JP2608633B2 - Dielectric multilayer filter, method of manufacturing the same, and optical element using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric multilayer interference filter used in optical communication and a component using the same.

[0002]

2. Description of the Related Art In optical communication, a component in which a thin dielectric multilayer filter is disposed in a minute gap in an optical path is used, and a thin dielectric multilayer filter required for this is sometimes required. FIG. 21 shows an example in which a dielectric multilayer filter is inserted between optical fibers (H. Yanagawa, et. Al., 'Filter-Embedded D).
esign and Its Applications to Passive Co
mponents', IEEEJ. Rightwave Technol. , vo
l. LT-7, pp. 1646-1653, 1989). In this figure,
(a) is a plan view, (b) is a cross-sectional view along AA ', and reference numerals 1 and 2 denote optical fibers, 3 denotes a dielectric multilayer filter flake, and 4 denotes a dielectric multilayer filter. Groove for
Denotes a substrate for fixing the optical fiber and the dielectric multilayer filter. With this configuration, if, for example, a dielectric multilayer filter flake 3 having a characteristic of transmitting light of wavelength λ1 and reflecting light of wavelength λ2 is used, two wavelength components λ1 and λ2 propagating in the optical fiber 1 are used. Only the unnecessary wavelength component λ2 can be removed, and only the necessary wavelength component λ1 can be propagated to the optical fiber 2. Normally, in order to allow the light reflected back in the direction of the input fiber to escape to the cladding of the input fiber 2, the dielectric multilayer filter is disposed at a required angle from the direction perpendicular to the optical axis of the optical fiber. In order to manufacture the optical fiber with a filter, first, the optical fibers 1 and 2 (in this state, both optical fibers are not cut) are fixed in a groove provided in the substrate 5 with an adhesive. Next, a groove 4 traversing the optical fiber is formed, and the dielectric multilayer filter 3 is inserted into the groove 4 and fixed with an adhesive.
As can be seen from this method, the optical fiber 1 and the optical fiber 2 are originally the same fiber, and were cut in a fixed state. No need arises.

Also, as shown in FIG. 21, a dielectric multilayer filter is provided not on a straight optical fiber but on a part of a device having a function of controlling guided light such as a directional coupler. Something to do is also possible. FIG. 22 shows an example thereof. In this figure, reference numerals 6 and 7 denote input side optical fibers, 8 and 9 denote output side optical fibers, 10 denotes an optical coupling portion of a directional coupler, and 11 and 12 denote dielectric fibers. Body multilayer filter flakes,
Reference numeral 13 denotes a groove for disposing the dielectric multilayer filter, and reference numeral 14 denotes a substrate for fixing the optical fiber and the dielectric multilayer filter. As is well known, since the degree of coupling of the directional coupler has wavelength dependence, for example, one wavelength component of the two-wavelength multiplexed light propagating through the input optical fiber 6 is
And the other wavelength component is output from the optical fiber 9. That is, wavelength separation can be performed. However, since the wavelength separation is not sufficient with only the directional coupler alone, a configuration in which the dielectric multilayer filter thin pieces 11 and 12 are inserted into the output fiber is an effective means.

In addition to these, various configurations are conceivable, such as one in which the optical fiber shown in FIGS. 21 and 22 is replaced with an optical waveguide.

In the conventional example described above, the light guided through the input optical fiber has its intensity distribution expanded in the groove due to diffraction, and only a part of the light is coupled to the output optical fiber. However, if the width of the groove in which the filter is provided is made sufficiently small, the loss of light can be reduced to such an extent that there is no problem. For example,
When an optical fiber having a core diameter of 10 μm and a relative refractive index difference of 0.3% is used, by setting the groove width to several tens μm or less, the diffraction loss caused by the gap between the input optical fiber and the output optical fiber is reduced to 0.5 dB. It can be suppressed to the extent.
That is, in order to realize these components with low loss, a thin dielectric multilayer filter is required.

As shown in FIG. 23, a conventional dielectric multilayer filter comprises a hard substrate 15 and a dielectric multilayer film 16 formed thereon. The substrate 15 is transparent, has a smooth surface, and requires a certain degree of strength. For this reason, a flat optical glass, for example, a material such as synthetic quartz glass or BK-7 is used, and the thickness of the substrate 15 is 0.1 mm. 5 mm or more. The dielectric multilayer film 16 is formed by alternately stacking low-refractive-index dielectric layers 17 and high-refractive-index dielectric layers 18. In addition, not only two types of dielectric layers but also three or more types of dielectric materials including a low refractive index dielectric, a high refractive index dielectric, and a dielectric layer having a refractive index between them are used. The thickness of each layer increases as the operating wavelength increases, and more layers are stacked to approximate the required spectral characteristics. In a wavelength range of 1.31 to 1.55 μm, which is often used in optical fiber communication, there is a case where the total thickness of the multilayer film reaches about 10 μm. When the thickness of this conventional dielectric multilayer filter using glass as a substrate is reduced to several tens μm or less, the substrate 15 is polished from the back surface where the dielectric multilayer film 16 does not exist to a desired thickness,
Next, it was cut into a predetermined size.

[0007]

However, the prior art for obtaining such a thin filter has two major drawbacks. The first disadvantage is that it requires skilled labor for polishing and processing,
Filters can be very expensive.
Further, when the thickness of the filter as a whole is several tens μm or less, the thickness of the substrate is extremely thin and easily cracked, requiring a great deal of labor for cleaning and mounting the surface. That is, even with a simple configuration as shown in FIGS. 21 and 22, the dielectric multilayer filter used therein is expensive,
In addition, since highly skilled personnel are required, there is a limit in reducing the cost of the entire part.

A second disadvantage of the prior art is that when a known ion-assisted vapor deposition method is used to obtain a dense multilayer film having no wavelength fluctuation, compressive stress remains in the multilayer film and the filter warps. This means that polishing cannot be performed thinly. This is clear from the measured data in FIG. 24, for example.
FIGS. 24A and 24B show the results obtained by the tally step with the multilayer film surface of the dielectric multilayer film filter facing upward. FIG. 24A shows the result obtained by the ion assist method, and FIG. 24B shows the result obtained by the ordinary vapor deposition method without using the ion assist. Things. (A),
(B) Both substrates have BK-7 glass with a thickness of 0.5 mm,
The multilayer film portion is about 10 μm thick and is composed of alternating layers of TiO ₂ and SiO ₂ and separates the wavelengths of 1.3 μm and 1.55 μm. In (A), the multilayer film was greatly warped so as to be convex. Further, the change in humidity in (A) and (B) (0 to 100)
%), The change in the spectral characteristics was measured.
The following results were obtained. In (B), the wavelength changes by 25 nm with respect to the change in humidity, whereas in (A), extremely stable characteristics are shown. The reason why the large humidity characteristic is shown in (B) is that moisture according to the surrounding humidity flows into and out of the pores in the multilayer film, thereby changing the refractive index of the film. On the other hand, the reason why excellent moisture resistance is exhibited in (A) is that the multilayer film is so dense that there are no pores that cause moisture to enter and exit. Cause.

[0009] Then, when the polishing workability of (A) and (B) was examined, the one of (A) was broken apart and several tens μm.
No one with a thickness of less than m was obtained. on the other hand,
(B) could be polished to a thickness of 20 μm. Due to such circumstances, the type (B) that can be polished has conventionally been used, but wavelength fluctuations due to changes in ambient humidity during handling, processing, or storage have been forced.

[0010] First, as a method of obtaining an inexpensive filter instead of the above-mentioned conventional product, the present inventors studied a method of forming a multilayer film on a thin plastic film. As a result of the investigation, an attempt to form a multilayer interference film thereon using a plastic film as a substrate has been reported by, for example, Sugiyama et al. (JP-A-63-64003, JP-A-63-8).
No. 8505), J. Amer. A. Dobrowlski et al. (Applied Optics, vol. 28, n.
o. 14, p2702). The filters in these examples are intended for use in the visible range,
Also, the required accuracy of the spectral characteristics is not so strict. Therefore, the thickness of each layer and the number of layers should be at most 0.2
μm, about 20 layers. In the above example, for forming a multilayer film,
A so-called roll coating method is used in which both ends of the film are held by a winding mechanism and the film is formed while the film is stretched straight. However, in this method, a multilayer film having a uniform thickness controlled with high precision cannot be obtained. When the film on which the multilayer film is formed is taken up, the multilayer film is peeled off or cracks occur. Also, the film used as the substrate needs to have a certain thickness to have some strength,
In fact, in the example of Sugiyama et al., The thickness of the polyester film is 100 μm. Taking these factors into consideration, it has been determined that this method cannot provide the dielectric multilayer filter desired by the present inventors.

The inventors of the present invention have conducted intensive studies on a method for forming a highly accurate and highly stable multilayer film on a plastic film. A method of forming a multilayer film by an ion assist method, and finally peeling the multilayer film from a glass substrate, was invented. Polyimide was selected because it can be formed in close contact with a plate-like substrate by a coating method such as spin coating, and can withstand a temperature rise during vapor deposition due to its excellent heat resistance. That is, there has been an expectation that a multilayer film having the same performance can be formed by the same vapor deposition process as in the related art, except that a thin polyimide thin film adheres to the substrate. Therefore, BK-7 with a thickness of 0.5 mm was obtained from a commercially available polyimide thin film forming material.
Form a polyimide thin film on glass by spin coating,
On top of that, SiO ₂ and Ti are deposited by ion-assisted evaporation.
A multilayer film made of O ₂ was formed. The adhesion between the multilayer film and the polyimide substrate was good. However, finally, in the step of separating the BK-7 glass from the polyimide substrate to which the multilayer film has adhered, the adhesion between the polyimide thin film and the BK-7 glass was so strong that separation was impossible.

Therefore, the glass substrate is made of S
Instead of the i substrate, a polyimide thin film and a multilayer film were formed on the polished surface in the same manner as described above. When the polyimide thin film on which the multilayer film was formed was gradually peeled off with the knife edge, bare peeling was possible. However, the exfoliated filter was curled to several mm in diameter, and was extremely poorly handled. The direction of the curl was such that the surface of the multilayer film became convex. The cause of the curl was considered to be the coefficient of thermal expansion of the polyimide thin film used. That is, since the temperature was increased by ion bombardment during the formation of the multilayer film (about 200 ° C.), the thermal expansion coefficient of the polyimide thin film (about 2 × 10 ⁻⁵ / ° C. in catalog value) and the thermal expansion coefficient of the multilayer film (TiO ₂ the difference of the expected near 0.4 to 0.5 × 10 ^{over 5} / ° C. approximately to the average value of the thermal expansion coefficient of the SiO _2), the polyimide thin film in a state was returned to room temperature shrinkage of the multilayer film It was surmised that the shrinkage exceeded the shrinkage, which further promoted the warpage due to the compressive stress of the multilayer film. In fact, when the temperature of the obtained film was raised on a hot plate, the curl tended to return. From the above, it is clear that in order to realize the method originally invented by the present inventors, it is important that peeling of the polyimide thin film and the substrate can be performed in the final step and that warpage is reduced. Was.

[0013]

In order to solve the above problems, the present inventors used a fluorinated polyimide thin film as a substrate, and formed a dielectric film having a multilayer film formed by ion-assisted vapor deposition on the polyimide thin film substrate. A multilayer filter is proposed. As a manufacturing method for realizing this, a liquid fluorinated polyimide material is applied to a required thickness on a temporary substrate having a smooth surface, dried and cured to form a fluorinated polyimide thin film. After a dielectric multilayer film is formed on the substrate, a method of peeling the fluorinated polyimide thin film having the dielectric multilayer film formed on the surface from the temporary substrate is proposed.

The function of the dielectric multilayer filter according to the present invention is as follows. First, since the substrate can be made thinner from the beginning, the conventional expensive polishing step can be omitted. Second, the multilayer film is formed by ion-assisted vapor deposition. It is stable because it is formed with
Third, since the substrate has a lower thermal expansion property than the multilayer film portion, the compressive stress of the ion-assisted vapor-deposited film is canceled when the temperature is returned to room temperature after vapor deposition due to the difference in the coefficient of thermal expansion between the substrate and the multilayer film.
Fourth, a filter having less warpage can be formed. Fourth, since the fluorinated polyimide thin film is used for the substrate, the filter has transparency and can be easily peeled from the temporary substrate. As a result, it is possible to supply inexpensive filter components using a thin dielectric multilayer filter.

[0015]

FIG. 1 shows an embodiment of a dielectric multilayer filter according to the present invention. In FIG. 1, reference numeral 19 denotes a fluorinated polyimide thin film serving as a filter substrate. On the upper surface of the fluorinated polyimide thin film 19, a dielectric multilayer film 20 is formed.
Are formed, and the dielectric multilayer filter 21 is formed.

Fluorinated polyimide for forming the above thin film
(Hereinafter abbreviated as polyimide) is an acid dianhydride represented by chemical structural formulas (1) to (15) shown in Chemical formula 1, and a diamine represented by chemical structural formulas (1) to (31) shown in Chemical formula 2. Synthesized from

[0017]

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That is, the acid dianhydride shown in Chemical formula 1 and Chemical formula 2
One or several kinds of acid dianhydrides selected from diamines shown below and one or more kinds of diamines, such that the acid dianhydride group and the diamine group are in a molar ratio of 1: 1. N-
Liquid polyimide material obtained by reacting in a polar solvent such as methylpyrrolidone (NMP) or N, N-dimethylacetamide (DMAc) (in terms of chemical components, a solution of polyamic acid which is a precursor of polyimide), solvent After the polyamide acid soluble in water is converted into a solid polyimide by imidation treatment such as heating and dehydration, or a liquid polyimide material dissolved in a solvent during the imidization treatment can be used.

The production of this dielectric multilayer filter is performed in the order of steps shown in FIGS. 2 (a), 2 (b), 2 (c) and 2 (d). That is, first, a liquid polyimide material is applied to a required thickness on a temporary substrate having a smooth surface. This coating is performed by spin coating in order to apply thinly to a uniform thickness. Next, the liquid polyimide material applied on the temporary substrate is dried and cured to form a polyimide thin film 19 as shown in FIG. Next, as shown in FIG. 2B, a dielectric multilayer film 20 is formed on the surface of the polyimide thin film 19 by an ion assisted vapor deposition method. Next, as shown in FIG. 2C, a cut 23 having a depth to reach the temporary substrate 22 is formed, and finally, as shown in FIG. Peel off.

Further, the order of peeling and cutting is changed, and FIG.
(a), (b), (c), and (d) may be manufactured. In this case, the dielectric multilayer filter 21 is peeled off in FIG. Cut in (d).

The polyimide thin film 19 obtained by the polyimide thin film forming step shown in FIGS. 2 (a) and 3 (a)
The coefficient of linear expansion is -0.5 to 10 * 10 < ^-5 > / [deg.] C. depending on the combination of the acid dianhydride and the diamine, and can cover the thermal expansion coefficient of most dielectrics used for the optical multilayer film. The refractive index becomes close to that of glass having a refractive index of about 1.5 to 1.7 depending on the magnitude of the fluorine content. As the temporary substrate, for example, silicon, BK-7 glass, quartz glass, ceramics, and the like can be cited, but since they are not finally included in the filter,
The cheaper the better. 2 (b) or FIG. 3 (b) in which the filter 21 is attached to the temporary substrate 22 for the purpose of measuring and inspecting the spectral characteristics of the filter. Preferably, a transparent temporary substrate which does not affect the optical characteristics of the filter in measurement and inspection is desirable.

(Experimental Example 1) A dielectric multilayer filter was actually manufactured based on the above manufacturing method. Acid dianhydride of formula 1 on BK-7 (temporary substrate) having a diameter of 30 mm and a thickness of 0.5 mm
The polyamic acid solution obtained by mixing (1) and the diamine (5) of Chemical formula 2 in DMAc and reacting them is spin-coated,
2 hours at 70 ° C, 1 hour at 160 ° C using oven
Drying and curing treatment were performed at 250 ° C. for 30 minutes and further at 350 ° C. for 1 hour to obtain a polyimide represented by Formula 3 below.

[0023]

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The fluorine content of this polyimide was calculated to be 23% from formula 3. Although the obtained polyimide thin film on BK-7 had a slightly yellowish color,
In the wavelength range of 1.7 μm, the transmittance was almost 100%. The thickness of the polyimide thin film is about 10 μm, and the refractive index is 1.
61 (λ = 1.532 μm). A multilayer interference film of about 10 μm made of TiO ₂ / SiO ₂ was formed thereon by ion-assisted vapor deposition. As shown in FIG. 4, the spectral characteristics of the resulting dielectric multilayer filter exhibited characteristics equivalent to those using an optical glass substrate, and were almost as designed. In addition, the long-wavelength band pass type (1.3 / 1.55 μmL WPF) shown in FIG. 5 and the narrow band type (half width at about 4 nm) shown in FIG. 6 also exhibited the same spectral characteristics as those of the glass substrate. From these characteristics, it was confirmed that the film thickness accuracy of the multilayer film formed on the polyimide thin film was equivalent to that using a conventional glass substrate. Further, no change in the wavelength of the multilayer film formed on the polyimide thin film with respect to the ambient humidity was observed. The adhesion between the polyimide thin film and the multilayer film was so good that it did not peel off even when rubbed with the tip of tweezers. Further, the temporary substrate and the polyimide thin film substrate adhered to each other so as not to be easily peeled off by ordinary handling, and the adhesion did not decrease even after being immersed in water for 3 to 7 days. However, it can be easily peeled off from the edge by a thin sharp object such as a knife edge, and has a diameter of 30 mm and a thickness of 20 mm.
A μm nearly flat filter was obtained. The warpage of the filter peeled from the temporary substrate at room temperature was slightly warped in the direction in which the multilayer film surface became convex, and the radius was about 0.3 m. For this reason, cutting with scissors and adhesion on glass were possible. A filter having almost no warpage was obtained because the polyimide film used here had a negative coefficient of thermal expansion (about -0.5 ×
10 ⁻⁵ / ° C.), the temperature difference between the multilayer film and the room temperature during deposition of the multilayer film has a remarkable effect that the elongation of the polyimide thin film becomes larger than the elongation of the multilayer film. This is because they completely canceled out. This is because the filter peeled off from the temporary substrate is placed on a hot plate at about 100 ° C, the warpage increases, and when the temperature is returned to room temperature, the magnitude of the warp returns to its original state. It was proved from showing.

Next, the filter on the temporary substrate was cut with a dicing saw so as to form a 2 mm square in a grid pattern while flowing water. Even in this cutting, the polyimide thin film did not peel off from the temporary substrate. However, the cut 2 mm square chip was easily peeled from the temporary substrate without being broken by a thin sharp object such as a knife edge. That is, about 150 filter chips having a size of 2 mm square and a thickness of 20 μm were easily obtained from a dielectric multilayer film filter formed on a temporary substrate having a diameter of 30 mm. As a result of measuring the thickness of each of the obtained filter chips one by one with a linear gauge, the thickness distribution was as shown in FIGS. 7 and 8. Here, FIG.
8 shows a filter having the characteristics shown in FIG. 4, and FIG. 8 shows a filter having the characteristics shown in FIG. In FIGS. 7 and 8, the most frequent 2
Thicknesses of 1 μm and 15 μm were obtained from the central portion of a wafer having a diameter of 30 mm, and thicker ones were obtained from the peripheral portion. Most of the thickness distribution was within about ± 2 μm with respect to the center value, which was almost the same as the accuracy of the method for polishing a glass substrate. Such high film thickness uniformity was obtained by using a spin coating method for forming a polyimide thin film. In addition, it was confirmed that the thickness can be selected according to the application because a polyimide thin film of 1 μm to 80 μm is obtained by one spin coating.

(Experimental Example 2) The same as Experimental Example 1 except that a liquid polyimide material obtained by reacting the acid dianhydride (5) of Chemical formula 1 with the diamine (13) of Chemical formula 2 in DMAc was used. Thus, a dielectric multilayer filter was manufactured. The polyimide in this case had the structure of the following formula 4, the fluorine content was 11%, and the coefficient of thermal expansion was 1 × 10 ⁻⁶ / ° C.

[0027]

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The warpage of the dielectric multilayer filter peeled off from the temporary substrate was slightly larger than in the case of Experimental Example 1, but could be used sufficiently.

(Comparative Example) Acid dianhydride (4) of Chemical formula 1 and Chemical formula 2
A dielectric multilayer filter was manufactured in the same manner as in Experimental Example 1 except that a liquid polyimide obtained by reacting the diamine (5) of Example 1 in DMAc was used. In this case, the polyimide had a structure represented by the following formula 5, and had a large fluorine content of 31%, was transparent even in the visible region, and had a refractive index of 1.5, which was close to that of glass.

[0030]

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Although the polyimide thin film after the formation of the multilayer film could be easily peeled off from the temporary substrate, the adhesion between the multilayer film and the polyimide thin film was insufficient, and the multilayer film partially peeled off when rubbed with tweezers. However, practical problems remained. Since the fluorine content was large, sufficient adhesion between the multilayer film and the polyimide thin film could not be obtained, and the coefficient of thermal expansion of the polyimide thin film was as large as 8 × 10 ⁻⁵ / ° C., and the coefficient of thermal expansion of the multilayer film was 0%. .
The difference is remarkable and from 4 to .5 × 10 ^{over 5} / ° C. approximately,
This was considered to be caused by the fact that a stress that promotes peeling remained at the interface between the two.

Examples of optical elements using the above-described dielectric multilayer filter will be described below.

FIGS. 9A and 9B are views showing an optical fiber with a filter as a first embodiment of the optical element according to the present invention. In this figure, (a) is a plan view, and (b) is a cross-sectional view along the optical axis AA 'of the optical fiber. In the figure, reference numerals 24 and 25 denote optical fibers from which the coating of the central portion 26 has been removed. 27 is a thin film filter whose substrate is made of polyimide. 28 is a groove for disposing a filter, 29
Is a substrate that holds the fiber and the filter. As a manufacturing method for obtaining the structure of the filter-containing optical fiber, first, the optical fibers 24 and 25 are arranged and fixed in a groove provided in the substrate 29 in advance (the optical fibers 24 and 25 are not cut at this stage). ), Fix with adhesive. Next, the groove 28 is formed so as to completely cut the core portion of the optical fiber along a straight line BB ′ perpendicular to or inclined to the optical axis of the optical fiber. Next, a thin film filter 27 using a polyimide thin film as a substrate is inserted into the formed groove 28 and fixed with an optical adhesive.

FIG. 10 is a graph showing the characteristics of the optical fiber with a filter, in which the output fiber light when white light is introduced from the input fiber is separated by an optical spectrum analyzer. The polyimide thin-film filter used here was of the short-wavelength-pass type obtained in Experimental Example 1 described above, and the thickness obtained by the process of FIG.
It is 0 μm in size and 2 mm square. This size is shown in FIG.
It is obtained by making a cut with a commercially available dicing saw in the step (c). The optical fiber has a core diameter of about 10 μm, a clad outer diameter of about 125 μm,
The one having a relative refractive index difference of about 0.3% between the core and the clad was used. As compared with the characteristics of the dielectric multilayer filter of FIG. 4, the loss in the transmission region increased by the diffraction loss. In addition, since the dielectric multilayer filter was disposed at an angle of 8 degrees with respect to the direction perpendicular to the optical axis of the optical fiber, the filter moved in a shorter wavelength direction than the spectral characteristics shown in FIG. As a result of producing 50 filter-containing optical fibers by the same process and measuring the transmission loss, any of them was 0.5 dB or less at 1.3 μm and 5 dB at 1.55 μm.
It was 5 dB or more. This characteristic is, for example, the wavelength multiplexing O
In failure detection of an optical fiber transmission line using TDR (optical time domain reflectometry),
It has practicality as a filter that prevents OTDR light from entering the light receiving / emitting element (H. Takasugi et.all.'Des
ign and Evaluation of Autmatic Optical Fiber Opera
tion Support System ', Proceedings of 39th Internatio
nal Wire and Cable Symposium, 1990, pp.632). Furthermore, they exhibited stable characteristics without deterioration in characteristics even after 200 cycles of a thermal cycle test (4 hours / cycle) at -25 to 70 ° C.

FIG. 11 shows a second embodiment of the optical element according to the present invention, which differs from the first embodiment in that a multi-core optical fiber is used. In this drawing, reference numeral 30 denotes a multi-core optical fiber, and as shown by a cross-sectional structure taken along the line CC ′, optical fibers arranged at equal intervals have a coating 3.
1 is coded into one. As the multi-core optical fiber, for example, a fiber having an outer diameter of about 125 μm and a length of about 2 to 8 cores arranged at 250 μm intervals can be used (for example, Proceedings of the IEICE Spring National Convention, B-649). , B-654, B-655, etc.). In the figure, reference numeral 32 denotes a thin film filter, the substrate portion of which is made of polyimide. Reference numeral 33 denotes a groove, and reference numeral 34 denotes a substrate for holding a fiber and a filter flake. In this embodiment, a large number of filter-containing fibers can be obtained in the same steps as in the first embodiment, and the cost per fiber can be further reduced.

FIG. 12 shows a third embodiment of the optical element according to the present invention, showing an application example as a polarizer. In this figure, reference numeral 35 denotes a polarization maintaining optical fiber,
Reference numeral 36 denotes a polarization separation film using a polyimide thin film as a substrate, 37 denotes a groove, and 38 denotes a substrate. Here, the groove 37 is inclined at an angle of about 45 degrees with respect to the optical axis of the fiber and is formed perpendicular to the substrate surface. Further, the main axis of the polarization maintaining optical fiber is set to be 0 degree or 90 degrees with respect to the substrate surface. As a result, of the polarized light components propagating through the incident side fiber, only the polarized light component parallel to the substrate surface is output from the output side fiber while maintaining its polarization direction.

FIG. 13 shows a fourth embodiment of the optical element according to the present invention. Reference numerals 39 and 40 denote a zirconia ceramic fitting portion and a stainless steel flange portion constituting a ferrule, 41 denotes an optical fiber, 42 is a filter whose substrate portion is a polyimide, 43 is a groove for disposing the filter, and 44 is an adhesive. In this embodiment, a filter 42 having a polyimide thin film as a substrate is provided in a ferrule for terminating a fiber. By applying a housing (not shown) to the ferrule, a plug for an optical connector is obtained. The structure according to this embodiment has an advantage that a filter function can be added to existing standard components.

FIG. 14 shows a fifth embodiment of the optical element according to the present invention, in which a polyimide thin film filter is sandwiched between butting portions of optical fiber end faces in an optical connector. In this figure, reference numeral 45 is an optical fiber, 46 is a ferrule for housing an optical fiber terminal, and 47 is a filter using a polyimide thin film as a substrate. The center of the ferrule, that is, the center of the fiber core, is matched to the required accuracy by the sleeve 48. The ferrule end face of the butted portion is polished perpendicularly, obliquely, or spherically with respect to the optical axis. This embodiment has an advantage that a function by a filter can be added to existing standard parts, and has a particularly simple configuration that does not require formation of a groove.

FIG. 15 is a view showing a sixth embodiment of the optical element according to the present invention, in which a dielectric multilayer filter having a polyimide thin film as a substrate is provided with a directional coupler (a so-called fiber coupler) formed of an optical fiber. ) Output terminal. In this figure, reference numerals 49 and 50 denote input-side optical fiber terminals, 51 and 52 denote output-side optical fiber terminals, 53 denotes an optical coupling part, 54 and 55 denote filter thin pieces having a polyimide thin film substrate, and 56 denotes a filter. The groove 57 is a substrate for fixing the optical fiber and the filter. here,
A polyimide thin film filter is used for the purpose of improving the wavelength separation degree of the fiber coupler used as the wavelength separation element. Also, when the same configuration is used with the light propagation direction reversed, that is, when two different wavelength lights are multiplexed, the polyimide thin film filter can be used. The filter in this case is used for removing a part of the spectrum of the light input to the fiber coupler or for removing a specific wavelength component of the light returning toward the light source by reflection.

FIG. 16 shows a seventh embodiment of the optical element according to the present invention, in which a polyimide thin film filter 60 is provided between an optical fiber 58 and a light receiver 59. Reference numeral 61 denotes a glass window surface of the light receiver, and the polyimide thin film filter is fixed here by an optical adhesive. Reference numeral 62 denotes a semiconductor light receiving element. In this case, the optical fiber 5
8 and the light receiver 59 are not connected, it is necessary to align the optical axes of the two so as to maximize the light coupling.

FIG. 17 is a view showing an eighth embodiment of the optical element according to the present invention, and shows a structure in which a dielectric multilayer filter having a polyimide thin film as a substrate is disposed in a glass optical waveguide. In this figure, reference numeral 63 denotes the core of the optical waveguide, 64 denotes the cladding of the optical waveguide, 65 denotes a substrate for forming the optical waveguide, 66 denotes a filter using a polyimide thin film as a substrate,
67 is a groove. In the case of this optical waveguide, since the core and the clad portion of the optical waveguide are originally integral with the substrate, the step of fixing the optical fiber to the substrate can be omitted as compared with the case where an optical fiber is used. Further, as in the case of the second embodiment, a structure in which a large number of optical waveguides are formed in parallel and filter thin pieces are collectively provided is of course possible. These can form a pigtail type filter by connecting a fiber to the optical waveguide.

FIG. 18 is a view showing a ninth embodiment of the optical element according to the present invention, for obtaining a function as a polarizer. In this case, the polarization separation film 70 having a polyimide thin film as a substrate is in a groove 71 which is approximately 45 degrees with respect to the optical axis of the optical waveguide core 68 and perpendicular to the substrate surface (not shown). It is arranged in. In the case of a normal optical waveguide, the optical waveguide has a polarization maintaining property, and the main axis of polarization is parallel to the substrate (TE).
This is advantageous in that it is not necessary to align the polarization main axes as in the case of the third embodiment.

FIG. 19 is a view showing a tenth embodiment of the optical element according to the present invention, in which a filter having a polyimide thin film as a substrate is disposed at an output terminal or an input terminal of a directional coupler formed by an optical waveguide. It is to establish. Reference numeral 7 in FIG.
2, 73 are filters, 74, 75 are optical waveguide cores, 7
6 is a cladding of the optical waveguide, 77 is a groove, and 78 is an optical coupling portion. The role of these filters is the same as in the sixth embodiment.

FIG. 20 is a view showing an eleventh embodiment of the optical element according to the present invention, which shows an optical fiber with a filter in which a plurality of thin pieces of a filter having a polyimide thin film as a substrate are arranged. In the figure, reference numerals 79 and 80 denote filters using a polyimide thin film as a substrate, 81 and 82 denote optical fibers,
83 and 84 are grooves, and 85 is a substrate. This configuration is an effective method when the amount of attenuation in the stop band for the wavelength component to be removed is insufficient for one filter. This method can be applied to all of the above-described first to tenth embodiments.

[0045]

As described above, according to the present invention,
An inexpensive component including a dielectric multilayer filter in an optical fiber or an optical waveguide can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a dielectric multilayer filter of the present invention.

FIG. 2 is a cross-sectional view illustrating a method for manufacturing a dielectric multilayer filter of the present invention in the order of steps.

FIG. 3 is a cross-sectional view showing another manufacturing method of the dielectric multilayer filter of the present invention in the order of steps.

FIG. 4 is a graph showing spectral characteristics of a dielectric multilayer filter manufactured in an experimental example.

FIG. 5 is a graph showing spectral characteristics of a long-wavelength bandpass filter.

FIG. 6 is a graph showing spectral characteristics of a narrow band filter.

FIG. 7 is a graph showing an example of a thickness distribution of a filter manufactured in an experimental example.

FIG. 8 is a graph showing another example of the thickness distribution of the filter manufactured in the experimental example.

FIGS. 9A and 9B are views showing a first embodiment of the optical element according to the present invention, wherein FIG. 9A is a plan view of an optical fiber containing a filter, and FIG.
It is sectional drawing.

FIG. 10 is a graph illustrating the spectral characteristics of the optical fiber with a filter shown in FIG. 11;

FIG. 11 is a plan view showing a second embodiment of the optical element according to the present invention.

FIG. 12 is a plan view showing a third embodiment of the optical element according to the present invention.

FIG. 13 is a sectional view showing a fourth embodiment of the optical element according to the present invention.

14A and 14B show a fifth embodiment of the optical element according to the present invention, wherein FIG. 14A is a partial sectional view, and FIG. 14B is a sectional view taken along the line DD ′.

FIG. 15 is a plan view showing a sixth embodiment of the optical element according to the present invention.

FIG. 16 is a side view showing a seventh embodiment of the optical element according to the present invention.

FIG. 17 shows an eighth embodiment of the optical element according to the present invention, wherein (a) is a plan view and (b) is a side view.

FIG. 18 is a plan view showing a ninth embodiment of the optical element according to the present invention.

FIG. 19 is a plan view showing a tenth embodiment of the optical element according to the present invention.

FIG. 20 is a plan view showing an eleventh embodiment of the optical element according to the present invention.

FIGS. 21A and 21B are diagrams showing one example of an optical element using a conventional dielectric multilayer filter, wherein FIG. 21A is a plan view and FIG. 21B is a cross-sectional view along AA ′.

FIG. 22 is a plan view showing another example of an optical element using a conventional dielectric multilayer filter.

FIG. 23 is a sectional view of a conventional dielectric multilayer film.

FIG. 24 is a graph comparing warpages generated in filters manufactured by two types of multilayer film forming techniques.

FIG. 25 is a graph showing the characteristics of the filters A and B shown in FIG. 24.

[Explanation of symbols]

1,2,6,7,8,9,24,25,41,45,49,50,51,52,58,81,82 Optical fiber 3,11,12 Dielectric multilayer filter flake 4,13, 28,33,37,43,56,67,71,77,83,84 groove 5,14,29,34,38,57,85 Fixing substrate 10,53,78 Optical coupling part of directional coupler 15 Glass substrate part of dielectric multilayer filter 16,20 Dielectric multilayer film 17 Low refractive index dielectric layer 18 High refractive index dielectric layer 19 Polyimide thin film 21,27,32,36,42,47,54,55,60 , 66,70,72,73,79,80 Dielectric multilayer film filter 22 Temporary substrate 23 Break 26 Optical fiber coating removal part 30 Multi-core optical fiber 31 Multi-core optical fiber coating 35 Polarization holding fiber 39 Ferrule fitting Joint 40 Ferrule flange 44 Adhesive 59 Light receiver 61 Glass window surface 62 Semiconductor light receiving element 63,68,74,75 Optical waveguide core 64 Optical waveguide clad 65,69,76 Optical waveguide substrate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shiro Nishi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Nobuo Tomita 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Within Telegraph and Telephone Co., Ltd. (72) Noriyoshi Yamada, Inventor 1-6-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (56) References JP-A-51-93237 (JP, A) JP-A-63- 64003 (JP, A) JP-A-63-88505 (JP, A) JP-A-55-65239 (JP, A) JP-A-63-116106 (JP, A) JP-A-1-182324 (JP, A) JP-A 1-217037 (JP, A) JP-A 1-226137 (JP, A)

Claims (7)

(57) [Claims] To 1. A substrate, in the dielectric multilayer film filter which multilayer portion is provided with different dielectric refractive index which is formed is laminated by ion-assisted deposition, the substrate is Tsu der fluorinated polyimide thin And the fluorine
A multi-layer dielectric film filter characterized in that the functionalized polyimide thin film has a smaller thermal expansion property than the multilayer film portion . 2. The dielectric multilayer filter according to claim 1, wherein the fluorinated polyimide has a fluorine content of 10 to 30%. 3. A step of applying a liquid fluorinated polyimide material to a required thickness on a temporary substrate having a smooth surface, drying and curing to form a fluorinated polyimide thin film; Forming a dielectric multilayer film, and peeling off the optical filter comprising the dielectric multilayer film and the fluorinated polyimide thin film from the temporary substrate. 4. A manufacturing method of a dielectric multilayer film filter of fluorinated polyimide material of the liquid is claim 3, wherein a solution of the fluorinated polyamic acid which is a precursor of the fluorinated polyimide. 5. The method of manufacturing a dielectric multilayer filter of fluorinated polyimide solution of the liquid is claim 3, wherein a solution of a soluble fluorinated polyimide. 6. A process of removing the optical filter from the temporary substrate, the manufacturing method of the dielectric multilayer filter according to claim 3, characterized in that it comprises a step of cutting the optical filter. 7. An optical element comprising an optical element having a minute gap formed in an optical path and an optical filter disposed in the gap, wherein the optical filter is a dielectric multilayer filter according to claim 1. An optical element characterized in that: