Solus: Another Coretek?

Solus Micro Technologies Inc. is hoping to turn the heat up under Nortel Networks Corp. (NYSE/Toronto: NT) in a couple of weeks' time, when it briefs analysts in a hotel suite near the NFOEC show in Baltimore.

The startup plans to pitch itself as a future competitor of Coretek, the startup acquired by Nortel last year (see Nortel Gambles $1.43 Billion On Tunable Lasers). It's confident its tunable filters will be just as good as, if not better than, Coretek's – and cost 30 to 40 percent less. So says Ben Jamison, VP of marketing and sales.

Note the future tense there. Solus expects to have samples of its filters in July and ship commercial products in the first or second quarter of next year. In contrast, Nortel has already shipped Coretek tunable filters to about 100 customers, according to Tom Dudley, previously Coretek's head of marketing and business development, now with Nortel. Dudley says he doesn't know enough about Solus to comment on its plans.

So, what makes Solus so sure that it can give Coretek a run for its money?

One of the reasons appears to be miniature trampolines (seems obvious, now that we mention it, no?). Coretek and Solus use MEMS (micro-electro-mechanical system) technology to make their tunable filters, but Solus incorporates a special elastic polymer membrane in its device to create something akin to a miniature trampoline.

Jamison says the trampolines are easier to manufacture than Coretek's MEMS-based filters, which are etched out of solid silicon. That translates into "higher yields and significantly lower costs," he says.

Polymer is also less likely to be damaged from constant flexing, he adds: "With silicon, you have to push the material properties to the limit."

The miniature trampolines also deflect farther when pulled by electrostatic forces, and that translates into exceptionally wide tuning ranges, according to Jamison. He claims Solus has made devices with 100-nanometer tuning ranges, more than double Coretek's 40nm range.

Solus and Coretek's products are Fabry-Perot filters, comprising two mirrors face to face. Light enters through one of the mirrors and bounces to and fro in the cavity between them in a way that results in a single wavelength of light eventually passing on its way though the mirror on the other side. The wavelength of the light coming out can be changed by altering the distance between the mirrors by minute amounts.

Solus makes these tiny adjustments in distance by mounting one of the mirrors on one of its tiny trampolines, shown in the middle wafer in the following diagram of its tunable filter.

Solus image When a voltage is applied to the electrodes in the lower wafer, electrostatic forces pull the trampoline downwards. Solus says this can be controlled very precisely, which equates to being able to filter very closely spaced wavelengths.

This is reflected in the filter contrast figure of 40 decibels cited by Solus. The startup also says insertion losses are low – less than 2.5dB.

Solus expects to use its tunable filters in subsystems that scan DWDM (dense wavelength-division multiplexing) systems monitoring the quality of the signal on each wavelength.

Jamison says the same basic concept could be used to make a wide range of other components, including gain flattening filters, tunable lasers, and tunable multiplexers.

Solus is another startup that began developing MEMS-based display technology and then discovered telecom applications, in much the same way as Silicon Light Machines (see Cypress Flexes MEMS Muscles).

Like Silicon Light Machines. Solus has friends in high places. One of its investors is JDS Uniphase Inc. (Nasdaq: JDSU; Toronto: JDU).

So far, Solus has raised a total of $26 million. VCs backing the startup include Enterprise Partners, Sierra Ventures, East River Ventures LP, Citigroup, and Essex Investment Management Co. LLC.

— Peter Heywood, Founding Editor, Light Reading
http://www.lightreading.com For more information on NFOEC, please visit the Light Reading NFOEC Site.

RazorDude 12/4/2012 | 8:14:26 PM
re: Solus: Another Coretek?
Can anyone help me understand reliability of this product? It's still MEMS but does that elastic piece do anything to help?

sridude 12/4/2012 | 8:14:24 PM
re: Solus: Another Coretek? The polymer membrane is certainly a reliability
concern. For example, moisture absorption over its lifetime can significantly change its mechanical properties and hence the tuning behavior.

Additionally I dont understand why the cost of this filter should be any different from Coretek's. Typically chip costs are small compared to the cost of the package, and unless Solus has some dramatically different packaging technology the costs are likely to work out to about the same number.

I also noticed that they havent mentioned qualification in their web site.

- Sri-dude
abacus 12/4/2012 | 8:12:37 PM
re: Solus: Another Coretek? Well, let's be clear on a few things: polymers are softer than silicon so they take less electrostatic voltage to deform. But then they require a much more fastidious control circuitry to maintain position - a hard thing to do when you are working with rubber bands. Silicon has creep, although very little. Can you imagine what kind of creep - read "sag" - a partially crosslinked polymer will have. Over time it will sag like your unwashed underwear. And rubber bands - like underwear elastic - get dry and brittle.

Then there is the matter of maintaining parallelism in the mirrors, one of which is suspended on a trampoline of rubber. Good luck! I suppose the control circuitry and the tripod of electrodes is supposed to do that. Speaking of which, did you see the latest photo of what is represented as Solus' tunable filter? Where are the electrodes? Since they are spouting a data sheet with such great perfomance, let's see a mechanical drawing and pin-out specification.

Speaking of performance - 40 dB cross talk suppression sounds a bit much to me. In a F-P cavity with only one mode at that wavelength, the cavity size has to be about 9 microns. That puts impossible requirements on the reflectivity of the multilayer mirrors - which I assume they use since a metal won't cut it for the finesse and channel cross talk suppression they need.
One last thing: The recent appointment of Nasir Partovi as COB is interesting: He is a partner in Enterprise Ventures, which is an investor in Solus. Bill Stensrud, of EV, is the prime mover in the investment. The arrival of Partovi suggests that the investors want to hold a tighter rein on the company. One classic scenario is that the investors come in, clean up the place to sell it off and get their money out when it looks like a losing proposition to stay. Know when to hold, know when to fold.

Now I am only speculating, you understand. The predicted performance is being put on the street almost a year before the device is. What state can the packaging and manufacturing be in to predict that kind of performance NOW, when it won't be ready, certified and able for two, three or four more quarters.

For such a little device they seem to be taking such a long time, and Lightreading is giving them such noteworthy coverage.
bjamison 12/4/2012 | 8:10:04 PM
re: Solus: Another Coretek? Thanks for your spirited comments regarding the article on Solus. I wanted to take a moment to respond to some of the questions you raised.

Regarding the statement that polymers are softer, require less voltage to deform and --a much more fastidious control circuitry to maintain position--, the Solus tunable Fabry-Perot is designed to operate at voltages that are commonly found in optical performance monitors that use tunable filters. The control electronics for all high performance tunable filters, including ours, rely on closed loop feedback. Thus the control electronics are not significantly different than those used in other tunable filters.

You had some concerns regarding the stability of our elastomer materials and that they would --sag-- over time. Silicon and most other materials will exhibit creep when stressed to near their limit. Rubber is in its natural form a carbon-based material with elastic, fatigue, and durability problems that we are all familiar with. The elastomer material that Solus has selected to suspend our mirror is a synthetic, silicon-based material, developed by one of the world--s leading chemical companies, and used in essentially a fully crosslinked configuration. It was specifically developed to be chemically, thermally and mechanically stable over hundreds of millions of cycles. Silicon supported tunable filters see stress which is a significant fraction of the total elastic limit of silicon. The material properties of the elastomer result in stress levels a fraction of a percent of the elastic limit. Using a closed loop (optical) feedback control to stabilize the position of the movable mirror compensates for any other variances in the parallelism of the mirrors over the life of the component.

You asked where the electrodes are in the design. Clearly they are shown in the illustration on the bottom wafer. The corresponding electrode on the underside of the movable mirror is connected to the drive circuitry using a very innovative process that provides maximum flexibility and a very robust drive design.

Regarding your questions about filter contrast, Solus plans to provide a family of tunable filters, each providing the appropriate performance levels required for different segments of the market and for each different application. The optical gap between our high reflectivity dielectric mirrors is indeed ~9+m to ~30+m depending on the desired free spectral range which is in this case 120nm and 45nm respectively. Achieving high reflectivity and low loss does make the fabrication of the dielectric mirrors demanding, but is well within the state of the art and exactly equivalent to other flat planar Fabry-Perot designs. We are producing filters with an optical contrast ratio of >40 dB with dielectric mirrors of 99.86%.

As for our performance predictions, they are actually de-rated from the performance already achieved in multiple prototype devices here at Solus. We are currently completing the development the external package of our tunable filter. We plan to meet all of the appropriate Telcordia requirements for hermeticity, vibration and thermal cycling. We believe this requires a significant testing cycle and therefore are being conservative about delivery until such time as that testing has been completed to our satisfaction and that of our customers.

Finally, I don--t know quite how to respond to your final comments other than to say that we are thrilled to have someone of Naser--s stature in the optical networking industry involved in our company. He has been involved with many significant events in this industry, and has had a great track record of success in his career. We--re confident he will participate with another winner here at Solus. Only time will tell.
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