Recent Projects

Internal Developments

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.)

PMTs have been around since the 1930s, and remain the undisputed champs for the very lowest light levels.  We love PMTs, but we have to admit that they're delicate and not that easy to use—they tend to be bulky, they need high voltage, and they need regular replacement.  Most of all, PMTs are very expensive.

In Part 1, we discussed ways to get better measurements by improving the signal to noise ratio (SNR), and saw that although it was often a win to measure more slowly and use lowpass filters, going too far actually makes things worse, because of the way noise concentrates at low frequency.  Here we introduce a more sophisticated approach that generally works better: the lock-in amplifier.

In building an ultrasensitive instrument, we're always fighting to improve our signal-to-noise ratio (SNR).  The SNR is the ratio of signal power to noise power in the measurement bandwidth, and is limited by noise in the instrument itself and the noise of any background signals, such as the shot noise of the background light or the slight hiss of a microphone. 

Thermoelectric (Peltier) Coolers

A thermoelectric cooler is a solid-state device made from two alumina ceramic plates with an array of metallized pillars in between.  The pillars are also ceramic--they're made of alternating p-type and n-type bismuth telluride (Bi₂Te) semiconductors, alloyed with antimony telluride (p-type) or bismuth selenide (n-type), and connected in series electrically.  The Peltier effect makes them electric-powered solid state heat pumps.   (Thermocouples work the other way round, via the Seebeck effect, but the physics is the same.)

At EOI, we've been building advanced instruments for a long time. One reason for our success is our large inventory of working designs, and another is the way we go about doing it. This post walks through a typical sort of development plan for a challenging customer requirement, in the form of a hypothetical email proposal outline for a fibre-coupled noninvasive glucose sensor similar to the one we did in 2013.
(You can also read about a recent project that went a lot like this, except with a single prototype stage.)

Drift and 1/f Noise at 70-90 °C
Sometimes you have to find out things that aren't in the datasheet, and even the manufacturer may not know.

Thermoacoustic fridges are magic: you heat one end, and the other end gets cold. (Of course you have to sink all that heat from the middle.) They can easily be made long and skinny, and so are a natural for use down drillholes. They're also made entirely of metal, and have no moving parts, so they will survive bouncing around in the back of a truck.

Use of my laser noise canceller to achieve shot-noise limited performance in SPR spectroscopy (in cooperation with Xi Wang and Andre Knoesen of UC Davis, and a bunch of my friends at IBM Almaden Research Center).

This was a photon budget for an OCT system—interesting primarily for the effect of path delay in turning FM noise in the superluminescent diode (SLD) into AM noise in the measurement.

This was for a midsize start-up making very large, high resolution touchscreen displays—they needed an outside pair of eyes to do some sanity checking of a couple of their proposed designs.

This was a patent and trade secret case concerning lidar (laser radar) technology for self-driving cars and trucks.  It was the biggest case I've worked on, with potential damages over $2 billion, and also one of the most fun.  I was the defendant's expert on the patent side, and we beat Google--they dropped all their patent assertions.  (This was made a lot easier by the fact that Uber wasn't infringing, of course.) 

In the spring of 2017, I was approached by lawyers from two technology companies working in civil avionics (instruments for airplanes).  I can't say who they were due to NDA restrictions, but the job was an unusual and interesting one.  The two companies had been joint development partners, but the relationship had soured and trust had now broken down completely.  Both were concerned that the other was misusing intellectual property disclosed during the joint venture, and they asked me to do do an audit to see whether this was in fact true.  The situation was made more complicated because one company was several hundred times as large as the other, and of course there was no court-ordered discovery and no one was under oath.

Testifying defense expert representing Samsung in an action for patent infringement concerning optical storage, holographic optical elements, tracking servos, and signal integrity.

This was another fun one with a lot of reverse engineering.  This time round I was working with the plaintiff, Industrial Technology Research Institute, which is a research lab owned by the Taiwanese government.  It was an action for patent infringement in the focusing and tracking servos of optical disc drives, as well as in the arrangement of the laser sources.  The patent claims at issue concerned the way the magnetic "voice coil" actuators simultaneously adjusted focus, tracking, and tilt, so I needed to take several of the accused products apart and run the head servos by themselves in my lab.  I also had to cut apart some of the coils to show how they were wired, and decap the lasers to show that there were two chips side-by-side in the CD/DVD source and one in the BluRay source.

Testifying expert representing ThinkOptics in an action for patent infringement concerning video games, specifically the human interface of the Nintendo Wii.
February 15, 2015: Settled after an inter partes re-examination.