Signal Stability in Periodically Amplified Fiber Transmission Systems Using Multiple Quantum Well Saturable Absorbers for Regeneration

The use of multiple quantum well (MQW) saturable absorbers (SAs) for signal regeneration in periodically amplified fiber transmission systems is explored. A systematic study of signal destabilization resulting from incomplete saturation of MQW SAs used for regeneration, and of means of overcoming such destabilization, is presented. A computer model for MQW SAs, which considers the asymmetric Fabry-Perot (AFP) cavity structure commonly employed to increase the contrast of such devices, is presented. The model is used to simulate nitrogen-implanted MQW SAs with 7000 km when the two components are combined.</p

InP integrated optical frequency comb generator using an amplified recirculating loop

A novel realisation of photonically integrated optical frequency comb generation is demonstrated on indium phosphide (InP) using a generic foundry platform. The architecture, based on the amplified recirculating loop technique, consists of cascaded electro-optic phase modulators embedded within a short waveguide loop. While an injected continuous wave laser signal is recirculated by the loop, the modulators are driven with a modulation frequency corresponding to the round-trip loop length frequency. This results in many phase coherent, evenly spaced optical comb lines being generated. The choice of InP as an integration platform allows immediate optical amplification of the modulated signal by embedded semiconductor optical amplifiers, enabling loop losses to be compensated and expanding the comb across broad optical bandwidths. This approach reduces the requirement for external, high-power optical amplifiers, improving the compactness and power efficiency of the full system. The system was modelled to identify off-resonance behaviour, outlining limits in matching both the modulation frequency and seed laser frequency to the round-trip loop frequency for optimal comb line generation to be achieved. The experimental device occupied a fraction of the 6 x 2 mm2 InP chip and operated at round-trip loop frequencies of 6.71 GHz to produce 59 comb lines within a 20 dB power envelope. All comb lines exhibited strong phase coherence as characterised by low composite phase noise measurements of -105 dBc/Hz at 100 kHz. A second device is also presented with a shorter loop length operating at ~10 GHz which generated 57 comb lines. Both loop configurations included short waveguide phase shifters providing a degree of tunability of the free spectral range with a tuning range of 150 MHz for small injection currents of less than 2.5 mA.This research work has been supported by the UK Engineering and Physical Sciences Research Council (EPSRC) through the Integrated Photonics and Electronic Systems (IPES) Centre of Doctoral Training and PICSat project (EPSRC Reference: EP/S000976/1)

Pilot-tone assisted 16-QAM photonic wireless bridge operating at 250 GHz

A photonic wireless bridge operating at a carrier frequency of 250 GHz is proposed and demonstrated. To mitigate the phase noise of the free-running lasers present in such a link, the tone-assisted carrier recovery is used. Compared to the blind phase noise compensation (PNC) algorithm, this technique exhibited penalties of 0.15 dB and 0.46 dB when used with aggregated Lorentzian linewidths of 28 kHz and 359 kHz, respectively, and 20 GBd 16-quadrature amplitude modulation (QAM) signals. The wireless bridge is also demonstrated in a wavelength division multiplexing (WDM) scenario, where 5 optical channels are generated and sent to the Tx remote antenna unit (RAU). In this configuration, the full band from 224 GHz to 294 GHz is used. Finally, a 50 Gbit/s transmission is achieved with the proposed wireless bridge in single channel configuration. The wireless transmission distance is limited to 10 cm due to the low power emitted by the uni-travelling carrier photodiode used in the experiments. However, link budget calculations based on state-of-the-art THz technology show that distances >1000 m can be achieved with this approach.Comment: 13 pages, in Journal of Lightwave Technolog

Photonic systems for tunable mm-wave and THz wireless communications

In this paper we present two different techniques for photonic generation of millimeter and THz waves. Each of them tackles the phase noise problem associated with optical sources in a different way. The first one relays on the heterodyne down-conversion of two phase noise correlated optical tones. The correlation is achieved by generation of an optical frequency comb. To select one of the optical lines we use an optical phase lock loop, which besides enabling a frequency offset between output and input, can provide optical gain and is highly selective. The second one relays on the envelope detection of a single sideband-with carrier signal. In this approach the photonic remote antenna unit is implemented as monolithically integrated photonic chip

Generation of continuous wave terahertz frequency radiation from metal-organic chemical vapour deposition grown Fe-doped InGaAs and InGaAsP

We demonstrate the generation of continuous wave terahertz (THz) frequency radiation from photomixers fabricated on both Fe-doped InGaAs and Fe-doped InGaAsP, grown by metal-organic chemical vapor deposition. The photomixers were excited using a pair of distributed Bragg reflector lasers with emission around 1550 nm, and THz radiation was emitted over a bandwidth of greater than 2.4 THz. Two InGaAs and four InGaAsP wafers with different Fe doping concentrations were investigated, with the InGaAsmaterial found to outperform the InGaAsP in terms of emitted THz power. The dependencies of the emitted power on the photomixer applied bias, incident laser power, and materialdoping level were also studied

Coherent terahertz photonics

We present a review of recent developments in THz coherent systems based on photonic local oscillators. We show that such techniques can enable the creation of highly coherent, thus highly sensitive, systems for frequencies ranging from 100 GHz to 5 THz, within an energy efficient integrated platform. We suggest that such systems could enable the THz spectrum to realize its full applications potential. To demonstrate how photonics-enabled THz systems can be realized, we review the performance of key components, show recent demonstrations of integrated platforms, and give examples of applications

The 2017 Terahertz Science and Technology Roadmap

Science and technologies based on terahertz frequency electromagnetic radiation (100GHz-30THz) have developed rapidly over the last 30 years. For most of the 20th century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to “real world” applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2016, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 17 sections that cover most of the key areas of THz Science and Technology. We hope that The 2016 Roadmap on THz Science and Technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies

Optical injection locking to optical frequency combs for superchannel coherent detection

Optical injection locking characteristics of a distributed feedback laser are experimentally investigated for multiple-wavelength injection. Using a three-wavelength source generated by intensity modulation as the injected signal, it was found that the presence of adjacent lines could cause disturbance to the locking if a minimum guard band between the respective locking limits of two adjacent lines was not observed. With a 21-line comb with 20 GHz line spacing as the injected signal, the injection locking range was observed to become asymmetrical in relation to the laser free-running frequency under high-power injection conditions and was found to be dependent on whether the laser was locked to lines located at centre and or edges of the comb. Finally, the use of the injection locked laser as a seed laser for generating a local oscillator (LO) comb for superchannel coherent detection was investigated and the phase error between the input and LO combs analysed23215471557CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP308553/2010-1BEX 3364/11-9não temThe authors would like to thank CAPES (grant BEX 3364/11-9), FAPESP, Padtec S.A., and CNPq (grant 308553/2010-1), Brazil, and EPSRC (COSINE project, EP/I012702/1), U

Signal Stability in Periodically Amplified Fiber Transmission Systems Using Multiple Quantum Well Saturable Absorbers for Regeneration

The use of multiple quantum well (MQW) saturable absorbers (SAs) for signal regeneration in periodically amplified fiber transmission systems is explored. A systematic study of signal destabilization resulting from incomplete saturation of MQW SAs used for regeneration, and of means of overcoming such destabilization, is presented. A computer model for MQW SAs, which considers the asymmetric Fabry-Perot (AFP) cavity structure commonly employed to increase the contrast of such devices, is presented. The model is used to simulate nitrogen-implanted MQW SAs with &lt; 5 ps recovery time in a transmission system. A comparison is made with results previously obtained for a 10 Gb/s standard single-mode fiber (SMF) recirculating loop transmission experiment using MQW SAs and temporary soliton propagation for signal regeneration. The simulations allow the benefits derived from the two parts of the regenerator to be identified, as well as their contributions to the destabilization of the propagating signal. The error-free transmission distance is improved from similar to 2000 to &gt; 7000 km when the two components are combined.</p