We study the quiet Sun magnetic fields using spectropolarimetric observations of the infrared and visible Fe i lines at 6301.5 , 6302.5 , 15648 and 15653 Å .
Magnetic field strengths and filling factors are inferred by the simultaneous fit of the observed Stokes profiles under the MISMA hypothesis .
The observations cover an intra-network region at the solar disk center .
We analyze 2280 Stokes profiles whose polarization signals are above noise in the two spectral ranges , which correspond to 40 % of the field of view .
Most of these profiles can be reproduced only with a model atmosphere including 3 magnetic components with very different field strengths , which indicates the co-existence of kG and sub-kG fields in our 1 \farcs 5 resolution elements .
We measure an unsigned magnetic flux density of 9.6 G considering the full field of view .
Half of the pixels present magnetic fields with mixed polarities in the resolution element .
The fraction of mixed polarities increases as the polarization weakens .
We compute the probability density function of finding each magnetic field strength .
It has a significant contribution of kG field strengths , which concentrates most of the observed magnetic flux and energy .
This kG contribution has a preferred magnetic polarity , while the polarity of the weak fields is balanced .