J.L. Corral

Continuously variable true time-delay optical feeder for phased-array antenna employing chirped fiber grating

In this paper, we present and demonstrate a novel approach of a true time-delay (TTD) optical feeder for phased-array antennas (PAAs). A continuously variable TTD is achieved by employing tunable lasers and a wide-bandwidth chirped fiber Bragg grating (FBG) as the dispersive element. The results show that a very high resolution performance (equivalent to a 6-b microwave phase shifter) is obtained for an L-band PAA employing narrow-tuning bandwidth lasers with a wavelength stability of 0.005 nm and a 4-nm bandwidth chirped grating with a dispersion of 835 ps/nm.

General expressions for IM/DD dispersive analog optical links with external modulation or optical up-conversion in a Mach-Zehnder electrooptical modulator

A general derivation of the optical modulation process in a dual-drive Mach-Zehnder modulator (DD-MZM) is introduced. The expressions include all harmonics and are entirely general in terms of bias point. Chromatic dispersion is also included allowing the prediction of a number of important phenomena in photonic signal transmission. Examples of special cases of these general equations are then presented. Similar expressions are introduced for harmonic optical up-conversion through a photonic mixer based on a DD-MZM covering any bias point or phase shift between DD-MZM drives.

True time-delay scheme for feeding optically controlled phased-array antennas using chirped-fiber gratings

A novel approach of true-time delay (TTD) optical feeder for phased-array antennas is proposed and demonstrated. A compact size continuously variable TTD is achieved by employing tunable lasers and one wide bandwidth chirped-fiber grating as dispersive element. A high-resolution performance (5.3 ps) is obtained for a 26-GHz phased-array antenna employing narrow tuning bandwidth lasers with a wavelength stability of 0.005 nm and a 4 nm bandwidth chirped grating.

Optically beamformed beam-switched adaptive antennas for fixed and mobile broad-band wireless access networks

In this paper, a 3-bit optical beamforming architecture based in 2/spl times/2 optical switches and dispersive media is proposed and demonstrated. The performance of this photonic beamformer is experimentally demonstrated at 42.7 GHz in both transmission and reception modes. The progress achieved for realizing these architectures with integrated optics is also reported. Due to its advanced features (i.e., potential fast-switching, huge bandwidth, and immunity to electromagnetic interference), the architecture is a very promising alternative to traditional beamforming technologies for implementing beamformed base-station antennas in fixed and mobile broad-band wireless access networks operating in the millimeter-wave band. The study presented here has been carried out in the frame of the IST 2000-25390 OBANET project.

Novel tunable photonic microwave filter based on laser arrays and N/spl times/N AWG-based delay lines

In this letter, a novel tunable and flexible photonic microwave filter architecture based on the use of laser arrays and the periodicity of N/spl times/N arrayed-waveguide-gratings optical response is proposed. Filter coarse and fine-tuning capabilities are experimentally demonstrated showing an excellent agreement with theory.

Diversity techniques for OFDM based WLAN systems

This paper presents different spatial diversity techniques that can be employed in an OFDM based WLAN system to improve the system performance. We present some results obtained by simulation when a HIPERLAN/2 transceiver is employed.

Generalized study of dispersion-induced power penalty mitigation techniques in millimeter-wave fiber-optic links

The authors present a comprehensive analysis of the chromatic dispersion effects in harmonic upconverted millimeter-wave (mm-wave) fiber-optic links. The optical upconversion is performed through a photonic mixer based on a Mach-Zehnder electrooptical modulator. It is shown that by biasing the electrooptical modulator either at the maximum or at the minimum transmission bias points, the dispersion-induced power penalty effect on the upconverted signal may be sharply mitigated, which results in increasing the frequency-length product of the fiber-optic link. Experimental results are provided for the three different types of bias.

Generation of Multi-Gigabit-per-Second MQAM/MPSK-Modulated Millimeter-Wave Carriers Employing Photonic Vector Modulator Techniques

In this paper, two photonic vector modulator (PVM) architectures are presented, and their use in generating multi-gigabit-per-second M-ary quadrature amplitude modulation/M-ary phase shift keying modulated RF carriers in the millimeter-wave frequency regime is experimentally demonstrated. First, a highly scalable photonic quadrature amplitude modulation (QAM) architecture based on vector summation and dispersive delay lines, which directly generate multilevel signals from parallel in-phase and quadrature components, is proposed and experimentally demonstrated by generating up to 3-Gb/s quadrature phase shift keying (QPSK), four-level amplitude shift keying, and eight-level QAM at 39-GHz-modulated carriers. The possibility of also detecting the baseband components is shown, which allows the simultaneous feeding of baseband/RF signals over the same infrastructure. This architecture is limited to a certain length of fiber, as the quadrature condition is obtained for a certain aggregated dispersion. To overcome this limitation, a second PVM architecture is proposed, which is based on the use of two Mach-Zehnder modulators in parallel and an optical delay line to obtain the quadrature condition. The generation of a 2-Gb/s QPSK signal is experimentally demonstrated, including a 1-km standard single-mode-fiber transmission.

All-optical WDM microwave filter with negative coefficients

A novel all-optical incoherent microwave filter with negative coefficients based on multiple optical carriers and a dispersive medium is presented. Negative coefficients are obtained by means of the /spl pi/ phase inversion in a single electrooptic Mach-Zehnder modulator and the modulator V/sub /spl pi// dependence with wavelength. In this way, negative coefficients can be implemented using a single modulator. Finally, experimental results for a notch filter showing the feasibility of the technique are provided.

Harmonic suppressed photonic microwave filter

This paper proposes a photonic microwave filter based on wavelength-division multiplexing (WDM) of multiple optical carriers and dispersive media. Harmonic suppression is obtained using nonuniform tap spacing to extend the filter free spectral range by a Vernier effect. The experimental results presented are in excellent agreement with theory.