Michele Midrio

Coupling and decoupling of electromagnetic waves in parallel 2D photonic crystal waveguides

The behavior of two nearby straight photonic crystal waveguides is analyzed. It is shown that the two guides, considered as a single system, may realize a very efficient wavelength selective directional coupler, that may be used as a channel interleaver in a WDM communications system. In addition, we also show that, by properly designing the geometry of the dielectric region between the guide cores, waveguide decoupling can be obtained. Necessary conditions for this feature to be obtained are analytically derived, and an electromagnetic explanation of the decoupling process is given.

Y junctions in photonic crystal channel waveguides: high transmission and impedance matching

We investigate the efficiency of transmission through photonic crystal Y junctions and show the importance of matching mode symmetries. Furthermore, we show that by adding tuning holes to the input waveguide it is possible to achieve almost perfect impedance matching, leading ideally to unitary transmission through the junction. The model system is based on a triangular photonic lattice of holes in dielectrics to reflect experimental reality.

The space filling mode of holey fibers: an analytical vectorial solution

We tackle holey fibers in full vectorial terms. From Maxwells equations, we derive the dispersion relations of the modes guided by an infinitely self-similar air hole lattice. We focus in particular on the fundamental mode (the so-called space filling mode), and show that previous numerical results based on vector methods are accurate, but scalar ones are not. We also find the field flow lines, intensity distribution in the cross section, and linear polarization ratio vs. wavelength.

Numerical analysis of propagation and impedance matching in 2D photonic crystal waveguides with finite length

A novel way of approaching wave propagation in two-dimensional (2-D) photonic crystal guides with finite length is presented. It is shown that the main propagation features can be captured by borrowing simple concepts of propagation in transmission lines and combining them with other concepts taken from the theory of periodic structures.

Role of third-order dispersion on soliton instabilities and interactions in optical fibers.

We analyze the role of third-order dispersion on the propagation, stability, and interactions of solitons in optical fiber transmission links and fiber lasers.

Compact polarization converter in InP-based material

We present a polarization converter using one-dimensional grating principles. The device is based on slanted slots etched deeply into an InP/InGaAsP heterostructure. Almost complete polarization conversion, with a 14 dB extinction ratio, is observed for a device less than 2 microm long.

Graphene-assisted critically-coupled optical ring modulator.

Graphenes conductivity at optical frequencies can be varied upon injection of carriers. In the present paper, this effect is used to modulate losses of an optical wave traveling inside a ring cavity. This way an optical modulator based on the critical-coupling concept first introduced by Yariv can be realized. Through numerical simulations, we show that a modulator featuring a bandwidth as large as 100 GHz can be designed with switching energy in the order of few fJ per bit. Also, we show that operations with driving voltages below 1.2 volt could be obtained, thus making the proposed modulator compatible with requirements of low-voltage CMOS technology.

Time-domain Fourier optics for polarization-mode dispersion compensation

We report on a novel technique to compensate for all-order polarization-mode dispersion. By means of this technique, based on a suitable combination of phase modulation and group-velocity dispersion, we compensated for as much as 60 ps of differential group delay that affected a 10-Gbit/s return-to-zero data stream.

Tunable erbium–ytterbium fiber sliding-frequency soliton laser

We characterize the soliton-train emission from an Er–Yb-doped fiber loop laser. We discuss the self-starting dynamics and pulse-repetition-rate control in this sliding-frequency soliton laser. We show that the laser truly self-starts after only one cavity round trip. In the steady state the laser emits a closely spaced train of solitons. We also show that the output pulse width may be controlled by the interplay of continuous frequency shifting, bandwidth-limited amplification, and nonlinear polarization rotation of the circulating solitons. The repetition rate is fixed by means of a weak intracavity feedback. The laser is tunable by shifting of the filter wavelength through the whole spectral band of the active fiber.

A Compact MIMO Array of Planar End-Fire Antennas for WLAN Applications

An approach to the design of multiple-input multiple-output (MIMO) arrays exploiting planar directive antennas is presented. It is well known that pattern orthogonality is a key aspect to reach low correlation, and thus to improve channel capacity in rich multipath environments. However, attention is often focused on reducing mutual coupling rather than optimizing the active element patterns. In this communication a planar MIMO array of printed Yagi-Uda antennas with integrated balun is presented. The end-fire radiation mechanism of the Yagi-Uda is exploited to obtain a triangular array of three sectoral antennas. This allows to achieve nearly orthogonal patterns, while keeping a low mutual coupling among radiating elements. A properly shaped ground at the feeding points allows to increase the isolation between the antennas, even in such a compact layout. A laboratory model has been characterized experimentally, and the effectiveness of the proposed design in terms of theoretical achievable capacity is demonstrated through numerical simulations considering IEEE 802.11n multipath fading channel models.