摘要:
A differential laser Doppler velocimeter is based on the use of a modified fibre optic Sagnac Interferometer 1,2. The interferometer phase is dependent not on the target displacement, but on its velocity. The output intensity of the interferometer may be modulated by control means PC which controls loop birefringence introducing a phase bias and polarization offset between counter-propagating beams.
摘要:
A sensor system in an interferometric arrangement has a sensor arm and a reference arm. The reference arm is in a stable environment and the sensor arm is arranged to be subject to variations in strain and/or temperature. Radiation from a broadband source propagates through the arrangement and a broadband interferogram is generated as an air gap is scanned. The interferogram is recorded on an oscilloscope and analyzed using signal processing software on a computer. From the analysis the changes in group delay and optical dispersion of the light in the sensor arm due to strain and temperature changes is measured, and values for the strain and/or temperature changes calculated. A narrowband light source may be used for accurate calibration of path length differences during scanning. The strain and temperature on the sensor arm may be calibrated or tested using clamps and a thermal enclosure. The system may also be configured in a tandem interferometry arrangement including a sensing interferometer and reference interferometer.
摘要:
An interferometric sensor includes an optical fiber polarimetric sensing element (5) for detecting a required measurand and is configured so as to derive interference output signals, which are simultaneously monitored by photodetectors (9, 11), from both conventional, for example, Michelson, and polarimetric interferometer arrangements. The sensor therefore offers the high resolution of a conventional interferometer in conjunction with the increased dynamic range of a polarimetric device.
摘要:
Optical pressure sensing apparatus comprises an optical fibre interferometer arranged to sense the movement of a pressure responsive element and produce an interference signal at its output which can be monitored and processed to measure changes in the pressure applied to the pressure responsive element. The interferometer comprises a signal arm coupled to the pressure responsive element and a fixed reference arm. A light source supplies light to the input of the interferometer via an optical fibre and monitoring and processing electronics connected to the output determine the optical phase shift between the light beams propagated in the signal and reference arms and produce a pressure reading.
摘要:
A laser system comprises a laser (500) whose output beam is delivered to a workpiece (504) by an optical fiber (502). A transducer (506) detects the power of light propagating in the cladding layer of fiber (502) at a position near its input end. The transducer (506) also strips out the light travelling in the cladding layer. The output of transducer (506) is divided by the output of a transducer (507), which detects the power of the output beam of laser (500), to produce a signal indicative of misalignment between the laser beam and the core of fiber (502) at the input face. A transducer (505) comprises a second fiber (508) optically coupled with the cladding layer of fiber (502). Light emitted from the ends of fiber (508) is detected by a pair of detectors (509, 510), whose outputs are indicated on displays (512, 514). Display (512) provides information on the integrity of transmissions of the laser beam through fiber (502). Display ( 514) provides information on the material processing operation performed on workpiece (504), and also on the focus of the beam onto the workpiece.
摘要:
A flowmeter for measuring the velocity of fluid flow by monitoring the vortex shedding frequency of the fluid flow comprises a single mode optical fibre sensing element (1) for detecting vortex shedding and utilizes interferometric techniques for producing an electrical output signal corresponding to the vortex shedding frequency. The sensing element (1) comprises at least part of the signal arm (2) of an interferometer (3) which also includes means (12) for deriving a reference signal from the illuminating light source (4). The flow induced oscillation of the sensing element (1) caused by vortex shedding produces modulations of the interferometer output which is monitored by a photodetector (14) which, in turn, produces a modulated electrical output signal which can be processed by a signal processing system (16-19) to identify the vortex shedding frequency and, hence, produce a measurement of the flow velocity.