JP2516980B2 - Optical matrix switch - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical matrix switch having a small size, a high degree of integration, and a small insertion loss.

[Prior Art] An example of a conventional optical matrix switch composed of a waveguide having a PN junction is shown in FIG. Here, 21 to 37 are optical waveguides, 1 is an N-type InP substrate, 2 and 2'are optical input waveguides 21 and 29 and 25 and 31 having PN junctions,
3 and 3'are optical output terminals of the optical output waveguides 28 and 31 and 34 and 36 having a PN junction, and 41 to 48 are electrodes for injecting current into the separated waveguide portions. Here, the optical waveguides 21 to 37, the terminal portions 2, 2'and 3, 3 ', and the electrodes 41 to 37
Numerals 48 are arranged on the substrate 1, and each of them is an N-type cladding layer 101 of N-type InP having a shape corresponding to the pattern of each portion.
And an active layer 102 made of InGaAsP and a P-type clad layer 103 made of P-type InP covering the active layer.

Now, it is assumed that the input signal light I ₁ is incident on the input terminal 2 '.
When the forward current J ₁ is injected into the electrode 42, the optical waveguides 25, 26, 27 and 28 in the cross shape change from the absorption medium to the gain medium, and the incident optical signal is guided to the optical waveguide 26. Further electrode 48
If current J ₂ ′ is injected into the optical waveguide 36
Becomes a gain medium, and an optical signal is emitted from the optical output terminal 3 '. In order to emit the light from the light output terminal 3, a current J ₂ may be applied to the electrode 47.

6 (A) and 6 (B) show optical output waveforms when a pulsed optical signal is incident. FIG. 6 (A) shows waveforms in the waveguide 26, and FIG. 6 (B) shows output terminals. The waveform at 3'is represented. The direct current component of the optical power is shown in the waveform of FIG. 6 (A) because the spontaneous emission light component due to the forward current in the optical switch at the optical output terminal 3 is added. In the output waveform of FIG. 6B, the spontaneous emission light component further increases because it passes through the two switch portions 42 and 3 '. In the switch section, when the spontaneous emission light component increases, the phenomenon that the gain is saturated occurs, so that the signal light component also slightly decreases as shown in FIG. 6 (B). Therefore, there is a drawback in that the more spontaneous light passes through the optical switch section in multiple stages, the more spontaneous emission light component with respect to the signal light component increases, and noise on the transmission of the optical signal increases.

[Problems to be Solved by the Invention] Therefore, an object of the present invention is to provide an optical matrix switch in which a spontaneous emission light component in an optical output signal is reduced and a signal / noise ratio is significantly improved.

[Means for Solving Problems] In order to achieve such an object, according to the present invention, optical switch elements for injecting a current and controlling a passing state of an optical signal are arranged in a matrix, and the optical switch element is arranged. 1 unit is PN
In an optical matrix switch that is configured by bonding and couples optical switches with a waveguide, and connects the predetermined waveguides of the waveguides to the optical input terminal and the optical output terminal respectively, the optical output surface of the optical output terminal is The output light from the optical output terminal is an optical output terminal that is configured to be inclined with respect to the plane perpendicular to the light emission direction, and an element having optical differential characteristics is optically connected to the optical output terminal. Is led to an element having an optical differential characteristic.

[Work]

According to the present invention, the output end of the output terminal is inclined and the element having the optical fine powder characteristic is arranged at the output terminal, whereby the spontaneous emission light component can be reduced and the signal light can be amplified. None, so that the signal / noise ratio can be significantly improved.

The element having an optical differential characteristic used in the present invention is a hysteresis curve when the relationship between the input light and the output light of this element is expressed in a characteristic curve with the input light on the horizontal axis and the output light on the vertical axis. It is an element that does not show a loop and has a characteristic that the output light jumps up nonlinearly with respect to a certain threshold input light.

EXAMPLES The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a schematic configuration of an embodiment of the present invention. Here, 5 and 5'are elements having an optical differential gain, which are arranged adjacent to the optical output terminals 3 and 3 ', respectively. First
Other configurations in the figure are similar to those of the optical waveguide circuit having the PN junction shown in FIG. 5, and are denoted by the same reference numerals.
In FIG. 1, details of the electrode portions 41 to 48 and the waveguide structure are omitted.

FIG. 2 shows a sectional view of a concrete embodiment of the optical output terminal 3 and the element 5 (5 ') having an optical differential gain. In FIG. 2, 6 is a P-side electrode, 7 is a P-type cladding, 8 is an active layer, 9 is an N-type cladding, and 10 is an N-side electrode.

Here, the cladding 9, the active layer 8, the cladding 7 and the electrode 6 are arranged in this order on one main surface of the substrate 1, and the electrode 10 is arranged on the other main surface of the substrate 1. In this embodiment, the P-side electrode 6 in the element 5 having the differential gain is used.
Are separated into two, and the currents Jc and Jc ′ can be independently injected into the separated electrodes 6A and 6B, respectively.

The output end of the optical output terminal 3 is configured to be inclined, so that the optical signal guided to the optical output terminal 3 is output without being reflected by the inclined end surface, and the active layer 8 of the adjacent element 5 is emitted.
Is injected as a light input P _in . The relationship between the optical output of the device 5 and the injection current gain in the forward direction is widely known as an optical bistable characteristic. That is, one electrode 6A (or 6
When the current is injected into B), the light output sharply increases at a certain threshold current, and a light output of a certain constant value is obtained. Even if it increases further, the light output does not increase so much and shows a saturation tendency. On the contrary, when the injection current is decreased, the light output suddenly decreases at a certain current value. Then, by controlling the current injected into the other electrode 6B (or 6A), the hysteresis loop can be controlled. In this case, the hysteresis loop is used while being suppressed so as to have a differential gain. The simplest condition is achieved by setting the current Jc 'of electrode 6A to zero.

Therefore, the input / output characteristics of the optical signal when the injection current Jc is biased immediately before the threshold current will be described.

FIG. 3 is a characteristic diagram showing characteristics of the optical output P _out with respect to the optical input power P _in under the above conditions. When the optical signal injected into the element 5 exceeds a certain threshold P _{in, 0} , the optical output P _out rapidly increases and the optical output P _{out, 0} is emitted.

In the experimental example, when P _{in, 0} is 1.2 mW, the optical output P _{out, 0} is about 4 m.
W got. Further, the optical output tends to be saturated, and the fluctuation range is almost P _{out, 0} + 10%.

Further, the value of the light output P _{in, 0} can be controlled by controlling the current Jc ′ injected into the control electrode 6A.
This is because the absorption coefficient in the saturable region can be controlled by the injection current Jc '. Therefore, the spontaneous emission light component in the optical signal from the optical output terminal 3 is now P
_If it is set to be very close to _{in, 0} or less, the element 5
As shown in FIG. 3, the optical output signal from the optical output signal is reduced in optical power corresponding to the spontaneous emission light component, and the optical pulse corresponding to the signal light component is amplified and emitted.

FIG. 4 is a structural diagram showing the structure of another embodiment of the present invention, and shows an example in which a Fabro-Perot element structure is used as the element 5 having optical differential characteristics. Here, 11 is a high reflection film. Reference numeral 12 denotes a saturable absorbing medium, for example, a multiple quantum well structure (MQW) medium of GaAs and GaAlAs can be used. The MQW medium 12 with the high-reflection film 11 on both main surfaces is
Arrange them so that they are perpendicular to the P _in direction.

The element 5 is manufactured by, for example, a thin film 1 having a high reflectance on both principal surfaces of the MQW medium 12 formed by the molecular beam epitaxial method.
The easiest method is to attach the vapor-deposited 1 to the optical output terminal 3 externally.

The optical input / output characteristics of the Fabry-Bello type element are similar to those shown in FIG. 3, but since the element 5 of this example is a passive element, no gain can be obtained. However, the optical power corresponding to the spontaneous emission light component can be reduced.

[Effects of the Invention] As described above, according to the present invention, the following advantages can be obtained by disposing the element having the optical differential characteristic at the optical output terminal.

(1) It is possible to improve S / N deterioration due to an increase in spontaneous emission light components that occurs when a large matrix having a multi-stage structure is formed.

(2) The output optical signal level can be made constant.

(3) A memory operation using the bistable function can be performed.

[Brief description of drawings]

FIG. 1 is a schematic view showing a schematic configuration of an embodiment of an optical matrix switch of the present invention, FIG. 2 is a sectional view showing an embodiment of an element having an optical differential characteristic in the present invention, and FIG. 3 is FIG. FIG. 4 is a characteristic view showing an optical input / output waveform in the element shown in FIG. 4, FIG. 4 is a sectional view showing another embodiment of the element having the optical differential characteristic of the present invention, and FIG. 6 is a perspective view showing a structural example of a matrix switch, and FIGS. 6 (A) and 6 (B) are operation explanatory views showing an example of optical output waveforms in a conventional optical matrix switch. 1 ... N-type InP substrate, 2,2 '... optical input terminal of optical input waveguide having PN junction, 3,3' ... optical output terminal of optical output waveguide having PN junction, 21-37 ... … Optical waveguide, 41 to 48 …… electrodes, 5,5 ′ …… elements with optical differential characteristics, 6,6A, 6B …… P side electrode, 7 …… P type cladding, 8 …… active layer, 9 ...... N-type cladding, 10 ... N-side electrode, 11 ... High-reflection film, 12 ... Saturable absorption medium, 13 ... Waveguide, 101 ... N-type cladding layer, 102 ... Active layer, 103 ... P-type clad layer.

Claims (3)

(57) [Claims] 1. An optical switch element for controlling a passing state of an optical signal when a current is injected is arranged in a matrix, and one unit of the optical switch element is composed of a PN junction, and a waveguide is provided between the optical switches. In the optical matrix switch in which predetermined waveguides of the waveguides are coupled to the optical input terminal and the optical output terminal, respectively, in the optical matrix switch, the optical output surface of the optical output terminal is perpendicular to the light emitting direction. And an element having an optical differential characteristic is optically connected to the optical output terminal, and the output light from the optical output terminal has the optical differential characteristic. An optical matrix switch characterized by being led to an element. 2. The optical matrix switch according to claim 1, wherein the element having the optical differential characteristic is a waveguide formed of a PN junction having a current non-injection region. . 3. The optical matrix switch according to claim 1, wherein the element having the optical differential characteristic is a Fabry-Perot element.