Heterodyne interferometric optical fiber displacement sensor for measuring displacement of an object

A heterodyne interferometric optical fiber displacement sensor, comprising:

• a laser diode;
• a modulation current generating means for outputting a modulation current whose value varies periodically at an internal of T.sub.s (in frequency f.sub.s);
• first, second, and third optical fibers;
• a first lens for guiding a laser beam from said laser diode to the tip of said first optical fiber;
• an optical fiber coupler that optically couples said first, second, and third optical fibers, said optical fiber coupler routing light transmitted through said first optical fiber to said second optical fiber, and also routing light returned through said second optical fiber to said third optical fiber;
• a second lens that is attached to the tip of said second optical fiber, and that reflects part of light at the exit surface and transmits the remaining light which will irradiate an object surface;
• a photoelectric transfer device that is attached to the tip of said third optical fiber and that photoelectrically transfers incident light coming through said optical fiber;
• a divider that divides the output of said photoelectric transfer device by the output of said modulation current generating means;
• a bandpass filter for extracting a frequency component, whose center frequency is nf.sub.s that is n-fold of the frequency f.sub.s of said modulation current, from the output of said divider;
• a first pulse output means that outputs a pulse signal having a frequency which is m-fold of the frequency of the output wave of said bandpass filter;
• a second pulse output means that outputs a pulse signal having a frequency which is m-fold of the same frequency as said frequency nf.sub.s ;
• and
• a counter for accumulating the difference in frequency between pulse signals provided by said first and second pulse output means, which is attributable to the relative movement between said second lens and said object surface.

A heterodyne interferometric optical fiber displacement sensor, comprising:

• a laser diode;
• a modulation current generating means for outputting a modulation current whose value varies periodically at an interval of T.sub.s (in frequency f.sub.s);
• first, second, and third optical fibers;
• a first lens for guiding a laser beam from said laser diode to the tip of said first optical fiber;
• a first photoelectric transfer device that is contained in the package of said laser diode and that photoelectrically transfers the laser beam from said laser diode;
• an optical fiber coupler that optically couples said first, second, and third optical fibers, said optical fiber coupler routing light transmitted through said first optical fiber to said second optical fiber, and also routing light returned through said second optical fiber to said third optical fiber;
• a second lens that is attached to the tip of said second optical fiber, and that reflects part of light at the exit surface and transmits the remaining light to provide parallel light which will irradiate an object surface;
• a second photoelectric transfer device that is attached to the tip of said third optical fiber and that photoelectrically transfers incident light coming through said third optical fiber;
• a divider that divides the output of said second photoelectric transfer device by the output of said first photoelectric transfer device;
• a bandpass filter for extracting a frequency component, whose center frequency is nf.sub.s that is n-fold of the frequency f.sub.s of said modulation current, from the output of said divider;
• a first pulse output means that outputs a pulse signal having a frequency which is m-fold of the frequency of the output wave of said bandpass filter;
• a second pulse output means that outputs a pulse signal having a frequency which is m-fold of the same frequency as said frequency nf.sub.s ;
• and
• a counter for accumulating the difference in frequency between pulse signals provided by said first and second pulse output means, which is attributable to the relative movement between said second lens and said object surface.

A heterodyne interferometric optical fiber displacement sensor, comprising:

• a laser diode;
• a modulation current generating means for outputting a modulation current whose value varies periodically at an interval of T.sub.s (in frequency f.sub.s);
• first, second, and third optical fibers;
• a first lens for guiding a laser beam from said laser diode to the tip of said first optical fiber;
• an optical fiber coupler that optically couples the backs of said first, second, and third optical fibers, said optical fiber coupler routing light transmitted through said first optical fiber to said second optical fiber, and also routing light returned through said second optical fiber to said third optical fiber;
• a second lens that is attached to the tip of said second optical fiber, and that reflects part of light at an exit surface and transmits the remaining light which will irradiate an object surface;
• a photoelectric transfer device that is attached to the tip of said third optical fiber and that photoelectrically transfers incident light coming through said third optical fiber;
• a bandpass filter for extracting a frequency component, whose center frequency is nf.sub.s that is n-fold of the frequency f.sub.s of said modulation current, from the output of said photoelectric transfer device;
• a first pulse output means that outputs a pulse signal having a frequency which is m-fold of the frequency to the output wave of said bandpass filter;
• a second pulse output means that outputs a pulse signal having a frequency which is m-fold of the same frequency as said frequency nf.sub.s ;
• and
• a counter for accumulating the difference in frequency between pulse signals provided by said first and second pulse output means, which is attributable to the relative movement between said second lens and said object surface.