Public Goods, Public Gains: Calculating the Social Benefits of Public R&D by albert n. link & john t. scott

Author:albert n. link & john t. scott
Language: eng
Format: epub
Publisher: Oxford University Press
Published: 2011-03-19T16:00:00+00:00

7

Wavelength References for Optical Fiber Communications

7.1. Background Information

The Optoelectronics Division of the Electronics and Electrical Engineering Laboratory (EEEL) at the National Institute of Standards and Technology (NIST) began research on optical communications in the mid-1970s and expanded its research program substantially in the late 1980s. 1 The Optical Fiber and Components Group of the Division began research on standard reference materials (SRMs) in 1991. The group’s first SRM became available in 1993 with SRM 2520, an optical fiber diameter standard. Since then the group has produced a number of optoelectronic standards. SRM 2517 was issued in 1997; it was intended for use in calibrating the wavelength scale of wavelength-measuring equipment in the spectral region from 1,510 nm to 1,541 nm.

In 1998, Dr. Sarah Gilbert in the Optical Fiber and Components Group began a 2-year ATP-sponsored intramural project to develop a more accurate version of SRM 2517. She received $145,000 over 2 years — $70,000 in fiscal year 1998 and $75,000 in fiscal year 1999.

The project produced the new SRM for calibration of wavelengths in the spectral region from 1,510 nm to 1,540 nm. The references in the 1,500 nm region are important to support wavelength division multiplexed (WDM) optical fiber communications systems. In a WDM system, many channels, each associated with a different wavelength, of communications information are sent down the same fiber. Thus, wavelength division multiplexing in effect increases the bandwidth of the communications system because any given spectral region will support more channels through which communications information can be sent. A WDM system requires stable wavelengths throughout the components of the system, and equipment must be calibrated to measure those wavelengths. The wavelength references provided by NIST are needed to calibrate the instruments — such as optical spectrum analyzers, tunable lasers, and wavelength meters — that are used to characterize the components of WDM optical fiber communications systems. The wavelength references are also used to monitor the wavelengths of the channels while the system is in use; if one channel’s wavelength were to shift, crosstalk could occur between it and a neighboring channel, thus disrupting the accurate flow of communications information through the channels of the system.

The output of Dr. Gilbert’s Advanced Technology Program (ATP)-funded NIST research with William Swann was SRM 2517a, High Resolution Wavelength Calibration Reference for 1,510 nm to 1,540 nm Acetylene (12C2H2). NIST’s description of the new SRM provides an exact description of the artifact — an absorption cell filled with acetylene gas that produces characteristic absorption lines in the readouts resulting when lasers project light of various wavelengths through the gas-filled cell. The absorption lines observed can then be used to identify the wavelengths for the laser emitting device being calibrated. 2 NIST’s description of the artifact is as follows:

Standard Reference Material 2517a is intended for wavelength calibration in the spectral region from 1510 nm to 1540 nm. It is a single-mode optical-fiber-coupled absorption cell containing acetylene (12C2H2) gas at a pressure of 6.7 kPa (50 Torr). The absorption path length is 5 cm and the absorption lines are about 7 pm wide.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.