Jun-Hyuk Seo

SOA-EAM frequency up/down-converters for 60-GHz bi-directional radio-on-fiber systems

We investigate a frequency up/down-converter based on a single cascaded semiconductor optical amplifier (SOA)-electroabsorption modulator (EAM) configuration for bi-directional 60-GHz-band radio-on-fiber (RoF) system applications. SOA cross-gain modulation and photodetection in EAM are used for frequency up-conversion, and EAM nonlinearity is used for frequency down-conversion. In our scheme, both 60-GHz local-oscillator (LO) signals and IF signals are optically transmitted from a central station to base stations. We characterize the dependence of frequency up/down-conversion efficiencies on EAM bias and optical LO power. For frequency up-conversion, maximum conversion gain of approximately 8 dB was obtained and, for frequency down-conversion, more than approximately 18-dB conversion loss was measured. Utilizing this frequency up/down converter, we demonstrate a 60-GHz bi-directional RoF link. Optically transmitted downlink 10-Mb/s quadrature phase-shift keying (QPSK) data at 100-MHz IF are frequency up-converted to the 60-GHz band at the base station, and uplink 10-Mb/s QPSK data in the 60-GHz band are frequency down-converted to 150-MHz IF and transmitted to the central station. In addition, the dependence of error vector magnitudes on IF signal power and wavelength is investigated.

60-GHz bidirectional radio-on-fiber links based on InP-InGaAs HPT optoelectronic mixers

We demonstrate 60-GHz band bidirectional radio-on-fiber (RoF) links based on InP-InGaAs heterojunction phototransistor (HPT) optoelectronic mixers. They employ remote up/down conversion scheme with optical local oscillator signals distributed from the central office and intermediate frequency (IF) fiber transmission for both up- and down-links. Since frequency up/down conversions and photodetection are carried out by a single HPT optoelectronic mixer, base station architecture is greatly simplified. In order to validate its feasibility, both up- and down-link RoF transmissions of 16 quadrature amplitude modulator data are successfully demonstrated at 60-GHz band using 1.25-GHz IF for down-link and 2.0-GHz IF for up-link.

Photonic frequency-upconversion efficiencies in semiconductor optical amplifiers

We investigated the characteristics of the photonic frequency-upconversion process in semiconductor optical amplifiers. We derived a simple analytical expression for the upconversion efficiency, and investigated its dependence on various parameters. We experimentally confirmed our results.

Remote optoelectronic frequency down-conversion using 60-GHz optical heterodyne signals and an electroabsorption Modulator

A new optoelectronic frequency down-conversion method for radio-on-fiber (RoF) uplink transmission is demonstrated by using an electroabsorption modulator, which down-converts uplink millimeter-wave signals into optical intermediate frequency (IF) using remotely fed optical local oscillator signals. Using this optoelectronic frequency down-converter, an RoF uplink is demonstrated in which quadrature-phase-shift keying uplink data signals in 60-GHz band are frequency down-converted to the 500-MHz optical IF signals and transmitted to the central station.

1.244-gb/s data distribution in 60-GHz remote optical frequency up-conversion systems

We experimentally demonstrate 63-GHz 1.244-Gb/s radio-on-fiber downlink data distribution using the remote optical frequency up-conversion technique. Sixty-three-gigahertz optical heterodyne local oscillator signals are cross-gain modulated by optical baseband signals inside a semiconductor optical amplifier. After photodetection, frequency up-converted signals at 63 GHz are generated. The bit-error-rate performance is investigated as a function of optical baseband signal power in a wide wavelength range

Spurious-free dynamic range characteristics of the photonic up-converter based on a semiconductor optical amplifier

We investigate nonlinear intermodulation distortion characteristics of the photonic up-converter based on a semiconductor optical amplifier for multifrequency signal up-conversion. The third-order intermodulation distortions are measured with two-tone intermediate frequency signals for the photonic up-converter under various conditions. The spurious-free dynamic range is determined to be larger than 72 dB/spl middot/Hz/sup 2/3/.

Nonlinear distortion suppression in directly modulated DFB lasers by sidemode optical injection

We demonstrate a new method of suppressing nonlinear distortions in directly modulated DFB lasers. In our scheme, external laser light is injected into the sidemode of the DFB laser. Using this scheme, we achieved significant reduction in nonlinear distortions such as the second harmonic distortion (SHD), second order intermodulation distortion (IMD2), and third order intermodulation distortion (IMD3). In addition, we enhanced the external light detuning range.

Nonlinear characteristics of an SOA photonic frequency up-converter

We investigate nonlinear distortion characteristics of the photonic up-converter using a semiconductor optical amplifier for multi-frequency signal up-conversion. The third order intermodulation distortions are measured and spurious free dynamic ranges are determined under various conditions.

Nonlinear distortion suppression in directly modulated distributed feedback lasers by sidemode optical injection locking

We demonstrate a new nonlinearity reduction method in directly modulated distributed feedback (DFB) semiconductor lasers. By injecting external light into a DFB laser sidemode, the nonlinear distortion of the laser is significantly reduced. Compared to the previously reported main-mode optical injection locking scheme, greater distortion suppression and a wider stable locking range can be achieved.

60 GHz radio-on-fiber downlink systems using optically injection-locked self-oscillating optoelectronic mixers based on InP/InGaAs HPTs

A 30 GHz hybrid-type optically injection-locked self-oscillating optoelectronic mixer is implemented with a high-performance InP/InGaAs heterojunction photo-transistor. Using this mixer as a harmonic up-converter, 60 GHz radio-on-fiber downlink transmission of 20 Mbps 16QAM data is successfully demonstrated. The link performance is uniform over a wide range of optical LO powers.