J. Capmany

Space-quest: experiments with quantum entanglement in space

Quantumentanglement is, according to Erwin Schrodinger in 1935, the essence of quantumphysics. It inspires fundamental questions about the principles of nature. By testing the entanglement of particles,we are able to ask fundamental questions about realism and locality in nature. Local realismimposes certain constraints in statistical correlations ofmeasurements onmulti-particle systems. Quantummechanics, however, predicts that entangled systems havemuch stronger than classical correlations that are independent of the distance between the particles and are not explicablewith classical physics.

Multiwavelength single sideband modulation for WDM radio-over-fiber systems using a fiber grating array tandem device

We demonstrate the generation of high-quality multiwavelength single sideband (SSB) signals for wavelength-division-multiplexing radio-over-fiber systems using a tandem of two identical arrays of fiber Bragg grating devices placed in a serial arrangement. SSB is confirmed by spectral measurements and also by the simultaneous cancellation of the radio-frequency fading effect in three different wavelengths. The results show a considerable improvement both in terms of insertion losses, carrier supression effect, and bandwith (extensible from the millimeter to the whole microwave band) over the previously reported configuration based on arrayed-waveguide grating devices.

1 Tb/s·km Multimode fiber link combining WDM transmission and low-linewidth lasers

We have successfully demonstrated an error-free transmission of 10 x 20 Gb/s 200 GHz-spaced ITU channels through a 5 km link of 62.5-microm core-diameter graded-index multimode silica fiber. The overall figure corresponds to an aggregate bit rate per length product of 1 Tb/s x km, the highest value ever reported to our knowledge. Successful transmission is achieved by a combination of low-linewidth DFB lasers and the central launch technique.

Transfer function of multimode fiber links using an electric field propagation model: Application to Radio over Fibre Systems

We present a closed-form expression for the evaluation of the transfer function of a multimode fiber (MMF) link based on the electric field propagation model. After validating the result we investigate the potential for broadband transmission in regions far from baseband. We find that MMFs offer the potential for broadband ROF transmission in the microwave and millimetre wave regions in short and middle reach distances.

Tunable radio-frequency photonic filter based on an actively mode-locked fiber laser

We propose the use of an actively mode-locked fiber laser as a multitap optical source for a microwave photonic filter. The fiber laser provides multiple optical taps with an optical frequency separation equal to the external driving radio-frequency signal of the laser that governs its repetition rate. All the optical taps show equal polarization and an overall Gaussian apodization, which reduces the sidelobes. We demonstrate continuous tunability of the filter by changing the external driving radio-frequency signal of the laser, which shows good fine tunability in the operating range of the laser from 5 to 10 GHz.

Self-frequency doubling in Yb3+ doped periodically poled LiNbO3:MgO bulk crystal

Continuous-wave laser action from an Yb3+ doped periodically poled LiNbO3:MgO bulk crystal at 1.06 μm is reported. In addition, efficient and stable self-frequency-doubled laser action at 531 nm was obtained by quasiphase matching. Up to 10.5 mW of green output power is obtained from a total laser output power of 58 mW. The experiments were carried out by end pumping with a Ti:sapphire laser, as a surrogate source for a diode laser, at 980 nm. Laser operation was stable at room temperature. The results are compared with those corresponding to single-domain Yb-doped crystals.

Ultra-fast quantum randomness generation by accelerated phase diffusion in a pulsed laser diode.

We demonstrate a high bit-rate quantum random number generator by interferometric detection of phase diffusion in a gain-switched DFB laser diode. Gain switching at few-GHz frequencies produces a train of bright pulses with nearly equal amplitudes and random phases. An unbalanced Mach-Zehnder interferometer is used to interfere subsequent pulses and thereby generate strong random-amplitude pulses, which are detected and digitized to produce a high-rate random bit string. Using established models of semiconductor laser field dynamics, we predict a regime of high visibility interference and nearly complete vacuum-fluctuation-induced phase diffusion between pulses. These are confirmed by measurement of pulse power statistics at the output of the interferometer. Using a 5.825 GHz excitation rate and 14-bit digitization, we observe 43 Gbps quantum randomness generation.

Bulk periodically poled lithium niobate doped with Yb3+ ions: Growth and characterization

We have obtained Yb3+-doped bulk periodically poled LiNbO3 crystals grown by adding Yb2O3 to the congruent melt. The structures obtained have been characterized by scanning electron microscopy, x-ray fluorescence, optical absorption, and second-harmonic generation. About 100 nm of fundamental tunable quasi-phase-matched second-harmonic generation at the pm/V level is obtained in some of the samples.

All silicon waveguide spherical microcavity coupler device

A coupler based on silicon spherical microcavities coupled to silicon waveguides for telecom wavelengths is presented. The light scattered by the microcavity is detected and analyzed as a function of the wavelength. The transmittance signal through the waveguide is strongly attenuated (up to 25 dB) at wavelengths corresponding to the Mie resonances of the microcavity. The coupling between the microcavity and the waveguide is experimentally demonstrated and theoretically modeled with the help of FDTD calculations.

High-Q microwave photonic filter with a tuned modulator

We propose the use of tuned electro-optic or electroabsorption external modulators to implement high-quality (high-Q) factor, single-bandpass photonic filters for microwave signals. Using this approach, we experimentally demonstrate a transversal finite impulse response with a Q factor of 237. This is to our knowledge the highest value ever reported for a passive finite impulse-response microwave photonic filter.