JPH11191656A - Photosemiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain satisfactory light-off ratio by forming at least one part of an optical waveguide into a curved shape in a photosemiconductor device that has the optical waveguide for outputting light which is inputted from one end to the other and functions as a photo amplifying medium, where light is amplified by at least one part of the optical waveguide. SOLUTION: An activation layer 3 for forming an optical waveguide of a photosemiconductor device (SOA) 1 is formed in an S-shaped curved shape, linear light input and output parts 11 and 12 are provided in one piece at the both ends, and the light input and output parts 11 and 12 are offset in parallel and are formed in a tapered structure, where the thickness of the layer is gradually thinned toward an end part. Then, the size of a light spot on an end face is enlarged, thus obtaining a satisfactory optical coupling. Also, a pair of element end faces opposite each other is positioned in parallel, and an AR coat 13 is formed as non-reflecting covering by an SiON film, thus quenching signal light being inputted for preventing it from being outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication technology, and more particularly to an optical semiconductor device having functions of amplifying and quenching signal light.

[0002]

2. Description of the Related Art Optical semiconductor devices (hereinafter, SOA: Semiconduct
or an Optical Amplifier) is an element having an optical amplification medium of a striped optical waveguide and amplifying signal light without electrical conversion. Although its structure is basically common to that of the semiconductor laser, it is designed so that the light reflectance at the end of the element is suppressed by a non-reflection coating or the like so that an optical resonator structure is not formed. For this reason, even if carriers are injected, the laser oscillation of the SOA itself is suppressed, and the amplified light is emitted by stimulated emission by the input signal light.

[0003] Examples of reports on SOA as described above include: (1) I. Cha. Et. Al., Electr. Lett. Vol. 25, pp124.
1-1242 (1989) (2) CE Zah, et. Al., Electr. Lett. Vol.23, pp9
90-991 (1987) (3) S. Kitamura, et. Al., IEEE Photonics Technol.
Lett. Vol. 7, pp147-148 (1995) (4) LF Tiemeijer, OAA '94 Technical Digest 34 /
WD1-1 (1994) (5) P. Doussiere, et. Al., ECOC '96, Proceeding V
ol.3, WeD 2.4 (1996) (6) S.Chelles, et. al., ECOC '96, Proceeding Vo
l.4, ThB 2.5 (1996).

Among the documents (4) to (6), SO
It is disclosed that A is modularized with an optical fiber. In that case, it has been reported that the gain between the optical fibers can be set to 20 dB or more, and the saturation output of the amplified signal light becomes close to 10 dBm.

On the other hand, the SOA is characterized in that it functions as a carrier injection type optical gate in addition to the above-described amplification of the signal light. That is, the active layer of SOA
While light is amplified at the time of ON (at the time of current injection), high optical absorption occurs at the time of OFF (at the time of no current injection). Therefore, the optical waveguide having the active layer as the core layer can turn on and off the guided light. .

In future optical communication networks, matrix optical switches are strongly desired for signal light cross-connects, and SOAs are currently most promising as optical gate elements for the matrix optical switches. SOA
Has a larger extinction ratio at ON / OFF than an electric absorption type semiconductor modulator or an optical coupling coupler type switch. For this reason, if a matrix optical switch is configured using the SOA as an optical gate element, an optical communication network with extremely small crosstalk can be realized.

[0007] Reports on the optical gate function of SOA include: (7) S. Kitamura, et. Al., ECOC '96, Proceeding Vo.
l.3, WeP 17 (1996) (8) G. Soulage, et. al., ECOC '96, Proceeding Vo
l.4, ThD 2.1 (1996), etc., and an extinction ratio of 50 dB or more has been reported.

[0008]

The above-mentioned prior arts (4) to (4)
Since the SOA disclosed in (8) is modularized using a lens system, an extinction ratio of 50 dB or more is easily realized.

However, in this case, since the structure of the lens system is complicated and the productivity is low, the SOA and the optical fiber are directly coupled without using the lens system as a structure for easily modularizing the SOA and the optical fiber. Has been addressed in recent years. In this case, the signal light input from the optical fiber to the SOA cannot be focused by the lens system.
It has been attempted to provide a light spot size conversion structure on the SOA side.

However, when an optical fiber is directly connected to both ends of an SOA without using a lens system, the S
Part of the signal light incident on the OA does not optically couple to the optical waveguide, but passes through the surroundings and directly reaches the other optical fiber. This is called stray light, and does not receive light absorption in the active layer when the SOA is turned off (when current is not injected). For this reason, when the SOA is used as an optical gate element of a matrix optical switch, the extinction ratio is deteriorated.

For this reason, the aforementioned conventional examples (4) to (8)
In the SOA modularized by the lens system like
An extinction ratio of 50 dB or more can be easily realized. However, in an SOA in which the structure is simplified by directly optically coupling an optical fiber, the extinction ratio becomes about 30 dB. Therefore, when a multi-by-many matrix switch is formed using such an SOA, the deterioration of the extinction ratio causes a problem such as signal crosstalk.

The present invention has been made in view of the above problems, and has as its object to provide an optical semiconductor device having a good extinction ratio.

[0013]

According to the present invention, there is provided an optical waveguide for outputting a light beam input from one end to an output light from another end, and at least a part of the optical waveguide functions as an optical amplification medium for amplifying the light beam. In the semiconductor element, at least a part of the optical waveguide is formed in a curved shape.

Therefore, when an optical fiber is directly optically connected to the optical semiconductor device of the present invention without using a lens system, at least a part of the optical waveguide is curved, so that the optical fibers on the input side and the output side are not connected. The two end faces are arranged so as not to face each other. In such a state, a light beam that enters the optical waveguide from one optical fiber is guided inside the curved optical waveguide and is emitted to the other optical fiber. At this time, the light emitted from the optical fiber on the input side to the periphery of the optical waveguide becomes non-guided stray light, but this stray light goes straight and enters the other optical fiber located at the other end of the curved optical waveguide. do not do.

In the present invention as described above, the following various modifications are possible. For example, by inclining the optical axis direction between the light input portion and the light output portion of the optical waveguide from the normal direction of the element end face, it is possible to prevent the extinction ratio from deteriorating due to stray light and to reduce the effective reflectivity at the element end face. And a high gain structure can be obtained.

Further, by forming the optical waveguide in an S-shape and offsetting the optical input portion and the optical output portion, the optical fibers to be optically connected to both ends of the optical waveguide are positioned at positions which are parallel to each other but do not face each other. Can be placed. In particular, there is a structure in which the offset distance between the light input portion and the light output portion of the optical waveguide is 20 μm or more. In this case, if the diameter of the optical fiber is about φ9 μm in general and the total length of the optical semiconductor element is less than about 1 mm in general, it is preferable that the stray light emitted from one optical fiber is incident on the other optical fiber. Can be prevented. Here, the offset referred to in the present invention means a deviation of a parallel portion, and corresponds to, for example, a distance between an extension of the central axis of the light input portion of the optical waveguide and the center point of the end face on the light output side. I do.

Also, a light-shielding portion may be provided in a gap between an extension of the central axis of the optical input portion of the optical waveguide and the optical output portion, or a light-shielding portion may be provided between the extension of the central axis of the optical output portion of the optical waveguide and the optical input portion. It is also possible to provide a light shielding portion in the gap. In these cases, the stray light emitted from the optical fiber on the input side to the periphery of the optical input portion of the optical waveguide is blocked by the light shielding portion before reaching the position of the optical output portion of the optical waveguide, so that it is located here. Not incident on the output side optical fiber.

It is also possible to form the light-shielding portion as described above with a concave groove. In this case, the light-shielding portion for blocking stray light is realized with a simple structure. Further, the optical waveguide may have a structure composed of a layer film formed on the substrate, and the light shielding portion may be formed to a depth of 4 μm or more from the surface to the inside of the substrate. In this case, the diameter of the optical fiber is generally 9
If it is about μm, the deepest part of the light shielding part is located outside the end face of the optical fiber, so that stray light is well blocked. In addition,
In the present invention, the layer film formed on the substrate may be a layer film laminated on the surface of the substrate by a thin film technique.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment and modifications of the present invention will be described below with reference to the drawings. 1 and 2 show an optical semiconductor device according to an embodiment of the present invention. FIG. 1 is an internal structural diagram showing the position and shape of an optical waveguide in the optical semiconductor device according to the present embodiment. FIG. FIG. 2 is a sectional view showing the internal structure of the optical semiconductor device. FIG. 3 is a schematic diagram showing a state of an experiment for measuring stray light. FIG. 4 is a graph showing the relationship between the offset and the extinction ratio as a result obtained by the experiment of FIG. FIG. 5 is a graph showing the relationship between the deterioration of the receiving sensitivity due to crosstalk in the matrix optical switch and the extinction ratio of the optical gate element constituting the matrix optical switch.

FIG. 6 is an internal structure diagram showing the position and shape of the optical waveguide of the SOA of the first modification, as viewed from above the substrate. FIG. 7 is an internal structure diagram showing the position and shape of the optical waveguide of the SOA of the second modified example, as viewed from above the substrate. FIG. 8 is an internal structure diagram showing the position and shape of the optical waveguide of the SOA of the third modification, as viewed from above the substrate. FIG. 9 is a sectional view taken along the line bb ′ of FIG.

First, as shown in FIG. 2, an SOA 1 as an optical semiconductor device of the present embodiment is formed on a substrate 2 by MOVPE.
(BH: Burried Head Structual) type LD by the (metal oxide vapor phase epitaxy) method
The active layer 3 having a wavelength band of 1.55 μm, which is an optical waveguide, is embedded in the cladding layer 4.

More specifically, the substrate 2 is made of n-InP, and on the lower surface thereof, an n-side electrode 5 is formed of Au / Ti. On the upper surface of the substrate 2, an active layer 3 is formed in a predetermined shape via a buffer layer 6, and these are embedded in a cladding layer 4. The active layer 3 is made of bulk InG
It is composed of an aAsP layer, has a thickness of 3000 ° and a width of 450.
It is formed in a rectangular cross section of 0 °, and the amplification gain has a shape independent of polarization. The cladding layer 4 is made of p-type InP, and the thickness of the buried portion is 5 μm.

On the upper surface of the cladding layer 4, a layer thickness of 100
A cap layer 7 made of ⁰ ° p ⁺ -InGaAs is formed, and current blocking layers 8 are provided on both sides of these layers 4 and 7. The clad layer 4, the cap layer 7, and the current block layer 8 are simultaneously laminated by MOVPE.

After laminating these layers, except for the cladding layer 4 having a width of 10 μm, they were converted into insulating layers by proton implantation. A passivation 9 made of SiO ₂ is formed on the upper surface of the passivation 9, and a portion corresponding to the active layer 3 is removed.
/ Ti forms p-side electrode 10.

In the above-described laminated structure, the active layer 3 forming the optical waveguide of the SOA 1 according to the present embodiment has a structure shown in FIG.
As shown in FIG. 5, the shape is curved in an S-shape. The SOA 1 of the present embodiment has a total length of 800 μm, and the active layer 3 has a length of about 350 μm and a radius of a curved portion of 1.5 mm.

At both ends of the active layer 3, a light input portion 11 as a linear light input portion and a light output portion 12 as a light output portion having a length of about 200 μm are integrally provided. Since the active layer 3 is curved in an S-shape as described above, the light input / output units 11 and 12 are offset by a distance of 50 μm in a parallel state.

The thickness of the light input portion 11 and the light output portion 12 is 3000 ° near the active layer 3 but is 500 ° at the position of the end face. That is, the optical input / output unit 11,
12 has a tapered structure in which the layer thickness gradually decreases toward the end, so that the light spot size at the end face is enlarged. Since the light spot size is enlarged in this manner, the SOA 1 of the present embodiment can obtain good optical coupling with the optical fiber 15 having a flat end face by a direct optical coupling method without using a lens system. I have.

In the SOA 1 of the present embodiment, a pair of element end faces facing each other are located in parallel, and an AR coat 13 is formed on these element end faces as a non-reflective coating with a SiON film. In order to further effectively reduce the reflectance, a window region 14 having a total length of 25 μm is provided at both ends of the element so that the active layer 3 is interrupted near the element end face. By the action of the window region 14 and the AR coat 13, the reflectance of the end face is suppressed to about 0.1%.

In the above-described configuration, the optical fibers 15 having flat end faces are arranged and optically coupled to the element end faces on both sides of the SOA 1 of this embodiment. In such a state, the SOA 1 of the present embodiment amplifies the signal light input from one optical fiber 15 and outputs the amplified signal light to the other optical fiber 15, or extinguishes the input signal light and does not output it. be able to.

At this time, in the SOA 1 of the present embodiment,
Since the active layer 3 forming the optical waveguide is curved in an S-shape, the end faces of the pair of optical fibers 15 disposed opposite to the element end faces on both sides do not face each other. Therefore, non-guided stray light is prevented from being input to the optical fiber 15 on the output side.

Here, the results of experiments performed by the present inventors will be described below. First, as shown in FIG.
The sample 21 in which only the layer film corresponding to
A single-mode optical fiber 15 having a flat end face and a diameter of 9 μm was individually arranged at a height of 50 μm in the thickness direction at both ends thereof.

Then, the sample 2
The optical fiber 15 on the output side was sequentially moved while the signal light was input to 1 and the intensity of the signal light output to the other optical fiber 15 was measured as the magnitude of the stray light. Then, when the extinction ratio with respect to the offset distance of the optical fiber 15 between the input side and the output side was estimated, as shown in FIG. 4, these relations were substantially directly proportional, and the extinction ratio was about 40 dB at a distance of 20 μm. Was confirmed.

For example, in the case of an optical gate element of a current 8 × 8 matrix optical switch, as shown in FIG.
The extinction ratio must be at least 40 dB, and if it is not satisfied, the reception sensitivity is significantly deteriorated. That is, when the optical fibers 15 are arranged on both sides of the SOA 1, if the offset is 20 μm or more, an extinction ratio of 40 dB required as an optical gate element of the matrix optical switch can be realized.

Therefore, as shown in FIG. 1, an SOA 1 with an offset of 50 μm was prototyped and optical fibers 15 were arranged at both ends. Here, one optical fiber 15 outputs SO
The signal light was input to A1 and the photocurrent flowing through the SOA1 was measured. The optical coupling loss between the optical fiber 15 and the SOA1 was estimated to be 3 dB on one side. We could join.

Next, when a current of 30 mA was injected into the SOA 1 and a signal light having λ = 1.55 μm and an intensity of 0 dBm was input through the optical fiber 15, there was no insertion loss (the gain between the optical fibers 15 was 0 dB), and the light on the output side was output. The signal light was output from the fiber 15. When no current is injected (in the case of OFF), the output from the output side optical fiber 15 is −50 d.
Bm or less.

That is, the SOA 1 according to the present embodiment has a 50 dB even when it is directly optically coupled to the optical fiber 15.
It was confirmed that a high extinction ratio as described above could be obtained, and that it functioned well as an optical gate element. Moreover, in the SOA 1 of the present embodiment, since the curved active layer 3 is formed in an S shape, it is sufficient to connect the pair of optical fibers 15 at a right angle to the end face of the SOA 1 while keeping the pair of optical fibers 15 parallel. It is.

The present invention is not limited to the above-described embodiment, but allows various modifications without departing from the gist of the present invention. For example, in the above embodiment, the curved shape of the active layer 3 is S
Although the arrangement of the optical fibers 15 is facilitated as a letter shape, the curved active layer 32 may be formed in an arch shape as in the SOA 31 shown as a first modification in FIG.

In this case, since the directions of the optical axes of the pair of optical fibers 15 are different, further improvement of the extinction ratio can be expected. When the extinction ratio of this SOA 31 was measured and measured in the same manner as in the above-described SOA 1, a 50
It was confirmed that an extinction ratio of dB or more could be secured.

Also, like the SOA 41 illustrated as a second modified example in FIG.
It is also possible that the optical axis direction of the light input section 11 and the light output section 12 is inclined with respect to the normal direction of the element end face while forming 2 in an S-shaped curved shape.

The above-described SOAs 31 and 41 can not only realize a sufficient extinction ratio as an optical gate but also reduce the effective reflectivity of light rays at the element end face.
It is easy to obtain a higher gain between optical fibers. Note that this SO
When A41 was actually manufactured as a prototype and an extinction ratio was measured by injecting a current of 0 to 30 mA, it was confirmed that an extinction ratio of 50 dB or more could be secured. In addition, the injection power is set to 10
Assuming 0 mA, an extinction ratio of 15 dB or more could be obtained as the gain between optical fibers.

However, since the end face of the optical fiber 15 optically connected to the SOAs 31 and 41 as described above needs to be polished at an angle, the mounting and modularization are performed in comparison with the SOA 1 described above. Productivity will decrease. That is, the above-described SOA1 and SOA3
1 and 41 have advantages and disadvantages, and it is preferable to select them in consideration of necessary performance and productivity.

As described above, SOA1 or SOA41
Although the transmission of the stray light is prevented by offsetting the pair of optical fibers 15, there is still a concern that a part of the stray light is transmitted. Therefore, if this poses a problem, it is preferable to form the light shielding portions 52 and 53 at positions where stray light passes, as in the SOA 51 shown as a third modification in FIGS.

More specifically, in this SOA 51, FIG.
As shown in FIG. 5, a first light-shielding portion 52 is provided in a gap between an extension of the central axis of the light input portion 11 of the active layer 3 and the light output portion 12. A second light-blocking portion 53 is provided in a gap between an extension of the central axis of the light input portion 12 and the light input portion 11. As shown in FIG.
Reference numerals 2 and 53 each include a concave groove and extend from the surface of the substrate 2 to the inside.
It is formed to a depth of at least μm.

In the SOA 51 described above, stray light emitted from the optical fiber 15 on the input side to the periphery of the optical input section 11 of the active layer 3 is blocked before reaching the position of the optical output section 12 of the active layer 3. Since the light is blocked by the sections 52 and 53, the light does not enter the output side optical fiber 15 located here, and the extinction ratio is further improved.

Further, since the above-mentioned light-shielding portions 52 and 53 are formed by concave grooves, their formation is easy. Further, since the light shielding portions 52 and 53 are formed at a depth of 4 μm or more from the surface to the inside of the substrate 2, if the diameter of the optical fiber 15 is generally about 9 μm, the deepest portions of the light shielding portions 52 and 53 are provided. Is located outside the end face of the optical fiber 15,
Stray light can be blocked almost certainly. Note that this SO
When the extinction ratio was measured in the same manner as in the case of SOA1, the extinction ratio was further confirmed to be better.

[0046]

Since the present invention is configured as described above, it has the following effects.

According to a first aspect of the present invention, there is provided an optical semiconductor device comprising an optical waveguide for outputting a light beam input from one end to the other end, wherein at least a part of the optical waveguide functions as an optical amplification medium for amplifying the light beam. At least a part of the optical waveguide is formed in a curved shape, so that even if an optical fiber is directly optically connected without using a lens system, stray light input from one optical fiber is Since transmission to the optical fiber can be prevented, a good extinction ratio can be realized when used as an optical gate element.

According to a second aspect of the present invention, in the optical semiconductor device according to the first aspect, the optical axis direction of the light input portion and the light output portion of the optical waveguide is inclined from the normal direction of the end face of the device. Thus, the effective reflectivity of light rays at the element end face can be reduced, so that a high gain between optical fibers can be obtained.

The third aspect of the present invention is the first or second aspect.
The optical semiconductor device according to claim 1, wherein the optical waveguide is formed in an S-shape, and the optical fibers disposed at both ends of the optical waveguide are positioned in parallel by offsetting the optical input portion and the optical output portion. The arrangement of the optical fiber is simple.

According to a fourth aspect of the present invention, in the optical semiconductor device according to the third aspect, the offset distance between the light input portion and the light output portion of the optical waveguide is at least 20 μm.
If the overall length of the optical semiconductor element is less than 1 mm in general, the extinction ratio can be made about 40 dB or more, and the performance required as an optical gate element can be realized.

According to a fifth aspect of the present invention, in the optical semiconductor device according to the third aspect, a light-shielding portion is provided in a gap between an extension of the central axis of the optical input portion of the optical waveguide and the optical output portion. Thereby, stray light can be blocked by the light shielding portion, so that a better extinction ratio can be realized.

According to a sixth aspect of the present invention, in the optical semiconductor device according to the third aspect, a light-shielding portion is provided in a gap between an extension of the central axis of the optical output portion of the optical waveguide and the optical input portion. Thereby, stray light can be blocked by the light shielding portion, so that a better extinction ratio can be realized.

The invention according to claim 7 is the invention according to claim 5 or 6.
In the optical semiconductor device described above, since the light shielding portion is formed of a concave groove, the light shielding portion for blocking stray light can be realized with a simple structure.

The invention described in claim 8 provides the invention according to claims 5 to 7
The optical semiconductor device according to any one of the above, wherein the optical waveguide is formed of a layer film formed on the substrate, and the light-shielding portion is formed at a depth of 4 μm or more from the surface to the inside of the substrate. If the fiber diameter is about 9 μm,
Since the deepest part of the light shielding part is located outside the end face of the optical fiber, stray light can be blocked almost certainly.

[Brief description of the drawings]

FIG. 1 is an optical semiconductor device S according to an embodiment of the present invention.
FIG. 3 is an internal structure diagram showing the position and shape of an OA optical waveguide,
It is the figure seen from the substrate.

FIG. 2 is a sectional view showing the internal structure of the SOA.

FIG. 3 is a schematic diagram showing a state of an experiment for measuring stray light.

FIG. 4 is a graph showing a relationship between an offset of an optical waveguide and an extinction ratio.

FIG. 5 is a graph showing a relationship between deterioration of reception sensitivity due to crosstalk in a matrix optical switch and an extinction ratio of an optical gate element included in the matrix optical switch.

FIG. 6 is an internal structure diagram showing a position and a shape of an optical waveguide of an SOA of a first modified example, as viewed from above a substrate.

FIG. 7 is an internal structure diagram showing a position and a shape of an optical waveguide of an SOA of a second modified example, as viewed from above a substrate.

FIG. 8 is an internal structure diagram showing a position and a shape of an optical waveguide of an SOA of a third modified example, as viewed from above a substrate.

FIG. 9 is a sectional view taken along the line bb 'of FIG.

[Explanation of symbols]

1, 31, 41, 51 SOA 2 substrate (n-InP) as an optical semiconductor element 3, 32, 42 Active layer as an optical waveguide (λ = 1.5
5 mm, composition u-InGaAsP; layer thickness 3000 mm × width 5000 mm) 4 cladding layer (p-InP; embedded height 5 mm) 5 buffer layer 6 n-side electrode (Au / Ti) 7 cap layer (p ⁺ -InGaAs) 8 current Block layer (proton implantation into InP layer) 9 passivation film (SiO ₂ film) 10 p-side electrode (Au / Ti) 11 light input part which is light input part of optical waveguide 12 light output part which is light output part of optical waveguide 13 AR coating 14 Window area 15 Optical fiber (single mode) 52, 53 Shielding part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification code FI G02B 6/12 B

Claims (8)

[Claims] 1. An optical semiconductor device comprising: an optical waveguide for outputting a light beam input from one end to an output from the other end, at least a part of the optical waveguide functioning as an optical amplification medium for amplifying the light beam. An optical semiconductor device characterized in that at least a part thereof is formed in a curved shape. 2. The optical semiconductor device according to claim 1, wherein an optical axis direction of a light input portion and a light output portion of the optical waveguide is inclined from a normal direction of an end face of the device. 3. The optical semiconductor device according to claim 1, wherein said optical waveguide is formed in an S-shape, and said optical input section and said optical output section are offset. 4. The optical semiconductor device according to claim 3, wherein the offset distance between the light input portion and the light output portion of the optical waveguide is 20 μm or more. 5. The optical semiconductor device according to claim 3, wherein a light shielding portion is provided in a gap between an extension of the central axis of the light input portion of the optical waveguide and the light output portion. 6. The optical semiconductor device according to claim 3, wherein a light-shielding portion is provided in a gap between an extension of the central axis of the optical output portion of the optical waveguide and the optical input portion. 7. The optical semiconductor device according to claim 5, wherein said light shielding portion comprises a concave groove. 8. The optical waveguide comprises a layer film formed on a substrate, and the light-shielding portion extends from the surface to the inside of the substrate.
The optical semiconductor device according to claim 5, wherein the optical semiconductor device is formed to a depth of at least μm.