Signal-to-Noise Ratio on ElectroOptical Innovations

Laser Noise Cancellers

Tue, 10 Dec 2019 02:08:57 +0000

Laser noise is very often the primary limiting factor in making high-accuracy optical intensity measurements. There are ways of making your laser quieter, but they won’t get to the shot noise level. On the other hand, what we actually measure is the photocurrent, not the laser power, and that we can improve.

Laser Noise Cancellers are extremely powerful devices that allow us to make shot-noise limited measurements at baseband, even with very noisy lasers. With zero adjustments, they will reliably suppress the effects of laser residual intensity noise (RIN) by 55 or 60 dB from dc to several megahertz, and with a bit of (optical) tweaking, will do 70 dB or more at low frequency, which is where it’s most needed (see the picture above, which shows > 70 dB suppression of noise intermodulation). There’s a New Focus app note which surveys applications of noise cancellers.

The laser noise canceller has two operating modes, linear and log-ratio. The linear mode produces a replica of the photocurrent minus the noise. The log ratio mode also suppresses the intermodulation of the laser noise with the signal, allowing (for example) tunable diode laser spectroscopy to achieve 1-ppm sensitivities even when the laser power is varying by >30% over a scan line, as shown here.

SiPM Module

Wed, 24 Feb 2021 20:21:59 +0000

Specifications


3dB Bandwidth	From DC–200 kHz to DC–300 MHz
Rise Time	4ns (highest bandwidth configuration)
Gain Control Method	Gain settable by serial or analog voltage. Analog voltage control profile mimics behaviour of similar PMT modules.
Detector Type	Hammamatsu S13361/S13362 series or On Semi MicroFC series SiPm
Coupling	DC
Output Impedance	50 Ω
Dynamic Range	All configurations support analog and photon counting
Power Requirements	+5V 100mA, -5V 10mA
Signal Output	SMA
Applications	Flow cytometry, Microplate readers, TOF Lidar

In the last year or two we’ve been doing a lot of work aimed at replacing photomultiplier tubes (PMTs) in instruments, using avalanche photodiodes (APDs) and silicon photomultipliers (SiPMs). These devices are arrays of single-photon detectors, so they’re also known as multi-pixel photon counters (MPPCs). Our main application areas include biomedical instruments such as flow cytometers and microplate readers, which have to measure low light levels very precisely but don’t need the ultralow dark current of PMTs. (Follow-on articles will talk about our SiPM work in airborne lidar and SEM cathodoluminescence, as well as on improving the performance of actual PMTs.)