JP2010266541A - Optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element having stable coupling efficiency by reducing generation of variance of coupling efficiency with an outside optical element, even in the occurrence of variance in the cutting position of the optical element. <P>SOLUTION: The optical element 1 has a spot size conversion optical waveguide part in the upper part of a substrate 2. The element is characterized in that the spot size conversion optical waveguide part is provided with at least a first region B and a second region C which are adjacent to each other, wherein the first region B is situated inside the element in a light propagation direction and provided with a first core 6 and a clad 3B, and wherein the second region C is situated on the tip end side of the element in the light propagation direction and provided with a second core 21. The first core 6 has an inverse tapered shape in which the width in the direction nearly in parallel with the bottom face of the substrate 2 diminishes toward the second region C. Also, the second core 21 has a height lower than the sum of the heights of the first core 6 and the clad 3B, in a direction nearly vertical to the bottom face of the substrate 2, in the joining face between the first region B and the second region C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical element that is used for optical communication or the like and has a spot size conversion optical waveguide portion.

In recent years, an increase in information processing speed accompanying an increase in the amount of content transmitted in optical communication has further increased the need for high-speed optical information processing technology. Accordingly, an optical element that responds at high speed is required. ing. By the way, when the optical waveguide in the optical element has a plurality of transverse modes, the time width of the optical pulse traveling in the optical waveguide is widened due to the difference in propagation speed for each mode. As a result, the front and rear light pulses overlap on the time axis, causing crosstalk.
Accordingly, an optical element used in high-speed optical communication is configured to include a single mode optical waveguide having only one transverse mode.

By the way, in the optical element, a material having a high refractive index such as silicon is often used, and the mode field of the single mode optical waveguide included in the optical element is generally very small. For example, in the case of the wavelength dispersion correction element described in Patent Document 1, the cross-sectional area of the optical waveguide is about 0.5 μm × 1.0 μm. On the other hand, in the single mode optical fiber, the cross-sectional area of the core is about 64 μm ² (= 4.5 × 4.5 × π).
That is, the mode field of the single-mode optical waveguide of the optical element is about 1/128 of the cross-sectional area of the core of the optical fiber. For this reason, when the optical fiber and the single mode optical waveguide of the optical element are simply coupled, the optical energy is greatly attenuated at the coupled portion. Therefore, increasing the efficiency of optical coupling between the optical fiber and the single mode optical waveguide of the optical element leads to a reduction in the loss of the entire optical communication system including a plurality of optical elements, which is an important issue.

To deal with such a problem, for example, Patent Document 2 discloses a high-refractive-index light transmission unit made of SiN whose tip portion has an inversely tapered shape and a low-refractive-index light made of SiON surrounding the high-refractive index light transmission unit. A technique relating to an optical transmission line that effectively takes in light from an optical fiber by a coupling unit having a transmission unit is disclosed.
With such a structure, light taken from an optical fiber or the like can be converted from a large mode field in the optical fiber to a small mode field in a waveguide made of SiN having a high refractive index along the propagation direction. The optical coupling between the single mode optical waveguide of the optical element and the optical fiber can be reduced in loss.

Further, Patent Document 3 discloses a structure in which the width of the core is narrowed toward the tip of the element, the thickness is thinned, and the clad is widened toward the tip of the element.
Further, Patent Document 4 includes a first optical waveguide, a mode field size conversion unit, and a second optical waveguide, and an overclad layer of the first optical waveguide, a mode field size conversion unit, and a second optical waveguide. The core material is simultaneously formed, and the overcladding layer and the core are simultaneously manufactured. When the core is manufactured, the core material is removed by using two regions symmetrical to the light traveling direction of the core as etching regions. In other regions, a structure is disclosed in which the core material is left uncut.

Japanese Patent No. 3917170 JP 2007-047694 A JP-A-6-67043 JP 2004-184986 A

  In the manufacturing process, an optical element having a spot size conversion optical waveguide section is cut at an appropriate position, and the cut surface is used as an end face connected to an external optical element. At this time, the position for cutting the optical element inevitably varies in manufacturing due to the accuracy of the equipment to be cut. As a result, for each of the following reasons, there is a problem in that the variation in the cutting position causes the variation in coupling efficiency with an external optical element.

In the structure described in Patent Document 2, when the end face is cut at the time of manufacture, the cross-sectional structure differs depending on the cutting position if the element inner side is cut from the reverse taper portion. Even considering a structure in which a low-refractive index waveguide made of a clad material of an inversely tapered portion continues, a high-order mode is excited at this boundary, and the mode field changes with respect to the light propagation direction due to the interference. Therefore, in any case, variations in coupling efficiency occur due to variations in the cutting position.
In the structure described in Patent Document 3, since the structure continuously changes toward the tip of the element, the cross-sectional structure changes depending on the cutting position, and the coupling efficiency changes.
In the structure described in Patent Document 4, high-precision processing is required at the tip of the reverse taper, and due to variations during manufacturing, at the boundary between the reverse taper structure (element region) and the first region, Higher-order modes are excited, and the interference causes a change in the mode field shape with respect to the light propagation direction. Therefore, even in the structure described in Patent Document 4, variations in coupling efficiency occur due to variations in the cutting position.

  The present invention has been made in view of the above-described problems, and even when variations occur in the cutting positions of optical elements, it is possible to reduce the occurrence of variations in coupling efficiency with external optical elements, and to stabilize An object of the present invention is to provide an optical element having a reasonable coupling efficiency.

The optical element of the present invention is an optical element having a spot size conversion optical waveguide part above the substrate, and the spot size conversion optical waveguide part has at least a first region and a second region adjacent to each other, The first region is located on the inner side of the element in the light propagation direction, and has a first core and a cladding, and the second region is located on the element tip side in the light propagation direction, The first core has an inversely tapered shape in which a width in a direction substantially parallel to the bottom surface of the substrate decreases toward the second region; The core has a height lower than the total height of the first core and the clad in the first region in a direction substantially perpendicular to the bottom surface of the substrate at the connection surface between the first region and the second region. It is characterized by having.
In the optical element of the present invention, it is preferable that the second core is made of the same material as the cladding of the first region.
In the optical element of the present invention, the second core is preferably made of a material different from that of the first core and the clad in the first region.
In the optical element of the present invention, it is preferable that the second core has a portion formed such that a width in a direction substantially parallel to the bottom surface of the substrate is widened toward the tip of the element.
In the optical element of the present invention, the first region further includes a third core and a fourth core, and the third core is made of a material having a higher refractive index than the first core, The cross-sectional area in a direction substantially perpendicular to the light propagation direction is formed so as to continuously decrease toward the tip direction of the element, and the fourth core has a direction substantially perpendicular to the light propagation direction. The first core or the fourth core is formed so as to be continuous with the first core so that the cross-sectional area is constant, and the first core or the fourth core is stacked above the substrate with respect to the third core. It is preferable.

According to the present invention, the light propagates in the second region with a mode field that is less changed with respect to the traveling direction of the light, and is thus connected to the outside of the second region in the light propagation direction. The occurrence of variation in coupling efficiency with the optical element can be reduced, and an optical element having stable coupling efficiency can be provided.
In addition, since light propagates in the second region with a mode field that has little change with respect to the traveling direction of the light, it is assumed that the second region is cut and used when the optical element is manufactured. Even when the cutting position varies before and after the light propagation direction, it is possible to reduce the occurrence of variation in coupling efficiency with the connected optical element, and to provide an optical element having stable coupling efficiency. Can be provided.

In the present invention, the material of the second core is the same as the cladding of the first region, or the material of the second core is different from the first core and the cladding of the first region. Thus, it is possible to provide an optical element that is more efficiently coupled to an external optical element.
In the present invention, the second core has a portion formed such that the width in a direction substantially parallel to the bottom surface of the substrate is widened toward the tip of the element, so that the spot size of the external optical element and the present invention are increased. It is possible to match the spot sizes of the optical elements, and in that case, it is possible to provide an optical element that is coupled to an external optical element with higher efficiency.

  In the present invention, since the first region further includes a third core and a fourth core, the height in the vertical direction of the second core, the third core, The vertical height of the core composed of the four cores can be changed individually, and the effective refractive index change in each core is moderated, and it can be coupled to external optical elements more efficiently. Will be able to. In addition, by using different materials for the third core, the fourth core, and the second core, the change in the effective refractive index between these cores is further moderated, and the external optics can be made more efficient. An optical element that can be coupled to the element can be provided.

It is explanatory drawing which shows 1st embodiment of the optical element which concerns on this invention. It is sectional drawing of the single mode waveguide part of the area | region of the element in the optical element of the embodiment. FIG. 3A is a partially enlarged view of the optical element according to the embodiment, FIG. 3A is a cross-sectional view of the element region and the first region of the optical element shown in FIG. 1, and FIG. 3B is FIG. 2 is a cross-sectional view of the zy plane of the element region and the first region in the central portion of the high refractive index optical transmission unit of the optical element shown in FIG. FIG. 4 is a cross-sectional view of a boundary surface between a beam focusing part D and a beam focusing part E in FIG. 3. It is sectional drawing in the single mode waveguide part of FIG. It is sectional drawing shown including the ridge part, slab part, and trench part of the optical element of the embodiment. It is sectional drawing in the 2nd area | region of the optical element of the embodiment. It is a figure which shows the calculation result of the coupling efficiency by the dispersion | variation in the cutting position based on the structure of the optical element of the embodiment. It is a figure which shows the calculation result of the coupling efficiency by the dispersion | variation in the cutting position based on the structure of the optical element of a conventional structure. It is sectional drawing which shows the structure of the optical element which calculated | required the calculation result shown in FIG. It is sectional drawing which shows the core structure in the optical element of 2nd embodiment which concerns on this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The embodiment described below is an embodiment in which an optical element having a spot size conversion optical waveguide portion of the present application is applied to an optical element including a photonic crystal layer.
FIG. 1 is an explanatory diagram of an optical element according to the present embodiment. The optical element 1 of the embodiment shown in FIG. 1 is an interface for propagating light from a single mode waveguide unit to an external optical element. It provides highly efficient optical coupling.
As shown in FIG. 1, the optical element 1 in the present embodiment is mainly composed of an element area A, a first area B, and a second area C. The region A of the element is a single mode waveguide portion located inside the element in the light propagation direction. The first region B is located on the inner side of the element in the light propagation direction, and has an inversely tapered core whose width gradually decreases toward the second region. The second region C is located at the forefront of the element in the light propagation direction, and is cut at this position when the element is manufactured, and is in a single mode. The element region A, the first region B, and the second region C are all configured with the substrate 2 as the lowest layer.

Next, an outline of each of the regions A, B, and C will be described, and then details of the present embodiment will be described with reference to the drawings.
The element region A plays a role of guiding light from a part having another function in the element to the element tip.
Another function is a function that uses light and has an external connection, such as a light-receiving / emitting device or an interferometer. In addition, the case where other functions are included in the region of the element is also conceivable. In the present embodiment, as another function, a dispersion compensation function may be included in the element region. In particular, the waveguide in the region A of the element according to the present invention does not need to have a low refractive index ratio, and is effective even in a waveguide having a high refractive index ratio such as silicon.

  The first region B has an inversely tapered core whose width gradually decreases toward the tip of the device in the light propagation direction, and has an effect of gradually increasing the spot size toward the tip of the device. The reverse taper structure does not necessarily have to be one stage, and in the present embodiment, a two-stage reverse taper structure is adopted.

  The second region C is a portion cut in the middle of this region in the manufacturing process of the optical element of the present invention, and is composed of a single mode waveguide. The structure of the second region C does not need to be particularly limited by the structure of the adjacent first region B. By appropriately selecting the material, height, and width of the core and the clad, the light traveling direction can be selected. Thus, a structure with little change in the mode field can be obtained. Here, the mode field refers to the intensity distribution of the electromagnetic field in the cross section when light is propagated. In the present specification, the height refers to a height in a direction substantially perpendicular to the clad laminate surface (bottom surface) of the substrate 2 unless otherwise specified. Further, the width refers to a width in a direction substantially parallel to the clad laminate surface (bottom surface) of the substrate 2.

In the present embodiment, the second cladding 22 in the second region C has a different cross-sectional shape from the cladding 3 in the first region. Furthermore, the second cladding 22 in the second region C has a different cross-sectional shape from the low refractive index optical transmission portion 5 that can be referred to as an overcladding in the first region.
In addition, by appropriately increasing the cross-sectional area of the cladding 22 in the direction substantially perpendicular to the light propagation direction, the influence of higher-order modes is reduced, and the change in coupling efficiency with external optical elements is reduced. Has the effect of
For example, in the present embodiment, as will be described later, as shown in FIG. 7, for example, the cladding 22 is used for each size of the claddings 3A and 3B in the first region shown in FIG. A design example in which the cross section of the trench portion 22c is 28 μm in width and the entire height of the clad 22 including the trench portion 22c is 36.95 μm (21.25 μm + 15.7 μm) can be shown. The size is not limited, and an optimum size can be set according to the structure of the external optical element to be connected and the refractive index of the material used for each constituent member.

Hereinafter, an embodiment of an optical element according to the present invention will be described in detail with reference to the drawings.
FIG. 2 is a cross-sectional view of the single mode waveguide portion in region A of the element of the present invention.
The substrate 2 is made of, for example, silicon having a refractive index of about 3.4. The clad 3 (3A) functions as a clad of the first region B and a clad of the second region C in the present invention, and has a lower refractive index than that of the low refractive index optical transmission unit 5, for example, silicon oxide (refractive The ratio is about 1.45), and is laminated on the substrate 2.

  3 is a partially enlarged view of the optical element, and FIG. 3A is a cutaway view of the xy plane of the element area A and the first area B of the optical element 1 in FIG. The ridge part 5a and the slab part 5b of the refractive index optical transmission part 5 are omitted from the illustration. FIG. 3B is a cross-sectional view of the element area A and the first area B in the center of the high refractive index optical transmission section 6 of the optical element 1 in FIG. It is sectional drawing in the FF part illustrated with the dashed-dotted line in FIG. In FIG. 3B, of the clads 3, the clad that functions as the first clad in the present invention is illustrated as the clad 3A, and the clad that functions as the second clad in the present invention is illustrated as the clad 3B. I decided to.

As shown in FIG. 3, on the bottom surface side of the substrate 2, a trench groove 2a is formed at the element tip side portion of the first region B, and a clad 3B (to be described later) and a low refractive index so as to fill the trench groove 2a. The trench portion 5 c of the rate light transmission portion 5 is provided up to the portion immediately before the second region C.
The silicon layer 4 is composed of silicon layers 4a and 4b, and is a base material of the photonic crystal layer 7. The silicon layer 4 is a material having a higher refractive index than that of the high refractive index optical transmission unit 6 made of SiN, for example, a refractive index. It is a thin film formed of about 3.4 silicon or the like.

Next, the photonic crystal layer 7 will be described more specifically with reference to FIG.
As shown in FIG. 3B, the photonic crystal layer 7 is laminated on the clad 3A as the first clad in the present invention. The photonic crystal layer 7 has a plurality of holes formed in a planar shape in a base material formed of silicon as a second material, and a refractive index (dielectric constant) different from the refractive index (dielectric constant) of the base material in the hole. ) Is filled with a silicon oxide film (SiO ₂ film) or the like as a first substance having a predetermined size and a predetermined arrangement interval in silicon to form a plane. is there. The base material made of silicon is formed on the cladding 3A continuously with the silicon layers 4a and 4b. The planar shape means a planar shape or the like arranged in a two-dimensional direction in the photonic crystal layer 7 and has an effect as a photonic crystal that imparts chromatic dispersion fluctuation to the optical pulse. In the case of exhibiting, when the photonic crystal layer 7 has a curved surface or a shape in which a flat surface and a curved surface are combined in the manufacturing process, the arrangement along the shape is also included. A dispersion compensation element for a photonic crystal layer using silicon as a base material is disclosed in a patent application (Japanese Patent Application No. 2004-315167: Japanese Patent No. 3917170).

  The silicon layer 4b formed of silicon which is the base material of the photonic crystal layer 7 has a cross-sectional area (xz plane in FIG. 1) in a direction substantially perpendicular to the light propagation direction. It is formed in a reverse taper shape (in other words, protruding to the beam converging part D of the coupling part) that gradually decreases gradually (in the element tip direction, -y direction in FIG. 1), It functions as a part of the reverse taper structure in the first region B. The silicon layer 4b having the reverse taper structure can be referred to as a third core.

  More specifically, the silicon layer 4b has a small cross-sectional area as shown in FIG. 4 which is a cross-sectional view at the boundary surface between the beam converging part D and the beam converging part E shown in FIG. As shown in (A), the cross-sectional area gradually increases toward the region A side of the element, and finally, the beam converging part D and the single mode waveguide part G of the coupling part shown in FIG. As shown in FIG. 5, which is a cross-sectional view at the interface, it is integrated with the photonic crystal layer 7 of the single mode waveguide portion G.

  The high-refractive-index optical transmission unit 6 extends from the top of the photonic crystal layer 7 to the element tip side portion of the silicon layer 4b via the silicon layer 4b, and has a base core (fourth fourth) whose width is uniform. 6A) and a tapered portion (referred to as a first core) 6B tapered from the tip of the base core 6A. Around the high refractive index light transmission section 6, a low refractive index light transmission section 5 having a ridge portion 5a, a slab portion 5b, and a trench portion 5c described below is formed. The high refractive index optical transmission unit 6 is made of a material having a higher refractive index than the low refractive index optical transmission unit 5 described later, such as silicon nitride (SiN) having a refractive index of 2.0. The silicon layer 4b is preferably made of a material having a higher refractive index than the first core.

The low refractive index optical transmission unit 5 functions as an optical transmission unit in the present invention together with the high refractive index optical transmission unit 6 and has a lower refractive index than the high refractive index optical transmission unit 6, for example, a refractive index of about 1 It is formed by silicon oxynitride adjusted to .5. Then, in the beam converging part E of the coupling part, it is arranged around the high refractive index light transmission part 6 and, as shown in FIG. 6, is horizontal with respect to the high refractive index light transmission part 6 (x direction in FIG. 1). And a ridge portion 5a and a slab portion 5b projecting in the vertical direction (z direction in FIG. 1), and further having a trench portion 5c, which is a clad functioning as a second clad. 3 (shown as the cladding 3B in FIG. 3B), that is, the cladding 3B and the trench portion 5c are stacked so as to fill the trench groove 2a of the substrate 2 described above. Yes.
In addition, the ridge portion 5a and the trench portion 5c, which are portions protruding in two directions perpendicular to the high refractive index optical transmission portion 6 (± z direction in FIG. 1), are provided with predetermined widths. These are configured to function as a light confinement portion for confining light.

FIG. 7 is a cross-sectional view of the second region C in a direction substantially perpendicular to the light propagation direction.
The cutting position portion cladding 22 in the second region C is formed on the substrate 2 common to the device region A and the first region B, and is made of, for example, silicon oxide. The cutting position clad 22 fills the trench groove 2b formed on the bottom surface side of the substrate 2A in the second region C, and the low refractive index light transmission unit in the first region B above the substrate 2A. 5 are stacked up to the same height as the ridge portion 5a. In the present embodiment, the trench 2b of the substrate 2A is formed so that the depth and width of the trench 2b in the cross section are larger than the slab portion 5b of the low refractive index optical transmission unit 5 in the first region B. Yes. Accordingly, the trench portion 22c formed in the trench groove 2b is formed to have a larger width in the cross section than the trench portion 5c in the first region B. Further, the width of the trench portion 22c protruding upward from the trench groove 2b is also formed to be larger than the slab portion 5b of the low refractive index optical transmission portion 5 in the first region B in the cross section.

In the substantially central portion of the cut position portion cladding 22 in the cross section, the rectangular parallelepiped block-shaped cut position portion core 21 is positioned so as to come into contact with the tip portion of the high refractive index optical transmission portion 6 in the first region B. Has been provided. More specifically, the tip portion of the high refractive index light transmission unit 6 is aligned with the substantially central portion of the end surface of the cutting position core 21 on the first region B side.
The cutting position portion core 21 in the second region C is made of, for example, silicon oxynitride used in the low refractive index optical transmission unit 5 in the first region B. The material of the cutting position core 21 may be the same as or different from that of the clad 3, and may be the same as or different from that of the high refractive index optical transmission unit 6. However, in the present invention, the material of the cutting position core 21 is preferably the same as that of the clad 3 or different from that of the clad 3 and the high refractive index optical transmission unit 6. By doing in this way, the optical element of this invention can be combined with an external optical element more efficiently.
The cutting position portion core 21 and the cutting position portion cladding 22 are configured to satisfy the single mode condition. And the cutting position part core 21 can be called a 2nd core.

  In the second region C, the cross-sectional shape of the cutting position portion cladding 22 in a direction substantially perpendicular to the light propagation direction is determined without being bound to the device region A and the first region B. For example, as shown in FIG. 6, in the first region B, the depth of the trench 5c is 4.2 μm, whereas in the second region C, as shown in FIG. The thickness is 15.7 μm. Such a relationship between shape and size produces the effects described below.

  When the light propagating from the optical element 1 of the present embodiment to the external optical element propagates from the first area B to the second area C, most of the propagation mode is the only propagation mode of the second area C. And the remainder penetrates into the cutting position cladding 22 in the second region C, and the remainder is reflected to the first region B. At this time, by taking the structure of the present embodiment, the light coupled to the only propagation mode propagates stably. Further, since the light that has entered the cut position portion cladding 22 in the second region C spreads outward in the xz plane of FIG. 1, interference with the propagation mode in the second region C is reduced. Therefore, the light that has entered the second region C has a mode field that is stable in the y direction. Conversely, the light incident on the optical element 1 of the present embodiment from an external optical element similarly has a stable mode field in the y direction.

  In order to achieve this effect, in the optical element 1 of the present embodiment, as shown in FIGS. 1, 3, 6 and 7, etc., the first region B and the second region C are connected at the first surface. The cutting position portion core (second core) 21 in the second region C is arranged in a direction substantially perpendicular to the bottom surface of the substrate 2 (z direction in FIG. 1), and the first core 6B in the first region B and The clad 3B has a height lower than the total height. And in the said connection surface, the height of the cutting position part core (2nd core) 21 of the direction (z direction in FIG. 1) substantially perpendicular | vertical with respect to the bottom face of the board | substrate 2 is as shown in FIG. It may be lower than the height of the clad 3B in the same direction or may be higher.

Although not shown here, the cut position portion core (second core) 21 is first in the direction substantially perpendicular to the bottom surface of the substrate 2 (z direction in FIG. 1) on the connection surface. Even if it has the same height as the total height of the core 6B and the clad 3B, the same effect can be obtained. Also in this case, the height of the cutting position core (second core) 21 may be lower or higher than the height of the clad 3B on the connection surface. In this case, the width of the cutting position portion core (second core) 21 in the direction substantially parallel to the bottom surface of the substrate 2 (the x direction in FIG. 1) is as shown in FIGS. As shown, it may be smaller than the total width of the first core 6B and the clad 3B, or vice versa.
In the single mode waveguide, the mode field spread of the fundamental mode increases as the cross-sectional area of the core in a direction substantially perpendicular to the light propagation direction increases. By gradually narrowing the cross-sectional area, the cross-sectional area can be increased. Therefore, with respect to the cutting position portion core (second core) 21 in the second region C, the height in the direction substantially perpendicular to the bottom surface of the substrate 2 (the z direction in FIG. 1) and the direction substantially parallel to the figure (FIG. Even if at least one value of the width in the x direction in 1) is made smaller than that of the low refractive index optical transmission unit 5 in the first region B, the same effect as described above can be obtained.

The optical element of the present invention is cut at a specific position at the time of manufacture, and is connected to an external optical element using that as an end face. At this time, manufacturing variations inevitably occur at the positions to be cut. The optical element 1 of the present invention is cut in the second region C. However, as described above, the optical element 1 has a mode field in the light propagation direction and in the opposite direction (± y direction in FIG. 1). Thus, stable coupling efficiency can be exhibited even if the cutting position varies.
6 and 7, high-efficiency optical coupling is possible when a single mode fiber having a core diameter of 8 μm, a cladding diameter of 125 μm, and a relative refractive index difference of 0.34% is assumed as an optical element connected to the outside. The design example (dimension example) of each structural member is shown. However, the size of each component and the size ratio between the components in the present invention are not limited to the design example. The structure of the external optical element to be connected and the refractive index of the material used for each component Of course, the optimum type and size can be set according to the above.

"Calculation example in this embodiment"
According to the present invention, it is possible to reduce a change in coupling efficiency with another optical element with respect to a change in cutting position. FIGS. 8 and 9 show calculation examples of the change in coupling efficiency due to variation in the cutting position in the optical element of the present invention described above and the optical element of the prior art.
Here, the optical element of the prior art has the same area as the element area A and the first area B in the present invention. Further, instead of the second area C, the cross section illustrated in FIG. An optical element having a second region having a cross section in a direction substantially perpendicular to the direction. The cross section shown in FIG. 10 has a structure in which the high-refractive-index light transmission unit 6 is deleted from a part of the first region B shown in FIG. is doing.

  The calculation of the change in the coupling efficiency due to the variation in the cutting position means the coupling efficiency between each of the two optical elements and the single mode fiber having a core diameter of 8 μm, a cladding diameter of 125 μm, and a relative refractive index difference of 0.34%. It is a simulation calculation based on the step connection method for the length of the second region in the y direction in FIG.

  Further, the cutting positions shown in FIGS. 8 and 9 indicate the positions at which the respective optical elements are cut at the time of manufacture, and the distance from the boundary with the first region B to the element end face, that is, the above-described optical elements. The second region C (second region) is shown corresponding to the length in the y direction in FIG.

From the comparison of the results shown in FIGS. 8 and 9, when the rate of change of the coupling efficiency in the 0-100 μm range of the cutting position is compared, the optical element of the prior art is 14.6%, whereas the optical according to the present invention. According to the device, it is 3.7%, and it can be seen that the change rate of the coupling efficiency is improved.
That is, when the structure of the optical element according to the present invention is adopted, even if the cutting position in the second region C varies, it is clear that the rate of change in coupling efficiency can be reduced as compared with the optical element of the prior art. is there.

"Second Embodiment"
In the optical element 1 according to the first embodiment, in the second region C, the cross-sectional shape is constant along the light propagation direction, but the present invention is not limited to this, and the second region C In the region C, the cross-sectional shape may be changed so as to satisfy the single mode condition.
More specifically, as shown in FIG. 11, in the second region C, the cutting position core 21 </ b> A has a width in a direction substantially parallel to the bottom surface of the substrate so as to continuously spread toward the tip of the element. The formed cutting position portion tapered core 21a, and then the cutting position portion steady core 21b formed so that the cross-sectional shape in a direction substantially perpendicular to the light propagation direction is constant toward the tip of the element. You may form so that it may have. About another structure, it is the same as the structure of embodiment shown in FIGS.
However, in 2nd embodiment, the site | part in which the cutting position part stationary core 21b exists is made into a cutting position.

  According to the second embodiment, the spot size at the boundary between the first region B and the second region C can be further enlarged in the second region C, and the change in coupling efficiency due to the cutting position is reduced. The coupling efficiency can be further increased while keeping it.

  A: Element region (single mode waveguide part), B: First region, C: Second region, D, E ... Beam focusing unit, 1 ... Optical element, 2 ... Substrate, 3 ... Cladding, 3A ... 1st clad, 3B ... 2nd clad, 4 ... Silicon layer, 4a ... Silicon layer, 4b ... Silicon layer (third core), 5 ... Low refractive index optical transmission part, 5a ... Ridge part, 5b ... Slab part, 5c ... trench part, 6 ... high refractive index light transmission part (first core), 6A ... base core (fourth core), 7 ... photonic crystal layer, 21 ... cutting position part core (second) Core 21), cutting position portion tapered core, 21b ... cutting position portion steady core, 22 ... cutting position portion cladding.

Claims (5)

An optical element having a spot size conversion optical waveguide part above the substrate,
The spot size conversion optical waveguide part has at least a first region and a second region adjacent to each other;
The first region is located inside the element in the light propagation direction, and has a first core and a cladding,
The second region is located on the element front end side in the light propagation direction, and has a second core,
The first core has an inversely tapered shape in which a width in a direction substantially parallel to the bottom surface of the substrate decreases toward the second region;
The second core has a total height of the first core and the clad of the first region in a direction substantially perpendicular to the bottom surface of the substrate at the connection surface between the first region and the second region. An optical element having a height lower than the height.   The optical element according to claim 1, wherein the second core is made of the same material as that of the clad in the first region.   The optical element according to claim 1, wherein the second core is made of a material different from that of the first core and the clad in the first region.   The said 2nd core has a site | part formed so that the width | variety of the direction substantially parallel to the bottom face of the said board | substrate may spread toward an element front-end | tip, The Claim 1 characterized by the above-mentioned. The optical element described. The first region further comprises a third core and a fourth core;
The third core is made of a material having a refractive index higher than that of the first core, and the cross-sectional area in a direction substantially perpendicular to the light propagation direction is continuously reduced toward the element tip direction. Formed,
The fourth core is formed continuously with the first core so that a cross-sectional area in a direction substantially perpendicular to the light propagation direction is constant,
The optical element according to claim 1, wherein the first core or the fourth core is stacked above the substrate with respect to the third core.

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