Naming Modes

Naming Modes

Detailed discussion and analysis of modal propagation is well outside the scope of this book. However it is useful to understand some of the terminology used in the literature and standard texts. Later it will be seen that multiple modes form in any waveguide situation. This is not limited to fibre propagation but includes, for example, the behavior of light within planar waveguides and within a laser’s cavity etc.

Transverse Electric (TE) Modes

TE modes exist when the electric field is perpendicular to the direction of propagation (the z-direction) but there is a small z-component of the magnetic field. Here most of the magnetic field is also perpendicular to the z-direction but a small z-component exists.

This implies that the wave is not travelling quite straight but is reflecting from the sides of the waveguide. However, this also implies that the “ray” path is meridional (it passes through the centre or axis of the waveguide). It is not circular or skewed.

Transverse Magnetic (TM) Modes

In a TM mode the magnetic field is perpendicular to the direction of propagation (z) but there is a small component of the electric field in this direction. Again this is only a small component of the electric field and most of it is perpendicular to the z-axis.

Rather than talk about field components here it might be better to say that the orientation of the electric field is only a few degrees away from being perpendicular to the z-axis.

Transverse ElectroMagnetic (TEM) Modes

In the TEM mode both the electric and magnetic fields are perpendicular to the z-direction. The TEM mode is the only mode of a single-mode fibre.

Helical (Skew) Modes (HE and EH)

In a fibre, most modes actually travel in a circular path of some kind. In this case components of both magnetic and electric fields are in the z-direction (the direction of propagation). These modes are designated as either HE or EH (H = magnetic) depending on which field contributes the most to the z-direction.

Linearly Polarised (LP) Modes

It turns out that because the RI difference between core and cladding is quite small much can be simplified in the way we look at modes.²³ In fibre propagation you can use a single-mode designation to approximate all of the others. Thus TE, TM, HE and EH modes can all be summarised and explained using only a single set of LP modes

http://www.imedea.uib.es/~salvador/coms_optiques/addicional/ibm/ch02/02-13.html

Glass story—Corning

Watch and share “A Day Made of Glass 2: Unpacked,” to see how Corning’s highly engineered glass, with companion technologies, will help shape our world. Take a journey with our narrator for details on these technologies, answers to your questions, and to learn about what’s possible — and what’s not — in the near future.

Here is the question, how much does Corning contribute to those charming technology? Is that the glass only choice?

 

Invisibility cloaking, metamaterial.

A team led by scientists at Duke University’s Pratt School of Engineering has demonstrated the first working “invisibility cloak.” The cloak deflects microwave beams so they flow around a “hidden” object inside with little distortion, making it appear almost as if nothing were there at all.
[Schurig et al., SCIENCE VOL 314, 977-980, 2006]

Li-Fi, Wi-Fi replacement?

Researchers have used rapid pulses of light to transmit information at speeds of over 500 megabytes per second  at the Heinrich Hertz Institute in Berlin. Dubbed Li-Fi (not to be confused with Light Fidelity) is this a viable competitor to conventional wifi ?

“At the heart of this technology is a new generation of high-brightness light-emitting diodes” says Harold Hass from the University of Edinburgh ”Very simply, if the LED is on, you transmit a digital 1, if it’s off you transmit a 0. They can be switched on and off very quickly, which gives nice opportunities for transmitting data.”

It is possible to encode data in the light by varying the rate at which the LEDs flicker on an off to give different strings of 1s and 0s. The modulation is so fast that the human eye doesn’t notice.

“There are over 14 billion light bulbs world wide, they just need to be replaced with LED ones that transmit data”.

This may solve issues such as the shortage of radio-frequency bandwidth and also allow internet where traditional radio based wireless isn’t allowed such as aircraft or hospitals. One of the shortcomings however is that it only work in direct line of sight.

[http://the-gadgeteer.com/2011/08/29/li-fi-internet-at-the-speed-of-light/]

Will Li-Fi be the new Wi-Fi?

FLICKERING lights are annoying but they may have an upside. Visible light communication (VLC) uses rapid pulses of light to transmit information wirelessly. Now it may be ready to compete with conventional Wi-Fi.

“At the heart of this technology is a new generation of high-brightness light-emitting diodes,” says Harald Haas from the University of Edinburgh, UK. “Very simply, if the LED is on, you transmit a digital 1, if it’s off you transmit a 0,” Haas says. “They can be switched on and off very quickly, which gives nice opportunities for transmitting data.”

It is possible to encode data in the light by varying the rate at which the LEDs flicker on and off to give different strings of 1s and 0s. The LED intensity is modulated so rapidly that human eyes cannot notice, so the output appears constant.

More sophisticated techniques could dramatically increase VLC data rates. Teams at the University of Oxford and the University of Edinburgh are focusing on parallel data transmission using arrays of LEDs, where each LED transmits a different data stream. Other groups are using mixtures of red, green and blue LEDs to alter the light’s frequency, with each frequency encoding a different data channel.

Li-Fi, as it has been dubbed, has already achieved blisteringly high speeds in the lab. Researchers at the Heinrich Hertz Institute in Berlin, Germany, have reached data rates of over 500 megabytes per second using a standard white-light LED. Haas has set up a spin-off firm to sell a consumer VLC transmitter that is due for launch next year. It is capable of transmitting data at 100 MB/s – faster than most UK broadband connections.

Once established, VLC could solve some major communication problems. In 2009, the US Federal Communications Commission warned of a looming spectrum crisis: because our mobile devices are so data-hungry we will soon run out of radio-frequency bandwidth. Li-Fi could free up bandwidth, especially as much of the infrastructure is already in place.

“There are around 14 billion light bulbs worldwide, they just need to be replaced with LED ones that transmit data,” says Haas. “We reckon VLC is a factor of ten cheaper than Wi-Fi.” Because it uses light rather than radio-frequency signals, VLC could be used safely in aircraft, integrated into medical devices and hospitals where Wi-Fi is banned, or even underwater, where Wi-Fi doesn’t work at all.

“The time is right for VLC, I strongly believe that,” says Haas, who presented his work at TED Global in Edinburgh last week.

But some sound a cautious note about VLC’s prospects. It only works in direct line of sight, for example, although this also makes it harder to intercept than Wi-Fi. “There has been a lot of early hype, and there are some very good applications,” says Mark Leeson from the University of Warwick, UK. “But I’m doubtful it’s a panacea. This isn’t technology without a point, but I don’t think it sweeps all before it, either.”

 

[http://www.newscientist.com/article/mg21128225.400-will-lifi-be-the-new-wifi.html]

Verizon launches 100G Ethernet network

Verizon (March 4, 2011) successfully deployed a 100G Ethernet network on a large section of one of its Internet backbones in Europe.

This deployment makes Verizon the first backbone carrier to deploy the new Ethernet standard with speeds of up to 100 gigabits per second, according to Verizon. The company was able to establish the 100-Gigabit Ethernet network between routers on a 555-mile stretch between Paris and Frankfurt.
In Verizon’s words, this marks the first “standards-based, multivendor 100G Ethernet link for an IP backbone,” and it will increase capacity for business customers and organizations that tap into the backbone.

Internet Protocol backbones use high-speed fiber-optic lines to connect the major routers across the Internet, enabling different networks to talk to each other. Separate IP backbones are maintained by different companies and organizations, including telecom providers such as Verizon and AT&T. Providing a major performance boost over the older 1G and 10G Ethernet and the more recent 40G Ethernet, the 100G Ethernet standard itself was ratified by the IEEE (the Institute of Electrical and Electronics Engineers) last summer.

Wellbrock ( director of optical transport network architecture and design for Verizon) confirmed that although different enterprises may be launching 100G Ethernet networks within their own organizations, Verizon believes it’s the first backbone carrier to successfully deploy it. But Verizon was not alone in the effort as two other companies contributed critical pieces, making this a true multivendor project.

See more of the story:
http://news.cnet.com/8301-11386_3-20039383-76.html?tag=mncol;title
http://ioptic.blogspot.com/2011/08/verizon-launches-100g-ethernet-network.html

Google 1Gbps network near Stanford is live [CNET]

By: Marguerite Reardon, August 23, 2011 3:17 PM PDT

Some residents near Stanford University in Palo Alto, Calif., are getting the first taste of Google’s 1-gigabit-per-second broadband service.

The service has been live in the market for about a month, and it will continue to be rolled out to homes in the community, where mostly Stanford professors and faculty live. The service is free to residents for the first year.

Google is building the Stanford fiber-to-the-home network and a larger network inKansas City, Kansas, as sort of test beds for ultra-high speed broadband. So far, residents in the Stanford community are the first to get access to the high-speed networks that Google is building.

Stanford economics professor Martin Carnoy, who was one of the first people in the neighborhood to get the high-speed access, said he has been loving his new high-speed service. He frequently sends and receives big data files of 20MB or greater from his home computer.

“It used to take several minutes to send big files with the AT&T broadband service I had before,” he said. “I felt like I was always waiting around when I was sending or receiving files. But now it takes seconds. There’s no waiting.”
Carnoy hasn’t tested his connection to see how fast the service is, but Engadgetreports that at least one Stanford resident says he has tested the network and is getting about 150Mbps download speeds and upload speeds around 92Mbps.

The idea behind the Google Fiber initiative is to provide 100 times faster speed broadband connections to businesses and homes so that entrepreneurs can use these networks to innovate and test new ideas for Internet services and applications.

“High-speed Internet access must be much more widely available,” Eric Schmidt, Google’s chairman, said when the company first announced the project. “Broadband is a major driver of new jobs and businesses, yet we rank only 15th in the world for access. More government support for broadband remains critical.”
Getting broadband and super fast broadband to Americans is a stated goal of the Federal Communications Commission. The agency said in its National Broadband Plan that it plans to extend broadband to every American and it promises to offer 100 Mbps broadband to 100 million people by 2020.

A separate initiative called GigU driven by 29 universities in the U.S. is also looking to build 1Gbps networks in and around universities.

Most major universities already have access to cutting edge Internet technology, and many are involved in research and development networks such as Internet 2, which is used to connect universities throughout the world to share data and test new Internet technologies. But Google Fiber and Gig.U are extending this kind of high speed Internet access outside the university to the private sector.

Read more: http://news.cnet.com/8301-30686_3-20096300-266/google-1gbps-network-near-stanford-is-live/#ixzz1VxYAcJXa

http://ioptic.blogspot.com/2011/08/google-1gbps-network-near-stanford-is.html

Optical Buffer

Today, computer network consist of optical fibre links, interconnected by electrical nodes. The data transport in the backbone is done in the form of light (Laser etc.) Dense wavelength division multiplexing (DWDM) technologies enable bitrate well beyond 1 Tbit/s. however, at the nodes; this light has to be converted to the electronic domain, in order to switch all data to their separate destinations. Due to rapidly increasing channel capacities, the switching capacity is becoming bottleneck of the system. Currently, research activities focus on optical switching technologies that involve fewer or no conversions from the optical to the electronic domain. An important problem is the buffering.

An optical buffer is a device that is capable to temporarily store light; it serves to store data that was transmitted optically without converting into electronic domain.

[wikipedia: Optical buffer. http://en.wikipedia.org/wiki/Optical_buffer%5D

CUDOS Australia Launching video

CUDOS Australia Launching video

E-book display business [Nature Photonics]

E Ink Holdings (Hsinchu, Taiwan, world’s largest supplier of displays to the e-book market), whose power-efficient display technology is used in the Amazon Kindle as well as a range of other electronic book (e-book) readers, says sales of its products nearly doubled in the last quarter of 2010. [Nature Photonics, 2011, Business News]

Sonoluminescent bubble lighted with laser