Fiber Optic equipment from Vistek

By Pavel Platov

Review contents:

Fiber Optic technologies in broadcast sphere Profitt Company equipment for Fiber Optic links of video, audio and data transmission Axon equipment BKtel equipment for Fiber Optic networks Fiber Optics in TV and Radio broadcasting Kramer Electronics equipment for Fiber Optic lines of TV signal transmission Network Electronics equipment Snell & Wilcox Fiber Optic receivers and transmitters Equipment of Telecast Fiber Systems Company Optical node getting closer to the household Fiber Optic equipment from Vistek

In recent years broadcast technology has changed dramatically; digital signals became wide used in this industry. And many gained opinion that for reliable operation of digital systems cable features are not so important yet.

But conventional cables with copper core cause serious limitations to high speed transmission of digital signals. Although there are copper cables designed especially for digital signals transmission the return loss these cables suffer from limit their use on distances over 500 m and in a case of high definition signals this value is even less.

An alternative to copper cables and to transmission electric signals over them is the use of Fiber Optic links and transmission light signals over them.

Transmitters, receivers and transceivers

To provide maximum systems flexibility Vistek Company has developed wide range of converters which allow combine copper-core cables and Fiber Optic cables. HD/SD V1674 models (designed for transmission both standard and high definition signals) and SD V1673 (aimed for transmission standard definition signal only) can be used as two channel transmitters, two channels receivers or in combining configuration with one transmitting and one receiving channel on each module (as a transceiver). On each transmitting channel one can set up to nine wavelengths in 1310…1610 nm range. Receiving channels designed with regard potential operation in full wavelengths range.

All converters operate under control of Vistek managing system which tracks their status and performs monitoring of alarm situations. Being connected to ViewNet client/server system developed by Vistek such a monitoring can be easily spread to third party systems supporting WAN operation via IP XML and SNMP network protocols.

Link budget

Despite of that the Fiber Optic cable transmits signals very effectively any Fiber Optic system have some loss. Developing the system it is necessary pay attention to total loss sum which may appear on particular communication path to make the transmitter’s output power appropriate to receiver’s input sensitivity. In simple systems with low number of physical connections the value of such loss can be very minor and even negligible. Meanwhile in large systems and especially if the line has passive optical devices these loss can affect pretty sufficient. Entire loss sum on the link path is called Link Budget and its calculation is the key moment for successful system’s developing.

Doubled single mode HD-SDI V1674 transceiver

V1679 — a converter of serial data signals to optical signal

For all devices included into Vistek catalog the calculated loss sum is given appeared at plugging the device to the line. But in calculation one should regard loss both in optical cable itself and in each connection link. For performing such calculations Vistek web site offer “Link budget calculator” in format of Microsoft Excel which can be downloaded from this site free of charge.

Over Fiber Optic networks not only video signals can be transmitted but also audio signals although in most systems digital video signals with embedded audio are used yet. But Vistek Company can offer also Fiber Optic transceiver containing module for audio embedding and de-embedding as a separate module.

Audio signal is only one from the elements with which broadcast companies have to work today. For them important roles play broadcast monitoring and control and control signals transmission over Fiber Optic cables always looks as native extension to program signals transmission. Vistek Company manufactures Fiber Optic converters supporting various formats from simplest GPI to Ethernet.

Passive processing

After conversion of electric signal to light beam the possibility arise to correct the method of this light beam transmission. At the simplest level the light beam from single Faber Optic cable can be divided in several ways and most often by means of opto-coupler. Usually such device has one input and two or four output ports. Incoming beam divides between output ports as a rule in equal parts (50/50) although uneven division is available at which less part of signal (10…20%) directs to one port for monitoring and testing while second parts goes to another port for transmission on long distances.

Another way is use of WDM — Wavelength-Division Multiplexer. This device can separate or combine two light waves with different lengths. WDM device in its design while looks like two output optical couplers differs from them because provides very low loss between input and output.

Optical couplers as well as WDM devices are duplex and balanced. If connect light source to one of output ports of a device than this signal will appear also in both second output port and input port. This feature allows single WDM device be both multiplexer and de-multiplexer.

V6705 — CWDM optical multiplexing module (left) and V6755 — optical multiplexer/de-multiplexer of SDI/audio signals

In those cases when more than two signals are involved the additional CWDM (Coarse Wavelength-Division Multiplexer) device is used. It just widens number of channels WDM device is able to work with and for Vistek products — up to 5 or 9. Nine is maximum number of channels which CWDM devices can provide because acceptable deviations of laser diodes do not allow wavelength reproduction with precision more than ±3 nm. In telecommunication industries there is wide used technology called DWDM (Dense Wavelength-division Multiplexing) but it presumes cooled lasers use which increases expenses pretty much.

CWDM modules which also feature duplex mode are used in complex systems of re-distribution where lots of signals involved.

In those cases when multiple Fiber Optic cables connections take place it is more reasonable to use optical routers allowing select redundant cables. Usually routers have 2×1 and 2×2 commutation schemes.

System integration

All Vistek Fiber Optic products are included to V1600 modular system range that’s why upon desire it is possible to combine very different modules: high definition and standard definition, video, audio, control. All they can be fitted to the same frame slot (mounted to 19" rack) along with other Vistek V1600 system modules. It allows integrate Fiber Optic inputs/outputs as an integral part of a general purpose system instead of directing signals to exact racks with Fiber Optic equipment.

Material provided by Oltbert Company