JP2001033641A - Variable wavelength optical filter element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make obtainable a variable wavelength mechanism by external stress by integrating a variable wavelength mechanism with a diffraction grating type optical filter using a polymer material. SOLUTION: The diffraction grating type optical filter comprises a core 3' having a diffraction grating 4 formed thereon, which is nipped by clads 2, 5. As the filter material, fluorinated polyimide is used. An air-gap 9 is inserted from one side between the lower clad 2 and a substrate to lay the lower clad 2 in a cantilever-shaped floating state, so that an element is longitudinally expansible and contractible. A super-magnetostrictive alloy plating film 8 is integrally laminated on the upper clad 5 to function as a wavelength variable mechanism. An external magnetic field is applied to the super-magnetostrictive plating film 8 to impart the change in length by the magnetostrictive effect to the diffraction grating type optical filter, changing the period of the diffraction grating 4 of the core 3', thereby, Bragg wavelength can be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a tunable optical filter element and a method for manufacturing the same. In particular, the present invention relates to enhancement of the function of a diffraction grating optical filter element using a polymer material such as polyimide, which can be expected to be reduced in size and cost.

[0002]

2. Description of the Related Art Diffraction grating filters that selectively reflect light of a specific wavelength (Bragg wavelength) are widely used, including adaptation to wavelength selection filters in wavelength division multiplexing communication systems for high speed and large capacity. Expected. The wavelength characteristics of these optical filters are determined by the pitch (period) of the diffraction grating and the effective refractive index of the waveguide, and by changing them simultaneously or one of them by some means, the Bragg wavelength of the filter, that is, the center wavelength, is changed. Can be changed.

In general, the center wavelength of the filter is changed by applying mechanical stress from the outside to cause the diffraction grating to expand or contract, or by changing the temperature of the element to change the refractive index of the waveguide. It has been done as. A typical example of a diffraction grating filter is a fiber black grating (FBG) in which a core of a quartz optical fiber is irradiated with ultraviolet light to form a diffraction grating. Since this material has a small change in the refractive index with respect to temperature, a large change in the center wavelength due to temperature control cannot be obtained, but it is also possible to give an external stress such as tension to cause a wavelength tunable effect.

[0004] A fiber black grating is fixed to both ends of a giant magnetostrictive alloy rod containing a lanthanoid element such as samarium or dysprosium, and a magnetic field is applied from the outside to cause a length displacement due to the magnetostriction effect on the diffraction grating to change the wavelength. An effect can be provided (Suzuki et al., Spring 1997, IEICE C-3-149). In this method, the wavelength can be changed much faster than the change in the refractive index due to temperature, and application to a wavelength sweep light source, a high-speed wavelength switch, or the like is expected depending on the intensity of the applied magnetic field. On the other hand, a waveguide-type diffraction grating filter using a polymer material represented by polyimide or epoxy can be manufactured by a wide range of wavelength tunable characteristics due to the magnitude of the refractive index change with temperature and a relatively simple method. For this reason, attention has been paid to miniaturization and cost reduction of the wavelength variable filter.

[0005]

However, in the conventional waveguide diffraction grating filter made of a polymer material, a wavelength tunable method for heating the entire device is possible, but the wavelength tunable effect due to external stress such as tension is structurally disadvantageous. It is difficult, and therefore, the high-speed tunable operation that is an advantage of the present method is not possible. As described above, in the conventional diffraction grating type wavelength tunable filter made of a polymer material, the wavelength variable means is limited due to structural limitations, and high-speed wavelength variable operation is impossible. The present invention solves the above-mentioned conventional problems,
A variable wavelength mechanism of a giant magnetostrictive alloy film by a plating method is laminated on a diffraction grating type filter element, thereby realizing a wavelength variable mechanism by an external stress which has been impossible in the past.

[0006]

According to a first aspect of the present invention, there is provided a wavelength tunable optical filter element for achieving the above object, wherein a wavelength tunable mechanism is integrated with a diffraction grating type optical filter using a polymer material such as polyimide. It is characterized by having A wavelength tunable optical filter element according to claim 2 of the present invention that achieves the above object has a structure in which a part of the diffraction grating optical filter according to claim 1 is floated from a substrate to freely expand and contract in a longitudinal direction. Features. A wavelength tunable optical filter element according to claim 3 of the present invention that achieves the above object uses a giant magnetostrictive alloy plating film that causes a period change of a diffraction grating due to a magnetostrictive effect as the wavelength tunable mechanism in claim 1. Features.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a wavelength tunable optical filter element, wherein a wavelength tunable mechanism is integrated with a diffraction grating type optical filter using a polymer material such as polyimide. It is characterized by the following. A wavelength tunable optical filter element according to a fifth aspect of the present invention, which achieves the above object, has a structure in which the diffraction grating optical filter according to the fourth aspect is partially laminated on a substrate with a sacrificial layer interposed therebetween. And a part of the filter is made to float from the substrate. A wavelength tunable optical filter element according to claim 6 of the present invention that achieves the above object is characterized in that a giant magnetostrictive alloy plating film that causes a periodic change in a diffraction grating due to a magnetostrictive effect is used as the wavelength variable mechanism in claim 4. And

[0008]

1 and 2 show a tunable filter element according to an embodiment of the present invention. FIG. 1 is an overall perspective view of a tunable optical filter element, and FIG. 2 is a sectional view thereof. In this embodiment, a giant magnetostrictive alloy plating film, which is a wavelength variable mechanism, is integrated on an element. Fluorinated polyimide (FLUPI) was used as the filter material.

That is, a diffraction grating optical filter comprising a core 3 'having a diffraction grating 4 sandwiched between claddings 2 and 5 is formed on a substrate, and a space between the lower cladding 2 and the substrate is formed from one side. The gap 9 is inserted and floats in a cantilever manner, and the element can freely expand and contract in the length direction. Further, a giant magnetostrictive alloy plating film 8 is integrally laminated on the upper clad 5 so as to function as a wavelength variable mechanism.

Therefore, by applying a magnetic field from the outside to the giant magnetostrictive alloy plating film 8 to give a change in length due to the magnetostrictive effect to the diffraction grating type optical filter and changing the period of the diffraction grating 4 of the core 3 ′, Bragg wavelength can be changed. In the method of giving the length change by the magnetostriction effect as in the present embodiment, the wavelength can be changed much faster than the refractive index change by temperature. In addition, a waveguide-type diffraction grating filter using a polymer material such as polyimide or epoxy can be manufactured using a wide range of wavelength tunable characteristics due to the magnitude of refractive index change with temperature and a relatively simple method. is there.

The tunable filter element according to the present embodiment having the above configuration is manufactured by the steps shown in FIGS. First, as shown in FIG. 3, a metal such as Ti serving as a sacrificial layer 1 is formed on a part of a silicon substrate by an ion beam sputtering method or the like. Next, as shown in FIG. 4, a fluorinated polyimide material is spin-coated on the sacrificial layer 1 so as to have a thickness of 20 μm.
By performing a baking treatment at about ° C to imidize, a lower clad layer 2 made of a transparent polyimide film is formed.

Subsequently, as shown in FIG.
A core layer 3 is similarly formed by spin coating and baking a larger fluorinated polyimide material for a core to a thickness of 7 μm. A resist for ultraviolet light such as silicon photoresist (SPP) is applied to the surface of the core layer 3 and is directly drawn by an electron beam, or is periodically formed using ultraviolet (X-ray) light such as excimer laser or SOR light and a phase mask. A diffraction grating pattern of about 500 nm is exposed on the resist.

After the development, oxygen reactive ion etching (O ₂ -R
Using a means such as IE), the diffraction grating 4 is transferred and formed on the surface of the core film as shown in FIG. After that, as shown in FIG. 6, a silicon photoresist is applied again to the surface of the diffraction grating, and the ridge type having a width of 7 μm is formed by means such as oxygen reactive ion etching similar to the photo step using a normal photomask. A single mode waveguide core 3 'is formed. Further, as shown in FIG. 7, the same material as that of the lower cladding layer 2 is applied thereon again, and a core stripe is embedded with an upper cladding layer 5 having a thickness of about 15 μm.
The baking process is performed again to obtain a waveguide diffraction grating filter substrate with a buried three-layer structure.

Then, as shown in FIGS. 8 to 11, a giant magnetostrictive alloy plating film is formed on the filter substrate. First, as shown in FIG. 8, a metal film such as Ni different from the sacrificial film 1 is deposited on the entire surface of the filter substrate by an ion beam sputtering method or the like to form a plating underlayer 6. Next, as shown in FIG. 9, a mold 7 made of a photoresist having a desired pattern is formed by a photolithography technique.
Subsequently, as shown in FIG. 10, a giant magnetostrictive alloy thick plating film 8 is deposited on the photoresist mold 7 by electrolytic plating.

After removing the resist mold 7 with acetone,
The excess plating base layer 6 is removed by a dry etching method or a wet etching method using hydrochloric acid or the like, and thereafter, the substrate is cut and separated by a diamond cutter or the like to form individual elements. Finally, as shown in FIG. 11, a void 9 is formed by removing the sacrifice layer 1 by a wet etching method using an etchant such as hydrofluoric acid, and a structure is created in which a part of the filter is floated from the substrate. Complete.

[0016]

As described above, the present invention provides a filter using a polymer material such as polyimide, which can be expected to be reduced in cost because a wavelength variable mechanism is provided in a diffraction grating type optical filter using a polymer material. By integrating the external stress applying mechanism of the giant magnetostrictive alloy plating film into the element, it becomes possible to have a wavelength tunable characteristic that changes the period of the diffraction grating, which was not possible in the past. Functionalization is obtained.

[Brief description of the drawings]

FIG. 1 is an overall perspective view showing a tunable filter element according to one embodiment of the present invention.

FIGS. 2A and 2B are a longitudinal sectional view and a transverse sectional view showing a tunable filter element according to one embodiment of the present invention.

FIGS. 3A and 3B are a cross-sectional view and a vertical cross-sectional view illustrating a step of depositing a metal film for a sacrificial layer.

FIGS. 4A and 4B are a cross-sectional view and a vertical cross-sectional view showing a step of forming a lower cladding layer.

FIGS. 5A and 5B are a cross-sectional view and a vertical cross-sectional view illustrating a step of forming a core layer.

FIGS. 6A and 6B are a cross-sectional view and a vertical cross-sectional view illustrating a process of manufacturing a diffraction grating and a ridge waveguide.

7 (a) and 7 (b) show the formation of an upper cladding layer and the formation of an upper cladding layer; FIG.
It is the cross-sectional view which shows the process of completing a layer buried waveguide, and a longitudinal cross-sectional view.

FIGS. 8A and 8B are a cross-sectional view and a vertical cross-sectional view showing a step of depositing a plating underlayer.

FIGS. 9A and 9B are a cross-sectional view and a vertical cross-sectional view showing a step of forming a plating resist template.

FIGS. 10A and 10B are a cross-sectional view and a vertical cross-sectional view illustrating a step of forming a plating film.

FIGS. 11 (a) and 11 (b) are a cross-sectional view and a vertical cross-sectional view showing steps of removing a template, etching a base layer, and etching a sacrifice layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sacrificial layer 2 Lower clad layer 3, 3 'core layer 4 Diffraction grating 5 Lower clad layer 6 Plating underlayer 7 Resist mold 8 Giant magnetostrictive alloy plating layer 9 Void

Claims (6)

[Claims] 1. A wavelength tunable optical filter element, wherein a wavelength tunable mechanism is integrated with a diffraction grating type optical filter using a polymer material such as polyimide. 2. The tunable optical filter element according to claim 1, wherein a part of the diffraction grating type optical filter is floated from a substrate to freely expand and contract in a longitudinal direction. 3. The tunable optical filter element according to claim 1, wherein the tunable mechanism is a giant magnetostrictive alloy plating film that causes a change in the period of the diffraction grating by a magnetostrictive effect. 4. A method for manufacturing a wavelength tunable optical filter element, wherein a wavelength tunable mechanism is integrated with a diffraction grating type optical filter using a polymer material such as polyimide. 5. The method of manufacturing a diffraction grating optical filter according to claim 1, further comprising: laminating the diffraction grating optical filter on a substrate with a sacrifice layer interposed therebetween, removing the sacrifice layer, and floating a part of the filter from the substrate. The method for manufacturing a wavelength tunable optical filter element according to claim 4, wherein 6. The method according to claim 4, wherein the variable wavelength mechanism is a giant magnetostrictive alloy plating film that causes a periodic change in the diffraction grating due to a magnetostrictive effect.