Unique multi-diffraction structures using electronically controlled Bragg
diffraction devices such as acousto-optic (AO) devices to accomplish optical beam
attenuation control functions. These variable optical attenuator (VOA) modules
can be fully inertialess as they can use electronically programmable sub-microsecond
speed AO devices to implement optical gain controls. These VOAs deliver desirable
capabilities in one optically reversible unit, making high dynamic range, low loss,
high power handling, ultra-fast, high optical isolation, broadband operation, self-aligning
robust modules. These VOAs can be made essentially independent of the optical polarization
of the incident light by the use of a unique fixed waveplate compensation technique
within the VOA configuration that suppresses polarization dependent loss. Broadband
gain control operation over several wavelengths can be achieved by controlling
the frequency and electrical drive power of the chosen frequencies feeding the
acousto-optic devices. Interleaver devices can be cascaded with the acousto-optic
modules to improve wavelength selectivity of the overall VOA modules. Alternative
embodiments can use electrically programmable Bragg gratings in polymer dispersed
liquid crystal and acousto-optic tunable filter devices as Bragg grating devices.
Embodiments are proposed using independently controlled Bragg diffractions using
multiple drive signals connected to multiple device transducers. Drive signal formats
can be digital, analog, or a combination for simultaneously driving the VOA modules.
Dual-mode VOA module designs are also described using mirror positioning.
