Showing papers by "Giuseppe Coppola published in 2001"

Analysis of feasibility on the use of fiber Bragg grating sensors as ultrasound detectors

Abstract: The spectral response changing of a Fiber Bragg grating due to the interactions with an ultrasound wave have been numerically analyzed by a transfer matrix approach has been used, taking into account the geometrical and elasto-optic effects. Numerical analysis show that it's possible to characterize the ultrasound wave, only if the ratio between the ultrasonic wavelength and the length of the used grating exceeds an established value, which depends on both the characteristics of the Bragg grating and the ultrasound amplitude itself.

Simulation and analysis of a high-efficiency silicon optoelectronic modulator based on a Bragg mirror

Abstract: We describe the operating principle of a silicon optoelectronic modulator based on the plasma dispersion effect used in conjunction with a distributed Bragg reflector, which converts the phase shift, in- duced by the free carriers injected by a P-i-N diode, into variations of its reflectivity. The device is integrated in a low-loss silicon-on-insulator waveguide. Two different approaches in the driving schemes are pro- posed. Moreover, we show how it is possible to reach a theoretical 100% modulation depth by exploiting in a concurrent way both the variations of the refractive index and the increased optical absorption. An exhaustive description of the optical structure and its guiding properties, together with the analysis of the electrical behavior of the modulator, is given. Finally, a comparison with other interferometric structures is analyzed, and it is shown how this kind of modulator exhibits satisfactory charac- teristics in terms of dissipated power and reduced occupation of area on a chip. © 2001 Society of Photo-Optical Instrumentation Engineers.

Temperature optical sensor based on a silicon bimodal Y branch

Abstract: A novel temperature optical sensor configuration, based on mode mixing principle, is theoretically discussed. The sensing element consists of a single-mode all-silicon waveguide, followed by a two-modes section, which acts as sensing region, and an output Y branch to separate the two output channels. The fundamental mode coming from input waveguide excites both the fundamental mode and the first higher order mode in the sensing region. The interference between the two propagating modes in the sensing region produces a periodically repeated optical intensity distribution along the propagation axis. It is possible to observe a light steering from one output channel to the other caused by the temperature change of the structure itself. This fact is related to the variation of the material refractive index with the temperature, that is the thermo-optic effect, which implies a variation of the mode effective refractive indices, and, consequently, a phase shift between the modes themselves. In this way, a continuous variation of the power distribution on the two output waveguides as a function of the temperature can be observed. A simultaneous acquisition of both output signals, followed by a simple elaboration, allows obtaining a temperature evaluation independent on light source instability. Moreover, it is possible to design the device in order to obtain the desired initial output power distribution on two channels. This permits to design sensors characterized by greater accuracy, if we use the linear part of the optical transfer function, or larger measure range, if we utilize the whole output excursion.

All-silicon mode-mixing router based on the plasma-dispersion effect

Abstract: This paper reports on the theoretical and numerical description of an optoelectronic router integrated in a silicon-on-silicon waveguide structure. The device is based on the mode-mixing principle together with the injection-induced optical phase shift. The structure consists of a single-mode all-silicon input waveguide, followed by a two-mode section, which acts as the active region, and a single-mode output Y-branch to separate the two output channels. The fundamental mode from the input waveguide excites both the fundamental mode and the first higher-order mode in the active region. The spatial interference between these propagating modes produces a periodically repeated optical intensity distribution along the propagation axis. Moreover, the active region is designed to allow a π shift between the two modes when a bipolar mode field effect transistor, which injects and controls the free carrier plasma inside the active region, is driven from the OFF state to the ON state. By doing so, it is possible to steer light from one output channel to the other. Electrical and optical simulations have been carried out for the evaluation of the performance of the device. These simulations show optical propagation losses around 3 dB cm-1, an overall crosstalk of -10 dB, a transient rise time of 8.2 ns and a fall time of 7.2 ns.

Optoelectronic switch and continuously tunable filter based on a liquid crystal waveguide

Abstract: In this paper the possibility of using ferroelectric liquid crystals in active waveguide devices is explored through the analysis of an integrated electro-optic switch and a continuously tunable filter. The design and the analysis of tow electro-optical devices, based on a Bragg grating integrated in a glass waveguide having liquid crystal as cover, are presented. The integrated optics structure allows to change the reflectivity of the Bragg mirror by means of electro-optic effects of smectic liquid crystals. The integrated fast electro-optic switch is based on electro- optic properties of smectic C * in the Surface Stabilized liquid crystal structure and on the selective properties of integrated Bragg grating. It presents the output directly in the frequency domain, overcoming the typical problems of intensity dependent devices, without requiring external electronic circuit. Moreover the possibility to realize a novel continuously tunable integrated filter, combining the linear electro-optic effect of smectic A * and the selective property of Bragg grating, has been explored. The proposed filter is characterized by a narrow bandwidth, desired feature for WDM technique. The principal advantages of such device include fast tuning speed, wide tuning range, low power consumption and low cost.

Numerical simulations of a silicon-based optoelectronic filter based on a Bragg grating and p-i-n diode for DWDM optical networks

Abstract: An electrically controlled filter for the selection of channels in a DWDM optical network is proposed. The wavelength selectivity is obtained by combining the electrical injection of free carriers in a forward biased p-i-n diode with a Bragg grating realized over the top of a Silicon on Insulator (SOI) rib waveguide. Apodization of the duty-cycle of the grating has been investigated in order to reduce the crosstalk between adjacent channels; in this way the performances of the filter in terms of spectral bandwidth for 100 GHz and 50 GHz DWDM spacing become attractive.

Optoelectronic router based on a liquid crystal waveguide

Abstract: A novel configuration for an optoelectronic integrated router based on a waveguide with a liquid crystal over- layer, working at the wavelength of 1.55 micron, is theoretically discussed for the first time. The device is based on the mode-mixing principle together with the electro-optic effect of a smectic A * liquid crystal. The device is composed by a single mode input optical channel waveguide, a bimodal active region, with a liquid crystal over-layer as cover, and an output Y branch to separate the two output channels. The active region is designed to allow a (pi) shift between the two modes that it supports, by means the variation of the effective refractive index of guided modes due to molecular reorientation of liquid crystals indued by an electrical field. By doing so it is possible to steer light from one output channel to the other one. Exhaustive detail about the design both of the input waveguide and of the active region has been given together with the description of the optical behavior of our device. Numerical simulations have shown how this kind of router exhibits satisfactory performances.