Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1996-03-18
2001-01-23
Negash, Kinfe-Michael (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06178024
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a two-way optical space communication apparatus provided with a function to adjust an angle of transmitting light or receiving light, which performs two-way (bidirectional) information transmission by propagating a light signal in a beam shape in a free space.
2. Related Background Art
In conventional optical space communication apparatus, a transmission-side device transmits a signal in which a pilot signal is superimposed on a main signal (transmission signal), and a reception-side device detects the pilot signal to detect an angular deviation between the optical axis of a receiving optical system and an arrival direction of the receiving light, thereby adjusting the angle upon start of operation or correcting the angle during operation. The pilot signal is a signal having a frequency band different from and narrower than that of the main signal. An example of the pilot signal is a sinusoidal signal.
A generally employed method for detecting the angular deviation is one arranged in such a manner that a receiving light spot focused by the receiving optical system is guided onto a photodetector and the photodetector detects a position of the spot. The photodetector employed is a PSD (Position Sensitive Detector) or a CCD (Charge Coupled Device), which demonstrates weakness with respect to the response speed when the frequency of the pilot signal is high. For overcoming it, generally employed is a method using an array of plural photodetectors comprised of photodiodes with fast response speed and detecting differences of outputs from the photodiodes, in which the photodetectors with same characteristics are located in the four quadrants and the position of the receiving light spot is obtained from a sum and a difference between the outputs from the photodetectors.
The reason why the pilot signal is used is that high-sensitive reception is possible because of its narrower band than that of the main signal and that the control function can be maintained even if the main signal becomes weak or even if there is no input of the main signal. Further, influence of background light can be decreased when the angular deviation is detected with the pilot signal having a certain high frequency component, different from low frequency components such as dc light.
The background light is all light other than the light transmitted from the transmission-side device, in the light entering the reception-side device. For example, the background light includes sunlight, lights of buildings, etc.
However, when the background light greatly increases, for example if the direct rays of the sun are incident on the light receiving elements for detecting the main signal and angular deviation signal, these light receiving elements could be damaged in the worst case. There is another problem that the angular deviation detector fails to discriminate the desired receiving light from the background light so as to erroneously correct the angle with respect to the arrival direction of the background light, which results in failing to recognizing the arrival direction of the desired receiving light even after the background light decreased, thereby failing to returning to the normal communication condition.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical space communication apparatus which is arranged to prevent damage on the light receiving elements and erroneous operation of the angle correcting function due to the background light, as overcoming the above problems.
In order to achieve the above object, the present invention provides an optical space communication apparatus for performing communication by propagating a light beam in a free space, comprising:
multiplexing means for multiplexing a first pilot signal with a transmission signal;
first converting means for converting a first electric signal from the multiplexing means into a first light signal;
a transmitting optical system for transmitting the first light signal to a party apparatus;
a receiving optical system for receiving a second light signal containing a second pilot signal, having been transmitted from the party apparatus;
second converting means for converting the second light signal into a second electric signal;
adjusting means for adjusting an angle of the receiving optical system;
control means for controlling the adjusting means; and
excessive light stopping means for stopping excessive light from entering the second converting means, wherein the excessive light stopping means is arranged also to serve as the adjusting means.
In order to achieve the above object, the present invention further provides a two-way optical space communication apparatus, which is provided with a function to adjust an angle of a receiving optical system so as to keep the optical axis of a transmitting optical system aligned with the optical axis of the receiving optical system and which performs two-way information transmission with light signals between apparatus opposed to each other at a predetermined distance, the optical space communication apparatus comprising generating means for generating a first pilot signal in a sinusoidal form, multiplexing means for multiplexing the first pilot signal with a transmission signal, electro-optical converting means for converting a first electric signal from the multiplexing means into a first light signal, a transmitting optical system for transmitting the first light signal to a party apparatus, a receiving optical system for receiving a second light signal containing a second pilot signal, having been transmitted from the opposed party apparatus in order to detect an angular deviation between the receiving optical system and an arrival direction of the receiving light, a plurality of photo-electrical converting means for receiving the second light signal and converting the second light signal into a second electric signal, angular deviation correcting means for correcting the angular deviation, excessive light detecting means for detecting input of excessive light due to the background light or the like, and excessive light stopping means for stopping the excessive light from entering the photo-electrical converting means, wherein the excessive light stopping means is arranged also to serve as the angular deviation correcting means.
In the optical space communication apparatus having the above configuration, the multiplexing means multiplexes the first pilot signal of sinusoidal wave from the generating means with the main signal of the transmission signal, the electro-optical converting means converts this electric signal into a light signal, and the transmitting optical system transmits the light signal to the party apparatus located as opposed at the predetermined distance from the transmitting optical system. The plurality of photo-electrical converting means receive the light signal from the party apparatus in order to detect the angular deviation between the arrival direction of the receiving light from the party apparatus and the optical axis of the receiving optical system, the angular deviation correcting means corrects the angular deviation, and at the same time, the background light detecting means detects input of excessive light due to the background light, thereby stopping the excessive light from entering the photo-electrical converting means.
REFERENCES:
patent: 4867560 (1989-09-01), Kunitsugu
patent: 5142400 (1992-08-01), Solinsky
patent: 5594580 (1997-01-01), Sakanaka et al.
patent: 5684614 (1997-11-01), Degura
patent: 59-126341 (1994-07-01), None
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Negash Kinfe-Michael
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