3.2. Wavefront with Obscuration or Irregular Edge Retrieved from Seed-Algorithm The algorithm given in subsection 2.2. is applied to retrieve the measured wavefront from several phase-shifting fringe patterns using our software package written in visual C++ language [4]. Figure 5 shows the wavefront with obscuration. Figure 6 shows the wavefront with irregular edge induced by a mechanical tool for fixing the tested optical elements. 3.3. Interferogram and Angle Error of a CCR A CCR can be tested using a portable phase-shifted interferometer. Its exit wavefront and angle error can be calculated via computer using the mathematical model described in subsection 2.3. Figure 7 shows the CCR results. 4. CONCLUSION The portable phase-shifted interferometer with small size and light weight can be taken from one place to another easily. There are four important parts in this interferometer: (i) the integrated PZT’s driver in a thin circuit board; (ii) a seed-algorithm for retrieving the wavefront with obscurations or irregular edges; (iii) software for the exit wavefront and angle error of a CCR; (iv) several reference transmission spheres for testing a large spherical surface. Figures 3 and 4 show that the phase-shifting driver can work effectively. Figures 5 and 6 show that the seed-algorithm is able to retrieve the wavefront with obscurations or irregular edges successfully. Ac- cording to Figure 7, the CCR can be tested in this interferometer. REFERENCES 1. J.B. Chen, et al., Large-aperture high-accuracy phase-shifting digital flat interferometer, Opt Eng 35 (1996), 1936 –1942. 2. D. Malacara, Optical shop testing, 2 nd ed., Wiley, New York, 1992. 3. Z.S. Gao, et al., Computer-aided alignment for a reference transmission sphere of an interferometer, Opt Eng 43 (2004), 69 –74. 4. D.J. Kruglinski, Programming Microsoft visual C++,5 th ed., Mi- crosoft Press, Seattle, WA, 2004. © 2004 Wiley Periodicals, Inc. 40 Gb/s SHORT-REACH TRANSMISSION IN NORMAL DISPERSION REGIME USING AN ERBIUM-DOPED WAVEGUIDE AMPLIFIER Mo ˆ nica L. Rocha, Mario T. Furtado, Mariza R. Horiuchi, Ju ´ lio C. R. F. Oliveira, Joa ˜ o B. Rosolem, Fa ´ bio Donati Simo ˜ es, Miriam R. X. Barros, and Sandro M. Rossi CPqD–Rodovia Campinas-Mogi Mirim (SP340) km 118,5 Campinas, SP, Brazil, CEP 13086-902 Received 4 May 2004 ABSTRACT: We report the short-reach transmission of a single chan- nel, which is positively prechirped and externally modulated in NRZ format at 40 Gb/s by an electro-optical Mach–Zehnder modulator. The signal, amplified by a low-cost waveguide amplifier, propagates in the normal dispersion regime with near error-free performance. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 419 – 423, 2004; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/mop.20488 Key words: fiber optics; normal dispersion regime; optical communica- tion; intra-office application INTRODUCTION The potential market for short-reach (SR) and very-short-reach (VSR) applications has attracted much attention recently [1–3] and the benefits may be proved first in metropolitan area because the spans are short enough to eliminate the need for special solutions [4 – 6]. Some carriers have already identified a near-term applica- tion of metro core rings, interconnecting a variety of systems within data centers, long-distance points-of-presence (POPs), and collocation centers within a metro area and transporting them via STM-256 systems [7]. High-speed VSR interconnects may be adopted for reducing the number of ports and cards in a way that, for the same capacity, equipment can be made smaller, which will require less power and cooling and will reduce the number of fibers. These factors decrease expenses with operation and inven- tory for the manufacturing processes and spares. Technical ad- vances are targeted at VSR interfaces in order to interconnect switches, routers, and transport equipment within a central office (CO), where each signal may use its own fiber and existing fibers may be capable of supporting 40 Gb/s over these short distances. A key development enabling 40-Gb/s interfaces are the standards “Serializer/Deserializer (SerDes) Framer Interface Level 5” (SFI- 5), “OIF VSR-5,” and “ITU-T G.693” [8 –12]. Applications are usually specified with target distances of 0.6 and 2 km and various loss budgets for G.652 (STD), G.653 (DS), and G.655 (NZD) fibers, although one should keep in mind that the dispersion tolerances for STD fibers make their use more restricted. The interest in those three fibers stems from the fact that they are Figure 6 Wavefront with irregular edge: (a) wrapped; (b) unwrapped Figure 7 Tested CCR results: (a) interferogram; (b) contour; (c) surface; (d) angle error MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 43, No. 5, December 5 2004 419