JPH067623B2 - Optical bistable integrated device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical bistable integrated element used as a main constituent element of an optical switching device or an optical information processing device using a semiconductor.

(Prior art and its problems) Optical bistable elements that have been recently studied as optical storage, optical logic, and optical amplification elements necessary for optical switching / optical information processing may operate at low energy and high speed. It is attracting attention as an element in the future.

An optical bistable element is an element that can have two stable states, one for the intensity of the incident light or the intensity of the emitted light for the intensity of the emitted light. Semiconductor devices such as liquid crystals and dielectrics have been studied as such devices.
The one using a semiconductor material has been attracting attention because it can best exhibit its high speed. Among them, there is an optical bistable element formed by laminating an optical transistor and a light emitting diode on the same substrate as an element which has a small wavelength dependency and whose characteristics are not affected by fluctuations in ambient temperature. For this, please refer to "IE E TRANSACTION ON ELECTRON DEVICES (IEEE TRANSACTIO
N ・ ON ・ E _- LECTRON ・ DEVICES), 1982, ED-29.
Volume, No. 9, pp. 1382-1388 gives a detailed report. In order to explain the principle of this operation, its block diagram is shown in FIG. Incident light is transmitted through the n-InP substrate 1 and the n-InP emitter layer 2 of the phototransistor 8 to be p-In.
The electrons are absorbed by the GaAsP base layer 3 and the n-InGaAsP collector layer 4 to generate electrons and holes. Of these, electrons flow into the n-InGaAsP active layer 6 of the light emitting diode 9 and p of the uppermost layer
The light is recombined with the holes that have flowed into the n-InGaAsP active layer 6 from the -InP clad layer 7 to emit light. Part of the emitted light at this time is returned to the phototransistor 8. The phototransistor 8 normally has a characteristic that the photocurrent generated by the incident light is saturated with respect to the light intensity. Therefore, when the incident light having a certain intensity is coupled to the phototransistor 8 and the light emitting diode 9 starts to emit light, the light is injected into the light emitting diode 9 until the photocurrent of the phototransistor 8 reaches a saturation state due to the effect of optical feedback. The current increases. in this case,
Letting a be the light output exchange efficiency with respect to the injection current in the light emitting diode 9 and k be the light exchange efficiency with respect to the light input in the phototransistor 1, the optical bistable characteristics are obtained when the condition of ak> 1 is satisfied. It is known to be observed. In this case, since the value of a is usually in the order of 10 ⁻³ mW / mA, it is necessary to set the current amplification factor of the phototransistor 8 to 1000 or more in order to satisfy ak> 1. The phototransistor 8 having such a current amplification factor can be realized by optimizing the thickness of the base layer 3, the semiconductor material forming the emitter layer 2 and the base layer 3, the size of the energy gap, and the impurity concentration. However, since there is a trade-off relationship with the response speed, it is necessary to lower the current amplification factor by at least about one digit when giving priority to high-speed operation. Therefore, if a semiconductor laser is used instead of the light emitting diode 9, the value of a becomes about 0.4, so that a large current amplification factor is not required. Therefore, it has been desired to realize an optical bistable integrated element which can be integrated by combining a semiconductor laser and an optical transistor, and which has a structure capable of optical feedback between both.

(Object of the Invention) An object of the present invention is to provide an optical bistable integrated device capable of operating at high speed by eliminating such a conventional defect and integrating a semiconductor laser and a light receiving device.

(Structure of the Invention) An optical bistable integrated device according to the present invention is a waveguide in which a semiconductor laser and a light receiving device are laminated on the same semiconductor substrate to form an optical integrated device, and light can be emitted in a plane direction as a semiconductor laser. It uses a distributed feedback semiconductor laser with a higher-order diffraction grating formed on the road, and has a light-receiving element stacked directly above the semiconductor laser so that the scattered light from the higher-order diffraction grating is reabsorbed. Further, it is characterized by having a light receiving surface so that incident light from the outside is absorbed by the light receiving element.

(Principle of the Invention) According to the present invention, following the growth of a distributed feedback semiconductor laser in which a higher-order diffraction grating is formed on a waveguide, a light receiving element such as an optical transistor is laminated along the layer. There is. For ease of explanation, FIG. 2 shows the period of the diffraction grating of the distributed feedback semiconductor laser and the state of scattered light. If the diffraction grating order is l and the light scattering angle is Ψ, Have a relationship. Here, i is an integer.

2 (a), (b) and (c) show the relationship between the light scattering angle Ψ and the diffraction grating order l.

When a first-order diffraction grating is used, the laser light is scattered only in the waveguide direction (Fig. 2 (a)), but when a second-order diffraction grating is used, the laser light is also scattered in the direction perpendicular to the waveguide. Received (Fig. 2 (b)). The same applies to the third order and above (second
(Figure (c)). About this, Casey (HCCASEY, Jr)
"HETEROSTRUCTURE LASERS", published by ACADEMIC PRESS by MBPANISH and
For details, please refer to pages 100 to 105 of Volume A. This makes it possible to emit laser light in a direction substantially perpendicular to the waveguide by setting the order of the diffraction grating to be second or higher. If a light receiving element, for example, a phototransistor is laminated on the emitting surface, the light emitted to the upper side is absorbed by the phototransistor. The photocurrent generated thereby is reinjected into the distributed feedback semiconductor laser as a bias current. Since the phototransistor has the characteristic that the photocurrent is saturated with respect to the intensity of the incident light as described above, this photofeedback effect is used to make the current flow to the distributed feedback semiconductor laser until the photocurrent reaches a saturation value. Continues to be injected. In this case, if incident light from the outside is injected from the light-receiving surface of the phototransistor, that triggers the optical bistable operation.
Therefore, in the present invention, since it is possible to integrate the semiconductor laser and the light receiving element on the same substrate,
A light receiving element having a structure suitable for high-speed operation can be formed, and an optical bistable element capable of high-speed operation can be formed.

(Example) Next, this invention is demonstrated in detail with reference to drawings. FIG. 1 is a perspective view of an embodiment of the present invention. The optical bistable integrated device 101 is composed of a distributed feedback semiconductor laser 102 and an optical transistor 103. In this case, the phototransistor 103 is laminated on a part of the distributed feedback semiconductor laser 102. The electrode for supplying the current to the distributed feedback semiconductor laser 102 and the electrode for the phototransistor 103 are provided with the groove
They are separated by 04, forming a so-called tandem electrode structure. As a method of manufacturing the optical bistable integrated device 101, first, the p-InP clad layer 1 is formed on the p-InP substrate 105.
06, non-doped InGaAsP active layer 107, n-InGaAsP guide layer 108 having a secondary diffraction grating, n-InP first
Clad layer 109, n-InP second clad layer 110, n
-InGaAsP collector layer 111, p-InGaAsP base layer 112, n
-InP emitter layer 113 is laminated. Next, the collector layer 111, the base layer 112, and the emitter layer 113, other than those which will become the phototransistor 103, are removed by etching so that current can be easily supplied to the distributed feedback semiconductor laser 102. Further, the first electrode 114 to the phototransistor 103
And the second electrode 115 to the distributed feedback semiconductor laser 102.
Are etched and removed so that they function independently of each other, and are separated by trenches 104. The reason for removing the n-InP second cladding layer 110 is to increase the resistance between the twelfth electrode 114 and the second electrode 115. Phototransistor 103
In order to enable high-speed operation, the first electrode 114 that surrounds the light-receiving surface 116 is formed so that the junction capacitance that affects the response speed becomes small. Since the distributed feedback semiconductor laser 102 has a secondary diffraction grating, a part of the laser light is scattered immediately above and absorbed by the phototransistor 103 immediately above the distributed feedback semiconductor laser 102.
Therefore, when incident light is injected into the phototransistor 103 from the light receiving surface 116 as a trigger, electrons of holes and electrons generated by absorption of light in the collector layer 111 and the base layer 112 are emitted from the first electrode 114. And the third electrode 117
The electric field between them pulls towards the third electrode 117. As a result, electrons are supplied to the active layer 107 of the distributed feedback semiconductor laser 102, and holes are supplied from the third electrode 117. As a result, the electrons and holes are recombined and the distributed feedback semiconductor laser 102 starts laser oscillation. In this case, if a current is injected from the second electrode 115 to some extent in advance to increase the gain, laser oscillation becomes easier. The oscillated laser light is scattered by the secondary diffraction grating and is optically returned to the phototransistor 103. As a result of repeating this optical feedback, the intensity of light emitted from the distributed feedback semiconductor laser 102 becomes a constant value when the photocurrent of the phototransistor 103 becomes saturated with respect to the intensity of incident light. In this embodiment, the laser oscillation threshold is 100 mA.
On the other hand, the injection current into the second electrode 115 was 80 mA, the incident light intensity was 30 μW, and the current amplification factor of the phototransistor 103 was 100. The applied voltage to the phototransistor 103 is 4V. Therefore, the remaining 20μ required for laser oscillation
A is due to light-electricity exchange of incident light. Once the laser oscillation is started, since ak> 1 is sufficiently satisfied, the emitted light intensity sharply increases until the photocurrent of the phototransistor 103 is saturated. After that, there was almost no change in the emitted light intensity even when the incident light intensity was increased. Next, when the incident light intensity was reduced, the emitted light did not change until the photocurrent of the phototransistor 103 reached the saturation point, and when it was further reduced, the emitted light intensity decreased sharply. There was a difference in the incident light intensity at the rising and falling edges, and optical bistable operation was observed. It was also found that it is effective for high-speed operation because it uses a semiconductor laser. In this embodiment, the distributed feedback semiconductor laser 102 has a resonance length of 350 μm and a width of 150 μm.
m, the length of the second electrode 115 is 250 μm, the length of the groove 104 is 50 μm, and the size of the phototransistor 103 is 20 μm in the size of the light receiving surface. Needless to say, the state of crystal growth greatly changes depending on the growth method, growth conditions, etc., and appropriate dimensions should be adopted together with them.

Embodiments of the present invention may have various forms other than the above-mentioned embodiments. An n-InP substrate may be used instead of the p-InP substrate. In this case, it is necessary to reverse p and n of the other layer in which the crystal grows. In addition, the distributed feedback semiconductor laser 10
2 is a full-surface electrode type in which a guide layer in which a secondary diffraction grating is provided on the active layer 107 is used. However, the order of the diffraction grating may be 2 or more, and the guide layer in which the diffraction grating is further provided is the active layer. It may be at the bottom of 107. Further, a buried hetero structure may be used so that the operating current can be suppressed small.
The semiconductor material is not limited to InP / InGaAsP, but GaAs / AlG.
Others such as aAs system may be used. Further, the emission side end face may be obliquely etched to form a total reflection end face so that the emission light from the semiconductor laser can be taken out in a direction perpendicular to the laminated surface. In the above embodiment, the distributed feedback semiconductor laser 102 is used.
Although the second electrode 115 is provided for the injection current into the phototransistor, if the current amplification factor of the phototransistor 103 is sufficiently large, it is not always necessary to provide it.

(Effects of the Invention) As described in detail above, according to the present invention, the distributed feedback semiconductor laser and the light receiving element are laminated on the same semiconductor substrate, so that high speed operation is possible. Thus, a stable optical bistable integrated device can be easily obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is a diagram showing a light scattering state by a diffraction grating for explaining the present invention, and FIG. 3 is a sectional view of a conventional example. 1 ... n-InP substrate, 2 ... n-InP emitter layer, 3 ...
p-InGaAsP base layer, 4 ... n-InGaAsP collector layer,
5 ... n-InP clad layer, 6 ... n-InGaAsP active layer,
7 ... p-InP clad layer, 8 ... Phototransistor, 9
...... Light emitting diode, 10 ... n side electrode, 10 ... p side electrode, 101 ... Optical bistable integrated device, 102 ... Distributed feedback semiconductor laser, 103 ... Optical transistor, 104 ... Groove, 105
... p-InP substrate, 106 ... p-InP clad layer, 107 ...
Non-doped InGaAsP active layer, 108 ... n-InGaAsP guide layer, 109 ... n-InP first cladding layer, 110 ... n-I
nP second clad layer, 111 ... n-InGaAsP collector layer,
112 ... p-InGaAsP base layer, 113 ... n-InP emitter layer, 114 ... first electrode, 115 ... second electrode, 116 ...
Light receiving surface, 117 ... Third electrode.

Claims (1)

[Claims] 1. An optical integrated device having a semiconductor laser and a light receiving element provided on the same semiconductor substrate, wherein a distributed feedback semiconductor laser having a diffraction grating formed on a waveguide is used as the semiconductor laser, and An optical bistable integrated device, wherein a light receiving device is provided directly above the distributed feedback semiconductor laser so that the scattered light of the above is reabsorbed.