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We report a nonlinear signal processing system based on a SiGe waveguide suitable for high spectral efficiency data signals. Four-wave-mixing (FWM)-based wavelength conversion of 10-Gbaud 16-Quadrature amplitude modulated (QAM) and 64-QAM signals is demonstrated with less than -10-dB conversion efficiency (CE), 36-dB idler optical signal-to-noise ratio (OSNR), negligible bit error ratio (BER) penalty and a 3-dB conversion bandwidth exceeding 30nm. The SiGe device was CW-pumped and operated in a passive scheme without giving rise to any two-photon absorption (TPA) effects. © 2017 Optical Society of America.

A new measure of complexity, time-scale independent permutation entropy, has been developed and applied to fully characterize the relative complexity of the emission of a four-section photonic integration chip (PIC) laser. The new technique allows the relative complexity of dynamics with different characteristic time scales to be compared. The analysis reveals the range of possible outputs the PIC device can produce over a three-dimensional operating parameter space. From the perspective of using such devices as synchronized transmitter and receiver pairs in chaos-based secure communication applications, a region of uninterrupted, highly complex, unpredictable dynamics has been identified for the device. Regions surrounding this desired complex state show intermittency, pulse packages, and limit-cycle oscillations. The effect of varying the laser's biasing current, feedback strength, and feedback phase reveals the extent of the short-cavity regime and provides insight to the fundamental physics driving the integrated device dynamics. © 2016 IEEE.

The fundamental properties of free space optical channels in the ultraviolet (UV) spectral range between 200 and 280 nm are the enhanced scattering and the solar blind operation. Exploiting these properties, point-to-point links in a non-line-of-sight (NLOS) regime were experimentally tested and the performance of pulse position modulation of fourth order (4-PPM) and flip-orthogonal frequency division multiplexing (Flip-OFDM) modulation formats was evaluated. At the transmitting side, light-emitting diodes (LEDs) emitting at 265 nm were used. At the receiving side, a photo-multiplier tube was combined with an optical filter. Distances up to 20 m were covered and kilobits/s rates were applied. The performance was also evaluated after modifying artificially the atmospheric conditions by the operation of a fog machine. In short, 4-PPM outperformed Flip-OFDM, whereas a medium that offers enriched scattering due to fog may boost the performance of short-range NLOS links in the UV spectral range. © 1989-2012 IEEE.

We theoretically and experimentally investigate the properties of a double sideband suppressed carrier modulation transmission scheme for long distance microwave frequency standard dissemination. The proposed method effectively doubles the transmitted frequency obtaining enhanced phase noise and stability performance. Suppressing the optical carrier also eliminates the dispersion induced signal fading. Important transmission parameters like optical modulation depth and linearity are also improved. Allan deviation and phase noise measurements prove the superior performance of the proposed modulation format. © 2016 Elsevier B.V.

We present a numerical analysis that focuses, for the first time to our knowledge, on the feedback-induced dynamics in a semiconductor passively mode-locked laser with sub-wavelength resolution. Our results and the corresponding theoretical explanations elucidate several aspects of the laser dynamics under self-injection including inherent properties of mode-locked lasers such as pulse intensity noise and timing jitter. We show that the dynamics of the laser exhibit a periodicity in the wavelength scale apparent only on integer multiples of the laser cavity and decays in the time scale of the pulse duration following the coherence of the mode-locked laser. The corresponding phenomena are dominant for external cavities that are shorter than the laser cavity and superimposed on the previously reported dynamics of the semiconductor mode-locked lasers for longer external delays. Since these dynamics are triggered by low feedback levels, our study could be useful for the optimization of the laser operation in cases where ultra-short external cavity lengths are involved (integrated designs, power collection with fiber tapers, etc.). © 2017, Springer-Verlag GmbH Germany.

We present experimental investigations of a novel mid-infrared gas sensor relying on a laser system consisting of two quantum cascade sources mutually coupled with each other. The free-space path between the two lasers contains the sensing cell which is filled with the gas of interest. This laser system proves to be a very interesting dynamical system which can offer enhanced detectivity when compared to a conventional direct absorption spectrometer utilizing a laser, the gas cell, and a detector. We present comprehensive investigations of the operation regimes under which the laser system behaves as an efficient sensor and demonstrate its dependence on critical parameters such as the coupling strength between the two lasers and their bias currents. The experimental study is supported by numerical simulations, which provide a theoretical understanding of the underlying mechanisms. A six fold improvement of the sensitivity in a N2O absorption spectroscopy experiment is demonstrated in comparison to a conventional direct absorption spectrometer. This sensitivity improvement is exhibited for a wide range of N2O concentrations. © 1995-2012 IEEE.

Error-free transmission of 10 Gbit/s non-return to zero optical signals along 2.5 cm long silicon germanium waveguides at a wavelength of 1.98 μm is demonstrated. Bit error rate measurements confirm the absence of penalty during the transmission through a subwavelength of 1.3 and 2.2 μm wide waveguides. © 2017 The Institution of Engineering and Technology.

We develop a framework for estimating the quality of transmission (QoT) of a new lightpath before it is established, as well as for calculating the expected degradation it will cause to existing lightpaths. The framework correlates the QoT metrics of established lightpaths, which are readily available from coherent optical receivers that can be extended to serve as optical performance monitors. Past similar studies used only space (routing) information and thus neglected spectrum, while they focused on oldgeneration noncoherent networks. The proposed framework accounts for correlation in both the space and spectrum domains and can be applied to both fixed-grid wavelength division multiplexing (WDM) and elastic optical networks. It is based on a graph transformation that exposes and models the interference between spectrum-neighboring channels. Our results indicate that our QoT estimates are very close to the actual performance data, that is, to having perfect knowledge of the physical layer. The proposed estimation framework is shown to provide up to 4 × 10-2 lower pre-forward error correction bit error ratio (BER) compared to theworst-case interference scenario,which overestimates the BER. The higher accuracy can be harvested when lightpaths are provisioned with low margins; our results showed up to 47% reduction in required regenerators, a substantial savings in equipment cost. © 2016 Optical Society of America.

The exploitation of optical wireless communication channels in a non-line-of-sight regime is studied for pointto-point and networking configurations considering the use of light-emitting diodes. Two environments with different scattering center densities are considered, assuming operation at 265 nm. The bit error rate performance of both pulsed and multicarrier modulation schemes is examined, using numerical approaches. In the networking scenario, a central node only receives data, one node transmits useful data, and the rest of them act as interferers. The performance of the desirable node's transmissions is evaluated. The access to the medium is controlled by a code division multiple access scheme. © 2016 Optical Society of America.

Neuro-inspired implementations have attracted strong interest as a power efficient and robust alternative to the digital model of computation with a broad range of applications. Especially, neuro-mimetic systems able to produce and process spike-encoding schemes can offer merits like high noise-resiliency and increased computational efficiency. Towards this direction, integrated photonics can be an auspicious platform due to its multi-GHz bandwidth, its high wall-plug efficiency and the strong similarity of its dynamics under excitation with biological spiking neurons. Here, we propose an integrated all-optical neuron based on an InAs/InGaAs semiconductor quantum-dot passively mode-locked laser. The multi-band emission capabilities of these lasers allows, through waveband switching, the emulation of the excitation and inhibition modes of operation. Frequency-response effects, similar to biological neural circuits, are observed just as in a typical two-section excitable laser. The demonstrated optical building block can pave the way for high-speed photonic integrated systems able to address tasks ranging from pattern recognition to cognitive spectrum management and multi-sensory data processing.

We report a low-power continuous wave-pumped phase sensitive amplifier (PSA)-based phase regenerator implemented in a passive silicon-based waveguide. A polarization assisted-PSA, consisting of two orthogonally-polarized pumps and a phase-locked signal copolarized to one of them, was implemented in a low-birefringence silicon germanium (SiGe) waveguide. The strong TE/TM modal symmetry of the waveguide and its large nonlinear coefficient enabled the achievement of an extremely large phase sensitive extinction ratio of approximately 29 dB for a total input power of only 21.3 dBm. This SiGe-based PSA was used to demonstrate phase regeneration on a 20 Gb/s differential phase-shift keying signal, thereby reducing its error vector magnitude and phase error by three and six times respectively and enabling a bit-error ratio improvement of up to 2 dB. © 1983-2012 IEEE.

We report the first demonstration of a single-pass dual-orthogonal-pump four-wave mixing-based wavelength conversion scheme in a silicon-based waveguide. The silicon germanium waveguide used was designed to exhibit strong TE/TM mode similarity across a broad wavelength range as well as a large nonlinear coefficient. A polarization-dependent loss of just 0.42 dB was measured, and the conversion of 40-Gb/s differential phase-shift keying signals was demonstrated with 1.5-dB power penalty at a bit error ratio of 10-9. © 1989-2012 IEEE.

One of the most critical parameters in free-space optical communications systems operating in a non-line-of-sight regime are the optical losses. In this Letter, we numerically calculate these losses taking into account the scattering effects using the Monte Carlo simulation technique. The obtained results are compared with experimentally obtained data at 265 nm (solar-blind UV regime). A large set of measurements at distances up to 20 m, for different elevation angles of the transmitter (UV-LEDs) and receiver (photo-multiplier tube) and for different atmospheric conditions has been taken for the characterization of the optical communications channel in terms of its loss properties. © 2016 Optical Society of America.

Ultrafast physical random bit generators based on broadband optical signals have been presented lately at astounding speeds. Some of the most popular mechanisms to obtain such random sequences are through signals that emerge from the coherence collapse operation of semiconductor lasers or from the photodetection signal beating of amplified spontaneous emission optical noise. Especially in the first case, the potential of chaotic signals to synchronize offers a great potential for secure communications. In this paper, we combine two unique properties of semiconductor lasers that operate at a chaotic regime: Their potential to become highly synchronized when optically coupled through appropriate configurations and their ability to seed ultrafast true random bit generators. The concurrent fulfillment of both conditions is shown in this paper and is used to demonstrate experimentally the one-time-pad encryption communication protocol. We report an error-free operation of such an encryption system, exceeding for the first time the Gb/s rate. Forward-error-correction coding is applied on the encryption scheme, in order to drastically reduce the errors of the synchronized true random bit sequences and optimize the decoding performance of the system, while securing the distribution of the random seed. © 1983-2012 IEEE.

Optically coupled semiconductor lasers (SLs) are known to exhibit chaotic properties in their emitted signals. Depending on the number of SLs and the coupling topology, their emissions can potentially show stable, synchronized behavior. The level of synchrony depends on numerous parameters and is the key factor to design secure communication systems based on synchronized chaotic signals. In this work we investigate a bidirectional coupling topology, with two or more SLs coupled with a common hub SL, which leads to an unprecedented level of synchronization. Cross-correlation (CC) values as high as 0.9961 are reported between SLs, when the latter operate at a fully chaotic regime and with spectral emission profiles that show minimized periodicities. Such conditions promote the proposed topology for cryptographic applications. © 1989-2012 IEEE.

In this Letter, we present and fully model a photonic scheme that allows the high-speed identification of images acquired through the dispersive Fourier technique. The proposed setup consists of a photonic reservoir-computing scheme that is based on the nonlinear response of randomly interconnected InGaAsP microring resonators. This approach allowed classification errors of 0.6%, whereas it alleviates the need for complex high-cost optoelectronic sampling and digital processing. © 2015 Optical Society of America.

We experimentally study the generation and amplification of stable picosecond-short optical pulses by a master oscillator power-amplifier configuration consisting of a monolithic quantum-dot-based gain-guided tapered laser and amplifier emitting at 1.26 μm without pulse compression, external cavity, gain-or Q-switched operation. We report a peak power of 42 W and a figure-of-merit for second-order nonlinear imaging of 38.5 W2 at a repetition rate of 16 GHz and an associated pulse width of 1.37 ps. © 2015 Optical Society of America.

A 4-section semiconductor laser with integrated optical feedback has been shown experimentally to be capable of operating in either the short- or long-cavity regime, by controlling the device relaxation oscillation frequency relative to the external cavity frequency. Systematic increase of the laser injection current, and the resulting increase in relaxation oscillation frequency, allowed the transition between the two regimes of operation to be observed. The system displayed a gradual transition from a dynamic dominated by regular pulse packages in the short-cavity regime to one dominated by broadband chaotic output when operating in the long-cavity regime. This suggests that the "short cavity" regular pulse packages continue to co-exist with the "long cavity" broadband chaotic dynamic in the system studied. It is the relative power associated with each of these dynamics that changes. This may occur more generally in similar systems. ©2015 Optical Society of America.

The intensity and timing noise of a 40-GHz quantum dot passively mode-locked laser with noncolliding cavity is numerically investigated and compared with the corresponding performance of the conventional self-colliding cavity. A detailed mapping of the pulse and noise properties versus the bias conditions shows that the devices based on the noncolliding cavities can generate shorter and stronger pulses with lower intensity and timing noise compared with the self-colliding counterparts if the gain to absorber length ratio is optimized. © 1989-2012 IEEE.

We propose and experimentally validate a new cost-effective optical receiver-regenerator scheme for long-distance microwave-frequency standard dissemination, based on the properties of dual-wavelength injection locked Fabry-Perot (FP) lasers. The regenerator FP laser is injection locked to one of its longitudinal modes by the incoming intensity-modulated light carrying the microwave-frequency standard. The light of a local CW laser is also injected in the regenerator FP, locking it to an adjacent mode. The dual-injection locked laser reproduces the sinusoidal microwave-frequency standard on both wavelengths. The regenerated original signal is transmitted to the next node, whilst the local wavelength is fed back to the previous node for phase error extraction and link compensation. The performance of the proposed regenerator is demonstrated with Allan deviation and phase-noise measurements. © 2015 Optical Society of America.

Mid-infrared silicon photonics emerge as the dominant technology to bridge photonics and electronics in multifunctional high-speed integrated chips. The transmission and processing of optical signals lying at the mid-infrared wavelength region is ideal for sensing, absorption-spectroscopy and free-space communications and the use of group IV materials becomes principally promising as the vehicle towards their realization. In parallel, optical forces originating from modes and cavities can reach to outstandingly large values when sizes drop into the nanoscale. In this work, we propose the exploitation of large gradient optical forces generated between suspended silicon beams and optomechanical transduction as a means of converting signals from the mid-infrared to the near-infrared region. A mid-infrared signal is injected into the waveguide system so as to excite the fundamental symmetric mode. In the 2-5 mu m wavelength range, separation gaps in the 100nm order and waveguide widths ranging from 300-600nm, the mode is mostly guided in the air slot between the waveguides which maximizes the optomechanical coupling coefficient and optical force. The resulting attractive force deflects the waveguides and the deflection is linearly dependent on the mid-infrared optical power. A simple read-out technique using 1.55 mu m signals with conventional waveguiding in the directional coupler formed by the two beams is analyzed. A positive conversion efficiency (>0dB) is foreseen for waveguides with suspending lengths up to 150 mu m. The converter could be ideal for use in sensing and spectroscopy rendering the inefficient mid-infrared detectors obsolete. The low-index unconventional guiding in mid-infrared could be a key component towards multifunctional lab-on-a-chip devices.

The intensity noise properties of injection locked mid-infrared quantum cascade lasers are experimentally investigated. The injection locking is realized below and near the threshold of the free running slave laser, resulting in an efficient technique to achieve low noise operation. It is found that below threshold the locking characteristics (locking range shape and bandwidth) are different in comparison to those above threshold. Furthermore, an alternative injection locking realization is also investigated: injection locking into longitudinal side modes of the slave laser. Here, similar characteristics were observed, however, with the potential to achieve even higher relative intensity noise reduction suppression with respect to the quantum noise limit. The measurements are confirmed by numerical simulations with a travelling-wave model which takes into account the multi-mode spectrum of the slave laser and the spectral profile of the material gain. The experiments give the perspective for the achievement of the relative intensity noise reduction of the slave laser of up to 10 dB (above threshold) and up to 20 dB (below threshold) in comparison to the free running slave laser noise level.

We present experimental investigations of the intensity noise properties of injection-locked midinfrared emitting quantum cascade lasers. Following the theoretical approach by Simos et al., the injection locking is realized below and near the threshold of the free running slave laser, resulting in an efficient technique to achieve low-noise operation. We find that below the threshold, the locking characteristics as locking range, shape and bandwidth, are different in comparison with those above threshold. In addition, we also investigate injection locking into longitudinal side modes of the slave laser apart by several longitudinal mode hops, and observe similar characteristics, however, with the potential to achieve higher relative intensity noise suppression. The measurements are confirmed by additional numerical simulations with a new model, which considers the multimode spectrum of the slave laser and the spectral profile of the material gain. Under the actual experimental conditions, a reduction of the relative intensity noise of the slave laser of up to 10 dB (above threshold) and up to 20 dB (below threshold) in comparison to the free running slave laser noise level is achieved. © 2014 IEEE.

In this work, a list of volatile organic compounds (VOCs) that are associated with targets susceptible to versatile security issues - such as drug trafficking, explosives carrying, or human presence in forbidden areas - are monitored and discriminated through algorithmic processing of their midinfrared (MIR) spectroscopic properties. Usually, such tasks are relatively straightforward by identifying the absorption peaks of the investigated compounds in extended spectral recordings, from a few hundred up to many thousands of wavenumbers (cm-1). Nevertheless, the physical mechanisms and instrumentation for obtaining so broad spectral profiles may prove to be complex, especially in field measurements, while data acquisition and processing may also prove to be time-consuming. In the proposed approach, support vector machine algorithmic training is applied in order to evaluate the potential of exploiting very narrow spectral MIR absorption bands that are optimal for reliable prediction analysis and training. The probabilistic classification performance of these bands is evaluated and compared with the prediction performance when using wider MIR absorption spectra. Depending on the data set and the list of the associated VOCs, spectral data recording within a span up to several tens of wavenumbers - at regions where absorption is detectable - prove to be enough for efficient VOC classification. © 2014 John Wiley & Sons, Ltd.

Bigger data is supporting knowledge discovery in nonlinear laser systems as will be demonstrated with examples from three semiconductor laser based systems - one with optical feedback, a photonic integrated circuit (PIC) chaotic laser and a frequency shifted feedback laser system.

We present a numerical analysis that focuses on the temporal pulse properties of a monolithic two-section passively mode locked quantum dot laser subject to optical feedback from a very long external cavity. Pulse duration, shape and intensity noise are studied for the first time to our knowledge versus feedback delay and strength for the case of a passively mode locked semiconductor laser. These temporal characteristics are correlated to the previously observed dependence of repetition rate and timing jitter on cavity parameters in order to highlight the dynamics and complete the corresponding theoretical explanations. © 2013 Elsevier B.V.

We demonstrate the design, fabrication and characterization of a highly nonlinear graded-index SiGe waveguide for the conversion of midinfrared signals to the near-infrared. Using phase-matched four-wave mixing, we report the conversion of a signal at 2.65 μm to 1.77 μm using a pump at 2.12 μm.©2013 Optical Society of America.

In this paper, we numerically investigate the effect of optical injection locking on the noise properties of mid-infrared quantum cascade lasers. The analysis is carried out by means of a rate equation model, which takes into account the various noise contributions and the injection of the master laser. The obtained results indicate that the locked slave laser may operate under reduced intensity noise levels compared with the free running operation. In addition, optimization of the locking process leads to further suppression of the intensity noise when the slave laser is biased close to the free-running threshold current. The main factors that significantly affect the locking process and the achievable noise levels are the injected optical power and the master-slave frequency detuning. © 1965-2012 IEEE.

Output characteristic mapping of a photonic integrated chaotic laser with three control currents has been completed. Visual maps allow identification of differentiated regions of dynamics and show systematic variation in complexity of the chaotic output.

A continuously growing number of municipalities has optical fiber networks supporting communications at their disposal. These fiber installations can also be utilized to convey low data optical signals from a large number of deployed sensing elements, usually positioned in critical infrastructure locations, providing a variety of useful information. Such information can be used in the context of a "smart city" to provide citizens with higher-level services or even to proactively ensure public security and safety. This work demonstrates a fiber sensing network based on low-cost fiber Bragg grating sensors that are able to appropriately oversee diverse monitoring parameters. © 2014 Taylor and Francis Group, LLC.

In this letter, rate-adaptive bit-loading techniques are explored for maximizing the transmission rate of spreading multicarrier modulation schemes over step index plastic optical fiber (SI-POF) short range transmission links. Both the discrete Fourier transform (DFT)-spread discrete multitone (DMT) and code division multiple access-DMT are experimentally evaluated and compared against conventional rate adaptive DMT, over a 50-m intensity modulation direct-detection (IM/DD) link of 1-mm PMMA SI-POF. It is shown that both schemes achieve better performance than DMT, whereas DFT-spread DMT behaves best among them, over the same experimental setup. © 1989-2012 IEEE.

We propose and experimentally demonstrate a novel receiver architecture based on injection locking for demodulating a DPSK/ASK orthogonally modulated signal. The receiver exploits the limiting amplification of an injection locked laser to discriminate the two data streams, enhance the performance of DPSK, and increase the ASK extinction ratio up to 8 dB, making this modulation format suitable for the cost-efficient capacity upgrade of metro networks. © 2013 IEEE.

Zero-lag synchronization in networks composed of semiconductor lasers with mutual coupling interaction has been investigated in much of the recent literature in the field. However, this type of synchronized behavior suffers from de-synchronization (bubbling) events. An analysis of these events and how they determine the laser network performance is presented. The duration and repetition rate of the intermittent de-synchronization events are quantified in order to be associated with the changes in the operating network's parameters. The role of the mediating element in the star network topology in defining leader or laggard dynamics is also under investigation. © 1989-2012 IEEE.

Proper thermal treatment of large core step index plastic optical fibers resulted in a transmission bandwidth improvement of > 35\% and optical loss decrease by approximately 7%. These improved properties remained after almost a year, with the fibers being subjected to environmental temperature variations of >30 Cover the year. The improvement of the fiber properties is attributed to the decreased accumulated modal dispersion resulting from the improved homogeneity of the PMMA material due to the thermal treatment. This interpretation has been experimentally verified. The impact of overfilled launching of light in the fiber has been examined as well. © 1989-2012 IEEE.

We demonstrate four wave mixing (FWM) based wavelength conversion of 40 Gbaud differential phase shift keyed (DPSK) and quadrature phase shift keyed (QPSK) signals in a 2.5 cm long silicon germanium waveguide. For a 290 mW pump power, bit error ratio (BER) measurements show approximately a 2-dB power penalty in both cases of DPSK (measured at a BER of 10-9) and QPSK (at a BER of 10-3) signals that we examined. © 2013 Optical Society of America.

In this paper, an alternative approach for an integrated photonic reservoir computer is presented. The fundamental building block of the reservoir is based on the nonlinear response of a ring resonator, where effects such as twophoton absorption and nonlinear refractive index variation were taken into consideration. In order to investigate the validity of this scheme, the response of a single add/drop micro ring was simulated through a traveling wave numerical model, and the parameters that affect the nonlinearity of the response were identified. Based on these results, a 5 × 5 matrix of randomly interconnected resonators was utilized in order to classify different high-bit-rate digital patterns. Simulations confirmed that the proposed system could offer a classification error of 0.5% for bit rates up to 160 Gbps and for 8-bit-length digital words. © 2013 Optical Society of America.

In this paper, we present a theoretical study on the optimization of passively mode-locked quantum dot lasers based on an alternative cavity design. In particular, we investigate a geometry in which the saturable absorber is located near the low reflection facet of the chip (output facet). The investigation is carried out by means of a time-domain traveling wave numerical model for quantum-dot active medium for both the gain and absorbing sections. The analysis shows superior performance in terms of pulsewidth and peak power of devices based on the new geometry compared to devices based on the conventional geometry, where the saturable absorber is placed near the high reflectivity facet. The optimization relies on the enhanced bleaching of the saturable absorber when the latter is located near the output facet, which prevents the generation of colliding or self-colliding pulse effects. © 2012 IEEE.

Microring cavities (diameter D = 2.7-7 μm) with an active region based on InAs/InGaAs quantum dots are fabricated and their characteristics are studied by the microphotoluminescence method and near-field optical microscopy. A value of 22 000 is obtained for the Q factor of a microring cavity with the diameter D = 6 μm. Lasing up to room temperature is obtained in an optically pumped ring microlaser with a diameter of D = 2.7 μm. © 2013 Pleiades Publishing, Ltd.