Interferometer on a Chip

About

Applications: The invention relates to liquid crystal (LC) devices that are used as the active modulation element in phase-shifting Point Diffraction Interferometer (LCPDI) which are used to accurately measure changes in optical path. These modulation elements are constructed to permit a reference beam and an object beam traversing a common optical path to induce a pattern of interference fringes. By addressing the LCPDI modulator with an electric field, the phase delay between the object and reference beams can be changed in real time. The LCPDI's compact size (less than 1 in. x 1 in.), near-solid-state robustness, and low-voltage requirements (1.5 Vrms) have led the device to be described as an 'Interferometer On-a-Chip' with the potential of offering comparable performance to commercial phase-shifting interferometers at a fraction of their size, complexity, and cost. The LCPDI cells with near solid-state robustness are provided with structured substrates, having diffractive element which are built integral with to the device. These structured substrates are prepared in accordance with the invention either by thin-film vapor deposition of an inorganic material or by photoresist processing techniques used in microelectronics. Additional attributes of the LCPDI include the capability to collect data at video frame rates and at a wide variety of wavelengths. This combination of unique attributes makes the LCPDI of special interest for diagnostic applications in the commercial, military, scientific, industrial, and biomedical sectors where physical size, robustness, rapid data collection, and low cost are of primary concern.   Advantages: Conventional phase-shifting interferometers are extremely sensitive to mechanical shock and transmitted vibration, are difficult and time consuming to set up, align, and maintain, and are costly due to the number of optical elements required for their dual-path design. Common-path interferometers such as the Point-Diffraction (PDI) type are much less sensitive to environmental disturbances but until recently have not been capable of phase-shifting. This invention provides for two major advantages over prior art. First, the improved device design maximizes both optical performance and enhances ease of manufacturing in production-scale quantities. Second, this device has a mixture of positive and negative dichroic dyes that are blended into the liquid crystal material to form a 'constant-compensated', non-dichroic mixture. This blend functions to attenuate the sample beam without the voltage-dependent changes in interference fringe contrast that normally occur when standard dichroic dyes are doped into a LC mixture.