JP3811774B2 - Optical switching device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical switching device that controls on / off of controlled light according to whether control light is incident or not, and in particular, enables the use of control light having the same wavelength as that of the controlled light. In addition, the present invention relates to an optical switching device that realizes various new functions such as integration.
[0002]
[Prior art]
With the spread of optical communication systems, various optical switching devices are being provided. As one of them, an optical switching device called an optical coupler is widely used at present.
[References] T. Takizawa et.al., "Switching Operation of GaInAs / InP Multiple-Quantum-Well Directional-Coupler-Type All-Optical Switch", Jpn.J.Appl.Phys.Vol.36 (1997) pp .L110-L113.
[0003]
The optical coupler described in this reference is composed of two waveguides A and B as shown in FIG. 12. When input light is introduced from one end of one of the waveguides B, two waveguides are provided. When A and B are in a coupled state, the light input to the waveguide B moves to the waveguide A and is output to output1.
[0004]
At this time, when the control light is input to the waveguide A, the refractive index of the waveguide A changes due to absorption in the waveguide A, the coupling state of the waveguides A and B collapses, and the input light passes through the waveguide B. By passing, it is output to output2.
[0005]
In this way, the optical coupler described in this reference operates as an optical switch.
[0006]
[Problems to be solved by the invention]
However, such an optical switch according to the prior art must use light having a wavelength different from that of the control light as input light.
[0007]
That is, in the example of FIG. 12, since the input light needs to propagate through the waveguides A and B, it must not be absorbed by the waveguides A and B. Needs to be absorbed by the waveguide A because it is necessary to break the coupling state of the waveguides A and B.
[0008]
Accordingly, as the input light is Ino Rana name without using light of a wavelength different from the wavelength of the control light.
[0009]
From this point of view, according to the prior art, when it is necessary to connect optical switches in multiple stages, there is a problem that a wavelength converter must be prepared in order to generate control light to be input to the subsequent optical switch.
[0010]
In other words, the light output from the optical switch at the front stage is light having the same wavelength as that of the input light, and is different from the wavelength of the control light required by the optical switch at the rear stage. It must be done.
[0011]
Furthermore, since the optical switch as shown in FIG. 12 requires a long waveguide, the structure of the optical switch becomes large and there is a problem that it is not suitable for integration.
[0012]
The present invention has been made in view of such circumstances, and realizes various new functions such as enabling the use of control light having the same wavelength as that of the controlled light and enabling integration. An object of the present invention is to provide a new optical switching device.
[0013]
[Means for Solving the Problems]
In order to achieve this object, the optical switching device of the present invention totally reflects the controlled light in order to realize on / off control of the passage of the controlled light according to whether the control light is incident or not. Upper and lower surface layers having a refractive index to be formed, and an inner layer formed between the surface layers and having a refractive index larger than those surface layers and changing the refractive index in response to incidence of control light And the inner layer of which changes the refractive index in response to the incidence of control light, and the layer whose refractive index changes less by the control light than the layer or the refractive index change by the control light It is composed of an optical device that has a function of tunneling controlled light, and is made incident on the optical device at an angle that causes total reflection and control light. Incident / non-incident In response, either by total reflection without tunneling the controlled light and configured to tunnel without totally reflecting the controlled light.
[0014]
In the optical switching device of the present invention configured as described above, the control light is incident on the optical device at an angle that does not cause total reflection, so that the refractive index of the inner layer of the optical device changes.
[0015]
According to this change in refractive index, the condition of the incident angle of the controlled light that causes light tunneling changes.
[0016]
The optical switching device of the present invention employs this phenomenon to prevent the control light from being normally incident. (A) When the control light is not incident, the total light is reflected without tunneling the controlled light. When the control light is incident, the control light is tunneled without being totally reflected. (B) When the control light is not incident, the control light is tunneled without being totally reflected. An optical switching operation is realized by operating so that the controlled light is totally reflected without being tunneled when incident.
[0017]
In addition, the optical switching device of the present invention employs a structure in which control light is normally incident using this phenomenon. (C) When control light is incident, the controlled light is not tunneled. When the control light is not incident, the control light is tunneled without total reflection, or (d) when the control light is incident, the control light is tunneled without total reflection. When the control light is not incident, the optical switching operation is realized by operating so that the controlled light is totally reflected without being tunneled.
[0018]
Thus, according to the present invention, a surface layer having a refractive index that totally reflects the controlled light, and a refractive index larger than that surface layer, the refractive index is adjusted in response to the incidence of the control light. Because the optical switching operation (optical inverter operation) is realized by using the optical tunneling phenomenon of the optical device having the basic structure including the inner layer to be changed, the control light has the same wavelength as the controlled light. Light having a wavelength (light having different wavelengths may be used) can be used, and integration can be realized by having a structure suitable for integration.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail according to embodiments.
[0020]
FIG. 1 illustrates an exemplary embodiment of an optical switching device comprising the present invention.
[0021]
According to this embodiment example, the optical switching device of the present invention is the guide layer having the refractive index “3.32794” in which the component ratio value x of ₍₁₎ Al _x Ga _(1-x) As is “0.491”. 10 and {circle around ₍ 2)} Al _x Ga _(1-x) As component ratio value x of “1.000”, a thickness of 500 nm, a barrier layer 11 having a refractive index of “3.01404”, and {circle around (3)} Al _x Ga _(1-x) component ratio value x of As is constituted thickness at 210nm with "0.000", with has a refractive index "3.69882" active to change its refractive index in response to incident light layer 12 And ₍ 4 _{) the} drain layer 13 having an Al _x Ga _(1-x) As component ratio value x of “0.419” and a thickness of 240 nm and having a refractive index of “3.37692”, and (5) Al _x Ga. _(1-x) component ratio value x of as is constituted with 500nm thickness by "1.000", a barrier layer 14 having a refractive index "3.01404", ▲ 6 ▼ Al x Ga (1-x) a The s component ratio value x is “0.491”, and the guide layer 15 has a laminated structure having a refractive index “3.32794”.
[0022]
As described in the following reference, an optical element as shown in FIG. 2 having a laminated structure in which a high refractive index layer is sandwiched between two low refractive index layers is mediated by an evanescent wave. It is known that light tunnels due to the resonant tunneling phenomenon of light.
[References] Masato Hayashi, "Light Tunneling-Resonant Tunneling in Multilayer Systems", Optics, 28, 9, pp.496-501, (1999)
The optical switching device of the present invention includes a material in which the active layer 12 changes its refractive index in response to the incidence of light (a material having a large nonlinear refractive index) in addition to the laminated structure of the refractive index described in this reference. ), And a drain layer 13 (a layer that does not change its refractive index in response to the incidence of light) having a refractive index larger than that of the barrier layer 11 is stacked on the active layer 12. Adopted.
[0023]
Further, the optical switching device of the present invention is directed to the input light (controlled light) incident from the guide layer 10 toward the barrier layer 11 at an angle θ larger than the critical angle, and from the guide layer 10 toward the barrier layer 11. Thus, a configuration is adopted in which the control light incident perpendicularly is incident.
[0024]
Since the input light is incident at an angle θ larger than the critical angle, if light tunneling does not occur, it is totally reflected at the boundary surface with the barrier layer 11 as shown by Output-A in FIG. become.
[0025]
Here, the input light and the control light may be light having the same wavelength, or may be light having different wavelengths. This is because in either case, the refractive index of the active layer 12 can be changed.
[0026]
Further, it is preferable that the control light is incident vertically, but it is only necessary to be able to reach the active layer 12, and in principle, the incident light may be incident at any angle as long as it is not totally reflected.
[0027]
Next, an optical tunneling phenomenon that occurs in the optical switching device of the present invention having the refractive index laminated structure shown in FIG. 1 obtained by theoretical analysis will be described.
[0028]
This theoretical analysis was performed by solving Maxwell's electromagnetic wave equations shown in FIGS.
[0029]
FIG. 6 illustrates the results of this theoretical analysis.
[0030]
In the analysis result of FIG. 6, the horizontal axis represents the incident angle θ, and the vertical axis represents the reflectance (intensity ratio of Output-A to Input in FIG. 1).
[0031]
Here, the wavelength of the input light and the wavelength of the control light are assumed to be the same wavelength, and the theoretical analysis was performed assuming that the wavelength is 780 nm. Further, theoretical analysis (analysis using the theoretical analysis formula of FIG. 4) was performed assuming TM waves as polarized light. The critical angle at the interface of the guide layer 10 / barrier layer 11 is 64.9 degrees.
[0032]
As is apparent from the analysis results of FIG. 6, the reflectance is almost 100% in most angle regions above the critical angle, but a sharp valley structure as shown in A and B in the figure was calculated.
[0033]
The sudden drop in reflectivity occurring in the total reflection region is as if input light tunneled through the barrier layers 11 and 14 between the upper and lower guide layers 10 and 15 via the active layer 12 / drain layer 13. This is due to the “resonant photon tunneling phenomenon” that behaves.
[0034]
In the analysis result shown in FIG. 6, the reflectance does not drop to 0 at the location where the light tunneling phenomenon occurs, but this is due to the resolution of the calculation and actually falls to 0. is there.
[0035]
FIG. 7 shows the incident angle dependence of the transmittance (intensity ratio of Output-B to Input in FIG. 1) near the resonance angle at the resonance angle “75.413 degrees (B resonance angle shown in FIG. 6)”. .
[0036]
FIG. 7 also shows the transmittance spectrum when the refractive index change Δn of the active layer 12 is ± 0.011.
[0037]
As can be seen from the analysis result of FIG. 7, when there is no change in the refractive index of the active layer 12 (Δn = 0), the transmittance having a sharp peak at an incident angle of 75.413 degrees is calculated. If the refractive index of the active layer 12 changes ± 0.011 from this state, the resonance angle is shifted by about ± 0.17 degrees. At this time, a slight difference is observed in the tail of the transmittance spectrum, but it can be seen that the spectrum shape close to the Lorentz curve is almost retained.
[0038]
As can be seen from this analysis result, in the optical switching device of the present invention having the structure shown in FIG. 1, when the incident angle is constant at 75.413 degrees, the refractive index change Δn = 0.011 of the active layer 12 is about 45 dB. It was revealed that the extinction ratio was extremely high.
[0039]
The optical switching device of the present invention having the structure shown in FIG. 1 operates as an optical switching device that performs on / off control of the passage of controlled light according to the incidence / non-incidence of control light according to this characteristic.
[0040]
That is, as shown in FIG. 8A, a configuration in which the control light is not normally incident is adopted, and at that time, the incident angle θ of the input light is set near the resonance angle (not the resonance angle). When the control light is incident, if the incident angle θ is made to be the resonance angle in accordance with the change in the refractive index of the active layer 12, the input light is changed from total reflection to transmission. It will be switched.
[0041]
Also, as shown in FIG. 8 (b), the control light is not normally incident, and at that time, the incident angle θ of the input light is set to the resonance angle, and the control light is transmitted. If the incident angle θ is configured to deviate from the resonance angle in accordance with the change in the refractive index of the active layer 12 when incident, the input light is switched from transmission to total reflection.
[0042]
Further, as shown in FIG. 9A, a configuration is adopted in which the control light is normally incident, and at that time, the incident angle θ of the input light is set near the resonance angle (not the resonance angle). When the control light is blocked, if the incident angle θ is configured to be a resonance angle in accordance with the change in the refractive index of the active layer 12, the input light is changed from total reflection to transmission. It will be switched.
[0043]
Further, as shown in FIG. 9 (b), a configuration is adopted in which the control light is normally incident. At that time, the incident angle θ of the input light is set to the resonance angle, and the control light is supplied. If the incident angle θ deviates from the resonance angle in accordance with the change in the refractive index of the active layer 12 when blocking, the input light is switched from transmission to total reflection.
[0044]
In this manner, the optical switching device of the present invention having the structure shown in FIG. 1 operates as an optical switching device that controls on / off of the passage of the controlled light according to whether the control light is incident or not. .
[0045]
Next, the reason why the drain layer 13 is provided in the optical switching device of the present invention will be described.
[0046]
10 and 11 show the results of theoretical analysis when the drain layer 13 is not provided.
[0047]
Here, the analysis result shown in FIG. 10 shows the result of the analysis with the stacked structure in which the drain layer 13 is omitted from the stacked structure shown in FIG. Therefore, the active layer 12 used in this analysis has an Al _x Ga _(1-x) As component ratio value x of “0.000”, a thickness of 210 nm, and a refractive index of “3.69882”.
[0048]
On the other hand, the analysis results shown in FIG. 11 are obtained by analyzing the analysis results for a layered structure in which the drain layer 13 included in the layered structure shown in FIG. 1 is replaced with the material of the active layer 12. Show. Therefore, the active layer 12 used in this analysis has an Al _x Ga _(1-x) As component ratio value x of “0.000”, a thickness of 450 nm, and a refractive index of “3.69882”.
[0049]
In the analysis results shown in FIG. 11, the reflectance does not drop to 0 at the location where the light tunneling phenomenon occurs, but this is due to the resolution of the calculation and actually falls to 0. is there.
[0050]
From this analysis result, it is clear that the light tunneling phenomenon does not occur when the thickness of the active layer 12 is small.
[0051]
Therefore, from the viewpoint of occurrence of the light tunneling phenomenon, the thicker the active layer 12 is, the better.
[0052]
However, if the thickness of the active layer 12 is increased, control light having a large power is required to cause a change in the refractive index of the active layer 12, which is not practical.
[0053]
Therefore, the optical switching device of the present invention employs a configuration in which a drain layer 13 that is a layer that does not absorb control light is provided as shown in FIG.
[0054]
As can be seen from a comparison between the analysis result shown in FIG. 6 and the analysis result shown in FIG. 11, when the drain layer 13 is provided, the light tunneling phenomenon occurs even when the thickness of the active layer 12 is small. Became clear.
[0055]
Unlike the active layer 12, the drain layer 13 can be made of a material that does not exhibit a nonlinear refractive index. From this, according to the optical switching device of the present invention adopting the configuration in which the drain layer 13 is provided, it becomes possible to use control light having a small power.
[0056]
Here, as the drain layer 13, it is preferable to use a material that does not cause a change in refractive index due to the control light, but a material that causes a change in refractive index due to the control light as compared with the active layer 12 may be used.
[0057]
As described above, the optical switching device of the present invention operates so as to control on / off of the passage of controlled light according to whether the control light is incident or not.
[0058]
From this, it can be used as a NOT gate having an optical configuration, and an AND gate can be configured by overlapping two stages of this gate.
[0059]
Further, the optical switching device of the present invention is basically configured to have a reflection surface that totally reflects.
[0060]
From this, it becomes possible to implement an optical fiber type optical switch because it can be mounted on an optical fiber that is composed of a core and a clad and propagates light while being totally reflected.
[0061]
Although the present invention has been described according to the illustrated embodiment, the present invention is not limited to this. For example, in the embodiment, the description has been given of the laminated structure in which the refractive index distribution is changed in the vertical direction. It may be guided horizontally.
[0062]
【The invention's effect】
As described above, according to the present invention, a surface layer having a refractive index that totally reflects the controlled light, and a refractive index that is higher than the surface layer and responds to the incidence of the control light. The optical switching operation (optical inverter operation) is realized by using the optical tunneling effect of the optical device with the basic structure including an inner layer that changes the wavelength, so that the control light has the same wavelength as the controlled light It is possible to use light having a wavelength of (which may be light having a different wavelength) and to achieve integration by having a structure suitable for integration.
[Brief description of the drawings]
FIG. 1 is an example of an embodiment of the present invention.
FIG. 2 is an explanatory diagram of an optical element that generates resonant tunneling of light.
FIG. 3 is an explanatory diagram of Maxwell's electromagnetic wave equation used in the theoretical analysis of the optical tunneling phenomenon.
FIG. 4 is an explanatory diagram of Maxwell's electromagnetic wave equation used in the theoretical analysis of the optical tunneling phenomenon.
FIG. 5 is an explanatory diagram of Maxwell's electromagnetic wave equation used in the theoretical analysis of the optical tunneling phenomenon.
FIG. 6 is an explanatory diagram of a theoretical analysis result.
FIG. 7 is an explanatory diagram of a theoretical analysis result.
FIG. 8 is a diagram showing an example of the operation of the optical switching device of the present invention.
FIG. 9 is a diagram showing an example of the operation of the optical switching device of the present invention.
FIG. 10 is an explanatory diagram of a theoretical analysis result.
FIG. 11 is an explanatory diagram of a theoretical analysis result.
FIG. 12 is an explanatory diagram of the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Guide layer 11 Barrier layer 12 Active layer 13 Drain layer 14 Barrier layer 15 Guide layer

Claims (4)

An optical switching device that controls on / off of controlled light according to whether control light is incident or not,
Upper and lower surface layers having a refractive index for totally reflecting the controlled light, are formed between the surface layer, has a greater refractive index than the surface layer, the refractive index in response to incidence of the control light A layer that has a laminated structure with an inner layer to be changed , and that inner layer changes the refractive index in response to the incidence of control light, and a layer with less refractive index change due to control light or control light than that layer It is composed of an optical device having a function of tunneling controlled light by being composed of a double layer structure with a layer that does not cause a refractive index change due to
Together to be incident on the optical device to be controlled light at an angle causing total reflection, in accordance with the incident and non-incident control light, either totally reflects without tunneling the controlled light, without totally reflecting the controlled light To be configured to tunnel to
Features an optical switching device. The optical switching device according to claim 1 .
The control light is configured to be incident on the optical device at an angle that does not cause total reflection.
Features an optical switching device. The optical switching device according to claim 2, wherein
That the control light is configured to be incident perpendicular to the optical device;
Features an optical switching device. The optical switching device according to any one of claims 1 to 3 ,
It is configured that light having the same wavelength as the controlled light is used as the control light.
Features an optical switching device.

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