Tailoring second-harmonic generation in birefringent poled fiber via Twist

We predict theoretically and demonstrate experimentally the ability to generate and control the strengths of various second-harmonic signals in birefringent poled fiber. This is done by simply twisting the fiber

Advances and prospects of frequency doublers based on periodically poled silica fibres

Record high efficient frequency doublers in periodically poled silica fibres are demonstrated for light generation at 532 nm and 775 nm. The onset of nonlinear conductivity is shown to limit the maximum χ(2) in glass

Broadband polarization-entanglement in a poled fiber

Broadband polarization-entanglement over 100 nm is demonstrated in a poled fiber phase-matched for type-II downconversion in the 1.5µm telecom-band. Two-photon interference and Hong-Ou-Mandel interference are used experimentally to confirm the broadband nature of the entanglement

Fibre Bragg grating fabrication in germanosilicate fibres with 244nm femtosecond laser light

The ability to fabricate strong and extraordinarily stable Bragg gratings in any type of fibre using femtosecond laser light has attracted much interest in the recent past. The induced index change has been attributed to glass densification brought about by nonlinear multiphoton ionisation resulting in bond breaking, local melting and rapid cooling occurring after optical breakdown by the high-energy femtosecond light. In this paper, a preliminary comparative study between fibre Bragg grating fabrication in germanosilicate fibre using 244nm femtosecond source with a repetition rate of 250kHz and 200fs pulse duration and a 244nm CW frequency doubled argon-ion source is presented. The reflectivities achieved in both cases were close to identical for similar writing fluences, as were the isochronal annealing profiles. This indicated that despite the very high repetition rate used, the collective heat generated by the femtosecond radiation plays no role in the compaction of the glass matrix. The index change observed in this case is a result of single photon absorption into known defect centres - the laser intensity was insufficient to excite the glass band edge leading to glass compaction. No qualitative difference in index change between CW and short-pulse excitation of these defects is found

From type II upconversion to SPDC: a path to broadband polarization entanglement in poled fibers

We report type II sum-frequency and second-harmonic generation in a 24-cm-long periodically-poled silica fiber. Quasi-phase matching is achieved for orthogonally-polarized signal and idler over 1520-1575 nm, demonstrating the path to in-fiber broadband polarization-entangled photon pair generation

Recent advances in material modification by strong fields: from poling to femtosecond laser writing

Recent progress in poling, femtosecond laser direct writing and related nanostructuring of glass is reviewed

Femtosecond pulsed 244nm versus CW 244nm grating writing in boron codoped germanosilicate optical fibres operating within the one photon absorption regime

We compare the performances of low intensity (~18 nJ/pulse) femtosecond 244 nm grating writing with that of CW (20 mW) 244 nm grating writing for fixed fluencies. We find no evidence of any improvement using pulsed light with duration commensurate with phonon-assisted relaxation away from the excited state

Tuneable second harmonic generation in long periodically poled optical fibres

A widely tuneable second harmonic generator in a periodically poled germanosilicate optical fibre is demonstrated for the first time. Broadband wavelength tuning of 27.8nm is achieved using a highly efficient compression tuneable package demonstrated with fibre Bragg gratings