PIN (positive intrinsic negative) photodiodes and analog-to-digital converters (ADC) are commonly used on visible light communication (VLC) receivers in order to retrieve the data on detected signals. In this paper, a visible light communication receiver based on a light to frequency converter (LTF) is proposed. We characterized the LTF and derived an equation for signal-to-noise ratio (SNR) estimation in terms of its input optical power, and the frequency of the output periodic signal. The experiments show that the periodic signal of the LTF converter has a maximum output frequency of 600 kHz at a distance of 6.2 cm. In this setup, measured SNR reached 18.75 dB, while the lowest obtained SNR with 1.1 m length was roughly −35.1 dB. The results obtained suggest that a bit rate of 150 kbps can be achieved with an on-off keying (OOK) modulation format. We analyzed the results and discuss the advantages and limitations of the LTF converter for optical wireless communication purposes.

Colour-shift keying (CSK) is a visible light communication (VLC) modulation scheme used in the existing IEEE 802.15.7 standard. In CSK, information is transmitted by changing the light intensities of the RGB LEDs. In this work, a low-complexity VLC system is proposed using CSK modulation and a novel receiver based on a light-to-frequency (LTF) converter. At the receiver, CSK symbols are interpreted and decoded in terms of frequencies, which are processed by a counter module of a generic microcontroller, thus avoiding the use of analog-to-digital converters (ADCs), which results in a low-cost VLC system. The main contributions of this work are summarized in the following key points: (1) A low-complexity receiver for CSK modulation is introduced; (2) A particle swarm optimization (PSO) algorithm for CSK constellation design is suggested considering the restrictions of the LTF based receiver; (3) Experimental and theoretical validation is perfomed for the proposed multi-colour VLC system. The results show that this system can provide a transmission speed of 100 kbps using a 4-CSK-LTF constellation for a symbol error rate (SER) of 10 − 4 and a signal to noise ratio (SNR) around 35 dB. These results suggest that the analysed system could find applications on those scenarios where low transmission speeds and ease of deployment are the goals.

No abstract

In this paper, the capabilities of chromatic dispersion compensation of a photonic crystal fiber with a hexagonal distribution of circular air holes was investigated. The vector finite element method with scattering boundary condition was used to analyze a set of configurations of the fiber in which the distance between air holes’ centers was modified. With this method it was possible to obtain the values of chromatic dispersion and confinement factor in the C fiber band. The best suited configurations were tested in a 160 km optical link with a bit rate of 40 Gbps. The performance was evaluated by measuring the bit error rate for a set of 20 channels with channel spacing of 100 GHz. The simulation results showed that is possible to reach values of chromatic dispersion as low as $- 850{{{\rm{ps}}} \over {{\rm{nm}} \middot {\rm{km}}}}$ , confinement losses close to 10−3 dB/km and good BER results in the order of 10−17 for a wavelength of 1550 nm.

We introduce a new scheme for the detection of terahertz pulses based on the frequency selective optoelectronic downconversion of its individual modes with a continous-wave (CW) ErAs:InGaAs photoconductive antenna (PCA) driven by a comb-based CW photonic signal. The detection scheme can be used as metrology tool for the analysis of the fundamental resolution and stability limits of terahertz pulses and the mode-locked-lasers (MLLs) that drives them, as well as an ultra-high-resolution measurement technique for terahertz components or gas spectroscopy. We demonstrate both applications by measuring the linewidth of two frequency components of the particular terahertz pulse analyzed here (one at 75 GHz and one at 340 GHz) and by measuring a very narrowband filter between 70 and 80 GHz. The main advantage of this technique with respect to other terahertz pulse detection schemes is its capability of performing ultrahigh-resolution measurements without the need of unpractically long scanning ranges or synchronization of two MLLs.