馬可曾德爾干涉儀,可以利用信號光與參考光的干涉,來獲得量測樣品的光學厚度。過去研究顯示,若在干涉儀信號端加入色散物質,會使包絡增寬,由於光經過色散物質,不同的折射率產生不同的波長,干涉信號強度會週期性的震盪,這會產生拍頻效應,這個效應會使低同調干涉儀信號產生多重分裂,這個現象雖然會使量測解析度降低,但量測曲線會較平滑,使量測多層結構時,正確度提升,我們發現在光信號端進行編碼可以產生類似的情形。我們將用空間光調變器架設於馬可曾德爾干涉儀的信號臂,經由干涉信號去量測樣品的光學厚度,會使用七種不同的編碼來量測樣品,比較與討論。
當空間光調變器使用適合的編碼會使光訊號加寬的現象,可以使用這個現象來量測多層結構,當光入射多層結構時會產生光信號分裂,產生許多峰值, 雖然光訊號會加寬使解析度降低,但卻只會取得所需的峰值,且取得的曲線較平滑,有效提升正確信, 假如我們可以完全地把它與影像處理作結合，那麼它就可以被廣泛的使用在醫界。此外，它也可以被使用在工業界，來量測樣品的一些性質。

Mach-Zehnder Interferometer (MZI) can be used to acquire the optical thickness of samples by utilizing the interference of two lights. Recently, some researchers mentioned that if a dispersion element is put in front of the interferometer, the coherence envelope of the signal will be broadened. The reason is that when the light passes the dispersion element, different refractive indices of different wavelengths in the dispersive medium. The intensity of the interference signal will oscillates, which leads to beat effect. As a result, multiple splitting of the partial-coherence interference (PCI) signal will be induced. Although the resolution of measurement decreases, the curve of the results will be smoother. Therefore, the precision of measuring multi-layer structures can be improved. We observe that the similar effect happens when encoding the signal.
In this paper, we set up the spatial-light modulator (SLM) at the signal arm of the MZI to measure the optical thickness of the sample. Different coding patterns are used and discussed in this study. When proper encoding scheme is used in SLM, the signal peaks will be broadened. This effect can be utilized to measure multi-layer structures of object samples. When the incident light passes multi-layer structures, the signal is split into multiple peaks. Though the broadening of the signal decreases the resolution, we can acquire the desired peak and the curve becomes smoother. Therefore, the precision of the measurement can be improved. If this effect is combined with image processing, it can be used in medical fields. It can also be used in industry fields to measure the properties of samples.

[1] A.M. Weiner, D.E. Leaird, J.S. Patel, and J.R. Wullert, “Progammable femtosecond pulse shaping by use of a multi-element liquid-crystal phase modulator”, Opt. Lett., Vol. 15, pp. 326-328, 1990.
[2] A.M. Weiner, D.E. Leaird, J. S. Patel, and J. R. Wullert, “Progammable shaping of femtosecond optical pulses by use of a 128-element liquid crystal phase modulator,” IEEE J. Quantum Electron., vol. 28, pp. 908-920, 1992.
[3] A.M. Weiner, “Femtosecond pulse shaping using spatial light modulators”, Review of Scientific Instruments, vol. 71, pp. 1929-1960, 2000.
[4] M.M. Wefers and K.A. Nelson, “Space-Time Profiles of Shaped Ultrafast Optical Waveforms,” IEEE J. of Quantum Electronics, vol. 32, p. 161, Jan. 1996.
[5] Z. Kostic and E.L. Titlebaum, “The design and performance analysis for several new classes of codes for optical synchronous CDMA and for arbitrary-medium time-hopping synchronous CDMA communication systems,” IEEE Trans. Commun., vol. 42, pp. 2608-2617, Aug. 1994.
[6] M. Arumugam, “Optical fiber communication – An overview,” Pramana-J. Phys., vol. 57, no. 5-6, pp. 849-869, Nov.-Dec. 2001.
[7] M. Veeraraghavan, R. Karri, T. Moors, M. Karol, and R. Grobler, “Architectures and protocols that enable new applications on optical networks,” IEEE Commun. Mag., vol. 39, no. 3, pp. 118-127, Mar. 2001
[8] P. Urquhart, “Component technologies for future optical networks,” IEE Proc. Optoelectron., vol. 150, no. 1, pp. 3-8, Feb. 2003.
[9] H. Kogelnik, “High-capacity optical communications: personal recollections,” IEEE J. Sel. Top. Quantum Electron, vol. 6, no. 6, pp. 1279-1286, Nov.-Dec. 2000.
[10] Y. Sasaki, “Optical fiber devices,” Transparent Optical Networks,” the 2nd International Conference on June 5-8, pp. 9-12, 2000.
[11] K. Nakagawa and S. Shimada, “Optical amplifiers in future optical communication systems,” IEEE, vol. 1, no. 4, pp. 57-62, Nov. 1990.
[12] R. Giles and L.T. Ye, “Optical amplifiers transform long-distance lightwave telecommunications,” Proc. IEEE., vol. 84, no. 6, pp. 870-883, June 1996.
[13] Z. Kostic and E.L. Titlebaum, “The design and performance analysis for several new classes of codes for optical synchronous CDMA and for arbitrary-medium time-hopping synchronous CDMA communication systems,” IEEE Trans. Commun., vol. 42, pp. 2608-2617, Aug. 1994.
[14] C.C. Yang, “Code Space Enlargement for Hybrid Fiber Radio and Baseband OCDMA PONs,” IEEE Trans. Commun., vol. 57, no. 8, pp. 2402-2409, Aug. 2009.
[15] B.E.A. Saleh and M.C. Teich, “Fundamentals of photonics”, 2nd Edition, 2007.
[16] S. Tolansky, “An introduction to Interferometry”, Wiley, 2nd ed., 1973.
[17] M. Feancon, “Optical Interferometry”, Academic Press, 1966.
[18] M.J. Cobb, X. Liu, and X. Li, “Continuous Focus Tracking for Real-Time Optical Coherence Tomography,” Opt. Lett., vol.30, pp. 1680-1682, 2005.
[19] P. Hariharan, “Optical Interferometry” , Academic press, 2nd Edition, 2003.
[20] P. Hariharan, “Basic of Interferometry”, Academic press, 1992.
[21] C.K. Hitzenberger, A. Baumgartner, A.F. Fercher, “Dispersion induced multiple signal peak splitting in partial coherence interferometry”, Opt. Commun. 154, pp. 179-185, 1998.