AO Modulators0 pages

Sintec Optronics Technology Pte Ltd

Sintec Optronics Technology Pte Ltd
10 Bukit Batok Crescent #07-02 The Spire Singapore 658079
Tel: +65 63167112 Fax: +65 63167113

Acousto-Optic Modulators
By virtue of having no moving parts our acousto-optic modulators (AOMs) are able to amplitude
modulate a laser beam at very high speed. For example modulation bandwidths in excess of
50MHz are readily achievable.
In an AOM a laser beam is caused to interact with a high frequency ultrasonic sound wave inside
an optically polished block of crystal or glass (the interaction medium). By carefully orientating the
laser with respect to the sound waves the beam can be made to reflect off the acoustic wavefronts
(Bragg diffraction). Therefore, when the sound field is present the beam is deflected and when it is
absent the beam passes through undeviated. By switching the sound field on and off very rapidly
the deflected beam appears and disappears in response (digital modulation). By varying the
amplitude of the acoustic waves the intensity of the deflected beam can similarly be modulated
(analogue modulation).
It is usual to choose the deflected beam as the one that is used in the optical system because it
can be switched on and off with high extinction ratio (typically >40dB) and intensity can be varied
from zero to more that 85% of the incident beam. The rate at which the beam can be modulated is
governed by the time it takes the acoustic wavefronts to traverse the laser beam, which depends
on the beam diameter and the acoustic velocity in the interaction medium.
The sound waves are generated by a transducer, usually a thin wafer of lithium niobate, that is
bonded onto the interaction medium using a highly efficient cold-weld metallic bonding process.
When a high frequency electrical signal is applied to the transducer it vibrates, generating the
acoustic wave. The signal is derived from an RF driver, which generates a high frequency carrier
that is itself modulated by an analogue or digital input signal.

AO Modulator Cell Schematic

Fiber-coupled AO Modulator Cell Schematic

Principal applications for AO modulators are pre-press (putting image and text data onto films or
plates as part of the printing process), laser imaging and displays, switching in telecom fibres,
instrumentation and research.

http://www.SintecOptronics.com http://www.SintecOptronics.com.sg

Tel: +65 63167112

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