Optical: systems and elements – Optical modulator
Reexamination Certificate
1999-05-21
2001-01-23
Mack, Ricky (Department: 2873)
Optical: systems and elements
Optical modulator
C359S264000
Reexamination Certificate
active
06178032
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a waveform modulator, and more particularly to an optic intensity modulator.
2. Description of Related Art
Currently, fiber optic sensors have been developed for a wide range of applications, in which a time division multiplexing (TDM) technology is a typical technology used in modern communications and fiber optic sensor network. TDM of the fiber optic sensor network has advantages of low crosstalk and simple construction. Particularly, TDM of fiber optic interferometric sensors has been shown to have the lowest crosstalk and optimum sensitivity as referred to a published paper on “J. Lightwave Technol., LT-5,pp. 1014-1023, 1987”. In a TDM fiber optic sensor system, a continuous-wave laser source can be externally modulated by an intensity modulator to generate an optic pulse. The output optic pulse of the intensity modulator with high extinction ratio (ER) is a key issue to increase the sensor sensitivity and to reduce the sensor crosstalk, especially for a TDM fiber interferometric sensor system, as referred to a published paper on J. Lightwave Technol., VOL. 14, NO.6, 1488-1500,1996.
It is very important in a TDM fiber optic sensor system to select an intensity modulator with high ER (typical ER≧30 dB) and to control the output optic pulse of an intensity modulator with optimum ER.
SUMMARY OF THE INVENTION
It is at least an objective of the present invention to provide an optical intensity modulator with optimized ER so as to obtain an optimum ER of an output optical pulse.
It is at least still another objective of the present invention to provide an optical intensity modulator with optimized ER by adjusting a direct current (DC) bias so as to obtain an optimum ER of an output optical pulse.
It is at least still yet another objective of the present invention to provide an optical intensity modulator with optimized ER, which is controlled by an automatic method.
In accordance with the foregoing and other objectives of the present invention, an optical intensity modulator with optimized ER is provided. The optical intensity modulator includes a modulator used to receive a light source, such as a laser source, and export an optical pulse. An optical divider, such as a fiber coupler, is used to receive the optical pulse and divide it into a first optical pulse and a second optical pulse. An optical receiver is used to receive the first optical pulse and convert it into an electrical pulse signal. A signal processor is used to receive the electrical pulse signal from the optical receiver and digitize it into a digital reference signal. A DC-bias generator coupled to the signal processor and the modulator is used to provide a DC bias to the modulator according to an output of the signal processor. The optical intensity modulator further includes a pulse generator used to provide a pulse signal for the modulator and a trigger signal to the signal processor. The pulse signal and the trigger signal can, for example, come from the pulse output and the trigger output of the pulse generator, respectively.
In the foregoing, a continuous-wave laser light is externally modulated into an optical pulse signal by the modulator. The optical pulse is received by the optical receiver and converted into an electrical pulse signal. The electrical pulse signal is processed by the signal processor so as to produce a reference signal. According to the reference signal, the DC-bias generator produces a feedback of precise DC bias to the modulator so as to optimize an ER ratio of the optical pulse. A current one of thereference signal is also compared with a previous one of the reference signal and is adjusted in the signal processor so as to obtain the precise DC bias.
REFERENCES:
patent: 4910458 (1990-03-01), Forsyth et al.
patent: 5132828 (1992-07-01), Conner et al.
patent: 5652669 (1997-07-01), Liedenbaum
Huang Shih-Chu
Tsay Jiunn-Song
Chung-Shan Institute of Science and Technology
Huang Jiawei
Mack Ricky
Patents J. C.
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