Page 472 - Tunable Lasers Handbook

432 Paul Zorabedian

high-performance instrument-grade tunable source. A WDM link containing a
fiber optic amplifier is a good example of a system that an ECL might be used to
test. Such a system contains both passive and active components.
7 8.2. 7 Testing of Passive Components

Passive components include such devices as filters, couplers, isolators, and
wavelength multiplexers. It is often necessary to measure the wavelength depen-
dence of the transmittance, splitting, and isolation of these devices [150]. Mea-
surements of the fiber chromatic dispersion [ 15 l, 1521 and polarization-mode
dispersion [ 1531 in fiber and in optical components also require tunable ECLs.
7 8.2.2 Testing of Optical Amplifiers
ECLs are used to test the gain, polarization sensitivity, and saturation char-
acteristics of traveling-wave semiconductor amplifiers [ 1541 and rare-earth-
doped optical fiber amplifiers [155]. At present, optical fiber amplifiers are com-
mercially dominant over semiconductor amplifiers. Low noise, high output
power, and wide tuning range are important requirements of the tunable laser
used for amplifier testing.

7 8.2.3 Swept-Source Measurements
The ability to observe the transmission or reflection spectrum in real time
would be of considerable value for making adjustments to optical components
and systems. The wavelength agility of the acousto-optically tuned ECL makes
it viable as a swept source for optical network analysis (Fig. 50). Swept-source
measurements have been made on A0 filters serving as devices under test [46].
The measured transmission characteristics were in good agreement with results
obtained using a grating-tuned ECL (Fig. 5 1).

1 8.3 High-Resolution Atomic Spectroscopy
The ease of use and broad tunability of ECLs makes them attractive replace-
ments for dye and Ti:sapphire lasers in a number of high-resolution atomic spec-
troscopy applications. Absorption lines of calcium cesium. iodine, oxygen, neon,
and uranium vapors lie within the tuning ranges of 650-, 780-, and 850-nm
ECLs [37,156,157].

18.4 Gas Monitoring
ECLs with InGaAsPDnP and InGaAsflnP gain media can tune to transitions
in a number of molecular gas species, for example HF (1.31 pm), H,O (1.39
pm), HO, (1.5 pm), H,F (1.57 pm), and CH, (1.65 pm). Carbon monoxide can
also be detected using its vibrational overtones at around 1.65 ym. Applications