Highly stable broadband light source and suitable stabilization method therefor
A highly stable broadband light source includes a semiconductor light source having a specific emission spectrum, an optical filter having a specific bandpass filtering function and a predetermined bandwidth and a coupling element, to which the light emissions of the semiconductor light source and of the optical filter are fed. The light emission of the broadband light source occurs at the output of the coupling element. The spectrum of the light emission of the broadband light source is composed of the emission spectrum of the semiconductor light source and the bandpass filtering function of the optical filter. The wavelength of the optical filter is temperature-stabilized so that the spectrum of light emission of the broadband light source is essentially determined solely by the filtering function of the optical filter.
1. A highly stable broadband light source, comprising:
a semiconductor light source with a specific emission spectrum;
a number of optical filters having specific bandpass filtering functions and predetermined bandwidths;
a coupling element, to which the light emissions of the semiconductor light source and of the optical filters are fed and at the output of which the light emission of the broadband light source is effected,
the spectrum of the light emission of the broadband light source being composed of the emission spectrum of the semiconductor light source and the bandpass filtering function of the number of optical filters; and
the wavelengths of the number of optical filters being stabilized in such a way that the spectrum of the light emission of the broadband light source is essentially determined only by the filtering functions of the number of optical filters
characterized in that
the number of optical filters is two, and
two photodetectors are provided, one of which in each case is assigned to each optical filter and detects the spectrum transmitted by the assigned optical filter and feeds it to a divider, in which the detected spectra are compared.
2. The highly stable broadband light source as claimed in claim 1 , characterized in that the bandwidths of the optical filters overlap.
3. The highly stable broadband light source as claimed in claim 1 , characterized in that the divider is a digital signal processor or logarithmizer in which a quotient formation is effected for the intensities of the two spectra fed.
4. The highly stable broadband light source as claimed in claim 1 , characterized by a control device, which receives an output signal of the divider and controls the wavelength of the semiconductor light source with feedback in such a way that the intensities detected by the two photodetectors remain the same.
5. The highly stable broadband light source as claimed in claim 1 , characterized in that the semiconductor light source is a superluminescence diode.
6. The highly stable broadband light source as claimed in claim 1 , characterized in that the optical filter is a fiber Bragg grating operated in reflection.
7. The highly stable broadband light source as claimed in claim 1 , characterized in that the coupling element is a 2×2 coupler.
8. The highly stable broadband light source as claimed in claim 1 , characterized in that an optical isolator is arranged between the semiconductor light source and the coupling element.
9. The highly stable broadband light source as claimed in claim 1 , characterized in that the optical filters are two identical fiber Bragg gratings operated in reflection, of which one feeds its light emission to the coupling element directly and the other feeds is light emission to the coupling element via an optical delay line.
10. The highly stable broadband light source as claimed in claim 9 , characterized in that the length of the optical delay line is chosen such that a second coherence spike generated by the latter does not correlate with other light paths in the coupling element.
11. A method for highly stabilizing a broadband light source, comprising the following steps:
emission of light by means of a semiconductor light source with a specific emission spectrum;
emission of light by means of a number of optical filters with specific bandpass filtering functions and specific bandwidths;
coupling of the emitted light in a coupling element, to which the light emissions of the semiconductor light source and of the number of optical filters are fed and at the output of which the light emission of the broadband light source is effected,
the spectrum of the light emission of the broadband light source being composed of the emission spectrum of the semiconductor light source and the bandpass filtering functions of the number of optical filter; and
stabilization of the wavelengths of the number of optical filters in such a way that the spectrum of the light emission of the broadband light source is essentially determined only by the filtering function of the optical filters
characterized by the steps of:
choosing the number of optical filters to be two;
providing two photodetectors;
assigning a respective one of the optical filters to a respective one of the photodetectors and detecting the spectrum transmitted by the assigned optical filter;
feeding the spectrum to a divider; and
comparing the detected spectra in the divider.