Fibre-grating-stabilized diode laser
First Claim
Patent Images
1. An optical feedback system comprising:
- a gain medium having a first optical cavity and having an output;
at least a first reflecting component in said first optical cavity and having an output facet providing a first reflectivity level for reflecting a portion of propagating light in said first optical cavity back into said cavity, said facet also providing a light output;
an optical fibre optically coupled to said first cavity to receive said light output;
a reflective element accompanying said optical fibre, said reflective element having a supplemental reflectivity level for reflecting a portion of said output over a narrow band of wavelengths back into said first cavity;
said supplemental reflectivity level approximately equal to or less than said first reflectivity level;
said fibre reflective element positioned in said optical fibre an optical distance from said first optical cavity sufficient to induce multiple longitudinal mode operation of said gain medium to suppress longitudinal mode hoping.
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Abstract
A fibre Bragg grating is used to stabilize the intensity and frequency fluctuations of a diode laser. The diode laser is connected with an opto-mechanical apparatus to the fibre which contains the grating. The grating is formed in the guided-mode region of the optical fibre. The wavelength of maximum grating reflectivity is selected to lie near the maximum of the diode laser gain bandwidth. The magnitude and bandwidth of the grating reflectivity stabilizes the diode laser output without appreciably reducing the optical output power from the end of the fibre. The bandwidth of the optical spectrum of the diode laser is selected depending on the distance of the grating from the diode laser.
78 Citations
63 Claims
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1. An optical feedback system comprising:
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a gain medium having a first optical cavity and having an output; at least a first reflecting component in said first optical cavity and having an output facet providing a first reflectivity level for reflecting a portion of propagating light in said first optical cavity back into said cavity, said facet also providing a light output; an optical fibre optically coupled to said first cavity to receive said light output; a reflective element accompanying said optical fibre, said reflective element having a supplemental reflectivity level for reflecting a portion of said output over a narrow band of wavelengths back into said first cavity; said supplemental reflectivity level approximately equal to or less than said first reflectivity level; said fibre reflective element positioned in said optical fibre an optical distance from said first optical cavity sufficient to induce multiple longitudinal mode operation of said gain medium to suppress longitudinal mode hoping. - View Dependent Claims (2, 3, 5, 6, 7, 8, 10, 13, 14, 15)
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4. An optical feedback system comprising:
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a gain medium having a first optical cavity and having an output; at least a first reflecting component in said first optical cavity and having a first reflectivity level; an optical fibre optically coupled to said first cavity; a reflective element accompanying said optical fibre, said reflective element having a supplemental reflectivity level for reflecting a portion of said output over a narrow band of wavelengths back into said first cavity; said supplemental reflectivity level approximately equal to or less than said first reflectivity level; said fibre grating positioned in said optical fibre an optical distance from said first optical cavity sufficient to induce multiple longitudinal mode operation of said gain medium; said gain medium is a semiconductor laser having a gain band at least a portion of which overlaps with said reflectivity band; said supplemental reflectivity level sufficient to induce coherence collapse in said laser. - View Dependent Claims (11)
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9. The optical feedback system of 8 wherein said reflective element has a reflectivity peak which is within 10 nm of the peak gain of said gain medium.
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12. An optical feedback system comprising:
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a gain medium having a first optical cavity and having an output; at least a first reflecting component in said first optical cavity and having a first reflectivity level; an optical fibre optically coupled to said first cavity; a reflective element accompanying said optical fibre, said reflective element having a supplemental reflectivity level for reflecting a portion of said output over a narrow band of wavelengths back into said first cavity; said supplemental reflectivity level approximately equal to or less than said first reflectivity level; said fibre grating positioned in said optical fibre an optical distance from said first optical cavity sufficient to induce multiple longitudinal mode operation of said gain medium; said gain medium is a semiconductor laser having a gain band at least a portion of which overlaps with said reflectivity band; said supplemental reflectivity level about 2 to 3 times less than said first reflectivity level.
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16. Apparatus for generating a stable laser source comprising:
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a laser source having a lasing cavity and a light beam output at a laser facet, said laser facet also providing a level of partial reflectivity for a portion of said light beam in said laser cavity for optical feedback therein, said light beam output comprising a wavelength band of light dependent upon the instantaneous operating characteristics of said laser source; an optical fibre having an input end coupled to said laser source to receive said light beam into said fibre; a grating formed in said optical fibre, said grating having a reflectivity band for partially reflecting selected wavelengths defined by said reflectivity band back into said laser cavity; the reflectivity level of said optical fiber grating being approximately equal to or less than the reflectivity level of said laser source facet; said fibre grating is sufficiently spaced from said laser source to induce multiple longitudinal mode operation of said laser source for enhancing optical spectrum stability and intensity. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24)
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24. The apparatus of claim 16 wherein the spacing of said grating from said fibre input end is greater than the coherence length of said light beam output.
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25. Apparatus for generating a stable laser source comprising:
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a laser source comprising a semiconductor laser having an output facet for reflecting a portion of propagating light in the laser cavity back into said cavity, said facet also providing a light output; a bias current means for excitation of said laser to operate over a bias current range within a given temperature range; an optical fiber optically coupled to receive said laser light output; a grating in said optical fiber providing partial reflection over a narrow band of wavelengths, said wavelengths at least partially overlapping the wavelength emission band of said laser, said reflection providing optical feedback to said laser; the bias current and temperature range of said laser and the reflectivity band of said grating selected so that said laser source operates in multiple longitudinal modes such that the longitudinal mode hopping noise of said laser source is reduced providing enhanced optical spectrum stability. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35, 36)
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26. Apparatus for generating a stable laser source comprising:
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a laser source comprising a semiconductor laser having an output facet for providing a light output; a bias current means for excitation of said laser to operate over a bias current range within a given temperature range; an optical fiber optically coupled to receive said laser light output; a grating in said optical fiber providing partial reflection over a narrow band of wavelengths, said wavelengths at least partially overlapping the wavelength emission band of said laser, said reflection providing optical feedback to said laser; the bias current and temperature range of said laser and the reflectivity band of said grating selected so that said laser source operates in multiple longitudinal modes such that the longitudinal mode hopping noise of said laser source is reduced; the reflectivity of said grating is less than or equal to the reflectivity of said laser output facet.
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37. Apparatus for generating a stable laser source comprising:
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a laser source having an output facet providing optical feedback and for providing an output, said output optically coupled to an optical fibre; a grating in said fibre providing a narrow wavelength band including wavelengths that are at least partially overlapping said wavelength emission spectrum of said laser source, absent said grating, and at least partially reflected to provide optical feedback to said laser source via said grating; separation between said grating and laser source and magnitude of optical feedback from said grating being selected such that said laser source is constrained to operate at the peak wavelength of said grating and within the multiple longitudinal modes of the grating bandwidth so that longitudinal mode hopping of said laser source is suppressed. - View Dependent Claims (38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 59, 60)
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48. Apparatus for generating a stable laser source comprising:
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a laser source having a lasing cavity and a light beam output at a laser facet, said output optically coupled to an optical fibre; a grating in said fibre such that a narrow band of wavelengths are reflected which at least partially overlaps a wavelength emission band of said laser source absent said grating; a reflectivity level of said grating being approximately equal to or less than a reflectivity level of said laser source output facet with said fibre grating spaced from said laser source for enhancing optical spectrum stability and intensity. - View Dependent Claims (49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 61, 62, 63)
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Specification