Bell Labs Scientists Demonstrate Record-Setting Ultra-High-Power Single-Mode Fiber Lasers

Donna Cunningham
802-482-3748 (office)
802-482-2933 (home)
donnac@lucent.com

Carl Blesch
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cblesch@lucent.com

FOR RELEASE WEDNESDAY, MAY 28 , 1997

MURRAY HILL, N.J. -- Bell Labs scientists, working with colleagues at Opto Power Corp. in Tucson, Ariz., have demonstrated record-setting output powers from optical-fiber lasers. The fiber lasers, each pumped by a single semiconductor laser and with the output coupled directly into a single-mode fiber, produced 8 to 21 watts of power.

The research team has built a cascaded Raman fiber laser with an output power of 8.5 watts at 1472 nanometers; the laser could be used to boost communications signals in long-haul communications systems. Conventional lasers used for this purpose typically produce only one tenth of a watt.

They’ve also built fiber lasers, with ytterbium-doped fiber cavities defined by two fiber Bragg gratings, that yield 16.4 watts of power at 1065 nanometers and 20.4 watts at 1101 nanometers into a single-mode fiber. The lasers’ output power levels are about 80 and 300 percent higher than other single-mode fiber lasers operating at 1065 and 1100 nanometers, respectively.

The fiber lasers were pumped by a single high-power laser-diode array with more than 40 watts of optical power at 915 nanometers.

In these high-power fiber lasers, light from a semiconductor laser is guided within the outer layer, or cladding, of a specially developed fiber with a single-mode core containing the rare-earth element ytterbium. The light is absorbed by the ytterbium, which changes its wavelength and makes it possible to “pump” optical amplifiers that boost communications signals. They make it possible for the signals to travel longer distances and are powerful enough to be used as a single source for distribution of the signals, through a router, to many users.

“The ability to have these high output powers coupled into a single-mode fiber is unprecedented in telecommunications technology,” said Kenneth Walker, head of the Bell Labs Optical Fiber Research department. “Their power levels are so high that they may be more practical as very high-power amplifiers in free-space communications than in traditional terrestrial fiber systems. It takes a lot of power to transmit signals through fog, snow, and/or rain without degradation or for the distances of greater than 10,000 kilometers that are necessary for satellite-to-
satellite communications.”

The lasers have potential applications in telecommunications, materials processing, printer and medical fields.

“In principal, the ytterbium-doped lasers can operate at any wavelength from 1050 to 1140 nanometers, “ said researcher Daryl Inniss. “Our results suggest that even higher diffraction-limited continuous-wave output power can be produced in the 1050-to-1700-nanometer wavelength region. Cascaded Raman lasers can be used to efficiently convert these output powers to wavelengths as long as 1.7 micrometers.

Inniss presented the research team’s latest experimental results in a talk at the joint Conference on Lasers and Electro-Optics (CLEO '97) and Quantum Electronics and Laser Science Conference (QELS '97) in Baltimore last week.

Other members of the research team are D.J. DiGiovanni, T.A. Strasser, A. Hale, C. Headley, A.J. Stentz, R. Pedrazzani, D. Tipton, S.G. Kosinski, D.L. Brownlow, K.W. Quoi, K.S. Kranz, R.G. Huff, R. Espindola, J.D. LeGrange and G. Jacobovitz-Veselka, working with D. Boggavarapu, X. He, D. Caffey, S. Gupta, S. Srinivasan, K. McEuen and R. Patel of Opto Power Corp., Tucson, Ariz.

"Breakthroughs in record, reliable, CW high-power laser-diode arrays have unleashed the high-power potential of fiber lasers," said Rushi Patel, vice president, engineering, Opto Power Corp.

Lucent Technologies designs, builds and delivers a wide range of public and private networks, communications systems and software, consumer and business telephone systems and microelectronics components. Bell Labs is the research and development arm for the company.

Bell Labs has a long history of laser invention and innovation, beginning in 1958 with publication of the scientific paper describing the concept of the laser by Arthur Schawlow and Charles Townes. Both worked for Bell Labs at the time, Schawlow as a researcher and Townes as a consultant.

Further information about the company is available at http://www.lucent.com.

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BELL LABS ULTRA-HIGH-POWER SINGLE-MODE FIBER LASERS
ADDITIONAL TECHNICAL INFORMATION

Bell Labs researchers, working with colleagues at Opto Power Corp., have demonstrated ultra-high-power single-mode fiber lasers from 1.065 to 1.472 micrometers, using ytterbium-doped cladding-pumped and cascaded Raman lasers.

They have demonstrated the highest reported output powers at multiple wavelengths with well defined spectral outputs in a conventional single-mode fiber. They have shown that ytterbium-doped fiber cavities defined by two fiber Bragg gratings are both efficient and versatile when lasing at either 1065 or 1101 nm. They have built and operated cascaded Raman fiber lasers with an output power of 8.5 watts at 1472 nm, demonstrating that these output powers can be efficiently converted to any desirable wavelength between 1.1 and 1.7 micrometers.

The fiber lasers were assembled with Yb-doped cladding pumped fiber having a low index polymer coating. The high reflector (99.9 percent reflectivity) was UV-induced in D2 sensitized fiber by conventional phase mask exposure at 242 nm. The output coupler of the cavity was a similar UV-induced grating in a standard high-index coated fiber. The cavities were assembled by fusion spicing the fiber gratings to the Yb-doped fiber. The fiber laser was pumped by a single Opto Power 915 nm one-centimeter-wide high-power semiconductor laser bar in a specially designed beam-shaper configuration for optimal fiber coupling. Power levels of more than 40 watts from a 400-micrometer 0.22 NA fiber were achieved.

At 1065 nm, 16.4 W is the highest power reported from any cladding-
pumped fiber laser. The previous highest power reported is 9.2W from a Nd-doped cladding-pumped fiber laser pumped with 40W, with an output bandwidth of 13 nm. At 1101 nm, the 20.4 W is the highest conventional fiber-coupled single-mode output power from a fiber laser; the 8.5 W output power of the cascaded Raman laser is the highest power available for pumping a conventional Er amplifier.

The researchers have demonstrated the great flexibility and excellent performance of Yb-doped cladding-pumped cavities defined by fiber Bragg gratings. In principal, this laser can operate at any wavelength from 1050 nm to 1140 nm, where Yb is a quasi-four-level system. Cascaded Raman lasers can be used to efficiently convert these output powers to wavelengths as long as 1.7 microns.

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