GaAs-based surface-normal optical modulator compared to Si and its wavelength response characterization using a supercontinuum laser.

A GaAs-based surface-normal optical modulator using the free-carrier effect is demonstrated for the first time to our knowledge. The device exhibits ~43% modulation depth compared to 24% for a previously demonstrated Si-based device with twice the interaction length. Simulations predict ~1.8 times the speeds for GaAs-based devices compared to Si. Operation in conjunction with a supercontinuum source is used to characterize the wavelength response of the modulator. Potential for colorless operation makes the modulator a candidate for wavelength-division multiplexed networks with broadband light sources.

Third order cascaded Raman wavelength shifting in chalcogenide fibers and determination of Raman gain coefficient.

Cascaded Raman wavelength shifting up to three orders from 1553 nm to 1867 nm is demonstrated in As(2)S(3)-chalcogenide fibers. Due to a long zero dispersion wavelength for the sulfide fiber (>4.5 mum), pumping the fiber at 1553 nm results in generation of cascaded Stokes orders based on stimulated Raman scattering. Using the threshold power for the Raman orders, we estimate the Raman gain coefficient for the As(2)S(3) fibers to be ~5.7x10(-12) m/W at 1550 nm. Observation of higher Raman orders is limited by damage to the fiber at input intensities >1 GW/cm(2).

Mid-infrared supercontinuum generation to 4.5 microm in ZBLAN fluoride fibers by nanosecond diode pumping.

A mid-infrared supercontinuum (SC) is generated in ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF...) fluoride fibers from amplified nanosecond laser diode pulses with a continuous spectrum from approximately 0.8 microm to beyond 4.5 microm. The SC has an average power of approximately 23 mW, a pump-to-SC power conversion efficiency exceeding 50%, and a spectral power density of approximately -20 dBm/nm over a large fraction of the spectrum. The SC generation is initiated by the breakup of nanosecond laser diode pulses into femtosecond pulses through modulation instability, and the spectrum is then broadened primarily through fiber nonlinearities in approximately 2-7 m lengths of ZBLAN fiber. The SC long-wavelength edge is consistent with the intrinsic ZBLAN material absorption.