Centennial Honors College
Western Illinois University
Undergraduate Research Day 2012
Poster Presentation
Modulation of Laser Intensity Using Electro-Optic Effect
Timothy Woodworth
Faculty Mentor: Pengqian Wang
Physics
The electro-optic effect refers to the phenomenon that when an external electric field is
applied on a crystal, the optical properties of the crystal, especially its refractive index
will be changed. This effect has a short response time of less than one nanosecond.
This has brought many important applications in modern science and technology, such
as laser pulse generation, high-speed photography, laser communication and optical
data processing. In this poster we will present our experiment of modulating the
intensity of a laser beam using the transverse electro-optic modulation in a lithium
niobate crystal. We measured the half-wave voltage of the crystal used in the
experiment, at which the electro-optic effect induces a phase shift of half a wave
between the two polarization modes of the light inside the crystal. The polarization plane
of the input light is rotated by a right angle. Linear modulation of light intensity is
achieved when the crystal is working at one half of the value of its half-wave voltage,
where the output light intensity faithfully follows the electronic modulation signal.
Frequency-doubling distortion occurs at certain applied voltages where the output light
is minimized or maximized. We measured the electro-optic coefficient of the lithium
niobate crystal. We also studied the characteristics and the variation of the interference
pattern of polarized light in the crystal and demonstrated the feasibility of optically
transferring music signals using electro-optic modulation.