JP3282162B2 - Method of manufacturing tunable filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a wavelength tunable filter capable of selectively and variably extracting an optical signal of an arbitrary wavelength from a wavelength-multiplexed optical signal in an optical fiber. The present invention relates to a method of manufacturing a wavelength tunable filter that can manufacture a high performance wavelength tunable filter at very low cost.

[0002]

2. Description of the Related Art Optical communication using an optical fiber has recently been rapidly put into practical use because it can transmit a large amount of information at a high speed. However, at the moment, only an optical pulse of a specific wavelength is transmitted. If a large number of optical pulses of different frequencies can be transmitted, a larger amount of information can be transmitted. This is wavelength multiplexed (W
DM) and is currently being actively researched. In wavelength multiplex communication, a wavelength tunable filter that selectively selects only light of an arbitrary wavelength from optical signals of many wavelengths is required.

Conventionally, as this type of filter, a grating filter for controlling an angle by a motor, a wavelength variable filter for moving a dielectric filter by a motor, an etalon filter for controlling a resonator length by a piezo element, and the like are known. However, these wavelength tunable filters are very expensive (currently, about 100,000 yen to 1,000,000 yen at present), which causes wavelength multiplex communication to not be widely used.

On the other hand, a low-cost and highly reliable filter with a fixed wavelength optical fiber has been developed (T. Oguchi,
J. Noda, H. Hanafusa, and S. Nishi "Dielectric multil
ayered interference filters deposited on polyimide
films, "Electronics Letters., Vol.27, p.706-707,
(1991)).

In this filter with an optical fiber having a fixed wavelength, a dielectric mirror film is formed on a polyimide film, cut into several mm squares, and embedded in a groove formed in the optical fiber. By using a polyimide film instead of glass for the substrate, the filter with an optical fiber having a fixed wavelength enables the dielectric mirror film, which accounts for the majority of the cost, to be cut into several mm square, and the thickness is reduced to several tens of mm.
It is possible to make it as thin as μm, and by inserting a groove in the optical fiber and inserting it there is no need for optical components such as lenses and no complicated alignment is required, so it is very cheap and stable fixing A wavelength filter can be realized. However, it is difficult to tunably control the filter transmission wavelength of the filter with the fixed wavelength optical fiber.

[0006]

As described above, a grating filter for controlling an angle by a motor, a tunable filter for moving a dielectric filter by a motor, an etalon filter for controlling a resonator length by a piezo element, and the like are inexpensive. There was a problem that it was very expensive.

[0007] In the case of a filter with an optical fiber having a fixed wavelength, there is a problem that it is difficult to tunably control the filter transmission wavelength.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art, and an object of the present invention is to provide a method of manufacturing a tunable filter, in which a film-like polymer-dispersed liquid crystal layer is formed in a cavity. It is an object of the present invention to provide a technique capable of manufacturing a very inexpensive and high-performance tunable filter using the used Fabry-Perot etalon filter.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0010]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

In a method for manufacturing a wavelength tunable filter, a step of manufacturing a Fabry-Perot etalon filter using a polymer dispersed liquid crystal layer having a liquid crystal particle diameter of 150 nm or less in a cavity, and fixing an optical fiber or an optical fiber array. Forming a groove so that the core region of the optical fiber or the optical fiber array is exposed in the substrate, forming the Fabry-Perot etalon filter in the groove, and fabricating the fiber inserted in the groove. Fixing the Perot etalon-type filter and the substrate with an adhesive having a refractive index matching that of the Fabry-Perot etalon-type filter, and attaching a means for applying a voltage to the transparent conductive film of the Fabry-Perot etalon-type filter And characterized in that:

The step of manufacturing the Fabry-Perot etalon filter includes the steps of: forming a first layer comprising a transparent conductive film and a dielectric mirror film on a transparent substrate having a thickness of 250 μm or less; A step of uniformly applying and curing a polymer dispersed liquid crystal layer having a liquid crystal particle diameter of 150 nm or less on the film, and a step of forming a transparent conductive film and a dielectric mirror film on the polymer dispersed liquid crystal layer. And a step of cutting the filter produced in each of the above steps into a size of 5 mm square or less.

In the step of manufacturing the Fabry-Perot etalon filter, the diameter of the liquid crystal particles is 150 nm on the substrate.
A step of uniformly applying and curing the following polymer dispersed liquid crystal layer, a step of peeling the polymer dispersed liquid crystal layer from the substrate, and a transparent conductive film on both surfaces of the polymer dispersed liquid crystal layer. Forming a first layer and a second layer made of a dielectric mirror film, and cutting the filter manufactured in each of the steps into a size of 5 mm square or less. .

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In all the drawings for describing the embodiments, those having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

[Embodiment 1] First, a Fabry-Perot etalon-type wavelength tunable filter using a polymer-dispersed liquid crystal layer in a cavity will be described. The polymer-dispersed liquid crystal layer, which is a mixture of a polymer such as an adhesive and a nematic liquid crystal, is used as a scatterer when no voltage is applied and a transparent body when voltage is applied. Have been.

The inventors of the present invention consider that the factor of the scattering is related to the size of the liquid crystal particles, and by reducing the size of the liquid crystal particles to 150 nm or less, which is shorter than the wavelength of light, low loss (0.1%
dB / cm to 0. Several dB / cm) and the refractive index change Δn =
4 × 10 ~ ⁵ E ² (Here, the unit of E is μm / V) We are developing a nano-sized liquid crystal particle dispersion (S.Matsum
oto, M. Houlbert, T. Hayashi and K. Kubodera, "Fine d
roplets of LCs in atransparent polymer and their r
esponse to an electric field, "Appl. Phys. Lett.,
vol.69 (8), pp.1044, 1996.).

Further, the present inventors have devised a Fabry-Perot etalon type variable wavelength filter using a polymer-dispersed liquid crystal layer in a cavity, and have already filed a patent application for the basic structure thereof (Japanese Patent Application No. 9-1997). 205896). The Fabry-Perot etalon type wavelength tunable filter using the polymer-dispersed liquid crystal layer for the cavity is polarization-independent and has a very fast response speed of 10 μsec.

The polymer-dispersed liquid crystal is not a liquid but a solid, and has an excellent feature that it can be formed into a thin film. By using a Fabry-Perot etalon filter using a polymer-dispersed liquid crystal film in the cavity or a Fabry-Perot etalon filter using the polymer-dispersed liquid crystal formed on a thin glass substrate in the cavity The process for producing a polyimide fixed wavelength filter described above can be applied as it is, and a very inexpensive wavelength tunable filter can be realized.

FIG. 1 is a perspective view for explaining a method of manufacturing a filter according to a first embodiment of the present invention, and a sectional view of a main part thereof. Hereinafter, a method of manufacturing a filter according to the present embodiment will be sequentially described with reference to FIG.

(1) First, a thin transparent glass substrate 101 of 250 μm or less is prepared. Here, 200 μm
Was used.

(2) Next, on the transparent glass substrate 101,
The transparent conductive film 102 is formed by a vacuum evaporation method or a sputtering method.
Is formed, and further, a dielectric mirror film (dielectric multilayer film mirror) 103 is formed.
A first layer is formed on 1.

(3) Next, a liquid obtained by mixing a polymer solution and a nematic liquid crystal is applied on the first layer by a spinner, and then cured to form a polymer dispersed liquid crystal layer 104. The polymer solution used here is suitably an adhesive. That is, it is an ultraviolet curable adhesive or a thermosetting epoxy adhesive.

The polymer-dispersed liquid crystal layer 104 is formed by spin-coating a mixed solution of a thermosetting or photocurable prepolymer and a liquid crystal, and then heating or irradiating the mixed solution. It is produced by spin coating a liquid mixed with a nematic liquid crystal and rapidly removing the solvent.

These polymers are not particularly limited as long as they are light-transmitting materials, but polymers having good light-transmitting properties and no optical anisotropy, such as PMMA-based polymers and polystyrene-based polymers Polymers, polycarbonate polymers, thermosetting or photocurable acrylic polymers, epoxy polymers, polyurethane polymers, polyisocyanate polymers, polyenepolythiol polyimides and the like can be mentioned. Further, a nematic liquid crystal having a particle size of 150 nm or less is used.

The thickness of the polymer-dispersed liquid crystal layer 104 is about 10 μm to several tens μm, depending on the FSR (interval between wavelengths of resonating light) of the completed tunable filter. In addition, since the polymer-dispersed liquid crystal layer 104 forms the cavity of the wavelength tunable filter, the uniformity of the film of the polymer-dispersed liquid crystal layer 104 is very strongly required. The allowable thickness unevenness is
It is 0.5 μm / cm or less.

(4) Next, a dielectric mirror film 105 is formed on the polymer-dispersed liquid crystal layer 104 by vacuum evaporation or sputtering, and a transparent conductive film 106 is formed. A second layer is formed on the liquid crystal layer 104.

(5) Finally, the filter 107 is cut out into a 5 mm square or less together with the glass substrate using a dicing saw.

The filter 107 manufactured by the method shown in FIG. 1 has a polymer-dispersed liquid crystal layer (10) comprising a transparent conductive film (102, 106) and a dielectric mirror film (103, 105).
By forming a Fabry-Perot etalon type filter sandwiching 4) and applying a voltage to the transparent conductive films (102, 106), the transmission wavelength can be changed.

FIG. 2 is a perspective view for explaining a method of manufacturing the tunable filter module with an optical fiber according to the first embodiment of the present invention. Hereinafter, a method of manufacturing the wavelength tunable filter module with an optical fiber according to the present embodiment will be sequentially described with reference to FIG.

(1) First, an optical fiber 201 having connectors 203 at both ends is prepared. In order to reduce the loss of the wavelength tunable filter, the optical fiber 201 is desirably a core-enlarged optical fiber having an enlarged core at the center as shown by 202 in FIG. However, a normal optical fiber without an enlarged core can also be used.

(2) Next, a substrate such as a glass substrate, a plastic substrate, or a ceramic substrate is prepared. In this case,
It is preferable that these substrates have grooves formed therein for embedding the optical fiber 201, as in the case of the grooved substrate shown at 204 in FIG. However, a flat substrate indicated by 205 in FIG. 2 can also be used.

(3) Next, these substrates (204, 20)
5) Attach the optical fiber 201 and fix it with the adhesive 206.

(4) Next, the substrates (204, 205)
Insert the groove 208 for inserting the filter 209 into the dicing saw 2
07 to expose the core region of the optical fiber 201. At this time, it is preferable that the groove 208 is inclined (about 80 °) with respect to the optical fiber 201 in order to reduce the reflected light returning from the filter 209. The width corresponds to the thickness of the filter 209.

(5) Next, a filter 209 (the filter 107 manufactured in FIG. 1) cut into several mm squares is prepared, and the upper transparent conductive film 106 and the polymer dispersed liquid crystal layer 10 are prepared.
4 and only the end portions of the dielectric mirror films (103, 105) are peeled off, and a lead electrode 210 is attached to the glass-side transparent conductive film 102 with a conductive paste or solder 211.

(6) Next, the filter 209 is mounted on the substrate (2
04, 205) and adhesively fixed with an adhesive 212 having the same refractive index as the filter 209. In this case, two or more filters 209 are stacked as necessary.

(7) Finally, the extraction electrode is attached to the filter upper transparent conductive film 106 by pressing the contact metal rod 213 to which the extraction electrode 214 is attached against the upper transparent conductive film 106 of the filter 209. In addition, using a conductive paste, the filter upper surface transparent conductive film 10 is used.
The electrode may be taken out of the filter 6, but the conductive paste may soak into the filter 209 and cause a short circuit.

FIG. 5 shows the applied voltage dependence of the wavelength tunable filter module with an optical fiber thus manufactured according to the present embodiment. As shown in FIG. 5, the wavelength tunable filter module with an optical fiber according to
By applying a voltage of 00V, the transmission peak becomes 10
It can be seen that the shift is at least nm.

In this embodiment, the substrate (204,
Although the case where only one optical fiber 201 is mounted on the substrate (205) has been described, it is also possible to mount many optical fibers on the substrate (204, 205) to form an array.

[Embodiment 2] FIG. 3 is a perspective view for explaining a method of manufacturing a filter according to Embodiment 2 of the present invention.
FIG. In the first embodiment,
The first layer, the polymer-dispersed liquid crystal layer, and the second layer were laminated on a thin glass substrate to form a filter. In this embodiment mode, a film-shaped polymer dispersion was used without using a glass substrate. This is a method for producing a filter using the liquid crystal layer.

Hereinafter, a method of manufacturing a filter according to the present embodiment will be sequentially described with reference to FIG.

(1) First, the film forming substrate 30
Prepare 1

(2) Next, a liquid in which a polymer solution and a nematic liquid crystal are mixed is applied onto the film forming substrate 301 by spin coating, and then cured by irradiation with ultraviolet light or heating to form a polymer dispersed liquid crystal layer. Form 302.
The polymer solution used here is desirably resistant to heat because of the following vapor deposition process, and may be an ultraviolet curable adhesive used as an adhesive or a thermosetting epoxy adhesive.

The thickness of the polymer-dispersed liquid crystal layer 302 is about 10 μm to several tens μm. Since the polymer-dispersed liquid crystal layer 302 serves as a cavity of the wavelength tunable filter, the uniformity of the film of the polymer-dispersed liquid crystal layer 302 is very strongly required, and the allowable film thickness unevenness is 0.5 μm / cm or less. is there.

(3) Next, the film-shaped polymer-dispersed liquid crystal layer (hereinafter referred to as polymer-dispersed film) 302 is peeled from the substrate 301.

(4) Next, the peeled polymer dispersed film 302 is attached to a frame 303 and is stuck uniformly without wrinkles.

(5) Next, the polymer dispersed film 302
A first layer and a second layer composed of a dielectric mirror film 304 and a transparent conductive film 305 are formed on both surfaces of the substrate by vacuum evaporation or sputtering.

(6) Finally, a film-like filter (hereinafter, referred to as a film filter) 306 is cut out into a 5 mm square or less.

The film filter 306 manufactured by the method shown in FIG. 3 also constitutes a Fabry-Perot etalon type filter in which the polymer dispersed liquid crystal layer 302 is sandwiched between the transparent conductive film 305 and the dielectric mirror film 304. Transparent conductive film 3
By applying a voltage to 05, the transmission wavelength can be changed.

FIG. 4 is a perspective view for explaining a method of manufacturing a wavelength tunable filter module with an optical fiber according to Embodiment 2 of the present invention. Hereinafter, a method of manufacturing the wavelength tunable filter module with an optical fiber according to the present embodiment will be sequentially described with reference to FIG.

The process up to the step (4) is the same as that of the first embodiment shown in FIG. 2, and the description thereof is omitted.

(5) Prepare a film-shaped filter 401 (the film filter 306 manufactured in FIG. 3) cut into a few mm square.

(6) Next, the film filter 401 is
It is inserted into the groove 208 formed on the substrate (204, 205), and is fixed with an adhesive 402 having the same refractive index.

(7) Finally, both surfaces of the film filter 401 are sandwiched between two contact metal rods 403 to which the extraction electrodes 404 are attached.
An extraction electrode is attached to the transparent conductive film 305.

The dependence of the applied voltage on the wavelength tunable filter module with the optical fiber of the present embodiment manufactured in this manner is almost the same as the characteristic shown in FIG.

In this embodiment, the substrate (204,
Although the case where only one optical fiber 201 is mounted on the substrate (205) has been described, it is also possible to mount many optical fibers on the substrate (204, 205) to form an array.

The cost of the tunable filter module with an optical fiber in each of the above manufacturing methods is estimated as follows.

The highest cost in the above process is the step of forming the dielectric mirror films (103, 105, 304) and the transparent conductive films (102, 106, 305), which is about 300,000 yen at present. . Assuming that a 1 mm square filter (107, 306) is cut out from a 3-inch substrate, the cost is about 70 yen per sheet. Therefore, the cost of the wavelength tunable filter module with an optical fiber of each of the above embodiments is mainly the cost of the optical fiber 201, the connector 203, and the trenching work, and the total cost is estimated to be about 10,000 yen. Since the cost of the current tunable filter is about one million yen, the cost is reduced to 1/100.

Further, the filter (2
09, 401) is in the form of a film, so that it is easy to laminate in multiple layers, and by laminating in multiple layers, the extinction ratio of the filter (209, 401) can be greatly increased. Furthermore, the filters (2
09, 401) has the advantage that light beam alignment is not required.

As described above, the invention made by the present inventor is:
Although a specific description has been given based on the above-described embodiment, the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the invention.

[0061]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) According to the present invention, a high-performance wavelength tunable filter can be manufactured at low cost.

(2) According to the present invention, a Fabry-Perot etalon-type filter using a polymer-dispersed liquid crystal layer in a cavity can be laminated in multiple layers, so that the extinction ratio of the Fabry-Perot etalon-type filter can be greatly increased. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a perspective view for explaining a method for manufacturing a filter according to a first embodiment of the present invention, and a cross-sectional view of a main part thereof.

FIG. 2 is a perspective view for explaining a method of manufacturing the wavelength tunable filter module with the optical fiber according to the first embodiment of the present invention.

FIG. 3 is a perspective view for explaining a method for manufacturing a filter according to a second embodiment of the present invention, and a cross-sectional view of a main part thereof.

FIG. 4 is a perspective view for explaining a method of manufacturing a wavelength tunable filter module with an optical fiber according to a second embodiment of the present invention.

FIG. 5 is a graph showing a relationship between a wavelength and an applied voltage of the wavelength tunable filter module with an optical fiber manufactured by the method of the first embodiment.

[Explanation of symbols]

101: transparent substrate, 102, 106, 305: transparent conductive film, 103, 105, 304: dielectric mirror film, 10
4,302: Polymer dispersed liquid crystal layer, 107, 209, 3
06, 401: Filter, 201: Optical fiber, 202
... Enlarged portion of optical fiber core, 203 ... Connector, 20
4 ... grooved substrate, 205 ... plane substrate, 206, 212,
402 ... adhesive, 207 ... dicing saw, 208 ...
Grooves, 210, 214, 404 ... Extraction electrodes, 211 ...
Conductive paste or solder, 213, 403: metal bar for contact, 301: substrate, 303: film attachment frame.

Continuation of the front page (56) References JP-A-8-160412 (JP, A) JP-A-8-94987 (JP, A) JP-A-4-220618 (JP, A) JP-A-9-33878 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/13 505 G02B 5/20

Claims (7)

(57) [Claims] 1. A step of manufacturing a Fabry-Perot etalon filter using a polymer dispersed liquid crystal layer having a liquid crystal particle diameter of 150 nm or less in a cavity, and a step of fixing an optical fiber or an optical fiber array to a substrate.
Forming a groove so that the core region of the optical fiber or the optical fiber array is exposed; inserting the Fabry-Perot etalon-type filter into the groove; and inserting a Fabry-Perot etalon-type filter into the groove. And fixing the substrate with an adhesive having a refractive index matching that of the Fabry-Perot etalon-type filter, and mounting a means for applying a voltage to the transparent conductive film of the Fabry-Perot etalon-type filter. A method for manufacturing a tunable filter, comprising: 2. The step of manufacturing the Fabry-Perot etalon filter includes the steps of: forming a first layer made of a transparent conductive film and a dielectric mirror film on a transparent substrate having a thickness of 250 μm or less; A step of uniformly applying and curing a polymer-dispersed liquid crystal layer having a liquid crystal particle diameter of 150 nm or less on the film of No. 1; and a transparent conductive film and a dielectric on the polymer-dispersed liquid crystal layer. The wavelength according to claim 1, further comprising: a step of forming a second layer made of a mirror film; and a step of cutting the filter produced in each of the steps into a size of 5 mm square or less. Manufacturing method of variable filter. 3. The step of manufacturing the Fabry-Perot etalon filter includes forming a liquid crystal particle having a diameter of 150 nm on a substrate.
m, a step of uniformly applying and curing a polymer dispersed liquid crystal layer, a step of peeling the polymer dispersed liquid crystal layer from the substrate, and a transparent conductive film on both surfaces of the polymer dispersed liquid crystal layer. Forming a first layer and a second layer comprising a film and a dielectric mirror film; and cutting the filter produced in each of the steps into a size of 5 mm square or less. The method for manufacturing a wavelength tunable filter according to claim 1. 4. The method for uniformly applying a polymer-dispersed liquid crystal layer by a spin coating method.
A method for manufacturing a wavelength tunable filter according to claim 3. 5. The tunable filter according to claim 1, wherein two or more Fabry-Perot etalon filters are stacked and inserted into the groove. Method. 6. The method according to claim 1, wherein the groove is inclined with respect to the optical fiber or the optical fiber array. . 7. The optical fiber according to claim 1, wherein the optical fiber or the optical fiber of the optical fiber array is a core-expanded optical fiber having a core portion partially enlarged. 3. A method for manufacturing a tunable filter according to claim 1.