Coherent multi-band MIMO radar: robustness analysis to SSMF-based RF signal delivery.

A numerical evaluation is conducted to assess the impact of distributing radio frequency (RF) signals through optical fiber links on the performance of a coherent multi-band multiple-input multiple-output (MIMO) radar system. The analysis focuses on scenarios where the antennas are widely separated in comparison to the employed signal wavelengths. The development of a model to quantify the phase noise (PN) induced on each RF band due to the signal transmission through optical fiber links between the centralized base station and each radar peripheral is described.

Phase noise mitigation in photonics-based radio frequency multiplication.

Two photonics-based radio frequency multiplication schemes for the generation of high-frequency carriers with low phase noise are proposed and experimentally demonstrated. With respect to conventional frequency multiplication schemes, the first scheme induces a selective cancelation of phase noise at periodic frequency-offset values, whereas the second scheme provides a uniform 3-dB mitigation of phase noise. The two schemes are experimentally demonstrated for the generation of a 110-GHz carrier by sixfold multiplication of an 18.

Coherent MIMO radar network enabled by photonics with unprecedented resolution.

The conventional concept of radar is based on stand-alone and independent apparatuses. Superior performance is possible, exploiting distributed points of view (i.e.

Penetration capability of near infrared Laguerre-Gaussian beams through highly scattering media.

The higher capability of optical vortex beams of penetrating turbid media (e.g., biological fluids) with respect to the conventional Gaussian beams is, for the first time to our knowledge, demonstrated in the 1.

Software-defined reconfigurable VCSEL-based transmission.

We propose and demonstrate a programmable and self-adaptive VCSEL-based transponder for short-reach applications that is easily extensible up to access and metro scenarios. The transponder presents a monitoring system that feeds the transponder controller in order to maintain the proper transmission performance. The emerging NETCONF protocol including the YANG model controls and manages the transponder.

Dual use architecture for innovative lidar and free space optical communications.

An innovative and effective architecture for lidar systems is presented and experimentally demonstrated. The proposed scheme can also be easily exploited for optical communications. In particular, the system includes an innovative lidar software-defined architecture based on optically coherent detection, overcoming current drawbacks of time of flight incoherent systems.

3 × 3 optical switch by exploiting vortex beam emitters based on silicon microrings with superimposed gratings.

A silicon-on-insulator microring with three superimposed gratings is proposed and characterized as a device enabling 3×3 optical switching based on orbital angular momentum and wavelength as switching domains. Measurements show penalties with respect to the back-to-back of <1  dB at a bit error rate of 10 for OOK traffic up to 20 Gbaud. Different switch configuration cases are implemented, with measured power penalty variations of less than 0.

Frequency-agile dual-frequency lidar for integrated coherent radar-lidar architectures.

We propose a novel architecture for implementing a dual-frequency lidar (DFL) exploiting differential Doppler shift measurement. The two frequency tones, needed for target velocity measurements, are selected from the spectrum of a mode-locked laser operating in the C-band. The tones' separation is easily controlled by using a programmable wavelength selective switch, thus allowing for a dynamic trade-off among robustness to atmospheric turbulence and sensitivity.

Pachymetry-guided intrastromal air injection ("pachy-bubble") for deep anterior lamellar keratoplasty: results of the first 110 cases.

Purpose: To report intraoperative and 1-year postoperative results of the pachy-bubble technique for deep anterior lamellar keratoplasty (DALK).

Methods: This prospective interventional case series included 110 eyes of 107 patients with anterior corneal pathology who underwent DALK, including 78 with keratoconus. Outcome measures included the rate of bubble formation, rate of completing DALK, bubble types, complications, and visual and keratometric parameters.

Flexible frequency comb generation in a periodically poled lithium niobate waveguide enabling optical multicasting.

We propose and demonstrate a technique for the generation of a coherent optical comb, with tunable line spacing in a periodically poled lithium niobate (PPLN) waveguide. A single continuous wave laser is modulated to generate three phase-locked seed lines, which are injected into a PPLN waveguide, to obtain line multiplication. The line spacing is set acting on the frequency of the electrical signal driving the modulator.

Generation of a flexible optical comb in a periodically poled lithium niobate waveguide.

We propose and demonstrate a technique for the generation of an optical comb with tunable line spacing in a periodically poled lithium niobate (PPLN) waveguide. The technique is implemented with four input continuous waves (CWs), which generate a 19-line comb tuned to the spacing of 25 and 20 GHz. We show that each additional CW switched on out of the quasi phase-matching band at the PPLN waveguide input generates the growth of six new lines.

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.

Photonic generation and independent steering of multiple RF signals for software defined radars.

As the improvement of radar systems claims for digital approaches, photonics is becoming a solution for software defined high frequency and high stability signal generation. We report on our recent activities on the photonic generation of flexible wideband RF signals, extending the proposed architecture to the independent optical beamforming of multiple signals. The scheme has been tested generating two wideband signals at 10 GHz and 40 GHz, and controlling their independent delays at two antenna elements.

PPLN-based OOK and DQPSK optical grooming by amplitude and phase-signal multiplexing through pump depletion.

We propose and characterize a simple, integrable, and wavelength-preserving scheme able to groom a 40 Gbps (D)QPSK signal with a 20 Gbps OOK one into a 20 Gbaud (60 Gbps) 8-APSK signal. The proposed all-optical scheme is based on the second-order nonlinear signal-depletion effect in a single periodically poled lithium niobate (PPLN) waveguide. Performance of the device, characterized by means of BER measurements, attests error-free operation and a power penalty below 4.

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.

Nodular epithelial hyperplasia after photorefractive keratectomy followed by corneal collagen cross-linking.

This study describes a case of nodular epithelial hyperplasia and stromal alterations in a patient with keratoconus who was submitted to topography-guided photorefractive keratectomy (PRK) followed by corneal collagen cross-linking. Debridement of the epithelial nodule was performed. After a 2-year followup, a new topography-guided PRK was indicated.

Corneal ectasia secondary to LASIK after arcuate keratotomy.

Purpose: To present a case of corneal ectasia after LASIK in a patient with previous arcuate keratotomy.

Methods: Case report.

Results: The patient underwent arcuate keratotomy in both eyes in 1997 for with-the-rule regular hyperopic astigmatism and uneventful bilateral LASIK for residual astigmatism 5 years later.

Flexible receiver for multiband orthogonal frequency division multiplexing signals at the millimeter waveband based on optical downconversion.

A novel (to our knowledge) and flexible photonics-based downconversion scheme is proposed for wireless receivers in base stations. It allows simultaneous detection of multiple signals at carriers up to tens of gigahertz, enabling communications at millimeter waves. Experiments demonstrate the effective downconversion of Wi-Fi signals at 2.

Colorless all-optical sum and subtraction of phases for phase-shift keying signals based on a periodically poled lithium niobate waveguide.

A colorless all-optical scheme performing the subtraction and addition of phases between phase-shift keying (PSK) signals exploiting cascaded sum and difference frequency generation in a periodically poled lithium niobate waveguide is introduced and experimentally demonstrated. The subtraction of phases of two 40 Gb/s differential quadrature PSK signals has been experimentally tested and performances have been analyzed in terms of bit error rate measurements.

All-optical simultaneous drop and wavelength conversion of DPSK data.

We demonstrate an all-optical scheme for the simultaneous drop and wavelength conversion of bursts of data from a continuous stream of differential phase-shift keyed (DPSK) signals. This function is obtained in a single semiconductor optical amplifier Mach-Zehnder interferometer thanks to proper nonlinear interaction of the data stream and an optical gate signal at different wavelength. Fast switching-time enabling wavelength shifting operation on continuous DPSK data stream at 10 and 40 Gb/s without any bit loss is reported.

High-speed addition/subtraction/complement/doubling of quaternary numbers using optical nonlinearities and DQPSK signals.

We propose an innovative approach to implementing multiple arithmetic functions of quaternary numbers using optical nonlinearities and differential quadrature phase-shift keying (DQPSK) signals. By adopting 100 Gbit/s DQPSK signals (A, B) and exploiting nondegenerate four-wave mixing (FWM) for addition/subtraction and degenerate FWM for complement and doubling in a single highly nonlinear fiber, we demonstrate 50 Gbaud/s simultaneous quaternary addition (A+B), dual-directional subtraction (A-B, B-A), complement (-A, -B), and doubling (2B). Power penalties less than 4 dB (addition), 3 dB (dual-directional subtraction), 2 dB (complement), and 3.

160 Gbit/s binary-to-quaternary amplitude shift keying encoding in the optical domain.

160 Gbit/s all-optical binary-to-quaternary amplitude shift keying format conversion is carried out in a nonlinear optical fiber. This scheme, which also acts as a 2 bit digital-to-analog convertor, has been confirmed through Q-factor measurements.

640 Gbits/s photonic logic gates.

We demonstrate 640 Gbits/s all-optical A AND B, and Ā AND B logic functions using pump depletion in a periodically poled lithium niobate waveguide. Bit-error-rate measurements show the effectiveness of the scheme, with a penalty of <2 dB.

Bit-rate-variable and order-switchable optical multiplexing of high-speed pseudorandom bit sequence using optical delays.

We experimentally demonstrate high-speed optical pseudorandom bit sequence (PRBS) multiplexing with coarse and fine bit-rate tuning capability and a switchable order using optical delays. Data multiplexing of 80 Gbit/s and 160 Gbit/s is shown, each with a tunable rate using a conversion/dispersion-based continuously tunable optical delay and tunable PRBS order with large switchable fiber delays. A 7% bit-rate tunability, i.

Eightfold 40-320 Gbit/s phase-coherent multiplexing and 320-40 Gbit/s demultiplexing using highly nonlinear fibers.

We experimentally demonstrate 40-320Gbit/s phase-coherent multiplexing based on cross-phase modulation and subsequent 320-40Gbit/s demultiplexing using cross-phase-modulation-induced frequency shift in highly nonlinear fibers. An average penalty of approximately 7dB at a 10(-9) bit-error rate is observed after the nonlinear processes. We also show the generation of a phase-coherent 320GHz optical pulse train.