Optical loop-back attenuator

Details Optical loop-back attenuator Optical loop-back attenuator

2001-12-27

2004-03-16

Sanghavi, Hemang (Department: 2874)

Optical waveguides

Accessories

Attenuator

Reexamination Certificate

active

06707979

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical attenuators, and particularly to a loop-back attenuator used for testing optical equipment either prior to installation or after installation.
2. Description of Prior Art
Optical fibers are utilized to transmit optical signals among various items of optical equipment in optical communications systems. Testing of the items of optical equipment is necessary to assure proper functioning. In testing, test conditions must accurately simulate the anticipated operating environment. In operation, optical communications systems generally experience unavoidable attenuation in the optical fibers. That is, loss of optical power transmitted through the fibers. Such systems are specified in terms of maximum optical attenuation that can occur between transmitting and receiving devices while still providing information transfer with substantially no error. Typically, an emitter and a detector of an item of optical equipment to be tested are connected to a device that simulates the optical system that the item of optical equipment is intended to be installed in. The device simulates the system's characteristic attenuation, among other things.
Loop-back attenuators are used to provide a communication signal path that forms a loop from the emitter to the detector of the same item of optical equipment. Optical signals transmitted from the item under test are looped back to that same item and internally transmitted among its component parts. Consequently, communication from a transmitter to a receiver within the item of equipment can be accomplished without operation of other items of equipment. The loop-back attenuators simulate a loss of signal intensity expected of a communications system in which the item is to be installed for “on-line” operation.
Referring to
FIGS. 1 and 2
, a loop-back attenuator
1
disclosed in U.S. Pat. No. 4,952,798 comprises an upper cover
11
, a lower cover
12
, a screw nut
13
, an optical fiber
14
and two optical fiber connectors
15
. Each optical fiber connector
15
comprises a ferrule
151
for retaining a distal portion of the optical fiber
14
. The optical fiber
14
is formed as a loop, and a film
152
is formed on an end surface of the optical fiber
14
. The loop and the film
152
provide controlled attenuation of optical power. The upper and lower covers
11
,
12
cooperate to define a space for accommodating and securing the optical fiber
14
and the optical connectors
15
therein. The upper and lower covers
11
,
12
are attached to each other and fastened by the screw nut
13
. Unfortunately, the film
152
needed for attenuation increases costs. Furthermore, manufacturing of the attenuator
1
is unduly time-consuming. U.S. Pat. No. 5,475,781 also discloses the attenuator.
SUMMARY OF THE INVENTION
In view of the above, an object of the present invention is to provide a loop-back attenuator having a bent optical fiber which provides desired attenuation.
In order to achieve the object set above, an optical loop-back attenuator in accordance with the present invention comprises a frame, a cover attached to the frame, an optical fiber, an optical fiber fixture retaining and fixing the optical fiber, and two subscriber connector (SC) plug connectors receiving and retaining opposite ends of the optical fiber therein. The frame and the cover cooperate to fittingly receive the optical fiber, the optical fiber fixture and portions of the SC plug connectors therein. The optical fiber has a bent part which is configured to be semicircular or to have another suitable shape that achieves a desired attenuation.


REFERENCES:
patent: 4979793 (1990-12-01), Bowen et al.
patent: 5259045 (1993-11-01), Azuma et al.
patent: 5311614 (1994-05-01), Caron et al.
patent: 5475781 (1995-12-01), Chang et al.
patent: 5677977 (1997-10-01), Smith
patent: 6454464 (2002-09-01), Nolan

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