Lab equipment/NE43500

NE43500

Description

NE43500 is a differential photocurrent amplifier that outputs both photocurrent difference and sum. With the sum output. The reason to have the sum output is to cancel the laser power noise when the polarimeter is misbalanced. The polarization rotation angle $\varphi$ can be found as:

${\frac {\Delta }{\Sigma }}=\tan \varphi$,

Where $\Delta$ is the difference and $\Sigma$ is the sum of photocurrents.

Schematics

• File:20161003135550907.pdf

Daniel Thrasher says these are sketches from the SPICE simulation code. The first is the completed circuit, the other two are the custom op am simulators that Bob rigged up in order to make a better simulation of the circuit as a whole.

Circuit boards

We have several PCBs of this device. The boards are using tiny components, including surface mount 0204 elements. This makes the boards hard to handle and impossible to modify. We need to redesign the PCBs so that they have more reasonable size.

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  Newer version

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  Older version

Problems

Zack mentioned that this board doesn't have enough gain and that it exhibited some drifts.

Daniel Thrasher says there are the following problems with this circuit:

1. The response was not as advertised. We found that the when we modulated the light incident on one of the photodiodes, the response of the difference output fell much more quickly then the 200 kHz advertised (I cant remember its 3 dB point, but I am sure it is on the myNotebook website). We found this was the case even with smaller (lower capacitance) photo diodes. This bandwidth was also dependent on the size of the beam incident on the photo detectors. This disqualified the detector for the NMR gyro because we needed a higher bandwidth.
2. Investigations with you and Ibrahim revealed that despite excellent noise suppression with the Griffiths, the detection noise did not decrease. We concluded that this was because the noise we were measuring was honest to goodness polarization noise although its source was not clear (fibers, optics, convection currents, etc).