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MIT Scientists Reach Fiber-Optic Breakthrough
kcurtis writes "The AP (via boston.com) has a story about how MIT scientists have detailed a breakthrough in optics that could lead to cheaper, more efficient optical communications. From the story: 'Like polarizing sunglasses that block light waves oriented in different directions, the MIT researchers created a clever device that splits the light beams as they pass through a circuit. The device then rotates one of the polarized beams, before both beams are rejoined on their way out of the circuit, retaining the signals' strength.
But it's not just that device that the researchers are touting.
They're also trumpeting the innovative method they devised to integrate the optical circuitry with electronic circuitry on the same silicon chip.'"
Death Ray?!? Naw - not important enough.. These MIT guys have figured out how to split, twist and rejoin light - so optical signal loss over distance is nearly eliminated. This means that a light pipe can stretch MUCH farther and provide near light speed transmission of information because the light pipe is directly integrated to the semiconductor switch. When one considers the circuitry in the brain, one can begin to imagine a world mind - all the free computing capacity connected at near light speed in a similar manner - and a Dinkum Thinkum like Mike (Moon is a Harsh Mistress - Heinlein) becomes truly possible - an important time to be "not stupid", yah?!
Lost in space at an early age. Survived the vacuum. Now rebuilding castle in air.
This sounds a lot like balanced audio connections.
It seems what the MIT scientists have created is a purely optical equalizer in a convention CMOS process. This would probably be used at the receiving end of a single mode fiber link. Most of the equalization done today is done electronically using fancy optical receivers (expensive but very robust).
The article is light on details but the idea of integrating photonics and electronics in a conventional CMOS process isn't a new idea. Maybe the way they did the integration is a breakthrough. A company called Luxtera demonstrated (with products) integrated photonic and electronic transmitters way back in 2005. Their press release from March 2005 http://www.luxtera.com/news_press_2005_0328.htm reveals that they created an optical modulator (a transmitter) in Freescale's CMOS process. The optical modulator they created is also based on the same idea of splitting light and combining it to create on/off pulses at extremely high speeds.
If you want to read more about their technology and why integrating photonics with electronics is important visit: http://www.luxtera.com/technology_faq.htm
Something this article didn't even allude to, since the journalist probably had no clue about optics, is that these devices are used for tuneable polarization over long distance spans of fiber. Polarization Mode Dispersion (PMD), where different polarization "angles" travel at slightly different speeds through the fiber, makes it necessary for frequent regeneration devices, PMD correction operations, etc., over hundreds of kilometers, especially with older fiber. New fiber is available with very low PMD characteristics, but a lot of what's deployed 'round the world isn't that type. If you can tune the polarization of the laser feeding the fiber, you can, in effect, pre-compensate for the PMD characteristics of the fiber. I.e., if Polarization Mode A experiences X picoseconds of differential delay relative to a defined norm, this device would induce that same delay in the emitter. In effect, the emitter creates an optical signal with various skewed polarization modes, and the shitty fiber "fixes" it so that the signal received on the other end has minimum PMD characteristics, increasing your optical signal-to-noise ratio (SNR).
Devices like this are going to be the future of long distance backbone networks, where they will enable the operators to remove most of the expensive regenerators, reshapers, and some of the Erbium-Doped Fiber Amplifiers (EDFAs). However, MIT is not the first to create these devices; all they have done is develop a new technique for building them on Si, which could reduce their cost and increase their reliability, while decreasing their size. Size is an issue with the current generation of these devices, which are often too large to fit on the smaller modular interface cards on new Internet core routers from Vendor C.
The article didn't give a whole lot of detail, and also exaggerated the importance of this work. I'm fairly sure the work being discussed in the article is work being done at MIT on splitting and rotating polorazations in using silicon nitride waveguides. There are a number of research groups (including Luxtera, as someone mentioned) looking at using silicon (and other silicon CMOS materials such as silicon nitride) to make highly integrated optical devices. A lot of progress has been made in the past few years on making modulators, detectors, wavelength splitters, and Raman lasers and amplifiers. One of the problems with these devices is most of them really only work on one polarization. For a telecom system however, you often can't control the incoming polarization. So, this work is a device that splits and rotates the two polarizations so they can be dealt with separately. (And can be integrated on the same chip as the rest of the devices). An important acheivement, but this achievement alone isn't going to make an impact. (It's all the pieces together that might). I've also seen that Luxtera has their own different way of dealing with this.
The work is also over a year old (unless there's a new development I'm not aware of). I know two of the students who did the work, and they've gotten their PhDs and moved on.