Abstract
This chapter, divided in six sections, begins with the naturally modulated sources: lasers that are modulated due to principle of operation—pulsed modulated solid-state lasers and sinusoidally modulated Zeeman two-frequency lasers. The Zeeman laser presents an exceptional possibility of creating monochromatic sinusoidally modulated light source. With some straightforward mathematics, the conditions of most efficient modulation are derived and experimental oscilloscope traces are presented. This forms the basis for the technology of measuring the cutoff frequency of photoreceivers. Mechanical modulators with perforated rotating wheel are simple devices that are suitable for modulation of any optical beams. But even they can be further optimized by some simple practical tricks. Electro-optical modulators (EOMs) described in the third section are compact, reliable, and surprisingly versatile devices being used for amplitude, polarization, phase and frequency modulation of laser beams. However, their performance can only be fully understood with detailed mathematics, explaining interaction of laser beams with electrically active birefringent crystals. Various types of artifacts may compromise modulation, and this section shows how to avoid it. Numerical computations help to realize these phenomena. Another widely used and also physically complicated device is the acousto-optical modulators (AOMs). The nature of interaction between light and acoustic wave can only be understood with differential equations and special functions, describing periodical solutions for the diffracted beam. Nonetheless, even with this theoretical complexity, it is possible to explain the principle of acousto-optical diffraction in simple terms of reflection from a periodical structure. In this section, deep theory is followed by very practical explanation of the design features of a typical AOM. The next section describes simple and efficient practical solutions for modulating LEDs and LDs, supporting the conclusions by real oscilloscope traces. It is not widely known that even white-light LEDs can be modulated at high frequencies, and temporal evolution of their spectrum is presented, obtained with the help of the gated spectrometer outlined in Chap. 9. The last section of this chapter guides the reader through basics of demodulation techniques and filtering: LC filters, crystal filters, diode rectifiers, active rectifiers, synchronous demodulation (lock-in amplifiers). Along with necessary theoretical explanation, practical circuits and schemes are presented, ready for implementation.
Not everything is possible in optics, and optical modulation has many limitations. This chapter advises on how to choose the proper technique for the specific application.
This is a preview of subscription content, log in via an institution.
Buying options
Tax calculation will be finalised at checkout
Purchases are for personal use only
Learn about institutional subscriptionsFurther Reading
M. Born, E. Wolf, Principles of Optics, Cambridge University Press, 7th ed., 1999.
V. Protopopov, Laser Heterodyning, Springer, 2009.
B.E.A. Saleh, M.C. Teich, Fundamentals of Photonics, Wiley, 1991.
E.F. Schubert, Light-Emitting Diodes, 2nd ed., Cambridge University Press, 2006.
P. Horowitz, W. Hill, The Art of Electronics, Cambridge University Press, 2nd ed., 2001.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
Copyright information
© 2014 Springer International Publishing Switzerland
About this chapter
Cite this chapter
Protopopov, V. (2014). Modulation-Demodulation Techniques. In: Practical Opto-Electronics. Springer Series in Optical Sciences, vol 184. Springer, Cham. https://doi.org/10.1007/978-3-319-04513-9_4
Download citation
DOI: https://doi.org/10.1007/978-3-319-04513-9_4
Published:
Publisher Name: Springer, Cham
Print ISBN: 978-3-319-04512-2
Online ISBN: 978-3-319-04513-9
eBook Packages: Physics and AstronomyPhysics and Astronomy (R0)