Mitigation of optical signal noise using a multimode transmit fiber

An apparatus for measuring a combustion parameter in a zone, the apparatus comprising:

• a laser generating a transmit beam of light of a select wavelength;
• a multimode optical fiber optically coupled to the laser;
• a transmitting/receiving optic optically coupled to multimode optical fiber;
• and
• a reflecting surface in the zone, the reflecting surface being constructed and arranged to reflect at least a portion of the transmit beam transmitted from the transmitting/receiving optic back to the transmitting/receiving optic;
• wherein the multimode optical fiber carries both the transmit beam and the at least a portion of the transmitted beam reflected back to the transmitting/receiving optic;
• and
• wherein the transmitting/receiving optic is configured to transmit the transmit beam into the zone, and receive the at least a portion of the transmitted beam reflected from the reflecting surface.

A method of measuring a property within a zone, the method comprising:

• transmitting a beam of light of a select wavelength through a multimode optical fiber and a transmit optic optically coupled to the zone;
• reflecting at a reflecting surface at least a portion of the transmitted beam to a receiving optic;
• receiving from the reflecting surface a reflection of the at least a portion of the transmitted beam with the receiving optic optically coupled to the transmit optic;
• the transmitting optic and the receiving optic being the same optic;
• and
• averaging modal noise induced signal level variations of the beam of light propagating within the multimode optical fiber.