JPH02116820A - Optical switch - Google Patents

Abstract

PURPOSE:To expand the operation wavelength region of the optical switch having a gain at the time of on and to allow the use of the switch for wavelength multiplex transmission by constituting an active layer of a semiconductor having plural kinds of composite structures and controlling the amplification and absorption of the light signal to be implanted to the active layer by the minority carriers to be implanted to the active layer. CONSTITUTION:The material and well layer width of the quantum well structure are controlled to control the concn. of the carriers to be implanted so that isolation is assured over a wide wavelength region. Namely, the active layer 4 sandwiched by the p type and n type semiconductors 3, 5 is constituted of the semiconductor of plural kinds of the composite quantum well structures. The amplification and absorption of the light signals implanted to the active layer 4 are controlled by the minority carriers to be implanted to the active layer. The sufficiently large gain is, therefore, obtd. over a wide wavelength region and the sufficiently large absorption loss is obtd. at the time of on. The application to a wavelength multiplex transmission system as the ultra-wide band optical switch is enabled in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a small optical switch made of semiconductor material and having low loss.

<Prior art and problems to be solved by the invention> Figure 1 shows that a forward current is injected into the active layer sandwiched between P-type and N-type semiconductors, and the incident optical signal is amplified and absorbed. This figure shows the basic configuration of an optical switch that turns on and off (gates). In the figure, 1 is an optical waveguide for input, 2 is a leading waveguide for output, 3 is a cladding made of a P-type semiconductor material, 4 is an active layer, 5 is a cladding made of an N-type semiconductor material, and 6 is a reflection It is a preventive film.

In this type of conventional optical switch, the active layer 4 is made of a non-doped semiconductor material and generally has a thickness of about 0.15 μm. When a forward current is injected into this optical switch, a population inversion of carriers is formed, and the active layer 4 changes into a gain medium similarly to a semiconductor laser. Therefore, when an optical signal is injected through the input optical waveguide 1 within the gain width, the input optical signal is amplified by the induced amplification effect and outputted through the output lunar optical waveguide 2. On the other hand, when no current is injected, the incident optical signal is attenuated by induced absorption and is not emitted to the output optical waveguide 2. Therefore, it functions as an optical switch that turns on and off the incident optical signal by turning on and off the forward injection current.

FIG. 3 shows the output-wavelength characteristics of a conventional optical switch in which the active layer 4 is made of a non-doped semiconductor having a bandgap energy wavelength of 1.3 .mu.m when the switch is on and off.

The amount of minority carriers injected when turned on is 6 x 10”ell
The carrier concentration is approximately 0.2 μm for the thickness of the active N4, 3 μm for the convergence of the active layer 4, and 20 μm for the element length I.
Assuming that the life time of a 0 μm carrier is about 1 ns, this corresponds to a current injection amount of about 120 to 150 mA. Assuming now that the optical signal wavelength λg is 1.3 μm, a gain of about 20 dB is obtained when it is on, and an absorption loss of about 35 dB when it is off. That is, the isolation thin is approximately 55
A dB optical gate switch is obtained.

However, if the signal light wavelength is 1.55 μm, there will be a loss of about 3 dB both when on and off, and it will not function as an optical switch.

Incidentally, in optical communication systems using optical fibers, a wavelength multiplexing transmission system in which optical signal wavelengths range from 1.3 μm to 1.55 μm or more will occupy an important position as a future transmission system. Therefore, the emergence of a low-loss, high-speed, and compact optical switch 4 that can be used in such a wavelength division multiplexing transmission system has been awaited.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, an object of the present invention is to provide an optical switch that can be used for wavelength multiplexing transmission by expanding the operating wavelength range of an optical switch that has a gain when turned on.

Figure 4 shows the output of a quantum well semiconductor laser having a quantum well structure in which the wavelength corresponding to the band gap energy in the active layer is 1.55 μm and the well layer radiation W = 200 nm. This shows the wavelength characteristics. In the figure, the carrier concentration is I
The figure shows something that oscillates at a wavelength of 0.56 .mu.m at a wavelength of about 10 "am-".

As is clear from the figure, at an oscillation light wavelength of 1.56 μm, the amount of absorption in the off state is 5 dB or less. At this time,
In the quantum well structure, the peak wavelength of gain was considered to be almost fixed at the quantum energy level of the oscillation wavelength, so it was considered that the isolation characteristics were poor and it could not be used as an optical switch.

The present invention makes it possible to ensure isolation over a wide wavelength range by controlling the material and well layer width of the quantum well structure and controlling the injection carrier concentration.

The structure of the present invention that achieves the above object is such that the active layer sandwiched between P-type and N-type semiconductors is composed of a semiconductor with a multilayer composite quantum well structure, and the light injected into the active layer is Signal amplification.

Features: Absorption is controlled by minority carriers injected into the active layer <Function> According to the present invention having the above configuration, a sufficiently large gain can be obtained over a wide wavelength range, Sometimes there are sufficiently large absorption losses.

Practical example Embodiments of the present invention will be described in detail below based on the drawings.

The optical switch according to this embodiment is externally the same as the optical switch shown in FIG. Ground carrier concentration = 4
A first quantum well layer of X 10 "am-3, pack gap energy wavelength λg = 1.33 μm, and well layer width W = 10 nm.

P-type background carrier concentration = 4 XIO”am
-3 second quantum well layers;
The almanac ratio of the well layer is 1:2.5 and the injected minority carrier concentration n == 4. OX 10'8 am-3.

FIG. 2 shows the output-wavelength characteristics calculated for the optical switch having a composite quantum well structure according to this embodiment. The calculation is a density matrix analysis that takes into account both heavy holes and light holes.

Further, the characteristics indicated by the broken line in the same figure also show similar characteristics in the case where the active layer 4 has a normal DH structure that is not a quantum well structure.

As is clear from the figure, n = 4. OX10”
1.3 μm with low injection carrier concentration below cm-'
A gain of 25 dB or more was obtained in the wavelength range from 1.55 μm to 1.55 μm. In addition, since the absorption loss in the off state is 30 dB or more at a wavelength of 1.55 μm, good isolation characteristics of 55 dB or more can be obtained from 1.3 μm to 1.55 μm.

On the other hand, with an optical switch having a normal DH structure, the same absorption characteristics can be obtained, but the same level of gain cannot be obtained with this minority carrier concentration. However, even if the concentration of injected minority carriers is increased, it is difficult to increase the gain due to gain saturation due to heat, increase in non-radiative recombination processes, etc., and therefore it is difficult to widen the band with the active layer 4 having a normal structure.

It goes without saying that a wideband optical matrix switch can be constructed by combining the optical switches of this embodiment in multiple stages to construct an integrated optical matrix switch.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, it is possible to obtain a sufficiently large gain over a wide wavelength range, and also to obtain a sufficiently large absorption loss during off-time. , it can also be applied to wavelength division multiplexing transmission systems as an ultra-wideband optical switch. Furthermore, it is possible to construct a compact and high-speed integrated optical switch network, and it is also possible to use it as an optical amplifier and optical switch in a wavelength division multiplexing transmission system.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram conceptually showing the general structure of an optical switch having a PN junction, Fig. 2 is a graph showing the output-wavelength characteristics of an optical switch according to an embodiment of the present invention, and Fig. 3 is a conventional diagram. A graph showing the output-wavelength characteristics of an optical switch related to the technology,
FIG. 4 is a graph showing the output-wavelength characteristics of a semiconductor laser having an active layer having a quantum well structure. In the drawings, 1 is an input optical waveguide, 2 is an output optical waveguide, 3 is a P-type cladding, 4 is an active layer, 5 is an N-type cladding, and 6 is an antireflection film.

Claims (1)

[Claims] The active layer sandwiched between P-type and N-type semiconductors is composed of multiple types of composite quantum well structure semiconductors, and the amplification and absorption of optical signals injected into the active layer are injected into the active layer. An optical switch characterized by being controlled by minority carriers.