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Quadrature Amplitude
Modulator
QAM

1 – Description
Kylia proposes two QAM products: QAM16 and QAM64.
The QAM16 emulator is a device that enables to emulate a QAM16 signal from a QPSK signal. The device has
one PM input by which a QPSK signal is launched. First the signal is split in a very precise 80/20 ratio. One
part is delayed by 1ns in order to de-correlate both parts of the signal. Then the two parts are combined tomake them interfere and thus emulate a QAM16 signal which is injected in the PM output fiber. A phasetuning element enables to adjust the delay between both arms to a multiple of bit-time in order optimize
the interferences pattern. Moreover an ON/OFF switch enables to visualize only one arm of the QAM16emulator.
The QAM64 emulator is a device that enables to emulate a QAM16 or QAM64 signal from a QPSK signal. Thedevice has one PM input by which a QPSK signal is launched. It is then split twice thanks to tunable couplers
and the three parts are finally recombined together after one has been delayed by 500ps and another by1ns. The interference of these three signals enables a QAM654 signal injected in the PM output of thedevice.
Phase tuning elements enable to precisely adjust the delay between the several arms depending on thewavelength used.

QAM64

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QAM

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QAM : Quadrature Amplitude Modulator

2 – Block diagram

Block diagram: QAM16

Block diagram: QAM64

3 – Absolute maximum ratings
Parameter
Maximal optical input power
Storage temperature range
Humidity
Fiber bend radius
Maximal input voltage

SymbolOpIn
STR
RH

Min

Typ.

-10.0
520VmaxMax
300
80854UnitmW°C%mm
VMax
1570
704Unitnm°C
VRemarks/Conditions

nonon condensing

4 – Operating conditions
Parameter
Operating wavelength
Operating temperature range
Operating tuning voltage

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Symbol
OWR
OTR
OTV

Min
1530
0-4Typ.

QAM

Remarks/Conditions

2

QAM : Quadrature Amplitude Modulator

5 – Specifications
QAM16 specifications:Parameter
Insertion loss
Splitting ratio
Path difference
Switch attenuation
Tuning range

SymbolILR
DAttTuning voltage

OTV

Power consumption
OTV connectorPεMin
3.2
78990
60
360

Typ.
4.5
80
1000

2.5

Max
5.5821010

Unit
dB%
psdB
deg

3.5

V

0.5WMax
2.0
3.0
4.0505505

520

UnitdBdBdB
pspsdBdB
deg

Remarks/Conditions
Including 3dB from BS

360deg is equivalent toapprox. 5fs at 1550nm
Voltage needed for a360deg tuning range

BNC

QAM64 specifications:Parameter
Insertion Losses path 1
Insertion Losses path 2
Insertion Losses path 3
Optical path delay 2-1
Optical path delay 3-2
Polarization Extinction Ratio
Optical Return LossTuning rangeSymbol
IL1IL2IL3
OPD21
OPD32PERORLMinTyp.

Tuning voltage

φ3.0V

Tuning time constantΤ1.0sPower consumption
OTV connector

P0.5

W

495495
1935

Remarks/Conditions
Measured with tunable
couplers optimized

Voltage needed to reachthe tuning range
To reach 50% of the finalstateBNC

OTV : The tuning voltage feeds a 33 Ohms heater attached to low thermal latency optical element. Whenheated, this element changes its refraction index, and adds an additional delay of several femtoseconds. Thisfeature enables to finely tune the phase of both arms for a perfect QAM figure.

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QAM

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QAM : Quadrature Amplitude Modulator

6 – Principle Mathematics
Let us call AIN(t) the electromagnetic field (EMF) of the input. Then for a QPSK signal we have:

AIN (t ) = eik ( t ).

π2Where k(t)t) is an integer that changes every T seconds. T is the bit-time
bit time and equals 1/F where F is themodulation frequency of the signal. Typically, for a QPSK signal modulated at 40GHz, we have T=2.5ps andk(t) can take a value between [0,1,2,3] and will change every 2.5ps.
At the output of the QAM16, the EMF can be expressed by:

AOUT (t ) = R .e

πik ( t ).

2+ (1 − R) .eπi  ω .( D +ε ) + k (t + D +ε ). 2

Where:••••

R is the splitting ratio (R=0.8)
ω=2πf with f the optical frequency (for example f=193400GHz)
D is the delay between both arms of the interferometer (D=1000ps)
ε is the delay added by the tuning phase element (ε<5fs hence it does not change the value ofk(t+D+ ε) but it enables ω*(D+ε) to be a multiple of 2π)

By now, let us call k’(t)=k(t+D+ ε) to simplify the notations. Then one can plot the EMF in phase
phandamplitude for the output as follow:

The spacing between the 16 points of the constellation is determined by the splitting ratio (R). The
orientation of the sub-constellation
constellation k’ has to be adjusted, depending on the modulation frequency, with thephase tuning element.
With a 80/20 ratio, when the tuning element is correctly adjusted, points are equidistant one to each otherthen emulating a QAM16 signal. With the +/-2%+/ 2% precision on R of the QAM16 emulator, the error made on
the QAM16 constellation willill not induced a penalty of the BER vs OSNR more than 0.5dB.

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QAM4

QAM : Quadrature Amplitude Modulator

The same reasoning applies for the QAM64 output with a third EMF adding to the first two.
Below are some results obtained with a QAM16 emulator:

Figure 1: QAM16 constellation

Figure 2: Eye diagram of the QAM16 signal emulated

Figure 3: Measurement of the Q² factor

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QAM5QAM : Quadrature Amplitude Modulator

7 – Package layout

QAM16 packaging

QAM64 packaging

8 – Revision
daterdFebruary 3 , 2015

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versionQAM V1.0

ObjectCreation

QAM

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