Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
1999-04-05
2001-10-23
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C385S037000, C356S401000, C430S022000
Reexamination Certificate
active
06307617
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and system for aligning an ultraviolet beam and an optical fiber preparatory to the manufacture of an optical filter in the optical fiber.
Optical filters comprising Bragg gratings formed in optical fibers are useful for dispersion compensation in optical communication systems, and for various other applications. A known method of manufacturing such filters illuminates a photosensitive optical fiber with ultraviolet light through a phase mask, thereby imprinting a modulation pattern in the refractive index of the fiber core. To obtain uniform modulation, the manufacturing process preferably uses a highly stable ultraviolet light source, such as a continuous-wave argon ion laser apparatus emitting an ultraviolet beam by second harmonic generation.
The beam emitted by this type of light source is relatively weak. To increase the beam intensity, the beam is focused to a width comparable to the diameter of the optical fiber, and scanned lengthwise along the fiber. The fiber diameter is only about one hundred twenty-five micrometers (125 &mgr;m), so successful scanning requires careful alignment between the beam and the fiber. In particular, the fiber must be accurately aligned at the beginning of the scan, so that the fiber is centered under the beam and the fiber axis is aligned in the scanning direction.
During the scanning process, alignment can be maintained by the known method of monitoring visible light produced by fluorescence when the core of the optical fiber is illuminated by the ultraviolet beam. Some of this visible light propagates through the fiber core, and can be measured by an optical power meter connected to one end of the optical fiber. The measured value can be fed back to an automatic positioning system that keeps the beam centered on the fiber core.
It would be advantageous if the initial alignment of the fiber could also be carried out by automatic control.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to align a photosensitive optical fiber automatically, in an initial position suitable for scanning with an ultraviolet beam to form an optical filter.
Another object of the invention is to align the photosensitive optical fiber accurately.
The invented alignment method comprises the steps of:
(a) holding the photosensitive optical fiber in a plane having an X-axis and a Y-axis;
(b) scanning the ultraviolet beam repeatedly across the photosensitive optical fiber, parallel to the Y-axis, at successively decreasing speeds;
(c) detecting light returned from the photosensitive optical fiber;
(d) thereby determining first X- and Y-coordinates at which the photosensitive optical fiber is centered under the ultraviolet beam;
(e) repeating steps (b) and (c) at a different location on the photosensitive optical fiber, thereby determining second X- and Y-coordinates at which the photosensitive optical fiber is centered under the ultraviolet beam; and
(f) rotating the photosensitive optical fiber through an angle determined from the first and second X- and Y-coordinates.
The invented method preferably comprises the additional steps of:
(g) repeating steps (b) and (c) again after step (f), thereby determining a third Y-coordinate at which the photosensitive optical fiber is centered under the ultraviolet beam; and
(h) moving the photosensitive optical fiber parallel to the Y-axis according to the third Y-coordinate, thereby aligning the photosensitive optical fiber with the ultraviolet beam.
When step (b) is carried out, the scans can be performed in identical directions, or at least two of the scans can be performed in mutually opposite directions. In either case, the scans can be performed at a fixed X-coordinate, or at different X-coordinates.
The Y-coordinate in step (d) can be determined from the last scan in step (b), or from the last two scans in step (b). In either case, the Y-coordinate can determined by finding a coordinate at which peak light power is detected during a scan, or by finding a coordinate centered between a pair of half-power coordinates.
The invented alignment system comprises at least one fiber holder for holding the photosensitive optical fiber, a first scanning stage for scanning the ultraviolet beam parallel to the X-axis, a second scanning stage for scanning the ultraviolet beam parallel to the Y-axis, a third scanning stage for rotating the photosensitive optical fiber about an axis perpendicular to the X- and Y-axes, an optical transducer for detecting light returned from the photosensitive optical fiber when illuminated by the ultraviolet beam, and a computing device controlling the first, second, and third scanning stages to carry out the steps described above.
REFERENCES:
patent: 4506947 (1985-03-01), Tatekura et al.
patent: 4608494 (1986-08-01), Kobayashi et al.
patent: 4676649 (1987-06-01), Phillips
patent: 5367588 (1994-11-01), Hill et al.
patent: 5862273 (1999-01-01), Pelletier
patent: 5914207 (1999-06-01), Nishiki et al.
patent: 6038358 (2000-03-01), Nishiki
Anderson et al., “Production of in-fibre gratings using a diffractive optical element”, Electronics Letters, vol. 29, No. 6, Mar. 18, 1993, pp. 566-568.
Komukai et al., “Fabrication of high-quality fiber gratings by the fluorescence monitoring method”, Ninth Meeting on Applied Fiber Optic Technology, pp. 1-4.
Inoue et al., Fiber Bragg grating and its applications, Oyo Butsuri, vol. 66, No. 1, 1997, pp. 33-36.
Fujii Kozo
Nishiki Akihiko
Adams Russell
Bindingnavele Raghuveer
Frank Robert J.
OKI Electric Industry Co., Ltd.
Sartori Michael A.
LandOfFree
Initial alignment system for use in manufacturing an optical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Initial alignment system for use in manufacturing an optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Initial alignment system for use in manufacturing an optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2564494