Evangelos Pikasis

Implementation of 140 Gb/s true random bit generator based on a chaotic photonic integrated circuit

In the present work a photonic integrated circuit (PIC) that emits broadband chaotic signals is employed for ultra-fast generation of true random bit sequences. Chaotic dynamics emerge from a DFB laser, accompanied by a monolithic integrated 1-cm long external cavity (EC) that provides controllable optical feedback. The short length minimizes the existence of external cavity modes, so flattened broadband spectra with minimized intrinsic periodicities can emerge. After sampling and quantization--without including optical de-correlation techniques and using most significant bits (MSB) elimination post-processing--truly random bit streams with bit-rates as high as 140 Gb/s can be generated. Finally, the extreme robustness of the random bit generator for adaptive bit-rate operation and for various operating conditions of the PIC is demonstrated.

Sub-Tb/s Physical Random Bit Generators Based on Direct Detection of Amplified Spontaneous Emission Signals

The most common optical amplified spontaneous emission sources can become the ultimate tools for the generation of ultra-broadband truly random bit sequences (TRBS). By using a straightforward configuration we experimentally prove that the amplified spontaneous emission noise of an optical amplifier-either an Er+3 -doped fiber amplifier (EDFA) or an InGaAs semiconductor optical amplifier (SOA)-is an efficient source for TRBS generation. A bit rate up to 560 Gb/s has been recorded, seeded by the direct detection of the unfiltered spontaneous-spontaneous (sp-sp) optical intensity beat noise on a broadband photoreceiver. The generation rate is practically limited only by the detection bandwidth, the electronic digitization process and the post-processing circuitry. The proposed mechanism passes the existing benchmarks of randomness.

DFT-Spread DMT Modulation for 1-Gb/s Transmission Rate Over 100 m of 1-mm SI-POF

In this letter, the discrete Fourier transform-spread discrete multitone modulation (DFT-spread DMT) scheme has been used for the first time in laser-based short range optical transmission (over 100 m) with 1-mm step-index plastic optical fiber link, and its superior performance, compared with the standard DMT scheme, was demonstrated. The DFT-spread DMT combines the advantages of both single carrier and multicarrier transmission together with a lower peak-to-average power ratio. Under the same experimental conditions, a lower bit-error-rate is achieved with DFT-spread DMT compared with standard DMT for transmission rates in the 1-Gb/s range.

Space-time block code based MIMO encoding for large core step index plastic optical fiber transmission systems

The performance of Space-Time Block Codes combined with Discrete MultiTone modulation applied in a Large Core Step-Index POF link is examined theoretically. A comparative study is performed considering several schemes that employ multiple transmitters/receivers and a fiber span of 100 m. The performance enhancement of the higher diversity order configurations is revealed by application of a Margin Adaptive Bit Loading technique that employs Chows algorithm. Simulations results of the above schemes, in terms of Bit Error Rate as a function of the received Signal to Noise Ratio, are provided. An improvement of more than 6 dB for the required electrical SNR is observed for a 3 × 1 configuration, in order to achieve a 10(-3) BER value, as compared to a conventional Single Input Single output scheme.

Power losses in diffuse ultraviolet optical communications channels.

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 (photomultiplier tube) and for different atmospheric conditions has been taken for the characterization of the optical communications channel in terms of its loss properties.

Enhanced Multi-Level Phase Quantizer for the Optical Processing of M-PSK Signals

This paper presents a novel multi-level phase quantizer with the potential of almost ideal step like transfer function. Its operation relies on the proper combination of phase sensitive amplification in highly nonlinear fibers and amplitude limitation offered by injection locked lasers. Thorough investigation of the quantization properties of the scheme is theoretically and numerically conducted under ideal and non-ideal operating conditions. The properties of the limiter and their impact on the quantization performance are highlighted. The regenerative operation is demonstrated numerically by showing that a regenerated differentially decoded quaternary shifted keyed signal exhibits almost identical bit error rate performance with homodyne detection.

Performance Evaluation of CDMA-DMT for 1-mm SI-POF Short-Range Transmission Links

In this letter, the code division multiple access discrete multitone (CDMA-DMT) modulation scheme is experimentally investigated for transmission over an intensity modulation direct-detection link of 100 m of 1-mm polymethyl methacrylate step-index plastic optical fibers. CDMA-DMT is a multicarrier modulation scheme combining the merits of both CDMA and DMT and in which CDMA is utilized to perform a spreading operation of the data symbols in the frequency domain using orthogonal spreading codes. It is experimentally shown that CDMA-DMT performs better than conventional DMT in terms of achieved bit-error rate, for transmission rates in the range of 1 Gbps and over the same experimental configuration.

OFDM, SC-FDMA AND MC-CDMA educational wireless transceivers using Matlab and the TMS320C6713 DSK

In this paper we describe the design and implementation of real-time wireless transceivers for advanced multicarrier modulation schemes, namely OFDM, SC-FDMA and MC-CDMA. The baseband system level design is done using Matlab/Simulink and the implementation is done using the TMS320C6713 DSK from Texas Instruments Inc. Cooperation of Matlab IDE and Code Composer Studio IDE allow for automatic code generation directly from Simulink blocks, offering a flexible way from system level design and simulation to actual implementation and verification. The wireless (RF) part is based on conventional components. For all multicarrier schemes we explore most of the basic building blocks that constitute them. The implemented testbed is intended primarily for educational demonstration and experimentation purposes offering the means for highlighting and studying several concepts and phenomena regarding not only the modulation schemes but the wireless link as a whole. Typical results concerning the experimental demonstration, evaluation and verification of the testbed are presented.

Experimental Evaluation of Modulation Formats’ Performance in Diffuse UV Channels

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.

Comparison of CAP and DFT-spread DMT for high speed transmission over 50m SI-POF

Over the recent years many modulation schemes were proposed for laser based high-speed short-range transmission over step-index plastic optical fiber (SI-POF). Among these schemes, CAP and DFT-Spread DMT demonstrated a good performance for intensity modulation direct-detection transmission via SI-POF. In this work, for the first time, we report on the progress and initial experimentation regarding the comparison of CAP and DFT-Spread DMT for transmission over 50m of 1-mm SI-POF. It is shown that CAP and DFT-Spread DMT achieve a comparable transmission rate for a given bit error rate over the same experimental configuration.