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MEMS Deformable Mirrors vs. Liquid Crystal-Based Devices

Posted by Angelica Perrone on Tue, Sep 30, 2014 @ 03:00 PM

Tags: deformable mirror, adaptive optics, boston micromachines, product information, response time, mirror technology, SLM, spatial light modulator, BMC, segmented, speed, Reflectivity


New Mini mount resized 600Before Deformable Mirrors became popular in the Adaptive Optics industry, consumers would generally turn to liquid crystal-based device (LCOS) spatial light modulators to confront their challenges. Here at BMC, we regularly receive questions on how all deformable mirrors, in addition to our MicroElectroMechanical (MEMS) deformable mirrors, compare to LCOS devices. Below I have touched upon some of the top differences between the two devices that I believe should play an important factor in one’s decision to purchase a wavefront shaping device.

1)      LCOS devices are only available in a segmented architecture, where MEMS DMs offer both continuous and segmented styles in various styles and options. Although both layouts have their own advantages, most researchers favor the continuous model. Due to discontinuities between the actuators, it prevents any sharp edges within the image, making it well suited for imaging applications. Claire Max at UC Santa Cruz has explained and presented calculations on how you can achieve higher level of correction capability with a continuous mirror. Check out slide 47, which goes over her calculations here.  

2)       With MEMS DMs, we are able to offer strokes up to 5.5um (1.5um, 3.5um and 5.5um available), while LCOS SLMs are generally limited to only a stroke of 2PI in the visible region. This can be a major inconvenience for certain applications with higher amplitude aberrations. 

3)      The response time of our devices have always been much faster than any liquid crystal device on the market, while recent updates to our product line achieve even FASTER rates than before. Our devices can operate up to 60 kHz with our new high speed Kilo-S Driver or our Low-Latency Driver, whereas LCOS devices are limited to only a few hundred Hertz at best.  

4)      For the most part, LCOS devices are transmission based, causing light to be absorbed by the medium and resulting in lost light. There have been reflective devices introduced recently, however, they tend to scatter large amounts of light due to the small segment sizes. With a MEMS device, our segmented mirrors are over 98% reflective and our continuous mirrors are greater than 99%. Of course, this is the case only with the appropriate coating for the wavelength at which you are operating.  

If you're interested in learning more about the differences between MEMS DMs and LCOS devices or the differences between any other mirrors currently on the market, please feel free to contact us here.  

Reflective Optical Chopper Outperforms the Rest

Posted by Angelica Perrone on Thu, Jun 20, 2013 @ 02:11 PM

Tags: adaptive optics, boston micromachines, product information, response time, BMC, free-space communication, modulating retroreflector, optical chopper, optical modulator, chopper, pulse, ultrafast lasers, CLEO, AOM, acousto-optic modulator, SNR, signal-to-noise, speed, shutter

As Boston Micromachines' newest member, I would first and foremost like to introduce myself. My name is Angelica and I have joined the BMC team as their Marketing and Communications Associate. It has been some time now since our last blog and I thought it would be appropriate to discuss our most recent product; The Reflective Optical Chopper, or ROC.ROC with driver 130326 No Logo

               Optical Choppers, being frequently used for signal recovery in improving signal-to-noise ratio, are used to convert a continuous laser beam into a chopped one. Traditional Optical Choppers offer various pains, such as the need to alter the beam size to fit through wheel spokes, challenging stability at low speeds, the need for costly lock-in amplifier equipment and complex calibration procedures. The innovative, low-cost ROC simply eliminates all of these, outperforming traditional optical choppers.

                Drive electronics are paired with BMC’s MEMS Optical Modulator technology to create the ROC. The ROC provides beam chopping at impressive speeds without beam size modification. With a frequency range of DC to 150 kHz with better than 40 µs response time, control increments of .01 Hz and a contrast ratio exceeding 90% up to 100 kHz, the value of the ROC ‘speaks’ for itself. For signal-to-noise ratio improvement, the drive signal can be used as the sync signal, allowing it to be painlessly synchronized.

                Many industrial, scientific, medical, aerospace and military applications call for the need of reliable and advanced equipment. The ROC has superior capabilities such as high speed, large frequency range, reliability, stability and usefulness in SNR improvement applications. Basically, the Reflective Optical Chopper is an advance in optical chopping technology which is available at a low price.

What Do You REALLY Want in a Deformable Mirror?

Posted by Michael Feinberg on Wed, Oct 17, 2012 @ 04:00 PM

Tags: deformable mirror, adaptive optics, response time, laser science, mirror technology, microscopy, astronomy

This past summer, Boston Micromachines Corporation conducted a survey of nearly 300 members of the business and scientific community to find out what features were valued in a deformable mirror for adaptive optics and other wavefront correction applications.  Respondents came from our three major vertical markets: microscopy, deformable mirror survey resized 600astronomy and laser science.  In this survey, we asked some fundamental questions and had respondents choose between three DMs with properties varying in categories of actuator count, stroke, response time and price in various combinations. We were able to drill down to what each respondent valued.  Here are some of our key findings:

1)      Actuator count was the most valued property

Across all verticals, this was true.  Overall, respondents preferred an  average of 1000 actuators. While microscopists preferred 140 actuators by almost 2 to 1 over other models, those who identified as laser scientists were looking for an average of 1001 actuators and astronomers preferred, on average, 1800 actuators.

This was very interesting to us considering we are the only player in the market to provide deformable mirrors with these actuator counts as standard products or are developing DM systems which meet these specific needs (we have a 2000 element mirror in the works).

2)      High speed is important

The most frequently chosen option for response time amongst laser scientists was 50μs and all other disciplines preferred average response better than 300μs. This is great news for the industry considering that most mirror architectures can respond adequately to meet the needs of the users. Our DM architectures are available with response times up to 22μs and we are able to drive these mirrors with our X-Driver (response time down to 4μs), satisfying high speed requirements as well.

3)      Low price is desired

As we hear so often, most users were looking for low-priced devices. This was the second    preferred property after actuator count. While those of us in the industry talk about lower prices with higher volumes, the volumes just haven’t been there yet to make this prophecy come true.  The hope in the future is that the DMs based on scalable technologies, such as MEMS, will take off and lower-priced devices will be available.

We definitely learned a lot from this survey, above and beyond what is mentioned above.  If you have any questions about our methods or are interested in discussing more specifics about the responses, I would be glad to chat further.  Just contact me at support@bostonmicromachines.com.

 

How to select the right deformable mirror for you Part 2: Beam Shaping

Posted by Michael Feinberg on Tue, Jan 11, 2011 @ 12:37 PM

Tags: deformable mirror, adaptive optics, boston micromachines, resolution, response time, laser beam, SLM, spatial light modulator, turbulence, pulse, pulse width, peak power, CW, average power

Laser spotIn our second installment of this series designed to boil down the questions that need to be answered before selecting the right mirror, we will review some of the past categories with alterations specific to laser beam shaping and introduce a few new ones that pertain only to beam shaping.  We plan to focus on pulse shaping applications in our third and final installment of this series.

So you have a beam (CW or pulsed) and you want to control it.  Below are the fundamental questions that need to be asked in order to ensure that you’re on the path to obtaining great results in your research or manufacturing application.  This list should be combined with Part 1 of this series to get the total picture of what’s needed.  I have left out the “pitch” and “response” categories, assuming that you have read the previous installment.  Click here, in case you haven’t.

1)      Aperture:  How big is your beam?

The size of the wavefront is the first and foremost issue to understand.  Some applications have no control over this while others can change the size of their wavefront through the use of some simple focusing optics.  Before doing research into your alternatives, you should figure out what your limitations are in relation to this.

2)      Control:  Phase control? Beam steering?

This will greatly affect the basic type of mirror you will need.  For phase control, most modern phase-only mirrors will work, depending on your requirement of resolution (see “2. Resolution” from Part 1 of this series).  However, if you get into beam steering, the amount you need to move your beam will greatly affect the type of mirror you need.  For example, if you’re trying to move the beam multiple degrees, a fast-steering mirror is probably a good place to start.  However, if you’re looking to only make very fine adjustments (milliradians), you can benefit from MEMS-based solutions which are usually referred to as tip-tilt-piston (TTP) devices or piston-tip-tilt, if you’re from one other particular company out there (you know who you are J).  Many customers have come to us asking about using our entire mirror surface to steer a beam.  For those asking for big angles, we unfortunately have to turn them away, but some want to steer it a very slight angle at high levels of precision and we can do that.  

3)      Speed:  Do you want to make fine adjustments?  Are you looking to phase-wrap?

If you’re shaping a beam that is pretty much static, then some low-cost solutions will work.  However, if you’re looking to change the profile at high speeds with high precision, MEMS solutions are a great bet.  The stroke is sufficient to accomplish phase-wrapping, using our SLM model (segmented surface). With sub-nanometer precision, very precisely-shaped beams are possible.

4)      PowerVisible laser

This is a biggie:  If you have a high-powered laser, your options become limited very quickly as most of the very precise devices are a bit fragile as well.  Lots of research is being conducted to steer big, powerful lasers and the bulk of the technologies out there fall short due the fact that they are made of thin-film surfaces and temperature-sensitive materials. My recommendation for this is to make sure you know the “big three” properties and contact individual manufacturers to see what their experience is. They are:

1)      Peak power (in W/cm2)

2)      Average power

3)      Pulse width (if applicable)

Most manufacturers probably can’t guarantee much, but if your application has beam characteristics close to some of the data points they have, then it will make you much more comfortable that you won’t be frying mirrors when you fire things up.  BMC has a database that is constantly being updated with new experience that we would be happy to discuss.  Also, see this paper for the latest published results from our friends at the UCO/Lick Observatory.

As I mentioned before, this is not exhaustive, but if you have these questions answered, your first conversation with either us or one of our competitors will be a pleasant one which will make you more confident of your purchase.

Please chime in and let me know what you think of this series!   Again, stay tuned for the final installment where I will talk about pulse-shaping and the different ways that deformable mirror technologies can be used to create the perfect pulse!

How to select the right deformable mirror for you Part 1: Imaging

Posted by Michael Feinberg on Tue, Jun 15, 2010 @ 02:10 PM

Tags: deformable mirror, adaptive optics, boston micromachines, Boston University, product information, Woofer Tweeter, resolution, response time

deformable mirrorIn this multi-part series, I will be exploring the basic questions that one needs to answer in order to determine which type of deformable mirror is best suited for their application. This list is by no means exhaustive, but if one has an understanding of these topics, the journey to creating spectacular images will be much smoother and equally as rewarding. I am starting with imaging since this is a field that is constantly expanding to new disciplines and often involves researchers who are not familiar with adaptive optics. The next topic will be beam shaping, with further topics to be introduced in the future.
Potential customers come to us at Boston Micromachines to design an adaptive optics system for many different applications: Confocal microscopy, conventional microscopy, astronomy, etc. However, many of them don't know their options when selecting the right mirror. We think we've reduced the questions you need to ask to four simple topics. If each customer reviews this list before giving us a call, finding a mirror best suited for their application will be as exciting as viewing that killer image you're trying to get:

1) Aperture: How big is your image? How big (or small) can you make it?
The size of the wavefront is the first and foremost issue to understand. Some applications have no control over this while others can change the size of their wavefront through the use of some simple focusing optics. Before doing research into your alternatives, you should figure out what your limitations are in relation to this.

2) Resolution: How complex are your aberrations? zernike
Having the right aperture is great, but if your mirror does not have a high enough level of precision, your image improvement will be greatly limited. In the deformable mirror industry, we call this distance between control points, "pitch." In our devices, it is the distance between actuators. In membrane-type mirrors, it will be the distance between electrodes that are underneath but not directly connected to the surface. If your aperture can be manipulated, the precision to which you can control the wavefront will most likely be directly affected by this adjustment. Also, the size of the pitch can affect the price of the mirror. So, understanding what the relationship is between aperture, pitch and price can help you not only find the right mirror, but minimize your costs.

3) Aberration: How big (deep) are your aberrations?DM  Profile
While aperture and resolution cover you in two dimensions, depth is the final critical physical dimension. The size of your aberrations will directly impact the necessary stroke (the distance the surface of the mirror can travel up and down). If you have very small aberrations and require a high level of precision to correct your wavefront, you can focus on MEMS-based solutions, like those provided by Boston Micromachines (available stroke is between 1.5 and 5.5um). However, if you require larger stroke, you may need to focus on more flexible electro-static or piezo-electrically motivated membrane surfaces. Most recently, some have executed what we call a woofer-tweeter approach where a larger mirror corrects for the larger aberrations (the woofer) and a smaller, more precise mirror fine-tunes the image (the tweeter). You can see an article on this in the June 2010 issue of Photonics Spectra: "Dual Deformable Mirror Systems Take the High and Low Roads to Imaging Success." Size of the aberrations is a critical point to understand due the fact that if you don't have enough stroke or high enough level of precision, your image may not improve enough to be impactful.

4) Response: How fast do your aberrations move?
If you're dealing with static medium, then this is not an issue. However, if you are dealing with atmospheric turbulence, as in astronomy, or in vivo conditions in live specimens, then this is a critical parameter. While this is dependent on the structural composition and design of the mirror, it is also dependent on the drive electronics and controller. So, make sure that both your system (PC or other controller) and the electronics associated with the mirror are up to snuff for your application.

Purchasing a deformable mirror should be an exciting endeavor: The images obtained to date have been astounding. I'm sure that with proper preparation and understanding, it can be successful for you as well.