High Power Pulsed

Fiber Lasers

Colin Diehl, Yevgeniy Krasnitskiy, Doug Lyons, Jered Richter

Basic Components of

Lasers• Power Source

• Gain Medium

• Feedback

Mode Locking• Mode locking is a technique to create

very short periodic pulses by locking modes in phase

Additive-pulse Mode

Locking• Nonlinear phase shifts in a single-mode fiber.

• Pulses returning from the fiber resonator into the

main laser resonator interfere with those pulses

which already are in the main resonator.

• Constructive interference near the peak of the

pulses, but not in the wings, because the latter have

acquired different nonlinear phase shifts in the fiber.

• Peak of the circulating pulse is enhanced, whereas

the wings are attenuated.

The Kerr effect

• Nonlinear polarization generated in the medium,

which modifies the propagation properties of the light.

• The refractive index for the high intensity light beam is

modified according to

Δn = n2 ∙ I

with the nonlinear index n2 and the optical intensity I.

Kerr Mode Locking

Kerr Mode Locking

Measurements

Stable pulses but unstable background

After removing passive fiber and splicing isolator to WDM

DC coupled

~70 ns repetition rate

AC Coupled

WDM Problems

• Single-mode pigtail of WDM broke, too

small to be re-spliced

• Unprotected fusion splice of double-clad to

single-mode caused coating to burn

• Splice protector submerged in water

stopped burning, cooled splice

MOPA (Master Oscillator

Power Amplifier)• This fiber laser will consist of three

stages:

• 1st: Master Oscillator (this is the

stage that will contain the

graphene and will produce the

pulsing)

• 2nd: Single-Mode Power Amplifier

• 3rd: Double-Clad Power Amplifier

Application of Graphene to the Tip of a

Fiber Connector

• We want to use graphene as a

saturable absorber for our MOPA

• In order to do that, we need to get

graphene onto the tip of a fiber

connector

Cut Out a Small Square From the

Graphene Sample

• To cut the graphene

sample, use an exacto

blade and press firmly

onto the foil, no sawing

motion

• Once the small square

is free, place it onto a

glass slide and with

another glass slide

cover it

• Press the two slides

together to flatten the

foil so that hopefully the

suction in the next step

will be strong enough to

hold it in place

Put a Droplet of Isopropyl Alcohol onto the

Copper Square

• Careful not to wet the copper square,

a bead is needed in order to adhere

to the target substrate

• Once there is a bead of Isopropyl on

the copper square, lower the fiber

connector slowly down to it. We used

a translation stage to lower the fiber

connector down slowly and smoothly

• When the tip of the fiber connector

breaches the top of the bead, the

copper square should be sucked

upward and flatten on the surface of

the fiber connector tip

Bake the Fiber Connector on a Hot Plate

• Place the whole translation

stage onto a hot plate set to

120C

• Lower the translation stage

so that the tip of the fiber

connector is right above the

hotplate

• Let it bake for an hour and a

half

Etch the Copper Substrate

• Fill a glass petri dish with

copper etchant (we used

sodium persulphate)

• Lower the fiber connector tip

into the copper etchant slowly

• Let it sit for an hour, and then

dip the fiber connector into DI

water the same way to remove

excess etchant

Attempts at Imaging Graphene on the Tip

of the Fiber Connector