Patent ID: 6788410
Filing Date: 2004-09-07
Classification: G01J,G01M

Abstract:
A delay time measurement apparatus for an optical element, comprising:a pulse light source which can vary a wavelength of light to be output, and outputs an optical pulse having a predetermined repetition period (T); wavelength setting means for setting the wavelength of the light to be output from said pulse light source; an optical power divider for dividing the optical pulse output from said pulse light source into a first optical pulse and a second optical pulse, the second optical pulse being input to an optical element as an object to be measured; optical delay means for changing a spatial optical path length along which the first optical pulse divided by said optical power divider travels, wherein the optical delay means receives the first optical pulse and outputs a reference optical pulse after a predetermined delay corresponding to the spatial optical path length of the optical delay means; control means for changing the spatial optical path length of said optical delay means, wherein the control means includes a spatial optical delay element controller which is adapted to control the spatial optical path length of the of the optical delay means and is adapted to arbitrarily set a relative delay amount of the reference optical pulse with respect to an output optical pulse which has passed through the object to be measured by changing the spatial optical path length in the spatial optical delay element controller and thereby changing an optical path length through which the first optical pulse passes; and a detector comprising: sampling means for receiving the output optical pulse that has passed through the object to be measured and the reference optical pulse delayed by said optical delay means, and for obtaining an autocorrelation intensity signal proportional to a light intensity of the output optical pulse at a given position every time said optical delay means changes the relative delay amount of the reference optical pulse; and signal processing means for obtaining an autocorrelation waveform of the output optical pulse from the autocorrelation intensity signals sequentially obtained by said sampling means; wherein the signal processing means includes means for outputting an optical delay element drive signal to the spatial optical delay element controller for sequentially changing the spatial optical path length of the optical delay means by a predetermined small distance &Dgr;L, where &Dgr;L corresponds to an increment &Dgr;T of delay time, and where &Dgr;T<wherein said detector detects a delay time of light that has passed through the optical element as the object to be measured based on the relative delay amount of the reference optical pulse delayed by said optical delays means, said delay time being required for obtaining a peak of the obtained autocorrelation waveform of the output optical pulse.