JPH0697593A - Semiconductor optical amplification element - Google Patents

Abstract

PURPOSE:To contrive the realization of a wide-band and high-gain semiconductor optical amplification element by a method wherein the total thickness of the well layers of an active layer and the width of the stripe of the active layer are set so as to have a specified relation and the active layer of a strained quantum well structure is used. CONSTITUTION:A active layer 16 of a strained quantum well structure is provided on an N-type InP substrate 10. A P side electrode 20 for injecting a current in this active layer 16, an N side electrode 21, an active layer stripe 14 for leading and amplifying light inputted in the layer 16 and an emitting surface 11 for taking out the light amplified in the layer 16 are provided. In the case where the total layer thickness of In0.7Ga0.3As well layers 22 of the layer 16 and the width of a stripe of the layer 16 are respectively assumed d[nm] and W[mum], the d[nm] and the W[mum] are set so as to satisfy the relation between (d-7)W<12 and (d-40)<2>/10000+(W-1.0)<2>/0.8<1. Thereby, a wide-band and high-gain semiconductor optical amplification element, which is capable of amplifying light of a wide range of wavelength, can be realized. Moreover, by applying this element, an increase in the multiplicity of a laser and the simplification of the constitution of the laser are contrived and moreover, the improvement of the reliability of the laser and a reduction in the cost of the laser are also contrived.

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 device, and more particularly to a semiconductor optical amplifier device which is required to have a high gain over a wide wavelength range used in the fields of wavelength multiplexed optical integrated devices and optical wavelength multiplexed systems. Regarding improvement.

[0002]

2. Description of the Related Art Conventionally, research and development of optical communication technology have been actively conducted. This is because optical signal transmission is superior to electrical signal transmission in terms of transmission speed and interference between signals. Also in the field of optical communication technology, the development of optical wavelength multiplexing technology has been particularly remarkable in recent years.

In a wavelength-multiplexed optical integrated device or an optical wavelength-multiplexed system (optical transmission, optical switching, optical recording, optical calculation, optical measurement, etc.), loss due to branching or multiplexing is large, so that optical amplification of multiple wavelengths is possible. An amplifier is desired.

However, the ultimate wavelength range that can be covered by the optical amplifier is limited by the width of the stimulated emission gain spectrum of the amplification medium of the optical amplifier. Today, Er ³⁺ doped optical fiber amplifiers are widely used as one of the optical amplifiers, but even if the gain wavelength band is wide, it is 1.
It is limited to 52 to 1.57 μm, and there is a disadvantage that the wavelength dependence of the gain is large in this range. Further, the optical fiber amplifier has not realized the excellent characteristics of a practical level for light other than the 1.55 μm band.

Further, when a traveling wave type semiconductor optical amplifier is used as an optical amplifier, its gain spectrum is said to be wider than that of an optical fiber amplifier.
The P-type traveling wave type optical amplification element has a half-value width of at most 60.
It was about nm. Therefore, in order to amplify light in a wide wavelength range by this type of optical amplifier, it is necessary to divide into a plurality of branches according to the wavelength range and perform amplification for each wavelength band, which causes a problem that the configuration becomes complicated. is there.

In a semiconductor optical amplifier device using an active layer having a strained quantum well structure, the density of states near the apex of the valence band of the active layer is smaller than that in the case of no strain. The change in the Fermi level of the band becomes large. Therefore, the spread of the gain spectrum toward the short wavelength side due to band filling in the high carrier injection state becomes large.

Further, when the active layer is made thin, the volume of the active layer and the light confinement coefficient become small. Therefore, a higher carrier density is required to obtain the same mode gain as compared with the conventional semiconductor optical amplifier device using the active layer. You will need it.

As a result, the carrier density becomes extremely high below the oscillation threshold current value of the semiconductor optical amplifier device, and the spectrum spread by band filling can be used. Here, the active layer of the strained quantum well structure has a larger gain than that of the conventional active layer, so that even an active layer having such a small optical confinement coefficient can obtain a sufficient gain in a normal current range. it can.

However, there is generally a trade-off between wide gain spectrum and maximum gain,
There is a problem that it is difficult to achieve a sufficient gain, an output level, and wide bandwidth.

[0010]

As described above, Er ³⁺ doped optical fiber amplifiers and traveling wave type semiconductor optical amplifiers have been conventionally used as optical amplifiers. However, wavelength multiplexed optical integrated devices and optical wavelengths have been used. There is a problem that it is difficult to collectively amplify multiple wavelengths which is desired in a multiplex system.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor optical amplifier device having a large gain over a wide wavelength range.

[0012]

In order to achieve the above-mentioned object, a semiconductor optical amplifier device of the present invention has a strained quantum well structure active layer formed on a semiconductor substrate and a current is injected into this active layer. Means, a means for introducing light into the active layer, and a means for extracting the light amplified in the active layer, and the total layer thickness of the well layers of the active layer is d [n
m] and the stripe width of the active layer is W [μm], the total layer thickness of the well layer and the stripe width are
(D-7) W ≦ 12 , (d-40) 2/1000 + (W
It is characterized by satisfying two inequalities of −1.0) ² /0.8≦1.

Here, the active layer having a strained quantum well structure refers to an active layer having a quantum well structure composed of a semiconductor thin film having a lattice constant different from that of the substrate.

It is preferable that the p-type cladding layer is in contact with the side surface of the active layer.

Further, the well layer of the quantum well is made of In _1-x G
In the case of a _x As _y P _1-y (0 ≦ x <1, 0 <y ≦ 1),
The barrier layer of the quantum well is made of In _1-u (Ga _1-v Al _v ) _u
As (0 ≦ u <1, 0 <v ≦ 1) is preferable.

[0016]

According to the research conducted by the inventors, (d-7) W <12
A wide gain spectrum within the range that satisfies
m or more) is achieved, ^{also, (d-40) 2/} 1000
It was found that the maximum gain (20 dB or more) was realized in the range where + (W-1.0) ² /0.8<1 was satisfied.

Therefore, if an active layer having a strained quantum well structure that simultaneously satisfies the above two inequalities is used, a broadband and high gain optical semiconductor amplifier device can be realized.

[0018]

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

FIG. 1 is a perspective view showing a semiconductor optical amplifier device according to a first embodiment of the present invention with a part thereof cut away.

In the figure, reference numeral 10 denotes an n-type InP substrate, and a strained quantum well laser having an active layer 16 having a buried structure is formed on the n-type InP substrate 10.

On the emitting surface 11 for taking out the amplified light, a broadband antireflection coating 1 made of a multilayer film is formed.
2 and a region where the active layer 16 is removed, a so-called window structure 13 is provided, and the active layer stripe 14 is inclined several degrees from the direction perpendicular to the cleavage plane. With such a structure, the end face reflectance is suppressed to 0.1% or less over a wide wavelength range of 1.3 to 1.6 μm, and oscillation of the laser chip alone is suppressed.

Further, along the active layer stripe 14 for guiding the light introduced from the end surface on the side opposite to the emission surface 11 to the active layer, the n-type InP buffer layer 15, the active layer 16, p.
The type InP clad layer 17 and the p-type InGaAsP side ohmic contact layer 18 are formed, and the side surface of the active layer stripe 14 is covered with the p-type InP clad layer 17.

A region 19 of the p-type InP clad layer 17 separated from the active layer stripe 14 is formed with a semi-insulating region 19 by proton injection. And
A p-side electrode 20 is provided on the P-side ohmic contact layer 18, and an n-side electrode 21 is provided on the back surface of the n-type InP substrate 10. Holes and electrons are injected into the active layer 16 from the p-side electrode 20 and the n-side electrode 21, respectively, and population inversion occurs, so that stimulated emission gain occurs.

The active layer 16 is made of n-type InP.
An In _1-x Ga _x As _y P _1-y barrier layer 23 having a composition equivalent to a wavelength of 1.15 μm, which lattice-matches the buffer layer 15, and an In _0.7 Ga _0.3 As well layer 22 having a thickness of 4 nm are laminated on each other. 4 layers of In _0.7 Ga _0.3 As well layers 22 (total layer thickness is 16 nm) and 5 layers of In _1-x Ga _x.
It has a quantum well structure including the As _y P _1-y barrier layer 23. The width of the active layer 16 is about 1 μm, and the optical confinement coefficient considering the lateral direction of the active layer 16 is 1% or less.

In _1-x Ga _x As _y P _1-y barrier layer 23
Has a lattice mismatch of about 1% with the n-type InP substrate 10, but is sufficiently thinner than the critical film thickness (about 20 nm), so that it is elastically strained so as to be compressed in the plane and extend in the direction of the line. Therefore, defects such as dislocation hardly occur.

In the In _0.7 Ga _0.3 As well layer 22, electrons and holes are quantized. Generally, the valence band of a quantum well has a complicated dispersion structure because a heavy hole band and a light hole band are mixed. However, when there is a compressive strain as in this example, the degeneracy of the heavy hole band and the light hole band is canceled by the effect of this strain, and the contribution of heavy holes is dominant near the top of the valence band. Be correct. Despite its name, the heavy hole band has a small effective mass in the in-plane direction of the well, so its density of states is small.

FIG. 2 shows changes in the valence band structure depending on the presence or absence of the compressive strain. This is In _0.53 Ga _0.47 As
/ In _1-x Ga _x As _y P _1-y system quantum well, FIG. 2A shows the wave number (wave number parallel to the well layer) and hole energy in the case of a compressive strain quantum well. 2B, and FIG. 2B shows that in the case of a strain-free quantum well. The thickness of In _0.53 Ga _0.47 As is 4 nm.
Further, in the figure, HH indicates a band that becomes a heavy hole at a point where the wave number is 0 (Γ point), and LH indicates a band that becomes a light hole at a Γ point. The subscripts of these symbols indicate different band bands.

From the shape of the dispersion characteristic curve in this figure, it can be seen that the density of states is smaller in the case of the compressive strained quantum well than in the case of the strainless quantum well.

FIG. 3 is a diagram showing changes in the quasi-Fermi level of the valence band due to carrier injection with and without compressive strain. From this figure, it is understood that the change in the pseudo Fermi level due to carrier injection is larger in the case of the compressive strained quantum well than in the case of the non-strained quantum well. This is because the compressive strained quantum well has a smaller state density than the non-strained quantum well.

Due to the above effects, in the strained quantum well having compressive strain, the symmetry between the conduction band and the valence band is improved, so that the utilization efficiency of carriers is increased and compared with the strainless quantum well having the same well width. And a large stimulated emission gain is realized.

Both heavy holes and light holes are involved in TE mode gain, and only light holes contribute to TM mode gain. Due to the compressive strain, the vicinity of the top of the valence band is dominated by heavy holes. Therefore, in a strained quantum well having compressive strain, the TE mode gain becomes particularly large.

Further, in the case of the compressive strained quantum well, as described above, the change in the quasi-Fermi level of the valence band due to carrier injection is large. Get wider. However, since the light actually guided to the active layer penetrates into the cladding layer, the mode gain is the product of the optical confinement coefficient to the well layer and the gain of the active layer. Therefore, by reducing the optical confinement coefficient and suppressing the increase in mode gain,
A very broad and flat spectrum can be achieved.

FIG. 4 is a characteristic diagram showing the relationship between the wavelength and the gain in the TE mode showing this. Maximum gain is 2
At 3 dB, the half-value width of the gain is about 180 nm, and 3 dB
The saturation output is 14 dBm.

FIG. 5 shows the width W (μm) of the active layer 16, In
It is a plot of the relationship between the total layer thickness d (nm) of the _0.7 Ga _0.3 As well layer 22 and the characteristics.

In the figure, the curve I is represented by (d-7) W = 12, and the area below the curve I, that is, (d-7) W <12.
The area of (hereinafter, also referred to as Expression 1) indicates an area where a high gain half width of 60 nm or more is obtained.

In the figure, the curve II is (d-40) ² /
1000+ (W-1.0) is represented by ² /0.8=1, the area above the curve I, ^{i.e., (d-40) 2/} 1000
The area of + (W-1.0) ² /0.8<1 (hereinafter, also referred to as Expression 2) indicates the area where the maximum gain of 20 dB or more is obtained.

It is considered that the equation 1 gives a limitation on the optical confinement coefficient, and the equation 2 gives a limitation on the carrier density and its distribution.

That is, in the range satisfying both equations (1) and (2), it is possible to keep the optical confinement coefficient in the thickness direction and the width direction small, the carrier density high, and the carrier distribution nonuniformity small.

The active layer 16 of the semiconductor optical amplifier device of this embodiment.
D and w at the positions shown by the black dots in FIG.
Since both expressions of Expression 2 are satisfied, high gain is realized over a wide wavelength range.

Further, in the semiconductor optical amplifier device of this embodiment,
Since the p-type cladding layer 17 is in direct contact with the side surface of each In _0.7 Ga _0.3 As well layer 22, uneven carrier distribution between multiple well layers hardly occurs even at a high output level, and the saturation output level becomes high.

The reason why the saturation output level becomes high is considered as follows. When the output is high and the internal carriers are insufficient, the carrier distribution inside the well becomes non-uniform, resulting in gain saturation. In particular, InGaAs (P) / InGa
In the case of an AsP-based optical amplification element, due to the large band discontinuity on the valence band side and the low mobility of holes, etc., holes are sufficiently supplied from the p-side cladding to the far well. I can't.

However, in this embodiment, each In _0.7 Ga
_{Since the} p-type clad layer 17 is in direct contact with the side surface of the _0.3 As well layer 22, holes are supplied from this p-type clad layer 17, and under the conditions that both equations 1 and 2 are satisfied. Then, the non-uniformity of the carrier distribution becomes small because the carrier can be easily redistributed in the width direction in the well. Therefore, the saturation level becomes higher than that of the conventional structure.

For comparison, FIG. 6 shows an example of a gain spectrum in a TE mode of a semiconductor optical amplifier device using a conventional strain-free quantum well. Even in this case, it was found that a broad spectrum cannot be obtained unless Formula 1 is satisfied. FIG. 7 shows the stimulated emission gain spectrum of TE mode when the number of quantum wells is 10 (total layer thickness 40 nm). It can be seen that both the gain spectrum of FIG. 7 and the gain spectrum of FIG. 6 have a small wavelength band.

FIG. 8 is a schematic diagram showing a schematic configuration of a semiconductor optical integrated device (broadband wavelength variable light source) according to the second embodiment of the present invention.

This semiconductor optical integrated device is roughly classified into
Oscillation wavelength tunable laser 61 that oscillates at 16 different wavelengths from 1.45 μm to 1.65 μm, 2 × 2 optical switch 62 for selecting the emitted light of these oscillation wavelength tunable laser 61, and quantum well optical waveguide And a semiconductor optical amplifier 63 for amplifying the light guided by 64, and these are integrated on the InP substrate 60.

The oscillation wavelength tunable lasers 61 each have about 2
It is a multi-electrode DFB laser that covers the wavelength range of 0 nm, and the center wavelength is shifted by about 12.5 nm. As a result, one of 16 oscillation wavelength tunable lasers 61 is oscillated, and the path of the optical switch 62 is selected.
The wavelength range of 5 to 1.65 μm can be continuously covered.

The active layer structure of the semiconductor optical amplifier device 63 is the first
This is the same as that of the above embodiment, the input light can be amplified by about 10 times, and a large power required for optical measurement or optical heterodyne reception can be output.

Further, the semiconductor optical amplification element 63 is manufactured by arranging the active layer stripes thereof to be displaced by 5 ° from the vertical direction with respect to the emission end face, and further, the emission end face has a window structure. Since the coating 65 is formed, the end face reflectance is suppressed to 0.2% or less over the wavelength range of 1.45 μm to 1.65 μm. The quantum well optical waveguide 64 is connected to the incident side of the semiconductor optical amplification element 63, and the reflectance of the connecting portion is also 0.2% or less.

As described above, the active layer structure of the semiconductor optical amplifier device 63 is the same as that of the first embodiment, and the structure shown in FIG.
Has a gain spectrum similar to. Therefore 1.4
It is possible to suppress the gain variation due to the wavelength within 4 dB over the wavelength range of 5 to 1.65 μm. As a result, an integrated wavelength tunable laser light source capable of obtaining sufficient output power over a wide wavelength range of 1.45 μm to 1.65 μm with one chip is realized.

FIG. 9 is a schematic diagram showing a schematic configuration of a semiconductor optical integrated device for optical wavelength division multiplexing transmission according to a third embodiment of the present invention.

The main difference between the semiconductor optical integrated device of this embodiment and that of the previous embodiment is that it is 1.47 μm to 1.6.
In the wavelength range of up to 2 μm, different semiconductor lasers 71 each oscillate by 10 nm at the same time.

This semiconductor optical integrated device is used for a low-cost optical parallel link for transmitting information between racks of computers or between boards.

The semiconductor optical amplifier element 63 of this embodiment is the second one.
It has the same configuration as that of the embodiment of 1.47.
Light of 16 wavelengths of 1.62 μm can be collectively amplified. The operating principle is the same as in the previous two embodiments.

In the application of the semiconductor optical integrated device of this embodiment, since the transmission distance is usually a short distance of several hundred meters or less, so high output is not required, but by passing the Y-type optical multiplexer 72 through three stages, Approximately 1 for light attenuated below / 16
It can be amplified by 0 times and output.

The gain variation due to the wavelength is within 3 dB, and the output of each semiconductor laser 71 is the semiconductor optical amplifier device 6.
By adjusting it according to the gain of 3, the output powers of the respective wavelengths can be easily equalized. A power monitor and the like can be integrated if necessary.

Each semiconductor laser 71 is about 630 Mb.
It operates at / s and can transmit a total of about 10 Gb / s of information. Therefore, compared to the time division multiplexing, a high speed multiplexer and a high speed signal processing unit are not required, which is economical. Moreover, since it is not necessary to use an expensive interference film filter for multiplexing, there is an advantage that the size is compact.

Further, since the wavelength interval is relatively wide at 10 nm, the limitation on the laser beam spectrum width of each wavelength is looser and separation on the receiving side is easier than in optical frequency division multiplexing (optical FDM) transmission.

FIG. 10 is a schematic diagram showing a schematic configuration of a semiconductor optical integrated device for bidirectional optical multiplex communication according to the fourth embodiment of the present invention.

The semiconductor optical integrated device of this embodiment is used as a low-priced one-chip electrical / optical conversion device for an optical subscriber terminal.

Each optical integrated device is formed on an InP substrate 80, and has a 1.3 μm band DFB laser 81 for transmission, a waveguide coupling type pin photodiode 82, and 1.56 μm.
A band integrated optical FDM signal receiver 83, a wide band semiconductor optical amplifier 84, a 1.3 μm band / 1.55 μm band wavelength division type optical multiplexer / demultiplexer 85 and a Y branch 86 are integrated on one chip.

1.3 μm band transmission DFB laser 81 and p
The in-photodiode 82 is a 1.3 μm band upstream /
The 1.56 μm band integrated optical FDM signal receiver 83, which is used for transmission / reception of the 1.52 μm band downlink bidirectional communication line,
It is used to receive broadcasting lines such as high definition optical CATV.

The 1.3 μm band DFB laser 81 for transmission is integrated with the output light monitor 87. The integrated optical FDM signal receiver 83 is composed of a DFB optical amplifier type tunable filter 88 and a waveguide coupled pin photodiode 89.

The optical FDM signal has a tunable filter 8
Selected by 8. The optical FDM signal is frequency-modulated, and by shifting the gain peak wavelength of the tunable filter 88 from the wavelength of the selection signal, it is converted into an intensity signal by utilizing the gain change depending on the frequency. That is, the tunable filter 88 has a wavelength selection function, an amplification function, and an FM-
It has IM conversion function at the same time.

The pin photodiode 89 receives only the light selected and amplified by the tunable filter 88 and IM-converted. On the other hand, in addition to the intensity-modulated 1.52 μm band light, the frequency-modulated and optical frequency-multiplexed 1.56 μm band light also enters the pin photodiode 82. However, since the intensity change of 1.56 μm light is small,
It becomes background light and is intensity-modulated 1.5
Only the 2 μm band signal is received by the pin photodiode 82.

The input power of light in the 1.52 μm band is 1.
It is set so as to be compatible with the total input power of the light subjected to the optical FDM in the 56 μm band. By this method, the 1.52 μm and 1.56 μm duplexers are Y-branched 86
Since it is replaced with, the chip can be made smaller and the price can be reduced.

The semiconductor optical amplification element 84 is used to compensate for the waveguide loss, the multiplexing / demultiplexing loss, etc. of this optical integrated element. The active layer of the broadband semiconductor optical amplifier 84 has the same structure as that of the semiconductor optical amplifier element of the previous embodiment, and the active layer stripe has an end face reflectance on the optical fiber coupling system side of 1.3. 0.2 for 1.56 μm band
% Or less. Since the return light from the waveguide side is small, the oscillation of the broadband semiconductor optical amplifier element 84 itself is effectively suppressed.

As described above, since the active layer of the semiconductor optical amplifier device 4 of this embodiment has the same structure as that of the semiconductor optical amplifier device of the previous embodiment, as shown in FIG.
It has a sufficient and similar gain to the light in the 1.3 μm band and the light in the 1.52 to 1.56 μm band, and can cover an unprecedented wide band wavelength. The principle of obtaining such a wide gain is the same as in the previous embodiment.

FIG. 11 is a perspective view showing a semiconductor optical amplifier device according to the fifth embodiment of the present invention with a part thereof cut away. The parts corresponding to those of the semiconductor optical amplifier device in FIG. 1 are designated by the same reference numerals as those in FIG. 1, and detailed description thereof will be omitted.

This semiconductor optical amplifier device has a strained quantum well laser structure of a buried hetero structure formed on an n-type InP substrate 10, and a traveling wave whose oscillation threshold is raised by suppressing the end facet reflectance to a low level. Type semiconductor laser amplifier.

Further, in order to suppress the end face reflectance to 0.1% or less over a wide wavelength range of 1.35 to 1.55 μm, not only the multi-layer antireflection coating 12 is applied to the entrance / exit surface 11, but also The window structure 13 is adopted, and the active layer stripe 14 is inclined from the direction perpendicular to the cleavage plane. This semiconductor laser amplifier is modularized with a Peltier cooling element, an optical isolator, an optical fiber coupling system and the like.

The active layer stripe 14 comprises an n-type InP buffer layer 15, a strained quantum well structure active layer 16, and a p-type InP.
The active layer stripe 14 includes a p-type InP layer 24, an n-type InP layer 25, and a p-side InGaAsP ohmic contact layer 18.
The InGaAsP layer 26 is embedded.

P on the P-side ohmic contact layer 18
A side electrode 20 is provided, and an n-side electrode 21 is provided on the n-type InP substrate 10. Holes and electrons are injected into the active layer 16 from the p-side electrode 20 and the n-side electrode 21, respectively, and population inversion occurs, so that stimulated emission gain occurs.

The active layer 16 is composed of four In _0.7 Ga _0.3 As well layers 22 each having a thickness of 4 nm, as in the first embodiment.
It has a quantum well structure sandwiched between n _0.53 Ga _0.23 Al _0.24 As barrier layers 27. The In _0.53 Ga _0.23 Al _0.24 As barrier layer 27 substantially lattice-matches with InP, and its forbidden band width corresponds to about 1.1 μm in terms of wavelength. In addition, the active layer 1
The width W of 6 is about 1 μm, and the total layer thickness d of the well layer 22 is 16 n.
m. That is, both equations 1 and 2 described in the first embodiment are satisfied at the same time.

FIG. 12 shows InGa lattice-matched to InP.
It is a figure explaining the difference of the band discontinuity of AsP system and InGaAlAs system.

In the InGaAsP system, the band discontinuity ΔEc of the conduction band is about 30% of the band gap difference ΔEg, whereas it is about 70% in the InGaAlAs system.

FIG. 13 shows In _1-x Ga _x As _y P
_1-y (composition equivalent to a wavelength of 1.1 μm) barrier layer and In _0.53 G
a _0.47 As strain-free quantum well consisting of a well layer and In _0.525
Ga _0.235 Al _0.24 As barrier layer and strained In _0.70 Ga _0.30 A
It is a figure which shows the change of the pseudo-Fermi level of the electron by carrier injection of the strained quantum well which consists of an s well layer.

The InGaAlAs / strained InGaAs strained quantum well has a larger discontinuity in the conduction band than the InGaAsP / unstrained InGaAs strained quantum well. Therefore, the overflow of electrons at the high injection level is small, and the change in the pseudo-Fermi level of the conduction band with respect to the carrier injection becomes large even at the high injection level used in the optical amplification element. As a result, the shift of the gain toward the short wavelength side due to the band filling of electrons also becomes large, and a wide-band optical amplification element can be realized.

However, InGaAlAs / strained InGa
In an As strained quantum well, band discontinuity in the valence band is reduced. However, due to the effect of compressive strain, which will be described later, the change in the quasi-Fermi level of holes due to carrier injection can be changed by InGa.
It can be maintained at about the same level as that of the AsP / strain-free InGaAs-based strain-free quantum well.

Since the band discontinuity on the valence band side is small, holes can be easily injected into the well. Therefore, in the InGaAlAs / strained InGaAs strained quantum well, the band barrier against holes is smaller than in the InGaAs (P) / strained InGaAsP strainless quantum well, and the hole distribution between the wells is small. Since unevenness is less likely to occur, the saturated output level can be kept high.

In the strained quantum well of InGaAlAs / strained InGaAs system, the density of states near the top of the valence band becomes small due to the effect of the strained quantum well. Therefore, even if the band discontinuity in the valence band is small, the change in the pseudo-Fermi level with respect to the holes when the carrier density is increased by passing a current is InGaAsP / strain-free In _0.53 Ga
_{It is} about the same as that of a _0.47 As-based strain-free quantum well, and a wide gain spectrum can be obtained by comparison with the same injected carrier density.

Further, by reducing the optical confinement coefficient according to the equation (1) to suppress the increase of the mode gain, it is possible to realize a broad gain spectrum as compared with the conventional semiconductor optical amplifier device.

Even when the quantum well is strained, the valence band in which the holes with large effective mass contribute to the valence band has a higher density of states, and electrons are more likely to overflow. Therefore, even when compressive strain is introduced, the gain due to the band filling of the conduction band is higher when the InGaAlAs-based semiconductor material is used for the barrier layer than when the InGaAsP-based semiconductor material having the same forbidden band width is used. The shift of the spectrum to the short wavelength side becomes large.

FIG. 14 shows the mode gain spectrum of the semiconductor optical amplifier device of this example.

The wavelength band is 150 nm, which is improved by 2.5 times or more as compared with the conventional semiconductor optical amplifier device shown in FIG. Further, the maximum gain is 20 dB or more and the saturation output level is 10 dBm or more.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the semiconductor material of the active layer is InGaAs / InGaAsP / In
P-based semiconductor materials, InGaAs (P) / InGaA
Although the case of using the 1As-based semiconductor material has been described, the present invention is applicable to other semiconductor materials such as various III-V.
It can also be applied to a semiconductor material in which a group semiconductor mixed crystal is combined and a semiconductor material in which a group II-VI semiconductor mixed crystal is combined.
Further, when a strained quantum well with extension strain is used, the amplification characteristic of the TM mode can be improved.

In addition to the semiconductor optical amplifier device in the above-mentioned field, the present invention also provides a wavelength tunable laser having an external resonator, a wavelength multiplexing optical transmission system, a wavelength multiplexing optical switching system, a wavelength multiplexing optical operation system, a wavelength multiplexing. It can be applied to semiconductor optical amplifiers in various fields such as optical recording systems and multi-wavelength optical measurement systems.

In addition, various modifications can be made without departing from the scope of the present invention.

[0088]

As described in detail above, according to the present invention,
It is possible to realize a semiconductor optical amplifier device having a wide band and high gain capable of amplifying light in an extremely wide wavelength range. Further, when the semiconductor optical amplifier device of the present invention is applied to a semiconductor optical integrated device or an optical wavelength multiplexing system, it is possible to collectively amplify light in an extremely wide wavelength range. It is possible to simplify the configuration, improve reliability, and reduce cost.

[Brief description of drawings]

FIG. 1 is a perspective view showing a semiconductor optical amplifier device according to a first embodiment of the present invention with a part thereof cut away.

FIG. 2 is a diagram for explaining changes in the valence band structure due to the presence or absence of compressive strain.

FIG. 3 is a diagram for explaining a change in quasi-Fermi level of a valence band due to carrier injection due to a difference in presence or absence of compressive strain.

4 is a characteristic diagram showing a relationship between a wavelength and a gain in a TE mode of the semiconductor optical amplifier device of FIG.

FIG. 5 is a diagram for explaining the effect of the present invention.

FIG. 6 is a characteristic diagram showing a relationship between a wavelength and a gain in a TE mode of a semiconductor optical amplifier device using a conventional uncompressed strained quantum well.

FIG. 7 is a diagram showing a stimulated emission gain spectrum when the number of quantum wells in the semiconductor optical amplifier device in FIG. 1 is 10.

FIG. 8 is a schematic diagram showing a schematic configuration of a semiconductor optical integrated device according to a second embodiment of the present invention.

FIG. 9 is a schematic diagram showing a schematic configuration of a semiconductor optical integrated device according to a third embodiment of the present invention.

FIG. 10 is a schematic diagram showing a schematic configuration of a semiconductor optical integrated device according to a fourth embodiment of the present invention.

FIG. 11 is a perspective view showing a semiconductor optical amplifier device according to a fifth embodiment of the present invention with a part thereof cut away.

FIG. 12: InGaAsP system lattice-matched to InP and I
The figure for demonstrating the difference of the band discontinuity of nGaAlAs system.

FIG. 13 InGaAsP / strainless InGaAs system and In
The figure which shows the change of the pseudo Fermi level of the electron by carrier injection of GaAlAs / strained InGaAs system.

14 is a diagram showing a stimulated emission gain spectrum of the semiconductor optical amplifier device of FIG.

[Explanation of symbols]

10 ... n-type InP substrate, 11 ... Emitting surface, 12 ... Broadband antireflection coating, 13 ... Window structure, 14 ... Active layer stripe, 15 ... N-type InP buffer layer, 16 ... Active layer, 1
7 ... p-type InP clad layer, 18 ... p-type InGaAsP
Side ohmic contact layer, 19 ... Semi-insulating region, 20 ... P-side electrode, 21 ... N-side electrode, 22 ... In _0.7
Ga _0.3 As well layer, 23 ... In _1-x Ga _x As _y P
_1-y barrier layer, 24 ... p-type InP layer, 25 ... n-type InP
Layer, 26 ... p-type InGaAsP layer, 27 ... In _0.53 Ga
_0.23 Al _0.24 As barrier layer, 60 ... InP substrate, 61 ... Oscillation wavelength variable laser, 62 ... Optical switch, 63 ... Semiconductor optical amplification element, 64 ... Quantum well optical waveguide, 65 ... Antireflection coating, 71 ... Semiconductor laser, 72 ... Y type optical multiplexer,
80 ... InP substrate, 81 ... DFB laser for transmission, 82 ...
Waveguide coupled pin photodiode, 83 ... Integrated optical FDM signal receiver, 84 ... Semiconductor optical amplifier element, 85 ... Optical multiplexer / demultiplexer, 86 ... Y branch, 87 ... Output light monitor, 88 ...
Tunable filter, 89 ... Waveguide coupled pin photodiode.

Claims (1)

[Claims] 1. An active layer having a strained quantum well structure formed on a semiconductor substrate, means for injecting current into the active layer, means for introducing light into the active layer, and amplification in the active layer. And a means for extracting the generated light, wherein the well layer of the active layer has a total layer thickness of d [nm] and the stripe width of the active layer is W [μm], the well layer total layer thickness and the stripe width of the layer is, (d-7) W ≦ 12, (d-40) 2/1000 + (W
-1.0) A semiconductor optical amplifier element characterized by satisfying two inequalities of ^{2 /} 0.8≤1.