Optical: systems and elements – Optical modulator – Light wave temporal modulation
Utility Patent
1999-03-08
2001-01-02
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S108000
Utility Patent
active
06169625
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a saturable absorption type optical switch including a semiconductor element provided with a saturable absorption region and a controlling method therefor suitable for use with optical communication, optical information processing, optical measurement and so forth.
2. Description of the Related Art
In recent years, demand has been increasing for development of technology of a transmission system for a data train composed of optical pulses having a time width smaller than several [ps] or a repetition frequency exceeding several tens [Gb/s] to hundred [Gb/s] and a controlling method therefor as basic technology for very high speed optical communication or optical information processing. It is to be noted that [b/s] is a representation of a quantity of pulses per second in units of a bit.
In such a situation as described above, it is required to produce stable and coherent optical pulses as well as to establish production technology for a very high speed optical pulse data train, technology for dividing and extracting a very high speed optical pulse data train, and technology for recovery of the waveform of a very high speed pulse data train which has been distorted with respect to time during transmission. Particularly for the division and extraction and the recovery of the waveform of a very high speed optical pulse data train, an optical switch which operates at a very high speed is required. Normally, since it is difficult to electrically control such an optical switch as mentioned above from a restriction in the response speed, it is desirable to control it with an optical signal.
As an optical switch of the type mentioned, an optical switch has been proposed which includes a semiconductor element (hereinafter referred to as saturable absorption type optical element) provided with a saturable absorption region. The optical switch is hereinafter referred to as saturable absorption type optical switch. The saturable absorption type optical switch is a semiconductor optical element whose output power characteristic with respect to an input power has some non-linearity as shown in
FIG. 1
due to its saturable absorption effect.
If signal light of a low optical power is inputted to a saturable absorption type optical element whose output power characteristic has some non-linearity, then the signal light is acted upon and attenuated by a strong absorbing action (absorption region). On the other hand, if signal light of a high optical power is inputted, then the signal light is transmitted through the saturable absorption type optical element because the absorbing action of the saturable absorption type optical element is saturated (transmission region). Detailed technology of the saturable absorption type optical element is disclosed, for example, in Yoichi Hashimoto, “Optical noise reduction by a semiconductor waveguide saturable absorber”, Technical Digest of CPT'98, Jan. 12-14, 1998, in corporation with IEICE Electronics society & IEEE LEOS & OSA, pp.215-216.
As shown in
FIG. 2
, a conventional saturable absorption type optical switch is composed only of a saturable absorption type optical element. If signal light (wavelength &lgr;S) and control light (wavelength &lgr;C) are inputted to the saturable absorption type optical switch with the power of the signal light set within the absorption region shown in FIG.
1
and with the total power of the signal light and the control light set within the transmission region shown in
FIG. 1
, then absorption or transmission of the signal light can be controlled by ON/OFF of the control light.
However, such a conventional saturable absorption type optical switch as described above has a problem in that, if an optical amplifier which is popularly used in an optical communication system to control the output power to a fixed level is disposed in a preceding stage, then even if the power of the control light is controlled ON/OFF, since the power of the control light inputted to the saturable absorption type optical element is controlled to the fixed value by the optical amplifier, the saturable absorption type optical switch cannot operate as an optical switch.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a saturable absorption type optical switch and a controlling method therefor which allow ON/OFF control of signal light without controlling the power of control light ON/OFF.
In order to attain the object described above, according to the present invention, there is provided a saturable absorption type optical switch, comprising a saturable absorption type optical element provided with a saturable absorption region, and a band-block optical filter to which signal light composed-of at least one wavelength light having an optical power in the absorption region of the saturable absorption type optical element and control light whose optical power is set such that a total power of the signal light and the control light comes within a transmission region of the saturable absorption type optical element and which is composed of either one of two wavelength lights different from that of the signal light are inputted and which transmits therethrough the signal light and the control light which is composed only of one of the wavelength lights and outputs the transmitted signal light and control light to the saturable absorption type optical element.
In the saturable absorption type optical switch having such a construction as described above, since the optical power of the signal light is within the absorption region of the saturable absorption type optical element, even if only the signal light is inputted to the saturable absorption type optical element, it cannot be transmitted through the saturable absorption type optical element. Meanwhile, since the optical power of the control light is set such that the total power of the signal light and the control light may be within the transmission region of the saturable absorption type optical element, if the control light and the signal light are inputted simultaneously to the saturable absorption type optical element, then they are transmitted through the saturable absorption type optical element.
Since the band-block filter allows transmission therethrough only of the signal light and the control light which is compose of the one wavelength light, the control light which is composed of the other wavelength light is not inputted to the saturable absorption type optical element. Accordingly, transmission or absorption of the signal light by the saturable absorption type optical element can be controlled by varying the wavelength of the control light.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with references to the accompanying drawings which illustrate examples of the present invention.
REFERENCES:
patent: 6091536 (2000-07-01), Usami et al.
patent: 0942319 (1994-09-01), None
patent: 2776083 (1999-12-01), None
patent: 61-38935 (1986-02-01), None
patent: 8-082813 (1996-03-01), None
Optical Noise Reduction by a semiconductor waveguide Saturable Absorber, Hashimoto, 998, Technical Digest of CPT '98 in Cooperation with IEICE Electronics Society & EEE LEOS & OSA, pp. 215-216.
Watanabe Seiji
Yamaguchi Shohei
Hellner Mark
NEC Corporation
Scully Scott Murphy & Presser
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