Unlike conventional balanced receivers, the Nirvana’s electronic gain compensation automatically results in balanced detection, even if the average optical intensities on the two detectors are different and time-varying. The auto-balancing technology allows elimination of background noise from dynamically changing systems, including thermal drifting and wavelength dependence, enabling you to achieve the perfect power balance between reference and signal beams.

Newport's balanced optical receivers are ideal for optical detection applications that require sensitive measurements and increased signal-to-noise. Balanced photodetection is a method that can very effectively cancel common mode noise and detect small signal fluctuations on a large DC signal. Detection methods in the time domain (such as femtosecond ultrasonics and frequency modulation spectroscopy) and frequency domain (like absorption spectroscopy), and coherent heterodyne detection (such as optical coherence tomography) can be substantially improved by using Newport balanced photoreceivers and can allow detection of signals not otherwise possible with other means. For more information, please see our application note A Survey of Methods Using Balanced Photodetection.

Nirvana photoreceivers operate in signal mode, balanced mode, or auto-balanced mode. The output of the photodetector (A) can be expressed as A=(IS – g x IR) x Rf. Here, IS the signal photodiode current, IR is the reference photodiode current, Rf is the value of the feedback resistor, and g is the current-splitting ratio, which describes how much of the reference current comes from the subtraction node (Isub) and how much comes from ground. In signal mode, g is zero and no reference photocurrent comes from the subtraction node. Here, the output A is simply an amplified version of the signal current. In balanced mode, g is equal to 1, and all the reference photocurrent comes from the subtraction node. In this mode, A=(IS–IR)•Rf, the photodetector behaves as an ordinary balanced photoreceiver, where laser noise is cancelled if the DC photocurrents are equal. In auto-balanced mode, g is electronically controlled by a low-frequency feedback loop to maintain equal DC photocurrents cancelling laser noise regardless of the photocurrent.