Young-Kwang Seo

All-optical signal up-conversion for radio-on-fiber applications using cross-gain modulation in semiconductor optical amplifiers

The authors present a novel scheme of up-converting optical intermediate frequency (IF) signals with an optical local oscillator (LO) signal using cross-gain modulation in a semiconductor optical amplifier. This scheme provides high conversion efficiency and is independent of the incident light wavelength and polarization. It can be useful for radio-on-fiber transmission system applications in which one remote LO signal is provided for several wavelength-division-multiplexing IF signals.

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.

Dispersion-tolerant transmission of 155-Mb/s data at 17 GHz using a 2.5-Gb/s-grade DFB laser with wavelength-selective gain from an FP laser diode

We present a novel scheme of overcoming laser diode (LD) intensity modulation bandwidth limitation by effectively improving modulation depth and simultaneously generating optical single sideband for radio-on-fiber applications. Our scheme uses wavelength-selective amplification characteristic of an LD under modulated light injection. The 17-GHz optical single sideband signals are generated with a 2.5-Gb/s-grade distributed feedback laser with wavelength-selective gain from a Fabry-Perot LD. The 155-Mb/s data transmission at 17 GHz is successfully achieved.

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/.

A 622-Mb/s Mixed-Mode BPSK Demodulator Using a Half-Rate Bang-Bang Phase Detector

A new mixed-mode binary phase shift keying (BPSK) demodulator is demonstrated using a half-rate bang-bang phase detector commonly used in clock and data recovery (CDR) applications. This demodulator can be used for new home networking applications using already installed CATV lines. A prototype chip realized by 0.18-mum CMOS process can demodulate 622-Mb/s data at 1.4-GHz carrier frequency. At this data rate, the demodulator core consumes 27.5 mW from a 1.8 V power supply while the core chip area is 210 times 150 mum2. The transmission over 20-m CATV line using the prototype chip is successfully demonstrated.

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.

Optical single sideband modulation using an injection-locked semiconductor laser as an optical filter

We propose a new technique of generating optical single sideband (SSB) signals using an injection-locked semiconductor laser (SL). The injection-locked SL acts as an optical filter which filters out the undesired mode from the double sideband signals. 30 GHz optical SSB signals with our scheme are successfully generated.