Guess the caption II

*Note the scale bar ;-)

What is MEMS ?

For all those who are wondering about what we do and why we do...this is an interesting article to start with:

http://www.semiconductor.net/article/CA6571814.html?nid=3572

Microlen part II - Classification

Microlens, as discussed in my post “Microlens part I” is one of the most important elements in the field of microoptics. Based on the refraction or diffraction phenomena at the optical interface, it can be classified as refractive microlens or diffractive microlens. In refractive microlens, the light is manipulated by analog phase element of considerable thickness in relation with the optical wavelength. In diffractive microlens light is diffracted at the periodic microstructure of the element.

Fabrication techniques for diffractive microlens have a good control over process parameters, and produce microlenses with good reproducibility and uniformity, which is a difficult task in refractive microlens production. However, from a system point of view, refractive microlens offers several advantages such as: reduced wavelength sensitivity as compared to diffractive microlens (a necessity for broadband applications), possibility of realizing large numerical aperture, and high light efficiency.

Now there is another kind of microlens which is called Graded Index microlens, and is basically a different type of refractive microlens. Rather than being refracted at the surface profile, in GRIN lenses, the light is deflected by a refractive index gradient within the surface. This in general leads to superior aberration characteristics of GRIN microlenses than that of conventional refractive microlenses. However, the major drawback with these kinds of lenses lies in the difficulty in fabrication. The precise formation of pre-specified graded index profile requires a very complex technology. Based on the terminology of GRIN lenses, we can define refractive microlens with a varying surface profile as Graded Thickness Microlenses. The idea seems appropriate since grading of thickness is the most prominent feature here, and the reason for the functionality of these lenses. It also helps to draws an analogy with GRIN lenses.

Both the diffractive microlenses and the graded index microlens have particular benefits, and can be used for certain type of application. However, as a best compromise between simple manufacturing techniques, high speed, low cost and good quality of microlenses produced, gives graded thickness microlens an edge over other kind of microlenses.

Guess the caption I

Whosoever identifies this picture and gives the best caption will win a dinner for one in River Walk Tandoor-Clark Quay, Singapore. Competition is open to all, and the winner can claim his/her price from me @ MMC-MAE, NTU.

Answer will only be accepted in the form of comments in my blog. I will be the only deciding factor for the competition. Based on the responses I will post more of my (work) pictures to further the game, and prizes.

Dinner can be claimed not more than 1 week later after the winner is announced, unless I agree to do so. Any doubts, discrepancy, controversy over the choice of winner will not be entertained, unless I agree to do so.

Microlens part I - Introduction

Warning: It's a technical post

In my article, “what are POEMS, technically?” I discussed about the different emerging fields (some of them are already commercially viable) based on the miniaturization of the various mechanical, electronic and optical component, along with the changes in approach in terms of processes, techniques and materials. Albeit superficially we mange to get some idea about the vast (but very small) fields of MEMS, MOEMS and POEMS.

Today I will try to enlighten you about microlens, which can be considered as one of the most important components in the field of microoptics.

Starting with the definition: Simply speaking microlens is a lens whose geometrical size or aperture is less than 1 mm. So, most of the time when we say microlens, we mean lens which is small...smaller than the conventional lens. That’s that for the time being. I will introduce complexities in the definition later.

Having understood about the basic defining criteria for a lens to be known as microlens, let me throw some light on how it all started. I mean the background: Conventional lenses have been an area of interest for long. Even in the mid of 17th century, geniuses like Robert Hooke had already produced their own lenses. However, it was not until the arrival of fiber optics that brought with itself the trend of miniaturization for optical components. The important fabrication techniques, nevertheless, were still based on classical way of grinding and polishing. More recently (1970s), the development of IC fabrication techniques and its adaptation in the field of optics, has helped the idea of miniaturization to be realised, which in turn helped to generate optical components in the micrometer range.

The synergy of fiber optics with IC fabrication techniques, along with their potential applications, produced the basic thrust that lead to idea of producing smaller dimension optical components, (microlens being most important of them).

What are POEMS, technically?

This one is a bit technical, but not difficult. I posted this piece to create some awareness about MEMS and related fields, as I have been referring to them in my earlier posts. This is also a reason for my love for POEMS. How? You will see once you read this paragraph:

“Miniaturization of optical components and their integration with the existing micro-electro-mechanical system (MEMS) has emerged as a new discipline in the last 2 decades, and is progressively making its way towards commercialization in a number of fields. It offers significant possibilities for achieving the micro-opto-electro-mechanical system (MOEMS) functionality necessary to meet the performance needs of a number of emerging applications, such as, imaging, sensing, communications, and control. Realization of these applications requires the development of a set of microoptical components and processes suitable for integration with MEMS and supporting microelectronics. The resulting MEMS “optical toolbox” will provide the standard building blocks with which photonic functions can be achieved within MOEMS. However, the traditional materials used for MEMS fabrication (silicon and derived compounds) can not provide high quality optical components. Apparently much better results can be obtained by using polymers, which have shown promising results for the fabrication of converging lenses, creating a whole new field of polymer based miniaturised optical systems as polymer-opto-electro-mechnical systems or POEMS.”