General Error-Signal-Generation Schemes | TOPTICA Photonics AG

Considering a spectral peak, e.g. obtained from the transmission through a spectroscopy cell or through an optical resonator, a straight forward way to obtain an error signal is to add or subtract a constant offset. Figure 5 illustrates this scheme. Then there will be two zero crossings, one at the left and the other at the right side of the peak. In the vicinity e.g. of the left zero crossing, the signal will be positive if the frequency is larger than the frequency at the zero crossing and the signal will be negative if the frequency is smaller than the frequency at the zero crossing. Consequently this can be used as an error signal for stabilizing the laser to the frequency at the zero crossing. Because the laser will be locked to the side of the peak, this locking scheme is called side-of-fringe locking. A problem of this scheme is that amplitude fluctuations will cause the position of the zero crossing to fluctuate, i.e. the lock will convert amplitude noise of the laser into freq

Considering a spectral peak, e.g. obtained from the transmission through a spectroscopy cell or through an optical resonator, a straight forward way to obtain an error signal is to add or subtract a constant offset. Figure 5 illustrates this scheme. Then there will be two zero crossings, one at the left and the other at the right side of the peak. In the vicinity e.g. of the left zero crossing, the signal will be positive if the frequency is larger than the frequency at the zero crossing and the signal will be negative if the frequency is smaller than the frequency at the zero crossing. Conseq