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

NRZ/RZ 40 Gbit/s optical regenerator based on a photonic two-level nonlinear device

A compact device with a two-level transfer function (TF) implemented with two semiconductor optical amplifier (SOA)-based stages is proposed and characterized. Each stage exploits nonlinear polarization rotation and self-phase modulation. The obtained improved TF with very flat top and bottom levels makes the scheme suitable for working as a reshaper in all-optical regeneration. The effectiveness of the device is verified in regenerating both nonreturn-to-zero (NRZ) and return-to-zero (RZ) data signals up to 40 Gb/s. Bit error rate measurements demonstrate increased threshold margin and extinction ratio improvement

Hitless reconfiguration of a PPLN-based multiwavelength source for elastic optical networks

Elastic optical networks may significantly take advantage of reconfigurable multiwavelength sources in order to maximize spectral efficiency and throughput. A multiwavelength source based on the line multiplication process taking place in a periodically poled lithium niobate waveguide has been recently proposed as a generator of tunable frequency combs. This source is stable and compact with respect to fiber-based solutions and does not require high radio frequency power. A transmitter employing the multiwavelength source is implemented and characterized in the static and dynamic regime, thus demonstrating hitless reconfiguration. The source also is tested within a three-node testbed employing commercial transceiver cards

All-Optical SOA-Assisted 40 Gbit/s DQPSK-to-OOK Format Conversion

An SOA-assisted 40 Gbit/s DQPSK-to-OOK format converter is presented. An SOA-based amplification stage, after conversion, provides negative penalty (>1.5 dB) and extinction ratio improvement (up to 6 dB), also after propagation, making the converted OOK-signals suitable for optical processing. © 2013 Springer-Verlag

Polarization-Independent All-Optical Regenerator for DPSK Data

We demonstrate polarization-independent simultaneous all-optical phase-preserving amplitude regeneration and wavelength conversion of NRZ differential phase shift keying (DPSK) data by four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). The dependence upon polarization state of the signals is eliminated by using a co-polarized dual-pump architecture. Investigation on the regenerative capability vs. pumps detuning shows significant BER threshold margin improvement over 6 nm conversion range

Review on phase preserving amplitude regeneration for phase-coded signals exploiting FWM in a saturated SOA

All-optical phase-preserving amplitude regeneration is an effective method to reduce nonlinear phase noise in long-haul transmission of phase-modulated signals. Here we review the latest results on a proposed differential phase shift keying (DPSK) regeneration scheme exploiting a compact architecture based on a saturated semiconductor optical amplifier. The scheme allows for amplitude-only signal regeneration with limited excess phase-noise contribution. Both the pass-through (PT) and the four wave mixing (FWM) signals exhibit enhanced Q-factor and margin improvement in bit error rate vs receiver threshold measurements, making the configuration suitable for both wavelength-preserving optical regeneration and wavelength regenerative conversion. The regeneration through FWM has an higher resilience to noise than the PT and its polarization dependency can be eliminated with the implementation of a dual co-polarized pump scheme. Preliminary experiments of simultaneous regeneration of two DPSK data streams are also provided