News Column

Patent Issued for Asymmetric Multi-Channel GRIN Optical Connector

July 23, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- Corning Cable Systems LLC (Hickory, NC) has been issued patent number 8774579, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Benjamin, Seldon David (Painted Post, NY); Fortusini, Davide Domenico (Ithaca, NY); Zhang, Chi (Evanston, IL).

This patent was filed on September 21, 2012 and was published online on July 8, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "The present disclosure relates to optical connectors and in particular to optical connectors that utilize gradient-index (GRIN) lenses.

"Certain types of fiber optics-based telecommunication systems and data communication systems require the optical connection of multiple optical fibers that carry information on multiple channels from transmitters to receivers, or between transceivers. The optical connections are made using optical-fiber connectors ('optical connectors') configured to direct light from output optical fibers to corresponding input optical fibers so that the light can be efficiently relayed from a light source (transmitter) to a photodetector (receiver).

"Optical connectors that utilize gradient-index (GRIN) lenses have been used in the past wherein a pair of confronting GRIN lenses is utilized to optically couple light between optical fibers. Multiple input and multiple output fibers could be used for a given GRIN lens pair. However, in such a configuration, cross talk can arise when light from one fiber is reflected by the exposed endfaces of the GRIN lenses and back into another optical fiber. In particular, since the cross-talk light arises from reflection, the cross talk happens between optical fibers that are symmetrically arranged relative to the optical axis of the GRIN lens. The effect is that light traveling in one channel ends up in another channel. If the cross-talk light reaches a receiver in another channel, it adversely affects the communication for that channel. If the cross-talk light reaches a laser light source, it can make the laser light source unstable, which also adversely affects the communication for that channel.

"Known methods for mitigating reflection-based cross talk in optical connectors include the use of anti-reflection coatings, index-matching materials and angled GRIN endfaces. Unfortunately, the use of anti-reflection coatings is relatively expensive and difficult to implement on the small GRIN endfaces. Additionally, the use of index-matching materials adds cost and complexity to the optical connectors without fundamentally addressing the source of the cross talk. The use of angled GRIN endfaces is problematic because the azimuths of the GRIN lenses must be tightly controlled in the sense that any rotational misalignment degrades optical performance."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "An aspect of the disclosure is a GRIN optical connector that includes a GRIN lens having a central optical axis and front and back opposite endfaces. A plurality of optical fibers optically are coupled to the back endface of the GRIN lens to define a first optical fiber bundle having an asymmetric arrangement relative to the central optical axis of the GRIN lens. The GRIN lens has a refractive index profile generally defined by an alpha profile having an alpha parameter .alpha. that in one example is in the range 1.92.ltoreq..alpha..ltoreq.1.98.

"Another aspect of the disclosure is an optical fiber connector assembly. The assembly has first and second GRIN lenses, with each GRIN lens having front and back endfaces, an optical axis and a same refractive index profile. The first and second GRIN lenses are interfaced at their front endfaces so that their optical axes are substantially coaxial. The assembly also includes a first optical fiber bundle of a first plurality of optical fibers optically coupled to the back endface of the first GRIN lens and having a first asymmetric configuration relative to the substantially coaxial optical axes. The assembly further includes a second optical fiber bundle of a second plurality of optical fibers optically coupled to the back endface of the second GRIN lens and having a second asymmetric configuration relative to the substantially coaxial optical axes. The first and second asymmetric configurations are either the same or rotated by 180.degree. and define a plurality of channel pairs of first and second optical fibers. The channel pairs of first and second optical fibers have a coupling loss that varies among the channel pairs by no more than 0.1 dB.

"Another aspect of the disclosure is a method of performing an optical connection between first and second optical fiber bundles. The method includes interfacing respective front endfaces of first and second GRIN lenses, each having a back endface, a same refractive index profile based on an alpha profile having an alpha parameter .alpha. in the range 1.92.ltoreq..alpha..ltoreq.1.98, and optical axes that are made substantially coaxial by said interfacing. The method also includes optically coupling a plurality of first optical fibers to the back endface of the first GRIN lens in a first asymmetric arrangement relative to the coaxial optical axes, and optically coupling a plurality of second optical fibers to the back endface of the second GRIN lens in a second asymmetric arrangement relative to the coaxial optical axes. The first and second asymmetric arrangements are the same or are rotated relative to one another by 180.degree. to define a plurality of channel pairs of first and second optical fibers. The method also includes transmitting light between first and second optical fibers within only the respective channel pairs and through the first and second GRIN lenses.

"Additional features and advantages are set forth in the Detailed Description that follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exemplary, and are intended to provide an overview or framework for understanding the nature and character of the claims."

For the URL and additional information on this patent, see: Benjamin, Seldon David; Fortusini, Davide Domenico; Zhang, Chi. Asymmetric Multi-Channel GRIN Optical Connector. U.S. Patent Number 8774579, filed September 21, 2012, and published online on July 8, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8774579.PN.&OS=PN/8774579RS=PN/8774579

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Source: Journal of Engineering


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