
All-optical repetition rate multiplication of pseudorandom bit
sequences based on cascaded TOADs
Zhenchao Sun
n
, Zhi Wang, Chongqing Wu, Fu Wang, Qiang Li
Key Laboratory of Education Ministry on Luminescence and Optical Information Technology, Institute of Optical Information, Beijing Jiaotong University,
Beijing 100044, China
article info
Article history:
Received 31 August 2015
Received in revised form
24 October 2015
Accepted 26 October 2015
Keywords:
Pseudorandom bit sequences (PRBS)
Tera-Hertz Optical Asymmetric Demulti-
plexer (TOAD)
All-optical logic gate
All-optical wavelength conversion
All-optical repetition rate multiplication
abstract
A scheme for all-optical repetition rate multiplication of pseudorandom bit sequences (PRBS) is de-
monstrated with all-optical wavelength conversion and optical logic gate ‘OR’ based on cascaded Tera-
Hertz Optical Asymmetric Demultiplexers (TOADs). Its feasibility is verified by multiplication experi-
ments from 500 Mb/s to 4 Gb/s for 2
3
1 PRBS and from 1 Gb/s to 4 Gb/s for 2
7
1 PRBS. This scheme can
be employed for rate multiplication for much longer cycle PRBS at much higher bit rate over 40 Gb/s
when the time-delay, the loss and the dispersion of the optical delay line are all precisely managed. The
upper limit of bit rate will be restricted by the recovery time of semiconductor optical amplifier (SOA)
finally.
& 2015 Elsevier B.V. All rights reserved.
1. Introduction
The pseudorandom bit sequences (PRBS) is widely applied to
optical transmission systems and optical communication net-
works, such as for the purpose of error rate measurements, en-
coding/decoding (scrambler, perturbation solution), encryption/
decryption (secure communications), simulations of white noises,
spread spectrum modulation (CDMA: code division multiple ac-
cess), and so on. As the traffic of the communication networks
grows explosively with the rapid development of optical fiber
telecommunications [1], the higher bit rate PRBS for system per-
formance monitoring is required. High-speed PRBS generator is
very complicated with high cost in electric domain for the bit rate
over 40 Gb/s. Though several methods of all-optical PRBS genera-
tion have been shown recently [2–4], there were also a number of
problems with these solutions. For instance, Wagemans has pro-
posed a scheme of PRBS generator based on double-loop flip-flop
with a complex structure and a low rate at 10 kb/s [5]. Zoiros has
proposed a PRBS generator by the TOAD-based D flip-flops [6], and
Ma also has proposed a PRBS generation based on quantum-dot
semiconductor optical amplifiers [7]. However, they were just
realized by theoretical simulation without any experimental result
and their structures are complex [5,6]. In this context, there is
another method to obtain a high rate of PRBS, which is the ultra-
speed all Optical repetition rate multiplication of PRBS.
According to the nature of the M-sequence extraction, every
proper decimation of an M-sequence is itself an M-sequence [8],
therefore the M-sequence PRBS can obtain 2
n
times repetition rate
multiplication with a T/2
n
delay feedback. Previously, Koulou-
mentas has used the NOLM rings to realize the repetition rate
multiplication of PRBS [9], However using NOLM rings entails a too
large energy consumption. The power of control light is very high
(the power of feedback control light is up to 620 mW in the ex-
periment) for the small nonlinear coefficient of optical fiber; sec-
ondly, it is unfavorable to integrate in the future. The length of
nonlinear fiber is too long (the length of nonlinear fiber is 180 m
and 260 m). Therefore, we demonstrate a scheme for all-optical
repetition rate multiplication of PRBS with all optical wavelength
conversion and optical logic gate ‘OR’ based on cascaded Tera-
Hertz Optical Asymmetric Demultiplexers (TOADs) [10].TOAD
reaps huge fruits, such as fast response speed, low energy con-
sumption and ease of integration. This paper introduces the
principle of the system, the key technologies and its feasibility is
verified by experiments, which will be shown by two multi-
plications for PRBS at different cycles 2
3
1 and 2
7
1 from
500 Mb/s to 4 Gb/s and from 1 Gb/s to 4 Gb/s respectively. This
scheme can be employed for rate multiplication for much longer
cycle PRBS at much higher bit rate over 40 Gb/s. The upper limit of
bit rate will be restricted by the recovery time of semiconductor
optical amplifier (SOA) finally.
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/optcom
Optics Communications
http://dx.doi.org/10.1016/j.optcom.2015.10.055
0030-4018/& 2015 Elsevier B.V. All rights reserved.
n
Corresponding author.
E-mail address: 11118409@bjtu.edu.cn (Z. Sun).
Optics Communications 363 (2016) 1–6