Abstract-Reduced dispersion-induced harmonics levels are reported for analogue radio-over-fiber systems by using a linearized receiver incorporating a memoryless electronic circuit with square root (SQRT)-like transfer function, and performing amplitude modulation (AM) at the transmitter. A practical implementation demonstrates the effectiveness of the AM-SQRT approach in linearizing the optical transmission system with respect to the conventional intensity modulation and direct detection system. Index Terms-Adaptive equalization, dispersion equalization, optical fiber communications, radio-over-fiber (RoF).

A simple and low cost method for wavelength control of economical random non-preselected independent ONU sources is shown to increase the number of users in an OFDMA-PON. The method is based on OLT monitoring and thermal tuning control; it has been validated through Monte-Carlo simulations and a probabilistic model. The minimum optical spectral gap between the ONUs wavelengths that guarantees a tolerable amount of optical beat interference has been determined through an experiment.

The statistical OFDM-PON concept with multiband Optical Network Units (ONUs) is experimentally tested with two users and an Optical Line Terminal (OLT) at 2.5 / 5 Gb/s total effective capacity with BPSK/QPSK modulation. Both downstream (DS) and uplink (UL) were measured based on intensity modulation and direct-detection (IMDD). The ONUs consisted of local non-preselected wavelength distributed feedback (DFB) laser sources centrally controlled to reduce overlapping probability. In addition, a radiofrequency (RF) mixing stage in the ONUs up/down-converts the user data to/from the OFDM signal reducing the computational effort. Compared with ONUs processing the whole signal, the multiband approach presents comparable results with almost symmetrical power budgets of around 25dB and 20dB with BPSK and QPSK respectively, which could increase up to 4.5dB by allocating a spectral guard interval between the optical carrier and the OFDM data. Furthermore, elastic bandwidth allocation is explored which is shown to compensate for up to 18dB differential link-loss.

Closed-form expressions explicitly relating modulation bandwidth and active length in electro-optic traveling wave modulators are presented which fully account for skin-effect electrode loss and optical-electrical wave velocities mismatch. Four Optical modulators based on the electro-optic (EO) Pockels effect are basic building blocks of optical systems, with applications continuously growing up. As compared to lumped electrode configurations, bounded by a fundamental sensitivity-bandwidth limit, traveling wave (TW) configurations allow pushing the limit by optimization of the TW structure and provide extended modulation bandwidth with reduced drive power [1,2]. In EO-TW modulators (EO-TWM) the Pockels electrically induced optical phase shift accumulates with the copropagated distance (L) and therefore, the modulation drive voltage, usually quantified as the voltage required for a π phase shift, V π , is reduced proportionally to increases in L [3]. However, as it is well known, this comes at the expense of a corresponding reduction in operative bandwidth (B), which in typical EO-TWM based on coplanar waveguides (CPWs) over LiNbO 3 substrates stems mainly from the combined action of two basic mechanisms, namely the skin-effect electrode loss and the optical-electrical wave velocity mismatch. When trying to elucidate the expected B reduction that a specific L increase could have, a constant BL product rule proportional to the inverse of the velocity matching (VM) constant (ν) has been shown to govern the low-loss (LL) limit [4], while in the VM limit, a constant BL 2 rule proportional to the inverse of the square of the loss constant (α) has been found more appropriate [5]. To the best of our knowledge, no simple B-L rules have been derived for the intermediate ranges in which both α and ν are relevant, nor have the LL and VM limits been quantified in a general way.In this Letter we present closed-form expressions that fully account for the effects of skin-effect electrode loss and optical-electrical wave velocities mismatch and that explicitly and in a biunivocal way relate the operative bandwidth and the electrode length in EO-TWM. From these, four B-L trade-off figures of merit are identified with different validity ranges which are seen to depend both on the TW cross-sectional parameters (i.e., skineffect constant and optical-electrical velocity mismatch) and on the target B and L values.In order to analyze the B-L relationship, we begin by considering the electrical modulation frequency response of an impedance matched EO-TWM in the presence of skin-effect electrical loss in the conducting electrodes of length L and optical-electrical velocity mismatch [6] Mf e

The electrical conductivity of two-dimensional (2D) materials without any electrical contact can be obtained using two different methods: the terahertz time domain spectroscopy (THz-TDS) method, in the range from GHz up to 2 THz, and with a rutile dielectric resonator (RDR), in which case the conductivity is obtained at the resonant frequency of the device, close to 9.0 GHz. In one case (THz-TDS in a transmission setup), the sample is directly focused. In the other case (RDR), the sample is placed inside the resonant cavity working at TE 011 mode and must have exactly the same surface size as the cavity, 12 Â 12 mm in our device. From the Q factor variation of the resonant cavity due to the sample, its surface resistance is extracted. These measurements are performed on different 2D materials: graphene and WS 2. Both methods are analyzed and compared. For few-layer 2D samples, the THz-TDS method is suitable.