JP2016126216A - Optical integrated element and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical integrated element in which internal variations in connection loss are small, and a manufacturing method therefor.SOLUTION: An optical integrated element comprises: a first waveguide type optical function element 140 formed on the same substrate 100a and having a first optical waveguide layer 140b; a second waveguide type optical function element 130 having a second optical waveguide layer 130b differing in thickness from the first optical waveguide layer 140b; and a connection optical waveguide 170 having a passive type connection optical waveguide layer 170b for connecting the first optical waveguide layer 140b and the second optical waveguide layer 130b. The connection optical waveguide has a thickness change section 170ba whose thickness changes, directing from the first end 170ba1 toward the second end 170ba2 of the connection optical waveguide 170b, so as to get closer to the thickness of the second optical waveguide layer 130b from the thickness of the first optical waveguide layer 140b, and a constant thickness section 170bb, connected to the second end 170ba2, being the same in thickness as the second end 170ba2 and having a fixed thickness in the waveguide direction of light.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an optical integrated device and a method for manufacturing the same.

  In order to respond to the increase in Internet traffic in recent years, introduction of digital coherent communication has been started in long-distance optical communication, and communication capacity has been increased. The next target of digital coherent communication is optical communication at short and medium distances, and miniaturization and low power consumption have been strongly demanded for optical transmission / reception devices. An LN (lithium niobate) modulator is used as a modulator for a current digital coherent communication transmitter, and a semiconductor modulator is a candidate for downsizing. For example, an InP-MZ (Mach-Zehnder) modulator using InP (indium phosphide) as a constituent material has a smaller chip size, a lower driving voltage, and a wider wavelength band that can be modulated compared to an LN modulator. Has been reported (see Non-Patent Document 1). In recent years, a low-power consumption and compact wavelength tunable laser module in which an InP-MZ optical modulator and a wavelength tunable laser are mounted on a multichip has been developed. Such a wavelength tunable laser module includes an optical integrated element in which optical functional elements having different functions of an optical modulator and a wavelength tunable laser are integrated on a single substrate.

  As an optical integrated element, an SOA (semiconductor optical amplification element) and an MZ optical modulator, which are different optical functional elements, are integrated on the same substrate (Patent Document 1), or on the same substrate, A device in which a DFB (distributed feedback type) laser element and an EA (electroabsorption type) optical modulator, which are different optical functional elements, are integrated (Patent Document 2) is disclosed.

JP 2009-198881 A JP 2002-324936 A

J. et al. S. Barton, et al. , “A Widely Tunable High-Speed Transmitter Using an Integrated SGDBR Laser-Semiconductor Optical Amplifier and Mach-Zehnder Modulator E, J. Sel. Topics Quantum Electron. , Vol. 9, no. 5, pp. 1113-1117, Sep. / Oct. 2003

  By the way, when integrating SOA and MZ optical modulator like patent document 1, it is desirable for the total thickness of the quantum well layer which is an optical waveguide layer of each element to be optimized according to each characteristic. . For example, for a phase modulator such as an MZ optical modulator, it is preferable to increase the total thickness of the quantum well layer in order to reduce the capacitance and increase the response characteristics. On the other hand, as for the SOA, when the total thickness of the quantum well layer is increased, the saturation output is lowered. Thus, when the total thickness of the quantum well layers of each device is optimized, the difference in the total thickness becomes large, and there is a problem that the connection loss increases at the junction portion of the device.

  In Patent Document 2, after the first quantum well layer having a large total thickness constituting the EA optical modulator is grown, the second quantum well layer having a thin total thickness constituting the DFB laser element is grown, and thereafter The portion between the first and second quantum well layers is removed by etching, and the optical waveguide layer connecting the first and second quantum well layers having different thicknesses is grown there. . At this time, the selective growth mask pattern is devised when growing the waveguide layer, the thickness of the waveguide layer is changed between the first quantum well layer side and the second quantum well layer side, and the connection loss is reduced. I try to decrease.

  However, in such a method, both the first and second quantum well layers having different thicknesses are etched during the etching for forming the optical waveguide layer. It is difficult to etch both by an appropriate etching amount. In particular, in Patent Document 2, the first quantum well layer constituting the EA optical modulator is an AlGaInAs-based multiple quantum well layer, and the second quantum well layer constituting the DFB laser element is an InGaAsP-based multiple quantum well layer. The etching for forming the optical waveguide layer is performed by dry etching and wet etching. In this case, since the material systems of the two quantum well layers are different, it is difficult to appropriately etch each quantum well layer by wet etching.

  In order to appropriately etch each quantum well layer, the first quantum well layer, the optical waveguide layer, and the second quantum well layer are grown in this order or in the reverse order in the light guiding direction. It is desirable to do. Specifically, first, a first quantum well layer is grown, a part of it is removed by etching, and an optical waveguide layer is regrown there. Further, a part of the optical waveguide layer is removed by etching, and the second quantum well layer is regrown there, or the steps are performed in the reverse order. By doing in this way, when etching, it can etch for every quantum well layer or every waveguide layer. However, the thickness of the optical waveguide layer continuously changes from the first quantum well layer toward the second quantum well layer. Therefore, when the part of the optical waveguide layer is etched to grow the next quantum well layer, if the position of the etching mask for etching the optical waveguide layer varies in the optical waveguide direction, The thickness of the optical waveguide layer in the etched cross section exposed to the side part varies. As a result, the thickness difference between the optical waveguide layer and the quantum well layer also varies at the junction between the optical waveguide layer and the quantum well layer formed by subsequent regrowth. There is a problem that the loss varies. Such variations in connection loss cause variations in internal connection loss in the optical integrated device.

  The present invention has been made in view of the above, and an object of the present invention is to provide an optical integrated device having a small variation in internal connection loss and a method for manufacturing the same.

  In order to solve the above-described problems and achieve the object, an optical integrated device according to an aspect of the present invention includes a first waveguide-type optical function having a first optical waveguide layer formed over the same substrate. A second optical waveguide element having a second optical waveguide layer having a thickness different from that of the first optical waveguide layer, the first optical waveguide layer, and the second optical waveguide layer; And a connection optical waveguide having a passive connection optical waveguide layer, wherein the connection optical waveguide layer includes a first end located on the first optical waveguide layer side and the second optical waveguide. A second end located on the layer side, from the thickness of the first optical waveguide layer to the thickness of the second optical waveguide layer from the first end toward the second end. A thickness changing portion whose thickness changes so as to approach the second end portion, and is connected to the second end portion and has the same thickness as the second end portion, and a light guiding method And having a Teiatsu of portion having a constant thickness in.

  In the optical integrated device according to one aspect of the present invention, the first waveguide optical functional element is a phase modulator, and the second waveguide optical functional element is a light emitting element or an optical amplifying element. Features.

  An optical integrated device according to an aspect of the present invention is characterized in that the first waveguide optical functional element has a high mesa structure, and the second waveguide optical functional element has a semiconductor buried structure. To do.

  The optical integrated device according to one aspect of the present invention is characterized in that the first and second optical waveguide layers have a multiple quantum well structure.

  The optical integrated device according to one aspect of the present invention is characterized in that the first optical waveguide layer is made of AlGaInAs or AlInAs, and the second optical waveguide layer is made of InGaAsP.

  The optical integrated device according to one aspect of the present invention is characterized in that the total thickness of the first optical waveguide layer is twice or more the total thickness of the second optical waveguide layer.

  An optical integrated device manufacturing method according to an aspect of the present invention includes a first waveguide-type optical functional device having a first optical waveguide layer formed on the same substrate, the first optical waveguide layer, Is a second waveguide type optical functional element having a second optical waveguide layer having a different thickness, and a passive connection optical waveguide layer connecting the first optical waveguide layer and the second optical waveguide layer. A connecting optical waveguide having a first optical waveguide layer, a first step of forming the first optical waveguide layer on the substrate, and a part of the first optical waveguide layer. A second step of removing the region and forming the connection optical waveguide layer in the removed region; removing a part of the connection optical waveguide layer; and forming a second optical waveguide layer in the removed region A first end located on the first optical waveguide layer side in the second step; A second end portion located on the second optical waveguide layer side, and the second light guide from the thickness of the first optical waveguide layer toward the second end portion from the first end portion. A thickness changing portion whose thickness changes so as to approach the thickness of the waveguide layer, and a thickness change portion connected to the second end portion, the same thickness as the second end portion, and constant in the light guiding direction The connecting optical waveguide layer is formed so as to have a constant thickness portion having a thickness, and in the third step, a part of the constant thickness portion of the connecting optical waveguide layer is removed. And

  According to the present invention, there is an effect that it is possible to realize an optical integrated device with small variation in internal connection loss.

FIG. 1 is a schematic plan view of the optical integrated device according to the first embodiment. FIG. 2 is a schematic cross-sectional view of the SOA shown in FIG. FIG. 3 is a schematic cross-sectional view of the optical modulator shown in FIG. 4 is a cross-sectional view of the optical integrated device shown in FIG. FIG. 5 is a diagram for explaining a method of manufacturing the optical integrated device shown in FIG. FIG. 6 is a diagram for explaining a method of manufacturing the optical integrated device shown in FIG. FIG. 7 is a diagram for explaining a method of manufacturing the optical integrated device shown in FIG. FIG. 8 is a diagram for explaining a method of manufacturing the optical integrated device shown in FIG. FIG. 9 is a diagram for explaining a method of manufacturing the optical integrated device shown in FIG. FIG. 10 is a diagram for explaining a method of manufacturing the optical integrated device shown in FIG.

  Embodiments of an optical integrated device and a method for manufacturing the same according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Moreover, in each drawing, the same code | symbol is attached | subjected suitably to the same or corresponding element. Furthermore, it should be noted that the drawings are schematic, and the relationship between the dimensions of each element, the ratio of each element, and the like may differ from the actual ones. Even between the drawings, there are cases in which portions having different dimensional relationships and ratios are included.

(Embodiment)
FIG. 1 is a schematic plan view of the optical integrated device according to the first embodiment. The optical integrated element 100 is formed on a substrate, receives seed light from a laser oscillation unit provided outside the optical integrated element 100, phase-modulates the seed light, and generates modulated signal light and local oscillation light (LO). Light) and a light modulator that outputs monitor light. As shown in FIG. 1, the optical integrated device 100 includes an optical input unit 110, optical waveguides 120, 121, 122, 123, two SOAs 130, 131, an optical modulator 140, and signal light output units 151, 152. And monitor light output units 151a and 152a and an LO light output unit 160.

  The optical waveguides 120, 121, 122, 123 are formed inside or on the surface of the substrate so as to extend along the surface of the substrate. One end of the optical waveguide 120 is connected to an optical input unit 110 that is a port for inputting seed light. The optical waveguide 120 branches at the branching portion 120 a, and one is connected to the SOA 130. The SOA 130 is further connected to the optical modulator 140 via a connection optical waveguide described later. The optical modulator 140 further outputs via the optical waveguides 121 and 122 signal light output units 151 and 152 which are ports for outputting signal light, and monitor light for monitoring the operation of the optical integrated device 100. The monitor light output units 151a and 152a are connected to the ports. The other branched side of the optical waveguide 120 is connected to the SOA 131. The SOA 131 is connected via an optical waveguide 123 to an LO light output unit 160 that is a port for outputting LO light.

  The optical modulator 140 includes four Mach-Zehnder interferometers (MZI) 141 formed by branching and joining optical waveguides by a plurality of optical couplers, and optical waveguides 142, 143, and 144. The optical waveguide 142 on the input side of the optical modulator 140 is branched into four by a two-stage waveguide type optical coupler and connected to the input side of the four MZIs 141. A 90-degree phase shifter (not shown) is connected to the output sides of the two MZIs 141 out of the four MZIs 141. Then, the MZI 141 to which the 90-degree phase shifter is connected and the MZI 141 to which the 90-degree phase shifter is not connected are joined as a pair by the waveguide type optical couplers of the optical waveguides 143 and 144, respectively. 122. Each of the optical waveguides 121 and 122 is branched, and one of the branched light is connected to the signal light output unit 151 or 152. With such a configuration, the signal light generated by performing the desired modulation by the optical modulator 140 is output from the signal light output units 151 and 152. The other branched side of the optical waveguides 121 and 122 is connected to the monitor light output units 151a and 152a.

  The SOA 130 optically amplifies one seed beam branched by the branching portion 120 a of the optical waveguide 120 and inputs the seed light to the optical modulator 140. The SOA 131 optically amplifies the other seed light branched by the branching part 120a of the optical waveguide 120, and outputs it from the LO light output part 160 as LO light.

  Next, the structure of the optical modulator 140 that is the first optical functional element and the SOAs 130 and 131 that are the second optical functional elements will be described. First, the SOA 130 will be described. Note that the SOA 131 also has the same cross-sectional structure as the SOA 130.

  FIG. 2 is a schematic cross-sectional view of the SOA 130 shown in FIG. 1 on a plane perpendicular to the light guiding direction. The SOA 130 includes a lower clad layer 130a made of n-InP that also serves as a buffer layer on a substrate 100a made of Fe-doped semi-insulating InP, which is a substrate of the optical integrated device 100. The active layer 130b, which is a second optical waveguide layer having a multiple quantum well structure composed of InGaAsP, and the upper cladding layer 130c composed of p-InP are sequentially stacked. The active layer 130b is formed by alternately laminating well layers and barrier layers made of InGaAsP having different compositions, and the composition of InGaAsP in the well layer is adjusted so that the emission wavelength is 1550 nm. . A part from the lower cladding layer 130a to the upper cladding layer 130c has a mesa structure, and both sides of the mesa structure are a lower current blocking layer 130da and n-InP made of Fe-doped semi-insulating p-InP. It is buried by a current blocking layer 130d composed of an upper current blocking layer 130db. Therefore, the SOA 130 has a semiconductor embedded structure. The current blocking layer 130d also functions as a cladding layer in the width direction with respect to the active layer 130b.

  The SOA 130 further includes an upper cladding layer 130e made of p-InP and a contact layer 130f made of InGaAs, which are sequentially stacked on the current blocking layer 130d and the upper cladding layer 130c. A p-side electrode 130h is formed on the contact layer 130f. In addition, a recess having a depth from the contact layer 130f to the lower cladding layer 130a is formed, and an n-side electrode 130i is formed on the surface of the lower cladding layer 130a at the bottom of the groove. The surface of the semiconductor layer constituting the SOA 130 is covered with a protective film 130g made of an insulator such as SiNx. In FIG. 1, the p-side electrode 130h, the n-side electrode 130i, and a wiring pattern for supplying power to them are not shown for the sake of simplicity.

  The operation of the SOA 130 will be described. When a seed light having a wavelength of 1550 nm, for example, is input to the SOA 130 with a voltage applied between the n-side electrode 130i and the p-side electrode 130h, the active layer 130b amplifies the seed light while guiding the seed light. And output. Thus, the SOA 130 is a waveguide-type optical functional element in which the active layer 130b, which is the second optical waveguide layer, has an optical amplification function.

  FIG. 3 is a schematic cross-sectional view of the optical modulator 140 shown in FIG. 1 on a plane perpendicular to the light guiding direction. 1 shows a cross section of one of the two arm portions of the MZI 141 constituting the optical modulator 140, the other arm portion also has the same cross-sectional structure. The MZI 141 is a substrate of the optical integrated device 100, on the same substrate 100a as the SOA 130, on the lower cladding layer 130a common with the SOA 130, and a well layer and a barrier layer made of AlGaInAs (or AlInAs) having different compositions, or An optical waveguide layer 140b which is a first optical waveguide layer having a multiple quantum well structure including an AlGaInAs well layer / AlInAs barrier layer, an upper cladding layer 140c formed of non-doped InP, and p-InP The upper clad layer 140e and the contact layer 140f made of InGaAs are sequentially stacked. The composition of the optical waveguide layer 140b is adjusted so that, for example, the emission wavelength is 1430 nm so as not to absorb the seed light. A modulation signal applying electrode 140h is formed on the contact layer 140f. The contact layer 140f to a part of the lower cladding layer 130a has a high mesa structure. That is, the optical modulator 140 has a high mesa structure. A ground electrode 140i is formed on the surface of the lower cladding layer 130a adjacent to the high mesa structure. The surface of the semiconductor layer constituting the optical modulator 140 is covered with a protective film 140g made of an insulator such as SiNx. Further, both sides of the high mesa structure are embedded with polyimide 140j. The surface of the polyimide 140j is also covered with a protective film 140g. The optical waveguides 142, 143, and 144 constituting the optical modulator 140 are covered with the protective film 140g without the modulation signal applying electrode 140h formed on the contact layer 140f, and the ground electrode 140i is formed. Except for this, it has the same cross-sectional structure as the arm portion of MZI 141 shown in FIG.

  The operation of the optical modulator 140 will be described. When high frequency modulation power is applied to the modulation signal application electrode 140h, the refractive index of the optical waveguide layer 140b changes due to the quantum confined Stark effect (QCSE) or the Pockels effect. Then, the phase difference of the light passing through the optical waveguide layer 140b of the two arms of the MZI 141 changes, and the interference state in the output side optical coupler of the MZI 141 changes. In such a configuration, by controlling the modulation power applied to the modulation signal application electrode 140h, the presence or absence of light output from the MZI 141 can be switched to modulate the light.

  As described above, the optical integrated device 100 includes the optical modulator 140 that is the first waveguide type optical functional device having the optical modulation function and the second optical amplifier that has the optical amplification function on the substrate 100a that is the same substrate. SOAs 130 and 131 which are waveguide type optical functional elements are integrated.

  Note that the optical waveguides included in the areas AA and BA separated by the broken line shown in FIG. 1 have different waveguide structures. That is, the optical waveguide in the region AA has a semiconductor buried structure like the SOA 130, and the optical waveguide in the region BA has a high mesa structure like the optical modulator 140.

  4 is a cross-sectional view of the optical integrated device shown in FIG. The XX line is a line along the light guiding direction. As shown in FIG. 4, a connection optical waveguide 170 is formed between the optical modulator 140 and the SOA 130, and the optical modulator 140 and the SOA 130 are connected by the connection optical waveguide 170. The connection optical waveguide 170 is a substrate of the optical integrated device 100, and is a passive type having a bulk structure composed of the lower cladding layer 130 a common to the SOA 130 and InGaAsP on the common substrate 100 a with the SOA 130 and the optical modulator 140. An optical waveguide layer 170b, which is a connection optical waveguide layer, an upper cladding layer 170c made of non-doped InP, an upper cladding layer 170e made of p-InP, and a contact layer (not shown) made of InGaAs are sequentially formed. It has a laminated structure. The composition of the optical waveguide layer 170b is adjusted so that, for example, the emission wavelength is 1300 nm so as not to absorb the seed light.

  As shown in FIG. 4, the total thickness of the active layer 130b, which is the second optical waveguide layer, is thinner than the total thickness of the optical waveguide layer 140b, which is the first optical waveguide layer. It is different. Thereby, the total thickness of the optical waveguide layer 140b is optimized so that the response characteristic of the optical modulator 140 is increased. Further, the total thickness of the active layer 130b is optimized so that the saturation output of the SOA 130 does not decrease.

  Furthermore, the optical waveguide layer 170b connects the active layer 130b and the optical waveguide layer 140b. Here, the optical waveguide layer 170b has a thickness changing portion 170ba and a constant thickness portion 170bb. The thickness changing portion 170ba has a first end 170ba1 located on the optical waveguide layer 140b side and a second end 170ba2 located on the active layer 130b side. The thickness of the first end portion 170ba1 is the same as or close to the thickness of the optical waveguide layer 140b, and the connection loss is in a sufficiently allowable range in consideration of the spot size of light at the connection portion. The thickness of the second end portion 170ba2 is the same as or close to that of the active layer 130b, and the connection loss is in a sufficiently allowable range in consideration of the light spot size at the connection portion. The thickness of the thickness changing portion 170ba changes from the thickness of the optical waveguide layer 140b toward the thickness of the active layer 130b from the first end 170ba1 to the second end 170ba2. On the other hand, the constant thickness portion 170bb is connected to the second end portion 170ba2, has the same thickness as the second end portion 170ba2, and has a constant thickness in the light guiding direction. Thereby, the optical waveguide layer 170b is connected to the active layer 130b at the constant thickness portion 170bb, and is connected to the optical waveguide layer 140b at the first end portion 170ba1 of the thickness changing portion 170ba.

  Here, consider the case where the optical waveguide layer 140b, the optical waveguide layer 170b, and the active layer 130b are grown in order by repeating etching and regrowth of the semiconductor layer when manufacturing the optical integrated device 100. Assume that the optical waveguide layer 170b is formed of only the thickness changing portion 170ba. In this case, when a part of the region of the thickness changing portion 170ba is removed by etching and the active layer 130b is regrown in the region, the position of the etching mask for etching the thickness changing portion 170ba is set to the optical waveguide. If it varies in the direction, the thickness of the thickness changing portion 170ba in the etching cross section exposed to the side portion due to etching varies. As a result, the thickness difference between the thickness change portion 170ba and the active layer 130b also varies at the junction between the thickness change portion 170ba and the active layer 130b formed by regrowth thereafter. The connection loss at the part varies. In addition, the etching depth may be shifted due to the variation in the thickness of the thickness changing portion 170ba, and a vertical shift may occur in the joint portion. Thereby, the junction loss in a junction part will vary.

  On the other hand, in the present embodiment, since the optical waveguide layer 170b has the constant thickness portion 170bb, even if the position of the etching mask varies in the light waveguide direction, There is almost no variation in the thickness of the constant thickness portion 170bb in the etching cross section exposed to the side portion. Therefore, there is almost no variation in connection loss at the joint between the optical waveguide layer 170b and the active layer 130b formed by subsequent regrowth. Further, when the constant thickness portion 170b is etched, since the thickness is constant, the controllability of the etching depth is remarkably increased, and the vertical shift at the joint portion does not occur. Therefore, there is almost no variation in the junction loss at the junction. As a result, the variation in connection loss inside the optical integrated device 100 is also reduced.

  Note that the total thickness of the optical waveguide layer 140b is t1, the thickness of the first end 170ba1 of the thickness changing portion 170ba of the optical waveguide layer 170b is t2, and the thickness of the second end 170ba2 and the constant thickness portion 170bb. Assuming that the total thickness of the active layer 130b is t3 and t4 is an example, t1 is 500 nm, t2 is 400 nm, t3 is 200 nm, and t4 is 150 nm. That is, the thickness of the thickness changing portion 170ba changes from 400 nm to 200 nm. Note that the thicknesses of the connected portions (for example, the total thickness t1 of the optical waveguide layer 140b and the thickness t2 of the first end 170ba1) are not necessarily equal, and the light spot size at the connection portion is taken into consideration. Thus, there may be a difference in the degree that the connection loss is within the allowable range.

  In addition, the constant thickness portion 170bb having a constant thickness means that the change in the thickness t3 is within a range of about 5% or less in the light guiding direction. This change is preferable because the light guided through the constant thickness portion 170bb is not affected by the change in thickness, so that the above-described variation in connection loss is eliminated. Further, the length L1 of the thickness changing portion 170ba in the light guiding direction is 500 μm so that the mode field diameter changes smoothly, but is not particularly limited. Further, if the length L2 of the constant thickness portion 170bb in the light guiding direction is 10 μm or more, it is larger than the actual value of the above-described variation in the position of the etching mask, so that the variation in the connection loss is eliminated. Is preferable. In addition, L2 may be about 100 μm or less.

  4 is a cross-sectional view taken along the line XX of the optical integrated device 100 shown in FIG. 1, and the cross-sectional view taken along the line YY shown in FIG. 1 is similar to FIG. 120 optical waveguide layers may be connected by a connection optical waveguide having a thickness changing portion and a constant thickness portion.

  As described above, the optical integrated device 100 has a small variation in internal connection loss.

(Production method)
Next, a method for manufacturing the optical integrated device 100 will be described. 5 to 10 are diagrams for explaining an example of a manufacturing method of the optical integrated device 100 shown in FIG.

  First, as shown in FIG. 5A, the lower cladding layer 130a, the optical waveguide layer 140b, and the upper cladding layer 140c are sequentially grown on the substrate 100a using an MOCVD crystal growth apparatus. Next, a mask M1 made of SiNx that protects the region BA is formed on the upper cladding layer 140c. Subsequently, as shown in FIG. 5B, using the mask M1 as an etching mask, the upper cladding layer 140c and the optical waveguide layer 140b on the region AA side where the mask M1 is not formed are removed by etching. Subsequently, as shown in FIG. 5C, using the mask M1 as a growth mask, the optical waveguide layer 170b and the upper cladding layer 170c are formed by butt joint growth in the region removed by etching. Here, as shown in FIG. 5D, the mask M1 has an opening O extending in the direction D1, and the width W1 of the mask M1 changes on both sides of the opening O. The direction D1 is matched with the light guiding direction of the optical waveguide to be formed. As a result, immediately below the opening O, the optical waveguide layer 170b and the upper cladding layer 170c can be selectively grown so that the thickness decreases from a portion having a large width W1 toward a narrow portion. Thereby, the optical waveguide layer 170b having the thickness changing portion 170ba and the constant thickness portion 170bb can be formed.

  Subsequently, as shown in FIG. 6A, after the mask M1 is removed, a mask M2 made of SiNx for forming the active layer 130b is formed on the upper clad layers 140c and 170c. Subsequently, as shown in FIG. 6B, using the mask M2 as an etching mask, the upper cladding layer 170c and the optical waveguide layer 170b in the region where the mask M2 is not formed are removed by etching. Here, since the optical waveguide layer 170b has the constant thickness portion 170bb, even if the position of the end portion of the mask M2 varies, the thickness of the optical waveguide layer 170b at the etching end face is the thickness of the constant thickness portion 170bb. And is substantially constant. Subsequently, as shown in FIG. 6C, using the mask M2 as a growth mask, an active layer 130b and an upper clad layer 130c are formed by butt joint growth in a region removed by etching.

  In this way, by forming the optical waveguide layer 140b, the optical waveguide layer 170b, and the active layer 130b in this order, the optical waveguide layer 140b and the active layer 130b having different thicknesses and different constituent materials are formed. Etching both at the same time can be avoided. As a result, the optical waveguide layer 140b and the active layer 130b can be appropriately etched with respect to each layer by optimizing the etching material and etching time.

  Subsequently, as shown in FIG. 7, a mask M3 made of SiNx is formed on the entire surface. The mask M3 has a mask part M3a formed in the area AA and a mask part M3b formed in the area BA. The mask portion M3a is for forming a mesa structure of an optical waveguide having a semiconductor embedded structure to be formed in the region AA, and is formed in a pattern of the optical waveguide to be formed. The mask width is set in consideration of the amount of side etching during etching, for example, so as to realize a predetermined mesa width in the semiconductor buried structure. For example, when the mesa width is 2.0 μm, the mask width is set to about 3.0 μm assuming that the side etching amount is 0.5 μm on one side. On the other hand, the mask portion M3b is for protecting a portion where the high mesa structure is to be formed in order to form a high mesa structure of the optical waveguide to be formed in the region BA in a subsequent process. Formed into a pattern. The mask width of the mask portion M3b is preferably set wider than the mesa width of the high mesa structure to be formed.

  Subsequently, as shown in FIG. 8, using the mask M3 as an etching mask, etching is performed to a depth reaching the lower cladding layer 130a to form a mesa structure. Thereafter, a lower current blocking layer 130da and an upper current blocking layer 130db are grown on both sides of the mesa structure to form a current blocking layer 130d, and the mesa structure is embedded. Thereby, a semiconductor buried structure in the region AA is formed. When a semi-insulating semiconductor is used for the current blocking layer, a single layer current blocking layer may be used. Note that a semiconductor buried structure is also formed in the region BA, but is processed to a high mesa structure in a later step. Thereafter, upper cladding layers 130e, 170e, 140e are grown on the upper cladding layers 130c, 140c, 170c, and the current blocking layer 130d, and contact layers (on the contact layers 130f, 140f, and the upper cladding layer 170e) are further formed thereon. Contact layer).

  Subsequently, as shown in FIG. 9, a mask M4 made of SiNx is formed on the entire surface. The mask M4 has a mask part M4a formed in the area AA and a mask part M4b formed in the area BA. The mask portion M4a is for protecting the optical waveguide of the semiconductor embedded structure formed in the region AA during the later-described etching, and is formed in the pattern of the optical waveguide of the semiconductor embedded structure. The mask width is set to a width that covers the current blocking layer, which is a buried portion on both sides of the mesa structure, with a desired width. On the other hand, the mask portion M4b is for forming a high mesa structure of the optical waveguide to be formed in the region BA, and is formed in the pattern of the optical waveguide to be formed. The mask width is set in consideration of the amount of side etching during etching, for example, so as to realize a predetermined mesa width. For example, when the mesa width of the high mesa structure is 3.5 μm, the mask width is set to about 3.7 μm assuming that the side etching amount is 0.1 μm on one side.

  Subsequently, as shown in FIG. 10, etching is performed to a depth reaching the lower cladding layer 130a using the mask M4 as an etching mask. Thereby, a high mesa structure in the area BA is formed. This etching also forms a recess structure for forming the n-side electrode 130i on the surface of the lower cladding layer 130a in the region AA.

  Subsequently, a protective film such as a protective film 130g or 140g is formed by CVD or the like, an insulating resin layer 141j such as polyimide is formed by spin coating or the like, and a protective film such as 140g or the like is further formed by CVD or the like. Form. Thereafter, openings are formed in the protective films 130g and 141g, a metal film is deposited on the openings, and lift-off forms a p-side electrode 130h, an n-side electrode 130i, a modulation signal applying electrode 140h, and a ground electrode 140i. By forming the wiring pattern, the optical integrated device 100 is completed.

  In the above embodiment, the first waveguide type optical functional element is a phase modulator and the second waveguide type optical functional element is an optical amplifying element. However, the present invention is not limited to this. The first and second waveguide type optical functional elements may be optical functional elements configured to exhibit a predetermined function by applying voltage, injecting current, heating, or the like. For example, the second waveguide type optical functional element may be a light emitting element such as a semiconductor laser element.

  In the above embodiment, the first waveguide type optical functional element has a high mesa structure, and the second waveguide type optical functional element has a semiconductor buried structure. However, the first and second waveguides The waveguide structure of the type optical functional element is not limited to these, and may be a low mesa structure, for example.

  In the above embodiment, the total thickness of the first optical waveguide layer of the first waveguide type optical functional element is greater than the total thickness of the second optical waveguide layer of the second waveguide type optical functional element. However, the total thickness of the first optical waveguide layer may be thinner than the total thickness of the second optical waveguide layer of the second waveguide type optical functional element. Also in this case, if the ratio of the thickness is twice or more, the effect of the present invention becomes more effective.

  Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

DESCRIPTION OF SYMBOLS 100 Optical integrated device 100a Substrate 110 Optical input part 120, 121, 122, 123, 142, 143, 144 Optical waveguide 120a Branch part 130, 131 SOA
130a Lower cladding layer 130b Active layer 130c, 130e, 140c, 140e, 170c, 170e Upper cladding layer 130d Current blocking layer 130da Lower current blocking layer 130db Upper current blocking layer 130f, 140f Contact layer 130g, 140g Protective film 130h P side electrode 130i n-side electrode 140 optical modulator 140b, 170b optical waveguide layer 140h modulation signal application electrode 140i ground electrode 140j polyimide 141 MZI
151, 152 Signal light output unit 151a, 152a Monitor light output unit 160 LO light output unit 170 Connection optical waveguide 170ba Thickness changing unit 170ba1 First end 170ba2 Second end 170bb Constant thickness AA, BA region D1 direction M1 , M2, M3, M4 Mask M3a, M3b, M4a, M4b Mask part O Opening

Claims (7)

A first waveguide type optical functional element having a first optical waveguide layer formed on the same substrate, and a second optical waveguide layer having a second optical waveguide layer having a thickness different from that of the first optical waveguide layer. A waveguide-type optical functional element, and a connection optical waveguide having a passive connection optical waveguide layer that connects the first optical waveguide layer and the second optical waveguide layer,
The connection optical waveguide layer has a first end located on the first optical waveguide layer side and a second end located on the second optical waveguide layer side, from the first end to the Connected to the second end portion and a thickness changing portion whose thickness changes so as to approach the thickness of the second optical waveguide layer from the thickness of the first optical waveguide layer toward the second end portion And a constant-thickness portion having the same thickness as the second end portion and a constant thickness in the light guiding direction.   2. The optical integrated device according to claim 1, wherein the first waveguide optical functional element is a phase modulator, and the second waveguide optical functional element is a light emitting element or an optical amplifying element. .   3. The optical integrated device according to claim 1, wherein the first waveguide optical functional element has a high mesa structure, and the second waveguide optical functional element has a semiconductor buried structure. .   The optical integrated device according to claim 1, wherein the first and second optical waveguide layers have a multiple quantum well structure.   5. The optical integrated device according to claim 4, wherein the first optical waveguide layer is made of AlGaInAs or AlInAs, and the second optical waveguide layer is made of InGaAsP.   6. The integrated optical device according to claim 1, wherein a total thickness of the first optical waveguide layer is twice or more a total thickness of the second optical waveguide layer. . A first waveguide type optical functional element having a first optical waveguide layer formed on the same substrate, and a second optical waveguide layer having a second optical waveguide layer having a thickness different from that of the first optical waveguide layer. Optical waveguide device and a connection optical waveguide having a passive connection optical waveguide layer for connecting the first optical waveguide layer and the second optical waveguide layer. Because
Forming a first optical waveguide layer on the substrate;
A second step of removing a part of the first optical waveguide layer and forming the connection optical waveguide layer in the removed region;
A third step of removing a part of the connection optical waveguide layer and forming a second optical waveguide layer in the removed region;
Including
The second step includes a first end located on the first optical waveguide layer side and a second end located on the second optical waveguide layer side, and the first end portion A thickness changing portion whose thickness changes so as to approach the thickness of the second optical waveguide layer from the thickness of the first optical waveguide layer toward the two end portions; Forming the connection optical waveguide layer to have a constant thickness portion having the same thickness as the second end portion and a constant thickness in the light guiding direction;
In the third step, a partial region in the constant thickness portion of the connection optical waveguide layer is removed.

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