Choong Keun Oh

A photonic up-converter for a WDM radio-over-fiber system using cross-absorption modulation in an EAM

A photonic frequency up-converter with a wide wavelength bandwidth is demonstrated. The up-converter is based on wavelength conversion by cross-absorption modulation in an electroabsorption modulator. A two-tone measurement is performed to investigate the linearity of the proposed up-converter. Moreover, its dependence on the wavelength and bias voltage are found to be suitable for wavelength-division-multiplexing-based radio-over-fiber application. The proposed up-converter has a spurious free dynamic range larger than 73.8 dB/spl middot/Hz /sup 2/3/ throughout the 30-nm range of the local oscillator wavelength. Also, the up-converted signal at 26 GHz has a phase noise of -76.8 dBc/Hz at a 10-kHz offset.

Tunable Photonic Microwave Notch Filter With Negative Coefficient Based on Polarization Modulation

A novel tunable photonic microwave notch filter with negative and positive coefficients is proposed and experimentally demonstrated. The coefficients can be achieved by polarization modulation along with an electrical signal. The two polarization-modulated signals, which have a relative time delay, are combined, and detected by a photodetector. The transfer response of the filter shows a very stable operation irrespective of the coherence length of the source used. Moreover, the free spectral range of the filter, which shows a sharp notch, can be changed by using a tunable differential group delay generator over the range of 3.16-4.31 GHz

Photonic microwave notch filter using cross polarization modulation in highly nonlinear fiber and polarization-dependent optical delay in high birefringence fiber

A novel photonic microwave notch filter with both negative and positive coefficients is proposed and demonstrated using a single optical source. These coefficients are generated in a highly nonlinear fiber by cross polarization modulation effect and guided through a high birefringence fiber, and finally detected. Due to the orthogonal polarity between the two coefficients, the proposed filter has a stable transfer response and no resonance peaks at baseband. The experimental results showed a stable notch filter characteristic with the free spectral range of 3.97 GHz over the range of 15 GHz.

All-optical transversal filter with tap doubling and negative coefficients based on polarization modulation.

A novel all-optical transversal filter with negative coefficients and tap doubling is proposed and experimentally demonstrated. Based on polarization modulation using the anisotropy of the electro-optic coefficient of LiNbO(3) crystals, negative and positive coefficients are simultaneously generated. Tap doubling is also achieved by using wavelength- and polarization-dependent time delays in fiber. Due to the orthogonal polarity between the two coefficients of each wavelength, the proposed filter is free from coherent interference and the synthesis of filter taps is performed in the optical domain. The experimental results demonstrated that stable 6-tap bandpass filter characteristics can be obtained by using only three optical sources.

Multiple RF-carrier Generation Using the Wavelength-dependent Stokes Shift and Selective Amplification of Stimulated Brillouin Scattering

We present an optical method that can simultaneously generate multiple RF-carriers. The generated RF-carriers meet the requirements of channel separation in fixed wireless services. The proposed method utilizes the wavelength-dependent Stokes shift and selective amplification of stimulated Brillouin scattering in an optical fiber. Four RF-carriers at 10.851, 10.831, 10.811, and 10.791 GHz, which have the narrow linewidth and the 20-MHz separation, are generated using four optical sources spaced 2.78 nm apart.

Optical frequency tripling method by use of selective amplification of stimulated Brillouin scattering and Brillouin re-injection

A simple optical method of frequency tripling is proposed and experimentally demonstrated. The proposed method is based on Brillouin selective amplification characteristic of stimulated Brillouin scattering and Brillouin re-injection using a single optical source in an optical fiber. The first sideband optically generated by a r-f signal is selectively amplified by stimulated Brillouin scattering and reused for the generation of the second Stokes wave to selectively amplify the second side band. In a same manner, the third sideband is selectively amplified and other sidebands are suppressed. Finally, copropagating sideband and optical carrier generate a frequency-tripled signal. The experimental results show that the r-f signal of 32.493 GHz can be obtained from the modulation frequency of 10.831 GHz with an 8 GHz optical modulator. Also, the linewidth is the same as that of the modulation signal. The frequency-tripled signal was amplified by 20 dB and the fundamental r-f signal was suppressed by 25 dB.

A tunable photonic microwave notch filter using a self-injection locked reflective semiconductor optical amplifier

We propose a tunable photonic microwave notch filter using a self-injection locked reflective semiconductor optical amplifier (RSOA) and fiber Bragg gratings. Tunable filter characteristic is obtained by changing the center wavelength of one of the gratings. The achievable tuning range is determined by the gain profile of the RSOA and the tuning range of the grating.

UWB monocycle pulse generation based on transfer curve of Two Mach-Zehnder modulators

A novel ultra -wideband monocycle pulse generation method based on transfer curve of two Mach-Zehnder modulators (MZMs) is proposed. By changing the bias voltage of MZMs, positive and negative polarity monocycle pulse s are generated.

Coherence Free All Optical Microwave Notch Filter with Negative Coefficient Based on Polarization Modulation in an Electro-optic Phase Modulator

We propose a coherence-free all-optical microwave notch filter with negative and positive coefficients from single optical source based on polarization modulation. The experimental result shows the stable notch filter characteristics with FSR of 3.97 GHz.

A novel photonic microwave notch filter with negative coefficient based on cross polarization modulation in a highly nonlinear fiber

A novel photonic microwave notch filter with both negative and positive coefficients is proposed and demonstrated using a single optical source as a probe beam. Due to the change in birefringence induced by another modulated pump beam, both non-inverted and inverted signals are generated in a highly nonlinear fiber. These are separated by using a polarization beam splitter and recombined with optical time delay given to one of them. From the generation of both coefficients and the orthogonal property between them, no resonance peaks were observed at baseband and the optical coherence could be avoided independently of the source coherence length. The experimental results show a stable transfer response with the free spectral range of 65 MHz and 1.32 GHz when the optical path difference is given to 3.19 m and 0.19 m, respectively.