>Conversion relationship between line width frequency Hz and length nm
A very important parameter for narrow linewidth lasers is line width. FWHM can be used to quantify line width, that is, Full width at half maximum, the full width at half maximum of the light pulse.
Line width can be expressed in either frequency (MHz or kHz) or length (nm). The specific conversion relationship is as follows:
Speed of light: c
Coherence length: △ x
; (1) c = v * λ ;
* λ )*△ λ ; (2) △ v = c / ( λ * λ ) * △ λ ;
(3) △ x = c / △ v
Where Δv is the line width expressed in Hz, and Δ & lambda; is the line width expressed in nm.
For example: a narrow linewidth laser with a wavelength of 1550nm. If the linewidth is expressed in Hz as 100Mhz, the conversion is expressed in nm as 0.0008nm and the coherence length is 3m. This is a very narrow linewidth laser. However, the narrower laser line width can currently reach 5Khz.