KEYWORDS: Optical filters, Signal processing, Scanning transmission electron microscopy, Nonlinear filtering, Image processing, Digital signal processing, Signal to noise ratio, Optical computing, Nonlinear optics, Electronic filtering
We present an integrated photonic reservoir computing scheme that relies on the use of passive optical filters inside waveguide loops. The filters-in-a-loop nodes aim to provide an alternative all-optical non-linear activation function, circumventing previous power-hungry or bandwidth-limiting approaches. The non-linear transformation of the incoming optical signal relies, firstly on multiple spectral slicing and secondly on the non-linear mapping of phase information to the outputs’ amplitude, through the existence of resonant optical cavities. The efficiency of the approach has been evaluated numerically, through two demanding applications. Transmission impairment amendment of 224 Gbps PAM signals with superior to HD FEC performance for short-reach networks and secondly, MHz rate all-optical classification of time-stretched scans depicting objects with different spatial features.
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.
KEYWORDS: Waveguides, Mid-IR, Sensors, Free space optics, Signal to noise ratio, Silicon, Polarization, Silicon photonics, Photonics, Free space optical communications
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 midinfrared
signal is injected into the waveguide system so as to excite the fundamental symmetric mode. In the 2-5μm
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 midinfrared
optical power.
A simple read-out technique using 1.55μm 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 150μm. 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.
In this study two types of coplanar waveguide (CPW) array antennas are designed and analyzed for use in a 60GHz
Radio over Fiber indoor network. The first one is based on high permittivity Rogers 6010 and Indium Phosphide (InP)
substrates incorporating slots as radiating elements. The second one utilizes stacked geometry based on the above
substrates. Both arrays present more 1 GHz bandwidth and 10dBi gain. Furthermore they can provide beam-forming
operation by properly adjusting the signal’s amplitude and phase. A Least Mean Square (LMS) algorithm is generated
for this purpose and the radiation pattern is steered accordingly. At last, a photodiode is simulated using equivalent
circuit and is adopted with the proposed arrays, and an optical beam forming scenario is discussed.
A thorough study of an all-optical chaotic communication system, including experimental realization real-world testing
and performance characterization through bit-error-rate analysis, is presented. Pseudorandom data that are effectively
encrypted in the chaotic emitter and sent for transmission are recovered at the receiver with bit-error-rate (BER) values
as low as 10-7 for 1 Gb/s data rate. Different data code lengths and bit-rates at the Gb/s region have been tested. Optical
transmission using 100km fiber spools in an in-situ experiment and 120km in an installed optical network showed that
chaotic communication systems does not act as a considerably deteriorating factor in the final performance.
A novel all-optical regeneration approach based on fiber-optic parametric amplification operating under the strong pump depletion regime is numerically demonstrated. The key point for the regenerator's operation is related to the fact that a high-power intensity modulated signal depletes the continuous wave pump in such a manner that the latter becomes intensity modulated and inverted compared to the signal. Using a cascade of two such devices a non-inverted, either wavelength converted or not, amplitude modulated output, which exhibits regenerative characteristics with respect to the input signal can be provided. Extended numerical simulations have been carried out on one hand to estimate the transfer characteristics of the regenerator and on the other hand to assess the cascadability performance on a typical 40Gb/s transmission system. Through the latter analysis very promising results have been derived proving the potential of the proposed device for all-optical regeneration in cascaded operation for both return to zero and non-return to zero data transmitted along 1Mm of optical fiber at 40Gb/s.
The performance of an all-optical closed-loop chaotic communication system in a transmission link consisting of single mode fibers (SMF) applying two different dispersion management techniques is numerically studied. The first technique is implemented by the usage of dispersion compensating fibers (DCFs), while the second utilizes optical phase conjugators (OPCs). The latter is implemented by means of four wave mixing (FWM) in a dispersion shifted fiber (DSF), where the chaotic carrier corresponds to the signal wave and a high power continuous wave corresponds to the pump wave. Calculation of the recovered message Q-factor values obtained from the corresponding eye diagrams has been carried out applying chaotic modulation (CM) and chaos shift keying (CSK) encryption techniques for two repetition rates (2.4Gbps, 5Gbps). It is shown that the optical phase conjugation is an effective dispersion and non-linear effects compensation technique even if high-bit rate message encoding is applied. The superiority of a transmission system including OPCs to that utilizing (DCFs) is presented. The influence of key system parameters such as optical power, OPC spacing, pump power level, etc. to the transmission performance has been investigated. Acceptable system performance is presented for approximately 600Km at 2.4Gbps and 400Km at 5Gbps.
A detailed investigation of the decoding properties of different receiver configurations in an all-optical chaotic transmission system is presented for two data-encoding techniques and for various dispersion compensation maps. A semiconductor laser subjected to optical feedback generates the chaotic carrier while data is encoded either by Chaotic Modulation (CM) or Chaotic Shift Keying (CSK) methods. The complete transmission module consists of various dispersion management maps, in-line amplifiers and Gaussian optical filters. The receiver, employing a high facet reflectivity laser, is either forming a closed-loop configuration operating at the non-amplification regime or a strongly injected open-loop one. For the latter configuration the possibility of utilizing an anti-reflection (AR) coated laser is also investigated. System's performance is numerically tested by calculating the Q-factor of the eye diagram of the 1 Gb/s received data. The influence of the optical power launched into fibre or the transmission distance to the quality of the decoded message has been investigated. The closed-loop scheme had better performance relative to the open-loop, while CSK method and maps utilizing Dispersion Shifted Fibres are superior to CM and that employing Dispersion Compensating Fibres respectively. When an AR-coated laser is used in the open-loop receiver setup, improved decoding performance occurs.
A novel approach for realization of all-optical pulse reshaping in an integrated microring resonator is proposed. The concept presented in this study is based on four-wave mixing in a passive GaAs/AlGaAs microring resonator side coupled to a bus waveguide, taking into account all higher order non-linear effects such as self-phase modulation (SPM), cross-phase modulation (XPM), pump depletion and two-photon absorption (TPA), the latter being the dominant process here. We also include in the description changes in absorption and refractive indexes induced by free-carriers generated by TPA. This scheme is investigated for its regenerative characteristics using an optical pump modulation scheme. The application of the modulation bit stream in the pump wave leads in a conjugate wave power being proportional to the square of the pump power, resulting in a corresponding extinction ratio improvement. Because of the strong TPA, enhanced by the resonance effect, the converted signal power saturates as pump power increases, providing noise suppression at high power levels. A detailed study of the static and dynamic reshaping characteristics of the wavelength converter has been carried out. Its performance, evaluated by extinction ratio (ER) and Q factor calculations, showed satisfactory regenerative properties up to 10Gb/s.
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