Claudio Porzi

A fully photonics-based coherent radar system

The next generation of radar (radio detection and ranging) systems needs to be based on software-defined radio to adapt to variable environments, with higher carrier frequencies for smaller antennas and broadened bandwidth for increased resolution. Today’s digital microwave components (synthesizers and analogue-to-digital converters) suffer from limited bandwidth with high noise at increasing frequencies, so that fully digital radar systems can work up to only a few gigahertz, and noisy analogue up- and downconversions are necessary for higher frequencies. In contrast, photonics provide high precision and ultrawide bandwidth, allowing both the flexible generation of extremely stable radio-frequency signals with arbitrary waveforms up to millimetre waves, and the detection of such signals and their precise direct digitization without downconversion. Until now, the photonics-based generation and detection of radio-frequency signals have been studied separately and have not been tested in a radar system. Here we present the development and the field trial results of a fully photonics-based coherent radar demonstrator carried out within the project PHODIR. The proposed architecture exploits a single pulsed laser for generating tunable radar signals and receiving their echoes, avoiding radio-frequency up- and downconversion and guaranteeing both the software-defined approach and high resolution. Its performance exceeds state-of-the-art electronics at carrier frequencies above two gigahertz, and the detection of non-cooperating aeroplanes confirms the effectiveness and expected precision of the system.

Sliceable transponder architecture including multiwavelength source

A multiflow transponder in flex-grid optical networks has recently been proposed as a transponder solution to generate multiple optical flows (or subcarriers). Multiflow transponders support high-rate super-channels (i.e., connection composed of multiple corouted subcarriers contiguous in the spectrum) and sliceability; i.e., flows can be flexibly associated to the incoming traffic requests, and, besides composing a super-channel, they can be directed toward different destinations. Transponders supporting sliceability are also called sliceable transponders or sliceable bandwidth variable transponders (SBVTs). Typically, in the literature, SBVTs have been considered composed of multiple laser sources (i.e., one for each subcarrier). In this paper, we propose and evaluate a novel multirate, multimodulation, and code-rate adaptive SBVT architecture. Subcarriers are obtained either through multiple laser sources (i.e., a laser for each subcarrier) or by exploiting a more innovative and cost-effective solution based on a multiwavelength source and micro-ring resonators (MRRs). A multiwavelength source is able to create several optical subcarriers from a single laser source. Then, cascaded MRRs are used to select subcarriers and direct them to the proper modulator. MRRs are designed and analyzed through simulations in this paper. An advanced transmission technique such as time frequency packing is also included. A specific implementation of a SBVT enabling an information rate of 400 Gb¿s is presented considering standard 100 GbE interfaces. A node architecture supporting SBVT is also considered. A simulation analysis is carried out in a flex-grid network. The proposed SBVT architecture with a multiwavelength source permits us to reduce the number of required lasers in the network.

Polarization and wavelength-independent time-division demultiplexing based on copolarized-pumps FWM in an SOA

A novel optical time-division demultiplexer based on copolarized-pumps four-wave mixing in semiconductor optical amplifiers is presented. The scheme is polarization and wavelength independent. Effective 10-Gb/s channel extraction from an optical time-division multiplexed 40-Gb/s aggregate frame is experimentally demonstrated.

Impedance-detuned high-contrast vertical cavity semiconductor switch

We report an all-optical semiconductor gate optimized for high-contrast switching. Using a pump signal with an intensity of less than /spl sim/25 KW/cm/sup 2/, we demonstrate a 30-dB contrast ratio for 10-GHz pulses with energy of 0.05 pJ.

Modeling and measurement of noisy SOA dynamics for ultrafast applications

A complete and effective tool for the analysis of semiconductor optical amplifiers (SOAs) in ultrafast telecommunication applications is presented. This model includes gain dynamics, the current induced gain saturation effect, the current-dependent gain dispersion, and the amplified spontaneous emission. Experimental results concerning both stationary and dynamic conditions confirm the model accuracy and its effectiveness in the design of all-optical signal processing schemes based on SOAs. Finally, we study the characteristic times and the efficiencies of SOA fast dynamics in order to investigate the bandwidth limits of these devices. A numerical evaluation, validated by high-resolution measures makes the SOAs suitable to process optical signals up to 160 Gb/s.

All-Optical nand / nor Logic Gates Based on Semiconductor Saturable Absorber Etalons

We propose a method to implement NAND and NOR logical operations using nonlinear vertical-cavity semiconductor gates based on saturable absorption in semiconductor quantum wells. The device is designed to exhibit an inverse saturable absorber behavior, i.e., high throughput at low input energy and low throughput at high input energy level. The effects of different design parameters on the device performance are discussed. Numerical simulations are carried out to demonstrate dynamic operation of the device. The main advantages of the proposed implementation rest on key features of the semiconductor gate, such as passive and polarization-independent operation, and compactness.

Binary-to-Quaternary ASK Encoding in the Optical Domain With Semiconductor Optical Amplifiers

Quaternary amplitude-shift-keying signal is all-optically generated from binary signals exploiting gain compression in two semiconductor optical amplifiers. The scheme is suitable for phase-control-free all-optical digital-to-analog conversion. Only two semiconductor amplifiers, a single optical filter, and no assist probe light are required for 2-bit operation. In addition, the input wavelength is preserved at the output of the device. Dynamic operation is experimentally demonstrated. The quality of the level-converted signal is confirmed by the high Q -factor of the output eye diagrams.

Regenerative Wavelength Conversion of DPSK Signals Through FWM in an SOA

We experimentally investigate broadband regenerative capability of four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) for nonreturn-to-zero differential phase-shift keying signals at 10 Gb/s. This scheme exploits the amplitude-limiting properties of the FWM process, when proper SOA gain saturation and α-factor depletion result in almost negligible additional phase noise for the converted signal after delay-interferometer demodulation. We report characterization in both the wavelength down- and up-conversion operations, demonstrating sound Q-factor improvement (through a factor comprised between 1.4 and 2.4) over a conversion range of about 50 nm.

All-Optical Gated Wavelength Converter-Eraser Using a Single SOA-MZI

We propose and experimentally demonstrate an original scheme for simultaneous all-optical wavelength conversion and data erasing under an optical gate signal, suitable for on-off keying (OOK) signals. This function is obtained in a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) exploiting nonlinear interaction between a continuous data stream and an optical gate signal at a different wavelength. In correspondence of the gate signal, a burst of data from the optical stream is converted at the optical gate wavelength and, at the same time, cancelled at the input stream wavelength. Fast switching time enabling selective wavelength shifting on a data stream at 10 Gb/s without any bit loss is demonstrated. Error-free operation with 0.2-dB power penalty for the wavelength-preserved output data and 1.8 dB for the shifted data is reported.

Optical Digital Signal Processing in a Single SOA Without Assist Probe Light

By exploiting nonlinear effects in a single semiconductor optical amplifier, different functionalities for all-optical digital signal processing applications are implemented. In particular, we demonstrate all-optical exclusive-OR (XOR) logical operation and all-optical binary-to-quaternary ASK format conversion suitable for 2-bit all-optical digital-to-analog conversion (DAC). Both operations are performed without the use of any extra probe light beam. Beside the advantage of reduced complexity in terms of number of active elements the proposed architecture allows to preserve the input signal wavelength at the gate output and is suitable for photonic integration. Error-free operation at 10 Gb/s is demonstrated for the all-optical XOR gate, whereas correct dynamic operation, always at 10 Gb/s is observed for the binary-to-quaternary ASK format converter. Based on the proposed single semiconductor optical amplifier architecture a possible implementation of 3-bit DAC scheme with reduced number of active gates with respect to previously reported schemes is also presented.