tiny profiles

11.7.11

(i do like a palindromic date) 

Back in the lab. Briefly. I bumped into L in the corridor, and asked if she was going to be in the cleanroom, which she was, and so asked if I could accompany her, which I could. So I did. Her task of the moment was to measure the thickness of a film on a substrate. She hence coated said substrate, which looks extremely like a piece of glass (about 1.5 cm square) by adding her solution (a clear one, a couple of drops) and spinning it for 30s in a centrifuge-type machine. All of this took place in one of the clean boxes with her manipulating the sample and equipment via the arm-long black rubber gloves (they are the arm equivalent of thigh-high boots, but I cannot think what the word to describe them in that way would be. Were they boots they would be very kinky – stretchy, close fitting, limb-long rubber - but as gloves they are somehow so very prosaic. Nonetheless I cannot resist the temptation to see how it feels.). I put my arm into one of the gloves, fingers into inverted fingers then rolling into it from there up – already ensconced in two pairs of shoe covers, a full length Tyvek suit, two hoods, gloves and spectacles I felt somewhat encumbered. Goodness only knows how they conduct any subtle actions buried under so many layers. Prior to working on her sample L had to get it into the clean box, which requires it going in through a little evacuated ante-chamber. This chamber was flushed three times with nitrogen gas (that’s what is in the clean box), and then the sample moved into the chamber. She explained her process as she went along, and I struggled to hear amidst the rustlings of many layers of clothing and background machine noise. L is working with Ravi Silva, who is the director of the ATI, and who works (in part) on solar cells, his group exploring new materials and methods to make them more efficient, longer lived, smaller, etc. After the transparent fragment is coated with the transparent coating L removes the sample from the clean box and scratches the surface, in order to be able to measure the profile across it. This is undertaken using a profilometer. A profilometer is basically a probe that is dragged across the surface of something and which records the topography of the surface. I love that kind of technology; I imagine it to have been around for hundreds, maybe thousands, of years in almost the same form. The form of this one is somewhat twentieth century, being a rather fetching brown and beige computer-looking machine. On the label it says 1994, but to me it is reminiscent of a computer my dad bought in the early 1980s, all ergonomic curves and a small, embedded, flickery screen. Apparently it is so knackered that they can’t switch it off, and must simply turn the brightness and contrast down. L measures the profile and I get caught up in drawing the machine – as ever in the cleanroom I am restricted to using the shed-free paper and biros and pens. In the university shop on the way in to the lab I had stumbled upon a cherryade-scented pen, and so my drawing becomes a multi-sensual event. The profiling completed L must go to have a meeting with Ravi. We leave the clean room, disrobing in the ante-chamber as we flush back into the audible, unclean world.

prime days

5.7.11

A prime date. 

5, 7 and 11 are consecutive prime numbers, but I wonder if 5,711 is one too? I guess the internet would be able to tell me in a flash. But I am not online at the mo. Somehow 5,711 does sound a suitably awkward number that it may be a prime. Let me see – is it divisible to an integer by 3? No. 5, no, don’t need to use a calculator for that. 7? No, but that’s a nice looking number 815.857142857142857142... 9, no. 11? No. 13, no. 15? No. 17, 19, 21, 23, 27? No, no, no, no, no. I’m beginning to wonder if I am going to have to try every odd number up into the hundreds...  maybe so. 35 (being a multiple of 7?) has a similarly good looking answer at 163.171428571428571428571... The forties and fifties and sixties give no integer divisible solutions, but the numbers by which they must be multiplied to get to 5711 are falling, and drop below 100. When I get up to trying 73 the answer is in the seventies, which means that I must be nearly there. 75? No, that is a 76.146666666666666666666666666666666666666666666666666666666667^th of 5711. And so, seemingly all of a sudden, I know that it is indeed a prime day.

Last week a trip to the museum at Porthcurno whilst in the area to drop off a silicon photonics drawing. Porthcurno is a small bay on the south coast of Cornwall, down beyond Penzance, where, from 1870 onwards, early international and transatlantic telegraph cables crossed from the land into sea; submerged copper wires taking messages around the world. The first successful trans-Atlantic cable had been laid between the UK and USA in 1865. Submarine copper cables were insulated using gutta percha, a substance similar to rubber, which had recently been discovered. By 1900 Cornwall was connected to India, North and South America, South Africa and Australia via such cables at Porthcurno. Messages were transferred using Morse, or other coded systems; text messages being distributed via a global network more than a hundred years ago. 

And some interesting art. A piece called ‘Soundings’ by Penny Nisbet at the Porthcurno museum (http://www.porthcurno.org.uk/), in which audio signals are generated from a dormant, but largely intact, submarine cable, since it acts “as a giant antenna in the sea of electromagnetic waves we are continually immersed in”. She further says “The prospect of the ancient telegraph cable resting silently on the seabed adds something to the fascination of listening to the sound of the radio energy it is receiving, including natural radio emissions of cosmic and atmospheric origin as well as those from man-made power sources.”

At the nearby Newlyn Art Gallery I pop in to a related exhibition of sounds and sculptures, co-curated by students at Falmouth Art College, called Down There Among the Roots (see http://downthereamongtheroots.wordpress.com for more info). In the Lower Gallery the sounds, by Chris Watson, include those made by hydrophones submerged “at the point where the ocean breaks upon the land and burying equipment into the earth beneath a series of wires”. These noises accompany Phoebe Cummings’ un-fired clay sculpture in a vitrine (and I must admit I’m a sucker for a vitrine – if your tastes are of a similar vein take a look at Marielle Neudecker’s tank works sometime) of a scene incorporating Malaysian Isonandra Gutta trees, producers of the aforementioned gutta percha. Upstairs, larger miniature un-fired sculptures of the Cornish landscape are accompanied by sounds captured from stretched wires in Australia and Cornish field recordings. And the view from the cafe, it being a sunny, turquoise-seaed, cloud-rushingly breezy day, provides other sensory fulfilment.

Art, science and Cornwall on a sunny day – a prime combination.

Eye balls

Last week I was back in the lab again. A highlight of my time In Residence was sitting quietly drawing the experimental rig and an eye, while DT was back and forth conducting experiments on the ring resonator, answering my intermittent questions and explaining subtleties of the process. The setup was one that I am now familiar with, the laser light emitted from an electronic box on a raised shelf, passing through various optic fibres to the point where it meets the wafer, on a table that is damped from external vibration by means of hydraulic legs. The piece of silicon disc (wafer) is clamped down and the light carefully aligned along the microscopic silicon grooves and mounds etched within it to pass through, in this case, a ring resonator. This device modifies light. When first in the lab that sentence did not falter as it encountered my brain, but with time I am becoming more perplexed by the process of altering light; it seems a rather fundamental thing to do, even if technically simple, to change, for example, the wavelength of a ray of light.

The eye diagram is a standard output format for this type of work and is indicative of the level of clarity of binary information transfer, a widely open eye being a sign of good data transfer with a low error rate. DT has recently used one of his silicon photonics devices to transmit data at 40Gbit per second (with a modulation depth up to 10dB, which may be of interest to the initiated), which is pretty quick. (see http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-19-12-11507 for the paper) (Incidentally, “pretty quick” in the former sentence actually means unprecedentedly fast rates for optical modulation in silicon with a large modulation depth, and hence also useful in a practical sense). The eye was all seeing as I drew.

But it’s not all work. The lab meeting that I attend the next day is followed by a group tennis doubles tournament. My partner and I are the unrivalled losers, but strangely are the only pair to take a game off the boss and second in command (who, weirdly since they are the two best players, were drawn (by the second in command) to play together) – I think that we discombobulated them with our atrociousness. Or maybe it was simple pity (although I’m not convinced by this second suggestion, the boss has a penchant for fiendish spin which, when on the receiving end of it, doesn’t seem to have any possible connection with pity). (Is it possible that it is connected to the spintronics I’ve heard mention of around the ATI?)

As ever my return home is in a state of mental disintegration – the transition between these two worlds seems to have the kind of impact on me that I imagine teleportation would. And the tang of tennis weary legs on the train is a physical memory, reminding me that it seems I need to work on my tennis as well as my maths.

Potential realities

The estuary at St Germans as stunning as ever, the bright sun glinting from the freshly rain-touched greenery and the river; the Tamar. Separating Cornwall from the rest of the country the beautiful inlets and waterways coming to a head, from the perspective of the train at least, as we pass over the Brunel Bridge at Saltash, and out to the sea beyond. As we cross the bridge I leave behind the gentle comforts of home, and pass the ‘realities’ of militarisation, dockyards, the urbanisation of Plymouth, heading into other versions of the world beyond, up country.

I have started reading Werner Heisenberg’s ‘Physics and Philosophy’, first published in 1962. In the late 1920s Heisenberg was famously uncertain about the possibility of knowing where anything is and the concurrent speed at which it is travelling, although, apparently paradoxically, was able to accurately know the probabilities of these attributes. Einstein was unconvinced by the idea of this fundamental unpredictability in the physical world, famously retorting “God does not play dice with the universe” to the notion. Heisenberg’s view, known as the Copenhagen interpretation of quantum mechanics, tells us that the observations of, for example, an electron, are what result in the existence of the electron. Measurement of the position of an electron creates an electron-with-a-position; test its momentum and an electron-with-momentum is created. An electron, in this view, is not a physical entity, but it and other fundamental particles “form a world of potentialities or possibilities rather than one of things or facts”. The reality, apparently, is the observation, not the electron.

And with such thoughts and words I am firmly back on my path into the world of electronic physics, striding out as if wearing high platform shoes with super-wobbly blancmange soles. Off I lurch, to observe the silicon photonics laboratory, wondering what art realities will result. It sure is good to be back.

A pause

Due to circumstance there is a break in these words, in this process. However it will continue in June, and rather than wrapping up in August, as previously planned, the residency will instead continue until October. The next post will be on, or before, June 7th, so please come back sometime after that and see if this pause has proved to be thought provoking.

Increasing the clarity of the unclear clearly

The light half.

Day 44. (already) A brief meeting with the boss. What a difference ten minutes makes. He has been reading the blog and is evidently appalled by the woeful lack of understanding and factual content therein; he specifically mentions the unclear “Clearly, this implies that...” which I referred to some weeks ago. It’s time for me to learn something. Only a few minutes later I leave the office with real comprehension about that formerly incomprehensible page turn (not least that the vertical lines either side of the letter r, the r representing the reflection coefficient, are the math shorthand for ‘the magnitude of’, so I can now at least write out the sentence in English rather than mathematics: Clearly this implies that the magnitude of the reflection coefficient is equal to one. (Why didn’t he just say that in the first place?)). But I’m also a little sad to have lost the infinitely intriguing imagined interpretation of imaginary numbers, having had them tied down to the mundane conceptual realities of axes on a graph (although as I write the understanding of why one would want to map the imaginary on the perpendicular axis to the real is again disappearing in a fog of misunderstanding, so that’s ok). Anyway, for the moment I don’t think it’s necessarily important to know the mathematician’s rationale for the perpendicularisation of real and imaginary, of import is that electronic engineers use the fact that real and imaginary numbers are plotted on the x- and y- axes (respectively) as an analogue for impedance in circuits. In capacitors the voltage and current are 90 degrees out of phase, and so these components (as well as the roles of resistors and inductors, the three collectively comprising impedance) can be mapped out on the axes (resistance is represented by the positive x-axis (the real equivalent), inductance by the positive y-axis (the imaginary equivalent), and capacitance the negative y-axis (imaginary equivalent). Bother, that seems to describe the roles of three of the four axes, but begs the question of what it is represented by the negative x-axis?). Anyway, it is evidently clear that by this means the overall impedance of a circuit can readily be calculated. You see?

 
As I write I am sitting on the train heading back home – again my reserved “window” seat was next to a piece of non-transparent train structure that largely obscures any view of the outside world, and someone else was already sitting in it anyway (having evidently also switched the seat tickets around to make it look like his!); but he is welcome to his falsely acquired sliver of view. It’s almost dark anyway, and I am now sitting at a forward facing window seat at a table, where I have spread out all over the place, and with relative acres of darkening glass next to me. I am riding high on the knowledge that I’ve acquired knowledge, and desperately trying to think of what to ask for the tutorial we have timetabled for next week; it seems that this art tomfoolery can remain obdurately obfuscated no longer.

Miniscule devisive shoes

About time.

I left the house at dawn this morning, at that very moment of its occurrence. The blackbirds were just starting their chorale and the sky was lightening. As I travelled to the station the mist rested in the valleys, and hung in the trees on the hillsides; approaching the turning, a long view through to a low east horizon showed a disc of deep luminous red hanging within the grey fog, the sun making its local debut for the day, stunning. Even as I saw it the news on the car radio reported of the evacuation of the Fukushima Daiichi power station because of a “spike of radioactivity” following explosions and a fire. On hearing the news I am stupefied in sadness and horror – what we do to ourselves, what we do to this earth.

As I write I am en route back up to the lab, a two day stint of residing. The train creaks and trembles as it rattles along the warming tracks, the day outside increasingly sunny, the warmth and light burning off the vestiges of water vapour, giving the day a bright golden clarity. I have decided that the time, being half way gone, is apposite for revisiting the copy of nature photonics that Graham handed me that first trip to the University (the Silicon Photonics special, August 2010, volume 4, number 8). 

[Low tide at St Germans as we pass, the muddy slivers of estuary snaking between the breast-like hummocky hills.] 

I can still remember my first naive fumblings between its sheets, sitting in the doctor’s surgery waiting room, trying to make some sense of it and recording my wonder at the words. I wonder how the experience of the time spent so far amidst the silicon photonicists will have affected my abilities in that realm.

Even as I open the covers I can’t help the smile as I read the words “Towards fabless silicon photonics” – doesn’t it sound like they’re trying to take the fun out of it? and I’m afraid that “Mid infra-red photonics in silicon and germanium” just makes me think of the silicon geranium photos I have taken. But enough mucking around, time to redive into Reed, Mashanovich, Gardes and Thompson, and their small world of silicon optical modulators (pages 518 to 526).

[Unbelievably low tide on the Plym as we pass, the sunshiny mudflat thronging with birds; it is the equinox this weekend, so I guess we’re due big springs soon, but the moon last night was a bright and clear more-than-semicircle, so I should think it’s pretty much fully neaps. Perhaps we are passing at the moment of its lowest ebb.]

In the review abstract they report that “Modulators have been improved dramatically in recent years, with a notable increase in bandwidth from the megahertz to the multigigahertz regime in just over half a decade.”, which I think sounds pretty amazing when you think that such a shift must be supported by actual physical technological and fabrication developments (this latter the word responsible for the dour, truncated fab in fabless), as well as the conceptual and ideological drivers involved.

[I just went and squeezed in next to a guy facing the right way in order to take my customary photograph of the “Teignmouth Electron” as we passed (a long series of muzzy and largely imperceptible images of a (currently rather rapidly and man-assistedly) decaying boat on the banks of the Teign). This “Teigmouth Electron” is a boat that is reminiscent to me of the real Teigmouth Electron, which is apparently slowly dissolving on a Caribbean beach, and to which I was introduced by a piece of Art made by Tacita Dean. In the book about it she tells the story of Donald Crowhurst who went out alone onto the watery surface of this world, on his final earthly journey, in the little vessel, on a partially-faked round the world race. It is a haunting tale that is beautifully told by her, delving into the realms of hope and expectation and time. An inspiring work. Just before he got off at Exeter the man came to thank me - he’d looked it up on the internet via his phone and thought it was a great picture (I recommended he look up the book and read the words...).  Very satisfying to have passed on the awareness of something wonderful, especially so geographically close to the location of the doppelganger craft.]

Back in the journal I grasp what the abstract is trying to tell me, although there are still some words that are yet mysterious. I am not clear as to what the modulation depth refers (I assume it is more than simply a physical depth in the wafer), and do not know how the energy requirement per bit can be altered, although with such increases in numbers of bits presumably it is something of a major consideration. As for the size of the device footprint, I do not know it but assume, given the scales at which they are working, that it must be very tiny, and very fast; miniscule devisive running shoes?