February 10, 2011 / Vol. 9, No. 2 / CHINESE OPTICS LETTERS 020606-1
Design and analysis of flexible colorless remote node using
RSOA- assisted Michelson interferometer
Lei Liu (
444
[[[
)
∗
, Min Zhang (
ÜÜÜ
¬¬¬
), Mingtao Liu (
444
²²²
777
), Xiaopin Zhang (
ÜÜÜ
ªªª
),
and Peida Ye (
)
Key Laboratory of Information Photonics and Optical Communications, Ministry of Education,
Beijing University of Posts and Telecommunications, Beijing 100876, China
∗
Corresponding author: liulei098332@gmail.com
Received June 12, 2010; accepted November 6, 2010; posted online January 28, 2011
A scheme of flexible colorless remote note with reflective semiconductor optical amplifier (RSOA) assisted
Michelson interferometer is proposed. This is capable of generating an optical carrier su ppressed signal at
a specific radio frequency to suppress the penalty brought about by Rayleigh backscattering and reflection
in a full-duplex single fiber transmission network. Simulations are conducted, and the validation of the
proposal is discussed by observing the penalty eye opening factor. The results are useful for designing
cost-effective multi-wavelength passive optical network (PON ) or radio-over-fiber (RoF) systems.
OCIS codes: 060.4510, 060.2360.
doi: 10.3788/COL201109.020606.
Deploying colorless re mote nodes (RNs) in multi-
wavelength passive optical network (PON) has been
considered as an effective solution to the problems of
cost and complexity reduction
[1−3]
. In this environ-
ment, many schemes have been prop osed to develop low-
cost, colorless RNs us ing tunable lasers , spectrum sliced
light sources
[4]
, injection locked lasers, such as Fabry-
Perot laser diodes (FP-LDs)
[5]
, or remodulatio n de-
vices, such as reflective semiconductor o ptica l amplifiers
(RSOAs), and reflective electronic absorption modula-
tors (REAMs)
[6]
. With good amplification and modula-
tion characteristics, the RSOA has beco me a promising
candidate as a remote modulator in colorless RNs. With
the help of extra electrical equalization a nd for ward er-
ror correction (FEC)
[7−10]
, the modulation bandwidth of
RSOA can be enlarged to 10 GHz, indicating a promis-
ing pro spec t for large-scale application. However, the
reported RSOA-assisted RNs are vulnerable to crosstalk
brought about by the Rayleigh backscattering (RB) and
reflections in case of full-duplex communication over a
single fiber sharing a single wavelength
[11−13]
. Some
schemes have been prop osed, such as frequency-shift key-
ing (FSK) mo dulation
[14]
or optical carrier suppressed
(OCS) modulation
[14−16]
with Mach-Zehnder modulato r
(MZM) in the transmission link, in order to create a fre-
quency shift between the upstrea m and downstream sig-
nals suppressing the crosstalk.
In this letter, a flexible and cost-effective RN with
RSOA-assisted Michelson interferometer (RSOA-MI) is
presented to generate an OCS signal at radio frequency
(RF) loc ated in the upstream that can suppress the
crosstalk introduced by RB and reflection by producing
a frequency shift between the upstream and downstream.
A schematic diagram of the proposed colorles s RN us-
ing RSOA-MI is given in Fig. 1, where two RSOAs are
located at the ends of the two arms in MI, with one of
the arm embedded an optical phase shifter. A group
of electronic components, such as local oscillator, mix-
ers, and phase shifters, were applied to generate the up-
stream RF sig nals. In the downstream direction, the
baseband optical signal was split equally into two parts;
these e ntered the upper and lower arms of RSOA-MI,
respectively. These two parts of the signal serving as
the seeding light in the RSOAs were remodulated by the
upstream electronic RF s ignals and then reflected after-
wards. When the reflected sig nals re-coupled together,
a phase shift was added at the lower ar m using an opti-
cal delay line. By adjusting the electrical phase shifter
and optical delay line, destructive or constructive inter-
ference may occur a t the coupler with an appropria te
phase difference between the two parts of the signals,
after which the optical single-sideband (OSSB) or OCS
signal emerges at the fiber end from the RSOA-MI. In the
OSSB case, the spectrum overlap between the upstream
and downstream exists; thus, the penalty intro duced by
the RB and reflection is still residual. As the simulation
results show, about 5-dB-high power is needed to obtain
the same performance as in the case of the OCS.
Given that the modulation in RSOA is the result of
the interactive process of the photon carrier, the carrier
density in the device can be descr ibed as
[17−19]
dN(z, t)
dt
=
J
input
q
−
N(z, t)
τ
s
− v
g
gS, (1)
where the carrier density N is a function of time t and
position z along the active layer. T he first term on the
right is the carrier injection rate, where J
input
is the in-
jection current density indicating the mo dulation sig nal,
and q equals the electron charge. The second term is
due to spontaneous recombination characterized by the
sp ontaneous carrier lifetime τ
s
. The third term repre-
sents the stimulated recombination le ading to optical
amplification, v
g
is the group velocity of the optical s ig-
nal, g is the gain coefficient, and S is the photon density
in the RSOA.
In Eq. (1), the spontaneous carrier lifetime and the
1671-7694/2011/020606(4)
c
2011 Chinese O ptics Letters