KEYWORDS: Signal to noise ratio, Picosecond phenomena, Polarization, Transmitters, Receivers, Signal processing, Signal detection, Optical engineering, Modulation
The impact of polarization mode dispersion (PMD) on the performance of coherent transmission systems employing different digital nonlinearity compensation (NLC) schemes is numerically investigated for a seven-channel PM-16QAM Nyquist-wavelength division multiplexing system at 256 Gbit / s. In these nonlinearity compensation schemes, the digital signal processing is divided between the transmitter (Tx) and receiver (Rx) with different splitting ratios. We demonstrate that by splitting the NLC equally between the Tx and Rx, one can always obtain the best performance improvement regardless of whether PMD is present or not. Results of 1000-km dispersion-unmanaged transmission show that when fiber PMD is equal to 0.05 ps / km, splitting the NLC can give a signal-to-noise ratio improvement of 1.1-dB over receiver-side NLC, while it is 0.9 dB for 0.1 ps / km of the fiber PMD coefficient.
Aiming at the problem of the low sensitivity of conventional optical fiber-based gas refractive index sensors, an ultrasensitive tapered optical fiber coupler-based gas refractive index sensor enhanced by the Vernier effect is proposed and demonstrated. The birefringence property of the tapered optical fiber coupler allows it to support two passes of interferences in two orthogonal polarized states, and the superposition of these two interferences forms the Vernier effect. Theoretical analysis and numerical calculations indicate that, for the fiber couplers working in the gas medium when the waist width is within the range of 1.2 to 2.0 μm, the group birefringence difference between the even mode and odd mode equals zero. Thus the sensitivity toward the ambient gas refractive index can be enhanced significantly. To demonstrate these theoretical results, a tapered fiber coupler with a width of 1.6 μm and a length of 16.5 mm was fabricated, and ultrahigh sensitivities up to 22015.4 and −22690.0 nm / RIU were experimentally achieved. The proposed sensor has the merits of being easy to fabricate, having compact structure, and being cost effective. It has significant application prospects in the petrochemical and biomedical detection fields.
An all-optical frequency-upconversion based on fractional talbot effect is experimentally reported. The 2.5-Gb/s
baseband signal carried on 10GHz pulse trains is upconverted to 40GHz millimeter wave after 18.49km transmission via
repetition frequency multiplication of pulse trains. The phase noise of the 40GHz is as well as -92dBc/Hz at 10kHz
frequency detuning. This scheme can operate in 60GHz band by employing the appropriate fiber length based on
fractional talbot effect.
A novel scheme to realize all-optical logic gates is proposed bases on nonlinear polarization rotation (NPR) in high
nonlinear fiber (HNLF). Two optical signals A and B with return-to-zero data format are injected into the HNLF together
with a continuous wave C. Thanks to the optical power variation in HNLF, nonlinear birefringence will be induced
between the two polarization axes. Thus it results in the nonlinear polarization rotation of the lightwave in the HNLF.
Both the optical signal and continuous wave are filtered out at the output of HNLF using optical band-pass filter. By
adjusting the optical power and polarization of the optical signal as well as the polarization of the polarizer with respect
to the polarization of optical signal/continuous wave, multiple all-optical logic gates can be realized. Theoretical analysis
of the simultaneously realization of the multiple optical logic gates based on NPR in HNLF is provided. And we
demonstrated the feasibility of the scheme by realizing all optical
"and", "not", "nxor", "A•B", "A•B ", half-adder and
half-subtracter at 10Gb/s operation.
A high frequency optoelectronic oscillator (OEO) using only low frequency optical and microwave devices is attractive
as it provides a low cost and high quality solution at the same time. In this paper, a novel OEO scheme is reported. The
proposed optoelectronic oscillator includes a 5GHz directly modulated DFB laser, an optical circulator, a 10GHz
photodetector, a 10GHz RF amplifier, and a bandpass RF filter with a central frequency at 5GHz. The OEO oscillates at
the 5GHz and with a continuous wave injected into the directly modulated DFB laser, higher harmonics will be
generated. The harmonic order can be controlled by the frequency difference between the free running DFB laser and
injection lightwave. An optical domain combined dual-loop configuration with polarization-beam splitter and a
polarization-beam combiner is employed to suppress the sidemodes in each single loop. Experiment results are proposed
to verify the scheme, in which 40GHz microwave is obtained.
40 Gb/s optical demultiplexing with amplitude regeneration is demonstrated based on data pump fiber-optical parametric
amplification(FOPA) while a 10 GHz short pulse is used as the probe. Four 10 Gb/s output channels with at least 14 dB
extinction ratio enhancement and an average 5.5 Q factor is obtained after demultiplexing.
40-Gb/s 2-Channel all-optical 3R regeneration has been realised by a fiber optical parametric amplication(FOPA). Using
degraded data signals rather than clock as the pump, all-optical 40Gb/s 2-Chanel 3R regeneration is realized with
improved performance of eliminating the unequal suppression of noise between bit0 and bit1, which is different in
mechanism from previous regeneration schemes. Theoretical analysis of the noise suppression mechanisms under
different pump power (corresponding to "0" code or "1" code) is provided. By properly adjusting the parameters of
FOPA, amplitude noise on both "0" code and "1" code can be suppressed simultaneously. The clock extraction is based
on wavelenth conversion and a Fabry-Perot (F-P) filter with a high Q value of 1000. The theoretical analysis conclusions
are verified through experiments, and the imbalance of the 3R regeneration using fiber optical parametric amplication is
eliminated. The root mean square (RMS) jitter of the clock extracted is only 180fs. Signal to noise ratio is improved
respectively from 2.7,2.4 to 4.9,5.2.
Radio-frequency (RF) oscillators are key components in many radio and also radio-over-fiber (RoF) systems. Here, we
propose a novel technique to extent the tunable range of the radio frequency generated by optoelectronic oscillators. The
proposed optoelectronic oscillator includes an intensity modulator, a photodetector, an optical circulator, a Febry-Perot
laser diode, and a broad band RF amplifier. All those devices compose a single feedback loop. The key device in the
system is the Febry-Perot laser. By utilizing injection locking of Febry-Perot laser diode rather than the commonly used
radio-frequency band-pass filter, a high Q microwave filter is formed in optical domain. Theoretical analysis of the
optoelectronic oscillator as well as the tunablity of microwave filter is provided. The central frequency of the microwave
filter is a function of the optical wavelength and effective injection power, i.e. the injection power at the transverse-electric
(TE) mode of the F-P laser. Thus, the central frequency of the high Q band-pass can be simply tuned by tuning
the wavelength and the injection power of the injection light. Experiment is done to verify the theoretical analysis, and a
tunable range from 11.074 GHz to 39.400GHz is demonstrated experimentally.
Proc. SPIE. 7988, Optical Transmission Systems, Switching, and Subsystems VIII
KEYWORDS: Optical amplifiers, Oscillators, Extremely high frequency, Modulation, Polarization, Interferometers, Radio over Fiber, Single mode fibers, Polarizers, Microwave radiation
We propose a novel technique to achieve optical frequency up-conversion in millimeter wave band without any local
microwave oscillator. It is hard to directly get mm band carrier frequency because the efficiency of the mode-locking
decreases as the carrier frequency increases. Thanks to the dynamic charge carrier density response during the injection
locking of Febry-Perot Laser diode (FP-LD), the wavelength of the leading part of carrier will be red-shifted while that
of falling part will be blue-shifted. With a suitable negative dispersion device, the carrier will be pulse compressed and
the 2nd harmonic of the carrier will be greatly enhanced. Thus it makes the RoF frequency up-conversion in mm band
feasible. By utilizing injection locking of Febry-Perot Laser diode, a suitable negative dispersion device and polarization
interferometer, a 2.5Gb/s baseband signal is frequency up-conversed to a subcarrier modulation signal at 30.8GHz.
All-optical logic NOT gate is demonstrated based on cross phase modulation in highly nonlinear fiber while using a
negatively pre-chirped pulse as the probe light, with the output logic NOT signals of improved extinction ratio.
Assessment of 10 Gb/s Operation is carried out using pulse probe with and without pre-chirping stage. At least 3 dB
extinction ratio improvement is obtained compared to the implementation using chirp free pulse probe.
A novel approach is proposed to reduce the cross phase modulation between multiple clock pump in the
multi-wavelength optical decision based optical fiber parametric amplifier. The dispersive media is used to
preprocess the pump clock, and then the clock pump is changed from intensity modulation into phase modulation. In
our experiment, cross phase modulation is obviously restrained between the adjacent channels.
A novel photonic technique of 60-GHz millimeter-wave subcarrier generation base on four-wave mixing effect in a semiconductor optical amplifier (SOA) and a dual-frequency Brillouin fiber laser configuration is proposed. In this system, two new harmonic components with six times spacing of the microwave source frequency are created when an optical signal, generated by carrier-suppressed intensity modulation, is launched into the SOA. The two residual modulation sidebands are then suppressed by stimulated Brillouin scattering process, and the leaved idlers provide an millimeter-wave subcarrier signal.
A time- and wavelength-interleaved optical pulse source, which is based on spectral slicing and dispersion management, is proposed and experimentally demonstrated. The pulse source has a simple configuration, and both the repetition rate and the wavelength channels can be tuned easily.
A time- and wavelength-interleaved optical pulse source, which is based on spectral slicing and dispersion management,
is proposed and experimentally demonstrated. The pulse source has a simple configuration, and both the repetition rate
and the wavelength channels can be tuned easily.
We demonstrate a tunable chromatic dispersion (CD) compensation technique using a semiconductor optical amplifier
(SOA) and a coil of dispersion compensation fiber (DCF). Based on cross-phase modulation (XPM) in the SOA, the
transient chirp of the received signal can be adjusted by tuning the drive current of the SOA and the power of clock
pulse. In this way, a 10-Gbit/s tunable CD compensation setup, ranging from -40ps/nm to 60ps/nm, is realized without
changing the length of the DCF.
A time- and wavelength-interleaved (T- W-interleaved) optical pulse source based on optoelectronic oscillator is
presented. By utilizing spectral slicing, a multi-loop configuration is formed in OEO system, which can effectively
suppress side-modes. In addition, this configuration is able to generate multi-wavelength optical pluses which can be
arranged T- W-interleaved optical pulse stream at different nodes. In this system, 10-ps-wide optical pulses at 5GHz
repetition rate are generated with 1ps timing jitter (in the 100Hz-1MHz range) and -100dBc/Hz spurious modes
suppression, Along with the optical outputs, 5GHz electrical signal with low phase noise (-113dBc/Hz at 10kHz offset
from the carrier) is also obtained.
Short locking and unlocking time is essepecially important in the packet clock recovery, as it determines the network
resource utilization. This paper presents a novel 10-GHz all-optical packet clock extractor with ultrafast locking and
unlocking time via self-phase modulation (SPM) effect of the semiconductor optical amplifier (SOA). Low finesse
Fabry-Perot (F-P) filter and a saturated SOA, in cascade, are used to directly extract the packet clock from the data
stream. An optical bandpass filter(OBPF) is used to filter out the red-shifted parts of the packet clock in order to reduce
the locking and unlocking time. We analytically investigate the impact of the locking and unlocking time thanks to the
self-gain modulation (SGM) effect and self-phase modulation(SPM) effect induced by the SOA, and demonstrate 10GHz
clock extraction with the establishing time of 200ps and vanishing time of 600ps experimentally.
A novel 10Gbit/s all-optical packet clock extractor, which comprises a Fabry-Perot (F-P) filter and a semiconductor
optical amplifier (SOA), is proposed in this paper. Low Finesse Fabry-Perot (F-P) filter was used to directly extract the
packet clock from the data packet stream, which ensures that the clock locks fast and vanishes quickly. The clock,
amplitude modulated as a result of low-Q filter, then goes into SOA to reduce the low-frequency amplitude noise. The
impact of F-P filter and SOA on the locking and unlocking time of the packet clock is theoretically analyzed. The result
shows that the locking time is reduced while the unlocking time is increased, due to the self-gain modulation (SGM)
effect. We demonstrate instantaneous 10.075GHz clock extraction experimentally with the establishing time of about 8
code-periods and vanishing time of about 22 code-periods.
We demonstrate a novel 40-Gb/s all-optical serial to parallel converter (AOSPC), which can convert 40-Gb/s serial
optical signals to 4-channel 10-Gb/s parallel optical signals. Moreover, based on the sequential multi-wavelength
conversion the AOSPC shows the regeneration ability.
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