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Training Videos

 

Acousto-optic diffraction

This is a continuation from the previous tutorial - photoelastic effect. We see from the preceding two tutorials that the space- and time-dependent periodic permittivity changes induced by a traveling plane acoustic wave of the form given in (8-1) [refer to the elastic waves tutorial] can be generally expressed as \[\tag{8-34}\Delta\boldsymbol{\epsilon}=\Delta\tilde{\boldsymbol{\epsilon}}\sin(\mathbf{K}\cdot\mathbf{r}-\Omega{t})\] where \(\mathbf{K}\) depends on both the polarization and the propagation direction of the acoustic wave. In general, \(\Delta\tilde{\boldsymbol{\epsilon}}\) is a function of the strain and the rotation generated by the acoustic wave in the medium, the elasto-optic coefficients of the medium, the mode and direction of the acoustic wave,...

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Photoelastic effect

This is a continuation from the previous tutorial - elastic waves. Mechanical strain in a medium causes changes in the optical property of the medium due to the photoelastic effect.  The basis of acousto-optic interaction is the dynamic photoelastic effect in which the periodic time-dependent mechanical strain caused by an acoustic wave induces periodic time-dependent variations in the optical properties of the medium. The photoelastic effect is traditionally defined in terms of changes in the elements of the relative impermeability tensor caused by strain: \[\tag{8-7}\eta_{ij}(\mathbf{S})=\eta_{ij}+\Delta\eta_{ij}(\mathbf{S})=\eta_{ij}+\sum_{k,l}p_{ijkl}S_{kl}\] where \(p_{ijkl}\) are dimensionless elasto-optic coefficients, also called strain-optic coefficients or photoelastic coefficients, and they...

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Elastic Waves

This is a continuation from the previous tutorial - guided-wave magneto-optic devices.   Introduction Scattering of light by acoustic waves was first investigated by Brillouin. The acoustic frequencies involved in Brillouin scattering fall in the ultrasonic and hypersonic regions. Hypersonic waves in a medium are caused by thermal excitation, whereas ultrasonic waves can be excited electronically using piezoelectric transducers. The acoustic waves used in acousto-optics are generally ultrasonic waves that have frequencies in the range between about 100 kHz and a few gigahertz. The basic principles of acousto-optic devices are based on the scattering of light by the periodic index...

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Guided-wave magneto-optic devices

This is a continuation from the previous tutorial - magneto-optic recording. It is possible to implement various kinds of guided-wave magneto-optic devices for optical modulation, switching, and many other functions. Nevertheless, there has been very little interest in developing such devices because equal or better performance of the functions provided by such devices can be accomplished by their electro-optic or acousto-optic counterparts. Among devices of equal performance, the magneto-optic ones have certain disadvantages. Magneto-optic waveguides are not compatible with the dielectric and semiconductor waveguides used in most photonic devices because they have to be fabricated with magnetic materials, most commonly...

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Magneto-optic recording

This is a continuation from the previous tutorial - magneto-optic modulators and sensors. In magneto-optic recording, digitized information stored in a magnetic thin film is read using the magneto-optic Faraday or Kerr effect. There are certain similarities between the principle of magneto-optic recording and that of the magneto-optic spatial light modulator. Indeed, because of its nonvolatility, a magneto-optic spatial light modulator also has the ability to hold digitized information for later access. Reading of the recorded information is performed using the magneto-optic Faraday effect. However, while the application of a magneto-optic spatial light modulator is primarily dynamic information processing, the...

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