Abstract: An optical flame-sensor includes an optical circulator, an optical-fiber cavity, and a first optical sensor. The optical circulator includes a first port, a second port, and a third port. The first port is configured to receive an optical signal. The second port is configured to output the optical signal received at the first port. The third port is configured to output the input to the second port. The optical-fiber cavity includes a cavity proximal-end optically coupled to the second port, and a mirror at a cavity distal-end, such that a cavity optical signal output by the optical-fiber cavity is the input to the second port. The first optical sensor is optically coupled to the third port to quantify the cavity optical signal.

Abstract: A method of sensing a process utilizing a sensing apparatus consisting of more than one diode laser having select lasing frequencies, a multiplexer optically coupled to the outputs of the diode lasers with the multiplexer being further optically coupled to a pitch side optical fiber. Multiplexed laser light is transmitted through the pitch side optical fiber to a pitch optic operatively associated with a process chamber which may be a combustion chamber or the boiler of a coal or gas fired power plant. The pitch optic is oriented to project multiplexed laser output through the process chamber. Also operatively oriented with the process chamber is a catch optic in optical communication with the pitch optic to receive the multiplexed laser output projected through the process chamber. The catch optic is optically coupled to an optical fiber which transmits the multiplexed laser output to a demultiplexer.

Abstract: A diode laser spectroscopy gas sensing apparatus having a diode laser with a select lasing frequency, a pitch optic coupled to the diode laser with the pitch optic being operatively associated with a process chamber and oriented to project laser light along a projection beam through the process chamber. This embodiment additionally includes a catch optic in optical communication with the pitch optic to receive the laser light projected through the process chamber and an optical fiber optically coupled to the catch optic. In addition, the catch optic is operatively associated with a catch side alignment mechanism which provides for the alignment of the catch optic with respect to the projection beam to increase a quantity of laser light received by the catch optic from the pitch optic and coupled to the optical fiber and a detector sensitive to the select lasing frequency optically coupled to the optical fiber.

Abstract: A pitch side optical system for use in diode laser spectroscopy consisting of more than one diode laser having select lasing frequencies with each diode laser being coupled to an end of a distinct input optical fiber. The pitch side optical system further consists of a multiplexer optically coupled to the other end of less than all of the input optical fibers with the multiplexer outputting multiplexed laser light to a pitch side optical fiber. The pitch side optical system further consists of a coupler optically coupled to the far end of the pitch side optical fiber and the far end of an unmultiplexed input optical fiber with the coupler combining the multiplexed laser light and the unmultiplexed laser light and outputting the combined light to a transmission optical fiber. Typically, the coupler is located near the combustion process. The pitch side optical system further consists of a pitch optic coupled to the transmission optical fiber.

Abstract: A catch side optical system for use in diode laser spectroscopy consisting of a catch side optic optically coupled to a catch side multimode optical fiber and means to mechanically manipulate a section of the catch side multimode optical fiber to minimize catch side mode noise. The mechanical manipulation may consist of twisting the catch side multimode optical fiber around its longitudinal axis. The means to mechanically manipulate the section of the catch side multimode optical fiber in the above fashion may consist of a motor associated with the catch side multimode optical fiber such that a section of fiber is held fast relative to a shaft position of the motor and the motor shaft is repetitively swept through +360 degrees and ?360 degrees of motion. The frequency of the motor shaft sweep may be at least 10 Hz to enable effective averaging of the transmitted signal and thereby reduce the effect of catch side mode noise.

Abstract: A sensing apparatus consisting of more than one diode laser having select lasing frequencies, a multiplexer optically coupled to the outputs of the diode lasers with the multiplexer being further optically coupled to a pitch side optical fiber. Multiplexed laser light is transmitted through the pitch side optical fiber to a pitch optic operatively associated with a process chamber which may be a combustion chamber or the boiler of a coal or gas fired power plant. The pitch optic is oriented to project multiplexed laser output through the process chamber. Also operatively oriented with the process chamber is a catch optic in optical communication with the pitch optic to receive the multiplexed laser output projected through the process chamber. The catch optic is optically coupled to an optical fiber which transmits the multiplexed laser output to a demultiplexer.