1. Multi-wavelength 40 GHz pulse source based on saturated optical parametric amplifier
David Dahan and Gadi Eisenstein
Technion - Israel Institute of Technology
Department of Electrical Engineering
The title of this talk is multiwavelength 40Ghz pulse source based on saturated optical parametric amplifierץ
My name is d. Dahan and I would like to take my advisor G. E. for his contribution to this work.
OAA - June San Francisco

2. Outlines Motivations Multi-wavelength pulse source
principle of operation
Experimental set up and results
Conclusion
Here are the outlines of this presentation :
First of all, I will explain the motivation of this work
Secondly I will explain the principle of operation of this all optical multiwavelength pulse source: it is based the generation of multiorder FWM product through saturation of OPA.
Then I will describe the ex se up and result and I will draw the conclusion
OAA - June San Francisco

3. Motivations
How can we cope with the increasing demand in information capacity?
Development of multi-wavelength optical pulse sources at high repetition rate
The increasing demand in information capacity has initiated intense research efforts to generate new optical source with the capability of providing optical narrow pulse at high repetition rate. 2 techniques based of the fiber nonlinearities can be used : supercontinuum generation and FWM
Super-continuum generation
Optical parametric amplification
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4. Using the exponential dependence of the OPA on the Pump power, the pulsed pump can be replaced by a sinusoidally modulated pump *
For G>>1
* J. Hansryd et al. “ Simple and robust 40 GHz RZ pulse source based on a fiber optical parametric amplifier “, OFC 2001, paper WA.5
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5. Multi-wavelength pulse source : principle of operation
Pump MZ CW
HNLF λp λs
λid1
λid2
λid3
λid5
λid4
Signal CW
The proposed multi-wavelength pulse source pumped OPA at saturation. An sinusoidally intensity modulated pump is launched with a CW signal into a HLNF. For sufficiently high , several FWM products are generated, each using a spectrally adjacent signal as its pump. Under optimized conditions, the generated pulses should shorten with the increasing FWM order. λp λs
A high input CW signal saturates the OPA : high FWM orders are generated
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6. Multi-wavelength pulse source : Experimental set up
OSC
OSA / Auto
BPF3
50/50 TL
HNLF (4km)
AWG
BPF2
BPF1
EDFA1
EDFA3
EDFA2
EDFA4 PC
VOA
20GHz
Photo-detector Φ MZ
223-1 PRBS 2.5 Gb/s
Pump
λp=1543 nm
Signal
λs= nm
Generation of multi-wavelength pulses was demonstrated using the system shown schematically in Fig. 1. The tunable pump is set at 1543 nm and modulated at 40 GHz using a Mach-Zehnder modulator biased at Vπ and driven by a 20 GHz RF source. An Erbium doped fiber amplifier (EDFA1) acts as a preamplifier to a booster (EDFA2) which enables a launch power of +21 dBm into a 4 km long HLNF with an average λ0 of nm, a dispersion slope of ps/nm2 and a nonlinear coefficient γ=10.6 W-1/km. To avoid stimulated Brillouin scattering, the CW pump is phase modulated with NRZ data at 2.5 Gbit/s. The CW signal is set at nm and amplified (EDFA3) before being coupled to the HLNF through an array waveguide grating. A variable optical attenuator placed after EDFA3 allows to vary the signal input power. At the OPA output, in order to selected one of the FWM products while reducing the adjacent channel crosstalks, we employed two cascaded tunable band pass filters (BPF2 and BPF3) whose 3dB bandwidth are 3.45 and 2.8 nm, respectively. An amplifier (EDFA4) is inserted between the two filters to compensate for their losses as well to provide sufficient power to the 50 GHz photo-detector and the autocorrelator.
HLNF : λ0= nm, S=0.018 ps/nm2, γ = 10.6 W-1/km
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7. OPA spectrum Idler1 Pump Signal Idler3 Idler2 Idler4 Power [dBm]20
no signal
Psin = - 5 dBm
Psin = 0 dBm
Psin= -20 dBm
Psin =5 dBm 10
Psin = -15 dBm
Psin = -10 dBm
Psin =10 dBm
-10
Power [dBm]
-20
-30
Figure 2 shows the optical spectrum at the output of the OPA. The OPA exhibits a gain bandwidth larger than 20 nm. The input signal wavelength is located at the peak gain and its spectrum as well as the spectrum of 1st order FWM product (called idler1) occupy the entire sideband bandwidth. Several FWM products were generated, even at low input signal power, as indicated in figure 2. Indeed, the used of a long HLNF allows to reduce the launched pump power while enhancing the saturation effects. Since the tuning range of our filters was limited to ~ 40 nm we placed the pump 8 nm away from λ0 so that we could make use of several FWM products.
-40
Idler1
Pump
Signal
-50
Idler3
Idler2
Idler4
1510
1520
1530
1540
1550
1560
1570
1580
Wavelength [nm]
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8. Ps= -10 dBm Idler 1 Pump Signal Idler 2 Idler 4 TFWHM = 6.3 ps
Here, we show the pulse source obtained at the different wavelength for an initial input power of -10 dBm
The 40 GHz pulse trains are detected by a 50 GHz photo-detector for the idler, the pump , signal, the 2nd and the 4th idlers. The pulses remain stable over time with an RMS timing jitter smaller than 1 ps. The pulse widths, shown by the autocorrelation traces narrow with increasing FWM product order. At the signal and 1rst idler wavelength the pulses are 6.3 ps wide, At the pump wavelength the pulses are 6.5 ps wide, at the 2nd idler wavelength they are 4.9 ps wide. The 4th idler exhibits the narrowest pulse (4.2 ps). In spite of the long fiber length, there is no walk off between the pump and the different signals since they are synchronized to the pump through XPM effect [4] which enables the good compression quality. Because of the low input power the second and fourth idler have a OSNR lower than the one for the 1rst idler and signal after EDFA amplification needed for the detection.
TFWHM = 6.3 ps
TFWHM = 6.5 ps
TFWHM = 6.5 ps
TFWHM = 4.9 ps
TFWHM = 4.2 ps
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9. Ps=5 dBm Idler 1 Pump Signal Idler 2 Idler 4 TFWHM = 7.1 ps
When increasing the input signal power, the high order get a better OSNR before detection. Here again for Ps=5 dBm we can see pulse width FWM reduction with the FWM order
TFWHM = 7.1 ps
TFWHM = 7.75 ps
TFWHM = 7.1 ps
TFWHM = 5.1 ps
TFWHM = 4 ps
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10. Pump Spectrum Power [dBm] Wavelength [nm]10
no signal in
Psin= -10 dBm
Psin= 0 dBm
-10
Pump in
Psin = 5 dBm
-20
Power [dBm]
-30
-40
Here we present the optical spectra of the pump for different input signal power with a resolution of 0.01 nm.
The input pump spectrum presents spectral lines are 40 GHz apart but residual sub-lines at 20 GHz are also present with more than 15 dB attenuation. They result from the non perfect pump modulation at Vπ. At the fiber ouput, the pump spectrum is broadened due to soliton compression and is 6 nm large when no CW signal is launched with it into the HLNF. We selected one side band of the spectrum for detection. The input signal power changes the pump spectrum . Large saturation reduces the total pump spectrum bandwidth
-50
-60
-70
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
Wavelength [nm]
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11. Idler 1 Spectrum Signal Spectrum Power [dBm] Wavelength [nm]
-10
-20
Power [dBm]
-30
-40
Psin = -20 dBm
Psin= -15 dBm
Psin = -10 dBm
Psin= -5 dBm
-50
Psin= 0 dBm
Psin= 5 dBm
Psin= 10 dBm
-60
1531
1532
1533
1534
1535
1536
1537
1538
Wavelength [nm]
Signal Spectrum
1548
1549
1550
1551
1552
1553
1554
1555
-60
-50
-40
-30
-20
-10
Wavelength [nm]
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12. Idler 2 Spectrum Idler 4 Spectrum Power [dBm] Wavelength [nm]
1555
1556
1557
1558
1559
1560
1561
1562
1563
-60
-50
-40
-30
-20
-10
Wavelength [nm]
Power [dBm]
Psin= 0 dBm
Psin= 5 dBm
Psin= 10 dBm
Psin = -20 dBm
Psin= -15 dBm
Psin = -10 dBm
Psin= -5 dBm
Idler 4 Spectrum
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
-60
-50
-40
-30
-20
-10
Wavelength [nm]
Power [dBm]
Psin= -10 dBm
Psin = -5 dBm
Psin= 0 dBm
Psin= 5 dBm
Psin= 10 dBm
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13. Pulse width and TBP vs. Input signal Power
-20
-15
-10 -5 5 10 4
4.5
5.5 6
6.5 7
7.5 8
8.5
input signal power [dBm]
FWHM [ps]
signal
pump
idler1
idler2
idler4
-20
-15
-10 -5 5 10
0.4
0.6
0.8 1
1.2
1.4
1.6
1.8 2
2.2
2.4
Input signal power [dB]
TBP
By changing the input signal power while keeping the pump power constant, the pulse width changes at each wavelength. This figure shows the pulse width variation respectively for the pump, signal and the idlers 1, 2 and 4. When no signal is present the input sinusoidal pump build itself into soliton pulses whose pulse width is 8 ps. When the input signal increases, the complex interactions between the pump, signal and idler waves can make the pump pulses decrease up to 5.5 ps, The signal and idler1 have almost the same pulse width which increases with the input signal power but since idler1 is closest to λ0, its spectral broadening is the largest. The pulses at idler2 vary from 4.2 to 6 ps and the TBP varies from 0.7 to 1.1, indicating a chirped profile since it can also act as a pump. Only idler4 has an almost a transform limited profile for large input signal powers and it width varies from 4 to 5.1 ps.
OAA - June San Francisco

14. Conclusions
We have demonstrated a 40 GHz multi-wavelength pulse source using the saturation effect in OPA:
An OPA pumped by a sinusoidally modulated pump controlled by a 20 GHz RF source can be saturated by a single CW input signal
Generation of several orders FWM products , each being a 40 GHz pulse source
Under optimized condition the pulse width reduces with the increasing FWM order
OAA - June San Francisco