Long-Period Fiber Gratings as Band-Rejection Filters

sary step during packaging. For minimum
spectral shifts after recoating, one
should choose the grating periodicity
such that the LP 01, core mode couples to
the first cladding mode.
Conclusion
We have presented a new class of
long-period gratings that function as
spectrally selective loss elements.
Natural extensions of these gratings
are in spectral shape-shifting applications,
whereby the spectrum of an
existing system can be modified with
the use of these in-fibe’r devices.
Gain-flattening devices for erbiumdoped
liber amplifiers, and sensors
for measuring strain, temperature,
and refractive index have been
demonstrated. Other applications
such as switching and power monitoring
are currently being explored.
In summary, these all-fiber fillers are
versatile devices with low insertion
losses (< 0.2 dB), low back-reflections
(< −80 dB), excellent polarization
insensitivity (PMD < 0.01 ps,
PDL < 0.02 dB) and midband peak
losses (band rejection) reaching as
high as 30 dB.
Acknowledgment
The authors would like to thank V.
Mizrahi, K.L. Walker, and I.A.
White for useful discussions, W.A.
Reed for help in modeling fiber-dispersion
curves, G. Jacobovitz-
Veselka for providing the data in
Figure 11, D.S. Gasper for
PMD/PDL measurements, and S.G.
Kosinski for recoating gratings.
We are grateful to Photonetics, Inc.,
for the use of the high-sensitivity
OCDR.
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