Laboratory of Quantum Electronics

and Nonlinear Optics

Electronics Department - University of Pavia





Nonlinear Waveguides

V. Degiorgio, I. Cristiani, L. Tartara, P. Minzioni, F. Bragheri, A. Trita, J. Parravicini

Wavelength conversion based on a cascade of second-order effects in periodically-poled lithium-niobate (PPLN) crystals is important for many applications, including the design of optical-communication devices and of sources of coherent green-blue light. In order to operate devices at room temperature it is necessary to reduce photorefractivity at the lowest possible level. In collaboration with E.P. Kokanyan, measurements of linear and nonlinear optical properties of doped ferroelectric crystals are performed in order to find the optimum crystal for wavelength conversion. At present a very promising solution seems to be represented by 4% Hafnium-doped lithium niobate.

A new research line concerning silicon-germanium waveguides with silicon cladding was started, in a collaboration involving groups expert in epitaxial groth and in semiconductor physics. The aim is to obtain single-mode channel waveguides to be used as Raman amplifiers in the optical-communication frequency-band.
The nonlinear propagation of ultrashort laser pulses in microstructured optical fibers gives rise to a variety of phenomena generating new frequencies. A strong conversion from infrared to blue was observed by our group in a specific solitonic propagation regime. Further experiments and simulations are planned to study the origin of the observed effect and to optimize the blue-light generation.


Wavelength conversion and optical phase conjugation in optical communication systems

V. Degiorgio, I. Cristiani, P. Minzioni

This activity is focussed on the analysis of the nonlinear phenomena affecting the propagation of an optical pulse in a fiber communication system. The main target of the research is to demonstrate that the optical phase-conjugation of a signal, performed using a properly studied setup, can be used to compensate at the same time the fiber dispersion and nonlinearity. Moreover a theoretical study is being developed to include in the proposed model also the analysis of WDM and phase-modulated systems.
This research takes advantage of a strong collaboration with CoreCom (Milan, Italy), owner of the 1000km long transmission system used in the experiments, and with the University of Stanford (CA, USA), where the periodically-poled lithium-niobate (PPLN) waveguide used for the phase conjugation process is realized.



Nonlinear Propagation of Conical Waves

V. Degiorgio, L. Tartara, D. Grando, F. Bragheri

The activity in this research filed will concern the realization of nonlinear propagation experiments of ultrashort laser pulses having high intensity peak. These high energy pulses will be obtained by using both the regenerative (Quantronix) and the parametric (Topas – Light Conversion) amplifiers recently installed in our laboratory. In particular we will study the generation of dissipative conical waves, i.e. polychromatic non-dispersing and non-diffracting weakly localized wave-packets which are spontaneously generated in nonlinear media even in presence of losses. On the basis of already known experimental techniques, such as the 3D mapping technique used to characterize the spatio-temporal intensity profile and the FROG technique that gives information about amplitude and phase temporal profile, we will implement a new complete diagnostics in order to obtain the full characterization of the wave packet’s amplitude and phase with space-time and angle-frequency resolution. Finally we will test the possibility of exploiting conical waves, instead of standard Gaussian pulses, for femtosecond laser writing of waveguides in nonlinear bulk media.




I. Cristiani, P. Minzioni, F. Bragheri, L. Ferrara

Biophotonics acivity in mainly devoted to the realization of a miniaturized device working as tweezer and micromanipulator. The device is based on optical fibers and requires a very simple set-up that can be easily handled and makes possible the trapping of biological micro- and nano-particles in many different environments. The use of optical fibers to carry the light close to the object to be trapped overcomes some problems related to the medium turbidity and removes the limitations (size, cost, device complexity, X-ray compatibility) that prevents from using microscope-based tweezers in many applications. Multifunctions tweezers can be obtained by integrating in the device analysis-dedicated fibers, to carry additional beams at different wavelengths and to perform optical analysis, cutting or 3D imaging of the trapped elements. It is very important to outline that the proposed optical fiber device can be easily implemented as a probe for endoscopy, opening new frontiers for optical tweezers utilization, like ‘in vivo’ analysis or controlled drug delivery.