阅读说明：本技术 光集成元件以及光模块 (Optical integrated element and optical module ) 是由 斋藤裕介 清田和明 于 2019-02-07 设计创作，主要内容包括：光集成元件具备：基板；第1波导路区域,其在所述基板上依次层叠下部包覆层、与所述下部包覆层相比而折射率更高的第1芯层和与所述第1芯层相比而折射率更低的上部包覆层；和活性区域,其在所述基板上依次层叠所述下部包覆层、与所述下部包覆层相比而折射率更高的第2芯层、通过被注入电流来将光放大的量子阱层和所述上部包覆层,所述第2芯层与所述量子阱层之间在正在所述第2芯层进行波导的光的模场的范围内接近,所述第1芯层、和所述第2芯层以及所述量子阱层。(The optical integrated element includes: a substrate; a 1 st waveguide region in which a lower clad layer, a 1 st core layer having a higher refractive index than the lower clad layer, and an upper clad layer having a lower refractive index than the 1 st core layer are sequentially stacked on the substrate; and an active region in which the lower cladding layer, a 2 nd core layer having a higher refractive index than the lower cladding layer, a quantum well layer that amplifies light by an injection current, and the upper cladding layer are sequentially stacked on the substrate, wherein the 2 nd core layer and the quantum well layer are close to each other within a range of a mode field of light being waveguided by the 2 nd core layer, and the 1 st core layer, the 2 nd core layer, and the quantum well layer are formed on the substrate.)

1. An optical integrated device, comprising:

a substrate;

a 1 st waveguide region in which a lower clad layer, a 1 st core layer having a higher refractive index than the lower clad layer, and an upper clad layer having a lower refractive index than the 1 st core layer are sequentially stacked on the substrate; and

an active region in which the lower cladding layer, a 2 nd core layer having a higher refractive index than the lower cladding layer, a quantum well layer that amplifies light by an injection current, and the upper cladding layer are sequentially stacked on the substrate,

the 2 nd core layer and the quantum well layer are proximate within a range of a mode field of light being waveguided to the 2 nd core layer,

the 1 st core layer, the 2 nd core layer, and the quantum well layer are butt-joined.

2. The photonic integrated component according to claim 1,

an intermediate layer having a different composition from the 2 nd core layer and the quantum well layer is provided between the 1 st core layer and the quantum well layer.

3. The photonic integrated component according to claim 2,

the intermediate layer has the same composition as the lower cladding layer or the upper cladding layer.

4. A light-integrating element according to any one of claims 1 to 3,

the lower cladding layer has an n-type conductivity, and the upper cladding layer has a p-type conductivity.

5. A light integration component according to any one of claims 1 to 4,

the light integration element is provided with: a 2 nd waveguide region in which the lower clad layer, the 2 nd core layer, and the upper clad layer are laminated in this order on the substrate,

the 2 nd waveguide region is cascade-connected to the active region.

6. The photonic integrated component according to claim 5,

the 2 nd waveguide region includes: a 3 rd core layer which is laminated between the substrate and the lower clad layer and has a higher refractive index than the substrate and the lower clad layer,

at least a portion of the 2 nd waveguide region has a 1 st mesa region of the upper cladding layer mesa-like protruding low mesa structure,

the 2 nd waveguide region includes a spot size transition region having mesa structures where the 2 nd core layer, the lower cladding layer, and the 3 rd core layer mesa protrude,

the mesa width of the mesa structure in the spot size conversion region is wider than the mesa width of the low mesa structure in the 1 st mesa region, and the mesa width of the low mesa structure in the 1 st mesa region continuously changes in the spot size conversion region having the mesa structure.

7. The light integration element according to any one of claims 1 to 6,

the 1 st waveguide region has: a 2 nd mesa region of the lower mesa structure of the upper cladding layer mesa-like protrusion; and a 3 rd mesa region of a mesa-shaped protruding high mesa structure of a part of the upper clad layer, the 1 st core layer, and the lower clad layer,

the active region has a low mesa structure,

the active region and the 2 nd mesa region are connected in a low mesa structure,

the low mesa structure of the 2 nd mesa region and the high mesa structure of the 3 rd mesa region are optically connected.

8. The light integration element according to any one of claims 1 to 6,

the 1 st waveguide region on the substrate has: a modulator region functioning as a phase modulator for modulating the phase of light to be guided,

the 1 st core layer in the modulator region is a modulator core layer that waveguides light.

9. The photonic integrated component according to claim 8,

the phase modulator is a mach-zehnder type modulator.

10. An optical module is characterized in that a light source,

a light-integrated device comprising the light-integrated element according to any one of claims 1 to 9.

Technical Field

The present invention relates to an optical integrated element and an optical module.

Background

In response to the recent demand for miniaturization of optical communication devices, the level of demand for optical integrated devices in which optical elements having different functions, such as semiconductor optical amplifiers and phase modulators, are integrated on the same substrate has also increased (see, for example, patent document 1).

Prior art documents

Patent document

Patent document 1: JP 2016-126216A

Patent document 2: JP-A2014-35540

Disclosure of Invention

Problems to be solved by the invention

However, when semiconductor optical amplifiers, phase modulators, and the like are integrated on the same substrate, the thickness of each waveguide layer is preferably optimized according to the characteristics of each element. For example, in the case of a phase modulator, it is preferable to increase the thickness of the waveguide layer in order to reduce the capacitance and increase the response characteristic, and in the case of a semiconductor optical amplifier, it is preferable to reduce the thickness of the waveguide layer to a certain extent or less in order to suppress the decrease in saturation output.

If the thicknesses of the waveguide layers of the respective integrated elements are optimized in this manner, there is a problem that the difference in the thicknesses of the optimum waveguide layers becomes large, and the connection loss at the joint portion between the elements increases. Fig. 8 is a graph showing an example of connection loss of waveguide layers having different thicknesses. As shown in fig. 7, the connection loss increases as the ratio of the thicknesses of the waveguide layers of the connection destination and the connection source becomes farther from 1. Further, when the refractive index discontinuity occurs at the connection portion, reflection occurs at the connection portion, but the reflection increases as the ratio of the thickness of the waveguide layer at the connection portion is further away from 1, and the characteristics of the optical integrated device are further adversely affected.

Further, optimizing the thickness of the waveguide layer of each element integrated in the optical integrated device also affects the tolerance of the optical element with respect to the periphery of the optical integrated device. That is, since the light emitted from or incident on the optical integrated device is coupled to the optical fiber, the light source, and the like, and the difference between the spot size optimized in the waveguide layer and the spot size optimized in the optical fiber, the light source, and the like of each integrated device becomes large, the tolerance of the coupling lens between the optical integrated device and the peripheral optical device becomes strict.

Further, as a method for solving such problems such as increase in connection loss, there is a method of providing a spot size conversion region in which the thickness of a waveguide layer changes along the waveguide direction of light between waveguide layers having different thicknesses, and in order to provide such a spot size conversion region, a difficult processing is generally required.

The present invention has been made in view of the above, and an object thereof is to provide an optical integrated element and an optical module capable of suppressing problems caused by a spot size mismatch.

Means for solving the problems

In order to solve the above problems and achieve the object, an optical integrated device according to an aspect of the present invention includes: a substrate; a 1 st waveguide region in which a lower clad layer, a 1 st core layer having a higher refractive index than the lower clad layer, and an upper clad layer having a lower refractive index than the 1 st core layer are sequentially stacked on the substrate; and an active region in which the lower cladding layer, a 2 nd core layer having a higher refractive index than the lower cladding layer, a quantum well layer that amplifies light by injection of a current, and the upper cladding layer are sequentially stacked on the substrate, wherein the 2 nd core layer and the quantum well layer are close to each other within a range of a mode field of light that is being waveguided by the 2 nd core layer, and the 1 st core layer, the 2 nd core layer, and the quantum well layer are butt-joined to each other.

In the photonic integrated device according to one aspect of the present invention, an intermediate layer having a composition different from that of the 2 nd core layer and the quantum well layer is provided between the 1 st core layer and the quantum well layer.

In the optical integrated device according to one aspect of the present invention, the intermediate layer has the same composition as the lower clad layer or the upper clad layer.

In the optical integrated device according to one aspect of the present invention, the conductivity type of the lower cladding layer is n-type, and the conductivity type of the upper cladding layer is p-type.

An optical integrated device according to an aspect of the present invention includes: and a 2 nd waveguide region in which the lower cladding layer, the 2 nd core layer, and the upper cladding layer are stacked in this order on the substrate, wherein the 2 nd waveguide region is cascade-connected to the active region.

An optical integrated device according to an aspect of the present invention is the optical integrated device described above, wherein the 2 nd waveguide region includes: and a 3 rd core layer which is laminated between the substrate and the lower clad layer and has a higher refractive index than the substrate and the lower clad layer, wherein at least a part of the 2 nd waveguide region has a 1 st mesa region of a low mesa structure in which the upper clad layer mesa protrudes, the 2 nd waveguide region includes a spot size conversion region having a mesa structure in which the 2 nd core layer, the lower clad layer, and the 3 rd core layer mesa protrude, a mesa width of the mesa structure in the spot size conversion region is wider than a mesa width of the low mesa structure in the 1 st mesa region, and a mesa width of the low mesa structure in the 1 st mesa region continuously changes in the spot size conversion region having the mesa structure.

In an optical integrated device according to an aspect of the present invention, the 1 st waveguide region includes: a 2 nd mesa region of the lower mesa structure of the upper cladding layer mesa-like protrusion; and a 3 rd mesa region of a high mesa structure of a portion of mesa-like protrusions of the upper cladding layer, the 1 st core layer, and the lower cladding layer, the active region having a low mesa structure, the active region and the 2 nd mesa region being connected in the low mesa structure, the low mesa structure of the 2 nd mesa region and the high mesa structure of the 3 rd mesa region being optically connected.

In an optical integrated device according to an aspect of the present invention, the 1 st waveguide region on the substrate includes: and a modulator region functioning as a phase modulator for modulating a phase of light guided by the waveguide, wherein the 1 st core layer in the modulator region is a modulator core layer for guiding the light.

In the optical integrated element according to one aspect of the present invention, the phase modulator is a mach-zehnder type modulator.

An optical module according to an aspect of the present invention includes the above-described optical integrated element.

Drawings

The optical integrated element and the optical module according to the present invention have an effect of suppressing problems caused by mismatching of spot sizes.

Fig. 1A is a sectional view of the optical integrated device according to embodiment 1 in the waveguide direction.

Fig. 1B is a top view of the optical integrated device according to embodiment 1.

Fig. 1C is a cross-sectional view of the light integration element according to embodiment 1.

Fig. 2A is a sectional view of the optical integrated device according to embodiment 2 in the waveguide direction.

Fig. 2B is a top view of the light integration device according to embodiment 2.

Fig. 2C is a cross-sectional view of the light integration element according to embodiment 2.

Fig. 3A is a sectional view of the optical integrated device according to embodiment 3 in the waveguide direction.

Fig. 3B is a top view of the light integration device according to embodiment 3.

Fig. 3C is a cross-sectional view of the light integration element according to embodiment 3.

Fig. 4 is a schematic top view of the photonic integrated device according to embodiment 4.

Fig. 5 is a sectional view showing an example of formation of a passivation film and an electrode.

Fig. 6 is a schematic configuration diagram of an optical module according to embodiment 5.

Fig. 7 is a graph showing an example of connection loss of waveguide layers having different thicknesses.

Detailed Description

The optical integrated element and the optical module according to the embodiment of the present invention will be described in detail below with reference to the drawings. The embodiments described below do not limit the present invention. In the drawings, the same or corresponding components are denoted by the same reference numerals as appropriate. The drawings are schematic, and it should be noted that the thickness, the thickness ratio, and the like of each layer are different from those of the actual drawings. In addition, the drawings may include portions having different dimensional relationships and ratios from each other.

(embodiment 1)

Fig. 1A is a sectional view of the optical integrated device according to embodiment 1 in the waveguide direction, fig. 1B is a top view of the optical integrated device according to embodiment 1, and fig. 1C is a sectional view of the optical integrated device according to embodiment 1. Arrows (a) to (C) shown in fig. 1A and 1B correspond to the cross-sectional portions shown in fig. 1C.

The Optical integrated device 100 shown in fig. 1A to 1C is described as an example of a configuration used in a connection region from a phase modulator to a Semiconductor Optical Amplifier (SOA). However, the optical integrated device according to embodiment 1 is not limited to the combination with the phase modulator. The phase modulator is not limited to the phase modulator, and particularly, a suitable effect can be obtained in combination with a device having a thick core layer. Here, as an example of the phase modulator, a mach-zehnder type modulator is conceived. The optical integrated device 100 can also be used for an application in which light in a 1.55 μm wavelength band is incident from either of the left and right end faces of the paper surface.

As shown in fig. 1A, the integrated device 100 includes: a passive waveguide region R13 in which a lower cladding layer 102, a waveguide core 103, an upper cladding layer 104, and a contact layer 105 are laminated in this order on a substrate 101; and an active region R12 in which a lower cladding layer 102, a waveguide core 103, an intermediate layer 108, a quantum well layer 107, an upper cladding layer 104, and a contact layer 105 are laminated in this order on a substrate 101. The optical integrated device 100 includes a modulator region R11 in which a lower cladding layer 102, a modulator core 106, an upper cladding layer 104, and a contact layer 105 are laminated in this order on a substrate 101, and is an example of a configuration in which phase modulators are integrated in the same device. The modulator region R11 corresponds to the 1 st waveguide region, and the passive waveguide region R13 corresponds to the 2 nd waveguide region. The passive waveguide region R13 is cascade-connected to the active region R12. The modulator core 106 corresponds to the 1 st core layer, and the waveguide core 103 corresponds to the 2 nd core layer.

Specifically, in the optical integrated element 100, the lower clad layer 102 is laminated on the substrate 101. For example, the substrate 101 is an InP substrate, the lower cladding layer 102 is InP doped so that the conductivity type becomes n-type, and the layer thickness is, for example, 1500 nm.

In the optical integrated device 100, the modulator core 106 and the waveguide core 103 are formed on the lower cladding layer 102, and the modulator core 106 and the waveguide core 103 are butt-joined. For example, the modulator core 106 is formed of an AlGaInAs multiple quantum well having a band gap wavelength of, for example, 1.4 μm, and the layer thickness is, for example, 500 nm. The modulator core 106 is configured to have a higher refractive index than the lower cladding layer 102 and the upper cladding layer 104. In the figure, a curve shown overlapping the modulator core 106 visually illustrates a mode field of light waveguided in the modulator core 106.

Since the band gap wavelength is, for example, 1.4 μm, the modulator core 106 hardly absorbs light of 1.55 μm and functions as a core of a waveguide. That is, the modulator core 106 is a so-called passive waveguide, and the modulator region R11 can be said to be a passive waveguide region. As described above, the passive waveguide path is a concept including a waveguide path that changes the phase of light guided by applying a reverse bias voltage.

The waveguide core 103 is made of GaInAsP having a bandgap wavelength of 1.3 μm, for example, and has a higher refractive index than the lower cladding layer 102 and the upper cladding layer 104. The layer thickness of the waveguide core 103 is, for example, 200 nm.

In addition, as shown in FIG. 1A, in the active region R12A quantum well layer 107 is provided in the vicinity of the waveguide core 103. Here, the vicinity of the waveguide core 103 means a range of a mode field of light guided by the waveguide core 103, for example, 1/e of a peak intensity of the mode field²Within a half-width range. When a part of the quantum well layer 107 is located near the waveguide core 103, the waveguide core 103 and the quantum well layer 107 approach each other within a range of a mode field of light being guided by the waveguide core 103. The intermediate layer 108 is present between the waveguide core 103 and the quantum well layer 107, and the intermediate layer 108 has a composition different from that of the waveguide core 103 and the quantum well layer 107, and in the present embodiment, has the same composition as that of the upper cladding layer 104. The intermediate layer 108 may have the same composition as the lower cladding layer 102. The layer thickness of the intermediate layer 108 is, for example, 10 nm.

In the figure, the curves superimposed on the waveguide core 103 and the quantum well layer 107 visually illustrate the mode field of light being guided by the waveguide core 103. The modulator core 106, the quantum well layer 107, and the intermediate layer 108 are butt-bonded.

The quantum well layer 107 is formed of, for example, a GaInAsP multiple quantum well, and the layer thickness is, for example, 100 nm. The quantum well layer 107 has a higher refractive index than the lower cladding layer 102 and the upper cladding layer 104, and amplifies input light by injecting current. Here, the composition of the GaInAsP multiple quantum well is adjusted, for example, so that light in a wavelength band of 1.55 μm can be amplified.

The upper cladding layer 104 is stacked on the modulator core 106, the waveguide core 103, and the quantum well layer 107. The upper cladding layer 104 is, for example, InP doped so that the conductivity type becomes p-type, and the layer thickness is, for example, 2 μm. Further, a contact layer 105 is laminated on the upper cladding layer 104. The contact layer 105 is for example InGaAs doped P-type with a layer thickness of for example 500 nm.

The quantum well layer 107 functions as an active layer of the SOA. That is, since the mode field of light guided by the waveguide core 103 is expanded to the quantum well layer 107, when a current is injected into the quantum well layer 107 from an electrode (illustrated in fig. 5) not shown, the amplification effect (for example, a gain of about 10 dB) is also applied to the light intensity of light guided by the waveguide core 103. Such a configuration has an advantage that the quantum well layer 107 is provided at an interval from the waveguide core 103, and the material of the quantum well layer is laminated in the vicinity of the waveguide core 103, and the core layer (waveguide core 103) of the passive waveguide can be formed by etching only the quantum well layer 107 in the passive waveguide region R13, and therefore, additional crystal growth and etching are not required.

The optical integrated element 100 is a waveguide of a so-called mesa structure, specifically, a waveguide of a low mesa structure. As shown in fig. 1B and 1C, the mesa width of the low mesa structure in the optical integrated device 100 is fixed, for example, 2.0 μm. In the photonic integrated device 100 of this example, the mesa width of the low mesa structure is constant, but a difference may be provided in the mesa width of the low mesa structure in each region as necessary.

As shown in fig. 1C (a), in the modulator region R11 (1 st waveguide region) of the optical integrated element 100, a low mesa structure in which the contact layer 105 and the upper cladding layer 104 are mesa-shaped is formed. Therefore, as shown in fig. 1B, in a diagram of the modulator region R11 in the optical integrated element 100 viewed from above, the modulator cores 106 are shown on both sides of the contact layer 105, which is the uppermost layer of the low mesa structure.

As shown in fig. 1C (b), a low mesa structure in which the contact layer 105 and the upper cladding layer 104 are mesa-protruded is formed in the active region R12 in the optical integrated device 100. Therefore, as shown in fig. 1B, in a view of the active region R12 in the optical integrated device 100 from above, the quantum well layer 107 is shown on both sides of the contact layer 105, which is the uppermost layer of the low mesa structure.

As shown in fig. 1C, in the passive waveguide region R13 (2 nd waveguide region) in the optical integrated device 100, a low mesa structure in which the contact layer 105 and the upper cladding layer 104 are mesa-protruded is formed. Therefore, as shown in fig. 1B, in a diagram in which the passive waveguide region R13 in the optical integrated device 100 is viewed from above, the waveguide core 103 is shown on both sides of the contact layer 105 of the uppermost layer of the low mesa structure.

Here, the structure of the optical integrated device 100 will be described with reference to fig. 1A to 1C, in terms of a manufacturing method.

In the method of manufacturing the optical integrated device 100, first, n-InP as the lower cladding layer 102, an AlGaInAs multiple quantum well layer as the modulator core 106, and p-InP as a part of the upper cladding layer 104 are sequentially formed on an InP substrate as the substrate 101 by a Metal Organic Chemical Vapor Deposition (MOCVD) method.

Next, an SiNx film was deposited over the entire surface of the p-InP layer as a part of the upper cladding layer 104, and then patterned to have a slightly wider pattern than the phase modulator, and the AlGaInAs multiple quantum well layer was etched out of the region to be the modulator region R11 using the SiNx film as a mask, thereby exposing the n-InP layer as the lower cladding layer 102.

Next, using the SiNx film as it is as a growth mask, GaInAsP as a waveguide core 103, p-InP as an intermediate layer 108, GaInAsP multiple quantum wells as a quantum well layer 107, and p-InP as a part of an upper cladding layer 104 were stacked in this order in a region to be an active region R12 and a region to be a passive waveguide region R13 by MOCVD. This forms a butt-joint structure of the modulator core 106, the waveguide core 103, the intermediate layer 108, and the quantum well layer 107.

Next, the SiNx film is removed once, and a new SiNx film is formed over the entire surface and patterned so that a region to be the passive waveguide region R13 is opened. Then, the layer of p-InP and the layer of GaInAsP multiple quantum well are etched using the SiNx film as a mask. After that, after removing the SiNx film, p-InP as a part of the upper cladding layer 104 and p-InGaAs as the contact layer 105 were stacked by MOCVD.

Next, SiNx film was formed again on the entire surface, and patterning and etching were performed for a low mesa structure.

Then, a passivation film, a resin layer, an opening thereof, an electrode for current injection, voltage application, and the like are formed in each part by a known method. After the front surface is finished, the substrate is polished to a desired thickness, and if necessary, an electrode is formed on the back surface. Further, the end face formation is performed by the substrate dicing, and the end face coating and the element separation are performed to complete the optical integrated element 100.

As described above, in the structure of the optical integrated device 100, the phase modulator and the SOA can be based on one device by 3-time crystal growth and 1-time mesa formation.

In the optical integrated device 100 according to embodiment 1 described above, the modulator core 106, the waveguide core 103, and the quantum well layer 107 are joined in butt joint, and therefore the spot size or the mode field can be matched between the modulator core 106 having a large layer thickness and the waveguide core 103 and the quantum well layer 107 having a large layer thickness in total. As a result, even if a device having a thick waveguide layer such as a phase modulator and a device having a thin waveguide layer such as an SOA are integrated into one device, the optimum structure can be adopted for both the phase modulator and the SOA, and the spot size and the mode field can be matched.

In the active region R12, the field of light is closer to the lower cladding layer 102 side due to the influence of the waveguide core 103. As a result, optical loss due to absorption in the valence band (light absorption by the p-type cladding layer) in the p-InP upper cladding layer 104 can be suppressed, and thus the waveguide loss can be reduced.

In addition, when the passive waveguide region R13 is formed, the GaInAsP multiple quantum well as the quantum well layer 107 may be removed by etching in the region where the passive waveguide region R13 is formed, and p-InP as a part of the upper cladding layer 104 and p-InGaAs as the contact layer 105 may be stacked thereon, so that a passive element can be easily integrated in the subsequent stage of the SOA.

In the passive waveguide region R13, since the quantum well layer 107 is not present and light is guided only in the waveguide core 103, the confinement of light is weak and the mode field is expanded. This facilitates connection of an optical fiber or the like to the passive waveguide region R13 side of the optical integrated device 100. For example, if the peak value is 1/e²The full width of the location of the multiplied intensity defines the spot size of the light, and the passive waveguide region R13 enables the spot size of the light to be expanded from less than 1 μm weak to more than 1 μm (e.g., 0.7 μm to 1.3 μm) wide.

In the above embodiment, the modulator core 106, the waveguide core 103, and the quantum well layer 107 are exposed on the surface of both side surfaces of the low mesa structure, but the upper cladding layer 104 may be etched so as to be slightly left on the surfaces.

(embodiment 2)

Fig. 2A is a sectional view of the optical integrated device according to embodiment 2 in the waveguide direction, fig. 2B is a top view of the optical integrated device according to embodiment 2, and fig. 2C is a sectional view of the optical integrated device according to embodiment 2. Arrows (a) to (C) shown in fig. 2A and 2B correspond to the cross-sectional portions shown in fig. 2C.

The optical integrated device 200 shown in fig. 2A to 2C is described as a configuration example used in a connection region from the phase modulator to the SOA. However, the optical integrated device according to embodiment 2 is not limited to the combination with the phase modulator. The phase modulator is not limited to the phase modulator, and particularly, a suitable effect can be obtained in combination with a device having a thick core layer. Here, as an example of the phase modulator, a mach-zehnder type modulator is conceived. The optical integrated device 200 can also be used for an application in which light in a 1.55 μm wavelength band is incident from either of the left and right end faces of the paper surface.

As shown in fig. 2A, the optical integrated device 200 includes: and an active region R22 in which a lower cladding layer 202, a waveguide core 203, an intermediate layer 208, a quantum well layer 207, an upper cladding layer 204, and a contact layer 205 are laminated in this order on the substrate 201. The optical integrated device 200 includes a modulator region R21 in which a lower cladding layer 202, a modulator core 206, an upper cladding layer 204, and a contact layer 205 are laminated in this order on a substrate 201, and is an example of a configuration in which phase modulators are integrated in the same device. The modulator region R21 corresponds to the 1 st waveguide region. The modulator core 206 corresponds to the 1 st core layer, and the waveguide core 203 corresponds to the 2 nd core layer.

The substrate 201, the lower cladding layer 202, the waveguide core 203, the intermediate layer 208, the quantum well layer 207, the upper cladding layer 204, the contact layer 205, and the modulator core 206 are made of the same material and have the same layer thickness as those of the substrate 101, the lower cladding layer 102, the waveguide core 103, the intermediate layer 108, the quantum well layer 107, the upper cladding layer 104, the contact layer 105, and the modulator core 106, which are corresponding elements of the optical integrated device 100, and therefore, description thereof will be omitted.

In the figure, a curve shown overlapping the modulator core 206 visually illustrates a mode field of light being waveguided at the modulator core 206. The curves shown overlapping the waveguide core 203 and the quantum well layer 207 visually illustrate the mode field of light being waveguided at the waveguide core 203.

The optical integrated element 200 is a waveguide of a mesa structure. As shown in fig. 2B and 2C, the mesa width of the mesa structure in the optical integrated device 200 is constant, for example, 2.0 μm. In the light integration element 200 of the present example, the mesa width of the mesa structure is constant, but a difference may be provided in the mesa width of the low mesa structure in each region as necessary.

Here, as shown in fig. 2C (a), in the optical integrated element 200, unlike the optical integrated element 100, a contact layer 205, an upper cladding layer 204, a modulator core 206, and a lower cladding layer 204 are formed in a mesa structure in which part of the contact layer 205, the upper cladding layer 204, and the lower cladding layer 204 protrude in a mesa shape in a part (a region on the left side in the drawing) of the modulator region R21 (1 st waveguide region). By adopting a high mesa structure in a part of the modulator region R21, the capacitance of the modulator region R21 is reduced, and thus higher-speed modulation is possible. Therefore, as shown in fig. 2B, in a view of the 2 nd mesa region of the modulator region R21 in the optical integrated device 200 viewed from above, the lower cladding layer 202 is shown on both sides of the contact layer 205, which is the uppermost layer of the high mesa structure. On the other hand, in the other part (region (b) on the right side in the drawing) of the modulator region R21, a low mesa structure in which the contact layer 205 and the upper cladding layer 204 are mesa-protruded is formed. Therefore, as shown in fig. 2B, in a diagram in which the region (B) of the modulator region R21 in the optical integrated element 200 is viewed from above, the modulator cores 206 are shown on both sides of the contact layer 205, which is the uppermost layer of the low mesa structure. In the modulator region R21, the region of (b) (the 2 nd mesa region) and the region of (a) (the 3 rd mesa region) are optically connected. Here, in the modulator core 206, the waveguide having the high mesa structure and the waveguide having the low mesa structure are switched halfway. In general, since the characteristics relating to the confinement of light are different between the high mesa structure and the low mesa structure, loss occurs when the waveguide of the high mesa structure and the waveguide of the low mesa structure are connected to each other. Therefore, for example, as described in patent document 2, an intermediate region may be provided between the waveguide of the high mesa structure and the waveguide of the low mesa structure, and the loss in the optical connection between the waveguide of the high mesa structure and the waveguide of the low mesa structure may be reduced by realizing the light confinement in the intermediate region, which is different from that of the high mesa structure and the low mesa structure.

As shown in fig. 2C (C), a low mesa structure in which the contact layer 205 and the upper cladding layer 204 are mesa-protruded is formed in the active region R22 in the photonic integrated device 200. Therefore, as shown in fig. 2B, in a view of the active region R22 in the optical integrated device 200 from above, the quantum well layer 207 is shown on both sides of the contact layer 205, which is the uppermost layer of the low mesa structure. And the active region R22 and the 2 nd mesa region are connected in a low mesa structure.

The optical integrated device 200 can be manufactured through the same process as the optical integrated device 100. In this case, the etching removal of the GaInAsP multiple quantum well as the quantum well layer 207 is not performed. After patterning and etching of the low mesa structure, the SiNx film is once removed, and the SiNx film is deposited again over the entire surface, followed by patterning of the high mesa structure in modulator region R21. Then, a mesa structure is formed by dry etching using the SiNx film as a mask. Then, a passivation film, a resin layer, an opening thereof, an electrode for current injection, voltage application, and the like are formed in each part by a known method. After the surface is finished, the substrate is polished to a desired thickness, and if necessary, an electrode is formed on the back surface. Further, the end face formation is performed by the substrate dicing, and the end face coating and the element separation are performed to complete the optical integrated element 200.

As described above, in the structure of the optical integrated device 200, the phase modulator and the SOA can be integrated into one device by 3-time crystal growth and 2-time mesa formation.

In the optical integrated device 200 according to embodiment 2 described above, the modulator core 206, the waveguide core 203, and the quantum well layer 207 are butt-joined, and therefore, the mode field can be matched between the thick-layered modulator core 206 and the waveguide core 203 and the quantum well layer 207 having the total thickness. As a result, even if a device having a thick waveguide layer such as a phase modulator and a device having a thin waveguide layer such as an SOA are integrated into one device, mode field matching can be achieved by adopting an optimum structure for both the phase modulator and the SOA.

In the active region R22, the field of light is brought closer to the lower cladding layer 202 side by the influence of the waveguide core 203, so that the optical loss due to absorption in the valence band in the p-InP upper cladding layer 204 can be suppressed, and the waveguide loss can be reduced.

Further, by making a region of a part of the modulator region R21 have a high mesa structure, the parasitic capacitance in this region can be reduced, and higher-speed modulation can be performed.

In the above embodiment, the modulator core 206, the waveguide core 203, and the quantum well layer 207 are exposed on the surface of both side surfaces of the low mesa structure, but the upper cladding layer 204 may be etched so as to be slightly left on the surfaces.

(embodiment 3)

Fig. 3A is a sectional view of the optical integrated device according to embodiment 3 in the waveguide direction, fig. 3B is a top view of the optical integrated device according to embodiment 3, and fig. 3C is a sectional view of the optical integrated device according to embodiment 3. Arrows (a) to (e) shown in fig. 3A and 3B correspond to the cross-sectional portions shown in fig. 3C.

The optical integrated device 300 shown in fig. 3A to 3C is described as a configuration example used in a connection region from the phase modulator to the SOA. However, the optical integrated device according to embodiment 3 is not limited to the combination with the phase modulator. The phase modulator is not limited to the phase modulator, and particularly, a device having a thickness equal to that of the core layer can obtain a suitable effect. Here, as an example of the phase modulator, a mach-zehnder type modulator is conceived. The light integration element 300 can also be applied to an application in which light in a 1.55 μm wavelength band is incident from either of the left and right end faces of the paper surface.

As shown in fig. 3A, the optical integrated device 300 includes a passive waveguide region R33 in which a Spot Size Converter (SSC) core 309, a lower cladding layer 302, a waveguide core 303, an upper cladding layer 304, and a contact layer 305 are laminated in this order on a substrate 301. The optical integrated device 300 includes an active region R32 in which an SSC core 309, a lower cladding layer 302, a waveguide core 303, an intermediate layer 308, a quantum well layer 307, an upper cladding layer 304, and a contact layer 305 are laminated in this order on a substrate 301. The optical integrated device 300 includes a modulator region R31 in which an SSC core 309, a lower cladding layer 302, a modulator core 306, an upper cladding layer 304, and a contact layer 305 are laminated in this order on a substrate 301, and is an example of a configuration in which a phase modulator is integrated in the same device. As shown in fig. 3B and 3C, which will be described later, the passive waveguide region R33 includes a spot size conversion region R34 having a 2-step mesa structure. The modulator region R31 corresponds to the 1 st waveguide region. The passive waveguide region R33 corresponds to the 2 nd waveguide region. The passive waveguide region R31 is cascade-connected to the active region R32. The modulator core 306 corresponds to the 1 st core layer, and the waveguide core 303 corresponds to the 2 nd core layer. The SSC core 309 corresponds to the 3 rd core layer.

The substrate 301, the lower cladding layer 302, the waveguide core 303, the intermediate layer 308, the quantum well layer 307, the upper cladding layer 304, the contact layer 305, and the modulator core 306 are made of the same material and have the same layer thickness as those of the substrate 101, the lower cladding layer 102, the waveguide core 103, the intermediate layer 108, the quantum well layer 107, the upper cladding layer 104, the contact layer 105, and the modulator core 106, which are corresponding elements in the optical integrated device 100, and therefore, the description thereof is omitted.

The SSC core 309 is a core for spot size conversion stacked between the substrate 301 and the lower cladding layer 302. The SSC core 309 is configured to have a higher refractive index than the substrate 301 and the lower cladding layer 302, and is made of GaInAsP having a refractive index of 3.34, for example, and has a layer thickness of 100nm, for example. Instead of directly stacking the SSC core 309 on the substrate 301, another InP layer may be stacked on the substrate 301, and the SSC core 309 may be stacked thereon.

The optical integrated device 300 is a waveguide having a mesa structure, but there is a difference in the mesa structure in each region of the optical integrated device 300. For this reason, the mesa structure in each region of the optical integrated device 300 will be described with reference to fig. 3A to 3C side by side.

As shown in fig. 3B and 3C, there are 3 stages of mesa structures in the optical integrated device 300. That is, the optical integrated element 300 has, in a part of the modulator region R31 (the region of (a)): the contact layer 305, the upper cladding layer 304, the modulator core 306, and a portion of the lower cladding layer 302 mesa protrudes beyond the 1 st mesa structure M1 of the high mesa structure. In addition, the region other than the spot size conversion region R34 in the other part of the modulator region R31 (the region of (b)), the active region R32 (the region of (c)), and the passive waveguide region R33 (the region of (d)) has: a contact layer 305 and an upper cladding layer 304 mesa-like protruding low mesa structure 2 mesa structure M2. In addition to the 2 nd mesa structure M2, a part of the spot size conversion region R34 includes: a waveguide core 303, a lower cladding layer 302, an SSC core 309, and a 3 rd mesa structure M3 of a high mesa structure in which a part of the mesa of the substrate 301 protrudes. The region of the passive waveguide region R33 having the 2 nd mesa structure M2 and the 3 rd mesa structure M3 functions as a spot size converter as will be described later. The region having the 2 nd mesa structure M2 corresponds to the 1 st mesa region.

As shown in (a) to (d) of fig. 3C, the widths of the 1 st mesa structure M1 and the 2 nd mesa structure M2 are constant, for example, 2.0 μ M, in the region where the 3 rd mesa structure M3 is not formed. On the other hand, as shown in fig. 3C (e), in the region where the 3 rd mesa structure M3 is formed, the width of the 2 nd mesa structure M2 continuously decreases as the end surface approaches. That is, the mesa width of the 3 rd mesa structure M3 in the spot size conversion region R34 is wider than the mesa width of the low mesa structure (2 nd mesa structure M2) in the 1 st mesa region, and the mesa width of the 2 nd mesa structure M2 continuously changes in the spot size conversion region M34 having the 2 nd mesa structure M2. As shown in fig. 3B, the width of the 2 nd mesa structure M2 is preferably a constant width (e.g., 0.5 μ M) at the end portion, and is preferably a structure that is interrupted (the width is zero) halfway without extending to the end surface of the optical integrated element 300. This is to obtain an effect of reducing variation in spot size conversion.

The reason why the above configuration reduces the variation in spot size conversion is as follows. In the optical integrated device 300 having the above-described structure, as shown in fig. 3A, as the width of the 2 nd mesa structure M2 becomes narrower, the mode field of light being guided in the waveguide core 303 is shifted to the SSC core 309 while being insulated. In addition, the curves shown in the figures visually illustrate the mode field of light constantly shifting from the waveguide core 303 to the SSC core 309.

At this time, the mode field of the light that is continuously transferred from the waveguide core 303 to the SSC core 309 is shifted upward by the 2 nd mesa structure M2, but the magnitude of the action of the mode field of the light to the upper side is determined by the width of the 2 nd mesa structure M2. That is, the magnitude of the mode field of the longitudinal light becomes sensitive to the accuracy of the width of the 2 nd mesa structure M2. Therefore, if the 2 nd mesa structure M2 is not extended to the end face of the optical integrated device 300 but interrupted in the middle, a fine mesa structure which is more susceptible to the accuracy in the width direction is not formed, and therefore, an effect of variation in spot size conversion among the mesas is obtained.

Here, the structure of the photonic integrated device 300 will be described in terms of a manufacturing method.

In the method of manufacturing the photonic integrated device 300, GaInAsP as the SSC core 309, n-InP as the lower cladding layer 302, GaInAsP as the waveguide core 303, p-InP as the intermediate layer 308, GaInAsP multiple quantum well as the quantum well layer 307, and p-InP as a part of the upper cladding layer 304 are sequentially formed on an InP substrate as the substrate 301 by the MOCVD method.

Next, a SiNx film was deposited on the entire face of the layer of p-InP as a part of the upper clad layer 304, and thereafter, patterning was performed so that the passive waveguide region R33, which is not an SOA, was opened. The layer of p-InP and the layer of AlGaInAs multiple quantum well are then etched using the SiNx film as a mask. After the SiNx film is removed, p-InP as a part of the upper cladding layer 304 and p-InGaAs as a contact layer 305 are stacked by MOCVD.

Next, the SiNx film is formed again on the entire surface, patterning and etching of the 2 nd mesa structure M2 are performed, the SiNx film is once removed, and then the SiNx film is formed on the entire surface, and patterning and etching of the 1 st mesa structure M1 and the 3 rd mesa structure M3 are performed.

Then, a passivation film, a resin layer, an opening thereof, an electrode for current injection, voltage application, and the like are formed in each part by a known method. After the surface is finished, the substrate is polished to a desired thickness, and if necessary, an electrode is formed on the back surface. Further, the end face formation is performed by the substrate dicing, and the end face coating and the element separation are performed to complete the optical integrated element 300.

With the above structure, the optical integrated device 300 can integrate the SOA and the spot size converter, which can expand the spot size from less than 1 μm to about 3 μm, into one device.

In addition, as described above, the optical integrated device 300 can be easily manufactured because the SOA and the spot size converter can be integrated into one device by 3-time crystal growth and 2-time formation of the mesa structure. The photonic integrated device 300 has a 3-stage mesa structure, but the mesa structure is further multi-staged without departing from the spirit of the present invention.

In the optical integrated device 300 according to embodiment 3 described above, the modulator core 306, the waveguide core 303, and the quantum well layer 307 are butt-joined, and therefore the mode field can be matched between the thick-layered modulator core 106 and the thick-layered waveguide core 303 and quantum well layer 307 in total. As a result, even if a device having a thick waveguide layer such as a phase modulator and a device having a thin waveguide layer such as an SOA are integrated into one device, mode field matching can be achieved by adopting an optimum structure for both the phase modulator and the SOA.

In the active region R32, the field of light is closer to the lower cladding layer 302 side due to the influence of the waveguide core 303. As a result, optical loss due to absorption in the valence band in the p-InP upper clad layer 304 can be suppressed, and thus the waveguide loss can be reduced.

Further, by providing a region of a part of the modulator region R31 with a high mesa structure, the parasitic capacitance in this region can be reduced, and higher-speed modulation can be performed.

In addition, in the case of forming the passive waveguide region R33, the GaInAsP multiple quantum well as the quantum well layer 307 may be removed by etching in the region where the passive waveguide region R33 is formed, and p-InP as a part of the upper cladding layer 304 and p-InGaAs as the contact layer 105 may be stacked thereon.

In the above embodiment, the modulator core 306, the waveguide core 303, and the quantum well layer 307 are exposed on the surface of both side surfaces of the low mesa structure, but the upper cladding layer 304 may be etched so as to leave a little bit on the surface.

Further, for example, as described in patent document 2, it is also possible to reduce loss in the optical connection between the waveguide of the high mesa structure and the waveguide of the low mesa structure by providing an intermediate region between the waveguide of the high mesa structure and the waveguide of the low mesa structure and realizing restriction of light different from the high mesa structure and the low mesa structure in the intermediate region.

(embodiment 4)

The photonic integrated device 400 according to embodiment 4 is a photonic integrated device that uses the features of embodiment 3. Fig. 4 is a schematic top view of the photonic integrated device 400 according to embodiment 4.

As shown in fig. 4, the optical integrated device 400 according to embodiment 4 is an optical integrated device in which a mach-zehnder IQ modulator 420, an SOA430, and an SSC440 are integrated into one device. For example, photonic integrated device 400 as a pair of slave terminals T₁The incident light is modulated and passes through the end T₂The outgoing modulator is utilized. The IQ modulator modulates both the amplitude and the phase of light.

As shown in fig. 4, the optical integrated device 400 has a so-called U-shaped configuration in which the IQ modulator 420 is orthogonal to the arrangement of the SOA430 and SSC440, and the mounting area of the optical integrated device 400 can be reduced.

In addition, wet etching is facilitated when the optical integrated device 400 having the U-shaped structure is used to form the mesa structures of the IQ modulator 420, the SOA430, and the SSC440 according to the relationship between the plane orientations of the substrates. Specifically, the SOA430 and the SSC440 are preferably fabricated with a mesa structure in a direction parallel to the [011] direction of the substrate, and the IQ-modulator 420 is preferably fabricated with a mesa structure in a direction parallel to the [01-1] direction of the substrate. In addition, the IQ modulator 420 uses the quantum confined stark effect to cause a phase change, the pockel effect acting with the same sign as the stark effect in the [01-1] direction, and the pockel effect acting with the opposite sign to the stark effect in the [011] direction. Thus, if the mesa structure is formed in the [01-1] direction, the efficiency of the phase change on the IQ modulator 420 becomes good. That is, when the vertical direction of the paper surface is the [011] direction of the substrate and the horizontal direction of the paper surface is the [01-1] direction of the substrate, the arrangement of the IQ modulator 420 and the SOA430 and SSC440 is orthogonal to each other, the plane orientation of the substrate becomes appropriate.

In the photonic integrated device 400, the SOA430 and the SSC440 are inserted only at a stage before the IQ modulator 420, but may be inserted also at a stage after the IQ modulator. In addition, it is also possible to insert only at the subsequent stage.

Fig. 5 is a sectional view showing an example of formation of a passivation film and an electrode. Fig. 5 (a) corresponds to a cross section of the IQ modulator 420 perpendicular to the extending direction of the waveguide, and fig. 5 (b) corresponds to a cross section of the SOA430 perpendicular to the extending direction of the waveguide. As shown in fig. 5 (a), in the IQ modulator 420, an SSC core 409, a lower cladding layer 402, a modulator core 406, an upper cladding layer 404, and a contact layer 405 are stacked in this order on a substrate 401. In the mesa structure of the IQ modulator 420, the contact layer 405, the upper cladding layer 404, the modulator core 406, and a part of the lower cladding layer 402 have a mesa-like projecting mesa structure of SiO, for example₂And a passivation film 411 made of SiNx. Further, a resin layer 412 made of a resin such as BCB or polyimide is formed on the outer side of the passivation film 411. Further, a current flows from the electrode 410a formed on the contact layer 405 to the ground electrode GND formed on the lower clad layer 402. On the other hand, in the SOA430, as shown in fig. 5 (b), S is sequentially laminated on the substrate 401SC core 409, lower cladding layer 402, waveguide core 403, intermediate layer 408, quantum well layer 407, upper cladding layer 404, and contact layer 405. In the mesa structure of the SOA430, the low mesa structure in which the contact layer 405 and the upper cladding layer 404 are mesa-shaped and the high mesa structure in which the quantum well layer 407, the intermediate layer 408 and the waveguide core mesa are mesa-shaped are formed of, for example, SiO₂And a passivation film 411 made of SiNx. Further, a current flows from the electrode 410b formed on the contact layer 405 to the ground electrode GND formed on the lower clad layer 402.

According to the above structure, the optical integrated device 400 can integrate the device having the waveguide path layer thickness like the IQ modulator 420, the SOA430, and the SSC440 of the 2 stage into one device, and the spot size converter thereof can be realized by 1/e²The full width of (a) extends the spot size from less than 1 μm to around 3 μm.

As described above, the optical integrated device 400 can integrate a device having a thick waveguide layer such as the IQ modulator 420, the SOA430, and the SSC440 at 2-stage into one device. Further, although the photonic integrated device 400 has a 2-stage mesa structure, the mesa structure may be further multi-staged without departing from the spirit of the present invention.

Although the photonic integrated device 400 according to embodiment 4 described above can enjoy all the advantages of the photonic integrated devices according to embodiments 1 to 3, it has an advantage that the number of crystal growths and the number of mesas formed do not increase during manufacturing.

(embodiment 5)

Fig. 6 is a schematic configuration diagram of a transmitter module as an optical module according to embodiment 5. The optical transmitter module 500 according to embodiment 5 is an optical transmitter module using any one of the optical integrated devices according to embodiments 1 to 4, and here, an optical transmitter module using the optical integrated device 400 according to embodiment 4 is exemplified.

As shown in fig. 6, the optical transmitter module 500 includes a wavelength-variable semiconductor laser 501, 1 st lenses 502a and 502b, an optical integrated element 400, 2 nd lenses 503a and 503b, and an optical fiber 504.

The wavelength variable semiconductor laser 501 is a light source that outputs laser light as a carrier wave. The laser light emitted from the wavelength variable semiconductor laser 501 is collimated by the 1 st lens 502a, and then enters the entrance end surface of the optical integrated device 400 through the 1 st lens 502 b.

As described above, the optical integrated device 400 is an optical integrated device in which the IQ modulator, SOA, and SSC are integrated into 1 device, and laser light incident on the incident end surface of the optical integrated device 400 is converted in spot size by SSC, amplified in light intensity by SOA, and modulated by the IQ modulator.

The laser light emitted from the optical integrated device 400 is collimated by the 2 nd lens 503a, enters the end face of the optical fiber 504 through the 2 nd lens 503b, and is led out to the outside of the optical transmitter module 500 through the optical fiber 504.

The optical transmitter module 500 having the above-described configuration alleviates the tolerance of coupling when entering the optical integrated element 400 from the wavelength variable semiconductor laser 501 by the action of the SSC included in the optical integrated element 400. Further, the function of the SSC included in the photonic integrated device 400 also reduces the tolerance of coupling when light enters the optical fiber 504 from the photonic integrated device 400.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments. The present invention also encompasses a configuration in which the above-described respective components are combined as appropriate. Further effects and modifications can be easily derived by those skilled in the art. For example, the layer structure of the optical integrated device used in the description of the above embodiment may be in the order of description, and the present invention is also included even if another semiconductor layer is interposed therebetween. Therefore, the present invention in its broader aspects is not limited to the above-described embodiments, and various modifications can be made.

Industrial applicability

As described above, the optical integrated element and the optical module according to the present invention are suitably used for optical communication.

Description of the symbols

100. 200, 300, 400 optical integrated element

101. 201, 301, 401 substrate

102. 202, 302, 402 lower cladding layer

103. 203, 303, 403 waveguide core

104. 204, 304, 404 upper cladding layer

105. 205, 305, 405 contact layer

106. 206, 306, 406 modulator core

107. 207, 307, 407 quantum well layers

108. 208, 308, 408 intermediate layers

309. 409 SSC core

410a, 410b electrodes

411 passivation film

412 resin layer

420 IQ modulator

430 SOA

440 SSC

500 optical transmitter module

501 wavelength-variable semiconductor laser

502a, 502b 1 st lens

503a, 503b No. 2 lens

504 an optical fiber.