JP2010211032A - Parallel translation mirror and optical module using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a parallel translation mirror which is stably translated in parallel with excellent reproducibility, and to provide optical modules such as a variable wavelength optical filter and a variable wavelength light source which have a stable wavelength bandwidth by using the parallel translation mirror. <P>SOLUTION: The parallel translation mirror includes: a base 1 which has a through-hole 2 for the incidence of light; a movable layer 4 facing the base 1; an insulating layer 3 which connects the base 1 and the movable layer 4, which are electrically separated, gives a gap of a predetermined distance between both components, and is disposed not intersecting with the optical path of the light incident from the through-hole 2; an oscillation part 6 formed in the movable layer 4 and composed of a membrane 41 positioned above the through-hole 2 and a movable mirror 5 formed on the surface opposite to the base 1 of the membrane 41; a driving device 10 which oscillates an oscillation part 6 at a frequency equal to the resonant frequency f of the oscillation part 6; a metallic weight part 7 which is formed on the membrane 41 except the part on which the movable mirror 5 is formed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a translation mirror and an optical module such as a wavelength tunable optical filter and a wavelength tunable light source using the translation mirror.

  A wavelength tunable optical filter or a wavelength tunable light source is used as a wavelength sweeping means for a fiber sensing light source such as an optical communication line or optical communication device test or an FBG (Fiber Bragg Grating) sensor.

  Among these types of filters and light sources, Fabry-Perot type tunable optical filters and tunable light sources using them are limited to a narrow range, but themselves are very small. It has the feature that it can.

  For this reason, a Fabry-Perot type tunable optical filter comprising a pair of mutually opposing reflecting surfaces of a membrane 140 and a concave opposing mirror 160 as shown in FIG. 8 has been proposed (see, for example, Patent Document 1). This wavelength tunable optical filter performs filtering by displacing the membrane 140 and changing the gap length 180 by electrostatic attraction generated by applying a voltage between the electrode 120 and the membrane 140 from the variable voltage source 220. The wavelength of light can be changed.

  FIG. 9 shows an example of the membrane structure. The membrane 140 is composed of a flat plate portion 34F constituting one reflecting surface of a Fabry-Perot filter and a spring portion 32F arranged around the flat plate portion 34F. The electrode 120 shown in FIG. 8 is arranged so as to face the portion where light does not pass on the flat plate portion 34F, and an electrostatic attractive force for displacing the flat plate portion 34F is generated.

  In order to realize a wavelength tunable light source, a semiconductor laser may be disposed instead of the counter mirror 160 in FIG. 8 and an external resonator may be formed between the semiconductor laser and the membrane 140.

  In any case of these filters and light sources, since the parallelism of the membrane 140 and the counter mirror 160 determines their characteristics, a high parallelism is required for the movement of the membrane 140. This is because if the parallelism of the membrane is lowered, the filter characteristic is deteriorated in the case of a filter, and the wavelength of output light becomes unstable in the case of a light source.

US Pat. No. 6,373,632

  However, it is difficult to displace the membrane which is a movable part with high parallelism. As already mentioned, in conventional filters, etc., the membrane is moved in parallel by electrostatic attraction. However, the parallelism is not always maintained due to nonuniformity in applied voltage and changes in elasticity of the membrane over time. I don't mean. In order to maintain parallelism, it is conceivable to use multiple electrodes and adjust the voltage applied to each electrode pair. However, there is a problem that the method of controlling the applied voltage for each electrode is complicated. For this reason, high-speed parallel movement, that is, high-speed wavelength sweep is difficult. In addition, these conventional structures are capable of DC driving and are designed to respond to a wide range of frequencies, so that they are not only susceptible to external mechanical vibrations but also susceptible to electrical noise. there were.

  As a method for avoiding these problems, it is conceivable to operate the filter at a resonance frequency determined by the movable part including the membrane. If a vibration mode in which the membrane moves in parallel can be used, stable translation with extremely good reproducibility can be realized. In addition, such a structure is resistant to disturbances such as mechanical vibration and electrical noise.

  However, in order to realize such stable translation, the resonance Q value must be set high. A high Q value means that much of the energy applied to the membrane is concentrated in a particular vibration mode of translational displacement and other vibration modes are suppressed.

  However, the conventional filter or the like has a very low Q value, and it is impossible to realize a stable translation even when operated at a resonance frequency.

  The present invention has been made in order to solve such a conventional problem, and realizes a translation mirror that is capable of stable translation with good reproducibility, and uses the translation mirror to provide light. An object of the present invention is to provide an optical module such as a wavelength tunable optical filter having stable transmission characteristics and a wavelength tunable light source having stable output light characteristics.

  The translation mirror of the present invention includes a base having a through-hole for allowing light to enter, a movable layer facing the base, and the base and the movable layer being connected in an electrically separated state. An insulating layer arranged to give a gap of a predetermined distance between the two and not to intersect the optical path of the light incident from the through hole, and a movable thin film formed in the movable layer and positioned on the through hole And an electrostatic attractive force between the base and the movable layer at a period equal to the resonance frequency of the vibration part, and a vibration part formed of a movable mirror formed on a surface of the movable thin film opposite to the base A drive device that vibrates the vibration part by generating the vibration part, the vibration part further comprises a weight part made of a metal formed on the movable thin film excluding a place where the movable mirror is formed, The movable mirror is It has a structure that vibrates at the resonant frequency while maintaining a degree.

  With this configuration, by providing the weight part for increasing the Q value of resonance of the vibration part, it is possible to realize stable parallel movement with good reproducibility.

The translation mirror of the present invention has a configuration in which an elastically deformable support portion for supporting the movable thin film is formed in the movable layer.
With this configuration, the movable layer is easily deformed, so that the vibration width of the movable mirror can be expanded.

  Moreover, the translation mirror of this invention may have the structure by which the reflective surface of a movable mirror is concave shape.

  An optical module according to the present invention includes any one of the above-described translation mirrors, a counter plate facing the translation mirror, a fixed mirror formed at a position facing the movable mirror on the counter plate, and the movable mirror The mirror and the counter plate are connected to each other, and a gap of a predetermined distance is provided between the two and the gap layer is disposed so as not to intersect the light incident from the through hole. .

  With this configuration, an optical module such as a wavelength tunable optical filter having stable light transmission characteristics can be realized by using any one of the above-described translation mirrors.

The optical module of the present invention has a configuration including a semiconductor laser instead of the fixed mirror.
With this configuration, an optical module such as a wavelength tunable light source having stable output light characteristics can be realized by using any one of the above-described translation mirrors.

  The present invention realizes a translating mirror capable of stable translation with good reproducibility, and using the translating mirror, a wavelength tunable optical filter with stable light transmission characteristics and a wavelength tunable with stable output light characteristics. An optical module such as a light source is provided.

Sectional drawing which shows the 1st Embodiment of this invention Top view and cross-sectional view showing a structural example of the vibration part Top view showing another structural example of the vibration part Sectional drawing which shows a part of manufacturing process of the 1st Embodiment of this invention. Sectional drawing which shows a part of manufacturing process of the 1st Embodiment of this invention. Sectional drawing which shows the 2nd Embodiment of this invention Sectional drawing which shows the other structural example of the 2nd Embodiment of this invention. Sectional drawing which shows the structural example of the conventional wavelength tunable optical filter Sectional drawing which shows the structural example of the principal part of the conventional wavelength tunable optical filter

  Hereinafter, embodiments of a translation mirror and an optical module using the translation mirror according to the present invention will be described with reference to the drawings.

(First embodiment)
An embodiment of a translation mirror according to the present invention is shown in FIG. FIG. 1 is a cross-sectional view of the translation mirror 20 of the present embodiment.

  As shown in FIG. 1, the translation mirror 20 includes a base 1 having a through hole 2 for allowing light to enter, a movable layer 4 facing the base 1, and the base 1 and the movable layer 4 electrically. Are formed in the movable layer 4 and the insulating layer 3 disposed so as not to intersect the optical path of the light incident from the through hole 2. The vibration part 6 which consists of the movable mirror 5 formed on the surface opposite to the base 1 of the membrane 41 as a movable thin film located on the through-hole 2 and the membrane 41, and the resonance frequency f of the vibration part 6 And a driving device 10 that vibrates the vibration unit 6 at an equal cycle.

  The translation mirror 20 may further include an elastically deformable support portion 42 that is formed in the movable layer 4 and supports the membrane 41.

The base 1 and the movable layer 4 are made of, for example, Si, and the insulating layer 3 is made of, for example, SiO ₂ . Here, at least the movable layer 4 needs to be sufficiently transparent to incident light. The movable mirror 5 is made of a highly reflective (HR) coat of a dielectric multilayer film, and its reflecting surface may be concave or planar.

  The vibration part 6 is further provided with an annular weight part 7 formed on the membrane 41 other than the movable mirror 5 and for improving the Q value of resonance of the vibration part 6. The weight portion 7 is preferably made of a metal having a relatively high density such as Au. A metal such as Au can be easily deposited on the membrane 41 by vapor deposition, sputtering, plating, or the like.

  The drive device 10 responds to the resonance frequency f between the base 1 and the movable layer 4 by applying an AC voltage having a frequency equal to the resonance frequency f of the vibration unit 6 between the base 1 and the movable layer 4. An electrostatic attractive force is generated at the cycle. Thereby, the vibration part 6 can be vibrated with a large amplitude with a small electric power.

  2A and 2B are diagrams illustrating an example of the structure of the vibrating portion 6, in which FIG. 2A is a top view of the movable layer 4 and the vibrating portion 6, and FIG. 2B is an AA line in FIG. A cross section is shown. Another example of the structure of the vibration unit 6 is shown in FIG.

  As shown in these drawings, the structure of the vibration part 6 is complicated, and the resonance frequency f is determined by various parameters such as the shape and material of the membrane 41 and the weight part 7. Therefore, for the sake of simplicity, the role of the weight part 7 of the vibration part 6 will be described by replacing it with the simplest vibration system comprising a spring having a spring constant k and a weight m.

At this time, the resonance frequency f of the vibration part 6 is given by the following equation.

When the variable representing the resistance component generated in the vibration system is R, the resonance Q value is given by the following equation.

  As apparent from [Equation 2], in order to increase the Q value, the mass m or the spring constant k may be increased. Actually, in order to obtain a desired resonance frequency f, an appropriate combination of m and k matched with the resonance frequency may be selected, and f can be set to an arbitrary value from 10 Hz to several tens of kHz.

  As a means for increasing the spring constant, there is a method of increasing the layer thickness of the movable layer 4. Moreover, when the vibration part 6 has the support part 42, the shape of the support part 42 may be changed.

  Further, as a method of changing the mass m, a method of increasing the thickness of the movable layer 4 can be considered, but in this method, the spring constant k is also changed at the same time. For this reason, the mass m can be adjusted independently of the spring constant k by providing the weight portion 7 having an appropriate mass separately from the movable layer 4.

  Furthermore, if the weight portion 7 is made of a metal having a high density such as Au, the variable width of the mass m can be made larger than that of a metal having a low density, so that the selection range of the resonance frequency f and the Q value can be expanded.

  The resonance vibration mode that can be selected is not limited to one as long as the parallel movement of the vibration unit 6 is guaranteed.

  In addition, when a problem occurs in the processing accuracy of the membrane 41 or the support portion 42, a part of the weight portion 7 is trimmed with a laser or the like to balance the structure of the entire vibration portion 6 and the displacement is reduced. Parallelism can also be corrected. Thereby, a yield can be improved.

  In the above description, the driving device 10 vibrates the vibration part 6 by electrostatic attraction. However, a piezoelectric material is deposited on the support part 42 or the like, or the support part 42 itself is a piezoelectric material and a voltage is applied thereto. It is also possible to use mechanical vibrations generated by doing so. Moreover, the magnetic force by arbitrary combinations of a magnetic body, a magnet, and an electromagnet can also be used.

  Hereinafter, an example of a method for manufacturing the translation mirror 20 according to the present invention will be described with reference to the drawings.

First, a mask (not shown) is applied on the movable layer 4 of the SOI substrate shown in FIG. 4A, and a concave surface portion 4a is formed by etching (FIG. 4B). Here, the substrate 1 is made of Si, the insulating layer 3 is made of SiO ₂ , and the movable layer 4 is made of Si. In addition, you may form the concave surface part 4a by grinding | polishing etc. instead of an etching process.

  Next, a mask (not shown) is applied to the upper surface of the movable layer 4 having the concave surface portion 4a. And the support part 42 is formed in the movable layer 4 by an etching process (FIG.4 (c)).

  Next, an annular weight portion 7 made of a metal such as Au for improving the Q value of resonance is formed on the membrane 41 (FIG. 5A). Thereafter, the through hole 2 is formed by etching, and the insulating layer 3 in contact with the membrane 41 and the support portion 42 is removed by etching (FIG. 5B).

  The movable mirror 5 is formed by applying a high reflection (HR) coat to the concave surface portion 4a. Further, a non-reflective (AR) coat 8 is applied to the lower surface side of the membrane 41 (FIG. 5C). This AR coating 8 can suppress unnecessary reflection of light on the lower surface side of the membrane 41.

  The translation mirror 20 of the present embodiment configured as described above can be used as a movable mirror of various interferometers including a Michelson interferometer. Furthermore, if the mirrors are arranged in an array, the phase of light in the same beam cross section can be adjusted, so that it can also be used as a so-called beam profiler.

  Further, as will be described in the second embodiment, the translation mirror 20 of this embodiment can also be used as a movable mirror of a wavelength tunable optical filter or a wavelength tunable light source.

  As described above, the translation mirror according to the present embodiment includes the weight part for improving the resonance Q value of the vibration part, thereby realizing stable translation with good reproducibility.

(Second Embodiment)
Hereinafter, an embodiment of a wavelength tunable optical filter including the translation mirror 20 of the first embodiment will be described with reference to the drawings. Note that a description of the same configuration as in the first embodiment is omitted.

  As shown in FIG. 6, the tunable optical filter 50 according to the present embodiment connects the counter plate 12 facing the movable layer 4, the movable mirror 5, and the counter plate 12 in addition to the configuration of the first embodiment. In addition, a gap of a predetermined distance is provided between them, and the gap layer 11 is disposed so as not to intersect the light incident from the through hole 2 and the movable mirror 5 on the opposing plate 12 is opposed to the movable mirror 5. A fixed mirror 13.

The gap layer 11 is formed by, for example, curing an insulating layer such as SiO ₂ , an Si substrate, a glass plate, or an adhesive such as solder, epoxy, or acrylic used to fix the counter plate 12 on the movable layer 4. It may be. In the case of an adhesive, the curing method may be ultraviolet curing, thermal curing, or a combination thereof. The counter plate 12 needs to be sufficiently transparent to incident light. For example, in the case of light in a communication band such as a 1.5 μm band, Si can be used as a counter plate.

  As described in the first embodiment, since the AR coat 8 suppresses unnecessary light reflection on the lower surface side of the membrane 41, for example, a pair of the AR coat 8 is provided between the fixed mirror 13 and the lower surface side of the membrane 41. Formation of an optical wavelength filter composed of a mirror surface can be avoided, and the monochromaticity of light emitted from the wavelength tunable optical filter 50 can be improved.

  The fixed mirror 13 is made of, for example, an HR coat, and the reflection surface thereof may be concave or flat. When the reflecting surfaces of the movable mirror 5 and the fixed mirror 13 are both concave, the time during which light interferes in the optical filter constituted by the movable mirror 5 and the fixed mirror 13 is increased, so that the wavelength variable optical filter 50 This is particularly preferable because the monochromaticity of the emitted light is improved.

  In the wavelength tunable optical filter 50 of the present embodiment configured as described above, when an AC voltage having a frequency equal to the desired resonance frequency f is applied between the base 1 and the movable layer 4 by the driving device 10, it is movable. The membrane 41 having the mirror 5 vibrates at the resonance frequency f in the thickness direction of the wavelength tunable optical filter 50.

  At this time, the light incident from the through hole 2 of the base 1 passes through the membrane 41 and reciprocates in the optical filter constituted by the movable mirror 5 and the fixed mirror 13. Then, light having a wavelength corresponding to the distance between the movable mirror 5 that vibrates at the resonance frequency f and the fixed mirror 13 passes through the counter plate 12 and is emitted to the outside.

  Since the wavelength tunable optical filter 50 according to the present embodiment includes a translation mirror that is capable of stable translation with good reproducibility, the reproducibility of the filter characteristics for each sweep cycle of the resonance frequency f is extremely high, and the operation is stable. realizable.

  In this embodiment, the wavelength tunable optical filter 50 in which the fixed mirror 13 is formed on the counter plate 12 is taken as an example. However, as shown in FIG. 7, a semiconductor laser 14 such as a surface emitting laser is used instead of the fixed mirror 13. , A Fabry-Perot type wavelength-swept external resonator laser 60 can also be realized.

DESCRIPTION OF SYMBOLS 1 Base 2 Through-hole 3 Insulating layer 4 Movable layer 5 Movable mirror 6 Vibrating part 7 Weight part 10 Drive apparatus 11 Gap layer 12 Opposite plate 13 Fixed mirror 14 Semiconductor laser 20 Translation mirror 41 Membrane (movable thin film)
42 Supporting Section 50 Wavelength Tunable Optical Filter (Optical Module)
60 External cavity laser (optical module)

Claims (5)

A base (1) having a through hole (2) for allowing light to enter;
A movable layer (4) facing the base;
The insulating layer is arranged so that the base and the movable layer are connected in an electrically separated state, a gap of a predetermined distance is provided therebetween, and the optical path of the light incident from the through hole is not crossed. (3) and
A vibrating portion (6) comprising a movable thin film (41) formed in the movable layer and positioned on the through hole, and a movable mirror (5) formed on the surface of the movable thin film opposite to the base; ,
A drive device (10) that vibrates the vibration part by generating an electrostatic attractive force between the base and the movable layer at a period equal to the resonance frequency of the vibration part;
The oscillating portion further includes a weight portion (7) made of metal formed on the movable thin film excluding a portion where the movable mirror is formed, and the movable mirror is maintained at the resonance frequency while maintaining its parallelism. A translation mirror characterized by vibrating.   The translation mirror according to claim 1, wherein an elastically deformable support portion (42) for supporting the movable thin film is formed in the movable layer.   The translation mirror according to claim 1, wherein a reflecting surface of the movable mirror is concave. The translation mirror (20) according to any one of claims 1 to 3,
An opposing plate (12) facing the translation mirror;
A fixed mirror (13) formed at a position facing the movable mirror on the counter plate;
The movable mirror and the counter plate were connected, and a gap layer (11) was provided so as to give a gap of a predetermined distance between the movable mirror and the light incident from the through hole. An optical module characterized by   5. The optical module according to claim 4, further comprising a semiconductor laser (14) instead of the fixed mirror.

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