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Generation of broadly tunable picosecond mid-infrared laser and sensitive detection of a mid-infrared signal by parametric frequency up-conversion in MgO：LiNbO_3 optical parametric amplifiers
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How Remote Controls Work
Infrared Remote Controls: The Process
Sony TV remotes use a space-coding method in which the length of the spaces between pulses of light represent a one or a zero.
Pushing a button on a remote control sets in motion a series of events that causes the controlled device to carry out a command. The process works something like this:
You push the &volume up& button on your remote control, causing it to touch the contact beneath it and complete the &volume up& circuit on the circuit board. The integrated circuit detects this.The integrated circuit sends the binary &volume up& command to the LED at the front of the remote.The LED sends out a series of light pulses that corresponds to the binary &volume up& command.
One example of remote-control codes is the Sony Control-S protocol, which is used for Sony TVs and includes the following 7-bit binary commands (source: ):
Button 1 = 000 0000
Button 2 = 000 0001
Button 3 = 000 0010
Button 4 = 000 0011
Channel Up = 001 0001
Channel Down = 001 0001
Power On = 001 0101
Power Off = 010 1111
Volume Up = 001 0010
Volume Down = 001 0011
The remote signal includes more than the command for &volume up,& though. It carries several chunks of information to the receiving device, including:
a &start& commandthe command code for &volume up&the device address (so the TV knows the data is intended for it)a &stop& command (triggered when you release the &volume up& button)
So when you press the &volume up& button on a Sony TV remote, it sends out a series of pulses that looks something like this:
When the infrared receiver on the TV picks up the signal from the remote and verifies from the address code that it's supposed to carry out this command, it converts the light pulses back into the electrical signal for 001 0010. It then passes this signal to the microprocessor, which goes about increasing the volume. The &stop& command tells the microprocessor it can stop increasing the volume.
Infrared remote controls work well enough to have stuck around for 25 years, but they do have some limitations related to the nature of infrared light. First, infrared remotes have a range of only about 30 feet (10 meters), and they require line-of-sight. This means the infrared signal won't transmit through walls or around corners -- you need a straight line to the device you're trying to control. Also, infrared light is so ubiquitous that interference can be a problem with IR remotes. Just a few everyday infrared-light sources include ,
and the human body. To avoid interference caused by other sources of infrared light, the infrared receiver on a TV only responds to a particular wavelength of infrared light, usually 980 nanometers. There are filters on the receiver that block out light at other wavelengths. Still, sunlight can confuse the receiver because it contains infrared light at the 980-nm wavelength. To address this issue, the light from an IR remote control is typically modulated to a frequency not present in sunlight, and the receiver only responds to 980-nm light modulated to that frequency. The system doesn't work perfectly, but it does cut down a great deal on interference.
While infrared remotes are the dominant technology in home-theater applications, there are other niche-specific remotes that work on radio waves instead of light waves. If you have a garage-door opener, for instance, you have an RF remote.
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Weird & WackyInexpensive Detector Sees the Invisible, In Color
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NASA NewsText SizeInexpensive Detector Sees the Invisible, In Color&
An inexpensive detector developed by a NASA-led team can now see invisible infrared light in a range of "colors," or wavelengths.
The detector, called a Quantum Well Infrared Photodetector (QWIP) array, was the world's largest (one million-pixel) infrared array when the project was announced in March 2003. It was a low-cost alternative to conventional infrared detector technology for a wide range of scientific and commercial applications. However, at the time it could only detect a narrow range of infrared colors, equivalent to making a conventional photograph in just black and white. The new QWIP array is the same size but can now sense infrared over a broad range.
Image right: This is a false color image of a Goddard engineer in the far infrared (8-12 micrometer IR spectral band) taken with the 1 megapixel GaAs QWIP camera.
Warmer temperatures are orange, cooler temperatures are dark red. Notice the thermal handprint left on her lab coat as she removes her hand from her pocket. Credit: NASA
"The ability to see a range of infrared wavelengths is an important advance that will greatly increase the potential uses of the QWIP technology," said Dr. Murzy Jhabvala of NASA's Goddard Space Flight Center, Greenbelt, Md., Principal Investigator for the project.
Infrared light is invisible to the human eye, but some types are generated by and perceived as heat. A conventional infrared detector has a number of cells (pixels) that interact with an incoming particle of infrared light (an infrared photon) and convert it to an electric current that can be measured and recorded. They are similar in principle to the detectors that convert visible light in a digital camera. The more pixels that can be placed on a detector of a given size, the greater the resolution, and NASA's QWIP arrays are a significant advance over earlier 300,000-pixel QWIP arrays, previously the largest available.
NASA's QWIP detector is a Gallium Arsenide (GaAs) semiconductor chip with over 100 layers of detector material on top. Each layer is extremely thin, ranging from 10 to 700 atoms thick, and the layers are designed to act as quantum wells.
Quantum wells employ the bizarre physics of the microscopic world, called quantum mechanics, to trap electrons, the fundamental particles that carry electric current, so that only light with a specific energy can release them. If light with the correct energy hits one of the quantum wells in the array, the freed electron flows through a separate chip above the array, called the silicon readout, where it is recorded. A computer uses this information to create an image of the infrared source.
Image left: Another false color image with the QWIP camera of engineers and a seeing-eye dog (named Denver).
This image illustrates the slight difference in temperatures of the scene – dark red being coldest and orange the warmest.
Note the hand visible inside the labcoat pocket and the very warm tongue of Denver, curled in a yawn.
Also note the different hand temperatures of the people, some warm some cold. Credit: NASA
NASA's original QWIP array could detect infrared light with a wavelength between 8.4 and 9.0 micrometers. The new version can see infrared between 8 to 12 micrometers. The advance was possible because quantum wells can be designed to detect light with different energy levels by varying the composition and thickness of the detector material layers.
"The broad response of this array, particularly in the far infrared -- 8 to12 micrometers -- is crucial for infrared spectroscopy," said Jhabvala. Spectroscopy is an analysis of the intensity of light at different colors from an object. Unlike a simple photograph that just shows the appearance of an object, spectroscopy is used to gather more detailed information like the object's chemical composition, speed, and direction of motion. Spectroscopy is used in cri for example, to tell if a chemical found on a suspect's clothing matches that at a crime scene, and it's how astronomers determine what stars are made of even though there's no way to take a sample directly, with the stars many trillions of miles away.
Other applications for QWIP arrays are numerous. At NASA Goddard, some of these applications include: studying troposphere and stratosphere temperatures and identif tree canopy energy
measuring cloud layer emissivities, droplet/particle size, co SO2 and aerosol emissions fro tracking dust particles (from the Sahara Desert, e.g.); CO2 ocean/river thermal gra analyzing radiometers and other scientific equipment used in obtaining ground truthing and atmosphe gr and temperature sounding.
The potential commercial applications are quite diverse.
The utility of QWIP arrays in medical instrumentation is well documented
(OmniCorder, Inc. in N.Y.) and may become one of the most significant QWIP technology drivers.
The success of OmniCorder Technologies use of 256 x 256 narrow band QWIP arrays for aiding in the detection of malignant tumors is quite remarkable.
Other potential commercial applications for QWIP arrays include: location of forest fires and location of unwanted veg mo monitoring food processing contamination, ripeness, locating power line transformer fail monitoring effluents from industrial operations such as paper mills, mining sites, searching for a wide variety of thermal leaks, and locating new sources of spring water.
The QWIP arrays are relatively inexpensive because they can be fabricated using standard semiconductor technology that produces the silicon chips used in computers everywhere. They can also be made very large, because GaAs can be grown in large ingots, just like silicon.
The development effort was led by the Instrument Systems and Technology Center at NASA Goddard. The Army Research Laboratory (ARL), Adelphi, Md., was instrumental in the theory, design, and fabrication of the QWIP array, and L3/Cincinnati Electronics of Mason, Ohio, provided the silicon readout and hybridization. This work was conceived for, and funded by, the Earth Science Technology Office as an Advanced Component Technology development project.
&&Bill Steigerwald
NASA Goddard Space Flight Center&&&