JP2002323620A - Dielectric multilayered film filter element, method for manufacturing the same and optical filter device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a filter device without using a lens in a dielectric multilayered film filter. SOLUTION: The multilayered film filter element 21 is obtained by alternately laminating high refractive index films and low refractive index films on a glass substrate 22 to form a multilayered film 23. The refractive indices of the layers of the multilayered film 23 and the glass substrate 22 are increased with respect to the multilayered film filter element 21 to form an optical waveguide 24. Thus, the optical filter device is obtained without using a collimator lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric multilayer filter element having high wavelength selectivity which can be miniaturized, a method of manufacturing the same, and an optical filter device using the same.

[0002]

2. Description of the Related Art Conventionally, a dielectric multilayer filter element is formed by alternately stacking high-refractive-index dielectric films and low-refractive-index dielectric films on a glass substrate. When this filter element is used, light from an optical fiber 11 enters a collimator lens 12 as shown in FIG.
To convert parallel light into dielectric multilayer filter element 1
3 is incident. The dielectric multilayer filter element 13 transmits an optical signal component having a required wavelength. The light transmitted through the filter element 13 is returned to the collimator lens 14 again.
Through the optical fiber 15 for receiving light. The transmitted light signal is condensed again on the optical fiber 15 by the collimator lens 14 and transmitted through the optical fiber. The unnecessary wavelength component of the optical signal is reflected by the dielectric multilayer filter element 13 and returned to the original optical fiber 11 or propagated to another space.

Here, the dielectric multilayer filter element 13 is generally formed on a glass substrate having a thickness of 1 mm or more. The reason is that the dielectric multilayer filter used in ordinary optical communication requires high wavelength selectivity, so the number of multilayer films of the dielectric multilayer filter is large, and the film thickness is large, for example, 10 μm or more. Is done. If a similar dielectric multilayer filter is formed on a glass substrate having a thickness of less than 1 mm, cracks may occur in the glass substrate due to the stress of the film, or the glass substrate may be broken in some cases. Therefore, the thickness of the glass substrate to be used as an underlayer must be 1 mm or more.

The light beam emitted from the optical fiber 11 has a divergence angle θ (rad) determined by the following due to a diffraction phenomenon.
The beam spreads. θ = 2λ / πD (1) where λ is the light wavelength and D is the aperture diameter.

In an optical fiber, since the core has a small opening diameter, the spread angle θ becomes large. For example, an optical signal having an optical wavelength of 1.5 μm propagating through a single-mode optical fiber has an opening diameter of the core of about 10 μm. Therefore, the divergence angle θ from the end face of the optical fiber is about 6 ° according to Expression (1). Therefore, at a distance of 1 mm from the opening, the beam diameter becomes about 200 μm. Therefore, when optical fibers having the same aperture diameter are used at a distance of 1 mm, the optical signal component is attenuated by 20 dB or more. Therefore, the optical signal emitted from the end face of the optical fiber is
The light beam is converted into a light beam propagating through a space having a beam diameter of about 0.5 mm via the collimator lens 12. In this case, the beam divergence angle can be reduced to 1 ° or less, and transmission can be performed while maintaining the beam diameter substantially. Also, an optical signal can be propagated to the end face of the optical fiber 15 via the collimator lens 14 on the light receiving side within a practical range of a diffraction loss of 1 dB or less.

[0006]

As described above, in the conventional optical filter device, the beam is once converted into a beam that propagates through space through a lens. For this reason, the loss is large, and a member such as a collimator lens is required, and the filter element itself needs to have a size of, for example, about 1 mm square.

The present invention has been made in view of such a conventional problem. By forming an optical waveguide in a dielectric multilayer filter element itself, it is converted into a spatial beam using a lens or the like. It is an object of the present invention to provide a dielectric multilayer filter element capable of selecting a desired wavelength without using the same, a method for manufacturing the same, and an optical filter device.

[0008]

According to a first aspect of the present invention, there is provided a dielectric material formed by alternately laminating high refractive index films and low refractive index films on at least one surface of a glass substrate. In the multi-layer filter element, an optical waveguide for transmitting light formed by increasing the refractive index distribution of the multi-layer filter element is provided in the multi-layer filter element.

According to a second aspect of the present invention, in the dielectric multilayer filter element of the first aspect, the optical waveguide is formed substantially perpendicular to the dielectric multilayer film. It is.

According to a third aspect of the present invention, a dielectric multilayer filter is formed by alternately laminating high-refractive-index dielectric films and low-refractive-index dielectric films to a predetermined thickness on a glass substrate, Forming an optical waveguide by irradiating an ultraviolet laser beam to a path for forming an optical waveguide with respect to the dielectric multilayer filter, and increasing a refractive index of the irradiated portion using the color center effect by the ultraviolet laser beam; It is characterized by the following.

According to a fourth aspect of the present invention, an optical waveguide is formed by irradiating an ultraviolet laser beam onto a path of an optical waveguide on a glass substrate and increasing the refractive index of the irradiated portion by using a color center effect. A dielectric multilayer filter is formed by alternately stacking high-refractive-index dielectric films and low-refractive-index dielectric films on the glass substrate to a predetermined thickness.

According to a fifth aspect of the present invention, a high refractive index film and a low refractive index film are alternately laminated on at least one surface of a glass substrate, and a refractive index distribution is formed inside the dielectric film. A multilayer filter element provided with an optical waveguide through which light propagates by being raised from the other; and at least one core connected to the dielectric multilayer filter element and having a core arranged so that the optical waveguide and the core are coaxial. Optical fiber and
It is characterized by having.

The invention of claim 6 of the present application is characterized in that the dielectric multilayer filter element according to claim 1 or 2 is connected to the end face of the substrate on which the optical waveguide is formed so that the optical waveguide is aligned. Things.

The invention of claim 7 of the present application is directed to claim 5 or 6
In the optical filter device, the optical filter device is used for optical communication at an optical wavelength of 1.0 to 1.7 μm.

[0015]

FIG. 1 shows a first embodiment of the present invention.
1 shows a dielectric multilayer filter element according to the present invention. This invitation
The electric multilayer filter element 21 is, for example, B manufactured by Shott.
K7 borosilicate glass substrate 22 (refractive index n_S= 1.5
0) A high refractive index dielectric film H such as Ta_TwoO_Five(Crown
Folding ratio n_H= 2.1) and low refractive index film L, for example, SiO
_Two(Refractive index n _L= 1.45) alternately laminated
The body multilayer film 23 is formed. The dielectric multilayer film 23 is an ion
Sputtering, ion-assisted evaporation, ion play
For example, HL is formed on the glass substrate 22 by the
Like HLHLHLH4LHLHLHLHLHL,
Form with each other. Here, H and L are first and second dielectrics, respectively.
The thickness of the substance is shown, and each thickness is H = λ.₀/ 4n
_H, L = λ₀/ 4n_LIt is. λ₀Is the film setting wavelength
You. This wavelength λ₀Is 1500 nm, for example.
Are H = 197 nm and L = 259 nm. 4
L is a cavity layer. By increasing the number of layers H and L,
A sharper characteristic will be obtained. As high refractive index film
Is Si (n_H= 3.45), Nb_TwoO_Five(N_H=
2.20), MgO (n_L= 1.
72) and the like.

Next, an optical waveguide 24 is formed in the dielectric multilayer filter element. Since the optical waveguide 24 forms an optical waveguide in an optical signal path propagating through the dielectric multilayer filter element, a refractive index distribution is formed so that a desired optical waveguide has a high refractive index. That is, by forming a refractive index distribution in the filter element where the refractive index is high in the central portion of the optical waveguide where the light propagates and the refractive index decreases toward the periphery, the optical waveguide 24 can be formed. Since the light propagation mode system of the optical waveguide is determined by the distribution shape of the refractive index, the ultraviolet laser 25 focused to a small diameter is irradiated. By irradiating ultraviolet rays, molecular bonds of the dielectric multilayer filter and the glass substrate are decomposed. For example, a part of the SiO ₂ film is decomposed into SiO + O by ultraviolet irradiation,
Since the refractive index of iO is higher than that of SiO ₂ ,
The refractive index increases slightly according to the ratio between O ₂ and SiO. It is known that, due to such a color center effect, the refractive index increases in a region having a higher ultraviolet irradiation intensity. Ultraviolet laser has strong light intensity and can focus on a narrow area.
There is an effect of increasing the refractive index due to the color center effect with respect to the substance forming the dielectric multilayer film and the oxide glass used as the glass substrate.

The amount of increase in the refractive index can be adjusted according to the wavelength, light intensity, and irradiation time of the ultraviolet laser light source used, and various ultraviolet lasers can be selected. In addition, since short-wavelength light is used, the divergence angle is kept small even with a small beam diameter. By using a light source capable of selectively irradiating a minute region having a high light intensity as described above, an optical waveguide structure suitable for a propagation mode can be formed inside the dielectric multilayer filter element. Although the optical waveguide 24 can be formed at an arbitrary angle with respect to the dielectric multilayer film 23, it is often convenient in practice to make it substantially vertical.

In this embodiment, a third harmonic (light wavelength: 355 nm) of an Nd: YAG laser (fundamental wave: 1064 nm) that performs continuous oscillation operation is used. At this wavelength, the dielectric multilayer film Ta ₂ O ₃ film, SiO ₂ film, and glass substrate exhibit the above-described color center effect. Here, the light intensity is 1 MW / cm
^{The second} ultraviolet laser beam 25 was applied to the dielectric multilayer filter element 21 from below as shown in FIG. FIG. 2 shows the light intensity distribution of the YAG laser and the change in the refractive index with respect to the position of each layer. If the beam shape of this laser beam is set to a Gaussian distribution as shown in FIG. 2 and the beam diameter is set to, for example, 10 μm, the Gaussian shape is obtained for the distributions of the refractive indexes n _S , n _H and n _L , and the refractive index is increased. The cylindrical region can be used as the optical waveguide 24. By selecting the irradiation time from 10 seconds to 1 minute, the refractive indices n _S , n _H , and n _L of each layer can be set from 0.0001 to 0.01.
01 can be increased. If the irradiation time is too long, the substrate becomes opaque, which is not preferable. As a result, the optical waveguide 24 having a refractive index distribution can be formed in the dielectric multilayer filter element. Although a YAG laser is used here, another laser light source may be used as long as it has a desired wavelength and intensity. The wavelength of the laser light source is a wavelength at which the color center effect can be obtained, preferably 400 nm or less. For a glass substrate that is transparent to a shorter wavelength, it is preferable to use an ultraviolet laser having a shorter wavelength.

Although the refractive index distribution of the optical waveguide is of a graded type having a Gaussian distribution in which the refractive index continuously increases in FIG. 2, as shown in FIG. To have a single-mode structure. It is also possible to use a dispersion compensation type optical waveguide similar to an optical fiber.

FIG. 4 shows another method of forming an optical waveguide using an ultraviolet laser. Also in this method, the cubic dielectric multilayer filter element 21 is the same as that described above. Assuming that the front side is a multilayer filter surface in FIG. 4, the above-mentioned ultraviolet lasers 26 and 27 each having a flat slit shape are irradiated from two directions perpendicular to the multilayer filter surface. When the ultraviolet laser beam is irradiated in a direction orthogonal to the direction, a portion where these laser beams overlap is formed in a direction substantially perpendicular to the multilayer film 23, and the refractive index increase rate of the portion is increased. The optical waveguide 24 can be formed inside the element 21. In this case, it is preferable to simultaneously irradiate slit-shaped ultraviolet lasers 26 and 27 to form a waveguide. Thus, while monitoring whether or not the waveguide is formed, the ultraviolet light 26,
27 can be controlled. In this method, since a slit-shaped ultraviolet laser is used, it is possible to form a waveguide in which the diameter of the optical waveguide is smaller than that in the case of FIG.

In FIGS. 1 and 4, the optical waveguide is formed after the dielectric multilayer filter is formed. However, the thickness of the multilayer film 23 is extremely thin as compared with the glass substrate 2. Therefore, the optical waveguide may be formed only on the glass substrate. In this case, an optical waveguide is formed on the glass substrate before the formation of the multilayer film by the method shown in FIG. 1 or FIG. 4, and then the multilayer film 23 is formed to constitute a multilayer filter having the optical waveguide.

FIG. 5 shows an optical waveguide 24 of this multilayer filter.
FIG. 3 is a diagram showing the wavelength characteristics of light passing through the optical path. By forming the optical waveguide 24, the refractive index of the dielectric multilayer film 23 also slightly increases, so that it is about
The peak wavelength shifts to 1.5 nm longer wavelength side. Thus previously formed with a pre-offset with respect to the desired wavelength lambda _1, it is preferable that the peak wavelength is the desired wavelength at the stage of forming the optical waveguide. For example, for a desired wavelength λ ₁ = 1500 nm, the multilayer filter 2
If the design wavelength λ _{0 of} 1 is set to 1449 nm as shown by a broken line, a desired wavelength characteristic can be obtained after forming the optical waveguide.

FIG. 6 is a diagram showing an optical filter device using such a dielectric multilayer filter element 21. As shown in FIG. As shown in this figure, a pair of optical fibers 31 and 32 are connected so that the core of the optical fiber is located coaxially with the optical waveguide 24 formed inside the dielectric multilayer filter element.
The optical fiber 31 is an incident optical fiber, and is connected so that the core and the multilayer optical waveguide 24 are coaxial. The optical fiber 32 is an optical fiber for emission, and the glass substrate 2
Optical fiber 3 so that the core coincides with the optical waveguide 24
2 is connected.

In this way, the light incident from the incident side optical fiber 31 passes through the multilayer filter element 21 and directly enters the core side of the exit side optical fiber 32. Light not selected by the dielectric multilayer filter travels in the optical fiber 31 in the opposite direction as reflected light. As described above, in the present invention, it is not necessary to use a collimator lens, and an extremely small filter device can be realized. It goes without saying that an optical fiber may be used for only one of the incident side and the output side.

Since the core diameter of the optical fiber is usually about 10 μm, the filter element itself can be formed very small, for example, in a cubic shape of about 0.1 mm. Also, by cutting the optical fiber and inserting and fixing the filter element therein so that the core and the optical waveguide of the filter are located on a straight line, an ultra-small optical filter device can be realized.

FIG. 7 shows an optical filter device which uses a dielectric multilayer filter element having an optical waveguide structure and is used for add / drop of wavelength multiplexed optical fiber communication. An optical waveguide 42 as shown in the figure is formed on a glass substrate 41 in advance. An optical fiber 4 for transmitting wavelength-division multiplexed light is provided on the left end of the optical fiber waveguide 42a on the end face of the glass substrate 41.
3 is attached, and a multilayer filter element 44 is attached to the right end so that the optical waveguide 24 coincides therewith. Here, when light enters the optical fiber 43, the angle formed by the optical waveguides 42a and 42b is changed so that a part of the light is transmitted through the multilayer filter element 44 and reflects other wavelength components to enter the optical waveguide 42b. For example, it is set to about 1 to 2 °. Similarly, the angles of the optical waveguides 42b, 42c and 42c, 42d are similarly set to about 1 to 2 °, and the multilayer filter elements 45, 46 are attached to the respective end faces. Filter elements 44, 45, 46
Are λ ₁ , λ ₂ , and λ ₃ . When wavelength multiplexed light including λ ₁ , λ ₂ , λ ₃ ... Is incident as incident light, the desired wavelengths λ ₁ , λ ₂ ,. λ ₃・ ・ ・
By dropping only the signal, a signal of a desired wavelength can be extracted and output.

This optical system combines the optical signal components λ ₁ , λ ₂ , λ ₃ ... Into one optical transmission line by using the propagation of light in the reverse direction. Functions can also be provided.

[0028]

As described in detail above, according to the present invention, since the optical waveguide structure is formed in the dielectric multilayer filter element itself, the optical filter device does not use a collimator lens or the like, and is extremely useful. A small and high-precision filter element can be realized. Further, according to the invention of claims 5 to 7, when an optical filter device is constructed using this filter element, the whole can be extremely miniaturized,
A filter device can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a perspective view of a dielectric multilayer filter element according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a laser distribution and a change in refractive index of an ultraviolet laser applied to a dielectric multilayer filter element.

FIG. 3 is a diagram illustrating another example of a laser distribution and a refractive index change of an ultraviolet laser applied to a dielectric multilayer filter element.

FIG. 4 is a perspective view showing a second embodiment for manufacturing the dielectric multilayer filter element of the present invention.

FIG. 5 is a graph showing wavelength characteristics of a dielectric multilayer filter element.

FIG. 6 is a diagram showing an example of an optical filter device using the multilayer filter element.

FIG. 7 is a diagram showing another example of the optical filter device using the dielectric multilayer filter element according to the present embodiment.

FIG. 8 is a diagram showing a use state of a conventional optical filter device.

[Explanation of symbols]

 21, 44 to 46 Dielectric multilayer filter element 22, 41 Glass substrate 23 Dielectric multilayer film 24, 42a to 42d Optical waveguide 31, 32, 43 Optical fiber

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G02B 6/13 G02B 6/12 A F term (reference) 2H038 BA06 BA22 BA23 2H047 KA04 KA15 LA18 LA24 MA00 PA01 PA11 PA22 TA01 2H048 GA01 GA04 GA09 GA21 GA23 GA34 GA51 GA60 GA62 2H050 AA01 AB02Z AC90 AD16

Claims (7)

[Claims] 1. A dielectric multilayer filter element formed by alternately laminating high-refractive-index films and low-refractive-index films on at least one surface of a glass substrate, wherein: An optical waveguide for transmitting light formed by increasing the refractive index distribution of the dielectric multilayer filter element. 2. The optical waveguide according to claim 1, wherein the optical waveguide is formed substantially perpendicular to the dielectric multilayer film.
The dielectric multilayer filter element according to claim 1. 3. A dielectric multilayer filter is formed by alternately laminating high-refractive-index dielectric films and low-refractive-index dielectric films to a predetermined thickness on a glass substrate. A dielectric multilayer, comprising: irradiating an ultraviolet laser beam on a path for forming an optical waveguide, increasing a refractive index of an irradiated portion by using the color center effect by the ultraviolet laser beam, and forming an optical waveguide. A method for manufacturing a membrane filter element. 4. An optical waveguide is formed by irradiating an ultraviolet laser beam on a path of the glass substrate on which the optical waveguide is formed, and increasing the refractive index of the irradiated portion using a color center effect. A method for manufacturing a dielectric multilayer filter element, comprising forming a dielectric multilayer filter by alternately laminating high-refractive-index dielectric films and low-refractive-index dielectric films to a predetermined thickness. 5. A light-emitting device comprising a dielectric layer of a high-refractive-index film and a low-refractive-index film alternately laminated on at least one surface of a glass substrate, and having a higher refractive index distribution in the interior thereof than that of the others. And a at least one optical fiber connected to the dielectric multilayer filter element and having a core disposed so that the optical waveguide and the core are coaxial. An optical filter device comprising: 6. An optical filter device, wherein the dielectric multilayer filter element according to claim 1 or 2 is connected to an end face of a substrate on which the optical waveguide is formed, with the optical waveguide being combined. 7. The optical filter device according to claim 1, wherein the light wavelength is 1.0 to 1.0.
The optical filter device according to claim 5, wherein the optical filter device is used for optical communication at a distance of 1.7 μm.