We have proposed a novel evanescent field (EF) sensor without any additional functionalized material. The sensors were
fabricated by single mode fiber with a etched section on it. We study the properties of the optical intensities out of the
sensors in the condition of immersing them in water, placing into a vacuum chamber or a climatic chamber. It was
demonstrated that this EF sensors can senses the changes of the RI of water surrounding it. And the change of the output of
the sensors occurs with a oscillation mode. We also show that the EF sensor with 11μm of outer diameter is sensitive to a
change of RI with a magnitude of power of negative 7. Using this type of sensor, we demonstrate the vacuum sensing in the
range from 20 to 300Pa. It is also demonstrated that the output of the sensors can be obviously attenuated by the scattering
of the water vapor surrounding the sensing section. With adequate design of fiber, we believe that the new EF sensors can
offer a platform on which the EF directly interacts with the materials of liquid or gas surrounding the sensing section and
give the information of the changes in the RI of the materials and the scattering or obsorption to the evanescent field.
A new type of evanescent field sensors based on a doubly cladding single mode fiber is proposed. The theoretical
analysis shows that the measurable refractive index (RI) ranges for the sensors are limited in the single mode in the fiber
becoming leaky and the range is less than the RI difference between the core and the cladding of the fibers. Two
temperature sensors and a humidity sensor were fabricated. One temperature sensor showed a good linear response in a
range of 60°C, the modulation depth of 40 dB, and the insertion loss of -1.4 dB. The humidity sensors fabricated by
agarose gel had a measurable moisture range of 16 ~ 100% of RH. Its optical power variation with humidity is 8.5 dB
and insertion loss is 3.9 dB. We confirmed that the DC single mode fiber sensors became a new type of intensity sensors
characterized in good linear response, low insertion loss, high modulation depth, and low cost in fabrication.
Prisms are involved in many instruments of measurements of refractive indices. The optical feedback effect in a
semiconductor laser introduced by the reflection of a prism was applied to the determination of zero incident angle.
Without any additional optical components or calibration setups the angular resolution reached 0.00074°. This approach
was used in refractometers and prism coupling system. Prisms, water, wintergreen oil and a quartz plate were measured
by total internal reflection technique and the optical feedback effect. In the measurement of prism, we proposed that the
base angle of a detected prism should be appropriately prepared so as that the refractive index of an isosceles prism
made of any material can be precisely measured. The results for a SrTiO3 prism with a base angle 30.0169 degree was
2.3780 at 659 nm. The measurements of water and wintergreen oil were performed by a reference prism made of SrTiO3.
We found that the result for a quartz plate wouldn't be influenced by the index matching liquid between the plate and a
reference prism, which was intentionally introduced, only if the index of the liquid was larger than that of the quartz. The
refractive index of a polymer film was measured accurately and the maximum of deviation from mean was ±0.0001.
Fiber optical evanescent field sensors provide means of optical power sensitive to temperature. This paper proposed a
novel and practicable fiber optical temperature sensor with doubly cladding structure. It worked on the basis of optical
attenuation brought about by the outer cladding medium with a large thermooptic coefficient. As the external diameter of
the sensing section was less than 1mm, the sensors were sensitive to the temperature of ambient air. The doubly cladding
fiber optical sensors with different fabrication characteristics (basically length and the diameter of inner cladding of the
sensing section) and external medium were studied experimentally. The sensor obtained by an outer cladding of Dow
Corning OE-4110 showed a low insertion loss of -0.7dB, a peak value of power loss of -66dB at 51°C, and a linear
dynamic range of -53dB for a temperature interval of 5°C at 1550nm. The sensor obtained by SILRES®Ren60 had the
peak value of power loss at about 105°C and a temperature interval of 65°C in a linear dynamic range of -5 dB.
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