S214 CHINESE OPTICS LETTERS / Vol. 5, Supplement / May 31, 2007
All-optical fiber switching based on cross-phase modulation
in high-nonlinear photonic crystal fiber Sagnac loop mirror
Jianguo Liu (
)
1,2
, Lifang Xue (
DZDZDZ
)
2
, Guiyun Kai (
)
2
, and Xiaoyi Dong (
þþþ
þþþ
)
2
1
Atmospheric Optics Key Laboratory of National 863 Project, Anhui Institute of Optics and Fine Mechanics,
Chinese Academy of Sciences, Hefei 230031
2
Institute of Modern Optics, Nankai University, Tianjin 300071
We designed a novel and low switching-power all-optical fiber switch. The highly nonlinear photonic crystal
fiber (PCF) and the bidirectionally pumped Er
3+
doped fiber amplifier are inserted into the Sagnac loop
mirror simultaneously. Therefore, the symmetry of the loop is broken, and the switching function is realized
for the phase shift of the reversely propagating signal. The theoretical analysis shows that the switching
power is inversely proportional to the product of the amplifier gain and the PCF nonlinear coefficient. In
the experiment, 40 mW switching power and 15.9 dB switching extinction are obtained, furthermore, the
transmission of signal light is cosine proportional to the peak power of the pump pulse. The experimental
result agrees well with that from theory.
OCIS co des: 060.1810, 060.5060, 060.4370.
All-optical fiber switching has excited the interests of
most researchers in past years
[1−17]
, because it is the key
passive device to solve “electronic bottle-neck” and to re-
alize all-optical network. For example, the standard con-
ventional fibers or some high-nonlinear special fibers
[1,10]
(such as Yb
3+
-doped fiber
[1]
) are used in some fiber
functional device, such as Bragg grating
[1−4]
,longperiod
grating
[5−8]
, laser resonant cavity
[9]
,interferometer
[11,12]
,
coupler
[13]
and so forth, when the laser propagates in
above fiber functional device, the all-optical switch-
ing can be realized based on the nonlinear effect, such
as self-phase modulation (SPM), cross-phase modula-
tion (XPM), optical-brooming effect, four-wave mixing
(FWM) and so on. Most research demonstrated that
high switching threshold, low switching extinction and
low switching speed are three primary obstacles to block
the development and applications of all-optical switch-
ing.
The appearance of photonic crystal fiber (PCF)
provides possibility to solve these three obstacles
for its flexibly designed structure and its particular
properties
[14−18]
. Most researchers realized optical
switching by using PCF, e.g. the operation of a 2R
regenerative optical switching based on dispersion shift
in high-nonlinear PCF was reported by Petropoulos et
al.
[19]
in 2001; an all-optical switching based on cross-
phase modulation in microstructure fiber has also be
reported by Sharping et al
[12]
in 2002; an optical switch-
ing could be realized based on the PCF infiltrated with
liquid crystals in 2003
[20]
. Recently, Zheltikova pro-
posed an all-optical fiber switch based on Kerr effect of
bandgap PCF
[21]
and Salgueiro designed an all-optical
fiber switching by using dual-core PCF coupler
[13]
.
In this paper, all-optical fiber switch based on XPM by
inserting the high-nonlinear PCF (HN-PCF) and bidi-
rectionally pumped Er-doped fiber amplifier (BP-EDFA)
into the Sagnac loop mirror were proposed and demon-
strated simutaneously. The theoretical analysis shows
that the switching power is inversely proportional to
the product of BP-EDFA gain and HN-PCF nonlinear
coefficient. Therefore, in order to decrease the switching-
power we can improve the gain of BP-EDFA and the non-
linear coefficient of the HN-PCF. We got almost 40-mW
switching power and almost 15.9-dB switching extinction
in the experiment, furthermore, the transmission of the
signal light is cosine proportional to the peak power of
the pump pulse. All the results of experiment are in
good agreement with those by theory.
The experimental setup is shown in Fig. 1, the fiber
Bragg gratings (FBG1 and FBG2) are two identical
Bragg gratings fabricated in photosensitive fiber using
phase-mask-writing technique by ourselves, whose cen-
tral wavelength and reflection are 1547.5 nm and 100%,
respectively. C1 and C2 are 1 ×2and2×2 3-dB coupler,
respectively. CI1, CI2 are two circulators. Broadband
source (BBS) is in C band and the pump source’s central
wavelength is 1552.5 nm and its power is tunable, respec-
tively. The length of single-mode fiber (SMF) is 20 m
and HN-PCF is 20 m, the mode area and zero-dispersion
wavelength are 2.5 μm
2
and almost 1550 nm, respec-
tively. BP-EDFA is Er-doped fiber amplifier pumped
by two 980-nm laser diode in bidirectional, whose bi-
directional gains are almost identical and are 20 dB.
The light launched by BBS is filtered by FBG1 to
generate continuous signal whose central wavelength is
1547.5 nm, and the 1552.5 nm pump pulse is launched
by pump. The two beams are coupled into one SMF by
C1 and incident into C2, the spectra of incident signal
light and pump pulse are shown in Fig. 2. The incident
light is divided into two parts by C2, one part propa-
gates clockwise, and the other propagates anticlockwise.
Because the signal light and the pump pulse are located
at two sides of zero-dispersion wavelength symmetrically,
Fig. 1. Schematic diagram of experimental setup.
1671-7694/2007/S1S214-04
c
2007 Chinese Optics Letters