System and method for controlling the light source of a cavity ringdown spectrometer

1 ) A cavity ring-down spectrometer comprising:

i) a resonant optical cavity comprising at least two high reflectivity mirrors;

ii) a source for providing a continuous wave optical signal into said optical cavity, said source comprising an electrically pumped semiconductor gain medium;

iii) a SOA interposed between said optical signal source and said optical cavity said SOA receiving said optical signal from said optical signal source and transmitting it to said resonant optical cavity;

iv) a first detector for monitoring the intensity of radiation emitted from said cavity and generating a first detection signal based thereon;

iv) at least a first controller for deactivating said optical signal based on a comparison of said first detection signal and a predetermined threshold and for thereafter reactivating said optical signal after a delay period in excess of the ring-down time for said optical cavity, said deactivating and reactivating being achieved by respectively turning off and then turning on electrical current to said SOA.

2 ) A cavity ring-down spectrometer in accordance with claim 1 wherein said optical signal source comprises at least one Distributed Bragg Reflector (DBR) or a Distributed Feedback Diode (DFB) laser.

3 ) A cavity ring-down spectrometer in accordance with claim 1 wherein said optical signal source comprises an array of fiber coupled lasers.

4 ) A cavity ring-down spectrometer in accordance with claim 1 wherein said optical signal source comprises an array of lasers integrated on a single chip.

5 ) A cavity ring-down spectrometer in accordance with claim 2 wherein said optical signal source is a broadly tunable DBR laser.

6 ) A cavity ring-down spectrometer in accordance with claim 2 wherein said optical signal source is a narrowly tunable DFB laser.

7 ) A cavity ring-down spectrometer in accordance with claim 1 wherein said optical signal source and said SOA are copackaged.

8 ) A cavity ring-down spectrometer in accordance with claim 1 wherein said laser and said SOA are integrated on a single chip.

9 ) A cavity ring-down spectrometer in accordance with claim 1 wherein said detector comprises a photodiode or avalanche photodiode.

10 ) A cavity ring-down spectrometer in accordance with claim 1 which comprises the following additional components:

v) a monitor for measuring the wavelength of the reactivated optical signal and generating a second detection signal based thereon;

vi) a second controller coupled to said monitor which second controller adjusts both the temperature of, and the current to, said gain medium to thereby achieve a desired emission wavelength;

vii) means for adjusting the beam path length of the optical cavity to bring it into resonance with said desired emission wavelength.

11 ) A cavity ring-down spectrometer in accordance with claim 10 wherein said current to said gain medium is terminated by shunting the current to an alternative medium.

12 ) A cavity ring-down spectrometer in accordance with claim 10 wherein said monitor comprises an etalon, a beam splitter and a pair of photodiodes.

13 ) A cavity ring-down spectrometer in accordance with claim 1 wherein said resonant optical cavity comprises three or four mirrors.

14 ) A cavity ring-down spectrometer in accordance with claim 10 wherein said second controller includes means for substantially continuously monitoring the temperature of the gain medium, and look-up tables indicating the temperature and current required to cause a desired laser emission wavelength.

15 ) A cavity ring-down spectrometer in accordance with claim 10 , wherein said means for adjusting the beam path length of the optical cavity comprises a piezo-electric transducer capable of translating one of the cavity mirrors.

16 ) A cavity ring-down spectrometer in accordance with claim 1 wherein said optical signal source comprises a broadly tunable, external cavity diode laser.

17 ) A cavity ring-down spectrometer in accordance with claim 1 wherein said SOA is a Fabry-Perot or Traveling-wave SOA.

18 ) A cavity ring-down spectrometer in accordance with claim 1 wherein said SOA is a strained layer multi-quantum well SOA.

19 ) A method for detecting the presence of an analyte in a resonant optical cavity comprising at least two high reflectivity mirrors, said method comprising the steps of:

i) directing a continuous wave optical signal from an electrically pumped semiconductor gain medium through a SOA and thence into said optical cavity;

ii) detecting radiation emitted from said optical cavity through one of said mirrors and comparing the intensity of said emitted radiation with a predetermined threshold value;

iii) based on said comparison, generating a control signal which interrupts said optical signal into said optical cavity by terminating the flow of current to, or reverse biasing, said SOA for a period which is at least in excess of the ring-down time for said cavity;

iv) reactivating said current flow to said SOA to thereby again direct said optical signal into said optical cavity.

20 ) A method in accordance with claim 19 wherein said current flow is deactivated for a period of at least about three ring-down times.

21 ) A method in accordance with claim 19 comprising the additional steps of:

v) monitoring the wavelength of said optical signal;

vi) adjusting the temperature of, and current to, the source of said optical signal to thereby cause it to emit a signal having a desired wavelength;

vii) adjusting the beam path length of said optical cavity by translating at least one of said mirrors to thereby bring said cavity into resonance with said desired wavelength optical signal