FR2509054A1 - OPTICAL CONNECTOR - Google Patents

Abstract

The optical connecting piece for fibre/fibre, source/fibre or fibre/detector connection consists of two cylindrically formed lenses (1, 2) made from poly(methylmethacrylate), which have an elliptical surface on one side and a flat surface on the other side. The piece enables a very high efficiency of connection without regard to the dimension and numerical opening of the fibre (4) and is insensitive with respect to change in the mutual position in the longitudinal direction. It can be produced easily and at low cost, can be easily assembled and is capable of universal use.

Description

 The invention relates to an optical connector for connecting sources, fibers and optical detectors.

 When transmitting a light signal by optical fibers, optical connections between the source and a fiber, between two fibers and between a fiber and a photodetector are necessary. It is important that the light losses through these connections are as low as possible, that the connections are as sensitive as possible to fouling and variations in the mutual positions of the connected elements, and that the connections can be dismantled and used in a way repeated. Furthermore, the condition required for commercial success and the usefulness of optical connections on fibers is a reasonable cost of these connections and the possibility of assembling them in a simple manner.

We know two different solutions to solve the problem posed by these connections, these solutions can be divided into two groups - An electrical connection with direct contact, in
which the end of the fiber is placed as close as
possible from the source and two fibers touch each other
their respective surfaces in section. Because of its
simplicity and a relatively reasonable price, this
embodiment is widespread. However, she
is very sensitive to fouling and requires quality
very high treatment of contact areas (polished
fiber wise in ruby ferrules).
deny this type of connection is that, first of all,
high losses appear at source connection
fiber (approximately 10 dB), because the radiation angle of
source is great compared to digital openness
fiber.

Another way of using lenses, which are
usually microscope objectives, allows
obtaining a much higher efficiency of the
source-fiber connection (losses of 2 to 5 dB), the connection
being relatively insensitive to fouling and
not requiring any special treatment of the ends of
fibers. Since the lenses are in demand
a weak aberration of sphericity and that it is necessary to apply
quer high quality anti-reflective layers
on lens surfaces, this embodiment
is very expensive and therefore not widespread.

Given the possibilities mentioned above for
lens production, these connectors are also
relatively bulky and heavy.

 The connector according to the invention belongs to the second group. It is therefore insensitive to fouling, it does not require any special treatment of the fiber ends, and it gives a high efficiency of the source-fiber connection (maximum losses of 3 dB). Its advantage is a reasonable cost and simple assembly so that, from this point of view, it can in any case be compared to direct contact connectors.

 The main elements of the connector are "cylinders" made of polymethyl methacrylate, having, on a first side, an elliptical surface on which an anti-reflective layer for the corresponding wavelength is deposited in the vapor phase, and on the on the other side, a flat area. On the side facing the source, the "cylinder" lens has as large a digital aperture as possible or a digital aperture suited to the source, respectively, while on the side of the "cylinder" lens facing the fiber, the digital aperture is adapted to the fiber. The lens also has a bore formed in its front end and in which a fiber, immersed in a liquid for balancing the refractive index, is housed. The high efficiency of this type of connection comes precisely from the elliptical surfaces and the minimum number of reflective zones.

The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting example and in which
- Figure 1 schematically shows a source-fiber connection;
- Figure 2 schematically shows a fiber-fiber connection
- Figure 3 is an axial section of a source-fiber connector according to the invention; and
- Figure 4 is an axial section of a fiber-fiber connector according to the invention.

 Figure 1 shows the source-fiber connection.

The source 3 is placed at the focus of a corresponding elliptical lens 1 and, consequently, the rays emerge parallel to each other. Thus, the sensitivity of the device to the mutual longitudinal position of the two lenses is eliminated. The lens 2, into which a fiber 4 is inserted, captures these rays at an angle less than or equal to an angle defined by the digital aperture of the fiber. The end of the fiber 4 placed at the focal point of the lens 2, that is to say in its bore, is immersed in a liquid intended to balance the refractive index. In this way, the irregularities of the boundary surfaces of the fiber 4 as well as those of the lens 2 are filled, and the losses are substantially reduced.

Consequently, the polish required on the input and output surfaces, respectively, of the fiber 4 is reduced to a large extent.

 Figure 2 shows the fiber-fiber connection.

The main operation is the same as that carried out in the first connection, except that at present, lenses 2 equipped with fibers 4 are provided on both sides, these lenses 2 not necessarily being identical, because each of them is adapted to the corresponding fiber. This connection mode makes it possible to establish very good connections between fibers of different sizes and different digital openings. This is particularly advantageous compared to the different fiber-to-fiber direct contact connections, which require identical fibers on both sides to obtain a good quality connection.

The fiber-photodetector connection is essentially of the same configuration as the source-fiber connection, except that, on the side of the photodetector, the required lateral positioning is less strict, since the surface of conventional photodiodes is much larger than the active surface from the source,
Figures 3 and 4 show the connections made by source-fiber and fiber-fiber connections (the source support being shown at 5, the fiber support at 6, the source-fiber connector support at 7, the support of the fiber-fiber connector in 8). It is obvious that the devices have an axial symmetry. If the source (laser) is not optically centered in its housing, an adjustment of the source in the lateral direction is necessary relative to the optical axis of the assembly. The concentric position of the two lenses is obtained by means of the tubes (7 and 8, respectively) in which the lenses must be adjusted to each other with minimal play. The connector can be dismantled, its dimensions being relatively small and its assembly is simple.

 The three types of connectors were produced in the laboratory. The measurements show that, on five samples of source connectors (GaAs laser) - fiber, the losses are always less than 3 dB (average value 2 due). In the case of fiber-to-fiber and fiber-photocathode connections, the losses are less than 1 dB. The losses are attributed to imprecise positions of the source and the fiber, respectively, in the lateral direction relative to the axis of the assembly, while this connection method is practically insensitive to longitudinal shifts. The lenses can be made of different optical materials, the advantage of polymethyl methacrylate residing precisely in the unsophisticated technical treatment, required for elliptical surfaces and for the bore housing the fiber.

The present invention has in particular the following advantages - a very high coefficient of efficiency of the connection
source-fiber - the possibility of a high quality connection between
fibers of different sizes and digital openings
ques different; - a reasonable price - insensitivity to variations in mutual positions
longitudinal lenses -; - simple assembly; - a simple production technique (molding or turning); - universal use.

 It goes without saying that many modifications can be made to the connector described and shown without departing from the scope of the invention.

Claims (1)

 CLAIM  Optical connector intended to make a fiber-fiber connection, a source-fiber connection or a fiber-detector connection, characterized in that it comprises two elliptical cylindrical lenses (1, 2), the fiber (4), the source (3 ) or the detector being placed at the focal point of the lens (2).