Optics: measuring and testing – By light interference – Having light beams of different frequencies
Reexamination Certificate
1999-04-19
2001-12-04
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By light interference
Having light beams of different frequencies
C356S487000
Reexamination Certificate
active
06327037
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an optical rotation angle polarimeter, more particularly to a noninvasive optical rotation angle polarimeter, which can be used to investigate the optical activity of optically active materials or substances.
2. Description of the Related Art
Polarizers and analyzers, in combination with mechanical methods for generating intensity-modulated signals, have been used to measure directly the optical rotation angle introduced by an optically active material or substance on linear polarized light to determine a physical property of the optically active material or substance, such as the refractive index of solid optically active materials or the concentration of optically active substances in a solution. Because of the susceptibility of the intensity-modulated signals generated by conventional mechanical methods to vibrations, and the relatively low frequency of the intensity-modulated signals that make it difficult to achieve high measuring precision, and because of the relatively slow measuring speed that results when conventional mechanical methods are in use, the conventional mechanical methods are currently being replaced with optic modulators, such as acousto-optic, electro-optic or photoelastic modulators, as intensity-modulated incident light sources. With the use of optic modulators, the magnitude of the optical rotation angle can be obtained by measuring directly the amplitude or phase of an intensity-modulated output light signal. However, because optic modulators are unstable, the high frequency intensity-modulated signals or polarization modulation signals generated thereby are prone to errors. Although a relatively high modulating frequency and relatively high stability can be achieved when optical heterodyne interference is generated in conjunction with acousto-optic modulators, the interferometer is very sensitive to disturbance from the outside environment, which can lead to limitations in the measuring precision of the system.
In co-pending U.S. patent application Ser. No. 08/967,691, there is disclosed a method and apparatus for determining the concentration of an optically active substance in a medium. In the disclosed method, a laser beam with two eigen modes of two different frequencies and two orthogonal linear polarized states is generated and passed through the medium. Then, the laser beam that exits the medium is passed through an analyzing polarizer so as to generate an optical heterodyne of the orthogonal linear polarized states. The amplitude of the optical heterodyne is detected for subsequent conversion into the concentration of the optically active substance in the medium. The method and apparatus are suitable for noninvasive in vivo glucose monitoring of the aqueous humor in an eye of an animal.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an optical rotation angle polarimeter that can be used to measure the optical rotation angle introduced by optically active materials or substances, that is not easily disturbed by the outside environment, that has a relatively simple construction, that can achieve relatively high measuring precision, and that can permit real-time optical rotation angle measurement to monitor a physical property of the optically active materials or substances, such as the refractive index of solid optically active materials or the concentration of optically active substances in a medium.
More particularly, the object of the present invention is to provide an optical rotation angle polarimeter that utilizes a two-frequency laser with two orthogonal linear polarized states as a light source, in conjunction with a polarized beam splitter to generate an optical heterodyne interference signal, whose amplitude is subsequently measured to obtain the optical rotation angle.
According to the present invention, an optical rotation angle polarimeter is used to investigate optical activity of a test object, and comprises:
a two-frequency laser source for generating a laser beam with two eigen modes of two different temporal frequencies and two orthogonal linear polarized waves, the laser beam to be passed through the test object;
a polarized beam splitter adapted to receive and split the laser beam, which exits the test object, into first and second orthogonal optical heterodyne interference X-axis and Y-axis components;
first and second photo detectors, each of which receives a respective one of the first and second orthogonal optical heterodyne interference X-axis and Y-axis components from the polarized beam splitter and generates a corresponding optical heterodyne interference signal;
a signal processor, connected to the first and second photo detectors, for combining the optical heterodyne interference signals therefrom so as to obtain an optical heterodyne interference output; and
an amplitude detector for detecting amplitude of the optical heterodyne interference output, which serves as a measure of the optical activity of the test object.
Preferably, a computer is connected to the amplitude detector, and converts the amplitude of the optical heterodyne interference output detected by the amplitude detector into an optical rotation angle introduced by the test object into the laser beam that passes therethrough.
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Chou Chien
Han Chien-Yuan
Kuo Wen-Chuan
Chou Chien
Font Frank G.
Natividad Phil
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