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Just about every broadcast and audio visual system today has some sort of a video and audio routing switcher. The switcher gives the user the ability to control the source and destination of a given video and audio signal. As more and more video and communications migrate from copper to fiber, it makes sense that the need for an optical routing switcher arose. The optical routing switcher is a new concept for the video market, but it has been used for many years in the telecommunications industry. It has been used to route and control telephone traffic.

As video and broadcast television industries become more and more complex with dozens of different video and encoding formats, optical switching starts to make more sense. In broadcast or video application there may be analog video, component video, SDI, and HD-SDI. An optical switch can switch most signals in the optical domain. There are two basic types of optical switching.

Photonic Fiber-Optic Switcher

The first is 100% optical switching using 3D micro-electromechanical mirror (MEMS) technology. It uses electronically controlled mirrors to route optical signals. This type of switch has an optical input, an optical cross-point, and an optical output. The abbreviation for this technology is OOO. An OOO switch provides only point-to-point switching. One input cannot be multicast to many outputs. The mirrors cannot point to more than one output at a time. The use of mirrors does permit multiple wavelengths and wavelengths in both directions. Switches are available is sizes from 8 × 8 to 256 × 256. Pure optical switching is available for multimode and single-mode applications. Optical switching supports both analog and digital optical signals.

Pure optical switching is performed using 3D MEMS arrays. Tiny mirrors are fabricated out of silicon. The mirrors are positioned and controlled with electrostatic charges. The core of the optical switch is a 1 inch square cube. The cube has an array of up to 256 input fibers on the left side as shown in Figure 6.10-15. Each fiber has a lens that focuses the optical light onto a MEMS mirror. Each input has its own mirror. On the right side is an array of output fibers. Each output has a MEMS mirror. An optical connection is made when one input mirror aligns with one of the output mirrors.

Fiber-optic switching is ideal for video broadcast, production, security, and other video applications requiring transmission, switching, and replication of high-quality optical signals. The fiber-optic switcher revolutionizes how video is distributed and managed. It is based on state-of-the-art field proven photonic switching technology. Laser light is switched in a pure optical format, without electrical conversion, allowing it to support transparent connections compatible with any video or data format including uncompressed HD video at 1.5 Gbps. Also, since the switching is done optically, the switch eliminates video degradation. With a traditional electrical switcher, electrical-to-optical (EO) and optical-to-electrical (OE) conversions are required that cause signal degradation and jitter.

An optical switch supports a wide range of formats from 19.4 Mbps ATSC through 1.5 Gbps HDTV as well as NTSC, PAL, SECAM, SMPTE 259M serial digital (SDI) video, broadband analog, L-band, IF, and many more. The optical switcher will also transparently switch CWDM and DWDM signals.

FIGURE 6.10-15 Three dimensional MEMS pure optic switching element. (Photo provided by Calient Networks.)

Optical switcher technology can be used in the field to support applications requiring reliable, high-quality video distribution such as mobile production trucks, sports venues, and professional video facilities; campus video and surveillance networks; remote video monitoring; as well as government and military. Optical layer protection and fault tolerant switching can be configured for mission critical, nonstop applications.

Optical switching is cost effective for any applica- tions requiring 32 or more switched optical ports. It eliminates the need for expensive video transceivers to convert signals between electrical and optical formats. Switching the signals in optical format can substantially reduce the cost per port in fiber-optic transport equipment costs.

ElectroOptical Switch

The second type is the electro-optical switch. The electro-optical switch uses a hybrid approach. The input is optical, the cross-point is electrical, and the output is optical. The abbreviation for this technology is OEO. An OEO switch supports point-to-multipoint or multi- cast switching. Any input can be switched to every output if necessary. Since the optical signal is converted to electrical, only one wavelength can be switched at a time. Also an electrical cross-point only operates in one direction. Therefore, only one wavelength in one direction is supported.

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