JP4552821B2 - Method for manufacturing spot size conversion waveguide - Google Patents

Description

  The present invention relates to a spot size conversion waveguide that connects an optical waveguide (hereinafter referred to as a high Δ optical waveguide) having a relative refractive index difference (Δ) larger than 0.3% and a single mode fiber with low loss, and a method for manufacturing the same.

  The high Δ optical waveguide and the single mode fiber have different spot sizes (beam radii). In general, the spot size of a high Δ optical waveguide is about 2.5 μm when Δ = 1.5%, and the spot size of a single mode fiber is about 5 μm. For this reason, in order to connect the high Δ optical waveguide and the single mode fiber, it is necessary to use a special part or an optical waveguide having a complicated configuration.

  Conventionally, a high-mode optical waveguide having a large relative refractive index difference and a single mode fiber are connected using a TEC (core expansion) fiber.

  The prior art document information related to the invention of this application includes the following.

JP-A-6-160675 Japanese Patent No. 3607129

  By the way, when using a TEC fiber, it is necessary to connect the TEC fiber between the high Δ optical waveguide and the single mode fiber, which increases the number of connections, and increases the number of parts compared to the conventional fiber array. There was a problem that the production cost was increased.

  In addition, since the high Δ optical waveguide is connected to the single mode fiber, the tolerance of axial misalignment between the waveguide core and the single mode fiber is smaller than that of the conventional low Δ (0.3% or less) optical waveguide and the single mode fiber. There was a problem of becoming severe.

  On the other hand, as an ideal spot conversion waveguide, there is a tapered waveguide structure in which the core height and the core width gradually change over the light propagation direction. The spot conversion waveguide having the tapered waveguide structure can make the spot size at the core end face of the optical waveguide device close to the spot size of the single mode fiber, and can greatly reduce the coupling loss. However, the spot conversion waveguide having the tapered waveguide structure has a problem that the manufacturing process is complicated and the manufacturing cost increases.

  Accordingly, an object of the present invention is to provide an inexpensive spot conversion waveguide that can connect a high Δ optical waveguide and a single mode fiber with low loss without using a spot size conversion member such as a TEC fiber, and a method for manufacturing the same. is there.

In order to achieve the above object, a method for manufacturing a spot size conversion waveguide according to the present invention includes a low-loss optical waveguide having a core having a waveguide core on a substrate and a single mode fiber, each having a different spot size. In a method of manufacturing a spot size conversion waveguide for connection,
Forming a first core film on the substrate;
Etching the first core film to form a first core including the waveguide core;
Covering the substrate and the first core with a mask in a state separated from the first core, and exposing the substrate and the first core over a predetermined length from an end surface of the first core;
A second core film made of a material having the same or lower refractive index as that of the first core film is formed through the mask, and a uniform film having a constant film thickness is exposed on the portion exposed from the mask. And a step of forming an inclined film whose film thickness is gradually reduced in the lower part of the mask ,
By the film forming step of the second core film, the fiber-side spot size is the same as that of the single-mode fiber at the end of the waveguide core of the optical waveguide. The width and height of the ridge portion that is equivalent to the waveguide core and is formed by covering the central portion of the first core with the second core film is from the fiber side to the waveguide core side. a shall form a ridge portion of smaller cross section projecting shape headed.

Here, when the d etching process, performed overetching reaching the middle of the substrate, it may be formed the first core on the protruding portion of the substrate. Etching depth of the over-etching is preferably adjusted to be larger than the thickness of the uniform layer of the second core layer.

  According to the present invention, it is possible to connect the high Δ optical waveguide and the single mode fiber with low loss without increasing the number of parts.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a structural diagram of a spot size conversion waveguide according to a preferred embodiment of the present invention.

  As shown in FIG. 1, a spot size conversion waveguide 1 according to the present embodiment is a high Δ optical waveguide, and has a waveguide core 3 having a rectangular cross section on a quartz (or Si) substrate 2. The waveguide core 3 is provided with a ridge portion 10 having a convex cross section at the fiber connection end (the front end in FIG. 1). The waveguide core 3, the ridge portion 10, and the substrate 2 are covered with an upper clad (not shown). In the spot size conversion waveguide 1, a portion including the ridge portion 10 is a ridge waveguide 1f, and the remaining portion is a general mesa waveguide 1b.

  The ridge portion 10 is configured by covering a central portion (the waveguide core 3 at the fiber connection end portion) with a film 4 serving as a pseudo core. The film 4 is formed on a portion connected to the core of the single mode fiber on the substrate 2. Since the film 4 is generally formed by a CVD method, it is also called a CVD core. The spot size of the ridge portion 10 on the connection side with the single mode fiber is equivalent to that of the single mode fiber (not shown), and the spot size on the mesa waveguide 1b side is equivalent to that of the waveguide core 3.

  In the ridge portion 10, the width of the ridge core and the height of the ridge core are reduced from the fiber side (front side in FIG. 1) toward the mesa waveguide 1b side (back side in FIG. 1). Here, the width of the ridge core is [the width w of the waveguide core 3 + the film width d10 × 2 of the film 4], and the height of the ridge core is [the height h of the waveguide core 3 + the film thickness of the film 4]. d]. Since the waveguide core 3 has the same cross-sectional shape in the longitudinal direction, the cross-sectional shape of the film 4 actually changes in the light propagation direction. Specifically, as shown in FIGS. 2A to 2D, the film 4 gradually has a film thickness of d1 and d2 (<d1) from the single mode fiber side toward the ridge waveguide 1f side. The film thickness becomes zero at the boundary b1 between the ridge waveguide 1f and the mesa waveguide 1b.

  Here, the relative refractive index difference between the mesa waveguide 1b (core portion) and the ridge waveguide 1f (ridge portion 10) is made larger than the relative refractive index difference of the connected single mode fiber. The refractive index of the waveguide core 3 is higher than the refractive indexes of the substrate 2 and the upper clad, for example, 1.0 to 3.0%, preferably about 1.5 to 2.5%. The refractive index of the film 4 is the same as or slightly lower than the refractive index of the waveguide core 3. As the substrate 2, a quartz substrate, a Si substrate, or the like is used. When Si is used as the substrate, it is necessary to provide a lower cladding between the substrate 2 and the waveguide core 3.

  The cross-sectional shape of the waveguide core 3 and the ridge core of the ridge portion 10 is not limited to a rectangular shape, and may be, for example, a trapezoidal shape, a semicircular shape, a semielliptical shape, or the like.

  Next, a method for manufacturing the spot size conversion waveguide 1 according to the present embodiment will be described.

  First, as shown in FIG. 3A, a waveguide core film (first core film) 31 is formed on the substrate 2 by using a CVD method, a sputtering method, an FHD (flame deposition) method, or the like. (First core film forming step). The refractive index of the material constituting the waveguide core film 31 is set higher than the refractive index of the material constituting the substrate 2.

  Next, as shown in FIG. 3B, an optical circuit pattern 32 is formed on the waveguide core film 31. Thereafter, as shown in FIG. 3C, the waveguide core film 31 is etched using the optical circuit pattern 32 as a mask to form the waveguide core (first core) 3 (first core formation step). ). After the etching process, the optical circuit pattern 32 is removed.

  Finally, as shown in FIG. 3 (d), a film is formed on the fiber connection end (the end on the near side in FIG. 1) of the substrate 2 and the waveguide core 3 by CVD, sputtering, FHD, or the like. (Second core film) 4 is formed (second core film forming step), and the spot size conversion waveguide 1 shown in FIG. 1 is obtained.

  Here, when the film 4 is formed, the film is formed in a state where the mask 33 is disposed on the substrate 2 and the waveguide core 3. More specifically, as shown in FIG. 4, a mask 33 is disposed on the substrate 2 and the waveguide core 3 with a distance (height) H away from the waveguide core 3, and a predetermined length from the core end surface 3a. The substrate 2 and the waveguide core 3 are partially exposed over L (mask placement step). When the glass 33 is deposited through the mask 33 and the film 4 is formed in the state where the mask 33 is arranged in this manner, the glass is masked from the gap between the substrate 2 and the waveguide core 3 and the mask 33 (spaced portion). Go around below. The amount of glass that wraps around decreases as the distance from the core end surface (the left end surface in FIG. 4) of the mask 33 decreases.

  As a result, a uniform film 41 having a constant film thickness is formed on the substrate 2 and the waveguide core 3 (part of a predetermined length L) exposed from the mask 33. Further, an inclined film 42 with a gradually decreasing film thickness is formed on the substrate 2 and the waveguide core 3 (the lower portion of the mask 33) covered with the mask 33. That is, the film 4 is composed of the uniform film 41 and the inclined film 42. The tilt angle of the tilt film 42 can be freely adjusted by adjusting the height H of the mask 33. The greater the H, the smaller the tilt angle, and the smaller the H, the greater the tilt angle.

  Conventionally, in order to continuously change the height (thickness) of the ridge portion 10 in the light propagation direction, it has been necessary to perform an etching process with different etching amounts on the flat film in the light propagation direction. However, adjusting the etching amount of this etching process is a very difficult task. On the other hand, according to the present invention, by forming the film 4 using the mask 33, the film thickness of the film 4 to be formed can be changed over the light propagation direction, so that it can be easily performed without etching treatment. The height of the ridge portion 10 can be continuously changed over the light propagation direction. Further, by forming the film 4, not only the height of the ridge portion 10 but also the width of the ridge portion 10 can be continuously changed.

  The reason why the width of the ridge portion 10 continuously changes in the light propagation direction is that the total core width including the waveguide core 3 and the film 4 changes. For example, in the ridge-shaped waveguide 1f (see FIG. 1), the film thickness of the film 4 changes over the light propagation direction, which is shown in FIG. 2B, which is a cross-sectional view taken along line 2B-2B in FIG. As described above, the width of the ridge core is (the width w of the waveguide core 3 + the film width d11 × 2 of the film 4), and the height of the ridge core is (the height h + d1 of the waveguide core 3). Further, as shown in FIG. 2C, which is a cross-sectional view of 2C-2C in FIG. 2A, the ridge core width is (w + film 4 film width d12 × 2), and the ridge core height is (h + d2). Become. On the other hand, in the mesa waveguide 1b, as shown in FIG. 2D, which is a 2D-2D cross-sectional view of FIG. 2A, the film thickness of the film 4 is zero, so the core width (w ) And the core height (h) are constant.

  Next, the operation of the spot size conversion waveguide 1 according to the present embodiment will be described.

  The spot size conversion waveguide 1 according to the present embodiment has a ridge portion 10 on a fiber connection side connected to a single mode fiber. In this ridge portion 10, the ridge core height and ridge core width of the ridge portion 10, that is, the spot size changes continuously in the light propagation direction, and the spot size on the fiber connection side is equivalent to that of the single mode fiber. is there.

  Therefore, the spot size conversion waveguide 1 according to the present embodiment can optically connect a high Δ optical waveguide having a different spot size and a single mode fiber without using other members such as a TEC fiber. Is possible. In other words, the single mode fiber and the high Δ optical waveguide can be connected with a low loss at one connection portion.

  Further, since the film 4 has a ridge shape and has a structure of confining light, the skirt portions 14s and 14s (see FIG. 1) of the film 4 do not have a negative influence on the light transmission characteristics. This is because the projection 14p located at the center of the waveguide core 3 and the film 4 from the equivalent refractive index of the part composed of the skirt portions 14s and 14s of the film 4 and the substrate 2 and the upper clad (not shown). This is because the equivalent refractive index of the waveguide constituted by the substrate 2 and the upper clad (not shown) is increased.

  Next, another embodiment of the present invention will be described with reference to the accompanying drawings.

(Second Embodiment)
FIG. 5 is a structural diagram of a spot size conversion waveguide 51 according to another preferred embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the member similar to FIG. 1, and description is abbreviate | omitted about these members.

  As shown in FIG. 5, a spot size conversion waveguide 51 according to the present embodiment is a high Δ optical waveguide, and has a waveguide core 3 having a rectangular cross section on a quartz substrate 2, and the waveguide. A fiber connecting end portion (an end portion on the near side in FIG. 5) of the core 3 is provided with a ridge portion 50 having a convex cross section. The waveguide core 3, the ridge portion 50, and the substrate 2 are covered with an upper clad (not shown). In the spot size conversion waveguide 51, a portion including the ridge portion 50 is a ridge waveguide 51f, and the remaining portion is a general mesa waveguide 51b.

  The ridge portion 50 is formed by providing a film 54 serving as a pseudo core on the convex portion 53 p of the substantially ridge-shaped waveguide core 53. The waveguide core 53 is composed of a convex portion 53p located in the center in the width direction (left-right direction in FIG. 5) and skirt portions 53s and 53s located on both sides in the width direction of the convex portion 53p. The parts 53s and 53s are provided continuously and integrally. The film 54 is generally formed by a CVD method. The spot size on the fiber side of the ridge portion 50 is equivalent to that of a single mode fiber (not shown), and the spot size on the mesa-shaped waveguide 51b side is equivalent to that of the waveguide core 3. The fiber is connected.

  In the ridge portion 50, the width of the ridge core and the height of the ridge core decrease from the fiber side (front side in FIG. 5) toward the mesa waveguide 51b side (back side in FIG. 5). The width of the ridge core mentioned here is [the width w of the convex portion 53p], and the height of the ridge core is [the height h of the convex portion 53p + the film thickness d of the film 4]. The cross-sectional shapes of the waveguide core 53 and the film 54 in the ridge portion 50 change over the light propagation direction. Specifically, the film 54 gradually decreases in thickness from the fiber side toward the core side, and becomes zero at the boundary b5 between the ridge waveguide 51f and the mesa-shaped waveguide 51b. On the other hand, the bottom portions 53s and 53s in the waveguide core 53 gradually decrease in height from the fiber side toward the core side, and become zero at the boundary b5 between the ridge waveguide 51f and the mesa waveguide 51b. At this boundary b5, the convex portion 53p is completely exposed to become the waveguide core 3. Further, the height of the convex portion 53p in the waveguide core 53 is constant, and the width is determined in accordance with the planar shape of the optical circuit pattern 62 (see FIG. 6C) described later.

  Here, Δ of the mesa waveguide 51b and the ridge waveguide 51f (ridge portion 50) is made larger than Δ of the single mode fiber to be connected. Further, the refractive indexes of the waveguide cores 3 and 53 are set higher than those of the substrate 2 and the upper clad. The refractive index of the film 54 is the same as or slightly lower than the refractive index of the waveguide cores 3 and 53.

  Next, a method for manufacturing the spot size conversion waveguide 51 will be described.

  First, as shown in FIG. 6A, a waveguide core film (first core film) 31 is formed on the substrate 2 by using a CVD method, a sputtering method, an FHD (flame deposition) method, or the like. (First core film forming step). The refractive index of the material constituting the waveguide core film 31 is set higher than the refractive index of the material constituting the substrate 2.

  Next, as shown in FIG. 6B, the CVD method, the sputtering method, the FHD, and the like are formed on the fiber connection end portions (the front end portion in FIG. 6B) of the substrate 2 and the waveguide core film 31. A film (second core film) 64 is formed by a method or the like (second core film forming step).

  Here, when the film 64 is formed, the film is formed in a state where the mask 33 is disposed on the substrate 2 and the waveguide core film 31. The arrangement state of the mask 33 is basically the same as the arrangement state of the mask 33 in the method for manufacturing the spot size conversion waveguide 1 according to the previous embodiment. When the glass 33 is deposited through the mask 33 and the film 64 is formed in the state where the mask 33 is arranged in this manner, the glass is masked from the gaps (spaced portions) between the substrate 2 and the waveguide core film 31 and the mask 33. Go around below 33. The amount of glass that wraps around decreases as the distance from the one end surface 33a of the mask 33 increases.

  As a result, a uniform film 65 having a constant film thickness is formed on the substrate 2 and the waveguide core film 31 exposed from the mask 33. In addition, an inclined film 66 whose thickness is gradually reduced is formed on the substrate 2 and the waveguide core film 31 (the lower part of the mask 33) covered with the mask 33. That is, the film 64 is composed of the uniform film 65 and the inclined film 66. The tilt angle of the tilt film 66 can be freely adjusted by adjusting the height of the mask 33. The tilt angle decreases as the height increases, and the tilt angle increases as the height decreases.

  Next, as shown in FIG. 6C, the optical circuit pattern 62 is formed on the film 64. Thereafter, the film 64 and the waveguide core film 31 are etched using the optical circuit pattern 62 as a mask. In this etching treatment, the etching amount is adjusted so that the waveguide core film 31 is etched halfway along the waveguide core film 31 at the fiber connection end of the waveguide core film 31 (the end on the near side in FIG. 6C). The By this etching, as shown in FIG. 6D, a waveguide core (first core) 53 having a convex portion 53p and skirt portions 53s and 53s is formed (first core forming step) and the convex portion 53p. A wedge-shaped film 54 is formed thereon. Since the etching amount is uniform over the entire film formation region of the film 64, as a result of the etching, the surface shapes of the uniform film 65 and the inclined film 66 are directly reflected as the surface shapes (undulation patterns) of the bottom portions 53s and 53s. The The film 54 is thickest on the fiber connection end side and gradually decreases as it approaches the waveguide core 3 side. With the change in the film thickness of the film 54, the height of the convex portion 53p changes.

  After the etching process, the spot size conversion waveguide 51 is obtained by removing the optical circuit pattern 62.

  In the present embodiment, the case where the width W2 of the ridge core is constant and only the height h2 of the ridge core changes in the light propagation direction has been described. However, the present invention is not limited to this, and the width of the ridge core and the ridge core are not limited thereto. It is of course possible to change the height of the light beam over the light propagation direction. For example, in the etching process, an optical circuit pattern 69 (indicated by a one-dot chain line in FIG. 6B) having an enlarged diameter portion 68 on the fiber connection end side is used as an etching mask. Can be varied over the propagation direction of the. The enlarged diameter portion 68 decreases from the fiber connection end side toward the waveguide core 3 side.

  Also in the spot size conversion waveguide 51 according to the present embodiment, the same effects as the spot size conversion waveguide 1 according to the first embodiment can be obtained.

(Third embodiment)
FIG. 7 is a structural diagram of a spot size conversion waveguide according to another preferred embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the member similar to FIG. 1, and description is abbreviate | omitted about these members.

  As shown in FIG. 7, the basic structure of the spot size conversion waveguide 71 according to the present embodiment is the same as that of the spot size conversion waveguide 1 according to the first embodiment. Is different in that it is raised.

  Specifically, the waveguide core 3 in the ridge portion 10 is provided on a convex portion 72 made of a material having a lower refractive index than the core. The convex portion 72 is formed by etching the substrate 2. The film 4 is provided so as to cover the substrate 2 including the convex portion 72 and the waveguide core 3 in the ridge portion 10.

  Next, a method for manufacturing the spot size conversion waveguide 71 according to this embodiment will be described.

  First, as shown in FIG. 8A, a waveguide core film (first core film) 31 is formed on the substrate 2 by using a CVD method, a sputtering method, an FHD (flame deposition) method, or the like. (First core film forming step). The refractive index of the material constituting the waveguide core film 31 is set higher than the refractive index of the material constituting the substrate 2.

  Next, as shown in FIG. 8B, an optical circuit pattern 32 is formed on the waveguide core film 31. Thereafter, as shown in FIG. 8C, the waveguide core film 31 is etched using the optical circuit pattern 32 as a mask to form the waveguide core (first core) 3 (first core formation step). ). At this time, overetching is performed so that the substrate 2 is etched halfway. Overetching means that when the waveguide core film 31 shown in FIG. 8B is etched, the etching amount is not limited to the height of the waveguide core film 31 but is excessively etched until the substrate 2 is reached. Is to do. An excessive etching depth at this time is referred to as an overetching depth 101. By this overetching, a convex portion 72 formed by etching the substrate 2 is formed below the waveguide core 3. After the etching process, the optical circuit pattern 32 is removed.

  Finally, as shown in FIG. 8D, a CVD method, a sputtering method, and an FHD method are formed on the fiber connection ends of the substrate 2 and the waveguide core 3 (the front end in FIG. 8D). Thus, a film (second core film) 4 is formed (second core film forming step). The method for forming the film 4 is the same as the second core film forming step in the first embodiment. As a result, a spot size conversion waveguide 71 is obtained as shown in FIG.

  Next, the operation of the spot size conversion waveguide 71 according to this embodiment will be described.

  Also in the spot size conversion waveguide 71 according to the present embodiment, the same effects as the spot size conversion waveguide 1 according to the first embodiment can be obtained.

  Further, in the spot size conversion waveguide 71 according to the present embodiment, for example, as shown in FIG. 9, the waveguide core 3 has a convex portion whose overetching depth is H12 (≦ film thickness of the film 4). Since the waveguide core 3 is provided on the upper surface 72, the waveguide core 3 is raised from the surface 122 of the substrate 2 and floated. For this reason, the upper part of the waveguide core 3 comes to be located above the surfaces 124 of the skirt portions 14 s and 14 s of the film 4.

  As a result, the confinement effect of the light propagating through the waveguide core 3 in the lateral direction (left-right direction in FIG. 9) becomes stronger, and is lower than the spot size conversion waveguide 1 according to the first embodiment. It becomes a lossy waveguide. This light confinement effect becomes stronger as the over-etching depth becomes deeper. For example, as shown in FIG. 10, the waveguide core 3 provided on the convex portion 72 whose overetching depth is H13 (> film thickness of the film 4) is the same as that of the film 4. It comes to be located above the surface 124 of the bottom parts 14s and 14s. Thus, when the positional relationship between the waveguide core 3 and the bottom portions 14s and 14s of the film 4 is in the state shown in FIG. 10, the light confinement effect is maximized.

  Further, as shown in FIG. 9, when the overetching depth H12 is not very deep (for example, 0.5 to 1.0 μm), the width W12 of the film 4 located on both sides of the waveguide core 3 is the fiber connection end portion. At the end portion b7 between the waveguide core 3 and the ridge portion 10 (see FIG. 7, the end on the near side), the film thickness is about ½. However, as shown in FIG. 10, when the overetching depth H13 becomes deeper, the width W13 of the film 4 located on both sides of the waveguide core 3 becomes narrower.

  For this reason, as shown in FIG. 11, as the overetching depth 101 is increased, the width w of the waveguide core 143 at the fiber connection end (the front end in FIG. 11) is increased, It is necessary to form a tapered waveguide core 143 having an enlarged diameter portion 145. Needless to say, the waveguide core 143 is formed using an optical circuit pattern having the same shape as the waveguide core 143 (see FIG. 8B). By appropriately adjusting the width w of the enlarged diameter portion 145 in the waveguide core 143, as shown in FIG. 12, the overetching depth 101 is deep, and the width W15 of the film 4 located on both sides of the waveguide core 143 is Even with the narrow spot size conversion waveguide 71, the spot size of the ridge core width [w + 2 × W15] at the fiber connection end can be adjusted to an arbitrary size.

  As described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various other things are assumed.

  Next, although this invention is demonstrated based on an Example, this invention is not limited to these Examples.

Example 1
The spot size conversion waveguide 1 shown in FIG. 1 was produced. The spot size conversion waveguide 1 has a total length of 4 mm, a core width w of the waveguide core 3 of 4 μm, a core height h of 4 μm, a thickness d of the film 4 of 3 μm, and a film positioned on the left and right of the waveguide core 3. Each width y of 4 was set to 2 mm, and the refractive index of the waveguide core 3 was set to be 1.5%. For example, when the refractive index of a clad (not shown) covering the waveguide core 3 is 1.458, in order to set Δ of the spot size conversion waveguide 1 to 1.5%, the refractive index of the waveguide core 3 is 1.4602. Just do it. Δ is defined by the following equation.
Δ = {(refractive index of waveguide core) − (refractive index of clad)} × 100 / (refractive index of waveguide core)

(Comparative Example 1)
A mesa-shaped waveguide having the same size and structure as the spot size conversion waveguide of Example 1 was prepared except that the film 4 was not formed.

  A propagation loss (coupling loss or connection loss) was measured by connecting a single mode fiber to the core end face of each waveguide of Example 1 and Comparative Example 1.

  As a result, the propagation loss of the waveguide of Comparative Example 1 was 3 dB, whereas the propagation loss of the spot size conversion waveguide of Example 1 was about 1/3 of 1 dB, and the loss amount was significantly reduced. I was able to confirm.

  The spot size conversion waveguide 71 shown in FIG. 7 was produced. As shown in FIG. 13A, the spot size conversion waveguide 71 forms a polishing margin 161 having a polishing margin length x in consideration of workability, and a waveguide core at one end surface of the polishing margin 161. The core width w of the (first core) 3 is 4.3 μm, the core height h is 4.3 μm, the thickness of the film (second core) 4 is d, and the refractive index of the waveguide core 3 is Δ is 1.5%. The overetching depth e (height of the convex portion 72) was set to 1 μm.

  The length x of the polishing margin 161 is 1000 μm, the taper length of the film 4 (the length along the waveguide core 3 of the film 4 excluding the polishing margin 161) Tp is 500 μm, and the Δ and thickness d of the film 4 are various. Instead, the shape of the film 4 was examined by simulation. FIG. 13B shows the coupling loss variation from the taper end portion of the film 4 (the boundary portion b7 between the taper portion of the film 4 and the waveguide core 3) to the fiber connection end portion of the polishing bar 161.

  As shown by the enclosed area A in FIG. 13B, the optimum value is when the refractive index of the film 4 is set to Δ = 1.1 to 1.5% and the thickness d = 3 to 9 μm. When the coupling loss was about 0.5 dB or less, the loss was very low.

  Next, the optimum values of the thickness d of the film 4 and the taper length Tp when the refractive index of the film 4 was set to be Δ = 1.5% were examined in detail by simulation. The results are shown in FIGS. 14 (b) to 14 (d). However, as shown in FIG. 14A, the starting point (0 μm) of the polishing margin length is the boundary between the taper portion of the film 4 and the polishing margin 161.

  As shown in FIGS. 14B to 14D, the optimum values of the thickness d of the film 4 and the taper length Tp when the refractive index of the film 4 is set to Δ = 1.5% are as follows: The thickness d of the film 4 was 4 μm and the taper length Tp was 1000 μm or more. At this time, the coupling loss was about 0.25 dB, which was very low.

  Similarly, the optimum values of the thickness d and the taper length Tp of the film 4 when the refractive index of the film 4 was set to be Δ = 1.5, 1.3, and 1.1% were examined by simulation. The results are shown in FIGS. 15 (a) to 15 (c). Here, FIG. 15A is the same as FIG. 14C.

  As shown in FIG. 15B, the optimum value of the thickness d of the film 4 and the taper length Tp when the refractive index of the film 4 is set to Δ = 1.3% is the thickness d of the film 4. = 5 μm, taper length Tp = 1000 μm or more. At this time, the coupling loss was as low as about 0.2 dB.

  Further, as shown in FIG. 15C, the optimum values of the thickness d of the film 4 and the taper length Tp when the refractive index of the film 4 is set to Δ = 1.1% are the thickness of the film 4. The thickness d was 7 μm and the taper length Tp was 1000 μm or more. At this time, the coupling loss was about 0.2 dB, which was very low.

  From the above results, when the refractive index of the film 4 is set so that Δ is in the range of 1.1 to 1.5% and the thickness d is in the range of 3 to 9 μm, the refractive index of the film 4 is increased so that Δ is large. It can be seen that the optimum thickness d of the film 4 decreases as the value is set to, and the optimum thickness d of the film 4 tends to increase as the refractive index of the film 4 is set so that Δ decreases. It was. That is, the refractive index of the film 4 is set so that Δ is in the range of 1.1 to 1.5%, and the refractive index of the film 4 is set so that Δ is large when the thickness d is in the range of 3 to 9 μm. In this case, when the thickness d of the film 4 is smaller, the coupling loss is lower. Conversely, when the refractive index of the film 4 is set so that Δ is smaller, the larger the thickness d of the film 4 is, the smaller the coupling is. Loss is reduced. In addition, when the refractive index of the film 4 is set so that Δ is constant and the thickness d is also constant, it can be confirmed that the coupling loss decreases as the taper portion length Tp increases.

  The coupling loss between the spot size conversion waveguide 71 shown in FIG. 12 and the single mode fiber was obtained by simulation using the beam propagation method. The structural parameters of the spot size conversion waveguide 71 are such that the waveguide core 143 (first core) has a refractive index of Δ1.5%, the core height h of the waveguide core 143 is constant at 4.3 μm, and the waveguide core The width W of 143 is changed to 4.3 μm, 5.3 μm, and 6.3 μm, and the film 4 (second core) has a refractive index of Δ 1.5% and 1.3%, and the film thickness of the film 4 (second core height) ) D was 3-7 μm. In order to simplify the simulation parameters, the width W15 of the film 4 located on both sides of the waveguide core 3 is set to ½ of the film thickness d of the film 4 regardless of the etching depth.

  First, a simulation was performed with the overetching depth 101 set to 1 μm under the above conditions (see FIGS. 16A and 16B). As a result, as shown in FIG. 16A, when Δ of the film 4 is 1.5%, the coupling loss is reduced by setting the width W of the waveguide core 143 to 5.3 μm and the film thickness d of the film 4 to 4 μm. It became the minimum (0.22 dB). As shown in FIG. 16B, when Δ of the film 4 is 1.3%, the coupling loss is minimized by setting the width W of the waveguide core 143 to 5.3 μm and the film thickness d of the film 4 to 5 μm. (0.18 dB).

  Next, the simulation was performed with the overetching depth 101 set to 5 μm (see FIGS. 16C and 16D). As a result, as shown in FIG. 16C, when Δ of the film 4 is 1.5%, the coupling loss is reduced by setting the width W of the waveguide core 143 to 6.3 μm and the film thickness d of the film 4 to 5 μm. It became the minimum (0.12 dB). Further, as shown in FIG. 16D, when Δ of the film 4 is 1.3%, the coupling loss is minimized by setting the width W of the waveguide core 143 to 5.3 μm and the film thickness d of the film 4 to 5 μm. (0.12 dB).

  From the above results, it was confirmed that the higher the height of the convex portion 72 (the deeper the overetching depth 101), the stronger the light confinement effect and the lower the loss of the waveguide.

1 is a structural diagram of a spot size conversion waveguide shown in a preferred embodiment of the present invention. It is the top view and sectional drawing of FIG. 2 (a) is a plan view of FIG. 1, FIG. 2 (b) is a cross-sectional view taken along line 2B-2B of FIG. 2 (a), FIG. 2 (c) is a cross-sectional view taken along line 2C-2C of FIG. FIG. 2D is a cross-sectional view taken along line 2D-2D of FIG. It is a figure for demonstrating the manufacturing method of the spot size conversion waveguide shown in FIG. It is a longitudinal cross-sectional view explaining the film-forming process of a film | membrane. FIG. 6 is a structural diagram of a spot size conversion waveguide according to another preferred embodiment of the present invention. It is a figure for demonstrating the manufacturing method of the spot size conversion waveguide shown in FIG. FIG. 6 is a structural diagram of a spot size conversion waveguide according to another preferred embodiment of the present invention. It is a figure for demonstrating the manufacturing method of the spot size conversion waveguide shown in FIG. It is a cross-sectional view which shows the film-forming example of a film | membrane. It is a cross-sectional view which shows the other film-forming example of a film | membrane. It is a modification of FIG.8 (c). It is a spot size conversion waveguide formed by forming a film on the waveguide core shown in FIG. It is a figure which shows the relationship between the film thickness and coupling loss in [Example 2]. FIG. 13A is a structural diagram of the spot size conversion waveguide, and FIG. 13B is a diagram showing the relationship between the film thickness d and the coupling loss. It is a figure which shows the relationship between the polishing margin length and coupling loss in [Example 2]. 14A is a longitudinal sectional view of the spot size conversion waveguide shown in FIG. 13A, and FIGS. 14B to 14D are diagrams showing the relationship between the polishing margin length x and the coupling loss. It is. It is a figure which shows the relationship between the polishing margin length and coupling loss in [Example 2]. FIGS. 15A to 15C are diagrams showing the relationship between the polishing margin length x and the coupling loss. It is a figure which shows the relationship between the over-etching depth and coupling loss in [Example 3].

Explanation of symbols

1 Spot size conversion waveguide 2 Substrate 3 Waveguide core 10 Ridge part

Claims (3)

In the manufacturing method of a spot size conversion waveguide for connecting an optical waveguide having a waveguide core on a substrate and a single mode fiber with low loss, each having a different spot size,
Forming a first core film on the substrate;
Etching the first core film to form a first core including the waveguide core;
Covering the substrate and the first core with a mask in a state separated from the first core, and exposing the substrate and the first core over a predetermined length from an end surface of the first core;
A second core film made of a material having the same or lower refractive index as that of the first core film is formed through the mask, and a uniform film having a constant film thickness is exposed on the portion exposed from the mask. And a step of forming an inclined film whose film thickness is gradually reduced in the lower part of the mask ,
By the film forming step of the second core film, the fiber-side spot size is the same as that of the single-mode fiber at the end of the waveguide core of the optical waveguide. The width and height of the ridge portion that is equivalent to the waveguide core and is formed by covering the central portion of the first core with the second core film is from the fiber side to the waveguide core side. method for producing a spot size conversion waveguide characterized that you form a ridge portion of smaller cross section projecting shape toward.   2. The method for manufacturing a spot size conversion waveguide according to claim 1, wherein, during the etching process, overetching reaching the middle of the substrate is performed to form the first core on the convex portion of the substrate. 3.   3. The method for manufacturing a spot size conversion waveguide according to claim 2, wherein an etching depth of the over etching is adjusted to be larger than a thickness of the uniform film of the second core film.

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