wk14a - Holography Preamble: modulation and demodulation...

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MIT 2.71/2.710 Optics 12/06/04 wk14-a-1 Holography • Preamble: modulation and demodulation • The principle of wavefront reconstruction • The Leith-Upatnieks hologram • The Gabor hologram • Image locations and magnification • Holography of three-dimension scenes • Transmission and reflection holograms • Rainbow hologram
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MIT 2.71/2.710 Optics 12/06/04 wk14-a-2 Modulation & Demodulation • Principle borrowed from radio telecommunications • Idea is to take baseband signal (e.g. speech, music, with maximum frequencies up to ~20kHz) and modulate it onto a carrier signal which is a simple tone at the frequency where the radio station emits, e.g. 104.3 MHz (that’s Boston’s WBCN station) • One of the benefits of modulation is that radio stations can be multiplexed by using a different emission frequency each • After selecting the desired station, the receiver follows a process of demodulation which recovers the baseband signal and sends it to the speakers.
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MIT 2.71/2.710 Optics 12/06/04 wk14-a-3 Types of modulation • Amplitude modulation (AM) • Frequency modulation (FM) • Phase modulation (PM) • Digital methods (Amplitude Shift Keying – ASK, Frequency Shift Keying – FSK, Phase Shift Keying – PSK, etc.) used in radio at low frequencies only (“AM band” = 535kHz to 1.7MHz) ; as we will see, it is an almost-exact analog of holography dominant in commercial radio (“FM band” = 88MHz to 108MHz) ; there is an analog in optics, called “spectral holography,” but it is beyond the scope of the class
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MIT 2.71/2.710 Optics 12/06/04 wk14-a-4 Amplitude modulation () x f (baseband) ( ) () ( ) x u x f x f c 2 cos modulated π × = = u c : carrier frequency
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MIT 2.71/2.710 Optics 12/06/04 wk14-a-5 AM in the frequency domain ( ) x f of spectrum () x f modulated of spectrum
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MIT 2.71/2.710 Optics 12/06/04 wk14-a-6 AM in the frequency domain ( ) x f of spectrum () x f modulated of spectrum (zoom-in) (zoom-in)
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MIT 2.71/2.710 Optics 12/06/04 wk14-a-7 AM in the frequency domain () () () ( ) () [] () c c c c 2 2 c 2 1 2 1 e e 2 1 2 cos c c u u F u u F u u u u u F x f x u x f u F x f x u i x u i + = = + + × = δ π modulation in the space domain
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This note was uploaded on 04/17/2011 for the course ME 525 taught by Professor Lucth during the Spring '11 term at Purdue University-West Lafayette.

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wk14a - Holography Preamble: modulation and demodulation...

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