Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-10-01
2003-06-24
Pascal, Leslie (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06583904
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of optical communications. More particularly, the invention relates to a method and apparatus for aligning optical interconnections between printed circuit boards (PCBs), by controlling the polarization of an information carrying light beam using electrically controlled polarizer, such as a Spatial Light Modulator (SLM).
BACKGROUND OF THE INVENTION
Many data communication systems, such as computers, use printed circuit boards for the integration of their electrical components. The architecture of modern electronic systems, and particularly of data processing systems, requires modular design, which is implemented by a set of PCBs, each of which is designed to fulfill specific functions. This modular design enables to more easily detect failures in the system, and to reduce production costs. Each PCB, which is frequently termed a “card”, can be manufactured and tested separately, and then integrated into the system. Integration is carried out mainly by a main PCB that is often termed “motherboard” (in computers, such as a PC) or “backplane” (in other computerizes data communication systems), into which each card is inserted (using pins in each card, that are inserted into corresponding sockets in the backplane), and the electrical connection between them is established. The backplane provides to each card the basic required inputs, such as power lines, for operating its electrical components, and distributes a central clock signal to synchronize the operation between cards. In addition, the backplane collects digital information processed by each card via a corresponding data bus, and transfers this information to other components for further processing. The processing elements can be located on the backplane or on another card. In the example of a PC, the main processor is located at the motherboard, and memories are located on different cards. Therefore, high rate data is exchanged between each card and the motherboard, as well as between different cards, via electrical connection (data buses).
Several data communication systems require data exchange between cards in an extremely high rate. Available high speed data buses, such as a Gunning-Transceiver-Logic (GTL) (by Texas Instruments Inc., USA) bus operating at 100 MHz, allows data exchange at a rate of 100 Mb/Sec per each line. When a data rate of 2.5 Gb/Sec is required, more data lines are added to the bus and operate in parallel. However, as the demand for higher rates increases, the frequency bandwidth becomes wider, and cross-talk problems (i.e., the spectral components of the data propagating along each line overlap in frequency with those of other lines and interfere with each other) start to appear, and therefore the available bandwidth and the data rate of each line is limited. In addition, adding more lines in parallel becomes a practical solution only for very short distances.
In several data communication systems, ribbon cables are used to add more data lines externally to the printed data lines, so as to increase the rate of data exchange between cards, without exceeding bandwidth limitations due to cross-talk problems. However, using ribbon cables suffers from limitations when “hot” replacement (i.e., replacement of cards in an essentially “transparent” mode while the system is operating) of cards is required. In addition, using external ribbon cables to add data lines is also bandwidth-limited due to cross-talk problems. Therefore, backplane designs based on electrical data connections between cards are limited to a total throughput (the maximum data rate that can be processed without delaying incoming data) of 20 Gb/Sec. In addition, adding more electrical data lines to each card requires to increase the number of pins required to provide the electrical connection, which is also limited from mechanical and space aspects.
Another method for increasing the rate of data exchange between cards is to add an information-carrying optical link between the cards, in parallel to the electrical data bus. Such link is provided by modulating a light beam, such as a laser beam, with the data that should be transmitted. Using a light beam to carry the data almost removes the bandwidth limitations of a multi-line data bus. The modulated light beam is focused on the transmitting card and directed to a detector, which is normally a photo-diode detector, located at the receiving card. The laser beam is demodulated, and the data is recovered at the receiving card. However, since there are manufacturing and assembly tolerances, as well as mechanical effects caused by temperature changes of the cards and/or of the backplane, the alignment between the transmitting laser and the light receiving detector deteriorates with time, and should therefore be aligned.
Conventional techniques for the alignment of deflected light beams comprise using an array of optical devices, such as mirrors and prisms, which direct the beam back to the desired receiving point on the receiving card. “60 GHz board-to-board optical interconnection using polymer optical buses in conjunction with microprism couplers”, Chen et. al, Applied Physics, Letter 60 (5), February 1992 discloses a board-to-board interconnection with enhanced speed using microprisms, which eliminates the need for backplane interconnection.
“Holographic optical backplane operated at 20 Gb/Sec at 1.55 &mgr;m”, Vincensini et al., Proceedings 21st European Conference on Optical Communications, ECOC'95 Brussels, describes a realization of a holographic optical backplane, which performs interconnections and clock distribution for six electronic boards at 1.3 and 1.55 &mgr;m. High speed data transmission is provided at a data rate of 20 Gb/Sec.
“Holographic coupling elements for optical bus systems based on a light-guiding optical backplane”, Haumann et al., SPIE Vol. 1319, Optics in Complex Systems (1990), describes an optical backplane consisting of a light-guiding glass plate, with holographic coupling elements for coupling the light from sources into the backplane and from the backplane onto detectors with high efficiency. However, all these essentially optical techniques are costly and cumbersome. Moreover, optical alignment does not provide an optimal solution for alignment problems that are caused by changes in ambient conditions (e.g., temperature effects) or by aging of electrical components.
All the methods described above have not yet provided satisfactory solutions to the problem of aligning optical interconnections between printed circuit boards (PCBs), which overcome the drawbacks of the prior art.
It is an object of the present invention to provide a method and apparatus for aligning optical interconnections between printed circuit boards (PCBs), which employ electric control.
It is another object of the present invention to provide a method and apparatus for aligning optical interconnections between printed circuit boards (PCBs), which provide an adaptive compensation in response to varying ambient conditions.
It is a further object of the present invention to provide a method and apparatus for aligning optical interconnections between printed circuit boards (PCBs), which provide a simple compensation for mechanical tolerances.
Other objects and advantages of the invention will become apparent as the description proceeds.
SUMMARY OF THE INVENTION
The present invention is directed to a method for the alignment of optical interconnections between at least one optical data transmission point and at least one corresponding optical data receiving point. A collimated beam of data carrying light is polarized through an electrically-controlled light polarizer, such as a spatial light modulator or a liquid crystal, which comprises an array of pixels. A focused beam of data-carrying light is obtained by controlling the polarization of each pixel. More specifically, the method employs a data carrying light source, such as a laser diode for transmission from the transmission point, an optical sensor, such as a photo-diod
Mahlab Uri
Yehezkely Hertzel
Browdy and Neimark , P.L.L.C.
ECI Telecom Ltd.
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