JP2001066423A - Band pass optical filter made of dielectric multilayered film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a band pass optical filter made of a dielectric multilayered film having little decrease in the transmittance for the passed wavelength even when the dimensional error of the film thickness of each resonance cavity layer is large. SOLUTION: The filter is equipped with two basic blocks 51, 52 for the optical filter that a dielectric multilayered film having a structure in which two or three layers of resonance cavity layers are alternately laminated with reflection mirror layers is fixed to one of the exit or entrance faces of the optical filter substrate. The dielectric multilayered film face 51a of the basic block 51 for the optical filter and the dielectric multilayered film face 52a of the basic block 52 for the optical filter are joined by using an adhesive 2. The optical film thickness d1 of the adhesive 2 is decided to be equal to or less than 20 times of the center wavelength of the selected optical signals to be passed by the band pass optical filter 40 made of the dielectric multilayered film, and decided so that the ripple wavelength of the band pass optical filter 40 made of the dielectric multilayered film does not coincide with the wavelength of other selected light signals near the objective selected optical signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a narrow-band bandpass optical filter required when a high-density wavelength division multiplexing (DWDM) transmission system is constructed using devices such as optical fibers. The present invention relates to a dielectric multilayer film bandpass optical filter formed by forming a dielectric multilayer film on an optical filter substrate.

[0002]

2. Description of the Related Art In a high-density wavelength division multiplexing (DWDM) transmission system, high multiplexing in which optical signals of a plurality of wavelengths are superimposed on one optical fiber and transmitted is progressing. The intervals are getting smaller. For example, the ITU-T recommendation defines wavelength intervals of optical signals to be used at intervals of 1.6 nm, 0.8 nm, and 0.4 nm. Is widely used, and it is considered that a narrower wavelength interval of 0.4 nm will be used in the future. Further, in a communication device of a DWDM transmission system, since light of various wavelengths is multiplexed and transmitted by one optical fiber, an optical signal of a target wavelength is selected from the multiplexed optical signals (proximity). (Separated from the optical signal of the wavelength). Further, when separating an optical signal of a target wavelength (selection optical signal), it is necessary to reduce as much as possible a crosstalk signal generated from another optical signal whose wavelength is close to the selection optical signal. Therefore, in the DWDM transmission system, a signal (selection optical signal) of the target wavelength is selected and a crosstalk signal generated from an optical signal having a wavelength close to the target selection optical signal is reduced. for,
A narrow-band bandpass optical filter composed of a dielectric multilayer film is used. Further, in order to select a target wavelength from a plurality of signals having a narrow wavelength interval as described above, the band-pass characteristics of the band-pass optical filter are narrower, and the rising / falling characteristics are narrower. It is required to be steeper (sharp characteristics). For example, a standard in the United States requires that a bandpass optical filter used in a multiplex transmission apparatus having 32 or more channels has an attenuation of 50 dB or more in a range of ± 0.8 nm from the center wavelength. .

Conventionally, in order to reduce the attenuation in a range of ± 0.8 nm from the center wavelength to 50 dB or more, FIG.
As shown in the isolation column with a wavelength shift of 0.8 nm in the middle, the number of resonance cavity layers in the bandpass optical filter had to be four or more. However, when the number of layers of the band-pass optical filter increases, variations in the film thickness of each resonance cavity layer and problems resulting therefrom occur.
That is, if the thickness dimension of each resonance cavity layer varies, the transmittance of the wavelength band transmitting the bandpass optical filter decreases. For example, as shown in FIG. 20A showing the relationship between the error in the thickness dimension of the resonance cavity layer of each layer of the band-pass optical filter having four resonance cavity layers and the transmittance, as shown in FIG. When there is an error of 1/10000 between the thicknesses of the four resonance cavity layers,
The transmittance at the target wavelength (center wavelength 1550 nm) is 4
It becomes 0% or less. As shown in FIG. 20B, the error in the thickness of the four resonance cavity layers is
When it is reduced to / 100,000, the transmittance at the target wavelength (center wavelength 1550 nm) exceeds about 70%. Further, the error in the thickness of the four resonance cavity layers is reduced by 1/100 as shown in FIG.
When it is reduced to 000, the transmittance at the target wavelength (center wavelength 1550 nm) exceeds about 90%. Therefore, in order to use a bandpass optical filter using four resonance cavity layers in a multiplex transmission device, an error in the thickness dimension of the four resonance cavity layers must be reduced to 1/100000.
Unless controlled within a margin of error, sufficient transmittance could not be obtained for the target wavelength. Here, a configuration of a wavelength separation multiplexing unit of a DWDM transmission system using a bandpass optical filter having four resonance cavity layers and a configuration of a bandpass optical filter having four resonance cavity layers will be described with reference to the drawings. Shown.

FIG. 21 is a diagram showing a schematic configuration of a wavelength division multiplexing unit for multiplexing / selecting signals in a DWDM transmission system. FIG. 22 is a diagram showing a configuration of a bandpass optical filter having four resonance cavity layers. FIG. 2 is a sectional view showing
FIG. 3 is a sectional view showing the configuration of the reflection mirror layer of FIG. As shown in FIG. 21, a multiplexed optical signal λ1 + λ2 +... (Wavelength λ1, wavelength λ2,
Multiplexed optical signals) are passed through a lens 2a formed of optical glass or the like to a multiplexed optical signal input / output unit 1a of a substantially rectangular parallelepiped wavelength separation multiplexing unit 1, and to a vertical axis 5 thereof. Incident at an angle of about 8 degrees. The multiplexed optical signal incident on the wavelength division multiplexing unit 1 is
Are multiple reflected at an angle of about 16 degrees. The selection optical signal input / output units 1b, 1c,..., Which are reflection points when the multiplexed optical signal is multiple-reflected in the wavelength division multiplexing unit 1, have bandpass optical filters 4b, 4c,. Are provided at the tip end of each of the bandpass optical filters 4b, 4c,... And the selected optical signal input / output unit 1b,
1c,... Each of the band-pass optical filters 4b, 4c,... Is formed so as to selectively transmit only a signal of a desired wavelength from among the multiplexed optical signals λ1 + λ2 +. For example, the bandpass optical filter 4b is a multiplexed optical signal λ1 + λ2 that multiple-reflects the inside of the wavelength division multiplexing unit 1.
+ ... can selectively transmit (separate) only the target selected optical signal λ1 from inside, and similarly, the bandpass optical filter 4c multiple-reflects the inside of the wavelength division multiplexing unit 1. Can selectively transmit (separate) only the target selected optical signal λ2 from the multiplexed optical signals λ1 + λ2 +. Each of the above bandpass optical filters 4b, 4
The selected optical signals λ1 and λ2 selected at c are guided to signal processing units for processing the selected optical signals λ1 and λ2 by optical fibers 3b and 3c connected to the lenses 2b and 2c, respectively.
Demodulation processing and the like are performed on each of the selected optical signals λ1 and λ2. When a multiplexed signal is transmitted from the wavelength division multiplexing unit 1, the optical signals λ1, λ2, etc., modulated by each signal processing unit are transmitted to the selected optical signal input / output units 1b, 1
are input to the wavelength division multiplexing unit 1 and then multiplexed with other optical signals that multiple-reflect inside the wavelength division multiplexing unit 1, and are multiplexed from the optical fiber 3a.
+ Λ2 +... As the bandpass optical filters 4b and 4c shown in FIG. 21, for example, the conventional bandpass optical filter 4b having four resonance cavity layers shown in FIG. 22 is used.

The band-pass optical filter 4b shown in FIG. 22 has a four-layer resonant cavity layer 101 made of a dielectric material on one of the surfaces of an optical filter substrate (optical filter substrate) 31 on which an optical signal enters or exits. To 104 are laminated in a manner sandwiched by five reflection mirror layers 111 to 115 made of a dielectric material, and each layer is formed using an evaporation method. In the configuration of FIG. 22, the incident light 41 (multiplexed optical signal λ1 + λ) incident from the optical filter substrate 31 side is used.
2+...) Are reflected by the bandpass optical filter 4b except for the selected optical signal λ1. On the other hand, the λ1 component in the incident light 41 passes through the band-pass optical filter 4b as the selected optical signal λ1 (transmitted light) 44, and is emitted from the other end of the band-pass optical filter 4b as the output light 42 of the selected optical signal λ1.
And emitted. The reflection mirror layer 111 of FIG.
As shown in an enlarged view of a main part of No. 3, it is composed of a multilayer dielectric film. FIG. 23 shows, as an example, a case where the reflection mirror layer is formed of 11 dielectric films. The reflection mirror layer shown in FIG. 23 has high refractive index dielectric films 150 to 150 whose optical thickness dimension W1 is １ ／ of the center wavelength λ0 of the target wavelength band.
155 and low-refractive-index dielectric films 171 to 175 having the same optical film thickness W1 are alternately formed on one surface of the optical filter substrate 31 by using a vapor deposition method. The other reflection mirror layers 112 to 115 in FIG.
In the same manner as in No. 3, a high-refractive-index dielectric film and a low-refractive-index dielectric film are alternately formed using an evaporation method.

For example, the resonance cavity layer 101 shown in FIG.
This is a configuration in which a low-refractive-index dielectric film that is の of 0 is formed by an evaporation method. The other resonance cavity layers 102 to 104 in FIG. 22 also have a structure in which a low-refractive-index dielectric film is formed by a vapor deposition method in the same manner as described above. As described above, in order to form the band-pass optical filters 4b and 4c on the optical filter substrate 31, it is necessary to alternately form high-refractive-index dielectric films and low-refractive-index dielectric films by using a vapor deposition method or the like. The thickness of each film is controlled to a size such as １ ／ or １ ／ of the center wavelength λ0. The above-mentioned bandpass optical filter is designed so that a target transmission wavelength band falls within a range of about a center wavelength ± 0.2 nm. Specifically, first, since the isolation of the wavelength shift of 0.8 nm is 50 dB or more as described above, the resonance cavity layers 101 to 104 shown in FIG. The number of layers of the resonant cavity layer and the number of layers of the reflection mirror layer are determined as if they were layers. Next, by increasing or decreasing the number of dielectric films in the reflection mirror layers 111 to 115 shown in FIG. 23, the wavelength band falls within the range of about ± 0.2 nm of the center wavelength. Therefore, in FIG. 23, as an example, the reflection mirror layer 111 in which the number of dielectric films is 11 is shown. However, in order to keep the wavelength band within the range of about ± 0.2 nm of the center wavelength, the reflection mirror layer 111 is used. In some cases, 23 or 27 dielectric layers may be used. As described above, the band-pass optical filter is composed of a multilayer dielectric film formed by using the vapor deposition method, and the thickness of each dielectric film needs to be suppressed within a predetermined error. In particular, when a band-pass optical filter having four resonant cavity layers is used as described above, the thickness of each of the four resonant cavity layers must be adjusted in order to obtain a sufficient transmittance for a target wavelength. Error is 1/1
As described above, it was necessary to keep the error within about 00000.

[0007]

However, it is not possible to manufacture a band-pass optical filter having four resonance cavity layers with an error in the thickness of each resonance cavity layer within an error of about 1/100000. It is very difficult, and the production efficiency is deteriorated due to the low production yield. As a result, the bandpass optical filter has become expensive. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described conventional problems, and a dielectric multilayer film band in which a decrease in transmittance of a transmission wavelength is small even when an error in the thickness dimension of each resonance cavity layer is large. It is an object to provide a pass light filter.

[0008]

According to a first aspect of the present invention, there is provided a dielectric multi-layer bandpass optical filter device according to the first aspect of the present invention, wherein three resonant cavity layers are alternately arranged via a reflection mirror layer. Two optical filter basic blocks in which the dielectric multilayer film having a structure laminated on the optical filter substrate is fixed to one of the incident and incident surfaces of the optical filter substrate, and the dielectric multilayer film surface of one of the optical filter basic blocks is provided. A dielectric multilayer film bandpass optical filter having a configuration in which the dielectric multilayer film surface of the other optical filter basic block is connected with an adhesive, wherein the optical film thickness of the adhesive is The center wavelength of the selected optical signal to be passed through the dielectric multi-layer film bandpass optical filter is 20 times or less. According to a second aspect of the present invention, there is provided a dielectric multilayer film band-pass optical filter comprising: a dielectric multilayer film having a structure in which two resonant cavity layers are alternately stacked via a reflection mirror layer; Two optical filter basic blocks fixed to one of the two surfaces are provided, and the dielectric multilayer surface of one optical filter basic block and the dielectric multilayer surface of the other optical filter basic block are bonded to each other. A dielectric multilayer film band-pass optical filter having a configuration in which the optical film thickness of the adhesive is passed through the dielectric multilayer film band-pass optical filter. Characterized in that the center wavelength is not more than twice the center wavelength.

According to a third aspect of the present invention, there is provided a dielectric multilayer film band-pass optical filter according to the second aspect of the present invention, wherein two of the dielectric multilayer band-pass optical filters are provided as basic blocks for a second stage optical filter. The optical filter substrate surface on one side of the basic block for optical filter of the second stage is connected to the optical filter substrate surface on one side of the other basic block for optical filter using an adhesive. . According to a fourth aspect of the present invention, in the dielectric multilayer film band-pass optical filter according to the third aspect, an optical film thickness dimension of the adhesive and both optical filter substrates connected by the adhesive is adjusted. The center wavelength of the selected optical signal to be passed through the dielectric multilayer bandpass optical filter is set to 2000 times or less. According to a fifth aspect of the present invention, there is provided the dielectric multilayer band-pass optical filter according to any one of the first to fourth aspects, wherein the optical film thickness is adjusted by adjusting the ripple of the dielectric multilayer band-pass optical filter. The wavelength is set so as not to coincide with the wavelength of another selected optical signal to be suppressed which is close to the selected optical signal.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A dielectric multilayer film band-pass optical filter according to the present invention will be described below based on an illustrated embodiment. FIG. 1 is a cross-sectional view illustrating a schematic configuration of a dielectric multilayer film bandpass optical filter according to a first embodiment of the present invention.
FIG. 2 is a sectional view showing the configuration of the three-resonance cavity layer bandpass optical filter of FIG. 1 in further detail. In FIGS. 1 and 2, parts having the same functions as those of the conventional dielectric multilayer film bandpass optical filter shown in FIGS. 22 and 23 are denoted by the same reference numerals, and redundant description will be omitted. As shown in FIG. 1, the dielectric multilayer band-pass optical filter 40 of the present embodiment is formed by alternately stacking the three resonance cavity layers 101 to 103 and the reflection mirror layers 111 to 114 shown in FIG. In the same manner as the optical filter basic block 51 having the configuration in which the formed dielectric multilayer film (three resonance cavity layer bandpass optical filter) 11 is formed on one of the entrance / exit surfaces 31a of the optical filter substrate (optical filter substrate) 31. Dielectric multilayer film (3-resonance cavity layer bandpass optical filter)
An optical filter basic block 52 having a configuration in which 12 is formed on one of the light incident / incident surfaces 32 a of the optical filter substrate 32 is bonded using an adhesive 2. Specifically, the dielectric multilayer film 11 in the optical filter basic block 51
The filter side surface 51a, which is the surface on which the dielectric multilayer film 12 is formed, of the filter side surface 51a on the side where the dielectric multilayer film 12 is formed in the optical filter basic block 52 has a predetermined optical film thickness d1. The connection is made using the adhesive 2 adjusted to be a value. Next, a method of adjusting the optical film thickness d1 of the adhesive 2 to a predetermined value and fixing the same will be described with reference to FIGS. Here, the optical thickness is the product of the refractive index of the dielectric and the actual physical thickness.

FIG. 3 shows a schematic configuration of an adhesive film thickness adjusting device for fixing the optical film thickness d1 of the adhesive 2 constituting the dielectric multilayer film bandpass optical filter 40 after setting the optical film thickness d1 to a predetermined value. FIG. FIGS. 4A and 4B are diagrams showing the transmittance of the basic blocks 51 and 52 in the transmission wavelength band. FIG. 5 shows that the optical film thickness dimension d1 of the adhesive is the center wavelength λ.
FIG. 6 is a diagram showing the attenuation of light of each wavelength transmitted through the dielectric multilayer film band-pass optical filter 40 when the optical film thickness is five wavelengths of 0, and FIG. FIG. 7 is a diagram showing the attenuation of light of each wavelength transmitted through the dielectric multilayer film band-pass optical filter 40 when the thickness d1 is an optical thickness of 10 wavelengths of the center wavelength λ0. FIG. 9 is a diagram showing the attenuation of light of each wavelength transmitted through the dielectric multilayer film band-pass optical filter 40 when the optical film thickness d1 of the adhesive is the optical film thickness of 20 wavelengths of the center wavelength λ0. is there. The optical film thickness of the adhesive 2 is adjusted by, for example, an adhesive film thickness adjuster 90 shown in FIG. FIG.
The adhesive film thickness dimension adjusting device 90 of the first embodiment places a first ring-shaped reinforcing jig 63 having a round hole 63a on a pedestal 61 having a round hole 61a, and places the first ring-shaped reinforcing jig 63 thereon as shown in FIG. The blocks 52 and 51 are placed with the adhesive 2 therebetween. The adhesive 2 used in the embodiment of the present invention is a UV-curable adhesive having a low viscosity and a refractive index at the time of curing that is substantially equal to the refractive index of the optical filter substrates 31, 32 and the like. Further, a second ring-shaped reinforcing jig 63 is placed thereon, and the pressure is applied from above by a pressing unit 65a attached to the arm 65b of the manipulator 65 and having a round hole 65c. At this time, the white light 41 is generated from the white light emitting section 67 and radiated to the basic blocks 51, 52 and the like, and the emitted light transmitted by the white light 41 through the basic blocks 51, 52 and the like is monitored by the optical spectrum analyzer 73. While applying pressure. In particular,
The white light 41 emitted from the white light emitting section 67 passes through the round hole 65c of the arm section 65b of the manipulator 65 and enters the basic block 51. The white light 41 incident on the basic block 51 passes through the basic block 51, the adhesive 2, and the basic block 52 as transmitted light 44, and exits from the basic block 52 as emitted light 42. The emitted light 42 reaches the light receiving unit 71, is converted into an electric signal, and is input to the optical spectrum analyzer 73. While determining the content displayed on the spectrum analyzer 73, the manipulator 65 is operated to adjust the optical film thickness d1 of the adhesive 2. 5 to 7, the horizontal axis represents the wavelength, and the vertical axis represents the signal in order to use the signal input to the optical spectrum analyzer 73 in FIG. 3 to adjust the optical film thickness d1 of the adhesive 2. Transmittance (%) or transmission attenuation (d
This is a diagram illustrating the content displayed as B). After the optical film thickness d1 of the adhesive 2 is determined by adjustment using the manipulator 65, the adhesive 2 is irradiated with UV light from the UV light emitting unit 69.

FIG. 4A is a diagram showing an ideal transmittance when there is no error in the thickness dimension of each resonance cavity layer of the basic blocks 51 and 52 of the present embodiment shown in FIG.
FIG. 4B is a diagram illustrating transmittance when there is an error of 5/100000 in the thickness dimension of each resonance cavity layer of the basic blocks 51 and 52 of the present embodiment. In the present embodiment, as shown in FIG.
The center wavelength has a transmittance of 90% or more even if there is an error of 5/100000 in the film thickness of each resonance cavity layer. As shown in FIG. 5, the optical film thickness d1 of the adhesive 2 of the present embodiment is five times the center wavelength (for five wavelengths).
In this case, the wavelength range in which the ripple signal appears is about ± 2.8 nm from the center wavelength λ0, and “± 0% from the center wavelength” required for a bandpass optical filter used in a multiplex transmission apparatus having 32 or more channels. .8 nm or more at 50 dB or more ". There is a correlation between the optical film thickness dimension d1 of the adhesive 2 and the appearance wavelength interval of the ripple signal, and when the optical film thickness dimension d1 is increased, the appearance wavelength interval of the ripple signal becomes larger. It becomes shorter, and the ripple signal appearing in the same wavelength band increases.
When the optical film thickness d1 of the adhesive 2 of the present embodiment shown in FIG. 6 is ten times the center wavelength (for ten wavelengths), the wavelength range in which the ripple signal appears is ±± from the center wavelength λ0.
It is about 2.1 to 2.2 nm, which also satisfies the standard that “the attenuation at ± 0.8 nm from the center wavelength is 50 dB or more”.

The adhesive 2 of the present embodiment shown in FIG.
Is 20 times (20 wavelengths) the center wavelength, the appearance wavelength range of the ripple signal is about ± 1.5 to 1.6 nm from the center wavelength λ0, The wavelength coincides with the wavelength of the optical signal to be suppressed of the adjacent channel. In FIG. 7, the transmission attenuation of the ripple signal satisfies the standard that “the attenuation at ± 0.8 nm from the center wavelength is 50 dB or more”, but if the ripple signal value increases for some reason,
There is a possibility that the attenuation at a wavelength that is an integral multiple (× n) of the center frequency λ0 ± 0.8 nm may be 50 dB or less. Here, if the appearance wavelength of the ripple signal is closer to the center wavelength λ0 than shown in FIG. 7, the condition that “the amount of attenuation is 50 dB or more” may not be maintained.
It is not advisable to make the optical film thickness dimension d1 larger than 20 wavelengths. Accordingly, the optical film thickness dimension d1 of the adhesive 2 of the present embodiment is 20 times the center wavelength (for 20 wavelengths).
In addition, it is required to set the dimension so that the wavelength of the ripple signal does not match the wavelength of the optical signal to be suppressed in the channel adjacent to the target selected optical signal.

As described above, in the present embodiment, the transmission of the transmission wavelength of each of the basic blocks 51 and 52 is shown in FIG. 4 (b) even if the error in the thickness of each resonance cavity layer is increased to about 5/100000. ), It is 90% or more. For this reason, the optical thickness dimension d1 of the adhesive 2 is set to be equal to or less than 20 times (20 wavelengths) the center wavelength, and the wavelength of the ripple signal and the optical signal to be suppressed in the channel close to the target selection optical signal are to be suppressed. Is set to a dimension that does not coincide with the wavelength of “the center frequency λ0 ± 0.8 nm, an integral multiple (× n)”.
1. The basic structure including the three-resonance-cavity-layer band-pass optical filters 11 and 12 having the three-resonance-cavity layers 101 to 103 as shown in FIG. The filter surface 51a of the block 51 and the filter surface 5 of the basic block 52
2a can be secured by the adhesive 2 so that the transmittance is 80% or more. Therefore, in the present embodiment, it is possible to provide a dielectric multilayer film bandpass optical filter with a small decrease in transmittance.

Next, a second embodiment of the present invention will be described with reference to FIG. In the first embodiment shown in FIGS. 1 and 2, the basic block 51 is constituted by three resonance cavity layers, but in the second embodiment, the resonance cavity layer is constituted by two layers. . Also, since the wavelength at which the ripple signal is generated differs due to the difference in the number of resonance cavity layers as described above, the optical film thickness dimension d1 of the adhesive 2 shown in FIG. 1 also differs. FIG. 8 is a diagram showing a basic block 51b including two resonance cavity layers 101 and 102. The dielectric multilayer film bandpass optical filter of the present embodiment has a configuration in which the basic block 51b shown in FIG. 8 and the basic block 52b having the same configuration are connected by the adhesive 2 as shown in FIG. Become. FIG. 9 (a)
Are the basic blocks 51b, 5 and 5 of the present embodiment shown in FIG.
1 / 10,000 to the film thickness of each resonance cavity layer 2b
FIG. 9B is a diagram showing the transmittance when there is an error in FIG.
FIG. 9 is a diagram showing the transmittance when there is an error of 5/100000 in the thickness dimension of each resonance cavity layer of the basic blocks 51b and 52b of the present embodiment, and FIG. It is a figure which shows the transmittance | permeability when there exists an error of 1/100000 in the film thickness dimension of each resonance cavity layer of blocks 51b and 52b. In the present embodiment, as shown in FIG. 9B, an error of 1/100000 with respect to the thickness dimension of each resonance cavity layer in the basic blocks 51b and 52b shown in FIG. Even if the accuracy is lowered to the error of, both the transmittance and the transmission band hardly change. Therefore, the thickness accuracy of each resonance cavity layer of the present embodiment can be reduced to an error level of 5/100000. Further, in the present embodiment, as shown in FIG. 9A, even if the accuracy is lowered to an error of 1/10000, the center wavelength λ0 has a transmittance of 90% or more. Therefore, the thickness accuracy of each resonance cavity layer of the present embodiment can be reduced to an error level of 1/10000.

As shown in FIG. 10, when the optical film thickness d1 of the adhesive of this embodiment is the same wavelength (one wavelength) as the center wavelength, the wavelength range in which the ripple signal appears is It is about ± 5.4 to 5.8 nm from the center wavelength λ0, and the wavelength of the ripple signal whose attenuation is 50 dB or less does not match the wavelength of the optical signal to be suppressed in the adjacent channel, so that 32 channels or more are used. Satisfies the standard that the amount of attenuation at ± 0.8 nm from the center wavelength is 50 dB or more, which is required for the bandpass optical filter used in the multiplex transmission device of the above. Further, the optical film thickness dimension d1 of the adhesive 2 of the present embodiment shown in FIG.
In the case of double (for 1.5 wavelengths), the appearing wavelength range of the ripple signal is about ± 4.7 to 5.1 nm from the center wavelength λ0, and also in this case, the ripple signal whose attenuation is 50 dB or less. Is not coincident with the wavelength of the optical signal to be suppressed in the adjacent channel.
The amount of attenuation at 8 nm is 50 dB or more ". Further, the optical film thickness dimension d1 of the adhesive 2 of the present embodiment shown in FIG. 12 is twice the center wavelength (for two wavelengths).
In this case, the wavelength range in which the ripple signal appears is about ± 4.3 to 4.8 nm from the center wavelength λ0, and also in this case, the suppression of the channel adjacent to the wavelength of the ripple signal whose attenuation is 50 dB or less. Since the wavelength of the optical signal to be used does not match, the standard satisfies the standard that “the attenuation at ± 0.8 nm from the center wavelength is 50 dB or more”.

Here, if the appearance wavelength of the ripple signal is made closer to the center wavelength λ0 than shown in FIG. 12, the condition that “the amount of attenuation is 50 dB or more” may not be maintained. It is not advisable to make the target film thickness dimension d1 larger than two wavelengths. Therefore, FIG.
Since the transmission attenuation of each ripple signal in each embodiment shown in FIG. 12 does not satisfy the standard of “the attenuation is 50 dB or more”, the value of the optical film thickness dimension d1 of the adhesive 2 of this embodiment is not satisfied. Depending on the center frequency λ0 ± 0.
The ripple signal overlaps with a wavelength that is an integral multiple (× n) of 8 nm, and the attenuation at a wavelength that is an integral multiple (× n) of the center frequency λ0 ± 0.8 nm may be 50 dB or less.
That is, there is a possibility that the wavelength of the selected optical signal assigned to the wavelength of the center frequency λ0 ± (0.8 nm × n) and the appearance wavelength of the ripple signal having the attenuation of 50 dB or less match.
Therefore, the optical film thickness dimension d1 of the adhesive 2 of this embodiment is set to be equal to or less than twice the center wavelength (for two wavelengths), and the wavelength of the ripple signal and the suppression of the channel close to the target selected optical signal are suppressed. It is required to set the dimensions so that the wavelength does not match the wavelength of the optical signal to be performed. As described above, in the present embodiment, the transmittance of each of the basic blocks 51 and 52 at the passing wavelength is
Error of thickness dimension of each resonance cavity layer is reduced to 1/10000
Even if it is increased to about 90%, as shown in FIG.
The above can be secured. For this reason, the optical film thickness d1 of the adhesive 2 is set to be equal to or less than twice the center wavelength (for two wavelengths), and the wavelength of the ripple signal and the optical signal to be suppressed in the channel close to the target selected optical signal. Of the center frequency λ0 ± 0.8n
A configuration in which two basic blocks 51b and 52b are connected by an adhesive 2 as shown in FIG. 1 while satisfying the standard that the attenuation amount at a wavelength that is an integral multiple of m (× n) is 50 dB or more. In this case, the transmittance can be 80% or more. Therefore, also in the present embodiment, the first
Similarly to the embodiment, a dielectric multilayer film bandpass optical filter with a small decrease in transmittance can be provided.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 13 shows a third embodiment of the present invention.
FIG. 3 is a cross-sectional view illustrating a schematic configuration of a dielectric multilayer film bandpass optical filter according to an embodiment. As shown in FIG. 13, the dielectric multilayer film bandpass optical filter 40a according to the third embodiment of the present invention uses two dielectric multilayer film bandpass optical filters according to the second embodiment. Here, the two dielectric multilayer film band-pass optical filters are used as second-stage optical filter basic blocks 81 and 82, respectively, and the optical filter substrate surface on one side of one second-stage optical filter basic block 81 is used. 81a, the optical filter substrate surface 82a on one side of the other second stage optical filter basic block 82.
Are connected using an adhesive 22. In the present embodiment, only the optical film thickness of the adhesive 22 is not adjusted as in the first and second embodiments.
Optical filter substrates 3 on both sides connected by adhesive 22
The optical film thickness d2 including 2, 31c is to be adjusted. In the present embodiment, the combined thickness of the optical filter substrates 32 and 31c is 0.25 mm or more, that is, 250 wavelengths or more. This is because if the thickness of the optical filter substrates 32 and 32a is less than this, the flatness of the substrate may not be maintained due to the stress generated when forming the dielectric multilayer film.

Also in this embodiment, the thickness of the second-stage optical filter basic blocks 81 and 82 corresponding to the dielectric multilayer film band-pass optical filter of the second embodiment includes an adhesive. 2 is included, but the optical thickness d1 is very small compared to the optical thickness d2 of the present embodiment, so the optical thickness d2 is adjusted. Sometimes they can be ignored. Further, a correlation similar to the correlation between the optical film thickness dimension d1 of the adhesive 2 and the wavelength interval of the appearance of the ripple signal is present between the optical film thickness dimension d2 and the appearance wavelength interval of the ripple signal. In the case where the optical film thickness d2 is increased, the wavelength interval at which ripple signals appear becomes shorter, and ripple signals appearing in the same wavelength band increase. Further, the isolation value at a wavelength shifted by 0.8 nm from the center wavelength of the dielectric multilayer film bandpass optical filter 40a of the present embodiment is as follows:
As shown in FIG. 14, the value is 50 dB or more, which is a value close to that of a conventional dielectric multilayer bandpass optical filter having four resonance cavity layers.

As shown in FIG. 15, the optical film thickness d2 including the adhesive 22 and the optical filter substrates 32 and 31c of the present embodiment is 300 times the center wavelength (300 times).
Wavelength portion), the appearance wavelength range of the ripple signal is about ± 0.7 nm from the center wavelength λ0, and the center wavelength λ
It is about ± 2.7 nm from 0, but here the attenuation is 5
Since the wavelength of the ripple signal of 0 dB or less does not match the wavelength of the optical signal to be suppressed of the adjacent channel,
"± 0.8n from center wavelength required for bandpass optical filter used in multiplex transmission apparatus of 32 channels or more"
m is 50 dB or more. " When the optical film thickness d2 of the present embodiment shown in FIG. 16 is 1000 times the center wavelength (for 1000 wavelengths), the wavelength range in which the ripple signal appears is the center wavelength λ.
0 to ± 0.4 nm, center wavelength λ0 to ± 0.9 n
m, about ± 1.6 nm from the center wavelength λ0, and
The wavelength is about ± 2.3 nm from the center wavelength λ0, and in this case, the wavelength of the ripple signal of about ± 1.6 nm from the center wavelength λ0 matches the wavelength of the optical signal to be suppressed in the adjacent channel. , The amount of attenuation of the ripple signal is 50d
B or less, and thus satisfies the standard that “the attenuation at ± 0.8 nm from the center wavelength is 50 dB or more”. When the optical film thickness d2 of the present embodiment shown in FIG. 17 is 1500 times the center wavelength (for 1500 wavelengths), the wavelength range in which the ripple signal appears is about ± 0.3 nm from the center wavelength λ0. About ± 0.6 nm from center wavelength λ0, about ± 1.1 nm from center wavelength λ0, center wavelength λ0
± 1.6 nm from center wavelength, ± 2.1 nm from center wavelength λ0
And ± 2.5 nm from the center wavelength λ0. In this case as well, the wavelength of the ripple signal of about ± 1.6 nm from the center wavelength λ0 is equal to the wavelength of the optical signal to be suppressed in the adjacent channel. However, since the amount of attenuation of the ripple signal does not become 50 dB or less, it satisfies the standard that “the amount of attenuation at ± 0.8 nm from the center wavelength is 50 dB or more”.

When the optical thickness d2 of the present embodiment shown in FIG. 18 is 2000 times the center wavelength (for 2000 wavelengths), the wavelength range in which the ripple signal appears is ± 0 from the center wavelength λ0. 0.3 nm, center wavelength ± 0
About 0.5 nm, about ± 0.7 nm from center wavelength λ0,
About ± 1.2 nm from center wavelength λ0, about ± 1.5 nm from center wavelength λ0, about ± 1.9 nm from center wavelength λ0, about ± 2.3 nm from center wavelength λ0, and ± 2.7 nm from center wavelength λ0. Degree, and in this case,
Although the wavelength of the ripple signal of about ± 1.6 nm from the center wavelength λ0 is very close to the wavelength of the optical signal to be suppressed in the adjacent channel, the wavelength is slightly shifted. Attenuation at 8 nm is 50 dB or more "
It satisfies the standard. Here, if the appearance wavelength interval of the ripple signal is made narrower than that shown in FIG. 18, the probability that the wavelength of “± 0.8 nm (integer multiple) from the center wavelength” and the wavelength of the ripple signal are very high is extremely high. Therefore, it is not advisable to make the optical film thickness d2 larger than 2000 wavelengths. Therefore, the transmission attenuation of each ripple signal in each of the embodiments shown in FIGS. 15 to 18 does not satisfy the standard of “the attenuation is 50 dB or more”. Depending on the value of d2, the attenuation at a wavelength that is an integral multiple (× n) of the center frequency λ0 ± 0.8 nm may be 50 dB or less.
That is, there is a possibility that the wavelength of the selected optical signal assigned to the wavelength of the center frequency λ0 ± (0.8 nm × n) and the appearance wavelength of the ripple signal having the attenuation of 50 dB or less match.
Therefore, regarding the optical film thickness d2 of the present embodiment,
It is required to set the dimension to be equal to or less than 2000 times the center wavelength (corresponding to 2000 wavelengths), and to set the dimension such that the wavelength of the ripple signal does not match the wavelength of the optical signal to be suppressed in the channel close to the target selected optical signal. As described above, in the present embodiment, the transmittance of the passing wavelength of each of the basic blocks 81 and 82 in the second stage reduces the error in the thickness dimension of each resonance cavity layer by 1 /.
Even if it is increased to about 10,000, 80% or more can be secured as described in the second embodiment. For this reason, the optical thickness d2 is set to 2000 times or less of the center wavelength (for 2000 wavelengths) or less, and the wavelength of the ripple signal and the wavelength of the optical signal to be suppressed in the channel close to the target selected optical signal. By using dimensions that do not match, “center frequency λ0
As shown in FIG. 13, the two basic blocks 81 and 82 of the second stage are formed while satisfying the standard of “the attenuation at a wavelength of an integral multiple (× n) of ± 0.8 nm is 50 dB or more”. Even when the connection is made by the adhesive 22,
The transmittance can secure 60% or more. Therefore,
Also in the present embodiment, similarly to the first and second embodiments, it is possible to provide a dielectric multilayer film bandpass optical filter with a small decrease in transmittance.

[0022]

As described above, according to the present invention, even if there is a large error in the thickness dimension of each resonance cavity layer, the decrease in the transmittance of the transmission wavelength is small, and the production yield is improved. And a low-cost dielectric multilayer bandpass optical filter can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic configuration of a dielectric multilayer film bandpass optical filter according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the configuration of the three-resonance cavity layer bandpass optical filter of FIG. 1 in further detail.

FIG. 3 is a diagram showing a schematic configuration of an adhesive film thickness dimension adjusting device that fixes an optical film thickness of an adhesive constituting a dielectric multilayer film bandpass optical filter after setting the optical film thickness to a predetermined value;

FIGS. 4A and 4B are diagrams showing the transmittance of a basic block in a transmission wavelength band.

FIG. 5 is a diagram showing the attenuation of light of each wavelength transmitted through a dielectric multilayer film band-pass optical filter when the optical film thickness of the adhesive is an optical film thickness corresponding to five central wavelengths. It is.

FIG. 6 is a diagram showing attenuation of light of each wavelength transmitted through a dielectric multilayer film bandpass optical filter when the optical film thickness of the adhesive is the optical film thickness of 10 wavelengths of the center wavelength. It is.

FIG. 7 is a diagram showing the attenuation of light of each wavelength transmitted through a dielectric multilayer film bandpass optical filter when the optical film thickness of the adhesive is the optical film thickness of 20 wavelengths of the center wavelength. It is.

FIG. 8 is a diagram showing a basic block including two resonance cavity layers according to a second embodiment of the present invention.

9A is a diagram showing transmittance when there is an error of 1/10000 in the thickness dimension of each resonance cavity layer of the basic block of the present embodiment shown in FIG. 8, and FIG. It is a figure which shows the transmittance | permeability when there exists a 5/100000 error in a film thickness dimension, and (c) is a figure which shows the transmittance | permeability when there is a 1/100000 error in a film thickness dimension.

FIG. 10 is a diagram showing the attenuation of light of each wavelength transmitted through a dielectric multilayer film bandpass optical filter when the optical film thickness of the adhesive is the optical film thickness of one wavelength of the center wavelength. It is.

FIG. 11 shows that the optical film thickness of the adhesive is 1.5 at the center wavelength.
FIG. 4 is a diagram illustrating attenuation of light of each wavelength transmitted through a dielectric multilayer film bandpass optical filter when the optical film thickness dimension corresponds to a wavelength.

FIG. 12 is a diagram showing the attenuation of light of each wavelength transmitted through a dielectric multilayer film bandpass optical filter when the optical film thickness of the adhesive is the optical film thickness of two wavelengths of the center wavelength. It is.

FIG. 13 is a sectional view illustrating a schematic configuration of a dielectric multilayer film bandpass optical filter according to a third embodiment of the present invention.

FIG. 14 is a diagram illustrating an isolation value at a wavelength shifted by 0.8 nm from the center wavelength of the dielectric multilayer film bandpass optical filter.

FIG. 15 is a view showing a case where the optical film thickness including the adhesive and the optical filter substrate is the optical film thickness corresponding to the central wavelength of 300 wavelengths, and is transmitted through the dielectric multilayer film band-pass optical filter. It is a figure showing the amount of attenuation of light of a wavelength.

FIG. 16 illustrates a case where a dielectric multilayer film band-pass optical filter is used when the optical film thickness including the adhesive and the optical filter substrate is the optical film thickness when the center wavelength is 1000 wavelengths. It is a figure which shows the attenuation of the light of each wavelength which transmits.

FIG. 17 illustrates a case where a dielectric multilayer bandpass optical filter is used when the optical film thickness including the adhesive and the optical filter substrate is the optical film thickness when the center wavelength is 1500 wavelengths. It is a figure which shows the attenuation of the light of each wavelength which transmits.

FIG. 18 illustrates a case where a dielectric multilayer film bandpass optical filter is used when the optical film thickness including the adhesive and the optical filter substrate is the optical film thickness when the center wavelength is 2000 wavelengths. It is a figure which shows the attenuation of the light of each wavelength which transmits.

FIG. 19 is a diagram illustrating an isolation value at a wavelength shifted by 0.8 nm from the center wavelength of the dielectric multilayer film bandpass optical filter.

FIG. 20 (a) is a diagram showing the transmittance when there is an error of 1/10000 in the thickness dimension of each of the resonance cavity layers of the band-pass optical filter having four resonance cavity layers, and FIG. (b) is a diagram showing the transmittance when there is an error of 5/100000 in the film thickness dimension, and (c) is a diagram showing the transmittance when there is an error of 1/100000 in the film thickness dimension.

FIG. 21 is a diagram illustrating a schematic configuration of a wavelength division multiplexing unit that multiplexes / selects a signal in a DWDM transmission system.

FIG. 22 is a cross-sectional view illustrating a configuration of a bandpass optical filter having four resonance cavity layers.

FIG. 23 is a cross-sectional view showing the configuration of the reflection mirror layer of FIG.

[Explanation of symbols]

2, adhesive, 11, 12,... Bandpass optical filter having three resonant cavity layers, 31, 32,.
Optical filter substrate, 31a, 31b, 32a, 32b, etc.
・ Incoming / outgoing surface, 41 ・ ・ ・ incident light, 42 ・ ・ ・ outgoing light, 4
3 ... reflected light, 51, 52 ... basic block, 51
a, 52a: filter side surface, d1: optical film thickness of adhesive

Claims (5)

[Claims] An optical filter basic block in which a dielectric multilayer film having a structure in which three resonant cavity layers are alternately stacked via a reflection mirror layer is fixed to one of the outgoing and incident surfaces of an optical filter substrate. A dielectric multilayer film band-pass having a configuration in which two dielectric multilayer film surfaces of one optical filter basic block and a dielectric multilayer film surface of the other optical filter basic block are connected using an adhesive. An optical filter, wherein an optical film thickness of the adhesive is not more than 20 times a center wavelength of a selected optical signal to be passed through the dielectric multilayer film bandpass optical filter. Dielectric multilayer film bandpass optical filter. 2. An optical filter basic block in which a dielectric multilayer film having a structure in which two resonant cavity layers are alternately stacked via a reflection mirror layer is fixed to one of the outgoing / incident surfaces of an optical filter substrate. A dielectric multilayer film band-pass having a configuration in which two dielectric multilayer film surfaces of one optical filter basic block and a dielectric multilayer film surface of the other optical filter basic block are connected using an adhesive. An optical filter, characterized in that the optical film thickness of the adhesive is not more than twice the center wavelength of a selected optical signal to be passed through the dielectric multilayer film bandpass optical filter. Dielectric multilayer film bandpass optical filter. 3. The dielectric multilayer film bandpass optical filter according to claim 2 is used as a basic block for a second stage optical filter.
One of the second-stage optical filter basic blocks is connected to one side of the optical filter substrate surface of the other second-stage optical filter basic block using an adhesive. A dielectric multilayer film bandpass optical filter characterized by the above-mentioned. 4. The dielectric multilayer film band-pass optical filter according to claim 3, wherein an optical film thickness of the adhesive and both optical filter substrates connected by the adhesive are adjusted to the dielectric film thickness. A dielectric multilayer film bandpass optical filter, wherein the wavelength is not more than 2000 times the center wavelength of a selected optical signal to be passed by the multilayer film bandpass optical filter. 5. The dielectric multilayer bandpass optical filter according to claim 1, wherein the optical film thickness dimension and the ripple wavelength of the dielectric multilayer bandpass optical filter are the same. A dielectric multilayer film bandpass optical filter, which is set so as not to coincide with a wavelength of another selected optical signal to be suppressed which is close to the selected optical signal.