The Original Low-Latency, High-Throughput, Real-Time Interface

Choosing Analog Hardware

As the world grows more digital, increasingly advanced communications interfaces have been instituted in PI nanopositioning and micropositioning controllers and many other instruments.  Even the new E-709 compact, cost-optimized digital nanopositioning controller comes complete with an SPI interface for command communications at the servo update rate of the controller (in addition to standard USB and RS-232 interfaces and a wealth of TTL trigger and synchronization lines).  We discussed some of the newest novel interfaces and their applications in the presentation linked in our earlier blog post, Gleanings from SMB 2011.

But it's important not to overlook the benefits of the original fast, deterministic, real-time interface: analog.  Most of our nanopositioning controllers are equipped with analog interfaces for position or autofocus command input, plus a feedback sensor monitor output (for closed-loop units).  Even our current-generation digital nanopositioning controllers feature analog I/O options across-the-board.

There are many compelling advantages to analog interfacing:

• Generating analog position steps and waveforms is very easy with today's software tools and powerful multifunction analog I/O hardware for personal computers.
• The most popular analog I/O products, from National Instruments, share a common software interface between models.  So software written for one model will work on other models and is readily transportable across operating systems.
• Highly synchronous multichannel I/O is readily achieved in any of the popular programming languages, meaning nanopositioning processes can be performed in parallel with process metrology-- essential for improving throughput in scanning and other high-dynamic processes.

Programming analog I/O is straightforward enough for most users to do from scratch if they need to, but PI's Analog GCS LabVIEW library eliminates even that.  This library is the industry's first plug-and-play LabVIEW library for instant productivity with analog-interfaced nanopositioning controllers.  It is available without charge and allows the use of the same comprehensive and well-thought-out selection of subVIs as used with any of our other controllers.  The GCS (General Command Set) approach means only the initialization subVI specifies an interface (for example RS-232, USB, TCP/IP, GPIB or in this case analog).  So you can move from PI product to PI product or interface to interface simply by swapping out the initialization subVI.  Functionalities in the Analog GCS LabVIEW library include point-to-point and waveform position generation with synchronous acquisition, a wealth of synchronization and triggering options, and much more.

As to hardware, this link will open a window to a National Instruments product selector page that presents a wide variety of analog multifunction devices suitable for most nanopositioning applications.  The following criteria were used:

1. At least one analog input for process metrology or sensor acquisition
2. At least one analog output for commanding the position of open- or closed-loop nanopositioners
3. Waveform output capability (versus static-only updates for some other models. 
4. Compatibility with the NI-DAQmx driver, the gold standard for analog I/O programming in any language.

Additional selectors are available to tailor the selection to your application needs and budget.

Although we can of course only test our Analog GCS LabVIEW library with a subset of NI's extremely broad offering, all the devices shown should work since all work with the NI-DAQmx driver.

If your budget allows, our top recommendation of all the current NI offerings is the top-of-the-line USB-6259 BNC (see photo).  This is a portable, self-contained USB unit capable of astonishing throughput and microsecond-scale synchronization-- performance that frankly took us aback when we first used it, as we expected the USB interface would be a bottleneck.  It has since been our recommendation for our CyberAligner high-throughput modular alignment engine since it also allows the workstation to be run from a laptop or virtual machine.  It offers sixteen 16-bit differential analog inputs with an acquisition rate of 1.25 mega-samples/sec and four 16-bit analog outputs with a blistering update rate of 2.8 mega-updates/sec.  That fast analog output speed makes it the ultimate choice for enhanced-resolution HyperBit applications, and we have achieved 27 bit positioning resolution using this unit.  Its integrated BNC connectors are convenient and eliminate having to purchase a cable and BNC box.

Of course, all that functionality may be overkill for your application and budget.  Fortunately there are plenty of other models with different form factors, fewer I/O options, different resolution, and more moderate speeds.  There is even an unpackaged OEM version of the USB-6259.

There's lots of life left in analog, a venerable and truly real-time interface.

Read these papers for the latest on high-througput digital interfacing.

• Interfacing Fast Nanopositioners to Track-Following Servos
•  High-speed, low latency communications for  nanopositioning in Single-Molecule Biophysics

Celebrating Twenty Years of Digital Photonic Alignment

A cost-effective, modular alignment engine is updated

The first digital gradient search technique was developed two decades ago to allow fiber optic devices to be efficiently aligned using the micropositioning devices of the day, which were low in speed, resolution and synchronization capabilities compared to today's piezoelectric nanopositioners.  Systems based on this technology were the earliest of a decade-long wave of offerings targeted at industrial automated alignment applications. 

As the telecom boom crested, we were approached by a leading industrial player to provide an especially cost-effective, robust and flexible alignment platform for coarse/fine alignment of photonic devices such as waveguides and laser diodes.  The desire was for a simple stack of stages based on our NanoCube XYZ nanopositioning stage, which provides 100 microns of travel in three orthogonal axes with 2nm resolution.  The customer specified that the software was to be modular, open-source and based on LabVIEW.

We reviewed this and similar applications, noting challenges like fiber-through-tube package designs and irregular coupling cross-sections.  We decided that comprehensive application coverage together with highly time-efficient throughput was possible with a sequence of two operations:

1. A space-efficient double-spiral-scan, using motorized long-travel stages, for first-light capture and rough optimization, followed by
2. An extremely fast raster scan with synchronous data acquisition to compile the transverse coupling cross-section and identify the global maximum.

An advantage of the raster scan approach versus established gradient search techniques was its insensitivity to local maxima in the coupling-cross-section; this option had been unavailable a decade earlier due to the limitations of the motion devices of that day.  Put plainly: since our piezo devices are so fast, why not collect lots of data to localize the global maximum directly rather than inferring the vector to it from the limited data older architectures could provide?

We called the result CyberAligner, and a YouTube video of it in action is still viewable (see below).

Recently this architecture enjoyed many advancements:

• An upgrade to LabVIEW 2010,
• Leveraging of the latest I/O capabilities provided by today's multifunction analog/digital hardware, including incredibly fast USB units,
• Motion code based on PI's GCS General Command Set, allowing any type of motorized stages to be used for first-light seek and coarse alignment: cost-effective stepper-motor, robust DC servo-motor, stiff and stable NEXACT^®, swift PILine^®... and whatever will come next.

The update virtually doubles CyberAligner's speed from the already blazingly-fast version shown in the video, now allowing a full-field scan-and-align on the order of 250 milliseconds.  The coupling cross-section data can be saved to a local or network drive, providing valuable process and device diagnostics in production.   All-USB configurations are featured, cabling is simplified, and multiple workstations can be run off of one PC.  Source-code, compiled and .dll versions of the modular workstation software are offered.

Today, as the twentieth anniversary of the first digital aligners dawns, the photonics industry is reawakening after years in the doldrums after the telecom bubble popped.  With CyberAligner as part of PI's broad toolkit of solutions including the popular F-206 HexAlign six-degree-of-freedom hexapod alignment microrobot, we look forward to meeting a new generation of device and applications challenges.

Updated Version for Silicon Photonics
For even higher performance applications such as industrial silicon photonics alignment sub-systems, a new system is now available.  Read more on Fast Optical Alignment for SiP Production

Gleanings from SMB 2011

PI's SMB 2011 presentation
on fast interfacing  techniques
is available at this link.

Every two winters the leaders in the field of Single Molecule Biophysics gather at the Aspen Center for Physics for a fast-paced five days of presentations, networking, discussions and the occasional slalom down Buttermilk. The topic: the very latest in research and experimental approach in this most demanding and promising of fields.

Most of us view chemistry as the bulk behavior of macroscopic quantities of chemicals that interact according to sensible rules based on mass conservation, valence properties, and so on. Single Molecule Biophysics (SMB) takes chemistry quite a few steps deeper, combining clever optical, biochemical, instrumentation and computing approaches to allow observation of the activities of individual molecules as they go about their work making things happen... this thing called life, for example.  SMB applications allow us to observe the transport, replication and transcription processes that occur continuously in every living cell.  They also illuminate the fundamental processes of what can go wrong with life as well. Observing molecular behavior is already revealing the molecular foundations of many diseases, including dread afflictions like cancer and Parkinson's disease. With understanding will come cures.

Clearly this field is among the most "nano" of nanotechnologies, placing severe demands on performance and stability of the coarse and fine positioning equipment that is the foundation for many SMB applications. For the past two conferences, PI has been proud to be a sponsor and participant. For 2011 we presented a non-commercial review of fast interfacing techniques that have proven valuable for extending the capabilities of SMB-class applications. This paper has been reformatted for easy viewing and is now available at this link.  Though it primarily spotlights SMB applications, we hope its information is valuable for any advanced application that can leverage interface throughput and determinacy.

2011's conference showed fascinating progress in the field, exemplified not only by the standing-room-only attendance and ongoing refinement of our understanding of the molecular basis of life, but also by several fascinating presentations from early industrial adopters of SMB techniques. These entrepreneurs are going to market with the first therapies and machines that leverage the field's teachings, and their endeavors represent the first commercial fruits of a highly important young field. Given the rapid pace of this energetic and innovative community, it is very safe to say that your life and those of your loved ones will benefit from SMB-rooted understanding and technologies.

Our deep thanks go to the organizers and participants of this fascinating conference.

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