To eliminate the problems associated with manually balancing the reference and signal beams, Nirvana Auto-Balanced Optical Receivers feature a built-in low-frequency feedback loop that controls the electronic gain of one of the receivers and maintains automatic balance between signal and reference arms. You can effectively eliminate laser-intensity noise and make shot-noise limited measurements without using lock-in amplifiers and optical choppers.
Reduces common-mode noise by up to 50 dB
Maintains automatic DC balance between reference and signal arms
The Nirvana’s patented circuitry subtracts the reference and signal photocurrents, canceling noise signals that are common to both channels. This allow you to measure signal power with 50 dB less noise for the 125 kHz model and 25 dB less noise for the 1 GHz model than in a single-beam experiment.
Maintains Automatic DC Balance Between Reference and Signal Arms
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.
400-1070 nm or 800-1700 nm Versions
Two Nirvana photoreceivers are offered covering the 400-1070 nm or 800-1700 nm spectral ranges.
Auto-Balanced or Manual Balanced Modes
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.
The feedback loop in the Nirvana™ photoreceiver splits the reference photodetector current, IR, to generate the cancellation photocurrent, Isub. When the DC value of Isub equals the signal current, IS, the laser-amplitude noise is cancelled.
Ideal for Balanced Photodetection
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.
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