JP2000223793A - Semiconductor optical amplifier and optical gate switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor optical amplifier whose switching speed is fast and whose polarization dependence is small and to provide an optical gate switch. SOLUTION: On a substrate 20, an active layer 34 whose cross sectional shape is nearly rectangular is covered with an upper-part clad layer 35 whose cross sectional shape is nearly inverted U-shaped. The upper-part clad layer 35 is covered with an oxide layer 26 and a polymer layer 27 which are at a low permittivity and at a low refractive index. As a result, a parasitic capacitance becomes small, and a high-speed switching characteristic is obtained. In addition, since the distribution of the light intensity in the thickness direction and the widthwise direction of the active layer 34 can be made nearly uniformly large, the polarization dependence of a semiconductor optical amplifier can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical amplifier and an optical gate switch.

[0002]

2. Description of the Related Art Research and development of a high-speed, large-capacity, long-distance transmission system using wavelength division multiplexing transmission and an optical device used therefor have been actively conducted. To realize this type of system, an optical amplifier, an optical switch, a wavelength selection filter, and the like are essential optical devices.

Accordingly, semiconductor optical amplifiers have been reviewed as basic optical elements for realizing these optical devices.

FIG. 6 is an external perspective view of a conventional embedded semiconductor optical amplifier.

In this semiconductor optical amplifier, a lower cladding layer 2 of InP (n) is formed on an InP (n ⁺ ) substrate 1, and an active layer 3 having a substantially rectangular cross section is formed on the lower cladding layer 2. Then, an upper cladding layer 4 of InP (p), an InGaAsP contact layer 5,
nP (p) buried layer 6 and InP (n) buried layer 7
Has a laminated structure embedded therein.

An upper electrode 9 is formed on the upper surface of the laminate 8, and a lower electrode 10 is formed on the lower surface of the laminate 8. Antireflection coating layers 11-
1, 11-2 are formed.

In this semiconductor optical amplifier, an optical fiber (not shown) is abutted against the anti-reflection coating layers 11-1 and 11-2 of the laminated body 8, and an order of the threshold current or less is applied between the upper electrode 9 and the lower electrode 10. A directional current (in the direction of arrow 12) is injected from the current injection terminal 13, a signal light is made incident from one optical fiber to propagate in the active layer 3, and the amplified signal light is extracted from the other optical fiber. ing.

FIG. 7 is a block diagram showing a conventional example of a 1-input 2-output gate type optical switch constituted by using the semiconductor optical amplifier shown in FIG.

This optical switch outputs the signal light in the direction of arrow 15-1 incident on the input port 17 of the optical branch circuit 16 in the direction of arrow 15-2 via the output port 18-1 or outputs the signal light in the direction of arrow 15-2. Arrow 15-3 through -2
The output is switched in the direction.

The operation of switching between the direction of arrow 15-2 and the direction of arrow 15-3 for output is performed by the semiconductor optical amplifier 14-1 inserted in the middle of the output port 18-1 (18-2). This can be performed by controlling the semiconductor optical amplifier 14-1 (14-2) inserted in the middle of (14-2) to either ON or OFF. ON / OFF control can be performed based on whether or not a forward current is injected into the semiconductor optical amplifier 14-1 (14-2).

The switching speed of a conventional gate type optical switch using a buried semiconductor optical amplifier is about 1 nsec. To realize a higher switching speed, a ridge as shown in FIG. A semiconductor optical amplifier having a die structure is provided.

FIG. 8A is a front view of a semiconductor optical amplifier having a ridge-type structure proposed by the present inventor, and FIG.
FIG. 9 is a sectional view taken along line AA of FIG.

In this semiconductor optical amplifier, a slab-like InP (n) lower cladding layer 2 is formed on an InP (n ⁺ ) substrate 20.
1. InGaAsP active layer 22 is sequentially formed, and InGa
A ridge-shaped upper cladding layer 23 having a substantially rectangular cross section is provided on the AsP active layer 22, and the side surface of the upper cladding layer 23 and the upper surface of the InGaAsP active layer 22 are covered with an oxide layer 26 and a polymer layer 27. InGa
The contact layer 24 and the upper electrode 25 of AsP are formed.

In this semiconductor optical amplifier, a forward current less than a threshold current is supplied from a terminal 32 between a lower electrode 29 formed on the lower surface of the substrate 20 and an upper electrode 25 by an arrow 33.
The injection is performed in the direction.

In this configuration, light is incident on the InGaAsP active layer 22 directly below the upper cladding layer 23, whereby the light is intensively confined and propagated into the InGaAsP active layer 22 directly below the upper cladding layer 23, The signal light is amplified. The buried layer is an oxide layer 26 and a polymer layer 27
, The parasitic capacitance can be reduced, and a high switching speed can be obtained.

[0016]

However, the conventional semiconductor optical amplifier shown in FIG. 6, the semiconductor optical amplifier shown in FIG. 8, and the gate type optical switch shown in FIG. 7 have the following problems. I understood.

The gate type optical switch formed by using the buried type semiconductor optical amplifier has very little polarization dependence.
Slow switching speed. Conversely, a gate type optical switch using a ridge type semiconductor optical amplifier has a high switching speed but polarization dependence.

An object of the present invention is to solve the above-mentioned problems and to provide a semiconductor optical amplifier and an optical gate switch having a high switching speed and a small polarization dependency.

[0019]

In order to achieve the above object, a semiconductor optical amplifier according to the present invention comprises a slab-shaped lower cladding layer formed on an upper surface of a compound semiconductor substrate having a lower electrode formed on a lower surface. An active layer having a substantially rectangular cross-sectional shape is formed on the upper surface of the clad layer, an upper clad layer having a substantially inverted concave cross-sectional shape is formed so as to cover the active layer, and an upper electrode is formed on the upper clad layer via a contact layer. An anti-reflection coating layer is formed on both end surfaces of a laminate in which an oxide layer and a polymer layer are sequentially formed on the side and top surfaces of the upper clad layer, and a current between the upper electrode and the lower electrode is equal to or less than a threshold current. Flowing, the signal light incident on the active layer from one end face of the laminate is amplified when propagating in the active layer, and the amplified signal light is emitted from the other end face of the laminate. It is.

In addition to the above configuration, a buffer layer having a refractive index higher than the refractive index of the lower clad layer and lower than the refractive index of the active layer is formed between the lower clad layer and the active layer of the semiconductor optical amplifier of the present invention. Is preferred.

In addition to the above structure, it is preferable that the active layer and the upper clad layer of the semiconductor optical amplifier of the present invention are formed in a curved or polygonal line from one end face to the other end face of the laminate.

In addition to the above structure, the active layer and the upper cladding layer of the semiconductor optical amplifier of the present invention are formed in a pattern including an S-shaped portion or an oblique linear portion from one end face to the other end face of the laminate. Is preferred.

In addition to the above structure, it is preferable that SiO ₂ is used for the oxide layer of the semiconductor optical amplifier of the present invention, and polyimide is used for the polymer layer.

In addition to the above structure, the width of the active layer and the upper cladding layer of the semiconductor optical amplifier of the present invention is preferably tapered toward the end face on the signal light incident side and the signal light emitting side.

In addition to the above configuration, the active layer of the semiconductor optical amplifier of the present invention preferably has either a bulk structure or a multiple quantum well structure.

In addition to the above configuration, the upper electrode of the semiconductor optical amplifier of the present invention is divided into two by an electrode separation groove between the incident side and the outgoing side of the signal light, and a current is independently injected into each upper electrode. By doing so, the amplification gain of the signal light may be controlled.

In addition to the above configuration, a saturable absorber is formed on the emission side of the upper electrode of the semiconductor optical amplifier according to the present invention so that the noise of the amplified signal light is reduced when a reverse voltage is applied. preferable.

In addition to the above configuration, it is preferable that the input end face and the output end face of the signal light of the semiconductor optical amplifier of the present invention are formed obliquely at an angle of 10 ° or less.

According to the optical gate switch of the present invention, in addition to the above configuration, the semiconductor optical amplifier has N inputs and M outputs (N ≧ 1, M ≧ 2).
Of the optical branch circuit of FIG.

According to the present invention, an active layer having a substantially rectangular cross section is covered with an upper cladding layer having a substantially inverted concave cross section to form a substantially rectangular cross section, and the upper cladding layer has a low dielectric constant and a low refractive index. Since it is covered with the layer and the polymer layer, the parasitic capacitance is reduced, and high-speed switching characteristics can be obtained. Further, since the spread of the light intensity distribution in the thickness direction and the width direction of the active layer can be substantially uniformly increased, the polarization dependence can be suppressed.

[0031]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1A is a front view showing an embodiment of a semiconductor optical amplifier according to the present invention, and FIG.
1A is a cross-sectional view taken along the line BB, and FIG.
FIG. 4 is a sectional view taken along line C of FIG.

The present semiconductor optical amplifier is an optical amplifier having a wavelength band of 1.5 μm. A slab-shaped InP (n) lower cladding layer 21 is formed on an InP (n ⁺ ) substrate 20. An active layer (InG
an upper cladding layer (InP (p) layer) 35 having a substantially inverted concave cross-sectional shape is formed on the active layer 34 so as to cover the active layer 34 and have a substantially rectangular cross-sectional shape. An upper electrode 25 is formed on the upper cladding layer 35 via an InGaAsP contact layer 24, and an oxide layer (SiO ₂ or SiO ₂ on the side and upper surfaces of the upper cladding layer 35 and the lower cladding layer 21) is formed. , B, F
And a non-reflective coating layer 30-1, 30-2 formed on both end surfaces of a laminate formed with at least one kind of dopant such as) and a polymer layer (polyimide, F-added polyimide, etc.) 27. It is.

The thickness and width of the upper cladding layer 35 are preferably substantially the same as or larger than the thickness and width of the active layer 34. A lower electrode 29 is formed on the lower surface of the InP (n ⁺ ) substrate 20, and an upper electrode 25 and a lower electrode 29 are formed.
Between the terminal 32 and the terminal, a current equal to or less than the threshold current flows in the direction of arrow 33, and the signal is incident on the active layer 34 in the direction of arrow 40-1 from one end face (left end face in the figure) of the laminate. The light is amplified by propagating in the active layer 34, and the light from the other end face (the right end face in the figure) of the arrow 4
The light is emitted in the 0-2 direction.

Here, as shown in FIG. 3B, the active layer 34 and the upper clad layer 35 are not formed linearly from one end face to the other end face of the laminate, but are formed in a polygonal line shape. This is one of the features of the present invention.

That is, in the present semiconductor optical amplifier, the shift S between the active layer on the incident end side and the active layer on the output end side is preferably equal to or larger than the diameter (125 μm) of the optical fiber. It is configured to be large. By taking such a shift S, the signal light emitted from the optical fiber (not shown) on the incident side leaks and propagates to portions other than the active layer 34 (the lower clad layer, the upper clad layer, the oxide layer, and the polymer layer). In addition, it is possible to suppress leakage into the optical fiber (not shown) on the emission side.

Reference numerals 37-1 and 37-2 denote spot size converters, and the active layer 34 and the upper cladding layer 35 are tapered toward the end face to form a taper in the thickness direction of the active layer 34. In addition, the spread of the light intensity distribution in the width direction can be increased toward the end face.

That is, in the conventional buried type semiconductor optical amplifier, only the active layer 34 is only tapered toward the end face side, so that the light intensity distribution in the thickness direction and the width direction can be further expanded. , The propagation length of the spot size conversion units 37-1 and 37-2 had to be increased.

On the other hand, in the semiconductor optical amplifier of the present invention, since the upper cladding layer 35 has a substantially inverted concave cross section and is tapered, the light intensity in the thickness direction and the width direction of the active layer 34 is increased. The degree of spread of the distribution is substantially equal, and the distribution can be expanded with a shorter propagation length. For this reason, the coupling with the optical fiber can be realized with less polarization dependence.

Reference numerals 38-1 and 38-2 denote parallel linear portions, and reference numeral 39 denotes an oblique linear portion. That is, the straight portions 38-1 and 38-1 extend from one end face of the laminate to the other end face.
-2 and 39 are formed in a polygonal line shape. Diagonal straight section 3
The shift S can be increased by increasing the length and the inclination angle of 9.

The semiconductor optical amplifier shown in FIG. 1 is characterized in that the active layer having a substantially rectangular cross section is covered with an upper cladding layer 35 having a substantially inverted concave cross section, and the whole is made to have a substantially rectangular cross section. In this case, the parasitic capacitance can be reduced by covering the entire surface with the oxide layer 26 having a low refractive index and the polymer layer 27 to have a substantially rectangular cross-sectional shape. Can be achieved. Further, the characteristic of confining the signal light in the active layer 34 is improved, and a high gain characteristic can be obtained. Furthermore, the polarization dependence is about the same as or better than the embedded type, and
Cost reduction can be achieved. Compared with the ridge type, it has excellent gain characteristics, small polarization dependence, and excellent connectivity with optical fibers.

FIG. 2A is a front view showing another embodiment of the semiconductor optical amplifier according to the present invention, and FIG.
FIG. 2A is a cross-sectional view taken along line DD, and FIG.
FIG. 4 is a sectional view taken along line -E. The same reference numerals are used for members similar to those of the embodiment shown in FIG.

The difference from the embodiment shown in FIG. 1 is that, in the semiconductor optical amplifier, the refractive index between the lower cladding layer 21 and the active layer 34 is higher than that of the lower The point where the buffer layer 36 having a refractive index lower than that of the layer 34 is formed, and the active layer 34 and the upper cladding layer 35 are formed in a curved shape (S shape) from one end face to the other end face of the laminate. It is a point.

The buffer layer 36 changes the refractive index and thickness at the spot size converters 37-1 and 37-2 so that the light intensity distribution spread in the thickness direction and the width direction in the active layer 34. Can be made substantially equal. The buffer layer 36 is an effective layer for suppressing polarization dependence.
The thickness of the buffer layer 36 is preferably equal to or smaller than the thickness of the lower cladding layer 21.

FIG. 3A is a front view showing another embodiment of the semiconductor optical amplifier according to the present invention, and FIG.
3A is a cross-sectional view taken along line FF, and FIG.
It is a G line sectional view.

The difference from the embodiment shown in FIG. 1 lies in that the incident end face and the output end face of the signal light are formed obliquely by an angle θ.

The angle θ is preferably in the range of 2 ° to 10 °. The reason why the input end face and the output end face are inclined is to prevent the reflected light of the signal light at the end face from returning to the inside of the semiconductor amplifier or the optical fiber (not shown).

In such a semiconductor optical amplifier, FIG.
The same effects as those of the semiconductor optical amplifier shown in FIG.

FIG. 4A is a front view showing another embodiment of the semiconductor optical amplifier according to the present invention, and FIG.
FIG. 4A is a cross-sectional view taken along line HH, and FIG.
FIG. 2 is a sectional view taken along line I.

The difference from the embodiment shown in FIG. 1 is that an electrode separation groove 42 is formed in the upper electrode 25 to separate the upper electrode 25 into two upper electrodes 25-1 and 25-2.

In the present semiconductor optical amplifier, each upper electrode 25-
To 1,25-2, adjust the amplification gain of the signal light at the front and rear stages by injecting the following order threshold current direction current I _k1, I _k2 to the terminal 32-1 and 32-2 independently control I can do it.

FIG. 5A is a front view showing another embodiment of the semiconductor optical amplifier according to the present invention, and FIG.
5A is a cross-sectional view taken along the line JJ, and FIG.
FIG. 4 is a sectional view taken along line -K.

In this semiconductor optical amplifier, the upper electrode 25 is divided into two upper electrodes 25-1 and 25- by an electrode separating groove 42.
Separated into two, the one terminal 32-1 constitutes the optical amplifier by injecting a forward current I _k below the threshold current, the other terminal 32-2 reverse voltage -V _k The saturable absorption section is formed by applying the voltage, and a noise component included in the signal light amplified by the optical amplification section at the preceding stage is reduced.

The saturable absorber effectively functions to reduce unnecessary light leaking and propagating into the cladding layers 21 and 35 other than the active layer 34, the buffer layer 36 and the substrate 20. , Low noise characteristics can be realized.

The present invention is not limited to the above embodiment. For example, a multiple quantum well structure may be used for the active layer other than the bulk structure. With such a structure, a semiconductor optical amplifier having less polarization dependence can be realized.

As an example of the multiple quantum well structure, for example, a seven-period structure is given. Assuming that the wavelength band of the signal light is the 1.5 μm band, the seven-period structure has a well layer (about 7 nm thick, In
A GaAs layer) and a barrier layer (about 8 nm thick, InGaAs).
(sP layer). Further, the mode field diameter may be increased by forming waveguide layers above and below such an active layer. For example, an upper waveguide layer having a bandgap wavelength of 1.15 μm and a thickness of about 0.05 μm is formed, and a lower waveguide layer having a bandgap wavelength of 1.15 μm and a thickness of about 0.5 μm. 15μ
By forming m, a larger mode field diameter can be obtained. It is to be noted that the thickness and width of the active layer are preferably substantially equal for realizing low polarization characteristics (that is, it is preferable to have a substantially rectangular cross-sectional shape).

The semiconductor substrate 20 is made of GaAs in addition to InP.
May be used.

The semiconductor optical amplifier shown in FIGS.
By inserting it into the output port of an N-input M-output (N ≧ 1, M ≧ 2) optical branching circuit as shown in (1), an N-input M-output optical gate switch having a high extinction ratio and low crosstalk characteristics can be realized. be able to.

As described above, according to the present invention, (1) an active layer having a substantially rectangular cross-sectional shape is covered with an upper cladding layer so as to have a substantially rectangular cross-sectional shape, and the outer periphery of the upper cladding layer has a low dielectric constant and a low refractive index. By forming the oxide layer and the polymer layer, it is possible to realize an optical gate circuit having switching characteristics faster than a conventional embedded semiconductor optical amplifier. In addition, it is possible to realize a characteristic having the same or less polarization dependence, and in this regard, it is possible to obtain characteristics superior to the ridge-type semiconductor optical amplifier. Further, since the characteristics of confining light in the active layer are excellent, high gain characteristics can be obtained.

(2) Since the active layer and the upper cladding layer having a substantially rectangular cross section are not formed in a straight line from one end face to the other end face of the laminate, an optical gate circuit using such a semiconductor optical amplifier is used. With this configuration, an optical gate switch having a high extinction ratio can be realized.

(3) Since the widths of the active layer and the upper cladding layer having a substantially rectangular cross-sectional shape are tapered on the incident side and the output side of the signal light, the thickness direction and the width direction of the active layer Of the light intensity distribution can be increased substantially uniformly, and coupling with an optical fiber having little polarization dependence can be realized.

(4) According to the configuration (1), the signal light can be propagated with improved confinement characteristics in the active layer. Therefore, by adopting the configuration (2), the extinction ratio can be further increased. Properties can be obtained.

[0063]

In summary, according to the present invention, the following excellent effects are exhibited.

It is possible to provide a semiconductor optical amplifier and an optical gate switch having a high switching speed and a small polarization dependence.

[Brief description of the drawings]

1A is a front view showing an embodiment of a semiconductor optical amplifier according to the present invention, FIG. 1B is a cross-sectional view taken along the line BB of FIG. 1A, and FIG. FIG. 4 is a sectional view taken along line C of FIG.

2A is a front view showing another embodiment of the semiconductor optical amplifier according to the present invention, FIG. 2B is a sectional view taken along the line DD of FIG. 2A, and FIG. 2C is a sectional view of FIG. It is EE sectional drawing.

3A is a front view showing another embodiment of the semiconductor optical amplifier of the present invention, FIG. 3B is a sectional view taken along line FF of FIG. 3A, and FIG. 3C is a sectional view of FIG. It is GG sectional drawing.

4A is a front view showing another embodiment of the semiconductor optical amplifier according to the present invention, FIG. 4B is a sectional view taken along line HH of FIG. 4A, and FIG. FIG. 2 is a sectional view taken along line II.

5A is a front view showing another embodiment of the semiconductor optical amplifier according to the present invention, FIG. 5B is a sectional view taken along line JJ of FIG. 5A, and FIG. 5C is a sectional view of FIG. It is KK sectional drawing.

FIG. 6 is an external perspective view of a conventional embedded semiconductor optical amplifier.

7 is a block diagram showing a conventional example of a 1-input 2-output gate type optical switch configured using the semiconductor optical amplifier shown in FIG. 6;

8A is a front view of a ridge-type semiconductor optical amplifier proposed by the present inventor, and FIG. 8A is a front view of FIG.
FIG. 4 is a cross-sectional view taken along a line A.

[Explanation of symbols]

 Reference Signs List 20 substrate (semiconductor substrate) 26 oxide layer 27 polymer layer 34 active layer 35 upper cladding layer (cladding layer)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H079 AA02 BA01 CA05 CA09 DA16 DA25 EA03 EA07 EA08 EB04 HA04 HA13 HA15 KA11 KA18 5F073 AA22 AA35 AA61 AA74 AB22 AB25 AB28 BA03 CA12 EA14 EA22 EA27 EA29

Claims (11)

[Claims] 1. A slab-shaped lower cladding layer is formed on an upper surface of a compound semiconductor substrate having a lower electrode formed on a lower surface, and an active layer having a substantially rectangular cross section is formed on an upper surface of the lower cladding layer. An upper clad layer having a substantially inverted concave cross section is formed so as to cover the layer, an upper electrode is formed on the upper clad layer via a contact layer, and an oxide layer and a polymer are formed on the side and upper surfaces of the upper clad layer. An anti-reflection coating layer is formed on both end faces of the laminated body in which the layers are sequentially formed, and a current equal to or less than a threshold current is passed between the upper electrode and the lower electrode, so that one end face of the laminated body is formed. A semiconductor optical amplifier, wherein the signal light incident on the active layer is amplified when propagating in the active layer, and the amplified signal light is emitted from the other end face of the stacked body. 2. A buffer layer having a refractive index higher than that of the lower cladding layer and lower than that of the active layer is formed between the lower cladding layer and the active layer. 3. The semiconductor optical amplifier according to 1. 3. The semiconductor optical amplifier according to claim 1, wherein the active layer and the upper clad layer are formed in a curved shape or a polygonal shape from one end face to the other end face of the laminate. 4. The laminate according to claim 3, wherein the active layer and the upper cladding layer are formed in a pattern including an S-shaped portion or an oblique linear portion from one end face to the other end face of the laminate. Semiconductor optical amplifier. 5. The semiconductor optical amplifier according to claim 1, wherein SiO ₂ is used for said oxide layer, and polyimide is used for said polymer layer. 6. The semiconductor according to claim 1, wherein the widths of the active layer and the upper clad layer are tapered toward an end face on the signal light incident side and the signal light incident side. Optical amplifier. 7. The semiconductor optical amplifier according to claim 1, wherein said active layer has a bulk structure or a multiple quantum well structure. 8. The signal light amplification gain is obtained by independently injecting a current into each upper electrode, wherein the upper electrode is separated by an electrode separation groove between an incident side and an output side of the signal light. The semiconductor optical amplifier according to claim 1, wherein is controlled. 9. The semiconductor optical amplifier according to claim 8, wherein a saturable absorbing portion is formed on an emission side of said upper electrode to reduce noise of amplified signal light when a reverse voltage is applied. 10. The semiconductor optical amplifier according to claim 1, wherein an input end face and an output end face of the signal light are formed obliquely at an angle of 10 ° or less. 11. An optical gate comprising the semiconductor optical amplifier according to claim 1 inserted into an output port of an N-input M-output (N ≧ 1, M ≧ 2) optical branch circuit. switch.