Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1999-10-22
2001-10-02
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S559290
Reexamination Certificate
active
06297487
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for generating an electrical control signal according to a position of a light beam in relation to a border line or separating line extending transverse to the propagation direction of the light beam and, more particularly, to a device for generating an electrical control signal dependent on the position of the light beam in relation to the separating line which has two photodetectors, one which one is arranged to detect light falling on one side of the separating line and the other is arranged to detect light falling on the other side of the separating line.
2. Prior Art
A device for position determination of a light beam is required in a receiving unit, when information is transmitted between a transmitting unit and the receiving unit using the light beam. When the transmitting unit and/or receiving unit is movable, the beam direction must be continuously monitored during the transmission. The alignment of the beam must be performed with very slight angular tolerances, especially during transmissions over very large distances, such as between satellites.
Usually telescopes with lenses or mirror objectives are used for bridging very large distances. In order to transmit or receive a collimated light beam, the transmitting or receiving module must be mounted at the focal point of an objective. The image point of the received light beam moves in the focal plane of the objective during angular adjustment of the receiving telescope. The lateral spacing of the image point from the optical axis of the telescope is given by the product of the focal distance of the objective and the angular displacement between the beam propagation direction and the telescope optical axis. From the position of the image point the alignment of the telescope is determined and a control signal is generated for correction of the beam direction at the receiving device and/or transmitting device.
According to the state of the art there are several possibilities to determine the position of the light spot. For example the light spot can be received by a four quadrant diode, which detects the beam position by comparing the signals from the four quadrants. The beam alignment for coherent superimposed reception is described in European Patent Application EP-A-0831604. Light from a local oscillator is superimposed on the received signal and the overlapping signals are divided by means of beam splitter and sent along two light paths with an equal optical path length. Both beam parts are directed by separate optics comprising mirrors and lens onto two detection devices each comprising respective separate detector halves.
In the case of an ideal beam alignment both beam parts fall on the respective separating lines between the respective detector halves. A position deviation signal for the respective beam parts from their ideal or set positions is thus obtained by comparing the signal strengths from the detector halves of the respective detectors. This signal can be used for control. The separating lines between the detector halves of the respective detectors are displaced about 90° relative to each other, so that a first control signal from one pair of the detector halves can be used for correcting the X-axis deviation, while the other or second control signal from the other pair of detector halves can be used for correcting the Y-axis deviation.
Because of the size of the optical beam guiding elements for both beam parts both detector arrangements with the separate detector halves must be spaced several millimeters from each other. In order to obtain the required high accuracy for the alignment detection, the positions of both separating lines between the detector halves of the both detector arrangements relative to each other and to the optical beam guiding elements for the beam parts must have a positional accuracy of about 1 micrometer. This accuracy must be achieved at a spacing or distance of several millimeters to a few centimeters because of the size of the optical beam guiding elements.
In the known method of satisfying these requirements both detector arrangements are mounted on a common substrate. Since the detectors also operate to receive the transmitted data signals as well as produce the control signal, only small surface area photodiodes can be used because of the high bit rate of the data signal in the vicinity of up to 10 Gbit/s. Because of that aspect of the detectors the requirements for the positioning accuracy of the detector arrangements are further sharpened or increased.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved device for generating an electrical control signal according to a position of a light beam in relation to a border line or separating line extending transverse to the propagation direction of the light beam.
These objects, and others which will be made more apparent hereinafter, are attained in a device for generating an electrical control signal depending on or according to a position of the light beam in relation to the separating line, the device having two photodetectors, one of which being arranged to detect light falling on one side of the separating line and the other being arranged to detect light falling on the other side of the separating line.
According to the invention the separating line is an edge extending between two (1,1,1) crystallographic planes of a crystalline substrate and the (1,1,1) crystallographic planes reflect respective parts of the light beam to the respective photodetectors.
The device according to the invention has the advantage that the above-described specifications for positioning accuracy can be satisfied in a simple and reliable manner. Similarly the received light beam can be divided into two light beam parts as in the prior art method to obtain respective position controlling signals for control in two axes perpendicular to each other. Then the light sensitive surface of the detector is not divided into two separate halves, but each light beam part for producing the positioning signals is divided into two beam parts at an edge extending between two highly accurately aligned crystal planes, before it falls on a detector.
Advantageous further features are described in the detailed description and in the dependent claims appended hereinbelow.
In contrast to the device according to the prior art the device according to the invention has the advantage that the position adjustment tolerance of the beam dividing edges to each other and to the adjusting depressions for the beam forming module can be maintained with a very high accuracy, since the beam dividing edges in the adjusting depressions can be made in a common masking process.
REFERENCES:
patent: 5546374 (1996-08-01), Kuroda et al.
Hirche Klaus
Kuke Albrecht
Moess Eberhard
Scholz Werner
Schwaderer Bernhard
Le Que T.
Robert & Bosch GmbH
Striker Michael J.
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