Useful Information
- ♦ Application
- ♦ Cameras
- ♦ Lenses
- ♦ Light & CCTV
- ♦ Number Plate Recognition
- ♦ Thermal Imaging
- ♦ Housings
- ♦ Digital Images
- ♦ Digital Technology & Recording
- ♦ Video Compression
- ♦ Infrared
- ♦ IR & LED Lighting
- ♦ IP CCTV & Technology
- ♦ Monitors
- ♦ Motion Detection
- ♦ Multiplexers
- ♦ PIR Movement Sensor
- ♦ Remote Positioning Devices
- ♦ Video Motion Detection
- ♦ Police and Standards
- ♦ Multiple Screen Display
- ♦ Signal Noise Ratio
- ♦ Survellance Vechicle
- ♦ Three-dimensional (3D) design in CCTV & Security
- ♦ Transmission of Video Signals by Cable
- ♦ Transmission of Video Signals by Remote Methods
- ♦ Transmission of Video Signals by Fiber Optics
- ♦ Video Analysis
- ♦ Wireless CCTV
Transmission of Video Signals by Fiber Optics
Most people are familiar with the everyday use of light, X-rays, radio waves, microwaves, and Radar. All of these are actually examples of electromagnetic radiation, which is characterised by a radiation wavelength or oscillation frequency.
The 400 - 750 nm region of the spectrum is the region of visible light; this region is expanded in the lower part. The area of interest for fibre optic transmission extends from the red region of the spectrum out into the wavelengths much longer than those visible to the human eye, the infrared. Specific wavelengths used have been driven by the requirements of the fibre technology and by source and detector technologies. Particular wavelengths used are nominally 780nm, 850nm, 1310nm, and 1550nm.
The different parts of the spectrum have previously been described in terms of the wavelength. An alternative measurement is the frequency of the part being considered. Frequency is the number of crests of a wave that move past a given point in a given unit of time.
The most common unit of frequency is the hertz (Hz), corresponding to one cycle per second. The frequency of a wave can be calculated by dividing the speed of the wave by the wavelength. Thus, in the electromagnetic spectrum, the wavelengths decrease as the frequencies increase, and vice versa.
Different frequencies have different bandwidths and the higher the frequency the wider is the bandwidth. The wider the bandwidth then the more information can be carried. Frequencies above the visible part of the spectrum offer a wider bandwidth, therefore they provide more space for the multiplicity of TV signals and reams of data that need to be transmitted.
Transmission by Light:
In fibre optics, messages whether data or video are first converted from electrical impulses into pulses of light. This function is performed by a minute device that incorporates a laser chip or an LED (light emitting diode). The infrared light is switched on and off at incredibly high speeds, thereby creating the stream of light pulses. These are then focussed onto the end of the optical fibre. The lightwaves travel along the fibre to the receiving end. Here the light pulses are converted back into electrical pulses by a photodiode or avalanche photodiode.