Manuel Violas

A Comparison of Radio Over Fiber Link Types for the Support of Wideband Radio Channels

Three radio over fiber link types are compared to assess their relative performance for the optical transmission of next generation wireless signals having multiple wideband radio channels with high-level modulation. These links differ in their choice of modulation device; either a directly modulated laser (DML) or external modulation using a Mach-Zehnder modulator (MZM) or a reflective semiconductor optical amplifier (RSOA). The DML and RSOA link types are shown to suffer minimal degradation of the uplink wireless range compared to the baseline value without an optical link, using optimum components in terms of cost and performance. The optimum technology depends on the relative merits of simplicity (DML) or optical network architecture flexibility (RSOA).

Radio-Over-Fiber Access Network Architecture Based on New Optimized RSOA Devices With Large Modulation Bandwidth and High Linearity

Next-generation wireless communications systems need to have high throughputs to satisfy user demand, to be low-cost, and to have an efficient management as principal features. Using a high-performance, low-cost reflective semiconductor optical amplifier (RSOA) as a colorless remote modulator at the antenna unit, the wavelength-division multiplexing (WDM) technique can be used for supporting distributed antenna systems (DASs). Each antenna unit is connected to the central unit using optical fiber and all links are used to transmit radio signals. Due to a large optical bandwidth, RSOAs are potential candidates for cost effective WDM systems. In this paper, simulations are carried out to determine optimized RSOA devices for wireless technology. New RSOA structures are fabricated and evaluated. The optimized RSOA is electrically driven by a standard Wi-Fi input signal (IEEE 802.11 g) with a 64-quadrature amplitude modulation (QAM) format. A large modulation bandwidth and a high electrooptic gain are demonstrated, which are confirmed by good performance when using orthogonal frequency-division multiplexing techniques. Characteristics such as high linearity and large electrooptic modulation bandwidth of our RSOA are sufficient to ensure an error vector magnitude (EVM) lower than 5% with a dynamic range exceeding 35 dB in a back-to-back configuration (at 0 dBm). Uplink transmission over a 20 km of single-mode fiber is also demonstrated with EVM lower than 5% and a dynamic range exceeding 25 dB (at 5 dBm).

Experimental Validation of a Reflective Semiconductor Optical Amplifier Model Used as a Modulator in Radio Over Fiber Systems

We improve and validate the multisection model for a bulk reflective semiconductor optical amplifier (RSOA) as a modulator in radio over fiber (RoF) systems. The RSOA model was developed using the symbolically defined devices (SDD) component under Agilent advanced design systems (ADS) software. An accurate parameter extraction method based on ADS optimization tools is presented. The intrinsic parameters of RSOA are obtained. Here the model is used to assess the static characteristics, harmonic and intermodulation distortions, and transmission performance of RSOA. Simulations have been validated with experimental results providing good agreement.

Chirp Reduction in Directly Modulated Multi-Electrode RSOA Devices in Passive Optical Networks

We demonstrate that the use of an optimized bi-electrode reflective semiconductor optical amplifier as remote modulator reduces the chirp. Our simulation shows that the chirp reduction is due to the carrier density profile in multi-electrode reflective semiconductor optical amplifiers. As a result of the chirp reduction, penalties for transmission are reduced from 6 to 4.5 dB on standard fiber at 2.5 Gb/s over 50 km. Using tri-electrode devices, a penalty of 3 dB is obtained for the same transmission conditions.

Digital predistortion for RSOAs as external modulators in radio over fiber systems

Reflective semiconductor optical amplifiers (RSOAs) can be used as external modulators in radio over fiber (RoF) links due to their amplification and modulation characteristics and colorless property. The nonlinear distortion of RSOA, however, limits its dynamic range. In this paper we demonstrate digital predistortion (DPD) linearization techniques to improve the linearity of RSOA external modulators. 64 quadrature amplitude modulation (QAM) signals are utilized to extract the model parameters. The dynamic AM/AM and AM/PM characteristics and power spectral densities of the modulated signals from the RSOA are demonstrated without and with DPD. Experimental results show clearly that the nonlinear distortion of RSOA external modulators in RoF links can be compensated using DPD linearization techniques.

Mitigation of chromatic dispersion effects on optical single sideband signals by Butterworth filtering

We present a study on the application of electrical dispersion compensation on optical single sideband signals using Butterworth filters, which are optimized for this purpose. Three schemes are studied: pre-equalization, post-equalization and dual-equalization.

Tunable Optical Dispersion Compensator Based on Power Splitting Between Two Dispersive Media

In this paper, we propose and experimentally demonstrate a novel tunable optical dispersion compensator (TODC). Dispersion compensation is achieved by splitting the input signal between two dispersive media and adding the resulting signals thereafter. Tunable compensation is attained by controlling the power splitting ratio of the input signal between both dispersive media. The frequency response of the TODC is theoretically assessed considering signal addition in the optical and electrical domains. The latter case is enabled by using optical single sideband (OSSB) modulation, which allows preserving the phase information of dispersive media output signals after direct detection. This is the only case experimentally tested, since it avoids stability problems related with coherent addition of optical signals. A TODC with a tuning range of -340 to 0 ps/nm was designed and experimentally assessed for a 40 Gb/s nonreturn-to-zero OSSB signal. The tunable power splitter consisted of an automatic polarization controller and a polarization beam splitter, which offered a tuning time lower than 150 ¿s. A bit error rate lower than 10-8 was measured on the entire compensation range with a maximum power penalty of 3.3 dB relatively to an SSB signal in back-to-back.

High gain GaAs 10Gbps transimpedance amplifier with integrated bondwire effects

This paper outlines the design and performance of a GaAs MESFET MMIC front-end receiver circuit. Its main characteristics are a 17GHz bandwidth, 62dB/spl Omega/ gain and 10.3pA//spl radic/Hz input referred noise. Input sensitivity is -21dBm with a good linear response which extends to -3dBm. Tolerance to high input capacitance assures 10Gbps operation with input capacitance exceeding 260fF. Total power dissipated by the circuit is 280mW. The design approach focused on the effect of bond-wire inductance and its impact on manufacturing reliability. Special attention was given to noise analysis and optimisation, stability requirements, output impedance matching and layout. On-wafer characterization of this circuit shows good yield with high similarity among the results of different chips. Measured results for a bonded chip in a metal case agree well with simulation results, confirming the validity of the simulation models, the quality of the UMS PH15 process technology and of the proposed design.

Electronic post-detection filter for multigigabit optical communication systems

We will present the design and characterisation of a transversal microwave filter as a signal processor for 40 Gbits/s optical receivers. The filter was implemented using monolithic microwave integrated circuit (MMIC) technology. The main features are the electrical response tuning facility and signal gain. The work reports, for the first time the response in time domain of the packaged filter and also the adaptive control structure.

Postdetection Adjustable Simultaneous Compensation of DGD and GVD in a 40-Gb/s Optical Single-Sideband System

Results on postdetection compensation of group velocity dispersion (GVD) and differential group delay (DGD) in a 40-Gb/s optical single-sideband system are presented. An electrically adjustable transversal filter structure and a microstrip line are used as electrical compensators. Our results show that 408 ps/nm of GVD or 18 ps of DGD, considered separately, are compensated with less than 1.3-dB optical signal-to-noise ratio (OSNR) penalty to back-to-back without compensator, for an extinction ratio (ER) of 6 dB. The simultaneous effect of 12.3 ps of DGD and 374 ps/nm of GVD is compensated with less than 2-dB OSNR penalty, also for ER of 6 dB. Simulations performed support the experimental results.