Coherent light generators – Particular beam control device – Q-switch
Reexamination Certificate
1998-03-16
2001-04-03
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular beam control device
Q-switch
C372S018000, C372S037000, C372S098000
Reexamination Certificate
active
06212209
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to switchable lasers and, more particularly, to Q-switched lasers and mode-locked lasers.
BACKGROUND OF THE INVENTION
Pulsed lasers are used in a wide variety of applications ranging from signal sources in telecommunications systems to optical sources in sensing and measuring equipment. Q-switched lasers, for example, provide high power, short duration pulses for optical sensing functions, optical time domain reflectometry, and the measurement of nonlinearities in optical fibers. Illustratively, Q-switched lasers are capable of generating peak pulse powers of the order of a few hundred watts or more at repetition rates in the tens of kilohertz range. Pulse durations of about 1-100 nanoseconds are typical. Mode-locked lasers, on the other hand, may serve as high speed (e.g., multi-gigabit) signal sources in telecommunications systems, particularly soliton transmission systems. As such, the mode-locked laser may generate peak pulse powers of a few hundred milliwatts at repetition rates in excess of 10 Ghz. Pulse durations of a few picoseconds are typical.
Q-switched and mode-locked lasers have been extensively reported in the scientific literature. Two basic structures have been successfully demonstrated: a fiber laser ring topology of the type described by F. Fontana et al. in U.S. Pat. No. 5,381,426 issued on Jan. 10, 1995 and a Fabry-Perot (FP) fiber laser configuration of the type shown in U.S. Pat. No. 5,450,427 granted to M. E. Fermann et al. on Sep. 12, 1995. Most conventional laser designs rely on the use of an electro-optic, acoustic-optic or absorption modulators. These modulators are all bulk optic components, rendering the overall laser design less integrable, or limited to certain configurations or materials.
Thus, a need remains in the art for a relatively simple switched laser design.
SUMMARY OF THE INVENTION
The need remaining in the prior art is addressed by the present invention, which relates to a switched laser configuration and, more particularly, to a switched laser that uses a switchable Faraday rotator to control the switching activity in the laser.
In a preferred embodiment the switchable laser comprises a switchable Faraday mirror coupled to a gain medium, with a second reflective surface disposed beyond the output of the medium. The laser's cavity length is defined by the combination of the switchable Faraday mirror, gain medium and second reflective surface. The switching function within the Faraday mirror is controlled by an applied magnetic field. When no magnetic field is applied, the Faraday rotator isolates the first reflective surface from the second reflective surface and no lasing occurs. When a magnetic field is then applied, the Faraday rotator becomes transmissive and a lasing cavity is formed by the pair of reflectors on either side of the gain medium, providing lasing and gain at the frequency determined by the total cavity length. Therefore, the switching activity of the laser is controlled by switching the magnetic field applied to the laser. A current or voltage applied to a magnetic source is used to provide the switchable magnetic filed in the first instance.
In general, a Faraday rotator yields a 90° polarization rotation to the signal passing therethrough. Thus, in order to provide an appropriate aligned amplified output signal, the signal must make two passes through the laser cavity so that it is fully rotated 180°. In an alternative embodiment of the present invention, the Faraday rotator device may be formed to comprise twice its conventional length so that the signal will rotate through the full 180° before entering the laser gain medium. Additionally, the second mirror forming the laser may be a bandwidth-limited mirror including a grating (such as a UV fabricated grating) structure to produce the necessary wavelength selectivity.
Other and various features of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.
REFERENCES:
patent: 4637027 (1987-01-01), Shirasaki
patent: 4975918 (1990-12-01), Morton
patent: 5701319 (1997-12-01), Fermann
patent: 5732095 (1998-03-01), Zorabedian
patent: 5923686 (1999-07-01), Fermann
Arroyo Teresa M.
Inzirillo Gioacchino
Koba Wendy W.
Lucent Technologies - Inc.
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