Available Photonics Experiments:

P5874 Erbium doped fibre amplifier
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  • Erbium doped optical fibre
  • Pump laser diode
  • Coupling light to fibre
  • Optical Pumping
  • Signal laser diode
  • Optical amplification
  • Examples of investigations and measurements
Principle of operation
An Erbium doped fibre is optically pumped by a laser diode emitting at a wavelength of 980 nm. Due to the pump process a population inversion is created between two states with an energy difference corresponding to a wavelength around 1.5 µm. Signals having this wavelength will be amplified when passing the fibre. Such a signal is generated by a laser diode emitting a radiation of 1.5 µm which is also coupled into the fibre. For combining both emissions a dichroitic beam splitter plate (E) is used. The amplified or even fibre laser oscillation is detected by means of a InGaAs photodiode.
OX General set-up
The EDFA fibre (G) is terminated with ceramic ferrules fixed to the assembly. The pump as well as the signal radiation is coupled with the module (F) into the Erbium doped fibre. The module (F) is provided with four fine pitch screws for XY and фθ Adjustment. Turning the microscope objective results in a smooth translation to adjust the focus with respect to the entrance face of the fibre.
The module E combines the radiation of the signal as well as pump light by means of a dichroitic beam splitter plate. The plate is mounted into an adjustment holder for precise alignment of the reflected pump laser beam. The signal as well as the pump laser diode are mounted into precise 4 axes adjustment holder.
OX Optical pumping and fibre laser
The experiment starts with the optical pumping of the erbium doped fibre. The pump laser radiation is guided into the Erbium doped fibre. For simplification of the alignment process the modulation of the injection current is switched on and the oscilloscope is triggered with this signal. This allows the detection of even very small modulated signals when the oscilloscope is switched to AC mode. Once a transmission signal is detected the alignment can be improved and optimised. If this is done properly and the injection current of the pump laser diode set to the maximum laser oscillation at 1.5 µm can be observed since the gain is very high so that the Fresnel reflectivity of the fibre end surfaces is sufficient to form an optical cavity. Spiking as shown in the figure left will be observed.
Optical amplification measured with an oscilloscope
Spiking of the fibre laser operating at 1.5 µm
Optical amplification
Once the pump radiation has been launched to the fibre, the signal radiation needs to be fed through the fibre. The alignment strategy is the same as for the pump radiation. Once the signal radiation passes the fibre, the pump radiation (B) is modulated and the signal radiation not. As soon as amplification takes place of the amplitude of the signal radiation is measured for different pump power and signal power levels and the maximum amplification determined.
  • P5874 Erbium doped Fibre Amplifier consisting of:
13L-03701BNC connection leads, set of 3
24B-00101Microscope objective x 10, RMS
34B-06001Focusing optic, triplet, f=6 mm NA 0.6, click 25 mm
44S-09801Dimo diode laser 980 nm (�10), 80 mW module with Peltier cooler
54S-15501Dimo diode laser 1550 nm (�20), 5 mW module with Peltier cooler
68X-XP201Manual Erbium doped fibre amplifier (EDFA)
7ED-00202Digital diode laser controller
8ED-02101PIN Photodetector, BPX61 with connection leads
9ED-02201Photodetector, InGaAs with connection leads
10MC-02501Profile Rail MG-65, 300 mm
11MC-02601Optical rail MG 65, 500 mm
12PM-00701Infrared display card, spectral range 0.8 -1.6 �m
13XM-00361Module B - Collimating optics on carrier
14XM-05101Coupling optics, microscope objective x 20 with XY- adjustment holder
15XM-05601Dichroic beam combiner HR980, HT 1550 nm
16XM-05701Erbium doped fibre 17 m with holder
17XM-10902Mounting plate C25 with carrier 20 mm
18XM-11102Adjustment holder, 4 axes, carrier 20 mm
 Required Options:  
 TP-01001Oscilloscope 100 MHz digital, two channel