Method for studying a sample and optical interferometer for doing the same
The present invention relates to the study of internal structure of objects by optical means. The invention presents a bi-directional sampling optical path for the low coherent optical radiation directed to the sample, i.e. a bi-directional sampling arm, and two unidirectional reference beams directed along a reference path designed as a loop. One of the reference beams propagates clockwise and the other propagates counterclockwise in the reference loop. The beam splitters non-reciprocal or polarization-dependent and by placing polarization-changing elements between the beam splitters and/or into the sampling arm and the reference loop. Thus the developed method and optical interferometer make possible to ensure highly efficient use of optical source power together with optimal signal-to-noise ratio for a given optical source power and are simple and cost effective.
1. A method for imaging a sample, comprising the steps of:
forming a low coherent optical radiation;
splitting the low coherent optical radiation into a first beam of low coherent optical radiation and a second beam of low coherent optical radiation;
splitting the first beam of low coherent optical radiation into a third beam of low coherent optical radiation and a fourth beam of low coherent optical radiation;
directing the third beam of low coherent optical radiation towards the sample under study along a bi-directional sampling optical path, wherein the third beam of low coherent optical radiation propagates along the bi-directional sampling optical path in a forward and a backward direction;
directing the second beam of low coherent optical radiation and the fourth beam of low coherent optical radiation along a reference optical path, wherein the reference optical path is formed as a reference loop, the second beam of low coherent optical radiation passes through the reference loop in a first direction, and the fourth beam of low coherent optical radiation passes through the reference loop in a second direction;
forming a first combination optical radiation by combining the third beam of optical radiation that having passed along the sampling optical path in a forward and a backward direction carries information about the sample with the second beam of optical radiation that has passed through the reference loop in the first direction;
forming a second combination optical radiation by combining part of the first combination optical radiation with the fourth beam of optical radiation that has passed through the reference loop in the second direction; and
visualizing the intensity of the third beam of optical radiation, that having passed along the sampling optical path carries information about the sample, by using either a signal of interference modulation of the intensity of the first combination optical radiation, or a signal of interference modulation of the intensity of the second combination optical radiation, or both.
2. The method of claim 1 , wherein the first direction through the reference loop is counter-clockwise and the second direction through the reference loop is clockwise.
3. An optical interferometer comprising:
a source of optical radiation;
a first beam splitter for splitting the low coherent optical radiation into a first beam of low coherent optical radiation and a second beam of low coherent optical radiation;
a bi-directional sampling arm;
a reference arm formed as a loop for low coherent optical radiation to propagate along the reference arm in a first and second opposite directions;
a second beam splitter for splitting the first beam of low coherent optical radiation into a third beam of low coherent optical radiation and a fourth beam of low coherent optical radiation and forming a first combination optical radiation by combining the third beam of optical radiation that has passed along the bi-directional sampling arm in a forward and backward direction with the second beam of low coherent optical radiation, that has passed along the reference loop in a first direction;
the first beam splitter being optically coupled to a sample through the ports of the second beam splitter, the first beam splitter forming a second combination optical radiation by combining part of the first combination optical radiation with the fourth beam of low coherent optical radiation that has passed through the reference loop in the second direction; and
at least one photodetector, wherein at least one of the beam splitters is connected to a respective photodetector.
4. The optical interferometer of claim 3 , wherein at least one of the arms of the optical interferometer comprises an optical delay line.
5. The optical interferometer of claim 3 , wherein at least one of the arms of the optical interferometer comprises a phase modulator.
6. The optical interferometer of claim 3 , wherein the sampling arm is provided with a probe located at its distal end.
7. The optical interferometer of claim 3 , wherein at least one of the arms of the optical interferometer is designed fiberoptic.
8. The optical interferometer of claim 3 , wherein at least one of the beam splitters is designed fiberoptic.
9. The optical interferometer of claim 6 , wherein the probe is made detachable and connected with the optical interferometer by a connecter.
10. The optical interferometer of claim 3 , wherein the first beam splitter is designed nonreciprocal.
11. The optical interferometer of claim 3 , wherein the first beam splitter is polarization-sensitive and the sampling arm is provided with a polarization switch.
12. The optical interferometer of claim 6 , wherein at least a part of the sampling arm comprising the probe is designed fiberoptic.