Temporal variation of residual amplitude modulation in electro-optic phase modulators

Juna Sathian, Esa Jaatinen

Research output: Contribution to conferencePosterpeer-review


The electro-optic modulator (EOM) is a key optical component used for phase modulating an incident field in optical
frequency references and gravity wave detectors. However, all EOMs generate unwanted residual amplitude
modulation (RAM) which limits the sensitivity and resolution in these ultra sensitive applications.While the origins of
RAM are not fully understood, measurements reveal that it can be suppressed to the 10-5
level through adequate
control of beam and medium properties. Although a practical and useful outcome, our understanding of RAM is not
complete and observations such as its irreproducible temporal behaviour remain unexplained and prevent further
suppression of this noise.
This study describes a comprehensive experimental evaluation of the time dependence of RAM and its dependence
on input intensity. These measurements were performed with a continuous wave 532 nm Nd:YAG laser that was
phase modulated with an MgO doped lithium niobate EOM, with the output measured by a phase sensitive detector.
The results presented here demonstrate that both the magnitude and phase of the modulator RAM varied with time.
Our results show that the observed temporal fluctuations in R{M level are tied to the medium’s nonlinear optical
properties and in particular, to the continual evolution of the self-defocusing refractive index changes that occur in
the photorefractive medium. Using the results of this study, beam properties are identified that minimize the RAM
temporal fluctuations, which are important in low noise applications where RAM stability is demanded.
Original languageEnglish
Publication statusPublished - 4 Sept 2012
Externally publishedYes
EventPhoton12: IOP’s premier event in optics and photonics - Durham University, Durham, United Kingdom
Duration: 3 Sept 20126 Sept 2012


Country/TerritoryUnited Kingdom
Internet address


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