Christophe Lethien

On-chip and freestanding elastic carbon films for micro-supercapacitors

Flexible power for flexible electronics A challenge for flexible electronics is to couple devices with power sources that are also flexible. Ideally, they could also be processed in a way that is compatible with current microfabrication technologies. Huang et al. deposited a relatively thick layer of TiC on top of an oxide-coated Si film. After chlorination, most, but importantly not all, of the TiC was converted into a porous carbon film that could be turned into an electrochemical capacitor. The carbon films were highly flexible, and the residual TiC acted as a stress buffer with the underlying Si film. The films could be separated from the Si to form free-floating films, with the TiC providing a support layer. Science, this issue p. 691 Porous carbon-based supercapacitors are directly fabricated onto silicon substrates. Integration of electrochemical capacitors with silicon-based electronics is a major challenge, limiting energy storage on a chip. We describe a wafer-scale process for manufacturing strongly adhering carbide-derived carbon films and interdigitated micro-supercapacitors with embedded titanium carbide current collectors, fully compatible with current microfabrication and silicon-based device technology. Capacitance of those films reaches 410 farads per cubic centimeter/200 millifarads per square centimeter in aqueous electrolyte and 170 farads per cubic centimeter/85 millifarads per square centimeter in organic electrolyte. We also demonstrate preparation of self-supported, mechanically stable, micrometer-thick porous carbon films with a Young’s modulus of 14.5 gigapascals, with the possibility of further transfer onto flexible substrates. These materials are interesting for applications in structural energy storage, tribology, and gas separation.

Radio-over-fiber transport for the support of wireless broadband services [Invited]

Some of the work carried out within the EU Network of Excellence ISIS on radio-over-fiber systems for the support of current and emerging wireless networks is reviewed. Direct laser modulation and externally modulated links have been investigated, and demonstrations of single-mode fiber and multimode fiber systems are presented. The wireless networks studied range from personal area networks (such as ZigBee and ultrawideband) through wireless local area networks to wireless metropolitan area networks (WiMAX) and third-generation mobile communications systems. The performance of the radio-over-fiber transmission is referenced to the specifications of the relevant standard, protocol operation is verified, and complete network demonstrations are implemented.

Optically Powered Remote Units for Radio-Over-Fiber Systems

Optically powered radio-over-fiber remote units have been designed and constructed for distributed antenna system applications using separate fibers for power and signal transmission. The feasibility of this approach has been investigated through a series of transmission measurements, based on the IEEE 802.11g wireless local area networking standard at a frequency of 2.5 GHz using 64-QAM OFDM modulation at 54 Mb/s. These measurements show that high-quality multilevel signal transmission is possible with modest levels of optical power at the central unit. For example, an EVM of around 3% has been achieved for an RF output power of 0 dBm using a central unit optical power of 250 mW over a link length of 300 m.

Potentials of radio over multimode fiber systems for the in-buildings coverage of mobile and wireless LAN applications

We evaluate the transmission of digital signal modulated on radio-frequency subcarriers through multimode fiber (MMF) by using low-cost 850-nm vertical-cavity surface-emitting lasers and 50-/spl mu/m/62.5-/spl mu/m-core matched receptacle photodiodes. Several mobile telecommunication and wireless local area network standards have been transmitted through standard (500 MHz/spl middot/km) and high bandwidth (1500 and 2000 MHz/spl middot/km) Corning Infinicor SXi and SX+ MMF under different lengths (100, 300, and 600 m). Characterization has been carried out to measure error vector magnitude (EVM) variation as a function of fiber type and length. EVM minor to IEEE and ETSI requirements are obtained for all standards being tested such as IEEE 802.11 g with 1.8% root-mean-square for 300 m of 50-/spl mu/m-core standard MMF at 850 nm.

Simultaneous Dual Band Transmission Over Multimode Fiber-Fed Indoor Wireless Network

Performance measurements of different combinations of digital enhanced cordless telecommunications packet radio service, global system for mobile communications, universal mobile telecommunication service, and 802.11g (54 Mbps) signals in a dual band configuration transmitted over an indoor wireless network fed by a low-cost 850-nm vertical-cavity surface-emitting laser (VCSEL)-300m multimode fiber link are presented. The feasibility of such a system is demonstrated with error vector magnitude measurements which are within the required specifications

Review of Glass and Polymer Multimode Fibers Used in a Wimedia Ultrawideband MB-OFDM Radio Over Fiber System

In this paper, we have exhibited the potential of the glass- and polymer-based multimode fibers to be used in a radio over fiber (ROF) system in order to extend the indoor coverage of the Wimedia multiband orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) standard. After the design of a test setup operating at 850 nm, we have performed the physical characterization of the ROF system especially the mask test compliance, the error vector magnitude (EVM), or the relative constellation error (RCE) variation as a function of the system parameters [radio frequency (RF) power, optical attenuation, fiber length, laser bias current]. The transmission performance of both 200 and 480 Mb/s Wimedia signals is demonstrated through a 100 m link length of glass- and polymer-based multimode fibers: transmission penalties are quantified by RCE with values under the standard requirements. Two different behaviors depending on the core material of the fiber have been identified in this study.

A Distributed Antenna System for Indoor Accurate WiFi Localization

Specific infrastructures are a key challenge for indoor geo-localization systems. In particular, an accurate narrowband localization technique using 802.11 g WiFi signals is proposed in this letter. The related system architecture is built on the basis of radio over fiber topology of distributed antennas systems that are increasingly deployed in buildings. In particular, the system proposed collects the microwave signals using remote and local access points linked by 62.5-μm core diameter multimode fibers and enables to determine the location transmitter with an accuracy of less than 6.4 cm.

Energy-Autonomous Picocell Remote Antenna Unit for Radio-Over-Fiber System Using the Multiservices Concept

The study reported in this letter deals with the extension of the multiservices concept to radio-over-fiber systems with energy-autonomous picocell remote antenna units. Continuous-power, radio-frequency, and digital signals have been combined in a single multimode fiber for the first time. The results clearly demonstrate no impairment of the optically powered remote antenna unit compared to an electrically powered version. The proposed system complies with the classical baseband Ethernet high-data-rate network (10 GbE bit error rate 10-12). The measured error vector magnitude for the radio-frequency (IEEE802.11g) signal transmission through the designed system stays around 2%, including both the optical transmission over 100-m OM3 multimode fiber and a wireless coverage of 5 m.

Differential Mode Delay Measurements of Fluorinated Graded Index Polymer Optical Fiber

We have performed a detailed study of four different perfluorinated graded index polymer optical fibers issued from two manufacturers. After the description of the test bench that has been set up in order to measure the differential mode delays, we report on the corresponding measurements in time domain and the deduced ones in the frequency domain allowing us to get the optical modal bandwidth.

An optically powered radio over fiber remote unit using wavelength division multiplexing

Power over fiber and radio over fiber transmission have been combined in a single optical fiber using wavelength division multiplexing for the first time. It is shown that there is no impairment to the radio over fiber transmission performance from the power transmission link. There is however a power penalty caused by the insertion losses of the multiplexer and demultiplexer and potentially a further insertion loss depending on the type of transmission fiber used.