High performance fiber optic sensor
First Claim
1. A method for measuring high frequency analog signals of low amplitude using optical sensors to convert such signals into electrical signals containing the analog information comprising the steps of:
- (a) arranging a fiber optic coil made of single mode fiber optic material so as to have optical path modified by the analog signals;
(b) using polarizing preserving fibers made out of single mode fiber optic material in said fiber optical coil to operate as a depolarizer;
(c) Injecting counter rotating beams of low coherence light into the coil to be modulated by the analog signals;
(d) converting the light beams into electrical signals containing the analog information; and
(e) demodulating the electrical signals to recover the analog information.
2 Assignments
0 Petitions
Accused Products
Abstract
An optical sensor and method for measuring naturally occurring phenomena such as vibrations is disclosed. An optic fiber is wound as a coil and placed such that strain is introduced in it by the phenomena. Low coherence light is launched through a coupler and split to produce counter rotating beams in the coil. The counter rotating beams are phase modulated by an optical modulator driven by an oscillator and by naturally occurring phenomena. The sensitivity and response of the sensor increases dependent on the length of fiber in the coil and improves linearly as the frequency of source signal increases. The modulated counter rotating beams are recombined in the coupler to produce an intensity modulated optical signal on a photodetector. The output of the detector is an electrical signal containing the signal of interest as modulation which is recovered througth demodulating circuits mixing the fundamental and second harmonic frequencies.
23 Citations
14 Claims
-
1. A method for measuring high frequency analog signals of low amplitude using optical sensors to convert such signals into electrical signals containing the analog information comprising the steps of:
-
(a) arranging a fiber optic coil made of single mode fiber optic material so as to have optical path modified by the analog signals; (b) using polarizing preserving fibers made out of single mode fiber optic material in said fiber optical coil to operate as a depolarizer; (c) Injecting counter rotating beams of low coherence light into the coil to be modulated by the analog signals; (d) converting the light beams into electrical signals containing the analog information; and (e) demodulating the electrical signals to recover the analog information. - View Dependent Claims (2, 3, 4)
-
-
5. A sensor for measuring high frequency analog signals for low amplitude comprising in combination:
-
fiber optic sensing means comprising a coil of single mode of fiber optic material, the optical path length of which may be altered by the analog information, said coil including polarization preserving fibers made out of single mode fiber optic material arranged as a depolarizer; (b) a source of low coherence light; (c) optical interferometer means including said fiber coil for splitting and applying a beam of low coherence light from said source to each end of said coil such that counter rotating beams thus produced are modulated by the analog signals; (d) means for combining said counter rotating beams of light and converting them into electrical signals containing the analog information; and (e) demodulating means for recovering the analog information as electrical signals. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13)
-
-
14. A sensor for measuring high frequency analog signals of low amplitude such as a source of vibrations comprising in combination:
-
fiber optic sensing means including at least one fiber optic coil wound on a spool, with the spool connected to be affected by said analog signals to strain the fiber optic, said fiber optic sensing means including a depolarizer made out of single mode fiber optic material; (b) a source of low coherence light including means for injecting light from said source into both ends of said fiber optic coil as counter rotating beams and for combining said beams to produce an optical output signal, said means also including an optical modulator driven at a reference frequency to phase modulate one of said counter rotating beams; (c) photodetector means receiving said optical output signal and converting same into an electrical signal containing the analog information; and (d) demodulator means receiving the electrical signal and including means for splitting the electrical signal into a reference frequency and a second harmonic and recombining the signals to recover the analog information as an output signal.
-
Specification