JPH11135876A - Integrated semiconductor optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove the effects of stray light and to improve high-speed modulation characteristic by providing a dummy waveguide region for separating guided light from stray light, which is placed between and in contact with an oscillating region and an optical modulation region and has the same structure as that of the optical modulation region. SOLUTION: An integrated laser with a modulator has a dummy waveguide region 300 for separating guide light from stray light, which is placed between and in contact with an oscillation region 100 and an optical modulation region 200 and has the same structure as the optical modulation region 200. Each of the regions of 100, 200, and 300 are provided in a region which includes a common substrate 10. The dummy waveguide region 300 has the same structure as that of the optical modulation region 200 and is constituted by the substrate 10, an absorption layer 16 formed on the substrate 10, a clad layer 18, a contact layer 20 and a second p-type electrode 26. The material as well as the composition of the absorption layer 16 of the dummy waveguide region 300 are identical to those of the absorption layer 16 of the optical modulation region 200.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an integrated semiconductor optical device.

[0002]

2. Description of the Related Art Conventional integrated semiconductor optical devices (here,
Literature (Technical Report of IEICE, TECHNICAL) REPORT IEICE LEQ95-16 (1995-06)). This integrated laser is configured by integrating a distributed feedback (DFB) laser region and an optical modulator region. The DFB laser region has a stripe-shaped active layer as a waveguide, while the optical modulator region has a stripe-shaped absorption layer as a waveguide. The active layer and the absorption layer are linearly and integrally formed in the waveguide direction, and the waveguide including the active layer and the absorption layer is formed in a mesa shape. A high-resistance buried layer is provided on both sides of the active layer in the DFB laser region and the absorption layer in the optical modulator region. Further, p-type electrodes are individually provided above the DFB laser region and the optical modulator region, while a common electrode (n-type electrode) is provided below.

[0003]

However, in the integrated laser described above, since the DFB laser region and the optical modulator region are coupled, stray light (here, the active layer of the DFB laser region and the optical modulator region) are combined. (Referred to as light due to irregular reflection or leakage of the guided light generated by the coupling portion with the absorption layer), and this stray light overlaps with the guided light to deteriorate the extinction characteristic.

In the case where a DFB laser is coupled to an optical fiber, if stray light is generated, interference between the stray light and the guided light occurs. Due to this effect, alignment between the integrated laser and the optical fiber becomes difficult. For this reason, there has been a problem that the coupling efficiency between the integrated laser and the optical fiber is reduced.

Further, since the conventional integrated laser uses an Fe-doped InP layer as a buried layer, the buried layer is maintained at a high resistance. Therefore, the element capacitance (here, the capacitance formed by the p-type electrode and the buried layer in the DFB laser region or the optical modulator region) is large in all regions of the DFB laser region and the optical modulator region. Thus, there is a problem that high-speed modulation characteristics cannot be obtained.

Therefore, there has been a demand for the emergence of an integrated semiconductor optical device which eliminates the influence of stray light and has excellent high-speed modulation characteristics.

[0007]

Therefore, according to the integrated semiconductor optical device of the present invention, an oscillation region and an optical modulator region are provided, and the oscillation region and the optical modulation region are linearly and integrally coupled. Integrated semiconductor optical device that modulates and outputs the guided light oscillated in the oscillation region at high speed, and between the oscillation region and the optical modulator region, is connected to the oscillation region and the optical modulator region and has the same structure as the optical modulator region Wherein a dummy waveguide region for separating stray light and guided light is provided.

In the present invention, a dummy waveguide region is provided between the oscillation region and the optical modulator region. Therefore, by setting the waveguide length of the dummy waveguide region to a suitable length, stray light generated from a coupling portion (butt joint coupling portion) between the oscillation region and the dummy waveguide region and traveling straight other than the waveguide. And the guided light oscillated from the oscillation region and propagated through the waveguide can be separated on the output end face side of the optical modulator region. Therefore, it is possible to output from the optical modulator region side without deteriorating the extinction characteristic of the guided light.

Further, by using the integrated semiconductor optical device of the present invention, when an optical fiber is connected, only the guided light can be incident on the optical fiber. Can be improved.

In practicing the present invention, preferably, the oscillation region comprises at least a substrate and an active layer and a cladding layer provided on the substrate, and the optical modulator region and the dummy waveguide region have at least It comprises a substrate and an absorption layer and a cladding layer provided on the substrate, at least the cladding layer is formed in a mesa shape, and the optical modulator region and the dummy waveguide region are insulating layers embedded on both sides of the cladding layer. Preferably, a body layer and an island-shaped electrode provided over the upper surface of the insulator layer and the upper side of the clad layer are separately provided.

As described above, the island-shaped electrodes are provided on the upper surfaces of the dummy waveguide region and the optical modulator region, respectively, and the insulating layers are provided on both sides of the clad layer. By providing an insulator layer with low resistivity, the element capacity formed by the electrode and the insulator layer can be reduced.

In practicing the present invention, it is preferable that the absorption layer in the optical modulator region and the absorption layer in the dummy waveguide region have the same material and the same composition.

With such a configuration, light oscillated in the oscillation region propagates through the waveguides in the dummy waveguide region and the optical modulator region at the same refractive index, while the light between the active layer and the absorption layer is not reflected. The stray light generated at the coupling portion propagates through the substrate or the clad layer other than the waveguide in the dummy waveguide region and the optical modulator region with the same refractive index. Accordingly, the spot interval between the guided light and the stray light of the near-field pattern in the optical modulator region can be separated and separated by the length of the waveguide in the dummy waveguide region.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an integrated semiconductor optical device of the present invention, in particular, a semiconductor laser in which an optical modulator is integrated. FIGS. 1 to 5 and FIGS. 8 to 9 only schematically show the size, shape and arrangement of each component to the extent that the present invention can be understood, and are not limited thereto. is not.

[First Embodiment] A main structure of an integrated semiconductor optical device according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a perspective view for explaining the structure of the integrated semiconductor optical device according to the first embodiment.

An integrated semiconductor optical device of the present invention (hereinafter referred to as an integrated laser with a modulator) is provided between an oscillation region 100 and an optical modulator region 200 so as to be connected to the oscillation region 100 and the optical modulator region 200. A dummy waveguide region 300 having the same structure as the modulator region 200 for separating stray light and guided light is provided. In addition, each area 100,
200 and 300 are common substrates (here, n-InP
(Substrate) 10.

The oscillation region 100 includes a substrate 10 and an active layer 1 provided on the substrate 10 as in the conventional configuration.
4, the cladding layer 18, the contact layer 20, and the first p-type electrode 24. The oscillation region 1
In 00, the grating 12 is formed on the surface of the substrate 10. The active layer 14 includes a barrier layer (InGaAs).
P) and a well layer (InGaAs) having an appropriate period, for example, five layers.

The optical modulator region 200 includes a substrate 10 and an absorption layer 16, a cladding layer 18, a contact layer 20, and a third p-type layer provided on the substrate 10, as in the conventional configuration.
And a mold electrode 28. And the absorption layer 16
Are a barrier layer (InGaAsP) and a well layer (InGaAs).
sP). Here, the absorption layer 16 barrier layer and the well layer are made of the same material, and the compositions of the barrier layer and the well layer are changed.

The integrated laser of the present invention has a dummy waveguide region 300. This region 300 has the same structure as the optical modulator region 200, that is, the substrate 10 and the substrate 10
It comprises the absorption layer 16, the cladding layer 18, the contact layer 20, and the second p-type electrode 26 provided thereon. Further, the absorption layer 16 in the dummy waveguide region 300 and the absorption layer 16 in the optical modulator region 200 have the same material and the same composition.

In this embodiment, a stripe-shaped cladding layer 18 is provided on the upper surface of the active layer 14 of the oscillation region 100 and the absorption layer 16 of the optical modulator region 200 and the dummy waveguide region 300. The layer 18 is formed in a mesa shape. Furthermore, on the cladding layer 18,
A contact layer 20 is provided. An insulator layer (buried layer) 22 is buried on both sides of the clad layer 18 and the contact layer 20. Here, the cladding layer 18 is made of p-InP, and the contact layer 20 is made of p-InP.
Is phosphorus (P) -doped InGaAs, and the insulator layer 22
Is polyimide.

In this embodiment, the insulator layer 22
Although polyimide is used as the above, silicon dioxide may be used instead of polyimide. By using such polyimide, the device capacitance of the optical modulator region 200 and the dummy waveguide region 300 can be reduced.

In the first embodiment, the second p-type electrode 26 in the dummy waveguide region 300 is provided in an island shape so as to extend over the polyimide layer 22 as an insulator layer and the contact layer 20. is there. The width W of the second p-type electrode 26
Is preferably 0.5 μm or more here. In this embodiment, assuming that the integrated laser with the optical modulator is connected to the optical fiber, the width W of the second p-type electrode 26 is set to a width larger than the core radius (about 4 to 5 μm) of the optical fiber. It is.

On the back surface of the substrate 10, an n-type electrode 30
Is provided.

In this embodiment, as in the prior art, the first p-type electrode 24 of the oscillation region 100, the third p-type electrode 28 of the optical modulator region 200, and the dummy waveguide region 3 are formed.
Separation grooves 32 and 34 for separating the second p-type electrode 26 of FIG.

[Method of Forming First Embodiment] Next, referring to FIGS. 2 to 5, an integrated semiconductor optical device (also referred to as an integrated laser with an optical modulator) of the first embodiment will be described. The formation method will be described. 2 (A) to 2 (D), FIGS. 3 (A) to 3 (C), FIGS. 4 (A) to 3 (B), and FIGS. 5 (A) to 5 (B) FIGS. 7A and 7B are a cross-sectional view and a perspective view for describing a method of forming the integrated laser with an optical modulator according to the embodiment.

An n-type InP substrate is used as the common substrate 10 (FIG. 2A). After that, the gratings 12 are formed on a part of the substrate 10 at a predetermined pitch by using any suitable etching method (FIG. 2B).

Next, the substrate 10 including the grating 12
An active layer 14 composed of a barrier layer (InGaAsP) and a well layer (InGaAs) having five periods is formed thereon by using a metal organic chemical vapor deposition (MOVPE) method (FIG. 2C).

Next, the active layer 14 on the substrate 10 other than the grating 12 is removed by any suitable method (FIG. 2D).

Next, in the region from which the active layer 14 has been removed by the MOVPE method, an absorption layer 16 having a proper period, for example, seven periods, composed of a barrier layer (InGaAsP) and a well layer (InGaAsP), is selectively grown (FIG. (A of FIG. 3).
Here, it is preferable that the absorption layer 16 and the active layer 14 have substantially the same thickness and form a flat surface.

Next, a cladding layer (p-InP layer) 18 is formed on the active layer 14 and the absorption layer 16 by MOVPE.
And contact layer (phosphorus (P) -doped InGaAs)
Layers) 20 are sequentially formed (FIGS. 3B and 3C).

Next, a stripe-shaped etching mask (not shown) is formed at right angles to the joint between the active layer 14 and the absorbing layer 16. In this case, the width of the etching mask used here is about 2 to 3 μm. Thereafter, the contact layer 20 and the cladding layer 18 are removed by, for example, dry etching using this etching mask to form a mesa-shaped structure (FIG. 4A). In this embodiment, the mesa-shaped structure is composed of the cladding layer 18 and the contact layer 20.

Next, buried layers (polyimide layers as insulator layers) 22 are formed on both sides of the cladding layer 18 and the contact layer 20 by, for example, the CVD method (FIG. 4B). At this time, the polyimide layer 22 is embedded so as to be flat with the surface of the contact layer 20.

Next, after forming a p-type electrode preliminary film (not shown) on the polyimide layer 22 including the contact layer 20,
The preliminary film is etched using a lithography technique to form an island-shaped first p-type electrode 24, second p-type electrode 26, and third p-type electrode 28, respectively (FIG. 5A).

On the back surface of the substrate 10, for example, CV
The n-type electrode 30 is formed using the D method.

Next, the first p-type electrode 24 and the second p-type electrode 2
6 and the exposed contact layer 20 and the second p
The contact layer 20 exposed between the mold electrode 26 and the third p-type electrode 28 is removed by etching to form separation grooves 32 and 34 (FIG. 5B). In the present embodiment, such separation grooves 32 and 34 are formed to
between the p-type electrode 24 and the second p-type electrode 26 or
The separation resistance between the type electrode 26 and the third p-type electrode 28 is 1
0 KΩ or more.

[Operation of First Embodiment] Next, an operation method of the integrated laser with an optical modulator according to the first embodiment will be described with reference to FIG.

When a forward bias current is applied to the first p-type electrode 24 in the oscillation region 100, the oscillation region 100 emits laser light. This laser light is applied to the dummy waveguide region 300
Incident on the absorption layer 16. At this time, the laser light propagates through the absorption layer 16 in the dummy waveguide region 300 and further enters the optical modulator region 200. On the other hand, stray light generated at the junction between the active layer 14 and the absorption layer 16 travels straight through the substrate 10 or the cladding layer 18 at a predetermined angle. Here, since a forward bias voltage is applied to the second p-type electrode 26 of the separation waveguide region 300, the propagation loss can be reduced and the gain can be increased. Here, the dummy waveguide region 300 is also referred to as a separation waveguide region.

The light (guided light) output (emitted) from the absorption layer 16 of the separation waveguide region 300 is transmitted to the optical modulator region 200.
And is modulated and output from the end face side of the optical modulator area 200.

Next, the emission positions of stray light and guided light in the integrated laser of the present invention and the conventional laser will be described with reference to FIGS. FIGS. 6A and 6B are explanatory diagrams for explaining a stray light position when a conventional integrated laser is used, and FIGS. 7A and 7B are diagrams for explaining the integration of the present invention. FIG. 9 is an explanatory diagram for explaining a stray light position when a laser is used.

In the conventional integrated laser, the laser light oscillated from the transmission region (laser region) 100 propagates through the absorption layer 16 of the light modulator region 200 and becomes a guided light (WL) as an end face of the light modulator region 200. Output from the side. On the other hand, the stray light (SL) generated at the joint (butt joint joint) between the active layer 14 and the absorbing layer 16 travels straight through the medium of the substrate 10 at an elevation angle θ with the guided light.

Therefore, the position interval b between the near-field pattern of the guided light WL and the stray light SL is b = a × tan θ (FIGS. 6A and 6B).

On the other hand, in the integrated laser of the present invention, since the separated waveguide region 300 is provided, the waveguide length c (c) between the separated waveguide region 300 and the optical modulator region 200 is set.
> A) is longer than before. Accordingly, the distance d between the near field patterns of the guided light WL and the stray light SL is d =
c × tan θ, and the stray light positions of the stray light and the guided light can be separated from each other as compared with the related art (FIGS. 7A and 7B).

As described above, in the first embodiment, since the separation waveguide region 300 is provided as described above,
It is possible to separate the guided light from the stray light, and the gain can be increased by applying a forward bias voltage to the separated waveguide region 300. For this reason, S /
The N ratio is improved. Further, since polyimide is used for the buried layer 22, the device capacitance in the separation waveguide region 300 and the optical modulator region 200 can be reduced. Therefore, high-speed modulation characteristics can be obtained.

[Structure of Integrated Laser of Second Embodiment]
Next, the structure of an integrated laser with a modulator according to a second embodiment of the present invention will be described with reference to FIG. FIG.
FIG. 7 is a perspective view for explaining a main structure of an integrated laser with a modulator according to a second embodiment.

In the second embodiment, the first p-type electrode 40
The second embodiment is different from the first embodiment in that the shape of the second p-type electrode 42 is changed.

That is, in this embodiment, the first and second p-type electrodes 40 and 42 are made smaller than those of the first embodiment. For other components,
This is the same as in the first embodiment.

As described above, the first and second p-type electrodes 40
By reducing the size of and, the device capacitance can be reduced as compared with the first embodiment.

That is, as is well known, the element capacitance (C) is:
It can be represented by the following equation (Reference: Appl. Phys.
Lett. 51. (22), 30, 1987).

C = (εA ₁ + ρτA ₂ ) / t (1) where A ₁ is the oscillation region 100 and the optical modulator region 20
0, the pad areas of the first and second p-type electrodes, A ₂ is the mesa length × the element length, t is the thickness of the insulator layer, ε is the dielectric constant of the insulator layer, and ρ is the The resistivity, τ, is the carrier lifetime (寿命 3 × 10 ⁻⁷ ).

Here, since the pad areas of the first and second p-type electrodes in the oscillation region 100 and the optical modulator region 200 are reduced, the element capacitance is smaller than the expression (1). That is, in the second embodiment, the separation waveguide region 300
And the element capacity of the optical modulator region 200 can be reduced.

The method of forming the integrated laser according to the second embodiment and the operation principle thereof are the same as those of the first embodiment, and a detailed description thereof will be omitted.

[Structure of Integrated Laser of Third Embodiment]
Next, a main structure of the integrated laser with an optical modulator according to the third embodiment will be described with reference to FIG. In addition, FIG.
FIG. 14 is a partially cutaway perspective view for explaining a structure of an integrated laser with an optical modulator according to a third embodiment.

In the third embodiment, the contact layer 20
To a part of the substrate 10 on the lower surface of the active layer 14 and the absorption layer 16. Other components are the same as in the first embodiment.

In the third embodiment, since the polyimide layers 22 are formed on both sides of the active layer 14 and the absorption layer 16, the intensity of the guided light can be increased as compared with the first embodiment. .

Further, as the thickness t of the polyimide layer 22 is increased, the element capacitance of the above-described formula (1) can be reduced as compared with the first and second embodiments.

The materials used in the configuration of the above-described embodiment are merely examples, and other materials may be used to form an integrated laser with an optical modulator.

[0057]

As is apparent from the above description, according to the integrated semiconductor optical device of the present invention, a dummy waveguide for separating stray light and guided light is provided between an oscillation region and an optical modulator region. The provision of the waveguide region increases the element length of the dummy waveguide region. Therefore, the distance between the guided light and the stray light output to the end face of the optical modulator region can be more separated than before. Therefore, when coupling the optical fiber and the semiconductor optical element, stray light can be removed and only guided light can be incident on the optical fiber, so that the coupling efficiency between the optical element and the optical fiber is greatly improved.

Further, in the present invention, at least the clad layer is formed in a mesa shape, and both sides of the clad layer are buried with insulator layers. Since the insulator layer is made of a material (for example, polyimide) having a lower resistivity than in the related art, the element capacitance in the dummy waveguide region and the optical modulator region can be reduced. Therefore, an integrated semiconductor optical device having excellent high-speed modulation characteristics can be obtained by reducing the device capacitance.

[Brief description of the drawings]

FIG. 1 is a perspective view for explaining a main structure of an integrated semiconductor optical device according to a first embodiment of the present invention.

FIGS. 2A to 2D are cross-sectional process diagrams for explaining a method of forming the integrated semiconductor optical device according to the first embodiment;

FIGS. 3A to 3C are cross-sectional process views following FIG. 2 for explaining a method of forming the integrated semiconductor optical device according to the first embodiment;

FIGS. 4A and 4B are perspective views following FIG. 3 for explaining a method of forming the integrated semiconductor optical device according to the first embodiment;

FIGS. 5A and 5B are perspective views following FIG. 4 for explaining a method of forming the integrated semiconductor optical device according to the first embodiment;

FIGS. 6A and 6B are diagrams for explaining a stray light position when a conventional optical element is used.

FIGS. 7A and 7B are diagrams for explaining a stray light position when the optical element of the present invention is used.

FIG. 8 is a perspective view for explaining a main structure of an integrated semiconductor optical device according to a second embodiment of the present invention.

FIG. 9 is a partially cutaway perspective view for explaining a main structure of an integrated semiconductor optical device according to a third embodiment of the present invention.

[Explanation of symbols]

 10: n-InP substrate 12: grating 14: active layer 16: absorption layer 18: cladding layer 20: contact layer 22: buried layer (insulator layer, polyimide layer) 24, 40: first p-type electrode 26, 42: first 2p-type electrode 28: third p-type electrode 30: n-type electrode 32, 34: separation groove 100: oscillation region 200: optical modulator region 300: dummy waveguide region (separation waveguide region)

Claims (5)

[Claims] An integrated circuit comprising an oscillation area and an optical modulator area, wherein the oscillation area and the optical modulation area are linearly and integrally coupled to each other, and the guided light oscillated in the oscillation area is modulated at a high speed and output. In the semiconductor optical device, between the oscillation region and the optical modulator region, the optical modulator region is connected to the oscillation region and the optical modulator region and has the same structure as the optical modulator region. An integrated semiconductor optical device comprising a dummy waveguide region for performing the operation. 2. The integrated semiconductor optical device according to claim 1, wherein said dummy waveguide region has a waveguide length of 0.5 μm.
An integrated semiconductor optical device characterized by the above. 3. The integrated semiconductor optical device according to claim 1, wherein the oscillation region comprises at least a substrate and an active layer and a cladding layer provided on the substrate, and wherein the optical modulator region and the The dummy waveguide region includes at least the substrate, the absorption layer and the cladding layer provided on the substrate, and at least the cladding layer is formed in a mesa shape, and the optical modulator region and the dummy waveguide region Comprises an insulator layer embedded on both sides of the cladding layer, and an island-shaped electrode provided over the upper surface of the insulator layer and the upper side of the cladding layer. Integrated semiconductor optical device. 4. The integrated semiconductor optical device according to claim 3, wherein said insulator layer is made of polyimide or silicon dioxide. 5. The integrated semiconductor optical device according to claim 3, wherein said absorption layer in said optical modulator region and said absorption layer in said dummy waveguide region have the same material and the same composition. Integrated semiconductor optical device.