JP2007155965A - Variable wavelength optical filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable low voltage driving since a selection characteristic of a filter is excellent. <P>SOLUTION: A movable mirror 32 is arranged inside holes 31a to 31d formed on a second substrate 31 and a mirror driving means has three sets of driving mechanisms provided around the movable mirror 32 at an equal distance, and each of the three driving mechanisms comprises: a pair of axes 42 and 43 which are orthogonal to the line extending from the center of the mirror 32 to the outer fringe of the second substrate 31, extend straightly inward from respectively different points on the outer fringe of the holes 31a to 31d, and are freely torsionably deformable in the longitudinal direction; a turning disk 41 arranged in the holes 31a to 31d, of which the outer fringe is connected to the end of the pair of axes 42 and 43 and is supported freely turnably around the axes; a flexible hinge 35 which connects the outer fringe of the movable mirror 32 and one end side of the turning disk 41; and electrodes 46 and 49 for giving the turning disk 41 turning force around the axes 42 and 43 by applying an electric voltage between the other end side of the turning disk 41 and the outer fringe of the second substrate 31. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a Fabry-Perot type variable wavelength optical filter that changes the wavelength of light transmitted between mirrors by changing the distance between two mirrors facing each other in parallel. The present invention relates to a technique for greatly changing a wavelength by voltage.

  As a wavelength tunable optical filter, a Fabry-Perot type (cavity type) optical filter that changes the wavelength of light transmitted between mirrors by changing the distance between two mirrors facing each other in parallel is known. A so-called MEMS structure constituted by an etching technique for a semiconductor substrate or the like is realized.

  FIG. 10 shows a cross-sectional structure of a conventional MEMS structure optical filter. This optical filter has a structure in which a transparent first substrate 1 and a second substrate 10 are overlapped with a spacer 9 interposed therebetween, and is formed on the lower surface side center of the first substrate 1. The fixed mirror 2 is formed by the high reflectivity HR film 3 and the low reflectivity AR film 4 formed on the opposite side. A plurality of electrodes 5 are provided outside the HR film 3. Here, the first substrate 1 is made non-conductive. However, in the case of a conductive substrate, the non-conductive HR film 3 may be formed large and a plurality of electrodes 5 may be provided on the outer edge of the surface. .

  On the other hand, the second substrate 10 has conductivity, and a movable mirror 12 formed by removing the outer side by an etching process at the center is movable up and down by a plurality of flexible hinges 11. It is supported.

  The movable mirror 12 is composed of an HR film 13 formed on the upper surface side of the second substrate 10 and an AR film 14 formed on the opposite surface side, and the first substrate 1 and the second substrate 10 are integrally formed. When overlaid, the spacer 9 is supported in parallel with the spacer 9 being separated in thickness.

  In the optical filter having such a structure, as shown in FIG. 10A, when no voltage is applied to each electrode 5 of the first substrate 1 with respect to the second substrate 10 (V = 0), As described above, the movable mirror 12 is supported in parallel at the position where the thickness of the spacer 9 is separated from the fixed mirror 2, and in this state, for example, when broadband light P0 is input from the lower surface side of the movable mirror 12, Light P1 having a wavelength interval determined by the distance between the mirrors is emitted from the fixed mirror 2 side.

  As shown in FIG. 10B, when a voltage V having an absolute value greater than zero volts is applied to each electrode 5 of the first substrate 1, an electrostatic attractive force is generated between each electrode 5 and the movable mirror 12. As a result, the movable mirror 12 approaches the fixed mirror 2 side, and light P2 having a narrower wavelength interval is emitted from the fixed mirror 2 side than when no voltage is applied.

  Therefore, by changing the voltage applied to the electrode 5, the wavelength of light passing between the mirrors can be changed.

  In addition, the optical filter of the said structure is disclosed by the following patent document 1, for example.

US Pat. No. 6,373,632

  However, in the optical filter having the above structure, since force is applied to the movable mirror 12 itself, when the thickness is thin, the movable mirror 12 itself is distorted, the parallelism is deteriorated, and the selection characteristic as a filter is reduced. There was a problem of deterioration.

  Further, since the movable mirror 12 is moved by the voltage applied between the electrode 5 and the movable mirror 12, a very high DC voltage is required to obtain a large movement distance, resulting in an increase in manufacturing cost. There was a problem.

  An object of the present invention is to solve these problems, and to provide a variable wavelength optical filter that has good filter selection characteristics and can be driven at a low voltage.

In order to achieve the above object, the variable wavelength optical filter according to claim 1 of the present invention comprises:
A first substrate (21) having translucency;
A fixed mirror (22) formed on the first substrate and having one surface side formed with high reflectivity;
A second substrate (31) having translucency and disposed in a state of facing the first substrate in parallel;
A movable mirror (32) formed on the second substrate, the one side of which is formed with high reflectivity, and the high reflectivity surface is opposed to the high reflectivity surface of the fixed mirror;
In the wavelength tunable optical filter having a mirror driving unit that moves the movable mirror in a direction in which the distance to the fixed mirror changes, and changes a wavelength of light transmitted between the fixed mirror and the movable mirror,
The movable mirror is disposed inside holes (31a to 31d) formed in the second substrate,
The mirror driving means includes
A pair of pairs that are orthogonal to a line from the center of the movable mirror toward the outer edge of the second substrate and extend inward to form a straight line from different positions of the outer edge of the hole, and are twistable in the longitudinal direction. Shafts (42, 43);
A rotating plate (41) disposed inside the hole, the outer edge of which is connected to the distal ends of the pair of shafts, and is supported rotatably about the pair of shafts;
A flexible hinge (35) for connecting between the outer edge of the movable mirror and one end of the rotating plate;
Electrodes (46, 49) for applying a voltage between the other end side of the rotating plate and the outer edge of the second substrate to apply a turning force about the axis to the rotating plate. A set of drive mechanisms,
Three or more sets of the drive mechanisms are provided at equal intervals around the movable mirror.

The variable wavelength optical filter according to claim 2 of the present invention is the variable wavelength optical filter according to claim 1,
The opposite surface side of the one surface side of the fixed mirror is formed with a low reflectance, and the opposite surface side of the one surface side of the movable mirror is formed with a low reflectance.

  The variable wavelength optical filter according to claim 3 of the present invention is the variable wavelength optical filter according to claim 1 or 2, wherein slits (51A to 51C) are formed at outer edges of the movable mirror.

  As described above, the wavelength tunable optical filter of the present invention transmits the rotational force applied to the rotating plate indirectly to the movable mirror via the hinge without directly applying force to the movable mirror itself. The mirror is less likely to be distorted, and good selection characteristics can be maintained.

  Further, by bringing the rotation center of the rotation plate closer to the electrode side, the amount of movement on the tip side can be increased, and a large wavelength change can be given by low voltage driving.

  In addition, since the slit is formed in the outer edge portion of the movable mirror, it is possible to prevent the mirror from warping due to the deposition of the AR film or the HR film, and to obtain better selection characteristics.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 6 show a structure of a Fabry-Perot variable wavelength optical filter 20 (hereinafter simply referred to as an optical filter 20) having a MEMS structure to which the present invention is applied.

  In these drawings, the optical filter 20 has a structure in which a first substrate 21 and a second substrate 31 having the same outer shape (in this example, a square) and having translucency are overlapped.

The first substrate 21 and the second substrate 31 are formed by etching and vapor deposition on a two-layer SOI substrate having an insulating layer 101 made of silicon oxide (SiO ₂ ) and a conductive layer 102 made of silicon (Si). ing.

  A fixed mirror 22 is formed at the center of the first substrate 21. The fixed mirror 22 is composed of a conductive layer 102 left circularly by etching on the surface side (second substrate 31 side) of the first substrate 21, and a dielectric multilayer film or the like deposited on the surface in a circular shape. A highly reflective film 23 (hereinafter referred to as HR film 23) and a low reflectivity film 24 (hereinafter referred to as AR film 24) formed by vapor deposition on the back side of the conductive layer 102 at a position overlapping the HR film 23. It is comprised by.

  As shown in FIGS. 4 to 6, the central portion of the insulating layer 101 of the first substrate 21 where the fixed mirror 22 is formed is removed in a circular shape by etching to form a hole 21 a. Yes.

  On the other hand, the second substrate 31 is integrally formed with a movable mirror 32 and a mechanism for moving the movable mirror 32.

  That is, in the center of the second substrate 31, a circular hole 31a formed concentrically with the fixed mirror 22 when overlapped with the first substrate 21, and the second substrate around the circular hole 31a. A plurality (three in this example) of rectangular holes 31b to 31d extending radially and rectangularly to the outer edge of 31 are formed. The rectangular holes 31b to 31d are formed with an interval of 120 degrees with respect to the center of the circular hole 31a.

  A circular movable mirror 32 is concentrically disposed inside the circular hole 31a. The movable mirror 32 includes a conductive layer 102 left in a circle by the etching process, an HR film 33 deposited in a circle on the lower surface side (first substrate 21 side), and an AR film deposited in a circle on the opposite surface. 34.

  Extending in the direction of the respective rectangular holes 31b to 31d, one end side of the hinges 35A to 35C having flexibility is connected to the outer periphery of the movable mirror 32 in the length direction and the direction orthogonal thereto.

  The other end sides of the hinges 35A to 35C are connected to the tips of the rotation plates 41A to 41C arranged at the central portions of the rectangular holes 31b to 31d, respectively.

  Each of the rotating plates 41A to 41C is formed in a rectangular shape whose center line coincides with the rectangular holes 31b to 31d, and one end side of the hinges 35A to 35C is connected to the center of the tip side.

  Further, both side edges of each of the rotating plates 41A to 41C are orthogonal to a line from the center of the movable mirror 32 toward the outer edge of the second substrate 31, and different positions of the outer edges of the rectangular holes 31b to 31d (rectangular holes 31b to 31b). 31d) is supported by the tip of a pair of shafts 42A, 43A, 42B, 43B, 42C, and 43C that extend inward so as to form a straight line and can be torsionally deformed in the length direction. , 43A to 43C can be turned around.

Electrode portions 45A to 45C are formed at the rear ends of the rotating plates 41A to 41C.
In the electrode portions 45A to 45C, a plurality of electrodes 46 extending in parallel at intervals in a comb shape toward the back end direction of the rectangular holes 31b to 31d are formed. Here, for convenience of illustration, the number of the electrodes 46 is three, but in reality, it is desirable to provide more, and this is the same for the electrode 49 described later.

  On the other hand, on the surface side of the conductive layer 102 of the second substrate 31, electrode plates 48A to 48C having conductivity are provided via insulating plates 47A to 47C at positions near the back end portions of the rectangular holes 31b to 31d. ing.

  Each of the electrode plates 48A to 48C is formed with a plurality of electrodes 49 extending in a comb-like shape in the direction of the rotation plates 41A to 41C with a width and interval that enter the gaps of the electrodes 46 of the rotation plates 41A to 41C. ing.

  Here, the movable mirror 32, the hinges 35A to 35C, the rotating plates 41A to 41C, the shafts 42A to 42C, 43A to 43C, and the electrode portions 45A to 45C are formed of the conductive layer 102 of the second substrate 31, and the electrodes The plates 48A to 48C are in a state of being insulated from the conductive layer 102 at positions higher by the thickness of the insulating plates 47A to 47C.

  In the optical filter 20 having the above structure, mirrors are driven by the hinges 35A to 35C, the rotating plates 41A to 41C, the shafts 42A to 42C, 43A to 43C, the electrode portions 45A to 45C, the electrode plates 48A to 48C, and the control circuit 60. And the part excluding the control circuit 60 is a drive mechanism.

  In the optical filter 20 configured as described above, as shown in FIG. 3, the control circuit 60 applies DC voltages Va to Vc to the electrode plates 48A to 48C with reference to the conductive layer 102 of the second substrate 31. By applying, the distance between the fixed mirror 22 and the movable mirror 32 can be changed, and a selection characteristic corresponding to the designated selection wavelength information can be given.

  That is, when no DC voltage is applied to each of the electrode plates 48A to 48C, as shown in FIG. 7A, the distance of the movable mirror 32 to the fixed mirror 22 is the thickness of the HR film and the AR film. Is neglected, the thickness of the conductive layer 102 is subtracted from the thickness of the insulating layer 101 of the second substrate 31. In this state, both mirrors are in a parallel state by design, and in this state, the fixed mirror 22 The spectrum of the light P1 emitted from the movable mirror 32 when the broadband light P0 is incident from the lower surface side of FIG. 8 is an interval Δλ determined by the distance between the fixed mirror 22 and the movable mirror 32, as shown in FIG. It becomes a peak at each wavelength λ1, λ2,.

  For example, by applying the same voltage having an absolute value greater than zero volts to each of the electrode plates 48A to 48C, the electrodes 49A to 48C and the electrodes 46 of the rotating plates 41A to 41C are electrostatically connected. As shown in FIG. 7B, each of the rotating plates 41 </ b> A to 41 </ b> C rotates about the shafts 42 </ b> A to 42 </ b> C and 43 </ b> A to 43 </ b> C in a direction in which the tip side approaches the first substrate 21. .

  For this reason, the movable mirror 32 supported via the hinges 35A to 35C on the front end sides of the respective rotating plates 41A to 41C moves while maintaining a parallel state on the fixed mirror 22 side. At this time, the distance from the tip of each of the rotating plates 41A to 41C to the edge of the movable mirror 32 increases, but the hinges 35A to 35C extend due to the tension generated therebetween, so that the movable mirror 32 moves smoothly, It stops in a state where the attractive force generated between the electrodes 46 and 49 and the return force depending on the spring constants of the shafts 42A to 42C, 43A to 43C and the hinges 35A to 35C are balanced.

  When the broadband light P0 is incident from the lower surface side of the fixed mirror 22 in a state where the distance between the fixed mirror 22 and the movable mirror 32 is thus reduced, the spectrum of the light P2 emitted from the movable mirror 32 is as shown in FIG. As shown in (b), peaks occur at the wavelengths λ1 ′, λ2 ′,... At intervals Δλ ′ smaller than Δλ.

  Further, in the optical filter 20 having this structure, the rotational force given to the rotating plates 41A to 41C is transmitted to the movable mirror 32 via the hinges 35A to 35C without directly applying force to the movable mirror 32 itself. Therefore, the movable mirror 32 is hardly distorted, and good selection characteristics can be maintained.

  Furthermore, by moving the rotation center of the rotation plates 41A to 41C closer to the electrode side, the amount of movement on the tip side can be increased, and a large wavelength change can be given by low voltage driving.

  In addition, the parallelism of the movable mirror 32 with respect to the fixed mirror 22 slightly changes due to variations in the spring constants of the hinges 35A to 35C and the shafts 42A to 42C and 43A to 43C. This can be dealt with by finely adjusting the DC voltages Va to Vc applied to the plates 48A to 48C in accordance with the designated selection wavelength.

  In this embodiment, the movable mirror 32 is supported from three directions by the three rotary plates 41A to 41C via the hinges 35A to 35C. However, the drive mechanism including the rotary plate around the movable mirror 32. Four or more sets may be provided at equal intervals.

  In this embodiment, the rotating plate 41 is driven in the direction in which the movable mirror 32 is brought closer to the fixed mirror 22, but the electrode plate 48 is placed on the lower surface side (first substrate 21 side) of the second substrate 31. By disposing, the rotating plate 41 can be driven in a direction to move the movable mirror 32 away from the fixed mirror 22.

  Further, when an HR film or an AR film is deposited on the surface of the movable mirror 32, the outer edge portion may be warped and the parallelism may be lowered. In such a case, as shown in FIG. Thus, by forming the slits 51 </ b> A to 51 </ b> C at the outer edge portion of the movable mirror 32, it is possible to prevent the mirror from warping and to obtain better selection characteristics.

  Further, the shape of the mirrors 22 and 32 and the shape of the holes 31a to 31d of the second substrate 31 are not limited to the above embodiment, and various modifications can be made.

  In the above description, the AR film is formed on the surface of the fixed mirror 22 and the movable mirror 32 opposite to the surface on which the HR film is formed. However, the present invention is not limited to this. The structure in which the film | membrane is not formed may be sufficient. Even with this configuration, the level of the spectrum of the incident broadband light is only slightly reduced, and good selection characteristics can be obtained.

A perspective view of an embodiment of the present invention Exploded perspective view of the embodiment Plan view of the embodiment Back view of the embodiment A1-A2 cross-sectional view of FIG. A1-A3 cross-sectional view of FIG. Schematic for explaining the operation of the embodiment Wavelength selection characteristic diagram of the embodiment The figure which shows the example which provided the slit in the outer edge of a movable mirror Schematic cross-sectional view for explaining the configuration and operation of a conventional device

Explanation of symbols

  20... Tunable optical filter, 21... First substrate, 22... Fixed mirror, 23... HR film, 24... AR film, 31. Membrane, 34 ... AR membrane, 35A-35C ... Hinge, 41A-41C ... Rotating plate, 42A-42C, 43A-43C ... Shaft, 45A-45C ... Electrode section, 46 ... Electrode, 47A- 47C: Insulating plate, 48A to 48C ... Electrode plate, 49 ... Electrode, 51A to 51C ... Slit, 60 ... Control circuit

Claims (3)

A first substrate (21) having translucency;
A fixed mirror (22) formed on the first substrate and having one surface side formed with high reflectivity;
A second substrate (31) having translucency and disposed in a state of facing the first substrate in parallel;
A movable mirror (32) formed on the second substrate, the one side of which is formed with high reflectivity, and the high reflectivity surface is opposed to the high reflectivity surface of the fixed mirror;
In the wavelength tunable optical filter having a mirror driving unit that moves the movable mirror in a direction in which the distance to the fixed mirror changes, and changes a wavelength of light transmitted between the fixed mirror and the movable mirror,
The movable mirror is disposed inside holes (31a to 31d) formed in the second substrate,
The mirror driving means includes
A pair of pairs that are orthogonal to a line from the center of the movable mirror toward the outer edge of the second substrate and extend inward to form a straight line from different positions of the outer edge of the hole, and are twistable in the longitudinal direction. Shafts (42, 43);
A rotating plate (41) disposed inside the hole, the outer edge of which is connected to the distal ends of the pair of shafts, and is supported rotatably about the pair of shafts;
A flexible hinge (35) for connecting between the outer edge of the movable mirror and one end of the rotating plate;
Electrodes (46, 49) for applying a voltage between the other end side of the rotating plate and the outer edge of the second substrate to apply a turning force about the axis to the rotating plate. A set of drive mechanisms,
A variable wavelength optical filter, wherein three or more sets of the drive mechanisms are provided at equal intervals around the movable mirror.   2. The variable wavelength light according to claim 1, wherein an opposite surface side of the one surface side of the fixed mirror is formed with a low reflectance, and an opposite surface side of the one surface side of the movable mirror is formed with a low reflectance. filter.   The variable wavelength optical filter according to claim 1 or 2, wherein slits (51A to 51C) are formed in an outer edge portion of the movable mirror.

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