Active alignment – The process of aligning optical components in which the power of the optical signal is monitored and maximized before the components are finally attached. Assembly through active alignment is a significant source of the cost of today's optical components. Intel is researching passive alignment to reduce these costs.

Amplification – An increase in power. Also called gain. A net gain in an optical device means that this amplification exceeds all loss or attenuation in the device. This means it is possible to send an optical signal through the device and get a stronger signal at the output.

Channel – A wavelength of light that carries data. Optical fibers and waveguides can carry multiple simultaneous channels, increasing their information capacity.

Chirp – Changes in a laser's peak emission wavelength due to instabilities. For example, chirping occurs when directly modulating a laser to generate data. This causes the signal to become more distorted the farther it travels from the source. Using an external modulator, such the silicon modulator under development at Intel, greatly reduces chirp and improves the quality of the data.

Coherent light – A beam of light whose photons all have the same optical properties (wavelength, phase, and direction). Coherent light is important for communication because it travels much farther in optical fiber without distortion.

Complimentary Metal Oxide Semiconductor (CMOS) – A widely used type of semiconductor technology that uses both NMOS (negative polarity) and PMOS (positive polarity) circuits. Since only one of the circuit types is on at any given time, CMOS chips require less power than chips using just one type of transistor. Intel uses CMOS transistors to manufacture microprocessors and flash memory

dB (Decibel) – Usually used as a figure of loss or gain in an optical network. This is calculated as one-tenth of the logarithm of the output power divided by the input power. A gain of 3dB gain represents an increase of 100 percent.

Demultiplexing – The process of separating different wavelengths from a fiber utilizing multiple data channels. This is the opposite of multiplexing.

Electrical pump – An electrical current that is used to power a laser or optical amplifier. Electrical pumping is used for most semiconductor lasers, including the ones found in CD-ROMs, laser pointers, and most communication systems

External Cavity Laser (ECL) – A special laser built using a semiconductor laser and an external component. For example, a silicon filter can be added to improve the quality of a low-cost laser and to make it tunable (see tunable lasers). Intel researchers demonstrated such an ECL in 2002.

Fiber/Optical fiber – Very thin strands of pure silica glass through which laser light travels in an optical network. Optical fibers are used to bring light onto and off of a silicon optical chip. The core of the fiber can range from 6 to 125 microns. For reference, the diameter of human hair ranges from about 80 to 100 microns.

Filter – A device in an optical system that removes one or more particular wavelengths from a group of wavelengths. A filter can be used to isolate a specific data channel or to form an External Cavity Laser. Intel researchers demonstrated a silicon filter in 2002.

Frequency – The number of cycles of an electric signal per unit time, measured in Hertz (Hz). Frequency can be used to describe the lightwave itself and also to describe the rate of data modulation applied to a lightwave.

Gain – Gain - See Amplification.

Gallium Arsenide – GaAs. An exotic semiconductor compound used for making electronic and optoelectronic devices.

Gbps – Gigabit per second. 1 Gbps is 1 billion bits of data per second.

GHz – Gigahertz. Hertz describes the number of times an electrical signal completes a full cycle in one second. 1 GHz means the signal has changed cycles one billion times in one second.

Grating – A device used to separate different wavelengths. A grating can be used as a wavelength filter (see filter). By changing parameters of the grating (e.g. thermal tuning, or electrical tuning) the wavelength that is filtered can be changed. Intel demonstrated a thermally tuned grating in 2002.

Indium Phosphide – InP. An exotic semiconductor compound used for making electronic and optoelectronic devices.

Infrared – The region of the electromagnetic spectrum between red light and radio waves. This includes all wavelengths that are used in optical networks. Silicon is transparent to most infrared wavelengths used in optical communications, typically wavelengths from 1310 to 1610nm.

Integrated optical circuits – Similar in principle to electrical integrated circuits, but achieved by combining many miniature versions of optical components onto a single wafer, such as a silicon wafer.

Interconnect – An electrical or optical connection (or cable) connecting two devices. Examples of interconnects are the cable to connect a computer monitor to the computer, or the cable between the computer and the disk drive. There are many of these interconnects inside a typical computer.

Laser – Strictly speaking, Light Amplification though Stimulated Emission of Radiation. Today, a laser is considered to be any device that emits an intense, coherent beam of light (see Coherent light). Coherent light can carry data over great distances in optical fiber without distortion.

Lasing – The process by which lasers operate.

Mach-Zehnder Interferometer (MZI) – In general, an interferometer that splits an optical signal into two components and directs them down two separate paths, then recombines them. By inducing a phase delay between the two optical signals, the resulting interference can cause intensity changes. Such a device can modulate the optical power from 100% (constructive interference) to 0% (destructive interference). Intel's modulator operates using the Mach-Zehnder Interferometer approach to send optical 1s and 0s.

Mbps – Megabits per second. 1 Mbps per second is 1 million bits per second.

MHz – Megahertz. 1 MHz means the signal has changed cycles one million times in one second.

Micrometer/Micron – A measure of length: 1 µm = 0.000001 meter (1 millionth of a meter).

Modulation/Modulator – A modulator is a device that encodes data onto a beam of light at extremely high data rates by acting like a switch to turn the light off and on, similar to the way a transistor acts like a switch to turn the flow of electrons on and off. Intel's novel approach in Q1 2004 resulted in a silicon optical modulator operating at speeds in excess of 1GHz, 50 times greater than the previous world record of about 20 MHz. Fast modulation has been one of the critical barriers to making photonic devices out of silicon. Intel researchers have removed this barrier by designing an innovative new way to build an optical modulator out of silicon using Intel's standard manufacturing processes at an existing fab.

Monochromatic light – Light that contains only one color or a very narrow band of wavelengths. See also Coherent light.

Moore's Law – Gordon Moore's famous observation made in 1965. It projects the doubling of transistors every couple of years. Moore's Law has been maintained and still holds true today. Intel expects that it will continue to do so at least through the end of this decade. See Moore's Law.

Multiplexing – The combining of different wavelengths in a wavelength-division multiplexing system. By multiplexing different wavelengths in a single channel, the bandwidth – or amount of information that can be transmitted per unit time – is increased, much like a five lane highway supports more traffic than a single lane highway.

Multiplexing – See Wavelength-division multiplexing.

Nanometer (nm) – A nanometer is a measure of length. 1 nm = 0.000000001 meter (1 billionth of a meter).

Net gain – See Amplification.

Optical amplifier – A device that boosts an optical signal's intensity directly without performing an expensive optical-to-electrical signal conversion. Optical amplification extends the distance the signal will travel before it fades away.

Optical pump – A beam of light that is used to power a laser or optical amplifier instead of an electrical current. The first laser ever created used a flash bulb to optically "pump" a ruby crystal. Optical pumping is used in several applications, including Raman lasers and amplifiers.

Passive alignment – The process of aligning two or more optical components without actively monitoring the resulting output power. Contrasted with active alignment, in which the power of the optical signal is maximized before the alignment is finalized. In silicon, precise mechanical structures can be lithographically defined, which guide components into place. Passive alignment could eventually be used to attach an optical pump directly to a silicon laser.

Phase shift – A change in phase of a periodic signal with respect to another periodic signal or reference signal. Inducing a phase shift is at the heart of the Mach-Zehnder interferometer used for Intel's optical modulator.

Photodetector/Photodiode – A device that converts optical signals (photons) into electrical signals (electrons). A photodiode is used to read data from an optical fiber and send information to electronic devices. Intel has researched silicon-based photodetectors for optical communication.

Photon – The quantum unit of electromagnetic radiation. The elementary "particle" of light.

Photonics – The technology of transmission, control, and detection of light (photons). This is also known as fiber optics and optoelectronics.

PIN – a diode made from an intrinsic (un-doped) region surrounded by a p-doped and an n-doped region, hence P-I-N. Intel built a PIN into its Raman waveguides to sweep out electrons generated by two-photon absorption, which absorb light and prevent continuous amplification.

Rack to Rack – Refers to the connection, or cables, between one rack-mounted component and another.

Receivers – Devices placed at the end of an optical network with detectors to convert the laser light back into electrical form. In other words, converting the photons to electrons.

Refractive index – A property of a material that determines how fast light travels through it.

Silica – Very pure glass from which optical fibers are manufactured; a combination of silicon and oxygen—(Si02).

Silicon – The most common semiconductor for building integrated circuits, including microprocessors. Silicon can also be used to make photonic devices. The Raman effect in silicon is 10,000 times stronger than in glass fiber.

Silicon Photonics – Technology of making optical devices using silicon and standard CMOS manufacturing techniques.

Splitter – An optical device, typically a waveguide, designed to split an optical signal into two components.

Taper – A section of a waveguide or optical fiber that is tapered to allow for more efficient coupling into/out of a device. A taper is commonly used to minimize the amount of light lost between two optical elements, e.g. between a laser and a waveguide, or between a waveguide and an optical fiber.

III-V Semiconductor – Semiconductor alloys made from elements from Group III and Group V on the periodic table such as Gallium Arsenide (GaAs) and Indium Phosphide (InP), which are used to emit light in typical optical devices. Silicon is a Group IV element.

Transmitters – Devices placed at the beginning of an optical network to transmit light representing information. Usually consist of lasers and modulators. In other words, converting electrons to photons.

Tunable lasers – Lasers that can be adjusted to emit one of several different wavelengths or channels.

Two-photon absorption – A quantum mechanical process by which photons that would normally pass though an atom are instead absorbed because two photons arrived simultaneously with enough total energy to free an electron from the atom. This process can quickly generate free electrons in silicon, which can absorb even more light, and thereby counteract Raman amplification.

Waveguide – Guides light on a wafer in a way similar to optical fiber, acting like the optical equivalent of wires connecting different devices. These waveguides are constructed on silicon wafers by etching very precise silicon channels on the wafers. Through precise manufacturing, waveguides can be manufactured that will split the light into two beams (splitter), or the waveguides can be manufactured to focus the light into a narrower beam, (a taper).

Wavelength – The distance between successive crests of waves. All electromagnetic radiation (radio waves, microwaves, ultraviolet light, visible light, etc.) is transmitted in waves. In optical networks, different wavelengths are different colors of light.

Wavelength conversion – The process of taking light of one wavelength (color) and changing it to another wavelength (color). In communications, more data can be transmitted by sending multiple wavelengths of light down the same optical fiber. Wavelength conversion allows the switching of data from one wavelength to another. The Raman effect in silicon can produce such a wavelength conversion.

Wavelength-division multiplexing (WDM) – Transmitting many different colors (wavelengths) of laser light down a single fiber. By multiplexing, the bandwidth—or amount of information that can be transmitted per unit of time—is increased, much like a five-lane highway can support more traffic than a single-lane highway.