1

Fiber Amplifier 1

In this experiment you will characterize a semiconductor laser

operating at 980 nm, the performance of a WDM coupler at the

wavelength of 980 nm, and the absorption properties of an erbium-doped

optical fiber also at the wavelength of 980 nm.

Those characteristics will later be used (Experiment Fiber

Amplifier 2) to characterize an erbium-doped fiber amplifier unit. The

980-nm semiconductor laser will be used to excite (pump) erbium ions

that are doped on the optical fiber to boost the signal intensity of a

co-propagating light beam at 1550 nm through the process of stimulated

emission at this wavelength (1550 nm). The WDM coupler will combine

the 980-nm laser and the incoming 1550-nm signal so they co-propagate

through the erbium-doped fiber.

Experiments:

Semiconductor Laser (980 nm)

You will characterize the optical power versus the electric

current passing through the 980-nm semiconductor laser device. A

laser driver (a tunable electric power supply) will be used to drive

electric current through the semiconductor device. The 980-nm laser

can reach high optical powers and needs to be temperature controlled

to improve its lifetime. To maintain the laser operating at about 25

ºC, you will use the temperature controller TED 350 with the following

settings:

Sensor: Th << 20 kΩ

2

Mode: T/R constant

ITEC LIM = 1.407 A

TSET = 10.000 kΩ

TWIN = 1.00 kΩ

TSET LIM = 9.00 kΩ

After you have turned on the temperature controller, connect the

fiber coming out of the 980-nm laser to the detector head of a power

meter. Make sure you use a detector head that is suitable for the 980

nm wavelength. The optical power in the detector head S122C should not

exceed 40 mW. The 980-nm can provide about 300 mW if the electric

current reaches about 439 mA. In order not to exceed the detector head

(S122C) limit, you should limit the electric current to about 80 mA.

In the laser drive controller, before turning it on, first turn

counter-clockwise the variable knob to set the initial current to

zero. Then turn the laser driver on. Switch the display to read the

actual electric current. You should see a value close to zero mA at

this moment. Make sure the fiber output is connected to the detector

head and the power meter is on and reading optical power (which should

be essentially noise at this moment). In the laser driver, enable the

laser operation. From this point, start increasing in small steps the

electric current and measuring the optical power in the power meter.

Take note of both readings. The laser threshold is about 46.9 mA. Go

up to 80 mA in the electric current. Very important: as soon as you

finished your measurements, please bring the current down to zero and

disable the laser in the laser driver controller.

3

WDM Fiber Coupler

With the output fiber of the 980-nm laser connected to the

detector head, set the laser driver current to 70 mA and measure the

optical power. Take note of this value. Turn off the laser.

Identify the common port of the WDM coupler. Clean the tip of

this connector. Place this common port of the WDM coupler at the fiber

coupler adaptor. Clean the tip of the connector of the laser output.

Connect the output fiber from the 980-nm laser to the common port of

the WDM coupler using the fiber coupler adaptor. Now, place the 980-

nm port of the WDM coupler at the detector head to measure the light

throughput. Turn on the 980-nm laser and set the current to 70 mA.

Take note of

the measured

optical

power.

Remove the

980-port of

the WDM from

the detector

head and

place it in

a safe place

(remember:

there is

optical

power coming out of this port). Now place the 1550-nm port of the WDM

coupler into the detector head and measure the optical power. Ideally

we would like to see most of the 980-nm light injected into the common

port of the WDM coupler going into the 980-nm port and very little

4

into the 1550-nm port. Your values are important to characterize the

quality of the WDM coupler. Turn off the laser.

Absorption of the Erbium-Doped Fiber

Connect the output fiber of the 980-nm laser to the detector

head. Set the laser driver to 70 mA and measure the optical power out

of the fiber connected to the laser. Take note of this value. Turn

off the laser power.

By using the fiber adaptor, connect the output fiber of the 980-

nm laser to the cable that contains a piece of about 1 meter of

erbium-doped fiber. Then connect the other port of the erbium-doped

fiber cable to the detector head. Turn on the 980-nm laser and set the

electric current to 70 mA. Measure the optical power reaching the

detector head after passing the erbium-doped optical fiber.

Analysis:

Create a plot of the optical power against the electric current

injected into the 980-nm semiconductor laser. Identify the current

threshold of laser operation in the laser device. Determine the slope

(mW/mA) for the part of the curve above threshold. Estimate the

conversion efficiency from electric power to optical power of this

laser diode. For this purpose, take a look on the voltage

specification provided in the laser data sheet.

As we saw earlier, the throughput in fiber optical devices is

given in decibel units (dB) as defined below:

5

𝑑𝐵 = −10 log10 (𝑃𝑜𝑢𝑡

𝑃𝑖𝑛)

Characterize the throughput of the WDM device by using the dB

units. First, determine the insertion loss for light incoming from

the common port and exiting at the 980-nm port. Then, determine the

amount of 980-nm light incoming from the common port and crossing over

to the 1550-nm port.

Characterize the erbium-doped fiber section in terms of

absorption loss (in dB) as described above, optical transmission

𝑇 = 𝑃𝑜𝑢𝑡

𝑃𝑖𝑛, and absorbance 𝐴 = − log10 (

𝑃𝑜𝑢𝑡

𝑃𝑖𝑛).

Questions to consider:

1) What would happen to the absorption loss of the erbium-doped fiber

if we double the length of the erbium-doped fiber? Would the

absorption loss change? If so, by how much.

2) What would happen to the absorption loss of the erbium-doped fiber

if we double the power of the pump laser? Would the absorption loss

change? If so, by how much.

3) Based on you measurements, determine the insertion loss for the

980-nm pump laser going from the 980-nm port of the WDM to the common

port of the device.

Erbium Doped Fiber MetroGain™

Fibercore’s MetroGain™ range is designed for high efficiency ‘Metro-style’ Erbium Doped Fiber Amplifier (EDFA) configurations, single stage amplifiers, Amplified Spontaneous Emission (ASE) light sources and single channel or few channel EDFAs.

M-5(980/125) offers a relatively low level of doping to simplify EDFA manufacturing processes by reducing the sensitivity of the amplifier output to the precise gain length.

M-12(980/125) gives high absorption levels to allow short gain lengths and reduced material costs.

M-12(980/80) is an 80µm variant, benefitting from the higher absorption of the standard M-12(980/125) but allowing significantly longer mechanical lifetimes when used in small coil diameters, particularly important for small form factor EDFA designs such as mini EDFAs and micro EDFAs.

M-3(1480/125) is designed for pumping at 1480nm, accessing higher pump conversion efficiencies than pumping at 980nm.

VERSION: MD20/1

RELEASE DATE: 8 NOVEMBER 2013

Doped Fiber

Typical applications:

• Erbium Doped Fiber Amplifiers (EDFAs)• Amplified Spontaneous Emission (ASE) light sources• Single channel amplifiers• Mini and micro EDFAs

Advantages:

• High conversion efficiency• High absorption variants available for short amplifiers and EDFAs• 80µm variant for small coil diameter applications

T: +44 (0)23 8076 9893E: info@fibercore.comwww.fibercore.com

Datasheet

Related Products:

• Erbium Doped Fiber IsoGain™

•  Dual-Clad Erbium/Ytterbium Doped Fiber (CP1500Y)•  GainMaster™ Simulation Tool

Product Variants:

• M-3(1480/125) Designed for single channel C-band amplifiers

• M-5(980/125) Designed for single channel C-band amplifiers

• M-12(980/125) Designed for short length single channel C-bandamplifiersandL-bandamplifiers

• M-12(980/80) Designed for small package size C-bandandL-bandamplifiers

Supported by Fibercore’s GainMaster™ simulation software

Specifications

T: +44 (0)23 8076 9893E: info@fibercore.comwww.fibercore.com

Typical Absorption and Emission Spectra

M-3(1480/125) M-5(980/125) M-12

(980/125) (980/80)

Cut-Off Wavelength (nm) 1300 – 1450 900 - 970

Numerical Aperture 0.21 - 0.24

Mode Field Diameter (µm) 5.1 – 5.9 @1550nm 5.5 – 6.3 @1550nm 5.7 – 6.6 @1550nm

Absorption (dB/m) 2.8 – 3.8 @1480nm6.5 – 10.1 @1531nm

4.5 – 5.5 @980nm5.4 – 7.1 @1531nm

11.0 – 13.0 @980nm 16.0 – 20.0 @1531nm

Proof Test (%) 1 (100kpsi)

Attenuation (dB/km) ≤10@1200nm

Polarization Mode Dispersion (ps/m) ≤0.005

Cladding Diameter (µm) 125 ± 1 80 ± 1

Core Concentricity (µm) ≤0.3

Coating Diameter (µm) 245 ± 15 170 ± 10

Coating Type Dual Acrylate

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