JPH1048439A - Optical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the occupying space small and to reduce the size, by forming a groove crossing the optical waveguide of an optical waveguide substrate and changing the wavelength to be taken out by inserting, fixing, etc., of an optical filter element changed in thickness into the groove. SOLUTION: The groove 25 crossing the branch waveguide parts 241 to 244 is formed on the optical wavehguide forming surface of the optical waveguide substrate 21. The optical filter element 26 is inserted and fixed into the groove 25. The optical filter element 26 is formed into a thin film shape obtd. by alternately laminating films of a high refractive index and a low refractive index. The film thickness thereof is gradually changed along the groove 25. Namely, the thickness W2 at the other end of the optical filter element 26 less larger than the thickness W1 at one end and the film thickness gradually changed therebetween (A). Another method is to make the respective adjacent intervals of the branch waveguide parts 241 to 244 gradually larger the further from the main waveguide 23 in order to change the wavelength of the light to be taken out by making the film thickness of the optical filter element 26 constant and changing the angle of the incident light on the optical filter element 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical filter which is used in fields such as optical communication and optical measurement and performs wavelength selection, wavelength division, wavelength multiplexing, and the like.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional optical filter for wavelength demultiplexing.
Show. Wavelength λ₁~ Λ_FourIncident light 10 including the optical fiber 1
1 and one end of the optical fiber 11 is, for example, 4
Optical fiber 12₁~ 12_FourIs split into the split light
Fiber 12₁~ 12_FourThe free end of the support 13₁~ 13
_FourThrough the support 13₁~ 13_FourOutgoing light
Is the lens 14₁~ 14_FourWith parallel light
And enters the optical filter element 15. Optical filter
The element 15 is a multilayer in which a high refractive index layer and a low refractive index layer are laminated.
It is a membrane filter and its film thickness is gradually reduced in the longitudinal direction.
It is changing in various ways. Lens 14₁More optical filter elements
Wavelength λ incident on 15₁~ Λ_FourWavelength λ in the light of₁Light of
Only through the lens 16₁Is collected by the support 17₁
Optical fiber 18 in₁At one end. Similarly Len
14_Two~ 14_FourIncident on the optical filter element 15
Wavelength λ_Two, Λ_Three, Λ_FourOnly transparent
And each lens 16_Two~ 16_FourAre collected by
Support 17_Two~ 17_FourOptical fiber 18 inside_Two~ 18_Four
Of the optical fiber 18₁~ 18
_FourFrom each wavelength λ₁~ Λ_FourOne wavelength of light is extracted
It is.

[0003] A support 13 _{1 to} 13 ₄ , 17
_{1-17 4,} the lens 14 _{1-14 4, 161-164,}
The optical filter element 15 is mounted so as to maintain the relative relationship.

[0004]

In the conventional optical filter, the positioning of the support 13 ₁ , the lens 14 ₁ for making parallel light, the condenser lens 16 ₁ , and the support 17 ₁ is troublesome, and the occupied space is small. growing. As further shown in FIG. 3, when separating a plurality of wavelengths, support _131-134, 1
7 _{1 to} 17 ₄ , lenses 14 _{1 to} 14 ₄ , 16 ₁ to 1
6 _4, mutual alignment of the optical filter element 15, it takes considerably troublesome because it is apart from one another, and the variation of the ambient temperature, there is a possibility that the relative position of these parts is shifted. There is also a problem that the entire occupied space is large.

[0005]

According to the present invention, an optical waveguide is formed on the surface of an optical waveguide substrate, a groove is formed on the substrate surface so as to intersect with the optical waveguide, and an optical filter element is inserted into the groove. Fixed. The optical waveguide is composed of one main waveguide and a plurality of branch waveguides branch-connected to one end thereof and extended in substantially the same direction. The groove intersects the plurality of branch waveguides, and an optical filter. The element faces the end faces of all the branch waveguides.

[0006] The thickness of the optical filter element changes in the direction in which the groove extends. The intersection angle between the optical filter element and the branch waveguide is different for each branch waveguide. Further, the grooves are formed by a micromachining technique.

[0007]

FIG. 1A shows an embodiment of the present invention. The optical waveguide 22 is formed on one surface of the optical waveguide substrate 21. In this example, the optical waveguide 22 includes a main waveguide portion 23 and a plurality of branch waveguides 24 _{1 to} 24 ₄ connected to one end thereof.
The one end surface of the main waveguide portion 23 coincides with the one end surface of the substrate 21, and the branch waveguide portion 24 ₁
The end face of 24 ₄ are matched, and the branch waveguide portions 24 ₁ ~
24 ₄ are substantially parallel to each other.

[0008] groove 25 which intersects with the branch optical waveguide forming surface on the waveguide portion 24 _{1-24 4} of the optical waveguide substrate 21 is formed, the optical filter element 26 is inserted and fixed in the groove 25. In this example, the groove 25 is formed in a linear shape, and the optical filter element 26 is a thin plate formed by alternately stacking high-refractive-index and low-refractive-index films, and the film thickness gradually changes along the groove 25. Have been. That relative thickness W ₁ of one end of the optical filter element 26, the thickness between who thickness W ₂ of the other end is large it is gradually changed. The groove 25 is formed narrow by a micromachining technique.

[0009] The micro-machining technology refers to ceramic or
A thin diamond blade is rotated at high speed,
At the same time as grinding the substrate with the blade,
Polishing material such as colloidal silica contained in cutting fluid
Polishing the wall surface of the ground groove to obtain a mirror surface.
It is a construction method. Therefore, the optical waveguide substrate 21 has a narrow width.
The groove 25 can be formed and formed on the optical waveguide substrate 21.
Optical waveguide 24₁~ 24 _FourThe exit surface of the
Is characterized by the fact that there is little loss there.
is there.

An optical bandpass filter element will be described as an example of the optical filter element 26. The optical bandpass filter element is formed by alternately stacking films having a high refractive index n _H and a low refractive index n _{L so} as to have a thickness d = λ / 4n (λ: wavelength of light, n: refractive index). Spacer layer and thickness d = λ /
This is one in which a 2n absentee layer is inserted. For example, when light of 1560 nm is extracted by an optical band-pass filter element, titanium dioxide (n _H = 2.15) is used as a material for the high refractive index layer, and silicon dioxide (n _L = n) is used as a material for the low refractive index layer. When 1.46) is used, the respective film thicknesses may be set to 181.4 nm and 267.1 nm. In this embodiment, light of a plurality of wavelengths can be separated and extracted by one optical bandpass filter element 26. The method for that is shown below.

One method is to change the film thickness in accordance with the wavelength of the light to be extracted. The wavelength is 1 when made with the above materials
In the case of 550 nm, the thicknesses of the high refractive index layer and the low refractive index layer are 180.2 nm and 265.4 nm, respectively. FIG. 1A
When 250μm adjacent spacing of the branching waveguides 24 _{1-24 4} as shown in (in FIG. 1A shows the four optical waveguides), optical filter elements 26 at a position corresponding to the spacing
Of the light wavelengths of 1560 nm and 1550 n, respectively.
m so that the optical bandpass filter element 26
And then insert and fix it. Adjacent distance 250nm
In order to obtain a wavelength resolution of 10 nm, the film thickness may be changed by 1.7 nm.

Another method is to change the wavelength of light to be extracted by changing the angle of incident light with respect to the optical filter element 26, while the film thickness of the optical filter element 26 is constant. For example branch as shown in FIG. 1B waveguide portion 24 21 _to
4 each adjacent interval of _4, gradually so as to be larger as the distance from the main waveguide 23. Optical filter element 2
The thickness of 6 that each part is the same W _3. For example, when two wavelengths are separated, the thickness W ₃ of the optical filter element 26 is adjusted to the wavelength of 1560 nm, and the thickness is set to 181.4 n
m, 267.1Nm, and the refractive index of the optical waveguide section 24 _{1-24 4} and 1.46 (the same as quartz), be taken out the light of wavelength 1550nm at an incident angle 6.5 degrees to the optical filter element 26 it can.

[0013] As a method for varying the crossing angle between the optical waveguide 24 _{1-24 4} and the optical filter element 26 is not limited to that shown in FIG. 1B. For example, as shown in FIG. 2A, between adjacent branch waveguide portions 24 ₁ and 24 _2, between 24 ₂ and 24 ₃ ,
_3, 24 ₄ between the respective angle of the degree that the loss can be ignored, varies by manufacturing conditions of the optical waveguide, for example, it is provided by sequentially shifting the 0.5 ° about increments angle, adjacent intervals 2
The wavelength resolution can be 10 nm at 50 nm.

[0014] Alternatively, as shown in Figure 2B, with the main waveguide 23 branch waveguide portion 24 ₁ by extending the curvature of the extent that the loss of main waveguide 23 can be ignored, varies depending fabrication conditions of the optical waveguide Has a radius R = 25 mm,
Extended to 6.5 ° of arc-shaped, branching waveguide from the point of extension and further 6.5 ° the arc extension with its tangentially branch waveguide portion 24 ₂ is formed from that point tangentially part 24 ₃ is formed, may be sequentially formed branching waveguide portion in the same manner. Thus, the wavelength resolution is 10n
m wavelength separation becomes possible.

In optical communication, it is conceivable to multiplex a large number of lights by setting the wavelength interval of light to about 1 nm. In this case, the optical waveguide is gradually branched so that the incident angle with respect to the optical filter element 26 changes sequentially. However, to separate light different by 1 nm from 1559 nm, the angle may be set to 2.1 ° instead of 6.5 ° in FIG. 2B. 2A and 2B, a large number of branch waveguides can be produced with the optical waveguide substrate kept sufficiently small.

In the above description, the branch waveguide portions 24 _{1 to} 24
_The wavelength resolution can be further increased by changing the angles of incidence on the optical filter elements 26 and changing the transmission path lengths (thicknesses) of the portions where the respective optical filter elements 26 pass through. The insertion and fixing of the optical filter element 26 into the groove 25 can be prevented by fixing with an adhesive having the same refractive index as that of the optical waveguide substrate 11. Branch waveguide portion 24 _{1-24 4} is not limited to four, in one, or other plural. The optical filter element 26 may be configured not only as a bandpass filter but also as a high-pass filter or a region-pass filter.

[0017]

As described above, according to the present invention, the optical filter element is inserted and fixed in the groove of the optical waveguide substrate and intersects with the optical waveguide. If the alignment is performed, there is no possibility that the alignment is shifted thereafter. Moreover, the components are not spatially arranged, but the optical filter element is fixed to the optical waveguide substrate, and the occupied space is small and the device can be made small.

In particular, when a plurality of optical waveguides intersect an optical filter element, the shape and dimensions of the optical waveguide on the optical waveguide substrate can be easily made with high precision.
If one optical waveguide and the optical filter element are aligned, the alignment between the other optical waveguide and the optical filter element can be obtained automatically, and the adjustment is extremely simple. And can be made compact. By using both the change in the film thickness of the optical filter element and the change in the angle formed between the optical filter element and the optical waveguide, the thickness change is reduced and the angle change is also reduced to obtain a desired resolution. be able to.

Further, since the grooves are formed by the micro-machining technique, optical coupling between the optical waveguide and the optical filter element is performed with extremely small loss.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example for splitting an optical waveguide with a small loss.

FIG. 3 is a diagram showing a conventional optical filter.

Claims (5)

[Claims] An optical waveguide substrate having an optical waveguide formed on a surface thereof and a groove formed on the surface so as to intersect with the optical waveguide, a high refractive index layer and a low refractive index layer inserted and fixed in the groove. An optical filter comprising an optical filter element obtained by laminating the above. 2. The optical waveguide according to claim 1, wherein the optical waveguide comprises one main waveguide and a plurality of branch waveguides branch-connected to one end thereof and extending in substantially the same direction, and the groove intersects all of the branch waveguides. 2. The optical filter according to claim 1, wherein the groove is a single groove, and the optical filter element faces all of the branch waveguides. 3. The optical filter according to claim 2, wherein the thickness of the high refractive index layer and the low refractive index layer of the optical filter element change along the longitudinal direction of the groove. 4. The optical filter element according to claim 1, wherein the high-refractive-index layer and the low-refractive-index layer have a constant thickness along the longitudinal direction of the groove, and each intersection between the optical filter element and each of the branch waveguides is provided. The optical filter according to claim 2, wherein the angles are different from each other. 5. The optical filter according to claim 1, wherein said groove is formed by a micro-machining technique.