Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-01-19
2001-09-11
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Input/output coupler
C385S073000, C385S074000, C385S075000, C385S033000, C385S900000
Reexamination Certificate
active
06289149
ABSTRACT:
FIELD OF THE INVENTION
The field of the invention is spectroscopy, in particular, infrared spectroscopy.
BACKGROUND OF THE INVENTION
Infrared (IR) spectroscopy typically involves the transmission of light of a range of infrared frequencies through a sample, resulting in the detection of the absorption of certain frequency components by certain materials thereby indicating the presence of those components in the sample. It has been found that a “mid-IR” range of frequencies, corresponding to 2.5-25 microns in wavelength or 4000-400 in wavenumbers, is particularly useful for analyses of oils, lubricants, and beverages, particularly dairy products.
Remote infrared spectroscopic monitoring using optical fibers is useful in spectroscopy, as discussed, for example, in U.S. Pat. No. Re. 33,789 to Stevenson, U.S. Pat. No. 5,076,243 to Bornstein, U.S. Pat. No. 5,239,176 to Stevenson, U.S. Pat. No. 4,852,967 to Cook, and U.S. Patent No. 5,585,634 to Stevenson et al. The material being analyzed or monitored may be gaseous, liquid, or solid, and sampling may be readily performed outside the sample compartment of a conventional spectrometer thus permitting in situ, real-time spectroscopic measurements and eliminating the need to transport a sample to the spectrometer.
The components for a transmitting light in the mid-IR through a traditional transmission cell containing a sample are expensive, including expensive antireflection-coated germanium/zinc selenide lenses to collimate the light directed to the sample and the light transmitted from the sample. Moreover, such components are difficult to handle, requiring relatively precise alignment, but being prone to scratching and breaking.
Other solutions such as the use of parabolic mirrors also required relatively precise alignment, which presented problems in an industrial process environment where mid-IR spectroscopy can be put to good use.
Non-imaging concentrators, comprising highly reflective internal conical or compound parabolic surfaces have been used to collimate IR light in spectroscopy, for example, the “System Having Non-Imaging Concentrators for Performing IR Transmission Spectroscopy,” disclosed in U.S. Pat. No. 5,254,858, issued Oct. 19, 1993, to Wolfman et al. That system, however, calls for the use of two concentrators tapered towards each other to collimate a light source and does not appear adapted to an in-process configuration.
SUMMARY OF THE INVENTION
The invention, specifically adapted to an environment of samples taken in-process with varying viscosities and at various pressures, is a structure enclosing a sample cell, defined further by parallel infrared transmitting windows, through which sample fluid is circulated, and symmetric compound parabolic, concentrators abutting each of the parallel infrared transmitting windows at the wider ends of the concentrators. Fiber optic cables are connected to the narrower ends of the concentrators to an optical connection to a light source and detector. Ingress and egress fittings are provided in the structure to allow the input and output of the sample fluid.
In a preferred embodiment, one or more circumferential channels are provided in the cell cavity to facilitate circulation of more viscous sample fluids. Shafts in the structure may be provided to accommodate heating elements and a temperature sensor. Thus, the invention provides a robust and modular structure that is well suited for in-process use in industrial processes.
It has been found that the invention not only enjoys a significant cost advantage over the traditional lens approach, but performs 10-100 times better in the mid-IR region in terms of definition of percentage transmission of relevant absorption peaks. It has also been found that the invention does not suffer from interference patterns (manifested as “wiggles”) observed in the lens approach. Other advantages will be apparent from the detailed description and drawings.
REFERENCES:
patent: 4496787 (1985-01-01), Touchais et al.
patent: 5477322 (1995-12-01), Malinen
patent: 6163641 (2000-12-01), Eastgate
patent: 6219140 (2001-04-01), Kaplan
Curtiss Lawrence E
Druy Mark A.
Glatkowski Paul J.
Chow Stephen Y.
Font Frank G.
Foster-Miller Inc.
Mooney Michael P
Perkins Smith & Cohen LLP
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