1837 gets self adjusted or AUTOBALANCED (b) to improve signal purity compared to an unbalanced case (a)Auto-balancing circuit reduces noise by 50 dB so you can see your signal
Maintains automatic DC balance between reference and signal arms
Ideal for spectroscopy
Auto balanced or manual balanced modes
Uncompromised gain and bandwidth
Nirvana is a state of enlightenment characterized by the absence of the “noise” of worldly distractions. We named our auto-balanced photoreceiver “Nirvana” because its auto-balancing circuit lets you see the light even with the noisiest of lasers.
The Model 1837 Nirvana is the only photoreceiver in the world capable of automatic balancing. Our 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. And now we have achieved much higher bandwidth with uncompromising gain with our new GHz Nirvana Photo-receiver. The GHz Nirvana Photoreceiver also has a manual balancing option and fiber coupling, giving flexibility to your experiment.
1837 gets self adjusted or AUTOBALANCED (b) to improve signal purity compared to an unbalanced case (a)
The Models 2007 and 2017 auto-balanced photoreceivers can cut the effects of laser noise by 50 dB, making even very small signals easy to see. In spectroscopy, ellipsometry, or heterodyne-detection experiments, these photoreceivers can yield shot-noise-limited performance without the need for lock-in amplifiers or high-frequency modulation.
The auto-balancing circuit uses a low-frequency feedback loop to maintain automatic DC balance between signal and reference arms. In effect, the circuit behaves as a variable-gain beamsplitter. This, in conjunction with the subtraction node, cancels common-mode laser noise with greater than 50-dB rejection at frequencies less than 125 kHz. With the Nirvana photoreceiver, you won’t have to operate in the RF regime to avoid unwanted laser noise. And you can adjust the loop bandwidth for your particular application.
This auto-balancing circuit, invented by Phil Hobbs of IBM, is shown schematically on the next page. It consists of two photodiodes, a current splitter, a current subtraction node, a trans-resistance amplifier, and a feedback amplifier.
The photoreceiver operates in three distinct modes—signal mode, balanced mode, and auto-balanced mode. The output of the photodetector (A) can be expressed as A=(IS – g x IR) x Rf. Here, IS 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.
An FC-receptacle design allows for FC-fiber as well as free-space input, giving you added flexibility. To ensure safe operation, we strongly recommend our Model 0901 power supply.
The detected noise level with and without the auto-balancing circuit. The auto-balancing circuit reduces the detection noise floor by 50 dB. The red curve represents the shot-noise limit for the given input power.
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.