JPH07270606A - Manufacture of optical waveguide type diffraction grating - Google Patents

Abstract

PURPOSE:To use irradiation light having various wavelengths, to widen the applicable range thereof and to easily control the reflectivity thereof by making the light having a prescribed wavelength incident on the plural parts of the core of a glass optical waveguide. CONSTITUTION:This diffraction grating is provided with the core 41 being an optical waveguide part and a clad 42 having a lower refractive index than that of the core 41, and a light absorbing agent absorbing the light having a prescribed wavelength and melting a glass constituting the core 41 is contained in the core 41. Since the core glass of the part on which the light is made incident, is melted by making the light incident on the core 41 containing the light absorbing agent, the density of the glass at that part is locally raised. In accordance with it, the refractive index of the glass at that part is locally enhanced. Therefore, when the light having the prescribed wavelength is made incident on the plural parts of the core 41 of the glass optical waveguide, plural refractive index-enhanced parts 43 are arrayed along in an optical axis direction in the core 41, and the diffracting grating 44 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical waveguide type diffraction grating in which a diffraction grating is formed in an optical waveguide such as an optical fiber or a thin film waveguide.

[0002]

2. Description of the Related Art There are various types of diffraction gratings, which are a type of optical element, but when used in an optical communication system or the like, an optical waveguide that can be easily connected to an optical waveguide and has a low insertion loss. Type diffraction gratings are preferred.

As a conventional method for producing an optical waveguide type diffraction grating, the method described in Japanese Patent Application Publication No. 62-500052 is known. This is a method of forming a diffraction grating by irradiating a silica-based optical fiber in which germanium oxide is added to form a high-refractive index core with ultraviolet light to cause a periodical refractive index change in the core. .

Here, the mechanism by which the refractive index of the core is changed by irradiation with ultraviolet light has not been completely clarified. However, as an important cause, oxygen deficiency type defects related to germanium in glass are considered, and neutral oxygen mono-pores such as Si-Ge or Ge-Ge are assumed.

According to the Kramers-Kronig mechanism proposed as a mechanism for changing the refractive index, the refractive index change is explained as follows. That is, the above defects absorb ultraviolet light having a wavelength of 240 to 250 nm. And
Due to this absorption, the Si—Ge or Ge—Ge bond is broken, which causes a new defect. This new defect forms an absorption band centering around wavelengths of 210 nm and 280 nm. As a result, the refractive index of the glass changes according to the Kramers-Kronig relationship.

[0006]

However, in the above manufacturing method, since the wavelength of the irradiation light is limited to 240 to 250 nm, usable irradiation light is limited. Although the concentration of germanium defects depends on the dopant concentration of germanium oxide, it is uncertain whether germanium oxide will change to the above-mentioned oxygen deficiency type defects in glass, so the defect concentration in the manufacturing process must be accurate. Is difficult to control. Therefore, it is difficult to control the reflectance of the optical waveguide type diffraction grating to be manufactured.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to use an irradiation light of various wavelengths, a wide range of application, and an optical waveguide type diffraction grating whose reflectance can be easily controlled. It is intended to provide a manufacturing method.

[0008]

In order to solve the above problems, a method of manufacturing an optical waveguide type diffraction grating according to the present invention comprises a core which is an optical waveguide portion and a clad having a refractive index lower than that of the core. The core has a first step of preparing a glass optical waveguide containing a light absorbing agent that absorbs light of a predetermined wavelength and melts the glass forming the core, and a light absorbing agent for the glass optical waveguide. A second step of arranging a plurality of refractive index increasing portions in the core along the optical axis by irradiating the core with light having a predetermined wavelength and making the light incident on the core.

Here, quartz (Si
This includes a quartz glass optical waveguide containing O ₂ ) as a main component, and a multi-component glass optical waveguide including glass mainly containing quartz and including Na ₂ O, CaO and the like. The optical waveguide refers to a circuit or a line for confining and transmitting light in a certain area by utilizing the difference in refractive index between the core and the clad, which includes an optical fiber and a thin film waveguide.

Further, in the above method, the cladding of the glass optical waveguide may contain a light absorbing agent which absorbs light having a predetermined wavelength and melts the glass forming the cladding.

Further, it is possible to use a transition metal as the light absorbing agent, and it is also possible to use a rare earth element among the transition metals. Specifically, the core of the glass optical waveguide may contain 50 to 500 ppm of nickel as a light absorber.

[0012]

According to the structure of the present invention, the light absorber absorbs light to generate heat, and the temperature of the portion where the light is incident becomes locally high. As a result, the glass forming the core is locally melted.
When the irradiation of light is stopped, the melting of the glass also stops and then the glass solidifies. As a result, rearrangement of atoms occurs, and the glass density of the portion where the light is incident locally rises, and accordingly, the refractive index of that portion locally rises.

Therefore, when light of a predetermined wavelength is incident on a plurality of portions of the core of the glass optical waveguide, a plurality of refractive index increasing portions are arranged in the core along the optical axis direction of the optical waveguide, and the refractive index increasing portions of these portions are increased. The part constitutes a diffraction grating. Thus, the optical waveguide type diffraction grating is manufactured.

Since the wavelength of the irradiation light differs depending on the kind of the light absorbing agent, the wavelength of the irradiation light can be selected by selecting the light absorbing agent.

The amount of increase in the refractive index is determined by the concentration of the light absorber in the glass. Therefore, by controlling this concentration in the glass optical waveguide prepared in the first step, the increase in the refractive index of the glass constituting the core is increased. The quantity can be adjusted easily.

In the manufacturing method of the present invention, when an optical fiber containing a light absorber in the clad as well as the core is prepared and irradiated with light, a plurality of refractive index increases not only in the core but also in the clad. The parts are arranged along the optical axis to form a diffraction grating. Thus, an optical waveguide type diffraction grating having a diffraction grating on both the core and the clad is manufactured.

In this optical waveguide type diffraction grating, not only the guided light traveling through the core is reflected by the core diffraction grating, but also the light emitted to the clad during the guided wave is guided by the clad diffraction grating. Since it reflects and reflects the guided light over the entire mode field, it has a high reflectance.

[0018]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

First, as a first step, an optical fiber having a core containing nickel, which is a rare earth element, as a light absorber is prepared. In this embodiment, this optical fiber is replaced by a known M
It was manufactured using the CVD method and the liquid immersion method. The manufacturing method will be described below.

First, a pure silica pipe is prepared, and a porous glass layer doped with germanium oxide (GeO ₂ ) in an amount of 20 wt% is synthesized on the inner wall of the pipe by a usual process of the MCVD method.

To briefly explain this step, silicon tetrachloride (SiCl ₄ ) as a source gas and germanium tetrachloride (GeCl ₄ ) as a dopant source are introduced into the silica pipe while rotating the silica pipe. .
Along with this, the silica pipe is heated from outside using an oxyhydrogen flame burner, and quartz (Si
O ₂ ) Deposit a porous glass layer consisting of fine particles of glass.

Next, the porous glass layer is impregnated with nickel by a known liquid immersion method. FIG. 1 is a diagram showing this liquid immersion method. As shown in FIG. 1, in this example, 14 g of nickel chloride was dissolved in 1 liter of water to prepare a nickel chloride aqueous solution, and then the silica pipe 100 was immersed in this solution to remove the nickel chloride aqueous solution. Permeate into the porous glass layer 110 on the inner wall. As a result, nickel comes to be contained in the porous glass layer 110.

Next, the silica pipe 100 is placed in a constant temperature bath at about 50 ° C. and dried for about 20 hours. And
While allowing chlorine gas and oxygen gas to flow into the silica pipe 100, the flame of the oxyhydrogen burner is changed to the silica pipe 100.
Apply heat to the outer wall of. The flow rates of chlorine gas and oxygen gas were both about 50 cc / min.

As a result, the porous glass layer 110 becomes transparent. The fine particles of germanium oxide contained in the porous glass layer 110 are well mixed with quartz glass during this transparent vitrification. As a result, germanium oxide is doped into the quartz glass of the core.

After that, using a general MCVD apparatus,
The silica pipe 100 is solidified (collapse). Figure 2
FIG. 7 is a diagram showing this solidification step. In this step, the temperature of the burner flame is set higher than that in the clearing step, and the silica pipe 100 is heated while rotating. At the same time, the MCVD apparatus is operated to adjust the degree of pressure reduction of the internal pressure of the silica pipe 100. As a result, the cavity of the silica pipe 100 is crushed at the place where the burner flame is hit. Thus, the silica pipe 100 is solidified.

Through the above steps, the optical fiber preform is completed.
About 20 wt% germanium oxide is contained in the core of the base material,
The cladding is made of quartz glass containing about 100 ppm of nickel, while the cladding is made of pure quartz.

Here, if the nickel concentration in the core is too high, it becomes difficult to crystallize the core glass and it becomes difficult to form an optical fiber. Further, if the nickel concentration is too low, a sufficient increase in the refractive index does not occur, making it difficult to manufacture an optical fiber type diffraction grating with a sufficient reflectance. Therefore, the nickel concentration in the core is preferably 50 to 500 ppm.

The nickel concentration in the glass can be easily measured by a known EPMA method or the like. Further, the concentration of nickel contained in the core glass can be easily controlled by adjusting the concentration of the nickel chloride aqueous solution used in the liquid immersion method.

Next, the optical fiber preform produced as described above is heated in an electric furnace and drawn to obtain an optical fiber having a core containing nickel.

Next, the optical fiber is irradiated with laser light to form a diffraction grating on the core. In this embodiment, diffraction gratings with equal grating intervals are formed, and for this reason, laser light is irradiated onto the optical fiber while generating interference fringes with equal intervals. Hereinafter, this irradiation method will be described in detail.

FIG. 3 is a diagram for explaining the irradiation method. As shown in FIG. 3, the laser light output from the laser light source 10 is interfered by the interference means 20,
The optical fiber 4 containing nickel while producing interference fringes
It is irradiated to 0.

In this embodiment, the laser light is made to interfere by the holographic interferometry. In this method, the interference means 2
As shown in FIG. 3, 0 is composed of a beam splitter 21a and reflecting mirrors 21b and 21c. Further, as the laser light source 10, an argon laser light source 11 was used.

In this embodiment, the argon laser light source 11 is used.
Continuously oscillates coherent light having an output of 1 W and a wavelength of 488 nm. Here, the wavelength of the coherent light was selected according to the absorption wavelength of nickel which is a light absorber.

The coherent light emitted from the laser light source 11 is split by the beam splitter 21a into two light beams of transmitted light and reflected light. The branched light fluxes are reflected by the reflecting mirrors 21b and 21c, respectively, and both are irradiated onto the optical fiber 40 at an incident angle of 33 ° (angle formed by the incident light flux with the radial direction of the optical fiber 40).

The respective light beams interfere with each other in the interference region 30 and are irradiated onto the optical fiber 40 while forming interference fringes at predetermined intervals. The irradiated laser light is transmitted through the clad 42 and is incident on the core to which nickel is added to change the refractive index of the incident portion.

FIG. 4 is a diagram showing the irradiation of the optical fiber 40 with laser light. Using the incident angle θ of the laser light and the wavelength λ of the laser light, the interval Λ of the interference fringes is expressed as Λ = λ / (2sin θ) (1) Therefore, in the portions of the core 41 and the clad 42 where the laser light is incident, the refractive index increasing portions 43 whose refractive indexes are locally increased are arranged along the optical axis direction of the optical fiber 40 with the interval Λ of the interference fringes as a cycle. Then, the diffraction grating 44 is formed. In this way, the diffraction grating 44 with the grating interval Λ is formed on the core 41, and the optical fiber type diffraction grating is completed. The length of the manufactured diffraction grating 44 along the optical axis was about 4 mm.

If the refractive index n of the core 41 and the grating interval Λ of the diffraction grating 44 are used, according to the well-known Bragg diffraction condition,
The reflection wavelength λ _R of this fiber type diffraction grating is expressed as λ _R = 2nΛ = λn / sin θ (2) In this example, the reflection wavelength λ _R was set to 1300 nm.

In the present embodiment, during the laser light irradiation, L
The formation of the diffraction grating 44 was monitored in real time by injecting the light from the ED light source from one end of the optical fiber and measuring the transmission spectrum of this light with a spectrum analyzer connected to the other end. Here, the spectrum analyzer detects the relationship between the wavelength and the light intensity of the light transmitted through the diffraction grating 44.

When the irradiation of laser light is started, the diffraction grating 4
As the formation of 4 progresses, the intensity of the transmitted light in the transmission spectrum decreases around the reflection wavelength. If there is no change in the transmission spectrum, it is considered that the formation of the diffraction grating 44 has been saturated, so the irradiation of the laser beam is stopped at this point. In this example, the saturation time was about 20 minutes.

The reflection spectrum can be obtained from the transmission spectrum when the formation of the diffraction grating 44 is saturated. FIG. 5 is a graph showing the reflection spectrum thus obtained. As shown in FIG. 5, the reflection wavelength is about 13
The spectrum width was 00 nm and the spectrum width was about 1 nm. Further, the reflectance was about 90%, which was a good result.

Although the holographic interference method is used to form the interference fringes of the laser beam in the above embodiment, the phase grating method may be used instead.

FIG. 6 is a diagram for explaining the phase grating method. In this method, first, the phase grating 22, which is the interference means 20, is closely fixed to the optical fiber 40. As the phase grating 22, a quartz plate having grooves formed at equal intervals can be used. Since the groove of the phase grating 22 can be formed by lithography and chemical etching, the grating interval can be freely selected and a complicated shape is possible.

Next, for example, the KrF excimer laser light source 1
2, pulsed laser light with a predetermined intensity having a wavelength of 488 nm is output at a predetermined frequency, and the upper surface of the phase grating is irradiated for a predetermined time as shown in FIG. The laser light may be continuously oscillated.

When the laser light passes through the phase grating 22, interference fringes are formed at a predetermined interval and enter the core 41 with the interference fringes being formed. Therefore, the refractive index increasing portions 43 are arranged along the optical axis and diffracted. A grid 44 is formed on the core 41. In this way, an optical fiber type diffraction grating in which the diffraction grating is formed on the core 41 is manufactured.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, although an optical fiber is used as the optical waveguide for forming the diffraction grating in the above-described embodiment, a thin film waveguide having a core doped with a light absorber such as nickel may be used instead. Moreover, although nickel (Ni) is used as the light absorber, a transition metal can be used more generally, and among them, a rare earth element seems to be preferable. As such rare earth elements,
In addition to the nickel used in this example, erbium (Er)
And neodymium (Nd).

As the optical fiber for forming the diffraction grating, an optical fiber in which not only the core but also the clad contains a light absorbing agent such as nickel may be prepared and irradiated with light. In this case, since the diffraction grating is formed not only in the core but also in the clad, an optical fiber type diffraction grating having a high reflectance can be manufactured.

[0047]

As described above in detail, in the present invention, the light is made incident on the core containing the light absorber,
Since the core glass in the portion where the light is incident is melted, the glass density in that portion locally rises, and along with this, the refractive index of the glass in that portion locally rises.

Therefore, when light of a predetermined wavelength is incident on a plurality of portions in the core of the glass optical waveguide, a plurality of refractive index increasing portions are arranged in the core along the optical axis direction.
A diffraction grating is formed. Thus, according to the present invention, an optical waveguide type diffraction grating can be manufactured.

Since the wavelength of the irradiation light differs depending on the type of the light absorbing agent, the wavelength of the irradiation light can be selected by selecting the light absorbing agent. Therefore, irradiation light of various wavelengths can be used in the present invention, and thus has a wide range of applications.

Since the amount of increase in the refractive index is determined by the concentration of the light absorber, the amount of increase in the refractive index can be easily adjusted by controlling the concentration of the light absorber doped in the core. Therefore, the reflection wavelength of the optical waveguide type diffraction grating to be produced can be easily controlled.

When the light having a predetermined wavelength is applied to the optical waveguide in which the clad as well as the core contains the light absorber,
In addition to the above effect, an optical waveguide type diffraction grating having a diffraction grating not only in the core but also in the clad can be manufactured. Since this optical waveguide type diffraction grating reflects the guided light over the entire mode field, it has a higher reflectance than the conventional optical waveguide type diffraction grating. Therefore, according to this method, an optical waveguide type diffraction grating with high reflectance can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing nickel doping by a liquid immersion method.

FIG. 2 is a diagram showing a solidification process of a silica pipe.

FIG. 3 is a diagram showing laser light irradiation by holographic interferometry.

FIG. 4 is a diagram showing irradiation of laser light on an optical fiber.

FIG. 5 is a diagram showing a reflection spectrum of the manufactured optical fiber type diffraction grating.

FIG. 6 is a diagram showing laser light irradiation by a phase grating method.

[Explanation of symbols]

10 ... Laser light source, 20 ... Interference means, 21a ... Beam splitter, 21b, 21c ... Reflecting mirror, 22 ... Phase grating, 30 ... Interference region, 40 ... Optical fiber type diffraction grating, 4
1 ... Core, 42 ... Clad, 43 ... Refractive index increasing part, 44
... diffraction grating, 100 ... natural quartz tube, 110 ... porous glass layer, 120 ... oxyhydrogen flame burner.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masakazu Mobara 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works

Claims (5)

[Claims] 1. A light absorber having a core which is an optical waveguide portion and a clad having a refractive index lower than that of the core, the core absorbing light of a predetermined wavelength and melting glass constituting the core. A first step of preparing a glass optical waveguide containing a, irradiating the glass optical waveguide with light of the predetermined wavelength that the light absorber absorbs, and by making this light enter the core, And a second step of arranging a plurality of refractive index increasing portions along the optical axis, and a method of manufacturing an optical waveguide type diffraction grating. 2. The clad of the glass optical waveguide comprises:
2. The method for producing an optical waveguide type diffraction grating according to claim 1, further comprising a light absorber that absorbs light having a predetermined wavelength and melts the glass forming the clad. 3. The method of manufacturing an optical waveguide type diffraction grating according to claim 1, wherein the light absorber is a transition metal. 4. The method of manufacturing an optical waveguide type diffraction grating according to claim 3, wherein the transition metal is a rare earth element. 5. The method of manufacturing an optical waveguide type diffraction grating according to claim 1, wherein the core of the glass optical waveguide contains 50 to 500 ppm of nickel as a light absorbing agent.