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The light guidance characteristics of the fully and partially ethanol-filled photonic bandgap fibers (PBFs) are investigated and their applications as modal interferometers (MIs) for temperature sensing are demonstrated. Different from the ethanol-filled solid core photonic crystal fibers (PCFs), the ethanol-filled PBFs are much easier to excite more high order cladding modes, and the effective refractive index difference between the interference modes can reach 26.6 times bigger than that of the ethanol-filled solid core PCF. Without using special splicing techniques, just splicing a short section of the fully or partially ethanol-filled PBF between the single mode fibers, a PBG-based MI can be constructed with a high thermal sensitivity. Moreover, the thermal sensitivity can be adjusted within a large range by selectively filling the air core and/or air claddings of the PBF with ethanol. Experimental results show that the fully ethanol-filled PBF-based MI has the thermal sensitivity up to –292 pm/°C while that of the partially ethanol-filled PBF-based MI is changed to –120 pm/°C. They are 43.8 and 18 times bigger than that of the unfilled PBF-based MI.

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 fiber micro-displacement sensor based on an embedded fiber dual cladding modes interferometer. This type of interferometer has a very high extinction ratio (ER) of 27.7 dB, with only one very deep resonance dip within C and L bands, enabling it to be used as an intensity-modulated sensor. With it embedded in a cured carbon fiber composites based beam, it shows a high sensitivity response to micro-displacement in ER variation. Experimental results show that there is a quasi-linear relationship between the micro-displacement and its ER variation, with the measurement resolution of 4.67 μm, and the dynamic measurement range of 0∼200 Hz.

A new scheme for the distributed intrusion detection system based on the polarization optical time domain reflectometry (POTDR) for multi-event detection is proposed in this paper. In the scheme, a polarization maintaining fiber is employed as the distributed pressure sensor instead of the single mode fiber. The working principle of the system is described in detail, and an experimental system is set up to confirm the ability to detect several intrusion events happened at the same time along the sensing fiber by measuring the polarization mode coupling coefficient caused by the pressure and three simulated events. And from the final experimental result denoised using wavelet transformation, the three intrusion events can be significantly detected.

We demonstrate an arc discharge fabrication method for a high extinction-ratio (ER) single mode fiber (SMF) based dual thin-taper modal interferometer (MI) and investigate the performance of the MI as thermal and refractive index (RI) sensors. With the optimized discharge parameters of a commercial fusion splicer and a simple mechanical taper setup, the MI with about 24 dB ER could be achieved if fabricating two thin-tapers with 20-µm waist diameter on the common SMF. It can be used as a highly sensitive thermal sensor with a thermal sensitivity of −72.8 pm/°C. However, for the high ER MI, the propagation position of the cladding mode is more close to that of core mode in the MI. Hence, its sensitivity to ambient RI variation is not very high, about 10.299 nm/RIU. If using it for dual parameter measurement, its thermal and RI measurement resolutions are ±1.1 °C and ±0.009, respectively, and are 6.6 and 2.4 times bigger than those of the other fiber sensors.

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 demonstrate a 10 Gsymbol/s, 1024 quadrature amplitude modulation (QAM) 160 km coherent transmission with an injection locking technique. Our newly developed, pilot-assisted adaptive equalizer has greatly improved the precision of waveform distortion compensation, and this has enabled us to increase the symbol rate to 10 Gsymbol/s in a 1024 QAM transmission. Thus, we could realize a 200 Gbit/s, 1024 QAM transmission over 160 km with a potential spectral efficiency of 12.6 bit/s/Hz.

With the open-loop fiber optic gyro (OFOG) model, output voltage and angular velocity can effectively compensate OFOG errors. However, the model cannot reflect the characteristics of OFOG errors well when it comes to pretty large dynamic angular velocities. This paper puts forward a modeling scheme with OFOG output voltage and temperature as the input variables and angular velocity error as the output variable. Firstly, the angular velocity error is extracted from OFOG output signals, and then the output voltage , temperature and angular velocity error are used as the learning samples to train a Radial-Basis-Function (RBF) neural network model. Then the nonlinear mapping model over T, and is established and thus can be calculated automatically to compensate OFOG errors according to and . The results of the experiments show that the established model can be used to compensate the nonlinear OFOG errors. The maximum, the minimum and the mean square error of OFOG angular velocity are decreased by , and relative to their initial values, respectively. Compared with the direct modeling of gyro angular velocity, which we researched before, the experimental results of the compensating method proposed in this paper are further reduced by , and , respectively, so the performance of this method is better than that of the direct modeling for gyro angular velocity.

We demonstrate a pol-mux, 12 Gsymbol/s 512 QAM coherent transmission. An injection-locked homodyne-detection circuit enabled precise optical-phase locking, and 216 Gbit/s-data were successfully transmitted over 160 km with a potential spectral efficiency of 12 bit/s/Hz.

A novel temperature insensitive and intensity modulated microdisplacement sensor is demonstrated by cross-layerly embedding an FBG in carbon fiber composites. The reflection spectrum of the FBG is selfmodulated to be chirped spectrum if a microdisplacement is applied to the center of the sensor structure. By monitoring the optical power change due to the above chirped spectrum variation, the microdisplacement can be measured. Experimental results show that there are quasilinear relationships between the microdisplacement and optical power, the maximum measurement resolution of the sensor reaches 10.7 μm within the displacement range of 0–1050 μm, and the dynamic measurement range is within the range of 0–200 Hz.

A directional coupler structure formed by a nematic liquid crystal (NLC)-filled photonic crystal fiber (PCF) represents a promising configuration in sensing applications. Because of large refractive index difference between the NLC and silica material, the mode coupling between the NLC waveguide and the silica core is more complicated than the situation of coupling between two fundamental modes of the waveguides. Therefore, it is necessary to perform a theoretical investigation of the mode properties associated with the experimental studies of the coupling characteristics. In this paper, we present a thorough analysis, both theoretically and experimentally, of the directional coupler structure, including the mode properties, coupling characteristics, and thermal sensing properties. The temperature response of the device is experimentally measured, showing a polynomial curve in nematic phase and a linear curve in isotropic phase. The nonlinearity of the temperature response of the device in nematic phase and the linearity in isotropic phase are attributed to the temperature dependence of the refractive index of the NLC. Specifically, the sensitivity is -3.86 nm/°C in isotropic phase of the 6CHBT with good linearity and shows good agreement with simulation results.

We report the fabrication of a highly sensitive refractometer based on photonic crystal fiber (PCF) interferometry. Using fusion arc splicing technique, a short length of PCF (∼3 mm) was spliced to conventional single-mode fibers on both sides. The voids of the PCF were completely collapsed in the splice region, which acted as mode splitter and combiner on both sides. Microbubbles were formed in the splice region and acted as diverging lens for exciting cladding modes efficiently. The transmission spectrum exhibited detectable “dips” for refractive index (RI) sensing. The bulk liquid sensitivity can reach up to 320 nm/RIU (RI unit) based on the linear curve fit for RI ranging from 1.33 to 1.34. Biosensing experiment was carried out using streptavidin and biotin as respective analyte and receptor. To the best of authors’ knowledge, this is the first time of reporting bioaffinity test on the external surface of PCF using modal interferometry.

We realized a single-carrier, polarization-multiplexed 32 Gbaud 128 QAM coherent transmission. Digital frequency-domain equalization enabled us to achieve waveform distortion compensation of a wideband data signal with high frequency resolution. Thus, we successfully increased the QAM multiplicity to 128 at 32 Gbaud, and transmitted 448 Gbit/s data over 150 km with a potential spectral efficiency of 10.7 bit/s/Hz. This is the highest multiplicity and spectral efficiency yet achieved in a coherent QAM transmission at a baud rate of as high as 32 Gbaud.

We demonstrate an 80 Gbit/s, 5 Gsymbol/s 256 QAM coherent optical transmission by employing an injection-locked homodyne detection circuit based on both fiber lasers and LDs. With either circuit, low phase noise carrier-phase synchronization between the transmitted data signal and an LO were achieved with a phase noise variance of only 0.2 degrees. As a result, we have successfully transmitted an 80 Gbit/s data signal over 150 km with a simple receiver configuration. This is the highest QAM multiplicity yet realized with injection-locked homodyne detection.

We report a polarization-multiplexed 10Gsymbol/s, 64QAM (120Gbit/s) coherent transmission over 150km by using an optical phase-locked loop (OPLL) circuit employing narrow linewidth LDs. The OPLL realized low phase noise demodulation of 64QAM signal. As a result, 120Gbit/s data signal were transmitted with a bit error rate (BER) performance below a forward error correction (FEC) threshold of 2×10-3.

It is experimentally shown that six-channel C + L-band 80-GHz short pulse trains are generated based on parametric process in highly-nonlinear fiber (HNLF). By launching a pulsed pump and three-channel continuous wave (CW) lights into 1-km HNLF, three-channel signals are amplified and three-channel idlers are generated. The waveforms of the generated 80-GHz short pulses are measured by an auto-correlator. The bit-error-rate (BER) of each channel is analyzed numerically. In the back-to-back case, the power penalties of the generated channels are less than 1.5-dB.

A scheme for hi-fi all-optical continuously tunable delay is proposed. The signal wavelength is converted to a desired idler wavelength and converted back after being delayed by a high linear-chirp-rate (HLCR) fiber Bragg grating (FBG) based on four-wave mixing (FWM) in a highly-nonlinear photonic crystal fiber (HN-PCF). In our experiment, 400 ps (more than 8 full width of half maximum, FWHM) tunable delay is achieved for a 10 GHz clock pulse with relative pulse width broaden ratio (RPWBR) of 2.08%. The power penalty is only 0.3 dB at 10 −9 BER for a 10 Gb/s 2 31 −1 pseudo random bit sequence (PRBS) data.

In this paper, an optically controlled loop buffer is proposed and experimentally demonstrated. It utilizes a semiconductor optical amplifier (SOA) based loop mirror as a fast switch to realize the writing and reading of packets within this buffer and a circulator based optical reflector to achieve internal re-circulations. By adding fibers with different lengths between the loop mirror and the circulator, variable delay time per circulations can be obtained. We also demonstrate the performance of the 2.5 and 10 Gb/s data packets in this buffer structure, as well as the influence of the two different control signal formats on the packet signal degradation during buffering. This loop buffer has the merits of low cost and improved performance compared to other similar loop buffer structures. According to the obtained results, the achieved number of circulations is greatly increased.

An integrated configuration is proposed to convert tunable slow light from signal to another frequency in a wide bandwidth by using a 70 m-long highly nonlinear photonic crystal fiber (HN-PCF). A 10 GHz RZ signal is delayed by a 10 Gbit/s 231-1 pseudo random bit sequence (PRBS) stimulated Brillouin scattering (SBS) pump, and the slow light is converted to another frequency in a broadband by four-wave mixing (FWM). By this way, not only the slow light is converted, but the idler power is enhanced greatly. In our experiment, all-optical controlled 37.5 ps delay time is converted in a 40 nm bandwidth flatly, and 4.7 dB idler power is enhanced simultaneously. The experimental results are in good agreement with those of the theory.

We experimentally evaluate the performance of Fabry–Perot laser diodes (FPLDs) injection locked by spectrum sliced amplified spontaneous emission (ASE) noise for transmission at 1.25 Gb/s. We characterize the injection locked FPLDs in terms of front-facet reflectivity, operation temperature, bias current and injection locked mode location. Experiment results show that the FPLD performance is strongly dependent on the front-facet reflectivity. Therefore a reasonable range of front-facet reflectivity for FPLDs is recommended. Operating the lasers at low temperature has better receiver sensitivity, while operating at high temperature has slightly broader operation range for injected ASE power. There is an optimal bias for a given injection power and the operation range for bias current is increased for higher injection power. Injection locked mode location also affects the performance of FPLDs.

The idler is separated from the co-propagating pump in a degenerate four-wave mixing (DFWM) with a symmetrical parametric loop mirror (PALM), which is composed of two identical SOAs and a 70 m highly-nonlinear photonic crystal fiber (HN-PCF). The signal and pump are coupled into the symmetrical PALM from different ports, respectively. After the DFWM based wavelength conversion (WC) in the clockwise and anticlockwise, the idler exits from the signal port, while the pump outputs from its input port. Therefore, the pump is effectively suppressed in the idler channel without a high-speed tunable filter. Contrast to a traditional PALM, the DFWM based conversion efficiency is increased greatly, and the functions of the amplification and the WC are integrated in the smart SOA and HN-PCF PALM. (C) 2008 Elsevier B.V. All rights reserved.

We propose and demonstrate a 10 Gb/s wavelength division multiplexed passive optical network (WDM-PON) where subcarriers are employed to transmit the downstream data and optical carriers of the downlink subcarrier modulated (SCM) lights are reused to injection lock Fabry-Perot laser diodes (FP-LDs) for uplink transmission. Experiment results show that a very good BER performance can be achieved for both uplink and downlink at 10 Gb/s. The impact of optical carrier to subcarrier ratio and wavelength mismatching is also investigated.

In this paper, we analyze the survivability of wavelength division multiplexed (WDM) passive optical network (PON). We propose and experimentally demonstrate a novel survivable WDM-PON architecture with self-protection and in-service fault localization capabilities. Two WDM-PONs are combined together and multiple sub-ring architecture is formed. Protection switching is achieved automatically at optical network units (ONUs) when failure occurs. Fiber loss, fiber fault localization and automatic protection switching in each ONU are real-time monitored in central office (CO) without interrupting customer service. No signaling for failure notice or protection switching is required for either CO or ONUs. Extra fibers required for protection are minimized compared with previous protection schemes. The self-protection and in-service fault localization capabilities of the proposed WDM-PON architecture are experimentally verified.

This paper presents the generation and the performance evaluation of optical minimum shift keying (MSK) for high-speed and high-spectral-efficiency wavelength-division multiplexing systems. The detailed principle on optical MSK generation and detection is derived and analyzed. Optical MSK data (10.7 Gb/s) are successfully generated by an experiment using the proposed scheme. The results show that the optical MSK signal exhibits a very compact optical spectrum. The performance of the optical MSK modulated system is evaluated and compared with those of 50% duty-cycle return-to-zero differential phase shift keying (RZ-DPSK) and 50% duty-cycle return-to-zero on-off keying (RZ-OOK) modulated systems, via both simulation and experiment, in terms of dispersion tolerance, linear crosstalk, self-phase modulation (SPM) tolerance, stimulated Brillouin scattering (SBS) threshold, optimal receiver filter bandwidth, and optimal link launch power into single-mode fibers and dispersion compensation fibers. Experimental and simulation results show that the MSK signal exhibits the largest tolerance against fiber dispersion and SPM effect as compared with RZ-DPSK and RZ-OOK. Experimental results also confirm the negative penalty against the SPM effect. The SBS threshold of both the MSK and RZ-DPSK systems is more than 10 dB higher than that of the RZ-OOK system. The MSK that is generated with conventional carrier-suppressed return-to-zero (CSRZ) pulses exhibits a narrower optimal optical filter bandwidth but a wider electrical filter bandwidth compared with those of RZ-OOK and RZ-DPSK. The MSK signal that is generated with pure dual-mode pulses has a similar optimum range to RZ-OOK and RZ-DPSK at a high optical signal-to-noise ratio (OSNR) but has a narrower optimal optical filter bandwidth at a low OSNR. The optimum fiber launch power study shows that the MSK signal that is generated using the conventional CSRZ pulses exhibits higher optimum launch power, which agrees with the SPM tolerance study.

In this paper, we present an orthogonal labelling scheme using inverted return-to-zero (IRZ) as payload and differential-phase-shift-keying (DPSK) as label. Transmission performances of orthogonal labelling with 40 Gb/s IRZ payload and 10 Gb/s label are evaluated. Simulation results show that orthogonal labelling using IRZ as payload exhibits a much larger extinction ratio margin than that of using return-to-zero (RZ) as payload. The asynchronous effect between payload and label on the transmission performances of orthogonal labelling using IRZ and RZ as payload is evaluated. Simulation results show that the degradation of asynchronous orthogonal labelling using IRZ as payload is relatively worse than that of using RZ as payload. The impact of optical filter bandwidth before receivers is also investigated. Results show that the receiver sensitivities of label for IRZ/DPSK and payloads for both IRZ/DPSK and RZ/DPSK are degraded with the reduction of the filter bandwidth, while the label of RZ/DPSK exhibits an opposite trend.

The thermal characteristics of the ethanol-filled hollow core photonic crystal fiber (HCPCF) based modal interferometer (MI) is investigated theoretically and experimentally. The effective refractive index difference between the interference modes and thermal sensitivity are improved greatly after filling ethanol solution into the air core and claddings of the HCPCF.

We demonstrate an 80 Gbit/s-256 QAM coherent optical transmission with a fiber laser-based injection-locked homodyne detection circuit. The circuit enabled low phase-noise carrier-phase synchronization, and an 80-Gbit/s data signal was successfully transmitted over 150 km.

Based on dual-order stimulated Raman scattering (SRS) of a single 1395 nm Raman fiber laser in 75 km single mode fiber and its corresponding dispersion compensation module, a hybrid Raman/Erbium doped fiber amplifier (EDFA) for long wavelength band (L-band) amplification is realized by inserting a segment of EDF within the span. By comparing the performance of gain and noise in four hybrid amplifiers with different span configurations, we find that the distribution of the secondary L-band amplification obtained from the EDF along the link has a great influence on the performance of the hybrid amplifier. Both gain and noise performance of hybrid amplifier can be improved significantly by optimizing the location of the EDF. Moreover, we can extend the flat gain bandwidth from L-band to central wavelength band (C-band) plus L-band by recycling the residual first-order SRS to pump a segment of EDF with proper length.

We consider and investigate an improved chromatic dispersion monitoring method using two RF tones with an inserted dispersion offset. This improved technique can be used to monitor both the positive and negative accumulated dispersion caused by optical fibers as well as other optical components in optical networks. We experimentally demonstrate that the monitoring range of the improved technique can be greater than 1150 ps/nm and the monitoring sensitivity better than 0.064 dB/ps/nm by selecting appropriate RF frequencies and dispersion offsets. Our investigations reveal that the RF modulation index should be greater than 10% but less than 20% so as to acquire a large monitoring range with a small power penalty. We also examine the CD monitoring errors caused by polarization mode dispersion (PMD) and self-phase modulation, and show that the use of a dispersion offset can effectively reduce the PMD-induced monitoring errors.

This paper presents a design approach for multistage gain-flattened fiber Raman amplifiers (FRAs) utilizing the multiwavelength-pumping scheme. To the authors' best knowledge, it is the first time that Raman amplifiers of more than one stage are considered in the design process so as to optimize multistage amplifier performance simultaneously. It is shown both theoretically and experimentally that optical power path integrals among several stages can, in principle, be arbitrarily redistributed while maintaining its gain performance, as long as the consolidated sums at different pump wavelengths are unaltered. The overall gain spectrum of a multistage FRA is thus very close to the cumulative spectrum of chained identical single-stage amplifiers with span numbers equal to its stages. However, the traditional prerequisite to minimize gain flatness in every stage is no longer required. It provides flexibilities to take full advantage of pump lasers with moderate launched powers and allows the reduction of the number of pump lasers and/or wavelengths in most stages. By arranging small positive net gain to the first stages and enhancing it at shorter signal wavelengths, significant reduction and flattening of total noise figure (NF) is achieved even if a pure backward pumping scheme is utilized. Finally, various pumping configurations for Raman amplifiers with hybrid dispersion-compensating fiber (DCF) and standard single-mode fiber (SMF) are discussed, with the objective of realizing flattened gain and noise performance simultaneously without using forward pumps.

A new scheme of distributed intrusion detection system based on the polarization optical time domain reflectometry is proposed. In the experiment, three events along the fiber were successfully detected by measuring the polarization mode coupling.

We demonstrate a 140-Gbit/s, 128 QAM coherent optical transmission employing an LD-based injection-locked homodyne detection circuit. Low phase noise carrier-phase synchronization was achieved and a 140-Gbit/s data signal was successfully transmitted over 150 km.

We demonstrate 20 Gsymbol/s, 256 QAM polarization multiplexed (pol-mux) 320 Gbit/s coherent transmission. By employing an LD-based injection locking circuit, we achieved low noise optical carrier-phase locking between the LO and the data signal. Furthermore, frequency domain equalization and digital back-propagation enabled us to realize precise compensation for transmitted waveform distortions. As a result, a 320 Gbit/s data was successfully transmitted over 160 km with a potential spectral efficiency of 10.9 bit/s/Hz. This is the highest symbol rate yet achieved in a pol-mux 256 QAM coherent transmission. In addition, we also describe a pol-mux 256 QAM transmission at a symbol rate of 10 Gsymbol/s.

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 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.

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

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.

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.

We present here a stimulated emission based fluorescence lifetime imaging (FLIM) scheme using a pair of synchronized diode lasers operating at gain switched pulse mode. The two semiconductor lasers, with wavelengths at 635 nm and 700 nm, serve as the excitation and the stimulation light sources for the ATTO647N labeled sample, respectively. FLIM is readily achieved with their relative time delay controlled electronically. The coherent nature of the stimulated emission signal also allows FLIM at long working distance. In this way, a high performance all-semiconductor FLIM module is realized in a flexible, compact, and cost effective configuration.

We report a highly precise OPLL circuit employing an optical voltage controlled oscillator and a frequency-stabilized, narrow linewidth LD. An extended OPLL bandwidth of 4 MHz enabled a phase noise as low as 0.6 degrees.

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.