KEYWORDS: Modulation, Single sideband modulation, Radio over Fiber, Microwave radiation, Modulators, Signal detection, Eye, Single mode fibers, Phase shifts, Particle filters
To simultaneously modulate and transmit 10-Gb/s baseband and 20-GHz microwave signals on a single wavelength
using single-sideband (SSB) modulation technique, a novel ROF scheme is proposed and verified by simulation. Based
on a Dual-Parallel Mach-Zehnder Modulator (DPMZM) the scheme can carry the microwave signal on the upper
sideband(USB) and the baseband signal on the lower sideband(LSB). It is to be seen from the simulated results that the
crosstalk between the signals with dual services is very small. By means of subcarrier-multiplexing (SCM) technique, the
optical 20-GHz microwave wave carrier is generated to carry 155-Mb/s baseband signal and 10-Gb/s baseband signal is
imposed on the original optical carrier via SSB modulation. The simulated results of BER and the eye diagram are
achieved separately. The signals with dual services are successfully transmitted over 50-km single-mode fiber.
Simultaneous generation and transmission of 10-Gb/s baseband signal and 20-GHz microwave signal with 155-Mb/s
on-off-keying (OOK) data on a single wavelength over 50-km-long fiber link based on a dual-parallel Mach-Zehnder
modulator (DPMZM) are investigated. After simultaneous modulation of the baseband signal and microwave signal at
central office (CO), the hybrid signals are separated by interleaver(IL) or fiber Bragg grating (FBG) at base station (BS).
The center wavelength spacing and bandwidth of IL, also the reflection ratio, center wavelength and bandwidth of FBG
are to be considered carefully as the baseband and microwave signal are only tens of GHz spacing and hard to be
separated with each other. Through theoretical analyses and simulation, for the demonstrated hybrid transmission system,
the relations of Q factor with the reflection ratio and bandwidth of FBG are analyzed separately in different fiber links
(SMF and DSF).
A theoretical model for description of the cSFG/DFG is developed in this paper. The factors influence the poled period of
PPLN is studied and the result shows that the poled period decreases while the temperature increases, and the poled
period also changes while we choose different signal wavelengths. In our simulation, a pulsed light is injected into a
PPLN waveguide as the signal, and then the performances of the wavelength conversion structures with two continuous
waves and two pulsed lights are compared in detail by numerical simulation. The output of these two situations are
educed while depletion, walk-off and nonlinear effect are all considered. The walk-off effects of output and conversion
efficiency are studied in both cases. The results demonstrate that there is an obvious walk-off between input signal and
output in the pulse pumped case, and in the CW case the converted wave width is boarder than that of input signal due to
pulse dispersion. Factors that influence the conversion efficiency are also analyzed including the power of the pump light,
the length of the PPLN waveguide and the experiment structure.
Some experiments of optical performance monitoring (OPM) with uniform or nonuniform
quasi-phase matching (QPM) gratings waveguides have already been demonstrated during the last few
years. Theoretical analyses based on coupled-wave equations are carried out for nonuniform QPM
gratings. The generation process of SHG in nonuniform QPM gratings is simulated and the outcome
comparison between uniform and nonuniform QPM gratings, which demonstrate that nonuniform QPM
gratings are more suitable for the OPM systems, is carried out in this paper. The value of grating chirp
coefficient of the chirped PPLN has influence on the efficiency and band width of the output pulse. The
relation between them is also discussed. These are new simulative attemptation to apply the
nonuniform quasi-phase matching gratings into optical performance monitoring system.
We have simulated the OSNR sensitivity, filtering tolerance, chromatic dispersion tolerance, and nonlinear tolerance
of optical DPSK and DQPSK formats with and without RZ carving in 40Gbit/s transmission systems. The results show
that RZ-DPSK has the highest OSNR sensitivity, and is most robust against fiber nonlinearity in dispersion compensated
systems with moderate channel spacing. The DQPSK systems have the highest filtering tolerance and dispersion
tolerance, and is least affected by the reduction of the channel spacing. The simulations of long haul dispersion
compensated systems show that RZ-DPSK has better performance in single channel system and WDM system with
100GHz channel spacing, while RZ-DQPSK has better performance in WDM system with 50GHz channel spacing.
The MMI optical power splitters which are based on the self-imaging effect (SIE) have been
analyzed in the paper, and 1×4 MMI power splitter is designed. The designed device is simulated and
optimized by Beamprop software, the simulation results are basically agreement with the designed
effect, the excess loss induced by multimode interference is less than 0.04dB, uniformity is about
0.01dB.The low loss and fine uniformity MMI power splitter has been made by Lithium Niobate
annealed proton exchange technology, and the experiment sample measurement results are achieved.
In this paper, a nonlinear optical loop mirror (NOLM) based on photonic crystal fiber (PCF) is used for optical pulse
compression. The transmission of optical pulses in the fiber loop can be described by the nonlinear Schrodinger
equations. The crossing phase modulation (XPM) effect in NOLM is used for pulse compression. The theory of XPM
effect in NOLM is analyzed and the process of pulse compression is simulated. Comparing three different shapes input
pulses, it can be found that the Hyperbolic-Secant Pulses have the better compression quality than the other two shapes
pulses. Due to the characteristics of PCF, especially high nonlinear properties, the high quality compressed pulses can be
got. Compare with the self phase modulation (SPM) effect for optical pulse compression, it is shown that the input pulse
with low power can be compressed and the compression of the input pulse can be controlled by the control pulse. By
choosing the proper parameters of the NOLM, to some extent, the pedestal of the compressed pulse can be suppressed.
Based on the analysis of the result, proper parameters and the crystal fiber of the NOLM will be selected.
All-optical wavelength conversion of 10Gbit/s optical pulse was realized by using nonlinear
optical loop mirror composed by a dispersion-shifted fiber, the conversion wavelength range from
1520nm to 1558nm, the max wavelength span reach 38nm. Based on the Cross-Phase Modulation
(XPM) in the NOLM, the control optical peak power and the polarization of two light were
changed to achieve a large conversion wavelength range. And the converted optical spectrum was
measured and the experiment results were discussed.
By means of the coupling mode theory and the method of the extension of coupling coefficient, the corresponding coupling model is corrected for PBS. Considering the angle of the two Y-branch waveguides in PBS, the coupling length of 1430 is figured out, which is different from that of 2186μm without considering of the coupling in the Y branches in the previous design. And the simulation of the device performances are carried out by beam propagation method (BPM), the extinction ratio of the TE and TM mode is -26dB and -23dB, respectively.
Acousto-optic tunable filter (AOTF) is one of important optical switch components in optical networks. The possibility of tellurium dioxide acousto-optic tunable filter (TeO2 AOTF) as an optical add/drop multiplexer (OADM) is studied on the basis of the theory of the anomalous acousto-optic Bragg diffraction and the design principle of non-collinear AOTF. Its main performances and structure are analyzed and discussed, and the significance of incident angles and interaction lengths for its performances is presented. The model for optimization design is built under some limitation and the transducer areas is adopted as a regulator for performance, the designed example of the TeO2 AOTF for WDM systems is given by the optimized method.
In the paper, a weighted-coupling scheme of a SiO2 film-loaded Ti:LiNbO3 quasi-collinear integrated acousto-optic mode converter is reported, in which an angular offset between the acoustic and optical waveguides is introduced to implement an optimized Hamming weighted function for realization of ultralow sidelobe level. Acoustic wave guiding properties have been investigated for films such as SiO2, ZnO on LiNbO3 firstly. SiO2 film on LiNbO3 was selected as acoustic waveguide. With the mode analysis of the acoustic wave guide and the theory of coupling mode the limit of the width, weighted coupling coefficient and the characteristics of the conversion of acousto-optic modes are obtained. As the angle between acoustical and optical waveguides is 0.45°, the worst sidelobe level is -16dB and the theoretical values of bandwidths of -3dB and -10dB is 1.37nm and 2.31nm respectively, which have excelled the domestic reported level.
Optical add/drop multiplexers(OADMs) are finding their applications in future all-optical communication networks to link the network with local transmitters and receivers. A novel fully dynamic and reconfigurable OADM based on AOTF with low crosstalk is presented. The PMD compensation issue of AOTF is addressed as well.
The Integrated acousto-optic tunable filter have the potential to perform the OADM or OXC functions, which play significant role in WDM optical network. The characteristic of the acousto-optic mode conversion is sinc2-like functions with high sidelobe intrinsic. The high sidelobe level lead to serious crosstalk in the WDM optical network. The theory of weighted coupling for IAOTF has been presented. And the filter response using four suggested weighted
functions has been calculated with the matrix methods. Significant suppression of sidelobe level has been achieved by employing the techniques of weighted coupling. It is a valid approach to reduce the sidelobe of IAOTF by choosing propriety weighted function and a realized way.
In the coming new general optical network, tunable filter is one of important optical devices, and can be used to compose dynamically optical add/drop multiplexer (OADM). Polarization independent integrated acousto-optic tunable filter (IAOTF) is one of devices which have most potential to perform the function[1][2]. Mode splitting and merging are realized by using two symmetrically directional couplers in the IAOTF. Mode polarization is converted by the acousto-optic mode converter when the condition of phase matching is met at the specifically light wavelength. The light wavelength passing the filter can be easily adjusted by changing the frequency of acoustic wave. The Ti diffused technology is adopted to fabricate the device on the X-cut Y propagation LiNbO3 slice. The relation of index difference in the X-cut Y propagation LiNbO3 waveguide with different diffusion conditions is computed in this paper. And the theory of coupling mode is utilized to analyze and design the directional coupler, in which TE/TM mode splitting can be realized. The designed structure is simulated by using BPM software. The extinction ratio of TE/TM mode can be reached 25. 1 dB and 24.9 dB respectively.
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