A Fiber Optic Photoelastic Accelerometer has been designed and developed, which operates with a force transducer made from an optically birefringent material. Signal measurements are made by Photoelastic techniques using an LED as an incoherent light source. The Accelerometer has a sensitivity of 2 V/g’s, a resolution of 2.5 mg’s for a frequency range from 0 to 600 Hz; and a linear amplitude range of 0 to 5 g’s.
The Accelerometer housing is a hermetically sealed aluminum case 41 mm x 35 mm x 20 mm with the force transducer mounted inside. The sensing element is a Photo elastic material located between two crossed linear optical polarizes. The 20 gram copper seismic mass has support elements made of stainless steel shim stock. The remaining support structure is an aluminum alloy.
The radius of the seismic mass cylindrical surface is 0.5 mm at the point of contact. A preload is applied to the Photoelastic sensing element. Optical access to the transducer is provided by two 200µm diameter multimode Fiber Optics. Fiber Optic ferrules holds the Fiber Optics in place. A 0.5 pitch GRIN lens collimates the light source increasing the optical coupling efficiency.
Single Photon Detectors in Visible Range by id Quantique SA
id Quantique’s id100 consists of compact and affordable single-photon counting modules with best-in-class timing resolution. Based on a reliable silicon avalanche photodiode sensitive in the visible spectral range, these modules are able to detect weak optical signals down to the single photon level. The includes:
- two free-space versions, the id100-20 and id100-50 with a 20um, respectively a 50um diameter photosensitive area.
-a fiber-coupled version, the id100-MMF50, coming with a standard FC/PC optical Input
The free-space and fiber-coupled modules are easy-to-use, self-contained and can be integrated in every optical setup. With a timing resolution as low as 40ps and a remarkably short dead time of 45ns, these modules outperform existing commercial detectors in all applications requiring single-photon detection with high timing accuracy. Besides an extremely fast IRF (Instrument Response Function), the modules have an excellent timing stability up to count rates of at least 20MHz
The id100 consists of an avalanche photodiode (APD) and an active quenching circuit integrated on the same silicon chip. The chip is mounted on a thermo-electric cooler and packaged in a standard TO5 header with a transparent window cap. A thermistor is used to measure temperature. The APD is operated in Geiger mode, i.e. biased above breakdown voltage. A high voltage supply used to bias the diode is provided by a DC/DC converter . The quenching circuit is supplied with +5V. The module output pulse reflects the arrival of a photon with high timing resolution. The pulse is shaped using a hold-off time circuit and sent to a 50ohm output driver. All internal settings are preset for optimal operation at room temperature. No user adjustment is necessary. In the fiber-coupled version, the TO5 header and the optical fiber are included in the housing. The optical input consists of a FC/PC connector on the front side of the module.
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A Stereoscope 3-D Viewer has been designed and developed for television sets and computers. It can be viewed without headgear or special glasses. The Viewer uses a camera to track the viewer’s eyes, allowing the Viewer to change position and still maintain 3D imaging.
The Viewer consists of folded focusing optics, two liquid crystal display video projectors mounted behind a partially silvered screen and a reflective screen. The left image and the right image fields of a stereoscopic image are projected and reflected off a pair of 45° retroreflective mirrors at the bottom of the cabinet. The silvered mirror suspended at 45° is in front of a 50-inch rear projection screen. This provides for the passage of 50 percent of the reflected light.
A small TV camera is positioned under the cabinet and tracks the viewers eyes to ensure correct image focus in both eyes. The tracking is updated 25 times per second. This information is used to adjust the position of the projected images automatically keeping the images aligned for 3D viewing.
The two images are spaced at 32 mm, half an eye spacing, to prevent image spillover. The eye tracking system allows both vertical and lateral viewer motion. The internal mirror optics is controlled by a logic servomechanism from information signals analyzed from the TV camera inputs. The projectors move horizontally for viewer lateral movement and the silvered mirrors tilt for viewer vertical movement.
Source: Laser Focus World, 1996
Reference: Xenotech , Perth West, Australia