40 and 100 Gb/s Ethernet services have been recently defined and 400G and 1 Tb/s services are anticipated in the future.
Optical transport networks are capable of separating the services provided and the underlying optical transport; service
bandwidths may be larger or smaller than the bandwidth carried on a single optical 'wave'. In this work, we compare
different arrangements of optical transport systems using polarization division multiplexed (PDM) coherent modulation
formats of 4 to 8 bits/symbol for baud rates spanning 8 - 91 GHz. A nonlinear threshold has been defined and nonlinear
performances are compared over 20 uncompensated spans of SMF and NZDSF for various modulation formats. The
finding is that lower baud rate equates to slightly more reach at equal capacity. For example, for 100G using single
carrier vs. dual carrier on a 50 GHz BW, it is observed that for the EDFA-only case, using dual-carrier transmission
yields a reach improvement of 5%, whereas in the Raman-assisted EDFA case, a reach improvement of 4% in favor of
dual-carrier transmission. This shows that one can achieve the same or better optical performance without having to
drive up the baud rate and the speed of associated electro-optics.
We demonstrate experimentally that a fiber optic gyroscope (FOG) using an air-core fiber coil can be operated with a
laser and still exhibit a fairly low phase noise. This noise is measured to be 1000 μrad/√Hz with a single-frequency laser,
and 150 μrad/√Hz when the frequency is swept. When the fiber is replaced with SMF-28 fiber, these figures drop to 100
and 14 μrad/√Hz, respectively. This last value is 35 times lower than the previous record. Comparison to a new model
shows that this noise is limited by coherent backscattering, and that the backscattering coefficient inferred for the air-core
fiber is ~11 times higher than for the SMF-28 fiber. By reducing the air-core fiber loss from its current high value
(24 dB/km) to its theoretical limit (~0.15 dB/km), we predict that this laser-driven air-core FOG will have a noise of only
~0.3 μrad/√Hz, and thus outperform commercial FOGs in terms of not only noise, but also improved thermal and mean-wavelength
Long-period fiber gratings (LPFGs) have recently been utilized as optical bend sensors by observing changes in their transmission spectra as the fiber is bent. One such spectral change reported is the "splitting" of each attenuation notch into two. To date, explanations given for this apparent notch splitting have proven unsatisfactory. In this communication, we show that the apparent notch splitting is due neither to a splitting of degenerate cladding modes nor to the phase-matching condition being satisfied at multiple wavelengths for a given cladding mode. In contrast, bending causes new notches to be formed at nearby wavelengths as a result of coupling to asymmetric cladding modes that are not coupled to in a straight UV-induced LPFG. With increased bending, these new notches' central wavelengths shift in the opposite direction as the original notches, thus causing the apparent splitting of the latter. We use a numerical analysis to show that the cladding modes of a fiber undergo large spatial changes when the waveguide is bent. These changes allow coupling in a bent fiber between modes with differing azimuthal symmetry even with a uniform UV-induced index perturbation. All of the primary experimental effects published thus far are
well-described with this analysis. This improved understanding of bent LPFGs will be important for the development of devices and is also relevant whenever there is interaction with the cladding modes in a curved optical fiber.
We show theoretically and experimentally that the use of an air-core photonic-bandgap fiber in a fiber-optic gyroscope can drastically reduce the noise and phase drift caused by Rayleigh backscattering as well as non-reciprocal and thermal effects.