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Up-Conversion Fiber Laser Produces Visible Output

Photonics Spectra
Aug 2004
Anne L. Fischer

Lumics GmbH of Berlin has developed a visible-wavelength source based on an up-conversion fluorozirconate (ZBLAN) fiber laser that has emission lines comparable to those from an argon-ion laser. It works by exploiting the absorption of rare-earth ions in fluoride glasses, converting infrared radiation into visible light.

The frequency-conversion process involves the stepwise absorption of multiple photons in the rare-earth ions. An IR pump photon excites the ion to a higher state, and the ion relaxes into a lower level. If a second IR photon is absorbed within the lifetime of that energy level, the ion is bumped to an even higher excited state, and a transition to another low energy level can happen.

Up-Conversion Fiber Laser Produces Visible Output
The prototype of the up-conversion fiber laser uses a 0.5-m-long active fiber coupled with standard telecom connectors to the pump source. The pump wavelength depends on the dopant in the fluoride glass fiber.

Thus, the transition wavelength can be shorter than that of the IR pump transitions. For example, with optical output power of approximately 200 mW from a 970-nm pump laser, about 10 mW of green light can be converted within an a 0.5-m-long erbium-doped ZBLAN fiber.

These fiber-coupled lasers have several advantages over argon-ion lasers, including lower cost, maintenance, power consumption and heat dissipation; smaller size; and higher fiber-coupling efficiency. Advantages over frequency-doubled laser diode sources are the same except for maintenance requirements.

Visible-wavelength fiber lasers are used in confocal microscopy, in the bioanalytic market, in eye examinations and in large-area display technologies.


GLOSSARY
argon-ion laser
gas laser using ionized argon as the active medium and applying electronic excitation in order to produce the laser light
fiber laser
A laser in which the lasing medium is an optical fiber doped with low levels of rare-earth halides to make it capable of amplifying light. Output is tunable over a broad range and can be broadband. Laser diodes can be used for pumping because of the fiber laser's low threshold power, eliminating the need for cooling.
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