Grating Light Valve - Technology

Technology

The GLV device is built on a silicon wafer and consists of parallel rows of highly reflective micro-ribbons – ribbons of sizes of a few µm with a top layer of aluminium – suspended above an air gap that are configured such that alternate ribbons (active ribbons are interlaced with static ribbons) can be dynamically actuated. Individual electrical connections to each active ribbon electrode provide for independent actuation. The ribbons and the substrate are electrically conductive so that the deflection of the ribbon can be controlled in an analog manner: When the voltage of the active ribbons is set to ground potential, all ribbons are undeflected, and the device acts as a mirror so the incident light returns along the same path. When a voltage is applied between the ribbon and base conductor an electrical field is generated and deflects the active ribbon downward toward the substrate. This deflection can be as big as one-quarter wavelength hence creating diffraction effects on incident light that is reflected at an angle that is different from that of the incident light. The wavelength to diffract is determined by the spatial frequency of the ribbons. As this spatial frequency is determined by the photolithographic mask used to form the GLV device in the CMOS fabrication process, the departure angles can be very accurately controlled, which is useful for optical switching applications.

The switching from undeflected to maximum deflection of the ribbon is really fast; it can switch in 20 nanoseconds which is a million times faster than conventional LCD display devices, and about 1000 times faster than TI’s DMD technology. This high speed can be achieved thanks to the small size, small mass and small excursion (of a few hundreds of nanometers), of the ribbons. Besides, there is no physical contact between moving elements which makes the lifetime of the GLV as long as 15 years without stopping (over 210 billion switching cycles).