JP2008191695A - Method of manufacturing y branch waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a Y branch waveguide capable of reducing propagation loss while a light propagation mode is secured. <P>SOLUTION: This invention relates to a method of manufacturing a Y branch waveguide in which an in-branch light leak-preventing part 3 is formed in a prescribed region that is interposed between the outputting end cores 1a, 1b and that is near the inputting end core li, the in-branch light leak-preventing part comprising a photonic crystal having a refractive index periodic structure composed of a plurality of mediums of different refractive indexes. For manufacturing this Y branch waveguide, in a periodic structure forming process for forming the refractive index periodic structure, a prescribed region is formed by one kind of medium among a plurality of mediums. Then, the laser irradiation part is machined by convergently irradiating it with a pulsed laser having a pulse width that causes no heat damage around a laser irradiation part in the prescribed region, wherein an image forming optical system is utilized that is provided with a mask having a pattern similar to a machining shape corresponding to the refractive index periodic structure. By so machining the laser irradiation part, the refractive index thereof is adjusted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a Y-branch waveguide used in fields such as optical communication and optical information processing.

  2. Description of the Related Art Conventionally, a Y-branch waveguide in which a Y-shaped core composed of a linear input-side core and two linear output-side cores branched from the input-side core is provided in a cladding layer is known. Note that this type of Y-branch waveguide is designed with a core width dimension or the like so as to be a single mode waveguide, for example.

By the way, in this type of Y-branch waveguide, the branching angle (that is, the angle between the output side cores) is 1 ° or less in order to reduce the loss when the light propagating through the input side core branches to the output side core. Must be set to Here, in manufacturing such a Y-branch waveguide, for example, an impurity such as Ti is diffused into a core formation scheduled region in a substrate made of LiNbO ₃ to form a core having a refractive index higher than that of the cladding layer made of the substrate. Although it is formed, it is difficult to form a mask pattern in which the angle between the output cores is 1 ° or less, and the tip of the region (triangular region) sandwiched between the output cores There is a problem that the loss increases due to the shape of the (end on the input core side) being a rounded shape or a deformed shape. Further, although the waveguide mode is designed to be a single mode waveguide, a higher-order mode is generated and a propagation loss occurs.

Therefore, as shown in FIG. 10, the refractive index of the core 1 ′ is obtained at the tip of the region sandwiched between the output side cores 1 a ′ and 1 b ′ in the clad layer 2 ′ where the Y-shaped core 1 ′ is formed. There has been proposed a Y-branch waveguide in which a light propagation mode is improved by forming a tapered intermediate refractive index region 3 ′ having a refractive index intermediate to the refractive index of the cladding layer 2 ′ (for example, Patent Documents). 1).
JP-A-63-60405 (page 2, lower right column, line 7 to page 3, upper left column, line 11, line 1)

  By the way, in the Y branch waveguide, although it is desirable that the radius of curvature at the front end portion of the region sandwiched between the output side cores is desirably 0.5 μm or less, the Y branch waveguide is disclosed in Patent Document 1. In the Y-branch waveguide, the tip of the region sandwiched between the output-side cores 1a ′ and 1b ′ has a flat shape, so that light (leakage light) emitted to the outside of the core 1 ′ is sufficiently reduced. There was a bug that I could not do it.

  The present invention has been made in view of the above-described reasons, and an object of the present invention is to provide a method of manufacturing a Y-branch waveguide capable of reducing propagation loss while ensuring a light propagation mode.

  According to the first aspect of the present invention, a Y-shaped core comprising a linear input core and two linear output cores branched from the input core is provided in the cladding layer, and is interposed between the output cores. Photonic crystal having a refractive index periodic structure in which a guided mode of light of a specified wavelength propagating through each output side core is formed in a predetermined region near the input side core and is propagated through each output side core in a predetermined region near the input side core A method of manufacturing a Y-branch waveguide in which an intra-branch light leakage prevention portion is formed, wherein in the periodic structure forming step of forming the refractive index periodic structure, the predetermined region is defined as one of the plurality of media. A pulse laser having a pulse width that does not cause thermal damage to the periphery of the laser irradiation portion in the predetermined region after being formed of a kind of medium has a similar pattern portion having a similar shape to the processing shape corresponding to the refractive index periodic structure. Using the imaging optical system using a mask and adjusting the refractive index of the laser irradiated portion by processing the laser irradiation portion and irradiating light collecting.

  According to the present invention, it is possible to form the refractive index periodic structure in a non-contact manner in the predetermined region, and it is possible to prevent thermal damage from occurring around the laser irradiation portion, and the refractive index period The structure can be formed with high accuracy.

  Moreover, according to this invention, the said refractive index periodic structure can be formed collectively, and it becomes possible to improve mass-productivity.

  According to the first aspect of the present invention, it is possible to form the refractive index periodic structure in a non-contact manner in the predetermined region, and it is possible to prevent thermal damage from occurring around the laser irradiation portion, and the refractive index. There is an effect that the periodic structure can be formed with high accuracy.

(Embodiment 1)
As shown in FIG. 5, the Y-branch waveguide of this embodiment includes a linear input-side core 1i and two linear output-side cores 1a and 1b branched from the input-side core 1i in the cladding layer 2. A Y-shaped core 1 is provided.

  The clad layer 2 is composed of a lower clad layer 21 and an upper clad layer 22 laminated on one surface side of the lower clad layer 21. The lower cladding layer 21 and the upper cladding layer 22 are formed of a resin material having the same refractive index, and the core 1 is formed of a resin material having a higher refractive index than the lower cladding layer 21 and the upper cladding layer 22. As the resin material, for example, the refractive index of an acrylic resin, an epoxy resin, a Teflon (registered trademark) resin, an ABS resin, or the like may be appropriately adjusted and employed. In these resin materials, those containing a benzene ring or a sulfur-based material have a higher refractive index than those containing no benzene ring or sulfur-based material. It is possible to adjust the refractive index by mixing it with what is not.

  In the Y branch waveguide of this embodiment, each dimension (width dimension, thickness dimension) of the core 1 is designed so as to be a single mode waveguide satisfying the single mode waveguide condition. For example, when the refractive index of the core 1 is 1.506, the refractive index of the cladding layer 2 is 1.500, and the refractive index difference between the core 1 and the cladding layer 2 is 0.006, If the width and thickness dimensions of the output side cores 1a and 1b are set in the range of 6 μm to 10 μm, a single mode waveguide is formed.

  By the way, in the Y-branch waveguide of this embodiment, light having a wavelength propagating through each output-side core 1a, 1b is a region interposed between the output-side cores 1a, 1b and in a predetermined region near the input-side core 1i. An intra-branch light leakage prevention unit 3 made of a photonic crystal having a refractive index periodic structure in which no waveguide mode exists is formed. Here, the outer peripheral shape of the predetermined region in a plane orthogonal to the thickness direction of the core 1 (left-right direction in FIG. 5B) is an isosceles triangle whose apex angle is an angle formed by the output-side cores 1a and 1b. The angle θ between the output cores 1a and 1b is set to 1 ° or less (that is, set to not exceed 1 °).

  The photonic crystal constituting the intra-branch light leakage prevention unit 3 is formed of two types of media having different refractive indexes (hereinafter referred to as a first medium and a second medium for convenience of explanation). Here, the photonic crystal constituting the intra-branch light leakage prevention unit 3 is a two-dimensional photonic crystal, and the outer peripheral shape in the plane perpendicular to the thickness direction of the core 1 made of the first medium is an isosceles triangle. And a large number of columnar regions 3b made of a second medium and having a circular outer peripheral shape in a plane perpendicular to the thickness direction of the core 1. In the intra-branch light leakage prevention unit 3 in the present embodiment, the first medium that forms the base region 3a is formed of the same resin material as the core 1, but the first medium that forms the base region 3a is used as the first medium. The clad layer 2 may be formed of the same resin material, and in any case, it is desirable that the refractive index of the first medium be a value that is twice or more the refractive index of the second medium. Further, in the intra-branch light leakage prevention unit 3 in the present embodiment, a resin material is employed as the second medium, but in addition to the resin material, a semiconductor material such as GaN, GaAs, Si, or air is employed. Also good.

  By the way, if the light demultiplexed from the input-side core 1i to the output-side cores 1a and 1b is radiated to the region sandwiched between the output-side cores 1a and 1b in the cladding layer 2, there is a problem that propagation loss occurs, When a higher-order mode is generated as a wave mode, the optical path length varies depending on the mode and a shift occurs in transmission time. Therefore, the generation of a higher-order mode becomes a problem in a single mode waveguide.

  On the other hand, in the Y-branch waveguide of the present embodiment, the light demultiplexed from the input side core 1i to each of the output side cores 1a and 1b is emitted to the region between the output side cores 1a and 1b. Since it can be prevented by the intra-branch light leakage prevention unit 3 made of a photonic crystal, it is possible to reduce the propagation loss while ensuring the light propagation mode. In the Y-branch waveguide of the present embodiment, the angle θ between the output side cores 1a and 1b is set so as not to exceed 1 °, so that the input side core 1i is divided into the output side cores 1a and 1b. The propagation loss of the waved light can be reduced compared to the case where the angle θ is set to a value exceeding 1 °.

Here, in order to completely reflect and transmit the light having the specified wavelength propagating through the core 1 in the intra-branch light leakage prevention unit 3 described above, the number of periods of the refractive index periodic structure is at least 4 periods. The wavelength of the light propagating through the core 1 (specified wavelength) is λ, the angle between the output side cores 1a and 1b is θ, and the length of the refractive index periodic structure in the direction along the longitudinal direction of the input side core 1i. When the dimension is L, an imaginary isosceles triangle whose apex angle is the angle between the output side cores 1a and 1b (the point where the output side cores 1a and 1b intersect is the vertex and the output side cores 1a and 1b are Since the base length of the enclosed virtual isosceles triangle) needs to be 4λ or more,
L ≧ 2λ / tan (θ / 2)
L is set so as to satisfy the relationship. For example, when the angle θ is set to 1 ° and the specified wavelength λ is 1300 nm, L may be set to a value of 298 μm or more.

  Hereinafter, the manufacturing method of the Y-branch waveguide of the present embodiment will be described with reference to FIGS.

  First, by using a molding die in which a groove is formed in a region where the Y-shaped core formation scheduled region and the predetermined region are combined on one surface side of the lower cladding layer 21 made of the material of the cladding layer 2. By forming the clad layer 21, and then pouring the material of the core 1 into the groove formed in the lower clad layer 21 and filling the groove with the material of the core 1, the core material portion 11 is formed. The structure shown in FIG. 2A and FIG.

  Thereafter, by performing a periodic structure forming step of forming a refractive index periodic structure in a portion corresponding to the predetermined region in the core material portion 11, the intra-branch light leakage prevention unit 3 made of a photonic crystal is formed in the predetermined region. By forming the Y-shaped core 1 excluding the intra-branch light leakage prevention part 3 from the core material part 11, and subsequently laminating the upper clad layer 22 on the one surface side of the lower clad layer 21, The structure shown in 1 (b) and FIG. 2 (b) is obtained.

  As the above-described periodic structure forming step, for example, a method of forming a refractive index periodic structure by a mold transfer method or a method of forming a refractive index periodic structure by laser processing may be employed.

  In the mold transfer method, the resin may be molded using a mold having a concavo-convex shape according to the period of the refractive index periodic structure, but the aspect ratio of the concavo-convex shape formed on the mold according to the period of the refractive index periodic structure is large. If molding is difficult, a mold having a small aspect ratio may be manufactured and sequentially laminated in multiple stages. It is also possible to transfer by irradiating the predetermined area with a laser to soften the resin in the predetermined area and press the mold. It is also possible to simultaneously perform the process of irradiating the surface of the predetermined region through the mold with the laser to heat the predetermined region and the process of pressing the mold against the surface of the predetermined region. These two processes are performed simultaneously. This improves productivity. As the mold material, a material having a higher melting point and softening point than the material in the predetermined region may be employed. For example, quartz glass, sapphire, or the like may be employed. If the laser used in the mold transfer method has a wavelength that transmits the mold and that is absorbed by the resin, the above two processes can be performed simultaneously. When the refractive index periodic structure is formed by the mold transfer method as described above, there is an advantage that the throughput is increased and the mass productivity can be improved.

On the other hand, when a method of forming a refractive index periodic structure by laser processing is adopted, a portion corresponding to the cylindrical region in the predetermined region is removed or modified to change the refractive index of the cylindrical region. Compared with a method using a mold such as a mold transfer method, it is possible to form a refractive index periodic structure in a non-contact manner, so there is no contamination or deterioration of the surface due to mold contact and stable processing. Can be applied. Here, as a laser used in the periodic structure forming step, for example, a laser using a harmonic oscillation of a solid-state laser such as a SHG-YAG laser, a THG-YAG laser, or an FHG-YAG laser, a copper vapor laser, a HeCd laser, UV lasers such as KrF excimer laser, ArF excimer laser, and F ₂ laser can be used. Of these, lasers with shorter wavelengths can be processed more finely, and a refractive index periodic structure with a smaller period can be formed. It becomes possible. However, in the periodic structure forming step, it is desirable to perform processing using a pulse laser having a pulse width that does not cause thermal damage to the periphery of the laser irradiation portion, and a high-intensity ultrashort laser that oscillates with a pulse width of 1 ps or less. A pulse laser (so-called femtosecond laser) is suitable, and a Ti: sapphire laser or the like is known as the femtosecond laser. Here, when a high-intensity ultrashort pulse laser with a pulse width of 1 ps or less is condensed to a diameter of about 1 μm inside the predetermined region, a high energy density of TW / mm ² order can be secured. In energy density processing, multiphoton absorption occurs, light energy is converted into electron thermal energy, and a portion corresponding to the cylindrical region is locally heated in the predetermined region, thereby enabling processing. Even substances that are difficult to remove with energy can be removed by multiphoton absorption. In addition, when a laser beam is condensed, it is difficult to condense to a beam diameter less than the wavelength of the laser, and in general, processing with a size less than the wavelength of the laser beam cannot be performed, but multiphoton absorption is used. This makes it possible to perform processing that is less than the condensing diameter of the laser beam. That is, it is possible to process only a part having a beam size equal to or larger than the processing threshold due to multiphoton absorption. When the pulse width is as short as 1 ps or less, it is possible to perform processing while suppressing the thermal influence on the periphery of the laser irradiation portion. To explain further, in general, when removal processing is performed with a laser, it takes ns order time for heat to be transferred to the periphery of the laser irradiation portion, whereas in this embodiment, the laser irradiation is completed at 1 ps or less. Therefore, it is possible to prevent the occurrence of thermal damage around the laser irradiated portion.

  For example, when an acrylic resin is processed using a Ti: sapphire laser with a laser beam wavelength of 800 nm and a pulse width of 150 fs as the above-described pulse laser, the processing energy per pulse is about 2 to 15 μJ (processing energy is 2 (About 15 μJ / pulse), it is possible to process a cylindrical region having a diameter of approximately 1 μm and a length of approximately 16 μm (that is, forming a region having a circular shape in plan view and a diameter of 1 μm to a depth of 16 μm). can do). If the machining energy per pulse is 22 nJ, a circular region having a diameter of 0.5 μm or less can be machined. If conditions are set so that the processing energy is as described above and the laser beam is operated, groove processing is also possible. Moreover, even if it is resin other than acrylic resin, it is possible to obtain a target shape under substantially equivalent processing conditions.

  By the way, as described above, when laser processing is employed in the periodic structure forming step, if batch processing is performed, throughput is increased and mass productivity can be improved. In order to perform such batch processing, for example, as shown in FIG. 3, a mask 31 having a similar pattern portion 31a (see FIG. 4) having a similar shape to the target processing shape (processing shape corresponding to the refractive index periodic structure). Is used to separate the laser beam 8 having a relatively large beam diameter into a plurality of laser beams 8a, and the plurality of laser beams 8a are reflected by the mirror 32 and then reduced and imaged by the lens 33 to the workpiece A. What is necessary is just to transcribe | transfer (that is, it should just transcribe | transfer to the part corresponding to the said predetermined area | region in the said core material part 11). In short, an imaging optical system using the mask 31 having the similar pattern 31a having a similar shape to the target processing shape may be used. As shown in FIG. 4, the above-described mask 31 includes a similar pattern portion 31 a in which circular holes 31 b are formed in portions corresponding to the respective columnar regions 3 b in the photonic crystal constituting the in-branch light leakage prevention portion 3. Have. Here, when the reduction ratio is set to 1/10, the target shape can be formed if the mask 31 is formed with a dimension 10 times the target shape (target processed shape). Further, an imaging processing method using a phase shift mask may be employed. If the phase shift mask is used, the phase of the laser beam transmitted through the adjacent opening is shifted by 180 °, so that the diffraction image generated during fine imaging can be canceled by the adjacent laser beam, and the fine uneven shape It is possible to form a refractive index periodic structure with a small period.

  In addition, when laser processing is employed in the periodic structure forming step, the processing surface is irradiated in a lump if the surface processing by laser is performed instead of condensing and irradiating the laser beam. And productivity can be improved. For example, when a Ti: sapphire laser is used as the laser, a plurality of laser beams 9 branched as shown in FIG. Interference exposure processing for simultaneously irradiating a predetermined area) from a plurality of directions and causing the irradiation lights to interfere with each other may be performed. Here, the beam size of the branched laser beam 9 is made equal to the size of the processing target surface. In irradiation with two branches, striped processing with only one axis is possible, and processing with a hexagonal lattice shape with three branches and a tetragonal lattice shape with four branches is possible.

  According to the manufacturing method described above, it is possible to provide a Y-branch waveguide capable of reducing propagation loss while ensuring a light propagation mode. In the periodic structure formation process, when laser processing is performed, the laser irradiation part is focused and irradiated with a pulse laser having a pulse width that does not cause thermal damage to the periphery of the laser irradiation part, and the laser irradiation part is removed or modified for branching. If the refractive index periodic structure of the photonic crystal constituting the internal light leakage prevention unit 3 is formed, thermal damage or mechanical damage may occur around the laser irradiation portion with the formation of the refractive index periodic structure. The photonic crystal constituting the in-branch light leakage prevention unit 3 can be formed as designed without being generated.

(Embodiment 2)
Since the configuration of the Y-branch waveguide of this embodiment is the same as that of Embodiment 1 and only the manufacturing method is different, the manufacturing method will be described below with reference to FIGS.

  First, a defined region D set so as to overlap the planned region including the predetermined region from the Y-shaped core formation planned region on one surface side of the lower cladding layer 21 made of the material of the cladding layer 2; By forming the lower cladding layer 21 in a region excluding the overlapping portion using a molding die in which a groove 21a having a depth dimension set to match the thickness dimension of the core 1 is formed, FIG. The structure shown in FIG. 8A and FIG.

  Thereafter, by performing a periodic structure forming step of forming a photonic crystal 3 ′ having a refractive index periodic structure over the entire prescribed region D in the lower cladding layer 21, the structure shown in FIG. 7B and FIG. Get. The periodic structure forming step is the same as the periodic structure forming step described in the first embodiment.

  Subsequently, the remaining part of the photonic crystal 3 ′ is removed by removing a portion of the photonic crystal 3 ′ formed in the above-described defined region D that overlaps with the core formation scheduled region with a femtosecond laser having a pulse width of 1 ps or less. By forming the in-branch light leakage prevention portion 3 composed of a portion and making the above-described groove 21a a core groove 21b corresponding to the core formation scheduled region, the structure shown in FIGS. 7C and 8C is obtained. obtain. Note that, by using a femtosecond laser, it is possible to remove a minute region of 200 nm or less, and therefore the angle formed by the portion corresponding to the output side cores 1a and 1b in the core groove 21b is set to 1 °. However, the radius of curvature at the tip of the predetermined region sandwiched between the portions corresponding to the output-side cores 1a and 1b in the core groove 21b can be 0.5 μm or less.

  Next, the core 1 is formed by pouring and filling the core groove 21 b with the material of the core 1, and the upper clad layer 22 constituting the clad layer 2 is laminated on the lower clad layer 21 together with the lower clad layer 21. Thus, the structure shown in FIGS. 7D and 8D is obtained.

  Thus, according to the manufacturing method of the present embodiment, it is possible to provide a Y-branch waveguide that can reduce propagation loss while ensuring a light propagation mode. In the manufacturing method described above, when the refractive index periodic structure is formed, a large number of cylindrical regions are modified by a femtosecond laser. However, a large number of circular holes are formed by removal processing. When filling the core groove 21 with the material of the core 1, the material may be filled into the circular hole as the second medium.

(Embodiment 3)
The basic configuration of the Y-branch waveguide of this embodiment is substantially the same as that of Embodiment 1, and as shown in FIG. 9, a predetermined region (hereinafter referred to as a first predetermined region) interposed between the output-side cores 1a and 1b. The light having the specified wavelength is composed of a plurality of media having different refractive indexes in a region sandwiching a portion in the vicinity of the input side core 1i in each of the output side cores 1a and 1b. This is different in that the outside-branch light leakage prevention portions 4 and 4 made of a photonic crystal having a refractive index periodic structure in which no waveguide mode exists are formed. In addition, the same code | symbol is attached | subjected to the component similar to Embodiment 1, and description is abbreviate | omitted.

  The photonic crystal constituting each outside-branch light leakage prevention unit 4 is formed of a first medium and a second medium having different refractive indexes as in the photonic crystal constituting the inside-branch light leakage prevention unit 3. Yes. More specifically, the photonic crystal constituting each outside-branch light leakage prevention unit 4 is a two-dimensional photonic crystal, and includes a base region 4a made of a first medium and formed in a second predetermined region, The outer peripheral shape in the surface orthogonal to the thickness direction of the core 1 which consists of two mediums is comprised with many cylindrical area | regions 4b formed circularly.

  Thus, in the Y-branch waveguide of the present embodiment, the portion in the vicinity of the input-side core 1i in each of the output-side cores 1a and 1b is placed between the output-side cores 1a and 1b. Since the outside-branch light leakage prevention portions 4 and 4 to be sandwiched are formed, light loss can be further reduced as compared with the first embodiment. In manufacturing the Y-branch waveguide of the present embodiment, when the photonic crystal constituting the intra-branch light leakage prevention unit 3 is formed in the manufacturing method described in the first or second embodiment, the outside of the branch is formed. What is necessary is just to form the photonic crystal which comprises the light leak prevention parts 4 and 4. FIG.

  In each of the above embodiments, the in-branch light leakage prevention unit 3 is formed of two types of media. In the third embodiment, the outside-branch light leakage prevention unit 4 is formed of two types of media. The medium is not limited to the type of medium, and may be formed of a plurality of media. For example, the medium may be formed of three types of media.

FIG. 6 is a main process plan view for explaining the method for manufacturing the Y-branch waveguide of the first embodiment. It is principal process sectional drawing for demonstrating the manufacturing method same as the above. It is explanatory drawing of a manufacturing method same as the above. It is explanatory drawing of a manufacturing method same as the above. The Y branch waveguide same as the above is shown, (a) is a schematic plan view, (b) is a B-B 'sectional view of (a). It is explanatory drawing of a manufacturing method same as the above. It is a main process top view for demonstrating the manufacturing method of Embodiment 2. FIG. It is principal process sectional drawing for demonstrating the manufacturing method same as the above. 6 is a schematic plan view showing Embodiment 3. FIG. It is a schematic plan view which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core 1i Input side core 1a, 1b Output side core 2 Clad layer 3 Intrabranch light leakage prevention part 11 Core material part 21 Lower clad layer 22 Upper clad layer 31 Mask 31a Similar pattern part 32 Mirror 33 Lens

Claims (1)

  A Y-shaped core consisting of a linear input core and two linear output cores branched from the input core is provided in the cladding layer, and is an area interposed between the output cores and the input side Intra-branch light leakage prevention consisting of a photonic crystal with a periodic structure of refractive index that does not have a guided mode of light of specified wavelength propagating through each output-side core in a predetermined region near the core In the periodic structure forming step of forming the refractive index periodic structure, the predetermined region is formed by one type of the plurality of media. A pulse laser having a pulse width that does not cause thermal damage to the periphery of the laser irradiation portion in the predetermined region is bonded using a mask having a similar pattern portion having a processing shape corresponding to the refractive index periodic structure. The Y-branch waveguide manufacturing method, characterized by adjusting the refractive index of the laser irradiated portion by processing the laser irradiation portion and irradiating condensed light using an optical system.

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