Optical transmission calibration device and method for optical transmissiometer

In a method for calibrating an optical transmission measurement apparatus having means for splitting a first light bean into first and second components which have different polarizations, a first photo-detector means which detects the first component, means for splitting a second light beam into third and fourth components which have different polarizations, and a second photo-detector means which detects the third component, wherein the second and fourth components are transmitted through an object and detected by the second and first photo-detector means respectively to permit the apparatus to measure the transmittance of the object according to a percentage of light reaching the object that passes therethrough, the improvement comprising the steps of:

• transmitting the second component in addition to the first component to the first photo-detector means without either of the first and second components passing through the object, and transmitting the fourth component in addition to the third component to the second photo-detector means without either of the third and fourth components passing through the object;
• and
• detecting the second component in addition to the first component with the first photo-detector means, detecting the fourth component in addition to the third component with the second photo-detector means, and producing calibration signals based on the detected first through fourth components, the calibration signals being indicative of at least one calibration parameter for use in determining the percentage of the light reaching the object that passes through the object when light is transmitted through the object.

An optical transmission measurement apparatus for measuring optical transmission through an object, comprising:

• a first transmitter/receiver, including
• a first photo-detector,
• means for emitting a first light beam of predetermined polarization,
• means for splitting the first light beam into a first component and a second component of different polarizations, the second component propagating on a first path toward the object, and
• means for returning the first component to the first photo-detector;
• a second transmitter/receiver unit, including
• a second photo-detector,
• means for emitting a second light beam of predetermined polarization,
• means for splitting the second light beam into a third component and a fourth component of different polarizations, the fourth component propagating on a second path toward the object, and
• means for returning the third component to the second photo-detector;
• first reflecting means, movable into and out of the first path, for reflecting the second component back to said first photo-detector through said means for returning the first component, when said first reflecting means is in the first path;
• and
• second reflecting means, movable into and out of the second path, for reflecting the fourth component back to said second photo-detector through said means for returning the third component, when said second reflecting means is in the second path, the second component entering said second photo-detector through the object and the fourth component entering said first photo-detector through the object, when the first and second reflecting means are out of the first and second paths;
• the first and second photo-detectors producing calibration signals indicative of calibration values, in response to the second and fourth components received thereby when said first reflecting means is in the first path and said second reflecting means is in the second path, the first and second photo-detectors producing further calibration signals indicative of further calibration values, in response to the first and third components.

A method of calibrating an optical transmission measuring apparatus, comprising the steps of:

• emitting a first light beam of predetermined polarization;
• splitting the first light beam into a first component and a second component of different polarizations;
• directing the second component on a first path toward an object;
• directing the first component away from the object to a first photo-detector;
• emitting a second light beam of predetermined polarization;
• splitting the second light beam into a third component and a fourth component of different polarizations;
• directing the fourth component on a second path toward the object;
• directing the third component away from the object to a second photo-detector;
• reflecting the second component from a first mirror block disposed at a first position between the first photo-detector and the object, back to the first photo-detector, such that the second component does not pass through the object;
• reflecting the fourth component from a second mirror block disposed at a second position between the second photo-detector and the object back to the second photo-detector, such that the fourth component does not pass through the object;
• in the first and second photo-detectors, producing calibration signals indicative of calibration values, in response to the first and third components and the reflected second and fourth components;
• and
• measuring the optical transmission of the object, including the steps of:
• a. holding the first and second mirror blocks away from the first and second positions so that the second and fourth components do not reflect therefrom,
• b. during said step a passing the second component through the object to the second photo-detector and passing the fourth component through the object to the first photo-detector;
• and
• c. after said step b, detecting the second component with the second photo-detector and detecting the fourth component with the first photo-detector.