JP2003029023A - Wavelength selective light attenuating element and wavelength selective light attenuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a wavelength selective light attenuator having a wavelength selecting function and varying the attenuation at a specified wavelength according to external signals. SOLUTION: Low refractive index dielectric films L and high refractive index dielectric films H are alternately layered on a substrate 1, and a third dielectric film 4 is deposited in the layers. The dielectric film 4 is a layer having a photochromic effect so as to vary the transparency according to external light signals. Thus, a variable light attenuator having the wavelength selecting function is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength-selective optical attenuator and a wavelength-selective optical attenuator capable of varying the amount of light attenuation to a specific wavelength.

[0002]

2. Description of the Related Art As a conventional variable attenuator optical attenuator, for example, as shown in FIG.
An optical attenuator having vapor deposited is used. The film thickness of this metal thin film is vapor-deposited with a continuous gradient along a certain direction. This optical attenuator is movable by a moving stage 103 in the direction of the arrow whose thickness changes. In this way, when light is incident so as to pass through the variable wavelength attenuator and transmitted light is obtained, if the irradiation position is continuously changed by the moving stage 103, the corresponding transmittance as shown in FIG. 19 is obtained. can get. For example, if the irradiation position of the incident light beam is X
By changing from 1 to X2, the transmittance can be varied between T1 and T2, and an arbitrary attenuation amount can be obtained for the incident optical signal. The metal thin film has a low dependence on wavelength, and the wavelength used in optical communication is 1500n.
The dependency is particularly low near m. Therefore, it can be used without considering the wavelength dependence.

[0003]

In the field of optical communication, an optical wavelength division multiplexing system (WDM) for multiplexing a large number of wavelength components is used.
Communication method) is being adopted. In this method, there are cases in which it is desired to adjust the intensity of an optical signal of a specific wavelength component with respect to a multi-wavelength signal propagating in one optical fiber or to make the optical intensities of respective wavelengths uniform. Since a conventional optical attenuator does not have a wavelength selective function, only a desired wavelength component is branched and extracted (dropped) from a multi-wavelength signal transmitted in one optical fiber to obtain a desired light intensity. It must be attenuated to a level and then added back to the original optical fiber.
Therefore, a device for branching the wavelength and a device for adding the light have to be prepared respectively, and the device becomes expensive and complicated.

The present invention has been made by paying attention to such a conventional problem, and adjusts the light intensity level of a specific wavelength component of a multi-wavelength component and affects other wavelength components. It is an object of the present invention to provide a wavelength-selective variable optical attenuator that does not exist and a wavelength-selective optical attenuator used for the variable optical attenuator.

[0005]

According to a first aspect of the present invention, there is provided a first dielectric thin film having a refractive index n ₁ and a film thickness d ₁ formed on a substrate, and a first dielectric thin film having a refractive index lower than n ₁ . A dielectric multilayer film in which second dielectric thin films having a refractive index n _{2 of 2} and a film thickness d ₂ are alternately stacked; and a third dielectric film having a photochromic effect, which is stacked between the dielectric multilayer films, And the optical film thickness of the dielectric multilayer film is an integral multiple of λ / 4.

According to a second aspect of the present invention, in the wavelength selective optical attenuating element according to the first aspect, the third dielectric film is a dielectric thin film having an amorphous structure.

According to a third aspect of the present invention, in the wavelength selective optical attenuator according to the second aspect, the third dielectric film is a
-WO ₃ , a-MoO ₃ , a-V ₂ O ₅ , and a-NiO are one oxide selected from the group.

According to a fourth aspect of the present invention, in the wavelength-selective optical attenuating element according to the second aspect, the third dielectric film has an optical film thickness that is an even multiple of λ / 4. To do.

According to a fifth aspect of the present invention, a first dielectric thin film formed on a substrate and having a refractive index n ₁ and a film thickness d _1, a second refractive index n ₂ having a refractive index lower than n ₁ , A dielectric multilayer film in which second dielectric thin films having a film thickness d ₂ are alternately laminated, and a third layer having a photochromic effect formed between the dielectric multilayer films.
And the optical film thickness of the dielectric multilayer film is λ
A wavelength-selective light attenuator that is an integral multiple of / 4, and a light amount level variable-type light source that irradiates light toward the third dielectric film of the wavelength-selective light attenuator. To do.

According to a sixth aspect of the present invention, in the wavelength selective optical attenuator of the fifth aspect, the light amount level variable type light source is an ultraviolet ray having a wavelength of 400 nm or less.

According to the invention of claim 7 of the present application, wavelength-multiplexed light is incident, and the reflected light is sequentially connected in cascade as the incident light.
6. A plurality of wavelength-selective optical attenuators according to claim 5, which have different transmission wavelengths, and each have a transmission wavelength of at least a part of the multiplexed wavelengths of the wavelength-multiplexed light, and a wavelength-selective type of the last stage cascaded. A branching unit for branching a part of the light reflected by the optical attenuator, a light amount level detecting unit for detecting a light amount level of each wavelength component of the wavelength division multiplexed light branched by the branching unit, and a light amount of each wavelength component A level corresponding to each wavelength detected by the level detection unit is input, and a feedback circuit for supplying a control signal to the light source of the wavelength selective optical attenuator is provided, and the level of each wavelength component is fixed by feedback control. It is characterized by

According to the invention of claim 8 of the present application, wavelength-multiplexed light is incident, and the reflected light is sequentially connected in cascade as the incident light.
6. The plurality of wavelength selective optical attenuators according to claim 5, wherein the wavelengths of the wavelength multiplexed light are different from each other, and at least a part of the wavelengths in which the wavelength-multiplexed light is multiplexed are transmission wavelengths. A plurality of branching parts provided in the output part for branching a part of the transmitted light, a plurality of light amount level detecting parts for detecting a light amount level of each wavelength component of the wavelength division multiplexed light branched by each of the branching parts, and A level corresponding to each wavelength detected by the light amount level detector of each wavelength component is input, and a feedback circuit that gives a control signal to the light source of the wavelength selective optical attenuator, respectively.
Is provided, and the level of each wavelength component is made constant by feedback control.

[0013]

(Embodiment 1) In the present invention, in order to realize a wavelength selection function in an optical attenuator,
It is based on a thin-film dielectric multilayer filter and has a variable attenuation function added to it. The dielectric multilayer film filter can realize various filter characteristics such as a long wavelength pass filter, a short wavelength pass filter, a band pass filter, etc., depending on the film design. The dielectric multilayer filter is used as a filter for optical communication, and its high reliability such as environmental resistance has been proven. The conventional dielectric multilayer filter is a passive element, and the refractive index and extinction coefficient of the thin film do not show large changes with respect to temperature, humidity, light irradiation, voltage application, etc.
It was stable. On the other hand, if the extinction coefficient of the thin film forming the dielectric multilayer filter can be controlled by any method, a variable optical attenuator having a wavelength selection function can be realized.

Therefore, a specific substance having a photochromic effect is used. The photochromic effect is a reversible photoreaction that is colored by irradiation with light and returns to its original state when irradiation is stopped. Materials having this photochromic effect include, for example, "Handbook of Optical Properties volume
I, Thin films for Optical coatings, Chap. 5, edit
ed by Rolf E. Hummel and Karl H. Guenther, CRC Pre
ss 1995. ”, in the case of oxides Ag ₃ V
O ₄ , Ag ₄ SiO ₄ , Ag ₃ PO ₄ , a-WO ₃ , a
-MoO ₃ etc. have been reported. a- indicates that it is in an amorphous state.

As a material having a photochromic effect suitable for optical communication, it is necessary to satisfy the following conditions. (1) Excellent environmental resistance against temperature and humidity. (2) The loss of the thin film itself is small. (3) Stable operation for a long period of time. (4) The film forming conditions are reproducible and stable. (5) It does not require a large amount of rare metal substances. As a thin film material suitable for these conditions, attention was paid to substances having an amorphous structure. The amorphous structure has the advantages that the film is dense, the surface of the film is excellent in smoothness, the temperature dependence is extremely low, and long-term stability of the composition can be obtained.
In addition to the dielectric thin film, the ion beam sputtering method (IBS method) or the ion beam assisted vapor deposition method (IAD method) is most suitable for forming these thin films. This is because in these film formation methods, the kinetic energy of the film composition particles during film pressure is high, and the film structure easily forms an amorphous structure. The composition ratio can be easily controlled by adjusting the supply flow rate of the gas (oxygen gas) used, the beam current / voltage during film formation, and the degree of vacuum.

Next, an optical bandpass filter having a dielectric multilayer film structure will be described. As shown in FIG. 1, an optical bandpass filter having a dielectric multilayer structure is made of glass,
A dielectric multilayer film 2 is vapor-deposited and synthesized on a substrate 1 such as silicon. As shown in the enlarged cross-sectional view of FIG. 1B, the dielectric multilayer film 2 alternates a high refractive index film H which is a first dielectric film and a low refractive index film L which is a second dielectric film. It is laminated and vapor deposited. The film thickness of the high refractive index film H is d ₁ , and the low refractive index film L is
Where d _{2 is} the film thickness, n _{1 is} the refractive index of the high refractive index film H, n _{2 is} the refractive index of the low refractive index film L, and λ is the transmission wavelength.
The optical thickness of L is represented by n ₁ d ₁ and n ₂ d ₂ , respectively.
Then, the following relations are established between them. n ₁ d ₁ = λ / 4 n ₂ d ₂ = λ / 4 A bandpass filter can be formed by alternately stacking a high-refractive index film H and a low-refractive index film L, and increasing the number of layers allows transmission. The half-width of the rate peak is reduced. The uppermost layer is via a medium and is generally air or the like.

This dielectric multilayer filter can be expressed as follows. Substrate / (HL) ⁿ / medium (air) where (HL) is each layer of the high-refractive index film H and the low-refractive index film L, and indicates that a layer of a pair of HL is repeatedly laminated n times. .

In the bandpass filter, a large number of such dielectric multilayer films are alternately laminated and the spacer layer 3 is inserted in the middle of the dielectric multilayer films. The structure of the bandpass filter having the spacer layer 3 can be expressed as follows. Substrate / A / Medium (air) A = [(HL) ⁿ s _i L (LH) ⁿ L] ^m where m, n, s _i (i = 1, 2, ... M) is a positive integer ( = 1, 2, 3, ...). When m is 1, 2 and 3, they are called a single cavity, a double cavity and a triple cavity, respectively. The larger the order of m, the sharper the characteristics of the bandpass filter. Also, the larger the spacer layer 3, the narrower the transmission bandwidth. Therefore, in designing a bandpass filter, these parameters m, n, and
s _i are selected.

In the present invention, this spacer layer is replaced with the thin film 4 having the photochromic effect described above. The thin film 4 having the photochromic effect has wavelengths of λ, λ /
4 When the physical film thickness is P, the refractive index is n _P , and the optical film thickness is Pn _P , the following equation holds. Pn _P = λ / 4 and the actual film thickness is an integral multiple of P.

FIG. 2 is a view showing the structure of the wavelength selective optical attenuator according to the first embodiment of the present invention. As shown in the figure, three layers of high refractive index film layers H and low refractive index film layers L are alternately laminated on the substrate 1. Then, a third dielectric film 4 having a photochromic effect is formed in the middle of these multilayer films to a thickness of 4
P is laminated, and further, three low-refractive index films L and three high-refractive index films H are alternately laminated. When this is expressed as described above, it becomes as follows. A = (HL) ³ 4P (LH) ^{3 In} this example, the cross-sectional structure of a dielectric multilayer filter element having a film structure of n = 3, s ₁ = 4, and m = 1 is shown. The optical thickness of the third dielectric 4 is preferably an even multiple of λ / 4.

(Embodiment 2) Next, FIG. 3 shows a block diagram in the case of constructing a wavelength selective optical attenuator using the wavelength selective optical attenuating element 10 according to the first embodiment. The wavelength-selective optical attenuator is one in which the wavelength-selective element 10 having the wavelength-selecting function configured as described above and the light source for the dielectric layer having the photochromic effect are integrated.
In FIG. 3, a collimator lens 12 is provided at the tip of an optical fiber 11 that guides the incident light and guides it to the wavelength selective optical attenuator 10. A collimator lens 13 and an optical fiber 14 are arranged on the optical axis of the collimator lens 12 via a wavelength selective attenuation element 10. Here, the incident surface to the selective light attenuating element 10 is arranged with a slight inclination from the right angle direction. Then, the collimator lens 15 is arranged at a position where the reflected light is received so that the reflected light is condensed and incident on the optical fiber 16.

The ultraviolet laser light source device 17 irradiates the wavelength selective optical attenuating element 10 with ultraviolet laser light. The light source device 17 has a function of adjusting the irradiation light amount by a control signal from the outside. The wavelength suitable as irradiation light for producing the photochromic effect is mainly in a wavelength region shorter than visible light, and ultraviolet rays having a wavelength of 400 nm or less are effective irradiation light for a thin film having a photochromic effect. Then, an ultraviolet laser beam having light having a photochromic effect is applied to the third dielectric film 4 through which the incident light and the emitted light pass.

In this way, the attenuation factor of the wavelength-selective optical attenuating element 10 varies depending on the light intensity of the ultraviolet laser light.
It is possible to select a predetermined wavelength from the wavelength-multiplexed light and arbitrarily set the light amount level of the selected wavelength.
Further, since all the wavelength components not selected are reflected, they can be emitted to the reflection optical fiber 16 via the collimator lens 15.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIGS. In this embodiment, the plurality of wavelength selective optical attenuators 20 shown in FIG.
A, 20B, 20C, and 20D are used, and the respective transmission wavelengths are λ1, λ2, λ3, and λ4. The input wavelength-multiplexed optical signal propagates through one optical fiber, but the signal strengths do not match. FIG. 5A is a spectrum diagram showing the level of each wavelength of the input signal.
The wavelength-multiplexed signal light of λ4 to λ4 and the incident signal intensities of the wavelengths λ1 to λ4 are s1, s2, s3, and s4, respectively. Well, Figure 4
As shown in FIG.
This wavelength-multiplexed light is incident on 0A. Then the wavelength λ1
Part of the light is transmitted and the other is reflected. The reflected light is guided to the wavelength selective optical attenuator 20B having the selective wavelength λ2. Similarly, the wavelength selective optical attenuators 20C and 20D are connected in series as shown in the figure to separate some of the wavelength components λ1 to λ4. Variable wavelength variable optical attenuator 20
Wavelength components λ1 to λ4 that transmit A to 20D are shown in FIG.
In order to make the optical power levels shown in (a) uniform, wavelength components having a high level, that is, unnecessary components of λ1, λ3, and λ4 are used.

The light that has passed through the wavelength-selective optical attenuator 20D is guided to the branching coupler 21, and a predetermined ratio of all wavelength components, for example, 5%, is separated. The separated wavelength division multiplexed light is guided to the light amount level detection unit 22 of FIG. In the light amount level detection unit 22, band pass filters 23A to 23D, each of which transmits light of λ1 to λ4, are connected in series as illustrated. The bandpass filters 23A to 23D take out only the respective wavelength components λ1, λ2, λ3 and λ4 and detect them by the photodetectors 24A to 24D. In this way, among the wavelength-multiplexed light components branched by the branch coupler 21, the light quantity levels of the respective wavelength components can be detected by the photodetectors 24A to 24D. The outputs out1 to out4 of the photodetectors 24A to 24D are given to the feedback circuits 25A to 25D, respectively. Feedback circuit 2
5A to 25D control the level of the ultraviolet laser light of the light source device of the wavelength selective optical attenuators 20A to 20D. By appropriately setting the feedback circuits 25A to 25D, the light of the high-level wavelength component is attenuated. In this way, the levels of the respective wavelengths can be matched so as to match the level s2 of the incident light having the lowest level or a level slightly lower than this. FIG. 5B shows the light quantity level s of each wavelength.
It is a spectrum figure showing the state where 1 ', s2', s3 ', and s4' were made into the fixed value.

Here, even if the signal intensity s1 of the incident light wavelength component λ1 suddenly increases for some reason, the light intensity of each transmitted light is increased by adjusting the light intensity of the irradiation light to increase the attenuation amount. Feedback control can be performed so that the levels match. In gain correction by such negative feedback control,
A higher gain correction is possible as compared with a conventional passive filter, and a correction error of ± 0.01 dB or less can be realized in real time, for example.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIG. In the above-described third embodiment, the light amount level detection unit 22 detects the light amount level of each wavelength component, but the wavelength selective variable attenuators 20A to 20D output the wavelength components of λ1 to λ4. Therefore, the level can be adjusted based on the light amount level. In FIG. 6, the same parts as those in the third embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. In the fourth embodiment, as shown in FIG. 6, each wavelength λ1 to λ4 is separated by each wavelength selective variable optical attenuator 20A to 20D having multiple wavelengths, and a part of the separated wavelengths is branched to a coupler 26A to. Separate at 26D. Then, the signal level is monitored and added to the level adjusting ultraviolet laser light source device via the feedback circuits 25A to 25D. In each light source device, irradiation light is given according to the branched level so that λ1 to λ4 are at the same level. By doing so, the levels of the respective wavelengths emitted from the last wavelength selective variable optical attenuator 20D can be made uniform. However, in this case, the output stage does not monitor and adjust the level.
The accuracy is inferior to the configuration shown in FIG.

As described above, by adjusting the level of the irradiation light for adjusting the attenuation level for each wavelength-selective attenuator according to the light intensity of the branched wavelength, it is possible to obtain wavelength-multiplexed light with that level aligned. it can.

[0029]

EXAMPLES Example 1 Next, Example 1 of the wavelength selective variable optical attenuator will be described. This wavelength-selective variable optical attenuator 10A comprises a Nb ₂ O ₅ film (refractive index 2.20) and a low refractive index film L as a high refractive index film H on a silica glass substrate.
As SiO ₂ films (refractive index 1.45) are alternately laminated,
Further, as a thin film having a photochromic effect, a-WO
_Three films (refractive index 2.0) are laminated. The membrane structure is as follows. A = (HL) ⁷ 4P (LH) ⁷ However, the design wavelength λ ₀ was set to 1550 nm, and a single cavity type bandpass filter structure was used. In the single-cavity type, this layer is omitted because the spectrum becomes sharper without the last low refractive index film. FIG. 7 shows the transmittance characteristics of this wavelength selective variable optical attenuator. FIG. 8 is a diagram showing the transmittance characteristic in which the wavelength band of 1540 to 1560 nm is expanded, and FIG. 9 is a diagram showing the reflectance characteristic. Then, as the light for adjusting the light amount level, a YAG laser (basically 10
A laser light source used at 355 nm, which is a third harmonic of 64 nm) as an ultraviolet laser, was used. The same applies to the following examples. In these figures, the curves B,
C, D is the optical power of the ultraviolet laser beam to be irradiated to the amorphous (a-WO ₃₎ film each having a photochromic effect 0 mW (non-irradiated), 1 mW, showing a characteristic when the 10 mW. Also, the extinction coefficient of incident light at a wavelength of 1550 nm corresponds to these powers of × 10 ^-6 and × 1 respectively.
It increases to 0 ^-3 and × 10 ^-2 . As described above, the wavelength component of 1550 nm is selected with almost no attenuation in the non-irradiated state, but the transmittance continuously changes according to the intensity as the level of the ultraviolet laser light increases, showing a change of 20 dB or more. . Further, at other wavelengths, the spectral characteristic does not change significantly, and it functions as a variable optical attenuator having wavelength selectivity.

(Embodiment 2) Next, a wavelength selective variable optical attenuator
Example 2 of the child will be described. This wavelength selective optical attenuation
The device 10B was mounted on the silica glass substrate in the same manner as in Example 1.
Nb as the refractive index film H₂O_FiveFilm (refractive index 2.20) and
SiO as the low refractive index film L₂Cross the film (refractive index 1.45)
As a thin film with photochromic effect
a-MoO ₃A film (refractive index 1.9) is used.
The film structure is the same as in Example 1. Figure 10 shows this wave
7 shows the spectral characteristics of a long-selection type variable optical attenuator. See also Figure 1
1 expands the wavelength band of 1540 to 1560 nm
FIG. Curves B, C, and D are for the ultraviolet laser light, respectively.
When the optical power is 0 mW (non-irradiated), 1 mW, 10 mW
Amorphous with photochromic effect (a-M
oO₃) Shows the transmittance characteristics of the film. Again wavelength 155
The extinction coefficient of the incident light at 0 nm is
Correspondingly × 10^-6, × 10^-3, × 10^-2And increase. This
When there is no irradiation, the wavelength component of 1550 nm is almost
UV laser light is selected with almost no attenuation
If the level of the
It shows a change of 20 dB or more. At other wavelengths,
Has no significant change in the spectrum characteristics and has wavelength selectivity.
Function as a variable optical attenuator.

(Embodiment 3) Next, a wavelength selective variable optical attenuator
A third embodiment of the child will be described. This wavelength selective optical attenuation
The device 10C was mounted on the silica glass substrate in the same manner as in Example 1.
Nb as the refractive index film H₂O_FiveFilm (refractive index 2.20) and
SiO as the low refractive index film L₂Cross the film (refractive index 1.45)
As a thin film with photochromic effect
a-V₂O _FiveA film (refractive index 2.1) is used.
The film structure is the same as in Example 1. Figure 12 shows this wave
7 shows the spectral characteristics of a long-selection type variable optical attenuator. See also Figure 1
3 expands the wavelength band of 1540 to 1560 nm
FIG. Curves B, C, and D are for the ultraviolet laser light, respectively.
When the optical power is 0 mW (non-irradiated), 3 mW, 30 mW
Amorphous with photochromic effect (a-V
₂O_Five) Shows the transmittance characteristics of the film. Again wavelength 155
The extinction coefficient of incident light at 0 nm depends on these powers.
X10 for each^-6, × 10^-3, × 10^-2And increase
It As described above, the wavelength component of 1550 nm is generated when no irradiation is performed.
Minutes are selected with little attenuation, but the UV level is
As the laser light level increases, the transmittance becomes continuous depending on the intensity.
It changes continuously and shows a change of 20 dB or more. Other wavelength
In the case of wavelength selection
Function as a variable optical attenuating element having the property.

(Fourth Embodiment) Next, a fourth embodiment of the wavelength selective variable optical attenuator will be described. This wavelength-selective optical attenuator 10B has a Nb ₂ O ₅ film (refractive index 2.20) as a high refractive index film H and a SiO ₂ film (refractive index) as a low refractive index film L on a silica glass substrate as in the first embodiment. 1.45) are alternately laminated and an a-NiO film (refractive index 1.7) is used as a thin film having a photochromic effect. The film structure is the same as in Example 1. FIG. 14 shows the spectral characteristics of this wavelength selective variable optical attenuator. See also FIG.
FIG. 4 is an enlarged view showing the wavelength band of 1540 to 1560 nm. Curves B, C, and D are amorphous (a-) having a photochromic effect when the optical power of the ultraviolet laser light is 0 mW (non-irradiation), 10 mW, and 100 mW, respectively.
The transmittance characteristic which permeate | transmits a (NiO) film is shown. Again wavelength 155
The extinction coefficient of incident light at 0 nm increases to ^{x10 -6} , x10 ^-3 , and ^{x10 -2} corresponding to these powers, respectively. As described above, the wavelength component of 1550 nm is selected with almost no attenuation in the non-irradiation, but the transmittance continuously changes according to the intensity as the level of the ultraviolet laser light increases, and shows a change of 20 dB or more. . Further, at other wavelengths, the spectral characteristic does not change significantly, and it functions as a variable optical attenuator having wavelength selectivity.

(Fifth Embodiment) Next, a fifth embodiment of the wavelength selective variable optical attenuator will be described. Also in this embodiment, a Nb ₂ O ₅ film (refractive index 2.20) as a high refractive index film H and a SiO ₂ film (refractive index 1.45) as a low refractive index film L are alternately laminated on a silica glass substrate. A-WO as a thin film further having a photochromic effect as in Example 1.
₃ Laminate the film. The film structure is as follows. A = [(HL) ⁶ 4P (LH) ⁶ L] ³ Here, a triple-cavity bandpass filter structure having a design wavelength λ ₀ = 1550 nm was adopted. An ultraviolet laser having a wavelength of 355 nm, which is the third harmonic of the YAG laser, is used, and the irradiation light power is 0 mW (non-irradiation), 1 mW, 1
The extinction coefficient of the a-WO ₃ film at 0 mW is × 10 ^-6 , ×
It increases to 10 ^-3 and × 10 ^-2 . Curves B, C, D in FIG.
Shows the spectral characteristics near 1550 nm for the three cases of this thin film. FIG. 17 shows changes in reflectance with respect to wavelength of the thin film having the photochromic effect. In this case, unlike the above-mentioned embodiment, 155
A substantially flat transmittance characteristic is obtained at about 1 nm centered on 0 nm, and an attenuation rate of incident light of 50 dB or more is achieved. At other wavelengths, a large change in spectral characteristics is not obtained, and it functions as a wavelength tunable optical attenuator having wavelength selectivity. In this way, the change in output level can be increased with respect to the incidence of ultraviolet rays.

[0034]

As described above in detail, according to the inventions of claims 1 to 4 of the present application, it is possible to realize a characteristic having wavelength selectivity while varying the variable wavelength attenuation factor by using the photochromic effect. . Therefore, it is possible to obtain an excellent effect that only the light of a specific wavelength is extracted from the wavelength multiplexed light to adjust the intensity level of the wavelength, or the wavelength level of the wavelength multiplexed light can be kept constant. According to the fifth and sixth aspects of the present invention, by changing the light level with which the dielectric film of the wavelength selective optical attenuating element is irradiated by using the light source, the amount of attenuation in this element can be controlled from the outside. it can. Further, according to the inventions of claims 7 and 8, an excellent effect that the level of each wavelength-multiplexed light can be made constant without using an individual device such as add / drop is obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a dielectric multilayer filter of the present invention and an enlarged view of a multilayer part.

FIG. 2 is a perspective view of a wavelength selective light attenuating element according to a first embodiment of the present invention and an enlarged view of a multilayer film portion.

FIG. 3 is a diagram showing a configuration of a wavelength selective optical attenuator according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a wavelength-selective optical attenuator for keeping a light amount level constant for wavelength-division multiplexed light according to a third embodiment of the present invention.

FIG. 5 is a diagram showing power spectra of incident light and emitted light according to a third embodiment of the present invention.

FIG. 6 is a diagram showing power spectra of incident light and emitted light according to a fourth embodiment of the present invention.

FIG. 7 is a graph showing the relationship between wavelength and transmittance of the wavelength selective optical attenuator according to Example 1 of the present invention.

FIG. 8 is an enlarged graph showing the relationship between wavelength and transmittance of the wavelength-selective optical attenuator according to Example 1 of the present invention.

FIG. 9 is an enlarged graph showing the relationship between the wavelength and the reflectance of the wavelength selective optical attenuating element according to Example 1 of the present invention.

FIG. 10 is a graph showing the relationship between the wavelength and the transmittance of the wavelength selective optical attenuating element according to Example 2 of the present invention.

FIG. 11 is an enlarged graph showing the relationship between the wavelength and the transmittance of the wavelength-selective optical attenuator according to Example 2 of the present invention.

FIG. 12 is a graph showing the relationship between the wavelength and the transmittance of the wavelength selective optical attenuator according to Example 3 of the present invention.

FIG. 13 is an enlarged graph showing the relationship between the wavelength and the transmittance of the wavelength-selective optical attenuator according to Example 3 of the present invention.

FIG. 14 is a graph showing the relationship between wavelength and transmittance of the wavelength selective optical attenuator according to Example 4 of the present invention.

FIG. 15 is an enlarged graph showing the relationship between the wavelength and the transmittance of the wavelength-selective optical attenuator according to Example 4 of the present invention.

FIG. 16 is an enlarged graph showing the relationship between the wavelength and the transmittance of the wavelength-selective optical attenuator according to Example 5 of the present invention.

FIG. 17 is an enlarged graph showing the relationship between the wavelength and the reflectance of the wavelength selective optical attenuating element according to Example 5 of the present invention.

FIG. 18 is a schematic diagram showing an example of a conventional variable attenuation rate optical attenuator.

FIG. 19 is a graph showing the relationship between irradiation position and transmittance.

[Explanation of symbols]

1 substrate 2 Dielectric multilayer film 3 Spacer layer 4 Dielectric film 10 Wavelength selective optical attenuator 11, 14, 16 optical fiber 12, 13, 15 Collimator lens 17 Light source device 20, 20A-20D Wavelength selective variable optical attenuator 21 Branch coupler 22 Signal level detector 23A-23D bandpass filter 24A-24D, 27A-27D Photodetector 25A to 25D feedback circuit

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H038 BA30                 2H048 DA01 DA05 DA12 DA21 GA01                       GA04 GA13 GA18 GA19 GA24                       GA34 GA62                 2H091 FA01X FA01Z FA02X FA02Y                       FA02Z FA03X FA03Y FA03Z                       FA04X FA04Y FA04Z FB08                       FC02 LA03 LA16 LA17 LA20

Claims (8)

[Claims] 1. A refractive index n ₁ and a film thickness d formed on a substrate.
_1. A dielectric multilayer film in which a first dielectric thin film 1 and a second dielectric thin film having a second refractive index n ₂ having a refractive index lower than n ₁ and a film thickness d ₂ are alternately laminated, and a dielectric multilayer A third dielectric film having a photochromic effect laminated between the films, wherein the optical film thickness of the dielectric multilayer film is an integral multiple of λ / 4. element. 2. The wavelength-selective optical attenuator according to claim 1, wherein the third dielectric film is a dielectric thin film having an amorphous structure. 3. The third dielectric film is a-WO₃, A
-MoO₃, A-V ₂O_Five, A-NiO
A single oxide selected.
2. The wavelength selective optical attenuating element according to 2. 4. The wavelength selective optical attenuating element according to claim 2, wherein the third dielectric film has an optical film thickness that is an even multiple of λ / 4. 5. A refractive index n ₁ and a film thickness d formed on a substrate.
_1, a first dielectric thin film, a second dielectric thin film having a second refractive index n ₂ having a lower refractive index than n ₁ , and a second dielectric thin film having a film thickness d ₂ , and a dielectric multilayer film. A third dielectric film having a photochromic effect formed therebetween, wherein the optical thickness of the dielectric multilayer film is an integral multiple of λ / 4, and the wavelength selective optical attenuator A wavelength selective optical attenuator, comprising: a light amount level variable light source that emits light toward a third dielectric film of the optical attenuating element. 6. The variable light amount level type light source has a wavelength of 4
6. An ultraviolet ray having a wavelength of 00 nm or less.
The wavelength selective optical attenuator described. 7. The wavelength-multiplexed light is incident, and the reflected light is sequentially cascaded as the incident light, the transmission wavelengths of which are different from each other, and at least a part of the multiplexed wavelengths of the wavelength-multiplexed light is set as the transmission wavelength. A plurality of wavelength selection type optical attenuators according to claim 5, a branching part for branching a part of the light reflected by the wavelength selective type optical attenuators at the final stage in cascade, and a branching part for branching by the branching part. A light quantity level detection unit for detecting the light quantity level of each wavelength component of the wavelength-multiplexed light, and a level corresponding to each wavelength detected by the light quantity level detection unit of each wavelength component is input, respectively, of the wavelength selective optical attenuator. A wavelength selective optical attenuator, comprising: a feedback circuit for supplying a control signal to a light source, wherein the level of each wavelength component is made constant by feedback control. 8. The wavelength-multiplexed light is made incident, and the reflected light is sequentially cascaded as the incident light, the transmission wavelengths of which are different from each other, and at least a part of the wavelengths of the wavelength-multiplexed light made to be the transmission wavelengths. A plurality of wavelength selection type optical attenuators according to claim 5, a plurality of branching parts which are provided in an output part of each wavelength selection type optical attenuator, and which branch a part of transmitted light, and a branching at each said branching part. A plurality of light amount level detection units for detecting the light amount levels of the respective wavelength components of the wavelength-multiplexed light, and the levels corresponding to the respective wavelengths detected by the light amount level detection units of the respective wavelength components are input, and each is a wavelength selective type. And a feedback circuit for supplying a control signal to the light source of the optical attenuator, wherein the level of each wavelength component is made constant by feedback control.