Arduino's "analog outputs" actually are pulse width modulation, that is, the "analog voltage" is in reality the average value of an input that rapidly switches between 0 V and 5 V. The frequency of this switching is generally fixed while the duty cycle, that is, the relative duration of "on" and "off" changes. I've never heard "chirp" used to describe this, rather "chirp" is a time varying frequency.
PWM can be used to vary the intensity of a LED and is in fact one of the basic examples provided with the IDE. Without knowing your application, it's not clear whether is satisfies your particular need. To the human eye, such an LED can be indistinguishable to one driven by a fixed current, but to a faster receiver it looks like a series of pulses.