JPH08338919A - Formation of optical waveguide type diffraction grating and forming device therefor - Google Patents

Abstract

PURPOSE: To provide a forming device for optical waveguide type diffraction gratings having a reflection characteristic of good wavelength selectivity. CONSTITUTION: An optical fiber 1 has a core added with Ge and the refractive index of its core part increases when the core part is irradiate with light of a wavelength about 240nm. A UV laser beam 2 having such wavelength is bisected by a beam splitter 3 and the flank of the optical fiber 1 is irradiated with the respective beams via a mask 8 from mirrors 4, 5. The bisected laser beams interfere with each other in the core part of the optical fiber 1. The core part is irradiated with the interference fringes. The transmittance of the mask 8 is large in the middle and is smaller toward both sides and, therefore, the interference fringes formed in the core part of the optical fiber 1 have a gentle light intensity distribution. The changes in the refractive index are induced in the patterns meeting the same and the diffraction gratings are formed on the core.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art An optical waveguide type diffraction grating is one in which a Bragg diffraction grating is formed in a waveguide portion by using a photo-induced change in refractive index of a waveguide to which Ge or the like is added. This optical waveguide type diffraction grating can be used as a reflection filter that reflects only light of a specific wavelength, and is also expected to be widely used as a wavelength control element, a sensor element, and the like. Above all, a fiber grating using an optical fiber as an optical waveguide is important because it has good connectivity with an optical fiber used as a transmission line.

As a method for producing an optical waveguide type diffraction grating,
A method of projecting an ultraviolet interference pattern from the side surface of the waveguide to spatially change the refractive index at an arbitrary period, for example, 2
The light flux interferometry, the prism interferometry, the phase grating interferometry, etc. are known.

FIG. 7 is a block diagram of an example of the two-beam interference method. In the figure, 1 is an optical fiber, 2 is a laser beam, 3 is a beam splitter, and 4 and 5 are mirrors. Optical fiber 1
It has a Ge-added core and a wavelength of 240
Irradiation with light near nm increases the refractive index of the core.
Ultraviolet rays having such a wavelength are emitted as the laser light 2.
The laser light 2 is divided into two by the beam splitter 3, and the side surfaces of the optical fiber 1 are irradiated by the mirrors 4 and 5, respectively. The divided laser light interferes with the core portion of the optical fiber 1 and irradiates the core portion with interference fringes. In the core portion of the optical fiber 1, the refractive index changes in a pattern according to the interference fringes, and a diffraction grating is formed.

FIG. 8 is a block diagram of an example of the prism interferometry. In the figure, 1 is an optical fiber, 2 is a laser beam, and 6 is a prism. The optical fiber 1 has the above-mentioned Ge-doped core, and one surface of the prism 6 is irradiated with the ultraviolet laser light 2 onto the core, and the interference fringes generated by refraction in the prism 6 are generated by the optical fiber. Irradiate the core part of 1. In the core portion of the optical fiber 1, the refractive index changes in a pattern according to the interference fringes, and a diffraction grating is formed.

FIG. 9 is a block diagram of an example of the phase grating interference method. In the figure, 1 is an optical fiber, 2 is a laser beam, and 7 is a phase grating. By irradiating the core of the optical fiber 1 with the laser light 2 through the phase grating, it is possible to form a diffraction grating corresponding to the grating interval of the phase grating.

The change in the refractive index of the diffraction grating formed by the above-described conventional method shows a uniform change in a predetermined range, as shown in FIG. 11 (A). That is, the portion where the diffraction grating is not formed is connected to the portion where the diffraction grating is formed discontinuously. FIG. 11 shows the reflection characteristic with respect to wavelength when this diffraction grating is used as a reflector.
(B), the not only show a large reflectivity at the wavelength lambda _0, but not so large in the vicinity of the wavelength lambda _0, there is a wavelength at which the reflectance increases, shows a characteristic having a side lobe . Therefore, there is a problem that reflection occurs at an undesired wavelength.

There is also a demand to obtain various characteristics in the wavelength region near the wavelength λ ₀ exhibiting a large reflectance, but the refractive index of the diffraction grating is only periodically changed within a predetermined range. Then, there is also a problem that this request cannot be satisfied.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and provides a method and an apparatus for producing an optical waveguide type diffraction grating having a reflection characteristic with good wavelength selectivity. The purpose is to do.

In addition, there are provided an optical waveguide type diffraction grating producing method and apparatus, an optical waveguide type filter producing method and an optical waveguide type filter capable of producing an optical waveguide type diffraction grating having various reflection characteristics. That is the purpose.

[0011]

According to a first aspect of the present invention, light having a wavelength that causes a refractive index change in an optical waveguide portion of an optical waveguide is formed as an intensity distribution pattern having spatially periodic brightness. In the method of producing an optical waveguide type diffraction grating in which a diffraction grating is produced on the optical waveguide by irradiating the optical waveguide to produce a periodic modulation in the refractive index of the optical waveguide, the change in the refractive index is caused. The light of the selected wavelength has an intensity distribution pattern having spatially periodic brightness and darkness, and has a distribution in the light intensity of the irradiation light flux in the longitudinal direction of the optical waveguide. .

In the invention described in claim 2, the optical waveguide is irradiated with light having a wavelength that causes a change in the refractive index in the optical waveguide portion of the optical waveguide, as an intensity distribution pattern having spatially periodic brightness. In the optical waveguide type diffraction grating producing apparatus for producing a diffraction grating on the optical waveguide by producing a periodic modulation in the refractive index of the optical waveguide section, the light of the wavelength that causes the change in the refractive index is It is characterized in that it has an intensity distribution pattern having spatially periodic brightness and darkness, and has a distribution in the light intensity of the irradiation light flux in the longitudinal direction of the optical waveguide.

According to the third aspect of the present invention, the optical waveguide is irradiated with light having a wavelength that causes a change in the refractive index in the optical waveguide portion of the optical waveguide, as an intensity distribution pattern having spatially periodic brightness. In the optical waveguide type diffraction grating producing apparatus for producing a diffraction grating on the optical waveguide by producing a periodic modulation in the refractive index of the optical waveguide section, the light of the wavelength that causes the change in the refractive index is It is characterized in that it has an intensity distribution pattern having spatially periodic brightness and darkness and has a gentle light intensity distribution over the entire irradiation light flux in the longitudinal direction of the optical waveguide.

According to a fourth aspect of the present invention, in the optical waveguide type diffraction grating producing apparatus according to the third aspect, an optical system for irradiating the optical waveguide with an intensity distribution pattern having spatially periodic brightness and darkness. At least one of them has a gentle light intensity distribution over the entire irradiation light flux in the longitudinal direction of the optical waveguide.

According to a fifth aspect of the present invention, in the optical waveguide type diffraction grating producing apparatus according to the third or fourth aspect, the optical waveguide is irradiated with an intensity distribution pattern having spatially periodic brightness. A transmittance modulation mask is used in the optical system so that a gentle light intensity distribution is provided over the entire irradiation light flux in the longitudinal direction of the optical waveguide.

According to a sixth aspect of the present invention, in the optical waveguide type diffraction grating producing apparatus according to the third aspect, there is provided a moving means for moving the irradiation region, and the moving speed is changed to change the moving speed of the optical waveguide. Is characterized in that a gentle light intensity distribution is provided over the entire irradiation light flux in the longitudinal direction.

According to a seventh aspect of the invention, in the optical waveguide type diffraction grating producing apparatus according to the third aspect, there is provided a moving means for moving the irradiation region, and at least the moving speed or the light intensity of the light is used. It is characterized in that the intensity is changed so as to have a gentle light intensity distribution over the entire irradiation light flux in the longitudinal direction of the optical waveguide.

According to an eighth aspect of the present invention, in the optical waveguide type diffraction grating producing apparatus according to the second aspect, the light intensity of the irradiation light beam in the longitudinal direction of the optical waveguide is determined by the modulation cycle of the refractive index. Is characterized by having a light intensity distribution that changes in a substantially rectangular shape within a long predetermined interval.

According to a ninth aspect of the present invention, in the optical waveguide type diffraction grating producing apparatus according to the eighth aspect, the predetermined interval is 10 times or more the modulation cycle of the refractive index. To do.

According to a tenth aspect of the present invention, in the optical waveguide type diffraction grating producing apparatus according to the eighth or ninth aspect, the optical waveguide is irradiated with an intensity distribution pattern having spatially periodic brightness. It is characterized in that at least one of the optical systems has the light intensity distribution.

According to the eleventh aspect of the present invention, in the apparatus for producing an optical waveguide type diffraction grating according to any one of the eighth to tenth aspects, the optical waveguide has a spatially periodic intensity. A transmittance modulation mask is used in an optical system for irradiating the distribution pattern so as to have the above-mentioned light intensity distribution.

According to a twelfth aspect of the invention, in the optical waveguide type diffraction grating producing apparatus according to the eighth or ninth aspect, the irradiation area is moved and the moving speed thereof is changed to obtain the light intensity distribution. It is characterized in that it is adapted to.

According to a thirteenth aspect of the invention, in the optical waveguide type diffraction grating producing apparatus according to the eighth or ninth aspect, the irradiation region is moved, and at least the light intensity of the moving speed or the light intensity is changed. It is characterized by having the above-mentioned light intensity distribution.

In the fourteenth aspect of the present invention, the light having a wavelength that causes a change in the refractive index of the optical waveguide portion of the optical waveguide is formed as an intensity distribution pattern having a brightness and darkness in which the period spatially changes in the longitudinal direction. In the method for producing an optical waveguide type filter in which a diffraction grating is produced on the optical waveguide by irradiating the optical waveguide with the optical waveguide to generate a modulation in which the period changes in the longitudinal direction, The light having the wavelength to be generated has an intensity distribution pattern having a light and darkness in which the period spatially changes in the longitudinal direction, and the intensity of the optical waveguide decreases in a predetermined interval longer than the modulation period of the refractive index. It is characterized by having a light intensity distribution in the longitudinal direction.

According to the fifteenth aspect of the present invention, the light having a wavelength that causes a change in the refractive index in the optical waveguide portion of the optical waveguide is formed as an intensity distribution pattern having a spatially constant brightness and darkness in the longitudinal direction. To produce a constant modulation of the refractive index of the optical waveguide in the longitudinal direction.
In the method of manufacturing an optical waveguide filter in which a diffraction grating is formed on the optical waveguide, the light having a wavelength that causes the change in the refractive index has a spatially periodic intensity distribution pattern having a constant darkness and darkness in the longitudinal direction. In addition, the light intensity distribution in the longitudinal direction of the optical waveguide is such that the intensity decreases within a predetermined interval longer than the refractive index modulation period.

[0026]

According to the first aspect of the present invention, the light of the wavelength that causes the change in the refractive index has an intensity distribution pattern having spatially periodic brightness and darkness, and is irradiated in the longitudinal direction of the optical waveguide. Since the light intensity of the light flux has a distribution, the reflection and transmission characteristics of the diffraction grating can be changed as compared with the case where the light intensity distribution is constant.

According to the second aspect of the present invention, the light of the wavelength that causes the change in the refractive index has an intensity distribution pattern having spatially periodic brightness and darkness, and is irradiated in the longitudinal direction of the optical waveguide. Since the light intensity of the light flux has a distribution, the same operation as that of the first aspect of the invention is achieved.

According to the third aspect of the present invention, the light having the wavelength that causes the change in the refractive index can form a diffraction grating pattern by having an intensity distribution pattern having spatially periodic brightness and darkness. By providing a gentle light intensity distribution over the entire irradiation light flux in the longitudinal direction of the optical waveguide, a gently changing diffraction pattern is formed, and thus reflection characteristics with side lobes suppressed can be realized.

According to the invention described in claim 4, at least one of the optical systems for irradiating the optical waveguide with the intensity distribution pattern having spatially periodic brightness and darkness is provided with an irradiation light beam in the longitudinal direction of the optical waveguide. Since a diffractive pattern is formed gently by having a gentle light intensity distribution over the entire area, it is possible to realize a reflection characteristic in which side lobes are suppressed.

According to the fifth aspect of the present invention, the transmittance modulation mask is used in the optical system for irradiating the optical waveguide with the intensity distribution pattern having spatially periodic brightness and darkness. By gradually changing the spatial intensity and providing a gentle light intensity distribution over the entire irradiation light flux in the longitudinal direction of the optical waveguide, the diffraction pattern is formed gently, so side lobes are suppressed. It is possible to realize excellent reflection characteristics.

According to the sixth aspect of the invention, there is provided a moving means for moving the irradiation area, and by changing the moving speed of the irradiation area, the irradiation time is changed so that the entire irradiation light flux in the longitudinal direction of the optical waveguide is changed. Since the diffraction pattern is gently formed by providing the gentle light intensity distribution over the entire area, it is possible to realize the reflection characteristic in which the side lobes are suppressed.

According to the invention as defined in claim 7, there is provided a moving means for moving the irradiation region, and at least the irradiation intensity is changed by changing at least the light intensity of the moving speed or the light intensity, thereby changing the optical intensity. Since a gentle light intensity distribution is provided over the entire irradiation light flux in the longitudinal direction of the waveguide, the diffraction pattern is formed gently, so that the reflection characteristic with suppressed side lobes can be realized.

According to the invention described in claim 8, the light intensity of the irradiation light flux in the longitudinal direction of the optical waveguide has a light intensity distribution which changes in a substantially rectangular shape within a predetermined interval longer than the modulation cycle of the refractive index. Since it has, the reflection characteristic can be changed according to a predetermined interval.

According to the invention of claim 9, the predetermined interval is 10 times or more of the modulation cycle of the refractive index, and therefore the light intensity distribution is set independently of the periodicity of the intensity distribution pattern. You can

According to the tenth aspect of the invention, at least one of the optical systems for irradiating the optical waveguide with the spatially periodic intensity distribution pattern has a light intensity distribution. The light intensity distribution can be easily set.

According to the eleventh aspect of the present invention, a light intensity distribution is provided by using a transmittance modulation mask in an optical system for irradiating the optical waveguide with an intensity distribution pattern having spatially periodic brightness and darkness. By doing so, the light intensity distribution can be easily set.

According to the twelfth aspect of the invention, since the irradiation area is moved and the moving speed thereof is changed to give the light intensity distribution, the light intensity distribution can be easily set. .

According to the thirteenth aspect of the invention, the irradiation area is moved, and at least the light intensity of the moving speed or the light intensity is changed so as to have the light intensity distribution. Can be easily set.

According to the fourteenth aspect of the present invention, the light having a wavelength that causes a change in the refractive index has an intensity distribution pattern with a light and shade in which the period spatially changes in the longitudinal direction. Since a light intensity distribution is provided in the longitudinal direction of the optical waveguide, the intensity of which decreases within a predetermined interval longer than the modulation cycle, it is possible to create a bandpass type or bandstop type filter.

According to the fifteenth aspect of the invention, the light having a wavelength that causes a change in the refractive index has an intensity distribution pattern having a spatially periodic light and dark with a constant periodicity in the longitudinal direction, and the A Fabry-Perot filter can be created by providing a light intensity distribution in the longitudinal direction of the optical waveguide, the intensity of which decreases within a predetermined interval longer than the modulation period.

[0041]

FIG. 1 is a schematic configuration diagram of a first embodiment of an optical waveguide type diffraction grating producing apparatus of the present invention. 7, those parts that are the same as those corresponding parts in FIG. 7 are designated by the same reference numerals, and a description thereof will be omitted. 8 is a mask. In this embodiment, the present invention is applied to the two-beam interference method described in FIG. The transmittance of the mask 8 is large in the middle and becomes smaller toward both sides.

In this embodiment, the mask 8 is placed immediately before the optical fiber 1. Since the transmittance of the mask 8 is modulated, a gentle light intensity distribution can be provided over the entire irradiation light flux. The diffraction grating formed by such a light intensity distribution has the largest increase in the refractive index in the central portion, and the increase in the refractive index gradually decreases toward both sides thereof.

FIG. 10 (A) shows an outline of an example of the change in the refractive index of the formed diffraction grating. The portion where the refractive index rises gradually increases, reaches the maximum in the central portion, and then gradually decreases. Although the pattern is almost symmetrical with the center as the axis of symmetry, it does not have to be symmetrical. The point is that the envelope of the change in refractive index should gradually increase and then gradually decrease. Since such a change in the refractive index does not cause a discontinuous change in the refractive index, the reflection characteristic with respect to the wavelength when the diffraction grating is used as a reflector has a wavelength λ ₀ as shown in FIG. Shows a large reflectance and can suppress the generation of side lobes.

FIG. 2 shows a modification of the above-described first embodiment. In the figure, the same parts as those in FIG. In FIG. 2A, the mask 8 described in FIG. 1 is inserted into an optical system that transmits the beam splitter 3. In addition, in FIG. 2B, the mask 8 described in FIG. 1 is inserted into the optical system on the side where the beam splitter 3 is reflected. In any case, a gentle light intensity distribution can be provided over the entire irradiation light flux of the optical system in which the mask 8 is inserted, and a gentle light intensity distribution can be provided over the entire irradiation light flux with which the optical fiber 1 is irradiated. . Of course, the mask 8 may be inserted into both the optical system on the side of transmitting the beam splitter 3 and the optical system on the side of reflecting it.

In FIG. 2C, the mask 8 is inserted in the optical system which is incident on the beam splitter 3. Also in this modified example, a gentle light intensity distribution can be provided over the entire irradiation light flux of the optical system entering the beam splitter 3, and a gentle light intensity distribution can be achieved over the entire irradiation light flux with which the optical fiber 1 is irradiated. Can be made.

FIG. 3 is a schematic configuration diagram of the second embodiment of the optical waveguide type diffraction grating producing apparatus of the present invention. In the figure,
The same parts as those in FIG. 8 are designated by the same reference numerals and the description thereof will be omitted. 8 is a mask. In this embodiment, the present invention is applied to the prism interference method described in FIG. The mask 8 was placed immediately before the optical fiber 1. In this embodiment as well, as in the first embodiment, the transmittance of the mask 8 is modulated, so that a gentle light intensity distribution can be provided over the entire irradiation light flux. The diffraction grating formed by such a light intensity distribution has the largest increase in the refractive index in the central portion, and the increase in the refractive index gradually decreases toward both sides thereof. The mask 8 has the same structure as described with reference to FIG.
It may be inserted on the incident side, that is, in the optical system that enters the prism 6.

FIG. 4 is a schematic block diagram of the third embodiment of the optical waveguide type diffraction grating producing apparatus of the present invention. In the figure,
The same parts as those in FIG. 9 are designated by the same reference numerals and the description thereof will be omitted. 8 is a mask. In this embodiment, the present invention is applied to the phase grating interferometry described with reference to FIG. The mask 8 was placed immediately before the optical fiber 1. In this embodiment as well, as in the first embodiment, the transmittance of the mask 8 is modulated, so that a gentle light intensity distribution can be provided over the entire irradiation light flux. The diffraction grating formed by such a light intensity distribution has the largest increase in the refractive index in the central portion, and the increase in the refractive index gradually decreases toward both sides thereof. The mask 8 has the same structure as described with reference to FIG.
It may be inserted on the incident side, that is, in the optical system that is incident on the phase grating 7.

The mask used in these embodiments will be described. FIG. 5 is an explanatory diagram of a specific example of the intensity pattern. FIG. 5A is an example in which the intensity changes linearly. The horizontal axis X is the distance in the axial direction of the optical fiber, and the center of the diffraction grating formed is 0. The vertical axis Y is the relative value of intensity with the maximum value being 1.

If this is expressed by a function, Y = 1−a · | X | However, a is a constant.

FIG. 5B is an example in which the intensity changes in a curve, and is shown in the same manner as FIG. 5A. If an example of the curve is expressed by a function, then Y = 0.5 + 0.5 · cos (π · | X | / a). However, a is a constant.

In addition, even in the case of a trapezoidal intensity pattern that linearly changes only at a part of both ends, it is necessary to connect from the part where the diffraction grating is not formed to the part where the diffraction grating is continuously formed. You can

The intensity distribution of the laser beam transmitted through the pattern of the transmittance of the mask has a desired distribution characteristic, for example, as shown in FIG.
A desired diffraction grating can be created by selecting the intensity pattern shown in FIG. 5A or FIG.

That is, at the same time that a periodic intensity distribution pattern is generated by the interference fringes, the light intensity distribution characteristic over the entire irradiation light flux is set by the mask transmittance pattern to create an optical waveguide type diffraction grating. . Figure 5
The light intensity distribution characteristics shown in (A) and FIG. 5 (B) have a non-uniform distribution in the longitudinal direction of the optical fiber, and are gentle over a predetermined interval longer than the cycle of the change in the refractive index of the diffraction grating. The light intensity distribution characteristic changes. This predetermined interval is preferably 10 times or more the modulation cycle of the light refractive index.

FIG. 6 is a schematic configuration diagram of a fourth embodiment of an optical waveguide type diffraction grating producing apparatus of the present invention. In the figure,
The same parts as those in FIG. 9 are designated by the same reference numerals and the description thereof will be omitted. In this embodiment, the irradiation area of the laser light source (not shown) is reduced and the laser light source is moved. When the moving speed is high, the irradiation light amount decreases, and when the moving speed is low, the irradiation light amount increases. Therefore, the light intensity distribution of the irradiation light flux can be changed by changing the moving speed. The moving speed is, for example, as shown in FIG. 5 (A) or FIG. 5 (B).
The intensity pattern described in 1. is formed.

Further, instead of moving the laser light source,
The laser light source is configured to irradiate the area where the diffraction grating is formed with uniform intensity, and a shield is arranged between the laser light source and the optical fiber to prevent the laser light from directly irradiating the optical fiber. Even if the shield is provided with a slit and the slit is moved and the moving speed thereof is changed, the light intensity distribution of the irradiation light beam can be changed as in the fourth embodiment.

Alternatively, the mask 8 used in the third embodiment shown in FIG. 4 may be used together. Due to the change in the moving speed and the change in the light intensity due to the mask 8 whose transmittance is modulated, it is possible to provide a gentle light intensity distribution over the entire irradiation light flux. In particular, it is preferable to use one of the change in the moving speed and the change in the light intensity as the main component and the other as the correction. It is also possible to provide a gentle light intensity distribution over the entire irradiation light flux by keeping the moving speed constant and only changing the light intensity by the mask 8. In addition to the mask 8, the change in the light intensity can be realized by controlling the light intensity of the laser light source in synchronization with the movement of the laser beam.

Next, a diffraction grating having various reflection characteristics is produced by giving a desired light intensity distribution characteristic using the optical waveguide type diffraction grating producing apparatus described with reference to FIGS. 1 to 4 and 6. To do.

FIG. 12 is an explanatory diagram of the refractive index distribution and the reflection characteristics in the band-type optical waveguide type filter. 12
12A shows a change in the refractive index of the diffraction grating which is a prerequisite, FIG. 12B shows a relative value of light intensity, and FIG. 12C has an intensity distribution corresponding to FIG. 12B. FIG. 12 (D) shows the pitch of the diffraction grating, and FIG. 12 (E) is an explanatory view of the action of this optical waveguide type diffraction grating. All the explanatory views are also schematically shown. The horizontal axis is the position along the longitudinal direction of the optical fiber. In FIG. 12D, 1 is an optical fiber.

In this example, as shown in FIG.
A so-called chirped grating, in which the period of the refractive index gradually changes in the longitudinal direction of the optical waveguide, is created. Specifically, for example, the phase grating 7 of the phase grating interference method as shown in FIGS. 9 and 4 may be formed in a pattern that forms a chirped grating. In the two-beam interference method shown in FIG. 7, the wavefront of the plane wave may be bent using a lens, and in the prism interference method shown in FIG. 8, the incident surface of the prism may be bent.

At this time, the light intensity distribution has the characteristics shown in FIG. This light intensity distribution characteristic is shown in FIG.
The relative intensity is 0 in a region within a predetermined interval longer than the spatial period of the change in the refractive index of the diffraction grating shown in (A), and light is shielded, and in other regions, the relative intensity is 1 in a substantially rectangular shape. Therefore, it has a characteristic that it changes into a substantially square wave shape. The position and number of light-shielded regions are designed according to the desired filter characteristics, but the above-mentioned predetermined intervals are
It is preferably 10 times or more the modulation cycle of the refractive index. A desired diffraction grating is created by adjusting the intensity distribution of the transmittance of the mask so that the intensity of the laser light passing through the mask has the light intensity distribution characteristic shown in FIG. In this example, both ends of the diffraction grating are changed into a substantially square wave shape to shield the light.

Alternatively, as in the case of the fourth embodiment described with reference to FIG. 6, instead of a single mask, a change in the moving speed of the laser light source with a smaller irradiation area and a change in the light intensity due to the mask or the like are performed. The light intensity distribution of the irradiation light flux may be changed by at least one of the above.

FIG. 12C shows an outline of changes in the refractive index of the formed diffraction grating. Since it is a chirped grating, the pitch of the refractive index, that is, the period, gradually changes in the longitudinal direction of the optical waveguide as shown in FIG. 12D. Lack of change. Consider the case of using as a reflection type filter. When there is no change in the refractive index, the light from the wavelength λ ₁ to the wavelength λ ₃ is reflected in the incident direction, and the light of the other wavelengths is transmitted and absorbed by the non-reflection end (not shown). When the change in the refractive index is absent, FIG.
As shown in, the light of wavelength λ ₂ (λ1>λ2> λ3) that should have been reflected in the region where the change in the refractive index is absent passes through the core portion of the optical fiber 1 from left to right.

FIG. 13 is a characteristic diagram schematically showing the characteristic of the optical waveguide type filter shown in FIG.
Is a reflection characteristic, and FIG. 13B is a transmission characteristic diagram. Due to the above-described change in the refractive index, the reflection characteristic with respect to wavelength when this diffraction grating is used as a reflector is shown in FIG.
As shown in (1), the reflection type band stop filter has a reflectance that decreases in the vicinity of the wavelength λ ₂ . On the other hand, the reflection characteristics for wavelength when this diffraction grating is used as a transmitter are:
As shown in FIG. 13B, the transmission type bandpass filter has a transmittance increasing in the vicinity of the wavelength λ ₂ . Light may be made incident from the right side of the optical fiber 1 of FIG. 12D, and the wavelength and phase characteristics are opposite, but the reflectance and the transmittance are similar.

Incidentally, by making the slope of the square wave-shaped light intensity distribution characteristic shown in FIG. 12B gentle, the envelope of the change in the refractive index does not change discontinuously and side lobes are generated. It may be suppressed.

FIG. 14 is an explanatory diagram of the refractive index distribution and reflection characteristics in the optical waveguide type Fabry-Perot filter. FIG. 14A shows the change in the refractive index of the presumed diffraction grating, and FIG. 14B shows the relative value of the light intensity.
FIG. 14C shows a change in the refractive index of the diffraction grating formed by giving the light intensity distribution corresponding to FIG. 14B, and FIG.
FIG. 4 is an explanatory view of the operation of this optical waveguide type diffraction grating. All the explanatory views are also schematically shown. The horizontal axis is the position in the axial direction of the optical fiber. In FIG. 14D, 1 is an optical fiber.

In this example, as shown in FIG.
A uniform diffraction grating is created in the longitudinal direction of the optical waveguide. At this time, the light intensity distribution has the characteristics shown in FIG. This light intensity distribution characteristic has a relative intensity of 0 in a region within a predetermined interval longer than the spatial period of the change in the refractive index of the diffraction grating shown in FIG. It has a substantially rectangular shape with a relative intensity of 1, and has a characteristic of changing into a square wave shape. Normally, the number of light-shielding regions is one in the central portion, and the width of the light-shielding region is designed according to the desired filter characteristics. However, the above-mentioned predetermined interval is 10 times or more of the modulation cycle of the refractive index. Is preferred.

A desired diffraction grating is prepared by making the intensity distribution of the transmittance of the mask such that the intensity of the laser beam transmitted through the mask has the light intensity distribution characteristic shown in FIG. 14 (B). In this example, both ends of the diffraction grating are changed into a substantially square wave shape to shield the light. Alternatively, FIG.
The light intensity distribution of the irradiation light flux may be changed in the same manner as described with reference to.

FIG. 14C shows an outline of changes in the refractive index of the formed diffraction grating. The refractive index change is absent in the central region, and the Fabry-Perot filter with an incident angle of 0 ° is formed by multiple reflection in this portion. Consider the case of using as a reflection type filter. When there is no change in the refractive index, light of a predetermined wavelength corresponding to the period of the refractive index of the diffraction grating is reflected in the incident direction, and light of other wavelengths is absorbed by the non-reflection end (not shown). . When the change in the refractive index is absent, as shown in FIG.
A phase difference occurs between the reflected light R ₁ reflected by the left diffraction grating area and the reflected light R ₂ reflected by the right diffraction grating area due to the distance d corresponding to the width of the light shielding area. In addition, the phase states are matched in the left and right diffraction grating regions where the grating is continuous.

When the wavelength of light is λ, the refractive index of the optical waveguide is n, and m is a positive integer, the transmitted light becomes maximum when 2nd = mλ, and the transmitted light becomes minimum. This is when 2nd = (2m + 1) λ / 2. As a result, it is possible to maximize or minimize the transmittance or the reflectance of the light having the wavelength satisfying the above-mentioned conditions among the light having the wavelengths that are transmitted or reflected by the diffraction grating. The interval (wavenumber difference) Δσ between adjacent transmission peaks is Δσ = 1 / (2nd)
Therefore, in practice, smaller d makes it easier to separate and extract light of a single wavelength (wave number), but it is preferably 10 times or more of the modulation cycle of the refractive index.

[0070]

As is apparent from the above description, according to the present invention, there is an effect that it is possible to produce an optical waveguide type diffraction grating having side lobes suppressed and good reflection characteristics with good wavelength selectivity. In addition, there is an effect that an optical waveguide type diffraction grating having various reflection characteristics can be produced.

[Brief description of drawings]

FIG. 1 is a first embodiment of a device for producing an optical waveguide type diffraction grating of the present invention.
It is a schematic block diagram of the embodiment of.

FIG. 2 shows a modification of the first embodiment.

FIG. 3 is a second part of the apparatus for producing an optical waveguide type diffraction grating of the present invention.
It is a schematic block diagram of the embodiment of.

FIG. 4 is a third embodiment of a device for producing an optical waveguide type diffraction grating of the present invention.
It is a schematic block diagram of the embodiment of.

FIG. 5 is an explanatory diagram of a specific example of an intensity pattern.

FIG. 6 is a fourth embodiment of a device for producing an optical waveguide type diffraction grating of the present invention.
It is a schematic block diagram of the embodiment of.

FIG. 7 is a configuration diagram of an example of a two-beam interference method.

FIG. 8 is a configuration diagram of an example of a prism interference method.

FIG. 9 is a configuration diagram of an example of a phase grating interference method.

FIG. 10 is an explanatory diagram of a refractive index distribution and reflection characteristics in the diffraction grating according to the embodiment of the present invention.

FIG. 11 is an explanatory diagram of a refractive index distribution and a reflection characteristic in a conventional diffraction grating.

FIG. 12 is an explanatory diagram of a refractive index distribution and a reflection characteristic in the bandpass optical waveguide filter.

13 is a diagram schematically showing the characteristics of the optical waveguide filter shown in FIG.

FIG. 14 is an explanatory diagram of a refractive index distribution and a reflection characteristic in the optical waveguide type Fabry-Perot filter.

[Explanation of symbols]

1 ... Optical fiber, 2 ... Laser light, 3 ... Beam splitter, 4, 5 ... Mirror, 6 ... Prism, 7 ... Phase grating, 8
... mask, 9 ... laser light source.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Masumi Ito 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (72) Toru Iwashima 1 Taya-cho, Sakae-ku, Yokohama, Kanagawa Sumitomo Electric Ki Industry Co., Ltd. Yokohama Works

Claims (15)

[Claims] 1. The refractive index of the optical waveguide is irradiated by irradiating the optical waveguide with light having a wavelength that causes a change in the refractive index of the optical waveguide as an intensity distribution pattern having spatially periodic brightness. In the method of manufacturing an optical waveguide type diffraction grating in which a diffraction grating is formed on the optical waveguide by causing periodic modulation, light having a wavelength that causes the change in the refractive index produces a spatially periodic light and dark. A method for producing an optical waveguide type diffraction grating, characterized in that it has a given intensity distribution pattern and also has a distribution in the light intensity of the irradiation light flux in the longitudinal direction of the optical waveguide. 2. The refractive index of the optical waveguide is irradiated by irradiating the optical waveguide with light having a wavelength that causes a change in the refractive index of the optical waveguide as an intensity distribution pattern having spatially periodic brightness. In a device for producing an optical waveguide type diffraction grating that produces a diffraction grating on the optical waveguide by producing a periodic modulation, light having a wavelength that causes the change in the refractive index produces a spatially periodic light and dark. An optical waveguide type diffraction grating producing apparatus, characterized in that it has a given intensity distribution pattern and also has a distribution in the light intensity of the irradiation light flux in the longitudinal direction of the optical waveguide. 3. The optical waveguide is irradiated with light having a wavelength that causes a change in the refractive index of the optical waveguide as an intensity distribution pattern having spatially periodic brightness and darkness, and the refractive index of the optical waveguide is changed. In a device for producing an optical waveguide type diffraction grating that produces a diffraction grating on the optical waveguide by producing a periodic modulation, light having a wavelength that causes the change in the refractive index produces a spatially periodic light and dark. A device for producing an optical waveguide type diffraction grating, which has a given intensity distribution pattern and has a gentle light intensity distribution over the entire irradiation light flux in the longitudinal direction of the optical waveguide. 4. A gradual light intensity distribution over the entire irradiation light flux in the longitudinal direction of the optical waveguide to at least one of the optical systems for irradiating the optical waveguide with an intensity distribution pattern having spatially periodic brightness and darkness. The optical waveguide type diffraction grating producing apparatus according to claim 3, further comprising: 5. An optical system for irradiating an intensity distribution pattern having spatially periodic brightness and darkness on an optical waveguide, wherein a transmittance modulation mask is used, and a gradual light is radiated over the entire irradiation light flux in the longitudinal direction of the optical waveguide. The optical waveguide type diffraction grating producing apparatus according to claim 3 or 4, wherein the apparatus has an intensity distribution. 6. A moving means for moving the irradiation area,
4. The optical waveguide type diffraction grating producing apparatus according to claim 3, wherein the moving speed is changed so as to have a gentle light intensity distribution over the entire irradiation light flux in the longitudinal direction of the optical waveguide. 7. A moving means for moving the irradiation area,
4. The light guide according to claim 3, wherein at least the light intensity of the moving speed or the light intensity is changed so as to have a gentle light intensity distribution over the entire irradiation light flux in the longitudinal direction of the optical waveguide. Waveguide-type diffraction grating production device. 8. The light intensity of the irradiation light flux in the longitudinal direction of the optical waveguide has a light intensity distribution that changes in a substantially rectangular shape within a predetermined interval longer than the modulation cycle of the refractive index. Item 2. An optical waveguide type diffraction grating producing apparatus according to Item 2. 9. The optical waveguide type diffraction grating producing apparatus according to claim 8, wherein the predetermined interval is 10 times or more the modulation period of the refractive index. 10. At least one optical system for irradiating an optical waveguide with an intensity distribution pattern having spatially periodic brightness and darkness.
The optical waveguide type diffraction grating producing apparatus according to claim 8, wherein the optical intensity distribution is provided. 11. A light intensity distribution is provided by using a transmittance modulation mask in an optical system for irradiating an intensity distribution pattern having spatially periodic brightness and darkness on an optical waveguide. An apparatus for producing an optical waveguide type diffraction grating according to any one of claims 8 to 10. 12. The optical waveguide type diffraction grating producing apparatus according to claim 8, wherein the irradiation region is moved and the moving speed thereof is changed so as to have the light intensity distribution. 13. The light guide according to claim 8, wherein the irradiation area is moved, and at least the light intensity of the moving speed or the light intensity is changed so as to have the light intensity distribution. Waveguide-type diffraction grating production device. 14. The optical waveguide is irradiated with light having a wavelength that causes a change in the refractive index of the optical waveguide as an intensity distribution pattern having a brightness and darkness with a spatially varying period in the longitudinal direction. In the method for producing an optical waveguide type filter in which a diffraction grating is produced on the optical waveguide by producing a modulation in which the period of the refractive index of the optical element changes in the longitudinal direction, the light having a wavelength that causes the change in the refractive index is A light intensity distribution in the longitudinal direction of the optical waveguide in which the intensity decreases in a predetermined interval longer than the modulation period of the refractive index. A method for producing an optical waveguide type filter characterized by: 15. The optical waveguide is irradiated with light having a wavelength that causes a change in the refractive index of the optical waveguide as an intensity distribution pattern having a spatially constant brightness and darkness in the longitudinal direction. In the method of producing an optical waveguide type filter in which a diffraction grating is produced on the optical waveguide by producing a constant modulation of the refractive index of the optical element in the longitudinal direction, the light of the wavelength that causes the change in the refractive index is Has a light intensity distribution pattern with a constant brightness in the longitudinal direction, and has a light intensity distribution in the longitudinal direction of the optical waveguide whose intensity decreases within a predetermined interval longer than the modulation period of the refractive index. A method for producing an optical waveguide type filter characterized by: