Birefringent crystal Mach-Zehnder interferometer
Inventors
Assignees
Publication Number
US-9939249-B1
Publication Date
2018-04-10
Expiration Date
2037-01-30
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Abstract
A birefringent Mach-Zehnder interferometer (MZI) is provided for optically sensing a small fluctuation from an un-polarized light beam. The birefringent MZI includes first and second birefringent crystals arranged coaxially, the first crystal to receive the beam; and first and second 45° polarizers positioned behind respective the first and second crystals. The first crystal divides the beam into first ordinary and extraordinary rays. The first polarizer converts the first rays into first 45° rays. The second crystal divides the first 45° rays into second ordinary, extraordinary and recombination rays. The second polarizer converts the second rays into second 45° rays.
Core Innovation
The invention provides a birefringent Mach-Zehnder interferometer (MZI) designed for optically sensing small fluctuations from an un-polarized light beam. The birefringent MZI comprises first and second birefringent crystals arranged coaxially, where the first crystal receives the beam. The first crystal divides the beam into first ordinary and extraordinary rays, and a first 45° polarizer converts these rays into first 45° rays. The second crystal then divides the first 45° rays into second ordinary, extraordinary, and recombination rays, followed by a second 45° polarizer which converts these second rays into second 45° rays.
The problem addressed by the invention relates to conventional free-space Mach-Zehnder Interferometers which, although relatively simple, are typically not compact nor stable. This instability and lack of compactness arise from the opto-mechanical mounts used in conventional MZIs, which involve holders, springs, pivots, and micrometers mounted on optical tables with tapped holes. These mounts make alignment difficult, and the devices are not readily fieldable nor easily reproducible as sensors.
This invention solves the problem by utilizing birefringent crystals and a slotted base architecture to produce a free-space, compact, and stable MZI design. The birefringent crystals function to split and recombine polarized rays, and 45° polarizers erase path information to enable interference. The slotted base and matched cylindrical devices allow for rapid and convenient alignment by rotation, significantly enhancing both compactness and stability relative to conventional MZIs.
Claims Coverage
The patent contains one main independent claim that discloses several inventive features related to the optical components and arrangement of the birefringent MZI.
Coaxial arrangement of birefringent crystals and polarizers
The MZI comprises first and second birefringent crystals disposed coaxially with first and second 45° polarizers respectively positioned coaxially behind each crystal. A horizontal-and-vertical polarizer is disposed coaxially behind the second polarizer, followed by third and fourth birefringent crystals and a third 45° polarizer coaxially behind the fourth crystal.
Optical beam division and conversion by crystals and polarizers
The first birefringent crystal divides the un-polarized light beam into first ordinary and extraordinary rays. The first polarizer converts these rays into first 45° rays. The second birefringent crystal further divides these first 45° rays into second ordinary, extraordinary, and recombination rays, which are then converted by the second polarizer into second 45° rays. The combined action of the polarizers and crystals produces a pair of phase-shift rays.
Construction with specific crystal material and mechanical assembly
The crystals are composed of calcite. Crystals and polarizers are disposed within corresponding metal tubes where the crystals provide a square internal cross-section and the polarizers provide a circular cross-section to facilitate assembly and alignment.
The main inventive features cover the specific coaxial arrangement of birefringent crystals and polarizers that manipulate the polarization components of the light beam to produce phase-shift rays, as well as the material composition and mechanical packaging that enable the MZI's compactness and stability.
Stated Advantages
Enhanced performance via stability compared to conventional free-space MZIs.
Compact and stable design facilitating easier field deployment and reproducibility as sensors.
Rapid and convenient alignment achieved by rotation of cylindrical devices in a slotted base.
Documented Applications
Sensing and measuring extremely small fluctuations such as refractive index changes related to density changes in fluid flow (gas or liquid), heat transfer, and temperature distribution in plasmas.
Potential use in improvements in interference sensors and quantum optics.
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