JPH0760225B2 - Optical switch - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical switch which is small and can be integrated.

(2) Conventional Technology and its Problems As a conventional optical switch of this type, the configuration shown in FIG. 1 is known. (For example, literature S. Tarucha, H. Iwamur
a, T.Saku and H.Okamoto. “Wavequide-TypeOptical Mod
ulaton of GaAs Quantum Well Double Heterostructure
s Using Electric Field Effect on Exciton Absorpto
n, "Japanese Journal of Appl, Phys, vol.24.No.6.PP.L4
42-L444, 1985). Here, 1 is a p-side electrode, 2 is a p-type semiconductor cladding, 3 is an active layer having a quantum well structure, 4 is an n-type semiconductor cladding, 5 is an n-side electrode, 6 is a condenser lens, 7 Represents a negative power source for applied voltage.

FIG. 2 shows the absorption characteristics with respect to the wavelength of the GaAs element shown in FIG. The solid line shows the absorption characteristics when no voltage is applied, and the broken line shows the absorption characteristics when a reverse voltage of 1 V is applied to the pn junction. As can be seen from this figure, the absorption peak of excitons generated by the active layer of the quantum structure shifts by the application of a reverse electric field. This change in absorption is used for switching light. As a wavelength that has a small insertion loss as an optical switch element and a large isolation,
In this case, the signal light of 0.86 μm is selected. In this case, the absorption is about 60 when it is on (when no electric field is applied).
Since the absorption at cm ^-1 and off (when applying -1.0 V) is about 250 cm ^-1 , when the element length is 200 μm, the insertion loss when on is about 5.2 dB and the isolation is about 16.5 dB. Become. Even if the applied voltage was changed, there was no great difference in this value, and it was difficult to obtain good characteristics with small insertion loss and large isolation.

Further, as shown in FIG. 1, since the lens coupling is used for inputting / outputting the signal light, there is a drawback that it is difficult to construct a compact and highly integrated optical switch.

(3) Object of the Invention It is an object of the present invention to provide an optical switch having a structure capable of reducing insertion loss when turned on and increasing isolation to achieve high integration.

(4) Configuration of the Invention (4-1) Differences between Features of the Invention and Prior Art The present invention has the same structure of the waveguide section and the switch section,
In addition, the most main feature is that a current is injected in the forward direction when turned on and a reverse voltage is applied when turned off. It is significantly different from the conventional technique in that gain is obtained at the time of turning on.

(4-2) Example FIG. 3 is a diagram for explaining the structure of an element used in the present invention, in which 1 is a p-side electrode, 2 is p-type Al _0.3 Ga _0.7 As cladding, and 3 is a quantum well. Structure active layer, GaAs80Å, Al
A period of _0.2 Ga _{0.8 As} 50Å is composed of about 10 layers. 4 is n
A type Al _0.3 Ga _0.7 As cladding, 5 is an n-side electrode, 7 and 8 are electrodes for reverse and forward directions, respectively, and 9 is a P ⁺ type GaAs layer.

When a forward current is injected into the electrode, carriers in the active layer 3 have an inverted population. This is the same as the population inversion in the semiconductor laser, and the active layer 3 changes from the absorption medium to the gain medium.

The wavelength characteristic of the one-dot chain line in FIG. 2 shows the gain characteristic when a voltage is applied in the forward direction of 0.5V. In this case, a gain peak is observed at a wavelength of 0.86 μm,
The gain is m ^-1 . If an antireflection film is applied to the end face of the waveguide, oscillation is prevented, and a gain of about 26 dB can be obtained with a gain waveguide length of 200 μm. Therefore, 0.5V when on
By applying a forward voltage of 1.0V and a reverse voltage of 1.0V when the switch is off, the device length is 200μm and 26d
B gain and switch characteristics with isolation of 47.7 dB are obtained. In the actual device configuration, there is a loss in the waveguide of the input / output section and a coupling loss of the optical signal, so the gain at the time of ON is reduced, but it is impossible to compensate the total loss to obtain the overall gain. is not.

Fig. 4 shows the structure of the AA 'cross section in Fig. 3, and 10 is n-type A.
l _0.3 Ga _0.7 As buried layer, 11 is a p-type Al _0.3 Ga _0.7 As block layer, and 12 is a SiO ₂ layer. As shown in FIG.
By configuring the waveguide as a buried type waveguide, it is possible to enhance the scattering loss of light and the effect of confining the current in the active layer 3, but it goes without saying that it can also be configured by a ridge type waveguide structure. Yes.

FIG. 5 shows a structural diagram of an embodiment of the present invention. In this structure, since the ON electrode and the OFF electrode are configured separately, ON and OFF can be controlled independently. Therefore, it is possible to increase the switching speed by overlapping the on and off timings.

FIG. 6 shows an embodiment in which a 2 × 2 optical matrix switch is constructed. Reference numeral 13 denotes the waveguide section having the above structure, and 14 denotes the optical switch section having the above structure.

Now, when the signal light is input from P _in ¹ and the output waveguide of P ² _out is selected, a voltage in the reverse direction is applied to the electrode of 14 ₁₁ and 14 ₁₂
This is achieved by applying a forward voltage to each of the electrodes. Further, 14 ₁₁ and by applying a forward voltage simultaneously to both electrodes 14 _12, it is possible to emit signal light without insertion loss at both the output waveguide.

In this embodiment, the GaAs-based embodiment has been described.
It goes without saying that an InP optical switch can also be configured.

(5) Effects of the Invention As described above, in the optical switch of the present invention, an electrode is provided in a part of a waveguide having a quantum well structure in the active layer, and gain is generated when the waveguide is on, and absorption is generated when the waveguide is off. Since it is configured to perform switching, there are the following advantages.

i) Since the waveguide section and the switch section can be configured with the same structure, it is easy to create an integrated optical switch network.

ii) An optical switch network with gain without insertion loss can be obtained.

iii) A characteristic with large isolation is obtained.

iv) An optical switch network with small crosstalk can be constructed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a conventional optical switch, FIG. 2 is a characteristic diagram showing wavelength dependence of absorption coefficient, FIG. 3 is a sectional view for explaining a structure of an element used in the present invention, and FIG. A- in Figure 3
FIG. 5 is a sectional view showing a structure taken along the line A ', FIG. 5 is a sectional view showing an embodiment of the present invention, and FIG. 1 ... p-side electrode, 2 ... p-type semiconductor cladding, 3 ... active layer having quantum well structure, 4 ... n-type semiconductor cladding,
5 ... n side electrode, 6 ... condensing lens, 7 ... reverse direction power supply,
8 ... Forward power source, 9 ... P ⁺ ... Contact layer, 10 ... N-type buried layer, 11 ... P-type block layer, 12 ... SiO ₂ layer, 13 ... Waveguide section, 14 ... Switch section.

Claims (2)

[Claims] 1. A gate type optical switch for turning on / off an optical signal by a voltage applied to a semiconductor element having a pn junction, wherein a waveguide having a quantum well structure is provided as an active layer provided in the middle of the pn junction. The electrode is divided into two parts, one is a forward current injection electrode, the other is a reverse voltage application electrode, and the timing of turning on or off the current or voltage to the two electrodes is over. An optical switch characterized by being configured to wrap. 2. The optical switch according to claim 1, wherein the optical switch has a structure in which an antireflection film is applied to an end face of the waveguide.