14.2 Survey of Test Equipment
583
Fig. 14.2 Operation of a
grating-based optical
spectrum analyzer
most common implementation uses an optical filter based on a diffraction grating,
which yields wavelength resolutions to less than 0.1 nm. Higher wavelength accuracy
(±0.001 nm) is achieved with wavelength meters based on Michelson interferometry.
Figure 14.2 illustrates the operation of a grating-based optical spectrum analyzer.
Light emerging from a fiber is collimated by a lens and is directed onto a diffraction
grating that can be rotated. The exit slit selects or filters the spectrum of the light
from the grating. Thus it determines the spectral resolution of the OSA. The term
resolution bandwidth describes the width of this optical filter. Typical OSAs have
selectable filters ranging from 10 nm down to 0.1 nm. The optical filter characteristics
determine the dynamic range, which is the ability of the OSA to simultaneously view
large and small signals in the same sweep. The bandwidth of the amplifier is a major
factor affecting the sensitivity and sweep time of the OSA. In the O-band through
L-band the photodiode is usually an InGaAs device.
The OSA normally sweeps (scans in a certain time interval) across a spectral
band making measurements at discretely spaced wavelength points. This spacing
depends on the bandwidth-resolution of the instrument and is known as the tracepoint spacing.
14.2.3 Multipurpose Test Equipment
To reduce the number of individual pieces of test gear that a field support engineer
needs to carry around, manufacturers are producing compact test equipment with
units for multiple functions. Of particular interest are multipurpose handheld test
units for the installation, turn-up, and maintenance of optical fiber links in enterprise
networks, metro networks, and PONs. A typical single handheld instrument might
incorporate functions such as a power meter, a bidirectional dual-wavelength loss
tester, an optical return-loss tester, a visual fault indicator for locating breaks and
failures in a fiber cable, and a talk set for full-duplex communications between
field personnel. Test results can be displayed on a typical 5-in. high-resolution color
583
Fig. 14.2 Operation of a
grating-based optical
spectrum analyzer
most common implementation uses an optical filter based on a diffraction grating,
which yields wavelength resolutions to less than 0.1 nm. Higher wavelength accuracy
(±0.001 nm) is achieved with wavelength meters based on Michelson interferometry.
Figure 14.2 illustrates the operation of a grating-based optical spectrum analyzer.
Light emerging from a fiber is collimated by a lens and is directed onto a diffraction
grating that can be rotated. The exit slit selects or filters the spectrum of the light
from the grating. Thus it determines the spectral resolution of the OSA. The term
resolution bandwidth describes the width of this optical filter. Typical OSAs have
selectable filters ranging from 10 nm down to 0.1 nm. The optical filter characteristics
determine the dynamic range, which is the ability of the OSA to simultaneously view
large and small signals in the same sweep. The bandwidth of the amplifier is a major
factor affecting the sensitivity and sweep time of the OSA. In the O-band through
L-band the photodiode is usually an InGaAs device.
The OSA normally sweeps (scans in a certain time interval) across a spectral
band making measurements at discretely spaced wavelength points. This spacing
depends on the bandwidth-resolution of the instrument and is known as the tracepoint spacing.
14.2.3 Multipurpose Test Equipment
To reduce the number of individual pieces of test gear that a field support engineer
needs to carry around, manufacturers are producing compact test equipment with
units for multiple functions. Of particular interest are multipurpose handheld test
units for the installation, turn-up, and maintenance of optical fiber links in enterprise
networks, metro networks, and PONs. A typical single handheld instrument might
incorporate functions such as a power meter, a bidirectional dual-wavelength loss
tester, an optical return-loss tester, a visual fault indicator for locating breaks and
failures in a fiber cable, and a talk set for full-duplex communications between
field personnel. Test results can be displayed on a typical 5-in. high-resolution color