Forward-scatter frequency-derived distributed optical fibre sensing using the optical Kerr effect

A novel technique is proposed for forward-scatter frequency-derived distributed sensing along a birefringent singlemode optical fibre. This uses a pump probe scheme to generate a signal frequency in forward-scattered light by means of the optical Kerr effect. The sensing action has been demonstrated by applying transverse pressure to a section of the fibre.<>     

Liquid-core optical fibre for voltage measurement using Kerr effect

Liquid-core optical fibre for voltage measurement, based on the Kerr effect, is shown. The measurements are performed for 50 Hz alternating voltage, i.e. for 23?130 kV/m electric fields.     

Temperature dependence of second harmonic generation in germania-doped silica optical fibres

Seeded second harmonic generation (SHG) is compared between room temperature (RT) and liquid N/sub 2/ temperature (LNT) in GeO/sub 2/-doped silica fibres. At RT the SH power grows much more rapidly. The corresponding conversion efficiency after seeding for 2 h is over 20 times larger than at LNT.<>     

Progress in silica optical fibre photosensitivity

A comprehensive survey of photosensitivity in silica optical fibre is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fibre photosensitivity is discussed within the framework of the colour-center or photoelastic densification models.     

Angular dependence of the mode-coupling coefficient in a multimode optical fibre

We derive a simple relationship which gives the angular dependence of the mode-coupling coefficient when the steady-state radiation pattern of the fibre is known. The correlation length and the amplitude of the random bends are deduced for two naked fibres and one sheathed fibre.     

Nondegenerate optical Kerr effect in semiconductors

We calculate the nondegenerate bound electronic nonlinear refractive index n₂(ω₁;ω₂) (i.e., an index change at frequency ω₁ due to the presence of a beam at frequency ω₂) in semiconductors. We calculate this nonlinearity and its dispersion using a Kramers-Kronig transformation on the calculated nondegenerate nonlinear absorption spectrum due to two-photon absorption, electronic Raman and optical Stark effects. The calculated n₂ values and their dispersion are compared to new experimental values for ZnSe and ZnS obtained using a 2-color Z-scan     

Hydraulic pressure dependence of optical loss in jacketed optical fibre

Hydraulic pressure dependence of fibre loss is examined for several jacket structures. It is found that a liquid-filled pipe structure exhibits small loss increase, 0.9 dB/km at a pressure of 500 kg/cm2, and is promising for use in a submarine optical cable     

Signal-level dependence in the recovery rate of irradiated plastic-clad silica fibre

The optical recovery of a plastic-clad silica fibre after gamma irradiation was monitored at a wavelength of 850 nm. The recovery rate over the measured range of 10 s to > 1 h was found to be strongly dependent on the signal power passing through the fibre.     

Kerr effect in an optical passive ring-resonator gyro

The Kerr effect in an optical passive ring-resonator gyro (OPRG) is analyzed considering the optical source coherence. This effect causes the drift to be much greater than the theoretical limit of rotation sensing given by the detector shot noise for an OPRG with high sensitivity. The drift depends not only on the fluctuation of the power splitting ratio between two counter-propagating beams in the resonator, but also on the frequency modulation indices used to set the operating point. Square-wave intensity modulation of the incident beam is also discussed as a way to eliminate the drift. It is found that the ratio of the signal-beam round-trip time in the resonator to the modulation period must be an integer to optimize the drift elimination. From the practical viewpoint, the requirement for the modulation parameters is analyzed numerically.     

Limitations in long haul IM/DD optical fibre systems caused by chromatic dispersion and nonlinear Kerr effect

The power penalty induced by dispersion, Kerr nonlinearity and attenuation is numerically investigated for long haul IM/DD systems with cascaded optical amplifiers. The authors demonstrate that the eye opening is critically dependant on the input mean power.<>     

Analysis of the wavelength dependence of Raman backscatter in optical fibre thermometry

Presents an analysis of the Raman backscatter for optical fibre distributed temperature sensors to quantify the effect of varying the pump wavelength. An optimal pump wavelength was found based on maximising the anti-Stokes backscattered power from the endpoint of the fibre. This optimum pump wavelength was found to vary as the fourth root of the distance to the endpoint of the fibre. The sensitivity of the system response to non-optimum pump wavelengths was also analysed. Results are presented for both direct detection and photon counting schemes.<>     

Compensation for temperature dependence of Faraday effect in diamagnetic materials: application to optical fibre sensors

The temperature dependence of the Faraday effect in a diamagnetic material can be compensated for by varying the polarisation state of the light entering the material as a function of temperature. The authors demonstrate that this can be done automatically by exploiting the temperature dependence of a linear retarder (waveplate).<>     

Passive mode locking of lasers with the optical Kerr effect modulator

A detailed analytical investigation is presented of a nonlinear device termed the optical Kerr effect modulator (OKEM) which is used to passivelyQswitch and mode lock high-power lasers. Experimentally, an OKEM employing two standard quarter-wave plates is used to passively mode lock the Nd:glass laser. The mode-locking threshold dependence upon the parameters of the OKEM transmission function is definitively established. Pulsewidths and spectral measurements are given for the train of ultrashort pulses from the glass laser mode locked with the OKEM using two different Kerr liquids. The analytical and experimental results together indicate that the OKEM technique is a versatile and viable alternative and in addition overcomes most of the shortcomings intrinsic to the saturable absorber technique. The non-resonant nature of the OKEM suggests that it should find immediate application as a passiveQ-switching and mode-locking element for a Variety of lasers, including dye lasers, UV lasers, the CO2laser, and, notably, the high-power iodine laser.     

Infra-red optical loss increase for silica fibre in cable filled with water

Loss increase characteristics of optical fibre in cable filled with water are reported. Drastic loss increase around 1.24 ?m is observed for both graded-index and single-mode fibres. The origin of the loss increase is found to be due to hydrogen gas diffused into the silica glass interstitially.     

保偏SiO_2光波导环形谐振腔温度特性研究

利用低压化学气相淀积(LPCVD)技术研制了Si基SiO2保偏光波导环形谐振腔,通过测试不同温度下的谐振曲线,得到了谐振腔双折射率差温度系数,进而利用琼斯矩阵法建立了谐振腔温度特性分析模型,分析了温度波动对谐振腔两个偏振态输出谐振曲线的影响。分析表明,研制的Si基SiO2保偏光波导环形谐振腔芯片具有较好的温度特性,能在较大温度范围内避免温度波动带来的两个偏振态谐振谷的重叠现象。     

Temperature dependence of the optical properties of Hg1−xCdxTe

The alloy composition of Hg_1−xCd_xTe should be controlled during growth, so that the desired band gap and the lattice-matched layer may be obtained. In-situ spectroscopic ellipsometry, now commercially available, enables one to acquire spectral data during growth. If one knows the optical dielectric function as a function of alloy composition and temperature, the technique can be fully used to monitor and control temperature, the thickness, and the alloy composition. For this purpose, we first obtained temperature dependent spectral data of Hg_1−xCd_xTe by spectroscopic ellipsometry (SE). The spectral data of Hg_1−xCd_xTe with x = 1,0.235, and 0.344 were obtained from room temperature to 800Kin the photon energy range from 1.3 to 6 eV. The spectral data revealed distinctive critical point structures at E₀, E₀+Δ₀, E₁, E₁+Δ₁, E₂(X), and E₂(Σ). Critical point energies decreased and linewidths increased monotonically as temperature increased. The model for the optical dielectric function enabled (i) the critical point parameters to be determined accurately, and (ii) the spectral data to be expressed as a function of temperature within and outside the experimental range.     

Effect of annealing on creation of second-order nonlinearity in twin-hole optical fibre of pure silica

The effect of thermal pre-annealing on the creation of second-order nonlinearity in a pure twin-hole optical fibre thermally poled at 3.5 kV and 280degC for 30 min has been investigated. In unannealed as-drawn fibres, a SON of ~0.18 pm/V was induced at the core-cladding interface. The induced SON showed little polarisation dependence. In fibres pre-annealed at 400degC for 3 h, the induced SON was smaller, decreasing to ~0.09 pm/V in magnitude. In fibres pre-annealed at 800degC for 3 h, no detectable SON was found at the core-cladding interface. Electron-migration along connected existing defects at the core-cladding interface was postulated to be responsible for the frozen-in space-charge field that generated the effective SON observed. Thermal annealing is proposed to have caused defect-annihilation, which resulted in a smaller SON.