JP2003509732A - Method of forming grating in optical waveguide - Google Patents

Abstract

(57) [Summary] A fiber is placed in a tube (34). This tube is sealed. A grating is written to the fiber in the tube (38).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the manufacture of optical fiber elements, and more particularly to a method of forming a Bragg reflector grating within an optical waveguide to protect the optical fiber from contamination during the manufacturing process.

[0002]

BACKGROUND OF THE INVENTION

The sensitivity of optical waveguide fibers to certain wavelengths and strengths has been known since the late 1970s. This is because the loss properties and the index of refraction of the waveguide fiber allow for periodic fluctuations in the index of refraction of the optical fiber piece formed by exposing the waveguide to light of a given wavelength and intensity. It became clear that it could be changed. The periodic variation of the refractive index of the waveguide along the longitudinal axis is generally known as an optical waveguide grating. The fiber Bragg grating is an optical waveguide grating that selectively propagates a light beam having a wavelength twice the grating period. Such a fiber Bragg grating is useful as a wavelength filter.

Fiber Bragg gratings are formed through a multi-step process involving writing by actinic radiation, etching, or other mechanisms to produce periodic perturbations. Sidelighting is one technique for forming a grating in an optical waveguide fiber in which a ray, such as actinic radiation, forms periodic light and dark stripes along the longitudinal axis of the waveguide. An example of such periodic fringes is an interference pattern that is periodically formed on the side surface of the waveguide fiber or on a part in the longitudinal axis direction. The periodic intensity pattern created by light interference causes a periodic change in refractive index along the longitudinal axis of the waveguide fiber.

Exposing exposed fibers to contaminants in the manufacturing process of fiber gratings causes failure of the manufacturing equipment and reduces reliability. Further, it is somewhat difficult to hold the fiber in a sufficiently stable state in order to prevent the grating performance from being deteriorated due to the displacement of the fiber. Such fiber misalignment can occur because the fiber needs to be fixed by its polymer coating.

Accordingly, it would be highly advantageous to provide a process for making a fiber Bragg grating that prevents optical fiber misalignment in the grating lighting process.

[0006]

[Outline of the Invention]

The present invention provides a beneficial method for forming a grating in an optical waveguide. In the present invention, the grating is lit after the photosensitive light guide is placed in the package to hold the light guide stable and protect it from contamination during several steps of the manufacturing process. According to one feature of the invention, the method of the invention comprises placing an optical waveguide in an enclosing structure, sealing the structure to secure the waveguide, and forming a grating in a portion of the waveguide. Including the step of performing.

According to another feature of the invention, embodiments of the present invention provide for sensitizing the optical waveguide, testing for special performance of the grating, and adjusting the grating within the sealed structure. And heat treating the lattice and the structure. The optical waveguide according to the present invention may have a special mode such as a single mode or multimode optical fiber, a multicore fiber, and a groove type or a plane type.

The understanding of the present invention and further features and advantages of the present invention will be apparent from the following detailed description of the invention and the accompanying drawings.

[0009]

[Embodiment]

The invention will now be described in more detail by means of the preferred illustrated embodiment. However, the present invention can be implemented in various forms, and should not be construed as being limited to only the exemplary embodiments described herein. Rather, the detailed description of these exemplary representatives will enable the present disclosure to be thorough and complete, while at the same time providing those skilled in the art with the scope, structure, operation, functionality, and breadth of the invention. Indicates the possibility of use.

FIG. 1 is a cross-sectional view of a grating package 10 formed by the method described below according to the present invention. Here, for convenience of explanation, the waveguide is an optical fiber,
An example is described where the package is a tube structure. However,
The method of the present invention can also be applied to other types of waveguides, in which case the package shape and manufacturing steps are appropriately modified or changed. Optical fiber 12
Is partly surrounded by a tube-shaped structure 14 made of a material having a property of transmitting actinic radiation such as ultraviolet rays. As a material for the structure 14, boron-doped (doped) silica glass or other glass that transmits ultraviolet rays is suitable. The dimensions of the tube-type structure 14 are the inner diameter a in the figure.
(For example, 255 to 1000 μm), outer diameter b (for example, 3.0 mm), and length c (for example, 70 mm). The outer diameter of the optical fiber 12 including the coating portion 16 is d (for example, 250 μm).
The coating 16 has a length of the optical fiber that is contained in the hollow tube 14.
Stripped from twelve. Further, as the optical fiber 12, a fiber grating 18 is lit on a portion where the coating 16 is stripped off.

Two seals 20 and 21 are provided at both ends 22 and 23 of the hollow tube 14, respectively, to hold the optical fiber 12 provided with the fiber grating 18 with appropriate tension. The seals 20 and 21 may be frits including copper glass or other suitable material. The package 10 is also closed by providing plugs 24 and 25 of epoxy or other suitable material at both ends 22 and 23 of the tubular structure 14. Both ends of structure 14 22
And 23 have, for example, a funnel shape with an angle of 45 °, which facilitates the insertion of the optical fiber 12 and the placement (installation) of the plugs 24 and 25.

While the present specification discloses currently preferred materials, dimensions, etc., those skilled in the art will recognize that a variety of materials and sizes may be used for the grid package 10 of the present invention. It should not be construed as limited to only the geometries and examples described in the specification. These are just typical or general examples. Details of other grid packages and packaging methods that can be used in the present invention are described in the US patent application (Attorney Docket No. Carberry 6) filed September 16, 1999. This U.S. patent application is entitled "Method And Apparatus For Packaging Long-Period Fiber Grating", the disclosure of which is incorporated herein by reference. To do.

FIG. 2 illustrates a method 30 of forming a waveguide grating in a package (eg, package 10 of FIG. 1, etc.) in accordance with the present invention. In step 32 of imparting photosensitivity to a waveguide, photosensitivity is imparted to a waveguide (eg, an optical fiber). An example of the optical fiber used in the present invention is a high-delta (high-delta, meaning that the relative refractive index difference described later is large) is a germanium-doped step type fiber having a refractive index delta of about 2%. It is a thing. The term "refractive index delta" used herein refers to the relative difference in refractive index between the core portion and the cladding portion of an optical fiber expressed as a percentage. An example of a process for imparting photosensitivity to the optical fiber of FIG. 2 is to expose the optical fiber to a hydrogen atmosphere of 100 atm for 2 weeks. After this, part of the optical fiber is exposed to a large amount of ultraviolet light. A suitable UV laser for this exposure has a wavelength of 248 nm and is pulsed at 15 Hz. This exposure is performed, for example, for 30 minutes with a pulse intensity of 75 mJ / cm ² . After that, in the optical fiber
Anneal at 125 ° C for 24 hours is added. Another process applicable to the present invention is U.S. patent application Ser. No. 09 / 252,151, filed February 18, 1999 (Title of Invention: "Optical Waveguide Photosensitization")
, And the disclosure content is as described in this specification.

Next, in a packaging step 34, the optical fiber is placed in a hollow tube, such as shown at 14 in FIG. 1, and sealed to form a package. During this process, the package protects the optical fiber from contamination and at the same time holds it securely. The grating writing step 36 then writes the grating onto the optical fiber. At this time, any technique for side writing the grating on the optical fiber can be applied. As an example of the typical technique of the present invention, an excimer pumped frequency doubled dye laser system is used, which in this example is used as an ultraviolet light source at a wavelength of approximately 240 nm. A beam having a wavelength of 240 nm generated by the laser light of this example first passes through the silica slit. For a silica slit suitable for this method, see 1998
U.S. Patent Application No. 09 / 081,912 filed on May 19, (invention title "Spatial Filter For High Power laser Beam"), the disclosure content of which is As described in the specification. The beam with a wavelength of 240 nm passes through the silica slit, then through the phase mask, and then reaches the optical fiber in the silica tube. This phase mask is, for example, a transmission diffraction grating, and is a component whose structure and properties are known in the art. Further, the phase mask may be a substrate having a series of openings provided at regular intervals. In the grating writing step 36, the tube 14 shown in the example is placed approximately 4 mm from the phase mask and the pulse exposure from the beam emitted by the excimer laser is repeated for 25 minutes at a 10 Hz period. Be done. The intensity of this laser is approximately 75 mJ / cm ² at the position of the optical fiber. 3 and 4 show typical reflectance and transmittance curves of the grating. At this time, the average refractive index change during the exposure to the laser beam was about 2 × 10 ⁻⁴ .

Next, in a first test step 38, the spectral properties of the grating are tested. This spectral characteristic is corrected or adjusted in the initial tuning step 40. In a first tuning step 40, the grating is exposed in a large amount of UV light so as to have the required target spectrum. At this time, the ultraviolet rays are emitted from the excimer laser system at a wavelength of, for example, approximately 248 nm for 5 minutes. At the position of the optical fiber shown in the illustrated embodiment, the laser intensity is approximately 75 mJ / cm ² and its repetition rate (repetition rate) is 15 Hz. FIG. 5 shows a typical transmission (transmission) spectrum of a fiber grating when exposed to UV light for several (different) time intervals. The wavelength shifts about 0.15 nm overall (total) during exposure. Also, as seen in FIG. 5, as the exposure time increases due to the decrease in the amplitude of the grating modulation, the minimum value that can be transmitted (transmitted) also increases. This reduction in the grating modulation is caused by the increase in the refractive index by previously irradiating the valley portion of the grating with a light beam. Further, in an embodiment, a first heat treatment step 42 is then performed. In this step 42, 125
Heat treatment is performed at ℃ × 24 hours.

Depending on the embodiment, additional steps such as testing, conditioning and heat treatment may follow. A second test step 44 tests whether the grating has the desired spectral characteristics. If the grating does not have the desired spectral characteristics, a second tuning step 46 is performed to make the tuning of the grating. This is an exposure step that exposes the grating to a large amount of ultraviolet light emitted from an excimer laser with a wavelength of approximately 248 nm. As shown in the figure, the laser intensity at the position of the optical fiber is about 75 mJ / cm ^{2 in a} 15 Hz cycle. Then, in the final step 48, the package is heat-treated at 125 ° C. for 24 hours.

It will be apparent to those skilled in the art that various modifications, changes and variations in the present invention can be implemented without departing from the object and technical scope (spirit) of the invention. Therefore, the present invention also covers modifications, changes and variations that occur within the scope of the claims and their equivalents.

[Brief description of drawings]

1 is a cross-sectional view of a lattice package according to the present invention.

FIG. 2 is a flowchart showing a fiber grating forming method according to the present invention.

FIG. 3 is a graph of a reflectance curve of a fiber grating formed according to the present invention.

FIG. 4 is a graph of a transmittance curve for a fiber grating formed according to the present invention.

FIG. 5 is a graph of the transmission spectrum of a fiber grating formed by the present invention with various irradiation times.

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), AE, AG, A L, AM, AT, AU, AZ, BA, BB, BG, BR , BY, BZ, CA, CH, CN, CR, CU, CZ, DE, DK, DM, DZ, EE, ES, FI, GB, G D, GE, GH, GM, HR, HU, ID, IL, IN , IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, M G, MK, MN, MW, MX, MZ, NO, NZ, PL , PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, U Z, VN, YU, ZA, ZW (72) Inventor Wella Brophy Laura             New York, USA 14830               Corning Pine Lane 6 F term (reference) 2H047 KA03 LA02 PA22 QA03 QA04                       TA41                 2H049 AA34 AA45 AA59 AA62                 2H050 AA01 AB09X AC82 AC84                       AD00

Claims (22)

[Claims] 1. A method of forming a grating in an optical waveguide, comprising: disposing the waveguide piece in an enclosing structure; and sealing the enclosing structure to form a package to form the optical waveguide piece. Fixing in the package, and forming a grating in a part of the optical waveguide piece. 2. The method of claim 1, wherein the structure is substantially transparent to ultraviolet light. 3. The method according to claim 2, wherein the structure comprises silica glass to which boron is added. 4. The method of claim 2, wherein the optical waveguide comprises an optical fiber. 5. The method according to claim 2, wherein the optical waveguide is a planar waveguide. 6. The method of claim 2, wherein the optical waveguide is a grooved waveguide. 7. The method of claim 1, wherein the optical waveguide is photosensitive. 8. The surrounding structure is a substantially cylindrical structure.
The method described. 9. The method of claim 1, wherein the package protects the optical waveguide from contamination. 10. The step of forming the grid comprises:   Substep of exposing a portion of the optical waveguide length in the package to actinic radiation The method of claim 1, comprising: 11. The method of claim 10, wherein the ultraviolet light comprises a wavelength of approximately 240 nanometers. 12. The ultraviolet ray transmits through a silica slit, and
The method described. 13. The ultraviolet ray is transmitted through a phase mask.
Method described in 10. 14. The method of claim 10, wherein the ultraviolet light is pulsed for 25 minutes at a frequency of approximately 10 Hz. 15. After the step of forming the grid,   Further adjusting the grating to modify the spectral characteristics of the grating The method of claim 1, comprising: 16. The method of claim 15, wherein adjusting the grid comprises exposing the grid to a large amount of violet light. 17. After the step of adjusting the grid,   Further heat treating the lattice 16. The method of claim 15, comprising: 18. After the step of applying a heat treatment to the lattice,   A second adjusting step for adjusting the spectral characteristics of the grating 18. The method of claim 17, comprising: 19. The method of claim 18, wherein the second adjusting step comprises exposing the grating to a large amount of ultraviolet light. 20. The method of claim 19, wherein the wavelength of the ultraviolet light is approximately 248 nanometers. 21. The method of claim 20, wherein the ultraviolet light is pulsed for 5 minutes at a frequency of approximately 15 Hz. 22. After the second adjusting step,   And further applying a heat treatment to the second lattice 19. The method of claim 18, comprising: