Interaction forces among solitons in optical fibers.

The propagation of light pulses as solitons in optical fibers may form the basis of a viable means of communication. We show here from the general two-soliton function that solitons in fibers exert forces on their neighbors that decrease exponentially with the distance between them and depend sinusoidally on their relative phase. These forces account for the displacements suffered by solitons during collisions, and their effects must be taken into account in system design.

Theory of the soliton self-frequency shift.

Raman effects cause a continuous downshift of the mean frequency of pulses propagating in optical fibers. For solitons in silica fibers, the effect varies roughly with the inverse fourth power of the pulse width. At 1.5-microm wavelength in a fiber with 15 psec/nm/km time-of-flight dispersion, a soliton of 250-fsec duration is predicted to shift by its own spectral width after about l00m of propagation. The theory agrees well with recent measurements.

Optical resonator with negative dispersion.

Analysis of an optical ring resonator consisting of a prism and two mirrors demonstrates that such a resonator can have adjustable dispersion of either sign. The dispersion is proportional to the second derivative of the optical path length in the resonator with respect to wavelength. Adjustable dispersion may have important application to the production of ultrashort laser pulses.

Stability of radiation-pressure particle traps: an optical Earnshaw theorem.

We prove an optical radiation Earnshaw theorem: A small dielectric particle cannot be trapped by using only the scattering force of optical radiation pressure. A corollary is that the gradient or dipole force is necessary to any successful optical trap. We discuss the implications of the theorem for recent proposals for the optical trapping of neutral atoms.

Phase noise in photonic communications systems using linear amplifiers.

Spontaneous emission noise limits the capacity and range of photonic communications systems that use linear optical amplifiers. We consider here the question of phase detection in such systems. Amplitude-to-phase-noise conversion occurs owing to the nonlinear Kerr effect in the transmission fiber, resulting in optimal phase noise performance when the nonlinear phase shift of the system is approximately 1 rad. Error-free state-of-the-art systems that use phase detection at multigigabit rates are thereby limited to a range of a few thousand kilometers.

Birefringence-mediated timing jitter in soliton transmission.

We describe the only two significant effects of the residual birefringence of high-quality fibers on solitons in long-distance transmission: a possible gradual accumulation of differential transit time between orthogonally polarized solitons and a jitter in pulse arrival times, initiated by noise modulation of the polarization states of the pulses and mediated by the birefringence.

PMD fundamentals: polarization mode dispersion in optical fibers.

This paper reviews the fundamental concepts and basic theory of polarization mode dispersion (PMD) in optical fibers. It introduces a unified notation and methodology to link the various views and concepts in Jones space and Stokes space. The discussion includes the relation between Jones vectors and Stokes vectors, rotation matrices, the definition and representation of PMD vectors, the laws of infinitesimal rotation, and the rules for PMD vector concatenation.

Scheme for the characterization of dispersion-managed solitons.

We give a simple new derivation of the ordinary differential equations that describe approximately the behavior of dispersion-managed solitons, and a new scheme for their solution in which the nonlinear dispersive and spectral effects are clearly apparent.

Cooling and trapping of atoms by resonance radiation pressure.

The combined use of trapping and cooling laser beams for optical trapping and cooling of neutral atoms by the forces of resonance radiation pressure is examined. Calculations show that atoms can be held in traps as deep as 10(-4) eV at temperatures of ~10(-3) K, close to the minimum set by quantum fluctuations. Spatial confinement of atoms to a region a fraction of a wavelength in length should be possible.

Random walk of coherently amplified solitons in optical fiber transmission.

In an optical-communications system using soliton pulse transmission, periodic amplification is needed to maintain the energy of the solitons. We show that amplifier noise causes a soliton's group velocity to undergo a random-walk process. The resultant timing errors at the receiver limit the system's product of length times bit rate, in one example, to about 24 000 GHz-km.

Negative dispersion using pairs of prisms.

We show that pairs of prisms can have negative group-velocity dispersion in the absence of any negative material dispersion. A prism arrangement is described that limits losses to Brewster-surface reflections, avoids transverse displacement of the temporally dispersed rays, permits continuous adjustment of the dispersion through zero, and yields a transmitted beam collinear with the incident beam.

Theory of passively mode-locked lasers including self-phase modulation and group-velocity dispersion.

Closed-form analytical solutions are obtained for a passively mode-locked laser for the case in which self-phase modulation and group-velocity dispersion, in addition to the more conventional mechanisms of saturable absorption and gain, shape the laser pulses. Provided that the self-phase modulation and group-velocity dispersion are related in a manner similar to that which causes soliton formation in optical fibers, this additional pulse shaping can reduce the pulse duration below the limit otherwise set by the laser bandwidth.

Generation of optical pulses as short as 27 femtoseconds directly from a laser balancing self-phase modulation, group-velocity dispersion, saturable absorption, and saturable gain.

We describe an ultrasbort-pulse laser that, under specific operating conditions, balances the mechanisms of conventional passive mode locking and solitonlike pulse shaping in a single resonator to generate optical pulses that are to our knowledge the shortest yet emitted directly from a laser, 27 fsec.

Raman effect in birefringent optical fibers.

Equations governing the Raman effect in birefringent optical fibers are derived. Both the parallel and perpendicular Raman effects are taken into account. The evolution of solitons is discussed.

The sliding-frequency guiding filter: an improved form of soliton jitter control.

By gradually translating the peak frequency of guiding filters along its length, we create a fibertransmission line that is substantially opaque to noise while remaining transparent to solitons. This trick allows the use of stronger filters, and hence greater jitter reduction, without incurring the usual penalty of exponentially rising noise from the excess gain required to overcome filterloss.

Soliton trapping in birefringent optical fibers.

We show experimentally the trapping of orthogonally polarized solitons in birefringent optical fibers with polarization dispersions as high as 90 psec/km. Solitons along two axes of a fiber compensate for the polarization dispersion by shifting their frequencies, and we observe frequency splitting up to 1.03 THz for a polarization dispersion of 80 psec/km. For a 20-m fiber the energy required to compensate for the polarization dispersion is ~84 pJ, and for a 76m fiber the energy required reduces to ~64 pJ.

Modulation-instability-based fiber interferometer switch near 1.5 microm.

We demonstrate a modulation-instability-based fiber interferometer switch, an ultrafast all-optical fiber switch operating near 1.5-microm wavelength with more than 40dB of small-signal gain. Switching is accomplished.by seeding the modulation instability in one arm of a Mach-Zehnder interferometer, thus destroying its balance. Computer simulations, which include the effects of Raman self-frequency shifts, suggest that as much as 74% of the power input to the interferometer can be transferred to its (initially nulled) output arm when cw pumps are used. Even with an 80% loss at the output analyzer, we have gated 184 mW of power from a color-center laser using only 4.4 microW from a semiconductor laser.

Polarization scattering by soliton-soliton collisions.

We have discovered experimentally that soliton-soliton collisions in wavelength division multiplexing significantly alter the polarization states of the colliding solitons. Analysis shows that the change in polarization is according to the cross product of the Stokes vectors of the colliding solitons. Birefringence of the fiber spans can turn this polarization scattering into a significant source of timing jitter.

Effect of guiding filters on the behavior of dispersion-managed solitons.

We show that guiding filters fundamentally alter the behavior of dispersion-managed soltions by making the pulse energy nearly independent of path-average dispersion (D?) in the neighborhood of D?=0 . This fact enables one to design maps permitting adequate pulse energy with narrow-bandwidth, temporally broad pulses for the attainment of high spectral efficiency and reduced nonlinear penalties in wavelength-division multiplexing.

Extreme picosecond pulse narrowing by means of soliton effect in single-mode optical fibers.

We report the narrowing of pulses, initially 7 psec FWHM, to widths as small as 0.26 psec by various lengths, short relative to the soliton period, of single-mode, low-loss optical fiber. Since the ~1.5-microm wavelength lies in the region of negative group-velocity dispersion ( partial differentialv(g)/ partial differentiallambda < 0), no auxiliary dispersive element was required to complete the narrowing. Optimum compression was obtained for peak-pulse input powers of several hundred watts, corresponding to relatively high (N > 10) soliton number. We show these results to be in at least semiquantitative agreement with prediction based on the nonlinear Schrödinger equation.