to temperatures above 800°C. The loss achieved is 1+ / -0.5 dB / cm.

[0095] As shown in Figure 9b, the aluminum oxide waveguide core shown in Figure 9a was exposed to approximately 1150°C for approximately 4 hours in a nitrogen environment. The loss achieved was 0.7 ± 0.2 dB / cm.

[0096] The light intensity shown on the Y axis is an estimate derived from scattered light measured over the propagation length of the waveguide core. Without being bound by theory, those skilled in the art will understand that, due to the limitations of this estimate, it appears that while the light intensity increases, losses occur. These losses are estimated by fitting the measured data to a log-linear model using the MLESAC (Maximum Likelihood Estimator Sample Consensus) algorithm. A predetermined tolerance is determined by fitting different sections of the entire propagation. Those skilled in the art will understand that other methods are also available for estimating the light intensity within the waveguide core and deriving the average loss from the measured data.

[0097] In another embodiment, when aluminum nitride waveguide cores are laminated, the temperature values ​​of P1, P2, or P3 may differ from those of aluminum oxide waveguide cores, but the applicant has found that the same behavior occurs. Similar changes in the phases of the aluminum nitride, such as amorphous or (nano)crystallites, similar increases in the size of the (nano)crystallites, and conceptually equivalent loss profiles can be observed in aluminum nitride waveguide cores deposited at various temperatures. The teachings described in Figures 8a to 8c and Figures 9a to 9b are described based on the embodiment of the aluminum oxide waveguide core, but are also applicable to the embodiment of aluminum nitride.

[0098] A second possible embodiment is described below in which the aluminum oxide waveguide cores 11 are stacked so that nanocrystallites are formed. The conceptual description of the nanocrystallites shown in relation to Figures 8a to 8c also applies to this embodiment.

[0099] To deposit the waveguide core, an aluminum oxide film may be deposited using reactive magnetron sputtering. A 786 nm thick Al2O3:Er film with a refractive index of 1.739 at 1030 nm, measured using VASE (Variable Angle Spectroscopic Ellipsometry), may be deposited at an O2 flow rate of 2.8 sccm, a deposition rate of 3.74 nm / min, and a stage temperature of 760°C. 3+ A layer was deposited. Using calibrated sputtering power based on Rutherford backscattering measurements (RBS), the erbium concentration in the layer was found to be approximately 3.9 × 10⁻¹⁶. 20 Ions / cm 3 It is known that... To avoid OH- contamination, a known cause of recombination centers in erbium-doped amplifiers, samples were stored in an N2 atmosphere during the manufacturing steps. Electron beam lithography (EBL) was used, with an exposure of 1000 μC / cm² to the negative resist. 2Patterns were formed and used as etching masks to define helical, ring resonators, and linear waveguides for signal enhancement and background loss characteristic evaluation. Reactive ion etching (RIE) was performed to define the waveguides at a chamber pressure of 3 mTorr and RF power of 25 W, with BCl3 and HBr gas flow rates of 25 and 10 sccm, respectively. Plasma-enhanced chemical vapor deposition (PECVD) was used to deposit SiO2 cladding at a chamber pressure of 650 mTorr, a stage temperature of 300°C, and a power of 60 W, with SiH4 / N2 and N2O flow rates of 200 and 710 sccm, respectively, at a deposition rate of 37 nm / min. The chips were diced and annealed in a tubular furnace in an N2 atmosphere at 550°C. To reduce the bonding loss (αc) and the scattering loss, the tip sidewalls were polished using a KrellTech Flex Waveguide Polisher with various polishing pads of different roughness levels (3.0, 1.0, and 0.3 μm) moistened with demi water.

[0100] Using this particular example, Al2O3:Er exhibits a gain of 33.5 dB at 1532 nm and an on-chip power of 475 mW (26.1 dBm) in a 12.9 cm amplifier. 3+ Waveguides can be manufactured.

[0101] This can be derived using a configuration with bidirectional excitation using an off-chip WDM and an amplifier with a filter that cuts the spectrum below 1500 nm, as shown in Figure 10. In such a configuration, two signal sources may be used to switch from the low-power signal region to the high-power signal region. The resulting signal may be monitored using an optical spectrum analyzer (OSA). Measurements with helices of different lengths (see Figure 11) and various excitation and signal outputs showed that a 4.9 cm amplifier had a peak on-chip gain of 3.5 dB / cm per unit length at 1532 nm.

[0102] Reactive sputtering of Al2O3:Er 3+ The waveguide amplifier is 3.9 × 10 20 Ions / cm 3 Having an erbium concentration, and as can be observed with the configuration shown in Figure 10, using bidirectional excitation at 1480 nm, a gain of over 30 dB can be achieved at 1532 nm. The output of the chip shown here exceeds 120 mW, demonstrating the advantages achievable with optical waveguides manufactured according to the method of the present invention.

[0103] The concept of the present invention generally relates to providing a waveguide core having the minimum amount of extinction. This can be achieved based on the method described in claim 1.

[0104] Extinction can be said to be, to a greater or lesser extent, a result of clustering of rare earth ions. If most ions are part of a cluster, the photons emitted by spontaneous emission are more likely to be emitted within the cluster, which means that they are more likely to interact with other nearby ions within the cluster. Therefore, as an alternative, the method according to the present invention may include a step of forming nanocrystallites within the waveguide core in the step of stacking the waveguide core, wherein the minimum temperature at which the proportion of rare earth ions constituting the cluster increases significantly exceeds the predetermined maximum temperature, and the predetermined maximum temperature is about 400°C or higher.

[0105] If the cluster is large, the photons emitted from the ions by spontaneous emission are more likely to interact with other nearby ions simply because there are more ions in close proximity in a large cluster. Therefore, as an alternative, the method according to the present invention may be characterized in that the step of stacking the waveguide cores includes a step of forming nanocrystallites within the waveguide cores, the minimum temperature at which the average size of the ion clusters increases significantly exceeds the maximum temperature, and the predetermined maximum temperature is about 400°C or higher.

[0106] In the field of crystallography, clusters are sometimes described based on the number of ions they contain. For example, a monomer refers to an isolated ion in a matrix that is at least locally homogeneous. A dimer refers to a cluster consisting of two ions, and a trimer refers to a cluster consisting of three ions. If there are no clusters of rare earth ions, then any present rare earth ions can be affirmatively stated to be monomers. Therefore, as an alternative, the method according to the present invention may be characterized in that the step of stacking the waveguide cores includes a step of forming nanocrystallites within the waveguide cores, the minimum temperature at which monomer ions significantly increase exceeds the predetermined maximum temperature, and the predetermined maximum temperature is about 400°C or higher.

[0107] Although the present invention has been described above using embodiments, the scope of the present invention is defined by the claims and their equivalents. It will be apparent to those skilled in the art that these embodiments can be modified or improved in various ways without departing from the scope of the present invention.

Claims

1. The process of preparing the circuit board, A step of laminating an aluminum oxide waveguide core layer doped with rare earth metal ions onto the substrate, The process includes placing a cladding layer on the stacked waveguide core, The method for manufacturing an optical waveguide is characterized in that the step of stacking the aluminum oxide waveguide cores is to form nanocrystallites within the aluminum oxide waveguide cores, the nanocrystallites having a size in the range of about 1 nm to about 30 nm, preferably in the range of about 1 nm to about 10 nm, and accounting for at least 50% by weight of the aluminum oxide waveguide core, preferably at least 75%, more preferably at least 99%, and the cladding layer is a high-temperature cladding layer.

2. The method for manufacturing an optical waveguide according to claim 1, characterized in that the step of arranging the cladding layer includes at least one processing step in which the stacked waveguide core is exposed to a predetermined maximum temperature, where the predetermined maximum temperature is about 400°C or higher.

3. The method for manufacturing an optical waveguide according to claim 2, characterized in that, in the step of stacking the aluminum oxide waveguide cores, the extinction rate of the stacked waveguide cores does not increase significantly as a result of the subsequent step of arranging the cladding layer.

4. The method for manufacturing an optical waveguide according to claim 2 or 3, characterized in that the minimum temperature at which the extinction rate of the stacked waveguide cores increases significantly exceeds the predetermined maximum temperature.

5. The method for manufacturing an optical waveguide according to claim 3 or 4, characterized in that the increase in extinction rate is significant when it is about 20 percent points or more, and preferably in the range of about 5 percent to about 20 percent.

6. The method for manufacturing an optical waveguide according to any one of claims 2 to 5, characterized in that the predetermined maximum temperature is in the range of about 400 to about 1400°C, preferably in the range of about 500 to about 800°C, and more preferably in the range of about 550°C.

7. The method for manufacturing an optical waveguide according to any one of claims 2 to 6, wherein the step of arranging the cladding layer includes laminating the cladding layer onto the laminated waveguide core, and the at least one processing step includes annealing the combination of the substrate, the laminated waveguide core, and the laminated cladding layer at a predetermined maximum temperature.

8. The method for manufacturing an optical waveguide according to claim 7, characterized in that the extinction rate of the aluminum oxide waveguide core after lamination of the cladding layer and before annealing is in the range of about 5% to about 35%.

9. The method for manufacturing an optical waveguide according to claim 7 or 8, characterized in that the extinction rate of the waveguide core after the annealing treatment is in the range of about 0% to about 35%, preferably in the range of about 0% to about 5%.

10. The method for manufacturing an optical waveguide according to any one of claims 2 to 6, characterized in that the at least one processing step includes laminating the cladding layer onto the aluminum oxide waveguide core at the predetermined maximum temperature.

11. The method for manufacturing an optical waveguide according to claim 10, characterized in that the extinction rate of the aluminum oxide waveguide core after lamination of the cladding layer is in the range of about 0% to about 35%, preferably in the range of about 0% to about 5%.

12. The rare earth metal is preferably Er ３＋ Erbium such as Yb ３＋ Ytterbium such as, preferably, Tm ３＋ Thulium such as, and / or preferably, Nd ３＋ A method for manufacturing an optical waveguide according to any one of the above claims, characterized in that the lanthanoid is such as neodymium.

13. The aluminum oxide is chemically quantifiable, and / or the waveguide core is Al ｘ O ｙ A method for manufacturing an optical waveguide according to any of the above claims, characterized in that, thereafter, 1.5 < x < 2.5 and 2.5 < y < 3.5, for example, x = 1.6 and y = 3.4, preferably x = 2 and y = 3.

14. A method for manufacturing an optical waveguide according to any one of the above claims, characterized in that the waveguide core is grown using one of the following methods: reactive sputtering, atomic layer deposition, vapor deposition, or pulsed laser deposition.

15. A method for manufacturing an optical waveguide according to any one of the claims, characterized in that the cladding layer includes a TEOS layer, a silicon oxynitride layer, or a polymer layer.

16. A method for manufacturing an optical waveguide according to any one of the above claims, characterized in that the cladding layer is disposed using one of the following methods: plasma excitation deposition, low-pressure chemical deposition, deposition, sputtering, or atomic layer deposition.

17. The method for manufacturing an optical waveguide according to any one of the claims, characterized in that the substrate includes a silicon substrate, a silicon thermooxide substrate, or a quartz substrate.

18. The method for manufacturing an optical waveguide according to any one of the claims, characterized in that the optical waveguide is a slab waveguide or a channel waveguide.

19. A method for manufacturing an optical waveguide according to any one of the claims, further comprising, between the step of stacking the aluminum oxide waveguide cores and the step of arranging the cladding layer, a step of reducing the surface roughness of the aluminum oxide waveguide cores by, for example, chemical mechanical polishing.

20. A method for manufacturing an optical waveguide according to any one of the claims, further comprising defining the shape and / or size of the aluminum oxide waveguide core using, for example, lithography and etching, before arranging the cladding layer.

21. The process involves depositing layers of aluminum oxide doped with rare earth ions onto each substrate while varying the substrate temperature and / or substrate bias voltage during the deposition rate of aluminum oxide, A process of measuring the extinction rate for each layered aluminum oxide layer, As the optimal settings, the deposition rate, the substrate temperature on which the aluminum oxide layer was manufactured, and the substrate bias voltage are selected, and the process having the lowest extinction rate is performed. A method for manufacturing an optical waveguide according to any of the claims, comprising the step of using the optimal setting when stacking the aluminum oxide waveguide cores in order to manufacture the optical waveguide according to any of the claims.

22. circuit board and An aluminum oxide waveguide core doped with rare earth metal ions is placed on the substrate, An optical waveguide comprising a cladding layer disposed on the waveguide core, The aluminum oxide waveguide core contains nanocrystallites, the extinction rate of the optical waveguide is 5% or less, and the cladding layer contains a high-temperature cladding layer. The optical waveguide is characterized in that the size of the nanocrystallites is in the range of about 1 nm to about 30 nm, preferably in the range of about 1 nm to about 10 nm, and the nanocrystallites occupy at least 50%, preferably at least 75%, and more preferably at least 99% by weight of the aluminum oxide waveguide core.

23. The optical waveguide according to claim 22, characterized in that the high-temperature cladding layer is a cladding layer whose arrangement process includes at least one processing step in which the aluminum oxide waveguide core is exposed to a high temperature of 400°C or higher.

24. The optical waveguide according to claim 22 or 23, characterized in that the high-temperature cladding layer comprises at least one of a TEOS layer or a silicon oxynitride layer.

25. The optical waveguide according to any one of claims 22 to 24, characterized in that the optical waveguide is a slab waveguide or a channel waveguide.

26. The optical waveguide according to any one of claims 22 to 25, characterized in that the optical waveguide is manufactured by the method according to any one of claims 1 to 21.

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