Optical arrangement for determining the concentration of a substance in a fluid

1. An arrangement for determining a concentration of at least one substance in a fluid, the arrangement comprising:

a light source coupled to a pulse generating means, so that the light source generates primary light pulses within at least one wavelength interval comprising at least one predetermined wavelength that is absorbed differently in the fluid depending on the concentration of said substance;

a light pulse splitter coupled with an input terminal to the light source, said light pulse splitter to split the primary light pulses into at least one secondary light pulse comprising the at least one predetermined wavelength, said secondary light pulse(s) are separated in time as well as wavelength;

means for transmitting said secondary light pulse(s) via an output terminal of the light pulse splitter through the fluid;

a detector to detect the intensity of the secondary light pulse(s) of the at least one predetermined wavelength which have been at least partly absorbed in the fluid;

a reference light pulse generating device coupled between the output terminal of the light pulse splitter and the detector to generate at least one reference intensity that bypasses the fluid without passing through a reference sample, the at least one reference intensity comprising the at least one predetermined wavelength, and having a delay in time relative to the at least one secondary light pulse; and

a comparator connected to the detector to compare the intensity of the secondary light pulse(s) with the at least one reference intensity comprising the at least one predetermined wavelength to thereby determine the concentration of said at least one substance in the fluid.

2. The arrangement according to claim 1 , wherein the light pulse splitter is interconnected between optical fibres by one of a fibre optical circulator and an optical coupler.

3. The arrangement according to claim 1 , wherein the reference light pulse generating device comprises an optical fibre.

4. The arrangement according to claim 1 , wherein the light pulse splitter comprises at least one fibre Bragg grating for reflecting the at least one predetermined wavelength.

5. The arrangement according to claim 4 , wherein the at least one fibre Bragg grating is terminated by a low reflection termination.

6. The arrangement according to claim 1 , further comprising a measuring cell for the fluid to pass through, said measuring cell comprising a hollow fibre.

7. An arrangement for determining a concentration of at least one substance in a fluid, the arrangement comprising:

a light source coupled to a pulse generating means, so that the light source generates primary light pulses within at least one wavelength interval comprising at least one predetermined wavelength that is absorbed differently in the fluid depending on the concentration of said substance;

a reference light pulse generating device coupled to the output terminal of the light source to generate a second set of primary light pulses that bypass the fluid without passing through a reference sample, said reference light pulse generating device generating the second set of primary light pulses within a predetermined wavelength interval comprising the at least one predetermined wavelength, said second set of primary light pulses having a delay in time in comparison with the first set of primary light pulses;

a light pulse splitter to receive the primary light pulses which have been at least partly absorbed in the fluid and the second set of primary light pulses, said light pulse splitter to splits the primary light pulses which have been at least partly absorbed in the fluid into at least one secondary light pulse comprising the at least one predetermined wavelength, said secondary light pulse(s) are separated in time as well as wavelength, said light pulses splitter also splits the second set of primary light pulses into at least one reference intensity comprising the at least one predetermined wavelength;

a detector to receive the at least one secondary light pulse and the at least one reference intensity from the light pulse splitter, said detector to detect the intensities of the at least one reference intensity and the secondary light pulse(s) of the at least one predetermined wavelength; and

a comparator connected to the detector for comparing the intensities of the secondary light pulse(s) with the at least one reference intensity comprising the at least one predetermined wavelength to thereby determine the concentration of said at least one substance in the fluid.

8. The arrangement according to claim 7 , wherein the light pulse splitter is interconnected between optical fibres by one of a fibre optical circulator and an optical coupler.

9. The arrangement according to claim 7 , wherein the reference light pulse generating device comprises an optical fibre interconnected between optical fibres.

10. The arrangement according to claim 7 , wherein the light pulse splitter comprises at least one fibre Bragg grating for reflecting the at least one predetermined wavelength.

11. The arrangement according to claim 10 , wherein the at least one fibre Bragg grating is terminated by a low reflection termination.

12. The arrangement according to claim 7 , further comprising a measuring cell for the fluid to pass through, said measuring cell comprising a hollow fibre.