Graphene-based electrodes for silicon heterojunction solar cell technology

Transparent conductive electrodes based on graphene have been previously proposed as an attractive candidate for optoelectronic devices. While graphene alone lacks the antireflectance properties needed in many applications, it can still be coupled with traditional transparent conductive oxides, further enhancing their electrical performance. In this work, the effect of combining indium tin oxide with between one and three graphene monolayers as the top electrode in silicon heterojunction solar cells is analyzed. Prior to the metal grid deposition, the electrical conductance of the hybrid electrodes was evaluated through reflection-mode terahertz time-domain spectroscopy. The obtained conductance maps showed a clear electrical improvement with each additional graphene sheet. In the electrical characterization of the finished solar cells, this translated to a meaningful reduction in the series resistance and an increase in the devices’ fill factor. On the other hand, each additional sheet absorbs part of the incoming radiation, causing the short circuit current to simultaneously decrease. Consequently, additional graphene monolayers past the first one did not further enhance the efficiency of the reference cells. Ultimately, the increase obtained in the fill factor endorses graphene-based hybrid electrodes as a potential concept for improving solar cells’ efficiency in future novel designs.This research was funded by DIGRAFEN, grant number ENE2017–88065-C2-2-R. The APC was funded by the Ministry of Economy, Industry and Competitiveness from Spain. das-Nano and UPNA would also like to acknowledge the funding from the Government of Navarra and the European Regional Development Fund (ERDF), 2020 I + D projects: ref. 0011-1365-2020-000026 for das-Nano and ref. 0011-1365-2020-000045 for UPNA

Robust fiber-optic sensor networks

The ability to operate despite failure will become increasingly important as the use of optical sensor networks grows, and the amount of sensing information to be handled by a sensor network is increasing, especially for safety and security applications. In this review, the four categories of protection to allow service to be reestablished after a failure (dedicated/shared and line/path) are thoroughly discussed. This paper also presents an overview of the most representative robust fiber-optic sensor systems, discussing their schemes, pros and cons.The authors are grateful to the Spanish Government project TEC2010-20224-C02-01

Switchable multi-wavelength erbium-doped fiber laser for remote sensing

In this work, we present and experimentally demonstrate a switchable Erbium-doped fiber laser for remote sensing applications. The laser uses four Fiber Bragg Gratings (FBGs) for wavelength selection and for temperature sensing and a 2x4 optical switch. By adjusting the switch combinations, the laser can be switched among the four different wavelength lasing configurations. Stable one- and two- wavelength oscillations were achieved based on the use of this device. An output power instability analysis with the temperature for two different multi-wavelength configurations, one of them using the 2x4 optical switch and the other using a 1x4 coupler, was performed, for a cavity length of 50 km. A comparison between the performances of these topologies is carried out, and their temperature sensitivity and stabilization time are shown

Multiwavelength and switchable erbium-doped fiber lasers

In this work, an experimental stability comparison between two different switchable Erbium- doped fiber lasers (EDFL) is carried out. Both topologies use fiber Bragg grating reflectors in order to select the emission wavelengths and two 2x4 optical switches. By adjusting the switches combinations, the lasers can be switched among the sixteen different wavelength lasing configurations. An output power instability analysis with time for both topologies was performed. The experimental results confirm that the topology based on a serial configuration offers a better stability and higher optical signal to noise ratios (OSNR) than the one based on a parallel configuration