ElectroOptical Innovations Consulting

Phil Hobbs's Optics Page

News      Last major update: April 22nd, 2010.
Forthcoming Product: Ultrasensitive photoreceiver
Besides the do-it-yourself photoreceivers below, I am introducing a new line of electro-optical products in cooperation with a cutting-edge instruments company in California. The first product is a shot-noise limited free space photoreceiver with quantum-limited sensitivity from 30 nW to 100 μW and an honest 1 MHz bandwidth. For photocurrents below a microamp, it's even better than the bootstrapped cascode, and it comes in a nice module you can buy. More information in a few weeks.

I can often be found on the Usenet groups sci.electronics.design, sci.optics, and alt.lasers. Those are great places to talk about optics and electronics, if you have a reasonably thick skin and a mailer with decent spam filters. Talk to you there!

Resources from Usenet newsgroup sci.electronics.design
Cover
A volume in the John Wiley Series In Pure And Applied Optics: Second Edition, July 2009:

  Building Electro-Optical Systems:,
    Making It All Work, Second Edition

Praise for the First Edition:
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....
-- Prof. A. E. Siegman, Optics & Photonics News
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.
-- Bob Pease, Electronic Design
A look inside: Reviews:

Corrections to the First Edition:


Practical lore is useful only when it's correct, so careful attention to detail and prompt reporting of any errata is very important. Nothing is too small to be worth fixing. Errata are listed by the last printing in which they appear.

Consulting Services

In my years as a physicist and engineer at IBM Research, I have done small amounts of free, nonconfidential consulting for the many people who have asked me. This continues unchanged, but now in addition I am able to take on larger, fee-based engagements as a consultant, including confidential ones. 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 38 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 development projects appear below.

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. I've done groundbreaking work in thermal infrared imaging, in situ particle detection, computer input devices, simulation software, spectroscopy, atomic and magnetic force microscopy, heterodyne interferometry, trace metal detection, photolithography, laser scanning, plasmonics, and silicon photonics. I also have expertise in disk drives, quantum computing, inspection systems, and semiconductor processing.

I started EOI in February 2009. On the design side, my customers to date are mainly startup companies: three in biomedical instruments, building spectroscopic and optical coherence sensors for glucose, blood alcohol, and heart surgery; a European manufacturer of computer displays; and two others making laser microphones, acoustic, seismic, and gravity sensors; as well as larger firms in the defense and consumer products industries. I am also introducing a line of electro-optical instruments in cooperation with a cutting-edge instruments company in California. On the litigation side, I've done both patent infringement and trade secret misappropriation cases.

If you have a tough technical problem and need the right solution fast, give me a call at 845-480-2058 (9-6 Eastern time, preferably). As always, the first hour or two is free, so don't hesitate to call, e-mail, or tell a colleague. I'm always interested to hear what folks are working on.

Antenna-Coupled Tunnel Junctions for Optical Interconnection


At the IBM T. J. Watson Research Center, my colleagues and I combined 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 um region. This is the project that POEMS was written for. We demonstrated the first waveguide-integrated ACTJ detectors, which have achieved a 40-fold increase in both response and sensitivity over any previous ACTJ detector.

The details of the junctions and fabrication procedures are here.

Mode field picture

POEMS: Programmable Optimizing Electromagnetic Simulator


    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 microns square by 20 microns long. This requires multiprocessor capability and subgridding, i.e. different places in the simulation domain having different cell sizes. This is a challenge in FDTD, which naturally likes uniform cubical grids.
Lens design programs and circuit simulators have optimization capability--given a decent starting point (which may be hard to find sometimes), they will automatically adjust the lens prescriptions or circuit constants to achieve best performance by some criterion set by the user.
POEMS is a very capable FDTD simulator that brings this optimizing capability to the full EM world. It's currently fully operative, and I've been using it to design waveguide-coupled antennas. The current version uses either the well-tested Berkeley TEMPEST 6.0 FDTD code or my own clusterized FDTD code for its number crunching engine. Here's the manual.

Current Status (05/01/09):

The POEMS clusterized FDTD engine was working on a 14-Opteron processor IBM eServer 325 cluster until I left IBM at the end of February, 2009. On a 2-processor Xeon machine running a 1.5 GB simulation of a silicon waveguide, POEMS runs > 2.5x faster than the single-processor version of TEMPEST 6.0 (Intel C++ 7.1, all optimizations on). It now runs inhomogeneous cubical meshes stably, subgridding by factors of 2, 3, 4, or 5 at any given rectangular box boundary. The subgrids can themselves be subgridded if desired. There remain some residual problems where material boundaries cross mesh-size changes. When this is fixed, POEMS will be the only FDTD code I know of that will run arbitrary cubical subgrids.

Scaling performance on this small cluster was excellent, with less than 30% deviation from linear scaling of the single-machine version, due primarily to communications latency over the 1 Gb/s Ethernet connections. The reason for the speed appears to be that my code precomputes a strategy, which allows a very clean inner loop iterating over a list of 1-D arrays, whereas TEMPEST has a big switch statement inside its inner loop, making optimization and caching much more difficult.

Please e-mail me if you'd like to try POEMS.

Laser Noise Cancellers

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. These papers discuss simple circuits (would you believe 1 dual op amp and 3 transistors?) that can improve the quality of laser measurements enormously.
These 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). 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.

Low-Noise Photodiode Front Ends

Photodiodes are essentially perfect transducers--one photon gets you one electron. So why are photodiode front ends so hard to design well, and how can we get better results? These papers present garden-variety op-amp transimpedance amplifier (TIA) design rules, so that you can design your own shot-noise limited front end. When that isn't enough, you might want to try an unusual solution, the cascode transimpedance amplifier, or even the bootstrapped cascode transimpedance amplifier. Sometimes these circuits can get you a factor of 10 in bandwidth over the best-possible op-amp TIA, while staying at the shot noise level.

ISICL: In Situ Coherent Lidar for Submicron Particle Detection


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 particles 0.2 micron or even smaller, as they float around in the plasma. An interesting combination of homodyne interferometry, laser noise cancellation, and signal processing allows reliable operation at the shot noise limit in the face of a coherent background 106 times larger than the signal and an incoherent background 1010 times larger.

A $10 Thermal Infrared Imager


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 (there's also a mirrored version.)

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.


Mosaic image from 6 Footprints sensors, showing four people wandering underneath. Slightly smoothed to reduce the visual noise from all the little squares.

Heterodyne Confocal Microscopy


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 half the wavelength--ultraviolet resolution from a visible-light scope. Would you believe 90 nm 10%-90% edge rise intervals with almost no overshoot, at 514.5 nm wavelength? In air?
Read on.
hobbs @ electrooptical.net


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