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Light & Laser Blog

The Laser & Light Blog is the place for conversation and discussion about optoelectronics, fiber optics, lasers, light sources, optics, imaging, electro-optics, and anything else related to the photonics industry. Here, you'll find everything from application ideas, to news and industry trends, to hot topics and cutting edge innovations.

Construction Kicks Off for LSST Camera

Posted November 04, 2015 12:00 AM by IHS Engineering360 eNewsletter

It's official: the U.S. Department of Energy has given the go-ahead for the start of construction on the 3.2 gpix digital camera that will be the eyes of the Large Synoptic Survey Telescope (LSST). When finished, the telescope will conduct a 10 year sky survey that promises to reveal unknown astronomical objects and help unravel the mystery of dark matter. The three-ton camera will operate across the spectral band from 0.3 to 1 µm, accessed with an automatic filter-changing mechanism. Work is already underway on the enclosure and mounts, as well as some of the sensors. The optics contracts for the state-of-the-art camera are still being awarded, however, so if you are in the running, stay by your phone.

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1 comments; last comment on 11/07/2015
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Can Light Travel Infinitely Fast?

Posted October 21, 2015 2:00 PM by Quasar

Researchers have created for the first time an on-chip metamaterial with a refractive index of zero, meaning that the phase of light traveling through the material can move infinitely fast. The research was conducted at Harvard's John A. Paulson School of Engineering and Applied Sciences, and is published in the journal Nature Photonics.

You might be wondering how exactly light can travel infinitely fast when according to special relativity, the speed of light (~300 million km/s) is a hard limit that no matter or information can surpass. The catch here is that the infinite speed refers to the phase velocity of light, or how fast the crests of the wavelength move. As Sommerfeld pointed out way back in 1907, "the signal velocity and the process of propagation have nothing to do with the phase velocity," so relativity and causality are preserved.

Upon entering a standard material, like the glass in a window, light's phase velocity slows down as its wavelength is compressed. Exiting the material, the phase velocity speeds up as its wavelength stretches back out. The index of refraction (n) is the ratio of maximum speed of light (c) and the phase velocity (v) of the light traveling through a material (n = c / v).

Interesting behavior is observed when the refractive index is zero. Light stops acting as a wave with crests and troughs moving through space. Instead, a constant phase is created where all crests or all troughs stretch out in wavelengths of infinite length, oscillating only as a variable of time and not space. This phase velocity of infinite speed does not, however, allow information or matter to exceed the speed of light; phase velocity is distinct from the velocity of a complete signal carrying data.

New zero-index metamaterial consisting of silicon pillar arrays embedded in a polymer matrix and clad in gold film. (Image: Peter Allen/Harvard SEAS)

Metamaterials with a refractive index of zero have been developed before, but this particular breakthrough is unique in the fact that it is on-chip and can interface with standard photonic components and chips. Traditionally, integrated photic components have had ineffective optical energy confinement. With this new metamaterial, high internal phase velocity allows lossless energy transmission, permitting the light to be manipulated without losing energy.

The material will allow researchers to investigate the physics of zero refractive index in integrated photonic circuits, with potential applications in quantum computing and quantum optics. Entanglement between even distant quantum bits could be improved as incoming light waves are effectively spread infinitely long. Furthermore, photons from a quantum emitter in a zero-index waveguide would always be in phase with each other, enabling interesting research avenues in quantum optics.

33 comments; last comment on 10/23/2015
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Public/Private Partnerships Help Photonics Prosper

Posted October 03, 2015 12:00 AM by IHS Engineering360 eNewsletter

If you want demonstration of the value of public/private technology projects, look no further than the final report of the Integrated Disruptive Components for 2 µm Fiber Lasers (ISLA) project. The European program focused on the advancement of components and subsystems for this key class of industrial lasers. Developments include high-efficiency specialty fibers plus application-specific components such as amplitude modulators, tunable filters, and high-power pump lasers to be combined in a 0.5 kW system. Meanwhile, hoping for similar results, a 124 member consortium will invest more than $610 million in public/private funds to launch the Manufacturing Innovation Institute for Integrated Photonics in Rochester, NY.

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The Post-Incandescent Future

Posted August 19, 2015 2:59 PM by Jonathan Fuller
Pathfinder Tags: CFL graphene incandescent bulb

I've always admired incandescent light bulbs, and find it amazing that an electrified wire filament could hold a near-monopoly on commercial electric lighting for a century or so. Since the mid-1990s, though, many different lighting technologies have sprouted up, all vying to succeed the trusty Edison bulb.

The incandescent bulb's drawbacks are well known. To begin with, their luminous efficacy-the basic measure of how efficiently they produce light, in lumens per watt-in a word, sucks. A 40 W bulb has a luminous efficacy of about 12.6 lm/W for an overall efficiency of 1.8%. If that sub-2% figure doesn't sound terrible enough, it's only a little under 50 times brighter than a candle. Incandescent bulbs convert most of their energy into heat, which is wasteful unless you're using one to heat a terrarium or power an Easy-Bake Oven. This poor performance and new pushes toward energy efficiency have led governments worldwide to order phase-outs or bans on incandescent bulbs.

Swirly CFL bulbs have grown in popularity and dropped in cost, and they're roughly 3-5 times more efficient than traditional incandescents. LED bulbs are about the same efficiency-wise, although research points to a pretty high ceiling as far as possible luminous efficacy.

More recently, lighting researchers have begun experimenting with the celebrated supermaterial graphene. A graphene-coated LED bulb co-developed by the University of Manchester and its spin-off company Graphene Lighting PLC, both in the UK, will likely go commercial later this year. While the university claims the lamps will be "competitively priced" and manufactured using sustainable components, there's been no mention of a more precise retail cost. It's also worth noting that last month Canadian investors Oriana Resources Corp. signed papers to acquire Graphene Lighting PLC. How this will affect lamp production remains to be seen.

In June, researchers from Columbia University and two Korean organizations announced that they'd jointly developed an on-chip light source using a suspended graphene filament. The device requires little power to heat up to the point of emitting visible light, in this case around 2500° C, and despite being only one atom thick, the graphene strip emitted light visible to the naked eye. While the press release hints that the team's more interested in the lamp's potential heating abilities, it could be useful in transparent displays and optical communications. And in an ironic twist apparently not lost on the research team, graphene is derived from carbon-the same filament material used in Edison's original incandescent bulb.

Despite its history of fearmongering, the so-called US "light bulb ban" only applies to the manufacture of 40- and 60-watt incandescents that don't meet certain brightness standards and efficiency ratings, and there are plenty of other options as far as wattage and bulb type. Still, a select few manufacturers have been producing and marketing "rough service" bulbs that legally buck the US ban on general service bulb production. At most retailers these "newcandescent" bulbs carry a steep price tag (over $5 per bulb), so you're probably better off biting the bullet and getting the cheaper CFLs anyway.

As the era of incandescent bulbs winds down, it seems we're only certain of the fact that the dominant lamp of the future is still unknown.

Image credit: Vinovin/CC BY 2.0

32 comments; last comment on 11/03/2015
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Posted January 26, 2015 9:00 AM by CR4 Guest Author
Pathfinder Tags: optogenetics

Imagine you are going out with your shy single friend to a party, he / she is talking to a nice potential match, but your friend starts to melt down. Your role as the wing person is to save the conversation and you just do that, not with starting a new topic or saying something interesting, but simply by switching the light on and off again and instantly your friend returns to his/ her normal state. Is that totally freaky science fiction? Actually, it's not.

Genetics and optics were united to form the new field of optogentics to control events within chosen cells of living organisms. However, thanks to ethical regulations, the above scenario would not be seen in the foreseeable future. On the other hand, realistically, this approach could allow us to understand more about and treat complicated diseases such as anxiety and Parkinson disease.

So how does it work? Optogenetics is based on a simple concept, which is the transfer of certain genes that have the ability to invoke light response in cells from one organism to another. If we concentrate on the use of optogentics in the nervous system, we find that the brain consists of neuronal cells that form a circuit, continuously, passing information from one hub to another in the form of neuronal signals also known as action potentials. Action potentials are formed through the passage of ions from and into the cell membrane through special channels called ion channels.

An interesting protein called Channelrhodopsin-2 (ChR2) can open an ion channel if activated by light. This protein is added to the mammalian brain through an ingenious method:

1. The protein (in the form of its DNA sequence) is added to a virus genome.

2. The virus is injected into the mammalian (mouse) brain.

3. The virus (carrying our interesting gene) integrates its genome with the mouse genome.

4. The mouse genome machinery translate its own genome including the virus genome and our gene of interest into proteins making the particular area in the mouse brain in which this gene ends up in responsive to light.

Thus, we can control it by switching the light (in that case, blue light at 480 nm) on or off to induce action potential. Delivering the light inside the brain is done through fine electrodes that are surgically implemented in the brain region we want to investigate.

A nice example to illustrate the applications of this technique is its use in treating anxiety symptoms in mice. This is done by controlling the centromedial (CeM) part of the brain. This part when excited initiates anatomic and behavioural responses associated with fear. CeM itself is controlled by the basolateral amygdala (BLA) neurons that excite the centrolateral (CeL) neurons which in turn form a feed-forward loop to CeM neurons. The problem is that BLA controls other parts of the brain and up till recently there weren't any available methods that allowed us to control the signal coming from BLA to CeM, without affecting other behaviour aspects of the patients. In 2011 researchers at the bioengineering department at Stanford University found that optogenetics can actually control this pathway. By inhibiting the particular BLA terminals associated with CeL using light they could increase anxiety in the investigated mice. On the other hand, astonishingly, they found that optogenetic stimulation of the same region produced an antianxiety agent effect.

This exciting finding was reported in nature article in 2011 under the title "Amygdala circuitry mediating reversible and bidirectional control of anxiety". However it is fair to say that the field of optogenetics is still in its early stages, where much development could be done, on light sources, transfection methods and electrodes design.

4 comments; last comment on 01/27/2015
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Lighting Manufacturers Flock to LEDs

Posted December 22, 2014 12:00 AM by IHS Engineering360 eNewsletter

Amid falling revenues for incandescent and even halogen bulbs, lighting manufacturers are ditching conventional products for solid-state lamps and luminaires. Energy consciousness plays a part in the trend, but also government regulations in multiple countries either mandating energy efficiencies that effectively rule out incandescents or banning the technology outright. Meanwhile, the LED illumination market has broadened out from niche applications like architectural accents to general lighting products sold in retail outlets. Find out more about this dynamic market in this research note from IHS.

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