Optical circuit device

Abstract

An optical circuit device according to the present disclosure comprises two or more optical circuit chips each having an optical waveguide. At least one optical circuit chip among the two or more optical circuit chips of the optical circuit device has an optical waveguide which is provided with an antireflective structure in the vicinity of a connection end face for connection to an optical circuit chip adjacent to that optical circuit chip. The antireflective structure has at least two refractive index boundary surfaces that reflect an optical signal propagating through the optical waveguide, in a direction opposite to the direction of travel of the optical signal. The antireflective structure is configured such that interference between reflection light from each of the refractive index boundary surfaces and reflection light from the connection end face is in a light-extinguishing interference state.

Description

Optical circuit device

[0001] The present disclosure relates to the structure of an optical circuit device, and particularly to an optical waveguide structure for reducing losses caused by reflection when an optical circuit chip having an optical waveguide is connected.

[0002] Due to the spread of data communication networks such as the Internet, the optical communication network is further advancing in terms of increased capacity. For the high functionality and high integration of optical devices used in such optical communication networks, research and development of integrated devices using combinations of different materials have been carried out.

[0003] For example, in Patent Document 1, a high-functional optical modulator that combines a silica-based planar optical waveguide made of silica glass, which is the same material as an optical fiber and suitable for a low-loss passive circuit configuration, and a lithium niobate waveguide utilized for high-speed optical modulation, that is, an example of a polarization multiplexed IQ modulator used in coherent optical communication is disclosed. Further, in Non-Patent Document 1, an example of an optical switch in which a silicon waveguide is included inside the same silica-based planar optical waveguide is shown.

[0004] Thus, heterogeneous material integrated functional devices that combine different materials are expected to further progress as a means to achieve functions and performances that were difficult to realize with only a single material. In a heterogeneous material integrated device, an optical signal input to the device is optically coupled and propagated from one material to a different material.

[0005] For example, in the example of Patent Document 1, an optical signal propagates from the silica-based planar optical waveguide to lithium niobate, and further from lithium niobate to the silica-based planar optical waveguide.

[0006] In the example of Non-Patent Document 1, an optical wave propagates from the silica-based planar optical waveguide to the silicon waveguide, and further from the silicon waveguide to the silica-based planar optical waveguide. Generally speaking, there are two main principles of optical coupling for the propagation of optical signals between different materials.

[0007] In other words, when comparing the optical coupling between waveguides of different materials in Patent Document 1 and Non-Patent Document 1, the former is a butt joint (end face coupling), while the latter is an adiabatic (adiabatic coupling). Furthermore, as a manufacturing form of a dissimilar material integrated functional device, Patent Document 1 is classified as hybrid packaging, while Non-Patent Document 2 is classified as heterogeneous packaging.

[0008] Hybrid packaging is a method of constructing a heterogeneous material integrated functional device by connecting multiple optical circuit chips, each equipped with a pre-fabricated optical waveguide made of a different material. Heterogeneous packaging involves loading thin films of different materials during or immediately after the fabrication of the host waveguide wafer, thereby manufacturing heterogeneous waveguides on the device using photolithography, dry etching, and other techniques, and constructing a heterogeneous material integrated functional device at the wafer level.

[0009] Hybrid packaging allows for the pre-evaluation of each individually fabricated optical circuit chip before mounting, offering advantages in terms of manufacturing yield and other aspects. However, as shown in Patent Document 1, hybrid packaging generally employs an optical coupling method using end-face coupling of optical waveguides.

[0010] When optical signals propagate between optical circuit chips equipped with optical waveguides of different materials, coupling losses occur due to factors such as mismatch in the mode diameters of the optical modes in the two waveguides, and Fresnel reflection caused by differences in the refractive indices of the materials.

[0011] Figure 1 is a schematic diagram of the configuration of the connection portion between optical circuit chips of an optical component disclosed in Patent Document 1. The optical component 100 includes an LN waveguide 111, a waveguide 112 of a first silica-based planar optical circuit connected to the LN waveguide 111 to be optically coupled, and a fiber alignment member 113 connected to the waveguide 112 of the first silica-based planar optical circuit to be optically coupled.

[0012] In the aforementioned end-face coupling, both losses due to mode mismatch and losses due to Fresnel reflection pose challenges. Fresnel reflection, in particular, generates not only losses but also reflected backlight, which is problematic for optical communication systems. Therefore, as shown in Figure 1, Patent Document 1 discloses a configuration in which the angle of the optical waveguides with respect to the connection end face of the optical waveguides between the optical waveguide 112 and the LN waveguide 111 of the first silica-based planar optical wave circuit is shifted from 90° to prevent the reflected backlight from coupling back to the original waveguide mode. While this layout of the optical waveguides can suppress reflected backlight, it does not improve the issue of Fresnel loss.

[0013] The loss due to reflected light can be calculated by the following formula (1) disclosed in Patent Document 1.

[0014]

[0015] Using equation (1), and assuming a refractive index of 1.45 for the quartz plane wave circuit and a refractive index of 2.28 for the LN waveguide, the loss R due to reflected light is calculated to be R = 5%, or 0.22 dB. Considering the two optical couplings from the quartz plane wave circuit to the LN waveguide and back to the quartz plane wave circuit, a Fresnel loss of 0.44 dB occurs.

[0016] Furthermore, when performing similar end-face coupling in a quartz-based planar optical circuit and a silicon waveguide, if we calculate the loss R due to reflected light assuming a refractive index of 3.5 for the silicon waveguide, we get R = 17%, or a Fresnel loss of 0.81 dB, at one end. Similarly, considering two optical couplings, a Fresnel loss of 1.6 dB may occur.

[0017] Furthermore, even when multiple optical circuit chips equipped with optical waveguides of the same material are end-face coupled, some degree of reflection loss may still occur.

[0018] Japanese Patent Publication No. 2012-037731

[0019] Kei Watanabe, Ryoichi Kasahara, and Yasuaki Hashizume, "Silicon-Quartz Hybrid Optical Switch," NTT Technical Journal, December 2009, pp. 24-27.

[0020] One of the objectives of this disclosure is to improve the Fresnel reflection loss that occurred when optical circuit chips having optical waveguides were end-face coupled, which is one of the problems of the prior art described above.

[0021] To achieve this objective, one embodiment of the present disclosure is an optical circuit device comprising two or more optical circuit chips having optical waveguides, wherein at least one of the two or more optical circuit chips has an optical waveguide including an anti-reflective structure near the connection end face with an adjacent optical circuit chip, the anti-reflective structure has at least two refractive index boundaries that reflect the optical signal in the opposite direction to the direction of propagation of the optical signal propagating through the optical waveguide, and is characterized in that the interference state is such that the reflected light from each refractive index boundary and the reflected light from the connection end face are extinguished. Another embodiment of the present disclosure is an optical circuit chip having an optical waveguide, wherein the optical waveguide includes an anti-reflective structure near the connection end face, the anti-reflective structure has at least two refractive index boundaries that reflect the optical signal in the opposite direction to the direction of propagation of the optical signal propagating through the optical waveguide, and is characterized in that the interference state is such that the reflected light from each refractive index boundary and the reflected light from the connection end face are extinguished.

[0022] This configuration makes it possible to provide an optical circuit device that improves upon the Fresnel reflection loss that occurred when optical circuit chips were end-face coupled.

[0023] Figure 1 is a schematic diagram of the connection structure of a conventional optical component. Figure 2 is a schematic diagram of the connection structure of an optical circuit device according to the first embodiment of this disclosure. Figure 3 is a simplified diagram showing the structure of an optical waveguide near the connection portion of an optical circuit device according to the second embodiment of this disclosure, viewed from above. Figure 4 is a schematic diagram showing two refractive index interfaces formed by a gap. Figure 5 shows the reflected light intensity and transmitted light intensity for a wavelength range commonly used in optical communication in the case of a 3-layer device. Figure 6 shows the reflected light intensity and transmitted light intensity for a wavelength range commonly used in optical communication in the case of a 5-layer device. Figure 7 is a schematic diagram of the connection structure of an optical circuit device according to the second embodiment of this disclosure.

[0024] Embodiments of this disclosure will be described in detail below with reference to the drawings. The following description is illustrative, and embodiments with modified configurations are possible without departing from the gist of this disclosure. Identical or similar reference numerals indicate identical or similar elements, and repeated descriptions may be omitted. Numerical values ​​in the following description are illustrative, and other numerical values ​​may be used in carrying out this disclosure without departing from the gist of this disclosure.

[0025] (First Embodiment) The first embodiment of the present disclosure is an optical circuit device comprising two or more optical circuit chips having optical waveguides. In this embodiment, at least one of the two or more optical circuit chips has an optical waveguide with an anti-reflection structure near the connection end face with an adjacent optical circuit chip. This anti-reflection structure has at least two refractive index boundaries that reflect the optical signal in the opposite direction to the direction of propagation of the optical signal propagating through the optical waveguide, and is configured such that the interference between the reflected light from each refractive index boundary and the reflected light from the connection end face is extinguished.

[0026] Figure 2 shows a schematic configuration of a connection structure when two optical circuit chips having optical waveguides are end-face coupled to form an optical circuit device, as one aspect of this embodiment. The optical circuit device 200 shown in Figure 2, as one aspect of the embodiment of this disclosure, is described in which the first optical circuit chip 201 includes a silicon waveguide and the second optical circuit chip 202 includes an optical waveguide made of quartz material.

[0027] However, in other embodiments, the first optical circuit chip 201 and the second optical circuit chip 202 may be optical circuit chips containing optical waveguides made of the same material, or they may be optical circuit chips containing optical waveguides made of different materials. Furthermore, in the case of optical circuit chips containing optical waveguides made of the same material, for example, optical circuit chips containing waveguides made of a silica-based material, the difference in the relative refractive index of the optical waveguides may be the same or different.

[0028] In the example shown in Figure 2, the optical waveguides that optically couple the first optical circuit chip 201 and the second optical circuit chip 202, which constitute the optical circuit device, are illustrated as single input / output waveguides, where an optical signal is input from one end face and output as output light from the other end face. However, there may be two or more waveguides. Furthermore, the optical circuit chips 201 and 202 may include other optical waveguides and optical functional elements that form optical circuits other than the optical waveguides that optically couple the optical circuit chips. In addition, although the optical waveguide with the anti-reflection structure of the first optical circuit chip 201 is formed extending from one end face to the other connecting end face, any optical waveguide that is positioned in contact with the connecting end face can be similarly applied.

[0029] In Figure 2, the first optical circuit chip 201, which includes a silicon waveguide, has a silicon optical waveguide covered with a quartz glass cladding. The silicon optical waveguide is positioned in contact with the connection end face 210. An anti-reflective structure 208 is positioned near the connection end face 210 of the silicon optical waveguide. This anti-reflective structure 208 includes a first gap 204 and a second gap 206 formed in the silicon optical waveguide.

[0030] Thus, the silicon optical waveguide consists of a first silicon straight waveguide 203 which is the input waveguide, a first gap 204, a second silicon straight waveguide 205, a second gap 206, and a third silicon straight waveguide 207.

[0031] Furthermore, the second optical circuit chip 202, which includes an optical waveguide made of quartz material, similarly has a quartz-based glass optical waveguide covered with quartz glass. A quartz-based glass optical waveguide is generally constructed by adding germanium dioxide, hafnium dioxide, or the like to quartz so that it has a higher refractive index than the quartz glass covering the quartz-based glass optical waveguide.

[0032] The silica-based glass optical waveguide consists of a silica-based linear waveguide 209. Furthermore, a resin 212, whose refractive index is matched to that of the silica-based glass optical waveguide, is filled between the connection end face 210 of the first optical circuit chip 201 and the connection end face 211 of the second optical circuit chip 202. The resin 212 may also be an optical adhesive used to fix the first optical waveguide chip 201 and the second optical circuit chip 202.

[0033] In this embodiment, an anti-reflective structure 208 is provided near the connection end face 210 of the silicon optical waveguide (a first silicon straight waveguide, a first gap, a second silicon straight waveguide, a second gap, and a third silicon straight waveguide) that is in contact with the connection end face 210 of the first optical waveguide chip 201.

[0034] Furthermore, the third silicon linear waveguide and the silica-based linear waveguide in contact with the connection end face 211 of the second optical circuit chip 202 are optically coupled via a resin 212 filled between the connection end face 210 and the connection end face 211.

[0035] The main point of this disclosure is to provide an anti-reflective structure, as shown in Figure 2, that has at least one gap forming two refractive index interfaces near the connection end face of an optical waveguide positioned in contact with the connection end face of at least one of a plurality of adjacent optical circuit chips. In this embodiment, a first gap 204 and a second gap 206 are provided. This embodiment describes the case where there are two gaps, but the anti-reflective structure of this disclosure may have at least one gap, i.e., two refractive index interfaces. Furthermore, an anti-reflective structure with even more gaps may be provided.

[0036] Figure 3 is a simplified diagram showing the structure of an optical waveguide near the connection point formed from the connection end face 210 of the first optical circuit chip 201, the connection end face 211 of the second optical circuit chip 202, and the resin 212, as viewed from above.

[0037] As described above, an antireflection structure 208 is disposed near the connection end face 210 of the optical waveguide disposed in contact with the connection end face 210 of the first optical circuit chip 201. This antireflection structure 208 is formed by creating a first gap 204 and a second gap 206 in the optical waveguide, and its structure consists of a first gap 204 filled with quartz (SiO2), a second silicon straight waveguide 205, a second gap 206 filled with quartz, and a third silicon straight waveguide 207.

[0038] Thus, the antireflection structure 208 includes a refractive index boundary surface 303 between the first silicon straight waveguide 203 and the first gap 204, a refractive index boundary surface 304 between the first gap 204 and the second silicon straight waveguide 205, a refractive index boundary surface 305 between the second silicon straight waveguide 205 and the second gap 206, and a refractive index boundary surface 306 between the second gap 206 and the third silicon straight waveguide 207.

[0039] In FIG. 3, the optical signal 301 input from the left of the figure propagates through the first silicon straight waveguide 203, the first gap 204 filled with quartz (SiO2), the second silicon straight waveguide 205, the second gap 206 filled with quartz, the third silicon straight waveguide 207, the resin 212, and the quartz-based straight waveguide 209.

[0040] In this propagation, since there is a difference in the equivalent refractive index at the boundary between the silicon waveguide and the gaps 204 and 206 formed in the silicon waveguide, reflection as shown in Equation (1) occurs at the boundaries 303, 304, 305, and 306 between the silicon straight waveguide and each gap. As a result of multiple interference at each refractive index boundary surface 303, 304, 305, and 306, reflection in the left direction of the figure and transmitted light in the right direction are provided.

[0041] FIG. 4 is a schematic diagram showing two refractive index boundary surfaces 401 and a refractive boundary surface 402 formed by one gap. The portion surrounded by the dotted line in FIG. 4 indicates the unit from the refractive index boundary surface 401 to the vicinity of the next refractive index boundary surface 402. However, the next refractive index boundary surface 402 is not included.

[0042] In FIG. 4, let the electric field of the optical signal input to the refractive index boundary surface 401 from the left direction be a1, the electric field of the optical signal reflected by the refractive index boundary surface 401 be b1, the incident electric field from the left direction to the refractive index boundary surface 402 be a2, and the electric field of the reflected light reflected by the refractive index boundary surface be b2. Also, let the reflectance at the refractive index boundary surface 401 and the refractive index boundary surface 402 be R, the amplitude transmittance at the refractive index boundary surface 401 be κ, the propagation constant (real number) from the refractive index boundary surface 401 to the refractive index boundary surface 402 be β, the amplitude transmittance from the refractive index boundary surface 401 to the refractive index boundary surface 402 be α, and the length from the refractive index boundary surface 401 to the refractive index boundary surface 402 be L. Then, the following equations (2) and (3) hold.

[0043]

[0044]

[0045] By arranging equations (2) and (3), the following equation (4) can be obtained.

[0046]

[0047] The 2×2 matrix in equation (4) is a scattering matrix. Let the number of each interface be n, and suffix R, α, β, and L. The scattering matrix before and after the nth interface can be expressed by the following equation (5).

[0048]

[0049] Then, the optical signal passing through multiple interfaces can be expressed as in the following equation (6).

[0050]

[0051] Therefore, the reflected light b1 and the transmitted light a output from the multi-stage interface structure can be obtained as follows. First, transform equation (6) into equations (7) and (8). n can be obtained as follows. First, transform equation (6) into equations (7) and (8).

[0052]

[0053]

[0054] Given a1 = 1 as the incident optical signal and setting the input light from the right side of the figure to zero, that is, a nIf we set = 0, then reflected light b1 and transmitted light a n These are given as equations (9) and (10), respectively.

[0055]

[0056]

[0057] Here, s 11 s 12 s 21 s 22 These are values ​​obtained from equations (5) and (6), respectively. Furthermore, it is preferable to use a propagation constant β between each refractive index boundary that takes into account the waveguide modes of light.

[0058] The following numerical examples demonstrate that by using the anti-reflective structure according to the embodiment, reflected light from the connection end face is suppressed, and the loss is improved.

[0059] First, in the case where there is only one gap (hereinafter referred to as the three-layer case), Figures 2 and 3 show the case where the second gap 206 filled with quartz and the third silicon straight waveguide 207 are omitted, and the second silicon straight waveguide 205 is in direct contact with the connection end face 210 (resin 212).

[0060] For the case where the anti-reflective structure has three layers, the lengths L of the first gap 204 and the second silicon straight waveguide 205 were determined by performing optimization calculations to minimize reflected light in the target wavelength range (1.5 to 1.65 μm in this example).

[0061] In the case of a three-layer system, reflected light is reflected in the opposite direction to the propagation direction of the optical signal from the refractive index interface 303 between the first silicon linear waveguide 203 and the first gap 204, and from the refractive index interface 304 between the first gap 204 and the second silicon linear waveguide 205 and the connecting end face 210, and the system is configured to create an interference state in which the interference of these reflected lights is extinguished.

[0062] Numerical examples of the lengths of each layer in this three-layer case are as follows: L (first gap 204) = 1.17 μm L (second silicon straight waveguide 205) = 0.54 μm

[0063] Figure 5 shows the reflected and transmitted light intensity for the wavelength range commonly used in optical communication, based on this numerical example. In Figure 5, the transmitted and reflected light intensity for a single-layer connection structure without an anti-reflective structure is also shown.

[0064] As shown in Figure 5, in the case of three layers, reflection loss is reduced in the range of 1.5 μm to 1.65 μm, and it can be seen that the loss when connecting multiple optical circuit chips with a butt joint is reduced.

[0065] However, in the case of a three-layer design, the wavelength range over which connection loss due to reflection can be reduced is not very wide. For example, if the optical signal uses one band from the C-band or L-band, it is fine, but if two bands are used, there is a risk that connection loss will not be sufficiently reduced in that range.

[0066] Next, as shown in Figures 2 and 3, we present a numerical example of an optimization calculation performed to minimize the loss in the wavelength range covering the C-band and L-band for an anti-reflective structure (referred to as the 5-layer case) that has a first gap 204 and a second gap 206 near the connection end face of an optical waveguide arranged in contact with the connection end face 210 of the first optical circuit chip 201.

[0067] Numerical examples of the lengths of each layer in this five-layer case are as follows: L (first gap 204) = 1.3 μm L (second silicon straight waveguide 205) = 0.43 μm L (second gap 206) = 1.18 μm L (third silicon straight waveguide 207) = 0.55 μm

[0068] Figure 6, based on this numerical example, shows the reflected and transmitted light intensities for the wavelength range commonly used in optical communication, similar to Figure 5. The transmitted and reflected light intensities for a connection structure without the structure of the present invention are also shown for the single-layer case. As shown in Figure 6, in the case of five layers, it can be seen that the reflection loss is reduced over a wider wavelength band than in the case of three layers, and the loss can be reduced to a negligible level in the range of 1.4 μm to 1.8 μm.

[0069] The anti-reflective structure of this disclosure has the advantage of being easily constructed by simply laying out a first gap 204 and a second gap 206 near the connection end face of the optical waveguide that is optically coupled with an adjacent optical chip when laying out the optical waveguide of the optical circuit chip. Therefore, there is no need to add any steps, such as when forming an anti-reflective film made of a dielectric multilayer film on the connection end face.

[0070] In the above example, an anti-reflective structure is provided only in the optical waveguide of the first optical circuit chip 201. This is because a larger reflectivity R can be achieved when the refractive index difference between the silicon forming the core layer and the quartz forming the cladding layer of the optical waveguide of the first optical waveguide chip is greater than the refractive index difference between the core layer and the cladding layer of the quartz waveguide on the second optical waveguide chip 102 side.

[0071] However, an anti-reflective structure may be provided near the connection end face 211 of the optical waveguide of the second optical circuit chip 202 that is connected. Alternatively, an anti-reflective structure may be provided on both the first optical circuit chip 201 and the second optical circuit chip 202 to prevent reflection by creating an interference state that extinguishes the interference of reflected light from the refractive index boundary surface formed across both optical waveguides.

[0072] In the first embodiment, the connection between a silicon waveguide and a quartz waveguide was described, but it is clear that the method is also applicable to the connection of other optical waveguides, such as a silicon waveguide to a semiconductor waveguide, or a silicon waveguide to a dielectric waveguide such as a lithium niobate waveguide. In such connections of dissimilar materials, a larger difference between the equivalent refractive index of the optical waveguide and the refractive index of the cladding layer is preferable because it allows for a larger reflectivity R, resulting in a significant effect.

[0073] Furthermore, although three-layer and five-layer structures have been described in this embodiment, the number of layers may be further increased depending on the refractive index difference between the material constituting the optical waveguide and the cladding layer material, and the wavelength range of the optical signal used.

[0074] Furthermore, although this embodiment shows the connection of two optical circuit chips 201 and 202, the anti-reflective structure of this disclosure can be applied to multiple connection portions of three or more optical circuit chips.

[0075] In this embodiment, it was stated that a larger difference between the equivalent refractive index of the optical waveguide and the refractive index of the cladding layer is effective because it allows for a larger reflectance R. Increasing the reflectance R leads to a reduction in the number of layers (i.e., the number of gaps) in the anti-reflective structure.

[0076] On the other hand, there are also advantages to forming the anti-reflective structure of this disclosure when the equivalent refractive index of the optical waveguide is small. When the equivalent refractive index of the optical waveguide is small, the lengths of both the gap and the straight waveguide become longer, so the anti-reflective structure can be formed with a high tolerance without requiring strict manufacturing tolerances.

[0077] (Second Embodiment) Figure 7 shows a schematic configuration of an optical circuit device 700 according to the second embodiment of the present disclosure. This embodiment is an application of the anti-reflection structure of the present disclosure to a connection structure described in the prior art above, which is configured to shift the angle with respect to the connection end face of the optical waveguide from 90° in order to suppress reflected light.

[0078] In the optical circuit device 700 according to the second embodiment, at the connection portion between the first optical circuit chip 701 and the second optical circuit chip 702, the optical waveguide of the first optical circuit chip 701 and the optical waveguide of the second optical circuit chip 702 are connected with respect to the connection end face at angles θ1 and θ2, respectively.

[0079] The first optical circuit chip 701 has a silicon optical waveguide covered with a quartz glass cladding. Similar to the first embodiment, the silicon optical waveguide has a first gap and a second gap located near the connection end face. Thus, the silicon optical waveguide consists of a first silicon straight waveguide 703 which is the input waveguide, a silicon bent waveguide 704, a second silicon straight waveguide 705, a first gap 706, a third silicon straight waveguide 707, a second gap 708, and a fourth silicon straight waveguide 709.

[0080] The optical waveguide, positioned in contact with the connection end face of the first optical circuit chip 701, is equipped with an anti-reflective structure near its connection end face, comprising a refractive index interface between the second silicon linear waveguide 705 and the first gap 706, a refractive index interface between the first gap 706 and the third silicon linear waveguide 707, a refractive index interface between the third silicon linear waveguide 707 and the second gap 708, and a refractive index interface between the second gap 708 and the fourth silicon linear waveguide 709.

[0081] The second optical circuit chip 702 similarly has a silica-based glass optical waveguide covered with silica glass. The silica-based glass optical waveguide is generally constructed by adding germanium dioxide or hafnium dioxide to silica to give it a higher refractive index than the silica glass covering the waveguide. The silica-based glass optical waveguide consists of a first silica-based straight waveguide 710, a silica-based curved waveguide 711, and a second silica-based straight waveguide 712. Furthermore, a resin 713, whose refractive index is matched to that of the silica-based glass optical waveguide, is filled between the first optical circuit chip 701 and the second optical circuit chip 702. The resin 713 may also be an optical adhesive for fixing the first optical circuit chip 701 and the second optical circuit chip 702.

[0082] As shown in Figure 6, the silicon optical waveguide and the silica-based glass optical waveguide are connected at the connection point to the connection end faces of the first optical circuit chip 701 and the second optical circuit chip 702 at angles θ1 and θ2, respectively.

[0083] Here, θ1 is determined so that the Fresnel reflected light at the connection end face does not couple as reflected light to the silicon optical waveguide of the first optical circuit chip 701. θ2 is determined by the following equation (11), taking into account the equivalent refractive index n1 of the silicon optical waveguide of the first optical circuit chip 701 and the equivalent refractive index n2 of the second optical circuit chip 702.

[0084]

[0085] In this embodiment, the anti-reflective structure positioned near the connection end face of the optical waveguide of the first optical circuit chip 701 reduces reflection loss in the same way as in the first embodiment. Furthermore, in this embodiment, even if there is reflected light that cannot be completely removed by the anti-reflective structure, it is prevented from such reflected light returning to the first optical circuit chip 701 as backlight.

[0086] In an optical circuit device comprising two or more optical circuit chips having optical waveguides, it is possible to provide an optical circuit device and optical circuit chips that improve the Fresnel reflection loss that occurred when the optical circuit chips were end-face coupled.

[0087] Optical circuit devices...200,700 First optical circuit chip...201,701 Second optical circuit chip...202,702 First silicon straight waveguide...203,703 First gap...204,706 Second silicon straight waveguide...205,705 Second gap...206,708 Third silicon straight waveguide...207,707 Anti-reflective structure...208 Quartz-based straight waveguide...209 Connection end face...210,211 Resin...212 Refractive index boundary face...303,304,305,306,401,402 Silicon bendable waveguide...704 Fourth silicon straight waveguide...709 First quartz-based straight waveguide...710 Quartz-based curved waveguide...711 Second quartz-based straight waveguide...712

Claims

1. An optical circuit device comprising two or more optical circuit chips having optical waveguides, wherein at least one of the two or more optical circuit chips has an optical waveguide including an anti-reflective structure near the connection end face with an adjacent optical circuit chip, and the anti-reflective structure has at least two refractive index boundary surfaces that reflect the optical signal in the opposite direction to the direction of propagation of the optical signal propagating through the optical waveguide, and is in an interference state in which the interference between the reflected light from each of the refractive index boundary surfaces and the reflected light from the connection end face is extinguished.

2. The optical circuit device according to claim 1, characterized in that the optical waveguide including the anti-reflective structure is formed on the adjacent optical circuit chip where the difference between the equivalent refractive index of the optical waveguide and the refractive index between the cladding is larger.

3. The optical circuit device according to claim 1, characterized in that the optical waveguide including the anti-reflective structure is formed on the adjacent optical circuit chip with the smaller equivalent refractive index of the optical waveguide.

4. An optical circuit chip having an optical waveguide, wherein the optical waveguide includes an anti-reflection structure near the connection end face, and the anti-reflection structure has at least two refractive index boundaries that reflect the optical signal in the opposite direction to the direction of propagation of the optical signal propagating through the optical waveguide, and the interference state is such that the reflected light from each of the refractive index boundaries and the reflected light from the connection end face are extinguished.

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