JP4352373B2 - Fabry-Perot filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Fabry-Perot filter that selectively transmits light of any desired wavelength.
[0002]
[Prior art]
A Fabry-Perot filter is an optical filter in which a gap is formed between a fixed mirror and a movable mirror with high reflectivity and face each other. The movable mirror is displaced in the direction of the fixed mirror to change the size of the gap. The wavelength corresponding to the size of the gap is selected and transmitted.
[0003]
In a Fabry-Perot filter designed to operate at a specific center wavelength λ, the thickness d of each of the multilayer optical films constituting the fixed mirror and the movable mirror is λ / 4 = nd (n: refraction Rate).
The Fabry-Perot filter selects and transmits the light wavelength λ ′ that satisfies the condition 2nD = Nλ ′ (n: refractive index, N: integer, D: gap size).
[0004]
2A and 2B are longitudinal sectional views of a conventional Fabry-Perot filter.
2A and 2B, 20 is a Si substrate, 21 is a fixed mirror, and is formed of a multilayer optical thin film made of SiO 2 / TiO 2 or the like formed on the Si substrate 20.
Reference numeral 22 denotes a movable mirror disposed to face the fixed electrode, and is composed of a multilayer optical thin film made of, for example, SiO2 / TiO2.
[0005]
Reference numeral 23 denotes a fixed electrode formed on the fixed mirror 21 so that the central portion of the fixed mirror 21 is exposed as the optically active region 24, and is made of, for example, an Au film.
A support film 25 supports the movable mirror 22 and is connected to the fixed electrode 23 via spacers 26 a and 26 b made of polyimide for forming a gap between the fixed mirror 21 and the movable mirror 22.
The support film 25 is composed of a multilayer film of a movable electrode 25a made of an Al film and a SiN film 25b.
[0006]
Then, an arbitrary desired wavelength selection voltage (drive voltage) is applied between the fixed electrode 23 and the movable electrode 25a to generate an electrostatic force, thereby driving the movable mirror 22 so that the fixed mirror 21 and the movable mirror 22 can be driven. By changing the size of the gap to be formed, the Fabry-Perot filter selectively transmits light having an arbitrary desired wavelength corresponding to the size of the gap.
[0007]
In manufacturing the Fabry-Perot filter, a multilayer optical thin film constituting the fixed mirror 21 is deposited on the Si substrate 20, and then an Au film serving as the fixed electrode 23 is vapor-deposited, and then the central portion of the Au film is removed by etching. Thus, the optically active region 24 is formed. Then, after applying polyimide on the front surface as the spacers 26a and 26b, the Al film 25a and the SiN film 25b as the support film 25 are deposited, the central portion is removed by etching, and the multilayer optical that becomes the movable mirror 22 at the removed central portion. A thin film is deposited and supported by the support film 25.
Then, the polyimide is etched away leaving the spacers 26a and 26b, and an air gap structure is produced.
[0008]
When the Fabry-Perot filter is used for optical communication, for example, as shown in FIG. 2B, the optical fibers 27a and 27b are arranged above and below the Fabry-Perot filter, and the light incident from the optical fiber 27a is transmitted by the Fabry-Perot filter. The wavelength is selected and emitted to the optical fiber 27b.
[0009]
[Patent Document 1]
JP-A-7-243963 [Patent Document 2]
Japanese Patent Laid-Open No. 2000-162516
[Problems to be solved by the invention]
However, such a Fabry-Perot filter has the following problems.
(1) Since the movable mirror is supported by the support film, the movable mirror is warped due to the stress of the Si substrate, the stress of the movable mirror, etc., and the movable mirror is used to control the optical performance (half width, etc.). It is difficult to increase the number of layers of the multilayer optical thin film to be configured.
(2) Since TiO2 constituting the movable mirror is chemically stable, patterning is difficult, and when the movable mirror is formed, it is necessary to use a lift-off, use a hard mask at the time of vapor deposition, and the manufacturing process is restricted.
(3) Since it is arranged in a direction perpendicular to the substrate, its alignment is difficult.
[0011]
The present invention has been made to solve the above-mentioned problems, and provides a Fabry-Perot filter that can be easily manufactured and easily aligned with an optical fiber while reducing the number of layers of the multilayer optical thin film. Objective.
[0012]
[Means for Solving the Problems]
In claim 1 of the present invention,
In a Fabry-Perot filter that has a fixed mirror and a movable mirror that is opposed to the fixed mirror with a variable size gap, and selectively transmits light of any desired wavelength corresponding to the gap,
The fixed mirror is formed by photo-etching the single crystal silicon layer on an SOI substrate in which the single crystal silicon layer is formed on the single crystal silicon substrate via an insulating film,
The movable mirror is formed in a hollow beam shape floating on the SOI substrate by photo-etching the insulating film and the single crystal silicon layer on the SOI substrate, and in the surface direction of the SOI substrate. Placed opposite the fixed mirror,
In the single crystal silicon layer, a mirror forming portion and a fixed portion are formed separately from each other by photoetching, and the fixed mirror and the fixed mirror are opposed to each other through an air gap. The movable mirror is formed as
A plurality of comb-shaped portions intersect each other in a direction parallel to the arrangement direction of the fixed mirror and the movable mirror so that the movable mirror is sandwiched between the end faces facing each other at a predetermined distance between the fixed portion and the mirror forming portion. Are placed opposite to each other,
The movable mirror is driven in the direction of the surface of the SOI substrate by the electrostatic force applied between the opposing portions separated by applying a driving voltage between the mirror forming portion and the fixed portion 3, and the gap is made variable. It is characterized by that.
[0013]
According to a second aspect of the present invention, in the Fabry-Perot filter according to the first aspect, the fixed mirror and the movable mirror have silicon portions and gap portions that are alternately arranged in a plane direction of the single crystal silicon substrate. This is a Fabry-Perot filter.
[0014]
According to a third aspect of the present invention, in the Fabry-Perot filter according to the first aspect, at least one optical fiber is provided such that an end surface thereof is disposed opposite to the fixed mirror or the movable mirror in the surface direction of the SOI substrate. This is a Fabry-Perot filter.
[0015]
In claim 4 of the present invention,
2. The Fabry-Perot filter according to claim 1, wherein any one of the optical fibers is replaced with an edge emitting laser.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1A is a top view illustrating a configuration of a Fabry-Perot filter according to the present invention, and FIG. 1B is a cross-sectional view taken along line AA ′ of FIG.
[0017]
1A and 1B, a Fabry-Perot filter uses a semiconductor manufacturing technique to micromachine a SOI substrate 1 in which a single crystal silicon layer 1c is formed on a single crystal silicon substrate 1a via an insulating film 1b. It is formed by doing. In this case, the single crystal silicon layer 1c is highly doped with impurities and has conductivity.
[0018]
In the single crystal silicon layer 1c, the mirror forming part 2 and the fixed part 3 are formed separately from each other by photoetching, and the mirror forming part 2 is movable so as to be opposed to the fixed mirror 4 via the air gap g. A mirror 5 and comb-shaped portions 6a and 6b are formed.
[0019]
The fixed mirror 4 includes a silicon part 4a, a gap part 4b, a silicon part 4c, a gap part 4d, and a silicon part 4e. The silicon part 4a, the gap part 4b, the silicon part 4c, the gap part 4d, and the silicon part 4e are made of SOI. The single crystal silicon layers 1c on the substrate 1 are formed by photoetching, and are alternately arranged in the plane direction of the single crystal silicon substrate 1a.
[0020]
The movable mirror 5 includes a silicon part 5a, a gap part 5b, a silicon part 5c, a gap part 5d, a silicon part 5e, and connection parts 5f and 5g. The silicon part 5a, the gap part 5b, the silicon part 5c, the gap part 5d, The silicon portion 5e and the connection portions 5f and 5g are formed in a hollow beam shape floating from the single crystal silicon substrate 1a by photoetching the insulating film 1b and the single crystal silicon layer 1c, and are formed in the plane direction of the single crystal silicon substrate 1a. Alternatingly arranged.
[0021]
In this case, the silicon parts 5a, 5c, 5e are connected to each other by the connection parts 5f, 5g, the silicon part 5a is fixed at both ends of the end parts 7a, 7b, and the comb parts 6a, 6b are connected to the connection parts 5f, 5g. They are formed between the portions 7a and 7b in a state of floating from the single crystal silicon substrate 1a.
An air gap g is formed between the silicon portion 4e of the fixed mirror 4 and the silicon portion 5a of the movable mirror 5 by etching.
[0022]
Further, comb mold parts 8a and 8b are formed in the fixing part 3, and the comb mold parts 8a and 8b are arranged to face each other in a state of intersecting with the comb mold parts 6a and 6b of the mirror forming part 2, respectively. The mirror forming parts are spaced apart by a predetermined distance.
[0023]
The optical fiber 9a is embedded in a groove provided in the mirror forming portion 2, and is fixed to the silicon portion 4a of the fixed mirror 4 with one end face thereof facing the fixed mirror 4 in the surface direction of the SOI substrate 1. The optical fiber 9b is embedded and fixed in a groove provided in the fixed portion 3 with one end face of the optical fiber 9b facing the movable mirror 5 in the surface direction of the SOI substrate 1.
In this case, the fixed mirror 4 and the movable mirror 5 are arranged on a line connecting the central axes of the optical fibers 9a and 9b.
[0024]
By the way, in the Fabry-Perot filter designed to operate at a specific center wavelength λ, the silicon portions 4a, 4c, 4e, 5a, 5c, 5e and the gap portions 4b, 4d constituting the fixed mirror 4 and the movable mirror 5 are used. , 5b, 5d are manufactured so as to satisfy the condition of λ / 4 = nd (n: refractive index).
The Fabry-Perot filter selects and transmits the light wavelength λ ′ that satisfies the condition 2nD = Nλ ′ (n: refractive index, N: integer, D: gap size).
[0025]
Since the refractive index of silicon is about 3.4 and the refractive index of air is 1, when using light with an optical communication wavelength of about 1.5 μm, the thickness of the silicon portion (high refractive index) is about 108 nm, The thickness of the gap (low refractive index) is about 374 nm.
[0026]
However, since the core diameter of the optical fiber is about 10 μm, the thickness of the silicon portions 4a, 4c, 4e, 5a, 5c, and 5e is about 108 nm, and the thickness of the gap portions 4b, 4d, 5b, and 5d is about 374 nm. Manufacturing is difficult in terms of manufacturing technology.
Therefore, the thickness of the silicon portions 4a, 4c, 4e, 5a, 5c, and 5e is about 972 nm (9 times 108 nm), and the thickness of the gap portions 4b, 4d, 5b, and 5d so that the line and space is about 1 um. The thickness is designed to be about 1122 nm (3 times 374 nm).
[0027]
Although the structure as described above can be formed by using dry etching, anisotropic etching (wet etching) is performed using an SOI substrate in which the plane orientation of the single crystal silicon layer 1c is the (110) direction. ), A similar structure can be created.
[0028]
Next, the operation of the Fabry-Perot filter shown in FIG. 1 will be described.
When a driving voltage V is applied between the mirror forming part 2 and the fixed part 3, an electrostatic force is applied between the two opposing parts, and the movable mirror 5 is shifted in the direction of the optical fiber 9b, and the air gap g The size changes (becomes larger).
[0029]
In this case, the magnitude of the electrostatic force is proportional to the size of the area where the mirror forming portion 2 and the fixing portion 3 face each other, and the comb-shaped portions 8a and 8b of the fixing portion 3 are comb-shaped portions 6a and 6a of the mirror forming portion 2, respectively. Since the two are opposed to each other so as to cross 6b, the area where the two are opposed to each other is large, and the driving force of the movable mirror 5 can be increased.
[0030]
The light input from the optical fiber 9a has a wavelength selected according to the size of the air gap g, passes through the Fabry-Perot filter, and is output to the optical fiber 9b.
[0031]
Then, the desired voltage corresponding to the size of the air gap g is controlled by controlling the drive voltage V applied between the mirror forming portion 2 and the fixed portion 3 to control the size of the air gap g to an arbitrarily desired size. Can be selected and output by a Fabry-Perot filter.
[0032]
In such a Fabry-Perot filter, the fixed mirror 4 and the movable mirror 5 as optical thin films are formed with a structure in which silicon and air having a large refractive index difference are alternately arranged, so that a conventional TiO2 film and SiO2 film are combined. Compared with this structure, an optical thin film having a high reflectance can be obtained without increasing the number of layers.
[0033]
Further, since the alignment between the optical fiber and the Fabry-Perot filter is performed in the lateral direction (the surface direction of the SIO substrate 1) instead of the conventional vertical direction, the alignment accuracy can be easily increased.
[0034]
Moreover, since the Fabry-Perot filter as described above does not use TiO 2 that is difficult to pattern, it is excellent in consistency with the silicon manufacturing process and can be easily manufactured.
[0035]
In addition, by forming a plurality of Fabry-Perot filters as described above, such as two cavities and three cavities, between the optical fiber 9a and the optical fiber 9b, the entire half-value width is increased. A Fabry-Perot filter with improved characteristics can be obtained.
[0036]
Further, by replacing one of the optical fibers 9a and 9b with an edge emitting laser, the Fabry-Perot filter can be used as a wavelength tunable laser.
[0037]
【The invention's effect】
As described above, according to the present invention, since the optical thin film (fixed mirror and movable mirror) is formed with a structure in which silicon and air having a large refractive index difference are alternately arranged, the TiO2 film and the SiO2 film are combined. Compared to the conventional structure, an optical thin film having a high reflectance can be obtained without increasing the number of layers.
[0038]
Further, according to the present invention, since the alignment between the optical fiber and the Fabry-Perot filter is performed in the horizontal direction (the surface direction of the SIO substrate 1), the alignment accuracy can be increased.
[0039]
Further, according to the present invention, since TiO 2 that is difficult to pattern is not used and only silicon is processed, it is excellent in consistency with the silicon manufacturing process and can be easily manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a Fabry-Perot filter according to the present invention.
FIG. 2 is a longitudinal sectional view of a conventional Fabry-Perot filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 SOI substrate 1a Single crystal silicon substrate 1b Insulating film 1c Single crystal silicon layer 2 Mirror formation part 3 Fixed part 4 Fixed mirror 4a, 4c, 4e Silicon part 4b, 4d Gap part 5 Movable mirrors 5a, 5c, 5e Silicon part 5b, 5d Gap part 6a, 6b Comb type part 7a, 7b End part 8a, 8b Comb type part 9a, 9b Optical fiber g Air gap

Claims (4)

In a Fabry-Perot filter that has a fixed mirror and a movable mirror that is opposed to the fixed mirror with a variable size gap, and selectively transmits light of any desired wavelength corresponding to the gap,
The fixed mirror is formed by photo-etching the single crystal silicon layer on an SOI substrate in which the single crystal silicon layer is formed on the single crystal silicon substrate via an insulating film,
The movable mirror is formed in a hollow beam shape floating on the SOI substrate by photo-etching the insulating film and the single crystal silicon layer on the SOI substrate, and in the surface direction of the SOI substrate. Placed opposite the fixed mirror,
In the single crystal silicon layer, a mirror forming portion and a fixed portion are formed separately from each other by photoetching, and the fixed mirror and the fixed mirror are opposed to each other through an air gap. The movable mirror is formed as
A plurality of comb-shaped portions intersect each other in a direction parallel to the arrangement direction of the fixed mirror and the movable mirror so that the movable mirror is sandwiched between the end faces facing each other at a predetermined distance between the fixed portion and the mirror forming portion. Are placed opposite to each other,
The movable mirror is driven in the direction of the surface of the SOI substrate by the electrostatic force applied between the opposing portions separated by applying a driving voltage between the mirror forming portion and the fixed portion 3, and the gap is made variable. Fabry-Perot filter characterized by that. The Fabry-Perot filter according to claim 1,
The Fabry-Perot filter, wherein the fixed mirror and the movable mirror have silicon portions and gap portions that are alternately arranged in the plane direction of the single crystal silicon substrate. The Fabry-Perot filter according to claim 1,
A Fabry-Perot filter characterized in that at least one optical fiber is provided so that an end surface thereof is disposed to face the fixed mirror or the movable mirror in the surface direction of the SOI substrate. The Fabry-Perot filter according to claim 1,
A Fabry-Perot filter, wherein one of the optical fibers is replaced with an edge emitting laser .

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