Embedded optical waveguide structure, integrated semiconductor laser device, and method for manufacturing embedded optical waveguide structure

Abstract

In an embedded optical waveguide structure (100), for example, a waveguide (20) has: a first portion (20-1); a second portion (20-2) narrower than the first portion (20-1); and a third region (20-3) that is adjacent to the first region (20-1) in a third direction, is optically connected to the first region (20-1), and has an end surface in the third direction, the first direction being a crystal orientation [100] direction, the second direction being a crystal orientation [0-11] direction or a crystal orientation [01-1] direction, and the third direction being a crystal orientation [011] direction or a crystal orientation [0-1-1] direction. The normal direction at each position of the end surface (20a) faces the first direction, the second direction, or the direction opposite to the second direction and the third direction, and is inclined with respect to the crystal orientation [111] direction or the crystal orientation [1-1-1] direction.

Description

Technical Field

[0001] The present invention relates to an embedded optical waveguide structure, an integrated semiconductor laser device, and a method for manufacturing an embedded optical waveguide structure. Background Art

[0002] As a conventional embedded optical waveguide structure, a structure in which one waveguide having a wide width and one waveguide having a narrow width are optically connected is known (for example, Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: JP Patent No. 5100881 Gazette Summary of the Invention

[0006] -Problems to be Solved by the Invention-

[0007] Through intensive research by the inventors, it has been found that in such an embedded optical waveguide structure, voids are generated near the end face on the narrow waveguide side of the waveguide having a wide width, and sometimes the optical characteristics are degraded due to light reflection caused by the voids.

[0008] Therefore, one of the problems of the present invention is to obtain a new embedded optical waveguide structure, an integrated semiconductor laser device, and a method for manufacturing an embedded optical waveguide structure that can suppress, for example, a decrease in optical characteristics accompanying the generation of voids and are improved.

[0009] -Means for Solving the Problems-

[0010] The buried optical waveguide structure of the present invention is made of, for example, a semiconductor crystal, and includes: a waveguide including a first cladding layer, a core layer, and a second cladding layer laminated in a first direction; and a buried layer adjacent to the waveguide in a direction intersecting the first direction. The buried optical waveguide structure is characterized in that the waveguide has: a first portion extending in a third direction intersecting the first direction and the second direction along a first width in a second direction intersecting the first direction; a second portion located at a position deviated from the first portion in the third direction, optically connected to the first portion, and extending in the third direction along a second width narrower than the first width in the second direction; and a third portion adjacent to the first portion in the third direction, optically connected to the first portion, and having an end face in the third direction. The first direction is the crystal orientation

[100] direction, the second direction is the crystal orientation [0-11] direction or the crystal orientation [01-1] direction, the third direction is the crystal orientation

[011] direction or the crystal orientation [0-1-1] direction, the normal direction at each position of the end face faces the first direction, the second direction, or a direction between the opposite direction of the second direction and the third direction, and is inclined with respect to the crystal orientation

[111] direction or the crystal orientation [1-1-1] direction.

[0011] In the buried optical waveguide structure, it may also be that, when observed in the opposite direction of the first direction, there is a first angular difference between the positive projection of the vector along the normal direction at each position of the end face onto a virtual plane intersecting the first direction and the third direction.

[0012] In the buried optical waveguide structure, it may also be that the absolute value of the first angular difference that is an acute angle is 35° ± 5.5°.

[0013] In the buried optical waveguide structure, it may also be that the end face has a portion that goes toward the third direction as it goes toward the second direction.

[0014] In the buried optical waveguide structure, it may also be that the end face has a portion that goes toward the opposite direction of the third direction as it goes toward the second direction.

[0015] In the buried optical waveguide structure, it may also be that the end face includes a convex portion or a concave portion.

[0016] In the buried optical waveguide structure, it may also be that the tangent direction at each position on the boundary line in the cross-section of the end face intersecting the first direction is along the direction between the third direction and the second direction or the opposite direction of the second direction.

[0017] In the buried optical waveguide structure, it is also possible that the absolute value of the second angular difference, which is an acute angle between the tangential direction and the third direction, is 55° ± 5.5°.

[0018] In the buried optical waveguide structure, it is also possible that the first portion and the third portion constitute a multimode interference waveguide optically connected to one of the second portions.

[0019] In the buried optical waveguide structure, it is also possible that the waveguide and the buried layer are made of a III-V compound semiconductor having a zinc blende structure.

[0020] The buried optical waveguide structure is made of a semiconductor crystal and includes: a waveguide including a first cladding layer, a core layer, and a second cladding layer stacked in a first direction; and a buried layer adjacent to the waveguide in a direction intersecting the first direction. The buried optical waveguide structure is characterized in that the waveguide has: a first portion extending in a third direction intersecting the first direction and the second direction along a first width in a second direction intersecting the first direction; a second portion located at a position deviated from the first portion in the third direction, optically connected to the first portion, and extending in the third direction along a second width narrower than the first width in the second direction; and a third portion adjacent to the first portion in the third direction, optically connected to the first portion, and having an end face in the third direction. The first direction is the crystal orientation

[100] direction, the second direction is the crystal orientation [0-11] direction or the crystal orientation [01-1] direction, the third direction is the crystal orientation

[011] direction or the crystal orientation [0-1-1] direction, and the end face has a portion whose normal direction faces the first direction, the second direction, or the direction between the second direction and the opposite direction of the third direction and is inclined with respect to the

[111] direction or the [1-1-1] direction.

[0021] In the buried optical waveguide structure, it is also possible that the boundary line in the cross section intersecting the first direction of the end face has a portion whose tangential direction is along the direction between the second direction and the third direction.

[0022] The integrated semiconductor laser device of the present invention includes, for example: the buried optical waveguide structure; a plurality of waveguides optically connected to the first portion on the side opposite to the second portion with respect to the first portion; and a semiconductor laser optically connected to each waveguide on the side opposite to the first portion.

[0023] In addition, a method for manufacturing the buried optical waveguide structure of the present invention, for example, includes the following steps: forming a laminate of a first cladding layer, a core layer, and a second cladding layer laminated in the first direction on a substrate intersecting the first direction; etching the laminate in a direction opposite to the first direction to form a recess, and forming a waveguide adjacent to the recess; and burying the recess with a buried layer. The method for manufacturing the buried optical waveguide structure is characterized in that the waveguide has: a first portion extending in a third direction intersecting the first direction and the second direction with a first width in a second direction intersecting the first direction; a second portion located at a position deviated from the first portion in the third direction, optically connected to the first portion, and extending in the third direction with a second width narrower than the first width in the second direction; and a third portion adjacent to the first portion in the third direction, optically connected to the first portion, and having an end face in the third direction. The first direction is the crystal orientation

[100] direction, the second direction is the crystal orientation [0-11] direction or the crystal orientation [01-1] direction, the third direction is the crystal orientation

[011] direction or the crystal orientation [0-1-1] direction, and the end face has a portion whose normal direction faces the first direction, the second direction, or a direction between the opposite direction of the second direction and the third direction and is inclined with respect to the

[111] direction or the [1-1-1] direction.

[0024] -Advantages of the Invention-

[0025] According to the present invention, a new buried optical waveguide structure, an integrated semiconductor laser device, and a method for manufacturing a buried optical waveguide structure with improved performance can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is an exemplary and schematic top view of the buried optical waveguide structure of the first embodiment.

[0027] Figure 2 is Figure 1 sectional view taken along line II-II of

[0028] Figure 3 is an exemplary and schematic sectional view at an equivalent position showing a state in which a plurality of layers are laminated on a substrate to form a laminate in the method for manufacturing the buried optical waveguide structure of the first embodiment, Figure 2 equivalent to

[0029] Figure 4 is an exemplary and schematic sectional view at an equivalent position showing a state in which a waveguide is formed by etching the laminate of Figure 3 in the method for manufacturing the buried optical waveguide structure of the first embodiment, Figure 2An exemplary and schematic cross-sectional view at the same position.

[0030] Figure 5 It is an exemplary and schematic top view of an embedded optical waveguide structure of a reference example.

[0031] Figure 6 It is Figure 5 the cross-sectional view taken along VI-VI.

[0032] Figure 7 It is a graph showing an example of the relationship between the applied current to a laser element and the increase rate of the optical output of the laser element with respect to the applied current when the output light of the laser element is transmitted through the embedded optical waveguide structure of the reference example.

[0033] Figure 8 It is a graph showing an example of the relationship between the applied current to a laser element and the increase rate of the optical output of the laser element with respect to the applied current when the output light of the laser element is transmitted through the embedded optical waveguide structure of the first embodiment.

[0034] Figure 9 It is an exemplary and schematic top view of an embedded optical waveguide structure of the second embodiment.

[0035] Figure 10 It is an exemplary and schematic top view of an embedded optical waveguide structure of the third embodiment.

[0036] Figure 11 It is an exemplary and schematic top view of an embedded optical waveguide structure of the fourth embodiment.

[0037] Figure 12 It is an exemplary and schematic top view of an embedded optical waveguide structure of the fifth embodiment.

[0038] Figure 13 It is an exemplary and schematic top view of an embedded optical waveguide structure of the sixth embodiment.

[0039] Figure 14 It is an exemplary and schematic top view of an embedded optical waveguide structure of the seventh embodiment configured as an integrated semiconductor laser device. Detailed Embodiments

[0040] Hereinafter, exemplary embodiments of the present invention will be disclosed. The structures of the embodiments shown below, the actions and results (effects) brought about by these structures are examples. The present invention can also be implemented by structures other than those disclosed in the following embodiments. In addition, according to the present invention, at least one of various effects (including derivative effects) obtained by the structures can be achieved.

[0041] The following-described multiple embodiments have the same structure. Therefore, based on the structure of each embodiment, the same functions and effects based on this same structure can be obtained. In addition, hereinafter, the same reference numerals may be assigned to these same structures, and repeated descriptions may be omitted.

[0042] In this specification, ordinal numbers are given for the convenience of distinguishing directions, parts, etc., and do not represent priority order, sequence, nor limit the number.

[0043] In each figure, the X direction is indicated by an arrow X, the Y direction is indicated by an arrow Y, and the Z direction is indicated by an arrow Z. The X direction, Y direction, and Z direction intersect and are orthogonal to each other. In addition, the X direction is referred to as the extending direction, the Y direction is referred to as the width direction, and the Z direction is referred to as the height direction or the stacking direction.

[0044] In addition, each figure is a schematic diagram for illustrative purposes, and the scales and ratios in each figure and the actual object are not necessarily the same.

[0045] [First Embodiment]

[0046] [Basic Structure]

[0047] Figure 1 is a top view of the buried optical waveguide structure 100A (100) of the first embodiment.

[0048] As Figure 1 shown, the buried optical waveguide structure 100A (100) includes three waveguides 20-1 to 20-3 arranged in the X direction. The buried optical waveguide structure 100A (100) is made of a semiconductor crystal.

[0049] The waveguide 20-1 extends in the X direction with a substantially constant width W1 in the Y direction and a substantially constant height in the Z direction. The waveguide 20-1 is an example of the first part of the waveguide 20 (see Figure 2 ). In addition, the width W1 is an example of the first width.

[0050] The waveguide 20-2 extends in the X direction with a substantially constant width W2 in the Y direction and a substantially constant height in the Z direction. As Figure 1 can be seen, the width W2 is narrower than the width W1 of the waveguide 20-3. The waveguide 20-2 is located at a position offset in the X direction with respect to the waveguide 20-1. The waveguide 20-2 is an example of the second part of the waveguide 20. In addition, the width W2 is an example of the second width.

[0051] The waveguide 20-3 is located between the waveguides 20-1 and 20-2. In other words, the waveguide 20-3 is adjacent to the waveguide 20-1 in the X direction and adjacent to the waveguide 20-2 in the opposite direction of the X direction. The waveguides 20-1, 20-3, and 20-2 are arranged in sequence in the X direction.

[0052] The heights of the waveguides 20-1, 20-3, and 20-2 in the Z direction are the same. In addition, the width W3 of the waveguide 20-3 changes as it goes in the X direction. Specifically, in the present embodiment, at the position where it is connected to the waveguide 20-1, the width W3 is the same as the width W1, and at the position where it is connected to the waveguide 20-2, the width W3 is the same as the width W2. And the width W3 gradually narrows linearly from the width W1 to the width W2 as it goes in the X direction. The waveguide 20-3 with such a structure is optically connected to both the waveguide 20-1 and the waveguide 20-2. The waveguide 20-3 is an example of the third part of the waveguide 20.

[0053] In this case, the waveguides 20-1 and 20-3 can be, for example, multimode interference waveguides optically connected to the waveguide 20-2.

[0054] Figure 2 is Figure 1 a cross-sectional view taken along line II-II. As Figure 2 shown, the waveguide 20 has a first cladding layer 21, a core layer 22, and a second cladding layer 23 stacked in the Z direction on the substrate 10. The Z direction is an example of the first direction.

[0055] The first cladding layer 21 is made of, for example, n-InP, and the second cladding layer 23 is made of, for example, p-InP. In addition, the core layer 22 is made of, for example, GaInAsP. In addition, a buried layer 31 is provided adjacent to the waveguide 20 in a direction intersecting the Z direction. That is, the core layer 22 is surrounded by the first cladding layer 21, the second cladding layer 23, and the buried layer 31. In addition, the waveguide 20 and the buried layer 31 are all covered by the upper layer 32. The buried layer 31 is made of, for example, p-InP and n-InP, and the upper layer 32 is made of, for example, p-InP. In addition, the buried layer 31 is sometimes covered by an insulating layer (not shown). In addition, depending on the part, there are also cases where a contact layer and an electrode (not shown) are further provided on the upper layer 32.

[0056] Figure 1 The shapes of the waveguides 20-1 to 20-3 shown represent Figure 2 the shape at the position of I-I in

[0057] [Manufacturing method]

[0058] Figure 3 ,Figure 4 are cross-sectional views at equivalent positions showing the states of respective stages of a method for manufacturing an embedded optical waveguide structure 100A (100), and Figure 2 equivalent positions.

[0059] First, as Figure 3 shown, a laminate 50 is formed on a substrate 10, which is laminated with a first cladding layer 21, a core layer 22, and a second cladding layer 23 in the Z direction. Further, a dielectric mask 42 is formed on the second cladding layer 23. The dielectric mask 42 is formed into a given shape. The dielectric mask 42 may also be referred to as an etching mask or a mask.

[0060] Next, as Figure 4 shown, a portion of the laminate 50 that is exposed from the dielectric mask 42 is etched and removed in the direction opposite to the Z direction. The etching in this case is dry etching or wet etching. Through this process, a recess C is formed in the laminate 50, and a portion that remains without being removed as the recess C, that is, a portion adjacent to the recess C, becomes a waveguide 20.

[0061] After the state of Figure 4 , the recess C is buried by an embedded layer 31 through epitaxial growth. After the sacrificial layer 41 and the dielectric mask 42 are removed, it is covered with an upper layer 32 and becomes the state of Figure 2 .

[0062] Here, as Figure 4 shown, a side surface 20a of the waveguide 20 formed by etching the laminate 50 is inclined with respect to the Z direction. Specifically, the side surface 20a is inclined within a virtual plane Vp (see Figure 1 ) that is orthogonal to each position of the X-direction edge 42a of the dielectric mask 42 so as to approach the inside of the dielectric mask 42 as it goes in the Z direction. The side surface 20a is an example of an end surface.

[0063] [Generation of voids]

[0064] Figure 5 is a top view of an embedded optical waveguide structure 100R of a reference example, Figure 6 is Figure 5 a VI-VI cross-sectional view. In addition, Figure 5 the dashed line in Figure 6 represents the shape of the side surface 20r of the waveguide 20 at the V-V position in

[0065] The inventors et al. found through in-depth research that in the embedded optical waveguide structure 100R of the reference example, due to the relationship between the normal direction at each position of the side surface 20a and the crystal orientation, voids 50a, 50b may be generated in the embedded layer 31 and the upper layer 32 during the processes of forming the embedded layer 31 and the upper layer 32 (see Figure 6 ).

[0066] According to Figure 5 it can be seen that in the reference example, there is no waveguide 20-3, and the side surface 20r of the waveguide 20-1, which is the end surface in the X direction, extends substantially along the Y direction.

[0067] In the etching process of forming the above-mentioned recess C, a dielectric mask 42 with an edge 42a extending in the Y direction (refer to Figure 6 ) is used to form a side surface 20r extending in the Y direction. In this case, in this etching process, the side surface 20r is inclined in a virtual plane Vp (refer to Figure 5 , the XZ plane) orthogonal to the edge 42a extending in the Y direction so as to approach the inside of the dielectric mask 42 as it goes in the Z direction. In addition, in the buried optical waveguide structure 100R of the reference example, the X direction, that is, the extending direction of the waveguide 20, is the crystal orientation

[011] direction, the Y direction, that is, the width direction of the waveguide 20, is the crystal orientation [0-11] direction, and the Z direction, that is, the stacking direction of the waveguide 20 and the buried layer 31, is the crystal orientation

[100] direction. In this case, there may be a portion P1 on the side surface 20r where the normal direction Dr thereof faces the direction in the middle between the X direction and the Z direction, that is, the crystal orientation

[111] direction. In addition, the normal vector Vr is set as a unit vector facing the normal direction Dr.

[0068] Here, when the materials constituting the waveguide 20 and the buried layer 31 are made of, for example, a III-V group compound semiconductor having a zinc blende structure, at the portion P1 where the normal direction Dr faces the crystal orientation

[111] direction, the bonding force between the crystals becomes weak. Therefore, in the epitaxial growth of forming the buried layer 31, it is estimated that a region where the buried layer 31 does not accumulate, that is, a void 50a, appears on the portion P1 where the normal direction Dr faces the crystal orientation

[111] direction.

[0069] Furthermore, with the appearance of this portion P1 and the void 50a, in the epitaxial growth, in the direction orthogonal to the normal direction Dr, in Figure 6 the case of Figure 6 the direction between the opposite direction of the Z direction and the X direction ( Figure 6 the upper right direction in the paper surface of Figure 6 , hereinafter referred to as the growth direction), the stacking of the buried layer 31 is promoted. In this case, there may sometimes be a void 50b generated in the portion that becomes the back of the dielectric mask 42 in this growth direction.

[0070] The portion P1 is not limited to Figure 6The position may also be at other positions on the side surface 20r. Therefore, when the above-described gaps 50a and 50b appear relatively close to the core layer 22 of the waveguide 20, reflection and scattering of the guided light occur, and accordingly, the light transmission characteristics in the waveguide 20 deteriorate. In addition, the same problem also occurs in the portion where the normal direction faces the crystal orientation [1-1-1] direction.

[0071] [Structure capable of suppressing gaps]

[0072] Therefore, in the buried optical waveguide structure 100A (100) of the present embodiment, a waveguide 20-3 is provided, and the normal direction at each position of the side surface 20a of the waveguide 20-3 is set to a direction inclined with respect to the crystal orientation

[111] direction. As described above, the crystal orientation

[111] direction is the direction that is the midpoint between the X direction and the Z direction. Regarding this point, refer to Figure 1 , Figure 2 for description.

[0073] The side surface 20a is configured to include a portion 20a1 that goes in the opposite direction of the X direction as it goes in the Y direction and a portion 20a2 that goes in the X direction as it goes in the Y direction.

[0074] As Figure 2 shown, the normal vector Vn1 at the portion P1 (P) on the side surface 20a1 faces the direction between the X direction and the Z direction, and as Figure 1 shown, it faces the direction between the X direction and the Y direction. That is, the normal vector Vn1, in other words, the normal direction of the portion P1 faces the direction between the X direction, the Y direction, and the Z direction. Regarding the portion P1 (P), the X direction is an example of the third direction, and the Y direction is an example of the second direction.

[0075] In addition, as Figure 1 shown, the side surface 20a1 is configured such that, when viewed in the opposite direction of the Z direction, the positive projection of the normal vector Vn1 at each position on the side surface 20a1 onto the virtual plane (i.e., the XY plane) that intersects the Z direction (i.e., Figure 1 the arrow of Vn1 in

[0076] generates an angular difference θ between the X direction. The angular difference θ is an example of the first angular difference.

[0077] The normal vector Vn2 at the portion P2 (P) on the side surface 20a2 and Figure 2The indicated part P1 is the same, facing the direction between the X direction and the Z direction, and as Figure 1 shown, facing the direction between the X direction and the opposite direction of the Y direction. That is, the normal vector Vn2, in other words, the normal direction of the part P2, faces the direction between the opposite direction of the X direction, the Y direction, and the Z direction. Regarding the part P2 (P), the X direction is an example of the third direction, and the opposite direction of the Y direction is an example of the second direction.

[0078] In addition, as Figure 1 shown, the side surface 20a2 is configured such that, when viewed in the opposite direction of the Z direction, the positive projection of the normal vector Vn2 at each position on this side surface 20a2 onto the virtual plane (i.e., the XY plane) that intersects the Z direction (i.e., Figure 1 the arrow of Vn2 in

[0079] forms an angle difference θ with the X direction.

[0080] By forming the side surface 20a2 (20a) such that the normal vector Vn2 becomes the above state, a state can be obtained in which the normal direction of each part P2 on the side surface 20a2 (20a), that is, the direction in which the normal vector Vn2 faces, is inclined with respect to the crystal orientation

[111] direction.

[0080] Through in-depth research by the inventors and others, it was determined that the angle difference θ is preferably 35° ± 5.5°.

[0081] In addition, in the above structure, it can be said that the tangent direction at each position on the boundary line in the cross-section of the side surface 20a (20a1, 20a2) that intersects the Z direction, that is, the Figure 1 tangent direction of the dotted line at each position on the dotted line representing the side surfaces 20a1 and 20a2 in

[0082] extends in the direction between the X direction and the Y direction or the opposite direction of the Y direction.

[0083] Figure 7 is a graph showing an example of the relationship between the applied current If [mA] to the laser element and the increase rate dL / dI (W / A) of the light output of the laser element with respect to this applied current (hereinafter, referred to as the current-increase rate characteristic) when the output light of the laser element is transmitted through the buried optical waveguide structure 100R of the reference example. In addition, Figure 8 is a graph showing an example of the relationship between the applied current If [mA] to the laser element and the increase rate dL / dI (W / A) of the light output of the laser element with respect to this applied current when the output light of the laser element is transmitted through the buried optical waveguide structure 100A (100) of the first embodiment.

[0084] In Figure 7 the reference example shown, due to the appearance of the gaps 50a and 50b, as Figure 7 enclosed by the dashed-line box in, a disorder (kink) occurs in the current-increase rate characteristic. In contrast, in Figure 8 the present embodiment shown, the generation of the gaps 50a and 50b is suppressed, and accordingly, no Figure 7 disorder such as that shown in the current-increase rate characteristic occurs.

[0085] As described above, according to the present embodiment, it is possible to avoid a portion on the side surface 20a where the normal direction faces the crystal orientation

[111] direction. Therefore, it is possible to suppress the generation of the gaps 50a and 50b corresponding to the portion where the normal direction faces the crystal orientation

[111] direction, and further, it is possible to suppress a decrease in the light transmission characteristic in the waveguide 20 due to the reflection of light by the gaps 50a and 50b.

[0086] By setting the end edge 42a in the X direction of the dielectric mask 42 such that the tangential direction at each position of the end edge 42a extends in a direction between the X direction and the Y direction or the opposite direction of the Y direction, it is possible to form the side surface 20a that can obtain the above effects. In this case, the angular difference α that forms an acute angle between the tangential direction and the X direction at each position of the end edge 42a is preferably 55° ± 5.5°.

[0087] [Second Embodiment]

[0088] Figure 9 is a top view of the buried optical waveguide structure 100B (100) of the second embodiment. Comparing Figure 9 with that of the first embodiment Figure 1 it can be seen that in the present embodiment, the positions of the waveguides 20-2 and 20-3 relative to the waveguide 20-1 are opposite to those in the first embodiment. In the present embodiment, the opposite direction of the X direction, that is, the crystal orientation [0-1-1] direction, is an example of the third direction.

[0089] In the buried optical waveguide structure 100B (100) of the present embodiment, the normal direction at each position of the side surface 20a of the waveguide 20-3 is set to a direction inclined with respect to the crystal orientation [1-1-1] direction. The crystal orientation [1-1-1] direction is a direction that is the midpoint between the opposite direction of the X direction and the Z direction.

[0090] The normal vector Vn1 at the portion P1 (P) on the side surface 20a1 faces the direction between the opposite direction of the X direction and the Z direction in the same manner as in the first embodiment, and as Figure 9As shown, the direction between the opposite direction of the X direction and the Y direction. That is, the normal vector Vn1, in other words, the normal direction of the part P1 faces the opposite direction of the X direction, the direction between the Y direction and the Z direction.

[0091] In addition, as Figure 9 shown, the side surface 20a1 is configured such that, when observed in the opposite direction of the Z direction, the positive projection of the normal vector Vn1 at each position on the side surface 20a1 onto the virtual plane (i.e., the XY plane) that intersects the Z direction (i.e., Figure 9 the arrow of Vn1 in

[0092] generates an angular difference θ between the opposite direction of the X direction. By forming the side surface 20a1 (20a) such that the normal vector Vn1 is in the above state, it is possible to obtain a state where the normal direction of each part P1 on the side surface 20a1 (20a), that is, the direction in which the normal vector Vn1 faces, is inclined with respect to the crystal orientation [1 - 1 - 1] direction.

[0093] The normal vector Vn2 at the part P2 (P) on the side surface 20a2 is the same as that of the part P1 shown in Figure 9 and faces the direction between the opposite direction of the X direction and the Z direction, and as Figure 9 shown, it faces the direction between the opposite direction of the X direction and the opposite direction of the Y direction. That is, the normal vector Vn2, in other words, the normal direction of the part P2 faces the direction between the opposite direction of the X direction, the opposite direction of the Y direction, and the Z direction.

[0094] In addition, as Figure 9 shown, the side surface 20a2 is configured such that, when observed in the opposite direction of the Z direction, the positive projection of the normal vector Vn2 at each position on the side surface 20a2 onto the virtual plane (i.e., the XY plane) that intersects the Z direction (i.e., Figure 9 the arrow of Vn2 in

[0095] generates an angular difference θ between the opposite direction of the X direction. By forming the side surface 20a2 (20a) such that the normal vector Vn2 is in the above state, it is possible to obtain a state where the normal direction of each part P2 on the side surface 20a2 (20a), that is, the direction in which the normal vector Vn2 faces, is inclined with respect to the crystal orientation [1 - 1 - 1] direction.

[0096] Through in - depth research by the inventors and the like, it has been found that the angular difference θ is preferably 35° ± 5.5°, the same as in the above - mentioned first embodiment.

[0097] In addition, in the above - mentioned structure, it can be said that the tangent direction at each position on the boundary line in the cross - section of the side surface 20a (20a1, 20a2) that intersects the Z direction, that is, the one representing Figure 9At each position on the dotted line of the side surfaces 20a1 and 20a2 in [it], the tangential direction of the dotted line extends in a direction between the opposite direction of the X direction and the Y direction or the opposite direction of the Y direction.

[0098] Moreover, through in-depth research by the inventors and the like, it has been determined that the acute angle difference α between the tangential direction and the X direction is preferably 55° ± 5.5° in the same manner as in the above-described first embodiment.

[0099] According to the above-described second embodiment, the same effects as those of the first embodiment can also be obtained.

[0100] [Third Embodiment]

[0101] Figure 10 is a top view of the buried optical waveguide structure 100C (100) of the third embodiment. Figure 10 Comparing with that of the first embodiment Figure 1 it can be seen that in this embodiment, the positions of the two side surfaces 20a are opposite to those of the first embodiment. However, the shape of each side surface 20a is the same as any one of the side surfaces 20a of the first embodiment. Therefore, according to this embodiment, the same effects as those of the first embodiment can also be obtained.

[0102] [Fourth Embodiment, Fifth Embodiment, Sixth Embodiment]

[0103] Figure 11 is a top view of the buried optical waveguide structure 100D (100) of the fourth embodiment. Figure 12 is a top view of the buried optical waveguide structure 100E (100) of the fifth embodiment. Figure 13 is a top view of the buried optical waveguide structure 100F (100) of the sixth embodiment.

[0104] In the first to third embodiments, the side surface 20a is formed in a substantially planar shape. In contrast, as Figures 11 to 13 shown, in the fourth to sixth embodiments, each side surface 20a has a curved surface shape or a shape formed by bending a plurality of planes, and has a concave portion or a convex portion. In the fourth embodiment, the side surface 20a is formed in a concave curved surface shape. In the fifth embodiment, the side surface 20a is formed in a convex curved surface shape. In addition, in the sixth embodiment, a groove formed by the intersection of two planes extending in different directions is formed in the side surface 20a. Alternatively, a ridge line formed by the intersection of two planes extending in different directions may be formed in the side surface 20a.

[0105] As in the fourth to sixth embodiments, even when the side surface 20a includes a concave portion or a convex portion, as long as the normal direction of each position on the side surface 20a faces a direction inclined with respect to the crystal orientation

[111] direction or the crystal orientation [1-1-1] direction, the same effects as those of the first embodiment can be obtained. The shape of the side surface 20a is not limited to the shapes of the above embodiments.

[0106] [Seventh Embodiment]

[0107] Figure 14 FIG. 7 is a top view of the buried optical waveguide structure 100G (100) of the seventh embodiment. The buried optical waveguide structure 100G is configured as an integrated semiconductor laser device. The buried optical waveguide structure 100G includes: a plurality of waveguides 20-4 optically connected to the waveguide 20-1 on the side opposite to the waveguide 20-2; and a semiconductor laser 110 optically connected to each waveguide 20-4 on the side opposite to the waveguide 20-1. The semiconductor laser 110 is a laser element such as a DFB laser, for example. The waveguide 20-2 can be configured as a semiconductor optical amplifier. In addition, as the waveguide 20-1, in addition to the structures shown in the above embodiments, appropriately deformed structures, combined structures, etc. can also be adopted. The buried optical waveguide structure 100G of the present embodiment can be applied to the same structure as that of Japanese Patent No. 5100881.

[0108] The embodiments of the present invention have been illustrated above, but the above embodiments are examples and do not intend to limit the scope of the invention. The above embodiments can be implemented in various other ways, and various omissions, substitutions, combinations, and changes can be made without departing from the gist of the invention. In addition, various specifications (structures, types, directions, forms, sizes, lengths, widths, thicknesses, heights, numbers, arrangements, positions, materials, etc.) of each structure, shape, etc. can be appropriately changed and implemented.

[0109] For example, it is not necessary for the normal direction of all positions on the end face to be inclined with respect to the crystal orientation

[111] direction or the crystal orientation [1-1-1] direction.

[0110] Industrial Applicability

[0111] The present invention can be used for a buried optical waveguide structure, an integrated semiconductor laser device, and a method for manufacturing a buried optical waveguide structure.

[0112] -Description of Reference Numerals-

[0113] 10... Substrate

[0114] 20... Waveguide

[0115] 20-1... Waveguide (first part)

[0116] 20-2... Waveguide (second part)

[0117] 20-3... Waveguide (third part)

[0118] 20-4... Waveguide

[0119] 20a, 20a1, 20a2... Side surface (end surface)

[0120] 20r... Side surface

[0121] 21... First cladding layer

[0122] 22... Core layer

[0123] 23... Second cladding layer

[0124] 31... Buried layer

[0125] 32... Upper layer

[0126] 42... Dielectric mask

[0127] 42a... Edge

[0128] 50... Stacked body

[0129] 50a, 50b... Gap

[0130] 100, 100A~100F... Buried optical waveguide structure

[0131] 100G... Buried optical waveguide structure (integrated semiconductor laser device)

[0132] 110... Semiconductor laser

[0133] C... Recess

[0134] Dr... Normal direction

[0135] P1, P2, P... Part

[0136] Vn1, Vn2... Normal vector

[0137] Vp... Virtual plane

[0138] Vr... Normal vector

[0139] W1... Width (first width)

[0140] W2... Width (second width)

[0141] W3... Width

[0142] X... Direction (third direction, or the opposite direction of the third direction)

[0143] Y... Direction (second direction, or the opposite direction of the second direction)

[0144] Z... direction (first direction)

[0145] α... angular difference (second angular difference)

[0146] θ... angular difference (first angular difference).

Claims

1. An embedded optical waveguide structure made of a semiconductor crystal, comprising: a waveguide including a first cladding layer, a core layer, and a second cladding layer stacked in a first direction; and a buried layer adjacent to the waveguide in a direction intersecting the first direction. The embedded optical waveguide structure is characterized in that the waveguide has: a first portion extending in a third direction intersecting the first direction and the second direction along a first width in a second direction intersecting the first direction; a second portion located at a position deviated from the first portion in the third direction, optically connected to the first portion, and extending in the third direction along a second width narrower than the first width in the second direction; and a third portion adjacent to the first portion in the third direction, optically connected to the first portion, and having an end face in the third direction, the first direction is the crystal orientation [100] direction, the second direction is the crystal orientation [0-11] direction or the crystal orientation [01-1] direction, the third direction is the crystal orientation [011] direction or the crystal orientation [0-1-1] direction, the normal direction at each position of the end face faces the first direction, the second direction, or the direction between the opposite direction of the second direction and the third direction, and is inclined with respect to the crystal orientation [111] direction or the crystal orientation [1-1-1] direction.

2. The embedded optical waveguide structure according to claim 1, wherein when observed in the opposite direction of the first direction, there is a first angular difference between the positive projection of the vector along the normal direction at each position of the end face on a virtual plane intersecting the first direction and the third direction.

3. The embedded optical waveguide structure according to claim 2, wherein the absolute value of the first angular difference that is an acute angle is 35° ± 5.5°.

4. The embedded optical waveguide structure according to claim 1 or 2, wherein the end face has a portion that goes toward the third direction as it goes toward the second direction.

5. The embedded optical waveguide structure according to claim 1 or 2, wherein the end face has a portion that goes toward the opposite direction of the third direction as it goes toward the second direction.

6. The embedded optical waveguide structure according to claim 1 or 2, wherein the end face includes a convex portion or a concave portion.

7. The embedded optical waveguide structure according to claim 1 or 2, wherein the tangent direction at each position on the boundary line in the cross section of the end face intersecting the first direction is along the direction between the third direction and the second direction or the opposite direction of the second direction.

8. The embedded optical waveguide structure according to claim 7, wherein the absolute value of the second angular difference that is an acute angle between the tangent direction and the third direction is 55° ± 5.5°.

9. The embedded optical waveguide structure according to claim 1 or 2, wherein the first portion and the third portion constitute a multimode interference waveguide optically connected to one second portion.

10. The buried optical waveguide structure according to claim 1 or 2, wherein, the waveguide and the buried layer are made of a III-V compound semiconductor having a zinc blende structure.

11. A buried optical waveguide structure made of a semiconductor crystal, comprising: a waveguide including a first cladding layer, a core layer, and a second cladding layer stacked in a first direction; and a buried layer adjacent to the waveguide in a direction intersecting the first direction, the buried optical waveguide structure is characterized in that, the waveguide has: a first portion extending in a third direction intersecting the first direction and the second direction along a first width in a second direction intersecting the first direction; a second portion located at a position deviated from the first portion in the third direction, optically connected to the first portion, and extending in the third direction along a second width narrower than the first width in the second direction; and a third portion adjacent to the first portion in the third direction, optically connected to the first portion, and having an end face in the third direction, the first direction is the crystal orientation [100] direction, the second direction is the crystal orientation [0-11] direction or the crystal orientation [01-1] direction, the third direction is the crystal orientation [011] direction or the crystal orientation [0-1-1] direction, the end face has a portion whose normal direction faces the first direction, the second direction, or the direction between the opposite direction of the second direction and the third direction and is inclined with respect to the [111] direction or the [1-1-1] direction.

12. The buried optical waveguide structure according to claim 11, wherein, the boundary line in the cross section of the end face intersecting the first direction has a portion whose tangent direction is along the direction between the second direction and the third direction.

13. An integrated semiconductor laser device, characterized in that, Comprising: the buried optical waveguide structure according to claim 1 or claim 11; a plurality of waveguides optically connected to the first portion on the side opposite to the second portion with respect to the first portion; and a semiconductor laser optically connected to each waveguide on the side opposite to the first portion.

14. A method for manufacturing a buried optical waveguide structure, comprising the following steps: forming a laminate of a first cladding layer, a core layer, and a second cladding layer stacked in the first direction on a substrate intersecting the first direction; Etch the laminate in a direction opposite to the first direction to form a recess, and form a waveguide adjacent to the recess; and burying the recess by the buried layer, the method for manufacturing the buried optical waveguide structure is characterized in that, the waveguide has: a first portion extending in a third direction intersecting the first direction and the second direction along a first width in a second direction intersecting the first direction; a second portion located at a position deviated from the first portion in the third direction, optically connected to the first portion, and extending in the third direction along a second width narrower than the first width in the second direction; and a third portion adjacent to the first portion in the third direction, optically connected to the first portion, and having an end face in the third direction, the first direction is the crystal orientation [100] direction, The second direction is the crystal orientation [0-11] direction or the crystal orientation [01-1] direction. The third direction is the crystal orientation [011] direction or the crystal orientation [0-1-1] direction. The end face has a portion whose normal direction faces the first direction, the second direction, or the direction between the opposite direction of the second direction and the third direction and is inclined with respect to the [111] direction or the [1-1-1] direction.

Images