MIDINFRARED MODULATION THROUGH THE USE OF FIELD-INDUCED SCATTERING INFERROELECTRIC LIQUID-CRYSTALS

The feasibility of the use of modulation devices based on field-induce d transient scattering in ferroelectric liquid crystals (LC) to replac e mechanical choppers used in uncooled infrared-imaging systems was in vestigated. Devices fabricated with ITO-coated ZnSe substrates and a f erroelectric LC path length of 25 mu m were able to modulate optical r adiation by transient forward scattering at rates approaching 20 KHz, Through the use of a commercial arbitrary waveform generator and assoc iated PC-based software, drive waveforms were developed that produced a variable, square-wave optical-modulation pattern by the extension of the duration of the scattering state to periods ranging from hundreds of microseconds to milliseconds. The ability of these extended-scatte ring-mode (ESM) devices to modulate radiation in both the visible and midinfrared regions was verified in a simple experiment through the us e of a Fourier-transform infrared spectrometer, in which an unoptimize d ESM device displayed a 40% modulation depth for IR radiation in the 8-12-mu m region.