Optical waveguides – With disengagable mechanical connector – Structure surrounding optical fiber-to-fiber connection
Reexamination Certificate
2000-07-07
2001-07-24
Ngo, Hung N. (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Structure surrounding optical fiber-to-fiber connection
C385S147000, C385S031000, C385S025000
Reexamination Certificate
active
06264372
ABSTRACT:
The present invention relates to the field of connectors for polarization-maintaining fibres. In particular, the present invention relates to optical fibres within which light beams polarized in predetermined directions travel, and which are connected to optical devices by means of the said connectors.
Polarization-maintaining fibres (PMF) are characterized in that they maintain the polarization of the input signal throughout their length, if this polarization is orientated in one of the two directions of polarization of the fibre.
In particular, these fibres have two principal axes of propagation of the optical signal within them, called the “slow” axis and the “fast” axis. The said axes are substantially perpendicular to each other and have different characteristics. The fast axis has a refractive index which is substantially lower than that of the slow axis, and therefore enables the light beam polarized in the same direction to travel along the fibre at a higher phase velocity than that of the light beam polarized in the direction of the slow axis. In both directions, however, the signal is kept substantially unaltered at the output of the fibre.
The connectors for this type of fibre generally have a distinctive sign which identifies an axis with which the axis of polarization of the fibre has to be aligned. In this way, after the final assembly of the connector and fibre, the axis of polarization of the fibre can be recognized from the outside; consequently, if the signal sent along the fibre is polarized consistently with the said axis of the fibre, the polarization of the signal can be recognized by identifying this distinctive sign on the body of the connector. The said distinctive sign is also called the connector key.
Additionally, the connector key is generally associated with means for coupling the connector to an optical unit or to a bush which permits joining to another section of polarization-maintaining fibre. These means associated with the connector key provide a unique axial position of coupling to the exterior in such a way that the polarization of the signal is maintained beyond the connector.
A parameter which can be used to evaluate the efficiency of a polarization-maintaining fibre and the efficiency of the joint between the fibre and a connector is the extinction ratio (ER), defined as the logarithm of the ratio between the power connected to one of the two principal axes of the maintaining fibre and that connected to the other perpendicular axis along which power is not to be sent; (another conventionally used definition is the logarithm of the ratio between the power connected to the non-excited axis and the total power).
In particular, this parameter is of fundamental importance in the evaluation of the efficiency of a method for coupling these polarization-maintaining fibres to a connector. The connection provides for the alignment between one of the axes, slow or fast, of polarization of the fibre and that of the connector, defined by the position of the key. If this alignment is imperfect when the fibre has been connected to another fibre or to an optical unit, the extinction ratio decreases significantly and consequently the connection causes a degradation of the transmitted signal.
To obtain the best extinction ratio characteristics in terms of repeatability, it is known that, with polarization-maintaining fibres, it is preferable to use connectors called the SC type rather than connectors called the FC type. An SC type connector provides engagement by insertion, in a bush for example, while an FC type connector provides engagement by screwing the connector on to the bush, thereby carrying out a rotation which may generate residual torsions, resulting in a low repeatability of the connection operation.
In U.S. Pat. No. 4,792,205, the optical axes of the PMF are aligned by using a method of visual alignment of the geometrical axes of the fibre disposed inside the ferrule capable of rotating with the fibre inside it, by means of observation through a microscope and a fixed reference grid. Once the optimal visual alignment has been determined, the ferrule is finally locked inside the connector.
To obtain a greater precision of alignment, active alignment is used; this consists in sending a polarized light beam along the fibre and, by means of optical power meters, measuring at the output the power sent along the fibre emerging from the connector. This method requires a system comprising polarizers aligned with geometrical references with respect to which the axes of birefringence of the fibre are positioned.
U.S. Pat. No. 4,919,509 describes a connection between polarization-maintaining fibres comprising a first and a second ferrule, each of which has a longitudinal through hole which terminates in a vertical wall at one end of the ferrule; two polarization-maintaining fibres which are inserted into the ferrules, without their external protective covering and having the same cross section as the through holes in the ferrules, which terminate at the said vertical walls; means of position recognition associated with each ferrule, which enable the ferrules to be disposed in the preferred position for a polarization-maintaining connection; and means which enable the said first and second ferrule to be connected together longitudinally in the said preferred position in such a way that the axis of polarization of the first fibre is aligned with the axis of polarization of the second fibre.
U.S. Pat. No. 5,216,733 describes a polarization-maintaining connector which is capable of connecting two polarization-maintaining fibres or connecting one fibre of this type to an optical unit, and which comprises a ferrule having a through hole into which the fibre can be inserted, a flange having a key for fitting the said ferrule on to it, and means for engaging the said flange with the external circumference of the ferrule.
This patent also describes a method of assembling a connector to produce a connection between two polarization-maintaining optical fibres or between one fibre of this type and an optical unit, comprising the stages of:
fixing the end of a polarization-maintaining optical fibre to the end of the body of a ferrule by means of an adhesive;
grinding the said end of the ferrule and simultaneously the end of the fibre;
visually aligning a flange, by means of a key present on it, with the axis of polarization of the fibre;
fitting the said flange on to the body of the ferrule;
rotating the body of the ferrule in such a way as to align the key of the flange with the axis of polarization of the fibre in the ferrule, while observing the ground terminal part of the said fibre;
securing the flange in the body of the ferrule.
The patent application WO9637792 describes a connector subassembly for non-cylindrically symmetrical optical elements comprising a holding member for an optical element, wherein said holding member comprises at least an alignment feature, an inner sleeve member comprising at least one co-operative alignment feature adapted to engage the alignment feature on said holding member and a housing with an interior surface adapted to receive said holding member and said inner sleeve member, and an external surface comprising a rotational alignment reference. Said holding member is freely rotatable with respect to said housing to rotationally align said optical element at an optimal angle with respect to said reference on the housing.
According to the present invention, an alignment procedure has been discovered which enables a high-precision geometrical reference to be formed on a flat work surface by means of a polarized light beam sent along the fibre. The alignment process is based on the fact that the said geometrical reference, actively determined and coinciding with the axis of the connector key, is used to align the fibre with it.
It has also been discovered, in particular, that if the alignment of the connector with the axis of polarization of the fibre is carried out after the process of assembling the said connector, errors and imp
Pianciola Aurelio
Scotti Simona
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Ngo Hung N.
Pirelli Cavi E Sistemi S.p.A.
LandOfFree
Polarization-maintaining connector does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polarization-maintaining connector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polarization-maintaining connector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2555839