Microcosm study reveals the microbial and environmental effects on tributyltin degradation in an estuarine sediment.

Tributyltin (TBT) is one of the most harmful contaminants ever released into the aquatic environment. Despite being banned, it is still present at many locations throughout the world. Its degradation in sediment mainly occurs through microbial biodegradation, a process that remains unclear. This study therefore aimed at better understanding TBT biodegradation in estuarine sediment and the microbial community associated with it. Microcosm experiments were set up, embracing a range of environmental control parameters. Major community shifts were recorded, mainly attributed to the change in oxygen status. The highest percentage of degradation (36,8%) occurred at 4 °C in anaerobic conditions. These results are encouraging for the in-situ bioremediation of TBT contaminated muddy sediment in temperate ports worldwide. However, with TBT able to persist in the coastal environment for decades when undisturbed in anoxic sediment, further research is needed to fully understand the mechanisms that triggered this biodegradation observed in the microcosms.

Design and fabrication of elliptical-core few-mode fiber for MIMO-less data transmission.

We propose a design strategy of elliptical core few-mode fiber (e-FMF) that supports three spatial modes with enhanced mode spacing between LP11a and LP11b, to suppress intra-mode coupling during mode-division multiplexing (MDM) transmission. Our theoretical investigations show that there exist two optimization regimes for the e-FMF, as a comparison with traditional circular core FMF(c-FMF). At the regime of three-mode operation, there occurs a trade-off between mode spacing and bending-induced loss. Meanwhile, in terms of five-mode regime, a trade-off between mode spacing and high-order mode crosstalk happens. Finally, we fabricate 7.94 km e-FMF with the optimal parameters, based on the commercial fiber manufacture facility. The primary characterizations at 1550 nm show that three spatial modes of e-FMF can be transmitted with a loss less than 0.3 dB/km. Meanwhile, -22.44 dB crosstalk between LP11a and LP11b is observed, even when the 2 km e-FMF is under stress-induced strong perturbation.

Comparison of bandwidth and sensitivity of long-period gratings in single-mode and few-mode fibers.

We present a comparative study of the bandwidth and the sensitivity of the resonance wavelength of long-period gratings (LPGs) to external perturbation fabricated in single-mode fibers (SMFs) and few-mode fibers (FMFs), and their dependencies on the group indices and the dispersion properties of the phase-matched modes. Unlike SMFs, a relatively large core size of FMFs invariably leads to nonuniform index modulation across the fiber cross section under UV exposure, enabling the coupling between modes having dissimilar azimuthal symmetry. Simple analytical formulas for the group/effective index difference, dispersion difference, bandwidth, and wavelength sensitivities are derived for the case of SMFs where light is coupled from the fundamental core mode to the symmetrical cladding modes. Our results show that a two-mode fiber operating at a V-number close to 3 is capable of producing LPGs with broader bandwidth and higher sensitivity as compared with their SMF counterparts, except for a few special cases. Our analyses provide insights into the characteristics of LPGs and facilitate their designs for specific applications.

Role of wavelength dependent sensitivity in affecting the crosstalk mitigation of homogeneous multicore fiber: an analytical estimation approach.

The mitigation of both crosstalk and its wavelength dependent sensitivity for homogeneous multicore fiber (MCF) is theoretically investigated using an analytical evaluation approach. It is found there exists a performance trade-off between the crosstalk mitigation and its wavelength dependent sensitivity suppression. After characterizing the fabricated homogeneous MCFs, we verify that although the increasing core pitch can mitigate the crosstalk, the wavelength dependent sensitivity is drastically degraded from 0.07dB/nm to 0.11dB/nm, which is harmful to the dense wavelength division multiplexing (DWDM) transmission over C + L band using MCF.

Fiber-integrated 780 nm source for visible parametric generation.

We report the development of a fully fiber-integrated pulsed master oscillator power fibre amplifier (MOPFA) source at 780 nm, producing 3.5 W of average power with 410 ps pulses at a repetition rate of 50 MHz. The source consists of an intensity modulated 1560 nm laser diode amplified in an erbium fiber amplifier chain, followed by a fiber coupled periodically poled lithium niobate crystal module for frequency doubling. The source is then used for generating visible light through four-wave mixing in a length of highly nonlinear photonic crystal fiber: 105 mW at 668 nm and 95 mW at 662 nm are obtained, with pump to anti-Stokes conversion slope efficiencies exceeding 6% in both cases.

Phase sensitive SPR sensor for wide dynamic range detection.

Phase detection has been utilized to enhance the sensitivity of surface plasmon resonance (SPR) sensors for a long time. However, an inherent drawback for phase sensitive SPR sensors are their limited dynamic range, which has greatly hindered wide applications of such sensors. In this Letter, a design combining phase detection and angular interrogation has been proposed to provide an SPR sensor with both high sensitivity and wide dynamic range. As a result, a resolution of 2.2×10-7 RIU with a dynamic range of over 0.06 RIU has been achieved simultaneously. An added advantage of this design is the flexibility for sensitivity and dynamic range adjustment.

Effect of input states of polarization on the measurement error of Mueller matrix in a system having small polarization-dependent loss or gain.

For the measurement of Mueller matrix in an optical system with birefringence and small polarization-dependent loss or gain (PDL/G), we theoretically derive the statistical relationship between the Mueller matrix measurement error and three input states of polarization (SOP). Based on this theoretical relation and simulation results, it can be concluded that the three input SOPs, that are coplanar with an angle of 120 degrees between any two of them in Stokes space, can be considered as a substitute for the best input SOPs which can statistically lead to the minimum measurement error. This conclusion is valid when the PDL/G of the optical system under test is less than 0.35 dB.

Observation of spectral enhancement in a soliton fiber laser with fiber Bragg grating.

We demonstrate that soliton generation in a fiber laser containing a fiber Bragg grating exhibits spectral enhancement near the Bragg resonance wavelength. The Bragg grating leads to a spectral hole on the soliton spectrum while the observed enhancement is always located at the long wavelength side of the Bragg resonance.

Photonic-assisted microwave frequency measurement with higher resolution and tunable range.

A photonic-assisted approach to microwave frequency measurement is proposed based on frequency-to-power mapping with the help of the so-called amplitude comparison function. The key component is a dual-output Mach-Zehnder modulator (MZM) working at chirped modulation. The proposed scheme is characterized as having simplicity, higher resolution, and tunable measurement range. Owing to experimental constraint, an equivalent experiment has been carried out using a common single-output MZM at different bias points to prove the concept.

Coupled-mode analysis of Bragg-reflection filters based on asymmetric nonlinear dual-core fibers.

We demonstrate a Bragg-reflection grating coupler using a nonlinear dual-core fiber with a long-period grating (LPG) and a fiber Bragg grating (FBG) inscribed in different cores. The LPG couples light from the primary core to the cladding, while the FBG operating in reflection acts to drop the channel from the secondary core. The coupler is nonreflective along the launching core. Theoretical analysis of this structure demonstrates a design for obtaining a flat-top bandpass filter with high reflectivity, steep band transitions, and negligible sidelobes. By launching an intense pump beam into the individual cores, a switchable and a wavelength tunable passband can be achieved. The results demonstrate the usefulness of the device as a grating-based all-optical element.

Optimum input states of polarization for Mueller matrix measurement in a system having finite polarization-dependent loss or gain.

We present the theoretical and simulation results of the relationship between three input states of polarization (SOP) and the Mueller matrix measurement error in an optical system having birefringence and finite polarization-dependent loss or gain (PDL/G). By using the condition number as the criterion, it can be theoretically demonstrated that the three input SOPs should be equally-spaced on the Poincaré sphere and centered on the reversed PDL/G vector to achieve better measurement accuracy in a single test. Further, an upper bound of the mean of the Mueller matrix measurement error is derived when the measurement errors of output Stokes parameters independently and identically follow the ideal Gaussian distribution. This upper bound also shows that the statistically best Mueller matrix measurement accuracy can be obtained when the three input SOPs have the same relationship mentioned above. Simulation results confirm the validity of the theoretical findings.

Stress distribution and induced birefringence analysis for pressure vector sensing based on single mode fibers.

We propose a theoretical approach to analyze the pressure stress distribution in single mode fibers (SMFs) and achieve the analytical expression of stress function, from which we obtain the stress components with their patterns in the core and compute their induced birefringence. Then we perform a pressure vector sensing based on approximately 2 km SMF. Using Mueller matrix method we measure the birefringence vectors which are employed to compute the pressure magnitudes and their orientation. When rotating the pressure around the fiber, the corresponding birefringence vector rotates around a circle with double speed. Statistics show the average deviation of calculated pressure-magnitude to practical value is approximately 0.17 N and it is approximately 0.85 degrees for orientation.

Long path-length axial absorption detection in photonic crystal fiber.

In this paper, we present a long path-length axial absorption detection method in photonic crystal fibers (PCFs). A PCF, also called a holey fiber or microstructured fiber, is an optical fiber which consists of a periodic array of very tiny and closely spaced air holes on the scale of 1 microm running through the whole length of the fiber. Here, a PCF with porous microstructures was used as a sample container for absorption detection. Light was guided by total internal reflection and propagated axially in the air holes of PCFs that were filled with the solution of the absorbing species by vacuum pumping. Excellent linearity was obtained for different sample concentrations, and high sensitivity was achieved due to the long optical path length. In addition, as the dimension of the PCF is small, the sample volume is greatly reduced. Moreover, due to its robustness, the PCF can be coiled up to keep the footprint small, making it suitable for microchip absorption detection. It can be widely used for both off-chip and on-chip detection of absorbing species, such as ions, alkaloids, and biomolecules.

Experimental analysis of spectral characteristics of antiresonant guiding photonic crystal fibers.

Both numerical and experimental analyses are carried out to investigate the spectral characteristics of antiresonant guiding photonic crystal fibers. The transmission minima were observed at the wavelengths where LP(ml) (m

Photonic ultrawideband monocycle pulse generation using a single electro-optic modulator.

A compact approach to photonic-assisted ultrawideband (UWB) monocycle pulse generation is proposed and experimentally demonstrated based on the wavelength dependence of the half-wave voltage of a Mach-Zehnder modulator (MZM). By employing a single MZM with dual-wavelength injection at around 1310 and 1550 nm, a pair of polarity-reversed monocycle pulses with the full width at half-maximum of about 80 ps and the fractional bandwidth of greater than 160% can be generated. The experiment results agree well with the theoretical prediction. The simple setup and the convenience to control the monocycle pulse polarity are favorable for future applications.

Spectrally resolved reflectometric measurement of polarization mode dispersion in an optical fiber link with polarization-dependent loss.

In an optical fiber link with polarization-dependent loss (PDL), we demonstrate that although the complex polarization mode dispersion vector cannot be fully obtained by the reflectometric measurement, the spectrally resolved differential group delay (DGD) and differential attenuation slope (DAS) can be explicitly determined by such measurements performed simultaneously in the optical frequency domain and the fiber length domain. In principle, this technique can be used to realize the spectrally resolved and spatially resolved measurement of DGD and DAS in an optical fiber link having PDL based on distributed Rayleigh backscattering. We report the experimental result based on the far-end Fresnel reflection to confirm the validity of the proposed method.

Cascaded dynamic eigenstates of polarization analysis for piezoelectric polarization control.

We propose the cascaded dynamic eigenstates (DESs) of polarization to analyze multicomponent polarization control (PC) devices, and achieve the analytical expression of output state of polarization (SOP) as a function of voltage for piezoelectric polarization control (PPC). By measuring the DES at the output port of the device, the prestage DESs will rotate around subsequent ones. Experimental results in PPC confirm the validity of our analysis. The average error of our theoretical output SOP is 1.23 degrees, and the SOP response time is ~10 micros, which is promising to realize a quasi-open-loop high-speed PC.

Spectral-resolved backreflection measurement of polarization mode dispersion in optical fibers.

An improved backreflection technique is proposed to perform the spectral-resolved measurement of polarization mode dispersion (PMD) in optical fibers. This technique is based on the PMD dynamical equation and realized by measuring the polarization state evolutions of the reflected signal in both frequency and time domains. Two experimental setups, employing the far-end Fresnel reflection, are constructed to verify this technique. The agreement between the results of the proposed backreflection technique and the conventional forward technique is observed.

Ultrawideband monocycle generation using cross-phase modulation in a semiconductor optical amplifier.

We propose a novel scheme to generate ultrawideband (UWB) monocycle pulses based on cross-phase modulation (XPM) of a semiconductor optical amplifier (SOA). The proposed system consists of a SOA and an optical bandpass filter (OBF). Due to the XPM, a continuous wave (CW) probe signal is phase modulated by another optical Gauss pulse in the SOA. The OBF will convert the phase modulation to intensity modulation. A pair of polarity-reversed UWB monocycle pulses is achieved by locating the probe carrier at the positive and negative linear slopes of the OBF. Both cases conform to the UWB definition of the Federal Communications Commission.

40 Gb/s all-optical NRZ to RZ format conversion using single SOA assisted by optical bandpass filter.

We propose a novel all-optical format conversion from nonreturn-to-zero (NRZ) to return-to-zero (RZ) based on single semiconductor optical amplifier (SOA) and a detuning optical bandpass filter (OBF). By adopting the ultrafast SOA model associated with intraband mechanism, the 40Gb/s NRZ-to-RZ format conversion is successfully demonstrated with numerical simulation. We investigate the influence of the filter detuning, extinction ratio, conversion efficiency, output pulsewidth, and filter bandwidth. These simulation results confirm the feasibility of our scheme. The proposed scheme is robust and potential for applications in future optical networks.