Graphene-deposited photonic crystal fibers for continuous refractive index sensing applications.

We present a pilot demonstration of an optical fiber based refractive index (RI) sensor involving the deposition of graphene onto the surface of a segment of a photonic crystal fiber (PCF) in a fiber-based Mach-Zehnder Interferometer (MZI). The fabrication process is relatively simple and only involves the fusion splicing of a PCF between two single mode fibers. The deposition process relies only on the cold transfer of graphene onto the PCF segment, without the need for further physical or chemical treatment. The graphene overlay modified the sensing scheme of the MZI RI sensor, allowing the sensor to overcome limitations to its detectable RI range due to free spectral range issues. This modification also allows for continuous measurements to be obtained without the need for reference values for the range of RIs studied and brings to light the potential for simultaneous dual parameter sensing. The sensor was able to achieve a RI sensitivity of 9.4 dB/RIU for the RIs of 1.33-1.38 and a sensitivity of 17.5 dB/RIU for the RIs of 1.38-1.43. It also displayed good repeatability and the results obtained were consistent with the modeling.

Dark pulse generation in fiber lasers incorporating carbon nanotubes.

We demonstrate the generation of dark pulses from carbon nanotube (CNT) incorporated erbium-doped fiber ring lasers with net anomalous dispersion. A side-polished fiber coated with CNT layer by optically-driven deposition method is embedded into the laser in order to enhance the birefringence and nonlinearity of the laser cavity. The dual-wavelength domain-wall dark pulses are obtained from the developed CNT-incorporated fiber laser at a relatively low pump threshold of 50.6 mW. Dark pulses repeated at the fifth-order harmonic of the fundamental cavity frequency are observed by adjusting the intra-cavity polarization state.

Three-dimensional graphene based passively mode-locked fiber laser.

We present an all-fiber passively mode-locked fiber laser incorporating three-dimensional (3D) graphene as a saturable absorber (SA) for the first time to the best of our knowledge. The 3D graphene is synthesized by template-directed chemical vapor deposition (CVD). The SA is then simply formed by sandwiching the freestanding 3D graphene between two conventional fiber connectors without any deposition process. It is demonstrated that such 3D graphene based SA is capable to produce high quality mode-locked pulses. A passively mode-locked fiber laser is constructed and stable output pulses with a fundamental repetition rate of ~9.9 MHz and a pulse width of ~1 ps are generated from the fiber laser. The average output power of the laser is ~10.5 mW while the output pulse is operating at single pulse region. The results imply that the freestanding 3D graphene can be applied as an effective saturable absorption material for passively mode-locked lasers.

Graphene-based passively mode-locked bidirectional fiber ring laser.

We present an all-fiber bidirectional passively mode-locked soliton laser with a graphene-based saturable absorber for the first time to the best of our knowledge. Our design includes a four-port circulator to introduce different sections of cavity for the two counter-propagating pulses, so they have distinct output characteristics. Simultaneous bidirectional operation is achieved by appropriately adjusting the net cavity birefringence and loss. In the clockwise direction, the laser emits ~750 fs pulses at 1561.6 nm, with a repetition rate of 7.68 MHz. In the counter clockwise direction, the central wavelength, pulse width, and repetition rate are 1561.0 nm, ~850 fs, and 6.90 MHz, respectively.

Enhanced stability of dispersion-managed mode-locked fiber lasers with near-zero net cavity dispersion by high-contrast saturable absorbers.

We experimentally investigate the stability of dispersion-managed mode-locked fiber lasers using carbon-nanotube-based saturable absorbers (SAs) with different modulation depths. An unstable operation region of the mode-locked fiber laser with near-zero net cavity dispersion is observed, where the laser produces random pulse burst rather than stable pulse train. Through the implementation of high-contrast SAs in the laser, the unstable region is found to be shrunk by ~31.3% when the modulation depth of the SAs increases from 6.4% to 12.5%. The numerical simulation is consistent with the experimental observation.

Enhancement of thermal damage threshold of carbon-nanotube-based saturable absorber by evanescent-field interaction on fiber end.

We present a scheme of fiber-connector-type carbon-nanotube-based saturable absorber (CNT-SA) with enhanced thermal damage threshold, in which the CNTs are deposited on the fiber connector end in a ring pattern for evanescent-field interaction instead of direct interaction. The thermal damage threshold of such CNT-SA is found to be increased by around 130% compared with an evenly deposited one. An all-fiber Fabry-Perot (FP) linear cavity passively mode-locked laser is further constructed incorporating the prepared CNT-SA, where the optical power is confined in a relatively short laser cavity to investigate the thermal damage threshold and the performance of the CNT-SA. Stable output pulses with a fundamental repetition rate of 211.84 MHz and a pulse width of 680 fs are generated from the fiber laser. The mode-locking operation can be maintained an intra-cavity average power of 30 mW, indicating that the CNT-SA can withstand a relatively high optical power without performance degradation.

Four-wave-mixing-based wavelength conversion using a single-walled carbon-nanotube-deposited planar lightwave circuit waveguide.

We demonstrated a single-walled carbon-nanotube-deposited planar lightwave circuit (PLC) waveguide for four-wave-mixing (FWM)-based wavelength conversion. FWM is generated from the interaction between the propagating light through the PLC waveguide and the deposited carbon nanotubes (CNTs) on the overcladding-removed core of the waveguide. The third-order nonlinearity of the CNTs is originated from the interband transitions of the pi electrons causing nonlinear polarization similar to other highly nonlinear organic optical materials. FWM-based tunable wavelength conversion of a 10 Gbit/s non-return-to-zero signal is achieved with a power penalty of 3 dB in the bit-error-rate measurements. To our knowledge, this is the first demonstration of a CNT-technology-based device for integrated photonic applications.

Four-wave mixing in a single-walled carbon-nanotube-deposited D-shaped fiber and its application in tunable wavelength conversion.

We report the first experimental observation of four-wave mixing (FWM) in single-walled carbon nanotubes (SWCNTs) deposited on a Dshaped fiber. FWM-based tunable wavelength conversion of a 10 Gb/s nonreturn-to-zero signal is demonstrated using a 5-centimeter-long CNT-deposited D-shaped fiber. A power penalty of 4 dB power is obtained in the 10 Gb/s biterror- rate measurements.

A widely tunable wavelength converter based on nonlinear polarization rotation in a carbon-nanotube-deposited D-shaped fiber.

We demonstrate widely tunable wavelength conversion based on cross-phase modulation induced nonlinear polarization rotation in a carbon nanotubes (CNTs) deposited D-shaped fiber. A 5-centimeter-long CNT-deposited D-shaped fiber is used as the nonlinear medium for wavelength conversion of a 10 Gb/s non-return-to-zero signal. Wavelength tunable converted signal over 40 nm is obtained with around 2.5-dB power penalty in the bit-error-rate measurements.

Four-wave mixing based widely tunable wavelength conversion using 1-m dispersion-shifted bismuth-oxide photonic crystal fiber.

We demonstrate widely tunable wavelength conversion based on four-wave mixing using a dispersion-shifted bismuth-oxide photonic crystal fiber (Bi-PCF). A 1-meter-long Bi-PCF is used as the nonlinear medium for wavelength conversion of a 10 Gb/s non-return-to-zero (NRZ) signal. A 3- dB working range of the converted signal over 35 nm is obtained with around 1-dB power penalty in the bit-error-rate measurements.

Extinction ratio improvement by pump-modulated four-wave mixing in a dispersion-flattened nonlinear photonic crystal fiber.

We demonstrate extinction ratio improvement by using pump-modulated four-wave mixing in a dispersion-flattened nonlinear photonic crystal fiber. A 6-dB improvement in the extinction ratio of a degraded return-to-zero signal has been achieved. A power penalty improvement of 3 dB at 10(-9) bit-error-rate level is obtained in the 10 Gb/s bit-error-rate measurements.

A prospective study of group B streptococcal colonization in parturient mothers and their infants.

The objective of this study was to investigate the rates of group B streptococcal colonization among parturients within the 24 hours prior to delivery and colonization of their newborns. It was also to identify high risk factors. 204 parturients were randomly selected in the Alexandra Hospital, Singapore. Swabs for culture were taken from the maternal vagina and throat and the neonate's ears, throat and umbilicus. In this study it was found that vaginal colonization in the mother is significantly associated with neonatal colonization. Among the various ethnic groups, Malays and Indians/Pakistanis are at a higher risk of having vaginal colonization. All other factors studied, however, failed to show any influence on neonatal colonization and thus appear to have had no forewarning value.

Successful outcome in antepartum pulmonary embolism--a case report and review of incidence, diagnosis and management.

Antepartum pulmonary embolism is a condition carrying a high maternal mortality, yet treatment with anti-coagulation can reduce the mortality to less than 1%. The true incidence is difficult to establish because of problems in confirming the clinical diagnosis. We report here a case of maternal pulmonary embolism complicating pre-eclampsia and hypertension. The difficulties in establishing a firm diagnosis are high-lighted. A brief review of the incidence, predisposing factors, diagnosis and management is presented. The total management of the patient is discussed in some detail.

A questionnaire survey on attitudes and understanding towards mental disorders.

OBJECTIVES. To obtain information about basic knowledge towards mental disorders and to evaluate public attitudes towards mental disorders in the Hong Kong Chinese population. METHODS. Questionnaires which collected basic demographic information, opinions about potential stigmas and myths, and knowledge on case vignettes depicting fictional characters with symptoms of mental illness were delivered to subjects in a secondary school, 2 homes for the elderly, a private housing estate, and a public housing estate in Hong Kong. RESULTS. Completed questionnaires were collected from 1035 subjects. In general, the participants' acceptance of mental illness was good. Regular contacts with such patients were associated with better knowledge (t = -2.71, p < 0.01) and better acceptance (t = 2.77, p < 0.01) of mental illness. Younger participants aged 15 to 19 years had a lower level of knowledge about mental health problems compared with other age-groups (p < 0.001). CONCLUSIONS. Personal contact with people with mental illness may help to improve knowledge and acceptance. Younger people in secondary school should be the target and prioritised group for mental health education. Apart from the delivery of mental health knowledge, strategies to increase social contact of the public with people having mental illness could be considered in the design and implementation of anti-stigma programmes.

Prenatal diagnosis of cri-du-chat syndrome: importance of ultrasonographical markers.

Cri-du-chat syndrome is a chromosomal abnormality involving a 5p deletion and is characterised by a cat-like cry, mental retardation, microcephaly and abnormal facial features. We report a case of prenatally-diagnosed cri-du-chat syndrome. Although PAPP-A was low at first trimester screening (FTS), the combined risks of trisomies 21, 18 and 13 were low. Amniocentesis was, however, carried out following the ultrasonographical observation of a severely hypoplastic nasal bone, cerebellar hypoplasia, choroid plexus cyst and a single umbilical artery during the second trimester. This case report highlights the importance of careful examination of basic and extended foetal biometry and structures, as well as soft markers for the detection of rarer chromosomal abnormalities that may be missed at FTS.