LUHS - LT-0400 OTDR - Optical Time Domain Reflectometer


  • Pulse Laser Diode

  • Optical Fiber

  • Fiber Stripping

  • Fiber cutting

  • Speed of Light

  • Length of Fiber

  • Losses of Fibers

  • Losses of Connectorsv

  • 2 x 1000 m connectorized Fiber Spools

  • Fast Photo Detector

  • Light Echoes

LT-0400 OTDR - Optical Time Domain ReflectometerLT-0400 OTDR - Optical Time Domain Reflectometer

The whole worldwide communication is based on fiber optical networks encompassing the entire world and is extremely important in view of economical and security aspects. Meanwhile fiber optical networks lines already terminating at homes thus forming a complex structure. The proper working and condition is of vital mutual interest of the provider and customer.
Fiber lines can be damaged during road works, earth movements and even by late effects of production imperfections. Whatever the reason of the malfunction of communication networks are, the problems needs to be solved as soon as possible. This is the moment of the mission of the "Optical Time Reflectometry" (OTDR). An OTDR is an optoelectronic instrument that uses time-domain reflectometry to characterize and locate faults in optical fibers The underlying idea is so send a short pulse into the fiber and "listening" to any echoes coming back from it. At each fiber imperfection, especially at the face of a broken fiber a lot of light is reflected or scattered back into the fiber From the time of flight of the input pulse and the occurrence of the echoes the distance to the faulty position is found and the service team can do their job. However, the OTDR covers more possibilities, it is the only device which can measure the attenuation or losses of an optical fiber non-destructively. Such losses in optical fibers can be caused by several reasons, mainly due to optical and mechanical imperfections during the manufacturing process, or by extra mechanical stress on the fibers like unspecified bending or tension. These days OTDR devices a small and compact and an indispensable tool in optical fiber communication.
The aim of this experiment is to set up an OTDR in such a way that the trainees can identify, align and control the required components like the pulsed diode laser, coupling light into the fiber via a polarizing beam splitter. The path of the returning light is bended due to its changed polarization at the beam splitter cube towards the fast photodetector. The returned light intensity carries the information about the losses by an exponential decay in time, upward peaks for reflections and downward peaks for losses at joints caused either by splices or connectors. The experiment comes with two drums carrying each 1000 m of optical fiber The fibers are interconnected via two ST patch cable whereby one end of each fiber is left as it is to teach fiber stripping and cutting.

LT-0400 OTDR - Optical Time Domain Reflectometer

A. Principle of Optical Time Domain Reflectometer OTDR
Main reasons for losses in optical fiber are mechanical cracks, unavoidable scatter centers due to the production process and reflections (see Fig. B). These three imperfections creating backward oriented scatter light, where by optical connectors acting as a photon sink. The idea of an OTDR is to detect this back scattered light and analyze its amplitude and temporal behavior. For this purpose the pulse of the laser diode (PLD) is launched via a polarizing beam splitter plate into the optical fiber The polarization of the back scattered is changed so that it will be reflected at the beam splitter towards the detector. The quarter wave-plate further enhances the right polarization in order to get most of the back scattered light which anyhow has a very small power. This requires highly sensitive photodiodes and fast amplifier.
Within this experiment an extra photodetector as alignment aid is used. It serves as indicator for the coupling efficiency of the laser light into the fiber Further more in first experiments the time of flight inside the fiber can be measured with this photodetector as well.
OTDR back scatter signal
A. OTDR back scatter signal

Sources for light back scatter B. Losses in optical fiber

LT-0400 OTDR - Optical Time Domain Reflectometer, consisting of:
Item Code Qty. Description
1 CA-0060 1 Infrared display card 0.8 -1.4 µm
2 CA-0450 2 BNC connection cable 1 m
3 CA-0620 1 Optical fiber scriber and breaker
4 CA-0630 1 Adjustable plastic cover stripper
5 DC-0050 1 Pulsed laser diode controller MK1
6 DC-0124 1 Si-PIN Photodetector with ST jack and connection leads
7 DC-0220 1 SiPIN Photodetector, ultrafast with amplifier
8 DC-0384 1 Photodetector junction box w. amplifier
9 LQ-0350 1 Pulsed diode laser in housing
10 MM-0020 2 Mounting plate C25 on carrier MG20
11 MM-0090 1 XY adjuster on MG20
12 MM-0490 1 Translation stage with bare fiber holder
13 MP-0130 1 Optical Bench MG-65, 300 mm
14 MP-0150 1 Optical Bench MG-65, 500 mm
15 OC-0060 1 Biconvex lens f=60 mm in C25 mount
16 OC-0170 1 Collimator 808 nm in C25 mount
17 OC-0840 1 Quarter-wave plate in C25 mount
18 OC-2030 1 ST/ST MM Fiber patch cable, length 1 m
19 OC-2040 1 Set of 10 ST pigtailed MM fiber
20 OC-2450 2 Multi-mode fiber 1000 m, 50/125 µm, ST panel jacks
21 OM-0020 1 Adjustable beam splitter on tee-piece MG65
22 OM-0950 1 MO coupling optics, 4 axes kinematic mount
23 UM-LT04 1 Manual OTDR
Required Option (order separately)
24 CA-0200 1 Oscilloscope 100 MHz digital, two channel
Available Downloads
Media Type Title File Size [MBytes] Action
PDF  LT-0400 OTDR - Optical Time Domain Reflectometer
 Version:  2014
5.49 MB Download
PDF  Catalogue Page    
JPEG, PNG, SVG  Pictures    
MP4  Video