JPH0815621A - Optical switch - Google Patents

Abstract

PURPOSE:To reduce power consumption, to increase an optical path switch speed and to provide sufficient strength by miniaturizing and thinning an optical path switch mechanism part, utilizing an electrostatic force and driving the mechanism part. CONSTITUTION:A recessed part 6 is formed on a silicon substrate 1, and a deflection element of a silicon made cantilever 2 provided with a reflection mirror 3 and an upper electrode 5 are provided on the surface of the recessed part 6. A lower electrode 4 is formed on the bottom surface of the recessed part 6, and an electric charge is imparted between the upper electrode 5 and the lower electrode 4, and the cantilever 2 is fluxed, and by inclining the reflection mirror 3, an optical path of an outgoing beam from the reflection mirror 3 is switched. That is, the deflection element of the cantilever 2 provided with the upper electrode 5 and the reflection mirror 3 is provided with a structure as a capacitor, and when a voltage is applied between the upper electrode 5 and the lower electrode 4, attraction force occurs and the cantilever 2 is flexed, and the angle of the reflection mirror 3 is changed, and the optical path of the outgoing beam is changed. Since the deflection element is miniaturized and light in weight, and is driven by the electrostatic force, thereby, it is operated at high speed, and power consumption is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch, and more particularly to an optical switch which has low power consumption and improved optical path switching speed.

[0002]

2. Description of the Related Art A conventional optical switch is of a type in which an optical path is switched by mainly changing the position of an optical fiber itself or an optical component such as a prism by using an actuator such as a solenoid.

[0003]

However, in this type of optical switch, since the shape and weight of the movable part are large,
There are problems that the power consumption is large (for example, about 1 W), the switching speed is slow (for example, several tens of milliseconds), and it does not operate depending on the mounting direction.

In view of the above points, an object of the present invention is to reduce the size and weight of the optical path switching mechanism portion and drive the mechanism portion by utilizing electrostatic force to reduce the power consumption and the optical path switching speed. Another object of the present invention is to provide an optical switch that has sufficient strength for practical use.

[0005]

In order to achieve such an object, in the present invention, a recess is formed in a silicon substrate,
A deflection element of a silicon cantilever having a reflecting mirror and an upper electrode is provided on the surface of this recess, and a lower electrode is formed on the bottom of the recess, and an electric charge is applied between the upper electrode and the lower electrode to cause bending of the beam. It is characterized in that the optical path of the light emitted from the reflecting mirror can be switched by inclining the reflecting mirror. Another invention of the present invention is
A plurality of the optical switches according to the first aspect of the present invention are arranged in a two-dimensional array, and each reflecting mirror can individually switch the optical path.

[0006]

The deflecting element, which is a cantilever made of silicon with an upper electrode and a reflecting mirror, has a structure as a capacitor. When a voltage is applied between the upper electrode and the lower electrode, an attractive force is generated and the beam bends. The deflection of the beam changes the angle of the reflecting mirror, which changes the optical path of the emitted light. Since the deflection element is small and lightweight, and can be driven by static electricity, it operates at high speed and consumes less power. It also has practically sufficient mechanical strength.

[0007]

The present invention will be described in detail below with reference to the drawings.
First, an optical path switching device using the optical switch of the present invention will be briefly described. FIG. 9 is a simplified block diagram showing an example of the optical path switching device. In the figure, the light emitted from the optical fiber output end 41 a enters the deflection element 45 via the input section 42. The input section 42 is composed of a collimator lens 43a and a condenser lens 44a, and is for converging the divergent light emitted from the fiber on the deflecting element. The deflecting element 45 is a deformable portion of the optical switch and is a cantilever beam with a reflecting mirror (details will be described later). The surface of the deflecting element 45 is a reflecting mirror, and the light reflected here goes to the output 1 or the output 2.
Both the output 1 and the output 2 are made to enter the fiber input end 41b or 41c through a condenser lens and a collimator lens.

This deflection element has a capacitor structure,
When a voltage is applied between the electrodes, the beam bends and the angle of the reflecting mirror changes. The deflecting element bends so that the reflected light is reflected to the output 1 side as shown in FIG. 10A when the capacitor is discharged, and is reflected to the output 2 side as shown in FIG. 10B when the capacitor is charged. Bend.

Details of such an optical switch will be described below. FIG. 1 is a perspective view showing the structure of an optical switch according to the present invention, and FIG. 2 is a view showing an example of its dimensions.

[0010] cantilever 2 is made by using a selective epitaxial method and an anisotropic etching in the S _i recesses like recess 6 formed by anisotropic etching to the substrate 1. The portion of the reflecting mirror 3 on the surface of the cantilever 2 (approximately 20 μm × 20
(μm) is the beam part (thickness 2 μm) so that distortion does not occur
The plate thickness is thicker than that of (5 μm). The reflecting mirror 3 is supported by beams (two, each having a width of 5 μm), and has a structure ensuring stability against twisting.

Next, a method of making an optical switch having such a structure will be described step by step. (1) substrate etching n-type (100) silicon substrate a silicon oxide (S _i O ₂₎
Is used as a mask to perform anisotropic etching with an aqueous solution of potassium hydroxide (KOH) or the like to form a recess 6 for forming the beam 2 (the upper opening is approximately 50 μm × 50 μm). (2) Lower electrode formation A lower electrode layer is formed on the bottom surface of the recess 6 by sputtering, for example, using molybdenum (Mo), and the lower electrode 4 is formed in a stripe shape by photolithography.

(3) Growth of sacrificial layer (p ⁺ layer) While adding a p-type impurity (for example, boron B), a portion (sacrificial layer p ⁺ ) to be a cavity is formed by chemical vapor deposition (CVD).
Selective epitaxial growth is performed to fill in the holes. (4) make a mask S _i O ₂ on the creation sacrificial layer recess for the reflector, etched pits as the reflector, for example, hydrazine (N ₂ H _4). (5) Beam (p ⁺⁺ ) growth By adding a higher concentration of B than the sacrificial layer, p ^{++ of the} beam portion
Selective epitaxial growth of layers is performed. (6) Removal of sacrificial layer The sacrificial layer (p ⁺ layer) is anisotropically etched with hydrazine, which has the property that the etching rate varies depending on the impurity concentration.
Is removed. (7) Formation of Upper Electrode Finally, for example, aluminum (Al) having a high reflectance is sputtered on the portion to be the reflection mirror 3, and the upper electrode is formed by the photolithography method.

The operation of the deflecting element thus formed will be described. Deflection element (2 cantilever with reflector)
Since it has a capacitor structure, when a voltage is applied between the upper and lower electrodes, electric charges are accumulated between the beam and the reflecting mirror and the substrate, and the reflecting mirror 3 bends toward the bottom of the recess 6 to bend the beam. Occurs. Due to this deflection, the angle of the reflecting mirror changes, and the optical path of the reflected light can be changed.

The deflection and inclination of the reflecting mirror will be described below. The attractive force W generated between the reflecting mirror and the substrate due to the charge Q accumulated between the upper and lower electrodes is W = Q ² / (4πε ₀ d ² ) according to Coulomb's law, where ε ₀ is the dielectric constant of the vacuum. 85 × 10 ⁻¹² d is the distance between the reflecting mirror and the substrate. The charge Q accumulated by the external voltage V and the electrostatic capacitance C of the capacitor formed by the reflecting mirror and the substrate are given by the following equation. Q = CV C = ε ₀ BH / d where B is the width of the reflector and H is the length of the reflector.

Now, the suction force W when a voltage of 5 V is applied between the upper and lower electrodes is calculated as follows: W = ε ₀ V ² S ² / (4πd ⁴ ) = 1.76 × 10 ^-11 [N] V is the voltage applied between the upper and lower electrodes: 5V S is the area (B × H) of the reflecting mirror.

The inclination angle θ _b of the tip of the beam 2 is θ _b = Fl ² / (2EIz ² ). Here, F is the weight applied to the tip portion, and l is the length of the beam. In the present invention, since there are two beams, F = W / 2. Iz is the moment of inertia of area of the beam, and Iz = bh
^3/12 (where, b is the beam width, h is the thickness of the beam) is given by. E is the elastic coefficient, which is about 1 × 10 in the case of silicon.
¹¹ [dyn / cm ² ]. Substituting these values into the above equation yields θ _b = 30 °.

The displacement amount Yb at the tip of the beam is given by the following equation. Yb = Fl ³ /3EIz=7.04×10 ⁻⁶ [m].

As described above, when a voltage of 5 V is applied between the upper and lower electrodes, the tilt angle θb of the reflecting mirror is θb = 30 °. The displacement amount Ym = Yb + L · tan (θ
b) = 18.5 μm.

FIG. 3 is a cross-sectional view showing how the deflecting element is deformed. FIG. 3 (a) shows a state during discharge in which the electrodes are short-circuited,
FIG. 6B shows the state when 5 V is applied. At the time of discharge, the reflecting mirror 3 is horizontal and vertically reflects light that is incident vertically. When 5 V is applied, the tip of the reflecting mirror 3 is 18.
The light vertically displaced by 5 μm is reflected at a reflection angle of 60 °.

The optical switch having such a structure is much smaller and lighter than the conventional heavy moving part, is deformed at a higher speed, and the switching speed of the optical path is also higher. It also consumes less power.

The optical switch of the present invention is not limited to the embodiment, and the shape, dimensions, applied voltage, etc. can be appropriately changed without departing from the object of the present invention.

Next, a reflective spatial light control element using the optical switch of the present invention will be described. The reflective spatial light control element is an optical switch in which a plurality of the optical switches shown in FIG. 1 are two-dimensionally arranged, and is applied to, for example, a projection type display. FIG. 4 is a diagram showing an example of the configuration of the projection display. Light emitted from the light source 11 is turned on / off by the spatial light control element (a liquid crystal panel in this example) 12, and the lens group 1
An image is formed on the screen 14 through the screen 3.

However, when the spatial light control element is a liquid crystal panel, its light utilization efficiency is low and a light source with a large light quantity is required due to its low aperture ratio and low transmittance of each component. , Causing problems such as large power consumption and heat generation. There is also an example of using a mirror array created by micromachining technology on a Si wafer as a spatial light control element, but the mechanical strength of the mirror part is insufficient, and the strength in the mounting process and in actual use is insufficient. There was a problem. The reflective spatial light control element according to the present invention solves these problems all at once. The optical switches shown in FIG. 1 are arranged in a matrix in the vertical and horizontal directions as shown in FIG. The elements are commonly connected, and the lower electrodes 4 are commonly connected to each element in one column. When applied to a projection display, 1
The element corresponds to one pixel, and for example, in the case of forming a screen of 640 × 400 dots, 256000 elements are arranged.

This spatial light control element can be driven by the line sequential method used in a simple matrix display such as a liquid crystal display. An example of the drive circuit is shown in FIG.
A switch is provided on each of the upper and lower electrodes of the optical switch,
The data line can be switched to 5V / GND (GND is the potential of the common line), and the selection line can be switched to 2.5V / GND.

The selection of the display pixel is performed by the following two procedures. (1) Display line selection (selection line selection) Connect the switch of the line to be displayed to the GND side and the switch of the line not to display to the 2.5V side. (2) Selection of data line The switch of the data string is switched to 5V or GND according to the display data (data indicating whether to display or not).

With the above selection, 5V is applied between the upper and lower electrodes of the display pixel and 2.5V is applied between the electrodes of the non-display pixels.
Will be applied. FIG. 7 shows the reflection mirror and the reflected light of the display pixel and the non-display pixel at this time. In this way, the image data can be projected on the screen by sending the display data while sequentially operating the selection line.

FIG. 8 shows an example of the structure of the reflection type projection display. Display line switch 2 by control circuit 24
2 and the switch 23 of the data string are selected, the spatial light control element 21 is driven, and the incident light from the light source 11 is reflected. The display light reflected by the reflecting mirror of the display pixel is projected on the screen 14 through the projection lens system 13 (composed of a collimating lens and a condensing lens). The non-display light has a small reflection angle and does not enter the projection lens system 13 so as not to hit the screen 14. The power supply 25 supplies the switches 22 and 23 with 5V and 2.5V.

As described above, the spatial light control element in which the optical switches of FIG. 1 are two-dimensionally arranged is formed by surely connecting the reflecting mirror and the optical switch body with the support beam of silicon. It is resistant to vibration or shock during mounting, and has the effect of simplifying the mounting process and improving reliability.

[0029]

As described above, according to the present invention, an optical switch having the following effects can be easily realized. (1) Compact and lightweight. (2) High-speed operation is possible. (2) There are no restrictions on the mounting direction. (3) Power consumption is extremely low compared to conventional ones. (4) The reflector part has sufficient strength for practical use.

[Brief description of drawings]

FIG. 1 is a perspective view of a configuration showing an embodiment of an optical switch according to the present invention.

FIG. 2 is a diagram showing an example of dimensions of each part of the optical switch of the present invention.

FIG. 3 is a diagram showing how the deflection element is deformed.

FIG. 4 is a configuration diagram showing an example of a projection display.

FIG. 5 is a configuration diagram showing an example of optical switches arranged two-dimensionally.

6 is a diagram showing an example of a drive circuit of the optical switch of FIG.

7A and 7B are diagrams showing a reflection state of a display element and a non-display element in the optical switch of FIG.

FIG. 8 is a configuration diagram showing an embodiment of a reflective projection display.

FIG. 9 is a simplified configuration diagram showing an example of an optical path switching device.

FIG. 10 is a diagram for explaining the operation of the optical switch.

[Explanation of symbols]

 1 Substrate 2 Cantilever 3 Reflector 4 Lower electrode 5 Upper electrode 6 Recess 11 Light source 13 Projection lens 14 Screen 22, 23 Switch 24 Control circuit 25 Power supply

Claims (2)

[Claims] 1. A silicon substrate is provided with a concave portion, a surface of the concave portion is provided with a deflecting element of a silicon cantilever having a reflecting mirror and an upper electrode, and a lower electrode is formed on the bottom surface of the concave portion. An optical switch characterized in that an optical path of light emitted from the reflecting mirror can be switched by applying a charge between an electrode and a lower electrode to cause the beam to bend and tilt the reflecting mirror. 2. An optical switch in which a concave portion is formed in a silicon substrate, a silicon cantilever deflection element having a reflecting mirror and an upper electrode is provided on the surface of the concave portion, and a lower electrode is formed on the bottom surface of the concave portion. By arranging a plurality of two-dimensionally and applying an electric charge between the upper electrode and the lower electrode to cause the beam to bend and tilt the reflecting mirror,
An optical switch characterized in that the optical path of the light emitted from each reflecting mirror can be individually switched.