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Fiber Laser Sets a Record

Photonics Spectra
Aug 1997
Kathleen G. Tatterson

MURRAY HILL, N.J. -- A recent demonstration of optical fiber lasers with ultrahigh output powers could have implications for telecommunications, materials processing and medical applications, according to the scientists who developed the technology.
In their report, researchers at Bell Labs-Lucent Technologies and Opto Power Corp. of Tucson, Ariz., showed that ytterbium-doped fiber cavities defined by two fiber Bragg gratings are efficient and versatile when lasing at 1065 or 1101 nm. Also, the group has produced Raman cascaded fiber lasers with an output of 8.5 W at 1472 nm, demonstrating that these output powers can be converted efficiently to any wavelength between 1.1 and 1.7 µm, said Bell Labs researcher Daryl Inniss. The laboratory called these output powers record-setting at these wavelengths; in 1995, H. Zellmer, et al., reported an output of 9.2 W from a pumped fiber laser with Nd-doped cladding with 40 W and output bandwidth of 13 nm.

Researcher Daryl Inniss makes adjustments to Bell Laboratories' fiber laser system.
The laser system will allow transmission of optical signals over longer distances, which is suited for cable TV applications. "We envision architectures with trunk and branching using one transmitter and many receivers," Inniss said. The team presented its findings in May at the Joint Conference on Lasers and Electro- Optics/Quantum Electronics and Laser Science Conference in Baltimore.
These optical fiber lasers are small, compact devices (2 3 2 3 1 ft) that plug into standard wall outlets and operate at room temperature. They have an advantage over diode-pumped solid-state lasers, Inniss said, because fiber lasers do not experience thermal lasing problems and the output power is intrinsically single-mode. The size issue is also advantageous in the medical arena because the lasers eliminate the cumbersome water-cooling apparatus typically used. The system could be applied to optical coherence tomography imaging as well as microsurgery.
A single high-power laser diode array pumps the high-power fiber lasers with more than 40 W of optical power at 915 nm. The system guides the light from a Raman cascade laser within the cladding of a fiber with a single-mode core containing ytterbium, which absorbs the light, changing its wavelength through stimulated emission at a desired wavelength defined by the Bragg gratings. The output from the cladding-pumped fiber laser can be used to pump a cascaded Raman resonator cavity, making it possible to pump optical amplifiers that boost communications signals. Therefore, signals can travel longer distances and, through a router, can provide a single source for wide signal distribution.
Inniss said that Lucent, the laboratory's parent company, plans to commercialize the technology within the next 18 months, possibly in the form of high-end printers for the medical and graphic arts industries where ultrahigh resolution is key.


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