In-field Raman amplification on coherent optical fiber links for frequency metrology.

Distributed Raman amplification (DRA) is widely exploited for the transmission of broadband, modulated signals used in data links, but not yet in coherent optical links for frequency metrology, where the requirements are rather different. After preliminary tests on fiber spools, in this paper we deeper investigate Raman amplification on deployed in-field optical metrological links. We actually test a Doppler-stabilized optical link both on a 94 km-long metro-network implementation with multiplexed ITU data channels and on a 180 km-long dedicated fiber haul connecting two cities, where DRA is employed in combination with Erbium-doped fiber amplification (EDFA). The performance of DRA is detailed in both experiments, indicating that it does not introduce noticeable penalties for the metrological signal or for the ITU data channels. We hence show that Raman amplification of metrological signals can be compatible with a wavelength division multiplexing architecture and that it can be used as an alternative or in combination with dedicated bidirectional EDFAs. No deterioration is noticed in the coherence properties of the delivered signal, which attains frequency instability at the 10(-19) level in both cases. This study can be of interest also in view of the undergoing deployment of continental fiber networks for frequency metrology.

High responsivity SiGe heterojunction phototransistor on silicon photonics platform.

We report on a novel near infrared SiGe phototransistor fabricated by a standard silicon photonics foundry. The device is first investigated by simulations. The fabricated devices are characterized in terms of current-voltage characteristics at different optical power. Typical phototransistors exhibit 1.55µm record responsivity at low optical power exceeding 232A/W and 42A/W at 5V and 1V bias, respectively. A differential detection scheme is also proposed for the dark current cancellation to significantly increase the device sensitivity.

High-performance hybrid Raman/fiber Bragg grating fiber-optic sensor based on simplex cyclic pulse coding.

We propose and experimentally demonstrate the use of cyclic pulse coding to improve the performance of hybrid Raman/fiber Bragg grating (FBG) fiber-optic sensors, for simultaneous measurement of distributed static temperature and discrete dynamic strain over the same sensing fiber. Effective noise reduction is achieved in both Raman optical time-domain reflectometry and dynamic interrogation of time-division-multiplexed fiber FBG sensors, enhancing the sensing range resolution and providing real-time point dynamic strain measurement capabilities. The highly integrated sensor scheme employs broadband apodized low-reflectivity FBGs, a single narrowband optical source, and a shared receiver block.

Ion-exchanged Er3+/Yb3+ co-doped waveguide amplifiers longitudinally pumped by broad area lasers.

A multimode pumping scheme for Er(3+)/Yb(3+) co-doped waveguide amplifiers based on broad area lasers at around 980 nm is presented. The proposed amplifier is fabricated by ion-exchange (IE) technique on silicate and phosphate glasses. The highly efficient energy transfer from Yb(3+) to Er(3+) ions, combined with the use of low cost and high power broad area laser, allows the realization of high performance and cost-effective integrated amplifiers. The structure has been designed and numerically studied using a 3D finite element modelling tool, and over 3 dB/cm small signal gain has been predicted for an optimized amplifier. Preliminary characterization of an amplifier structure provides a first experimental evidence of the novel multimode longitudinal pumping.

Study of an efficient longitudinal multimode pumping scheme for Si-nc sensitized EDWAs.

We present an efficient multimode longitudinal pumping scheme which overcomes the main limitations of single-mode longitudinal pumping as well as top pumping in Si-nanoclusters sensitized Erbium-doped waveguide amplifiers. The proposed configuration is based on evanescent pump light coupling from a multimode waveguide to a Si-nanoclusters sensitized Er(3+)-doped active core. Theoretical predictions, based on propagation and population-rate equations for the coupled Er(3+)/Sinanoclusters system, point out that the proposed pumping scheme can provide high pump intensity within the active core, also ensuring good uniformity of the population inversion along the waveguide amplifier. Although longitudinal multimode pumping by high power LEDs in the visible can potentially lead to low cost integrated amplifiers, further material optimization is required. In particular, we show that when dealing with high pump intensities, confined carrier absorption seriously affects the amplifier performance, and an optimization of both Si-nc and Er(3+) concentrations is necessary.