Optics: measuring and testing – For optical fiber or waveguide inspection
Reexamination Certificate
2001-04-19
2002-04-16
Font, Frank G. (Department: 2877)
Optics: measuring and testing
For optical fiber or waveguide inspection
Reexamination Certificate
active
06373564
ABSTRACT:
CLAIM OF PRIORITY
This application claims priority to an application entitled, “Image Tracking Device and Method for Transverse Measurement of Optical Fiber,” filed in the Korean Industrial Property Office on Aug. 22, 2000 and there duly assigned Ser. No. 2000-48506.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an image tracking device in an optical communication system, and in particular, to a device and method for measuring the transverse characteristics, including the refractive index or residual stress, of an optical fiber or a fiber preform.
2. Description of the Related Art
Hereinafter, the term, “transverse section,” relating to an optical fiber (or preform) will refer to the section perpendicular to “the lengthwise section” of the optical fiber (or preform), whereas the term, “longitudinal section” will refer to the section that is parallel to “the length direction” of the optical fiber (or preform).
Various types of image-tracking techniques for tracking the transverse and longitudinal images of the optical fiber (or preform) are available. The transverse measuring device is typically utilized to detect the residual stress and refractive index of an optical fiber (or fiber preform). Despite having a low-image resolution, the transverse measuring device allows a non-destructive testing environment compared to other measurement techniques that are available in the industries related to fiber and fiber fabrication device. Moreover, unlike the longitudinal measuring technique, a polarization distribution effect can be measured accurately using the transverse measuring technique. Therefore, the transverse measurement is more preferred for measuring the characteristics of an optical fiber (or preform).
FIG. 1
illustrates a conventional measuring device for enabling the longitudinal measurement of an optical fiber. For the purpose of illustration, an optical fiber
14
is arranged along the z-axis direction, and the longitudinal section
15
of the optical fiber
14
is aligned in the x-y plane. Parallel light
13
, emitted from a light source
11
, is focused on the longitudinal section
15
of the optical fiber
14
by a first lens
12
. Some portion of the light
13
incident on the transverse section
15
is transmitted into the optical fiber
14
, while the other portion of the light
13
is reflected. The reflected light
13
from the fiber
14
is coupled into a second convex lens
16
in backward direction and thereafter determined by an optical detector
17
as light power. Accordingly, the optical detector
17
measures the power of the reflected light received thereon, and the measured power is used to obtain information about the refractive index of the parallel light
13
at the beam spot on the transverse section
15
of the fiber
14
. Hence, by implementing this type of parallel light measuring device, the refractive index distribution of the transverse section
15
of the fiber
14
can be derived using the power of the light detected at the detector
17
.
FIG. 2
illustrates another conventional measuring device for detecting the transverse characteristics of an optical fiber. As shown in
FIG. 2
, the optical fiber
23
is arranged along the z-axis direction, and the longitudinal section
24
of the optical fiber
23
is aligned along the x-z plane,. Light
22
emitted from a light source
21
passes through the fiber surface and the longitudinal section
24
of the optical fiber
23
and eventually arrives at the image sensor
25
. Accordingly, the image of the longitudinal section
24
can be measured and can determine whether the optical fiber
23
contains beam deflecting sections, which result from different refractive indexes by dopants. To achieve this, the conventional measuring device also includes an image sensor (i.e., CCD)
25
to measure the intensity distribution of light passing through the fiber component
24
. Hence, the image of the intended longitudinal section of an optical fiber, including the center of the optical fiber as well as the sectional profiles of an optical fiber, is detected.
However, there are some drawbacks with the above-identified conventional systems, which rely on the diffraction of an optical fiber image. Typically, the transverse image of an optical fiber is detected not by projecting light onto a sample but by transversely radiating the optical fiber with light and then detecting refracted light therefrom. When light is projected onto the outer circumferential surface of the optical fiber, the cylindrical core structure acts as a lens. That is, an optical fiber composed of a core and a cladding with different refractive indices and with a symmetrical cylinder shape has equivalent function as a lens. Thus, the light focusing effect and the light diffraction effect are generated when light passes before and behind the center of the core, respectively. Currently, there is no way to numerically analyze these focusing and diffraction effects caused by the fiber in the conventional image sensor. Therefore, there is a need for a new image-tracking method that is capable of detecting the focusing and diffraction effects caused by the fiber core member.
SUMMARY OF THE INVENTION
The present invention relates to an image-tracking device that can minimize measurement errors caused by the fiber core member in the transverse measurement method.
Accordingly, an image-tracking device that is capable of detecting the transverse characteristics of an optical fiber is provided and includes a linear object; a light source for emitting light onto the light object; a first convex lens for projecting the light received via the linear object onto the outer circumferential surface of the optical fiber and forming a primary image of the linear object penetrating the optical fiber; a second convex lens for converging the light received via the optical fiber and forming a secondary image of the linear object; an image sensor for detecting the secondary image; and, a controller for calculating the distance between the primary image and the center of the optical fiber based on the distortion degree on the detected secondary image.
The present invention provides a method for measuring the transverse characteristics of an optical fiber, a linear object is arranged to be inclined at an angle other than 90° with respect to the transverse direction of the optical fiber. Light is projected onto the linear object and the light that passes through the linear object is focused thereafter. A primary image of the linear object is generated to be within the optical fiber. A secondary image of the linear object is generated by focusing the light that has passed through the optical fiber with a lens
70
. As a consequence, the secondary image is detected and a differential curve is derived from the detected secondary image. Finally, the distance between the primary image and the center of the optical fiber is calculated according to the length of a distortion region and distortion peaks on the differential curve.
REFERENCES:
patent: 5215489 (1993-06-01), Nakamura
patent: 5770001 (1998-06-01), Nagayama et al.
patent: 6034779 (2000-03-01), Yamaura
Kim Dug-Young
Paek Un-Chul
Park Yong-Woo
Cha Steve
Font Frank G.
Klauber & Jackson
Nguyen Tu T.
Samsung Electronics Co,. Ltd.
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