Up-Conversion Fiber Laser Produces Visible Output

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.

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.