JPH04290485A - Optical semiconductor - Google Patents

Abstract

PURPOSE:To eliminate positioning of a light receiving element for monitoring emitted light from semiconductor laser by providing an absorption layer to be optically coupled with active layers of the semiconductor laser between the active layers and a modulator and extracting outside electric charge generated by light absorbed from the absorption layer. CONSTITUTION:An absorption layer 15 to be optically coupled with active layers of semiconductor laser 2 is provided between the active layers and a modulator 4, while an electrode 21 which extracts electric charge generated by light absorbed from the absorption layer 15 is formed, thereby constituting a monitor unit 3. Thus a part of light output from the semiconductor 2 is absorbed by the absorption layer 15 of the monitor unit 3 and the electric charge generated by the absorption is made to flow outside, so that an output state of the semiconductor laser 2 is detected by the magnitude of the electric charge. It is not necessary to secure an installation space for a light receiving element, thereby miniaturizing a package.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical semiconductor device.
More specifically, the present invention relates to an optical semiconductor device equipped with an optical modulator/DFB laser as a light source for an ultrahigh-speed optical transmission system.

As a light source for an ultrahigh-speed optical transmission system, an integrated light source in which a DFB laser light source with little wavelength chirping and an external modulator are combined into a single chip is promising. When applying such devices to actual systems,
It is essential to monitor the light output status and control the output to make it constant.

0003

2. Description of the Related Art As an optical semiconductor device serving as a light source, a structure as illustrated in FIG. 7 has been proposed, for example, and this device includes a DFB laser a on one side and an optical modulator b on the other
It is integrally formed.

In the figure, a diffraction grating e is formed on one upper surface of a semiconductor substrate d having an electrode c provided on its lower surface, and an optical waveguide layer f, an etching stopper layer g, an active layer h, and a cladding layer i are formed on the semiconductor substrate d. and electrode j are laminated in this order, thereby configuring the DFB laser a.

Further, the optical waveguide f and the etching stopper layer g are formed extending on the other flat surface of the semiconductor substrate d, and a light absorption layer k, a cladding layer l, and an electrode m are formed in this order on the optical waveguide f and the etching stopper layer g. These are stacked to form the modulator b. In this case, the light absorption layer k is formed on the same plane as the active layer h, and their end faces are joined, so that light output from the active layer h travels through the light absorption layer k. .

As a first device for monitoring the optical output of such an optical semiconductor device, as shown in FIG. 7, a photodetecting element w such as a large-diameter PIN photodiode is arranged behind the DFB laser a. A method has been proposed in which the optical output is determined based on the magnitude of the current flowing through the element w.

As a second device, as shown in FIG. 8, when the light emitted from the optical modulator b is incident on the fiber q through a plurality of lenses o, a deflection prism r is placed between the lenses o. A structure has been proposed in which a portion of the light extracted by the deflecting prism r is detected by a photodetecting element w.

[0008]

[Problems to be Solved by the Invention] However, these methods require high alignment accuracy of the photodetector element w;
There is a problem in that the adjustment takes time and effort.

In addition, according to the former method, the detection element w can be housed in the same package as the DFB laser/modulator, but there is a disadvantage that the installation space for the detection element w is required, which increases the size of the device. There is.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an optical semiconductor device that does not require alignment of a photodetector element and can further reduce the space for accommodating the device. do.

[0011]

[Means for Solving the Problems] As illustrated in FIG. a first absorption layer 15 formed on the semiconductor substrate 10 and having one end surface in contact with the end surface of the active layer 14 for optical coupling; a monitor unit 3 that extracts charges generated by light absorbed from the absorption layer 15 to the outside through the electrode 21; and a monitor unit 3 provided on the semiconductor substrate 10;
A second absorption layer 15 is provided which is optically coupled in contact with the other end surface of the first absorption layer 15, and the second absorption layer 15 is provided with a signal voltage applied to a cladding layer 16 on the second absorption layer 15. This is achieved by an optical semiconductor device characterized by having a modulator 4 that modulates light passing through the absorption layer 15.

Alternatively, as illustrated in FIG. 5, a semiconductor device comprising an active layer 14 partially provided on a semiconductor substrate 10 and operated by a current injected through a cladding layer 16 above the active layer 14 a laser 2; a first absorption layer 15 formed on the semiconductor substrate 10 and having one end surface in contact with the end surface of the active layer 14 for optical coupling; and a cladding layer on the first absorption layer 15. a modulator 5 that modulates light passing through the first absorption layer 15 by a signal voltage applied to the first absorption layer 16; An optical semiconductor device comprising a second absorption layer 15 that is optically coupled, and a monitor section 6 that extracts charges generated by light absorbed from the second absorption layer 15 to the outside through an electrode 31. achieved by.

Alternatively, as illustrated in FIG. 6, a semiconductor device comprising an active layer 14 partially provided on a semiconductor substrate 10 and operated by a current injected through a cladding layer 16 above the active layer 14 A laser 2 and a first absorption layer 15 formed on the semiconductor substrate 10 and having one end surface in contact with the end surface of the active layer 14 for optical coupling, the light absorbed from the first absorption layer 15 being The charge generated by
The first monitor section 7 is drawn out to the outside through the electrode 41 of the
and a second absorption layer 15 that is provided on the semiconductor substrate 10 and whose one end surface is optically coupled to the other end surface of the first absorption layer 15, The signal voltage applied to the cladding layer 16 of the second absorption layer 1
a modulator that modulates light passing through the semiconductor substrate 10;
A third absorption layer 15 is provided on the top of the second absorption layer 15 to be optically coupled in contact with the other end surface of the second absorption layer 15, and charges generated by light absorbed from the third absorption layer 15 are transferred to the second absorption layer 15. This is achieved by an optical semiconductor device characterized by having a second monitor section 9 that is drawn out through an electrode 43.

Alternatively, the present invention is achieved by an optical semiconductor device characterized in that the plurality of absorption layers 15 are formed of the same material.

[0015]

[Operation] According to the first invention, an absorption layer 15 is provided between the active layer of the semiconductor laser 2 and the absorption layer 15 of the modulator 4, and the absorption layer 15 is optically coupled to these layers. An electrode 21 is formed to draw out the electric charge generated by the emitted light, thereby forming the monitor section 3.

Therefore, a part of the light output from the semiconductor laser 2 is absorbed by the absorption layer 15 of the monitor section 3, and the charge generated by the absorption flows to the outside through the electrode 21, and the magnitude of this current changes. The optical output state of the semiconductor laser 2 can be detected. In addition, the monitor section 3
The remaining light that has passed through is modulated by the signal voltage of the modulator 4 and is emitted from its tip.

Therefore, not only is it unnecessary to align the light receiving element for monitoring the emitted light of the semiconductor laser 2, but also it is no longer necessary to secure a space for mounting the light receiving element in the optical semiconductor device storage package. Can be made smaller.

Further, according to the second invention, the absorption layer 15 is provided for optical coupling to the output end face of the absorption layer 15 of the modulator 5, and charges generated by light absorbed from the absorption layer 15 are transferred to the outside. A lead-out electrode 32 is formed, thereby configuring the monitor section 6.

Therefore, the light output from the active layer 14 of the semiconductor laser 2 is modulated by the modulation signal of the modulation section 5 and travels within the absorption layer 15, and then passes through the absorption layer 1 of the monitor section 6 at the next stage.
5 and is output to the outside. This monitor section 6 absorbs a portion of the light, and the charges generated thereby flow to the outside through the electrode 32. Therefore, depending on the magnitude of the photocurrent flowing from the electrode 32, it becomes possible to monitor the modulated light signal and the magnitude of the light output from the modulator 5.

[0020] Therefore, similarly to the first invention, alignment of the light receiving element is no longer necessary, and the package housing the optical semiconductor device can be made smaller.

According to the third invention, the absorption layer 1 of the modulator 8
Absorbing layers 15 for optical coupling are provided on both end surfaces of the electrodes 41 and 43, respectively, and two electrodes 41, 43 are provided to draw out charges generated by light absorbed from the absorbing layers 15 at both ends.
, thereby forming two monitor sections 7 and 9.

Therefore, a part of the light emitted from the semiconductor laser 2 is absorbed by the two monitor sections 7 and 9, and the electric charges generated thereby flow to the outside from the respective electrodes 41 and 43, and their current By detecting the magnitude of the light, it becomes possible to monitor the state of the light before and after modulation. As a result, when the optical output of the optical semiconductor device decreases, it can be easily determined whether it is caused by the DFB laser 2 or the modulator 8, and the laser drive current and modulation signal voltage can be adjusted appropriately to keep it constant. This means that the light output can be maintained.

According to the fourth invention, since the plurality of absorption layers 15 in the first to third inventions are made of the same material, the formation of the absorption layers becomes easy.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (a) Description of a first embodiment of the present invention FIG. 1 is a sectional view and a perspective view showing an apparatus according to a first embodiment of the present invention.

In FIG. 1, numeral 1 indicates one n-InP
This is an optical semiconductor device including a DFB laser 2, a monitor section 3, and a modulator 4 formed on a substrate 10.

The n-InP substrate 10 described above has a diffraction grating 11 formed on the upper surface of the laser region An optical waveguide layer 12 made of GaInAsP with a composition of 1 μm and an etching stop layer 13 made of n-InP are epitaxially grown to thicknesses of 0.15 μm and 0.01 μm, respectively.

Further, on the upper surface of the etching stop layer 13, in the laser region
An active layer 14 made of InAsP is laminated to a thickness of 0.15 μm, and the remaining region has a wavelength of 1.40 to 1.43 μm.
The absorption layer 15 made of GaInAsP with a composition of 0.
The absorption layer 15 and the active layer 14 are optically coupled at their end faces. The front end side of the absorption layer 15 in the light traveling direction becomes a modulation region Y, and the side toward the laser region becomes a monitor region Z.

Furthermore, the active layer 14 and the absorption layer 15 have p
A p-electrode 20 is formed on the surface of the laser region X via a GaInAsP cap layer 17, and the DFB laser 2 is constituted by this p-electrode 20 and each layer below it. In addition, GaInA is applied to the surfaces of the monitor area Z and the modulation area Y, respectively.
P-electrodes 21 and 22 are formed via the sP cap layers 18 and 19, and the two p-electrodes 21 and 22 and the layer below constitute a monitor section 3 and a modulator 4, respectively.

The p-electrodes 20 to 22 described above are made of Au and are separated from each other at intervals. The same potential as or a negative bias voltage is applied, and the monitor current is extracted from the bias voltage.

For example, the length of the p-electrode 20 of the DFB laser 2 is 300 μm, and the length of the p-electrode 21 of the monitor section 3 is 5 μm.
0μm, and the p-electrode 22 of the modulator 4 has a thickness of 150μm.
It is formed to have a length of m, and the interval between each is 25 μm.

Note that each layer on the n-InP substrate 10 from the optical waveguide layer 11 to the cladding layer 16 and the cap layers 17 to 19 is formed into a long strip in the direction of light propagation, forming a mesa shape. A high-resistance buried layer 24 made of InP containing Fe is formed on the side. Further, an anti-reflection film 25 made of Si3N4 with a thickness of 1/4 of the wavelength of the signal light is formed on the front end face of the modulator 4, while an anti-reflection film 25 made of Si3N4 is formed on the rear end face of the DFB laser 2 to improve efficiency. A film 26 is formed.

In the device of this embodiment, a direct current is injected into the p-electrode 20 of the DFB laser 2, and the direct current is
．． 55, light is output from this DFB laser 2, a part of which is absorbed by the absorption layer 15 of the monitor section 3, and charges generated by the Franz-Keldish effect are externally transmitted through the cladding layer 16 and the p-electrode 21. It will flow to Further, the remaining light that has passed through the monitor unit 3 is modulated by the high frequency signal voltage applied to the p-electrode 22 of the modulator 4, and is emitted from its tip.

By the way, with the p-electrode 21 of the monitor section 3 open, the voltage V applied to the p-electrode 22 of the modulator 4
When the relationship between the DFB laser drive current and the modulator optical output was investigated using mod as a parameter, the characteristics shown in FIG. 2 were obtained.

That is, during CW operation at 25° C., the oscillation threshold current is 13 mA, and the applied voltage Vmod of the modulator 4 is
When the voltage was set to 0V and a current of 150 mA was injected into the DFB laser 2, the optical output was 13.7 mW. Further, when the voltage Vmod applied to the modulator 4 was -5V, the total optical output extinction ratio was 30%.

Next, when the voltage Vmod applied to the modulator 4 is set to 0 V and the relationship between the modulator optical output and the monitor current is examined while the current can be drawn from the monitor section 3, the characteristics shown in FIG. 3 are obtained. and the monitor current efficiency is 0.14
mA/mW was obtained.

Furthermore, when the relationship between the laser drive current and the monitor current is examined using the applied voltage Vmod of the modulator 4 as a parameter, the characteristics shown in FIG. 4 are obtained. It can be seen that even if the voltage is varied within a range, the variation rate is as low as about 7% at maximum, and a monitor current that is almost unaffected by the magnitude of the voltage can be obtained.

Therefore, by checking the value of the current flowing through the p-electrode 21 of the monitor section 3, the magnitude of the optical output of the DFB laser 2 can be determined.

(b) Description of the second embodiment of the present invention The first embodiment described above detects the optical output of the DFB laser 2, but it is also possible to monitor the optical output of the modulator 4. FIG. 5 is a sectional view showing the apparatus of this embodiment.

This optical semiconductor device has a modulator 5 formed between the DFB laser 2 and the monitor section 6, and the first
As in the embodiment, n-GaInAsP is placed on an InP substrate 10 on which a diffraction grating 11 is provided on the upper surface of a region near one end.
Optical waveguide layer 12, n-InP etching stop layer 13
GaInAsP active layer 14 and GaInAsP are stacked in order on the upper surface of the etching stop layer 13.
An absorption layer 15 is formed continuously in the light traveling direction, and a p-InP cladding layer 16 is further formed to cover them, and these layers are etched into a mesa shape, with high-resistance buried layers on both sides. is formed.

In this case, the region where the active layer 14 is formed becomes a laser region, and the region of the absorption layer 15 near the tip in the light traveling direction becomes a monitor region, and the rest becomes a modulation region.

Further, a p-electrode 30 is formed on the cladding layer 16 in the laser region with a cap layer 27 interposed therebetween.
Furthermore, p-electrodes 31 and 32 are formed in the modulation region and the monitor region of the remaining cladding layer 16 via cap layers 28 and 29, respectively, and these three p-electrodes 30
.about.33 are separated at regular intervals.

Note that 23 is an n-electrode formed on the lower surface of the InP substrate 10, 25 is an anti-reflection film provided at the tip of the monitor section 6, and 26 is a reflective film formed at the rear end of the DFB laser 2. In this embodiment shown, the light output from the active layer 14 of the DFB laser 2 is modulated by the modulation signal of the modulation section 5, travels through the absorption layer 15, and is outputted to the outside through the next stage monitor section 6. .

In this monitor section 6, charges generated by absorbing part of the light are transferred to the cladding layer 16 and the cap layer 29.
, will flow to the outside through the p-electrode 32. Therefore, depending on the magnitude of the photocurrent flowing from the p-electrode 32, it is possible to monitor the state of the modulated light and the magnitude of the light output from the modulator 5.

(c) Description of Third Embodiment of the Present Invention In each of the above two embodiments, a case has been described in which one monitor section is formed in an optical semiconductor device in which a DFB laser and a modulator are integrated. It is also possible to install two monitors before and after the modulator, and an example device is shown in FIG.

This device has a DFB laser 2 in the light traveling direction.
, a first monitor section 7, a modulator 8, and a second monitor section 9 are formed in this order, and similarly to the first embodiment, an InP substrate 1 is provided with a diffraction grating 11 on the upper surface of the laser region.
0, n-GaInAsP optical waveguide layer 12, n-I
nP etching stop layer 13 is laminated in order, and GaInAs is formed on the upper surface of etching stop layer 13.
A P active layer 14 and a GaInAsP absorption layer 15 are formed continuously in the light traveling direction, and a p-InP layer is formed on them.
A cladding layer 16 is formed, these layers are etched into a mesa shape, and high-resistance buried layers are formed on both sides of the cladding layer 16.

In this case, the areas near the front and rear ends of the absorption layer 16 in the light traveling direction become first and second monitor areas, and the area between them becomes a modulation area.

Further, a p-electrode 40 is formed on the cladding layer 16 in the laser region with a cap layer 36 interposed therebetween.
Further, in the remaining cladding layer 16, p-electrodes 41, 42, and 43 are formed in the modulation region and two monitor regions, respectively, via cap layers 37, 38, and 39, and these four p-electrodes 40 to 43 are formed in the modulation region and two monitor regions, respectively. are separated at regular intervals.

For example, the length of the p-electrode 40 of the DFB laser 2 is 300 μm, and the length of the p-electrode 40 of the DFB laser 2 is 300 μm.
, 9 are each 50 μm thick, and the p electrodes 41 and 43 of the modulator 8 are
The electrode 42 has a length of 150 μm, and the interval between the four p-electrodes 40 to 43 is 25 μm.

Note that 23 is an n-electrode formed on the lower surface of the InP substrate 10, 25 is an anti-reflection film provided at the tip of the monitor section 9, and 26 is a reflective film formed at the rear end of the DFB laser 2. In this example device shown, DF
The light output from the active layer 14 of the B laser 2 is absorbed into the absorption layer 15.
After passing through the first monitor section 7, the output light is modulated by the modulator 8, and then passes through the second monitor section 9 and is emitted. It turns out.

The light absorption layers 15 of the two monitor sections 7 and 9 each absorb a portion of the light, and carriers generated thereby are transferred to the clad layer 16, the cap layers 37, 39,
The light flows to the outside through the p-electrodes 41 and 43, and by detecting the magnitude of these currents, it becomes possible to monitor the light before and after modulation.

Therefore, when the optical output of the optical semiconductor device decreases with the passage of time, the DFB laser 2
It is possible to easily determine whether the problem is caused by the problem or the modulator 8, and it is possible to maintain a constant optical output by adjusting the laser drive current and modulation signal voltage as appropriate.

(d) Description of other embodiments of the present invention In the embodiments described above, the light absorption layer 15 of the modulator and the monitor section were formed of the same material. The composition wavelength is made closer to the active layer, for example, 1.46 μm, to increase the photocurrent per unit area, and the length of the p electrode is 10 μm.
If the area is made small enough, the area can be made small without changing the amount of light absorption in this area.

Furthermore, in the above-described embodiment, the cladding layer 16 of the laser region, monitor region, and modulation region was integrally formed of the same material, but grooves were formed in the cladding layer between the monitor region or the modulator and the semiconductor laser. A high resistance buried layer may be formed in this groove.

[0054] The material, length, and
The wavelength and the like are not limited to these, and any device may be used as long as a monitoring electrode is formed in a region of the light absorption layer.

[0055]

[Effect of the invention] As described above, according to the first invention,
An absorption layer is provided between the active layer of the semiconductor laser and the absorption layer of the modulator to optically couple with these layers, and an electrode is formed to draw out the charge generated by the light absorbed from the absorption layer. Since the monitor section is configured with
There is no need to secure a space for mounting the light receiving element in the package, and the device can be made smaller. Moreover, since a monitor is provided on the output side of the semiconductor laser, the actual output can be monitored and the output value can be adjusted appropriately.

Further, according to the second invention, an absorption layer for optical coupling is provided on the output end face of the absorption layer of the modulator, and an electrode is formed to draw out the charge generated by light absorbed from the absorption layer. However, since this constitutes a monitor section, similarly to the first invention, it is not necessary to align the light receiving element, the package can be miniaturized, and the modulated light signal and the modulator can be It becomes possible to monitor the size of the light output from the

Furthermore, according to the third invention, absorption layers for optical coupling are provided on each of both end faces of the absorption layer of the modulator, and charges generated by light absorbed from these absorption layers are extracted to the outside. Since two electrodes are formed, thereby configuring two monitor sections, it is not only necessary to align the light receiving element and make the package smaller, similarly to the first invention. The two monitor sections make it possible to monitor the light before and after modulation, making it easy to determine whether the deterioration in the optical output of the optical semiconductor device is caused by the semiconductor laser or the modulator.

According to the fourth invention, since the plurality of absorption layers in the first to third inventions are made of the same material, the absorption layers can be easily formed.

[Brief explanation of the drawing]

FIG. 1 is a sectional view and a perspective sectional view showing an apparatus according to a first embodiment of the present invention.

FIG. 2 is a drive current/light output characteristic diagram of the device according to the first embodiment of the present invention.

FIG. 3 is an optical output/monitor current characteristic diagram of the device according to the first embodiment of the present invention.

FIG. 4 is a characteristic diagram showing fluctuations in monitor current in the device according to the first embodiment of the present invention.

FIG. 5 is a sectional view showing a device according to a second embodiment of the present invention.

FIG. 6 is a sectional view showing a device according to a third embodiment of the present invention.

FIG. 7 is a sectional view showing a first example of a conventional device.

FIG. 8 is a sectional view showing a second example of a conventional device.

[Explanation of symbols]

1 Optical semiconductor device 2 DFB laser 3, 6, 7, 9 Monitor section 4, 5, 8 Modulator 10 InP substrate 11 Diffraction grating 12 Optical waveguide layer 13 Etching stop layer 14 Active layer 15 Absorption layer 16 Cladding layer 23 N electrode 25 Anti-reflection film 26 Reflective film

Claims (4)

[Claims] 1. A semiconductor comprising an active layer (14) partially disposed on a semiconductor substrate (10) and operated by electric current injected through a cladding layer (16) above the active layer (14). a laser (2); a first absorption layer (15) formed on the semiconductor substrate (10) and having one end surface in contact with the end surface of the active layer (14) for optical coupling; A monitor part (3) draws out electric charges generated by light absorbed from the absorption layer (15) to the outside through an electrode (21).
), and a second layer provided on the semiconductor substrate (10) and optically coupled to the other end surface of the first absorption layer (15).
an absorption layer (15), modulating light passing through the second absorption layer (15) by a signal voltage applied to a cladding layer (16) above the second absorption layer (15); Vessel (4
) An optical semiconductor device comprising: 2. A semiconductor comprising an active layer (14) partially provided on a semiconductor substrate (10) and operated by electric current injected through a cladding layer (16) above the active layer (14). a laser (2); a first absorption layer (15) formed on the semiconductor substrate (10) and having one end surface in contact with the end surface of the active layer (14) for optical coupling; a modulator (5) that modulates light passing through the first absorption layer (15) by a signal voltage applied to a cladding layer (16) above the absorption layer (15); A second absorption layer (15) is provided above and optically coupled to the other end surface of the first absorption layer (15), and the light absorbed from the second absorption layer (15) A monitor section (6) draws out the generated charge to the outside through an electrode (31).
) An optical semiconductor device comprising: 3. A semiconductor comprising an active layer (14) partially provided on a semiconductor substrate (10) and operated by electric current injected through a cladding layer (16) above the active layer (14). a laser (2); a first absorption layer (15) formed on the semiconductor substrate (10) and having one end surface in contact with the end surface of the active layer (14) for optical coupling; a first monitor section (7) that extracts charges generated by light absorbed from the absorption layer (15) to the outside through a first electrode (41); is provided with a second absorption layer (15) optically coupled to the other end surface of the first absorption layer (15);
a modulator for modulating light passing through the second absorption layer (15) by a signal voltage applied to a cladding layer (16) on the absorption layer (15); , a third absorption layer (15) that is optically coupled in contact with the other end surface of the second absorption layer (15), and absorbs charges generated by light absorbed from the third absorption layer (15). Second
An optical semiconductor device characterized in that it has a second monitor section (9) drawn out to the outside through an electrode (43). 4. The absorbent layer according to claim 1, wherein the plurality of absorbent layers (15) are formed of the same material.
3. The optical semiconductor device according to 3.