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We propose a novel scheme for simultaneous strain and temperature measurement by mode division multiplexing (MDM) in a dual cladding modes fiber up-taper interferometer. The fiber interferometer, with a strong cladding mode and a weak cladding mode, can be constructed by fabricating two optimized adjacent fiber up-tapers along a single-mode fiber. With the MDM method, the temperature and strain measurement resolutions reach ±0.05 °C and $\pm 3.14~\mu \varepsilon $ , respectively, which are much higher than those of the other proposed dual-parameters (temperature and strain) measurement solutions.

We propose a novel dual cladding modes fiber up-taper interferometer-based surface-mounted acoustic sensor. It consists of two optimized fiber fusion up-tapers along a single-mode fiber that enable it to excite dual cladding modes, which leads to its interference pattern with an extinction ratio of more than 20 dB, guaranteeing it to be used as an intensity-modulated fiber acoustic sensor (FAS) with an ultrahigh sensitivity. Under an acoustic pressure, its simultaneous responses in wavelength shift and intermodal power coupling change contribute to its ultrahigh sensitivity. The sensitivity of the proposed FAS reaches 2.65 V/ $\mu $ Pa and is 33.5 times bigger than that of the piezoelectric acoustic sensor.

We propose a configuration for suppressing pumps in a broad-and flat-band tunable nondegenerate four-wave mixing (FWM) wavelength converter. The signal and pumps are coupled into a highly nonlinear photonic crystal fiber symmetrical Sagnac loop. After the FWM wavelength conversion in the loop, the idler is separated from the pumps without a filter. In our experiment, a flat wavelength conversion bandwidth of 36 nm, conversion efficiency of -11 dB, pump-to-signal suppression ratio of 48 dB, and idler-to-pump suppression ratio of 15 dB are achieved.

An ON-OFF-keying optical receiver with dual thresholds and an erasure zone is proposed. This configuration can be applied to track the optimized decision level adaptively and obtain additional coding gain from forward-error correction without increasing the code rate. Our analysis shows that in both unamplified and optically preamplified receivers, the required Q value for the bit-error rate of 10-12 can be reduced by 1.8 dB, if errors arise in burst nature and the optimized erasure zone width is around 7%-11% of the signal swing.

An extinction ratio tunable optical fiber polarization interferometer (OFPI) is proposed and implemented to increase the optical modulation depth in radio-over-fiber (RoF) systems by suppressing the optical carrier power. The extinction ratio of the OFPI can be simply tuned by adjusting the polarization state of the launched RoF signal. Experimental results illustrate that the receiver sensitivity and dynamic range of RoF systems are greatly improved using the proposed scheme.

We propose a novel optical carrier-reuse scheme for the wavelength-division-multiplexed passive optical network. The scheme is based on a single delay interferometer (DI) at the remote node and reflective semiconductor optical amplifiers (RSOAs) at optical network units as the colorless devices for upstream transmission. The downstream subcarrier signals are optically separated by the DI for baseband detection of the downstream data and the separated optical carriers are used for seeding the RSOAs. Eight-channel upstream and downstream transmission is demonstrated at 1.25 Gb/s using the proposed scheme. The impact of optical carrier-to-subcarrier ratio of downlink signal and seeding light power on performance is also investigated

Conventional on-off keyed signals, such as return-to-zero (RZ) and nonreturn-to-zero (NRZ) signals are susceptible to cross-gain modulation (XGM) in semiconductor optical amplifiers (SOAs) due to pattern effect. In this letter, XGM effect of Manchester-duobinary, RZ differential phase-shift keying (RZ-DPSK), NRZ-DPSK, RZ, and NRZ signals in SOAs were compared. The experimental results confirmed the reduction of crosstalk penalty in SOAs by using Manchester-duobinary signals

Four pi-phase shifts are introduced in a uniform fiber Bragg grating (FBG) structure to realize a quadruple-transmission-band filter with ultranarrow 40-pm wavelength spacing. Four separate single-wavelength lasings at 1552.60, 1552.63, 1552.67, and 1552.71 nm, and three pairs of dual-wavelength lasings among above four wavelengths, are achieved stably by incorporating the quadruple-transmission-band FBG filter in a fiber ring cavity with a tunable uniform FBG acting as coarse frequency selection. This new kind of laser will be very useful in applications requiring closely spaced and tunable single- or dual-wavelength components

A stable 50-pm-spaced triple-wavelength fiber ring laser with nearly equal output power at each lasing line is achieved experimentally by incorporating a triple-transmission-band fiber Bragg grating filter in the fiber ring cavity. Such a laser will be very useful in applications requiring closely spaced multiwavelength components

We experimentally study the impact of filter bandwidth of a spectrum-sliced amplified spontaneous emission (ASE) source on the injection-locking of a Fabry-Perot laser diode (FPLD) for passive optical network application. Optimal bandwidth of a spectrum-sliced ASE source was found in terms of receiver sensitivity after transmission. We also investigate the impact of intensity noise (IN) of the spectrum-sliced ASE source and its suppression for a wavelength-locked FPLD using a semiconductor optical amplifier. Experiment results show that the output performance of a wavelength-locked FPLD is improved by IN suppression

A Manchester-duobinary coding scheme is proposed to compact the optical spectrum compared with that using pure Manchester coding and thus demonstrate much larger tolerance against fiber dispersion. With this modulation format, the dispersion tolerance can be extended to nearly three times of that using pure Manchester coding. Dispersion tolerance of Manchester-duobinary is from -800 to +920 ps/nm at 2-dB power penalty

We investigate the effects of polarization-mode dispersion (PMD) and chirp on radio-frequency tone-based chromatic dispersion (CD) monitoring method, and show that the PMD and chirp induce significant CD monitoring errors. We propose a CD monitoring technique to suppress these effects. Experiment results show that the CD monitoring errors induced by PMD and chirp fluctuation are greatly suppressed.

To avoid significant stimulated Brillouin scattering (SBS) generation in a bidirectional Raman-pumped long single-span transmission system, the SBS threshold is studied in both return-to-zero on-off -keying (RZ-OOK) and RZ differential phase-shift keying (DPSK) systems. It shows that SBS threshold in an RZ-DPSK system is more than 10 dB higher than that in an RZ-OOK system, and SBS reflection is dominated by copumping, while counterpumping has minor effect. Error-free eight-channel single-span transmission is demonstrated over 310-km standard single-mode fiber using RZ-DPSK format and bidirectional Raman pumping, without applying forward-error correction and remote-pumping techniques.

A novel in-service signal quality monitoring technique for nonreturn-to-zero differential phase-shift keying signals using asynchronous amplitude histogram evaluation has been demonstrated. As a result of phase-to-amplitude modulation, there are three Gaussian distributions in the amplitude histogram. The widths of the Gaussian distributions are related to the amount of amplified spontaneous emission, while the separations between the Gaussian distributions increase monotonically with fiber dispersion. The amount of dispersion and optical signal-to-noise ratio can, thus, be directly extracted and discriminated from the amplitude histogram.

Novel phase-shift-keying (PSK)-Manchester coding scheme is suggested for the first time to be used in a 10-Gb/s wavelength-division-multiplexing passive optical network (PON) system. PSK-Manchester signal demonstrates much stronger tolerance to beat interference noise compared to that of differential phase-shift-keying and amplitude-shift-keying-Manchester signals. With this modulation format applied, the number of semiconductor optical amplifiers used as control gates in a PON system can be greatly reduced, which make the PON system more cost-effective.

An excellent polarization-dependent gain (PDG) suppression technique using a polarization scrambler is proposed in this letter. Investigations on PDG due to signal-to-signal Raman interaction among 40 wavelength-division-multiplexer signal channels were carried out experimentally to evaluate the system performance after incorporating a polarization scrambler in the system. It was confirmed by experiment that the use of polarization scrambler is an effective way to reduce PDG caused by signal-to-signal Raman interaction.

A multimode fiber Bragg grating (MMFBG)-based wavelength-switching erbium-doped fiber laser and its application in displacement sensing is proposed and demonstrated. According to the spatial-mode distribution in the multimode fiber (MMF), the modes reflected by the MMFBG at different wavelengths build a wavelength-dependent mode field on the transverse plane of the MMF. By varying spatial-launching position of the single-mode fiber against the MMFBG to achieve different mode group excitation and selection, single-wavelength lasing at 31 discrete wavelengths has been realized over a wide wavelength range.

To extend transmission distance using cascaded in-line semiconductor optical amplifiers (SOAs) and differential phase-shift-keying modulation format, optimal operation conditions for SOAs, such as input power and operation current, are studied. 16/spl times/10.709-Gb/s wavelength-division-multiplexing transmission over 640-km SSMF with the optimal system design parameters is demonstrated. This is, to the best of our knowledge, the largest bit-rate distance product reported.

We have performed eight-channel wavelength-division-multiplexing transmission over 1050-km single-mode fiber using cascaded in-line semiconductor optical amplifier and differential phase-shift keying modulation format for the first time; more than 6 dB of power margin was achieved over forward-error correction threshold. Factors that affect the transmission performance were discussed. It was found that four-wave mixing is the main factor that limits the maximum transmission distance. Larger capacity distance product can be realized by further optimizing the configuration of transmission link.

We have demonstrated ten-stage cascaded wavelength conversion together with 800-km transmission for 10-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) format using four-wave mixing (FWM) in semiconductor optical amplifiers. To the best of our knowledge, this is the first experiment reported on cascade wavelength conversion for RZ-DPSK format, which cannot be realized by methods based on cross-gain modulation and cross-phase modulation using a semiconductor optical amplifier. Compared with wavelength conversion using FWM for conventional on-off keying format, the signal-to-pump ratio for RZ-DPSK format can be increased to higher level to achieve better performance.

A novel method based on asynchronous sampling using sampling pulse with wide pulsewidth has been suggested for Q-factor estimation from amplitude histogram. The effectiveness of this method has been demonstrated through numerical simulation. It was found that, there exist a linear relationship between original Q value and the estimated Q factor using sample pulse with certain pulsewidth for both nonreturn-to-zero and return-to-zero signal format. This method is simple and easy to implement. It can be applied to either single channel or multi channel monitoring scheme.

We propose and demonstrate experimentally a novel microwave-photonic filter using a variable polarization delay line based on a high-birefringence linear chirped fiber Bragg grating. The filter is free from the problems associated with the optical coherence interference of the laser. It provides a continuous tuning capability without the need to change the wavelength of the input optical carrier, and offers high resolution filtering for real-time signal processing in radio frequency systems.

An analytical model of intraband optical crosstalk in an N/spl times/N fiber Bragg grating optical circulator-based optical cross connect (OXC) is presented. Results show that the worst-case coherent crosstalk is /spl sim/22-26 dB higher than incoherent crosstalk, depending on the switching state of 2/spl times/2 OXC. In addition, a novel scheme of OXC with improved intraband crosstalk performance is proposed.