Apparatus for enhanced evanescent field exposure in an optical fiber resonator for spectroscopic detection and measurement of trace species
An apparatus for detection and measurement of trace species in a gas or liquid sample. A sensor of a ring down cell formed from an optical fiber is exposed to the sample gas or liquid. A coherent source emits radiation into the optical fiber loop, which in turn is received at an output coupler. The fiber optic ring is coupled to a sensor which has a portion thereof, between the input and output, exposed to the sample gas or sample liquid. The sensor has an enhanced evanescent region. A processor is coupled to the receiver and determines the level of trace species in the gas or liquid sample based on the rate of decay of the radiation within the fiber optic ring.
1. A sensor for detection of trace species in at least one of a sample gas and a sample liquid, for use in cavity ring down spectroscopy comprising, the sensor comprising:
a continuous closed passive optical fiber ring having an first inner core and a cladding with respective first diameters;
a tapered portion formed from and in line with the optical fiber, the tapered portion having a second inner core and cladding with respective second diameters,
wherein the diameter the second inner core is less that the diameter of the first inner core, the diameter of the second cladding is less than a diameter of the first cladding, and the tapered portion is exposed to the at least one sample liquid and sample gas to detect the trace species.
2. The sensor according to claim 1 , wherein an evanescent field of the tapered portion is greater than an evanescent field of the optical fiber.
3. A sensor for detection of trace species in at least one of a sample gas and a sample liquid, for use in cavity ring down spectroscopy comprising, the sensor comprising:
a continuous closed passive optical fiber ring having an inner core and a first cladding with respective first diameters;
an abraded portion formed from and in line with the optical fiber ring, the abraded portion having a cladding with a substantially “D” shaped cross section,
wherein the abraded portion is exposed to the at least one sample liquid and sample gas to detect the trace species.
4. The sensor according to claim 3 , wherein an evanescent field of the substantially “D” shaped potion has a greater exposure to the trace species that an evanescent field of the optical fiber.
5. A sensor for detection of trace species in at least one of a sample gas and a sample liquid, for use in cavity ring down spectroscopy comprising, the sensor comprising:
a continuous closed passive optical fiber ring having an inner core and a first cladding with respective first diameters;
a tapered portion formed from and in line with the optical fiber ring, the tapered portion having the inner core and a second cladding, the second cladding having a diameter less than the diameter of the first cladding,
wherein the tapered portion is exposed to the at least one sample liquid and sample gas to detect the trace species.
6. The sensor according to claim 5 , wherein an evanescent field of the tapered portion is greater than an evanescent field of the optical fiber.