JP2003172886A - Optical attenuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an optical attenuator which is inexpensive and can operate fast and obtain a desired attenuation quantity and an arbitrary attenuation range even in an initial state without using a driving part such as a motor nor expensive optical crystal. <P>SOLUTION: The optical attenuator which attenuates and outputs input light is equipped with a Fabry-Perot filter which has a fixed mirror and a variable mirror arranged opposite to the fixed mirror across a gap and inputting the input light and varies the size of the gap by displacing the movable mirror to or away from the fixed mirror to output the input light as output light having been optionally attenuated to desired intensity corresponding to the size of the gap. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for adjusting the optical signal intensity of a DWDM (Dense Wavelength Division Multiplexing) system, an EDFA optical amplifier (erbium-doped fiber amplifier), an optical measuring device, etc. incorporated in an optical communication system. The present invention relates to an optical attenuator.

[0002]

2. Description of the Related Art FIG. 10 to FIG. 13 are schematic views showing the structure of a conventional optical attenuator. The optical attenuator shown in FIG. 10 mechanically obtains an attenuation effect, and collects the light incident from the optical fiber 30 by the collimator 31 and does not show the ND filter 32 having almost no wavelength dependence in the attenuation rate. It is mechanically driven by a stepping motor or the like to be attenuated to an arbitrary intensity, and emitted to the optical fiber 34 via the collimator 33.

The ND filter 32 is formed by forming filters having different light transmittances on a plate, and the transmittances are continuously different so as to obtain a continuous attenuation amount (for example, 0 to 15 dB) on the plate. When the filter is formed, a variable optical attenuator capable of selecting an arbitrary attenuation amount according to the position of the plate can be configured.

Also, a plurality of fixed attenuation values (for example, 5 dB,
10 dB, 15 dB). The ND filter 3 is formed by forming filters having different transmittances at a plurality of locations on the sea urchin plate.
In the case of configuring No. 2, it is possible to configure a fixed optical attenuator that obtains an arbitrary fixed attenuation amount according to the position of the plate.

The optical attenuator shown in FIG. 11 is a variable optical attenuator which obtains a thermo-optical attenuation effect, and two optical waveguides 3 are provided on a substrate 35 made of an optical crystal whose refractive index changes with temperature.
6a and 36b are provided to form a Mach-Zehnder interferometer structure, and one optical waveguide 36a is heated by the control electrode 37 to obtain an optical path difference. The light incident from the optical fiber 30 is emitted to the optical fiber 34 via the optical waveguides 36a and 36b, and the output light is attenuated depending on the optical path difference caused by the temperature difference.

The optical attenuator shown in FIG. 12 is a variable optical attenuator that obtains a light attenuating effect by using an electro-optical element whose refractive index changes by energizing. 38 is LiNbO2
The light incident from the optical fiber 30 and condensed by the collimator 31 is attenuated to an arbitrary light intensity via the electro-optical element 38 and emitted to the optical fiber 34 via the collimator 33. It

The optical attenuator shown in FIG. 13 is a variable optical attenuator that uses a magneto-optical element whose refractive index changes when a magnetic field is applied by an electromagnet or the like to obtain a light attenuating effect. Reference numeral 39 is a magneto-optical element such as a magnetic garnet, 40 is an electromagnet, 41 is a permanent magnet, and 42 is a wedge-shaped birefringent crystal. Light incident from the optical fiber 30 and condensed by the collimator 31 passes through the magneto-optical element 39. The light is attenuated to an arbitrary light intensity via the collimator 33 and is emitted to the optical fiber 34 via the collimator 33.

[0008]

However, such an optical attenuator has the following problems. (1) In the variable optical attenuator that mechanically drives the ND filter, it takes a long time for the attenuation amount to stabilize (for example, several hundred mse before stabilizing to 10 dB).
c). Further, when a surge is applied to the current that drives the motor, the operation of the filter may be affected by noise. (2) In a fixed optical attenuator that uses an ND filter, the degree of attenuation is 5 dB, 10 dB, and 15 dB, so the degree of freedom in setting the amount of attenuation is low. (3) In the variable optical attenuator that obtains the attenuation effect thermo-optically, the loss due to the joining of the optical fiber and the substrate is large.
(For example, 2 dB or more) When the current is turned off, the initial state is restored, and the damping effect cannot be obtained. (4) In the variable optical attenuator that obtains the attenuation effect electro-optically and magneto-optically, the optical element used is expensive. Further, when the current is turned off, the initial state is restored and the damping effect cannot be obtained. Further, in the variable optical attenuator that obtains the attenuation effect magneto-optically, the number of parts is large and the coupling loss is large.

The present invention has been made to solve the above-mentioned problems, and can be operated at low cost and at high speed without using a drive unit such as a motor or an expensive optical crystal, and a desired attenuation can be obtained even in the initial state. An object of the present invention is to realize an optical attenuator capable of obtaining a quantity and an arbitrary attenuation range.

[0010]

According to a first aspect of the present invention, there is provided an optical attenuator for attenuating input light and outputting the attenuated light.
A fixed mirror and a movable mirror that is arranged to face the fixed mirror in a state where a gap is formed between the fixed mirror and receives the input light; and by displacing the movable mirror with respect to the fixed mirror, An optical attenuator comprising a Fabry-Perot filter that makes the size of the gap variable and attenuates the input light to any desired intensity corresponding to the size of the gap to output as output light. .

According to a second aspect of the present invention, in the optical attenuator according to the first aspect, the output light is reflected light of the movable mirror or transmitted light of the fixed mirror. Is.

According to a third aspect of the present invention, in the optical attenuator according to the first aspect, an arbitrary attenuation range is selected by arbitrarily setting the size of the initial gap in which the movable mirror is not displaced. The optical attenuator is characterized by doing so.

According to a fourth aspect of the present invention, in the optical attenuator according to the first aspect, the fixed mirror is provided on a substrate, and the movable mirror is formed on the fixed mirror via a sacrificial layer. The optical attenuator is formed by removing the sacrificial layer to form a diaphragm with a gap corresponding to the thickness of the sacrificial layer formed.

According to a fifth aspect of the present invention, in the optical attenuator according to the fourth aspect, a fixed electrode formed on the fixed mirror and a movable electrode formed on the movable mirror are provided, and the movable mirror is The optical attenuator is driven by an electrostatic force generated by applying a voltage between the fixed electrode and the movable electrode.

A sixth aspect of the present invention is the optical attenuator according to the fourth aspect, wherein a plurality of the Fabry-Perot filters are integrated and provided on the substrate.

According to a seventh aspect of the present invention, in the optical attenuator according to the first aspect, a plurality of the Fabry-Perot filters are collectively provided in one module, and the plurality of Fabry-Perot filters respectively emit lights having different wavelengths. It is an optical attenuator characterized by attenuating and outputting.

According to an eighth aspect of the present invention, in the optical attenuator according to the first aspect, an optical adhesive which is provided around the Fabry-Perot filter and fixes the movable mirror to fix the size of the gap. , And attenuating the input light according to the size of the fixed gap and outputting the attenuated input light.

According to a ninth aspect of the present invention, in the optical attenuator according to the eighth aspect, the optical adhesive has a size of the gap such that the attenuation amount of the Fabry-Perot filter is an arbitrary desired attenuation amount. After being adjusted, the optical attenuator is provided around the optical attenuator.

According to claim 10 of the present invention, claim 9
The optical attenuator described in claim 1, wherein a plurality of Fabry-Perot filters fixed by the optical adhesive are provided so that the attenuation amounts are different from each other.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The optical attenuator according to the present invention obtains an attenuation effect by utilizing the wavelength selection characteristic of a Fabry-Perot filter. The Fabry-Perot filter is an optical filter that forms a gap between a fixed mirror having a high reflectance and a movable mirror and faces each other, and displaces the movable mirror in the direction of the fixed mirror to change the size of the gap. The wavelength is selected according to the size of the gap and transmitted.

In the Fabry-Perot filter designed to operate at a specific center wavelength λ, the thickness d of the fixed mirror and the movable mirror satisfies the condition of λ / 4 = nd (n: refractive index). Is manufactured as. Then, the Fabry-Perot filter selects and transmits the wavelength λ ′ of light that satisfies the condition of 2 n D = Nλ ′ ( n: refractive index , N: integer, D: size of gap).

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1A is a sectional perspective view of a Fabry-Perot filter used in the present invention, and FIG. 1B is an enlarged view of a main part thereof. 1A and 1B, 1 is a substrate, 2 is a fixed mirror, 3 is a sacrifice layer, 4 is a gap, 5 is a movable mirror, 6 is an etching hole, 7 is an interlayer insulating film, and 8 is an antireflection film. ,
Reference numeral 9 is an aperture and 10 is a light transmitting portion.

The substrate 1 is made of a material that transmits light in the transmission wavelength band, such as silicon, sapphire, or germanium. The fixed mirror 2 is formed on the substrate 1 and is composed of a single layer or a multilayer film having an optical film thickness corresponding to ¼ wavelength of the center wavelength λ of the filter. Examples of the multilayer film include those in which the high refractive index layer is formed of polysilicon and the low refractive index layer is formed of silicon oxide. A fixed electrode (not shown) for electrostatic driving is formed on the fixed mirror 2 by, for example, doping polysilicon with impurities.

The sacrificial layer 3 is a portion for forming the gap 4 necessary for constructing the Fabry-Perot filter, and by making the vertical cross-section substantially trapezoidal, the effect of relaxing stress concentration can be obtained. The sacrificial layer 3 is, for example, PSG.
It is formed of a substance that can be removed by a hydrofluoric acid-based etching solution such as (phosphorus glass) or a silicon oxide film.

The movable mirror 5 is a single-layer or multi-layer film reflecting mirror that transmits a specific wavelength of incident light (input light) due to interference with the fixed mirror 2. For example, Si / SI ₃ N ₄ / Si having upper and lower high-refractive-index layers of silicon and intermediate low-refractive-index layers of silicon nitride and having optical film thicknesses corresponding to ¼ wavelength of the center wavelength λ of the filter, respectively. It is formed of three layers. A movable electrode (not shown) for electrostatic driving is formed on the movable mirror 5 by, for example, doping silicon with impurities.

The etching hole 6 is a hole into which an etching solution for etching the sacrificial layer 3 is introduced, and the movable mirror 5 is provided.
Is formed in the center and the outer peripheral portion of the etching solution to facilitate diffusion, replacement and drying of the etching solution.

Then, a gap 4 is formed by etching the sacrificial layer 3, and the movable mirror 5 is arranged so as to face the fixed mirror 2 with the gap 4 formed between the movable mirror 5 and the fixed mirror 2, and is formed in a diaphragm shape. It In this case, the initial gap g0 becomes equal to the thickness of the sacrificial layer 3.

The inter-layer insulating film 7 is an insulating film that maintains insulation between a fixed electrode and a movable electrode (not shown), and is made of, for example, silicon nitride. The antireflection film 8 is a layer for increasing the transmittance of light transmitted from the substrate when a substrate having a high refractive index is used, and is a single layer or a multilayer having an optical film thickness that effectively transmits light in the transmission wavelength band. It consists of a membrane. For example, there is a combination of the substrate 1 made of silicon and the antireflection film 8 made of silicon oxide.

The aperture 9 is a layer that defines the light transmitting portion 10 and is made of a metal film such as Au. The light transmitting portion 10 is formed by etching the aperture 9. The light transmitting portion 10 is a light transmitting portion of the Fabry-Perot filter.

Next, the light attenuation operation of the Fabry-Perot filter will be described. 1A and 1B show a state in which an electrostatic drive voltage is not applied between a fixed electrode and a movable electrode (not shown). In this case, since the electrostatic force is not generated between the fixed electrode and the movable electrode, the movable mirror 5 is not displaced and the size of the initial gap g0 is maintained.

When an electrostatic drive voltage V is applied between the fixed electrode and the movable electrode, an electrostatic force is generated between the fixed electrode and the movable electrode as shown in FIGS. 2 (a) and 2 (b). The movable mirror 5 is displaced in the direction of the fixed mirror 2. And the gap 4
Is smaller than the size of the initial gap g0.

FIG. 3 shows a Fabry-Perot filter designed such that the center wavelength λ and the initial gap g0 are 1.60 μm, and the movable mirror 5 is electrostatically driven so that the size of the gap 4 is about 1.2 μm to 1. It is a figure which shows the result of having simulated the characteristic (spectral characteristic) of the transmittance | permeability by the wavelength of the incident light when changing to arbitrary 9 points within 6 micrometers.

In FIG. 3, when attention is paid to the size of one gap, it is shown that a mountain-shaped transmission characteristic has a peak at a wavelength where the transmittance is maximum (the attenuation is minimum). Then, when the driving voltage is increased and the gap is decreased, the mountain-shaped waveform moves in a direction in which the wavelength at which the transmittance becomes maximum decreases.

Then, in FIG. 3, when one wavelength is focused, it can be seen that the transmittance changes according to the size of the nine gaps. FIG. 4 is an attenuation characteristic diagram showing how the transmittance in FIG. 3 is replaced with an attenuation amount, and the attenuation amount changes in accordance with a change in the size of the gap for a arbitrarily selected specific wavelength. In addition, in FIG. 4, the C-band (wavelength of 1.53 μm
(1.56 μm), three wavelengths of 1.53 μm, 1.545 μm, and 1.56 μm, which are the wavelengths at both ends and the intermediate wavelength, are selected, and the attenuation characteristics at the three wavelengths are overlapped and shown.

In FIG. 4, the size of the gap that minimizes the attenuation (maximum transmittance) for all three wavelengths is 1.55 μm.
In the vicinity of m, there is shown a substantially V-shaped attenuation characteristic with the lowermost point in the vicinity of 1.55 μm. Then, if a wavelength shorter (longer) than C-band is selected in FIG. 3, the substantially V-shaped attenuation characteristic in FIG.
The size of the gap that forms the letter-shaped lower dot is 1.55 μm
Move in a direction smaller (larger) than the neighborhood.

As shown in FIG. 4, when light of a specific wavelength within C-band is incident on the Fabry-Perot filter, an electrostatic drive voltage for driving the movable mirror is applied to set the gap to the initial gap 1. When changing from 6 μm to around 1.55 μm, the attenuation amount of incident light decreases (transmittance increases), and the electrostatic drive voltage is further increased to about 1.55 μm.
When the gap is changed from near to 1.2 μm, the amount of attenuation of incident light increases (transmittance decreases).

In this way, the Fabry-Perot filter is
By controlling the electrostatic drive voltage and arbitrarily changing the size of the gap, the incident light can be attenuated by any desired attenuation amount.

It should be noted that FIG. 4 shows that the attenuation characteristics have wavelength dependence (characteristics in which the same gap gives different amounts of attenuation at different wavelengths). For example, 1.5
Gap 1.45 for wavelengths of 3 μm and 1.56 μm
The attenuation has a width of about 8 to 12 dB in the vicinity of μm.
However, if the application allows such an attenuation error,
The same Fabry-Perot filter can be used as an optical attenuator for light of a plurality of wavelengths within a specific wavelength band.

Then, the Fabry-Perot filter designed to have the attenuation characteristic as shown in FIG.
Has an attenuation range of about 2 dB to about 17 dB with respect to the wavelength inside, and attenuates the incident light of the wavelength within C-band within the full range (about 2 dB to 15 dB) effective as an optical attenuator. Is possible.

When a Fabry-Perot filter is designed with a center wavelength of 1.6 μm and an initial gap of 1.451 μm, the gap of 1.6 μm is obtained in FIG.
It is a characteristic diagram in which the mountain-shaped waveforms of m, 1.55 μm, and 1.501 μm are lost. In FIG. 4, the characteristics from the gap of 1.6 μm to the vicinity of 1.45 μm are lost, and the overall characteristics are not V-shaped but curve rising to the left, and the attenuation range of the Fabry-Perot filter is about 10 d.
It becomes B to 17 dB.

As described above, by arbitrarily setting the size of the initial gap (thickness of the sacrificial layer), the attenuation range of the Fabry-Perot filter can be designed to be a desired attenuation range. That is, it is possible to design a Fabry-Perot filter that attenuates incident light with a desired attenuation amount even in the initial state where the electrostatic drive voltage is not applied.

In the above case, the output light of the Fabry-Perot filter is the transmitted light transmitted through the fixed mirror. However, the amount of the incident light entering the Fabry-Perot filter is the transmitted light of the fixed mirror. It becomes equal to the sum of the amount of light and the amount of light reflected by the movable mirror. Therefore, not only the transmitted light that has been transmitted but also the reflected light of the movable mirror can be used as the output light of the Fabry-Perot filter.

Since the Fabry-Perot filter as described above is manufactured by a known semiconductor manufacturing technique using, for example, a silicon substrate, a plurality of Fabry-Perot filters are inexpensively integrated and formed on the substrate. be able to.

Next, an example of using the Fabry-Perot filter as an optical attenuator will be described. Figure 5
In this example, the optical fibers 12 and 13 are provided on the incident side and the transmitting side of the optical attenuator 11 (Fabry-Perot filter), respectively.

FIG. 6 shows an example in which the optical fiber 12 is provided on the incident side of the optical attenuator 11 and the photodetector 14 is provided on the transmitting side to monitor the amount of transmitted light. In this case, the amount of transmitted light can be optimized by adjusting the gap of the Fabry-Perot filter while monitoring the amount of light.

In FIG. 7, the optical fibers 12 and 13 are provided on the incident side and the transmitting side of the optical attenuator 11, respectively, and the photodetector 14 is provided on the optical path of the reflected light so that the amount of the reflected light can be monitored. It is an example. In this case, the amount of transmitted light can be optimized by adjusting the gap of the Fabry-Perot filter while monitoring the amount of reflected light.

FIG. 8 shows the incident side and the transmitting side of the optical attenuator 11.
This is an example in which optical fibers 12, 13, and 15 are provided on the reflection side, respectively, and both transmitted light and reflected light are used as output light with attenuated intensity.

Incidentally, FIG. 5 and FIG. In FIG. 8, since the optical fiber is provided on the transmission side and the optical path is limited, it is not necessary to provide the Fabry-Perot filter with an aperture for limiting the optical path.

In addition, a plurality of Fabry-Perot filters as described above are collectively provided in one module, and light of different wavelengths is input to each Fabry-Perot filter, so that multiple channels corresponding to a plurality of wavelengths can be obtained. Optical attenuator can be constructed.

FIG. 9 is a diagram showing the configuration of another embodiment of the present invention, which is a diagram showing the configuration of a fixed optical attenuator with a fixed amount of attenuation. In FIG. 9, 16 is a Fabry-Perot filter, 17 is an optical adhesive made of an ultraviolet curable resin that is cured by irradiation with light such as ultraviolet rays, and 1
8 and 19 are optical fibers, 20 and 21 are collimators, 22
Is a case for housing the Fabry-Perot filter 16, the optical adhesive 17, and the collimators 20, 21.

The Fabry-Perot filter 16 attenuates the intensity of incident light by any desired attenuation amount by controlling the electrostatic drive voltage and arbitrarily changing the size of the gap as described above. Since the optical adhesive 17 fixes the movable mirror (not shown) of the Fabry-Perot filter 16 so as not to displace, the size of the gap is also fixed. Therefore, the amount of light attenuation by the Fabry-Perot filter 16 is also fixed according to the size of the gap.

Further, a fixed electrode (not shown) of the Fabry-Perot filter 16 so that the attenuation amount becomes a desired attenuation amount.
And the movable electrode (not shown) are applied with an electrostatic drive voltage (the size of the gap is adjusted), the case 22
By filling the inside with an optical adhesive and curing it, the amount of light attenuation by the Fabry-Perot filter 16 can be fixed to an arbitrary value.

Therefore, it is possible to easily manufacture a plurality of fixed optical attenuators having an arbitrary amount of attenuation fixed between 1 and 15 dB with one type of Fabry-Perot filter. It is possible to realize an optical attenuator having a plurality of fixed attenuation amounts.

[0054]

As described above, according to the present invention,
Since the Fabry-Perot filter that is electrostatically driven is used as the optical attenuator, it is not necessary to use a driving unit such as a motor, and a stable and high-speed optical attenuator can be realized.

Further, according to the present invention, since the Fabry-Perot filter can be manufactured by integrating a plurality of silicon substrates on one substrate by a known semiconductor manufacturing technique, an expensive optical crystal should be used. Therefore, an inexpensive optical attenuator can be realized.

Further, according to the present invention, a desired amount of attenuation can be obtained even in the initial state where the electrostatic drive voltage of the Fabry-Perot filter is zero, and by setting the initial gap of the Fabry-Perot filter arbitrarily. The attenuation range can be set arbitrarily.

Further, according to the present invention, a plurality of Fabry-Perot filters are collectively provided in one module, and light of different wavelengths is input to each Fabry-Perot filter, so that multi-channels corresponding to a plurality of wavelengths can be obtained. An optical attenuator can be realized.

Further, according to the present invention, since the gap of the Fabry-Perot filter is fixed by the optical adhesive, the attenuation amount of the Fabry-Perot filter can be fixed according to the size of the gap.

According to the present invention, the electrostatic drive voltage is applied to the fixed electrode and the movable electrode of the Fabry-Perot filter so that the desired attenuation can be obtained (the size of the gap is adjusted). By filling the case with the optical adhesive and curing the case, the attenuation amount of the optical attenuator can be fixed to an arbitrary value.

[0060]

[Brief description of drawings]

FIG. 1 is a cross-sectional perspective view of a Fabry-Perot filter used in the present invention.

FIG. 2 is a diagram showing a state in which a movable mirror of a Fabry-Perot filter is displaced.

FIG. 3 is a diagram showing transmittance characteristics of a Fabry-Perot filter depending on the wavelength of incident light.

FIG. 4 is a diagram showing an attenuation characteristic of incident light due to a change in a gap of a Fabry-Perot filter.

FIG. 5 is a diagram showing a usage example of an optical attenuator.

FIG. 6 is a diagram showing a usage example of an optical attenuator.

FIG. 7 is a diagram showing a usage example of an optical attenuator.

FIG. 8 is a diagram showing a usage example of an optical attenuator.

FIG. 9 is a diagram showing a configuration of a fixed optical attenuator with a fixed attenuation amount according to the present invention.

FIG. 10 is a schematic diagram of a configuration of a conventional optical attenuator.

FIG. 11 is a schematic diagram of a configuration of a conventional optical attenuator.

FIG. 12 is a schematic diagram of a configuration of a conventional optical attenuator.

FIG. 13 is a schematic diagram of a configuration of a conventional optical attenuator.

[Explanation of symbols]

1 substrate 2 fixed mirror 3 sacrifice layer 4 gap 5 movable mirror 6 etching holes 17 Optical adhesive g0 initial gap

Claims (10)

[Claims] 1. An optical attenuator for attenuating input light and outputting the same, wherein a fixed mirror and a movable mirror which is arranged to face the fixed mirror with a gap formed between the fixed mirror and which receives the input light are provided. The size of the gap is made variable by displacing the movable mirror with respect to the fixed mirror, and the input light is attenuated to an arbitrary desired intensity corresponding to the size of the gap to be output light. An optical attenuator comprising a Fabry-Perot filter for outputting. 2. The optical attenuator according to claim 1, wherein the output light is reflected light of the movable mirror or transmitted light of the fixed mirror. 3. The optical attenuator according to claim 1, wherein an arbitrary attenuation range is selected by arbitrarily setting a size of an initial gap in which the movable mirror is not displaced. An optical attenuator. 4. The optical attenuator according to claim 1, wherein the fixed mirror is provided on a substrate, the movable mirror is formed on the fixed mirror via a sacrifice layer, and the sacrifice layer is removed. The optical attenuator is formed in a diaphragm shape with a gap corresponding to the thickness of the sacrificial layer being formed by. 5. The optical attenuator according to claim 4, wherein a fixed electrode formed on the fixed mirror and a movable electrode formed on the movable mirror are provided, and the movable mirror includes the fixed electrode and the movable electrode. An optical attenuator characterized by being driven by an electrostatic force generated by applying a voltage between the electrodes. 6. The optical attenuator according to claim 4, wherein a plurality of the Fabry-Perot filters are integrated and provided on the substrate. 7. The optical attenuator according to claim 1, wherein a plurality of the Fabry-Perot filters are collectively provided in one module, and the plurality of Fabry-Perot filters attenuate and output lights of different wavelengths, respectively. Characteristic optical attenuator. 8. The optical attenuator according to claim 1, further comprising an optical adhesive which is provided around the Fabry-Perot filter and fixes the movable mirror to fix the size of the gap. An optical attenuator which attenuates and outputs the input light according to the size of the formed gap. 9. The optical attenuator according to claim 8, wherein the optical adhesive adjusts the size of the gap so that an attenuation amount of the Fabry-Perot filter is an arbitrary desired attenuation amount, and then the optical attenuation is performed. An optical attenuator provided around the element. 10. The optical attenuator according to claim 9, wherein a plurality of Fabry-Perot filters fixed by the optical adhesive are provided so that the attenuation amounts are different from each other.