IEEE LEOS Annual M eeting (LEOS 2003), Invited Talk
Tucson, Arizona, October 26-30, 2003, vol. 1, pp. 380-381.

All-Optical Signal Processing for over-100-Gb/s Optical-TDM Networks
Yoshiyasu Ueno
Department of Electronic Engineering, University of Electro-Communications
1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan, email: y.ueno@ieee.org
Abstract: Recent semiconductor-based ultrafast signal processing results are reviewed. After
results regarding demultiplexing, 3R gating, and related topics are introduced, several scaling
rules that could govern the SOAs in such gating modes are given.
1. Current OTDM Component Technology
The large and ultrafast optical nonlinearity of millimeter-size semiconductor optical amplifiers (SOAs) has
led to the study of several types of gate functions at ultrahigh bit-rates beyond 40 Gb/s. Among these functions,
optical demultiplexing has been the most successfully demonstrated with 336 Gb/s RZ signals [1]. The
slow-recovery-induced phenomena that accompany the ultrafast nonlinear response inside each SOA do notslow down the gating speed, because their effects on the optical signals are dramatically removed by an opticalinterferometer incorporated in each ultrafast gate structure (e.g., SMZ, TOAD, PD-SMZ, UNI, or DISC).
Despite the use of optical interference, their stability will not be a problem in the building of network
systems. Integrated gates have shown excellent stability. Even when ultrafast gating with large extinction ratios
is required in long ter ms, the optical interference will precisely be stabilized with low-cost slow
optoelectronics inside each gate module (Fig. 1) [2].
One gate function that has attracted considerable attention from both OTDM and 40-Gb/s researchers isoptical 3R gating. Its noise-tolerant, jitter-tolerant regenerative properties have been observed experimentallywith 40- to 80-Gb/s signals by several research teams (Fig. 2) [3-6]. 3R regenerative gating with 160-Gb/ssignals is currently a particularly attractive research goal.
All-optical wavelength conversion for cross-connecting OTDM signals has also been demonstrated with
one of the above gate structures. To date, error-free wavelength conversion of 168-Gb/s signals has beenreported [7]. Importantly, all-optical gates in the wavelength-conversion mode, as well as those in the3R-gating mode, are driven with ultrafast-line-rate RZ signals, in good contrast to those gates in thedemultiplexing mode. The experimental demonstration of 168-Gb/s conversion, consequently, is considered amilestone along the way to 160-Gb/s 3R gating.
2. Possible Scaling Rules for nonlinear SOAs in the Ultrahigh-Frequency Gating Mode
The modeling and designs of SOAs for amplification purposes have been well established in the pastdecade. In contrast, those for ultrafast gating remain on-going subjects. Several types of straightforward
scaling rules that could govern such SOAs were proposed only recently, where the gating mechanism wasmodeled as simply as possible for deriving such rules. The simplest gating mode, i.e., the ‘periodical’ gating
mode as is used in demultiplexing, was assumed there as well. Systematically measured data in the frequency
range from 40 through 160 GHz have been reasonably representative of two of these scaling rules; the driving
force for the gating, i.e., the magnitude of the nonlinear response in an SOA, follows the rule,∆Φ ∝ f −1 × I op ,(1)

where f is the gating frequency and Iop is the injection current to the SOA (Fig. 3) [8].
3. Scaling Rules for 160-Gb/s optical-3R Gating
Because all-optical gates in the 3R-gating mode are driven by line-rate random signals, the slow recovery
time constant of SOAs inside these gates must be of the order of the bit separation (6 ps for 160-Gb/s gating).
Two alternative research directions for accelerating the SOA recovery have attracted attention. Recent resultsfrom sub-band-transition nanostructures suggest that less-than-one-picosecond-recovery SOAs will appear in
the future [9, 10]. For conventional SOAs, a remarkable acceleration of the recovery time has been reported,
where the SOA is pumped with a specifically designed light [11, 12]. We should emphasize, however, that thetolerance of optical 3R gating to input timing jitter will be lost if the SOA recovery is accelerated to that of thefiber nonlinearity. Thus, the SOA recovery time is clearly an important gate-design subject.
For the optical 3R gating mode, no scaling rule has been established. The experimentally observed 3R
properties (noise suppression and jitter tolerance) have been numerically demonstrated only very recently using
the latest 3R gating model (Fig. 4) [13]. A possible frequency-scaling rule derived from the latest model will bepresented at the talk. Scaling rules that can be derived from such modeling will be helpful for drawing
roadmaps for various types of on-going research ai med at 160-Gb/s signaling in the near future, and towards
higher bit-rates beyond that.
References: [1] S. Nakamura et al., OFC 2002, Anaheim, Postdeadline paper FD3, [2] Y. Ueno et al., IEEE Photon. Technol.
Lett. 14 (2002) 1692, [3] A. E. Kelly et al., Electron. Lett. 35 (1999) 1477, [4] Y. Ueno et al., ECOC 2001, Amsterdam, theNetherlands, Th.F.2.1, [5] B. Dagens et al., OFC 2003, Atlanta, ThX1, [6] M. Tsurusawa et al., OFC 2003, Atlanta, ThX3, [7] S.
Nakamura et al., IEEE Photon. Technol. Lett. 13 (2001) 1091, [8] Y. Ueno et al., J. Opt. Soc. Am. B19 (2002) 2573, [9] T.
Akiyama et al., Electron. Lett. 37 (2001) 129, [10] I. Waki et al., FST 2003, Makuhari, Japan, WB-2, [11] M. Tsurusawa et al.,Jpn. J. Appl. Phys. 41 (2002) 1199, [12] T.P. Hessler et al., Appl. Phys. Lett. 81 (2002) 3119, [13] Y. Ueno, submitted to Opt.
Comm.

Input Random Data
“non-uniform”-30-30-20+0+ 20

1579.5+40Time (ps)1580.01580.520 0 00

Cou nts

Regenerated

2 00 0 0

1 00 0 0

10 0 00-60-40

STREAK 0 01 11 0.SMP, No v 1 3 2 00 0
D4 1.DA N, Nov 10 20 00

30 0 00

Input-50-20

STR EAK 00 11 10 .SMP, N ov 1 3 2 00 0
D3 8 .D AN, No v 1 0 20 00

3 00 0 0

Opt. Spectrum

-40

-10

Output random data
“uniform”

Cou nts+0

Intensity (dBm)

Relative intensity (dB)

Demultiplexed01581.000

Wavelen gth (n m)

10 0

2 000Time (ps)

10 0

20 0

T ime (ps)Fig. 1: Interference control scheme
Fig. 2: Optical 3R gating with 84-Gb/s
demonstrated in the 16:1 168-Gb/s demultiplexing [2]. pseudorandom signals, observed with streak camera [4].

168 GHz0.50.50

168 GHz

0.1

1.010.0100.0

Input pulse energy (fJ)

+1.0+0.5∆Φ rec overs+0.0

0.100.100.4

Input

Intensity (a. u.)

0.50

84 GHzIntensity (a. u.)

84 GHzINPUT EYE A.SMP , Mar 27 2003
B IAS.TXT ,M ar 28 2003

+1.5

1.00

Phase shift, ∆Φ/πPhase shift, ∆Φ/π42 GHz

42 GHz1.00

1050

100500Injection current (mA)

Fig. 3: Observed scaling rules in the SOA's nonlinear
response in the frequency range from 42 to 168 GHz [8].

Regenerated

0.3
0.2
0.10.0-5.0+0.0

Time (ps)

+5.0

-5.0

+0.0

+5.0

Time (ps)Fig. 4: Calculated noise-suppression property
from the latest 3R gating model [13].