JP3493019B2 - Tunable bandpass filter module, tunable multiplexer, tunable duplexer, and tunable multiplexer / demultiplexer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable bandpass filter module used for add / drop of an optical network system, a wavelength tunable demultiplexer for demultiplexing light of an arbitrary wavelength from a wavelength multiplexing optical signal, and a wavelength multiplexing. The present invention relates to a wavelength tunable multiplexer that multiplexes light with an arbitrary wavelength and a wavelength tunable multiplexer / demultiplexer that also has these functions.

[0002]

2. Description of the Related Art In the optical communication system, various flexible optical transmission systems are required with the progress of optical wavelength division multiplexing and transmission techniques. In an optical transmission system, it is required to extract light having a desired wavelength from an optical signal wavelength-multiplexed at an arbitrary node, or add light having a desired wavelength and transmit it as wavelength-multiplexed light.

FIG. 7 shows the configuration of a conventional 4-channel optical add / drop device. In the figure, the wavelength-division multiplexed light is added to the optical demultiplexer 101 and the multiplexed wavelengths λ _{1 to} λ
Desired wavelengths such as λ ₁ , λ ₂ , λ ₃ and λ ₄ are demultiplexed from _n . The light of the demultiplexed wavelength is transmitted to the optical switch 102a-
It is incident on each of 102d. Optical switches 102a-10
Signals of newly modulated wavelengths λ _{1 to} λ ₄ are simultaneously incident on 2d. The optical switches 102a to 102d have two inputs and two output ends. One of the signals demultiplexed by the optical demultiplexer and the newly-modulated λ ₁ to λ ₄ based on a control signal from the outside. The signal and are selected and output from two output terminals. The outputs of the optical switches 102a to 102d are the variable optical attenuators 103a to 103d and the demultiplexer 10, respectively.
It is given to the multiplexer 105 via 4a-104d. The demultiplexers 104a to 104d are variable optical attenuators 103a.
A part of the output of ˜103d is extracted and output to the monitor 106. The wavelength intensity is set to be the same by adjusting the output from the variable optical attenuator on the monitor 106.

In the optical communication system (WDM communication system),
Multiple wavelength signal components (λ ₁ , λ ₂ ·
... and to propagate λ _n). In such wavelength division multiplexing optical communication, it is required that an optical node takes out (drops) a signal component of a position wavelength and introduces (adds) an optical signal component of the same wavelength. In the conventional optical add / drop module (OADM), the wavelength to add / drop is fixed to one wavelength or a certain number of wavelengths, but for the purpose of more flexible signal processing, an arbitrary signal channel is selected and its wavelength is changed. There is a need for an OADM device that can add and drop components. In such a device,
A bandpass filter having wavelength tunability is required instead of a bandpass filter that extracts only one wavelength.

A conventional wavelength tunable bandpass filter, for example, as shown in Japanese Unexamined Patent Publication No. 6-265722, forms a multilayer film in which two kinds of dielectric thin films having different refractive indexes are alternately laminated on a substrate. , A dielectric multilayer filter element. Then, in order to change the selection wavelength, the physical film thickness is made to have a gradient distribution along a predetermined direction of the dielectric multilayer film. This filter element is arranged on the moving stage so that it can be moved in the direction in which the film thickness changes. By doing so, the transmitted light signal with respect to the incident light signal exhibits continuous wavelength variability according to the position of the moving stage. In order to realize wavelength tunability in the wavelength range λ ₁ to λ _{2 in} the conventional wavelength tunable optical filter device, the inclination of the physical film thickness ratio (λ ₂ / λ ₁ ) in the movable range of the dielectric multilayer filter element is used. It should have a distribution. For example, wavelength 1 used in the field of optical communication
In order to realize wavelength tunability from 500 nm to 1530 nm, the film thickness distribution ratio is 1.02 (= 15 at maximum) in the movable range.
30 nm / 1500 nm). Further, it can be seen that when the operation range in the moving direction is 50 mm, the wavelength tunability per 1 mm corresponds to 0.6 nm.

In the band-pass filter, a cavity layer having a thickness of a plurality of times is provided in an intermediate portion of the dielectric multilayer film, and a multi-cavity structure having a plurality of cavity layers is used to improve selectivity. .

[0007]

In the current high-density WDM optical communication technology, the International Telecommunications Union (Internatio)
Optical communication is performed on the optical signal channel recommended by the Nal Telecommunication Union (ITU). The channel spacing is 0.8 near the wavelength of 1550 nm.
nm or 0.4 nm intervals. As described above, in order to perform optical signal separation at high speed with high accuracy and excellent signal separation characteristics for an optical signal having a narrow wavelength interval, a multi-cavity, that is, a bandpass filter type wavelength tunable filter with a narrow band of order 2 or more is used. Optical filter devices are desired.

The conventional wavelength tunable filter is considered to be used for such an application, but the optical thin film thickness is inclined in the longitudinal direction of the substrate used as the filter substrate, for example, the one-dimensional direction over 50 mm of the 50 × 4 mm substrate. Therefore, it is difficult to realize a dielectric multilayer filter having 100 layers or more over the entire surface of the substrate with a predetermined optical thin film thickness distribution. It is difficult to produce such a dielectric multilayer filter with a high yield, and there is a drawback that the cost becomes high. Further, in order to realize a narrow band wavelength bandpass filter having a bandwidth of 1 nm or less, which is used in the field of optical communication, it is required to form each layer to a desired film thickness with an error of 0.01% or less. . Due to the film thickness distribution deviation during film formation of the film forming apparatus, the change in the film formation state over time, etc., the length that can satisfy such accuracy is generally 3 to 1.
It is only in the range of 0 mm, and there is a drawback that it is difficult to realize a highly accurate wavelength tunable filter having a length longer than this length. Therefore, its use is generally limited to a single cavity bandpass filter. If the single cavity has insufficient selectivity, it is necessary to connect a plurality of the same single-cavity wavelength tunable filter devices in series to improve the separation characteristics of optical signals.

The present invention has been made by paying attention to such a conventional problem, and is a wavelength tunable bandpass used in a transmission node or the like in a wavelength division multiplexing optical transmission system for selecting an arbitrary wavelength. It is an object to provide a filter module, a wavelength tunable demultiplexer, a wavelength tunable multiplexer and a wavelength tunable multiplexer / demultiplexer.

[0010]

According to a first aspect of the present invention, a variable wavelength bandpass filter and m (m ≧ 2) for changing a voltage applied to the variable wavelength bandpass filter are provided.
A variable voltage source of a table and a voltage control unit for controlling the voltage of each variable voltage source, and the wavelength variable bandpass filter is formed on the transparent optical substrate and the transparent optical substrate. A dielectric multilayer film, wherein the dielectric multilayer film is formed by stacking m layers of cavities, each of the cavities having a different refractive index.
An electro-optical thin film whose refractive index changes due to an electro-optical effect is sandwiched between the first and second dielectric thin films and the first and second dielectric thin films, which are alternately stacked. The variable voltage source includes a variable refractive index layer,
The refractive index is changed by applying a voltage to the electro-optic thin film via the transparent conductor thin film of each cavity, thereby changing the selected wavelength of each cavity. The output voltage of the variable voltage source is the same first voltage, the selected wavelength is the first wavelength, the voltage of a part of the variable voltage source is the second voltage, and the output voltage is the same. The second voltage is controlled so as to switch the selected wavelength to the second wavelength.

The invention of claim 2 of the present application is the wavelength tunable bandpass filter module according to claim 1, wherein the first
The dielectric thin film of H is H, and the second thin film having a refractive index lower than H
Where L is the dielectric thin film, C is the transparent conductive thin film, and M is the electro-optical thin film, these are thin films that are transparent at the light wavelength used, and a substrate / A / medium is formed on the transparent optical substrate. film structure as shown in formula (1), where, m is a positive integer _{(2,3, ···), n 1} , n 2, ···, n m
Is a positive integer (1,2,3, ···), s _m is a positive even number (2,4,6,8, ···), k _m is a positive odd number (1, 3 , 5, 7, ...) and α ₁ , α ₂ , ...
.., α _m , β ₁ , β ₂ , ..., β _m , γ ₁ , γ ₂ ,
.., γ _m is a real number between 0 and 2 and has a film structure.

The invention of claim 3 of the present application is the same as claim 1 or 2.
In the wavelength tunable bandpass filter module, the first dielectric thin film is Ta ₂ O ₅ or Nb ₂ O ₅ , and the second dielectric thin film is SiO ₂ .

The invention of claim 4 of the present application is the same as claim 1 or 2.
In the wavelength tunable bandpass filter module, the transparent conductor thin film is made of Cd ₂ SnO ₄ , ZnO, (G
a, N): ZnO, and (Ga, N): ZnO contains 0.01% to 10% of GaO and N atoms as impurities in ZnO.
It is a substance added between%.

The invention of claim 5 of the present application is the invention of claim 1 or 2.
In the wavelength tunable bandpass filter module, the electro-optic thin film is made of BaTiO ₃ , KTN (KTa _X N
b _{1- X} O ₃ (X = 0.1 to 0.9)), LiNbO ₃ ,

[Chemical 2] Any one of the above substances is used.

The invention according to claim 6 of the present application is a wavelength tunable demultiplexer for adding wavelength-multiplexed light and extracting light of a part of the wavelengths, wherein the wavelength-multiplexed light is extracted. A wavelength tunable bandpass filter module, an incident unit that makes the wavelength multiplexed light enter the wavelength tunable bandpass filter module, and an emission unit that emits light that has passed through the wavelength tunable bandpass filter module, It is characterized in that different voltages are applied from the voltage controller according to the selected wavelength.

The invention of claim 7 of the present application is a wavelength tunable multiplexer which adds light of a desired wavelength not included in the wavelength of the wavelength multiplexed light to the wavelength multiplexed light. The wavelength tunable bandpass filter module according to any one of claims 1 to 3, a first incident section that makes the wavelength-multiplexed light enter the wavelength tunable bandpass filter module, and a wavelength-multiplexed light that is incident from the first incident section. A second incident part for injecting light having a wavelength not included in the wavelength multiplexed light into the wavelength tunable bandpass filter along an optical axis of reflected light reflected by the tunable bandpass filter module; Light incident from the second incident part and transmitted through the wavelength tunable bandpass filter module, and light incident from the first incident part and reflected by the wavelength tunable bandpass filter module. It is characterized in that it comprises an exit section for emitting superposed, the.

According to the invention of claim 8 of the present application, wavelength-multiplexed light is added, and light of a part of wavelengths is extracted, and
A wavelength tunable multiplexer / demultiplexer for adding another optical signal having the extracted wavelength, wherein the wavelength tunable bandpass filter module according to any one of claims 1 to 5 and the wavelength tunable band The first incident part that is incident on the pass filter module, the first emitting part that emits the light that has passed through the wavelength tunable bandpass filter module, and the wavelength multiplexed light that is incident from the first incident part is the wavelength A second incident part for injecting light having a wavelength not included in the wavelength division multiplexed light into the wavelength tunable bandpass filter along an optical axis of reflected light reflected by the tunable bandpass filter module; The light that is incident from the incident part and that has passed through the wavelength tunable bandpass filter module, and the first
And a second emitting portion that emits light that is incident from the incident portion and reflected by the wavelength tunable bandpass filter module in a superimposed manner.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) In the present invention, in order to realize a wavelength tunable bandpass filter having no mechanically movable portion, a thin film type dielectric multilayer filter is basically used. 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 are temperature, humidity, light irradiation,
It was stable with no significant change with respect to voltage application.

On the other hand, if the refractive index of the thin film forming the dielectric multilayer filter can be controlled by some method, a bandpass filter having a wavelength tunable function can be realized. Therefore, a specific substance having an electro-optical effect is used. The electro-optical effect is an effect of changing the refractive index by applying an external voltage, and the effect of linearly changing the refractive index with respect to the applied voltage is called a first-order electro-optical effect or Pockels effect. The change in which the refractive index is proportional to the square of the applied voltage is called the secondary electro-optical effect or the optical Kerr effect. Since the optical film thickness of the dielectric multilayer filter can be changed with the change of the refractive index,
The center wavelength of the bandpass filter can be shifted.

As a material having an electro-optical effect suitable for optical communication, it is necessary to satisfy the following conditions. (1) The electro-optic coefficient is large. (2) Excellent environmental resistance against temperature and humidity. (3) The loss of the thin film itself is small. (4) Stable operation for a long period of time. (5) The film forming conditions are reproducible and stable. (6) It does not require a large amount of rare metal substances. As a thin film material suitable for these conditions, BaTiO ₃ ,
KTN (KTa _X Nb _{1- X} O ₃ (X = 0.10 to 0.
9)) and so on. Since the electro-optic coefficient of each of these bulks is 1000 pm / V or more, a large refractive index change can be caused at a low voltage. In the case of KTN, by adjusting the composition ratio (X) between 0.1 and 0.9, it can be optimized so as to have the maximum electro-optic coefficient at the desired operating temperature. Other materials for the electro-optic thin film include LiNbO ₃ ,

[Chemical 3] There is.

In order to apply an electric field to the electro-optic thin film,
It is a transparent conductor thin film that is transparent in the light band using an optical thin film.
It's sandwiched. For the transparent conductor thin film, for example, Cd₂S
nO _Four, ZnO, (Ga, N): ZnO is used. this
Et al. Are transparent conductor thin film materials used in optical communication in the infrared region.
Is. Here, (Ga, N): ZnO is Ga in ZnO.
Atom and N atom as impurities from 0.01% each
It is a substance added between 10%. Concentration of these additives
Increasing the value lowers the transparency in the infrared region, but improves the conductivity.
Go up. Therefore, if the concentration is low within the range where the desired conductivity is obtained,
The amount added is gradually increased. The desired conductivity is, for example,
For example, it is 1 Ω · cm or less. You can adjust the concentration during this period.
Due to, it is transparent and highly conductive at the wavelength of light used.
Membrane characteristics are obtained.

The film quality to be formed is preferably an amorphous structure or a polycrystalline structure instead of a crystalline structure. The amorphous structure generally has a dense film and is excellent in smoothness of the film surface. Further, there is an advantage that humidity dependence is extremely low and long-term stability of the composition can be obtained. Further, as a method for producing these thin films, the ion beam sputtering method and the ion beam assisted vapor deposition method which have been conventionally used are suitable. This is because in these film forming methods, the kinetic energy of the film constituent particles during film formation is high, and the film structure easily forms an amorphous structure. Therefore, it has been used to manufacture conventional passive bandpass filters. It is relatively easy to control the composition ratio of the formed film by adjusting the supply flow rate of the gas (oxygen gas or the like) used, the beam current / voltage amount during film formation, the degree of vacuum, and the like. Further, the formed film itself has advantages such as low loss characteristics. Further, in these methods, it is possible to form a polycrystalline film by adjusting the film formation temperature using a glass substrate or a crystal substrate as the substrate. As a material for the substrate, oxide glass and optical crystals are suitable for use in the present film formation method because they are stable against temperature changes and environmental resistance during the film formation process.

On the contrary, when a single crystal structure is formed by epitaxial growth, optical anisotropy occurs due to the crystal structure, resulting in limiting the polarization state of the incident beam. Therefore,
A homogeneous and isotropic medium is desirable.

The disadvantage is that the medium is spatially isotropic, so that the polarization vectors are randomly arranged in a microscopic manner, and the effective voltage is 1/3 of the effective voltage.

The response speed of these electro-optical effects is 1n.
Since it is as fast as s (10 ^-9 seconds), it is used as a broadband optical modulator. In this method, the wavelength is changed by changing the refractive index, but the same 1 ns (10
High-speed ^{tunability of} about ^-9 seconds) can be obtained.

Next, the relationship between the change in the refractive index and the applied voltage will be described. [Handling of Micro System] Consider a case where an incident beam propagates in a grain (crystal) having a certain polarization. When the optical principal axes of the crystal are X, Y, and Z, the index ellipsoid is given by the following equation (1). X ² / n _X ² + Y ² / n _Y ² + Z ² / n _Z ² = 1 (1) When the externally applied electric field E exists, the following equation (2) is obtained. _{^{(1 / n 2) 1 X}} 2 + (1 / n 2) 2 Y 2 + (1 / n 2) 3 Z 2 + 2 [(1 / n 2) 4 YZ + (1 / n 2) 5 ZX + (1 / N ² ) ₆ XY] = 1 (2) Here, when E = 0, the following equation (3) is obtained. (1 / n ² ) ₁ = 1 / n _X ² (1 / n ² ) ₂ = 1 / n _Y ² (1 / n ² ) ₃ = 1 / n _Z ² (1 / n ² ) _i = 0 (i = 4, 5, 6) (3) Externally applied voltage E = (E ₁ , E ₂ , along the main axis direction)
The amount of linear change due to E ₃ ) is given by the following equation (4). Δ (1 / n ² ) _i = Σr _ij E _j (i = 1,2, ..., 6; j = 1,2,3) (4) where r _ij is 1 of the electro-optic crystal. It is the next electro-optic coefficient (Pockels coefficient).

The refractive index varies from n to n + Δ depending on an externally applied voltage.
When changing to n, the equation (4) can be expressed by the following equation (5). ^{_{Δn i = -Σ (n 3/}} 2) r ij E j (i = 1,2, ···, 6; j = 1,2,3) ··· (5) where n is no applied voltage The refractive index in the case of the following equation (6)
Given in. n = (n _X + n _Y + n _Z ) / 3 (6)

[Handling of Macroscopic System] When the grain size is small with respect to the incident beam cross-sectional area, the incident beam is affected by the randomly arranged polarization vector, so that the effective refractive index is treated isotropically. Need to do. When E = 0, n _eff = n (7) When there is an applied voltage E ≠ 0, when treated as an isotropic medium, n _eff becomes n _eff + Δn _{ef f} , and from equation (5), Δn _eff = _{(1/3) ΣΔn i = - (} 1/6) Σ i Σ j n 3 r ij E j (i = 1,2, ···, 6; j = 1,2,3) ··· (8 ) Is given by.

Therefore, according to the equation (8), the externally applied voltage is
(E_j) The refractive index by Δn_effOnly linear change
You can As an example, an electro-optic crystal with a point group of 4 mm
(Eg BaTiO 3₃, KTN) have non-zero coefficients
Do r₁₃, R_{twenty three}(= R₁₃), R ₃₆, R₄₂, R₅₁(=
r₄₂).

Now, the dielectric multilayer film structure for having wavelength selectivity will be described below. According to the film design of the optical filter, the dielectric thin film H having different first and second refractive indexes
When the refractive indices of L and L are n _H and n _L (n _H > n _L ), the film structure of the dielectric multilayer mirror having a high reflectance around a certain design wavelength λ ₀ is given by the following equation. Substrate / H L H L ... H L / medium (9) where the thickness d _H of the dielectric thin film H and L, d _L has a λ physical thickness of each quarter, the following Given by the formula. d _H = λ ₀ / 4n _H (10) d _L = λ ₀ / 4n _L (11) The uppermost layer L is a medium, and the medium is generally air, a resin solvent, or a solid substrate. Etc. are possible. Formula (9) is defined by two types of dielectric thin films H and L having optical film thicknesses d _H and d _L on a substrate.
Are alternately laminated. Expression (9) can be simply expressed as in the following expression. Substrate / (HL) ⁿ / medium (12) In this equation, H and L represent layers having the film thicknesses shown in equations (10) and (11). Where (12)
The formula means to repeatedly stack n layers of HL pairs on a substrate. That is, substrate / HLHLHL / medium is equivalent to substrate / (HL) ³ / medium.

By the way, when it is desired to separate only a certain specific wavelength component, a bandpass filter is often used. The film structure of the bandpass filter can be expressed by the following equation. Substrate / A / Medium (13)

[Equation 2] Here, α _m L, β _m H, γ _m L, s _m L are expressed by the formula (1
0) and (11) have film thickness coefficients α _m , β _m ,
It represents a layer having a thickness obtained by multiplying the γ _m, s _m. m is a positive integer (1, 2, 3, ...), n ₁ , n ₂ ,
· · ·, N _m is a positive integer (1,2,3, ···), s _m is a positive even number _{(2,4,6,8, ···), α 1} , α ₂ , ・ ・ ・, α _m , β ₁ , β ₂ , ・ ・ ・,
β _m , γ ₁ , γ ₂ , ..., γ _m are real numbers between 0 and 2.

The film structure of A is called a cavity structure, and an s _m L spacer layer is arranged next to the high reflection mirror part in which a pair of dielectric thin films H and L are laminated n _m times. m
, 1, 2, and 3 are called single cavity, double cavity, and triple cavity, respectively, and are generally called m-fold cavity. The larger the order of m, the steeper the characteristics of the bandpass filter. Further, there is a tendency that the more the transmission bandwidth the larger spacer layer s _m L is becomes narrow. The values of α _m , β _m , and γ _m are between 0 and 2 in order to realize loss reduction and high flatness in the transmission band of the bandpass filter, considering the refractive index of the boundary medium and the incident angle of the incident light. The value of is selected.

[0033] From the above, transmission width in the design of the bandpass filter, these parameters m in consideration of the separation of the other signal, n _m, s _m, alpha _m, beta _m, gamma _m is determined. In order to realize a wavelength tunable filter having a wavelength selection function by applying this feature, a spacer layer of the formula (14) is sandwiched between two layers of transparent conductor thin film (C) as shown below. It is replaced with an electro-optic thin film (M) having an electro-optic effect. The film structure is shown below.

[Equation 3] Here, the film thickness d of C and M_C, D_MIs the λ physical film thickness of 4 minutes
And is given by: d_C= Λ₀/ 4n_C  ... (16) d_M= Λ₀/ 4n_M  ... (17) m is a positive integer (2, 3, ...) And n₁, N₂，
..., n_mIs a positive integer (1, 2, 3, ...)
S_mIs a positive even number (2, 4, 6, 8, ...)
, K_mIs a positive odd number (1, 3, 5, 7, ...)
, Α₁, Α₂, ..., α_m, Β₁, Β₂・ ・ ・ ・ ・ ・
β_m, Γ₁, Γ₂・ ・ ・ ・ ・ ・ Γ_mIs a real number between 0 and 2
is there. n_C, N_MAre transparent conductor thin films (C) and
It is the refractive index of the electro-optic thin film (M). In equation (15)
Then, H, L, C, and M are equations (10), (11),
Representing a layer having a film thickness shown in (16) and (17)
Cage, coefficient α_m, Β_m, Γ _m, S_mThose marked with
It represents a layer having a film thickness multiplied by a coefficient of. This departure
In the Ming, in order to realize hitless, which will be described later,
Ta is an integer of 2 or more.

Next, the structure of this wavelength tunable bandpass filter will be described. For example, as shown in FIG. 1 as a double cavity film structure, the wavelength tunable bandpass filter is formed by depositing a dielectric multilayer film 2 on a substrate 1 such as glass of an oxidation system or optical crystal of an oxidation material such as silicon. Form. The dielectric multilayer film 2 has an enlarged cross-sectional view as shown in FIG.
A first dielectric thin film H having a high refractive index and a second dielectric thin film L having a low refractive index are alternately laminated. Then, instead of the spacer layer between them, the first refractive index variable layer 3A including the transparent conductor thin film C, the electro-optic thin film M, and the transparent conductor thin film C is inserted. Further, the refractive index variable layer 3B having the same structure as this
Insert. Here, the numbers of the first and second dielectric thin films H and L are not limited to the numbers shown.

Then, as shown in the figure, openings 4A and 4B are formed in the dielectric multilayer film 2 from two locations, and reach the transparent conductor thin film C above and below the electro-optic thin film M of the first refractive index variable layer 3A. Etching up to. Further, chromium and gold electrodes are formed on the upper and lower transparent conductor thin films, and the wires are connected to the respective electrodes through the openings 4A and 4B. A variable voltage source 5 is connected to the wire as shown. In addition, as shown in FIG.
C and 4D are formed, and etching is performed until the transparent conductor thin film C above and below the electro-optic thin film M of the second refractive index variable layer 3B is reached. Then, chromium or gold electrodes are formed on the upper and lower transparent conductor thin films C, and the wires are connected to the respective electrodes through the openings 4C and 4D. A variable voltage source 6 is connected to the wire as shown. A voltage control unit 7 for controlling the voltage is connected to the variable voltage sources 5 and 6 as shown in the figure.

Then, the voltages V ₁ and V ₂ are supplied to the variable voltage sources 5 and 6, respectively. Normally, these applied voltages are set to be the same, and the first and second refractive index variable layers 3A, 3
The transparent conductive thin film of B is configured so that the refractive index thereof changes in the same direction. As described above, the refractive index of the electro-optic thin film is changed by replacing the spacer layer of the band-pass filter with the three-layer structure of the two transparent conductor thin films C and the electro-optic thin film M having the electro-optic effect sandwiched between them. Can be made. Since the center wavelength of the bandpass filter is mainly determined by the optical film thickness of the spacer layer, if the optical film thickness of that portion can be changed, remarkable wavelength variability can be realized. Even in the case where the refractive index variable layer 3 is replaced as in the present invention, the wavelength variability can be realized because the optical film thickness changes with the change in the refractive index. Further, in this case, an electric field can be applied to the electro-optic thin film M, and wavelength variability can be realized with steeper characteristics.

FIG. 2 shows a general structure of a double cavity type wavelength tunable bandpass filter. In the figure, L and H in the dielectric multilayer film 2 indicate the film thickness of the dielectric layer. .
Here, 2-1 is the first cavity of the dielectric multilayer film 2,
Reference numeral 2 denotes the second cavity of the dielectric multilayer film 2. The wavelength tunable module using the double cavity type wavelength tunable bandpass filter is provided with variable voltage sources 5 and 6 for applying these voltages and a voltage controller 7 for controlling the voltage of the variable voltage source.

Next, the operation of the voltage controller will be described.
The voltage controller 7 applies the same voltage to the two cavities to set the refractive index of a predetermined electro-optic thin film to a predetermined value. In this way, the wavelength selection characteristic corresponding to it can be obtained. Then, when changing the wavelength, one of the voltages is once set to a voltage having a target wavelength. Then, both voltages are set to voltages corresponding to the target wavelength. In this way, the selected wavelength does not change continuously, and the wavelength selection characteristic can be changed.

(Second Embodiment) Next, a triple cavity type wavelength tunable bandpass filter according to a second embodiment will be described. However, the design wavelength λ ₀ was set to 1570 nm. A BK7 glass substrate was used as the substrate 1, and a dielectric thin film Nb ₂ O ₅ film (refractive index n _H = 2.24) was used as the first dielectric thin film H having a high refractive index. Other materials include Ta
_{A 2} O ₅ film (refractive index n _H = 2.13) can be used. Further, as the second dielectric thin film L having a low refractive index, SiO _{2 is used.}
A film (refractive index n _L = 1.45) was used. The transparent conductor thin film C has a Cd ₂ SnO ₄ film ((refractive index n _C = 1.9.
0) was used. This film operates as a transparent conductor thin film at a wavelength of around 1570 nm and has a resistivity of 1 × 10 ^-2 Ω.
・ Cm or less was obtained. The electro-optic thin film M having the primary electro-optic effect includes a KTN film (KTa _X Nb _1-X O ₃ (X
= 0.65)) was used. The refractive index (n _M ) is 2.30. The external medium is a medium having a refractive index of 1.50. KTN
Corresponds to a point group of 4 mm, and the following values are obtained for the primary electro-optic coefficient. _{r 42 = r 51 = 16000pm /} V r 13 «r 42 r 36 «r 42 this time (8) is, Δn _eff = -0.022 @E
= 1 V / μm. That is, when the thickness of the electro-optical thin film M in the spacer layer is 1 μm, the applied voltage is 1 to 0 V.
Changing to V corresponds to a 0.022 decrease in refractive index from 2.3 to 2.288.

The structure of the film structure A of this example is shown below. By using A = [(HL) ⁷ C4MC (LH) ⁷ L] ³ triple cavities, it was possible to realize a bandpass filter characteristic with top flatness and high wavelength selectivity. The full width at half maximum of the bandpass was 0.52 nm.

In this embodiment, because of the triple cavity, the voltages V ₁ , V ₂ and V _{3 are respectively} supplied from the three variable voltage sources.
To the electro-optic thin film of each cavity. FIG. 3 shows the wavelength variable characteristic. Transparent conductor thin film C in each cavity
Applied voltage of the same DC component from the outside (V ₁ = V ₂ = V
_{When 3} ) is added, wavelength selection characteristics corresponding to that voltage can be obtained. For example, when V ₁ = V ₂ = V ₃ = 1.2V, the refractive index of the KTN film changes to 2.26, which is decreased by 0.04 from 2.30 when no voltage is applied. In this case, the center wavelength of the filter appears at 1560.5 nm,
The wavelength variable amount corresponds to about 10 nm.

Similarly, when the applied voltage is 4.8 V, K
The refractive index of the TN film is 2.14, and the center wavelength of the bandpass filter appears at 1531 nm. As described above, it was possible to realize wavelength tunability of about 40 nm from 1570 nm to 1531 nm as the wavelength tunable range when the applied voltage was within 5 V.

Next, the operation for performing hitless wavelength tuning using the wavelength variable bandpass filter module will be described. Here, hitless means that when the wavelength is changed, it does not change continuously from a certain wavelength to the target wavelength, but once it has reflection characteristics for all wavelengths, and then the target wavelength. It is intended to obtain the property of selecting the light. The operation for hitless is executed in the following three steps.

(1) First, in step 1, the voltage controller 7
A predetermined voltage is set for the three variable voltage sources.
For example, the voltage applied to each cavity is V ₁ = V ₂ = V ₃ =
1.2V. At this time, the selected wavelength λ _i is adjusted to 1560.5 nm as shown in FIG.

(2) In the next step 2, the applied voltage to the first and third cavities of the triple cavity is switched to the applied voltage corresponding to the wavelength component of the voltage to be tuned.
For example, if the voltage is 3.6 V, V ₁ = V ₃ = 3.
Set to 6V. When only V ₂ is returned to the original state, the resonance wavelength of one of the cavities does not match, so that no selection characteristic is obtained for any wavelength component.
As shown in (b), it has a reflection characteristic of reflecting all the light in all wavelength bands.

(3) Next, in step 3, the applied voltage V _{2 to the second} cavity is set to 3.6V as in the other cavities. In this way, all applied voltages are V ₁ = V ₂ = V ₃ =
Since the resonant wavelength of each cavity is equal to 3.6 V, the wavelength selected by the bandpass filter is λ _j = 15.
It becomes 41.5 nm. Therefore, as shown in FIG. 4C, desired characteristics can be obtained at this wavelength.

On the other hand, when changing from a certain wavelength λ _i to λ _j , when the applied voltage in the initial state is directly changed to the voltage having the target wavelength, the selected wavelength also changes during this period due to the transient change of the voltage. there's a possibility that. However, if the voltage is switched through the steps (1) to (3), a desired wavelength, in this case, another wavelength between the wavelengths λ _i and λ _j is selected for a moment. Wavelength tunability can be realized without

In this embodiment, the voltage applied to the first and third cavities is set as the target voltage applied from the step of making the voltage applied to all cavities the same in the case of the triple cavity. In step 2, the voltage is changed to step 3 in which all the voltages are set to target voltages, and hitless wavelength shift is realized. However, in step 2, only the voltage applied to some of the cavities may be set to a voltage corresponding to the target wavelength. For example, in step 2, the applied voltage V ₂ to the second cavity is the target voltage,
In this case, the voltage may be set to 3.6V, and then all the voltages may be set to 3.6V in step 3. Further, in step 2, it may be possible to set only the voltage V ₁ applied to the first cavity to the target voltage.

(Embodiment 3) FIG. 5 shows a general structure of an m-fold cavity type wavelength tunable bandpass filter. As shown in FIG. 5, the m-fold cavity type wavelength tunable bandpass filter has cavities 2-1 to 2-m stacked on a substrate. Similarly, in the case of the bandpass filter module using the bandpass filter of the m-fold cavity, the voltage applied to the plurality of variable refractive index layers 3 is changed using m variable voltage sources. This makes it possible to realize a bandpass filter with steep characteristics.

In order to realize a hitless wavelength change with an m-fold cavity band-pass filter, the voltage applied to one of the cavities is changed to a voltage having the next target wavelength in step 2, and then step 3 is changed. The voltage applied to all the cavities is set to a wavelength at which the target wavelength is obtained. In this case, it is preferable that, for example, either an even number or an odd number is set as the target voltage in step 2, and the applied voltage to all the cavities is set in step 3 to a voltage at which the target wavelength is obtained. In this way, it is possible to secure the reflection characteristics for all wavelengths in step 2 and achieve hitless with desired wavelength selection characteristics in step 3.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIG. In this embodiment, a variable wavelength multiplexer / demultiplexer is realized by using the variable wavelength bandpass filter module described above. In the figure, an optical fiber 11 is an optical fiber to which wavelength-multiplexed light of λ ₁ to λ _n is added, and is connected to a two-core capillary 12 as shown in the figure. The two-core capillary 12 is a cylindrical member that holds the optical fiber 11 for incidence and the optical fiber 13 for emission, and the optical fibers 11, 1 at the lower end thereof.
The output end face of No. 3 is held substantially at the center position. The lower end is cut with a slight tilt from the central axis so that the reflected light does not return to the incident side. The two-core capillary 12 is attached to a cylindrical refractive index distribution lens (Graded Index Lens, hereinafter referred to as GRIN lens) 14 having the same diameter as the two-core capillary 12. GRIN lens 1
Reference numeral 4 denotes a lens configured such that the refractive index continuously increases from the periphery toward the central axis, and the light emitted from the optical fiber 11 can be made into parallel light by selecting the length thereof. . The upper end of the GRIN lens 14 is processed such that the surface in contact with the two-core capillary is slightly inclined, and has a series of cylindrical shapes together with the two-core capillary 12. Below the GRIN lens 14, the same triple cavity type wavelength tunable bandpass filter 15 as in the second embodiment is used.
Are placed. The wavelength tunable bandpass filter 15 is provided with variable voltage sources 16A, 16B, 16C and a voltage controller 17 for controlling the applied voltage. A GRIN lens 18 for one core is provided at a position where the light that has passed through the wavelength tunable bandpass filter 15 is received. An optical fiber 19 for emission is provided at the emission end of this lens.

The optical fiber 13 attached to the two-core capillary 12 guides the light reflected by the filter 14 to the capillary 21. Similar to the capillary 12, the optical fibers 13 and 22 are attached to the capillary 21 at symmetrical positions from the center thereof, and a GRIN lens 23 for two cores is provided coaxially with the capillary 21. The capillary 21 and GRIN lens 23 are the same as the above-described capillary 12 and GRIN lens 14, respectively. And GRI
A wavelength-tunable bandpass filter 24 is provided at the emission end of the N lens 23. The bandpass filter 24 is also a triple cavity type filter like the bandpass filter 15, and the same variable voltage sources 16A, 16B and 16C are used.
Shall be driven simultaneously by. A GRIN lens 25 for one core is provided on the emission end side of the bandpass filter 24, and an optical fiber 26 is connected thereto.
Here, the one-core GRIN lens 25 is arranged so as to join the wavelength tunable bandpass filter 24 from the optical fiber 13 through the GRIN lens 23 and emit light on the same optical axis as the reflected light. To do.

Here, the optical fiber 11, the cavity 12,
The 2-core GRIN lens 14 constitutes a first incidence part for making wavelength-multiplexed light incident on the variable wavelength bandpass filter module, and the 1-core GRIN lens 18 and the optical fiber 19 pass through this bandpass filter 15. A first emitting unit that emits the emitted light is configured. Further, the GRIN lens 25 for one core and the optical fiber 26 constitute a second incident section for adding the add light to the variable wavelength multiplexer / demultiplexer. Further, a 2-core GRIN lens 23, a capillary 21, an optical fiber 22
Constitutes a second emitting section for outputting the multiplexed wavelength multiplexed light.

Next, the wavelength tunable multiplexer / demultiplexer according to this embodiment
The operation of the container will be described. First, the optical fiber for incidence
11 for λ₁~ Λ_nWDM light is added up to
It A certain wavelength λ from this wavelength multiplexed light_iExtract only the components of
(Drop) and λ _iWave to wavelength multiplexed light excluding
Long λ_iThink about the case of adding (adding) another optical signal of
It In this case, first, the voltage controller 17 controls the variable voltage source.
A wavelength tunable band of the wavelength multiplexed light is transmitted through 16A to 16C.
The selected wavelength of the de-pass filters 15 and 24 is λ_iAnd This
If it is λ_iTunable bandpass filter 1
5 through the 1-core GRIN lens 18
It will be output to the optical fiber 19 for the optical fiber. λ_iSince
The optical signal of the outside wavelength component is reflected by the bandpass filter 15.
Through the 2-core GRIN lens 14 and the capillary 12.
It is incident on the optical fiber 13. This light goes through the capillary 21
It is added to the GRIN lens 23 via the
It joins the long variable bandpass filter 24. As mentioned above
The bandpass filter 24 also has a selected wavelength of λ_iSet to
Therefore, λ_iLight of all components except
Guided by Ba 22. On the other hand, the wavelength λ_iOther optical signals from the optical fiber
It is incident from the iva 26. At this time, it is guided from the optical fiber 26.
Wavelength λ_iLight is transmitted through the GRIN lens 25 for one core.
And added to the wavelength tunable bandpass filter 24,
Passes through the band-pass filter 24 and the optical fiber
It is added to the ba 22. Therefore, the new wavelength λ_iSignal of
Can be added to the wavelength division multiplexed light of the optical fiber 22 for irradiation.
It

When changing the selected wavelength from λ _i to λ _j , a voltage corresponding to the wavelength λ _j is applied to only some of the cavities, as shown in step 2 of the second embodiment. . Then, once the band pass filter 1
5, 24 are in a reflective state for all wavelengths. Next, in step 3, a voltage corresponding to the target wavelength λ _j is applied to the remaining cavities, and the selected wavelength is set to λ _j . This was dropped signal wavelength lambda _j if, it is possible to superimpose the optical signal in which the different wavelength lambda _j.

In the fourth embodiment, a wavelength tunable multiplexer / demultiplexer that extracts (drops) a predetermined wavelength from an optical signal and superimposes (adds) the same wavelength as this is explained. It can also be used as a wavelength tunable demultiplexer by using the members up to 19. It can also be realized as a wavelength tunable multiplexer that superimposes the signal of the removed channel of the wavelength multiplexed signal using the materials of the optical fiber 13 and the capillaries 21 to 26.

In the fourth embodiment, light is superposed on the bandpass filter by using the optical fibers for entrance and exit, the capillaries, and the GRIN lens, and the reflected light is guided to the filter of the next stage. Alternatively, the optical signal may be directly superimposed on the bandpass filter, and the reflected light may be guided to the next bandpass filter as it is or via a mirror or the like. As described above, a wavelength tunable optical multiplexer / demultiplexer, a wavelength tunable demultiplexer, and a wavelength tunable multiplexer can be realized without omitting the non-essential optical components.

[0058]

As described above, the wavelength tunable bandpass filter module according to the present invention uses the optical bandpass filter capable of changing the selected wavelength by the application of the voltage, and when the wavelength is switched, all the light is reflected once. After changing to the state, the wavelength is switched to the selected wavelength.Therefore, while moving the wavelength for the wavelength division multiplexed light, there are no wavelengths that continuously pass through it, and unnecessary interference due to wavelength change is prevented. You can Further, in the wavelength tunable multiplexer / demultiplexer, the wavelength tunable demultiplexer, and the wavelength tunable multiplexer, wavelengths are continuously added when adding or extracting light of a desired wavelength using such a wavelength tunable bandpass filter. It is possible to obtain an excellent effect that unnecessary interference due to the wavelength change can be prevented without changing the wavelength.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a double cavity type wavelength tunable bandpass filter according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a general configuration of a dielectric multilayer film of the double cavity type wavelength tunable bandpass filter according to the present embodiment.

FIG. 3 is a graph showing wavelength tunable characteristics of the wavelength tunable bandpass filter according to the second embodiment.

FIG. 4 is a graph showing changes in transmittance and reflectance when wavelengths are changed by using the wavelength tunable bandpass filter according to the second embodiment.

FIG. 5 is a diagram showing a general configuration of a dielectric multilayer film of an m-fold cavity type wavelength tunable bandpass filter according to a third embodiment.

FIG. 6 is a diagram showing a configuration of a variable wavelength multiplexer / demultiplexer according to a fourth embodiment.

FIG. 7 is a diagram showing a configuration of a conventional 4-channel optical add / drop device.

[Explanation of symbols]

1 substrate 2 Dielectric multilayer film 2-1 First cavity 2-2 Second cavity 2-m m-th cavity 3A, 3B refractive index variable layer 4A-4D opening 5, 6, 16A, 16B, 16C Variable voltage source 11,13,19,22,26 Optical fiber 7,17 Voltage controller 12,21 capillaries 14,23 2-core GRIN lens 15,24 Wavelength tunable bandpass filter 18,25 1-core GRIN lens H first dielectric film L second dielectric film C transparent conductor thin film M Electro-optic thin film

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 2001-91911 (JP, A) JP 10-221662 (JP, A) JP 61-88229 (JP, A) Optical / Thin Film Technical Manual Supplement Revised version, Optronics Co., Ltd., August 31, 1992, pp. 284-289 (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/01-1/03 JSTPlus (JOIS)

Claims (8)

(57) [Claims] 1. A variable wavelength bandpass filter, m (m ≧ 2) variable voltage sources that change the voltage applied to the variable wavelength bandpass filter, and a voltage that controls the voltage of each variable voltage source. And a dielectric multilayer film formed on the transparent optical substrate, wherein the dielectric multilayer film comprises m layers. The cavities are formed by stacking cavities, each of the cavities having a different refractive index and alternately stacked first and second dielectric thin films, and the first and second dielectric thin films. In between, the electro-optic thin film whose refractive index is changed by the electro-optic effect is sandwiched between transparent conductor thin films, and the variable voltage source includes the transparent conductor thin film of each cavity. The electro-optic The refractive index is changed by applying a voltage to each of the films, and the selected wavelength of each cavity is changed. The voltage control unit sets the output voltage of each variable voltage source to the same first voltage. A state in which the selected wavelength is the first wavelength, a state in which a part of the voltage of the variable voltage source is the second voltage, and an output voltage is the same second voltage, and the selected wavelength is the second wavelength. A wavelength tunable bandpass filter module, which is controlled so as to switch between different states. 2. When the first dielectric thin film is H, the second dielectric thin film having a lower refractive index is L, the transparent conductive thin film is C, and the electro-optic thin film is M, these Is a thin film that is transparent at the light wavelength used, and the following film structure substrate / A / medium Here, m is a positive integer (2, 3, ...),
n ₁ , n ₂ , ..., N _m are positive integers (1, 2, 3, ...
...), and, s _m is a positive even number (2, 4, 6, 8, ...
.), And k _m is a positive odd number (1, 3, 5, 7, ...
・), Α ₁ , α ₂ , ..., α _m , β ₁ , β ₂ ,
_{···, β m, γ 1,} γ 2, ···, the gamma _m is a real number between 0-2, tunable bandpass filter module according to claim 1 having a membrane structure. 3. The first dielectric thin film is Ta ₂ O ₅ ,
The wavelength tunable bandpass filter module according to claim 1, wherein the second dielectric thin film is Nb ₂ O ₅ , and the second dielectric thin film is SiO ₂ . 4. The transparent conductor thin film is Cd ₂ Sn
One of O ₄ , ZnO, and (Ga, N): ZnO is used as the constituent material, and (Ga, N): ZnO has a Ga atom and an N atom of ZnO as impurities of 0.01 and respectively. 3. The wavelength tunable bandpass filter module according to claim 1, which is a substance added in the range of 10% to 10%. 5. The electro-optic thin film is BaTiO 3.₃, K
TN (KTa_XNb _1-XO₃(X = 0.1 to 0.
9)), LiNbO₃, [Chemical 1] The wave according to claim 1 or 2 using any one of the substances
Long variable bandpass filter module. 6. A wavelength tunable bandpass filter module according to claim 1, wherein the wavelength tunable demultiplexer is a wavelength tunable demultiplexer to which wavelength-multiplexed light is added and light of a part of the wavelengths is extracted. An input unit that inputs the wavelength-multiplexed light into the wavelength tunable bandpass filter module, and an output unit that outputs the light that has passed through the wavelength tunable bandpass filter module, and the voltage according to the selected wavelength. A variable wavelength demultiplexer characterized in that different voltages are applied from a control unit. 7. A wavelength tunable multiplexer that adds light of a desired wavelength not included in the wavelength of the wavelength multiplexed light to the wavelength multiplexed light, the wavelength of any one of claims 1 to 5. A tunable bandpass filter module; a first incidence unit that makes the wavelength-multiplexed light incident on the wavelength tunable bandpass filter module; and a wavelength-multiplexed light that is incident from the first incidence unit. A light having a wavelength not included in the wavelength multiplexed light is incident on the wavelength tunable bandpass filter along the optical axis of the reflected light reflected by
Of the incident light, the light incident from the second incident portion and transmitted through the variable wavelength bandpass filter module, and the light incident from the first incident portion and reflected by the variable wavelength bandpass filter module. A variable wavelength multiplexer comprising: an emission unit that emits light in a superposed manner. 8. A wavelength tunable multiplexer / demultiplexer to which wavelength-multiplexed light is added, and light of a part of wavelengths thereof is extracted and another optical signal having the extracted wavelength is added.
5. The wavelength tunable bandpass filter module according to any one of 5, A first incident unit that makes the wavelength-multiplexed light enter the wavelength tunable bandpass filter module, and a light that has passed through the wavelength tunable bandpass filter module. A first emitting portion that emits light, and wavelength-multiplexed light that is incident from the first incident portion is included in the wavelength-multiplexed light along an optical axis of reflected light that is reflected by the wavelength tunable bandpass filter module. A second wavelength of variable wavelength band-pass filter is incident on the second wavelength
Of the incident light, the light incident from the second incident portion and transmitted through the variable wavelength bandpass filter module, and the light incident from the first incident portion and reflected by the variable wavelength bandpass filter module. A wavelength tunable multiplexer / demultiplexer comprising: a second emitting portion that emits in a superposed manner.