JP2011197453A - Semiconductor optical waveguide element, semiconductor optical waveguide array element, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor optical waveguide element and a semiconductor optical waveguide array element in which coupling loss is low, variation in values is less, and crystal quality is satisfactory, and a method for manufacturing the same.SOLUTION: A flush type semiconductor optical wave guide element is formed on a substrate and includes a taper waveguide with a core layer in which width and thickness decrease like a taper from a first end toward a second end, and in the core layer, layer thickness ratio between layer thickness at the first end and layer thickness at the second end is 1.5-2.5, and the width at the second end is ≥0.5 μm ≤1.0 μm.

Description

  The present invention relates to an embedded semiconductor optical waveguide device formed on a substrate, a semiconductor optical waveguide array device, and a method for manufacturing the same.

  Along with the spread and progress of optical communication networks, higher performance of optical components used in optical communication systems is progressing. Optical components include optical active components that emit or receive signal light, optical passive components that branch or combine signal light, and optical fibers that serve as signal light transmission lines. On the other hand, there is a growing need for higher functionality and lower costs.

  For optically active components, optical elements based on semiconductor materials such as semiconductor optical amplifiers, semiconductor lasers, semiconductor optical modulators, and semiconductor photodiodes are mainly used. A semiconductor-based optical active component is characterized by an optical amplification function, high-speed operation, and compact integration. Many of semiconductor lasers and optical modulators as light sources for optical communication are of the waveguide type, and the typical spot size of the optical waveguide is about 1 to 2 μm.

  Regarding optical passive components, planar lightwave circuit (PLC) elements, which are optical waveguides based on silica-based materials, have been commercialized and widely used. PLC waveguide-based optical passive components have the advantages of low loss and low polarization dependence. Although the spot size of the PLC waveguide varies depending on the relative refractive index difference (Δ) between the core layer and the cladding portion, the spot size is about 7 to 8 μm in the conventional PLC waveguide in which Δ is about 0.8%. Recently, a technique for increasing Δ to reduce the optical circuit size has been developed. For example, in a PLC waveguide having Δ of about 2.5%, the spot size is as small as about 4 to 5 μm. In addition, the optical fiber is mainly based on a silica-based material like the PLC waveguide, and recently, an optical fiber having a very low loss of 0.2 dB / km or less has been put into practical use. The spot size of a normal single mode optical fiber is about 9 to 10 μm.

  In this way, although optical waveguide technology is commonly used in optical active components, optical passive components, and optical fibers, the spot size of each optical waveguide varies depending on the refractive index and size of the material. Yes. Thus, when optical waveguides having different spot sizes are coupled to each other as they are butted together, a large coupling loss occurs due to spot size mismatch. Accordingly, when optical waveguides having different spot sizes are connected, it is often performed to join either one or both of the spot sizes in the vicinity of the connection portion so that the spot sizes are matched. The part responsible for changing the spot size is called a spot size converter, and various structures have been proposed.

  In a spot size converter for an optical element having an embedded optical waveguide structure on a substrate, a tapered waveguide having a tapered shape by gradually changing the shape of the embedded core layer along the light propagation direction is often used. . For example, Non-Patent Document 1 describes a spot size converter using a width-tapered waveguide in which the width of a core layer is gradually narrowed to have a tapered shape. Further, Patent Document 1 describes a spot size converter using a thickness-tapered waveguide having a taper shape by gradually reducing the thickness of a core layer using selective growth. Patent Document 1 describes a spot size converter in which the layer thickness ratio of the core layer is three times or more at one end and the other end.

JP-A-9-61652

P. J. Williams, D. J. Robbins, J. Fine, I. Griffith, and D. C. J. Reid, “1.55μm DFB lasers incorporating etched lateral taper spot size converters,” Electronics Letter, vol. 34, pp. 770-771, 1998.

  However, in a spot size converter using a width-tapered waveguide, a value on the order of submicrons is often required for the width of the core layer at the tapered tip. For example, the optical waveguide width of a typical semiconductor laser is about 2 μm, but at the tip of a tapered shape for a spot size converter for optimizing coupling with a single mode optical fiber or a PLC waveguide with a small Δ. The width of the core layer is a very small value of about 0.2 to 0.4 μm. In order to obtain good low coupling loss, it is necessary to control the width of the core layer at the tip within ± 0.1 μm of the optimum value. However, if the width of the core layer at the tip is made 0.5 μm or less, it becomes extremely difficult to perform processing accuracy by photolithography and etching with high accuracy. In addition, there is a problem that it is very difficult to control with good reproducibility.

  In addition, in a thickness tapered waveguide, when the layer thickness ratio of the core layer is increased to 3 times or more by selective growth, the crystal quality of the core layer is reduced due to the difference in the layer thickness, or the crystal growth itself There was a problem that became difficult.

  The present invention has been made in view of the above, and provides a semiconductor optical waveguide device and a semiconductor optical waveguide array device that have low coupling loss, little variation in value, and good crystal quality, and a method for manufacturing the same. For the purpose.

  In order to solve the above-described problems and achieve the object, a semiconductor optical waveguide device according to the present invention is a buried type semiconductor optical waveguide device formed on a substrate, and includes a first end to a second end. A tapered waveguide having a core layer whose width and thickness decrease in a tapered manner toward the portion, and the core layer has a layer thickness of a layer thickness at the first end and a layer thickness at the second end The ratio is 1.5 to 2.5, and the width at the second end is not less than 0.5 μm and not more than 1.0 μm.

  In the semiconductor optical waveguide device according to the present invention, in the above invention, the core layer of the tapered waveguide has a layer thickness ratio of 2 to 2.5, and a width at the second end is 0.8 μm. It is the above.

  In the semiconductor optical waveguide device according to the present invention, in the above invention, the second end is connected to the tapered waveguide, has the same width as the second end, and has a length of 15 to 80 μm. It further includes a straight connection waveguide having a certain core layer.

  The semiconductor optical waveguide device according to the present invention is characterized in that, in the above invention, the length of the core layer of the connection waveguide is 20 to 60 μm.

  Moreover, the semiconductor optical waveguide device according to the present invention includes the two tapered waveguides and the active core layer connected to the core layers at the first end portions of the two tapered waveguides. And a semiconductor active optical waveguide.

  Further, in the semiconductor optical waveguide device according to the present invention, in the above invention, the two tapered waveguides are connected to the semiconductor active optical waveguide via a bending waveguide, and the two tapered waveguides The end face of each second end portion is inclined with respect to the light incident / exit end face of the semiconductor optical waveguide device.

  The semiconductor optical waveguide device according to the present invention is characterized in that, in the above invention, the core layer of the tapered waveguide is formed by selective growth using a selective growth mask having a mask width of 80 μm or less. To do.

  A semiconductor optical waveguide array element according to the present invention is characterized in that the semiconductor optical waveguide elements according to any one of two or more of the above inventions are arranged in an array at intervals of 100 μm or less. .

  A method for manufacturing a semiconductor optical waveguide device according to the present invention is a method for manufacturing an embedded semiconductor optical waveguide device formed on a substrate, wherein the semiconductor optical waveguide device is selectively grown from a first end to a second end. A selective growth step of forming a core layer whose thickness decreases in a taper shape, and a taper width of the core layer in which the thickness is formed in a taper shape from the first end portion toward the second end portion. And an etching step of etching into a shape that decreases in a shape.

  In the method of manufacturing a semiconductor optical waveguide device according to the present invention, in the above invention, the selective growth step may be configured such that the core layer has a layer thickness at the first end and a layer thickness at the second end. The selective growth is performed so that the layer thickness ratio is 1.5 to 2.5, and the etching step is performed so that the width at the second end is 0.5 μm or more and 1.0 μm or less. Features.

  The method of manufacturing a semiconductor optical waveguide device according to the present invention is characterized in that, in the above invention, the selective growth step performs selective growth using a selective growth mask having a mask width of 80 μm or less.

  Moreover, the manufacturing method of the semiconductor optical waveguide array element according to the present invention includes manufacturing the semiconductor optical waveguide elements arranged in an array at intervals of 100 μm or less by the manufacturing method according to any one of the above inventions. Features.

  According to the present invention, it is possible to realize a semiconductor optical waveguide element and a semiconductor optical waveguide array element that have low coupling loss, little variation in value, and good crystal quality.

FIG. 1 is a schematic plan view of the semiconductor optical waveguide device according to the first embodiment. 2 is a cross-sectional view of the semiconductor optical waveguide element shown in FIG. FIG. 3 is a cross-sectional view of the semiconductor optical waveguide device shown in FIG. FIG. 4 is a cross-sectional view of the semiconductor optical waveguide device shown in FIG. FIG. 5 is a diagram illustrating characteristics of the semiconductor optical waveguide devices according to Examples 1 to 3 and Comparative Examples 1 to 4. FIG. 6 is a diagram for explaining an example of the method for manufacturing the semiconductor optical waveguide device according to the first embodiment. FIG. 7 is a diagram for explaining an example of the method for manufacturing the semiconductor optical waveguide device according to the first embodiment. FIG. 8 is a diagram for explaining an example of the method for manufacturing the semiconductor optical waveguide device according to the first embodiment. FIG. 9 is a diagram for explaining an example of the method of manufacturing the semiconductor optical waveguide device according to the first embodiment. FIG. 10 is a diagram showing the dependency of the layer thickness ratio on the mask width and the opening width. FIG. 11 is a diagram for explaining an example of the method for manufacturing the semiconductor optical waveguide device according to the first embodiment. FIG. 12 is a diagram for explaining an example of the method for manufacturing the semiconductor optical waveguide device according to the first embodiment. FIG. 13 is a schematic plan view of the semiconductor optical waveguide array device according to the second embodiment. 14 is a cross-sectional view taken along line DD of the semiconductor optical waveguide array element shown in FIG. FIG. 15 is a diagram for explaining an example of a method for manufacturing a semiconductor optical waveguide array device according to the second embodiment. FIG. 16 is a diagram for explaining a cleavage position in the semiconductor optical waveguide array device according to the second and third embodiments. FIG. 17 is a diagram illustrating a relationship between the cleavage position shift and the increase in coupling loss.

  Embodiments of a semiconductor optical waveguide device, a semiconductor optical waveguide array device, and a manufacturing method thereof according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments. In the description of the drawings, the same or corresponding elements are appropriately denoted by the same reference numerals. Further, the drawings are schematic, and it should be noted that the relationship between the thickness and width of each layer, the ratio of each layer, and the like are different from the actual ones. Also in the drawings, there are included portions having different dimensional relationships and ratios.

(Embodiment 1)
First, the semiconductor optical waveguide device according to the first embodiment of the present invention will be described. FIG. 1 is a schematic plan view of the semiconductor optical waveguide device according to the first embodiment. As shown in FIG. 1, the semiconductor optical waveguide device 100 includes a spot size converter 110 that is a tapered waveguide, a bending waveguide 120, and a semiconductor optical amplifier (SOA: Semiconductor) that is a semiconductor active optical waveguide, which are sequentially connected. Optical amplifier) 130, a bending waveguide 140, and a spot size converter 150 that is a tapered waveguide. FIG. 1 shows the shape in the width direction of the core layer (or active core layer) of these waveguides. The semiconductor optical waveguide device 100 has a light incident end face 100a and a light emitting end face 100b. The light incident end face 100a and the light emitting end face 100b are formed by cleavage, and a non-reflective coating is applied to the surface.

  The spot size converter 110 has a first end 110a and a second end 110b. The spot size converter 150 has a first end 150a and a second end 150b. The spot size converters 110 and 150 are connected to the SOA 130 via the bent waveguides 120 and 140 at the first ends 110a and 150a, respectively. Further, in order to suppress the reflection of light at the light incident end face 100a, the end face of the second end portion 110b of the spot size converter 110 is inclined by 7 degrees with respect to the light incident end face 100a. Similarly, the end surface of the second end 150b of the spot size converter 150 is inclined by 7 degrees with respect to the light emitting end surface 100b.

  Here, as shown in FIG. 1, the spot size converter 110 has a core layer whose width decreases in a tapered shape along the light propagation direction from the first end 110a to the second end 110b. is doing. Further, the spot size converter 150 has a core layer whose width decreases in a tapered shape along the light propagation direction from the first end 150a to the second end 150b.

  The width of the core layer at the second end 150b of the spot size converter 150 is 0.5 μm or more and 1.0 μm or less, preferably 0.8 μm or more. The width of the core layer at the first end 150a is the same as the width of the core layers of the bending waveguides 120 and 140 and the active core layer of the SOA 130. For example, light in the 1.55 μm wavelength band is transmitted in a single mode. Is set to 2 μm. Moreover, although the length of the light propagation direction of the spot size converter 150 is 300 μm, it can be, for example, 200 to 500 μm. The shape of the spot size converter 110 is the same as that of the spot size converter 150. That is, the width of the core layer at the second end portion 110b is 0.5 μm or more and 1.0 μm or less, preferably 0.8 μm or more, and the width of the core layer at the first end portion 110a is, for example, 2 μm. The length in the direction is, for example, 300 μm.

  Next, a cross-sectional structure of the semiconductor optical waveguide device 100 will be described. 2 is a cross-sectional view taken along line AA of the semiconductor optical waveguide device 100 shown in FIG. 3 is a cross-sectional view of the semiconductor optical waveguide device 100 shown in FIG. FIG. 4 is a cross-sectional view of the semiconductor optical waveguide device 100 shown in FIG.

  As shown in FIG. 2, this semiconductor optical waveguide device 100 has an n-type that also functions as a buffer layer on a common substrate 102 made of n-type InP, with an n-side electrode 101 having an AuGeNi / Au structure formed on the back surface. A lower clad layer 103 made of InP, a core layer 111, 121, 141, 151 made of non-doped InGaAsP, and InGaAsP, and a separate confinement heterostructure (SCH) above and below a multi quantum well (MQW) structure An active core layer 131 having an MQW-SCH structure in which a separate confinement heterostructure) is formed, upper cladding layers 112, 122, 142, and 152 made of non-doped InP, and an upper cladding layer 132 made of p-type InP, and p-type InP. A common upper cladding layer 105 and p-type InGaAsP A contact layer 133 made of AuZn and a p-side electrode 134 made of AuZn are sequentially stacked.

  The core layer 111 and the upper cladding layer 112 constitute a spot size converter 110. The core layer 121 and the upper clad layer 122 constitute the bending waveguide 120. The active core layer 131 and the upper clad layer 132 constitute the SOA 130. The core layer 141 and the upper clad layer 142 constitute the bending waveguide 140. The core layer 151 and the upper clad layer 152 constitute a spot size converter 150. Further, the p-type contact layer 133 and the p-side electrode 134 are formed in the upper region of the active core layer 131.

  As described above, the semiconductor optical waveguide device 100 is obtained by monolithically integrating the spot size converters 110 and 150, the bending waveguides 120 and 140, and the SOA 130 on the common substrate 102.

  Here, as shown in FIG. 2, the core layer 111 of the spot size converter 110 decreases in a taper shape along the light propagation direction from the first end 110a to the second end 110b. is doing. Further, the core layer 151 of the spot size converter 150 has a thickness that decreases in a taper shape along the light propagation direction from the first end 150a to the second end 150b.

  The layer thickness ratio (T1 / T2) between the layer thickness T1 of the core layer 151 at the first end 150a of the spot size converter 150 and the layer thickness T2 of the core layer 151 at the second end 150b is 1.5. -2.5, preferably 2-2.5. That is, when the layer thickness T1 is 200 nm, the layer thickness T2 is about 80 to 133.3 nm, preferably 100 nm or less. The layer thickness ratio between the layer thickness of the core layer 111 at the second end 110b of the spot size converter 110 and the layer thickness of the core layer 111 at the second end 110b is also 1.5 to 2.5, preferably 2 to 2.5. The thicknesses of the core layers 121 and 141 of the bending waveguides 120 and 140 and the active core layer 131 of the SOA 130 are the same as the layer thickness T1.

  Next, the sectional structure of the spot size converter 150 will be further described with reference to FIG. As shown in FIG. 3, a part of the lower cladding layer 103, the core layer 151, and the upper cladding layer 152 have a mesa structure. This mesa structure is buried by a current blocking layer 104 made of a semi-insulating layer 104a made of Fe-doped InP and an n-type InP layer 104b. That is, the spot size converter 150 is an embedded optical waveguide. Note that the spot size converter 110 and the bending waveguides 120 and 140, which are other passive optical waveguides, are also embedded optical waveguides having the same cross-sectional structure.

  Next, the cross-sectional structure of the SOA 130 will be further described with reference to FIG. As shown in FIG. 4, a part of the lower cladding layer 103, the active core layer 131, and the upper cladding layer 132 have a mesa structure, and a semi-insulating layer 104a and an n-type InP layer 104b made of Fe-doped InP. Embedded in a current blocking layer 104 consisting of That is, the SOA 130 is a buried optical waveguide and has a current confinement structure by the current blocking layer 104. Therefore, when a voltage is applied between the n-side electrode 101 and the p-side electrode 134 and current is injected, current can be injected into the active core layer 131 at a high density due to the effect of the current blocking layer 104.

  In addition, as shown in FIGS. 1 and 2, between the second end portion 110b of the spot size converter 110 and the light incident end surface 100a, and between the second end portion 150b of the spot size converter 150 and the light emitting end surface 100b. A window structure is formed between the semi-insulating layer 104a and the n-type InP layer 104b between them, and the end face reflection is further suppressed together with the above-described inclination of 7 degrees.

  The semiconductor optical waveguide device 100 is used by being connected to a PLC waveguide or a single mode optical fiber, for example. That is, for example, when light having a wavelength of 1.55 μm band output from the PLC waveguide on the input side is input to the second end portion 110b of the spot size converter 110 via the light incident end surface 100a, the spot size converter 110 is input. The spot size of the emitted light is converted so as to be close to the spot size of the SOA 130 and input to the SOA 130 via the bending waveguide 120. The SOA 130 amplifies the input light and inputs the amplified light to the spot size converter 150 via the bending waveguide 140. The spot size converter 150 converts the spot size of the input amplified light so as to be close to the spot size of the PLC waveguide on the output side, outputs the spot size from the second end 150b, and outputs it via the light emitting end face 100b. Output to the side PLC waveguide.

  Here, in the semiconductor optical waveguide device 100 according to the first embodiment, the core layer 151 of the spot size converter 150 is tapered in width and thickness from the first end 150a to the second end 150b. The layer thickness ratio of the layer thickness T1 at the first end 150a and the layer thickness T2 at the second end 150b is 1.5 to 2.5, preferably 2 to 2.5. When the width W1 of the second end 150b is 0.5 μm or more and 1.0 μm or less, preferably 0.8 μm or more, the coupling loss is low when connected to the PLC waveguide on the output side. There is an effect that there is little variation in values. In the spot size converter 110 as well, the core layer 111 has a shape in which the width and thickness decrease from the first end portion 110a toward the second end portion 110b in a tapered shape. The layer thickness ratio of the layer thickness at 110a to the layer thickness at the second end 110b is 1.5 to 2.5, preferably 2 to 2.5, and the width at the second end 110b is 0.5 μm or more. When the thickness is 1.0 μm or less, preferably 0.8 μm or more, when connected to the PLC waveguide on the input side, there are effects that the coupling loss is low and the variation in value is small.

  The above effect will be specifically described using examples and comparative examples. As Examples 1 to 3 and Comparative Examples 1 to 4 of the present invention, various taper-shaped embedded spot size converters were produced, and the characteristics of coupling loss with the PLC waveguide at a wavelength of 1.55 μm were measured. did. Specifically, in the spot size converter having the same cross-sectional shape as in the first embodiment, the layer thickness ratio between the layer thickness at the first end of the core layer and the layer thickness at the second end is set to 1 to 1. After making a spot size converter element on the substrate with the width of the taper shape changed in the vicinity of the optimum width for each ratio, and applying anti-reflective coating to both end faces formed by cleaving The characteristics of the coupling loss with the PLC waveguide were evaluated using light with a wavelength of 1.55 μm, using the narrow second end as the output end. Note that the PLC waveguide having a commonly used characteristic in which the relative refractive index difference Δ between the core layer and the clad portion is 1.2% and the size of the core layer is 6 μm × 6 μm is used. . In each spot size converter, the amount of increase in coupling loss when the core layer width at the output end deviates from the optimum width by 0.1 μm is also measured, and the effect of core layer width error on coupling loss A comparison was made. The taper shape of the core layer was formed by selective growth, and a specific method thereof will be described later.

  FIG. 5 is a diagram illustrating characteristics of the semiconductor optical waveguide devices according to Examples 1 to 3 and Comparative Examples 1 to 4. In FIG. 5, in the spot size converter having a layer thickness ratio of 1 that is Comparative Example 1, that is, the thickness of the core layer is constant, and has a tapered shape only in the width direction, the output end portion that has the lowest coupling loss is obtained. The optimum width was 0.3 μm, and the coupling loss with the PLC waveguide at this optimum width was slightly large, 0.9 dB. Further, when the width of the output end is shifted by ± 0.1 μm from the optimum width of 0.3 μm, that is, when the width error is 0.1 μm, the increase amount of the coupling loss from the optimum width is the larger increment side ( In this case, when the width is 0.2 μm, it is as large as 0.6 dB, and the tolerance for the width is very strict. Also, when the layer thickness ratio is 1.2 in Comparative Example 2, the coupling loss at the optimum width is slightly large as 0.8 dB, and the increase in coupling loss when the error is 0.1 μm is as large as 0.5 dB. It was.

  On the other hand, when the layer thickness ratio of Examples 1 to 3 was 1.5 to 2.5, the optimum width was 0.5 to 1.0 μm, but the coupling loss at the optimum width was 0. The increase in coupling loss when the error is as small as 0.4 to 0.6 dB and the error is 0.1 μm is as small as 0.3 dB or less, and the tolerance for the width is relaxed. In particular, when the layer thickness ratio is 2 to 2.5, the optimum width is 0.8 to 1.0 μm, but the coupling loss at the optimum width is as small as 0.4 to 0.5 dB, and the error is 0. The increase in coupling loss in the case of 1 μm was extremely small, less than 0.1 dB. Moreover, Examples 1-3 are wider than the case of the comparative examples 1 and 2, and manufacture is easy.

  However, in Comparative Examples 3 and 4, when the layer thickness ratio is 3 or when the layer thickness ratio is 4 and has a taper shape only in the thickness direction, the amount of increase in coupling loss due to error is small, but the optimum width The coupling loss at a high value was 0.8 dB or more. In Comparative Examples 3 and 4, there was variation in coupling loss between elements, and the yield of good elements was reduced. Further, in Comparative Examples 3 and 4, there was an abnormality that polycrystalline deposition partially occurred in the selective growth when forming the taper shape in the thickness direction. This abnormal growth was particularly remarkable in Comparative Example 4. In the case of Comparative Examples 3 and 4, it is considered that such abnormalities in selective growth occur and the subsequent manufacturing process is hindered, resulting in variations in characteristics. explain.

  From the above results, considering the coupling loss at the optimum width and the manufacturing tolerance for the width error, as well as the variation in the coupling loss, the core layer is tapered in the width direction and the thickness direction in the spot size converter. Preferably, it has a shape, a layer thickness ratio of 1.5 to 2.5, and a width of the output end (second end) of 0.5 to 1.0 μm. More preferably, when the layer thickness ratio is 2 to 2.5 and the width of the output end is 0.8 to 1.0 μm, the increase in coupling loss due to the width error can be suppressed to a very small value. Therefore, the characteristic of the coupling loss is stable and very suitable for manufacturing.

  As described above, the semiconductor optical waveguide device 100 according to the first embodiment has a low coupling loss and a small variation in value due to the effect of relaxation of tolerance.

(Production method)
Next, an example of a method for manufacturing the semiconductor optical waveguide device 100 according to the first embodiment will be described with reference to FIGS. First, as shown in FIG. 6, a lower clad layer 103, an active core layer 131, and an upper clad layer 132 are crystal-grown on a substrate 102 by using a metal organic chemical vapor deposition (MOCVD) method. .

  Next, after a SiNx film is formed on the entire surface, this SiNx film is patterned into a shape as shown in FIG. 7 to form a mask M1. In FIG. 7, reference numeral G1 indicates the shape in the width direction of the waveguide to be formed shown in FIG. This mask M1 is formed by simultaneously forming a mask for protecting the region where the SOA 130 is formed and a selective growth mask for forming a taper shape in the thickness direction. The selective growth mask portion of the mask M1 has an opening width Wg1, and has a wedge shape in which the mask width narrows from the mask width Wm1 toward the second end of the spot size converter. The setting of the mask width Wm1 and the opening width Wg1 will be described later. For example, the mask width Wm1 is set to 60 μm and the opening width Wg1 is set to 20 μm.

  Next, as shown in FIG. 8, using the mask M1 as a mask, etching is performed to a depth reaching the bottom surface of the active core layer 131, and the upper cladding layer 132 and the active core layer 131 in the region PA where the mask M1 is not formed, Remove. The area AA where the mask M1 is formed includes an area where the SOA 130 will be formed later, and the active core layer 131 and the upper cladding layer 132 remain.

  Next, as shown in FIG. 9, using the mask M1 as a selective growth mask, the core layers 111, 121, 141, 151 and the upper cladding layers 112, 122, 142, 152 are butted in the region PA by selective growth. Joint growth. In FIG. 9, only the core layers 141 and 151 and the upper cladding layers 142 and 152 are shown. At this time, the shape of the mask for selective growth of the mask M1 shown in FIG. 7 is a shape in which a mask that does not grow is provided on both sides of the opening portion where selective growth is performed. As a result, in the region corresponding to the second end portions 110b and 150b of the spot size converters 110 and 150, the mask M1 hardly exists, so that crystal growth is performed at a normal growth rate. On the other hand, the mask width becomes wider as the region corresponding to the first end portions 110a and 150a is approached. Since the crystal growth raw material supplied on the mask is not consumed there and migrates to the opening, more raw material is supplied to the opening in accordance with the mask width on both sides thereof. Therefore, the crystal growth rate gradually increases according to the mask width. As a result, the thicknesses of the core layers 111 and 151 are thicker on the first end portions 110a and 150a side, gradually become thinner toward the second end portions 110b and 150b side, and become tapered in the thickness direction.

  In addition, when the present inventors systematically experimented on the dependency of the layer thickness ratio of the core layer on the mask width Wm1 and the opening width Wg1 in the selective growth using the MOCVD method, the following results were obtained. FIG. 10 is a diagram showing the dependency of the layer thickness ratio on the mask width Wm1 and the opening width Wg1. As shown in FIG. 10, the layer thickness ratio increases almost linearly with respect to the mask width Wm1, and the inclination increases as the opening width Wg1 becomes narrower. Although there are some differences depending on the MOCVD crystal growth apparatus and growth conditions, the dependence of the layer thickness ratio on the mask width Wm1 and the opening width Wg1 shows a similar tendency.

  For example, if the mask width Wm1 is 60 μm and the opening width Wg1 is 20 μm as described above, the layer thickness ratio is about 2, as shown in FIG. Therefore, in the vicinity of the region corresponding to the first end portions 110a and 150a, the crystal growth rate is about twice that of the normal portion. In this case, if the thickness of the core layers 111 and 151 is 200 nm on the first end portions 110a and 150a side, the thickness is about 100 nm on the second end portions 110b and 150b side, and becomes a taper shape in the thickness direction.

  Next, after removing the mask M1 used for selective growth, a SiNx film is formed again on the entire surface, and a stripe pattern M2 for forming a waveguide shape as shown in FIG. 11 is formed from this SiNx. . The stripe pattern M2 is formed so as to pass through the center of the opening of the mask M1 shown in FIG. 7, and is tapered in the width direction so that the width becomes narrower as it approaches the end. Thereafter, using this stripe pattern M2 as a mask, dry etching is performed to a depth reaching a part of the lower cladding layer 103 (see FIGS. 3 and 4), and the core layers 111, 121, 141, 151 and the active core layer 131 are formed. A mesa structure is formed. Further, using this stripe pattern M2 as a selective growth mask, the semi-insulating layer 104a and the n-type InP layer 104b are embedded and grown to embed a mesa structure. As a result, the core layers 111, 121, 141, 151 and the active core layer 131 become buried waveguides.

  Next, after removing the stripe pattern M2, a common upper cladding layer 105 and contact layer are formed on the upper cladding layers 112, 122, 132, 142, 152 and the current blocking layer 104 as shown in FIG. 133 is crystal-grown. Next, as shown in FIG. 12B, the contact layer 133 other than the upper part of the region where the SOA 130 is to be formed is removed. Further, the p-side electrode 134 is formed on the contact layer 133, and the n-side electrode 101 is formed after the back surface of the substrate 102 is polished. Thereafter, the substrate on which the semiconductor layer has been grown is cleaved to form the light incident end face 100a and the light exit end face 100b, and after applying a non-reflective coating to the light incident end face 100a and the light exit end face 100b, each element is further separated. The semiconductor optical waveguide device 100 is completed.

  As can be seen from FIG. 10, when the layer thickness ratio is set to 3 as in Patent Document 1 and Comparative Example 3 described above, it is necessary to set the mask width Wm1 to about 100 μm when the opening width Wg1 is 20 μm. is there. Further, in the opening, since the mesa stripe shape of the optical waveguide is formed in a later process, it is difficult to make the opening width Wg1 extremely narrow. However, even when the opening width Wg1 is extremely narrow as 6 μm, the layer thickness In order to make the ratio 3, the mask width Wm1 needs to be about 70 μm. Here, considering the case where a plurality of spot size converters are arranged in an array, the arrangement interval between spot size converters cannot be less than or equal to the mask width, so the possible arrangement interval is restricted by the required mask width. become. Then, even if an attempt is made to produce a highly integrated spot size converter array with an arrangement interval of about 50 μm, a necessary mask width of 70 μm cannot be secured, and a layer thickness ratio of 3 or more cannot be realized. Problems arise.

  The layer thickness ratio or the crystal growth rate increases as the opening width Wg1 is narrowed or the mask width Wm1 is widened. However, if there is a large difference in the growth rate between the selective growth region and the other region, there will be a difference in the lattice strain of the crystal layer that grows in the growth plane, and crystal dislocations that reduce the reliability of the device to be produced will occur. Can be a factor. Further, when the mask width Wm1 is widened, as in Comparative Examples 3 and 4, there is a high probability that polycrystals are deposited due to abnormal growth in a mask region that should not be crystally grown. Such polycrystalline deposition hinders subsequent processes.

  Another problem is lattice strain that occurs during selective growth. Usually, in crystal growth, the composition is such that the lattice constant of the growth layer matches the lattice constant of the substrate (lattice matching composition). However, when the layer thickness ratio is changed by selective growth, a difference occurs not only in the layer thickness but also in the crystal composition between the thin layer portion and the thick layer portion where the layer thickness is thin. Normally, priority is given to lattice matching in the thick layer part, but if the layer thickness ratio increases, the effect of lattice mismatch in the thin layer part increases, causing defects in crystal growth, and possible layer thickness Is restricted. Crystal defects are problematic because they can affect the reliability of optical elements.

  On the other hand, in this Embodiment 1, by making both the width and thickness of the core layer into a tapered shape, a preferable layer thickness ratio is 1.5 to 2.5, particularly 2 to 2.5. The value is relatively small. As a result, the above problems of abnormal growth and crystal defects are suppressed, and the crystal quality is improved. In addition, since restrictions on the arrangement interval are relaxed, an array element integrated with high density can be realized.

  In the case of Comparative Examples 3 and 4, the mask width Wm1 of the selective growth mask was set to be as wide as 100 μm or more. However, polycrystals were deposited on a part of the mask, and normal from the vicinity of the deposited portion. The element which functions was not able to be manufactured. On the other hand, when the mask width Wm1 was 80 μm or less as in Examples 1 to 3, no abnormal growth such as polycrystalline deposition was observed. Therefore, the mask width Wm1 is preferably set to 80 μm or less. The lower limit of the mask width Wm1 is preferably set to 20 μm or more as can be seen from FIG. 10 in order to obtain a layer thickness ratio of 1.5 to 2.5.

  In the above embodiment, the current blocking layer for embedding the mesa structure uses an Fe-doped semi-insulating layer, but the pn-type current blocking layer composed of a p-type InP layer and an n-type InP layer is used. May be embedded.

  Moreover, in the said embodiment, the end surface of the 2nd end part of a spot size converter is inclined 7 degree | times with respect to the light incident / exit end surface by the bending waveguide arrange | positioned between SOA and a spot size converter. . Here, the 7 ° inclination may be formed by arranging the SOA itself obliquely with respect to the light incident / exit end face, or adopting a bent waveguide as a part of the waveguide constituting the SOA. . However, in order to realize the current confinement effect of the SOA with the embedded structure with good reproducibility or reliability, the component of non-coupled light generated in the butt joint part formed in the process shown in FIG. In order to prevent the light from being mixed in as stray light, a configuration in which a bending waveguide is disposed between the SOA and the spot size converter is preferable.

(Embodiment 2)
Next, a semiconductor optical waveguide array element according to the second embodiment of the present invention will be described. FIG. 13 is a schematic plan view of the semiconductor optical waveguide array element according to the second embodiment. As shown in FIG. 13, the semiconductor optical waveguide array element 1000 is configured by arranging the semiconductor optical waveguide elements 200 in an array with an arrangement interval P. The number of semiconductor optical waveguide devices 200 is not particularly limited, but is, for example, 2 to 128. Further, the arrangement interval P is not particularly limited, but the semiconductor optical waveguide elements 200 can be arranged at a high density as long as it is 100 μm or less, for example, about 50 μm. The lower limit of the arrangement interval P is preferably 10 μm or more from the viewpoint of reducing crosstalk between array elements and ensuring tolerance in the manufacturing process.

  In addition, the semiconductor optical waveguide device 200 includes a linear connection waveguide 260, a spot size converter 210, a linear waveguide 220, an SOA 230, a linear waveguide 240, and a spot size converter 250, which are sequentially connected. And a straight connection waveguide 270. FIG. 13 shows the shape in the width direction of the core layer (or active core layer) of these waveguides.

  FIG. 14 is a cross-sectional view taken along line DD of the semiconductor optical waveguide device 200 constituting the semiconductor optical waveguide array device 1000 shown in FIG. As shown in FIG. 14, the semiconductor optical waveguide device 200 is made of n-type InP that also functions as a buffer layer on a common substrate 202 made of n-type InP having an n-side electrode 201 with an AuGeNi / Au structure on the back surface. A lower clad layer 203, a core layer 261, 211, 221, 241, 251, 271, and InGaAsP made of non-doped InGaAsP, and an active core layer 231 having an MQW-SCH structure, and an upper clad layer made of non-doped InP 262, 212, 222, 242, 252, 272 and an upper clad layer 232 made of p-type InP, a common upper clad layer 205 made of p-type InP, a contact layer 233 made of p-type InGaAsP, and p made of AuZn The side electrodes 234 are sequentially stacked.

  Further, the core layer 261 and the upper cladding layer 262 constitute a connection waveguide 260. The core layer 211 and the upper clad layer 212 constitute a spot size converter 210. The core layer 221 and the upper clad layer 222 constitute a straight waveguide 220. The active core layer 231 and the upper clad layer 232 constitute the SOA 230. The core layer 241 and the upper clad layer 242 constitute a straight waveguide 240. The core layer 251 and the upper clad layer 252 constitute a spot size converter 250. The core layer 271 and the upper clad layer 272 constitute a connection waveguide 270. The p-type contact layer 233 and the p-side electrode 234 are formed in the upper region of the active core layer 231.

  Spot size converter 210, SOA 230, and spot size converter 250 each have the same structure and shape as the corresponding elements in semiconductor optical waveguide device 100 of the first embodiment. In other words, the spot size converters 210 and 250 have core layers 211 and 251 whose width and thickness decrease in a tapered manner along the light propagation direction from the first end toward the second end. Yes. Further, the width of the core layer at the second end of the spot size converters 210 and 250 is 0.5 μm or more and 1.0 μm or less, preferably 0.8 μm or more. The width of the core layer at the first end is 2 μm, for example. The layer thickness ratio of the core layer thickness at the first end of the spot size converters 210 and 250 to the core layer thickness at the second end is 1.5 to 2.5, preferably 2 to 2. 2.5. That is, if the layer thickness at the first end is 200 nm, the layer thickness at the second end is about 80 to 133.3 nm, preferably 100 nm or less. However, although the length of the spot size converters 210 and 250 is 260 μm, it can be set to 160 to 460 μm, for example.

  The straight waveguides 220 and 240 have a straight waveguide shape, but the other structures and shapes are the bent waveguide 120 and the corresponding elements in the semiconductor optical waveguide device 100 of the first embodiment. 140.

  The connection waveguide 260 has one end on the same plane as the light incident end face 1000a, the other end connected to the second end of the spot size converter 210, and the same width and thickness as the second end. A core layer 261 is included. The connection waveguide 270 has one end on the same plane as the light emitting end face 1000b, the other end connected to the second end of the spot size converter 250, and the same width and thickness as the second end. A core layer 271 is included.

  Here, the length of the connection waveguide 260 is, for example, 40 μm, and the combined length with the spot size converter 210 is 300 μm. Further, the length of the connection waveguide 270 is, for example, 40 μm, and the combined length with the spot size converter 250 is 300 μm.

  The semiconductor optical waveguide array element 1000 can be manufactured by the same manufacturing method as the semiconductor optical waveguide element 100 described above. Hereinafter, a process of forming a tapered shape in the thickness direction by selective growth will be particularly described. FIG. 15 is a diagram for explaining an example of a method for manufacturing a semiconductor optical waveguide array device according to the second embodiment.

  When the semiconductor optical waveguide array element 1000 is manufactured, a mask M3 made of a SiNx film is formed in a shape as shown in FIG. In FIG. 15, symbol G2 indicates the shape of the waveguide to be formed shown in FIG. 13 in the width direction. In this mask M3, the opening width Wg2 between the wedge-shaped portions of the selective growth mask is, for example, 6 μm, and the mask width Wm2 is narrower than 50 μm, which is the exemplified value of the arrangement interval P shown in FIG. 44 μm. Thereby, as shown in FIG. 10, the above-described preferable value of 2 as the layer thickness ratio can be realized. The setting of the opening width Wg2 and the mask width Wm2 can be appropriately set to a value narrower than the arrangement interval P based on FIG.

  In addition, since the semiconductor optical waveguide array element 1000 includes the connection waveguides 260 and 270, when the light incident end face 1000a and the light emitting end face 100b are formed by cleavage, even if the cleavage position is deviated from a predetermined position. Thus, an increase in coupling loss due to this shift is suppressed.

  Hereinafter, in the semiconductor optical waveguide array element 1000 according to the second exemplary embodiment, the lengths of the spot size converters 210 and 250 are both 260 μm, and the lengths of the connection waveguides 260 and 270 are both 40 μm. The amount of increase in coupling loss when the cleavage position was shifted was calculated. For comparison, as a third embodiment, a semiconductor optical waveguide array in which a connection waveguide is not provided in the semiconductor optical waveguide array element 1000 and the length of the spot size converter is 300 μm as in the first embodiment. For the element, the amount of increase in coupling loss when the cleavage position was shifted was calculated.

  FIG. 16 is a diagram for explaining a cleavage position in the semiconductor optical waveguide array device according to the second and third embodiments. When the semiconductor optical waveguide array element 1000 is manufactured, a large number of semiconductor optical waveguide array elements 1000 shown in FIG. 13 are arranged on a substrate, and this is separated into array elements by cleavage. Accordingly, when the substrate plane is viewed from above, as shown in FIG. 16, the spot size converter 250 and the connection waveguide 270 of a certain array element are connected to other adjacent array elements as indicated by broken lines. The connected connection waveguide 260 and the spot size converter 210 belong to each other.

  Here, when the cleavage position CP is just a boundary between the connection waveguide 270 and the adjacent connection waveguide 260, the cleavage position deviation is set to zero. In addition, when the cleavage position CP is shifted to the connection waveguide 270 side, the amount of cleavage position shift is represented by a negative sign. In this case, the connection waveguide 270 is shortened. On the other hand, when the cleavage position CP is shifted to the adjacent connection waveguide 260 side, the amount of cleavage position shift is represented by a positive sign. In this case, the connection waveguide 270 becomes long. Also in the case of the semiconductor optical waveguide array device according to the third embodiment, the cleavage position shift is caused when the cleavage position CP is just the boundary between the spot size converter 350 and the adjacent spot size converter 310 indicated by a broken line. Is set to zero, and the amount of cleavage position shift is given a negative sign when it is shifted to the spot size converter 350 side, and a positive sign is attached when it is shifted to the spot size converter 310 side.

  FIG. 17 is a diagram illustrating a relationship between the cleavage position shift and the increase in coupling loss. As shown in FIG. 17, in the case of Embodiment 3, the amount of increase in coupling loss increases in proportion to the cleavage position shift. On the other hand, in the case of the second embodiment, as compared with the third embodiment, even if there is a certain amount of cleavage position shift, the increase in coupling loss can be suppressed to a small value.

  For example, in the case of this calculation, the length of the connection waveguide 270 is 40 μm, but even if the cleavage position deviation is −25 to +40 μm and the length of the connection waveguide 270 is 15 to 80 μm, the coupling loss The amount of increase is 0.2 dB or less. In other words, if the length of the connection waveguide 270 is 15 to 80 μm, the coupling loss can be suppressed to a value within [(minimum value) +0.2] dB. More preferably, if the cleavage position deviation is within ± 20 μm, that is, if the length of the connection waveguide 270 is 20 to 60 μm, the coupling loss is suppressed to a value within [(minimum value) +0.1] dB. be able to. The same applies to the connection waveguide 260. Thus, by providing the connection waveguides 260 and 270, it is possible to prevent a sudden increase in the coupling loss even if the cleavage position is shifted by ± several tens of μm. Can be suppressed.

  As Example 4 of the present invention, a 16-channel semiconductor having a structure similar to that of the semiconductor optical waveguide array element according to the second embodiment and 16 semiconductor optical waveguide elements arranged in an array with an arrangement interval of 50 μm. An optical waveguide array element was manufactured. Then, this semiconductor optical waveguide array element is bonded to a 16-channel PLC waveguide array in which 16 PLC waveguides used in the measurement of characteristics shown in FIG. Channel coupling loss was evaluated. As a result, the coupling loss was within the range of 0.3 to 0.6 dB in all 16 channels, and it was confirmed that coupling with very low loss and small variation could be realized.

  One of the reasons for the small variation in coupling loss is that the semiconductor optical waveguide array element of the fourth embodiment has a large number of 16 semiconductor optical waveguide elements, which are arranged with a narrow arrangement interval (pitch) of 50 μm. This is because the arrangement can be made in a compact manner, and a compact junction with the PLC waveguide array can be achieved within a narrow width range of 750 μm in the arrangement direction. Thus, when the width of the entire semiconductor optical waveguide array element is narrowed by a narrow pitch, even if the array element is warped, the relative positional deviation of the light incident / exit end faces of each element due to the influence of the warp is reduced. Therefore, it is very effective for suppressing variation in coupling loss.

  As described above, the semiconductor optical waveguide array element of Example 4 can reduce the element pitch to about 50 μm by using the core layer having the taper shape in the width direction and the thickness direction in the spot size converter. It will be possible. Furthermore, since the core layer width at the narrow second end of the spot size converter can be increased to a desired spot size by making the width of the core layer relatively wide, such as about 0.8 μm, it is easy to manufacture and due to variations in width. An increase in coupling loss can be suppressed to a small level.

  In the above embodiment, since the core layer has a tapered shape over the entire length of the tapered waveguide in both the width direction and the thickness direction, the length of the tapered portion ( The taper length) is the same length in the width direction and the thickness direction. However, the present invention is not limited to this. For example, in accordance with the thickness or width of the core layer of the waveguide to be connected by the tapered waveguide, a taper shape is formed only in a part of the tapered waveguide, and the width direction The taper length may be different in the thickness direction. Note that the taper length is preferably set short enough to prevent radiation loss.

  In the above embodiment, the connection waveguide has a constant width and thickness in the length direction, but a connection waveguide that is tapered only in the width direction or only in the thickness direction may be employed. The effect of suppressing the variation in coupling loss to some extent against the cleavage position shift can be obtained.

  In the above embodiment, the semiconductor active optical waveguide is an SOA. However, the SOA may be replaced with another semiconductor active optical waveguide such as a semiconductor laser or an optical modulator.

  In the above embodiment, an InP-based material is used as a semiconductor material in order to use light having a wavelength of 1.55 μm. However, other semiconductor materials such as GaAs are used depending on the wavelength of light to be used. Can be used.

  Moreover, what combined each component of the said embodiment suitably is also contained in this invention. For example, in the semiconductor optical waveguide array element according to the second embodiment, the semiconductor optical waveguide element may be replaced with the semiconductor optical waveguide element provided with the bending waveguide according to the first embodiment. Further, the spot size converter itself in the above embodiment is also included in the semiconductor optical waveguide device according to the present invention.

100, 200 Semiconductor optical waveguide device 100a, 1000a Light incident end face 100b, 1000b Light exit end face 101, 201 n-side electrode 102, 202 Substrate 103, 203 Lower cladding layer 104 Current blocking layer 104a Semi-insulating layer 104b n-type InP layer 105, 112-152, 205, 212-272 Upper cladding layer 110-310, 150-350 Spot size converter 110a, 150a First end 110b, 150b Second end 111, 121, 141, 151, 211, 221, 241 271 Core layer 120, 140 Bending waveguide 130, 230 SOA
131, 231 Active core layer 133, 233 Contact layer 134, 234 P-side electrode 220, 240 Linear waveguide 260, 270 Connection waveguide 262 Upper cladding layer 1000 Semiconductor optical waveguide array element AA, PA region CP Cleavage position G1, G2 Conduction Waveguide shape M1, M3 Mask M2 Stripe pattern P Arrangement interval T1, T2 Layer thickness W1 Width Wg1, Wg2 Aperture width Wm1, Wm2 Mask width

Claims (12)

An embedded semiconductor optical waveguide device formed on a substrate,
A tapered waveguide having a core layer whose width and thickness decrease in a tapered manner from the first end toward the second end, wherein the core layer has a layer thickness at the first end and the second end; A layer thickness ratio with a layer thickness in the portion is 1.5 to 2.5, and a width in the second end portion is not less than 0.5 μm and not more than 1.0 μm.   2. The semiconductor optical waveguide according to claim 1, wherein the core layer of the tapered waveguide has a layer thickness ratio of 2 to 2.5 and a width at the second end of 0.8 μm or more. element.   A linear connection waveguide having a core layer connected to the tapered waveguide at the second end and having the same width as the second end and a length of 15 to 80 μm is further provided. The semiconductor optical waveguide device according to claim 1 or 2.   The length of the core layer of the said connection waveguide is 20-60 micrometers, The semiconductor optical waveguide element of Claim 3 characterized by the above-mentioned. Two tapered waveguides;
A semiconductor active optical waveguide having an active core layer connected to each core layer at each first end of the two tapered waveguides;
The semiconductor optical waveguide device according to any one of claims 1 to 4, further comprising:   The two tapered waveguides are connected to the semiconductor active optical waveguide via a bending waveguide, and end surfaces of the second end portions of the two tapered waveguides are used for light of the semiconductor optical waveguide device. The semiconductor waveguide device according to claim 5, wherein the semiconductor waveguide device is inclined with respect to an incident / exit end face.   The semiconductor optical waveguide according to claim 1, wherein the core layer of the tapered waveguide is formed by selective growth using a selective growth mask having a mask width of 80 μm or less. element.   8. A semiconductor optical waveguide array element comprising two or more semiconductor optical waveguide elements according to claim 1 arranged in an array at intervals of 100 [mu] m or less. A method of manufacturing an embedded semiconductor optical waveguide device formed on a substrate,
A selective growth step of forming a core layer whose thickness decreases in a tapered manner from the first end to the second end by the selective growth;
An etching step of etching the core layer having the tapered shape into a shape whose width decreases in a tapered shape from the first end portion toward the second end portion;
A method of manufacturing a semiconductor optical waveguide device, comprising:   In the selective growth step, the core layer is selectively grown so that a layer thickness ratio between a layer thickness at the first end and a layer thickness at the second end is 1.5 to 2.5, 10. The method of manufacturing a semiconductor optical waveguide device according to claim 9, wherein in the etching step, etching is performed so that a width of the second end portion is not less than 0.5 μm and not more than 1.0 μm.   11. The method of manufacturing a semiconductor optical waveguide device according to claim 9, wherein the selective growth step performs selective growth using a selective growth mask having a mask width of 80 [mu] m or less.   12. A method of manufacturing a semiconductor optical waveguide array element, comprising manufacturing the semiconductor optical waveguide elements arranged in an array at intervals of 100 [mu] m or less by the manufacturing method according to claim 9.

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