Eszter Udvary

Optical Wireless Communications: An Emerging Technology

Optical wireless communication (OWC) enables wireless connectivity using infrared, visible or ultraviolet bands. With its powerful features such as high bandwidth, low cost and operation in an unregulated spectrum, OWC can be, in some applications, a powerful alternative to and, in others, complementary to the existing wireless technologies. It is one of the most promising current areas of research with significant potentials for high-impact results which will considerably change the wireless market mostly dominated by the radio-frequency (RF) technologies. In this paper, we provide an overview of OWC highlighting the advantages and wide range of application areas of this emerging technology.

Transmission Characteristics of All Semiconductor Fiber Optic Links Carrying Microwave Channels

An experimental and theoretical study is presented for the transmission characteristics of all semiconductor fiber optic links carrying microwave channels. The nonlinear distortion and signal to noise ratio are investigated and evaluated in case of multi-carrier transmission. Extremely high spurious free dynamic range is presented achieved by a direct modulated semiconductor laser.

Optical subcarrier label swapping by semiconductor optical amplifiers

The semiconductor optical amplifier (SOA) can be used as an efficient high-speed modulator. The paper presents optical subcarrier multiplexed label swapping/reinsertion utilizing this device associated to the wavelength converter block in packet switched all optical networks. For that purpose the modulation response and nonlinear behavior of SOAs are analyzed and experimentally demonstrated.

Improvements in the Linearity of Semiconductor Optical Amplifiers as External Modulators

Semiconductor optical amplifiers (SOAs) can be advantageously utilized as external modulators because they can simultaneously perform two functions: amplification and modulation. When the SOA is used in a subcarrier multiplexed system, the modulation linearity is a crucial property. In this paper, theoretical and experimental investigations are presented with the result of improved modulation linearity. By proper adjustment of the operation point and by careful optical matching, a significant improvement in the modulation linearity and also in the spurious-free dynamic range is achieved, along with high modulation sensitivity and wide bandwidth.

Semiconductor Optical Amplifier for Detection Function in Radio Over Fiber Systems

This paper demonstrates that in broadband networks in-line semiconductor optical amplifiers (SOAs) beside providing system gain can also be used as simultaneous transceivers. The SOA branching stages are studied and presented for bus configuration. Using a steady-state model, we have made a small-signal approximation applying an equivalent circuit for detection based on the rate equations. The theory enables us to explain the detection functionality, the optimal working state of the multifunctional SOA, and to analyze noise properties. The measurements support the calculations. So the SOA-transceivers are potentially useful in subcarrier multiplexed access systems.

Harmonic distortion in dispersive fiber-optical transmission of microwave signals

Dispersion penalty has been investigated widely in 1550 nm fiber-optical links transmitting microwave (/spl mu/W) signals. However, less attention was addressed to the levels of harmonics. This paper presents theoretical and experimental results on estimation of harmonics in the transmission.

A new optical distribution approach for millimeter wave radio

In the proposed picocellular radio system a microwave reference and subcarrier multiplexed radio signals are distributed optically. The millimeter-wave carrier is generated by phase locking technique. This approach is not affected by dispersion and utilizes inexpensive devices.

Soliton propagation of microwave modulated signal through single-mode optical fiber

Sinusoidally modulated optical signal transmission is experimentally investigated over a 30 km standard single-mode fiber using a range of optical input powers. Experiments and computer simulations showed that fiber-induced self-phase modulation generates a chirp on the signal with an effect opposite to that induced by chromatic dispersion. Calculations were performed to investigate the distortions caused by simultaneous dispersion and non-linearity using a range of fiber parameters. Soliton propagation of the microwave/millimeter wave modulated signal is reported at elevated intensities in lossless and loss compensated cases.

Fiber-dispersion compensation techniques in optical/wireless systems

Carrier frequencies of point-to-multipoint systems are pushed into the higher microwave (MW) or millimeter-wave (mmW) range due to the increasing demand for broadband services and growing number of new subscribers as well as due to lack of sufficiently wide unused radio channels in traditional communication frequency bands. High free space loss of MM wave frequencies reduces the lengths of the wireless links in the radio access part of these systems. Therefore the need for involving fiber-optical techniques in point-to-multipoint systems becomes evident. Optical transmission and distribution of signals up to the last mile offer several advantages. In such combined optical/wireless systems the base stations are connected to the central station through optical fibers. Subscribers are accessed by only few hundred meters long wireless links in the picocells employing MM wave carriers.

Vertical cavity surface emitting lasers in radio over fiber applications

Theoretical and experimental study of using direct modulated vertical cavity surface emitting lasers in radio over fiber applications is presented. The nonlinear distortion and signal to noise ratio are investigated and evaluated in the case of short-range multi-carrier transmission. Nonlinear characterization and comparison of different kinds of semiconductor lasers are also presented.