Young-Shik Kang

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.

Development and RF characteristics of analog 60-GHz electroabsorption modulator module for RF/optic conversion

We developed an analog 60-GHz module for RF/optic conversion by using an electroabsorption modulator (EAM) device associated with a traveling-wave electrode. The impedance matching of the module was accomplished with the 30-/spl Omega/ termination such that the resonance was precisely located at 60 GHz and the fractional bandwidth at S/sub 11/=-15 dB was as large as 1.0 GHz. The RF/optic conversion gain of the EAM device revealed a strong dependence on the input optical power and was closely related with the slope change in the optical transmission characteristic with reverse bias. From the EAM module with the composite-type multiple-quantum-well electroabsorption core consisting of both 8- and 12-nm quantum wells, we obtained the optimal RF/optic conversion gain at the reverse bias between 1.5-2 V in a wide range of input optical power from -6 to +9 dBm. In the same bias range, the third-order intermodulation distortion was <-49.5 dBc as obtained with RF input of -7.5 dBm.

Analysis and characterization of traveling-wave electrode in electroabsorption modulator for radio-on-fiber application

Comparing with a lumped electroabsorption modulator (EAM), we show the merits of a long EAM with traveling-wave electrode with high radio-frequency (RF) gain that could be used in high-frequency analog application. By terminating the RF output port with the characteristic impedance of 30 /spl Omega/, the device exhibited a large enhancement of 6 dB above 10 GHz in the electrical-to-optical response and a wide fractional bandwidth as estimated from simulation. In addition, an input impedance matching circuit of stub embedded on the device chip was found to be very effective for improving RF characteristics in the narrow band of frequency.

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.

System-on-packaging with electro-absorption modulator for 60 GHz band radio-over-fiber link

We developed a system-on-packaging (SoP) with an electro-absorption modulator (EAM) for a 60 GHz band radio-over-fiber (RoF) link. It consists of an EAM device, a microstrip filter, and a low noise amplifier (LNA). The microstrip filter was used to achieve the impedance matching between the EAM device and the LNA and to reject the local oscillator (LO) frequency of the heterodyne system. The frequency response and the effect of the EAM bias voltage of a simple RF/optical link were measured. A 60 GHz band RoF link with 2.4 GHz intermediate frequency (IF) was prepared to measure the transmission characteristics of 16 QAM data

Optical coupling analysis of dual-waveguide structure for monolithic integration of photonic devices

We proposed the dual-waveguide structure (DWS) with spot size converters and demonstrated the monolithic integration of both photodetector (PD) and electroabsorption modulator (EAM) based on the DWS. The coupling loss between the device facet and a lensed fiber was as small as 2.13 dB. The responsivity of PD and the extinction ratio of EAM were 0.58 A/W and 20 dB at -4 V/sub dc/, respectively. From the optical coupling analysis, it was proved that the dual-waveguide scheme provided one of the best solutions for the monolithic integration of optoelectronic devices.

Development of Packaging Technologies for High-Speed (

We developed high-speed optoelectronics packaging technologies for a waveguide photodiode and a traveling wave electro-absorption modulator device for 40-Gb/s digital communication systems. The effects of the device and the packaging designs on the broadband performance were investigated to optimize broadband characteristics. For the receiver, inductive peaking was used for bandwidth control and an internal bias tee was implemented; in addition, two types of preamplifier devices were used to develop high-gain receiver and wide-bandwidth receiver. In the optical-to-electrical response, a 3-dB bandwidth of the high-gain module was about 32 GHz as compared to 42 GHz for the wide-bandwidth module. The clear 40-Gb/s nonreturn-to-zero (NRZ) eye diagrams showed a good system applicability of these modules. In addition, an optimized modulator module showed a 3-dB bandwidth of 38 GHz in the electrical-to-optical response, an electrical return loss of less than 10 dB at up to 26 GHz, an rms jitter of 1.832 ps, and an extinction ratio of 5.38 dB in a 40-Gb/s NRZ eye diagram

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TWEAM modulator modules optimized in 40 GHz and 60 GHz band, respectively, were developed. The bandwidth at the operating frequency can be controlled with the termination resistance. Impedance matching of the modules was achieved using the double stub design and the laser trimming process. The measured Electrical-to-optical (E/O) response showed the increase in the response near 40 GHz and 60 GHz, respectively. The third-order inter-modulation distortion (IMD3) was below -65 dBc at -7 dBm RF input and spurious free dynamic range (SDRF) was about 108 dB Hz/sup 2/3/.

Gb/s) Optical Modules

We experimentally demonstrate frequency up/down-conversion with cascaded SOA-EAM configuration. For frequency up-conversion, SOA cross-gain modulation and photo-detection characteristics of EAM are used and for frequency down-conversion, EAM nonlinearities are used.

Fabrication and characteristics of traveling-wave electro-absorption modulator (TWEAM) modules for millimeter-wave radio-over-fiber link

We developed a narrow band electroabsorption modulator (EAM) module for RF/optic conversion at 60-GHz band. Using this EAM module, we demonstrated radio-over-fiber link in which quadrature-amplitude-modulation data were transmitted.