JP2003302662A - Optical switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a small-size optical switch with low power consumption, responding to a multichannel system and excellent in low loss property. <P>SOLUTION: A low-loss type optical switch having three-dimensionally crossed optical paths is used for the optical switch which has a nonlinear optical thin film at the branch point of an optical path and which switches optical paths at the branch point by applying an excitation field on the branch point to reversibly change the refractive index of the nonlinear optical thin film. A high-speed optical switch with low loss and low power consumption and advantageous for minimizing can be obtained by this invention. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch with low loss and high speed response.

[0002]

2. Description of the Related Art In order to further develop the information society, it is necessary to construct an optical communication system capable of transmitting a large amount of information at high speed. Currently, wavelength division multiplexing (WD)
M) Systems have been developed, and network speeds are rapidly increasing.

The essential parts for higher speed optical communication are:
It is a switching means of optical information. In the conventional switching of optical information, a photoelectric conversion unit for converting optical information into electrical information and an electro-optical conversion unit for inversely converting electrical information into optical information are required at a relay point.

As the number of relay points increases, the total power consumption of the photoelectric conversion means and the electro-optical conversion means increases, and the switching speed decreases. Therefore, in order to construct a higher speed optical communication system, optical information is transmitted. It is preferable to use optical switches that switch directly.

[0005]

When the optical path is switched by the n × n type optical switch based on the above principle, the input optical signal basically passes through the 1 × 2 switch element n times. Therefore, the loss in each switch element is multiplied by n before being output. According to the market trend of optical switches,
The number is increasing, and it is expected that there will be a demand for 1000 × 1000 type switches.
There is a problem that the loss of the basic switch element is greatly amplified and output.

Further, since the electric driving force required for switching each 1 × 2 basic switch element is generally large, there is also a problem that the energy consumption increases as the number of n increases.

An object of the present invention is to provide a cross-connectable optical switch for an optical network system, which has low loss and low power consumption and is advantageous for miniaturization.

[0008]

In order to solve the above-mentioned problems, when the optical path is switched by an n × n type optical switch, an input optical signal basically passes through a 1 × 2 switch element once. It suffices to use an optical switch having such a structure. Specifically, in a matrix type optical switch having a 1 × 2 type optical switch at a branch point of an optical path, it is solved by using a low loss type optical switch characterized in that optical paths intersect three-dimensionally. An example of the structure of such a switch is shown in FIG. In the example shown in the figure, two optical paths for input and three optical paths for output intersect three-dimensionally, and there are six optical switches between them. The optical signal input from the optical path 1 is output to 2. Here, when the optical switch A is operated, the optical signal input from 1 is output to 3, and when the optical switches A and B are operated, the optical signal is output to 4. The same applies when an optical signal is input to another optical path. By using the matrix switch with such a structure, when selecting multiple output destinations,
There is only one optical switch through which the optical signal passes, and loss can be reduced. Although FIG. 1 shows a 2 × 3 optical switch structure example, the optical switch according to the structural principle of the present invention is not limited to the 2 × 3 type optical switch.

In order to reduce the size and power consumption of the low-loss optical switch, a nonlinear optical thin film is provided at the branch point of the optical path, and an external field for excitation is applied to the branch point of the nonlinear optical thin film. In the optical switch that reversibly changes the refractive index and switches the optical path at the branch point, a low-loss optical switch characterized in that the optical paths intersect three-dimensionally may be used. Alternatively, in the same optical switch, a low loss type optical switch characterized in that the branching shape is an arc shape or a polygonal shape may be used. Here, the nonlinear optical thin film has a high refractive index due to excitation by an external field, the refractive index in the non-excited state is smaller than that of the waveguide or the waveguide fiber material, and the refractive index in the excited state is Alternatively, it is the same as the refractive index of the waveguide fiber material. In any case, the low-loss optical switch has a nonlinear optical thin film at the branch point of the optical path and has a mechanism for applying an excitation external field to the branch point. Here, the external field may be light or electric field. The nonlinear optical material thin film at the branch point of the optical path is at least Co, F
It is more preferable that the thin film contains a metal oxide selected from e, Cr, Ni, V, Zn, and Cu and contains an oxide selected from silicon oxide, titanium oxide, and aluminum oxide. Further, when a rare earth oxide is contained, good characteristics can be obtained. The structure has an average particle size of 15
It is characterized by being below nm.

Here, the basic operation of optical switching is performed by utilizing the change in the refractive index of the nonlinear optical thin film, but the principle of switching does not have to be limited to the change in the refractive index of the thin film. A MEMS type switch may be used. Basically, by forming the structure of the present invention with 1 × 2 optical switch elements, a low loss matrix type optical switch can be obtained.

In the optical switch based on such a principle,
When a × n type optical switch is manufactured, the number of n is not limited in principle, and in that case, a high-speed response optical switch suitable for a time division type optical information system can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail.

(Embodiment 1) FIG. 2 shows a method of manufacturing an optical switch according to the present invention. First, the quartz glass-based glass substrate 9
A photoresist 20 is applied on the surface (a). A waveguide pattern is formed by photolithography (b). Then C
A material transparent to communication light by the VD method, for example, SiO
After depositing the ₂ type thin film, the resist is removed to form a SiO ₂ type waveguide, which is used as the lower waveguide 8 (c). After that, a SiO ₂ film 21 is deposited by the CVD method and an etching process is performed to obtain the state of FIG.

A Co ₃ O ₄ -nonlinear optical thin film 6 is attached to the substrate in this state by the sputtering method (e). The sputtering gas was argon + 20% oxygen mixed gas, the gas pressure was 0.67 Pa, the substrate temperature was 300 ° C., CoO was used as the target, and SiO ₂ —TiO ₂ was used as the glass component.
At the time of sputtering, a mask having a hole with a diameter of 50 μm was placed at a position to be an excitation spot of the optical switch so that a Co ₃ O ₄ thin film was sputtered on the excitation spot.

A photoresist is further applied to the substrate provided with the Co ₃ O ₄ type thin film (f), and a waveguide pattern is formed by photolithography so as to form an angle of 15 ° with the lower waveguide 8. Thereafter, the upper waveguide 7 is formed by the same method (g), and finally the SiO ₂ film is deposited by the CVD method to obtain an optical switch (h).

FIG. 4 shows a schematic structure of a 2 × 2 optical switch manufactured by the above method. In order to clearly show the positional relationship between the waveguide and the nonlinear optical thin film, a quartz substrate and Si
The O ₂ layer is not shown. 1 is an input terminal, 3, 4 and 5
Is an output terminal. C at the crossing interface of each waveguide
O ₃ O ₄ system thin films are sputtered, and these are used as excitation spots by an external field. In this example, a surface emitting laser having a wavelength of 775 nm was used as the external field.

FIG. 3 shows a method of irradiating the excitation light with the surface emitting laser. In FIG. 3, 22 is a surface emitting laser. The light 23 emitted from the surface emitting laser is applied to the branch point of each signal light. The surface emitting laser was mounted at a position perpendicular to the surface of the laminated body through which the optical signal passes, that is, at a position where laser light could be irradiated to a predetermined position of the nonlinear optical layer of the laminated body. The light emission timing of the surface emitting laser was determined based on the switching information written in the optical signal.

Input light was applied from 1 to the optical switch manufactured by the above method. The wavelength of the input light was 1550 nm, which is the wavelength of the communication light. When not irradiating, it was output from 3. Here, when the surface emitting laser is irradiated to the point A in FIG. 4 at an intensity of 0.3 MW / cm ² , the output light is 3 to 4
It was confirmed that the location was changed and switching was possible. Furthermore, when the response speed at this time was measured, it was a very high speed of 11 ns.

Furthermore, the intensity of the surface emitting laser is set to 0.5 MW.
When it was increased to / cm ² , the switching phenomenon was also observed, but it was confirmed that the response speed was as fast as 1.2 ps. This phenomenon is considered to have occurred because the refractive index change increased due to the intensity of the excitation light.

Next, the spots to which the surface-emitting laser is applied are set to two points A and B. As a result, the output light changed from 3 points to 5 points. At this time, the response speed was 1.1 ps, which was very high as before. From this, it was shown that the switching can be performed in different directions by increasing the irradiation position.

The material of the glass substrate and the waveguide used here was SiO ₂ having a refractive index of 1.5.
₂ was added to change the refractive index from 1.5 to 1.7. The result is shown in FIG. In this figure, from the left, TiO ₂
Shows the content of, the refractive index of the supporting substrate, and the output light intensity. Ti
It was found that when the O ₂ content exceeded 30% (weight ratio), the output light intensity drastically decreased to 10% or less. This phenomenon is considered to be because the refractive index of the supporting substrate exceeded 1.6 and the light leaked to the periphery to reduce the output light intensity.

The change in characteristics when the material of the nonlinear optical thin film was changed was examined. The measurement system is shown in FIG. In this case, first, in order to examine the refractive index of each substance and its response, a sample in which only the nonlinear optical thin film 6 was formed on the glass substrate 9 was prepared. The measurement light 11 is s-polarized with respect to the sample,
As the p-polarized light, an ellipsometry optical system for measuring the refractive index based on the difference in reflectance between the p-polarized light and the s-polarized light by the nonlinear optical thin film 3, that is, an ellipsoidal polarization method was used. The wavelengths of the excitation light 10 and the measurement light 11 can be changed arbitrarily.

In this measurement, a femtosecond laser having a wavelength of 775 nm, which is easy to control the oscillation drive, was used as the light source of the excitation light 10. The maximum output of this semiconductor laser was 8 mW. In addition, the measuring light 11 is used for communication 155.
A 0 nm femtosecond laser was used. Excitation light, measurement light,
In both cases, the frequency was 1 kHz and the laser irradiation time per cycle was 0.2 ps. The response time was calculated by changing the frequency interval between the two. Further, the measurement was performed with a laser power that was sufficiently weak with respect to the intensity of the excitation light 10 so that the sample was not excited by the measurement light 11. Here, 12 is a signal light source, 13 is a signal light receiver, 14 and 15 are collimator lenses, 16 is a polarizer, 17 is an analyzer, and 18 and 19 are condenser lenses. FIG. 7 is a diagram showing an example of a change in the refractive index when the excitation light 10 is irradiated on the nonlinear optical thin film 6. It was found that the refractive index of the thin film changed after the laser irradiation (with the change of the laser power), and then returned to the original value in two steps.

Therefore, 1.2p from the pulsed light power saturation
The refractive index after s (picosecond) was measured, and the dependence of the refractive index on the power of the excitation light 10 was measured. The result is shown in FIG. The refractive index without irradiation of the excitation light 10 was 3.2 at the measurement wavelength of 1550 nm. The refractive index decreases as the intensity of the excitation light 10 changes to 0.3 MW.
/ The strength of cm ² in the strength of the 3.13,0.5MW / cm ² was changed to 3.1. It is considered that the reason why the response speed changed with the excitation light intensity in the previous experiment is that the refractive index changed in two steps and the trend changed with the power.

FIG. 9 shows the changes in the refractive index and the refractive index of the nonlinear optical thin film (excitation light power 0.5 MW / c) investigated by the above method.
m ² ), switching characteristics and response time. In the figure, in the column of switching characteristics, the case where switching is possible is indicated by ⊚, and the case where switching is not possible is indicated by ×.
As a result, the same effect was obtained except for CoO and ZnO, and good switching characteristics were confirmed.

Since the change in the refractive index of CoO is 0.05% and the change in the refractive index of other substances is 2% or more, it is 2%.
It has been found that the characteristics are detected by the above. Furthermore, Co
_{When 3} O ₄ thin film and Fe ₃ O ₄ thin film are used, the change in refractive index is 3%.
Since it is very large as above, it switched at a very fast speed of 1.2 ps. This is considered to be a result of reflecting the two-stage transition described above.

When this example is seen from the structure of the crystal system, the refractive index change of Co ₃ O ₄ and Fe ₃ O ₄ having a spinel structure is 3% or more, and the change is on the order of ps (picosecond). It had a particularly noticeable change. From this, it was found that an oxide having a spinel structure is particularly preferable for this switch.

Further, the thin film (Er ₄ Fe ₆ O ₁₄ , Nd ₄ Fe ₆ O ₁₄ ) mixed with 40% of rare earth oxide has a refractive index of 1.
It turned out to be 9. Therefore, for these oxide thin films, SiO ₂ and Ti were used as a substrate for lamination.
A glass substrate having a refractive index of 1.9 containing 40% by weight of O ₂ was used. As a result, the same switching characteristics as the previous one were obtained. Further, when the intensity of output light was examined, it was found that the efficiency was 70% in the previous case, but it was 95% when the glass substrate was used, which was very efficient.

The case where the substances in the nonlinear optical thin film are changed variously has been described above. Further, in the switching characteristics, ZnO does not change, and Fe ₃ O ₄ changes. The composition was examined during this period.
This result is shown in FIG. In FIG. 10, the composition ratio, the average particle size, the refractive index change, and the switching characteristics are shown from the left.

First, looking at the relationship between the ZnO composition and the average grain size, it was found that the average grain size increased as ZnO was mixed. Furthermore, ZnO is added to Co ₃ O ₄ .
When 40% or more is added, the change in refractive index becomes small,
I couldn't switch. It can be inferred that this is because the average particle size exceeds 15 nm. As a result,
It has been shown that an average particle size of 15 nm or less is desirable for switching.

In this embodiment, the thin film is formed on the glass substrate, but a thin film having the same composition as Si or glass is formed on the upper surface of the thin film by the thickness of the substrate to obtain a similar result. Was given.

From the above results of this embodiment, by using the three-dimensional structure of FIG. 1, the response time is 1.2 ps to 11 ps.
It was shown that a matrix optical switch of ns and very high speed can be easily manufactured. Furthermore, it was found that the switch characteristics are greatly influenced by the thin film composition and the supporting substrate.

(Embodiment 2) The present embodiment 2 is a structure for using an electric field in contrast to the embodiment 1 which uses laser light (excitation light) as an external field. FIG. 11 shows a schematic diagram at that time. In this figure, 24 is Cr wiring and 25 is Cr
It is a glass plate with a thickness of 0.1 mm with wiring drawn. As shown in this figure, Cr wiring was drawn on the upper and lower surfaces of the nonlinear optical thin film, and a voltage was applied between them to apply a voltage to the nonlinear optical thin film.

When a voltage of 40 V is applied to the nonlinear optical thin film 3 via the upper electrode and the lower electrode, the optical path of the emitted light is changed from the core b to the core c as in the first embodiment in which the excitation light is irradiated.
I was able to observe that it changed to.

However, the response to the applied voltage pulse is 1
It was found that the speed was slower than that of Example 1, which was on the order of 000 ns (nanosecond). According to the second embodiment, it has been found that a voltage-driven optical switch can be manufactured, but it has been found that it is possible to manufacture a faster switch by using pumping light in the external field.

(Example 3) An experiment was carried out in which the fluorescent film ZnS was caused to emit light by a voltage and the change in the refractive index of the nonlinear optical thin film was caused by the light emission.

FIG. 12 shows the device structure used in the experiment. For simplicity, this figure shows a schematic diagram of a 1 × 2 switch. In FIG. 12, reference numeral 26 is ZnS attached as a phosphor, and is arranged so as to emit light when a voltage is applied between the electrodes. Before the switch verification experiment, it was confirmed that the ZnS thin film emits light when a voltage of 40 V is applied.

It was confirmed that when the refractive index of the nonlinear optical thin film was changed by utilizing this fluorescence, switching was performed at the same speed as in Example 2. From this result, it was found that the switching can be performed by the fluorescence applied by the electric field.

According to this embodiment, by providing the laminated structure using the non-linear optical thin film, it is possible to obtain a small matrix optical switch which is excellent in high-speed response and suitable for switching a large amount of information.

[0040]

According to the present invention, it is possible to obtain a high-speed optical switch which has low loss and low power consumption and is advantageous for miniaturization.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the structure of an optical switch according to the present invention.

FIG. 2 is a diagram showing a manufacturing process of the optical switch of FIG.

FIG. 3 is a schematic view showing a surface emitting laser.

FIG. 4 is a diagram schematically showing the structure of an optical switch according to the present invention.

FIG. 5 is a diagram showing the configuration and arrangement of a measurement optical system for measuring the optical characteristics of the optical switch according to the present invention.

FIG. 6 is a diagram showing an example of a change in the refractive index when the nonlinear optical thin film 2 is irradiated with the excitation light 10.

FIG. 7 is a diagram showing an example of a change in the refractive index when the nonlinear optical thin film 2 is irradiated with the excitation light 10.

FIG. 8 is a diagram showing a result of examining a nonlinear optical material most suitable for the optical switch of the first embodiment.

FIG. 9 is a diagram showing a result of examining a non-linear optical material most suitable for the optical switch of the first embodiment.

FIG. 10 is a diagram showing a result of examining a nonlinear optical material most suitable for the optical switch of the first embodiment.

FIG. 11 is a diagram showing a structure of an optical switch according to a second embodiment.

FIG. 12 is a diagram showing a structure of an optical switch according to a third embodiment.

[Explanation of symbols]

1 ... Input terminal, 3, 4, 5 ... Output terminal, 6 ... Non-linear optical thin film, 7, 8 ... Waveguide, 9 ... Quartz glass type glass substrate,
10, 23 ... Excitation light, 11 ... Measuring light, 12 ... Signal light source, 13 ... Signal light receiver, 14, 15 ... Collimator lens, 16 ... Polarizer, 17 ... Analyzer, 18, 19 ... Collecting light Lens, 20 ... Photoresist, 21 ... SiO ₂ film, 2
2 ... surface emitting laser, 24 ... Cr wiring, 25 ... glass plate,
26 ... ZnS phosphor.

Continued front page    (72) Inventor Keiro Ishikawa             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Takashi Naito             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. F-term (reference) 2K002 AA02 AB04 BA01 BA06 CA02                       EA00 EB01 HA15 HA16

Claims (13)

[Claims] 1. A non-linear optical thin film is provided at a branch point of an optical path, and a refractive index of the non-linear optical thin film is reversibly changed by applying an excitation external field to the branch point so that the optical path at the branch point is changed. An optical switch for switching, wherein the optical paths intersect three-dimensionally. 2. The optical switch according to claim 1, wherein the excitation external field is an electric field. 3. The optical switch according to claim 1, wherein the excitation external field is light. 4. A surface emitting laser for irradiating the light on the nonlinear optical thin film.
Optical switch described in. 5. The wavelength of the surface emitting laser is 700 nm to 9 nm.
The optical switch according to claim 4, wherein the optical switch has a thickness of 00 nm. 6. The optical switch according to claim 2, further comprising a voltage application electrode or wiring for applying the electric field on the nonlinear optical thin film. 7. The optical switch according to claim 1, wherein the response speed of the optical switch is 1 μs or less. 8. The optical switch according to claim 1, wherein the response speed of the switch is 12 ns or less. 9. The optical switch according to claim 1, wherein the response speed of the switch is 1.2 ps or less. 10. The non-linear optical thin film comprises at least C
The optical switch according to claim 1, wherein the optical switch comprises a metal oxide selected from o, Fe, Cr, Ni, V, Zn, Cu, and Mn, or a composite oxide containing the metal oxide. 11. The optical switch according to claim 10, wherein the nonlinear optical thin film contains at least an oxide selected from silicon oxide, titanium oxide and aluminum oxide. 12. The optical switch according to claim 11, wherein the nonlinear optical thin film contains a rare earth oxide. 13. The optical switch according to claim 1, wherein the nonlinear optical thin film is composed of an aggregate of particles and has an average particle diameter of 15 nm or less.