NIST/Lucent Team Develops Method For Ultraprecise Optical Frequency Measurements

Reported in tomorrow’s Science, the technique uses a single laser to measure optical frequency instead of a cumbersome and expensive multiple laser system. The measurements made by the NIST/Lucent system have a higher level of precision than conventionally derived ones because they are compared to the well-defined primary frequency standard of a cesium-133 atomic clock. Eventually, the researchers believe that the level of precision for their technology will be limited only by the performance of the primary standard itself.

The experiments were conducted at JILA, a joint research endeavor of NIST and the University of Colorado at Boulder.

The researchers "locked" a radio-frequency-clock-stabilized titanium-sapphire laser in a manner that generated a repetitive train of ultrashort optical pulses (referred to as a "repetition frequency"). Each pulse is so short that it contains only about three cycles of light.

The output spectrum of such a laser is a series of sharply defined spectral lines, separated by the repetition frequency. The scientists call this spectrum a "comb" because it has the appearance of a common pocket comb.

Ordinarily, there would be no fixed relationship between the envelopes of the pulses and the wavelength of the laser light, but in this work, the envelope and the wavelength are locked together with a controlled phase relationship. In addition, the repetition rate of the pulses is locked to the standard cesium microwave frequency (9.2 gigahertz). This makes it possible to determine the absolute frequency of each of the "teeth" of the comb, and provides a means of measuring optical frequencies with a single laser.

A visible continuum of lightwave frequencies is generated within a novel air-silica microstructure fiber. Light is very tightly confined to the glass fiber’s solid core by a ring of air holes surrounding the core. This unusual fiber creates an extremely small effective area, possesses special characteristics for light dispersion and keeps light loss to a minimum. This allows for generation of a frequency continuum with only one thousandth of the power previously needed.

As a non-regulatory agency of the U.S. Department of Commerce’s Technology Administration, NIST strengthens the U.S. economy and improves the quality of life by working with industry to develop and apply technology, measurements and standards through four partnerships: the Measurement and Standards Laboratories, the Manufacturing Extension Partnership, the Advanced Technology Program, and the Baldrige National Quality Program. For more information about NIST, see the agency’s web site at http://www.nist.gov. JILA’s web site is at http://jilawww.colorado.edu.

Lucent Technologies, headquartered in Murray Hill, N.J., designs and delivers the systems, software, silicon and services for next-generation communications networks for service providers and enterprises. Backed by the research and development of Bell Labs, Lucent focuses on high-growth areas such as optical and wireless networks; Internet infrastructure; communications software; communications semiconductors and optoelectronics; web-based enterprise solutions that link private and public networks; and professional network design and consulting services. For more information on Lucent Technologies and Bell Labs, visit the company’s web site at http://www.lucent.com or the Bell Labs web site at http://www.bell-labs.com.

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For more information about NIST, see our web site at http://www.nist.gov.