JPS5960407A - Optical filter - Google Patents

Abstract

PURPOSE:To eliminate the need to use adhesives, to improve reliability, and to facilitate manufacture by forming a TiO2 film and an SiO2 film on a substrate alternately and then forming an Si3N4 film over the outermost film. CONSTITUTION:The TiO2 film 2 and SiO2 film 3 are laminated on the substrate alternately. Further, the Si3N4 film 6 is vapor-deposited on the outermost film 3 on an air side. The refractive index of the film 2 is 2.3 and that of the film 3 is 1.46, so the film 6 having an intermediate refractive index between those of film 2 & 3 e.g. 1.8-1.9 is formed. Consequently, the obtained optical fiber is almost as good as or better than an optical filter having a glass substrate adhered to the outermost layer. Thus, no glass substrate is adhered, so the reliability is improved and the filter is formed by a method similar to the formation of a dielectric multi-layered film, thereby facilitating the manufacture.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to Tioz
, S1()z-based dielectric multilayer film.

Prior Art and Problems A band-pass optical filter having a TiO2, 5i02-based dielectric multilayer film is generally formed by alternately stacking TiO2°S i O2 on a glass substrate using techniques such as electron beam evaporation. It was something. For example, as shown in FIG. 1, an 'I'+02 film 2 is deposited on a glass substrate l, a 5I02 film 3 is deposited on a glass substrate, and this process is repeated alternately to form a multilayer film, with the outermost layer being TiO2 similar to the first layer
This is the film 2. The thickness of each film is λ/4, where λ is the wavelength of light (However, for some 5i02
).

If the optical filter having the above configuration is used as it is for a demultiplexer, it will not be possible to obtain the highly accurate characteristics required for the demultiplexer due to the optical asymmetry. Therefore, conventionally, as shown in FIG. 2, a glass substrate 5 is provided on the outermost layer film using an adhesive 4, and the dielectric multilayer film is sandwiched between glass substrates 1.5 degrees to achieve optical symmetry. This was to improve the characteristics of the passband.

FIG. 3 is a characteristic curve diagram for the configuration shown in FIGS. 1 and 2. Curve A shows the characteristic of the configuration shown in FIG. It can be seen that by providing the glass substrate 5 as in the configuration shown in FIG. 2, the characteristics of the passband are improved.

However, since the adhesive 4 is used, there are problems with reliability and it is not easy to bond the glass substrate 5 onto the outermost film with the adhesive 4 having a uniform thickness.

OBJECTS OF THE INVENTION It is an object of the present invention to make it possible to improve filter characteristics without bonding glass substrates. Examples will be described in detail below.

Embodiment of the Invention FIG. 4 is a schematic sectional view of an embodiment of the invention, and the same parts as in FIG. 1 are designated by the same reference numerals. Ti on the glass substrate 1
O2 membrane 2 and 5iO2N! f! 3 and 3 are stacked alternately as in the conventional example, but the outermost layer on the air side is SiO
A Si3N film 6 is formed on the second film 3 by vapor deposition or the like. The refractive index of the TiO2 film 2 is 2.3, and 5i
Since the refractive index of the 02 film 3 is 1.46, S i with a refractive index of 1.8 to 1.9, which is an intermediate refractive index between those refractive indexes.
A 3N4 film 6 is formed. It has been confirmed through simulations that it is possible to obtain an optical filter with characteristics comparable to or better than the optical filter having the configuration shown in FIG. 2 in which a glass substrate is bonded to the outermost layer.

FIG. 5 is a characteristic curve diagram of the optical filter, curve B is the characteristic of the conventional optical filter having the configuration shown in FIG. 2, curves C and D are
4 shows the characteristics of the optical filter according to the embodiment of the present invention having the structure shown in FIG. 4 when the Si3N4 film has a refractive index of 2 and 1.8. Considering only the improvement of passband loss, Si 3 formed in the outermost layer of the dielectric multilayer film
The refractive index of the N4 film can be selected within the range of 1.46 to 2.3, but since the bandwidth becomes narrow, the optimal refractive index is preferably about 1.8 to 1.9. be.

Further, since the thickness of the film 6 only needs to be λ/4 or more, manufacturing is easy.

As described in detail, the present invention includes a TiO2 film 2 and an S
Since the Si 3 N 4 film 6 is formed on the outermost layer of the dielectric multilayer film in which the iO2 film 3 is alternately formed on the glass substrate 1, the glass substrate is bonded to the outermost layer of the dielectric multilayer film. Compared to conventional methods, this method has the advantage of improving reliability by not using adhesives, and is easy to manufacture because it can be formed using the same method as that used for forming dielectric multilayer films. There are some advantages.

[Brief explanation of the drawing]

Figures 1 and 2 are schematic cross-sectional views of conventional optical filters, Figure m3 is a characteristic curve diagram of the optical filter having the configuration shown in Figures 1 and 2, and Figure 4 is a schematic cross-sectional view of an embodiment of the present invention. Figure, 5th
The figure is a characteristic curve diagram of an example of an optical filter of a conventional example and an optical filter of an embodiment of the present invention. l is the glass substrate, 2.3 is "I" constituting the dielectric multilayer film.
” + 02 crotch and 3i02 membrane, 6 is 3 i 3 N
There are 4 membranes. Patent applicant Fujitsu Ltd. Representative Patent Attorney Gobe Tamamushi and 3 others Figure 2 Figure 4

Claims (1)

[Claims] In an optical filter having a TiO2, Si02-based dielectric optical multilayer film, the above-mentioned 'r i
1. An optical filter comprising a Si3N4 film having a refractive index between 02 and 5102.