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.
Keep in mind this was designed in 2002 using technology that was considered rock-solid & mature at that time. Spacecraft technology always seems outdated because of the lead times required: on something like New Horizons, it's between 15 and 20 years from component design to being used for its primary mission.
In addition, as another commenter noted, the reference oscillator is used for REX (the radiometry experiment on board New Horizons) and quality of gathered measurements for this experiment was one of the primary needs here: being able to use the component for the communications subsystem is just good power/mass engineering at work.
I believe the main reason is for navigation. They need a stable frequency reference because they use its delta, due to Doppler shifting, as the measure of the spacecraft's radial speed relative to earth.
From the paper, even this amazing stability isn't good enough for their navigation needs, by itself:
7. NAVIGATION SUPPORT
The downlink frequency from the New Horizons transceiver is
derived from the USO, as discussed previously, but even this
excellent frequency reference is not sufficient to support
precise and accurate Doppler velocity measurements at the
target level of 0.1 mm/s throughout the mission. In order to
remove the impact of frequency drift and bias in the
reference oscillator, New Horizons has implemented the
noncoherent Doppler velocity measurement approach [2] which
was successfully demonstrated in 2002 during the demanding
Earth orbit phase of the CONTOUR mission [3].
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.
You're comparing a barrel of oil directly to electricity, a fallacy. Electric vehicles are extremely efficient photon to road compared to combustion vehicles.
"Tank-to-wheel efficiency of conventional Otto cycle car is only 16% as illustrated fellow. Here, Otto cycle engine loss is 72%, standby /idle loss is 10% and drive line loss is 2%. Accessories loss, such as air conditioning unit consumes 2% but for comparison purposes, it was assumed 0%."
That's right. You're losing almost 90% of your available energy to heat. In all practicalities, you use less than 1% of energy available in a barrel of oil to move a car forward.
The NREL have done this calculation, it comes out with a total figure of about 0.6% of the US landmass, 50 times less than the land allocated to growing crops. Although that figure includes Alaska, it gives a pretty good idea, and the state by state percentage areas to generate their share of US national electricity demand are also given:
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.
It's pretty common here (nl), you have to ask for it but it is usually available. I'd advise against it because you're deviating from the bulk but if you need it you can usually get it, especially at the larger colocation facilities.
This is true, however: 48V circuits are generally priced 'per-amp' just like 120V or 240V circuits. That translates into much higher cost-per-watt and with the efficiency of AC switching supplies being well over 90% you're probably better off from an economics point of view of getting the highest voltage supply that you can get and then to step down in your rack mounted devices.
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.
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