  We investigate the coherent population trapping resonance induced by a
polychromatic optical field with an asymmetric spectrum, i.e., whose sidebands
equidistant from the carrier have unequal powers. A situation is considered
where a modulation is used to provide the so-called in-phase and quadrature
signals in the optical field's transmission, which are used for stabilization
of the local oscillator's frequency in chip-scale atomic clocks. In a general
case, the frequencies of the signals nonlinearly depend on the optical field's
intensity due to the asymmetry of the resonance. In this work, we demonstrate
a) that this effect stems from a multi-peak structure of the resonance; b) a
linear dependence of the frequency on the optical field's intensity at high
modulation values; c) that the regime of the resolved structure has more
advantages than suppression of the frequency shift due to the spectrum
asymmetry.
