Posts by Justin Bertelsen

Overview Quantum Cascade Laser (QCL) is a semiconductor-based laser whose operation is unipolar meaning it only depends on the inter-band transition of electrons. QCLs have an optimum operation band between 3µm-100µm. These LongWave (LWIR) Infrared signals are in the atmospheric transparency window for FSO communications. Application of QCL technology to the communication field will prove…

Overview Optical Wireless Home Networks (OWHN), more commonly known as indoor FSO networks, is a wireless broadband communication within homes and office buildings. This technology relies on the use of infrared and visible light to transmit data as well as illuminate the space simultaneously. OWHN must be connected to a network backbone that allows individual…

Overview Error control coding (ECC) is the coding procedure done to control the occurrences of errors. These techniques help in Error Detection and Error Correction. There are many different error correcting codes depending upon the mathematical principles applied to them. [1] For free-space optics, ECC grants redundancy in laser uplink. The primary technique used for…

Overview Eye safety is a prominent topic for any optics technology. Since FSO products, especially in urban areas, will be directing laser beams into potentially populated areas, laser eye safety is a fundamental design concern. Although the damage threshold for ultraviolet light is much lower than it is for infrared, [1] infrared light is still…

Overview Smart antennae are antenna arrays with smart processing algorithms and are used in identifying spatial signals. A smart antenna takes advantage of the diversity effect at either the source (transmitter), the destination (receiver), or both. The diversity effect increases data speed and reduces error by combining the transmission and/or reception of multiple radio frequency…

Overview Free-Space Optics (FSO) communication, also called free-space optical communication, is an optical communication technology that uses light propagating in free space to wirelessly send a signal. For example, using a flashlight and turning it off and on to send Morse code is FSO communication. Another example is using a laser rapidly turning off and…

Overview FSO communications have built-in interception resistance due to the way information is sent. Consider first how a radio-frequency signal is sent. RF signals are broadcast over an area and are then funneled with point-to-point connections whereas FSO is exclusively point-to-point. Since RF is broadcast, an eavesdropper of an RF signal doesn’t sap much power…

Overview Wavelength division multiplexing (WDM) is the combination of many optical signals into one transmission medium. Rather than sending a signal at 1550nm or 630nm, or sending both using two individual terminals, WDM enables the signals to be combined and sent using one transmitter. WDM is commonly used in fiber-optics and is an emerging technology…

Some FSO Limitations include the following: Obstructions Flying birds, trees, and tall buildings can temporarily block a single beam when it appears in line of sight (LOS) of transmission in an FSO system. Scintillation There can exist temperature variations in the free space between a transmitter and receiver in FSO communications; they manifest as pockets…