JP2002071943A - Optical multilayer film filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute an optical multilayer film filter used in optical communications in such a way that total film thickness is made thin and the number of constituent layers is reduced without damaging the performance. SOLUTION: The optical multilayer film filter used in optical communications with a light in the near infrared region is manufactured by using niobium pentoxide (Nb2O5) as a high refractive index substance and silicon dioxide (SiO2) as a low refractive index substance and by alternately laminating the high refractive index substance layer and the low refractive index substance layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical multilayer filter which is formed by alternately laminating high-refractive-index material layers and low-refractive-index material layers, and is used for optical communication using light in a near-infrared region.

[Detailed Description of the Invention] Today, the spread and use of the Internet communication and the like are progressing, and the traffic of communication lines is rapidly increasing. At present, optical communication using optical fibers with large communication capacity is the mainstream, but it is required to increase the capacity that can be transmitted through each optical fiber, and it is easy to increase the communication capacity among optical communication technologies. Wavelength division multiplexing communication technology (WDM communication system: Wave-length Division Multplexing
Communication method) is being used. WD
In the M communication system, it is necessary to divide the light in the near-infrared region used for communication into a plurality of fine wavelength regions or to combine the light in the plurality of wavelength regions. In addition, a large number of optical multilayer filters are required.

[0003] Such an optical multilayer filter is disclosed in, for example, JP-A-7-198935.
It is made by alternately laminating high refractive index material layers and low refractive index material layers. This optical multilayer filter has a very complicated configuration in which the thickness of each layer formed by laminating dozens of layers is different from each other. Management is required.
As a film formation method for forming such a multilayer film, a vacuum deposition method has been well known. However, when a film is formed using the vacuum deposition method, the structure of the film becomes columnar, and the absorption and desorption of moisture in the gaps are reduced. This causes a problem that a shift in filter characteristics (a shift in a selected wavelength region) occurs.

In order to avoid such a problem, it is necessary to densify the film structure to such an extent that moisture is not absorbed and desorbed in the film. As a method for obtaining such a dense film structure, a vacuum evaporation method is used. An ion beam-assisted vapor deposition method with an ion gun and a plasma ion-assisted vapor deposition method that assists with ions extracted from a plasma source have been considered. In addition, it is necessary to use a material that is optimal for optical communication technology as a film material constituting the high refractive index material layer and the low refractive index material layer. In addition, as a substance used for an optical multilayer film in the near infrared region, an alternating layer film of titanium oxide and silicon oxide and an alternating layer film of tantalum oxide and silicon oxide are known. As a film forming method, an ion beam sputtering method or an RF sputtering method, in which a relatively stable evaporation distribution or sputtering distribution is easily obtained, may be adopted.

[0005]

In the ion beam assisted vapor deposition method and the plasma ion assisted vapor deposition method, the dissolution of a sample (target) in electron beam deposition tends to be unstable, and the evaporation distribution tends to fluctuate.
In the film forming process, it is necessary to constantly monitor and correct the film thickness while performing the film forming operation, which causes a problem that the film forming operation is difficult and the production cost increases. On the other hand, both the ion beam sputtering method and the RF sputtering method can form a film that is relatively stable, but the film forming rate is about 1/5 of that of the ion beam assisted vapor deposition method and the plasma ion assisted vapor deposition method. There is a problem that it is slow, production efficiency is low, and production cost is high.

An optical multilayer filter, particularly an optical multilayer filter used for optical communication, is used in various environments, and must transmit light to a distant place with low loss, so that stable optical characteristics can be obtained. Must have.
Therefore, a light-absorbing and light-scattering property is low, and a dense film is required. Further, an optical multilayer filter having a stable optical characteristic with a stable refractive index regardless of the film forming conditions is required. .

[0007] Further, optical communication filters are used in places where light is split or combined or light is amplified. And it is necessary to provide many such places everywhere in the optical communication network. Therefore, when forming an optical communication network, a large number of optical multilayer filters having desired conditions are required, and it is desired that a large number of optical communication filters can be obtained with high production efficiency. I have.

In general, when an optical multilayer filter is manufactured, if the thickness of each layer can be reduced and the number of layers constituting the filter can be reduced, the film forming time can be shortened and the production time can be reduced. It is thought that the efficiency can be increased and the production cost can be reduced. For this reason, there is a demand for a film material having a small total film thickness and capable of obtaining desired filter performance with a small number of layers.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an optical multilayer filter having a structure capable of reducing the total film thickness and the number of constituent layers without deteriorating the performance.

[0010] The present invention further provides an optical multilayer film filter which is formed by using a film forming method capable of forming a film at a high film forming rate and stably, so that the production efficiency is high and the production cost is low. The purpose is to do.

[0011]

In order to achieve the above object, the optical multilayer filter according to the present invention is used for optical communication using light in the near-infrared region. Niobium (Nb ₂ O ₅ ) is used, silicon dioxide (SiO ₂ ) is used as a low refractive index material, and high refractive index material layers and low refractive index material layers are alternately laminated.

Since the difference between the refractive indices of niobium pentoxide (Nb ₂ O ₅ ) and silicon dioxide (SiO ₂ ) is large, the use of such an optical multilayer filter having such a structure reduces the total film thickness and necessity. Desired filter performance can be obtained by reducing the number of layers. For this reason, the film formation time is shortened, the production efficiency is improved, and the production cost is reduced. As described above, the optical multilayer filter composed of niobium pentoxide and silicon dioxide has characteristics of low absorption and low scattering, and a stable refractive index can be obtained. It is suitable as a filter.

The optical multilayer filter comprising niobium pentoxide and silicon dioxide is particularly preferably used for wavelength division multiplex optical communication. The optical multilayer filter used for this wavelength division multiplexing optical communication has much severer wavelength selection performance. Therefore, the number of layers formed to satisfy the performance naturally increases. However, niobium pentoxide and silicon dioxide have characteristics of high refractive index stability, low absorption and low scattering, and have a large difference in refractive index. It is suitable as an optical multilayer filter used for wavelength division multiplexing optical communication.

It is preferable that the high refractive index material layers and the low refractive index material layers are alternately formed by AC dual cathode sputtering. The AC dual-cathode sputtering method does not have a problem that the melting of a sample (target) becomes unstable and the evaporation rate or the sputtering distribution fluctuates as in the case of the ion beam assisted vapor deposition method and the plasma ion assisted vapor deposition method, and the film formation is stable. It is possible to automate the film forming operation and reduce the production cost. Further, the film formation rate of the AC dual cathode sputtering method is almost equal to that of the ion beam assisted vapor deposition method and the plasma ion assisted vapor deposition method, and there is an advantage that higher production efficiency can be obtained as compared with the ion beam sputtering method and the RF sputtering method. .

In another aspect of the present invention, an optical multilayer filter used for optical communication using light in the near-infrared region is formed by alternately laminating high-refractive-index oxide compound layers and low-refractive-index oxide compound layers. At this time, a high-refractive-index oxide compound layer and a low-refractive-index oxide compound layer are formed by AC dual cathode sputtering.

In the production of an optical multilayer filter, it is required to control the thickness of each layer with very high accuracy. Therefore, unlike the conventional ion beam-assisted vapor deposition method and plasma ion-assisted vapor deposition method, In a film forming method in which fluctuations in the evaporation distribution are likely to occur, the presence or absence of film forming fluctuations is constantly monitored during the film forming operation.
This needs to be dealt with immediately. For this reason, there is a problem that a load for monitoring fluctuations in the film forming operation is large, production efficiency is easily lowered, and production costs are increased. However, as in the present invention, the AC dual cathode sputtering method is used. If the film work is performed, stable film formation without fluctuation in film formation is possible, and the film formation work can be automated. Further, the film formation rate is equivalent to that of the ion beam assisted vapor deposition method and the plasma ion assisted vapor deposition method, and according to the present invention, the production efficiency can be improved and the production cost can be reduced.

As described above, in the film forming method using the AC dual cathode sputtering method, tantalum pentoxide (Ta ₂ O ₅ ) is used as a high refractive index oxide compound, and silicon dioxide (SiO ₂ ) is used as a low refractive index oxide compound. ) Is preferably applied to an optical multilayer filter for optical communication using the method described in (1). An optical multilayer filter made of tantalum pentoxide (Ta ₂ O ₅ ) and silicon dioxide (SiO ₂ ) having a refractive index difference smaller than that of niobium pentoxide and silicon dioxide described above,
The number of layers is larger than that of the optical multilayer film filter of niobium pentoxide and silicon dioxide, but the film can be formed stably without film formation fluctuation, so that the manufacture of the filter with this material is simpler than the conventional manufacturing method, and Since it has high refractive index stability and also has characteristics of low absorption and low scattering, it is suitable as an optical multilayer filter for optical communication. Even when compared with the conventional method, when a multilayer film of tantalum pentoxide and silicon dioxide is formed so as to obtain desired wavelength characteristics, a reduction in the film formation time can be expected. Such an optical multilayer filter is particularly suitable for an optical multilayer filter for wavelength division multiplex communication in which the number of layers is large.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. Before describing the optical multilayer filter according to the present invention, a WDM communication system using such an optical multilayer filter will be described with reference to FIG.

This system comprises a plurality of laser emitters L1, L2, L2, each outputting an optical signal of a different wavelength.
, Ln, a signal combiner 1 for combining the signal lights emitted from these laser light emitters, and a transmission optical fiber 2 for transmitting the signal light combined and emitted by the combiner 1
And a predetermined interval (for example, 80
a plurality of amplifiers 3 (e.g., composed of optical fiber amplifiers) arranged at a distance (km intervals) and amplifying the transmission optical signal, and a plurality of different optical signals transmitted through the transmission optical fiber 2. A demultiplexer 5 for splitting the wavelength into optical signals,
.., Dn for detecting each optical signal divided by the demultiplexer 5. The detectors D1, D2, D3,.

In the system having such a configuration, on the transmitting side, each of the laser emitters L1, L2, L3,.
Optical signals are output from Ln, respectively, combined by the multiplexer 1 and transmitted as a collective optical signal through the transmission optical fiber 2. On the other hand, on the receiving side, after the optical signal emitted from the transmission optical fiber 2 is divided by the demultiplexer 5 into a plurality of optical signals, each optical signal is divided into the corresponding detectors D1, D2, D3,. Dn. With this configuration, one transmission optical fiber 2
Accordingly, a large number of optical signals can be transmitted in a superimposed manner, and the signal transmission efficiency is high.

Here, the configuration of the multiplexer 1 is shown in detail in FIG. The multiplexer 1 includes laser emitters L1, L
2, L3,..., Ln and a plurality of optical filters FL1, FL2, FL3,. The wavelength λ1 is output from the laser emitter L1.
Is emitted, and light having a desired wavelength width (for example, a narrow wavelength width of about 1 nm) is selected by the optical filter FL1 and emitted to the optical fiber OF1. Note that when laser signal light having a desired wavelength width is emitted from the laser light emitter L1, the optical filter FL1 may not be provided.

On the other hand, the wavelength λ2
Is emitted and enters the front side of the optical filter FL2. The optical fiber OF1 is guided to the rear surface side of the optical filter FL2, and the laser signal light having the wavelength λ1 is emitted toward the front surface of the optical filter FL2.
Here, as shown in FIG. 3, the optical filter FL2 is composed of an optical multilayer filter having a property of transmitting light of the wavelength λ2 but reflecting light of other wavelengths. The signal light of the wavelength λ2 is transmitted as it is, and the light of the wavelength λ1 from the optical fiber OF1 irradiated on the rear surface side is reflected.

An optical fiber OF2 is disposed opposite to the rear surface of the optical filter FL2, and the signal light transmitted through the optical filter FL2 and emitted from the optical fiber OF1 and reflected by the optical filter FL2 as described above. The signal light is incident on the optical filter FL2. As a result, the signal light obtained by combining the signal lights of the wavelengths λ1 and λ2 enters the optical fiber OF2.

Hereinafter, in the same relationship as described above, the optical filters FL3,.
FLn is provided, and the optical filter FL3 includes:
The combined signal lights of wavelengths λ1 and λ2 and the signal light of λ3 are respectively incident on different surfaces, the signal lights of λ1, λ2 and λ3 are combined, and then incident on the next optical fiber OF3. The optical filter FLn at the final position has λ1, λ2,
.lambda.n-1 and the combined signal light of all wavelengths .lambda.1, .lambda.2, .lambda.3... .lambda.n are incident on the optical fiber OFn. The optical fiber OFn is connected to the transmission optical fiber 2, and the signal light thus combined is transmitted via the transmission optical fiber 2.

As can be seen from the above description, each of the optical filters FL1, FL2, FL3,.
As shown in FIG. 3, it is required to transmit only the corresponding narrow-wavelength optical signal but reflect the other optical signals (that is, the performance as a narrow-band interference filter is required). In order to satisfy the above condition, an optical multilayer filter is used. Note that the demultiplexer 5 may be configured to perform an operation opposite to that of the multiplexer 1.
Also in the demultiplexer 5, the same plurality of optical multilayer filters as used in the multiplexer 1 are used.

In the optical communication system, the optical signal transmitted through the transmission optical fiber 2 is C-ba
It is known to use a signal in a band of wavelength 1525 to 1565 nm called nd and a signal in a band of wavelength 1565 to 1590 nm called L-band, and to use C-band and L-band optical signals. Transmission is performed through one transmission optical fiber 2 in a mixed state. When such an optical signal is transmitted, the amplifier 3 disposed in the middle of the transmission optical fiber 2 and amplifying the signal has C-ba.
It is required to amplify the nd and L-band optical signals with amplifiers suitable for each. For this reason, the amplifier 3 is configured as shown in FIG. 4, for example, and the optical filters 31 and 32 composed of optical multilayer filters are used here.

Here, the optical filters 31 and 32 are arranged as shown in FIG.
The optical signal mixed with C-band and L-band optical signals transmitted through the transmission optical fiber 2 from the left side in FIG.
The light is applied to the optical filter 31, and only the C-band optical signal passes through the optical filter 31 and is amplified by the first fiber amplifier 35 at a predetermined amplification factor. Then, the light is applied to the optical filter 32 and transmitted therethrough. On the other hand, the L-band optical signal is reflected by the optical filter 31 and is incident on the second fiber amplifier 36, where it is increased at a predetermined amplification factor.

As a result, the light is divided by the optical filter 31 and the first and second fiber amplifiers 35 and 36 are respectively provided.
C-band and L-amplified at a predetermined amplification rate in
The band optical signal is synthesized by the optical filter 32 and transmitted through the optical transmission fiber 2 on the right side in FIG.
In general, the gain of the C-band optical signal is larger than the gain of the L-band optical signal. Then, the optical filters 31 and 3
No. 2 is required to function as an edge filter.

As described above, many optical filters are used in the optical communication system. First, the optical filter FL used in the multiplexer 1 and the demultiplexer 5 will be described. By the way, in WDM optical communication in which optical signals having different wavelengths are superimposed and transmitted on one transmission optical fiber, the difference between adjacent wavelengths is as follows.
It is about 2 nm to 0.8 nm. When an optical signal is selected based on such a wavelength difference, it is necessary to sufficiently reduce the difference between the design data and the center wavelength of the manufactured optical multilayer filter and the difference in the width of the selected wavelength band. For this reason, it is necessary to reduce the light absorption and light scattering properties to suppress the loss of the optical signal, and of course, a dense film is required so that the change in the center wavelength and the selected wavelength band due to changes in the environment becomes sufficiently small. Further, there is a need for an optical multilayer filter having stable optical characteristics with a stable refractive index regardless of the film forming conditions.

The present inventors have developed an optical multilayer filter made of tantalum pentoxide and silicon oxide, an optical multilayer filter made of titanium oxide and silicon oxide, and an optical multilayer filter made of niobium pentoxide and silicon oxide. For three types of filters, filter performance was compared and examined.

First, tantalum pentoxide (Ta ₂ O ₅ ) is used as the high refractive index material layer and silicon dioxide (SiO ₂ ) is used as the low refractive index material layer, and (TiO ₂ ) is used as the high refractive index material layer. The optical multilayer filter is manufactured using ion beam assisted vapor deposition and plasma ion assisted vapor deposition, and the performance (density of the film) is compared with the case where silicon oxide (SiO ₂ ) is used as the low refractive index material layer. ,
An experiment for confirming light absorption, light scattering, and refractive index stability was performed. As a result, the optical multilayer filter using the combination of (Ta ₂ O ₅ ) and (SiO ₂ ) satisfies the desired performance, but the optical multilayer filter using the combination of (TiO ₂ ) and (SiO ₂ ) does not It was found that the specification was not satisfied in terms of scattering properties and refractive index stability. The optical multilayer filter of niobium pentoxide and silicon oxide also had the same performance as the optical multilayer filter of tantalum pentoxide and silicon oxide.

Therefore, both optical multilayer filters are described.
To manufacture an optical filter FL applicable to the multiplexer 1.
I decided that. First, as a high refractive index material layer (T
a_TwoO _Five) As a low refractive index material layer (SiO 2)_Two)
Ion beam assisted vapor deposition or plasma ion
These layers are alternately laminated by the cyst evaporation method.
Of the optical filter FL usable for the multiplexer 1
Built. This optical filter FL is (Ta_TwoO_Five) Layer
(SiO_TwoAnd a total of 96 alternately laminated layers
A filter having desired characteristics is obtained, and the total film thickness is 25.
1 micron.

However, in the ion beam assisted vapor deposition method or the plasma ion assisted vapor deposition method, the dissolution of the target (sample) in the electron beam deposition tends to be unstable, and the evaporation distribution tends to change. There is a problem that it is necessary to monitor and work. For this reason, the present applicant has tried to make the film formation operation as simple as possible, for example, by making the film formation stable and automating the film formation process. Further, the present inventors have sought and researched an optical filter having a configuration capable of reducing the number of layers to shorten the film formation time.

As a result, a film forming operation was performed using the AC dual cathode sputtering method, and niobium pentoxide (Nb ₂ O) was used.
₅ ) High refractive index material layer composed of silicon dioxide (SiO ₂ )
It has been found that an optical filter made by alternately laminating a low refractive index material layer made of The prototype optical filter is made by alternately laminating (Nb ₂ O ₅ ) layers and (SiO ₂ ) layers in total of 84 layers, and has a total film thickness of 20.9 μm. It was found that the filter had the performance required for the filter (density of the film, light absorption, light scattering, refractive index stability). FIG. 6 shows the light transmission characteristics (light transmission characteristics with respect to wavelength) of this optical filter.
The wavelength band in the range of -3 dB or more, at which the light transmittance is 50% or more, is approximately 1 nm.

As described above, in the case of an optical filter composed of niobium pentoxide and silicon oxide, the refractive index of niobium pentoxide is 2.22 with respect to the refractive index of tantalum pentoxide of 2.08. Even if the thickness was reduced by 10% or more and the total film thickness was reduced by slightly less than 20% as compared with the case of tantalum pentoxide, the same wavelength characteristics could be obtained as shown in FIG. in this way,
An optical multilayer filter used for optical communication such as a stack of dozens of layers, particularly an optical multilayer filter for WDM optical communication, is formed by using niobium pentoxide and silicon oxide. It has become possible to produce a large number of optical filters in a short time, and it has been found that the film configuration is very suitable for an optical communication component that requires a very large number of optical multilayer filters.

Next, an AC dual cathode sputtering apparatus used in the embodiment of the present invention will be described. In FIG.
FIG. 1 shows a schematic configuration diagram of an AC dual cathode sputtering apparatus to which an AC dual cathode sputtering method used in the present embodiment is applied. In this AC dual cathode sputtering apparatus, the substrate holder 1 is placed in a vacuum chamber 10.
1 is provided and rotates about a rotation axis 12. The substrate holder 11 has a disk shape. On the lower surface of the substrate holder 11, a substrate 13 on which a film is to be formed is formed.
Are mounted concentrically, but a monitor substrate is mounted at one place where the substrate 13 is mounted. A sputtering device 16 is provided below the vacuum chamber 10, and particles of the components constituting the film fly out from the sputtering device 16 and strike the surfaces of the substrate 13 and the monitor substrate to form a film.

Meanwhile, the sputtering device 16 has sputtering sources 61a and 61b, and an excitation member 63 provided below the sputtering sources 61a and 61b, respectively. And
A high frequency power supply 62 oscillating at 40 KHz is connected to both of the sputtering sources 61a and 61b.
The voltage output from 2 is applied to sputter sources 61a and 61b. When a high-frequency voltage is applied to the sputter sources 61a and 61b, the vacuum chamber 10 and the sputter source 61
Discharge occurs between a and 61b. At this time, since the argon gas and the oxygen gas are introduced into the vacuum chamber 10 from a gas inlet (not shown),
And an argon gas plasma is formed between the sputtering source 61a and the sputtering source 61b. This argon gas is supplied to the sputtering source 6
When any one of the negative potentials 1a and 61b has a negative potential, it collides with the sputter sources 61a and 61b to cause a sputter phenomenon to form a film on the substrate 13. In addition, the particles jumping out of the sputtering sources 61a and 61b combine with the oxygen gas in the vacuum chamber 10 and reach the substrate 13 in an oxidized state.

As described above, the AC dual-cathode sputtering apparatus according to the present embodiment is sputtered from a sputter source having a negative potential, but there are a plurality of the sputter sources, and the high-frequency power source is set so that the respective electrodes are opposite to each other. Since it is connected to 62, one of them always has a negative potential. Therefore, since the AC dual-cathode sputtering apparatus has a sputter source that is ready for sputter conditions, the deposition rate is extremely high.

On the other hand, a window 14 is provided on the upper and lower surfaces of a part of the vacuum chamber 10 of the AC dual cathode sputtering apparatus according to the present embodiment, and the light irradiated from the light projector 15 emits light from the substrate 13 or the monitor substrate. And the light is received by the light receiver 17 so that the film thickness can be measured.

The film formation of the optical element using the apparatus as shown in FIG. 8 is performed as follows. First, the material of the film, the number of layers, and the thickness of each layer are determined by calculation so as to obtain predetermined optical characteristics (reflectance, transmittance, phase characteristics, and the like). When the design is completed in this way, first, the first layer is formed. When the film thickness can be measured without stopping the rotation of the substrate holder 11, the monitor substrate is
And the film thickness is measured each time the light passes the position of the light receiver 17. Of course, the approximate time required to form a predetermined film thickness can be obtained by calculation, so that the film thickness measurement may be performed after a time close to this time has elapsed.

The film formation is continued while measuring the film thickness in this way, and when the film thickness is within the tolerance, the first layer film formation is completed. Then, the material used for sputtering is changed, and the second layer is formed in the same manner. Hereinafter, this is repeated to form a film up to the final film.

Such an AC dual-cathode sputtering method has the advantage that the fluctuation of the sputter distribution in the film forming process is small and stable, the film forming operation can be automated, and the film forming operation is simplified. Having.

The applicant of the present invention has proposed that the optical multilayer filter FL usable in the multiplexer 1 be composed of (Ta ₂ O ₅ ) as a high refractive index material layer and (SiO ₂ ) as a low refractive index material layer. An optical filter was prepared by performing film formation using an AC dual cathode sputtering method. In this case, by employing the AC dual-cathode sputtering method, the fluctuation of the sputtering distribution in the film forming process is small and stable, so that the film forming operation can be automated and the film forming operation is simplified. However, the number of laminated films is 96, and the total film thickness is 25.
1 micron. FIG. 6 shows the light transmission characteristics (light transmission characteristics with respect to wavelength) of the optical filter thus manufactured.
In this case, the wavelength band in the range of -3 dB or more, at which the light transmittance is 50% or more, is almost 1 nm.

Next, the present applicant has conducted similar research on the optical filters 31 and 32 used in the amplifier 3, and as a result, has performed a film forming operation using an AC dual cathode sputtering method, and has performed a niobium pentoxide (Nb _It has been found that an optical filter made by alternately laminating a high-refractive-index material layer made of ₂ O ₅ ) and a low-refractive-index material layer made of silicon dioxide (SiO ₂ ) is suitable. This optical filter has, for example, a total of 82 layers of (Nb ₂ O ₅ ) and (SiO ₂ ) alternately.
Made by stacking layers, the total film thickness is 20.6 microns,
It has been found that it has the performances required for the optical filter for the amplifier 3 (density of the film, light absorption, light scattering, refractive index stability, wavelength selectivity). FIG. 7 shows the light transmission characteristics (light transmission characteristics with respect to wavelength) of this optical filter.
Are indicated by broken lines. As you can see from this figure,
The wavelength band in the range of −3 dB or more, at which the light transmittance is 50% or more, is 1526 to 1563 nm, and almost only the C-band optical signal is transmitted, and the optical filters 31 and 32 for the amplifier 3 are used. It turns out that it is fully usable.

The present applicant further uses (Ta ₂ O ₅ ) as the high-refractive-index material layer and (SiO ₂ ) as the low-refractive-index material layer, and forms an optical filter by AC dual-cathode sputtering. Created. In this case, the performance (density of the film, light absorption, light scattering, and refractive index stability) required as the optical filter for the amplifier 3 was satisfied. In order to obtain desired filter characteristics, the number of laminated films is 9
There were two layers and the total film thickness was 22.9 microns. The light transmission characteristic (light transmittance characteristic with respect to wavelength) of the optical filter thus manufactured is shown by a solid line in FIG. As can be seen from this figure, the wavelength band in the range of -3 dB or more, at which the light transmittance is 50% or more, is 1526 to 156.
The optical filter has a wavelength of 3 nm, and almost transmits only the C-band optical signal. It can be seen that this optical filter can be sufficiently used as the optical filters 31 and 32 for the amplifier 3.

In the present invention, the optical multilayer filter for optical communication is not limited to the wavelength selection filter used for the multiplexer and the demultiplexer described above and the wavelength selection filter used for the amplifier 3. Absent. For example, there are various types such as an optical multi-layer filter used as an optical communication component, a gain flattening filter for making the optical signal output from the amplifier 3 the same intensity at any wavelength. All of these optical multilayer films require very strict wavelength characteristics,
In addition, one line requires a very large number. In particular,
Since the transmission gain performance that is inverted with respect to the amplification gain with respect to the wavelength of the fiber amplifier using the gain flattening filter is required, the wavelength characteristic becomes complicated, and a very large number of layers is required.

Therefore, by using the manufacturing method to which the AC dual cathode sputtering method is applied, the manufacturing cost can be reduced. Further, the gain flattening filter has the same refractive index stability as the above-described wavelength selection filter,
Since light absorption, light scattering properties, and environmental resistance are required, it is desirable to form a gain flattening filter using an alternate multilayer film of niobium pentoxide and silicon oxide that satisfies such conditions and reduces the number of layers. .

[0048]

As described above, according to the present invention,
An optical multilayer filter is made by alternately laminating a high refractive index layer made of niobium pentoxide (Nb ₂ O ₅ ) and a low refractive index material layer made of silicon dioxide (SiO ₂ ). Niobium pentoxide (Nb ₂ O ₅ ) and silicon dioxide (Si
Since the difference in refractive index from O ₂ ) is large, a desired filter performance can be obtained by reducing the total film thickness and the required number of layers, and the film formation time of this optical multilayer filter is shortened. It is possible to improve production efficiency and reduce production cost. This optical multilayer filter is suitable for use in wavelength division multiplexing optical communication.

It is desirable that the high refractive index material layer and the low refractive index material layer are alternately formed by AC dual cathode sputtering. The AC dual-cathode sputtering method enables stable film formation, and can automate the film formation operation to reduce the production cost. Furthermore, A
The film formation rate of the C dual cathode sputtering method is substantially equal to that of the ion beam assisted vapor deposition method and the plasma ion assisted vapor deposition method, and higher production efficiency can be obtained as compared with the ion beam sputtering method and the RF sputtering method.

According to another aspect of the present invention, an optical multilayer filter is manufactured by alternately stacking high-refractive-index oxide compound layers and low-refractive-index oxide compound layers by AC dual-cathode sputtering. If the film forming operation is performed by using the AC dual cathode sputtering method, a stable film forming without a film forming fluctuation can be performed, and the film forming operation can be automated. Further, the film formation rate is equivalent to that of the ion beam assisted vapor deposition method and the plasma ion assisted vapor deposition method, and according to the present invention, the production efficiency can be improved and the production cost can be reduced.

When a film is formed by using the AC dual cathode sputtering method, tantalum pentoxide (Ta ₂ O ₅ ) is used as a high-refractive-index oxide compound and silicon dioxide (SiO ₂ ) is used as a low-refractive-index oxide compound. _It is preferred to use ₂ ). An optical multilayer filter having a desired filter performance by reducing the total thickness and reducing the required number of layers by reducing the refractive index difference between tantalum pentoxide (Ta ₂ O ₅ ) and silicon dioxide (SiO ₂ ). Can be obtained. For this reason, the film formation time is shorter, the production efficiency is improved, and the production cost is reduced. This optical multilayer filter is suitable for use in wavelength division multiplexing optical communication.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the configuration of a WDM communication system configured using an optical multilayer filter of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a multiplexer constituting the system.

FIG. 3 is a graph showing light transmission characteristics of an optical filter used in the multiplexer.

FIG. 4 is a schematic diagram showing a configuration of an amplifier constituting the system.

FIG. 5 is a graph showing light transmission characteristics of an optical filter used in the amplifier.

FIG. 6 is a graph showing light transmission characteristics of an optical filter (optical multilayer filter) according to the present invention that can be used in the multiplexer.

FIG. 7 is a graph showing light transmission characteristics of an optical filter (optical multilayer filter) according to the present invention that can be used for the amplifier.

FIG. 8 is a schematic diagram showing a configuration of an AC dual cathode sputtering apparatus used for manufacturing an optical multilayer filter according to the present invention.

[Explanation of symbols]

Reference Signs List 1 multiplexer 2 transmission optical fiber 3 amplifier 5 demultiplexer 31, 32 optical filter (optical multilayer filter) L1, L2, L3, ..., Ln laser emitter D1, D2, D3, ..., Dn detector FL1, FL2, FL3,..., FLn Optical filter (optical multilayer filter)

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[Procedure amendment]

[Submission Date] September 8, 2000 (2000.9.8)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0002

[Correction method] Change

[Correction contents]

[0002]

2. Description of the Related Art Today, the spread and use of the Internet communication and the like are progressing, and the traffic of communication lines is rapidly increasing. At present, optical communication using optical fibers with large communication capacity is the mainstream, but it is required to increase the capacity that can be transmitted through each optical fiber, and it is easy to increase the communication capacity among optical communication technologies. Wavelength division multiplexing communication technology (WD
M communication system: Wave-length Division Multplexing communication system) has been used. In the WDM communication system, it is necessary to divide the light in the near-infrared region used for communication into a plurality of fine wavelength regions or to combine the light in the plurality of wavelength regions. In addition, a large number of optical multilayer filters are required.

Claims (6)

[Claims] 1. An optical multi-layer film filter which is formed by alternately laminating a high refractive index material layer and a low refractive index material layer, and is used for optical communication by light in a near infrared region, wherein the high refractive index material is niobium pentoxide (Nb ₂ O _5), the optical multilayer filter having a low refractive index material is characterized in that it consists of silicon dioxide (SiO _2). 2. The optical multilayer filter according to claim 1, wherein the optical multilayer filter is used for wavelength division multiplexing optical communication. 3. The optical multilayer filter according to claim 1, wherein the high refractive index material layer and the low refractive index material layer are formed by AC dual cathode sputtering. 4. An optical multi-layer film filter which is formed by alternately stacking high-refractive-index oxide compound layers and low-refractive-index oxide compound layers and is used for optical communication using light in a near-infrared region. An optical multilayer filter, wherein the refractive index oxide compound layer and the low refractive index oxide compound layer are formed by AC dual cathode sputtering. 5. The method according to claim 4, wherein the high-refractive-index oxide compound comprises tantalum pentoxide (Ta ₂ O ₅ ) and the low-refractive-index oxide compound comprises silicon dioxide (SiO ₂ ). Optical multilayer filter. 6. The optical multilayer filter according to claim 4, which is used for wavelength division multiplexing optical communication.