Optical module and connection method

Abstract

This optical module comprises: a planar lightwave circuit (101) having an optical waveguide (102); and a thin film (103). An optical fiber is optically connected to the planar lightwave circuit (101) at an input / output end (151). The thin film (103) is formed in the vicinity of the input / output end (151) of the planar lightwave circuit (101) to which the optical fiber is optically connected. Additionally, the thin film (103) is composed of a material that generates heat when irradiated with electromagnetic waves. The thin film (103) generates heat when irradiated with electromagnetic waves (for example, microwaves) having a frequency at which it would be difficult to heat the planar lightwave circuit (101).

Description

Optical module and connection method

[0001] The present invention relates to an optical module and a connection method.

[0002] Planar lightwave circuits, which have planar optical waveguides made of quartz-based materials, silicon, or semiconductors, are often used with an optical fiber connected to at least one of the input and output terminals. Hereinafter, a planar lightwave circuit connected to an optical fiber will be referred to as an optical fiber module. Optical fiber modules have the advantage of being easily incorporated into devices through optical connections using optical connectors attached to the optical fibers or optical connections by fusion splicing between optical fibers.

[0003] Conventionally, most optical fiber modules have been used as devices that use near-infrared light, such as components that make up optical communication networks. In recent years, it has been proposed to use optical fiber modules in optical devices that use visible light, such as small projectors and optical microscopes (Non-Patent Document 1). This is because replacing spatial optical systems for visible light, which are composed of components such as lenses and mirrors, with planar optical circuits makes it possible to miniaturize the device, improve vibration resistance, and increase the scale of the optical system. Hereinafter, optical devices that use visible light will be referred to as visible light devices.

[0004] However, the use of optical fiber modules in visible light devices is currently very limited. One reason for this is the difficulty of ensuring the reliability of optical connection points between planar lightwave circuits and optical fibers. Compared to the near-infrared light band, which has traditionally been used in optical fiber modules, the visible light band has a short wavelength and high energy, making optical connection points more susceptible to deterioration. For example, in conventional optical connection points, UV-curable resins are widely used as adhesives and fillers to reduce Fresnel loss at optical connection points (Patent Document 1). However, these resins are known to deteriorate when exposed to visible light, resulting in increased optical connection loss.

[0005] JP 2016-206628 A

[0006] J. Sakamoto et al., "Shape-optimized multi-mode interference for a wideband visible light coupler", Optics Communications, vol. 433, pp. 221-225, 2019.

[0007] To suppress optical connection loss due to the deterioration of the UV-curable resin, a connection technology has been proposed in which the optical connection point is made into a gap. However, making the optical connection point into a gap results in Fresnel loss. In addition, it is known that when the optical connection point is made into a gap, contaminants adhere to the end faces of the optical fiber or planar lightwave circuit that make up the optical connection point due to dust collection effects, etc., which increases optical connection loss.

[0008] To avoid these problems, a technique for fusing the optical connection points between a planar lightwave circuit and an optical fiber has been proposed. Hereinafter, the technique for fusing an optical connection point will be referred to as fusion splicing. Fusion splicing has the advantage that the optical connection point does not contain materials that are easily degraded by visible light irradiation, such as UV-curable resin, and the optical connection point is not an air gap, so there is no Fresnel loss or loss due to dust collection effects.

[0009] Fusion splicing is a common technique for forming optical splices between optical fibers. Dedicated equipment is widely available commercially, and the technique is also widely used when incorporating optical fiber modules into equipment.

[0010] However, it is known to be difficult to fusion splice optical fibers and planar lightwave circuits. This is because optical fibers and planar lightwave circuits often have different volumes and materials, which in turn result in significantly different heat capacities. Fusion splicing of optical fibers is generally achieved by simultaneously melting the end faces of two optical fibers using an arc discharge generated between a pair of opposing terminals, and then butting the end faces together.

[0011] When applying a similar technique to optical fiber and planar lightwave circuits, the large difference in heat capacity makes it difficult to simultaneously and appropriately melt both the optical fiber and the planar lightwave circuit using arc discharge. Specifically, the amount of heat required to melt the optical fiber to a state suitable for fusion splicing will not melt the planar lightwave circuit, making it impossible to achieve sufficient splice strength. Furthermore, the amount of heat required to fully melt the planar lightwave circuit will cause the optical fiber to melt excessively, resulting in deterioration of the core shape and increased splice loss.

[0012] To address the above issues, fusion splicing techniques have been proposed that compensate for the difference in heat capacity between the optical fiber and the planar lightwave circuit. Specifically, these techniques enable fusion splicing between the optical fiber and the planar lightwave circuit by providing sufficient heat from a separate heat source to melt the planar lightwave circuit. For example, one proposed technique involves preheating the planar lightwave circuit using a ceramic heater, a heating wire, or a torch flame, and then irradiating the optical connection point between the optical fiber and the planar lightwave circuit with laser light to achieve fusion splicing. Hereinafter, this technique of providing heat to the planar lightwave circuit using a heat source separate from the heat source used during fusion splicing is referred to as auxiliary heating. While this auxiliary heating compensates for the difference in heat capacity between the optical fiber and the planar lightwave circuit and enables fusion splicing, it has the disadvantage of damaging other elements integrated on the planar lightwave circuit, such as the photodetector and light-emitting element, because the entire planar lightwave circuit is preheated to a high temperature.

[0013] Techniques have also been proposed to compensate for the difference in heat capacity between an optical fiber and a planar lightwave circuit without preheating the entire planar lightwave circuit. Specifically, techniques have been proposed in which an arc discharge or focused laser light used to melt the optical connection point between the optical fiber and the planar lightwave circuit is slightly deflected toward the planar lightwave circuit. These techniques enable fusion splicing by applying more heat to the planar lightwave circuit to compensate for the difference in heat capacity. However, they have the disadvantage of requiring precise alignment, as the irradiation point of the arc discharge or laser light must be precisely deflected to match the heat capacity of the planar lightwave circuit.

[0014] The present invention has been made to solve the above problems, and its object is to enable fusion splicing between a planar lightwave circuit and an optical fiber without damaging other elements integrated in the planar lightwave circuit and without requiring precise alignment.

[0015] The optical module of the present invention comprises a planar lightwave circuit having an optical waveguide, and a thin film formed near an input / output end where an optical fiber of the planar lightwave circuit is optically connected, the thin film generating heat when irradiated with electromagnetic waves, the thin film generating heat when irradiated with electromagnetic waves of a frequency that does not easily heat the planar lightwave circuit.

[0016] Furthermore, a connection method according to the present invention is a connection method for optically connecting an optical fiber to an input / output end of an optical module, the connection end comprising a planar lightwave circuit having an optical waveguide, and a thin film formed in the vicinity of an input / output end to which an optical fiber of the planar lightwave circuit is optically connected and which generates heat when irradiated with electromagnetic waves, the thin film generating heat when irradiated with electromagnetic waves of a frequency that does not easily heat the planar lightwave circuit, the connection method comprising a first step of abutting the connection end of the optical fiber to the input / output end, and a second step of irradiating the thin film with electromagnetic waves to generate heat, thereby fusing the input / output end and the connection end of the optical fiber and optically connecting the optical fiber to the input / output end.

[0017] As described above, according to the present invention, a thin film that generates heat when irradiated with electromagnetic waves is provided, so that a planar lightwave circuit and an optical fiber can be fusion-spliced ​​without damaging other elements integrated in the planar lightwave circuit and without requiring precise alignment.

[0018] Fig. 1A is a cross-sectional view showing a partial configuration of an optical module according to an embodiment of the present invention. Fig. 1B is a cross-sectional view (a) and a plan view (b) showing a partial configuration of an optical module according to an embodiment of the present invention. Fig. 2 is a flowchart for explaining a connection method according to an embodiment of the present invention. Fig. 3 is a configuration diagram showing the configuration of a system for implementing the connection method according to an embodiment of the present invention.

[0019] An optical module according to an embodiment of the present invention will now be described with reference to FIG. 1A. FIG. 1 shows a cross section parallel to the thickness direction and the light propagation direction. This optical module includes a planar lightwave circuit 101 having an optical waveguide 102, and a thin film 103. An optical fiber is optically connected to the planar lightwave circuit 101 at an input / output terminal 151. The planar lightwave circuit 101 is formed on a substrate 110. The optical waveguide 102 is composed of a lower cladding layer 111, a core 112, and an upper cladding layer 113.

[0020] The substrate 110 may have a thickness of 460 μm. The lower cladding layer 111 and the upper cladding layer 113 may each have a thickness of 20 μm. The cross-sectional shape of the core 112 may be a square with sides of 2 μm. The length of the planar lightwave circuit 101 in the light propagation direction may be 3 cm. The length of the planar lightwave circuit 101 in the direction perpendicular to the light propagation direction may be 1 cm.

[0021] The planar lightwave circuit 101 can be made of, for example, a silica-based material and silicon. For example, the substrate 110 can be made of silicon. The core 112 can be made of germanium-doped SiO2. The lower cladding layer 111 can be made of pure SiO2 without any doping, and the upper cladding layer 113 can be made of SiO2 doped with boron or phosphorus. The refractive indices of the core 112, lower cladding layer 111, and upper cladding layer 113 can be controlled by changing the concentration of the dopant. The refractive index of the upper cladding layer 113 can be adjusted to be equal to that of the lower cladding layer 111. The concentration of germanium doped in the core 112 can be adjusted so that the refractive index of the core 112 is higher than that of the lower cladding layer 111 and the upper cladding layer 113. For example, the relative refractive index difference between the core 112 and each cladding layer can be 1.0%.

[0022] The thin film 103 is formed near an input / output terminal 151 to which an optical fiber of the planar lightwave circuit 101 is optically connected. The thin film 103 can be disposed near the input / output terminal 151, for example, embedded in the upper cladding layer 113 of the optical waveguide 102. Alternatively, the thin film 103 can be disposed on the upper surface of the optical waveguide 102 near the input / output terminal 151. The thin film 103 is made of a material that generates heat when irradiated with electromagnetic waves. The thin film 103 generates heat when irradiated with electromagnetic waves (e.g., microwaves) of a frequency that heats the planar lightwave circuit 101 less easily than the thin film 103. The thin film 103 can be made of, for example, AlGaN.

[0023] As described above, the thin film 103 generates heat when irradiated with electromagnetic waves such as microwaves, and the heat generated by the thin film 103 realizes fusion bonding between the input / output terminal 151 and the connection terminal of the optical fiber.

[0024] Heating by microwave irradiation (microwave heating) is achieved by irradiating an object with electromagnetic waves of a specific frequency, which are absorbed by the object and converted into heat. The absorption rate of this electromagnetic wave varies depending on the frequency of the electromagnetic wave, and the frequency dependence differs for each substance. Therefore, by irradiating a specific object (thin film 103) with electromagnetic waves of a frequency that is significantly absorbed by the specific object, it is possible to heat only the specific object.

[0025] Specifically, by selecting a frequency that is not absorbed by the silica glass or silicon (lower cladding layer 111, core 112, upper cladding layer 113) that constitute the planar lightwave circuit but is absorbed by the material that constitutes the thin film 103, only the thin film 103 will be heated even when the entire planar lightwave circuit 101 is irradiated with electromagnetic waves (microwaves). In this case, precise alignment is not required because the heated position is determined by the position of the thin film 103 formed on the planar lightwave circuit 101. However, because the heat generated in the thin film 103 by microwave heating is diffused throughout the entire planar lightwave circuit 101 by thermal diffusion, achieving localized heating requires a thin film 103 that is sufficiently small and capable of supplying the required amount of heat in a sufficiently short period of time.

[0026] The size and material of the thin film 103 can be determined as follows. Fusion splicing of the optical fiber and the planar lightwave circuit 101 can be performed by heating using arc discharge, similar to conventional techniques for fusion splicing optical fibers, and auxiliary heating using microwave heating with the thin film 103. When the planar lightwave circuit 101 and the optical fiber are fused together using arc discharge with the same output as conventional techniques for fusion splicing optical fibers without auxiliary heating, the temperature around the end face of the optical fiber rises to several thousand degrees Celsius and is sufficiently melted. In contrast, the temperature around the input / output terminal 151 of the planar lightwave circuit 101 only rises to several tens to several hundred degrees Celsius and is not sufficiently melted.

[0027] The temperature around the input / output terminals 151 of the planar lightwave circuit 101 during the above-described temperature increase (heating) is determined by the dimensions and material of the circuit. In the planar lightwave circuit 101 having the structure exemplified above, the temperature was only increased to about 100°C by a 2-second arc discharge heating process. Here, if the time for the arc discharge heating process were extended, it would be possible to further increase the temperature around the input / output terminals 151 of the planar lightwave circuit 101, but the optical fiber would melt excessively. For this reason, when arc discharge is performed under conditions similar to those for fusion splicing optical fibers, the discharge time (heating time) is limited to about 2 to 3 seconds.

[0028] Therefore, in this case, in order to bring the input / output terminal 151 of the planar lightwave circuit 101 into an appropriate molten state, it is necessary to apply a heat quantity of about 5 J to the input / output terminal 151 of the planar lightwave circuit 101 for about 2 to 3 seconds by auxiliary heating using the thin film 103. The heat quantity P (W / m) obtained by the thin film 103 per unit time per unit volume by dielectric heating due to microwave irradiation is 3 ) is expressed by the following formula (references):

[0029]

[0030] P is the amount of heat [W / m] obtained by the thin film 103 per unit time per unit volume. 3 ], f is the frequency of the microwave to be irradiated [Hz], ε" is the dielectric loss factor (relative permittivity x dielectric dissipation factor), and E is the electric field strength [V / m]. Based on equation (1.1), the volume of the thin film required to obtain approximately 5 J in 2 seconds can be expressed by the following equation.

[0031]

[0032] V is the volume of the thin film [m 3 ]. Here, the frequency selected was 2.45 GHz, which is in the ISM (Industrial Scientific and Medical) band and has relatively low absorption by silicon and quartz. The electric field strength was set to 200 kV / m, which can be achieved using a commercially available microwave generator. From equation (1.2), it can be seen that when the frequency and electric field strength are constants, the larger the dielectric loss factor, the smaller the required volume.

[0033] For example, AlGaN is used as the material for the thin film 103 in order to ensure the necessary amount of heat and to make the size of the thin film 103 sufficiently small. The dielectric loss factor of AlGaN is approximately 20 at a frequency of 2.45 GHz. Therefore, based on equation (1.2), the thin film 103 can have a flat plate-like structure with a thickness of 14 μm, a width of 900 μm, and a length in the light propagation direction of 900 μm. The thickness is determined by the microwave penetration depth, which is a value inherent to the material of the thin film 103, and the width and length can be determined from the relationship between the thickness and the volume of the thin film 103. By determining them in this way, a thin film 103 that is sufficiently small relative to the planar lightwave circuit 101 can be realized.

[0034] In the above description, the amount of heat compensated for by auxiliary heating using the thin film 103 was set to approximately 5 J. However, it is possible to further reduce the required amount of heat by changing the material of the substrate 110 of the planar lightwave circuit 101 to a material with lower thermal conductivity. For example, if the substrate 110 is made of pure SiO2, the required amount of heat can be reduced to several hundred mJ. In this case, if the microwave frequency is 2.45 GHz, the electric field strength is 200 kV / m, and the material of the thin film 103 is AlGaN, the shape of the thin film 103 can be further miniaturized to approximately 10 μm thick, 280 μm wide, and 280 μm long in the light propagation direction.

[0035] The material and dimensions of the substrate 110 and the thin film 103 can be changed depending on the application of the optical fiber module. In this way, the material and shape of the thin film 103 can be freely changed depending on the material and dimensions of the planar lightwave circuit 101.-12 fε”E 2 It is preferable that the relationship satisfy the following formula: x thickness T x width W x length L x number of heating seconds S ≥ heat deficit Q. More preferably, the width W and length L are 1 mm or less. Here, the heat deficit Q is set to 400 mJ.

[0036] Next, the arrangement of the thin film 103 will be described with reference to Fig. 1B. Fig. 1B (a) is a cross section perpendicular to the direction of light propagation at the location where the thin film 103 is formed. Fig. 1B (b) is a plan view of the location where the thin film 103 is formed, with the upper cladding layer 113 omitted.

[0037] The thin film 103 designed based on the formulas (1.1) and (1.2) is placed at a position sufficiently far away so as not to affect the light propagating through the core 112. Specifically, it can be placed 5 μm above the top surface of the core 112 in the thickness direction, and can be placed at a position 10 μm away from the input / output terminal 151 of the planar lightwave circuit 101 so as to enable auxiliary heating of the optical connection point.

[0038] Next, a method for fabricating an optical module according to an embodiment of the present invention will be described. First, a thoroughly cleaned substrate 110 with a thickness of 0.46 μm is prepared. In this example, a 6-inch silicon wafer is used as the substrate 110, but the substrate 110 may be of a different size. A layer of SiO2 glass particles is deposited on the substrate 110 using flame deposition, and a layer of germanium-doped SiO2 glass particles is deposited on top of this layer. The particle film is then made transparent by heating at 1000°C to 1300°C for approximately 2 to 4 hours. As a result, a lower cladding layer 111 is formed in the layer where only the SiO2 glass particles are deposited, and a core 112 is formed in the layer where the SiO2 glass particles and GeO2 glass particles are deposited (core-forming layer).

[0039] As exemplified above, the lower cladding layer 111 was fabricated to have a thickness of 20 μm, and the core forming layer serving as the core 112 was fabricated to have a thickness of 2 μm. The thicknesses of the lower cladding layer 111 and the core forming layer are generally determined according to the wavelength of light to be used and the core diameter of the optical fiber.

[0040] Next, a photoresist is applied onto the core-forming layer, and an optical waveguide pattern is formed by exposure and development (photolithography technology). Next, the core-forming layer is dry-etched using the formed optical waveguide pattern as a mask, and the resist residue is removed to form the ridge-shaped core 112.

[0041] Next, a cladding layer corresponding to a part of the upper cladding layer 113 is deposited on the lower cladding layer 111 including the core 112. As with the lower cladding layer 111 and the core 112, the cladding layer is deposited by flame deposition and transparent glass. For example, the cladding layer can be deposited to a thickness of 7 μm.

[0042] Next, an AlGaN layer is formed on the cladding layer. The AlGaN layer can be formed by depositing AlGaN using a sputtering method. For example, AlGaN is deposited on the cladding layer to a thickness of 14 μm to form the AlGaN layer. Next, the AlGaN layer is etched using a mask pattern formed by photolithography to form a thin film 103 having a width of 900 μm and a length of 900 μm in a planar view at a position 5 μm above the top surface of the core 112 in the thickness direction and 10 μm away from the input / output terminal 151 of the planar lightwave circuit 101. After forming the thin film 103 in this manner, the remaining cladding layer is deposited to a thickness of 13 μm using flame deposition and glass clarification to form the upper cladding layer 113.

[0043] Next, the planar lightwave circuit 101 formed up to the thin film 103 is cut by a dicing device. Thereafter, the input / output terminals 151 of the planar lightwave circuit 101 are polished to smooth the surfaces (end faces) of the input / output terminals 151.

[0044] Next, a connection method according to an embodiment of the present invention will be described with reference to Fig. 2. This connection method comprises a planar lightwave circuit 101 having an optical waveguide 102, and a thin film 103 formed near an input / output end 151 to which an optical fiber of the planar lightwave circuit 101 is optically connected, the thin film 103 generating heat when irradiated with electromagnetic waves, and is a method for optically connecting an optical fiber to the input / output end 151 of the planar lightwave circuit 101, the thin film 103 generating heat when irradiated with electromagnetic waves of a frequency that does not easily heat the planar lightwave circuit 101.

[0045] First, in a first step S101, the connection end of the optical fiber is brought into contact with the input / output end 151. Next, in a second step S102, the thin film 103 is irradiated with electromagnetic waves (e.g., microwaves) to generate heat, thereby fusing the input / output end 151 and the connection end of the optical fiber, thereby optically connecting the optical fiber to the input / output end 151.

[0046] In the second step S102, in addition to irradiating the thin film 103 with electromagnetic waves, the input / output terminal 151 and the connecting end of the optical fiber can be fused together by laser heating, thereby optically connecting the optical fiber to the input / output terminal 151.

[0047] In the second step S102, in addition to irradiating the thin film 103 with electromagnetic waves, the input / output terminal 151 and the connecting end of the optical fiber can be fused together by arc heating, thereby optically connecting the optical fiber to the input / output terminal 151.

[0048] The connection method will be described in detail below.

[0049] For example, the above-described multi-connection method can be implemented using the system illustrated in Fig. 3. This system includes a discharge device 201 using a pair of discharge electrodes, a microwave generator 202, a laser light source 203, a photodetector 204, and three three-axis stages 205a, 205b, and 205c.

[0050] The laser light source 203 is connected to a first optical fiber 206, which is connected to a second optical fiber 208 via a connector 207. The second optical fiber 208 is fixed to a three-axis stage 205a. The photodetector 204 is connected to a third optical fiber 209, which is fixed to a three-axis stage 205c.

[0051] The planar lightwave circuit 101 is disposed between the second optical fiber 208 and the third optical fiber 209, and is fixed to a three-axis stage 205b. The second optical fiber 208, which is directly fusion-spliced ​​to the planar lightwave circuit 101, is a glass optical fiber for visible light with a cladding diameter of 125 μm and a core diameter of 3 μm.

[0052] The discharge electrodes of the discharge device 201 are arranged to fuse the connection portion between the second optical fiber 208 and the planar lightwave circuit 101. The discharge electrodes are made of tungsten, and the distance between the two discharge electrodes is 1 mm. Between the two discharge electrodes, which are spaced 1 mm apart, a discharge occurs within an area with a diameter of 0.4 mm, centered on the axis of the discharge electrode. When the planar lightwave circuit 101 and the second optical fiber 208 are fused together, a discharge lasts for 2 seconds. Furthermore, a microwave generator 202 is arranged so that microwaves are irradiated onto the entire planar lightwave circuit 101.

[0053] The laser light source 203 is composed of a semiconductor laser with a wavelength of 445 nm. The laser light source 203 is used to align the planar lightwave circuit 101 and the second optical fiber 208. The output of the laser light source 203 is 1 mW, and the laser light output from the laser light source 203 is output from the first optical fiber 206. The output of the laser light source 203 is of a sufficiently weak intensity so as not to deteriorate the planar lightwave circuit 101. The wavelength of the laser light source 203 is not important, but visible light that can be seen with the naked eye is desirable because it is used for alignment.

[0054] The photodetector 204 is configured, for example, by a silicon photodiode capable of detecting a wavelength of 445 nm. The photodetector 204 is used to align the planar lightwave circuit 101 with the second optical fiber 208. Furthermore, by comparing the power detected by the photodetector 204 before and after fusion splicing, it is possible to evaluate the excess loss that occurred during splicing.

[0055] A magnetron capable of generating a frequency of 2.45 GHz was used as the microwave generator 202. The electric field strength was set to 200 kV / m, which can be achieved using a commercially available microwave generator 202.

[0056] The three-axis stages 205a, 205b, and 205c can be moved along three axes and have a resolution of 0.05 μm in the X, Y, and Z directions so that they can be used to align the planar lightwave circuit 101 and the second optical fiber 208.

[0057] Using the above-described system, first, the input / output end of the planar lightwave circuit 101 is brought into contact with (butted against) the connection end of the second optical fiber 208. First, the first optical fiber 206 and the second optical fiber 208 to be fused are connected with the connector 207, and the second optical fiber 208 is fixed to the three-axis stage 205a. The planar lightwave circuit 101 is fixed to the three-axis stage 205b so that the cores at the input / output ends of the planar lightwave circuit 101 face forward relative to (the connection end of) the second optical fiber 208.

[0058] A third optical fiber 209 is placed roughly close to the other input / output end of the planar lightwave circuit 101. The third optical fiber 209 is fixed to a three-axis stage 205c. The third optical fiber 209 fixed to the three-axis stage 205c is brought close to the planar lightwave circuit 101 in the light propagation direction. The other input / output end of the planar lightwave circuit 101 and the third optical fiber 209 are arranged so as to have a gap of 7 μm in the light propagation direction.

[0059] Next, the second optical fiber 208 is brought closer to the planar lightwave circuit 101 in the light propagation direction. At this time, the end face of the connecting end of the second optical fiber 208 and the end face of the input / output end of the planar lightwave circuit 101 are brought closer so that there is a gap of 7 μm in the light propagation direction. When aligning, the thin film 103 (not shown) formed on the planar lightwave circuit 101 serves as a guide, so that alignment can be visually confirmed to a certain extent.

[0060] The second optical fiber 208 is moved in a plane perpendicular to the light propagation direction to find the position where the optical power measured by the photodetector 204 is highest. The second optical fiber 208 is fixed at the position where the optical power measured by the photodetector 204 is highest. Similarly, the third optical fiber 209 is moved in a plane perpendicular to the light propagation direction to find the position where the optical power measured by the photodetector 204 is highest.

[0061] Next, the discharge device 201 is operated to discharge near the optical connection point between the second optical fiber 208 and the input / output end of the planar lightwave circuit 101 under the conditions of 1 second discharge and a discharge current value of 0.1 mA. This discharge serves to remove impurities present between the second optical fiber 208 and the planar lightwave circuit 101. After this, the distance between the second optical fiber 208 and the planar lightwave circuit 101 in the light propagation direction is set to 0 μm (they are in contact).

[0062] Next, the microwave generator 202 was operated to irradiate the entire second optical fiber 208 and the planar lightwave circuit 101 with microwaves at a frequency of 2.45 GHz for 2 seconds. At the same time, the discharge device 201 generated an arc discharge under conditions of a discharge current of 20 mA, a discharge voltage of 500 V, and a discharge time of 2 seconds. These current, voltage, and discharge time values ​​are those used in existing fiber fusion splicers. Simultaneously with the arc discharge, the second optical fiber 208 was pushed approximately 5 to 10 μm in the light propagation direction toward the planar lightwave circuit 101. This pushing was performed to prevent the splice from becoming thinner when melted by the discharge. As a result, a fusion splice in which both the planar lightwave circuit 101 and the second optical fiber 208 were melted was achieved.

[0063] The excess loss at the optical connection point between the planar lightwave circuit 101 and the second optical fiber 208 fusion-spliced ​​by the above-mentioned connection method was reduced by an average of 0.1 dB compared to a method that did not use preheating, and the tensile strength was improved by about 1.5 times. This shows that both the excess loss and tensile strength are superior to fusion splicing that does not use preheating using the thin film 103, and that the same levels of excess loss and tensile strength are obtained compared to heating that requires alignment of the heated area or heating that heats the entire fiber.

[0064] Furthermore, the maximum instantaneous temperature of the input / output end face on the side opposite to the input / output end where the second optical fiber 208 of the planar lightwave circuit 101 was optically connected was 200° C. or less, which was below the reflow temperature. As a result, damage to elements such as semiconductor lasers provided on the opposite input / output end face was prevented.

[0065] As described above, according to the present invention, a thin film that generates heat when irradiated with electromagnetic waves is provided, so that a planar lightwave circuit and an optical fiber can be fusion-spliced ​​without damaging other elements integrated in the planar lightwave circuit and without requiring precise alignment.

[0066] Fusion splicing between a planar lightwave circuit and an optical fiber requires, first, that precise alignment is not required. Second, it is necessary to heat a limited area around the optical connection point of the planar lightwave circuit to achieve localized heating. Furthermore, it is necessary to take into account the thermal diffusion that occurs during the heating process. Even if it is possible to heat only the area around the optical connection point, depending on the time it takes to heat up to the desired temperature, the entire planar lightwave circuit may be heated in a distributed manner due to thermal diffusion, potentially damaging other integrated elements. Therefore, to reduce the temperature of other elements integrated within the planar lightwave circuit, it is necessary to heat up the optical connection point to the desired temperature in a sufficiently short time, taking thermal diffusion into account. The above-mentioned problems can be solved by using a thin film that generates heat when irradiated with electromagnetic waves.

[0067] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0068] [Reference] X. Liao et al., "Dielectric properties and their application in microwave-assisted organic chemical reactions", McGill University, 2002.

[0069] 101...planar lightwave circuit, 102...optical waveguide, 103...thin film, 110...substrate, 111...lower clad layer, 112...core, 113...upper clad layer, 151...input / output terminal.

Claims

1. An optical module comprising: a planar lightwave circuit having an optical waveguide; and a thin film formed near an input / output terminal where an optical fiber of said planar lightwave circuit is optically connected, said thin film generating heat when irradiated with electromagnetic waves of a frequency that does not easily heat said planar lightwave circuit.

2. An optical module according to claim 1, wherein said thin film generates heat when irradiated with microwaves having a frequency that does not easily heat said planar lightwave circuit.

3. An optical module according to claim 1 or 2, wherein the planar lightwave circuit is made of a quartz-based material and silicon, and the thin film is made of AlGaN.

4. A connection method for optically connecting an optical fiber to an input / output end of an optical module, comprising a planar lightwave circuit having an optical waveguide and a thin film formed near an input / output end to which an optical fiber of the planar lightwave circuit is optically connected and which generates heat when irradiated with electromagnetic waves, the thin film generating heat when irradiated with electromagnetic waves of a frequency that does not easily heat the planar lightwave circuit, the connection method comprising: a first step of abutting the connecting end of the optical fiber to the input / output end; and a second step of irradiating the thin film with electromagnetic waves to generate heat, thereby fusing the input / output end and the connecting end of the optical fiber and optically connecting the optical fiber to the input / output end.

5. A connection method according to claim 4, wherein the second step involves irradiating the thin film with electromagnetic waves and optically connecting the optical fiber to the input / output end by fusing the input / output end and the connecting end of the optical fiber using laser heating.

6. A connection method according to claim 4, wherein the second step involves irradiating the thin film with electromagnetic waves and then fusing the input / output terminal and the connection terminal of the optical fiber by arc heating, thereby optically connecting the optical fiber to the input / output terminal.

7. A connection method according to any one of claims 4 to 6, wherein the second step involves irradiating the thin film with microwaves to generate heat.

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