The figure depicts the laboratory setup of an optical-fiber-coupled microsphere laser with an output in the 1.55-µm wavelength band used in some communication systems. This laser offers the obvious advantages of compactness and simplicity. In addition, as consequences of the high resonance quality factor (Q) and smallness of the microsphere, it also offers the non-obvious advantages of a high degree of spectral purity and a low threshold power level. This laser could be useful as a source of highly coherent infrared light or, if operated in a subthreshold regime, as a low-noise front-end amplifier in optical communication. Alternatively, with the addition of active mode locking, this laser could be the core of an ultra-compact optoelectronic oscillator that would generate a light signal modulated by a microwave signal according to the principle described in "Closed-Loop Microsphere Laser for Optoelectronic Oscillator" (NPO-20597),NASA Tech Briefs, Vol. 25, No. 9 (September 2001), page 14a.
The microsphere serves as both the resonator and the gain medium of the laser. It is made of a standard erbium-doped aluminosilicate glass ordinarily used as the core material of communication-band fiber-optic amplifiers. The pump light, at a wavelength of 977.6 nm, is generated by a diode laser. The pump light is supplied to the microsphere through a single angle-polished fiber-optic evanescent-wave coupler like the one described in "Simple Fiber-Optic Coupling for Microsphere Resonators" (NPO-20619), Vol. 25, No. 5 (May 2001), page 70.
Inside the microsphere, the pump light excites "whispering-gallery" waveguide modes that circulate by virtue of total internal reflection. In a standard erbium-doped-fiber laser or amplifier, the length of the active fiber must be at least a few meters to obtain enough absorption of the pump light. In the microsphere laser, the circulation of the "whispering-gallery" modes provides the necessary path length for absorption, thus making it possible to reduce the laser volume drastically. The 1.55-µm laser radiation is coupled back into the optical fiber and selected for output by a wavelength-division demultiplexer.
This work was done by Vladimir Iltchenko, Steve Yao, and Lutfollah Maleki of Caltech for NASA's Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
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Refer to NPO-20918.