JP2004045934A - Variable wavelength type optical filter and wavelength varying device for same filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a variable wavelength type optical filter from having a break of an intermediate wavelength. <P>SOLUTION: The variable wavelength optical filter has a band-pass filter main body 14 with a reflecting film 10 and a spacer layer 12, and a substrate 16. The reflecting film 10 is formed by laminating alternate dielectric layers differing in refractive index. The spacer layer 12 is sandwiched between a couple of reflecting films 10 at its front and rear parts and has tapered slope surfaces as its top and reverse surface so that the thickness continuously varies. The filter main body 13 varies in value of transmission wavelength λ as the thickness of the spacer layer 12 varies. To vary the transmission wavelength, the band-pass optical filter main body 13 is moved so that the position of incidence of incident light L<SB>in</SB>on the band-pass optical filter main body 14 changes to (1), (2), (3), and (4) in order. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wavelength tunable optical filter and a wavelength changing device for the filter, and in particular, when changing a transmission wavelength, can change the wavelength existing between before and after the change without interruption. The present invention relates to a wavelength variable optical filter and a wavelength changing device for the filter.
[0002]
[Prior art]
A wavelength tunable optical filter capable of changing a transmission wavelength among optical filters that separate a specific wavelength (transmission wavelength) from other wavelengths from light containing a large number of wavelength components, for example, wavelength multiplexed light. It has been known.
[0003]
This type of optical filter is used, for example, when extracting only light of a specific wavelength for maintenance in a wavelength division multiplexing communication system, or in an wavelength division multiplexing optical communication network for switching only a specific wavelength to another line. Applications to drop filters and the like are being considered.
[0004]
By the way, as a wavelength tunable optical filter used in such an application, a filter having a configuration as shown in FIG. 9 is conventionally known. The optical filter shown in FIG. 1 includes a bandpass filter main body 3 including a reflective film 1 in which dielectric layers having different refractive indexes are alternately stacked, and a spacer layer 2 sandwiched between a pair of reflective films 1. .
[0005]
The band-pass filter body 3 is mounted on a light-transmitting substrate 4 and transmits only a wavelength (λ) of 2 · ns · ds when the refractive index of the spacer layer 2 is ns and the thickness is ds. Let it.
[0006]
The spacer layer 2 is formed in a tapered shape so that the thickness varies continuously in one direction. In the optical filter configured as described above, when the incident position of the incident light L _{in on} the band-pass filter main body 3 is different, the thickness of the spacer layer 2 changes, and as a result, the wavelength (λ) of the transmitted light L _out Changes.
[0007]
For example, when the optical filter having the above configuration is applied to a wavelength division multiplexing communication system, an input port and a reflection port are arranged at one end of the bandpass filter main body 3 as shown in FIG. A transmission port is provided on the other end side of the filter body 3.
[0008]
In such a wavelength multiplex communication system, for example, when it is desired to take out a specific wavelength from the transmission port for maintenance, the bandpass filter body 3 is moved in the direction in which the transmission wavelength changes, that is, in the direction in which the thickness of the spacer layer 2 changes. To adjust the wavelength of the transmitted light from the transmission port to a predetermined value.
[0009]
However, such a conventional optical filter has a technical problem described below.
[0010]
[Problems to be solved by the invention]
That is, the wavelength changing method in the above-described conventional optical filter has a disadvantage that the light of the wavelength output to the reflection port is interrupted in the process of changing the wavelength.
[0011]
To explain this more specifically, for example, in FIG. 9, wavelength-multiplexed light (incident light L _in ) including a large number of wavelengths is incident from an incident port, and a specific wavelength of the incident light L _in For example, if the reflected light Lr of λ3 is discriminated and received from the reflection port and the transmitted light L _out of a specific wavelength, for example, λ2, is discriminated and received from the transmission port, the wavelength has a relationship of λ2>λ3> λ4. Assuming that there is, before changing the transmission wavelength, the reflection spectrum of the band-pass filter main body 3 is in a state where the portion of the transmission wavelength λ2 is missing as shown in FIG.
[0012]
From the state where such a reflection spectrum is obtained, the wavelength of the transmitted light L _out is changed from λ2 to λ4 by sliding movement, and the reflection spectrum is changed as shown in FIG. In this case, the light is moved to a position where the wavelength λ4 is transmitted through a position where the wavelength λ3 is transmitted.
[0013]
However, in this movement process, as shown in FIG. 10B, since light of wavelength λ3 passes through the filter body 3, this wavelength component is cut off from the reflection spectrum.
[0014]
Therefore, when the reflection port that is discriminatingly receiving the light of the wavelength λ3 is in the communication service state, there is a problem that the transmission wavelength cannot be changed unless the service is temporarily stopped.
[0015]
The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a tunable optical filter and a wavelength tunable optical filter capable of changing a transmission wavelength without interrupting an intermediate wavelength. It is to provide a filter wavelength changing device.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has a reflective film in which dielectric layers having different refractive indices are alternately laminated, and a spacer layer sandwiched between a pair of the reflective films, and a refractive index of the spacer layer. A band-pass filter body that transmits only a specific transmission wavelength corresponding to the thickness, wherein the thickness of the spacer layer is formed so as to be continuously changed along one direction, and the light is incident on the band-pass filter body. By changing the position, in a wavelength tunable optical filter in which the transmission wavelength is changed, a total reflection area that reflects all of the incident light is provided on the side of the band-pass filter body, and when changing the transmission wavelength, After passing through the total reflection area, the incident position is changed to another position on the band-pass filter body.
[0017]
According to the wavelength tunable optical filter configured as described above, the total reflection area that reflects all of the incident light is provided on the side of the band-pass filter body, and when the transmission wavelength is changed, the incident position is changed to the total reflection area. After passing through, the band-pass filter is changed to another position, so while the incident position exists in the total reflection area, the incident light is not transmitted at all, and the entire wavelength area is included in the reflected light. In addition, the intermediate wavelength sandwiched before and after the wavelength change is not interrupted from the reflection spectrum.
[0018]
The total reflection area may be arranged adjacent to the band-pass filter body in a direction in which the thickness of the spacer does not change.
[0019]
The total reflection region can be formed integrally with a part of the spacer layer by removing a part of the reflection film.
The total reflection area may be provided on the back side of the band-pass filter body for extracting the transmission wavelength (λ).
[0020]
Further, the present invention includes a stage capable of two-dimensional movement in a plane, and a movement mechanism for individually moving the stage in two-dimensional directions, wherein the band-pass filter body having a total reflection area on a side thereof is provided. Mounted on a stage, an input port and a reflection port are provided at one end of the band-pass filter main body, and a transmission port is provided at the other end of the band-pass filter main body. When changing, by the operation of the moving mechanism, the incident position on the bandpass filter main body through the incident port is changed to another position of the bandpass filter main body through the total reflection area. I made it.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1 to 4 show an embodiment of a wavelength tunable optical filter according to the present invention.
[0022]
The tunable optical filter shown in FIG. 1 includes a band-pass filter main body 14 having a reflection film 10 and a spacer layer 12, and a substrate 16. As shown in detail in FIG. 2, the reflection film 10 is formed by alternately laminating a plurality of dielectric layers having different refractive indexes, and includes a high refractive index dielectric layer 10a and a low refractive index dielectric layer 10b. And
[0023]
The high refractive index dielectric layer 10a is made of, for example, Ta ₂ O ₅ or TiO ₂ , and the low refractive index dielectric layer 10b is made of, for example, SiO ₂ . The high-refractive-index dielectric layer 10a and the low-refractive-index dielectric layer 10b of the reflection film 10 are set so as to satisfy the following conditions with respect to the operating wavelength λ.
[0024]
High refractive index dielectric layer 10a, when the refractive index _{n H,} the film thickness _{d H is, (λ / 4) / n} H so as to satisfy also the low refractive index layer 10b, the refractive index the When _{n L,} the thickness _{d L} are set so as to satisfy the _{(λ / 4) / n L} .
On the other hand, the spacer layer 12 is sandwiched between the pair of reflective films 10 at the front and rear sides thereof, and tapered inclined surfaces are provided on upper and lower surfaces so that the thickness ds continuously changes along one direction. I have.
[0025]
In the band-pass filter body 14 configured as described above, assuming that the refractive index of the spacer layer 12 is n _S (= n _L ) and its thickness is ds, the transmission wavelength λ is represented by the following equation.
_{λ = 2 · n S (=} n L) · ds
Therefore, when the thickness ds of the spacer layer 12 changes, the value of the transmission wavelength λ changes. The substrate 16 is selected from, for example, a light-transmissive glass substrate, and has an antireflection film 20 formed on one surface thereof.
[0026]
The basic configuration of the band-pass optical filter body 14 as described above is the same as that of a conventional filter of this type, but the optical filter of the present embodiment has the following remarkable features.
[0027]
That is, on the side of the optical bandpass filter body 14, the total reflection area 18 is provided for reflecting all incident light L _in. In the case of the present embodiment, the total reflection area 18 is arranged adjacent to a direction in which the thickness of the spacer layer 12 of the bandpass filter main body 14 does not change, that is, a direction orthogonal to the inclination direction of the spacer layer 12. .
[0028]
In the case of this embodiment, the total reflection area 18 is formed integrally with a part of the spacer film 12 by removing a part of the reflection film 10, that is, by removing the reflection film 10 on one side. .
[0029]
FIG. 3 shows an example of a method of manufacturing the bandpass optical filter main body 14 integrally provided with the total reflection region 18. In the manufacturing method shown in the figure, a filter film is formed by a lift-off method (one of typical etching techniques). First, as shown in FIG. The antireflection film 20 is formed by sputtering.
[0030]
The antireflection film 20 is manufactured by a widely used technique, for example, as described in “Thin Film Handbook” published by Ohmsha, pages 818 to 821, edited by the Japan Society for the Promotion of Science thin film 131st committee.
[0031]
Next, as shown in (2), the reflection film 10 is formed on the surface side of the glass substrate 16. The reflective film 10 is formed by alternately stacking high-refractive-index dielectric layers 10a and low-refractive-index dielectric layers 10b each having a predetermined thickness.
[0032]
Subsequently, as shown in (3), a dielectric spacer layer 12 is formed on the reflective film 10. In this case, for example, the distance between the deposition source and the substrate 16 is changed depending on the position in the substrate 16 by a method such as inclining the glass substrate 16 or the like, or a similar method. Sputtering is performed in this state, and the spacer layer 12 is tapered so that the thickness of the spacer layer 12 continuously changes in one direction. Such a film forming method is disclosed in, for example, JP-A-6-265722 and JP-A-8-227014.
[0033]
Next, as shown in (4), a mask layer 22 is formed and formed on the spacer layer 12, and after exposing approximately half the area, the part is removed with a developing solution. Next, as shown in (5), the high refractive index dielectric layers 10a and the low refractive index dielectric layers 10b are alternately laminated on the spacer layer 12 and the mask layer 22 again to form the reflective film 10. A film is formed.
[0034]
Finally, as shown in (6), when the mask layer 22 and the reflective film 10 laminated thereon are removed together with an etching solution, the band in which the total reflection region 18 is formed on the spacer 12 is formed. The transmitted light filter body 14 is obtained. In the example shown in FIG. 3, the shape of the substrate 16 is a rectangular shape, but the shape may be an arbitrary shape such as a round shape.
[0035]
When the bandpass optical filter 14 configured as described above is applied to, for example, a wavelength division multiplexing communication system, as shown in FIG. 1, an input port is provided on one end side (substrate 16 side) of the bandpass filter body 3. And a reflection port, and a transmission port is provided on the other end side (the back side of the reflection film 10) of the band-pass filter main body 3.
[0036]
Then, wavelength multiplexed light (incident light L _in ) containing a large number of wavelengths is incident from the incident port, and among the incident light L _in , reflected light Lr having a specific wavelength, for example, λ3, is discriminated from the reflection port. Then, when the transmitted light L _out having a specific wavelength, for example, λ2 is discriminated and received from the transmission port and the transmission wavelength is changed from λ2 to λ4, this is performed in the following procedure in the present embodiment.
[0037]
In this case, it is assumed that the relationship between the wavelengths is λ2 <λ3 <λ4. In the case of this embodiment, the incident position of the optical bandpass filter body 14 of the incident light L _in is, as shown in FIG. 1, ▲ 1 ▼ → ▲ 2 ▼ → ▲ 3 ▼ → ▲ 4 ▼ like comprising sequentially Then, the band-pass optical filter main body 14 is moved. In the following description, the case where the filter main body 14 is moved is illustrated, but the same result can be obtained even if the filter main body 14 is fixed and the incident position is moved.
[0038]
The incident position (1) is a position where the transmission wavelength λ2 is obtained, and the reflection spectrum does not have the transmission wavelength λ2 as shown in FIG. Incident position ▲ 2 ▼ and ▲ 3 ▼ is the total reflection region 18, these incident position, all wavelength components of the incident light L _in is reflected, the reflection spectrum is as shown in FIG. 4 (B) .
[0039]
The incident position {circle around (4)} is a position where the thickness of the spacer layer 12 is shifted in the x direction, which is thicker than the incident position {circle around (1)}. In this position, the transmission wavelength λ4 is obtained. As shown in FIG. 4C, the reflection spectrum does not have the transmission wavelength λ4.
[0040]
In this embodiment, when changing the transmission wavelength, the incident position is changed to another position on the band-pass filter main body 14 after passing through the total reflection area 18. More specifically, before moving from the incident position (1) to the incident position (4) where the transmission wavelength λ4 is obtained, first, the filter body 14 is moved in the y-axis direction.
In this case, since the y-axis direction is a direction in which the thickness of the spacer layer 12 does not change, the transmission wavelength λ2 does not change even if it is moved in that direction.
[0041]
Therefore, the reflection spectrum is maintained in the state shown in FIG. 4A until the incident position reaches the total reflection area 18, and when the incident position enters the total reflection area 18, the reflection spectrum becomes FIG. It becomes as shown in.
[0042]
When the incident position reaches (2) of the total reflection area 18, the incident position is moved in the x direction to a position (3) in the total reflection area 18. In such transfer process, the incident position, because the total reflection region 18, the reflection spectrum, all wavelength components of the incident light L _in is reflected is maintained the state shown in FIG. 4 (B).
[0043]
Next, the incident position is translated in the y-axis direction from (3) to (4) (4). In this case, when the incident position escapes from the total reflection area 18 and reaches the position (4) of the band-pass filter body 14, the reflection spectrum has a transmission wavelength λ4 as shown in FIG. And the change of the transmission wavelength is completed.
[0044]
In this way, after the incident position is made to pass through the total reflection area 18 and then changed from (1) to (4) of the band-pass filter body 14 and the transmission wavelength is switched from λ2 to λ4, the incident position In the process from ▼ to ２2, the direction in which the thickness of the spacer layer 12 does not change and the total reflection region 18 are provided, so that the reflection spectrum always includes the wavelength λ3.
[0045]
Further, until the light exits the total reflection area 18 in the process of the incident position (2) → (3) and the process of (3) → (4), the wavelength λ3 is included in the reflection spectrum because the wavelength is λ3. Always included.
[0046]
Accordingly, during the process until the transmission wavelength is changed from λ2 to λ4, the reflection spectrum always includes the wavelength λ3, so that this wavelength component is not interrupted at the reflection port side and transmitted at the transmission port side. It is possible to change the wavelength from λ2 to λ4.
[0047]
In the above embodiment, the total reflection region 18 is integrally formed on the side of the band-pass filter main body 14. However, the embodiment of the present invention is not limited to this. The formed total reflection area may be attached to the filter body 14. Further, the means for forming the total reflection area 18 is not limited to being formed by etching, but may be other means. Further, in the above-described embodiment, the incidence of light is set on the substrate 16 side. However, this may be on the reflection film 10 side. However, on the substrate 16 side, the light incident on the boundary between the filter region and the total reflection region 18 is formed. There is no step, and light scattering at this portion can be prevented.
[0048]
FIGS. 5 to 7 show measurement results obtained by experimentally producing a wavelength tunable optical filter of the present invention by the manufacturing method shown in FIG. 4 and measuring the characteristics thereof. In this prototype, the substrate 16 is made of BK-7 optical glass, the spacer layer 12 is made of SiO ₂ , the high-refractive-index dielectric layer 10 a of the reflection film 10 is made of Ta ₂ O ₅ , and the low-refractive-index dielectric is used. These were alternately formed using SiO ₂ for the layer 10b. Further, Cu was used for the mask layer 22.
[0049]
In this prototype, as shown in FIG. 5, the total reflection area 18 is formed in approximately half of a rectangular shape having a long side of 10 mm, and the incident position of the light beam is set at 39 places as shown in FIG. did.
[0050]
FIG. 6 is an optical spectrum measured at the reflection ports at the incident positions 1, 7, 20, 33, and 39 when the wavelength of the incident beam is changed. In this case, the incident positions 1 and 7 are on a straight line in the direction in which the thickness of the spacer layer 12 does not change, and the position 20 is located in the total reflection area 18.
The incident positions 33 and 39 are on a straight line in the direction in which the thickness of the spacer layer 12 does not change. This straight line and the straight line where the positions 1 and 7 are arranged are parallel to each other with an interval of about 7 mm. I have.
[0051]
As can be seen from the graph of FIG. 6, in the optical spectra at positions 1 and 7, a loss peak is observed at 1537 nm (corresponding to the transmission wavelength λ4), and at positions 33 and 39, 1532 nm (at the transmission wavelength λ2). (Equivalent), a loss peak is observed, and at position 20, no loss peak exists in the range of 1525 to 1545 nm.
[0052]
This means that when the incident position of the light beam is moved from 1 (transmission wavelength 1537 nm) → 7 → 20 → 33 → 39 (transmission wavelength 1532 nm), the loss increases at these intermediate wavelengths (eg, 1535 nm). You can see that it is not.
[0053]
FIG. 7 shows the measurement results of the light intensity measured at the reflection port for the three wavelengths of 1535 nm (the transmission wavelength at the position 1), 1532 nm (the transmission wavelength at the position 39), and the intermediate wavelength of 1535 nm.
[0054]
As can be seen from the figure, it was found that the 1535 nm light was hardly affected even if the incident position of the light beam was changed, and the effectiveness of the present invention was confirmed from the results of these characteristic measurements. We were able to.
[0055]
FIG. 8 shows an embodiment of the wavelength changing device for the tunable optical filter described above. The wavelength changing device shown in FIG. 1 includes a stage 30 that is movable in a two-dimensional direction, a moving mechanism 32 that moves the stage 30 in a two-dimensional direction, and a housing 34 that houses these components.
[0056]
The stage 30 is formed in a flat plate shape, and is supported by a housing 34 so as to be movable in two-dimensional x and y directions. On the stage 30, a band-pass filter main body 14 of a wavelength variable optical filter is mounted. ing.
[0057]
The filter main body 14 has the same configuration as that shown in FIG. 1, includes a reflection film 10, a spacer layer 12, and a substrate 16, and has a total reflection area 18 on the side. In the state shown in FIG. 8, the total reflection area 18 is hidden behind the main body 14.
[0058]
The filter main body 14 is mounted on the stage 30 so that the substrate 16 and the reflection film 10 are located at both ends. The entrance and reflection ports 36 and 38 are set in front of the substrate 16 side, and the rear of the reflection film 10 is provided. The transmission port 40 is disposed at the bottom.
[0059]
Each port 36, 38, 40 has collimator lenses 36a, 38a, 40a and optical fibers 36b, 38b, 40b coupled thereto so that the collimator lenses 36a, 38a, 40a are close to the stage 30. And is fixed to the housing 34.
[0060]
The moving mechanism 32 is composed of x-axis and y-axis moving mechanisms 32a and 32b. In the case of the present embodiment, a manual micrometer is used. As a result, the stage 30 moves in the x-axis or y-axis direction. The moving mechanism 32 need not be limited to a manual method using a micrometer, but may be, for example, an electric moving mechanism using a stepping motor or the like.
[0061]
When the transmission wavelength of the band-pass filter body 14 is changed, the position of incidence on the band-pass filter body 14 via the incident port 36 is moved by the operation of the moving mechanism 32 through the total reflection area 18 to change the band-pass filter. Change to another position on the body 14.
[0062]
This change process will be described in more detail. When changing the transmission wavelength, first, the y-axis moving mechanism 32b is operated to move the pass filter 14 in a direction orthogonal to the plane of FIG. The total reflection area 18 disposed on the back side of the 14 faces the collimator lens 36a of the entrance port 36.
[0063]
Thereafter, while maintaining this state, the x-axis moving mechanism 32a is operated to move in the x direction, and then the y-axis moving mechanism 32b is operated again, so that another portion of the filter 14 is moved to the entrance port 36. Of the collimator lens 36a.
[0064]
Such a movement process is substantially the same as the movement processes (1) to (4) shown in FIG. 1, and by moving in this manner, the intermediate wavelength is not interrupted. , The transmission wavelength can be changed.
[0065]
【The invention's effect】
As described above in detail, according to the tunable optical filter and the filter wavelength changing device of the present invention, the transmission wavelength can be changed without interruption of the intermediate wavelength.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of the entire configuration showing an embodiment of a wavelength tunable optical filter according to the present invention.
FIG. 2 is an enlarged view of a main part of FIG.
FIG. 3 is an explanatory diagram of a manufacturing process when manufacturing a wavelength tunable optical filter according to the present invention.
FIG. 4 is an explanatory diagram of a reflection spectrum when a transmission wavelength is changed in the wavelength tunable optical filter shown in FIG. 1;
FIG. 5 is an explanatory diagram of positions where characteristics of the wavelength variable optical filter according to the present invention are measured.
FIG. 6 is an explanatory diagram of a reflection spectrum at a representative light beam position of the wavelength tunable optical filter according to the present invention.
FIG. 7 is an explanatory diagram of a loss change in a reflection port when a light beam position is moved in the wavelength tunable optical filter according to the present invention.
FIG. 8 is an explanatory diagram of the entire configuration showing an embodiment of a wavelength changing device for a wavelength tunable optical filter according to the present invention.
FIG. 9 is an explanatory diagram of an overall configuration showing an example of a conventional wavelength variable optical filter.
FIG. 10 is an explanatory diagram of a reflection spectrum when the transmission wavelength is changed in the variable wavelength optical filter shown in FIG. 7;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Reflective film 12 Spacer layer 14 Band-pass filter main body 16 Substrate 18 Total reflection area 30 Stage 32 Moving mechanism 36 Incident port 38 Reflection port 40 Transmission port

Claims (5)

It has a reflective film in which dielectric layers having different refractive indexes are alternately laminated, and a spacer layer sandwiched between a pair of the reflective films, and transmits only a specific transmission wavelength corresponding to the refractive index and thickness of the spacer layer. With a bandpass filter body,
In the wavelength tunable optical filter, the thickness of the spacer layer is formed so as to continuously change along one direction, and the transmission wavelength is changed by changing the incident position on the bandpass filter body. ,
A total reflection area that reflects all of the incident light is provided on the side of the bandpass filter main body, and when changing the transmission wavelength, the incident position is passed through the total reflection area, and then the bandpass filter is used. A tunable optical filter characterized by being changed to another position on the main body. The tunable optical filter according to claim 1, wherein the total reflection region is disposed adjacent to the band-pass filter body in a direction in which a thickness of the spacer does not change. The tunable optical filter according to claim 2, wherein the total reflection region is formed integrally with a part of the spacer layer by removing a part of the reflection film. The tunable optical filter according to any one of claims 1 to 3, wherein the total reflection area is provided on a back side of the band-pass filter body that extracts the transmission wavelength. A stage capable of two-dimensional movement in a plane, and a moving mechanism for individually moving the stage in two-dimensional directions,
A band-pass filter body with a total reflection area provided on the side is mounted on the stage, and an entrance port and a reflection port are provided at one end of the band-pass filter body, and the other end of the band-pass filter body A transmission port is provided for
When changing the transmission wavelength of the band-pass filter main body, the operation of the moving mechanism causes an incident position on the band-pass filter main body via the incident port to pass through the total reflection region, and the band-pass filter A wavelength changing device for a wavelength tunable optical filter, wherein the wavelength changing device is changed to another position on a main body.

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