JPH11109156A - Optical waveguide, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable grating characteristic, and easily and uniformly form a plurality of gratings in a same plane light circuit by forming a phase grating mask directly on an outer surface of a clad of an optical waveguide, and irradiating the mask with the ultraviolet ray to form a light-induced grating in a core. SOLUTION: A resist is formed on an outer surface of an upper clad 6A, and a phase grating mask pattern is formed on the resist. The KrF excimer laser beam of 249 nm in wavelength is selected as the ultraviolet ray 1, and a phase grating mask 3 is manufactured by achieving the dry-etching to the depth of 244 nm from the outer surface of the upper clad 6A so as to satisfy the phase condition that the 0-th diffracted light intensity is zero on the phase grating mask 3. Finally, the phase grating mask 3 is perpendicularly irradiated with the ultraviolet ray 1 to form a light-induced grating 5 in a core 6C through two-beam interference caused by the primary diffracted light 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide and a method for manufacturing the same, and more particularly to an optical waveguide used for optical communication and optical information processing and having a light-induced grating in a core region, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a narrow band reflection filter, a quartz-based planar light wave circuit, and a fiber having a light-induced grating (Bragg grating) formed in a core utilizing a light-induced refractive index change using ultraviolet light have been developed. Application to a WDM multiplexer / demultiplexer is being studied. Conventionally, as a method of forming a light-induced grating using ultraviolet light for an optical fiber or a quartz-based planar lightwave circuit, KOHill
In general, a method using a phase grating mask proposed by the authors (for example, JP-A-7-14031)
No. 1).

In this case, as shown in FIG.
A phase grating mask 3 formed on A is disposed adjacent to and parallel to an optical waveguide or optical fiber (hereinafter, referred to as an optical waveguide) 4 including an upper clad 6A, a lower clad 6B, and a core 6C. Then, the parallel beam 1 of ultraviolet light is vertically incident on the phase grating mask 3 from the quartz substrate 3A side, and at this time, the light-induced grating 5 is placed in the core 6C of the optical waveguide 4 by an interference pattern generated by the phase grating mask 3. It is what forms.

[0004]

However, when such a conventional light-induced grating forming method is applied to an optical waveguide, there are the following two problems. First,
As a first problem, it is necessary to accurately position the optical waveguide and the phase grating mask. That is, when the grading is inclined with respect to the axis of the optical waveguide, it causes a decrease in the reflectance of the light-induced grating and a deterioration in the reflection spectrum.

In general, in a planar optical circuit,
Warpage occurs due to the difference in expansion coefficient between the substrate and the material forming the optical circuit. In particular, a quartz-based optical waveguide fabricated on a Si substrate by the FHD method has a very excellent function as a planar optical circuit, but warpage occurs due to a large difference in the expansion coefficient between quartz and Si. I do. In this case, considering formation of a long-period chirped grating that periodically changes the grating interval, there is a great problem in terms of the above-described alignment accuracy.

[0006] The second problem is that workability and uniformity of characteristics when forming a plurality of gratings having the same or different light-induced wavelengths in the same planar optical circuit are mentioned. For example, when forming a grating having a plurality of light-induced wavelengths by a conventional method, a phase grating mask corresponding to each is formed on a separate quartz substrate, and each of the gratings is individually irradiated with ultraviolet light to form the grating. Need to be formed.

In this case, for the formation of each grating, it is necessary to align the optical waveguide and the phase grating mask with high accuracy, which is the first problem described above, and the workability is reduced. In addition, as the number of gratings to be formed increases, there arises a problem that the uniformity of the characteristics also decreases at the same time.

Further, when gratings having different flag wavelengths are formed at close places, it is necessary to precisely control the irradiation position of ultraviolet light using a stencil or the like.
In other words, in the conventional method, the distance at which the gratings having different light-induced wavelengths can be approached is limited by the accuracy of disposing the stencil and the like.
The present invention is to solve such a problem,
It is an object of the present invention to provide an optical waveguide capable of obtaining stable grating characteristics and forming a plurality of gratings easily and uniformly in the same planar optical circuit, and a method of manufacturing the same.

[0009]

In order to achieve the above object, in the present invention, a phase grating mask is formed directly on the outer surface of a cladding of an optical waveguide, and the core is irradiated with ultraviolet light. We propose a method of forming a photo-induced grating in a cavity. Here, in this structure,
The distance accuracy between the phase grating mask and the core of the optical waveguide is determined by the film thickness accuracy of the core and the upper clad. For example, in a quartz-based planar lightwave circuit using the FHD method, the distance accuracy is 1 μm or less, and the distance accuracy is high. Can be controlled.

[0010] In addition, there is no problem with respect to the inclination in the in-plane direction because a photolithography technique such as electron beam (EB) exposure is used for manufacturing a phase grating mask.
Further, since a light-induced grating can be formed simply by irradiating a parallel beam of ultraviolet light perpendicularly to the phase grating mask, it is possible to remove an unstable element such as alignment of the conventional phase grating mask, and to obtain a grating characteristic. Is greatly stabilized.

In this simple grating forming method, since a plurality of gratings are formed in the same planar optical circuit, there is no restriction on the arrangement of the gratings, and a plurality of gratings are provided in a narrow area with arbitrary characteristics. It has the feature that a grating can be formed. Further, since there is no need to manufacture a phase grating mask corresponding to each light-induced wavelength, an expensive phase grating mask is not required, which is economically advantageous.

Further, as a method of manufacturing a phase grating mask on the outer surface of the cladding of the optical waveguide, a phase grating mask can be formed by dry etching using a photoresist as a mask material as in the related art. Furthermore, in addition to this method, a method of directly forming a phase grating mask pattern on the surface of an optical waveguide using a silicone-based photosensitive resin composition is proposed.

This eliminates the need for a dry etching step, and makes it possible to greatly simplify the formation of a phase grating mask. This is based on the fact that a glass (quartz) pattern can be directly formed by heating a pattern of a silicone-based photosensitive resin composition at a high temperature. Glass pattern direct formation '', J. Photoplym.Sci.
Technol., Vol. 4, 1991).

[0014]

Next, the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing a light-induced grating forming method for an optical waveguide according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing an example of a phase grating mask forming step of the present invention. First, as shown in FIG.
The upper clad 6A,
The optical waveguide 4 including the lower clad 6B and the core 6C is formed.

The structure of the optical waveguide 4 is such that the upper clad 6A and the lower clad 6B have a layer thickness of 30 μm, a core 6C of 6 μm square and a relative refractive index of 0.75%. At this time, the outer surface of the upper clad 6A and the core 6
The distribution of the distance from the C center was 1 μm or less.

Subsequently, as shown in FIG. 2B, a resist 8 for processing a phase grating mask is formed on the outer surface of the upper clad 6A using electron beam (EB) exposure. At this time, for a desired Bragg wavelength of 1550 nm, the thickness of the resist 8 is set to 0.2 μm.
Next, a phase grating mask pattern 8A having a pitch of 1068 nm is formed.

Then, as shown in FIG. 2C, the ultraviolet light 1 used for forming a photo-induced grating, which will be described later, is:
A KrF excimer laser having a wavelength of 249 nm is selected, and dry etching is performed to a depth of 244 nm from the outer surface of the upper cladding 6A so as to satisfy a phase condition such that the intensity of the 0th-order diffracted light in the phase grating mask 3 becomes zero. The fabrication of the grating mask 3 is completed. Finally, as shown in FIG. 1, the phase grating mask 3 is irradiated with ultraviolet light 1 vertically, and the light-induced grating 5 is formed in the core 6 </ b> C by two-beam interference by the first-order diffracted light 2.

In the above description, K as ultraviolet light 1
Although an rF excimer laser is used, an ArF excimer laser (wavelength: 193 nm) or a second harmonic (wavelength: 244 nm) of an Ar laser may be used. In this case, the 0th-order diffracted light becomes zero by the phase grating mask 3. Thus, the amount of etching on the outer surface of the upper clad 6A may be adjusted. In addition, electron beam (EB) is used for patterning the resist material.
Although the exposure method is used, a light exposure device (stepper) can be used.

The phase grating mask used for forming the photo-induced grating may be formed using a silicone-based photosensitive resin composition as shown in FIG. FIG. 3 is an explanatory view showing another example of a phase grating mask forming step of the present invention. First, as shown in FIG. 3A, an optical waveguide 4 is formed by the FHD method or the like, and then, as shown in FIG. 3B, a silicone-based photosensitive resin composition is formed on the outer surface of the upper clad 6A. An object, that is, a film 14 of a glass precursor (polysiloxane composition) made of a photosensitive organic material is formed by spin coating.

Then, by photolithography technology,
A phase grating mask pattern 14A made of a precursor film is formed. In this case, the pitch of the phase grating mask pattern 14A is 1068 n, as described above.
m.

Next, as shown in FIG. 3 (c), the phase grating mask pattern 14A is heat-treated at 1000 ° C. in an oxygen atmosphere to remove organic substances and change the composition of the precursor into glass (quartz). Then, the formation of the phase grating mask 3 made of the silicone-based photosensitive resin composition film 14 is completed. In order to set the depth of the phase grating mask 3 to 244 nm in the same manner as described above,
The film thickness of the silicone-based photosensitive resin composition film 14 was set to 813 nm in consideration of the pattern remaining film ratio (30%) during the heat treatment.

[0022]

Embodiment 1 A first embodiment of the present invention will be described with reference to FIG. In the first embodiment, an example of manufacturing an MZ type three-wavelength duplexer 9 as shown in FIG. 4 will be described as an application to an actual circuit. In a general MZ type interferometer, the wavelength λ1 (1.48 μm) input from the input port 9A,
The multi-wavelength signal lights of λ2 (1.55 μm) and λ3 (1.41 μm) are split by the arms 9X and 9Y on both sides, and the signal light of wavelength λ1 from the output port 9B (through port) and the output port 9C (cross Port) outputs a signal light of wavelength λ2.

Here, the phase grating mask 3 is formed by the above-described method, and the arms 9X and 9X of the MZ interferometer are formed.
A light-induced grating having a flag wavelength of 1.41 μm is formed in each of Y. Thus, the MZ type three-wavelength splitter 9 in which the signal light of the wavelength λ3 is split and output from the output port 9D can be realized.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, an example of manufacturing a hybrid integrated multi-wavelength light source 10 as shown in FIG. 5 will be described. Here, the configuration is such that the semiconductor laser 11 and the light-induced grating are combined based on a quartz-based planar lightwave circuit platform.

As the characteristics of the light sources, the wavelength multiplexing number is set to 4 and the wavelength interval is set to 1.6 nm. These light sources are combined by the multiplexer 12 and output. In this case, each phase grating mask 3 was formed by the above-described method, and each light-induced grating was individually formed by sequentially irradiating each ultraviolet light irradiation region 13A with ultraviolet light. Regarding the uniformity of the grating characteristics for the four wavelengths produced in this example, the average of the reflectance was 90%, the variation was within 5%, and the variation in the Bragg wavelength was within 0.1 nm.

In a similar grating forming experiment using the prior art, four grating characteristics were obtained.
The average reflectance was 78%, the variation was within 25%, and the variation in Bragg wavelength was within 0.3 nm (Tanaka et al., “UV Induced Grating and Spot Size Conversion L
Hybrid 4-wavelength laser using D ”, 1997 IEICE General Conference C-3-160). Therefore, it can be confirmed that the grating characteristics are significantly improved as compared with the conventional case.

Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, another example of manufacturing the hybrid integrated multi-wavelength light source 10 as shown in FIG. 6 will be described. Second Embodiment (see FIG. 5)
Then, each light-induced grating was individually formed by sequentially irradiating each ultraviolet light irradiation region 13A with ultraviolet light.

Here, each phase grating mask 3
Are arranged in close proximity to each other, and the light-induced gratings are simultaneously formed by simultaneously irradiating the ultraviolet light irradiation region 13B with ultraviolet light. This makes it possible to greatly simplify the manufacturing process, suppress variations in the conditions for forming the photo-induced grating, and make the grating characteristics more uniform.

[0029]

As described above, according to the present invention, the phase grating mask for producing the photo-induced grating is formed directly on the outer surface of the cladding of the optical waveguide by using the photolithography technique. The positional relationship between the mask and the core of the optical waveguide can be arranged with very high precision. Therefore, when a light-induced grating is formed in a core using ultraviolet light, characteristics such as reflectance and reflection spectrum can be greatly stabilized.

Further, even when a large number of light-induced gratings are formed on the same plane optical circuit, a phase grating mask can be formed collectively for each wafer. Further, when forming the photo-induced grating, it is not necessary to arrange each phase grating mask with high precision as in the related art, and the process of forming the photo-induced grating can be greatly simplified.

Further, since the phase grating mask is formed in advance by the lithography technique, the arrangement of the light-induced grating is not restricted, and a plurality of light-induced gratings can be arbitrarily formed in a narrow region. Further, when forming a phase grating mask on the outer surface of the cladding of the optical waveguide, the phase grating mask is formed using a silicone-based photosensitive resin composition, so that it is easier than a method using a general etching process. A phase grating mask can be formed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a method for forming a light-induced grating of an optical waveguide according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing an example of a forming process of a phase grating mask of the present invention.

FIG. 3 is an explanatory view showing an example of a forming process of another phase grating mask of the present invention.

FIG. 4 is an explanatory diagram showing an MZ type three-wavelength demultiplexer according to the first embodiment of the present invention.

FIG. 5 is an explanatory view showing a hybrid integrated multi-wavelength light source according to a second embodiment of the present invention.

FIG. 6 is an explanatory view showing another hybrid integrated multi-wavelength light source according to the third embodiment of the present invention.

FIG. 7 is an explanatory view showing a conventional light-induced grating forming method for an optical waveguide.

[Description of Signs] 1 ... Ultraviolet light, 2 ... First-order diffracted light, 3 ... Phase grating mask, 3A ... Quartz substrate, 4 ... Optical waveguide, 5 ... Light induced grating, 6A ... Upper cladding, 6B ... Lower cladding, 6C ... Core, 7: Si substrate, 8: silicone-based photosensitive resin composition, 9: MZ type three-wavelength demultiplexer, 9A: input port, 9B to 9D: output port, 10: hybrid integrated multi-wavelength light source, 11: semiconductor Laser, 12 ... combiner, 1
3A, 13B: UV light irradiation area.

Claims (6)

[Claims] 1. An optical waveguide comprising a core and a clad formed around the core and formed on a substrate, wherein the optical waveguide is provided on the outer surface of the clad and interferes with ultraviolet light to form a light-induced grating in the core region. An optical waveguide, comprising: a phase grating mask of (1), and a light-induced grating formed in a core region using the phase grating mask. 2. An optical waveguide formed on a substrate and comprising a core and a clad formed around the core, wherein the optical waveguide is provided on the outer surface of the clad and interferes with ultraviolet light to form a light-induced grating in the core region. An optical waveguide comprising the phase grating mask of (1). 3. The optical waveguide according to claim 1, wherein the phase grating mask is formed by repeating irregularities formed on the outer surface of the clad. 4. The optical waveguide according to claim 1, wherein the phase grating mask is formed by repeating irregularities formed on the silicone-based photosensitive resin composition disposed on the outer surface of the clad. Wave path. 5. The method of manufacturing an optical waveguide according to claim 3, wherein the irregularities formed on the outer surface of the clad are repeatedly formed by etching. 6. The method of manufacturing an optical waveguide according to claim 2, wherein the outer surface of the clad is irradiated with ultraviolet light to form a light-induced grating in the core region.