Vertical Cavity surface Emission Lasers (VCSEL) are lasers that emit light from their surface in contrast with regular ‘edge emitters’. Also they have got a vertical cavity , as the name suggests, which enables surface emission.â€Vixels†, as they are commonly called ,have several superior characteristics compared to their edge emitting counter parts.
VCSEL – Semiconductor micro laser diodes which emit light perpendicular to their PN junction in a cylindrical beam vertically from the surface of a fabricated wafer and feature circular low divergence beam
Earliest reported in 1965 by Melngailis
VCSEL was first demonstrated in 1979 at Tokyo Institute of Technology
Epitaxial mirrors for GaAs/ AlGaAs VCSELs
Distributed Bragg Reflection
If layers of alternating semiconductors are stacked periodically , each layer having a thickness
λo n , the reflections from each of the boundaries will be added in phase to produce a large reflectivity
Brag reflection condition
Periodicity of cladding layer is chosen so that
n1d1 + n2d2 = λo/2
n1 , n2 refractive indices
d1 , d2 thickness of layer
λo free space wavelength of the optical beam
Epitaxial growth of VCSEL
There are two methods
1 . Molecular beam epitaxy ( MBE )
xMax developed by xG Technology is a wireless communications technology whose developers claim is low power and provides a high data rate over a distance of about 13 miles.
“A fundamental paradigm shift in the way radio signals are modulated and demodulated.â€
Developed by xG Technology in Florida Rather than transmitting many RF cycles for each bit of data to be sent, xMax does it in a single RF cycle.
Power is saved not only in the transmission, but because receivers will only recognize single-cycle waveforms, power isn't wasted on un-intended RF signals
Privacy of personal data is an illusion in today’s complex society. With only passwords, or Social Security Numbers as identity or security measures every one is vulnerable to invasion of privacy or break of security. Traditional means of identification are easily compromise and enyone can use this information to assume another’s identity. Sensitive personal and corporate information can be assessed and even criminal activities can be performed using another name. Eye pattern recognition system provides a barrier to and virtually eliminates fraudulent authentication and identity privacy and safety controls privileged access or authorised entry to sensitive sites, data or material. In addition to privacy protection there are myriad of applications were iris recognition technology can provide protection and security. This technology offers the potential to unlock major business opportunities by providing high confidence customer validation. Unlike other measurable human features in the face, hand, voice or finger print, the patterns in the iris do not change overtime and research show the matching accuracy of iris recognition systems is greater than that of DNA testing. Positive identifications can be made through glasses, contact lenses and most sunglasses. Automated recognition of people by the pattern of their eyes offers major advantages over conventional identification techniques. Iris recognition system also require very little co-operation from the subject, operate at a comfortable distance and are virtually impossible to deceive. Iris recognition combines research in computer vision, pattern recognition and the man-machine interface. The purpose is real-time, high confidence recognition of a persons identity by mathematical analysis of the random patterns that are visible with in the iris. Since the iris is a protected internal organ whose random texture is stable throughout life, it can serve as a ‘living password’ that one need not remember but one always carries.
ZigBee is a published specification set of high level communication protocols designed to use small, low-power digital radios based on the IEEE 802.15.4 standard for wireless personal area networks (WPANs). The relationship between IEEE 802.15.4-2003 and ZigBee is analogous to that existing between IEEE 802.11 and the Wi-Fi Alliance. The ZigBee 1.0 specifications were ratified on December 14, 2004 and are available to members of the ZigBee Alliance. An entry level membership in the ZigBee Alliance costs US$ 3500 and provides access to the specifications. For non-commercial purposes, the ZigBee specification is available to the general public at the ZigBee Alliance homepage.
The technology is designed to be simpler and cheaper than other WPANs such as Bluetooth. The most capable ZigBee node type is said to require only about 10% of the software of a typical Bluetooth or Wireless Internet node, while the simplest nodes are about 2%. However, actual code sizes are much higher, more like 50% of Bluetooth code size. ZigBee chip vendors announced 128-kilobyte devices.
As of 2005, the estimated cost of the radio for a ZigBee node is about $1.10 to the manufacturer in very high volumes. Most ZigBee solutions require an additional micro controller driving the price further up at this time. In comparison, before Bluetooth was launched (1998) it had a projected price, in high volumes, of $4-$6. The price of consumer-grade Bluetooth chips are now under $3.
ZigBee has started work on version 1.1. Version 1.1 is meant to take advantage of improvements in the 802.15.4b (still in draft) specification, most notably that of CCM* as an alternative to CCM(CTR + CBC-MAC)CCM mode. CCM* enjoys the same security proof as CCM and provides greater flexibility in the choice of Authentication and Encryption.
ZigBee is a published specification set of high level communication protocols designed to use small, low-power digital radios based on the IEEE 802.15.4 standard for wireless personal area networks (WPANs). The relationship between IEEE 802.15.4-2003 and ZigBee is analogous to that existing between IEEE 802.11 and the Wi-Fi Alliance. The ZigBee 1.0 specifications were ratified on December 14, 2004 and are available to members of the ZigBee Alliance. An entry level membership in the ZigBee Alliance costs US$ 3500 and provides access to the specifications. For non-commercial purposes, the ZigBee specification is available to the general public at the ZigBee Alliance homepage.
The technology is designed to be simpler and cheaper than other WPANs such as Bluetooth. The most capable ZigBee node type is said to require only about 10% of the software of a typical Bluetooth or Wireless Internet node, while the simplest nodes are about 2%. However, actual code sizes are much higher, more like 50% of Bluetooth code size. ZigBee chip vendors announced 128-kilobyte devices.
As of 2005, the estimated cost of the radio for a ZigBee node is about $1.10 to the manufacturer in very high volumes. Most ZigBee solutions require an additional micro controller driving the price further up at this time. In comparison, before Bluetooth was launched (1998) it had a projected price, in high volumes, of $4-$6. The price of consumer-grade Bluetooth chips are now under $3.
ZigBee has started work on version 1.1. Version 1.1 is meant to take advantage of improvements in the 802.15.4b (still in draft) specification, most notably that of CCM* as an alternative to CCM(CTR + CBC-MAC)CCM mode. CCM* enjoys the same security proof as CCM and provides greater flexibility in the choice of Authentication and Encryption.
The basic idea behind this technology is to give the computer the human power. We all have some perceptual abilities. That is we can understand each others feelings. For example we can understand ones emotional state by analyzing his facial expression. If we add these perceptual abilities of human to computers would enable computers to work together with human beings as intimate partners. The “BLUE EYES†technology aims at creating computational machines that have perceptual and sensory ability like those of human beings.
Mesotechnology describes a budding research field which could replace nanotechnology in the future as the primary means to control matter at length scales ranging from a cluster of atoms to microscopic elements. The prefix meso- comes from the Greek word mesos, meaning middle, hence the technology spans a range of length scales as opposed to nanotechnology which is concerned only with the smallest atomic scales.
describes very well phenomena on the atomic to nanoscale while classical Newtonian Mechanics describes the behavior of objects on the microscale and up. However, the length scale in the middle ( Although the term itself is still quite new, the general concept is not. Many fields of science have traditionally focused either on single discrete elements or large statistical collections where many theories have been successfully applied. In the field of physics for example, Quantum Mechanicsmesoscale) is not well described by either theory. Similarly, psychologists focus heavily on the behavior and mental processes of the individual while sociologists study the behavior of large societal groups, but what happens when only 3 people are interacting, this is the mesoscale.
Z-Wave is the interoperable wireless communication standard developed by Danish company Zensys and the Z-Wave Alliance. It is designed for low-power and low-bandwidth appliances, such as home automation and sensor networks
Radio specifications
Bandwidth: 9,600 bit/s or 40,000 bit/s, fully interoperable
Radio specifics
In Europe, the 868 MHz band has a 1% duty cycle limitation, meaning that a Z-wave unit can only transmit 1% of the time. This limitation is not present in the US 908 MHz band, but US legislation imposes a 1 mW transmission power limit (as opposed to 25 mW in Europe). Z-wave units can be in power-save mode and only be active 0.1% of the time, thus reducing power consumption dramatically.
Topology and routing
Z-wave uses an intelligent mesh network topology and has no master node. A message from node A to node C can be successfully delivered even if the two nodes are not within range providing that a third node B can communicate with nodes A and C. If the preferred route is unavailable, the message originator will attempt other routes until a path is found to the 'C' node. Therefore a Z-wave network can span much further than the radio range of a single unit. In order for Z-wave units to be able to route unsolicited messages, they cannot be in sleep mode. Therefore, most battery-operated devices will opt not to be repeater units. A Z-wave network can consist of up to 232 units with the option of bridging networks if more units are required.
Application areas
Due to the low bandwidth, Z-wave is not suitable for audio/video applications but is well suited for sensors and control units which typically only transmits a few bytes at a time.
A graphics tablet is a computer peripheral device that allows one to hand-draw images directly into a computer, generally through an imaging program. Graphics tablets consist of a flat surface upon which the user may 'draw' an image using an attached stylus, a pen-like drawing apparatus. The image generally does not appear on the tablet itself but, rather, is displayed on the computer monitor. It is interesting to note that the stylus, as a technology, was originally designed as a part of the electronics, but later it simply took on the role of providing a smooth, but accurate 'point' that would not damage the tablet surface while 'drawing'.
A tablet PC is a notebook- or slate-shaped mobile computer. Its touchscreen or digitizing tablet technology allows the user to operate the computer with a stylus or digital pen instead of a keyboard or mouse. The form factor presents an alternate method of interacting with a computer, the main intent being to increase mobility and productivity. Tablet PCs are often used in places where normal notebooks are impractical or unwieldy, or do not provide the needed functionality. The tablet PC is a culmination of advances in miniaturization of notebook hardware and improvements in integrated digitizers as methods of input. A digitizer is typically integrated with the screen, and correlates physical touch or digital pen interaction on the screen with the virtual information portrayed on it. A tablet's digitizer is an absolute pointing device rather than a relative pointing device like a mouse or touchpad. A target can be virtually interacted with directly at the point it appears on the screen.
A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with the computer's CRT monitor. It allows the user to point to displayed objects, or draw on the screen, in a similar way to a touch screen but with greater positional accuracy. A light pen can work with any CRT-based monitor, but not with LCD screens, projectors or other display devices. A light pen is fairly simple to implement. The light pen works by sensing the sudden small change in brightness of a point on the screen when the electron gun refreshes that spot. By noting exactly where the scanning has reached at that moment, the X,Y position of the pen can be resolved. This is usually achieved by the light pen causing an interrupt, at which point the scan position can be read from a special register, or computed from a counter or timer. The pen position is updated on every refresh of the screen. The light pen became moderately popular during the early 1980s. It was notable for its use in the Fairlight CMI, and the BBC Micro. However, due to the fact that the user was required to hold his or her arm in front of the screen for long periods of time, the light pen fell out of use as a general purpose input device.
In computer hardware, Serial Attached SCSI (SAS) is a computer bus technology primarily designed for transfer of data to and from devices like hard disk, cd-rom and so on. SAS is a serial communication protocol for direct attached storage (DAS) devices. It is designed for the corporate and enterprise market as a replacement for parallel SCSI, allowing for much higher speed data transfers than previously available, and is backwards-compatible with SATA. Though SAS uses serial communication instead of the parallel method found in traditional SCSI devices, it still uses SCSI commands for interacting with SAS End devices. SAS protocol is developed and maintained by T10 committe. The current draft revision of SAS protocol can be downloaded from SAS 2 draft
Low voltage differential signaling, or LVDS, is an electrical signaling system that can run at very high speeds over cheap, twisted-pair copper cables. It was introduced in 1994, and has since become very popular in computers, where it forms part of very high-speed networks and computer buses.
LVDS uses the difference in voltage between two wires to signal information. The transmitter injects a small current, nominally 3.5 milliamperes, into one wire or the other, depending on the logic level to be sent. The current passes through a resistor of about 100 to 120 ohms (matched to the characteristic impedance of the cable) at the receiving end, then returns in the opposite direction along the other wire. From Ohm's law, the voltage difference across the resistor is therefore about 350 millivolts. The receiver senses the polarity of this voltage to determine the logic level. (This is a type of current loop signaling).
In computer networking a Media Access Control address (MAC address) is a unique identifier attached to most forms of networking equipment. Most layer 2 network protocols use one of three numbering spaces managed by the IEEE: MAC-48, EUI-48, and EUI-64, which are designed to be globally unique. Not all communications protocols use MAC addresses, and not all protocols require globally unique identifiers. The IEEE claims trademarks on the names 'EUI-48' and 'EUI-64'. (The 'EUI' stands for Extended Unique Identifier.)
ARP/RARP is commonly used to map the layer 2 MAC address to an address in a layer 3 protocol such as Internet Protocol (IP). On broadcast networks such as Ethernet the MAC address allows each host to be uniquely identified and allows frames to be marked for specific hosts. It thus forms the basis of most of the layer 2 networking upon which higher OSI Layer protocols are built to produce complex, functioning networks.
Native Command Queuing (NCQ) is a technology designed to increase performance of SATAhard disks by allowing the individual hard disk to receive more than one I/O request at a time and decide which to complete first. Using detailed knowledge of its own seek times and rotational position, the drive can compute the best order to perform the operations. This can reduce the amount of unnecessary seeking (going back-and-forth) of the drive's heads, resulting in increased performance (and slightly decreased wear of the drive) for workloads where multiple simultaneous read/write requests are outstanding, most often occurring in server-type applications.
TCQ stands for the Tagged Command Queuing technology built into certain PATA and SCSI hard drives. It allows the operating system to send multiple read and write requests to a hard drive. TCQ is almost identical in function to Native Command Queuing (NCQ) used by SATA drives. Before TCQ, an operating system was only able to send one request at a time. In order to boost performance, it had to decide the order of the requests based on its own, possibly incorrect, idea of what the hard drive was doing. With TCQ, the drive can make its own decisions about how to order the requests (and in turn relieve the operating system from having to do so). The result is that TCQ can improve the overall performance of a hard drive.
Differential signaling is a method of transmitting information over pairs of wires (as opposed to single-ended signalling, which transmits information over single wires). Differential signaling reduces the noise on a connection by rejecting common-mode interference. Two wires (referred to here as A and B) are routed in parallel, and sometimes twisted together, so that they will receive the same interference. One wire carries the signal, and the other wire carries the inverse of the signal, so that the sum of the voltages on the two wires is always constant. At the end of the connection, instead of reading a single signal, the receiving device reads the difference between the two signals. Since the receiver ignores the wires' voltages with respect to ground, small changes in ground potential between transmitter and receiver do not affect the receiver's ability to detect the signal. Also, the system is immune to most types of electrical interference, since any disturbance that lowers the voltage level on A will also lower it on B.
HyperTransport (HT), formerly known as Lightning Data Transport (LDT), is a bidirectional serial/parallel high-bandwidth, low-latency computer bus that was introduced on April 2, 2001[1]. The HyperTransport Technology Consortium is in charge of promoting and developing HyperTransport technology. The technology is used by AMD and Transmeta in x86 processors, PMC-Sierra, Broadcom, and Raza Microelectronics in MIPS microprocessors, ATI Technologies, NVIDIA, VIA, SiS, ULi/ALi, AMD, Apple Computer and HP in PC chipsets, HP, Sun Microsystems, IBM, and IWill in servers, Cray, Newisys, and PathScale in high performance computing, and Cisco Systems in routers. Notably missing from this list is semiconductor giant Intel, which continues to use a shared bus architecture.
