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    Optical fiber (or "fiber optic") is a glass or plastic fiber along which light travels through. The glass fiber is made of SiO2. The optical fiber is as thin as 0.1 mm in diameter and very light in weight. There are plenty of fiber optic resources that can be used for a variety of application.

      Light is kept in the fiber core by total internal reflection. Generally, optical fiber is not subject to electromagnetic interference and allows for long distance transmission at higher bandwidths (data rates). During fiber optic transmission, much less loss will occur than other types of communication and more information can be carried than conventional metal wires.

      Fiber optics is the combination of the design and application of optical fibers. Most telephone company long-distance lines are now made of optical fiber. Fibers are also designed specially for various applications including sensors and optical laser diodes. The latter are extensively exploited in fiber optical transmission equipment. For distances longer than 100 km, repeaters are required in fiber optic transmission.

      Two types of fibers are commonly used in fiber optics including single mode fiber and multi-mode fiber.Multi-mode fibers (MMF) support many propagation paths or transverse modes, whereas single-mode fibers (SMF) can only support a single mode. The wavelength used in fiber optic communication is in near infrared range from 0.8 to 1.8 μm including the short range 800 nm~900 nm, mid range 1250 nm~1350 nm and long rang 1500 nm~1600 nm. In these ranges, the performance of fiber optic transmission is optimal, especially for wavelength in the middle of each range. Thus, in order to obtain the best performance, 850 or 1300 nm is usually used in MMF transmission, while 1310 or 1550 nm is mostly employed in SMF transmission. Multi-mode fibers generally have a larger core diameter. They are used for short-distance communication links and for applications where high power transmission is required. Single-mode fibers are used for most communication links longer than 550 metres (1,800 ft).

      The core of a single mode fiber is very thin in diameter, only around 4~10 μm. As mentioned, single mode fiber only supports single mode transmission, which can completely avoid the mode dispersion leading to wider bandwidth, larger capacity and longer transmission distance than MMF. SMF transmission will become inevitable trend of optical fiber communication and optical technology development.

      Fiber optic communication has achieved rapid progress recently due to their incomparable advantages. The advent of fiber optic transmission is one of the milestones in the new technology revolution. Since 1980s, wideband optic fiber has been starting to replace the traditional narrow-band metal cable. Optic fiber is predicted to be the major medium for information network in the future.

      In the structural cabling, optical fiber supports not only the FDDI fiber optic backbone, 1000Base-FX backbone, 100Base-FX to the desktop, ATM backbone and ATM to the desktop, but also support CATV/CCTV as well as fiber to the desktop (FTTD). Therefore, together with traditional copper wiring, optical fiber will become another key player in structural cable wiring.

      Nevertheless, as everything has advantage and disadvantage, optic fiber can not avoid imperfection, either. More protection is required for the glass fiber within an outer cable than copper due to its low mechanic strength. More care should be taken when jointing lengths of optical fiber than jointing electrical wire or cable. The fibers must be carefully cleaved at the two end faces. Splicing two fiber ends together is also elaborate and delicate using either mechanical method or by electric arcfusion. Removable connections can be made by use of special connectors. Furthermore, careful treatment and sophistication in skill is required for a fiber optic engineer or technician when cutting, splicing, jointing, splitting and coupling fibers. For these reasons as well as labor-intensive property during the installation of any new cabling, few communities have installed optical fiber cables, from the phone company''''s branch office to local customers worldwide. However, with the development of new technologies, all these shortcomings can be overcome and will not be a factor to slow down the pace of fiber optic progress.

      Fiber optics is an extensively studied science. There are many aspects that can be covered and discussed in details for paragraphs. However, for concise consideration, the following sections just selectively describe several important issues that take effects on good fiber optic performance, including Fiber Optic Cabling, Notice for the Use of Optical Fiber, Fiber Optic Test Instrument, Optical Fiber Fusion Welding Technology, and Optical Passive Devices.


    Fiber Optic Cabling

      Fibers wrapped with protection layers can be used in bundles leading to fiber cables. Fiber optic cabling is the important component of the fiber optic communication system. The following section will focus on fiber optic cabling.

    1Feature of fiber optic cabling

      Fiber optic cabling project, whether it is between the relay wiring or in the state level or first-class long-distance backbone lines, shares the same property that a relay hop is an independent unit. In the point of view of cabling construction technology, there is no fundamental difference in multimode or single mode fiber that they select, or in laying methods such as pipes, overhead and buried type.

      The light weight and small diameter of fiber optic cable brings the convenience of construction. However, the thinness and softness in addition to cable length far exceeding the ordinary copper cable gives rise to new requirement in laying fiber cable. In particular, there is more stringent requirement for jointing technology and test instrument when handling optical fiber than copper wires.

    2、Range of fiber optic cabling

      Fiber Optical communication system includes two main parts: fiber optic cable lines and transmission equipment. The construction for fiber optic cable and equipment is demarcated based on fiber optic distribution frame (ODF frame). The exterior side of the optical connector is for cable wiring and the inner side is for equipment installation. Cable wiring part includes various optical fiber cables and connectors. Fiber optic cable wiring is constructed on the basis of regulations and customer request in order to make a complete transmission cable line meeting the designed requirement.

    3、Fiber optic cabling technology

      Fiber optic engineers, technicians and production staff, who are engaged in project management, engineering design, construction and maintenance, must know well the main cable line construction technologies. These key technologies include:

    1)Fiber optic laying technology for a variety of projects;

    2)Optical fiber and cable connection technology;

    3)Optical fiber and cable on-site testing techniques;

    4)Fiber optic cable maintenance technology.


    Cautions in the Use of Optical Fiber

      Both single mode and multimode fibers have to be used properly in order to get good transmission quality. Users must pay attention to the following aspects (but not limited to).

    1、The wavelength of receiving and transmitting optical modules at both ends of a jumper must be consistent, i.e. the optical modules connected via the same optical fiber must use the same wavelength.

    2、Do not bend or circle the fiber in use excessively. Or else it will give rise to more light attenuation during transmission.

    3、Do protect the two ends of optical fiber jumpers (when not in use) with rubber cover lest dust and oil damages the fiber optic coupling.

    4、There are many types of optical fibers commercially available with various interfaces. For example:

      ST-ST Fiber Jumper, SC-SC Fiber Jumper, 
      ST-SC Fiber Jumper, FC-SC Fiber Jumper, 
      FC-FC fiber jumper, FC-ST Fiber Jumper, 
      LC-LC fiber jumper, LC-SC Fiber Jumper, 
      LC-ST fiber jumper, MTRJ-2ST fiber jumper,
      MTRJ-MTRJ fiber jumper, MTRJ-2SC fiber jumper

    Fiber Optic Test Instrument

      Fiber optic test instrument plays key roles in the application of fiber optics. The commonly used fiber optic test instruments are: Optical Power Meter, Steady Light Source, Optical Multimeter, Optical Time Domain Reflectometer (OTDR) and Optical Fault Locator.

    1、Optical Power Meter

       Optical Power Meter is used to measure the absolute optical power or relative optical power loss transmitted over a certain length of optical fiber.

    2、Steady Light Source

      Steady Light Source is used to emit light with known power and wavelength. The combination of steady light source and optical power meter can measure optical loss in the entire fiber optic system.

    3、Optical Multimeter

     Optical Multimeter is used to measure optical power loss in fiber optic links.

    4Optical Time Domain Reflectometer (OTDR) and Optical Fault Locator

       Optical Time Domain Reflectometer (OTDR) and Optical Fault Locator are used to indicate a function of the fiber loss and distance. With OTDR, technical staff can observe the outline of the entire system to identify and measure the span of optical fiber, follow-up point and the connector. Trochoid OTDR shows the position and size of the system attenuation such as: the position and loss of any connector, follow-up point, special optical fiber, or fiber break. OTDR is especially useful in three aspects:

    1)To understand the property (length and attenuation) of fiber cable before laying it.

    2)To obtain a signal waveform over a section of optic fiber.

    3)To locate the point of failure when problems increase and connection is deteriorating.


    Optical Fiber Fusion Welding Technology

      Once fiber optic cable is ordered, the transmission loss of the fiber itself is determined. However, the fiber loss of fusion joint is related to the fiber itself and the on-site construction. To reduce the optical loss at the fusion welding joint as much as possible can increase fiber transmission distance relay and then improve the fiber optic link attenuation margin.

      Factors affecting the loss due to optical fiber fusion welding

       There are many factors that can affect the fusion welding loss. The impact factors can be divided into intrinsic and non-intrinsic factors of optical fiber. The intrinsic factors include:

     1) Diameter inconsistency in fiber mode field

     2) Core diameter mismatching between two fibers

     3) Cross-section of the fiber core is not round

     4)Poor concentricity between fiber core and cladding layer

      The last factor, diameter inconsistency in fiber mode field has the largest impact on fiber loss. According to CCITT (International Telegraph and Telephone Consultative Committee), the inconsistency tolerance of a single mode fiber is suggested as follows:

    Mode Field Diameter: (9 ~ 10μm) ± 10%, i.e. the tolerance is about ± 1 μm;

    Cladding diameter: 125 ± 3 μm;

    Mode field concentricity error ≤ 6%, cladding roundness error ≤ 2%.

    Optical Passive Devices

       Optical passive device is a kind of device without any need of any external optical or electrical energy but with its own ability to complete some optical functions. It works in compliance with the principle of geometrical optics theory and physical optics theory. All the technical parameters, formula and test methods are closely related to those of fiber optics and integrated optics.

       Optical passive device can be classified according to its production technology and functions. Based on production, optical passive device can be divided into fiber optic passive devices and integrated optic passive devices; Based on function, optical passive device can be divided into optical connector, optical attenuator, optical power distributor, optical wavelength distributor, optical isolator, devices, optical switch, optical modulators and other devices.

       The main technical parameters of optical passive device include: insertion loss, return loss, bandwidth, band fluctuation, power distribution error, wavelength isolation rate, channel isolation rate, channel width, extinction ratio, switching speed, modulation speed and etc. Different devices have different technical parameters. However, the vast majority of optical passive device requires low insertion loss, high return loss and broad bandwidth.


       Optic fiber has been achieving more and more attention nowadays. It is one of the main components of fiber optic transmission system, which consists of fiber optic transmitter, fiber optic receiver, optical fiber cable, fiber optic repeater, fiber optic connector and coupler etc. There are much more subjects worth of detailed discussion. In our on-line training programs, we will provide more such information in subsequent topics.



    Training section 2


     Fiber Optic Transmisson

       A fiber optic transmission system consists of fiber optic transmitter, fiber optic receiver, fiber optic repeater, fiber optic connector, coupler, etc. Among all the components, fiber optic transmitter and receiver are the hard-core equipment, whose performance directly affects the quality of the whole communication system.

       In a fiber optic communication system, the transmitter receives the electrical signal from signal source and converts it into optical signal before it transmits the optical signal to the remote receiver over an optical fiber. The receiver restores the electrical signal (by amplification, reshaping and regeneration) and outputs it to other devices such as LCD screen and PC. For long distance transmission (>100 meters), additional repeater(s) are required for extension because they can amplify weak optical signal after long-distance fiber attenuation to appropriate intensity and reshape distorted pulse wave. The resultant optical signal can be retransmitted continuously, ensuring good transmission quality.



    (1)Analog Video

       Analog video is a video signal transferred by analog signal. It contains the luminance (brightness) and chrominance (color) of the image, which may be carried in separate channels, as in component video (YPbPr) and S-Video, or combined in one channel, as in composite video and RF connector.

       Analog video is used in both consumer and professional applications. However, digital signal formats with higher quality have been adopted, recently.

    2Digtal Video

       Digital video is a type of video recording system that works by using a digital rather than an analog video signal. There are different digial video formats including serial digital interface (SDI), Firewire (IEEE1394), DVI and HDMI.

       Serial digital interface (SDI) refers to a family of video interfaces standardized by SMPTE. For example, ITU-R BT.656 and SMPTE 259M define digital video interfaces used for broadcast-grade video. A related standard, known as high-definition serial digital interface (HD-SDI), is standardized in SMPTE 292M and provides a nominal data rate of 1.485 Gbit/s.

       An emerging interface, commonly known in the industry as dual link HD-SDI and consisting essentially of a pair of SMPTE 292M links, is standardized in SMPTE 372M. Dual link HD-SDI provides a nominal 2.970 Gbit/s interface used in applications (such as digital cinema or HDTV 1080P) that require greater fidelity and resolution than standard HDTV can provide. A more recent interface, 3G-SDI, consisting of a single 2.970 Gbit/s serial link, is standardized in SMPTE 424M that will replace the dual link HD-SDI.

       These standards are used for transmission of uncompressed, unencrypted digital video signals (optionally including embedded Audio and/or Time Code) within television facilities and they can also be used for packetized data. SDI and HD-SDI are currently only available in professional video equipment because various licensing agreements, restricting the use of unencrypted digital interfaces to professional equipment, prohibit their use in consumer equipment. Serial digital interface uses BNC connectors as shown in Figure 2.


    (1)Analog Audio

       Sound is generated by mechanical vibration. The stronger the vibration, the greater the sound is. The mechanical vibration is converted into electrical signal via microphone. In the analog audio technology, the level of analog voltage indicates audio intensity.

    (2)Digital Audio

       Digital audio uses digital signals for sound reproduction. This includes analog-to-digital conversion, digital-to-analog conversion, storage, and transmission. By sampling and quantization, the analog audio is converted into digital audio that consists of a number of binary 1 and 0 components.

    (3)Difference between Analog Audio and Digital Audio

       Analog audio is continuous in time, while digital audio is discrete. The primary usefulness of a digital signal is that it can be corrected and reconstituted. The discreteness in both time and amplitude is curial to this reconstitution, which is unavailable for a signal in which at least one of time or amplitude is continuous.

    (4)Audio Connector and Definition

     1)RCA (Female/Male) 


      RCA connector is used for unbalanced analog audio. It consists of two components in white and red color for stereo.

     2) 6-position Terminal Block


    Figure 5 6-position Terminal Block


      6-position Terminal Block is employed for balanced audio signal.The pins are defined as 1-6 from the left to right: 1, 2, 3 for left channel (1 = “+”, 2 = “GND”, 3 = “–”) and 4, 5, 6 for right channel (4 = “+”, 5 = “GND”, 6 = “–”).



    Figure 6 XLR Connector


      There are female (left) and male (right) types of XLR connector as shown in Figure 6. The three-pin XLR3 is most commonly used as a balanced audio connector. The pins are defined as below: 2 = “+”, 3 = “–” and 1 = “GND”.


    (1)Data Standard

     1) RS-232-C

        RS-232-C is a serial physical connector standard instituted by EIA (Electronic Industry Association) in the USA. This standard is set for serial binary data signals connecting between a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). RS represents “Recommend Standard”, 232 is the identification code, and C indicates the current revised version. RS-232-C bus standard has 25 signal lines including one main channel and an auxiliary channel.

        The main channel is used in most cases. In general, for duplex data transmission, 3 lines are enough as one is used for transmitting line, one receiving line and one grounding line.

        RS-232-C standard specifies data transmitting rate:50, 75, 100, 150, 300, 600, 1200, 2400, 4800, 9600 and 19200 Baud per second.

        RS-232 data is suitable for short distance transmission (up to 20 m) mainly due to two reasons including load capacitance and single-ended transmission. RS-232-C standard specifies that the drive allows for load capacitance up to 2500 pF, which limits the communication distance. For example, when a communication cable of 150 pF/m is used, the maximum transmission distance is 15 m. If the capacitance per meter decreases, the communication distance will be increased. The other reason for the short transmission distance is that RS-232 is single-ended signal transmitting, leading to the existence of common-ground noise and common-mode interference

     2 RS-485

        RS-485 serial connector is widely employed when the communication distance is required to be up to 100 ~ 1000 meters

        RS-485 adopts differential transmitting and receiving, capable of attenuating common-mode interference. In addition, the high sensitivity of RS-485 bus transceiver enables to detect the voltage as low as 200 mV volt. Therefore, the transmission signal can be restored beyond 1000 meters.

        RS-485 works in half-duplex mode. Thus, only one end point can transmit signal at anytime, requiring signal control design in transmitting circuit.

        It is very convenient for RS-485 to interconnect multiple end points. It is an extension of RS-422 and can save a number of signal lines. Application of RS-485 can constitute a network of distribution system, which allows a maximum of 32 drives in parallel and 32 receivers.

     3) RS-422

        RS422 and RS485 use almost the same circuit principle. Both of them adopt differential transmitting and receiving, without the need of digital grounding line. However, the power supply has to be grounded well.

       Differential transmission and receiving is the reason for longer transmission distance at the same transmission rate. It is the fundamental difference between RS485/422 and RS232. Since RS232 supports only single-ended input and output, at least three lines including digital grounding line, transmitting and receiving lines are necessary for duplex transmission (Asynchronous transmission). Additional control lines can be used to achieve other functions like synchronization.

        RS422 can work in full duplex mode with two pairs of twisted-pair cable. There is no interference between transmitting and receiving. RS485 only works in half-duplex mode, i.e. transmitting and receiving can not work simultaneously. However, RS485 only needs one pair of twisted-pair cable.

        RS422 can also be exploited to interconnect multiple end points. Application of RS-422 can constitute a network s of distribution system, which allows a maximum of 10 drives in parallel and 10 receivers.

        RS422 and RS485 can transmit up to 1200 meter at 19 kbps.


    2Pin definition of Data Connector (Applicable to OPVISION Products)


     1) RJ45 Connector

       The standard RJ45 connector is shown in Figure 7. The pins are defined as 1-8 from the left to right, each for one color: 1 = white, 2 = grey, 3 = black, 4 = red, 5 = green, 6 = yellow, 7 = blue and 8 = brown.

     2) TRS Connector

       A standard TRS (terminal block) connector is shown in Figure 8. The pins are defined as 1-8 from the left to right, each for one color: 1 = white, 2 = grey, 3 = black, 4 = red, 5 = green, 6 = yellow, 7 = blue and 8 = brown.

       RJ45 or TRS connector labeled with “DATA” is used to input and output data signal. If there is no special requirement, data connection is made as the definition in Table 1. The definition of both RJ45 and TRS connections are the same.

    Table 1 Pin definition of RJ45 connector (the same as TRS connection) :


     3) Conditional Switch



      The principle of switch signal is indicated in Figure 9. A and B represents a RJ-45 connector or pin 1 and 3 of a TRS connector (See Table 1 for pin definition). The A and B in Rx is the mirror imagese of that in Tx. Thus, they represent AB input and AB output. There are two working modes for switch signal.

      (1) Normal mode: Rx is controlled by Tx.

      When Tx is turned on, Rx is on and the Rx will be off as Tx is turned off.

      (2) Abnormal mode

       When Tx is off, the Rx is turned on but the Rx will be on as the Tx is turned off.

     4) Pin Definition of Special Products

        TN 110: RS-485 Data connector


     (1) Card-cage type connectionRS485 data from the keyboard is connected to the most left port that is located at the most left side of the chassis and is used to distribute the data as shown in Figure 10. Thus, other cards inside the chassis can obtain data through automatic data distribution.

     (2) Standalone type connectionConnect the data port directly (-, GND and +) as shown in Figure10 for both transmitter and receiver.


    Table 2 Pin definition of VGA connector



    Table 3 Definition of 8-position TRS connector




    3.Troubleshooting for Equipment Operation

    (1)POWER indicator is off

     1)Check if the power connection is loosened.

     2)Check if the device connects to power supply correctly.

     3) Check if the external power supply (DC power or 220VAC) works properly.

    (2)Optical LINK indicator is off or flickering

     Power indicator light is on, but the fiber light is off

     1) Check if the right type of fiber is used (single mode or multimode)

     2) Check if there is damage on the fiber cable and its connectors.

     3) Check if the fiber is disconnected or fiber link loss exceeds the receiving sensitivity.

     4) Make sure to connect the transmitter and receiver only by optical fiber.

     5) Check if fiber connector is not connected properly.

     6) Check if fiber optic end faces are not clean.

    (3)Video Failure

     Video input signal indicator V is OFF

     If Power and LINK indicator lights are on and Video channel cannot work properly, please follow the steps below.

     1) Check if the signal input device is connected correctly.

     2) Assure the cable connects different devices at two ends but must connect to the same channel accordingly.

     3) Assure the cable is connected to the video channel of the equipment correctly and safely. Disconnect power and restart.

     4) When it is hard to figure out if the optical link works properly, just simply connect the transmitter and receiver with jumpers directly. If the transmission is normal, there must be something wrong with the optical link; otherwise, the optical link is the failure reason.

     5)Check whether the fiber has high dispersion.

    (4)Data Failure

     1) Check whether the input and output of data are in the proper connection.

     2) Check whether the polarity of data input or output are correct.

     3) The terminal “2” and “4” of RJ45 connector should be connected to “ground” of external data signal.

     4) Check if the data rate exceeds the standard value.

     5)Lightning and surges may damage the data interface. It is recommended to use an optocoupler so that the transmitter and receiver do not share the grounding. No electric connection between signals from the two equipment units can effectively protect the data interface from damage.

    (5)A udio Failure

    The volume is low after audio connection is established, but noise appears after the amplifier is connected.

     1) Assure the source signal is matched with the equipment requirement.

     2) If the source signal is balanced audio and the equipment supports unbalanced audio, problems will rise such as low volume and noise.

     3) Check if the transmitter and receiver share the grounding.

    (6)E xample: OPV5000 Troubleshooting

    Table 4 OPV5000 Troubleshooting



    4.Troubleshooting for Network Management Software

    (1)Search Equipment

     Can not search any equipment

     1) Check if the network connection is normal by using command PING as follows:

     2) Click START-->Select RUN manu-->Type “ping” (Device IP) in the RUN dialog box. The successful ping indicates proper network connection.

     3) Restart the equipment search to connect again.

     4) If the problem still exists, restart the NWM software and try again.

     5) If the problem can not be solved by all the above solutions, turn off the power and restart the device.

      Two or more devices have the same IP address in search result

     1) Keep only one device unit in the list by removing other equipment units having the same IP address from the network.. Then change its IP address.

     2) Take the same actions on the removed units in turn until all the IP addresses configured to each unit are different.

     IP address conflicts between searched equipment and computer

     Change the PC IP followed by changing equipment IP; or else, the communication between the PC and equipment fails.

    (2)Time switch

     1) All characters should be in English

     2) If the device transmits 8 channel video, the channel number should be 1- 8 instead of 0 -7.

     3) The device should remain connected if TIME SWITCH is set up, or else the present TIME SWITCH information will be lost.

     4) If TIME SWITCH has been set for one device but users need to monitor another device simultaneously, a new Netmanager software interface should be opened. 

    (3)Automatic Mode and Manual Mode

     1) Automatic Mode

        Under Automatic mode, user can set a time interval (the default time interval is 1 second). The software will request the instant status of devices at every time interval.

       Under Automatic mode, user cannot use those functions such as matrix switch and time switch, unless change to the manual mode.

     2)Manual Mode

      Under Manual mode, user should refresh the software to get instant status of devices.

     3) In general, we don’t recommend software working under automatic mode, for it might influence network speed. User can refresh the device status manually whenever necessary.

    .Maintenance and Notice

      The conditions below are applicable to all OPVISION fiber optic transmitters and receivers.

     1) Do not look at the optical connector of the equipment directly with naked eyes. The equipment adopts the high-power laser emitting invisible laser light, which may be harmful to eyes.

     2) Ensure to turn off the power before connecting the transmitter and receiver via the connectors and optical fibers.

     3) Do not expose the optical connectors of the equipment and the fibers to the air without any protection for a long time, lest the dust in the air affects the signal transmission (The dust may affect the optical coupling efficiency and shorten the transmission distance).

     4) Use the provided laser diode module protectors to cover the optical connectors of the equipment and protect the fibers with dustproof caps, whenever disconnect the optical fibers.

     5) Use a special tampon with 95% absolute ethanol to clean the optical connectors on the equipment or optical fiber when they become dirty. Do not use general alcohol for cleaning.

     6) Ensure to keep the fiber cable with the bending radius larger than the required curvature radius (30 times of the fiber diameter) for the consideration of protection due to the specialty of the fiber optical transmission.

     7) Properly use the data connector:

      Suggest using a protective device against overload voltage on the data cable to avoid induced faradism from damaging the transmitter or receiver.

       Do not disconnect or connect the data cable with power on.

     8) OPVISION products are high-precision electronic equipment.

       Do not put these products in environments such as outer field, high humidity, strong static electric field, strong magnetic field and high dust density.

       Do not smash or drop these products.









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