Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is currently the only available strictly transparent wavelength-conversion technique, which is not penalized by phase matching. The span of the conversion is limited primarily by conversion efficiency and signal-to-noise (SNR) issues, both of which are expected to improve with the use of longer SOAs. In this paper, we demonstrate significantly enhanced performance of long converters in a system experiment at 10 Gbit/s. The experiment shows for the first time, to our knowledge, that FWM wavelength down-conversions can span the full gain bandwidth of erbium-doped fiber amplifiers

D'Ottavi, A.

Dall'Ara, R.

Guekos, G.

Hunziker, Guido

Paiella, Roberto

Spano, P.

Vahala, Kerry J.

English

Caltech Authors - Main

108 0 Wednesday Morning OFC '98 Technical Digest 
I I I I I 
c2 
1556.8 1557.0 1557.2 1557.4 
Wavelength (nm) 
WB6 Fig. 2. Conjugate and suppressed signal at the output of a converter 
made using a 0.5-mm amplifier, after a polarizer suppressing the polarization 
parallel to P1. P1-S detuningis Af= 120 GHz. Dashedline is the component ofthe 
signal parallel to P1, hence orthogonal to C2, demagnified 2500 times. 
the same frequency is thereby possible. The frequency of C2 is tuned 
by tuning the frequency of PI  and P2, with fixed Af: Because FWM 
efficiency is expected to be almost independent of P1-P2 detuning, 
the frequency conversion efficiency is virtually flat. A high efficiency 
is obtained because the frequency of S is lower than that of PI for 
either up- or down-conversion of the signal. Assuming the optimal 
case of equal output pump intensities, efficiency and SNR are 6 dB less 
than the single pump scheme for the same saturated gain and the same 
A 5  independently of the P2 polarization. The polarizer at the SOA 
output also suppresses the amplified spontaneous emission noise 
generated by the in-line amplifiers downstream and amplified in the 
SOA. Our converter can be made polarization independent by a 
polarization diversity scheme in which two orthogonal components 
of the signal polarization are independently converted. 
Preliminary measurements with a 0.5-mm-long polarization- 
insensitive Opt0 Speed bulk amplifier show FWM efficiency virtually 
independent of the conversion range for fixed Af. The intensity of S 
was suppressed by the polarizer 5 dB below the intensity of C2 (see 
Fig. 2). With 2-mm-long amplifiers, the conversion efficiency is 
expected to increase by approximately 20 dB, the saturated gain by 
only 5 dB.' Suppression of S more than 15 dB below C2 is therefore 
attainable. Results on longer amplifiers will be presented at the con- 
ference. 
*Institute of Quantum Electronics, Swiss Federal Institute of Technology, 
8093 Zurich, Switzerland 
**Opt0 Speed SA, 6805 Mezzovico, Switzerland 
1. A. D'Ottavi, F. Girardin, L. Graziani, F. Martelli, P. Spano, A. 
Mecozzi, S. Scotti, R. Dall'Ara, J. Eckner, G. Guekos, IEEE J. Sel. 
Top. Quantum Electron. 3,522-528 (1997). 
A. D'Ottavi, E. Iannone, A. Mecozzi, S. Scotti, P. Spano, R. Dall'Ara, 
J. Eckner, G. Guekos, Appl. Phys. Lett. 65,2633-2635 (1994). 
J. Zhou and K. Vahala, in Conference on Lasers and Electro-optics, 
Vol. 15 of 1995 OSA Technical Digest Series, (Optical Society of 
America, Washington, D.C., 1995), p. 367. 
2. 
3. 
10:OOam WB7 
30-nm wavelength conversion at 10 Gbit/s by four- 
wave mixing in a semiconductor optical amplifier 
Guido Hunziker, Roberto Paiella, A. D'Ottavi,* P. Spano,* 
R. Dall'Ara,** G. Guekos,? Kerry J. Vahala, California 
Institute of Technology, Pasadena, California 91125 
Four-wave mixing (FWM) in semiconductor optical amplifiers 
(SOAs) is currently the only available strictly transparent wavelength- 
conversion technique, which is not penalized by phase matching.' The 
span of the conversion is limited primarily by conversion efficiency and 
signal-to-noise (SNR) issues,' both of which are expected to improve 
with the use of longer SOAs? In this paper, we demonstrate significantly 
enhanced performance of long converters in a system experiment at 10 
Gbit/s. The experiment shows for the first time, to our knowledge, that 
FWM wavelength down-conversions can span the full gain bandwidth of 
erbium-doped fiber amplifiers (EDFAs). 
The experiment is schematically shown in Fig. 1 and is similar to 
that described in Ref. 1. The SOA was a 1.5-mm-long bulk active layer 
structure, temperature controlled and biased at 670 mA. The maximum 
small signal fiber-to-fiber gain of the amplifier was 24 dB at 1565 nm 
(limited by amplified spontaneous emission (ASE) gain saturation), and 
the total optical power coupled into the device was + 15 dBm. To reduce 
the ASE noise from the high-power EDFA (located before the SOA) in 
the converted signal band, the input signal and the pump were also 
passed through a broad bandpass filter at the SOA input (15-nm band- 
width). The power ratio of the pump to the probe was about 10 dB 
(measured at the SOA output), a value which was found to minimize 
errors due to cross-gain modulation of the pump by the probe, while 
maintaining good conversion performance. 
The SOA output spectrum for three different up- and down-con- 
versions is shown in Fig. 2. For the down-conversion, the input signal was 
fxed at 1558 nm and the pump was tuned to achieve the desired shifts. 
Conversely, in the up-conversion, the pump was fixed at 1558 nm and 
the signal wavelength was tuned. This configuration was chosen to take 
full advantage of the spectral dependence of the SOA gain. The span of 
the 10 Gbit/s down-conversion was limited by the width of the 15 nm 
ASE prefilter, while for the up-conversion the limit was set by converted 
signal-to-ASE noise ratio. 
FWM Wavelenath Converter 
I EDFA EDFA 
Spectrum looh 
Analyser Preamplified Receiver 90% 
/J 
Detector ED; j I " 
WB7 Fig. 1. Schematic of the experimental setup. PC: polarization controller; 
EDFA erbium-doped fiber amplifier; BPF: bandpass filter (all 1-nm bandwidth, 
except the one just before the SOA); SOA semiconductor optical amplifier; B E R  
bit error rate. Dashed lines carry electrical (RF) signals. 
OFC '98 Technical Digest Wednesday Morning 0 109 
Wavelength in nm 
1550 1555 1560 1565 
Wavelength in nm 
WB7 Fig. 2. Spectra measured at the output of the SOA (0.1-nm resolution 
bandwidth). The upper shows the down-converted signals for the 30-, 20-, and 
10-nm shifts (fromleft to right). For the smallest shift, we also show the pump and 
the input signal. The pump wavelength was tuned to lower wavelengths at con- 
stant power to achieve the larger shifts. The lower figure shows the up-converted 
signals for the 5-, lo-, and 15-nm shifts (from right to left). In this case, we 
changed the input signal wavelength and the pump remained the same for all three 
shifts. The small peak near 1559.5 nm is a distributed feedback sidemode. 
m 
10 
-40 -38 -36 -34 -32 
Received Power (dBm) 
-36 -32 -28 -24 
Received Power (dBm) 
WB7 BER vs. received signal power for the shifts in Fig. 2. The received 
signal power was measured at the 10% tap after the attenuator with 0.2-nm 
resolution bandwidth. The eye diagram in the inset corresponds to the largest shift 
in each case, with no attenuation. 
Fig. 3. 
Figure 3 shows the bit error rates (BER) versus converted signal power 
measured at the output of the 10% bi-directional coupler in Fig. 1. There is 
almost no additional penalty when going from 10 to 30 nm shifts in the 
down-conversion, while for the up-conversion there is a 3 dB penalty going 
from 5 to 15 nm of up-shift. These record conversions are primarily attrib- 
uted to the long length of the SOA. Further improvements are expected 
going to even longer devices. The lower up-conversion performance stems 
from the well-known detuning asymmetry in the FWM nonlinearity,' as 
well as from the SOA and receiver EDFA gain spectrum. 
In conclusion, we have demonstrated a record 30 nm of wavelength 
down-shifts and 15 nm of up-shift for 10-Gbit/s optical signals. The 
improvements result from the use of long (1.5 mm) SOAs. Further 
improvements in performance are anticipated with yet longer devices. 
*Fondazione Ugo Bordoni, 00142 Roma, Italy 
**Opt0 Speed SA, 6805 Mezzovico, Switzerland 
tSwiss Federal Institute of Technology, 8093 Zurich, Switzerland 
1. 
2. 
D.F. Geraghty, R.B. Lee, K.J. Vahala, M. Verdiell, M. Ziari, A. 
Mathur, IEEE Photon. Technol. Lett. 9,452-454 (1997). 
F. Girardin, J. Eckner, G. Guekos, R. Dall'Ara, A. Mecozzi, A. 
D'Ottavi, F. Martelli, S. Scotti, P. Spano, IEEE Photon. Technol. 
Lett. 9,746-748 (1997). 
WE8 10:15am 
Wavelength conversion by four-wave mixing in a 
folded-path, self-pumped semiconductor optical 
amplifier 
Roberto Paiella, Guido Hunziker, Mehrdad Ziari,* 
Atul Mathur,* Kerry J. Vahala, Department of Applied Physics, 
Mail Stop 128-95, California Institute of Technology, 
Pasadena, California 91125 
Wavelength conversion is recognized as a key function for the imple- 
mentation of complex wavelength-division multiplexing (WDM) commu- 
nication systems. Of the approaches demonstrated so far, only four-wave 
mixing (FWM) in semiconductor optical amplifiers (SOAs) is M y  trans- 
parent to modulation format and bit rate while providing arbitrary wave- 
length mapping. Recent demonstrations',* have shown that the perfor- 
mance of FWM converters can be made technologically competitive. Here 
we present a novel wavelength conversion scheme that offers additional 
advantages while significantly reducing the complexity of the device. 
The converter consists of an external-cavity semiconductor laser, 
with a high-reflection coating on one facet, and a fiber Bragg grating 
pigtailed to the other facet (anti-reflection coated). The pump wave is 
Attenuator 
Fiber Bragg Grating 
coating coating 
Received Power Meter 
Preamplified 
Receiver and 
Error Rate Tester 
WB8 Fig. 1. Schematics of the experimental setup. 


30-nm wavelength conversion at 10 Gbit/s by four-wave mixing in a semiconductor optical amplifier

http://authors.library.caltech.edu/28564/1/HUNofc98.pdf

30-nm wavelength conversion at 10 Gbit/s by four-wave mixing in a semiconductor optical amplifier

Abstract

Similar works

Full text

Available Versions

Caltech Authors - Main