Myth 1: Fiber optic transmission systems require continuous maintenance. Twenty years ago, it was a true statement. The average fiber optic transmitter needed to be tuned and tweaked every six months or so due to the general loss of intensity of the optic emitter and the weaker, less stable fiber optic receiver. Today’s systems, however, use higher-grade electronics and, for the most part, monitor and self-correct for normal wear of the optic emitter. Additionally, the higher-quality receivers do not desensitize as quickly. The net result is low-maintenance fiber optic transmission/reception systems.

Myth 2: Fiber optic systems require extensive training to design, install and/or troubleshoot.

With today’s systems, an average Joe or Jane can run a fiber optic cable, attach connectors and power-up a simple system using nothing more than the instructions in the box. Granted, more involved systems require training and experience. But at the end of the day, common sense is the rule, not the exception, with designing fiber-optic systems. You do not need to be an engineer or technician to learn fiber optics. As for installation and troubleshooting, what can I say? We have simple crimp-on connectors that anyone can do, and many of our transmission/reception systems are totally self-diagnostic and even, in some cases, self-adjusting.

Myth 3: Fiber optic systems are extremely expensive. Granted, fiber optic systems may not necessarily save you money on the up-front or in a single-camera, short-run scenario. But it might.

Consider using a single coaxial cable for an outside camera application. Let’s make it simple and say that the run is 500 feet long. To properly install this single coaxial cable system outside, you should install a surge protector for lightning, and will probably require a ground loop corrector (GLC) of some sort. Well, you just ran the cost of that coaxial cable up by an average of $150. The fiber-optic system may require a fiber optic converter, but it will not require surge protection or a GLC. At the end of the day, your overall cost on this simple, single fiber run will be about 20 percent more than if you did the job with coaxial. Since fiber optic cable can be run in the same conduit as high voltage (depending upon local electrical codes), you could save a fortune not having to tear up your parking lots trenching for coax. Before you throw fiber optics out the door because of cost, you should do a serious comparison of both short-term and long-term expenses. In most cases, when fiber costs more on the up-front, it will save you a lot on the long-term.

Myth 4: Fiber optic cable is fragile and hard to work with. I think this myth came from the old days of grind-and polish connectors. Granted we still have and use these styles of connectors. When first learning to install them, the average person can break the optic glass … so it seems that the fiber is fragile. The fact is, however, that fiber cable is stronger and more flexible than coaxial cable because 98 percent of the fiber cable is designed for strength while less than 5 percent of the coaxial cable is designed for strength. Additionally, fiber optic cables are made with pure glass. Pure glass is flexible and strong.

Tale 5: Fiber is great, but we can only send a maximum of four video signals down a single fiber. Oh this is a really big one … We are able today to transmit up to 64, real-time, full-resolution video images, bidirectionally (128 actual video signals) on a single fiber simultaneously and … on the same fiber, at the same time, send 64 channels of stereo quality audio, bidirectionally (128 actual audio channels) and … on the same fiber, at the same time, send 64 data or control signals, bidirectionally (128 individual controlling signals). Now, daisy chain this system up to five times with up to five miles between points, and you have 320 bidirectional, real-time signals. Now expand the system and start adding things up. What a hoot! If nothing else, you should be able to see that there is a huge list of potentials for fiber-optic applications between a simple, single camera run and the end of your imagination

OK, with the myths out of the way, we can concentrate on the fiber optic transceiver.

Overall, I have developed a few “Golden Rules” of fiber-optic design that I live by. They are as follows:

Fiber-Optic Golden Rule 1: You will always be better off working with fiber-optic companies that specialize in CCTV and/or security applications – this versus telephone- and/or data transmission-related companies. Why? Telephone companies run hundreds of thousands of miles of fiber-optic cable each year. They handle millions of data and audio signals each hour. So why wouldn’t these folks be the best to go to for my surveillance fiber needs? Because your surveillance/security optic specialists will

- understand your applications better;

- have a wider, more applicable line of equipment designed especially for the CCTV security industry; and

- have a stronger base of knowledge and support available for the design, installation and servicing of surveillance/security-based fiber-optic systems.

Bottom line, if you have heart problems would you go to a general practitioner?

Fiber-Optic Golden Rule 2: Work with the best equipment and fiber-optic cable available. Pinching pennies on fiber-optic cable and/or equipment falls in the same category as pinching pennies on coaxial cable. You will save on the up-front, but will pay in the end. Ending payments come in the form of extensive system downtime, repeat problems, interruptions of security and extensive service costs.

Fiber-Optic Golden Rule 3: Verify the credentials of the individual(s) who are designing your fiber-optic transmission system. If you have a few cameras and a basic, run-of-the-mill application, it’s OK to let someone break their teeth on your system design. Fiber is that easy to work with! On the other hand: If you are planning a major system of 10 cameras or more, have extensive cable runs, and/or are looking for speciality or involved applications, you need to check credentials. Make sure that the individual(s) doing your design and/or installation work have the proper training, experience and manufacturer support to do the job right. Fiber is that involved! You notice that I mentioned manufacturer support. On the CCTV side of the fiber-optic industry, manufacturer support is available and unprecedented. A simple phone call can save hundreds of dollars in errors and hours of frustration. In the fiber industry, it is possible to speak directly to the experts you need on any level. The majority of the individuals you will speak with on this side of the industry have grown up with the industry. They have been here since fiber optics was nothing more than a prediction. No, theyre not that old. They have just been at if for the past 20 or 30 years. That’s about as long as fiber optics have been used in the CCTV industry.

CCTV over Fiber Optic Golden Rule 4: Plan, review, plan, review, and plan some more. Granted, on a simple, smaller fiber-optic system, there is little planning necessary to have a trouble-free environment – buy it off the shelf and put it in. However, the larger the system, the more planning and review you should do before buying a single piece of equipment. There are so many options for system interface and cooperative transmission that you need to plan carefully.

CCTV Fiber-Optic Golden Rule 5: To fully appreciate what the fiber systems of 2001 can do to enhance your CCTV system and security in general, you need to shop around and ask questions.

Learn about the technology that is available before you spend too much time or money designing the controlling, transmitting, and/or hardware side of your CCTV system or upgrade. The first step to any CCTV system is to lay out and design the purpose of the overall system and then each individual point of observation or camera. After that you go for the transmission media and controlling systems. It is at that fragile point between purpose and controlling systems that you should familiarize yourself with what is available from the surveillance optic groups. Learn about the potentials, advantages and applications where fiber optics can be applied, and I think you will be amazed at what you can do. Simple stuff like running long-distance cables parallel to high voltage without any interference.

Fiber-Optic Golden Rule 6: Don’t let the technology intimidate you. Fiber optic video transmitter is nothing more than turning electrical signals into modulated light and injecting that light into the end of a piece of glass or plastic. At the other end, the modulated light is transformed, through photosynthesis, back into electronic signals. You don’t need to understand the technology involved to take advantage of this medium. You do need, however, to investigate the advances that fiber optics have made over the past five or 10 years. These are the hidden assets that will take your overall surveillance security into and beyond the future at an affordable cost.

All right, we have covered the myths and the golden rules of fiber optics. It sounded a lot like common sense, didn’t it? What did you expect? At the end of the day, a truly good designer is nothing more than an experienced (sometimes), trained (sometimes) individual with a strong presence of common sense, a large reference library, and a lot of contacts. We pay these people to represent our best interests. However, as a designer of systems, I can honestly say that my best customers are those who take the time and effort to open their eyes and minds to their own dilemmas and take part in the decisions from an educated, common-sense perspective. Take a good look at fiber … take your time … it’s not that difficult, and the overall advantages are huge.

Benefits Include:

1. Fiber optical cable support higher bandwidth and faster data rate transmission than either copper twisted pair wire or coaxial cable.

2. As a result of low loss, fiber optic cable can transmit at much greater distances, than either twisted pair copper or coaxial cable. Commercially available fiber optic converter can transmit video, audio and data for many kilometers/miles without requiring a repeater. This is compared to a copper coaxial cable that requires repeaters almost every mile. A repeater consists of a fiber optic transmitter and fiber optic receiver or fiber optic transceiver and is used to regenerate a signal in order to increase distance.

3. Fiber is immune to electro-magnetic (EMI) and radio frequency interference (RFI), lightning strikes, and is not conductive. Unlike copper, it does not cause ground loops and since photons are transmitted, there is no possibility of a fire hazard from a spark. Optical cable may be installed next to high voltage electrical equipment and power or be lashed directly to telephone lines.

4. The materials in optical cables include glass, Kevlar, plastic and PVC. If the cable is specified as an “all dielectric” (non metallic), it is not affected when installed in and exposed to corrosive, chemical environments. It can also be specified for direct burial in the ground with rodent protection.

5. A multi-stranded fiber optic cable is always much smaller in diameter and lighter in weight than the equivalent multi-stranded copper or coaxial cable. It is easier to handle and can usually be installed in existing conduit or duct space – even when the conduits are already filled with other cables.

6. Fiber optic cable is ideally suited for secure communications systems because it is very difficult to tap. The equipment required to decode transmission through a fiber would have to decipher if the signal is analog AM or FM, Digital, LED or Laser based and the optical frequency employed. If the fiber is cut, the “leaking of light” may be picked up as loss of signal at the monitor end.

Figure 1. Optical System Design Consideration

1. Determine the correct optical transmitter and optical receiver based upon the signals to be transmitted – video, audio (bal/unbal 600, unbal 10k or 47k Ohm) data (over the Coax as Coaxitrontm and Proteustm , Manchester, Biphase, RS-232, RS-422, RS-485, Sensornettm, Ethernet, TTL, Open Collector or Contact Closure);

2. Determine the operating power available at remote locations (24VAC, 12VDC) and at the control rooms (120V, 240V);

3. Determine the type (multimode or singlemode) and number of available fiber strands and optical connectors installed on the cable (ST or FC);

4. Calculate the total optical loss (in dB) in the system from end to end; include cable, splices, patch panels and connector losses. Parameters should be available from the manufacturers of the optical cables, fiber accessory hardware (patch, splices) and/or the sub contractor who installed the cable network;

5. Compare the loss figure obtained with the optical loss budget of the electronics as per the manufacturer’s specifications. In order to account for ageing of light sources, add a safety margin factor of 3 dB to the entire system.

6. When transmitting multiple high bandwidth signals, as in video multiplexers, compare with the available bandwidth in the fiber, to ensure the signal will be transmitted.

Example # 1: we have a requirement for transmission of 1 video signal with bi-directional PTZ data, there is one fiber available and the distance required is 13,000ft or a little less than 4Km (1Km = 3381ft.). As the signal is carried through several buildings, there are a total of 6 patch panels from end to end. Let us assume the loss of the video/data link is 13dB and the center carrier is 70 MHz. The specifications indicate that the video signal is transmitted @ 1300nm and fiber loss and bandwidth are specified @ 1dB and 500 MHz, respectively. NTK3631 Series transceivers are specified.

Distance required is 13,000ft. or 4Km

Calculation # 1 – as to loss budget

Fiber rated @ 1dB loss per Km x 4 Km, loss in cable = 4dB
Connector loss is system @ 1dB/connector x 2 = 2dB
Patch Panel loss in system @ 0.5dB/adapter x 6 = 3dB
Safety Margin = 3dB
Total Loss = 12dB
Since the 3631 Series link budget of 13dB is better than the 12dB the system requires, the conclusion is
that, based on loss, video/data signals may be transmitted on the 1 fiber.

Calculation # 2 – as to available bandwidth
Fiber optic Bandwidth per Km @ 1300nm = 500MHz
Divided by Bandwidth of 3631 Series System = 70MHz
Total Distance System may Transmit = 7 Km
Since the video/data signals use 70MHz, one simply divides the available fiber bandwidth of 500 MHz by
the system bandwidth of 70MHz. The result indicates that, based on bandwidth, the video/data signals may
be transmitted on the existing fiber.

Example # 2: we have a requirement for transmission of 4 video signals, there is but one (1) fiber available and the distance required is 10,000ft or a little less than 3Km. As the signal is carried between two buildings, there are two (2) patch panels – one at each end. Let us assume the loss budget of the video multiplexer is 10dB and carrier (combined bandwidth) of the 4 video signals is 150 MHz. The specifications indicate that video signals are transmitted @ 1300nm and fiber loss and bandwidth are specified @ 1dB and 500 MHz respectively. NTK3644 Series transmitters and receivers are specified.

Distance required is 10,000ft or 3Km

Calculation # 1 – as to loss budget

Fiber rated @ 1dB loss per Km x 3 Km, loss in cable = 3dB
Connector loss is system @ 1dB/connector x 2 = 2dB
Patch Panel loss in system @ 0.5dB/adapter x 2 = 1dB
Safety Margin = 3dB
Total Loss = 9dB
Since the 3644 Series link budget of 10dB is better than the 9dB the system requires, the conclusion is that,
based on loss, 4 video signals may be transmitted on the existing fiber.

Calculation # 2 – as to available bandwidth
Fiber Bandwidth per Km @ 1300nm = 500MHz
Divided by Bandwidth of 3644 Series System = 150MHz
Total Distance System may Transmit = 3.33 Km

When fiber is rated @ 500MHz per Km, it does not mean that for every new Km, there is an additional 500MHz. Since the 4 video signals use 150MHz, one simply divides the available fiber bandwidth of 500 MHz by the system bandwidth of 150MHz. The result indicates that, based on bandwidth, the 4 video signals may be transmitted on the 1 fiber. If, after performing the calculations, it is discovered that the loss is greater or bandwidth is inadequate, it will be necessary to consider the installation of additional fiber.

Typical Applications

The following chart of typical applications includes the reasons, advantages and benefits when fiber optic transmission systems are installed over copper twisted pair or coaxial systems.

Making sure that transmission is able to cope with system requirements now and in the future is not only key to a future-proof security and surveillance system, it also allows for easy and cost-effective expansions.

There are, however, many transmission technologies and media available; hence, deciding and designing the appropriate solution is not necessarily straightforward.

This article highlights the advantages and disadvantages of different technologies and designs and will, hopefully, provide some guidance in terms of how one can avoid some of the usual integration and configuration bottlenecks.

With a completely new project with no legacy technology involved, the first thing you have to consider is which signal format you plan to use — that is, compressed or uncompressed video signals.

If you start a network from scratch, this decision has major implications for the transmission network and medium(a) you design your network around.

Depending on the distances involved, choices for compressed video signals include coaxial cables (Cat-5/6), fiber optic transmission (multi-mode optical fiber  or single-mode optical fiber, CWDM or DWDM), Ethernet, wireless transmission (unlicensed or licensed frequencies) or a mobile network.

If you need to transmit uncompressed video signals, media include coaxial, twisted pair, wireless and optical, depending on your requirements and distances.

The physical layout of the network — the topology — is often a function of the geographic distances and transmission medium(a). The topologies usually employed are star (also known as point-to-point), ring, bus (also know as spur) and mesh (a combination of star and ring. See <Figure 1>.

In many projects, however, there is either some legacy equipment involved in the transmission. Or, there may be other specific requirements which necessitate the consideration of one more element, namely the mixture of signals on the network:
* Uncompressed, all analog: analog cameras and analog transmission
* Compressed, all IP: network cameras and IP transmission
* Hybrid: analog cameras, analog and IP transmission
* Mixed: analog and network cameras, analog and IP transmission

Uncompressed
In an ideal world, an uncompressed network would be preferable, as it affords the highest video quality for PAL/NTSC cameras and is well-understood for easy installation and maintenance.

You have a number of vendors you can choose from, although some solutions are considered proprietary. <Table 1> shows the advantages/disadvantages of the various media for uncompressed transmission.

Uncompressed Transmission

Compressed
The main advantage in a compressed transmission network is that it allows video to fit into the global IP standard.

As HD cameras are beginning to gain traction, the technology will gradually offer resolution benefits over uncompressed PAL/NTSC video. It is important to note, however, that a compressed solution can be limited in frame rate, can have issues with the temperature range it is operating in, and may have low-light performance issues.

On the other hand, a compressed solution can use existing network infrastructure, such as Ethernet. Another thing to take into consideration is that historically compressed solutions have been troubled by algorithm obsolescence and vendor-dependent algorithm implementation. Further, there are trade-off issues with quality, latency and bandwidth.

Now, we are seeing more multivendor protocols emerging, requiring IT skills to install, commission and maintain networks. <Table 2> shows the advantages/ disadvantages of the various media for compressed transmission.

Compressed Transmission

Hybrid Networks
A hybrid solution employs analog cameras with analog transmission to a control point/room where you then apply video compression. An IP network is used to link the control points together. One could argue that a hybrid solution offers the best of both worlds. It gives you the largest choice of high-resolution cameras while retaining a high degree of security integrity because it keeps IP away from the edge of the network.

It allows for easy upgrades of compression equipment while retaining the benefits associated with analytic software, which you do not have to install at the edge of the network, providing you with the highest quality signals available for content analysis. You have the flexibility to install analytics on any camera in a controlled environment, even deploying different software on different cameras for easy upgrades. Best of all, you can work with a multivendor system.

Mixed Networks
Mixed networks tend to be legacy-based, and they allow you to mix HD compressed cameras with PAL/NTSC uncompressed cameras. This caters for the application of centralized analytics on PAL/NTSC cameras and allows you to choose the best-of-breed technology for each location need. It further allows you to build a multivendor system.

How to Decide?
Start by considering all the technologies and topologies available to make sure you design a network based on the requirements of your given project. Many users are not aware that the requirement specification is actually not a technology specification. You need to make informed decisions with respect to picture quality, maintainability, resilience, cost, security and future requirements.

Only when you have considered these elements can you effectively decide the technology best suited for your particular project. In terms of topology, a point-to-point system may require the lowest initial equipment cost, but may be expensive in terms of maintainability, resilience, scalability or manageability. The more significant the requirement is in terms of security, the more up time and resilience matter in the transmission topology selected.

An fiber optic transmitter converts electrical input signals into modulated light for transmission over a fiber optic cable. Depending on the nature of the signal, the resulting modulated light may be turned on and off or may be linearly varied in intensity between two predetermined levels. Figure (2) shows a representation of these two basic schemes.

The devices used as the light sources in optical transmitters are Light Emitting Diode (LED) and Laser Diodes. LEDs and Lasers are semiconductors mounted in a TO style can or microlens package that focus the beam of light right into the optical fiber connector. In the case of analog FM transmission, the Laser is “pigtailed” directly onto the surface of the emitter in order to reduce or eliminate back reflection and noise.

LEDs have a wide spectral frequency, are suited for large aperture multimode fibers and are used for short to moderate transmission distances. Lasers, on the other hand, feature a narrow band of wavelengths and can couple many times more power into the fiber than LEDs and therefore are useful in applications that require high speed, high bandwidth over long distances. Lasers are not stable over wide operating temperatures, however, with well-designed feedback circuitry, continuous stable output can be achieved.

Analog modulation takes a number of forms – see figure (3). The simplest is intensity modulation (IM) where the brightness of an LED is varied in direct step with the variations of the transmitted signal. In other methods, an RF carrier is first frequency modulated (FM) with another signal or, in some cases, several RF carriers are separately modulated, then are combined and transmitted as one complex waveform.

Fiber Optic Receivers

The fiber optic receiver converts modulated light coming from an optical fiber back into the original electronic signal applied to the transmitter.

The detector is a photodiode of either the PIN or the Avalanche type and is mounted in a similar package to the one used for the LED or Laser. Sensitivity of the receiver is specified as the minimum signal that it can receive (in dBm). Dynamic Range is the difference between the minimum and maximum acceptance levels. Receivers usually employ high gain internal amplifiers and require special circuitry to avoid saturation or distortion. When the optical dynamic range of the system is equal to the optical power budget, no saturation of the receiver can occur. Quality of signal transmission is equally good at short or long distances.

As in the case of fiber optc transmitters, fiber optic receivers are available in both analog and digital versions. Figure (4) is a functional diagram of a simple analog optical receiver.

This example illustrates the main features of any fibre optic system, which are as follows:

1. The fibre optic link and its associated terminal equipment fit between the camera and the associated monitor/controller and provide a transparent signal path i.e. the camera and controller do not know that the signals have been transmitted over fiber.

2. The camera output is a 1V peak to peak composite video signal.

3. Movable cameras have a telemetry receiver is mounted near to the camera movement mechanism. This telemetry receiver connects to the system controller to provide control of the camera pan/tilt and zoom PTZ functions.

4. At the control end of the link camera selection and movement is looked after by the system controller and video signal outputs from the controller are displayed on a local monitor(s).

5. Electrical to optical and optical to electrical converters provides the interfaces to the optical fibre transmission fibre.

6. At the camera end of the link the E/O converter is usually a single channel unit packaged in a small enclosure which can be conveniently mounted near to the camera or telemetry receiver. These E/O converters are not usually environmentally sealed and so need to be protected from the elements often mounting them in the telemetry receiver enclosure. In their most cost effective form a PTZ cameras E/O converter will use two multimode fibres to give a uni-directional video connection plus a bi-directional control data channel.

7. As an alternative these control and video link functions can be carried over a single fibre using optical transmission at two wavelengths, WDM – wavelength division multiplexing. These WDM links are more expensive than single wavelength links but they do save on fibre usage and they also can make the best use of a previously installed fibre infrastructure.

8. The E/O converter data interface must be compatible with that used by the system controller; these are often non-standard.

9. Fixed cameras can use a miniature E/O transmitter, which can connect directly to the camera BNC signal output. This link requires only one fibre.

10. The camera end E/O converter is connected to the transmission fibre through a patch box. This patch box provides a point of termination for the transmission cable and so prevents strain and wear and tear being placed on the transmission cable when installing, servicing or moving the terminal equipment. Optical connections between the E/O converter and the patch box are made with duplex patchleads (which are short fibre cable lengths terminated at each end with an optical connector). The patch box will only be a relatively small enclosure because it will only need to provide connectivity for a few fibre cores.

11. At the control room end of the link fibres from a large number of cameras will be concentrated. Equipment must therefore be packaged accordingly and most often this means the use of 19” rack mount units. E/O converters are manufactured in modular card format, which enables multiple video channels to be accommodated in a 19” cage. Typically one 3 U high rack can accept plug-in E/O converters for up to 30 video only channels or 10 video/data channels (or a mixture of both).

12. The fibre transmission cables are also handled in 19” rack enclosures because now we will be organising many fibre cores. These enclosures are called patch panels and they again provide a physical buffer between the transmission cable and the terminal equipment. Here the cable will be bought into the rear of the patch panel via a compression gland and the fibre cores will be broken out into the secondary coated cores. These cores will then be terminated with connectors, which are then connected into in-line adaptors mounted through the front bulkhead of the patch panel enclosure. This termination may either be carried out by the direct attachment of connectors to the fibre tails or factory terminated connectors tails will be spliced to the transmission fibre cores. If splices are used then the splice enclosures will be mounted in clips on the patch panel base. Patchleads then connect the patch panel bulkhead connections to the E/O converter optical connections. Copper leads then complete the connections to the system
controller and monitors.

As part of the cable installation the installer will have measured the installed cable loss, a function of position using a piece of test equipment called an OTDR (Optical Time Domain Reflectometer). This measurement serves to finger print the system and provides a point of reference for future system maintenance. It also provides the value of the end to end loss of each optical fibre used. The total loss must not exceed the optical margin specified by the equipment manufacturer, otherwise the transmitted picture quality may be impaired. In a correctly installed multimode system link lengths of 4 km for 850nm products and 8 km for 1300nm products are readily achieved.

The basic components of a CCTV fibre optic transmission system are as follows:

·  Electrical to Optical Converter (Transmitter) at the camera end of the link. This unit takes the analogue 1 v peak to peak signal from the surveillance camera and converts it into a light signal that varies in proportion to the camera output signal. The light signal is generated by an LED (light emitting diode) or laser transmitter which is designed to couple a maximum of the generated light into an optical fibre.

·  The optical transmission fiber and fiber optic cable. The optical fibre guides the light from the LED or laser transmitter with a minimum of loss to the monitor or matrix controller end of the link. The optical fibre itself is protected by a variety of sheathing materials to provide a cable construction appropriate to the specific application. The fibre cable is connected to the terminal equipment using de-mountable screw or bayonet fixing connectors.

·  Optical to Electrical Converter (Receiver) at the monitor end of the link. This unit takes the optical signal from the optical fibre and converts it into an analogue electrical signal that is compatible with the monitor input requirements. The light to electrical conversion is carried out by a semiconductor detector which is called a photodiode, or an avalanche photodiode. Subsequent electronic circuitry regenerates the output signal. Products from the better quality manufacturers compensate for optical fibre losses and transmitter output intensity variation with time and temperature by providing automatic gain control to give a standard 1 v peak to peak output format as generated at the camera output.

·  Control data and audio connections. Cameras in CCTV installations are either fixed, viewing a specific scene, or movable, so that different scenes can be viewed under the direction of the operator who would be sited in the remote control room. In the case of fixed cameras then the fibre optic link is required to transmit video only information from the camera to monitor, this requires only a single fibre link for each camera to monitor path. In the case of a movable camera then a return signal must be provided from the control room to the camera usually over a second optical fibre. It is usual for these return control links to provide remote control of the camera PTZ – pan, tilt and zoom functions plus
camera enclosure wash/wipe activation.

If camera control is used then the fibre optic link interface electronics must be compatible with the protocols used by the controller manufacturer. These functions are transmitted over the return fibre link using a standard digital transmission format such as RS232, RS485/422, 20 mA current loop and most recently Echelon Lonworks FTT10A. In addition some controller manufacturers require a return data channel from the camera to confirm camera movement. This return data is usually encoded by the camera optical transmitter electronics and sent over the same fibre as the video signal.

Help point and door entry installations require the transmission of two-way audio signals over the fibre link. Again optical transmitter and receiver units are available to provide this facility in addition to the video and control data links all over the same two fibres. It is also possible to provide all of these video, data and audio transmission functions over one fibre using different wavelength (colour) lights sources to transmit light in each direction. This technique is known as wavelength division multiplexing; it maximises the use of installed fibre cores but at the expense of more costly fiber optic transmitters and fiber optic receivers.

·  The maintenance of picture quality and control data integrity over extended distances:
This is the major reason for using fibre optics which have superior signal amplitude loss characteristics than copper cable. Typically co-axial cable attenuation at a signal frequency of 5 MHz can be 20 dB/km. In comparison fiber attenuation is between 0.3 and 3 dB/km meaning that fiber optic transmitter distances of 60 km+ can be achieved, depending on the precise details of the application. In addition this low fibre signal attenuation is achieved over a very wide signal frequency range so that optical fiber can be used for the transmission of multiple video signals over long distances.

·  Immunity to electromagnetic interference:
Optical fibre transmits signals as light pulses rather than electrical pulses. This light transmission is unaffected by the presence of electro-magnetic fields. As a consequence fiber optic transmission can be used in applications where links are routed near electrical conductors and electrical machines. This includes applications such as railways, tramways, power generation and vehicle manufacture with welding machinery. In addition the fibre cable usually has a metal free construction so that there are no ground loop problems between terminal equipment and the cable will not transmit lightning pulses. This elimination of ground loops makes fibre cable the media of choice for inter building links of whatever distance.

·  Security of Information and Operational Safety
Unlike copper cables fiber cables do not radiate any signals as a consequence fiber optical cables are virtually immune from “tapping” and so the signal content is difficult to access for unauthorised parties. As there are no emissions from optical fibre cable there is no risk that a fibre installation will act as a ignition source. This means that fibre can be used in explosive atmospheres such as chemical and petro-chemical sites providing a truly “Intrinsically Safe” transmission path. Note however, that this Intrinsic Safety, would not extend to the electro-optic termination modems which would need to be safety certified and protected the same as any other electrical equipment.

·  Efficient use of duct space.
Optical fibre itself is very small, each glass fibre being only 0.125mm diameter. Protective sheathing is then applied in stages, depending on the application area, to make up the fibre into a usable cable. Typically resulting cable would have a diameter of 3mm for a single fibre core patchlead or 8mm for a 8 fibre cable suitable for internal or external use. In contrast 75 Ohm CT100 coaxial copper cable has a diameter of 6.5 mm. It can therefore be seen that the small size of fibre cable gives significant savings over copper where installation space is in short supply or where duct space is limited. Along with the small fibre cable size comes a weight saving both of which give savings in storage and transportation costs prior to installation.

·  Multi-channel capability and “Future Proofing”.
While most CCTV fibers today will be used to transmit one video signal and perhaps a control data signal, the user may wish to upgrade the system to support more camera and control channels. Any glass optical fiber used today is able to transmit multiple optical channels either by using different optical carrier “colours” i.e. wavelength division multiplexing or by increasing the signal frequency using electrical multiplexing techniques. The transmission media is hence “future proofed” and the link will need only additional fiber optic converter equipment to expand the link capacity.

In these sections we will attempt to de-mystify fibre optic transmission as applied to CCTV system use. We will start by outlining why fibre optics should be used, go on to consider the basic elements of a fibre optic converter system and installation practice and finally outline the technology to extend CCTV systems from essentially local installations to extensive, distributed multi-channel signal transmission systems.

1: Defining criteria – Why do I want to install CCTV?

It’s essential to start with a clear idea of what you want your CCTV system to achieve. What suits your neighbour or another business may not suit you. Are you considering the investment as a deterrent to intruders and thieves? To record access to a building or car park? To monitor movement in particular areas of your property? To record activity round the clock or at specific times, for example when your property is unoccupied? You also need to think about what you want to do with the information once you have it. How long do you want to keep it? How often do you want to review it? With clear objectives, it’s easy to determine the criteria – such as picture resolution, camera focal length and image storage requirements – that will ensure your chosen system is fit for purpose.

2: Basic requirements – What equipment will I need?

Essentially, a CCTV system comprises one or more cameras and either a software- or hardware-based image recording facility. Until recently CCTV cameras operated by transmitting analogue video signals through copper cables or fiber optic cable to a central location where the video signal was recorded. While analogue cameras still have their place, today’s more sophisticated IP cameras produce digital output and use IP networks to relay their images. The number and type of cameras you choose will depend on the subject and the extent of the surveillance area.

3: Recording options – How can I store images?

Images can be stored on the camera itself, on a computer or on a digital video recorder (DVR). The output from an IP camera is digital and is recorded without change; the output from an analogue camera is first digitised and then stored. DVRs and computer software offer the ability to record multiple channels, ie images from several cameras at the same time, regardless of the camera type. With analogue cameras, the number of channels that can be recorded is limited by the number of physical connections on the DVR, whereas in an IP system it is usually limited by software licensing. The number of camera sources you want to record from, the image quality you require, and the length of time that you want to store those images will all influence which recording device is best for you.

4: Ongoing surveillance – How can I monitor images?

A key consideration in getting the right system is to know how you want to view the images from your cameras. Will you have a central control room with trained operators constantly monitoring screens? Do you want a third-party to monitor your property? Will you want to access your CCTV images remotely while abroad? Do you want to receive email or text alerts if suspicious activity is detected by your CCTV system? IP cameras can be connected to the internet to relay images anywhere, and both IP cameras and DVRs have the capability for motion detection.

5: Static or not – Do I need fixed or moving cameras?

Camera housings can either contain fixed cameras, trained on a single location, or PTZ (pan/tilt/zoom) cameras that can rotate 360° and provide pre-programmed ‘tours’ of an area. Motion detectors can be added to a PTZ camera system so that the camera can respond and focus in on suspicious activity. Depending on the rationale for your CCTV system, you might want a mixture of fixed and PTZ cameras to cover different zones and applications.

6: Camera features – Do I need IP or analogue cameras?

While an analogue camera is ideal if you want to monitor one location from a fixed position, an IP camera is more flexible and can enable more sophisticated surveillance, recording and review. IP cameras can deliver high definition or megapixel images, which give greater detail and can cover a greater range. They can also be powered over a network using Power over Ethernet (PoE), so do not require a separate power supply. Some IP cameras have audio recording built in which allows recorded messages to be broadcast automatically to warn people that they are being watched. However, this functionality can be integrated into any camera’s housing and is not a specific benefit of IP. Both types of camera can also feature infrared technology to capture full-colour images during the day and black-and-white images in low light or even complete darkness.

7: Intelligent security – Should I integrate my CCTV with my other security systems?

CCTV cameras can be easily integrated to enhance your security. When integrated with an intruder alarm, your CCTV system can be set to record images at a higher resolution when the alarm is set or activated. When integrated with an access control system, CCTV can provide additional visual verification that a person has authorised access. Your specific integration requirements will influence the type of camera and recording equipment you need.

8: Investing wisely – How do I make the most of my budget?

This depends on what you want your CCTV system to achieve. IP cameras are more expensive because their image quality is better and they are more flexible, but analogue cameras are often sufficient for the job. If you only need fixed-point monitoring, a low-spec, low-cost analogue system would be the right choice. On the other hand, if you need to monitor a large area, it may be more cost-effective to use one high-resolution PTZ camera in the place of several fixed analogue cameras.

9: Going digital – Should I upgrade to a digital system?

The need to upgrade will depend on what equipment you already have, your surveillance requirements and your budget. By replacing a VHS video recorder with a DVR, the feed from existing analogue cameras can be digitised and more easily stored. The system can then benefit from features, such as motion detection, which are supported by DVRs. IP cameras can also be introduced to work alongside analogue cameras allowing you to benefit from their technology where appropriate.

10: Industry validation – What accreditation or references should I look for in a CCTV installer?

Credible CCTV installers will have industry accreditation such as recognition by the NSI (National Security Inspectorate) which promotes compliance with relevant British and European Standards as well as the requirements of the police and the insurance industry. A reputable company will not have any problem with you asking for their credentials, and should also be able to introduce you to existing customers for reference.