The performance of an erbium-doped fiber (EDF) ring laser based intra-cavity gas sensor is investigated theoretically
and experimentally. A theoretical model for analyzing the effects of the EDF parameters and the system parameters on
the performance of this gas sensor was established using coupled rate equations and propagation equations. We
investigated a number of specific cases and suggested practical choices of their parameters. Experiments with two cavity
losses were conducted to test the system sensitivity enhancement and the trend of the results matched well with the
theoretical prediction. The results showed sensitivity enhancement factors ranged from 17-20 in the experimental system
can be achieved.
We present recent work and progress on Spectrally Coded Multiplexing (SCM). SCM as a generic multiplexing
technique adds new dimension of freedom and provides additional flexibility and channel capability needed for fibre and
fibre grating based sensor systems. We show a few examples of our newly developed SCM techniques based on
specially designed fibre gratings.
Fiber laser gas sensors based on the intra-cavity absorption spectroscopy require the use of gas cells. We propose a
simple and reliable gas cell using graded-index fiber lens (GFL) based all-fiber collimator. Conventional gas cells
usually utilize direct fiber-to-fiber coupling without collimators or graded-index (GRIN) lens as collimators. Direct fiberto-
fiber gas cell has simple configuration, but it suffers from high coupling loss and stray light interference. Gas cells
applying fiber pigtailed GRIN lens are advantageous to achieve low coupling loss. However, fiber pigtailed GRIN lens
requires accurate and complicated alignment and glue packaging which could compromise long term reliability and
thermal stability. The proposed technique fabricates all-fiber collimators by simply splicing a short section of gradedindex
fiber to single mode fiber which is both compact and durable. With that collimator, the gas cell can be fabricated
very thin and are suitable for extreme environments with high temperature and vibration. In this paper, we have carried
out experiment and analysis to evaluate the proposed technique. The coupling efficiency is studied versus different GFL
gradient parameter profiles using ray matrix transformation of the complex beam parameter. Experiments are also done
to prove the practical feasibility of the collimator. The analysis indicates that gas cell using GFLs can overcome the
disadvantages of traditional design; it may replace the conventional gas cells in practical applications.
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