These are great saws. The founder originally just wanted to sell his safety device to table saw manufacturers. He had no takers so he started his own company.
My next door neighbor lost 4 of his fingers in a table saw accident. I believe in personal responsibility but losing 4 fingers on your dominant hand is a pretty high price to pay for a mistake particularly when a viable safety technology is available.
Yet there was huge opposition to adopting this technology in table saws.
Firstly it's not at all equivalent to an AM radio. It is an AM modulated carrier but that's about it. The detection scheme direct detection and not coherent like in an AM radio.
Also your power spectral density would be fairly low as your AM modulation would be distributed over a huge wavelength range. So taking a narrow slice with a tunable optical filter (which aren't that narrow really) would mean the detector would see a very small signal indeed.
Given that it's so broadband, my guess is that it's probably not low intensity noise at all (modern communications lasers are ~-140dB/Hz) and thus wouldn't make a great direct detection OOK source. So this would limit ultimately the sensitivity of such an AM modulated system. Being so broadband means that it's not at all suitable for phase modulated signal because by definition it would have high phase noise. Overall the spectral efficiency of such a source as a communications device is abysmal.
Additionally the silicon detectors that are needed to convert the light signal back into an electrical signal have low responsivity and speed. So the poor detector speed places an upper bound on the supportable BW and poor Si responsivity places a limit on the overall sensitivity of the system.
It's much, much more efficient to use IR sources all the way around. Materials in the IR are really efficient for both light generation and detection. There are lots of other reasons why IR is better for free-space communications as well (less scattering and higher material transparencies generally).
No a white laser is good for other reasons. There are lots of places where we still use things like Xenon lamps for measurement of things.
While impressive it's not clear why such a low phase noise oscillator is needed. This oscillator looks like it takes up lots of space and power. So some justification for the device should be presented. Furthermore its possible to create a robust FEC that would be tolerant of burst errors due to phase noise. So the paper is incomplete without some mention of phase noise and the FEC used.
Other than the high end parts used in this device, it is fairly low-tech compared to most modern communications systems. That is a good thing for something like this I guess.
Let's figure out just how much area we need for solar panels.
The US consumes about 19.05M barrels of oil per day. Each barrel of oil is about 1.6 MWh of power.
So this is 31017210 MWh (3.1 x 10^10 kWh) of power just in oil every day..
The solar constant is 1.36kW/m^2 on average.
Solar panels convert solar energy into power with roughly a 14% efficiency or about 190W/m^2
or about 2.2kWh/m^2 in 12hrs.
Taking 3.1 x 10^10 kWh/(2.2kWh/m^2) I get 13 x 10^9 m^2. Converting this to miles gives us about 5240sq miles of solar panels just to get the same amount of energy we consume in oil.
Yes, a conventional 2-port MMI will generally give you a pi/2 phase shift of one port relative to another. If you combine the 2 ports again with another MMI, you have built a Mach-Zehnder interferometer with ideally pi phase difference (if you've perfectly matched the length of the 2 waveguides) between the top and bottom signal paths. If you insert a phase shifter in one or both arms you can control the light at the output of the MZ by varying the voltage applied to the phase shifter. You can then modulate the voltage and produce an AM or PM signal at the output of the MZM. This is currently how some commercially available photonic communication IC's send data over the network.
There are limitations on how good the extinction (cancellation) can be based on how well the losses are matched in the respective waveguides.
In this case of this paper, I imagine that the phase relationship will be much more complex and it will highly wavelength dependent.
She also spun out the original HP business of test and measurement equipment, chips, transceivers, etc as Agilent (now Keysight). I never ever thought of HP as a computer company. To me HP was oscilloscopes, spectrum analyzers, network analyzers, and lightwave measurement gear. Spinning Agilent out was shocking to many people at the time.
Kind of the stuff of science fiction but...I can imagine that if we could put someone in a medical induced coma for a long-period of time, sort of like suspended animation, we could perhaps find ways to treat the cancer while the brain is inactive or at least limit the tumor growth until a more viable treatment is available at a future date.
These big switch boxes typically end up being about thermal management and this box looks like thermal design was an afterthought. Also I'm not sure the power entry design is really all that smart. Generally speaking if you're in the market for a 640Gb/s switch (or 3.8Tb/s switch), does your data center really not have access to 48V power? The AC/DC conversion wastes power and space.
The QSFP's are "spaced for optimal airflow." However this spacing seems to neglect cooling the QSFPs themselves. Belly-to-belly mounting of modules is usually the most thermally challenging way to arrange them. The heat dissipated by the QSFP's is generally directed towards the top of the module. By placing open air channels between modules, they have effectively ensured that little to no air flows over the QSFP heat sinks (which is not shown). So there is probably a limitation on which reach codes are supported. My guess is that because of the thermal limitations of this design, it's not truly non-blocking in all reach configurations.
The Whole Foods in Almaden (affluent South San Jose) hires off-duty San Jose PD to provide security. The officers are in full uniform and carry their utility belt and service weapon.
Error Correction Coding is hardly mundane and in modern communication systems far from trivial. There is a lot more to ECC than Reed-Solomon. Basically nothing in our digital world today would work very long without it. You think of it as mundane only because it just works.
This guy built a fully functional scale model of a Ferrari 310 including the V12 engine all from photos. He built every part. He tuned the car so that it makes the sound of the "Ferrari Music."
Yep at Univ. of Rochester as physics undergrads we were often allowed a single sheet of paper with anything on it (we were told no microfiche!). I did a few open book exams but still made the "cheat" sheet. We all spent a great deal of time preparing that sheet. You had to study to really know what to put on the sheet. I often found that I did not need the sheet in the actual exam because the process of preparing it helped to bring the concepts forward in my mind.
In grad school as classes got more difficult, we had take home exams even. I always dreaded these because they were substantially more difficult than a regular exam. Generally if you didn't have the concepts down, having an entire library at your disposal was not helpful in that case.
It's easier to lay a subsea cable than to go overland in remote areas. Take a look at the subsea map of Africa as an example. In Africa the subsea links are there because it's too remote to run cables through the jungle or across the Sahara. Additionally terrestrial cables are more frequently cut than subsea cables. In India terrestrial fibers are cut routinely every day to the point that they have to allocate extra repair margin for the links.
In some cases the cable is buried on the sea floor by a special plow. It's incredible that the cable can be buried up to 6m deep in the mud on the bottom. Cable burial is intended to keep fishing equipment from snagging cables laid on the bottom.
Yes. It's a 100G service though. Infinera runs on 25G spacing so at 25G dual wave dual polarization is 100G in the same spectral efficiency as single wave.
So you have to separate the "wet" plant from the terminal gear. The speed of the terminal gear is completely disconnected from the wet plant these days. Nobody replaces wet plant to upgrade capacity. They run Ciena, Infinera, Alcatel gear over Tyco's old line system.
Essentially the issue with upgrading over the wet plant is basically the presence of nonlinearities on the fiber. The links are not noise limited. Some of these fibers are still running 10G OOK in half the band and that on NZ-DSF that's used for submarine cables basically causes huge nonlinear penalties. The new subsea fiber is 22ps/nm-km and essentially larger effective diameter for reducing nonlinear penalty.
Nope this will be 100G per wave not 40G. 40G was a stop-gap technology that never really shipped in large volume. With the advent of coherent optical, everyone just went to 100G (eg. Infinera, Ciena, Alcatel-Lucent)
EDIT: One caveat, depending on a particular link many of these systems will run at half-rate. A lot of legacy cables today are running BPSK at 50G in 2 waves (25G/wave) due to nonlinearities.
Nope, the new fiber will be high dispersion compared to the old fiber and also will not have dispersion compensation along its length. The old cable was designed for OOK signaling. Previously optical signaling was 1 bit per symbol OOK (on-off-keying) and direct detection meaning you did not have any optical phase information to make dispersion corrections so the dispersion compensation was done in a specially designed fiber with the opposite sign slope for dispersion (DCF).
This fiber was also relatively high loss and has a narrower core which leads to higher nonlinearities in the link. The old cable tries to keep the dispersion within the range that OOK technologies can operate error-free (post FEC) so there's a lot of it typical at each repeater (EDFA). The newer coherent optical technology can transmit multiple bits per symbol (BPSK, QPSK) by encoding the bits in the optical phase. Since the phase is recovered at the receiver the dispersion accumulated in the fiber can be undone in DSP with a long enough FIR filter. So the need for dispersion compensation is gone with coherent optical. Taking out the DCF also reduces loss along the link reducing EDFA (amplifier) count and increasing spacing. Also nonlinear penalties on the newer higher dispersion fiber are lower which improves something called cycle slips that can punch through the FEC and cause you to take post-FEC errors.
The net result is that you should be able to transmit QPSK at 32GBd in 2 polarizations in maybe 80 waves in each direction.
2bits x 2 polarizations x 32G ~128Gb/s per wave or nearly 11Tb/s for 1 fiber. If this cable has 6 strands, then it could easily meet the target transmission capacity.
My next door neighbor lost 4 of his fingers in a table saw accident. I believe in personal responsibility but losing 4 fingers on your dominant hand is a pretty high price to pay for a mistake particularly when a viable safety technology is available.
Yet there was huge opposition to adopting this technology in table saws.
The Colbert Report on Saw Stop http://thecolbertreport.cc.com/videos/hgxqxc/people-who-are-... stop