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Use of optical fibers in the pulsed time-of-flight laser rangefinding technique

The problems associated with the fibres used in pulsed time-of-flight rangefinders were studied, and particularly errors due to the transit time disturbances of step and graded index fibres as a function of fibre length, input numerical aperture and temperature. The cladding modes and leaky modes ofa fibre can affect the transit time oflight pulses under suitable conditions, so that fibres become sensitive to environmental effects. The effect of temperature is smaller and more linear for acryl-coated fibres than for nylon-coated ones. The main reason for the non-linear effect of temperature on a nylon fibre is the non-linear Young's modulus of nylon as a function of temperature. The increasing transit time of hard clad silica (HCS) fibres at lower temperatures (below +20°C), contrary to glass fibres, can be explained by the different thermal coefficient of the core and cladding, leading to increased non-homogenities on the core-cladding interface.