JP2011022464A - Optical waveguide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform an optical coupling more efficiently by using an optical waveguide which transforms spot size. <P>SOLUTION: The optical waveguide is characterized in that a second core 103 is tapered toward the beginning end (on the side of waveguide region 111) of a spot size transformation region 112. Because the second core 103 is tapered toward the beginning end of the spot size transformation region 112, the reflection and the loss of guided light occurring at the boundary between the waveguide region 111 and the spot size transformation region 112 are reduced. As a result, the optical coupling is more efficiently performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical waveguide for optically coupling two integrated optical waveguide elements.

  Currently, quartz-based planar lightwave circuits (PLCs) are widely used as key components in optical communications. Until now, arrayed waveguide diffraction gratings, ROADMs (Reconfigurable Optical Add / Drop Multiplexers), splitters, and the like have been commercialized as main elements of quartz-based PLCs. In recent years, the development of new functional elements such as a wavelength tunable laser in which a semiconductor optical amplifying element (SOA) and a silica-based PLC are integrated has progressed, and a small, inexpensive and highly functional element in which an active element and a passive element are mixedly mounted. Attempts to realize the system are active.

However, with the rapid increase in the amount of information transmitted, high integration of key components is inevitable, and limits have been seen in quartz PLCs in terms of device dimensions and power consumption. In order to cope with this, silicon photonics that enables miniaturization and low power consumption has attracted attention. Silicon photonics refers to a silicon photonics that uses a waveguide having a high refractive index difference, in which a core is formed from Si and a cladding is formed from SiO ₂ . Since this optical waveguide can reduce the bending radius as compared with the silica-based waveguide, the PLC can be miniaturized. In addition, it can be integrated with electronic circuits, and can be used in the same manner as LSI, and has the advantages of low cost and high productivity. It has become.

  However, since silicon photonics has extremely low light emission efficiency due to the material properties of silicon, it is indispensable to integrate a compound semiconductor laser diode, optical amplifier, or the like when used as an optical functional device. An example of a form that has been attracting attention in recent years is monolithic integration in which a compound semiconductor element is bonded to a substrate on which a Si waveguide is formed. Non-Patent Document 1 reports that laser operation was confirmed by providing an optical gain by evanescent coupling of an AlGaInAs multiple quantum well and a Si waveguide.

  The guided mode profile in this configuration overlaps both the III-V medium and the Si waveguide. For this reason, the waveguide mode can obtain gain from the III-V region, and at the same time, it is guided by the Si waveguide region under the III-V region. The greatest advantage of this configuration is that the III-V region has symmetry in the lateral direction, and therefore high-precision alignment is not necessary when the III-V wafer is bonded to a pre-formed Si waveguide. That's what it means. However, the characteristics of this form do not reach those realized by a single III-V medium, and in fact, the characteristics reported so far are inferior to those of conventional elements.

  In contrast to the above-described technology, the form in which compound semiconductor chips are integrated in a hybrid manner with respect to an SOI wafer still retains its importance particularly in optical communication that requires high performance. In this integration, in addition to reducing the optical coupling loss by matching the waveguide mode spot sizes of the waveguides to be matched, it is important to introduce a structure for reducing reflection at the coupling portion. In particular, the reflection at the coupling portion when the hybrid integration is performed becomes a factor that destabilizes a desired operation such as inducing unnecessary laser oscillation. This is particularly noticeable when an external cavity laser including a compound semiconductor and an optical circuit is configured.

  Until now, in order to efficiently obtain optical coupling between a silicon waveguide and an optical fiber, for example, Patent Document 1 has proposed a structure using a waveguide with a core made of SiON having a refractive index lower than that of silicon. Yes. In this structure, by connecting the silicon waveguide to a waveguide such as SiON, the spot size of the guided light is enlarged, and the coupling efficiency with the optical fiber is improved.

JP 2004-133446 A

Alexander W. Fang et al., "Electrically pumped hybrid AlGzInAs-silicon evanescent laser", Optics Express, Vol.14, No.20, pp.9203-9210, 2006.

  However, in the waveguide having the above-described configuration, reflection occurs at locations and end surfaces where the core shape such as silicon or SiON changes discontinuously along the propagation direction of the guided light. This is because the refractive index distribution changes discontinuously along the propagation direction. In addition, when the spot size is matched with a compound semiconductor using the same waveguide structure, it is generally necessary to design the spot size smaller than that of the fiber. Therefore, the refractive index of the core made of SiON or the like needs to be higher than when used for optical coupling with a fiber. If the refractive index of SiON or the like connected to the silicon waveguide is increased, reflection at a location where the core shape changes discontinuously becomes more remarkable, leading to a decrease in optical coupling efficiency. In particular, the remarkable reflection in optical coupling is a problem because it causes an unstable operation of the integrated device.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to make it possible to perform optical coupling more efficiently by using an optical waveguide that converts a spot size.

  An optical waveguide according to the present invention includes a lower clad layer and an end before a light incident / exit end that is formed from a waveguide region on the lower clad layer to a spot size conversion region and that is the end of the spot size conversion region. A first core; a second core formed on the lower cladding layer so as to cover the first core in the spot size conversion region; and an upper part formed on the lower cladding layer so as to cover the first core and the second core. At least one cladding layer, wherein the first core is tapered toward one end in a region covered by the second core, and the second core is tapered toward the start end of the spot size conversion region. Is smaller than the first core and larger than the lower cladding layer and the upper cladding layer.

  An optical waveguide according to the present invention is formed from a lower cladding layer and a waveguide region above the lower cladding layer to a spot size conversion region, with a light incident / exit end serving as a termination of the spot size conversion region as one end. A first core; a second core formed on the lower cladding layer so as to cover the first core up to the light incident / exit end; and an upper cladding layer formed on the lower cladding layer so as to cover the second core. At least the first core is formed to taper from one end of the light incident / exit end to one end, and the second core includes a shape inclined region that gradually increases from the spot size conversion region to the waveguide region; Is smaller than the first core and larger than the lower cladding layer and the upper cladding layer.

  As described above, according to the present invention, it is possible to obtain an excellent effect that optical coupling can be performed more efficiently by using an optical waveguide that converts a spot size.

FIG. 3 is a plan view showing a configuration of an optical waveguide in the first embodiment. FIG. 3 is a cross-sectional view showing a cross section parallel to the waveguide direction of the optical waveguide in the first embodiment. It is a top view which shows the structure of the optical waveguide in this Embodiment 2. FIG. 6 is a cross-sectional view showing a cross section parallel to the waveguide direction of the optical waveguide in the second embodiment. It is sectional drawing which shows the cross section of the cc 'line | wire of FIG. 2A. It is sectional drawing which shows the cross section of the dd 'line | wire of FIG. 2A. It is a top view which shows the example of application of the optical waveguide in Embodiment 1 of this invention. FIG. 6 is a process diagram for explaining the manufacturing method of the optical waveguide in the first embodiment. FIG. 6 is a process diagram for explaining the manufacturing method of the optical waveguide in the first embodiment. FIG. 6 is a process diagram for explaining the manufacturing method of the optical waveguide in the first embodiment. FIG. 6 is a process diagram for explaining the manufacturing method of the optical waveguide in the first embodiment. It is sectional drawing which shows the example of application of the optical waveguide in Embodiment 1 of this invention. It is a top view which shows the structure of the optical waveguide in this Embodiment 2. 10 is a plan view illustrating an application example of an optical waveguide according to Embodiment 2. FIG. It is a top view which shows the example of application of the optical waveguide in this invention. It is a top view which shows the example of application of the optical waveguide in this invention. It is a top view which shows the example of application of the optical waveguide in this invention. It is sectional drawing which shows the example of application of the optical waveguide in this invention. It is sectional drawing which shows the example of application of the optical waveguide in this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
First, Embodiment 1 of the present invention will be described with reference to FIGS. 1A and 1B. FIG. 1A is a plan view showing a configuration of an optical waveguide according to the first embodiment. FIG. 1B is a cross-sectional view showing a cross section parallel to the waveguide direction of the optical waveguide according to the first exemplary embodiment.

  This optical waveguide is formed first from the lower cladding layer 101 and the waveguide region 111 on the lower cladding layer 101 to the spot size conversion region 112, and before the light incident / exit end 103a which is the end of the spot size conversion region 112. And a second core 103 formed on the lower cladding layer 101 so as to cover the first core 102 with a spot size conversion region 112. The first core 102 is formed to be tapered toward one end in a region covered with the second core 103. In addition, an upper clad layer 104 formed on the lower clad layer 101 so as to cover the first core 102 and the second core 103 is provided. In FIG. 1A, the upper cladding layer 104 is omitted.

  As the cross-sectional area of the tapered tip portion of the first core 102 decreases, confinement of the waveguide mode profile with respect to the first core 102 decreases (containment with respect to the second core 103 increases). The waveguide mode profile by becomes dominant. Therefore, by reducing the cross-sectional area of the tip portion of the first core 102 as much as possible, reflection and loss of guided light generated at the tip portion of the first core 102 can be reduced.

  In addition to the above-described configuration, the optical waveguide according to the present embodiment is characterized in that the second core 103 is tapered toward the start end of the spot size conversion region 112 (waveguide region 111 side). As described above, since the second core 103 is formed to be tapered toward the start end of the spot size conversion region 112, according to the present embodiment, the second core 103 is generated at the interface between the waveguide region 111 and the spot size conversion region 112. Therefore, reflection and loss of guided light can be further reduced. As a result, optical coupling can be performed more efficiently.

  Here, the refractive index of the second core 103 is smaller than that of the first core 102 and larger than that of the lower cladding layer 101 and the upper cladding layer 104. For example, the lower clad layer 101 and the upper clad layer 104 may be made of silicon oxide, the first core 102 may be made of silicon, and the second core 103 may be made of silicon oxynitride.

  In the above description, in the tapered region of the second core 103, the height in the normal direction of the plane of the lower cladding layer 101 does not change as shown in FIG. 1B, as shown in FIG. 1A. The planar shape is tapered, but the present invention is not limited to this. The height direction may be smaller as it is closer to the start end of the spot size conversion area 112. The second core 103 may be formed in a world where the cross-sectional area gradually decreases as the spot size conversion region 112 is closer to the start end. This also applies to the tapered shape on one end side of the first core 102.

[Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 2A is a plan view showing a configuration of an optical waveguide according to the second embodiment. FIG. 2B is a cross-sectional view showing a cross section parallel to the waveguide direction of the optical waveguide in the second embodiment. 2C shows a cross section taken along line cc ′ in FIG. 2A, and FIG. 2D shows a cross section taken along line dd ′ in FIG. 2A.

  The optical waveguide is first formed from the waveguide region 211 on the lower clad layer to the spot size conversion region 212, and has a first core having one end before the light incident / exit end 203a serving as the end of the spot size conversion region 212. 202 and the second core 203 formed on the lower cladding layer so as to cover the first core 202 with the spot size conversion region 212. The first core 202 is formed to be tapered toward one end in an area covered with the second core 203. In addition, an upper clad layer formed on the lower clad layer so as to cover the first core 202 and the second core 203 is provided. Other configurations including the lower clad layer and the upper clad layer are the same as those in the first embodiment, and the lower clad layer and the upper clad layer are omitted in FIGS. 2A to 2D.

  Also in the present embodiment, the second core 203 is formed to be tapered toward the start end of the spot size conversion region 212 (on the waveguide region 211 side). . The cross-sectional view of FIG. 2D shows a case where the width of the start end of the second core 203 is reduced, resulting in a smaller width than the first core 202. FIG. 2D shows a cross section taken along the line dd ′ of FIG. 2A, and the first core 202 shows this cross section, but the second core 203 does not become a cross section because it is the starting end. For this reason, in FIG. 2D, the surface of the start end is shown for the second core 203.

  As described above, the smaller the cross-sectional area of the start end of the second core 203, the stronger the confinement of the waveguide mode profile with respect to the first core 202, and the state in which the waveguide mode profile is dominantly determined by the first core 202. It becomes. As a result, also in the present embodiment, it is possible to reduce reflection and loss that occur at the start end of the second core 203.

  In addition, in the present embodiment, the first core 202 includes a shape inclined region 213 that is a waveguide region before the start end of the spot size conversion region 212 and gradually increases toward the start end. The change in which the cross-sectional area of the first core 202 increases is within a range in which the fundamental mode of light guided toward the start end is maintained. With this configuration, low-reflection and low-loss optical coupling can be performed, and optical coupling can be performed more efficiently.

  The influence of reflection at the start end is particularly noticeable when the first core 202 in the waveguide region 211 is made of a thin silicon wire having a cross-sectional shape of several hundreds of nanometers. This is because the light confinement factor of the waveguide mode profile in the silicon wire core is relatively small. On the other hand, as described above, if the cross-sectional area of the first core 202 is increased at the start end of the spot size conversion region 212, the waveguide mode profile is confined in the silicon core (first core 202). The coefficient can be increased. As a result, the influence of reflection at the start end can be further reduced.

  Further, in the present embodiment, the second core 203 includes the shape inclined region 214 whose diameter gradually changes toward the light emitting end before the light incident / exiting end 203a. FIG. 2A shows a case where the thickness gradually decreases toward the light emitting end. In a region in the middle of the spot size conversion region 212 before the shape inclined region 214, it is desirable to increase the cross-sectional area of the second core 203 within a range where the single mode condition of the guided light is satisfied. . By producing such a waveguide, reflection and loss at the tip of the first core 202 can be reduced.

  In addition, by gradually changing the cross-sectional area (diameter) of the second core 203 by the shape inclined region 214, an appropriate waveguide in a state where optical coupling with other optical elements can be performed with low loss at the light incident / exit end 203a. A mode profile can be obtained. For example, in the shape inclined region 214, it is conceivable that the cross-sectional area of the second core 203 is increased toward the emission end and optically coupled to another optical element within a range in which the fundamental mode is maintained.

  For example, as shown in the plan view of FIG. 3, a waveguide-type compound semiconductor optical device 301 is used for an optical circuit 220 in which an optical waveguide including a waveguide region 211 and a spot size conversion region 212 in this embodiment is formed. Can be combined. The compound semiconductor optical device 301 is, for example, a waveguide type semiconductor laser. The light emitting end 302 and the light incident / exiting end 203a of the compound semiconductor optical element 301 are optically coupled to face each other.

  In the example shown in FIG. 3, the waveguide directions of the waveguide region 211 and the spot size conversion region 212 are arranged so as to be inclined from the right angle with respect to the plane of the light incident / exit end 203a. Similarly, in the compound semiconductor optical device 301, the emission direction of the emission light (laser light) is arranged so as to be inclined from the right angle with respect to the plane of the light emission end 302. Further, a refractive index matching agent 303 is disposed between the light exit end 302 and the light entrance / exit end 203a to reduce light reflection at each end face.

  Here, if the refractive index of the second core 203 is basically designed in accordance with the refractive index of the refractive index matching agent 303, reflection at the end face can be reduced. On the other hand, in order to reduce reflection at the tapered tip of the first core 202, the higher the refractive index of the second core 203, the more relaxed. This is an effect obtained as a result that the refractive index difference between the first core 202 and the second core 203 is reduced, and confinement of the waveguide mode profile with respect to the first core 202 is reduced. In addition, since reflection at the start end of the second core 203 is reduced as the confinement of the waveguide mode profile to the first core 202 is increased, the refractive index of the second core 203 is designed to be about the same as that of the cladding, or The size of the first core 202 may be increased. Considering these, the waveguide structure and the refractive index of the second core 203 are designed.

  The results of measuring the intensity reflectance of the guided light at the tapered tip (interface) of the first core 202 will be described. In the prototype for evaluation measurement, SiON having a refractive index of 1.55 is used as the second core 203. The cross-sectional dimensions of the second core 203 at the tip of the first core 202 are a width of 1.5 μm and a height of 1.4 μm. For the intensity reflectance measurement, a reflectometer using a light source having a wavelength of 1.5 μm is used.

  As a result of the measurement described above, an intensity reflectance of 0.32% is confirmed when the size of the tapered tip portion of the first core 202 is set to a width of 161 nm and a height of 270 nm. In principle, reflection can be further reduced by further finely processing the tip of the first core 202. Here, at the tip of the first core 202, it is more important in reducing reflection to reduce the height in addition to the width. Therefore, it is more effective in reducing reflection (reduction in loss due to reflection) that the tip portion of the first core 202 has a tapered shape so that the height is reduced in addition to the width. Further, the first core 202 may be formed by processing a thinner semiconductor layer.

  Next, the manufacturing method will be briefly described with reference to FIGS. 4A, 4B, 4C, and 4D. The optical waveguide in the present embodiment can be formed by using, for example, an SOI (Silicon on Insulator) substrate. For example, a resist for electron beam exposure is applied to the surface silicon layer on the buried insulating layer of the SOI substrate, and exposure and development are performed to form a mask pattern. Using this mask pattern as a mask, the surface silicon layer is dry etched. If the used mask pattern is removed, a silicon pattern 402 is formed on the buried insulating layer 401 as shown in the plan view of FIG. 4A. The formed silicon pattern 402 has the same shape as the mask pattern described above. In the figure, the portion of the silicon pattern 402 is gray to clarify the distinction from other portions.

  By the way, when using what is called a positive resist, it irradiates with an electron beam other than the part left as a pattern. On the other hand, when a negative resist is used, an electron beam is irradiated to a portion to be left as a pattern.

  The silicon pattern 402 includes a core portion 402a serving as a core, a frame portion 402b surrounding the periphery, and a connecting portion 402c connected to the frame portion 402b. The tapered tip end portion of the core portion 402a is formed by being connected to the frame portion 402b by a connecting portion 402c. For this reason, for example, even if the pattern is very thin with a width of 100 nm, the mask pattern at this location can be prevented from flowing and disappearing during development, and the tapered tip can be stably formed.

  Next, as shown in the plan view of FIG. 4B, a resist pattern 403 is formed to cover the core portion 402a to be the first core 202 described above. In this state, if other surface silicon layers (such as the frame portion 402b and the coupling portion 402c) exposed on the buried insulating layer 401 are selectively removed by etching, as shown in the plan view of FIG. 4C, the buried silicon layer is buried. A core portion 402 a can be formed on the insulating layer 401. The buried insulating layer 401 becomes a lower cladding layer, and the core portion 402a becomes a first core. Next, for example, a silicon oxynitride film is formed by sputtering or the like, and this film is patterned by a lithography technique and an etching technique by electron beam exposure similar to those described above, and as shown in FIG. The core portion 404 is formed. Thereafter, if the upper cladding layer is formed by depositing silicon oxide, the optical waveguide in the present embodiment can be obtained.

  The optical waveguide in the present embodiment may be combined with the compound semiconductor optical device 301 as shown in the cross-sectional view of FIG. An optical waveguide 510 is formed on the base portion 501 of the SOI substrate, and the compound semiconductor optical device 301 is mounted in a region where the base portion 501 is exposed. The optical waveguide 510 includes a lower cladding layer 502, a first core 503, a second core 504, and an upper cladding layer 505. The lower cladding layer 502 is formed by patterning the buried insulating layer of the SOI substrate. Further, the first core 503 is formed by patterning the surface silicon layer of the SOI substrate. The mounting portion 521 on which the compound semiconductor optical device 301 is mounted may be aligned (positioned) after the mount stage is formed.

  For example, if an optical amplifying element is used as the compound semiconductor optical element 301 and the waveguide formed by the first core 503 of the optical waveguide 510 has a variable wavelength filter function, a wavelength tunable laser including an external resonator in the optical waveguide 510 and can do. In particular, if a ring resonator is formed in the waveguide composed of the first core 503 of the optical waveguide 510, the size can be reduced as compared with the silica-based waveguide. In addition, when the wavelength is adjusted using the thermo-optic effect in the ring resonator, the power consumption can be reduced due to the difference in the coefficient.

  Reflection at the optical coupling portion when these two elements are integrated is particularly important in ensuring stable wavelength tuning operation. By using the optical waveguide of the present invention, low reflection and low loss optical coupling can be obtained, and stable variable wavelength laser operation can be realized.

[Embodiment 3]
Next, Embodiment 3 of the present invention will be described with reference to FIGS. 6A and 6B. 6A and 6B are plan views showing the configuration of the optical waveguide according to the third embodiment.

  The optical waveguide according to the present embodiment is formed from the lower cladding layer 601 and the waveguide region 611 on the lower cladding layer 601 to the spot size conversion region 612, and the light incident / exit end 613 serving as the end of the spot size conversion region 612. Is provided with a first core 602. In addition, a second core 603 formed on the lower cladding layer 601 is provided so as to cover the first core 602 up to the light incident / exit end 613. Although not shown, an upper cladding layer is provided on the lower cladding layer 601 so as to cover the second core 603.

  In the optical waveguide according to the present embodiment, the first core 602 is tapered from the front side to the one side of the light incident / exit end 613. Further, the second core 603 includes a shape inclined region 614 that gradually increases from the spot size conversion region 612 to the waveguide region 611. The refractive index of the second core 603 is smaller than that of the first core 602 and larger than that of the lower cladding layer 601 and the upper cladding layer.

  For example, as shown in the plan view of FIG. 6B, a waveguide-type compound semiconductor optical device 301 is used for an optical circuit 620 in which an optical waveguide including a waveguide region 611 and a spot size conversion region 612 is formed. Can be combined. The light emitting end 302 and the light incident / exiting end 613 of the compound semiconductor optical device 301 face each other and are optically coupled.

  In the example shown in FIG. 6B, the waveguide directions of the waveguide region 611 and the spot size conversion region 612 are arranged so as to be inclined with respect to the plane of the light incident / exit end 613 from a right angle. Similarly, in the compound semiconductor optical device 301, the emission direction of the emitted light is arranged so as to be inclined from the right angle with respect to the plane of the light emission end 302. Further, a refractive index matching agent 303 is disposed between the light emitting end 302 and the light incident / exiting end 613 to reduce the reflection of light at each end face.

  According to the optical waveguide in the present embodiment, since the entire area of the first core 602 is covered with the second core 603, there is no discontinuous change in the waveguide structure along the propagation direction of the guided light. For this reason, reflection and loss due to the presence of discontinuous portions can be suppressed. Further, by changing the cross-sectional area of the second core 603 by the shape inclined region 614, the light incident / exit end 613 can be appropriately coupled with the compound semiconductor optical element 301 (the light exit end 302) with low loss. A cross-sectional size is prepared so that a proper waveguide mode profile can be obtained. Further, if the change in cross-sectional dimension in the shape change region 614 is changed with a sufficient length along the propagation direction of the guided light, reflection and loss can be reduced.

  Next, application examples of the optical waveguide of the present invention will be described. 7A and 7B are plan views showing an example in which a Mach-Zehnder interferometer is configured by combining a semiconductor optical amplification element 702 with an optical waveguide 701 of the present invention. FIG. 7A shows a configuration when used as a wavelength conversion duplexer, and FIG. 7B shows a configuration when used as a time division multiplexing duplexer. In any configuration, two semiconductor optical amplifying elements 702, four sets of waveguide regions 111 and spot size conversion regions 112 are provided. Further, two light input / output portions of the semiconductor optical amplifying element 702 are optically coupled at the light incident / exit ends of the spot size conversion region 112 constituting the optical waveguide 701. Further, a coupler in which a part of the waveguide region 111 is provided on each side via the semiconductor optical amplification element 702 is provided.

  As shown in FIG. 7A, when a wavelength conversion demultiplexer is used, signals of two wavelengths are respectively input from different ports, and almost all the power of the pulse signal light is converted into Mach by a coupler on the input side.・ Design to move to one side of the Zender interferometer. In this design, signal light of another wavelength, which is continuous wave light, is equally distributed to both sides of the interferometer, so that pulse signal light that has been wavelength-converted through cross-phase modulation can be obtained.

  As shown in FIG. 7B, when a time division multiplexing duplexer is used, a clock signal is input from one port and is equally distributed to both sides of the Mach-Zehnder interferometer. From the difference in the arrangement of the two semiconductor optical amplifying elements 702, the timing of applying phase modulation in each semiconductor optical amplifying element 702 can be controlled by, for example, a difference of several picoseconds. can do.

  According to the Mach-Zehnder interferometer configured as described above, for example, by using a silicon waveguide, the interferometer can be made smaller than that formed by a silica-based waveguide, so that it has a larger scale and other functions. Monolithic integration with an optical circuit becomes possible. Further, according to the optical waveguide of the present invention, since reflection at the optical connection portion with the semiconductor optical amplifier 702 can be reduced, unnecessary laser oscillation and noise can be reduced.

  Next, another application example of the optical waveguide of the present invention will be described. FIG. 8 is a configuration diagram showing a configuration of an optical add / drop multiplexer (OADM) in which a plurality of optical waveguides are used and a wavelength multiplexer / demultiplexer 821 using a silica-based waveguide is combined therewith. The OADM includes two wavelength multiplexers / demultiplexers 821 and an optical circuit 801 disposed therebetween.

  The optical circuit 801 includes an optical waveguide 811 formed corresponding to each port of the wavelength multiplexer / demultiplexer 821. The optical waveguide 811 is the above-described optical waveguide of the present invention, and includes spot size conversion regions 812 at both ends thereof. In the optical waveguide 811, a waveguide type optical switch element 814 is formed in a waveguide region 813 between the two spot size conversion regions 812. For example, after all wavelength channels are demultiplexed by one wavelength multiplexer / demultiplexer 821, a specific signal light can be added, extracted or passed by the optical switch element 814, and then the entire optical signal is The other wavelength multiplexer / demultiplexer 821 multiplexes.

  In this case, as shown in the cross-sectional view of FIG. 9A, the optical circuit 801 may be mounted on the circuit board mounting region 822 of the substrate 820 on which the wavelength multiplexer / demultiplexer 821 is formed. In FIG. 9A, an optical circuit 801 mainly shows a spot size conversion region 812. A lower cladding layer 902, a first core 903, a second core 904, and an upper cladding are formed on the base 901 of the SOI substrate. Layer 905 is provided. 9B, the optical circuit 801 may be mounted on the circuit board mounting region 822 so that the base 901 side is directed upward and the upper clad layer 905 side is fixed.

  By using the wavelength multiplexer / demultiplexer 821 using a quartz-based waveguide, it is possible to use characteristics excellent in polarization dependence, crosstalk between wavelength channels, and the like. On the other hand, by using the optical waveguide 811 and the optical switch element 814 using silicon waveguides, a large-scale optical switch can be manufactured in a small size. Further, if the optical switch element 814 is a switch based on a thermo-optic effect, there is an advantage that power consumption can be reduced due to a difference in coefficient from a quartz material.

  In addition to these, by integrating a functional polymer waveguide element having an electro-optic effect and a ferroelectric element such as lithium niobate and an optical circuit using a silicon waveguide, each characteristic is utilized. A highly functional optical circuit element can be configured. By using the present invention, it is possible to reduce reflection and loss (optical coupling loss) at the optical coupling portion of different types of waveguides, and contribute to high performance for any application.

  For example, in the above description, the first core is made of silicon, but is not limited thereto. For example, germanium may be composed of a semiconductor material such as silicon germanium. The clad layer (upper clad layer) is not limited to silicon oxide, and may be composed of silicon oxynitride, silicon nitride, or a polymer medium (polymer material). The same applies to the second core. The second core may be made of a material having a refractive index smaller than that of the first core and larger than that of the lower cladding layer and the upper cladding layer.

  DESCRIPTION OF SYMBOLS 101 ... Lower clad layer, 102 ... 1st core, 103 ... 2nd core, 103a ... Light entrance / exit end, 104 ... Upper clad layer, 111 ... Waveguide area | region, 112 ... Spot size conversion area | region.

Claims (4)

A lower cladding layer;
A first core that is formed from the waveguide region on the lower cladding layer to the spot size conversion region and has one end before the light incident / exit end that is the end of the spot size conversion region;
A second core formed on the lower cladding layer so as to cover the first core in the spot size conversion region;
An upper clad layer formed on the lower clad layer so as to cover the first core and the second core;
The first core is formed to be tapered toward the one end in a region covered with the second core,
The second core is formed to be tapered toward the start end of the spot size conversion region,
The refractive index of the second core is smaller than that of the first core and larger than that of the lower cladding layer and the upper cladding layer. The optical waveguide according to claim 1,
The first core includes a shape inclined region that gradually increases in thickness toward the start end in a range in which a fundamental mode of guided light is maintained in the waveguide region before the start end. Optical waveguide. The optical waveguide according to claim 1 or 2,
The optical waveguide, wherein the second core includes a shape inclined region whose diameter gradually changes toward the light incident / exit end before the light incident / exit end. A lower cladding layer;
A first core that is formed from a waveguide region on the lower cladding layer to a spot size conversion region, and has a light incident / exit end serving as a terminal end of the spot size conversion region;
A second core formed on the lower clad layer covering the first core to the light incident / exiting end;
An upper clad layer formed on the lower clad layer so as to cover the second core, and
The first core is formed to be tapered from the front of the light incident / exit end to the one end,
The second core includes a shape inclined region that gradually increases from the spot size conversion region to the waveguide region,
The refractive index of the second core is smaller than that of the first core and larger than that of the lower cladding layer and the upper cladding layer.