JP3845922B2 - Manufacturing method of optical waveguide type diffraction grating - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an optical waveguide type diffraction grating in which the refractive index of a core periodically changes along the optical axis.
[0002]
[Prior art]
In recent years, with the progress of optical fiber communication technology, the complexity of networks and the multiplexing of signal wavelengths have progressed, and the system configuration is becoming more sophisticated. In such optical communication systems, the importance of optical circuit elements is increasing.
[0003]
A fiber-type element as one of general configurations in an optical circuit element has advantages such as being small and having a small insertion loss and being easy to connect to an optical fiber. A fiber type filter is known as such a fiber type element.
[0004]
Recently, it has been well known that when an optical fiber doped with germanium oxide in the core is irradiated with ultraviolet light, the refractive index of the core changes, and as a fiber-type filter using such a photo-induced change in refractive index. Optical fiber diffraction gratings have been developed.
[0005]
This optical fiber type diffraction grating reflects a light portion having a specific wavelength in the light traveling in the optical fiber. In general, the refractive index of the optical fiber core portion along the optical axis is irradiated by ultraviolet light irradiation. Manufactured by forming periodically varying regions.
[0006]
[Problems to be solved by the invention]
By the way, although the optical fiber having such a diffraction grating Bragg-reflects the fundamental mode of a specific wavelength, it has been confirmed that loss due to clad leakage of propagating light occurs in a wavelength region shorter than the reflection wavelength band (Electronics Letters, 28th April 1994, 730-732).
[0007]
This loss that occurs on the short wavelength side occurs because part of the signal light propagating in the optical fiber is converted to a higher-order mode in the region where the diffraction grating is formed, propagates as a cladding mode, and leaks to the outside. To do.
[0008]
Moreover, it has been clarified that the loss occurring on the short wavelength side greatly depends on the angle θ between the grating stripes of the diffraction grating and the perpendicular direction with respect to the axial direction of the optical fiber as shown in FIG. However, it is difficult to confirm the direction of the phase fringes of the phase grating during manufacturing, and the direction of the phase grating cannot be accurately adjusted.
[0009]
Accordingly, an object of the present invention is to provide a method of manufacturing an optical fiber type diffraction grating capable of adjusting the angle θ formed by the direction of the grating fringe and the axial direction of the optical waveguide with high accuracy.
[0010]
[Means for Solving the Problems]
The method of manufacturing an optical fiber type diffraction grating according to the present invention irradiates an optical waveguide of a glass material whose refractive index changes by irradiating light with interference light having a predetermined wavelength emitted from a light irradiation mechanism. In the method of manufacturing an optical waveguide type diffraction grating in which the refractive index of the core periodically changes in the core axis direction, a light irradiation mechanism and a projection plate are disposed on the side facing the light irradiation mechanism so as to sandwich the optical waveguide, An optical waveguide is irradiated with two light beams forming interference light, and two optical waveguide images are projected on a projection plate. An angle formed by a line connecting the two images and an axis of the projected optical waveguide image By adjusting θ, the direction of the light irradiation mechanism with respect to the optical waveguide is adjusted so that the angle θ formed by the normal line of the interference fringe of the refractive index formed in the core portion and the core axis is not more than a predetermined value. Method comprising adjusting step It is.
[0011]
According to the present invention, when changing the refractive index of the core by irradiating the core portion with interference fringes of a predetermined wavelength such as ultraviolet light, the ultraviolet light is passed through the phase grating or the like and the light beam traveling in two directions is guided. Since the light is transmitted through the waveguide, the image of the optical waveguide can be projected onto the projection plate . At this time, since the image of the optical waveguide is projected in a direction perpendicular to the lattice fringes of the phase grating, by measuring the angle θ between the direction connecting the two optical waveguide images and the axial direction of the optical waveguide image, The direction of interference fringes with respect to the optical axis direction can be accurately measured and adjusted.
[0012]
Further, by adjusting the angle θ in the present invention to 1.0 ° or less, the generation of higher order modes can be effectively suppressed.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Embodiments relating to a method for manufacturing an optical waveguide type diffraction grating will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.
[0014]
First, a method for manufacturing an optical waveguide type diffraction grating using a phase grating will be described with reference to FIGS. FIG. 1 is a configuration diagram of a manufacturing apparatus for manufacturing an optical waveguide type diffraction grating, and FIG. 2 is a diagram for explaining a manufacturing method. In FIG. 1, an optical fiber 1 having a core mainly composed of SiO ₂ in which GeO ₂ is uniformly doped in the axial direction is disposed on a projection plate 3, and a phase grating 2 is disposed immediately above the optical fiber 1. Arranged in parallel, the ultraviolet light 4 is irradiated from above the phase grating 2.
[0015]
In forming a diffraction grating in the core of the optical fiber 1 by the manufacturing apparatus of FIG. 1, when the ultraviolet light 4 passes through the phase grating 2, the ultraviolet light 4 travels in a direction perpendicular to the grating fringes 6 of the phase grating 2. The divided light beams 4-1 and 4-2 are divided into 4-1 and 4-2 and pass through the optical fiber 1 to reach the projection plate 3.
[0016]
When the lattice fringes 6 are arranged to be inclined with respect to the axis of the optical fiber 1, the light beams 4-1 and 4-2 travel in a direction perpendicular to the lattice fringes 6, so two optical fiber images 5-1 and 5-2. As shown in FIG. 2A, it appears on both sides of the optical fiber image 1-0 that appears light gray. Here, the optical fiber images 5-1 and 5-2 are images including the optical fiber images 1-1 and 1-2 and the diffracted lights 6-1 and 6-2 around them.
[0017]
When the optical fiber images 5-1 and 5-2 are projected away from the central axis as described above, the phase grating 2 is rotated in the horizontal plane on the optical fiber 1 as shown in FIG. The two optical fiber images 5-1 and 5-2 can be moved to the axis of the optical fiber image 1-0. By adjusting in this way, the interference light formed by the light beam 4-1 and the light beam 4-2 between the optical fiber 1 and the phase grating 2 becomes substantially perpendicular to the axial direction of the optical fiber 1, and the core axis A diffraction grating can be formed at a right angle. By this method, the positional relationship between the interference fringes and the axial direction of the optical fiber 1 can be easily adjusted to a desired angle θ.
[0018]
The two images projected on the projection plate 3 are enlarged in proportion to the distance between the optical fiber 1 and the projection plate 3. At this time, the sharpness of the enlarged image can be increased by using ultraviolet light with good linearity or by making the surface of the projection plate 3 white. It is also possible to place a thermal paper on the projection plate 3 to take an optical waveguide image and accurately measure the position.
[0019]
The angle θ formed by the axial direction of the optical fiber image 1-0 with respect to the direction connecting the optical fiber image 5-1 and the optical fiber image 5-2 is:
θ = tan ⁻¹ (L ₁ / L ₂ )
It is represented by
[0020]
The angle θ becomes zero when the grating fringes 6 of the diffraction grating 2 and the axis of the optical fiber 1 are perpendicular, and the two optical fiber images 5-1 and 5-2 are projected on the optical axis of the optical fiber image 1-0. The
[0021]
FIG. 3 is a diagram showing a specific configuration of the present manufacturing apparatus using a phase grating, and shows a side view (a) and a plan view (b). The phase grating 2 is attached to the center of a disk-shaped holder 13, and the holder 13 is provided on the frame 11 so as to be rotatable in the direction of the arrow 15. The frame 11 and the optical fiber 1 are fixed to the column 12.
[0022]
In forming the diffraction grating in the core of the optical fiber 1 using the manufacturing apparatus of FIG. 3, when the ultraviolet light 4 is incident on the phase grating 2, as shown in FIG. 2 is projected on both sides of the optical fiber image 1-0. In this case, the holder 13 is rotated in the direction of the arrow 15 to move the optical fiber images 5-1 and 5-2 to the axis of the optical fiber image 5-0, and the interference fringes of the ultraviolet light are reflected on the optical fiber axis. After adjusting so that it is at a right angle, irradiate with ultraviolet light.
[0023]
Next, in order to confirm the influence on the transmission characteristics when the optical waveguide type diffraction grating is tilted with respect to the optical fiber axis, the present inventors have made the relationship between the interference fringe normal line and the core axis 8 as shown in FIG. An optical fiber was produced when the angle θ formed was changed.
[0024]
First, the manufacturing method of these optical fibers is shown. A glass fiber having an 8 μm diameter core composed mainly of SiO ₂ with GeO ₂ uniformly doped in the axial direction and a clad having a diameter of 125 μm composed mainly of SiO ₂ on the outer periphery of the core is drawn at the same time as the resin. The optical fiber which gave was manufactured. This optical fiber was allowed to stand for 2 weeks in an atmosphere of a temperature of 25 ° C. and a hydrogen gas of 100 atm, and hydrogen was injected into the optical fiber to increase the refractive index change due to ultraviolet light irradiation.
[0025]
Next, a method for forming a diffraction grating in an optical fiber into which hydrogen is injected will be described. FIG. 6 is a block diagram of an apparatus for forming a diffraction grating using a phase grating. A phase grating 2 is arranged immediately above an optical fiber 1 mainly composed of SiO ₂ doped with GeO ₂ in the axial direction. The ultraviolet light is irradiated from above the phase grating 2. The ultraviolet light 4 is irradiated and interfered in the normal direction of the surface of the phase grating 2 in which the grating is arranged at a predetermined interval Λ ′. Therefore, the interval Λ of interference fringes in the core 9 is
Λ = Λ ′ / 2
It becomes. Accordingly, since the interference fringes having different refractive indexes are arranged in the axial direction of the core 9 with the interval Λ ′ / 2 as a period, the diffraction grating 10 is formed in the exposure region of the core portion 9.
[0026]
Based on the Bragg diffraction conditions, the refractive index n of the core 9 and the period Λ of the grating 10 are used, and the reflection wavelength λ _R of this diffraction grating is
λ _R = 2nΛ
= NΛ '
It becomes.
[0027]
Further, using the length L of the grating 10 and the refractive index difference Δn, the reflectance R of this optical fiber type diffraction grating is:
R = tanh ² (LπΔn / λ _R )
It becomes.
[0028]
Next, with respect to the case where the angle θ of the diffraction grating is 0 °, 0.17 °, 0.42 °, 0.85 °, 1.70 ° using the hydrogenated optical fiber, as shown in FIG. Formed by manufacturing equipment. The ultraviolet light source used was a KrF excimer laser, the irradiation beam was shaped to 20 mm × 8 mm, and the power intensity was 250 mJ / cm ² .
[0029]
Transmission spectrum characteristics of the optical waveguide type diffraction grating thus manufactured were measured. Of the measured characteristics, representative examples are shown in FIGS. It was confirmed that the loss occurring on the shorter wavelength side than the Bragg reflection wavelength tends to monotonously increase as the angle θ increases. From these measurement results, the relationship between the angle θ and the peak loss value on the short wavelength side is shown in FIG. From this graph, it can be seen that the increase in loss generated on the short wavelength side can be suppressed almost by making the inclination of the angle θ at 1.0 ° or less, preferably 0.5 ° or less.
[0030]
FIG. 11 is a configuration diagram of a manufacturing apparatus when an optical waveguide type diffraction grating is formed using a beam splitter. In this figure, the ultraviolet light emitted from the light source 20 is divided into two by a beam splitter 21, and each of the two divided ultraviolet lights is interfered by two mirrors 22 to form an interference space 24. A fiber 1 is installed, and a projection plate 3 is disposed below the optical fiber 1.
[0031]
In this apparatus, an interference mechanism 23 composed of a beam splitter 21 and two mirrors 22 arranged so as to sandwich the beam splitter 21 corresponds to the phase grating 2 shown in FIG. Has the same configuration as FIG.
[0032]
Therefore, in forming the diffraction grating by the manufacturing apparatus of FIG. 11, the optical fiber images 5-1 and 5-2 are formed of the optical fiber image 1-0 by the ultraviolet light emitted from the light source 20, as shown in FIG. Projected away on both sides. In such a case, by rotating / adjusting the interference mechanism 23 in the direction of the arrow 25, the optical fiber images 5-1, 5-2 are moved to the axis of the optical fiber image 1-0, and the interference fringes are cored. Can be adjusted at right angles to the axis.
[0033]
In the present invention, the optical waveguide and the light irradiation mechanism (the ultraviolet light 4 and the phase in FIG. 1 and the phase) are set so that the angle θ between the normal line of the interference fringe of the refractive index formed in the core portion and the core axis becomes a predetermined value. The wavelength of the light source in the case of adjusting the relative position of the grating 2 or the light source 20 and the interference mechanism 23 in FIG. 11 is not limited, and any wavelength can be used. When adjusting with ultraviolet light, the diffraction grating can be formed with ultraviolet light of the same wavelength, which is most preferable.
[0034]
【The invention's effect】
As described above, the method of manufacturing an optical waveguide type diffraction grating according to the present invention adjusts the direction of the light irradiation mechanism so that the two optical waveguide images initially projected on the projection plate are in a predetermined position, Then, since the refractive index is changed by irradiating with ultraviolet light, the direction of the diffraction grating can be formed accurately. By performing such adjustment, it is possible to suppress loss that occurs in a wavelength region shorter than the Bragg reflection band.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a manufacturing apparatus for forming an optical waveguide type diffraction grating according to the present embodiment.
FIG. 2 is a diagram for explaining a method of forming an optical waveguide type diffraction grating by the manufacturing apparatus shown in FIG.
FIG. 3 is a side view (a) and a plan view (b) showing a specific configuration of the manufacturing apparatus according to the present embodiment.
4 is a diagram for explaining a method of forming an optical waveguide type diffraction grating by the apparatus shown in FIG. 3. FIG.
FIG. 5 is a diagram showing a configuration of a diffraction grating.
FIG. 6 is a configuration diagram of an apparatus for forming an optical waveguide type diffraction grating by a phase grating.
FIG. 7 is a graph showing an example of transmission spectrum measurement using an optical waveguide type diffraction grating.
FIG. 8 is a graph showing an example of transmission spectrum measurement by another optical waveguide type diffraction grating.
FIG. 9 is a graph showing an example of transmission spectrum measurement using another optical waveguide type diffraction grating.
FIG. 10 is a graph showing a relationship between an inclination angle θ and a loss in a short wavelength band.
FIG. 11 is a diagram showing a configuration of another manufacturing apparatus for forming an optical waveguide type diffraction grating according to the present embodiment.
12 is a view for explaining a method of forming an optical waveguide type diffraction grating by the manufacturing apparatus shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 2 ... Phase grating, 3 ... Projection plate, 4 ... Ultraviolet light, 5 ... Optical waveguide image, 6 ... Grid stripe, 7 ... Direction of grid stripe, 8 ... axial direction of the core, 9 ... core, 10 ... diffraction grating, 11 ... frame, 12 ... strut, 13 ... holder, 14, 15 ... arrow (turn Rolling direction), 20 ... light source, 21 ... beam splitter, 22 ... mirror, 23 ... interference mechanism, 24 ... interference space, 25 ... arrow (rotation direction)

Claims (2)

A glass material optical waveguide whose refractive index changes by irradiating light is irradiated with a predetermined wavelength of interference light emitted from the light irradiation mechanism, and the refractive index of the core of the irradiation section periodically changes in the core axis direction In a method of manufacturing an optical waveguide type diffraction grating,
A projection plate is arranged on the side opposite to the light irradiation mechanism and the light irradiation mechanism so as to sandwich the optical waveguide, and the optical waveguide is irradiated with two light beams forming the interference light on the projection plate. By projecting two optical waveguide images and adjusting an angle θ formed by a line connecting the two images and the axis of the projected optical waveguide image, an interference fringe having a refractive index formed in the core portion. normal to, the angle between the core shaft forms θ is the diffraction grating, characterized in that it comprises an adjusting step of adjusting the direction of the light irradiation mechanism relative to the optical waveguide to be equal to or less than a predetermined value Production method.   2. The method of manufacturing an optical waveguide type diffraction grating according to claim 1, wherein the angle [theta] is adjusted to be 1.0 [deg.] Or less.

Images