Hybrid Wavelength Calibration Reference Demonstrated
Mary Rowe and Bill Swann have developed a multiple-wavelength calibration reference that incorporates the wavelength flexibility of fiber Bragg grating artifact references and the stability of fundamental molecular absorption references. A prototype wavelength calibration unit was demonstrated at the Navy Primary Standards Laboratory (NPSL), San Diego, in December 2002. The NIST prototype uses interleaved sampled fiber Bragg gratings to produce multiple peaks in the 1300 and 1550 nm regions, with one 1550 nm peak stabilized to a molecular absorption line. The unit provides 8 calibration references between 1297 and 1306 nm and 12 references between 1531 and 1550 nm. The wavelength of each grating peak is quite stable; we measured one of the 1300 nm gratings and found it had a standard deviation of 0.7 pm over a 70-days period. The hybrid reference has been extended to the 850 nm region and we plan to deliver a unit to NPSL containing certified calibration references in the 850, 1300, and 1550 nm regions.

Supercontinuum Amplitude Noise Study
Kristan Corwin, Nathan Newbury, and Brian Washburn have completed a study of the low frequency (technical) and broadband amplitude noise on supercontinua generated when femtosecond laser pulses propagate in microstructure fiber. Washburn has also developed a numerical simulation to predict the supercontinuum properties.

Raman Gain Measurements
We have developed and fully documented a simple technique to measure the full wavelength dependence of the Raman gain. We have also participated in a Telecommunications Industry Association round robin measurement intercomparison for Raman gain; measuring the Raman gain of 5 different fiber samples. As of February 2004, this round robin is still in progress.

Near IR Frequency Measurements Using Newly-Developed Frequency Comb
Kristan Corwin, Tasshi Dennis, Sarah Gilbert, Nate Newbury, and Bill Swann, in collaboration with staff of the Optical Frequency Measurements Group of the NIST Time and Frequency Division, have developed the capability to accurately measure optical frequencies across the near infrared region from 1100 to 2000 nm, including the important telecommunication window from 1300 to 1600 nm. The system is based on a stabilized infrared frequency comb, which comprises a mode-locked Cr:forsterite laser whose output is spectrally broadened in highly nonlinear fiber to generate a supercontinuum spanning from 1100 nm to beyond 2000 nm. Since the laser operates at a repetition rate of 430 MHz, the supercontinuum is actually a comb of individual frequency lines with 430 MHz spacing. By locking the frequency comb to both a hydrogen maser and the calcium optical frequency standard, an accurate frequency ruler is formed covering this entire near infrared region. Any unknown optical frequency can then be measured by simply comparing its frequency to that of the nearest tooth of the stabilized frequency comb. We have used this technique to make measurements of telecommunication optical frequency references, including three methane absorption lines in the 1300 nm region and a 1560 nm laser stabilized to a rubidium line. We have also used it to calibrate the physical length of a prototype compact length standard.

Fiber Laser-Based Frequency Comb for Frequency Metrology in the Infrared Developed
Nate Newbury and Brian Washburn, in collaboration with OFS Technologies and Scott Diddams of the NIST Time and Frequency Division have developed the first self-referenced phase-locked frequency comb in the 1100 to 2200 nm wavelength region. The phase-locked frequency comb is based on a mode-locked, erbium-doped fiber laser whose output is amplified and spectrally broadened in novel dispersion-flattened, highly nonlinear optical fiber to span this wavelength range. This supercontinuum actually comprises a comb of frequency lines, separated by the laser repetition rate and with an arbitrary frequency offset. Borrowing the now standard techniques used with Ti:sapphire laser-based systems, the researchers phase-locked both the comb spacing and offset to an RF oscillator, forming a frequency ruler covering the near infrared region from 1100 to 2200 nm. A fiber laser-based system can be much more compact, robust, power-efficient, and lighter than a bulk optic solid-state laser system, and can require less alignment.

SRM 2513
Mode Field Diameter Standard for Single-Mode Fiber; available.

SRM 2514
Wavelength Calibration Reference for 1560-1595 nm - Carbon Monoxide ¹²C¹⁶O; available.

SRM 2515
Wavelength Calibration Reference for 1595-1630 nm - Carbon Monoxide ¹³C¹⁶O; available.

SRM 2517a
High Resolution Wavelength Calibration Reference for 1510-1540 nm - Acetylene ¹²C₂H₂; available.

SRM 2519
Wavelength Reference Absorption Cell - Hydrogen Cyanide (H¹³C¹⁴N); available.

SRM 2520
Optical Fiber Diameter Standard; available.

Additional SRMs for optical fiber communications produced by NIST: SRMs 2522 & 2523 for optical fiber ferrule geometry and SRMs 2553-2555 for optical fiber coating diameter. Please visit our SRM page for more information.