EOI is a well-equipped small technical house whose mission is to enable our customers to produce advanced measurement products for their customers. As technology developers we find imaginative solutions to hard measurement problems in very many areas of optics, electronics, photonics, and mixed-technology systems, both for customers and for our own proprietary developments, as well as doing extensive expert witness work in optics and electronics cases.
One problem that comes up again and again in doing measurements is that we need the apparatus to be quieter than the thing we’re measuring, ideally by at least a factor of two. Besides quiet, it should be wideband, have an accurately known gain that’s flat with frequency, have a clean step response, and generally do its job while keeping itself out of the way. There’s a wealth of detail in our app note AN-1
on photoreceiver testing.
A quick plug for a little gem of a book that all fans of early radio should know about: “Super-Regenerative Receivers” by J. R. Whitehead (Cambridge University Press, 1950). It’s part of the Modern Radio Techniques series, where a bunch of the technical movers and shakers document the advances that were made during the war, e.g. centimeter radar. This one is about the theory and practice of superregenerative radios. I learned a lot from it and had a lot of fun.
The need to control temperature is everywhere, but getting it right is more difficult than one might expect. A domestic furnace controlled by a simple thermostat keeps a house comfortable in winter, but the inside air temperature swings irregularly over a range of a few degrees. That’s fine for a house—you can have a New Year’s party, with a bunch of people dissipating a hundred watts each, doors to hot ovens and the cold outside opening and closing, no worries whatsoever. The heating system keeps it comfortable.
Building Electro-Optical Systems: Making it all Work
This book is an attempt to provide a systematic and accessible presentation of the practical lore of electro-optical instrument design and construction: in other words, it’s the book I needed as a graduate student, but couldn’t find.
It’s intended in the first instance for use by oppressed graduate students in physics and electrical engineering, who have to get their apparatus working long enough to take some data before they can graduate. When they do, they’ll find that real-world design work has much the same harassed and overextended flavor, so in the second instance, it’s intended as a self-teaching guide and professional reference for working electro-optical designers.
For the third edition (February 2022), the book has been fully revised, and is almost a third again the size of the second edition, besides bringing in things learned in twelve years of consulting with EOI. The large format also made it possible to include a revised and expanded version of the thermal control chapter
, which makes the printed book complete.
Now a new laboratory bible for optics researchers has joined the list; it is Phil Hobbs’ Building Electro-Optical Systems: Making It All Work, aimed at providing “accessible presentation of the practical lore of electro-optical instrument design and construction.” I predict it will move to the front of the shelf.
This is a wonderfully practical book…. [It] is also a wonderfully entertaining read….
I like this guy’s attitude. He points out how most scholars…never write about the troubles they had getting the apparatus to work right, or the changes they had to make to get valid data. Mr. Hobbs talks about exactly that. Good man. …[I]f you work in this field, you ought to buy this book. If you don’t work in this field, then you should still read it.
I got started in consulting during my 20 years as a Research Staff Member at IBM T. J. Watson Research Center. I began in the Manufacturing Research department, building special instruments for unique manufacturing problems for which commercial solutions did not exist, such as scanned-probe and solid-immersion microscopy, and in-chamber particle detection. I also did a fair amount of firefighting, retrofitting semiconductor lithography equipment for new capabilities, and helping fix problems that were causing immediate revenue loss in manufacturing. Later I developed new classes of computer input device, advanced scanning technology, and a new class of photonic detector and switch for optical interconnection, based on metal-insulator-metal tunnel junctions.
Front of Watson Research
The clear practical emphasis has never left me. One of the reasons that I wrote three editions of Building Electro-Optical Systems was to help people to build better products and apparatus while staying out of all the potholes in the road, and that’s why I love consulting as well.
I do design consultation, expert witness work (testifying and consulting in patent and trade secret cases), contract design engineering, debug, and system bring-up tasks, as well as training in ultrasensitive detection methods and front end design. I hold 43 US patents and several foreign ones, and am thoroughly familiar with the patent process, both in prosecution (i.e. obtaining a patent) and litigation. Some of my earlier research and development projects appear below, and there’s also a list of recent projects for clients.
I’m expert in the design, debug, and refinement of electrooptical and mixed-technology systems. I’m also a leading designer of ultrasensitive optoelectronics and other low noise analog circuitry. Many of my designs have improved the state of the art by orders of magnitude in performance, in cost, or both (see below). I’ve done groundbreaking work in thermal infrared imaging, in situ particle detection, computer input devices, simulation software, spectroscopy, atomic and magnetic force microscopy, solid immersion microscopy, heterodyne interferometry, trace metal detection, photolithography, laser scanning, plasmonics, and silicon photonics. I also have expertise in downhole instruments (especially stabilized lasers), disk drives, inspection systems, and semiconductor processing. There’s more detail in my resume, as well as on the patents page, the recent work page and in the papers linked below.
On the design side, our customers to date are a mix of start-ups and larger companies, including some of the largest companies in the electronics, defense, oil-field services, and semiconductor equipment industries. We’ve worked as subcontractor or consultant on four defense contracts, for DARPA, the Office of Naval Research, and the Army. Our recent work page has some more details, but of course NDAs and other contractual obligations limit how much we can say about most of them. We’re also introducing electro-optical instruments in cooperation with Highland Technology, a cutting-edge instruments company in California. On the intellectual property side, I’m a testifying expert witness in both patent infringement and trade secret misappropriation cases, with experience doing depositions, declarations, and expert reports, in both claim construction through validity or invalidity and infringement or noninfringement.
EOI is well-equipped for design, prototyping, and testing of optical, electronic, and mixed-technology systems of many kinds. If you have a tough technical problem and need the right solution fast, give me a buzz at the lab, 914-236-3005 (9-6 Eastern time, preferably). As always, the first hour or two is free, so if you’d like to discuss your application, you’re invited to call, e-mail
, or tell a colleague. I’m always interested to hear what folks are working on.
My silicon photonics work at IBM centred on the idea of integrating submicron silicon optical waveguides with metal plasmonic antennas and metal-insulator-metal (MIM) tunnel junctions, to build optical detectors and modulators in the 1.55 μm region.
The X-shaped antenna arms, with the plasmonic travelling-wave structure that eliminates the effects of capacitance at optical frequencies in the middle.
There are a variety of EM simulation schemes in wide use, with different strengths and weaknesses. For free-space antennas at radio frequency, where dielectrics are simple and metals are excellent conductors, integral equation schemes such as the method of moments (MoM) win. At optical frequencies, particularly when metal is involved, partial differential equation methods are generally better. The two most common PDE schemes are finite element method (FEM) and finite difference, time domain (FDTD). The antenna-coupled tunnel junction work required simulations with very fine resolution (1 nm) in some places, to represent plasmons and metal surface discontinuities, and a very large simulation domain, at least 5 μm square by 20 μm long. This requires multiprocessor capability and subgridding, i.e. different places in the simulation domain having different cell sizes. Subgridding is a natural strength of FE, but presents a challenge in FDTD, which naturally likes uniform cubical grids. On the other hand, mesh generation can be very time consuming, and FEM doesn’t clusterize as well as FDTD and is much harder to get correct.
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.
The definitive summary of my early work on noise cancellers: Six easily-constructed circuits that can improve the SNR of bright-field laser measurements by as much as 70 dB at low frequency and 40 dB out to 10 MHz. Bright field measurements at the shot noise limit become much easier.
The circuits are simple to construct (as simple as 1 dual op amp and 3 jellybean transistors), so anyone who can handle a soldering iron can improve the quality of his laser measurements enormously. Detailed applications advice is provided.
A word of caution: these circuits are easy to build but fairly hard to improve. Even if you want some custom tweaks, build the circuit as described, test it, and then change it around. You will have to add the usual 0.1 μF bypass caps on the supplies, and replace the discontinued Analog Devices MAT04 matched quad with the MAT14, but no other changes are necessary. Use ground plane construction, e.g. dead bug on a piece of Cu-clad FR4, or perf board style on a Vector 8007 protoboard, use nice quiet power supplies and/or capacitance multipliers, and don’t put the photodiodes on cables. Bring the beams to them, instead.
Other important points: put a polarizer right at the laser to eliminate the spontaneous emission in the orthogonal polarization state, since it doesn’t split the same way as the laser light, causing imbalance in the subtraction; and whatever you do, don’t vignette the beams after splitting them. (Applied Optics36, 4 pp 903-920 [1 February 1997]).
In my consulting work, I’ve extended laser noise canceller technology out to higher speeds (10-100 MHz) and wider photocurrent ranges.
Use of the log ratio version of the laser noise canceller to achieve 10-6 absorption sensitivity in current-tunable diode laser spectroscopy, even when the laser power changes by 30% over a scan. This is shown by the pictures at right. Using the well studied rovibrational spectrum of molecular iodine allowed us a simple demonstration system for a widely applicable technique, subsequently used in many instruments.
Popular article on the laser noise canceller, from Optics&Photonics News, April 1991. An updated and somewhat chattier version of the SPIE paper below, with more discussion of applications. (Optics & Photonics News2 4, pp. 17-23 [April 1991])
First description of the laser noise canceller, including comparisons with heterodyne systems and use with helium-neon lasers showing mode beat suppression by >50 dB.
Particles in plasma etch chambers are a major source of yield loss in semiconductor manufacturing. Particles condensing from the plasma or spalling out of films on the chamber walls are levitated in the edges of the plasma sheath for long periods, and then (too often) drop on the wafer when the plasma excitation is turned off.
Process control and tool utilization can both be improved by knowing what’s happening inside the chamber while the process is going on—but how? The plasmas are usually too bright to look at, and there’s only one (poor quality) window in the typical chamber, so an optical particle detector would have to work in backscatter, with a huge background.
ISICL is capable of seeing and mapping individual particles of less than 0.2 μm diameter, as they float around in the plasma, a unique capability.
Calculation vs experiment for the photon budget, signal processing, and detection strategy of the ISICL sensor. Shows that a photon budget is worth following, even in a complicated instrument used in hostile conditions.
Optical phase is a wonderful thing—it can get you good topographical images of samples with no discernible amplitude contrast, for example, or allow you to disambiguate phase features from amplitude ones. My interest in phase-sensitive microscopes dates back to my graduate work—hence this paper. It gives design details and the theory of the heterodyne scanning laser microscope, including the point- and line-spread functions, plus a deconvolution method that can give resolution equivalent to an ordinary microscope working at λ0/2—ultraviolet resolution from a visible-light scope. Operating with a green Ar+2 laser (514.5 nm) and 0.9 NA, it attained a 10%-90% edge resolution of 90 nm.
This works because the interferometer makes it a confocal microscope, i.e. its amplitude point-spread function is the square of the illumination PSF. By the convolution theorem of Fourier transforms, that means that its bandwidth is twice as wide, i.e. ±2NA/λ. A bit of digital filtering turns the resulting nearly-triangular transfer function into something a bit more Gaussian-looking, which gives us a factor of 2 resolution improvement. Unlike the usual image processing ad-hockery, Fourier filtering makes absolutely no additional assumptions about the sample; the additional information comes from measuring both phase and amplitude, which is why you need an interferometer.
A low-resolution thermal camera with competitive sensitivity (0.13 K NETD) at very low cost. Easily built from scratch—it requires no special parts, except a screen-printed sheet of pyroelectric PVDF polymer (as used in automatic porch lights) and a moulded polyethylene Fresnel lens. This camera achieves a cost reduction of 2 orders of magnitude ($10 vs $1000) over the next cheapest, which is a 256-pixel PZT array from Irisys, while maintaining very good sensitivity. These are from a project called Footprints.
The design is simple: screen-printed carbon ink on a free-standing film of PVDF polymer, with a multiplexer made out of ordinary display LEDs with a few interesting optical and electronic hacks, as shown in these photos.
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.)
I can often be found on the Usenet groups sci.electronics.design and sci.optics. (There’s not a lot of activity at sci.optics these days, but there are still folks listening who can help. SED goes up and down, but is much more active.)
Those are great places to talk about optics and electronics, if you have a reasonably thick skin. There are a lot of smart people there who know their stuff and can help you. The clearer and more concise the question, the more helpful the answer, in general.
Usenet is generally unmoderated, which is a good thing in a busy group, because it keeps the discussion flowing. There are a few flamers, whom it’s best to ignore.
(I used to hang out in alt.lasers as well, but the whole crowd moved to photonlexicon, which is more applications-oriented. The subreddit r/Optics has some knowledgeable folks too, if you like Reddit.)
Google Groups dropped Usenet support in February 2024, but it wasn’t great for real use anyway. You’ll need a mailer with decent filters, such as Thunderbird or Forte Agent.
