geneous impedance cylinder using the MoM technique. The results are in good agreement, as depicted in Figures 2 and 3. It is also observed that the results converge when the number of coefficients N is increased (see Figs. 4 and 5). The exterior medium is assumed as free space for all examples. In all cases, the operation frequency is f = 33 MHz, the radius of the cylinder is a = 0.6, and the angle of incidence is  0 = 0. 4. CONCLUSION In this study, scattering from a general high-order inhomogeneous- impedance cylinder is investigated by series expansion of the surface impedance for an incident TM wave. A similar procedure can also be applied for the TE incidence case. It is observed that when N increases, the results converge more rapidly. The proposed method and the MoM technique are also applied for a 1 st -order inhomogeneous impedance cylinder. The obtained results are com- pared by those obtained using the numeric MoM technique and good agreement is observed. The proposed method also signifi- cantly reduces the computer calculation time according the MoM. For instance, using the same computer, the calculation times of Figure 2 by proposed method with N = 30 coefficients and discretization number N = 400 points (MoM) are 3.859 and 38.65 s, respectively. REFERENCES 1. M.A. Leontovich, Investigations of radio wave propagation Part 2, Academy of Sciences, USSR, 1948. 2. J.R. Wait, The scope of impedance boundary conditions in radio propagation, IEEE Trans Geosci Remote Sensing GRS-28 (1990), 721–723. 3. T.B.A. Senior and J.L. Volakis, Approximate boundary conditions in electromagnetics, IEE, London, 1995. 4. D.J. Hoppe and Y. Rahmat-Samii, Impedance boundary conditions in electromagnetics, Taylor and Francis, 1995. 5. T.B.A. Senior, J.L. Volakis, and S.R. Legualt, Higher-order impedance and absorbing boundary conditions, IEEE Trans Antennas Propagat 45 (1997), 107–114. 6. O. Marceaux and B. 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Paker, Electromagnetic scattering from arbitrary shaped inhomogeneous impedance cylinder using MoM, IEEE Trans Antennas Propagat (submitted). © 2006 Wiley Periodicals, Inc. ANALOG CHARACTERISTICS OF ELECTROABSORPTION MODULATOR FOR RF/OPTIC CONVERSION; RF GAIN AND IMD3 Yong-Duck Chung, Young-Shik Kang, Kwang-Seong Choi, Sung-Bock Kim, and Jeha Kim Basic Research Laboratory Electronics and Telecommunications Research Institute 161 Gajeong-dong, Yuseong-gu Daejeon, 305-700, Korea Received 22 November 2005 ABSTRACT: We design and fabricate a traveling-wave electroabsorp- tion modulator for RF/optic conversion. The RF gain is measured with a simple RF/optic link. It is related to the optical transfer curve. The input optical power causes the change of the transfer curve so that the RF gain varies accordingly. The RF/optic conversion gain shows a close relationship with the slope efficiency of transfer curve. Linearity is also one of the important characteristics for analog applications. We evalu- ate the linearity of the module from the 3 rd -order intermodulation distortion (IMD3). © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1151–1155, 2006; Published online in Wiley Inter- Science (www.interscience.wiley.com). DOI 10.1002/mop.21564 Key words: traveling-wave electroabsorption modulator; transfer curve; E/O response; IMD3; analog application 1. INTRODUCTION Until now, the radio-over-fiber (RoF) link has received much attention as a first-mile solution of the broadband wireless access network connected to the backbone trunk-line network [1–3]. Its technology is considered to fulfill the needs of broadband wireless data transport. It takes advantage of the excellent characteristics of single-mode optical fiber such as low optical loss of 0.5 dB/km, ultra-wide data bandwidth of 1 Tb/ps, no electromagnetic inter- ference, and so on. For the transport of analog RF data through fiber, it is necessary to modulate the optical intensity from either a laser diode at the RF frequency with digital data (subcarrier modulation, SCM). At the other end of the link, a receiver detects and directly converts the optical signal into RF data. An electroabsorption modulator (EAM) is well known to be a key component (among others) in an RF photonic link because of its various benefits, such as small size, low driving voltage, and large bandwidth, and its potential for monolithic integration with other devices (such as a photodetector, in particular) for a compact, cost-effective photonic remote antenna unit [4]. It can also be used as a full duplexer for both data transmission and detection [5]. As an electrical-to-optical (E/O) converter, the external modulator has various advantages for a photonic link because large nonlinear distortion can be avoided due to the frequency chirping that is common in a direct-modulation laser diode. In analog fiber radio applications, however, the optical-modulator module needs to be prepared and characterized differently from its application in dig- ital fiber-optic communication. Besides the static optical characteristics, it should be also evaluated in terms of the RF link efficiency, the RF bandwidth, and the 3 rd -order intermodulation distortion (IMD3). Thus, for analog RoF applications, the EAM device is required to have the excellent RF efficiency such as RF link gain, RF bandwidth, noise figure (NF), and RF spurious-free dynamic range (SFDR) that is closely related with the slope efficiency and the linearity of the transfer curve. In particular, the slope efficiency is critical for RF gain. The RF/optic conversion gain is of particular importance for obtaining DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 6, June 2006 1151