GAOTek OTDR 103, Visual Fault Locating

This portable and intelligent OTDR is designed for testing the distances and losses of the optical fiber and comes with built-in VFL (Visual Fault Locating) system.


Key Features

  • Handheld, portable and with high cost performance
  • Supports touch screen and easy to use
  • Average test mode and real-time test mode
  • 3 s starting time: tests as soon as the tester is opened
  • Built-in VFL function: a perfect combination with OTDR
  • Light warning function: automatically detects and protects the injection of light
  • Single port, double wavelength output: switch between 1310 nm/1550 nm wavelength
  • Hotkey function: swift location and analysis of events
  • Mass storage can save more than 10000 test waveforms
  • Low power consumption design: 50 h long battery life makes it suitable for field work
  • Adopts changeable OTDR output port: it becomes more convenient to clean the end face
  • Supports FC/SC/ST adapters
  • USB port: supports to upload test results and on-line upgrading
  • Dust-proof, moisture-proof and shock-proof design, suitable for field work
  • Auto, Manual and Real-time test: three test modes

Auto Test: automatically calculates fiber length, sets sampling parameters, gain curve, displays event list and gained curve

Manual Test: offers and operates all the tools of a complete OTDR test; user can also control all the test parameters

Real-time Test: real-time testing of fiber and then compares the current result with previously gained curve; it can save time when you are going to test large number of fibers

  • A secondary analysis of test results
  • Large color LCD touch screen: intuitive and easy to use
  • Real-time clock function: displays the current time and offer the recording time for data storage
  • Lithium polymer battery
  • Battery voltage monitoring display
  • Energy saving design: auto power off, low voltage detection, low voltage power off
  • Offers professional management software: analyzes, edits, prints curve via PC

Technical Specifications

Models GAO-OTDR-103-A




Wavelength 1310 nm/1550 nm
Dynamic Range 28 dB/26 dB 32 dB/30 dB
Pulse Width 10/20/50/100/200/500/1 us/2 us/5 us/10 us/20 us/Auto
Even Dead Zone ≤6.56 ft (2 m)
Attenuation dead zone ≤32.80 (10 m)
Linearity (dB/dB) ±0.05 dB
Loss Threshold 0.01 dB
Loss Resolution 0.01 dB
Sampling Resolution 1.83 ft-16.40 ft (0.16 m~5 m)
Uncertainty of Distance ± 3.28 ft (±1 m) + 0.005 % × distance + sample interval)
Curve Saving Capacity >10000 groups
Measuring Duration 5 s, 15 s, 30 s, 1 min, 2 min and 3 min
Power Consumption <3 W
Light Warning >1 uw (-30 dBm)
VFL 650 nm visual fault locator (>3 MW)
Output Connect FC/PC (SC/ST are optional)
USB Port Mini USB port
Battery Working Time Standby time: >50 h

Continuous test (peak power consumption): >20 h

Working Temperature 32 °F~122 °F (0 °C~50 °C)
Storage Temperature -4 °F~140 °F (-20 °C~60 °C)
Relative Humidity 0 % RH~95 % RH (non-condensing)
Size 8.66 in × 4.13 in × 2.36 in (220 mm × 105 mm × 60 mm)
Weight About 2.20 lbs (1 kg)

Additional Information

Working Principle of the OTDR

Optical time domain reflectometer tester is based on the design of a back-scattered optical test instruments. It carries out non-destructive measurement from one end of the fiber, and has good repeatability.

Backscatter method is to inject high-power laser pulse into the fiber, and then detect the scattered-light power returning along the optical fiber back at the same side.

If the density of the optical material fluctuates or consists unevenly, the degree of molecular lines is smaller than the wavelength of the light wave. Because of this, Rayleigh scattering appears. The main scattering mechanism is Rayleigh scattering, which is characterized by the wavelength of light having the same wavelength with the incident light wave. Its optical power is proportional to the point of incident light power, so according to the measurement of back-Rayleigh scattering optical power returning along the fiber, you can get the fiber loss information during transmission, which can also measure fiber attenuation. In addition, because the refractive index of the other side changes and then Fresnel reflection appears. According the principle, we can determine the position of the fiber end and the fault point. The distance between reflection point and injection point can be calculated by formula:

In this formula, C0 is the speed of light 3 × 108 m/s; n is the refractive index of the fiber core; t is the time from giving out to accepting the optical signal.

The microprocessor is the heart of the instrument, which bears a lot of work: controlling pulse launch, data acquisition, data processing and output display.

Principle block diagram

Typical backscatter curve

a– The curve area: is caused mainly by the optical fiber coupler and the front surface of the Fresnel reflection pulse.

b– The back-Rayleigh scattering curve area: when optical pulses along the transmission fiber segment with uniform properties.

c– High loss area: because of the loss caused by the welding head or some defects in optical fiber

d– Fresnel reflection pulse area: caused by the end of the optical fiber.

The measurements of distance and loss are two important functions of optical time domain reflectometer. For the optical fiber having connector or defective, the measured loss is not accurate due to the different sections of the backscatter coefficient and could have a huge bias. But for the fiber which is uniform continuous, without joints and defect-free, the loss measurement results will be accurate enough. Because the signal takes the logarithm, so the relative backscatter power curve is a logarithmic scale, which is the value of the level. And it is a value after two losses of the forward and reverse, so the average loss of the b section of optical fiber is as follows:

The length of the curve abscissa scale is converted through time scale. That is the conversed length value according to the light speed in optical fiber transmission and propagation time. Light velocity in vacuum is C0 = 3 × 108 m/s; fiber refractive index is n, so the velocity of light in the fiber is C = C0/n. Let the time interval between two points of the curve abscissa A – B is t. Because it is the time through the forward and reverse transmission time, so the distance between two points A-B is LA-B = C0t/2n.

Panel Description

Panel functions as below:

Key combinations: It is mainly used for quick operations during zoom-in or zoom-out in curve analysis.

Interfaces of the tester

Side Interface


“Menu” includes: OTDR parameter setting, OTDR file management and OTDR system setting.

Enter into menu by press【Menu】button or touch 【Menu. Press【▼】and【▲】or touch to choose the setting items. Press【OK】to confirm and press【ESC】to exit.

Main Menu Options

Options Functions
File Enter into submenu of file management.
Scan Setting Enter into submenu of OTDR parameter settings.
Sys Setting Enter into submenu of system settings
Analyze Do secondary analysis for current waveform or the opened record
Summary Check the parameter settings of current waveform or the opened record
Save Save the current test waveform
Help Enter into help menu to check product serial number and edition
Exit Exit the menu option.

File Option

Options Functions
Open File… Enter into the options of “open file”
Save As… Save the current curve
Delete File… Delete the file or file folder
Format Format the record storage area
Exit Exit file menu

Scan Setting Option

Setting Parameters Functions Note
Distance Range Set the testing range according to detailed requirements For more details, please refer to relative prompt.
Pulse Width Set the width of the laser pulse emitted by the OTDR For more details, please refer to relative prompt
Average Time Duration of the average mode testing For more details, please refer to relative prompt
Laser Wavelength Choosing the laser wavelength for measurements 1310 nm/1550 nm
Measurement Mode Working condition of the current OTDR test Average Mode or Real-Time Mode
Index of Reflection Set the index of reflection of the optical fiber The value will be offered by fiber manufacturer
Scattering Coefficient It has an impact on the backscattering power of light in the optical fiber The value will be offered by fiber manufacturer
Non-reflection Threshold The events with an insertion loss larger than this threshold will be in the event list. Judge attenuation event
Reflection Threshold The reflection events with reflection strength equal to or larger than this threshold will be in the event list. Judge reflection event
Ending Threshold The first event with an insertion loss equal to or larger than this threshold will be regarded as end of the optical fiber and all the events following it will be ignored. Judge end event
Restore Defaults Defaults set for the setting parameters before delivery.

System Setting Option

Setting Parameters Functions
Auto Off Choosing between Shut, 10 min, 30 min and 1 h
Brightness Adjusting the LCD contrast
Date Date setup
Time Time setup
Length Units Unit used in measurements by the instrument
Storage Format Choose standard SOR format or customized JSN format.
Light Warming Open or close light warning function
Screen Calibration It is used to calibrate the screen.
Restore Defaults Defaults set for the system parameters before delivery


1. Test Fiber Link

Procedures are as followed:

  • Firstly, please make sure that the battery is installed well or the power adapter has been inserted; there is no light injected into the fiber; press【 】button for 3 s to switch on the tester.
  • Choose the test wavelength.
  • Set test mode and testing parameters.
  • Clean the fiber; clean the connectors; clean fiber adapters; and check the adapter is FC/PC type.
  • Connect the fiber with the OTDR output port.
  • Pressbutton to gain the waveform.
  • After the test is finished, the tester will list the events automatically according to the set event threshold.

The testing result can be checked from the event list when the curve analysis is completed.

Caution: Before testing, please make sure that there is no operating light in the optical fiber, otherwise the measurement result will be inaccurate or even result in the permanent damage of the instrument. The dimension of the fiber is very tiny, so, even a very small dirt on the fiber connector can affect the accuracy of the testing result. So please clean the fiber connector, as well as the interface before testing.

The optical fiber connector can be cleaned by ordinary industrial alcohol and the cleaning cotton swabs (standard accessories). Stretch a cleaning cotton swab with industrial alcohol into the port of an optical fiber connector, turn it gently and repeat the operation with another clean and dry cleaning cotton swab.

2. Testing mode and parameter

  • Press or touch Menuto enter the menu.
  • Press 【▲】 and【▼】to move the curse to the “Parameter set”.
  • Press 【 OK 】button or touch to confirm to enter the interface of parameter setting.

2.1 Set testing range

Usually, the corresponding predefined range in the setup of distance range is chosen in line with the actual optical fiber length to guarantee high measurement accuracy.

Setup of the distance range of the instrument: Auto, 1 km -120 km (or 1 km-160 km); it is different from different sub models

Please operate as following:

  • Please touch or press 【▲】 and【▼】button, and move the curse to the “distance range”, and press 【】to switch to the parameter, then press 【OK】to enter to pop up a pull-down menu.
  • Touch or press 【▲】 and【▼】to choose the item to be set, and press 【OK】to confirm the parameter to be set.

2.2 Set Pulse width

The pulse width has an impact on the dynamic range and the resolution of the measured trace. If a narrower pulse width is chosen, a higher range resolution and a smaller dead zone will be realized, but the dynamic range will have a loss; if a wider pulse width is chosen, a larger dynamic range and a longer optical fiber length will be realized, but the range resolution and the dead zone parameter will be both affected.

The “Setup of the Pulse Width” option has 10 pre-defined items in all:10 ns, 20ns, 50 ns, 100 ns, 200 ns, 500 ns, 1000 ns, 5 us, 10 us, 20 us. The setup is valid in the manual measurement mode only. Please operate as following:

  • Press or touch 【▲】 and【▼】to switch to the “Pulse width” option and 【】to switch to the parameter.
  • Press 【OK】, a pull-down box menu of range will pop up after that. Touch or press 【▲】 and【▼】to choose the item to be set, and click 【OK】 to confirm the item to be set.

2.3 Set Average time

The average time has a direct effect on the signal-to-noise ratio of the measured trace. A larger time corresponds to a longer measuring duration, a higher signal-to noise ratio and larger dynamic range. Thus, choose the maximum average time as much as possible when measuring a long optical fiber or viewing a remote event.

The operation method is same as in 2.1

2.4 Set Laser wavelength

Choose the wavelength of OTDR, and 1310 nm and 1550 nm are optional. The factory default of laser length is 1550 nm.

The operation method is same as that in 2.1

2.5 Set Measuring mode

The optional modes are Average mode and Real-time mode. Under the real time mode, the OTDR can measure the connectivity of the optical fiber and update the testing curve in real time. And the testing will not stop unless you press 【 】 or 【】to stop the testing; Under the Average mode, based on the average time to be set, the instrument will accumulate and average the testing data, when the testing time is longer than the predefined time, the testing is stopped.

2.6 Set Index of reflection

The index of the optical fiber influences the transmission speed of the laser in the optical fiber. So an accurate index of reflection can affect all of the OTDR testing referring to distance, such as the location of event, attenuation, section length and the total length. Generally speaking, the index of reflection is provided by the manufacturer of the optical fiber. A default index of reflection for each wavelength. And user can set according to their need, and please check the parameter before each testing. It can be set to be any value between 1.0 and 2.0 and correct to four decimal places. Its factory default is 1.4666.

Please operate as following:

  • Touch or press 【▲】 and【▼】to switch to the “Index of Reflection” option and

】to switch to the parameter value, press【OK】to pop up the Edit of Index of reflection.

  • Touch soft keyboard directly or press 【】、【】、

【▲】 ,【▼】move curse to the software, press 【OK】to edit the value or “”to delete the value. Finally, touch “save” directly or move the curse to “save”, and then touch 【OK】 to confirm the set.

2.7 Set Scattering Co-efficient

The Scattering coefficient is used to show the backscattering amount of specific optical fiber. And the scattering coefficient is used to calculate the event loss and reflectivity. And the scattering coefficient is provided by the manufacturer of the optical fiber. And the default is 60.50 dB, and customer can modify according to their needs.

The operation method is same as that in 2.6

2.8 Non-reflection threshold

Setup of the non-reflection threshold has a direct bearing on the existence of the insertion loss events in the event list. The loss events equal to or larger than the threshold are listed in the event list. It is 0.20 dB by default.

The operation method is same as that in 2.6

2.9 Reflection threshold

Setup of reflection threshold: It has a direct bearing on the existence of reflection events in the event list. Only the events with a reflection value equal to or larger than the threshold are listed in the event list. It is 60.50 dB by default.

The operation method is same as that in 2.6

2.10 Ending threshold

Set up the minimum value of ending event, it is used to judge the end of the optical fiber, and it is 3 dB by default.

And the operation method is same as 2.6.

2.11 Restore the defaults

Restore parameters of the OTDR to factory default.

System Setting

Auto Shutdown

This function is mainly designed for saving the battery capacity.

Backlight brightness

The backlight brightness of the LCD has been pre-adjusted. It can be reset by user to adapt to his visual habits.

Light Waring

Open the Light Warning before the official measurement to detect if there is optical signal in the optical fiber. It will help to prevent damage to the lasers by light.

Screen Calibrate

To calibrate the touch screen, after the calibration is completed automatically return to the main menu.


Trace display window

  1. Each horizontal grid refers to a kilogram value; each vertical grid refers to a dB value. User cannot change the zoom-in and zoom-out of the trace window.
  2. Name of the trace file. A newly measured trace has no file name, but a file name may be set for it when it is saved (see the file saving setup). After a saved file is opened, the file name of the trace will be displayed.
  3. Remaining battery capacity
  4. Current time
  5. Trace window. Through the trace window, the measured traces can be displayed and show the characteristics of the optical fiber link.
  6. Information about markers A and B. It includes their distance, losses and attenuation coefficients.
  7. Event list
  8. Current trace parameters

The instrument displays the measurement range, the measured wavelength and the measured pulse width only.

Press the “Info” key to enter the “Summary Info” box for the detailed information.

Marker instruction: Marker number + distance between the marker and initial position of the measured optical fiber

【Operate】Switching between markers A and B

Marker switching: Press the “Marker” key. Markers A and B will switch automatically after that and the chosen marker will become blue.

Instruction: When marker A or B is moved, the marker information bar will change.

Types and icons of events:

Event list

Press OK to view the whole event list.

Trace zoom in or out

By operating the composite key, you can enlarge or reduce the traces. Or touch “ctrl” to activate trace control menu to zoom in or out traces.

“ctrl” to activate trace control menu

In the case of trace premise touch “ctrl” can activate traces control menu, as below:

[Operation]Quick View Event

Press 【▲】 and【▼】 keys to quickly find the event you need, at this time the bench mark should be on the event.
Using composite key one can quickly zoom in or out.

Trace records upload to PC

  • Connect the OTDR and the USB interface of a PC through mini USB cable.
  • Start the OTDR, there will be a USB icon on the top left of the screen.
  • Copy the trace file.

Visual Optical Fault Locating

The instrument can realize visual optical fault locating. The output wavelength and frequency are 650 nm and CW/1Hz, respectively.

Operating steps: Connect an optical fiber with the red light output interface. CW red light and 1 KHz red light will be output after VLS is pressed for the first and second time, respectively, and red light output will be disabled after the key is pressed for the third time.

Mode of Power Supply

The instrument can be powered by lithium battery or a power adapter.

The instrument is chargeable. In normal conditions, its lithium battery can stand by 50 hours, continue work 20 hours.

When the instrument is powered by a lithium battery, there is a battery capacity icon on top left of the LCD.

Note: Charge with the designated power adapter only, through the red LED 【】 key to indicate charge status, charging status is also displayed at the top of the main menu.

If the instrument is not used in a long time, better to take the battery out, charge it every three months.

After the battery is exhausted, connect it with a power adapter. A power adapter icon () will appear on top right of the LCD. If a power adapter is used while the battery is still high and on the instrument, the instrument will be powered by the power adapter first.

Note: Please use the power adapter that comes with the instrument, other types of adapters may cause damage to the instrument!

Computer Aided Analysis Software

Installation of bundled software

Run the CD provided with the instrument, enter the “OTDRsoftware” directory and double click the “SetupOTDRsoftware.msi” setup file to run it. The application is installed as below.

Use of OTDR software


The OTDRSOFTWARE is bundled software of the instrument. It can be used for reading the data acquired by the instrument and displaying data curves and information. Through it, user can realize more intuitional data validation and analysis. Schematic diagram and function of the main interface of the program are briefly introduced below.

Functions of Views of the Main Interface
No. Functional area Function
1 Function button Applicable to special models
2 List of the Opened Files For displaying the opened files. Click the “List Item” to activate (thickened) and display the corresponding curves in views. The cross can capture coordinate information.
3 Resource Browsing For browsing resources.

Directory choosing can be done for easy browsing of all the files under a directory.

4 Curve View For displaying the data curves of the opened files.

The X coordinate is the distance value; the Y coordinate is the dB value.

5 Data Parameter For displaying the configuration information in data acquisition by the instrument
6 Analysis Result For displaying the analysis result of the instrument
7 AB Label The AB label is made up of two mobile locating lines with adjustable positions. This field displays the information of AB in a dynamic way.

Operation of data curve view

Curve views are the main tool for manual data analysis. Skilled use of curve views guarantees quicker and more perfect understanding of data characteristics. Some fast operations of curve views are introduced below.

No. Function Operation
1 Show All Double click any position of the view.
2 Operating mode switching There is an operating mode switching button on top left of the curve view. The current icon shows the corresponding current operating mode.
3 X-coordinate zooming in the “mobile mode” Move the mouse to the needed position and roll the mouse wheel up to zoom in or down to zoom out.
4 Curve moving in the “mobile mode” At any position of the curve view, press the left key of the mouse and move the mouse.
5 Zooming in the “zoom mode” Press the left key, move the mouse to choose the needed position from the pull-down box for and zooming in. Double click the “Show All” function to view the detail of each position of the curve quickly.
6 Curve moving in the “zoom mode” Move the mouse to the data cable position. When there is a small square at center of the cross coordinates, press the left key and move the mouse at the same time.
7 AB label locating Click the event list. The instrument will obtain the focus automatically and realize dragging through the mouse.
8 Direct A/B label locating Move the mouse to the position needing to be located. Click the right key of the mouse to pop up the following menu. An A label and a B label can be set or removed.

Common Faults

Breakdown Reasons Solutions
No display

on the LCD

1.Power off

2.Power is not enough

1.Press key

2.Change batteries

Wrong measured value 1. Optic fiber connector is dirty.

2.Optic fiber is connected improperly

3.Improper setting of measurement parameters

1.Clean the connectors

2.Reconnect optic fiber

3.Reset parameters


  • Frequently clean end face of the sensor to keep it clean and from grease and other pollutants. Do not use dirty or non-standard optical fiber adapter connector or insert an end face with a poor polished surface, otherwise end face of the sensor will be damaged and the performance of the whole system will be very poor.
  • Use one kind of optical fiber adapter as much as possible.
  • After the instrument is used, fit the dust cap over it immediately to keep the end face clean and avoid measurement errors due to dust as a result of long-term exposure to air.
  • Plug and unplug the optical fiber adapter connector carefully to avoid scratches of the port.
  • Clean the optical fiber adapter connector regularly. Wipe gently along the circumferential direction with special cleaning cotton swabs.

Important points

AC/DC charger

Please use the charger that comes with the standard package as the power supply. Any other chargers may damage this tester.

Lithium ion battery

  1. In order to make Li-ion battery reach better function, please ensure the battery to use up the electricity and at full charge during the first 3 use. If the battery is not used for a long time, you should also follow the above rules.
  2. In order to prolong the lifespan of battery, please remember remove it after charging; use battery to supply power for the tester. In this way, you can ensure to gain better-qualified wave form.
  3. If you don’t use the battery for a long time, please take it out of the tester and charge the battery every 3 months
  4. It is not suitable to charge for a long time. Because it can reduce the lifespan of battery and even damage the battery.

LCD display screen

  1. So as not lead to invalidity or damage of the LCD screen, please don’t use pointed objects to click on the LCD screen and don’t strike it with strength.
  2. Don’t drop organic solvents or pollutants on the LCD screen and don’t clean it with organic solvents but you can use silk or soft textile.

Usage of OTDR

  1. Before connecting the under test optical fibers with the port, you must clean end face of the under test optical fibers in order not to affect result.
  2. During the test, please keep light output port clean and avoid pollutants like oil to pollute ports. Or it can lead to test error and even failure of the test.
  3. When connecting the tested optical fiber with the test port, please keep horizontal and push it gently. Don’t use great strength and don’t screw the connector tightly not to damage end face of the port.
  4. When the tester is not used, please close the dust cap immediately to keep end face clean and protect it from adhering dust due to expose in the air for a long time in order not lead to test error.
  5. Keep optical fiber end face clean. The end face should be without dust and pollution. Don’t use uncleanly and substandard adapter connector. Don’t insert into the end surface with bad polished face or it can damage the end face of the connector.


Clean the optical output port

The function of cleaning optical fiber connector and output port:

  • As the fiber core is very small, so the dust and particles attached to the fiber optical connectors and optical output port may cover part of the output of the fiber core, and results in the decline of the instrument performance.
  • Dust and particles may wear the end face of the output fiber connector, which will reduce the accuracy and repeatability of the tester.

The principles of security before cleaning:

  • Please ensure that the power is turned off during cleaning.
  • Disobeying the regulation or procedure may result in hazardous radiation injury.
  • When cleaning any optical interfaces, make sure to disable the laser source

Clean the optical output ports and connector tools:

  • You can use the optical cleaner, fiber cleaning rods and other tools to clean the optical fiber output interface and connector.
  • If you don’t have the professional tools, please prepare: cotton ball, anhydrous ethanol.
  • Do not use sharp objects or liquids in addition to ethanol to clean optical output connectors, and fiber optic jumpers within the instrument’s face. Or it will lead to the decline of the accuracy and repeatability of the instrument, and even lead to the instrument not to be properly tested.

The procedure of cleaning the optical output connector:

  • Switch off the power supply.
  • Loosen the flange cap security.
  • Gently pull out the flange, just as the following picture shows.

  • Dip appropriate amount of ethanol with clean cotton ball to clean the optical output connector and the flange connector.
  • After cleaning, gently push the flange into the optical output port, and then tighten it


When you remove and access flange, the force should be uniform and not too much force, so as not to damage the optical output end.

When you clean, please gently wipe the fiber end face, so as not to damage the fiber end face.

When you clean, please ensure that rayon balls and absolute ethyl alcohol is clean, or they will pollute the end face of the fiber and will lead to the inaccuracy of the test.

The Maintenance and Exchange of the Battery

  • The work environment and storage environment of the tester (including battery) must comply with the regulations of this manual to ensure the normal operation of the tester.
  • You had better store the equipment (including battery) at room temperature 59 °F~86 °F (15 °C~30 °C), and place it in a dry place to maintain the best equipment performance.
  • When not using the instrument for a long time, please charge and discharge the battery every 3 months. Otherwise, the excessive self-discharge will lead to damage of the battery.
  • Do not charge the battery for a long time, or this may decrease the life of the battery or damage.

The exchange of the battery is as the followings:

  • Unscrew the battery cover on the bottom of the instrument with a cross screwdriver and remove the battery cover. As shown below:

  • Remove the batteries from the battery box, and then replace the battery. Note that location of the battery reed and the battery box reed must be accordant.
  • After covering the battery box, use a cross screwdriver to tighten the screws.

Rechargeable battery specification

The battery in this tester is Li-ion rechargeable battery.

Five Parameter Settings to Protect OTDR Precision

  • Test wavelength selection

OTDR is service for optical fiber communication, so before the optical fiber test, should select the wavelength firstly, single mode fiber only select 1310 nm or 1550 nm. The 1550 nm wavelength of fiber bending loss is more sensitive than 1310 nm wavelength, so whether the construction of optical cable line or cable maintenance or experiment, teaching, the use of OTDR a cable or an optical fiber transmission link for the whole optical back scattering signal curve test, generally choose 1550 nm wavelength.

The test curves shape of 1310 nm and 1550 nm wavelength is same, optical fiber splicing loss measured values are basically same. If there is no problems at a wavelength of 1550 nm testing, then the 1310 nm wavelength test is certainly no problem. Select the 1550 nm wavelength measurement can be easily found the existence of fiber bending over situation.

If found somewhere that the curve has loss step larger, then use 1310 nm wavelength measure, if 1310 nm wavelength loss step disappear, it means bending over have, need to find and eliminate. If in 1310 nm wavelength loss step is same, may also have other problems in the fiber, also need to find out. In the fiber line test, try to use the wavelength of 1550 nm, the effect will be better.

  • Optical fiber refractive index selection

Use the single-mode fiber refractivity in the 1.4600 to 1.4800 range, according to the fiber or fiber manufacturers who provide the actual value to accurately select. The refractivity is not accurate, caused by the length of the test, due to the error. In the optical cable maintenance and troubleshooting when very small mistake will bring obvious error, testing must be done carefully.

The pulse width measurement select

Setting pulse width larger, can produce strong Finel reflection and will make the blind increase. Narrow test pulses of light although have smaller blind area, the test pulse is too narrow; optical fiber power certainly too weak, the corresponding backscatter signal is weak, and the backscattering signal curve will be bumpy, test error big. Setting optical pulse width must be able to guarantee no big blind area effect, but also ensure the backscatter signal curve has sufficient resolution and can see the situation along with the fiber on each point. Generally, according to the measured optical fiber length, select a proper test pulse width, pre-tested one or two times, determine one of the best values. Through bidirectional test or several tests take the average value, it can reduce the effective of blind area.

  • Test range selection

The OTDR range is the maximum distance which OTDR abscissa can reach. The test should be measured according to the length of the optical fiber selection range, the best range is 1.5 times the length of the measured fiber. Select range is too small, OTDR cannot display all information; select range is too large, the abscissa compression of OTDR cannot be seen clearly.

According to experience, the test range selection can make the backscatter curve about the OTDR display screen 70%, regardless of length of the test or loss test can get better visualization and accurate test results. In optical fiber communication system testing good result can be achieved if proper OTDR range is selected.

  • Average time selection

Due to the backscattering signal is very weak, generally used to multiple statistic average method to improve the SNR. OTDR testing curve takes samples of reflected signal of each output pulse, and takes more samples to average to eliminate random events averaging; the average time is longer, the noise level is more closer to the minimum value, the dynamic range bigger. Usually, the average time is longer, the accuracy test is higher. In order to improve the test speed, reasonably use test average time.

Standard Accessories

Items Names Qty
Host GAO-OTDR-103 1
Standard Accessory Adapter (FC standard) 1
User manual 1
CD (including management software) 1
USB Data Cable 1
Carrying Bag 1

Ordering Information

The optional modules of GAO-OTDR-103 are as the below table shows.

Model Wavelength Fiber Type Dynamic range


GAO-OTDR-103-A 1310 nm/1550 nm

±20 nm

SMF 28 dB/26 dB
GAO-OTDR-103-B 1310 nm/1550 nm

±20 nm

SMF 32 dB/30 dB

Optional Accessories

The optional accessories of GAO-OTDR-103 are as the below table shows:

NO. Name QTY Note
1 SC Connector 1pc Adapter
2 ST Connector 1pc Adapter

Additional information


GAO-OTDR-103-A (1310/1550nm; 28/26dB

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