JP4279227B2 - Manufacturing method and manufacturing apparatus for optical waveguide Bragg grating - Google Patents

Description

The present invention relates to a method and an apparatus for forming an optical waveguide Bragg grating, which is a diffraction grating that reflects light of a specific wavelength, on an optical waveguide by irradiating with ultraviolet laser light.

A Bragg grating formed on an optical waveguide consisting of a planar waveguide or optical fiber is a periodic refractive index change applied to the core of the optical waveguide. It reflects only incident light of a specific wavelength, and other light. Is a light filter that allows all to pass through. For example, as described in Non-Patent Document (1) and Non-Patent Document (2), an optical waveguide Bragg grating has low transmission loss, excellent reflection characteristics and transmission characteristics, and uses optical signals. Widely applied to various devices, apparatuses, and systems, for example, high-density wavelength multiplexing optical communication equipment, laser diode external resonators, fiber laser resonators, various sensors such as temperature and strain.

として決まる。光導波路の屈折率をその長手方向に周期的に変化させてグレーティングを形成するには、通常、被覆樹脂を除去した光導波路にその長手方向に側面から、グレーティング周期に対応する周期的な強度分布を持たせた紫外線を照射し、光導波路（光ファイバー）のコア部にドープされているゲルマニウム（Ｇｅ）の紫外線に対する光誘起反応に基づく屈折率上昇の現象を利用してなされる。形成される屈折率変調の周期Λは、例えば、光ファイバーの実効屈折率ｎ_effが約１．４４７で、光通信によく用いられる波長の約１５５０ｎｍに対しては、式（９）の関係式から、Λ＝０．５３６μｍとなる。良好な光信号の反射特性を得るためにファイバーブラッググレーティングは、通常、この大きさの周期を約５ｍｍから約数１０ｍｍの長さに渡って形成され、１０ｍｍ長のファイバーブラッググレーティングではその周期の個数は、１０ｍｍ／０．５３６μｍとなり、すなわち約１９０００個のグレーティングが形成されている。 The reflection wavelength λ _FBG of the optical waveguide Bragg grating (also referred to as fiber Bragg grating in the case of an optical fiber) depends on the effective refractive index n _eff of the core portion of the optical waveguide and the period of refractive index modulation, that is, the grating period Λ.

Determined as. In order to form a grating by periodically changing the refractive index of the optical waveguide in its longitudinal direction, the periodic intensity distribution corresponding to the grating period is usually applied to the optical waveguide from which the coating resin has been removed from the side in the longitudinal direction. This is done by utilizing the phenomenon of refractive index increase based on the photo-induced reaction of germanium (Ge) doped in the core portion of the optical waveguide (optical fiber) with respect to the ultraviolet light. The refractive index modulation period Λ is, for example, that the effective refractive index n _eff of the optical fiber is about 1.447, and for the wavelength of about 1550 nm often used for optical communication, the relational expression of Equation (9) , Λ = 0.536 μm. In order to obtain good optical signal reflection characteristics, a fiber Bragg grating is usually formed with a period of this size ranging from about 5 mm to a length of about several tens of millimeters. Is 10 mm / 0.536 μm, that is, approximately 19000 gratings are formed.

As a method for forming such an optical waveguide Bragg grating, for example, as described in Non-Patent Document (1) and Non-Patent Document (2), a phase mask method and a two-beam interference method are roughly classified. Are known. The former phase mask method is disclosed in Patent Document (3), Non-Patent Document (4), and Non-Patent Document (5). In this phase mask method, an optical fiber is placed close to or in contact with the phase mask, the optical fiber is irradiated with ultraviolet laser light through the phase mask, and the + 1st order light and the −1st order diffracted by the phase mask are converted into the optical fiber. In this method, an ultraviolet light intensity distribution composed of interference fringes having a period Λ is formed by causing interference at a position, thereby forming a periodic refractive index modulation in the core portion in the longitudinal direction of the optical fiber.

In the latter two-beam interferometry, the ultraviolet laser beam is split into two beams, and then the two beams are crossed and interfered at the position of the optical waveguide to form an ultraviolet light intensity distribution consisting of interference fringes of period Λ. In this way, a periodic refractive index modulation is formed in the core portion in the longitudinal direction of the optical waveguide. The most basic method for realizing this method is disclosed in Patent Document (6), Patent Document (7), and Non-Patent Document (8), in which incident ultraviolet laser light transmits about 50% and remains. Two beams are split using a beam splitter that reflects about 50% of the beam, and each beam is crossed at the position of an optical waveguide (optical fiber) using a mirror. In the two-beam interference method, by changing the angle at which two beams intersect at the position of the optical waveguide, the period Λ of the interference fringes can be changed, and the reflection wavelength λ _FBG of equation (4) changes in proportion to this. Therefore, it has a feature that the reflection wavelength of the optical waveguide Bragg grating to be manufactured can be easily controlled. Various methods have been devised for beam splitting and crossing.

In Non-Patent Document (9), as described in Patent Document (3), Non-Patent Document (4), and Non-Patent Document (5), incident ultraviolet laser light is + 1st order by a phase mask. The two beams are split by using the fact that the light and the −1st order light are diffracted and split into two beams, that is, the phase mask has the function of a beam splitter. A method is disclosed in which a fiber Bragg grating is manufactured by making an incident on a square quartz block, reflecting the light from the side of the inner wall of the quartz block, emitting the light from the quartz block, and intersecting at the position of the optical fiber to form interference fringes. Further, in Non-Patent Document (10) and Non-Patent Document (11), in addition to the contents of Non-Patent Document (9), a Lloyd mirror method using a triangular prism is also described.
In order to cross the two beams branched by the beam splitter using two mirrors to obtain an interference fringe, it is necessary to invert one of the two diffraction grating images of the phase mask to achieve parity matching. It is disclosed in Non-Patent Document (12).
In the non-patent document (13), an ultraviolet laser beam is split into two beams using a phase mask as a beam splitter, and each beam is reflected by two mirrors and crossed at the position of the optical waveguide to cause interference. It has been shown by experiment that a strong fiber Bragg grating whose transmission blocking amount reaches -28 dB can be obtained by changing the reflection wavelength of the fiber Bragg grating over about 250 nm simply by changing the angle of the mirror. Non-Patent Document (16) shows the fabrication of an optical waveguide Bragg grating with the same configuration and the reflection wavelength changed from 600 nm to 1350 nm, and further inserts a cylindrical lens for wavefront control between the phase mask and two mirrors. We are also manufacturing fiber Bragg gratings with chirp.
Patent Document (14) and Patent Document (15) include Patent Document (3), Non-Patent Document (4), Non-Patent Document (5), Non-Patent Document (9), Non-Patent Document (10) and As disclosed in Non-Patent Document (11), an ultraviolet laser beam is split into two beams using a phase mask, and symmetrical as disclosed in Non-Patent Document (10) and Non-Patent Document (11). A method is described in which two mirrors arranged in the above are rotated to form fiber Bragg gratings with different reflection wavelengths as disclosed in Non-Patent Document (10) and Non-Patent Document (11).

In order to produce a good strong optical waveguide Bragg grating, interference fringes cannot be obtained unless the two beams strongly interfere with each other. Therefore, an ultraviolet laser with a longer coherent length indicating the degree of coherence is more reliably formed. be able to. Examples of ultraviolet lasers often used for optical waveguide Bragg grating fabrication include argon ion laser (oscillation wavelength 244 nm), KrF excimer laser (oscillation wavelength 248 nm), ArF excimer laser (oscillation wavelength 193 nm), etc. The coherent length is about several centimeters for an argon ion laser (oscillation wavelength 244 nm), and is about 1 mm or less for a KrF excimer laser and an ArF excimer laser. In many of the two-beam interference methods disclosed in the above-mentioned documents, an argon ion laser having a long coherence length is usually used. In the phase mask method, the optical waveguide Bragg grating is formed by bringing the optical fiber close to or in contact with the phase mask, so it is possible to easily and reliably form the optical waveguide Bragg grating even with an excimer laser beam having a short coherent length. It is. However, in the phase mask method, since the diffraction grating interval of the phase mask is fixed, the reflection wavelength of the optical waveguide Bragg grating to be manufactured is basically only one reflection wavelength with one phase mask, and different reflections. In order to fabricate an optical waveguide Bragg grating having a wavelength, it is necessary to prepare a large number of phase masks having different diffraction grating periods. In contrast, in the two-beam interference method, the angle at which the two beams intersect can be easily changed by adjusting the reflection angle of the mirror, so that optical waveguide Bragg gratings having different wavelengths can be easily manufactured. Has great features.

(1) Raman Kashyap: “Fiber Bragg Gratings”, Academic Press, (1999).
(2) Andreas Othonos, Kyriacos Kalli; “Fiber Bragg Gratings”, Artech House, Inc., (1999).
(3) Kenneth O. Hill, Bernard Y. Malo, Francois C. Bilodeau, Derwyn C. Johnson; “Method of creating an index grating in an optical fiber and a mode converter using the index grating”, USP-5,367,588, November 22 , 1994.
(4) KO Hill, B. Malo, F. Bilodeau, DC Johnson, J. Albert; “Bragg gratings fabricated in monomode coated optical fiber by UV exposure through a phase mask,” Appl. Phys. Lett. Vol. 62, No 10 (1993) 1035-1037.
(5) KO Hill, F. Bilodeau, B. Malo, T. Kitagawa, S. Theriault, DC Johnson, J. Albert; “Chirped in-fiber Bragg gratings for compensation of optical-fiber dispersion,” Opt. Lett. Vol. 19, No. 17 (1994) 1314-1316.
(6) William H. Glenn, Gerald Meltz, Elias Snitzer; “Method for impressing gratings within fiber optics”, USP-4,725,110, February 16, 1988.
(7) William H. Glenn, Gerald Meltz, Elias Snitzer; “Method for impressing gratings within fiber optics”, USP-4,807,950, February 28, 1989.
(8) G. Meltz, WW Morey, WH Glenn; “Formation of Bragg gratings in optical fibers by a transverse holographic method,” Optics Letters, Vol. 14, No. 15, pp. 823-825 (1989).
(9) R. Kashyap, JR Armitage, R. Wyatt, ST Davey, DL Williams; “All-fibre narrowband reflection gratings at 1500 nm,” Electron. Lett. Vol. 26, No. 11, pp. 730-732 (1990 ).
(10) R. Kashyap, JR Armitage, RJ Campbell, DL Williams, GD Maxwell, BJ Ainslie, CA Miller; “Light-sensitive optical fibers and planar waveguides”, BT Technol. J., vol. 11, No. 11, pp. 150-160 (1993)
(11) R. Kashyap, “Photosensitive optical fibers: Devices and applications,” Optical Fiber Technol. No. 1, pp. 17-34 (1994).
(12) CG Askins, TE Tsai, GM Williams, MA Putnam, M. Bashinsky, EJ Friebele; “Fiber Bragg reflectors prepared by a single excimer pulse,” Opt. Lett. Vol. 17, No. 11, (1992) 833 -835.
(13) R. Kashyap; “Assesment of tuning the wavelength of chirped and unchirped fiber Bragg grating with single phase mask,” Electronic Letters, Vol. 34, No. 21, pp. 2025-2026 (1998).
(14) Robert A. Modavis; “Method of forming a grating in an optical waveguide”, USP-5,818,988, October 6, 1998.
(15) Robert Adams Modavis; “Method of forming a grating in an optical waveguide”, JP-A-10-54915, (1998).
(16) Y. Wang, J. Grant, A. Sharma, G. Myers; “Modified Talbot interferometer for fabrication of fiber-optic grating filter over a wide range of Bragg wavelength and bandwidth using a single phase mask”, Journal of Lightwave technology , vol. 19, No. 10, pp. 1569-1573 (2001).
(17) Koji Teruse, Hiroyoshi Saito, Shunichi Tanaka, Junpei Takiuchi, Takeshi Namioka; “Optical Engineering Handbook”, Asakura Shoten, pp. 475-476 (1986).

In the two-beam interference method, it is necessary to fix optical components such as a beam splitter, phase mask, and mirror and an optical waveguide with high precision, and it is easy to adjust the mirror angle to obtain optical waveguide Bragg gratings with different reflection wavelengths. As described in Non-Patent Document (13), the phase mask and the optical waveguide are arranged in parallel, the ultraviolet laser beam is incident vertically, and the two mirrors are arranged at symmetrical positions. It is desirable to do. The reason for this is that the arrangement of the component parts and the optical waveguide is simplified due to symmetry, so that the position adjustment is facilitated and a highly accurate arrangement is possible. However, in this method, in order to obtain optical waveguide Bragg gratings with different reflection wavelengths, as shown in FIG. 1, two mirrors are rotated symmetrically by the same angle, and then the two beams interfere with the position of the optical waveguide. You must move to the position where you want to go. In FIG. 1, the rotation angle of the mirror 2, the diffraction angle of the two beams by the phase mask, etc. are exaggerated for easy understanding, and the horizontal ratio is not accurate. In order to realize optical waveguide Bragg gratings with high reproducibility by using the two-beam interferometry method, which requires high-precision optical component placement, and to produce with a high yield, change the placement of optical components as much as possible. is required. The problem of the present invention is that when obtaining optical waveguide Bragg gratings of different wavelengths as seen in the prior art, instead of changing the position of the optical waveguide each time, the optical waveguide is fixed at one position and It is to obtain optical waveguide Bragg gratings of different wavelengths simply by rotating the mirror symmetrically.

The theory underlying the present invention for solving this problem will be described below, and then the features of the present invention will be described.
First, the relationship of the arrangement of optical components in the conventional mirror center rotation method will be described, and then the relationship of the arrangement of optical components in the mirror rotation axis eccentricity method of the present invention will be described. Here, the mirror center rotation method is a configuration in which the reflection position on the mirror that reflects the two beams and the position of the mirror rotation axis for adjusting the mirror reflection angle are substantially the same position. The core system is defined as a configuration in which the position of the mirror rotation axis for adjusting the mirror reflection angle is in the vicinity of the optical waveguide away from the mirror reflection position.

である。ここでｐは位相マスクの回折格子の周期で、λ_Ｅは照射する紫外線レーザーの波長である。位相マスク１による回折で２つのビームに分岐された±１次光は垂直方向から角度αだけ傾いたミラー２で反射され、光導波路４の位置で重なる。角度βで光導波路に入射する＋１次光と角度−βで入射する−１次光が干渉し、干渉縞の間隔Λは

で規定され、屈折率変調の周期がΛの光導波路ブラッググレーティングが形成される。実効屈折率ｎ_effの光ファイバーでは反射波長λ_FBGは式（１１）のΛを式（９）に代入して、

となる。図２に示すように、２つのミラーの間隔を２ｓ、ミラー回転軸３と位相マスク１の垂直方向距離をＬ_１、ミラー回転軸３と光導波路４の垂直方向距離をＬ_２、位相マスク１と光導波路４の距離をＬとし、ミラー２の回転角をαとしたとき、

が得られ、このＬの位置で２つのビームが干渉し、その位置に光導波路４を設置すれば光導波路ブラッググレーティングが形成される。この場合、位相マスク１とミラー回転軸３の間の垂直方向距離ｕはＬ_１である。光導波路ブラッググレーティングの反射波長λ_FBGは、２光束の入射角

を式（１２）に代入して、

となる。実効屈折率ｎ_effは標準的なシングルモードファイバーＳＭＦ２８では、ｎ_eff＝１．４４７である。
以上が従来技術のミラー中心回転方式における関係式である。次に、本発明のミラー回転軸偏芯方式について説明する。 FIG. 2 shows an arrangement of optical components in a conventional mirror center rotation system (for example, Non-Patent Document (13)). The ultraviolet laser incident on the phase mask 1 is diffracted into + 1st order light and −1st order light at an angle θ and emitted left and right as shown. This angle θ is

It is. Here, p is the period of the diffraction grating of the phase mask, and λ _E is the wavelength of the ultraviolet laser to be irradiated. The ± first-order light branched into two beams by diffraction by the phase mask 1 is reflected by the mirror 2 inclined by an angle α from the vertical direction and overlaps at the position of the optical waveguide 4. The + 1st order light incident on the optical waveguide at an angle β interferes with the −1st order light incident at an angle −β.

And an optical waveguide Bragg grating having a refractive index modulation period of Λ is formed. For an optical fiber having an effective refractive index n _eff , the reflection wavelength λ _FBG is calculated by substituting Λ in equation (11) into equation (9),

It becomes. As shown in FIG. 2, the distance between the two mirrors is 2 s, the vertical distance between the mirror rotation axis 3 and the phase mask 1 is L ₁ , the vertical distance between the mirror rotation axis 3 and the optical waveguide 4 is L ₂ , and the phase mask 1 And the distance of the optical waveguide 4 is L, and the rotation angle of the mirror 2 is α,

The two beams interfere with each other at the position L, and an optical waveguide Bragg grating is formed by installing the optical waveguide 4 at that position. In this case, the vertical distance u between the phase mask 1 and the mirror rotating shaft 3 is L _1. The reflection wavelength λ _FBG of the optical waveguide Bragg grating is the incident angle of the two beams.

Is substituted into equation (12),

It becomes. The effective refractive index n _eff is n _eff = 1.447 for a standard single mode fiber SMF28.
The above is the relational expression in the conventional mirror center rotation method. Next, the mirror rotation shaft eccentricity system of the present invention will be described.

が成り立つから、

が得られ、

となり、位相マスク１と光導波路４の垂直方向距離Ｌは

となり、このＬの位置で２つのビームが干渉し、その位置に光導波路４を設置すれば光導波路ブラッググレーティングが形成される。式（２２）でｕ＝Ｌ_１と置けばミラー中心回転方式におけるＬが得られ、式（１４）と同じになることが確認できる。位相マスク１と光導波路４の垂直方向距離Ｌは、式（２２）を用いてミラー回転軸間隔の半値ｓ、位相マスク１とミラー２のビーム反射の垂直方向距離ｕ、ミラー回転角α、および位相マスクによる±１次光回折角度θから決まる。位相マスクの回折角θは紫外線レーザーの波長λ_Ｅと位相マスクの回折格子の周期ｐから式（１０）で求められる。光導波路ブラッググレーティングの反射波長λ_FBGは、ミラー中心回転方式と同じように、式（１５）で規定される２つのビームの光導波路への入射角βを用いて、式（１６）で求まる。請求項記載の式（１）、式（３）、式（５）および式（７）は、式（２２）と同じである。以下に、式（２２）を用いて計算した結果を述べ、異なる波長の光導波路ブラッググレーティングを形成するためにミラーを回転させるとき、ミラー回転軸を適切な位置に偏芯させることで、光ファイバーの位置は、その都度調整する必要はなく固定して行うことが出来ることを証明する。 FIG. 3 shows the arrangement of optical components according to the mirror rotation axis eccentricity system of the present invention. The vertical distance from the phase mask 1 to the beam reflection position on the surface of the mirror 2 is L ₁ , the vertical distance from the beam reflection position to the optical fiber 4 is L ₂ , and the vertical distance from the phase mask 1 to the optical waveguide 4 is L, if the vertical distance from the phase mask 1 to the mirror rotation axis 3 is u, and the distance between the two mirror rotation axes is 2 s,

Because

Is obtained,

The vertical distance L between the phase mask 1 and the optical waveguide 4 is

Thus, the two beams interfere with each other at the position L, and an optical waveguide Bragg grating is formed by installing the optical waveguide 4 at that position. If u = L ₁ is set in Expression (22), L in the mirror center rotation method can be obtained, and it can be confirmed that it is the same as Expression (14). The vertical distance L between the phase mask 1 and the optical waveguide 4 is obtained by using equation (22), the half value s of the mirror rotation axis interval, the vertical distance u of the beam reflection between the phase mask 1 and the mirror 2, the mirror rotation angle α, and It is determined from the ± first-order light diffraction angle θ by the phase mask. The diffraction angle θ of the phase mask is obtained by the equation (10) from the wavelength λ _{E of the} ultraviolet laser and the period p of the diffraction grating of the phase mask. The reflection wavelength λ _FBG of the optical waveguide Bragg grating is obtained by Expression (16) using the incident angles β of the two beams defined by Expression (15) to the optical waveguide, as in the mirror center rotation method. The formula (1), formula (3), formula (5) and formula (7) described in the claims are the same as the formula (22). In the following, the results calculated using Equation (22) are described, and when the mirror is rotated to form optical waveguide Bragg gratings of different wavelengths, the optical axis of the optical fiber is decentered at an appropriate position when the mirror is rotated. It proves that the position can be fixed without having to adjust each time.

The wavelength λ _E of the irradiating ultraviolet laser is set to the wavelength 248 nm of the KrF excimer laser, the period p of the diffraction grating of the phase mask is set to 1072.34 nm, the half value s of the mirror interval is set to 29.7143 mm, and several phase masks and mirror rotations The results of calculating the vertical distance L between the phase mask and the optical waveguide with respect to the vertical distance u between the axes are shown in FIGS. 4A and 4B. The optical waveguide Bragg grating reflection wavelength λ _FBG and the mirror rotation are shown in FIGS. The dependence of the angle α on the vertical distance L between the phase mask and the optical waveguide is shown. # 1 in the figure is the result for the mirror center rotation method when u = L ₁ = 125 mm. In the figure, # 2, # 3, # 4, # 5, and # 6 are the results calculated for u = 227 mm, 242 mm, 257 mm, 272 mm, and 287 mm, respectively, for the mirror rotation axis eccentricity method. For the effective refractive index n _{eff, the} value n _eff = 1.447 for a standard single mode fiber SMF 28 was used. In the phase mask method in which an optical waveguide Bragg grating is formed by using a phase mask having a diffraction grating period p of 1072.34 nm and bringing the optical waveguide close to or in contact with the phase mask, the diffraction grating of the phase mask is directly used as the optical waveguide. Since the grating period Λ becomes p / 2 due to the transfer, an optical waveguide Bragg grating having a reflection wavelength of λ _FBG = 2 × 1.447 × 1072.34 / 2≈1552 nm is formed from the equation (9). As can be seen from FIG. 4A, in the two-beam interference method, the optical waveguide Bragg grating of this reflection wavelength is obtained at α = 0 where the phase mask and the mirror are at right angles. FIGS. 4A and 4B show the results of calculating the reflection wavelength λ _FBG for an extremely wide band from 800 nm to 2000 nm.
FIG. 5 shows the result obtained by calculating the dependence of the reflection wavelength of the optical waveguide Bragg grating on the mirror rotation angle α from the equation (16). The reflection wavelength λ _FBG is determined by the incident angle β = θ−2α, the effective refractive index n _eff, and the wavelength λ _E of the ultraviolet laser with respect to the optical waveguide, as can be seen from the equation (16). Since there is no direct dependence on the vertical distance u between the rotation axes, there is no difference between the mirror center rotation system and the mirror rotation axis eccentricity system.
As can be seen from curve # 1 in FIGS. 4A and 6B, in the conventional mirror center rotation method, the vertical distance L between the phase mask and the optical waveguide is large in order to change the reflection wavelength. You have to change and adjust each time. On the other hand, in the mirror rotation axis decentering method of the present invention, even if the reflection wavelength λ _FBG is changed, it can be made substantially constant with respect to the vertical distance L between the phase mask and the optical waveguide, so L is adjusted. Doing so can be unnecessary. That is, as shown in # 2, # 3, # 4, # 5, and # 6 in the figure, the vertical distance u between the phase mask and the mirror rotation axis can be changed so that the curve becomes almost vertical. In the case of the figure, when u = 257 mm of # 4, it is optimized so as to be almost vertical, and the reflection wavelength λ _FBG does not depend on the vertical distance L between the phase mask and the optical fiber. Of course, it cannot be made completely constant, but it is not necessary to adjust the vertical distance L between the phase mask and the optical waveguide in order to produce optical waveguide Bragg gratings with different reflection wavelengths. It is possible to fix.
FIG. 6A and FIG. 6B show the results obtained by enlarging FIG. 4A and FIG. 4B with respect to the 1500 nm to 1600 nm band that sufficiently covers the C band band (1530 to 1570 nm). Show. With respect to this wide bandwidth of 100 nm, when u = 257 mm of # 4, it is almost completely vertical. The result of further enlarging the horizontal axis L with respect to # 4 is shown in FIGS. The vertical distance L between the phase mask and the optical waveguide changes only by 0.0067 mm as shown by the arrows over a wide band of 100 nm. However, in the case of # 1 of the mirror center rotation method, it can be seen from FIG. 6A that the wavelength width must be changed by about 8 mm.

When an excimer laser is used as the light source of the ultraviolet laser, the coherent length is around 1 mm or less, and the difference in the optical path length from the phase mask of the two beams to the optical waveguide is sufficient for realizing sufficient interference. It must overlap within a length of around 1mm. For an allowable amount of around 1 mm, the change amount 0.0067 mm of the vertical distance L between the phase mask and the optical waveguide in the mirror rotation axis eccentricity method of the present invention can be completely ignored, and the position of the optical waveguide is No adjustment is necessary.

In the mirror center rotation system of the prior art, the mirror rotation axis is arranged at the substantially middle point of the mirror, but in the mirror rotation axis eccentricity system of the present invention, it is in the vicinity of the optical waveguide. Here, the vicinity means a position where the mirror rotation axis is decentered to the front and back of the position of the optical waveguide with a very large vertical distance L from the phase mask as shown in FIG. When the mirror rotation axis is decentered in this way, the position where the beams reflected by the two mirrors intersect and interfere, that is, the position where the optical waveguide is disposed is ∂L / ∂α≈0. This is realized by selecting the optimum value of u. In the above calculation, when the half value s between the two mirrors is 29.7143 mm, and the distance L from the phase mask to the optical waveguide is 250 mm, the vertical distance u from the phase mask of the two mirror rotation axes is It became optimal at 257 mm.

From the above theory, in the mirror rotation axis eccentricity system of the present invention, the position of the optical waveguide is not adjusted, and if it is fixed at one position according to the value calculated from the above theory, then the mirror can be simply rotated. It was proved that optical waveguide Bragg gratings with different wavelengths can be fabricated. Next, the characteristics of the present invention developed based on this theory will be described.

The first feature of the present invention is that ultraviolet laser light is incident on a phase mask, is split into two beams using the diffraction phenomenon of the phase mask, and the two split beams are transferred from the phase mask to the phase mask. Are emitted symmetrically with respect to the incident axis of the ultraviolet laser light, and two beams are reflected by two mirrors arranged symmetrically at substantially right angles to the phase mask surface, and the two beams reflected by the mirrors are reflected on the optical waveguide. Using two-beam interferometry that intersects two beams by crossing at positions, two mirrors are rotated symmetrically to adjust the period of interference, and gratings with different reflection wavelengths are formed in the optical waveguide for reflection. In a method of manufacturing optical waveguide Bragg gratings with different wavelengths, the rotation axes of the two mirrors are decentered from the midpoint of the phase mask and the optical waveguide and placed in the vicinity of the optical waveguide. , In which position the two beams intersect, characterized in that it is substantially independent to the mirror rotation angle.
Here, the reason why the relative angle between the phase mask surface and the two mirrors is substantially perpendicular is that in FIG. 6 where the reflection wavelength λ _FBG is changed over 100 nm, the mirror rotation angle is ± 0.2 degrees. This is because even in the case of FIG. 4 changed over 1200 nm, the angle is as small as −6 to +2 degrees. The fact that the position of the optical waveguide is substantially independent of the mirror rotation angle means that if the position of the optical waveguide is fixed at the position required by the above theory, in order to obtain an optical waveguide Bragg grating with a different reflection wavelength, This means that it becomes possible by simply rotating the lens, and it is unnecessary to readjust the position of the optical waveguide.
In the description of the present invention, the method and apparatus for forming the optical waveguide Bragg grating on the most typical optical fiber of the optical waveguide is mainly described. However, the optical waveguide Bragg grating is applied to the optical waveguide such as a planar waveguide. Of course, it can be applied to the forming method and manufacturing.

この式は、２つのミラーを平行からα度回転させたとき、式（２２）に沿って、位相マスクと光ファイバーの垂直方向距離Ｌを∂Ｌ／∂α＝０となるように最適化した値からのズレ量ΔＬに対する許容量を規定するものであり、許容される量は実験から求めなければならない。これについては後述する我々が行った実施例２で述べる。式（２２）で規定されるＬおよびｕを選んだとき、Ｌのミラー回転角度αに対する依存性が式（２３）を満たすようにｕを選定すれば良好な光導波路ブラッググレーティングを形成することが可能となる。式（１）と式（２２）は同じであり、式（２）と式（２３）は同じである。 The second feature of the present invention is that, in the first feature described above, u satisfying the equation (22) and the following equation (23) in the positional relationship between the phase mask, the two mirrors, the mirror rotation axis, and the optical waveguide is obtained. It is characterized by being selected.

This equation is a value obtained by optimizing the vertical distance L between the phase mask and the optical fiber so that ∂L / ∂α = 0 along the equation (22) when the two mirrors are rotated from the parallel by α degrees. The allowable amount with respect to the deviation amount ΔL is defined, and the allowable amount must be obtained from experiments. This will be described in Example 2 which was performed later. When L and u defined by equation (22) are selected, a good optical waveguide Bragg grating can be formed if u is selected so that the dependency of L on the mirror rotation angle α satisfies equation (23). It becomes possible. Expressions (1) and (22) are the same, and expressions (2) and (23) are the same.

この式は、２つのミラーを平行からα度回転させたとき、式（２２）に沿って、位相マスクと光ファイバーの垂直方向距離Ｌを∂Ｌ／∂α＝０となるように最適化した条件において、位相マスクと光導波路の垂直方向距離ｕに対する許容量を規定するものであり、許容される量は実験から求めなければならない。これについては後述する我々が行った実施例２で述べる。式（２２）で規定されるＬおよびｕを選んだとき、Ｌのミラー回転角度αに対する依存性が式（２４）を満たすようにｕを選定すれば良好な光導波路ブラッググレーティングを形成することが可能となる。式（３）と式（２２）は同じであり、式（４）と式（２４）は同じである。 According to a third feature of the present invention, in the first feature described above, u satisfying Expression (22) and the following Expression (24) is satisfied in the positional relationship between the phase mask, the two mirrors, the mirror rotation axis, and the optical waveguide. It is characterized by being selected.

This equation is a condition in which the vertical distance L between the phase mask and the optical fiber is optimized so that ∂L / ∂α = 0 along the equation (22) when the two mirrors are rotated from the parallel by α degrees. In this example, an allowable amount with respect to the vertical distance u between the phase mask and the optical waveguide is defined, and the allowable amount must be obtained from an experiment. This will be described in Example 2 which was performed later. When L and u defined by equation (22) are selected, a good optical waveguide Bragg grating can be formed if u is selected so that the dependency of L on the mirror rotation angle α satisfies equation (24). It becomes possible. Expressions (3) and (22) are the same, and expressions (4) and (24) are the same.

A fourth feature of the present invention relates to an optical waveguide Bragg grating manufacturing apparatus that realizes the first feature described above. As a result, a high-performance optical waveguide Bragg grating can be manufactured with high reproducibility and can be manufactured with a high yield.

この式は、２つのミラーを平行からα度回転させたとき、式（２２）に沿って、位相マスクと光ファイバーの垂直方向距離Ｌを∂Ｌ／∂α＝０となるように最適化した値からのズレ量ΔＬに対する許容量を規定するものであり、許容される量は実験から求めなければならない。これについては後述する我々が行った実施例２で述べる。式（２２）で規定されるＬおよびｕを選んだとき、Ｌのミラー回転角度αに対する依存性が式（２５）を満たすようにｕを選定すれば良好な光導波路ブラッググレーティングを形成することが可能となる。式（５）と式（２２）は同じであり、式（６）と式（２５）は同じである。 According to a fifth feature of the present invention, in the fourth feature described above, u satisfying Expression (22) and the following Expression (25) is satisfied in the positional relationship between the phase mask, the two mirrors, the mirror rotation axis, and the optical waveguide. It is characterized by being selected.

This equation is a value obtained by optimizing the vertical distance L between the phase mask and the optical fiber so that ∂L / ∂α = 0 along the equation (22) when the two mirrors are rotated from the parallel by α degrees. The allowable amount with respect to the deviation amount ΔL is defined, and the allowable amount must be obtained from experiments. This will be described in Example 2 which was performed later. When L and u defined by Expression (22) are selected, a good optical waveguide Bragg grating can be formed if u is selected so that the dependency of L on the mirror rotation angle α satisfies Expression (25). It becomes possible. Expressions (5) and (22) are the same, and expressions (6) and (25) are the same.

この式は、２つのミラーを平行からα度回転させたとき、式（２２）に沿って、位相マスクと光ファイバーの垂直方向距離Ｌを∂Ｌ／∂α＝０となるように最適化した条件において、位相マスクと光導波路の垂直方向距離ｕに対する許容量を規定するものであり、許容される量は実験から求めなければならない。これについては後述する我々が行った実施例２で述べる。式（２２）で規定されるＬおよびｕを選んだとき、Ｌのミラー回転角度αに対する依存性が式（２６）を満たすようにｕを選定すれば良好な光導波路ブラッググレーティングを形成することが可能となる。式（７）と式（２２）は同じであり、式（８）と式（２６）は同じである。 The sixth feature of the present invention is that in the fourth feature described above, u satisfying Expression (22) and the following Expression (26) is satisfied in the positional relationship between the phase mask, the two mirrors, the mirror rotation axis, and the optical waveguide. It is characterized by being selected.

This equation is a condition in which the vertical distance L between the phase mask and the optical fiber is optimized so that ∂L / ∂α = 0 along the equation (22) when the two mirrors are rotated from the parallel by α degrees. In this example, an allowable amount with respect to the vertical distance u between the phase mask and the optical waveguide is defined, and the allowable amount must be obtained from an experiment. This will be described in Example 2 which was performed later. When L and u defined by equation (22) are selected, a good optical waveguide Bragg grating can be formed if u is selected so that the dependency of L on the mirror rotation angle α satisfies equation (26). It becomes possible. Expressions (7) and (22) are the same, and Expressions (8) and (26) are the same.

Note that the light diffracted from the phase mask is usually diffracted not only with ± first-order light but also with high-order diffracted light such as zero-order light, ± second-order light, and ± third-order light, although the intensity is weak. Since the high-order diffracted light is emitted outside the apparatus and discarded, it does not affect the fiber grating fabrication. The zero-order light is irradiated onto the optical fiber. In this case, the influence can be easily and easily removed by placing a shielding object between the two mirrors.

Ultraviolet laser light is incident on the phase mask, and is split into two beams using the diffraction phenomenon, symmetrically arranged with respect to the ultraviolet laser light incident axis to the phase mask and symmetrically at a right angle to the phase mask surface. The two mirrors reflect the two beams respectively, the two beams intersect at the position of the optical waveguide, the two beams interfere, the two mirrors rotate symmetrically, and the period of interference is adjusted to be different. In a method of manufacturing an optical waveguide Bragg grating in which an optical waveguide Bragg grating having a reflection wavelength is formed on the optical waveguide, the mirror center rotation method of the prior art changes the mirror angle to obtain an optical waveguide Bragg grating having a different reflection wavelength. Each time, the position of the optical waveguide must be changed and adjusted so that the two beams interfere with each other. On the other hand, the rotation axis of the two mirrors is decentered from the midpoint of the phase mask and the optical waveguide and arranged in the vicinity of the optical waveguide, and the position where the two beams intersect is substantially independent of the mirror rotation angle. According to the mirror rotation axis eccentricity system of the present invention, it is not necessary to change the position of the optical waveguide at all, and it is possible to obtain optical waveguide Bragg gratings having different reflection wavelengths with high accuracy simply by changing the mirror rotation angle. Is possible. At this time, if the position where the mirror rotation axis is decentered is selected so as to satisfy Expression (23) or Expression (24) with respect to L defined by Expression (22), a good optical waveguide Bragg The grating can be manufactured with high accuracy.
In the two-beam interference method, optical components such as beam splitters, phase masks, mirrors, and optical waveguides need to be arranged with high precision, and optical waveguide Bragg gratings can be manufactured with high reproducibility and manufactured with high yield. Therefore, it is necessary to avoid changing the arrangement of the optical components as much as possible. If the mirror rotation axis eccentricity method of the present invention is adopted, the position of the optical waveguide is fixed, so that high reproducibility can be realized and an optical waveguide Bragg grating can be manufactured with a high yield.
Furthermore, in the optical waveguide Bragg grating manufacturing apparatus based on the mirror rotation axis eccentricity system of the present invention, the drive mechanism for changing the position of the optical waveguide and its control become unnecessary, and the number of parts of the apparatus can be reduced. The device can be simplified, and the manufacturing cost of the device can be reduced.

In the best mode of the present invention, in the positional relationship of the phase mask, the two mirrors, the mirror rotation axis, and the optical fiber arranged as shown in FIG. 3, L defined by Equation (22) changes the mirror rotation angle α. Is realized by selecting u so that ∂L / ∂α≈0. We designed the optical waveguide Bragg grating manufacturing equipment to meet this requirement.
With the apparatus manufactured in this way, we conducted an experiment for manufacturing a fiber Bragg grating and confirmed the effect of the present invention. The experimental results are described below.

本実施例の実験により、ミラー回転軸偏芯方式のファイバーブラッググレーティング形成装置を作製して、光ファイバー位置を固定して、ミラー回転角だけを変えて異なる反射波長のファイバーブラッググレーティングが高い波長精度で作製できると言う本発明の方法の有効性が、充分に実証された。 In the manufactured fiber Bragg grating manufacturing apparatus, a phase mask, two mirrors, a mirror rotation axis, and an optical fiber were arranged as shown in FIG. The diffraction grating period p of the used phase mask is 1072.34 nm. The half value s of the distance between the rotation axes of the two mirrors is 29.7143 mm, and the vertical distance u between the phase mask and the mirror rotation axis is 257 mm. The position of the optical fiber was fixed at a position where the vertical distance L from the phase mask was 250 mm. Note that the line connecting the mirror 2 and the mirror rotation axis 3 intersects the optical fiber 4 in FIG. 3, but in the configuration of the apparatus in which these are arranged, the mirror rotation axis mechanism is perpendicular to the paper surface of FIG. If arranged by changing the height, they will not interfere with each other. These positional relationships were determined by designing so that ∂L / ∂α = 0 in the formula (22) of the mirror rotation axis eccentricity system of the present invention.
The ultraviolet laser used was a KrF excimer laser with a wavelength λ _E of 248 nm (Compex-102MJ manufactured by Lambda Physics, with unstable resonator), and the emitted beam was shaped with a 7.5 mm x 7.5 mm slit, and the following experiment Then, the emission energy density was 30 mJ / (7.5 mm × 7.5 mm), and the repetition frequency was 20 Hz. The length of the produced fiber Bragg grating is determined by the width of the slit and is 7.5 mm. The optical fiber used was the most standard single mode fiber SMF28, and in order to increase the sensitivity to excimer laser light, prior to the experiment, it was kept in a hydrogen gas atmosphere at 100 atm for 10 days at room temperature and subjected to hydrogen loading treatment. . In the incidence to the fiber Bragg grating manufacturing apparatus, after being squeezed with a cylindrical lens having a focal length of 451.9 mm, it was incident as shown in FIG. The aperture by the cylindrical lens was stopped in the direction perpendicular to the plane of the beam branched into two by the phase mask and the optical axis of the incident excimer laser beam, and the energy per unit area was increased about 12 times at the position of the optical fiber. The influence of the 0th-order light diffracted from the phase mask was removed by placing a shield between the two mirrors.
In the experiment, the distance L from the phase mask was fixed at a position of 250 mm without changing the position of the optical fiber, and only the mirror rotation angle α was changed to produce seven fiber Bragg gratings. The reflection and transmission spectra of the fiber Bragg grating were measured with two spectrum analyzers (Q8384 manufactured by Advantest Co., Ltd.) by putting light of an ASE light source (ASE-FL7701 light source manufactured by Fiber Lab Co., Ltd.) into the optical fiber. Excimer laser light was irradiated for 2.5 minutes.
FIG. 8A shows the transmission spectrum of the seven fiber Bragg gratings obtained in the experiment, and FIG. 8B shows the reflection spectrum. Table 1 shows the mirror rotation angle α and the reflection wavelength λ _E (experimental values and theoretical values calculated by the equations (15) and (16)). FIG. 9 shows the dependence of the reflection wavelength λ _{FBG on} the mirror rotation angle α, where the ● mark is an experimental value and the solid line is a theoretical value. In the device we fabricated, the mirror rotation angle α can be varied sufficiently in the corresponding range from the reflection wavelength λ _FBG = 800 nm to 2000 nm, but the light source used to see the transmission and reflection spectra (manufactured by Fiber Labs) Since the ASE-FL7701 light source) only outputs light having a wavelength in the range of 1500 to 1620 nm, seven fiber Bragg gratings were produced within this range. As can be seen from FIG. 9 and Table 1, the variation in the difference between the experimental value and the theoretical value of the reflection wavelength was as low as 0.15 nm among the seven fiber Bragg gratings, and it was possible to fabricate with very high accuracy. The depth of the transmission blocking amount varies between about 5 dB between different fiber Bragg gratings as shown in FIG. 8A, but this can be made uniform by adjusting the laser irradiation time. It is easily possible with the device according to the invention.

According to the experiment of the present embodiment, a fiber Bragg grating forming device of the mirror rotation axis eccentricity type is manufactured, the position of the optical fiber is fixed, and only the mirror rotation angle is changed, so that the fiber Bragg gratings of different reflection wavelengths have high wavelength accuracy. The effectiveness of the method of the present invention that it can be produced has been fully demonstrated.

と表される。このことは、ミラー回転軸の位置に関しては、位相マスクからミラー回転軸ｕに対して、我々の前述理論計算と実験ではｕ＝２５７ｍｍであるから、許容範囲ΔＬに対して

とも表すことが出来る。
ここで求めたＬの許容量ΔＬは、２つのビームの干渉しやすさに依存しており、これは使用する紫外線レーザーのコヒーレント長に比例する（非特許文献（１７））。エキシマレーザーのコヒーレント長は数ｍｍあるいはそれ以下であり、ファイバーブラッググレーティング作製に用いられる他の紫外線レーザー、例えば波長２４４ｎｍのアルゴンイオンレーザーではその約１０倍のコヒーレント長を有しており、この場合は、Ｌの許容量ΔＬは約１０倍となり、式（２７）の約１０倍の

が許容量となる。同じように式（２８）の許容範囲も約１０倍となり、ｕ／Ｌが１．０２８±０．０４の範囲にあればよいことになる。これはＬに対する許容量であるばかりでなく、ｕに対する許容量でもあるため、

となる。式（２９）は式（２３）および式（２５）と同じで、式（３０）は式（２４）および式（２６）と同じである。
本実施例の実験により、光ファイバーの位置およびミラー回転軸の位置が上述の範囲内にあれば、ミラー回転角だけを変えて異なる反射波長のファイバーブラッググレーティングが高い波長精度で作製できると言う本発明の方法の有効性が実証された。 In the first embodiment, the position of the optical fiber is fixed at a position where the vertical distance L from the phase mask is 250 mm. However, in this embodiment, the position of the optical fiber is intentionally changed to change the position of the fiber Bragg grating. An experiment was conducted to examine how the strength, that is, the amount of transmission blocking changes, and the sensitivity was examined.
In the experiment, the mirror rotation angle α is set to 0.019 degrees, and the vertical distance L from the optical fiber phase mask is offset within the range of −2.5 mm to 3.5 mm with reference to the optimum value of 250 mm. A Bragg grating was produced. The excimer laser had the same energy and frequency as in Example 1, and the irradiation time was 3 minutes. The result is shown in FIG. Here, the offset amount ΔL is defined as + in the direction in which the position of the optical fiber moves away from the phase mask, and in the direction in which it approaches. When this offset amount ΔL was zero, a strong fiber Bragg grating with a transmission blocking amount of −34 dB could be produced. When the offset amount ΔL is changed from this state, if ΔL is ± 2 mm or more, the transmission blocking amount is shallower than about −10 dB, but if ΔL is ± 1 mm or less, a deep fiber Bragg grating can be produced. It was.
From this experiment, it was found that the allowable amount of deviation from the optimum value with respect to the vertical distance L from the optical fiber phase mask in our apparatus is ± 1 mm or less. This experimental result means that in FIG. 6A of the theoretical calculation, a good fiber Bragg grating can be produced if the deviation ΔL from the value optimized by L on the horizontal axis is within a range of ± 1 mm. The mirror rotation angle α corresponding to this is Δα = ± 0.2 degrees from FIG. 6B. Therefore, since L is 250 mm, the allowable range for L is

It is expressed. This is because, with respect to the position of the mirror rotation axis, from the phase mask to the mirror rotation axis u, in our previous theoretical calculation and experiment, u = 257 mm.

Can also be expressed.
The permissible amount ΔL of L obtained here depends on the ease of interference between the two beams, which is proportional to the coherent length of the ultraviolet laser used (Non-patent Document (17)). The excimer laser has a coherent length of a few millimeters or less, and other ultraviolet lasers used to fabricate fiber Bragg gratings, such as an argon ion laser with a wavelength of 244 nm, have a coherent length of about 10 times that. , L allowance ΔL is about 10 times, about 10 times that of Equation (27)

Is the allowable amount. Similarly, the allowable range of equation (28) is about 10 times, and u / L should be in the range of 1.028 ± 0.04. Not only is this a tolerance for L, but also a tolerance for u,

It becomes. Formula (29) is the same as Formula (23) and Formula (25), and Formula (30) is the same as Formula (24) and Formula (26).
According to the experiment of the present embodiment, when the position of the optical fiber and the position of the mirror rotation axis are within the above-mentioned range, it is said that the fiber Bragg grating having different reflection wavelengths can be manufactured with high wavelength accuracy by changing only the mirror rotation angle. The effectiveness of this method was demonstrated.

It is a figure which shows mirror rotation and the position adjustment of an optical waveguide in the case of manufacturing an optical waveguide Bragg grating using the 2 light beam interference method of a prior art. It is a figure which shows the positional relationship of the optical component and optical waveguide in the mirror center rotation system of the 2 light beam interference method of a prior art. It is a figure which shows the positional relationship of the optical component and optical waveguide in the mirror rotating shaft eccentricity system of the 2 light beam interference method of this invention. It is a figure which shows the dependence with respect to the perpendicular direction distance of a phase mask and an optical waveguide of the reflection wavelength (a) and mirror rotation angle (b) of an optical waveguide Bragg grating. It is a figure which shows the dependence with respect to the mirror rotation angle of the reflective wavelength of a fiber Bragg grating. FIG. 5 is an enlarged view of FIG. 4. It is the figure further expanded with respect to # 4 of FIG. It is a figure which shows the transmission spectrum (a) and reflection spectrum (b) of the fiber Bragg grating produced with the manufacturing apparatus based on the fiber Bragg grating manufacturing method of this invention. It is a figure which shows the mirror rotation angle dependence of the fiber Bragg grating reflection wavelength of FIG. It is a figure which shows the change of the transmission blocking amount of a fiber Bragg grating when the position of an optical fiber is intentionally offset in the fiber Bragg grating manufacturing apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Phase mask 2 Mirror 3 Mirror rotation axis 4 Optical waveguide 5 Ultraviolet laser beam

Claims (6)

Ultraviolet laser light is incident on the phase mask, and is split into two beams using the diffraction phenomenon of the phase mask. The two split beams are output from the phase mask to the ultraviolet laser light incident axis to the phase mask. The two beams are reflected by two mirrors that are emitted symmetrically and arranged symmetrically at substantially right angles to the phase mask surface, and the two beams reflected by the mirrors are crossed at the position of the optical waveguide to obtain the two beams. Using two-beam interferometry to interfere, rotate two mirrors symmetrically to adjust the period of interference to form gratings with different reflection wavelengths in the optical waveguide to produce optical waveguide Bragg gratings with different reflection wavelengths In the way to
The rotational axis of the two mirrors is decentered from the center point of the phase mask and the optical waveguide, and is arranged in the vicinity of the optical waveguide, and the position where the two beams intersect is substantially independent of the mirror rotation angle. A method for manufacturing a featured optical waveguide Bragg grating. An optical waveguide Bragg grating comprising: the phase mask according to claim 1; and u satisfying the expressions (1) and (2) in the positional relationship between the two mirrors, the mirror rotation axis, and the optical waveguide. Production method.

Here, the phase mask and the optical waveguide are arranged in parallel at a distance of L, the ultraviolet laser is incident on the phase mask at a substantially right angle, θ is an emission angle of ± first-order diffracted light by the phase mask, and α is a mirror Is the angle from the direction perpendicular to the phase mask, u is the vertical distance between the phase mask and the mirror rotation axis, and s is half the distance between the rotation axes of the two mirrors. An optical waveguide Bragg grating comprising: the phase mask according to claim 1; and u satisfying the expressions (3) and (4) in the positional relationship between the two mirrors, the mirror rotation axis, and the optical waveguide. Production method.

Here, the phase mask and the optical waveguide are arranged in parallel at a distance of L, the ultraviolet laser is incident on the phase mask at a substantially right angle, θ is an emission angle of ± first-order diffracted light by the phase mask, and α is a mirror Is the angle from the direction perpendicular to the phase mask, u is the vertical distance between the phase mask and the mirror rotation axis, and s is half the distance between the rotation axes of the two mirrors. Ultraviolet laser light is incident on the phase mask, and is split into two beams using the diffraction phenomenon of the phase mask. The two split beams are output from the phase mask to the ultraviolet laser light incident axis to the phase mask. The two beams are reflected by two mirrors that are emitted symmetrically and arranged symmetrically at substantially right angles to the phase mask surface, and the two beams reflected by the mirrors are crossed at the position of the optical waveguide to obtain the two beams. Using two-beam interferometry to interfere, rotate two mirrors symmetrically to adjust the period of interference to form gratings with different reflection wavelengths in the optical waveguide to produce optical waveguide Bragg gratings with different reflection wavelengths In the apparatus, the rotation axes of the two mirrors are decentered from the midpoint of the phase mask and the optical waveguide and arranged in the vicinity of the optical waveguide, and the two beams intersect. An optical waveguide Bragg grating fabrication apparatus characterized by that position is substantially independent to the mirror rotation angle. An optical waveguide Bragg grating comprising: the phase mask according to claim 4; and u satisfying the expressions (5) and (6) in the positional relationship between the two mirrors, the mirror rotation axis, and the optical waveguide. Manufacturing equipment.

Here, the phase mask and the optical waveguide are arranged in parallel at a distance of L, the ultraviolet laser is incident on the phase mask at a substantially right angle, θ is an emission angle of ± first-order diffracted light by the phase mask, and α is a mirror Is the angle from the direction perpendicular to the phase mask, u is the vertical distance between the phase mask and the mirror rotation axis, and s is half the distance between the rotation axes of the two mirrors. An optical waveguide Bragg grating comprising: a phase mask according to claim 4; and u satisfying the expressions (7) and (8) in the positional relationship between the two mirrors, the mirror rotation axis, and the optical waveguide. Manufacturing equipment.

Here, the phase mask and the optical waveguide are arranged in parallel at a distance of L, the ultraviolet laser is incident on the phase mask at a substantially right angle, θ is an emission angle of ± first-order diffracted light by the phase mask, and α is a mirror Is the angle from the direction perpendicular to the phase mask, u is the vertical distance between the phase mask and the mirror rotation axis, and s is half the distance between the rotation axes of the two mirrors.

Images