JP2001135887A - Optical semiconductor device and optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical semiconductor device having high coupling efficiency to an optical waveguide, and an optical semiconductor device which has high coupling efficiency to an optical waveguide while optical output is ensured within a desired dimension. SOLUTION: A representative figure of this invension is an optical semiconductor device which is provided with a light output and a beam spot converter constituting butt joint with the light output. Film thickness of an optical waveguide of the beam spot converter is continuously reduced toward an output end surface, and at least one butt joint is arranged in the optical waveguide of the beam spot converter. As a result, an optical semiconductor device having high coupling efficiency to an optical waveguide, e.g. an optical fiber, can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device having an optical waveguide layer and a method of manufacturing the same. Further, the present invention relates to an optical transmission system using an optical semiconductor device.

[0002]

2. Description of the Related Art An optical transmission device including an optical transmission module, an optical fiber, an optical reception module, and the like has been introduced not only to a trunk system but also to a subscriber system. In this subscriber optical communication system, coupling light generated from a semiconductor laser device used as a light source to an optical fiber or an optical waveguide with high efficiency without using an optical lens can reduce the cost of an optical transmission device. This is an important task for planning.
As a method for this, there is a method of integrating a beam spot converter in a semiconductor laser device.

As an example of this beam spot converter integration method, a taper type beam spot converter in which the thickness of an optical waveguide layer is continuously reduced toward an emission end face is used in a butt joint for a semiconductor laser device or the like. (Joint) (Butt-
Joint). In addition, Butt-Jo
The int is sometimes referred to as a butt joint connection, but is described as a butt joint or (connection) in this specification. This method has a small loss in a beam spot conversion unit and is suitable for metal organic chemical vapor deposition (MOCVD: Metal).
-Organic Chemical Vapor De
By using the selective growth technique based on the position method, it is easy to integrate with an optical element such as a semiconductor laser device. In this film thickness tapered beam spot converter, the light propagating in the core of the optical waveguide spreads to the outside of the core without being confined in the core due to the decrease in the core film thickness, and the beam spot diameter at the emission end face is reduced. It is enlarged. As a result, the divergence angle of the laser light from the emission end face is reduced, and the function of improving the coupling efficiency with an optical fiber or the like is provided.

As an example of such a conventional beam spot converter integrated device, for example, Y. Itaya et al., I
EEE J. Selected Topics in
Quantum Electronics, Vol.
3, p. 963, 1997, "Spot-Size C
inverter Integrated Laser
Diodes ".

A method of integrating this tapered beam spot converter into a semiconductor laser device will be described with reference to the drawings. FIG. 1 is a cross-sectional view taken along the waveguide direction shown in the order of steps for explaining the structure and manufacturing method of a tapered beam spot converter and an integrated element of a semiconductor laser device.

First, a lower I-type substrate is placed on an n-InP substrate 101.
nGaAsP light guide layer 102, multiple quantum well (MQ
W: Multi-Quantum Well) active layer 1
03, the upper InGaAsP light guide layer 104 is sequentially
OCVD growth. Next, the dielectric film 105 of SiN
Is formed (FIG. 1A).

A SiN pattern 105 'having a desired shape is formed by using a conventional photolithography and etching technique, with the film thickness taper forming region as an opening. Using the SiN pattern 105 'as a mask, the optical waveguide layers (102 to 104) at the mask openings are removed by etching (FIG. 1B).

Further, an InGaAsP layer having a band gap wavelength shorter than the light generated in the gain region is grown by selective growth using the MOCVD method using the SiN pattern 105 'as a mask. At this time, the thickness of the InGaAsP layer at the portion where the butt joint is connected to the laser gain region is set to be substantially equal to the thickness of the optical waveguide layers (102 ′ to 104 ′). Thereby, the SiN
A tapered InGaAsP layer 106 in which the film thickness and the band gap wavelength are continuously reduced is formed in the mask opening formed by the method (FIG. 1C). The laser gain region 11 of the tapered InGaAsP layer (106) formed in this manner.
FIG. 2 shows the relationship between the film thickness and the distance from the butt joint (coupling) portion to zero. The horizontal axis in FIG.
The vertical axis indicates the thickness of the tapered portion 106 of the beam spot converter 111.

After that, the SiN pattern 105 'is removed, and the p-InP cladding layer 107 is grown by MOCVD. Thereafter, the electrodes 108, 109 and the like are formed by the same steps as those for manufacturing a normal semiconductor laser device, and a semiconductor laser device integrated with a tapered beam spot converter is completed (FIG. 1D).

At this time, the optical waveguide layers (102 'to 104') of the laser gain region 110 and the tapered InGaAs
By the butt joint (coupling) of the sP layer 106, the light generated in the laser gain unit 110 is efficiently guided to the film thickness tapered beam spot converter unit 111 and from the beam spot converter side end face. The emitted light has an enlarged beam spot diameter, and can be easily and efficiently coupled to an optical fiber or an optical waveguide.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical semiconductor device having a high coupling efficiency to an optical waveguide. Still another object of the present invention is to provide an optical semiconductor device having high coupling efficiency to an optical waveguide within desired dimensions. It is still another object of the present invention to provide an optical semiconductor device having high coupling efficiency to an optical waveguide while ensuring a desired optical output within a desired dimension.

More specifically, the present invention overcomes the limitations of the conventional film thickness tapered beam spot converter. That is, the present invention is an optical semiconductor device having a high coupling efficiency with an optical waveguide within a desired dimension required in a current optical system. In the present invention, the thickness of the film thickness taper region to ensure high coupling efficiency with the optical waveguide in the conventional film thickness tapered beam spot converter,
Avoid lowering of light output.

Another object of the present invention is to provide an optical module and an optical transmission system having an optical semiconductor device having a high coupling efficiency with an optical waveguide within a desired size required for a current optical system.

[0014]

The main aspects of the present invention are as follows.

According to a first aspect of the present invention, there is provided a light emitting portion, a first optical waveguide crystallographically joined to the light emitting portion,
At least a second optical waveguide that is crystallographically joined to the emission end face side of the first optical waveguide is provided, and at least the first and second optical waveguides have a film thickness continuously toward the emission end face. An optical semiconductor device characterized in that it decreases.

According to a second aspect of the present invention, there is provided a light emitting section, a beam spot converter section forming a butt joint (coupling) with the light emitting section, and a film of an optical waveguide of the beam spot converter section. An optical semiconductor device characterized in that the thickness is continuously reduced toward the emission end face and that one or more butt joints (couplings) are provided inside the optical waveguide of the beam spot converter. In contact with the end face of the optical waveguide layer area on the emission end face side, the beam spot conversion is performed so that the thickness of the optical waveguide layer area is gradually reduced in the waveguide direction at least in the direction intersecting the light waveguide direction. The optical waveguide of the container is formed. The present invention can provide an optical semiconductor device having a high coupling efficiency to an optical waveguide, for example, an optical fiber.

Of course, the present invention may have a plurality of tapered optical waveguide regions. That is, at least the first tapered optical waveguide region is in contact with the end surface on the emission end surface side of the first tapered optical waveguide region.
The second thickness of the tapered optical waveguide region is gradually reduced in the waveguide direction from the thickness in the direction crossing the light waveguide direction.
May be provided, as well as a third tapered optical waveguide region.

Another embodiment of the present invention is an optical semiconductor device, wherein the light emitting portion is a semiconductor light emitting device portion. As the semiconductor light emitting device, a semiconductor laser device is usually used. This embodiment is extremely useful for use in an optical communication system. Of course, as shown in the first and second embodiments, the present invention is also applicable to an embodiment in which light from other regions is transmitted to the beam spot converter unit through the light emitting unit. Specific examples of configuring the light emitting unit applicable to the present invention include a semiconductor laser device, an optical modulator,
Various optical elements such as an optical amplifier, an optical waveguide, and an optical switch can be given. Also, an optical waveguide is used as the light emitting portion, and light from various optical elements such as the semiconductor laser device, the optical modulator, the optical amplifier, the optical waveguide, and the optical switch is guided to the optical waveguide. Can be used in the present invention.

In the present invention, the type of the laser resonator is a Fabry-Perot resonator, a DFB (Distribut).
uteedfeedback), DBR (Difrac)
Tion Bragg Reflection) can be used in response to such a request.

Still another aspect of the present invention is an optical semiconductor device, characterized in that the bandgap wavelength of the optical waveguide layer is shorter from the butt joint (coupling) portion toward the emission end face. is there. In order to shorten the wavelength, it is preferable that the wavelength is continuously changed.

According to still another aspect of the present invention, there is provided a light emitting unit,
Having an optical waveguide crystallographically bonded to the light emitting portion,
The optical waveguide has at least a first optical waveguide, and a second optical waveguide that is crystallographically bonded to an emission end face side of the first optical waveguide, and has at least the first and second optical waveguides. The length of the waveguide in the waveguide direction is 300 μm or less;
The thickness of at least the first and second optical waveguides decreases toward the emission end face, and the thickness at the interface between the light emission portion and the first optical waveguide and the light guide at the emission end face are reduced. An optical semiconductor device, wherein the thickness ratio of the waveguide is 3: 1 or more. The present invention can provide an extremely practical optical semiconductor device in which an optical waveguide can be formed particularly in a desired size and the coupling efficiency to the optical waveguide is high.

Still another embodiment of the present invention is a light emitting unit,
A beam spot converter that forms a butt joint (coupling) with the light emitting unit, wherein the length of the beam spot converter in the waveguide direction is 300 μm or less, and the optical waveguide of the beam spot converter is The thickness of the butt joint (coupling) decreases continuously toward the emission end face.
The light guide has a film thickness ratio of 3: 1 or more at the emission end face, and has at least one butt joint (coupling) inside the light guide of the beam spot converter section. It is a semiconductor device. The present invention can provide an extremely practical optical semiconductor device having a high coupling efficiency to an optical waveguide.

Further, it goes without saying that the various aspects of the invention can be used in any combination.

Still another embodiment of the present invention has an optical waveguide and an optical semiconductor device, and the optical semiconductor device comprises a light emitting portion, and a beam spot converter forming a butt joint (coupling) with the light emitting portion. The beam spot converter has a length of 300 μm or less in the waveguide direction, and the light coupling efficiency between the optical semiconductor device and the optical waveguide is −3 dB.
The optical transmission system is characterized by being an optical semiconductor device not exceeding.

It is preferable that the thickness of the optical waveguide of the beam spot converter part decreases continuously toward the emission end face. It is a practical form to have at least one butt joint (coupling) inside the optical waveguide of the beam spot converter. By making the thickness ratio between the butt joint (coupling) and the optical waveguide at the emission end face 3: 1 or more, it is useful for ensuring the desired optical coupling efficiency between the optical semiconductor device and the optical waveguide. It is.

Further, the optical semiconductor device is characterized in that the band gap wavelength of the optical waveguide layer is shorter from the butt joint (coupling) portion toward the emission end face. In order to shorten the wavelength, it is preferable that the wavelength is continuously changed.

In the optical semiconductor device, wherein the light emitting portion is a semiconductor light emitting device, it is preferable that a semiconductor laser device is used as the semiconductor light emitting device. This embodiment is extremely useful for use in an optical communication system. The present invention can improve the coupling efficiency between an optical semiconductor device and an optical fiber or an optical waveguide,
By using the optical semiconductor device for an optical transmission device, the cost of the optical transmission device or the optical transmission system can be reduced.

Further, it goes without saying that the various aspects of the invention can be used in any combination.

According to a mode relating to the manufacturing method of the present invention, there is provided a step of removing a part of an optical waveguide layer region formed on a semiconductor substrate on an emission end face side, and adding the optical waveguide to the removed region of the optical waveguide layer. In contact with the end face on the emission end face side of the layer region,
An optical semiconductor device having at least one step of crystal-growing a tapered optical waveguide region such that the thickness of the optical waveguide layer region is gradually reduced in the waveguide direction from the thickness of the optical waveguide layer region in a direction intersecting the light waveguide direction. It is a manufacturing method.

The output end face of the optical waveguide layer region and the tapered optical waveguide region form a so-called butt joint (coupling).

It is optional to have a plurality of butt joints (couplings) inside the tapered optical waveguide region. That is, another mode related to the manufacturing method of the present invention is a step of removing a part of an optical waveguide layer region formed on a semiconductor substrate on an emission end face side, and adding the optical waveguide layer to the removed region of the optical waveguide layer. The first tapered light guide is in contact with the end face on the emission end face side of the waveguide layer area so as to gradually reduce its thickness in the waveguide direction at least in the direction intersecting the light guide direction of the optical waveguide layer area. Crystal growing a waveguide region, removing a part of the first tapered optical waveguide region on the emission end face side,
In the region where the first tapered optical waveguide region is removed,
In contact with the end face of the first tapered optical waveguide region on the emission end surface side, the thickness of the first tapered optical waveguide region is gradually increased in the waveguide direction more than the thickness of the first tapered optical waveguide region in the direction intersecting the light waveguide direction. And a step of crystal-growing the second tapered optical waveguide region so as to reduce the size of the optical semiconductor device.

For the crystal growth of each of the tapered optical waveguide regions, selective growth by the metal organic chemical vapor deposition method is useful. During the crystal growth of the compound semiconductor layer, the band gap wavelength of the optical waveguide layer of the tapered beam spot converter is continuously reduced from the butt joint (coupling) portion with the optical semiconductor element toward the emission end face. Is preferred.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing individual embodiments of the present invention, specific details of general embodiments of the present invention will be described.

One example of the present invention is, as described above,
When integrating a film thickness tapered beam spot converter, M
It can be obtained by repeating the step of forming the tapered optical waveguide layer by the OCVD selective growth twice or more in the waveguide direction. That is, in addition to the butt joint (coupling) part of the optical semiconductor element and the tapered beam spot converter, one or more butt joint (coupling) part is provided inside the tapered beam spot converter. It is characterized in that the thickness ratio is increased.

The optical waveguide in the above-mentioned tapered region is composed of a single layer, and the material layers above and below the optical waveguide serve as cladding layers. It is also possible to configure the optical waveguide in the film thickness taper region with a plurality of laminates.

As described above, since the film thickness distribution of the film thickness taper region formed by the selective growth by the MOCVD method decreases exponentially, for example, the film thickness ratio to an infinitely distant position becomes 3. 300 μm
The film thickness ratio at a film thickness taper region length of m is smaller than 3. However, since the film thickness distribution decreases exponentially, for example, the film thickness ratio in the region of 150 μm is 2
Then, by repeating the same process twice, 300 μm
The film thickness ratio in the region of m can be set to 4.

On the other hand, the bandgap wavelength of the InGaAsP crystal in the tapered film thickness region is smaller than that of the butt joint (coupling) portion with the thick optical semiconductor device due to the effect of selective growth by the MOCVD method. To shorten the wavelength. This shortening of the wavelength is generally about several tens of nm. For this reason, in the second and subsequent steps of forming the tapered optical waveguide layer, the butt joint (coupling) portion has
By sequentially setting the wavelength to be short so that the band gap wavelength of the nGaAsP crystal becomes continuous, the optical loss does not increase even when the number of steps of forming the tapered optical waveguide layer is increased twice or more. Therefore, it is possible to increase only the beam spot diameter without impairing the laser characteristics.

As is known, the shortening of the wavelength is caused by the diffusion ratio of In and Ga on the silicon nitride film. Therefore, the compound semiconductor material InGaAsP
The number of bad joints (couplings) inside the beam spot converter realized in the crystal, the InGaAs crystal, or the InGaAsP crystal depends on the practical length of the light traveling direction of the optical waveguide of the beam spot converter. −
Two are practical. Needless to say, the number is designed depending on the length of the beam spot converter, the required thickness ratio of the optical waveguide at the butt joint (coupling) and the output end face, and the like.

Here, the beam spot converter section includes:
Based on an optical waveguide that sandwiches a usual core layer between cladding layers,
A configuration in which the thickness of the optical waveguide in the vertical direction crossing the traveling direction of light changes along the traveling direction of the light (so-called ve).
rtally tapered waveguide
Using e) is sufficient. Also, a so-called butt joint (coupling) refers to a coupling having a second optical waveguide crystallographically connected to the first optical waveguide. Specific examples thereof include coupling of the laser active layer region as the first optical waveguide to the laser active layer region as the first optical waveguide, and coupling of the second active region to the laser active layer region as the first optical waveguide. Coupling of an optical waveguide of a beam expander as an optical waveguide, coupling of an optical waveguide of a beam expander as a second optical waveguide to the optical waveguide as the first optical waveguide, or light coupling as an optical waveguide of the first optical waveguide Coupling of an optical waveguide as the second optical waveguide to a waveguide region can be mentioned. Usually, such a butt joint (coupling) is formed by removing a part of the first optical waveguide layer by, for example, etching or the like, and then crystal-growing the second optical waveguide layer connected to this part.

In the following, the invention of the present application and a device in which a beam spot converter is integrated with the above-described conventional semiconductor laser device will be compared and studied. It will be appreciated from this that the present invention is useful.

In the conventional tapered beam spot converter, the beam spot diameter at the exit end face is further increased by increasing the thickness ratio of the optical waveguide layer at the butt joint connection portion and the other exit end face. Let
It is possible to further increase the coupling efficiency with an optical fiber or an optical waveguide.

However, in the conventional integrated device of the film thickness tapered beam spot converter and the semiconductor laser device,
In the manufacturing stage, selective growth by the MOCVD method is used only once in order to butt joint (coupling) the two. The principle of forming a film thickness taper by MOCVD selective growth utilizes the fact that an organic metal material used for growth diffuses laterally on a mask near a dielectric mask, thereby increasing the growth rate of a mask opening region. Therefore, the film thickness distribution around the dielectric mask by the selective growth has an exponential distribution shape as shown in FIG. Therefore, the usual M
The film thickness obtained under the OCVD growth conditions is about 1/3 at a position infinitely distant from the dielectric mask, assuming that the vicinity of the dielectric mask is 1.

As a result, for example, a film in a film thickness taper region obtained by a film thickness taper type beam spot converter of 300 μm or less as used in an actual film thickness taper type beam spot converter and an integrated element of a semiconductor laser device. The maximum thickness ratio is about 2.5 at the maximum. Therefore, for example, in a device in which a beam spot converter is integrated in a semiconductor laser device, the coupling efficiency with a single mode fiber is limited to about -3 dB at the maximum.

On the other hand, as is clear from FIG. 2, it is possible to increase the thickness ratio of the tapered region to about 3 by making the length of the tapered region sufficiently long, for example, 1 mm. However, in this case, an increase in the thickness taper region having no gain causes an increase in optical loss and a decrease in the output of laser light. Further, since the size of the integrated device is greatly increased, the number of devices to be obtained from a wafer having the same area is reduced, which causes a problem in cost reduction.

It will be appreciated that the present invention avoids these difficulties of the prior art.

First Embodiment A tapered beam spot converter integrated semiconductor laser device was fabricated on an n-type InP substrate. FIG. 3 is a perspective view showing the present embodiment. FIG. 4 is a sectional view taken along the waveguide direction for explaining the element structure and the manufacturing method.

In this example, a so-called embedded type (BH type: Buried) in which the light emitting portion is embedded with a semiconductor material.
1 shows an example of a semiconductor laser device of a Hetero-structure type. This aspect of the lateral mode control is not directly related to the present invention.

First, an optical guide layer (band gap wavelength: 1.10 μm, thickness: 0.1 μm) under n-type InGaAsP 2 on an n-type (100) InP substrate 1 by a conventional MOCVD method, and a strained MQW active layer (Oscillation wavelength 1.3μ
m) 3, and an optical guide layer (bandgap wavelength 1.10 μm, thickness 0.1 μm) 4 on the upper side of the p-type InGaAsP is sequentially formed. An example of the strained MQW active layer is InGaAsP
(6 nm thick) is a strained MQW active layer having a well layer and InGaAsP (band gap wavelength 1.10 μm, 10 nm thick) as a barrier layer, and its period is 7 periods.

In the present invention, practically, the semiconductor laser device uses an active layer region having a quantum well structure, an active layer region having a multiple quantum well structure, or an active layer region having a strained multiple quantum well structure. Conventional structures are sufficient for these structures. The same applies to other embodiments.

Next, a first dielectric film made of SiN is formed, and an SiN pattern 5 having a desired shape is formed using a well-known photolithography and etching method, with the film thickness tapered region as an opening. I do. Thus, this SiN
Using the region of the pattern 5 as a region to be masked, the optical waveguide layers (2 to 4) at the mask opening are removed by etching (FIG. 5A).

Further, the region of the SiN pattern 5 is used as a region to be masked, and the InGaAsP optical waveguide layer (the band gap wavelength of the butt joint (coupling) portion is 1.10 μm, the thickness is 3) by the well-known MOCVD selective growth.
(00 nm) 6 (FIG. 5B). Then S
InGa mask whose film thickness continuously decreases is formed in the iN mask opening.
An AsP film thickness tapered optical waveguide layer 6 is formed. The distance from the first butt joint portion of the tapered optical waveguide layer is 15
The film thickness at the position of 0 μm is about 150 nm, and the band gap wavelength is about 1.07 μm. The InG of the present example
The n-type InP substrate 1 and the p-InP cladding layer 9 above and below the aAsP optical waveguide layer 6 serve as a so-called cladding layer to guide light.

After removing the dielectric film 5 made of SiN, a second dielectric film made of SiN is formed on the semiconductor laminated body. Then, a SiN having a position of 150 μm from the first butt joint (coupling) portion as a tip of the opening by well-known photolithography and etching.
The pattern 7 is manufactured (FIG. 5C).

Next, the InGaAsP layer 6 in the mask opening is removed by etching using the SiN pattern 7 as a region to be masked. At this time, the thickness of the InGaAsP layer 6 ′ at the opening is about 150 nm. Further, an InGaAsP optical waveguide layer (a band gap wavelength of a butt joint (coupling) portion of 1.07 μm and a thickness of 150 nm) is grown by MOCVD selective growth using the region of the SiN pattern 7 as a region to be masked (FIG. 5). (D)). At this time, an InGaAsP film thickness tapered optical waveguide layer 8 whose film thickness is continuously reduced is formed in the opening of the SiN mask. The film thickness of this tapered optical waveguide layer at a position 150 μm from the second butt joint is about 7 μm.
5 nm, and the bandgap wavelength is about 1.04 μm.
Thereafter, the SiN pattern 7 is removed, and the p-InP cladding layer 9 is grown by MOCVD (FIG. 5E).

Thereafter, the wafer is taken out into the atmosphere, and a silicon oxide (SiO ₂ ) mask having a stripe shape (width of about 2 μm) is obtained.
To form a ridge-type structure. Thereafter, the substrate is again introduced into the MOCVD apparatus, and the p-type buried layer 14, the n-type block layer 15, and the p-type clad layer 16 are formed with the compound semiconductor material InP. Thus, a so-called BH type light confinement region is formed.

After that, the SiO ₂ mask is removed and LD
The p-type electrode 11 was formed immediately above the part. Further, after forming the n-type electrode 10 on the back surface of the substrate, the optical semiconductor laser device in which the taper type beam spot converter is integrated is completed through a cleavage process of both end faces (FIG. 5 (f)). . In this example, the length of the laser gain section 12 is 300 μm, and the length of the beam spot conversion section 13 is 300 μm.

As described above, the film thickness ratio of the film thickness tapered beam spot conversion region 13 obtained by repeating the formation process of the film thickness tapered optical waveguide layer by MOCVD selective growth twice in the waveguide direction is shown in FIG. As shown in FIG.
/ 75 nm = 4. This value corresponds to 1 for the conventional forming process.
(Only 300 times / 120 nm = 2.5)
It is increasing compared to. The horizontal axis in FIG. 5 is the distance from the junction with the laser unit 12, and the vertical axis is the beam spot converter unit 1.
3 shows the thickness of the tapered portions 6 ′ and 8.

The InGaAs of the film thickness tapered region 13 is formed.
As shown in FIG. 6, the bandgap wavelength of the P crystal is continuously shortened from 1.10 μm at the first butt joint to 1.04 μm at the emission end face. The horizontal axis in FIG. 6 is the distance from the junction with the laser unit 12, and the vertical axis is In.
The wavelength corresponding to the band gap of the GaAsP crystal is shown.

As a result, the characteristics of the tapered beam spot converter integrated semiconductor laser device were comparable to those in the case where no beam spot converter was integrated, and the coupling efficiency with a single mode fiber was -2 dB. This result shows that the conventional formation process is performed only once, and the optical waveguide of the beam spot converter does not have a butt joint therein.
The coupling efficiency with a single mode fiber in the case of a single optical waveguide was improved from -3 dB.

Embodiment 2 This embodiment is an example in which two butt joints (coupling) are provided inside the waveguide of the beam spot converter.

An optical semiconductor laser device in which a taper type beam spot converter was integrated on an n-type InP substrate was manufactured. FIG. 7 is a sectional view taken along the waveguide direction of the optical semiconductor laser device.

First, an n-type (10
0) On the InP substrate 21, an n-type InGaAsP lower optical guide layer (bandgap wavelength 1.10 μm, thickness 0.1 μm)
m) 22, strained MQW active layer region (oscillation wavelength: 1.3 μm)
23, a p-type InGaAsP upper light guide layer (bandgap wavelength 1.10 μm, thickness 0.1 μm) 24 is sequentially formed. This strained MQW active layer region 23 is made of InGaAsP.
(6 nm thick) is a strained MQW active layer having a well layer and InGaAsP (band gap wavelength 1.10 μm, 10 nm thick) as a barrier layer, and its period is 7 periods.

Next, a first dielectric pattern of SiN is formed, and a part of the tapered optical waveguide layer is removed by etching.
An nGaAsP film thickness tapered optical waveguide layer 25 is grown. At this time, the thickness of the tapered optical waveguide layer at a position 100 μm from the first butt joint is about 180 nm, and the band gap wavelength is about 1.08 μm. The In
The band gap wavelength of the butt joint (coupling) portion of the GaAsP film thickness tapered optical waveguide layer 25 is 1.10 μm.
m, thickness 300 nm.

Next, after removing the dielectric film made of SiN, a second dielectric pattern made of SiN is formed.
After removing a part of the tapered optical waveguide layer by etching, selective growth is performed by MOCVD to form an InGaAsP tapered optical waveguide layer (a band gap wavelength of a butt joint (coupling) portion is 1.08 μm and a thickness is 180 nm).
Grow. At this time, the film thickness at a position of 100 μm from the second butt joint portion of the tapered optical waveguide layer is about 1 μm.
00 nm, and the band gap wavelength is about 1.06 μm.

Next, after removing the SiN dielectric film, the third
After forming a second SiN dielectric pattern and removing a part of the tapered optical waveguide layer by etching, the MOCV
An InGaAsP film thickness tapered optical waveguide layer (band gap wavelength of a butt joint (coupling) portion 1.06 μm, thickness 100 nm) 27 is grown by the D method selective growth. At this time, the horizontal width of the opening of the dielectric pattern is set to the first time,
By making it wider than the second dielectric pattern,
The thickness was set so that the change in film thickness due to the selective growth was small.
This is for stabilizing the mode of light in the optical waveguide by reducing the change in the film thickness of the optical waveguide near the emission end face. At this time, the film thickness at a position 100 μm from the third butt joint of the film thickness tapered optical waveguide layer is about 9
0 nm, and the band gap wavelength is about 1.05 μm.
Incidentally, the InGaAsP optical waveguide layers (25, 2
6, 27) are the upper and lower n-type InP substrates 21 and p-I
The nP cladding layer 28 serves as a so-called cladding layer and guides light.

Thereafter, the SiN pattern is removed, and pI
The nP cladding layer 28 is grown by MOCVD. After that, the wafer is taken out into the atmosphere and striped silicon oxide
Mesa etching is performed using a (SiO ₂ ) mask (about 5 μm in width) to form a ridge type structure. After this, MOC again
The semiconductor device is introduced into a VD device, and a p-type buried layer 14, an n-type block layer 15, and a p-type clad layer 16 are formed using a compound semiconductor material InP. Thus, a so-called BH type light confinement region is formed.

Thereafter, the SiO ₂ mask is removed, and the LD
A p-type electrode 30 was formed immediately above the portion. Further, after the n-type electrode 29 is formed on the back surface of the substrate, the semiconductor laser device in which the tapered beam spot converter is integrated is completed through a step of cleaving both end faces. The length of the laser gain section 31 is 300 μm, and the length of the beam spot conversion section 32 is 30 μm.
0 μm.

The thickness ratio of the tapered beam spot conversion region 32 obtained by repeating the process of forming the tapered optical waveguide layer by selective growth using the MOCVD method three times in the waveguide direction according to this method is shown in FIG. As shown in FIG.
m / 90 nm = 3.3. As a result, the coupling efficiency of the tapered beam spot converter integrated semiconductor laser device with the single mode fiber was -2.5 dB. The horizontal axis in FIG. 8 is the distance from the junction with the laser unit 31, and the vertical axis is the tapered part 25 of the beam spot converter 32.
A film thickness of -27 is shown.

In each of the above embodiments, the case where the semiconductor laser device and the beam spot converter are integrated has been described. However, various optical elements such as an optical modulator, an optical amplifier, an optical waveguide, an optical switch, and a beam spot are integrated. The present invention is similarly effective when integrating converters.

Also, since the present invention has at least one butt joint (coupling) portion inside the beam spot converter,
As shown in Step 3 of the second embodiment, an arbitrary thickness taper shape can be designed and manufactured by changing the shape of a dielectric mask pattern used for selective growth. .

An optical communication system can be configured by mounting the optical semiconductor device exemplified in the first and second embodiments of the present invention as a light source in a transmission system device system. In particular, the optical semiconductor device of the present application is useful for use in a subscriber optical system. By using the optical semiconductor device of the present application of the optical module, an optical lens which has been required between the semiconductor laser device and the optical waveguide is unnecessary. The present invention is advantageous for low cost requirements.

By using the present invention, it is possible to provide an optical module and an optical transmission system having an optical semiconductor device having a high coupling efficiency with an optical waveguide within a desired size required for a current optical system.

[0072]

According to the present invention, an optical semiconductor device having a high coupling efficiency to an optical waveguide can be provided. Furthermore, the present invention can provide an optical semiconductor device having high coupling efficiency to an optical waveguide within a desired size.

The present invention secures high coupling efficiency with an optical waveguide in a film thickness tapered beam spot converter and avoids a decrease in optical output.

The present invention can further provide an optical module and an optical transmission system having an optical semiconductor device having a high coupling efficiency with an optical waveguide within a desired size required for a current optical system.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view taken along a plane parallel to the waveguide direction of a device shown in the order of manufacturing a semiconductor laser device in which a conventional beam spot converter is integrated.

FIG. 2 is a diagram for explaining a film thickness distribution of a conventional film thickness tapered beam spot converter.

FIG. 3 is a perspective view of a semiconductor laser device in which a beam spot converter according to the first embodiment of the present invention is integrated.

FIG. 4 is a cross-sectional view taken along a plane parallel to the waveguide direction of the device shown in the order of steps for manufacturing the beam spot converter integrated semiconductor laser device according to the first embodiment of the present invention.

FIG. 5 is a diagram for explaining a film thickness distribution of an optical waveguide of the film thickness tapered beam spot converter according to the first embodiment of the present invention.

FIG. 6 is a diagram for explaining a crystal bandgap wavelength distribution of an optical waveguide of the film thickness tapered beam spot converter according to the first embodiment of the present invention.

FIG. 7 is a cross-sectional view of a beam spot converter integrated semiconductor laser device according to a second embodiment of the present invention, taken along a plane parallel to the waveguide direction.

FIG. 8 is a diagram for explaining a film thickness distribution of a film thickness tapered beam spot converter according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Compound semiconductor substrate, 2 ... Lower light guide layer, 3 ... MQ
W active layer region, 4 ... upper light guide layer, 5 ... dielectric film,
6, 6 ': first thickness tapered optical waveguide layer, 7: dielectric film, 8: second tapered optical waveguide layer, 9: cladding layer, 10: n electrode, 11: p electrode, 12 ... Laser gain unit, 13: beam spot conversion unit, 14: buried layer, 15
... block layer, 16 ... cladding layer, 21 ... compound semiconductor substrate, 22 ... lower light guide layer, 23 ... MQW active layer region, 24 ... upper light guide layer, 25 ... first thickness tapered optical waveguide layer, 26 ... second thickness tapered optical waveguide layer, 27 ...
Third film thickness tapered optical waveguide layer, 28 ... clad layer, 29
... n electrode, 30 ... p electrode, 31 ... laser gain part, 32 ...
Beam spot converter, 101 ... compound semiconductor substrate, 1
02, 102 '... lower light guide layer, 103, 103' ...
MQW active layer region, 104, 104 ': upper light guide layer, 105, 105': dielectric film, 106: tapered optical waveguide layer, 107: clad layer, 108: n electrode, 1
09 ... p electrode, 110 ... laser gain section, 111 ... beam spot conversion section.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazunori Shinoda 1-280 Higashi-Koigabo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 2H037 AA01 BA02 DA03 5F073 AA22 AA45 AA74 AB25 AB28 BA02 CA12

Claims (9)

[Claims] 1. A light emitting portion, a first optical waveguide crystallographically bonded to the light emitting portion, and a second optical crystallographically bonded to an emission end face of the first optical waveguide. An optical semiconductor device having at least an optical waveguide, wherein the film thickness of at least the first and second optical waveguides decreases continuously toward the emission end face. 2. A light emitting section, and a beam spot converter section forming a butt joint with the light emitting section, wherein the thickness of the optical waveguide of the beam spot converter section is continuously increased toward an emission end face. An optical semiconductor device having a reduced number and one or more butt joints inside an optical waveguide of the beam spot converter. 3. The optical semiconductor device according to claim 1, wherein the light emitting unit is a semiconductor light emitting device unit. 4. The light emitting device according to claim 1, wherein the light emitting portion is at least one member selected from the group consisting of an optical modulator, an optical amplifier, an optical waveguide, and an optical switch. Optical semiconductor device. 5. A method according to claim 1, wherein a band gap wavelength of the optical waveguide layer of the beam spot converter is shorter from an interface of the optical waveguide layer with the light emitting portion toward an emission end face. The optical semiconductor device according to claim 1. 6. A light emitting portion, and an optical waveguide that is crystallographically joined to the light emitting portion, wherein the optical waveguide is a first optical waveguide, and an emission end face side of the first optical waveguide. At least a second optical waveguide that is crystallographically bonded to the first optical waveguide, at least the first and second optical waveguides have a length of 300 μm or less in the waveguide direction, and at least the first and second optical waveguides
The thickness of the optical waveguide having the thickness decreases toward the emission end face, and the film thickness ratio at the interface between the light emission part and the first optical waveguide and the thickness of the optical waveguide at the emission end face becomes 3 An optical semiconductor device having at least one pair. 7. A light emitting unit, and a beam spot converter unit forming a butt joint with the light emitting unit, wherein the length of the beam spot converter unit in the waveguide direction is 300 μm.
m, the thickness of the optical waveguide of the beam spot converter decreases toward the emission end face, and the thickness ratio of the optical waveguide between the butt joint and the emission end face is 3: 1.
An optical semiconductor device comprising the above, and having one or more butt joints inside the optical waveguide of the beam spot converter. 8. An optical waveguide having an optical waveguide and a light emitting section, wherein the light emitting section has a beam spot converter section forming a butt joint with the light emitting section. An optical transmission system characterized in that a film thickness is continuously reduced toward an emission end face and one or more butt joints are provided inside an optical waveguide of the beam spot converter. 9. An optical semiconductor device comprising: an optical waveguide; and an optical semiconductor device, wherein the optical semiconductor device includes a light emitting unit, and a beam spot converter unit forming a butt joint with the light emitting unit. 300 μm
An optical transmission system comprising: an optical semiconductor device, wherein the optical coupling efficiency between the optical semiconductor device and the optical waveguide does not exceed -3 dB.