• Optical Shutter
• LCBM

	Description Device Operation Characteristics Datasheet Price/Delivery

DEVICE OPERATION AND APPLICATIONS
As shown below, the diffractive optical shutter consists of a thin, metal-coated membrane mirror, suspended over a 2-D array of wells. The membrane mirror is electrostatically deformed, thus creating a diffractive grating. The MMLS is driven by a high-voltage, high-bandwidth amplifier & controller that can be fed by a signal/pulse generator. One version of the amplifier can also provide a DC offset that is necessary for certain operating modes of the MMLS. The spatial filter is either a circular aperture or a circular opaque disc positioned at the center of the focal plane of the Fourier lens.

ZERO-ORDER PASS OPERATION

In zero-order-pass operation, the Fourier-plane spatial filter is a circular aperture. The light to be modulated or chopped (incoherent or coherent, polarized or unpolarized) is nominally collimated before it reaches the MMLS (see Fig. 1). Typically up to 100 full cone angle of divergence can be tolerated. When there is no voltage across the wells, the membrane mirror is flat and the light reflecting off the shutter surface maintains its collimation. Thus, the Fourier transform lens focuses this light to a single zero-order spot which passes through the spatial filtering aperture and is recollimated by the second lens as shown. This corresponds to the on state of the shutter. In this case, essentially all the light reaching the modulator is recovered as on-state radiance. If a small-diameter laser beam is used (e.g., 2-5 mm) no lenses are necessary. Generally, in this case, the zero order light is well separated from the higher orders and is easily filtered out.

When a voltage waveform is applied to the electrodes, the resulting electrostatic forces deform the membrane mirror into the underlying wells, and the membrane mirror becomes a 2-D diffraction grating. As the voltage across the wells increases, the deformation of the membrane-mirror increases, and more and more light is scattered out of the zero order into higher orders leading to lower and lower zero-order output intensity. Thus, gray-scale intensity modulation of the zero-order light is achieved. At some specific applied voltage, Vxt , the zero-order light is extinguished and the off state is achieved. The modulator may be driven with square waves or pulses for binary on/off operation, or with sine waves, triangular waves, or any arbitrary waveform.

APPLICATIONS

• Laser-pulse grating
• Phase modulation
• High-speed laser printing
• Broad-band image chopping
• Adaptive optics
• Two-port beam switching
• High-speed photography
• Beam spoiling
• Variable beam splitting