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. Typically, all optical fibers used in the
pitch side optical system are single mode optical fibers.