Optical communications – Transmitter and receiver system – Including alignment between transmitter and receiver
Reexamination Certificate
1998-09-02
2003-11-18
Pascal, Leslie (Department: 2633)
Optical communications
Transmitter and receiver system
Including alignment between transmitter and receiver
C398S140000, C398S141000, C398S151000, C398S153000, C398S165000
Reexamination Certificate
active
06650843
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to devices for optical signal transmissions between a transmitter unit and a mobile receiving unit, which are optically coupled to each other via an optical transfer medium.
Optical systems are frequently employed to transmit data and signals. Such systems are fundamentally composed of a transmitter unit and a receiver unit which are interconnected via an optical transfer medium. When the optical transfer medium is free space or air, an arrangement similar to a light barrier is achieved.
However, optical fibers, such as glass or synthetic fibers, are more frequently used to guide the light. In both cases, the length of the optical path between the transmitter unit and the receiving unit is, as a rule, constant. As a result, the amplitude of the signal received in the receiver unit is not subject to significant variations with respect to time. This furnishes a uniform transmission quality.
In the case of transmission paths which have a variable optical path length between the transmitter unit and the receiving unit, the signal level at the receiver may vary accordingly. This is, inter alia, a consequence of the attenuation along the optical path, which may give rise to a varying transmission quality. In advanced digital transmission systems, in particular, this may result in an undesirable increase of the bit error rate.
Another disadvantage of prior art optical transmission systems is due to the finite transit time of the light through the optical transfer medium. This transit time depends on the distance between the transmitter and the receiver, and varies within a range of almost zero when the transmitter is located in the immediate proximity of the receiver, up to a maximum value which occurs when the transmitter unit is located at that end of the optical medium which is remote from the receiver.
When the transmitter moves along the length of the medium, starting from the receiver up to the end of the optical medium, the transit time increases. In the case of a transition of the transmitter from that end of the optical medium which is remote from the receiver, to the medium close to the receiver, initially the light passes through the entire length of the optical medium, resulting in a long transit time prior to arrival at the receiver. When the path length is short, on the one hand, the light arrives at the receiver almost without any transit time. This abrupt difference in transit time, which may occur during the transition, may give rise to a discontinuity in phase, restricting the bandwidth which can be transmitted, and possibly resulting in transmission errors.
Particularly, when optical signals are transmitted via an optical transfer medium shaped in the form of a closed curve, an overlapping at the beginning and the end of the optical medium is unavoidable unless a failure in transmission can be accepted in this position. That is, two signals are superimposed in the receiver, at the beginning and simultaneously at the end of the medium. The first signal reaches the receiver after a short path, and thus also after a short time. The second signal passes over a longer distance, and thus arrives at the receiver with a substantial delay. Both signals are now superimposed and produce an incorrect cumulative signal. As a result, the transmission is adversely affected. Specifically, with high frequencies where the signal transit time corresponds to one half of the period, the signal is extinguished. In such a case a sensible data transmission is no longer possible.
It is therefore an object of the present invention to improve a device for optical signal transmission between a transmitter unit and a mobile receiving unit (that is, moveable relative to the transmitter unit), which are coupled to each other via an optical transfer medium, such that interferences upon the transmission quality may be largely eliminated.
Another object of the invention is to provide an arrangement, in which the transmission quality is independent of relative movements between the transmitter unit and the receiving unit.
Still another object is to provide such an arrangement in which no signal overlapping occurs at the location of the receiving unit which could interfere with the data transmission. Finally, another object of the invention is to provide a device which requires a small space, involves moderate costs, and is specifically appropriate for wide-band signal transmission.
These and other objects and advantages are achieved by the invention, which is based on the proposition that, a desired independence of the bandwidth of the signal transfer times can be achieved only when the signals are prevented from arriving at the receiver along several paths with different transit times. This means that the independence of the bandwidth of the signal transit times is ensured if only a single signal reaches the receiver. This may be the case, for instance, on a linear path. Independence may equally be achieved when several signals arrive at the receiver, but all signals have the same transit times to the receiver. In the current object of the invention, both features are combined.
In the apparatus according to the invention the light beam propagates within the optical transfer medium such that either optical signals progress along different paths within the transfer medium, so that they arrive concurrently at the location of the receiving unit and can thus be combined to form a single signal, or the transfer medium is designed such that a separate three dimensional signal transmission of the individual light signals is ensured in order to avoid signal overlapping.
In accordance with the objects of the invention, the curve of the optical medium or the transfer medium, respectively, is severed at one location and closed as free of reflections as possible. This separating point is located at that site of the curve from where the signal transit times in all directions of propagation to the receiver are equal. Hence, the light arrives at the receiver along both paths when the transmitter is positioned above the separating point. Here, the signal transit times are precisely equal and signal distortion does not occur. At all other transmitter positions the light progresses along one path to the receiver and along the other path to the separating point where it is absorbed. Hence there is only one light path from the transmitter to the receiver. With such a provision signal transmission over a substantially larger bandwidth is possible.
The inventive relates equally to an optical signal transmission between moving parts. The movement may here be circular, linear or along any other optional curve on the condition that sufficient signal coupling from the transmitter unit to the optical transfer medium is ensured. In the event of linear travel of parts, the term “path length of travel” denotes that length of the path along which the transmitter unit and the receiving unit may be moved relative to each other. In the event of circular movements, it denotes the corresponding part along the periphery of the circle. At maximum, however, it denotes the complete circumference of the circle. The same applies also to any other curve along which a movement may be carried out.
Pursuant to the object of the invention, in order to allow for a simple low-cost implementation of the amplifiers in the receiving unit, the optical path length must be as short as possible. Moreover, optical signals with different transit times must be definitely prevented from arriving at the receiving unit in order to achieve a high bandwidth in transmission.
Of note, due to the shortness of the optical medium, the transmission bandwidth is also substantially wider in the case of reception of several signals with different transit times. This is because the transmission bandwidth is inversely proportional to the length of the optical medium.
Another important aspect of the present invention is the fact that optical transmitters can be produced at low costs while optical receivers are v
Lohr Georg
Poisel Hans
Stark Markus
Pascal Leslie
Schleifring und Apparatebau GmbH
Sedighian M. R.
St. Onge Stewart Johnston & Reens LLC
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