Telefonaktiebolaget Lm Ericsson (Publ)

Tomas Adeback

Wei-Ping Huang

Ellef Hersoug

Wenxin Zheng

Lars Wiik

Jan Magnusson

In the manufacture of an optical attenuator having a desired value of the optical loss end regions of two optical fibers are placed with an offset in the traverse direction in relation to each other and having their end surface at each other. Thereafter the region at end surfaces is heated to make the ends melt to each other and the heating is then further continued. To achieve the desired loss in the finished attenuating splice the further heating is stopped for an optical loss exceeding the desired loss by a calculated value. This value can be obtained from measurements in real time of the loss for the splice during the continued heating. The measurements can be made at the beginning and end of an interrupt of the further heating. An attenuator manufactured in this way obtains an attenuation that accurately agrees with the desired value.

Optical attenuator and method of manufacture

When an optical fiber (') is heated by an electrical discharge generated between electrodes () thermal light emission from the core and cladding of fiber forms a hot image which can be observed by an optical imaging system (). Since the concentration of dopants in the core is significantly higher than in the cladding, the light emitted from the core gives a peak structure in the light intensity profile of a hot image. The peak width of the core image increases significantly when dopants diffuse out of the core such as in heating the fiber. The increase of peak width is found to be highly correlated to the expansion of the mode field diameter (MFD) of fiber. This correlation can be experimentally determined at well-defined fusion conditions for any given type of fiber and thereby used to give a measure of the MFD by observing the peak width in hot images. Measures of MFD can be used for improving the quality of estimation of losses in splices of optical fibers.

Determining MFD of optical fibers

Optical fibers (') are fusion spliced to each other by using a CO2 laser () having an emission wavelength of 9.3 microm. The heat absorption of the fibers is higher and the variation of the absorption for small deviations of the wavelength is smaller than at the conventional wavelength of 10.6 microm. As a result, less laser power is needed, the laser construction may be more compact and safety problems can easier be handled. The optical arrangement for the light beam of the CO2 laser includes deflecting and focusing the collimated laser beam () emitted by the laser using a mirror () having a curved surface of concave nearly paraboloid shape, the splice position () located at a small distance of the focus of the mirror and well outside the collimated beam.

Fiber splicer

A technique is provided for automatic optimization of a splice loss estimator of a fiber splicer (), where the splice loss estimator is adapted, in a splice loss estimation procedure, to estimate the splice losses (L) of splices (i) of optical fibers as produced by the fiber splicer from images taken of the optical fibers at the splicing thereof, and the splice loss estimation procedure includes the use of splice loss estimation parameters (P). The estimator estimates splice losses based on information (C) obtained from the images and the estimation parameters. Further, the splice losses are measured by means of a measurement instrument (). The estimated (L) and measured (L) splice losses, and the information obtained from the images are uploaded () into an off-line computer () and the key estimation parameters are automatically optimized by the selection of any solution within the Bellcore accuracy criteria (), whereafter the optimized estimation parameters are downloaded () to the splicer.

Automatic optimization of a splice loss estimator for optical fiber splicers

In a device () for continuously varying the extinction ratio, ER, a laser diode () is connected to a first end of a PZ fiber (). At a second end, the PZ fiber is connected to a connector (). At the other end of the connector a PM fiber () is connected. The two fibers meet in the connector, which means that opposite end facets of the fibers are located at a very close distance of each other. A rotation is produced by a rotator (), mechanically coupled to the connector. The device can be used for: selecting a desired ER of the PM fiber; achieving high accuracy of angular alignment between the principal axes of two PM fibers (); evaluating the quality of angular alignment of a splice between two PM fibers made by a splicer; and setting the adjustment/calibration of a PM fiber.

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Jarfalla, Sweden

Tomas Adeback