Renato Caponi

Polarization measurements on single-mode fibers

An overview of current measurement techniques on conventional and polarization maintaining single-mode fibers is presented. The various methods are discussed and classified with respect to the relevant polarization parameters. Applicability ranges and resolution are pointed out for different types of fibers. >

Modeling of nonlinear absorption and refraction in quantum-well structures for all optical switching

A realistic model of the electromagnetic response in excited, type-I semiconductor quantum wells is presented. A multisubband analysis of the room temperature band edge spectra, in which the plasma effects are determined through an iterative, numerical solution of a generalized Bethe-Salpeter equation, is introduced. The method allows the treatment of situations in which transitions higher than the first give sizeable contributions to the nonlinear optical properties, as in coupled quantum wells or in the propagation of TM modes within waveguides based on quantum confined structures. Further, the method accounts for the effects of finite quantum-well thickness and incorporates a phenomenological description of the width of the resonance lines. The behavior is compared to that exhibited by more idealized models introduced in earlier works, where single-subband, purely 2-D systems were treated. Computer generated spectra are compared with absorption spectra experimentally obtained for moderately strained InGaAs-InP QWs. >

Nonlinear absorption and refraction in strained InGaAs/InP multiple quantum wells for all-optical switching

Absorption spectra of strained InGaAs/InP quantum wells exhibit a single, unusually large exciton feature. 60% quenching is obtained for 4.3 mW Nd:YAG effective pump power at a wavelength of 1.064 mu m. A simple two-level formula fits well the behaviour at the exciton peak, and absorption spectra are reasonably approximated by a standard two-dimensional exciton model. Saturation intensities calculated with these techniques range around 200 W cm-2. Finally the Kramers-Kronig relations are used to calculate the associated refractive index change.

Coherent Transmission With Polarization Modulation: Experimental Results And System Analysis

The polarization modulation technique with two different detection schemes is analyzed. A first experimen-tal test for demonstrating the principle of differential heterodyne detection has been performed. Many computer simulations at high and low bit-rates yield a performance complete equality of the two systems.

A new approach to investigating mode coupling phenomena in graded-index optical fibres

To study mode coupling in optical fibres a new technique is developed, based on mode selective excitation and output near-field analysis. Experimental results support decoupling of the problem into two phenomena which are effective on different scales of propagation length: azimuthal and longitudinal mode mixing. A statistical model providing a simulation of the experimental near-field patterns is developed. Comparison with measurements shows that azimuthal mixing is complete before 1 km propagation, while effects of uncomplete axial coupling are accounted for. This approach also suggests a method for measuring the steady-state distribution length, with useful system implications.

Steady-state and dynamic characteristics of bistable DFB amplifiers for all optical switching

The steady-state and dynamic properties of a DFB amplifier have been analyzed from theoretical and experimental viewpoints. The linewidth enhancement factor has been estimated from the experimental hysteresis cycle using an inversion technique of the device transmissivity. The dynamic behavior of the DFB has been tested at 622 Mbit/s and the experimental results are supported by numerical simulations based on an assessed model.

High-speed polarimetric measurements for fiber-optic communications

A high-speed heterodyne polarimeter at 1.55 micrometers wavelength with an intermediate frequency of 1 GHz is demonstrated. To verify the good performance of the instrument, birefringence measurements on a polarization maintaining fiber with a submillimetric beat- length have been performed. The repeatability of the measurement is excellent, and the precision ranges around 0.3%.

A heterodyne interferometric polarimeter for the detection of jones and stokes polarization vectors

Abstract A heterodyne interferometric polarimeter for detection of the Jones components and Stokes parameters is demonstrated. The measurement of both sets of quantities for various polarization states is achieved with excellent precision. The details of the corresponding Lissajous picture (ellipse) can be visualized in real time. Finally, the polarization data collected at the output of a highly birefringent fiber have been used for submillimetric beat-Length measurements.

Optical Heterodyne Communications With Polarization Modulation

The heterodyne systems with polarization modulation presented so far are reviewed both from the theoreti-cal and experimental viewpoint. The probability distribution for the basic schemes is determined through a rigorous derivation. Consequently the detection sensitivity for these particular cases is shown equal to that of FSK (although with reduced bandwidth occupancy) . This fundamental equivalence is also extended in a qualitative way to all the configurations using orthogonal polarization vectors for modulation. Open problems regarding the analy-sis of advanced versions and the development of numerical simulations are also discussed in detail.

Interferometer measurement of polarization-mode dispersion statistics

A new relationship between polarimeter and interferometer measurements of polarization mode dispersion is proposed. This model bridges the gap between interferometer patterns and probability density function of the principal states of polarization group delay. Experimental results supporting the theory are presented.