Optical: systems and elements – Lens – With reflecting element
Reexamination Certificate
2003-06-30
2004-07-20
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With reflecting element
C359S730000, C359S615000, C359S868000
Reexamination Certificate
active
06765730
ABSTRACT:
INCORPORATED BY REFERENCE
The present application is based on patent application No. 2002002-194760 filed in Japan, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dispersion compensator for compensating for a deterioration in an optical signal which is caused by a dispersion of a light which is transmitted in an optical transfer element such as an optical fiber which is used for an optical communication. The present invention particularly relates to a dispersion compensator which can compensate a chromatic dispersion and a dispersion slope which are caused in the optical transfer element.
2. Description of Related Art
There has been an increasing requirement for larger capacity in an optical communication system as a traffic in a communication increases according to an Internet which is rapidly used commonly. Conventionally, larger communication capacity has been realized by increasing a transmission speed based on a faster processing speed in an electronic circuit. However, a recent request for increasing the communication traffic exceeds what can be realized by making use of faster processing speed in such an electronic circuit. Presently, it is inevitable to use a wavelength division multiplexing (hereinafter called WDM) method together with the higher speed processing operation by an electronic circuit.
Presently, an optical transmission speed which is commercially realized has a limit such as 10 Gb/s. According to the latest status in this area in the art, a transmission speed such as 40 Gb/s has already been realized under non-commercial condition such as under a Research and Development condition because of an improved electronic device using a composite-semiconductor. Regarding a medium which us used for an optical communication, there is a serious problem wider width in a transmission pulse width caused by a dispersion in that a transmission speed of a light which exists in a transmission medium alters based on a wavelength or a polarization condition of a light in case of a high transmission over 10 Gb/s. It is understood that it is necessary to reduce a decrease an entire system for transmitting a light to zero.
For Methods for decreasing such a dispersion, following methods can be commonly used for example. In a method, dispersion in an optical fiber is reduced by using a dispersion shift fiber which adjust a zero-dispersion wavelength in a fiber to a transmission wavelength. In other method, a dispersion compensation fibers (hereinafter called DCFs) which have an opposite characteristics to an optical fiber such as a single mode fiber (hereinafter called SMF) are disposed in constant intervals have been used commonly.
On the other hand, more strict control for dispersion is required under condition of transmission speed such as 40 Gb/s; thus, it is necessary to correct the dispersion in an optical fiber which is caused by a temperature condition dynamically.
In order to solve such problems, a fiber brag-grating (hereinafter called an FBG) and a virtually-imaged-phased-array (hereinafter called a VIPA) have been proposed. For a dispersion compensator using a VIPA, a dispersion compensator can be named which is disclosed in a patent document such as Published Japanese Translation No. 2000-511655 of PCT. In this dispersion compensator, a light which is ejected from an optical fiber is collimated. After that, the collimated light is condensed and transmitted through a VIPA which is disposed in a focal point of the transmitted light. Thus, a light flux which can be identified according to each wavelength therein is generated so as to be a parallel light. The parallel light is condensed and reflected by a reflection mirror which is disposed in a focal point. The reflected light returns to an optical fiber by reversing the reflected light in the same optical system thereabove.
According to such a dispersion compensator, a light which is outputted from the VIPA is condensed in a different point on the reflecting mirror, and a surface on on the reflection is formed in a certain shape. By doing this, it is possible to generate an optical path length difference. Thus, a chromatic dispersion is compensated because different wavelengths transmit for different distances.
For a member to compensating the dispersion slope, a dispersion compensator which is disclosed in a patent document such as U.S. Pat. No. 6,301,048 is proposed. According to the document, a method is disclosed by which a dispersion and a dispersion slope are compensated concurrently by using a VIPA and a diffracting grating.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a dispersion compensator which can compensate a chromatic dispersion and a dispersion slope under condition that an insertion loss can be restricted in a minimum level.
Another object of the present invention is to provide a dispersion compensator and a dispersion compensating system which do not need a large space for realizing functions for varying a dispersion to be compensated and a dispersion slope.
A dispersion compensator according to the present invention is characterized in comprising an angular dispersion element for changing an angle of a light which is ejected from an optical transfer element according to a wavelength in the ejected light, a diffracting optical element having at least a concave reflecting surface so as to diffract the ejected light, and a reflecting mirror having a reflecting surface which is disposed near a focal point in an entire optical system of which surface shape of the reflecting mirror changes in a dispersing direction of the ejected light according the wavelength in the ejected light.
Also, a dispersion compensator according to the present invention is characterized in comprising an angular dispersion element for changing an angle of a light which is ejected from an optical transfer element according to a wavelength in the ejected light, an optical element having a light-condensing function, a diffracting optical element having at least a concave reflecting surface so as to diffract the ejected light, and a reflecting mirror having a reflecting surface which is disposed near a focal point in an entire optical system of which surface shape of the reflecting mirror changes in a dispersing direction of the ejected light according the wavelength in the ejected light.
Also, it may be acceptable that the focal point in which an image is focused by the optical element and the reflecting surface of the reflecting mirror are disposed on a circumference which is formed according to a radius of curvature in the concave reflecting surface in the diffracting optical element.
Also, according to the present invention, a dispersion compensator is characterized in comprising an angular dispersion element for changing an angle of a light which is ejected from an optical transfer element according to a wavelength in the ejected light, an optical element having a light-condensing function, an optical deflecting device for deflecting a light which is ejected from the optical element near a focal point in which the light which is ejected from the optical element is focused, a diffracting optical element having at least a concave reflecting surface so as to diffract the ejected light, and a reflecting mirror having a reflecting surface which is disposed near a focal point in an entire optical system of which surface shape of the reflecting mirror changes in a dispersing direction of the ejected light according the wavelength in the ejected light.
Also, according to the present invention, it may be acceptable that the reflecting surface on the optical deflecting device and the reflecting surface on the reflecting mirror are disposed on a circumference which is formed according to a radius of curvature in the concave reflecting surface in the diffracting optical element.
Also, it may be acceptable that the diffracting optical element is a concave-surfaced diffracting grating, and a grating pitch in the co
Kenyon & Kenyon
Olympus Optical Co,. Ltd.
Schwartz Jordan M.
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