DS-OCDMA encoder/decoder performance analysis using optical low-coherence reflectometry

Direct-sequence optical code-division multiple-access (DS-OCDMA) encoder/decoder based on sampled fiber Bragg gratings (S-FBGs) is characterized using phase-sensitive optical low-coherence reflectometry (OLCR). The OLCR technique allows localized measurements of FBG wavelength and physical length inside one S-FBG. This paper shows how the discrepancies between specifications and measurements of the different FBGs have some impact on spectral and temporal pulse responses of the OCDMA encoder/decoder. The FBG physical lengths lower than the specified ones are shown to affect the mean optical power reflected by the OCDMA encoder/decoder. The FBG wavelengths that are detuned from each other induce some modulations of S-FBG reflectivity resulting in encoder/decoder sensitivity to laser wavelength drift of the OCDMA system. Finally, highlighted by this OLCR study, some solutions to overcome limitations in performance with the S-FBG technology are suggested.     

Jaggedness-free millimeter-resolution low coherence reflectometry

We report a millimeter resolution optical low coherence reflectometer (OLCR) that exhibits reduced jaggedness in the Rayleigh backscatter signal. This OLCR was achieved by using an erbium-doped superfluorescent fiber source that can tune narrow-band superfluorescence (~0.2 nm full-width at half-maximum) over a 3-nm range with an output of -8 dBm, The signal averaging that resulted from wavelength tuning with this source efficiently reduced the jagged fluctuation to ±1.4 dB. The spatial resolution was 1.2 mm, and the hidden spaces defined by the full-widths at -20 dB and -60 dB maximum of a Fresnel response of the OLCR were 6 mm and 1.2 cm, respectively. These two hidden spaces are at least ten times narrower than those of a previously reported photon-counting OTDR, although their spatial resolutions are roughly the same. The OLCR enabled the weak Rayleigh backscattering near a connector joint to be measured with a dynamic range of 18 dB without any deconvolution. We confidently expect that this OLCR will be applied to short-haul optical fiber fault location     

New methodology to evaluate the performance of ring resonators using optical low-coherence reflectometry

This paper describes the efficient implementation of optical low-coherence reflectometry (OLCR) measurements to evaluate the performance of InP-based high-index contrast ring resonators. Using examples of racetrack ring resonators, this paper shows here for the first time that all characteristic parameters relevant to resonator design (coupling coefficient k, propagation losses a, and optical cavity length L), and ultimately its performance, can be extracted in a straightforward manner. This is accomplished by introducing a new methodology that implicates OLCR measurements in transmission and also reflection modes as an alternative approach, in comparison with conventional spectral analysis, to extract resonator design parameters.     

Optical low coherence reflectometer with a 47-dB dynamic rangeachieved by using a fluoride-based erbium-doped fiber amplifier

We describe a jaggedness-free optical low coherence reflectometer (OLCR) with a high power tunable narrow-band light source which employs a fluoride-based erbium-doped fiber amplifier. The use of the amplifier simplifies the structure of the source and enables us to generate narrow-band light with a power of 18±0.2 dBm in the 1530-1560 nm wavelength range and with a reduced background level in each spectrum. The OLCR achieves a dynamic range of 47 dB and the signal fluctuations caused by residual speckle-like noise in the Rayleigh backscattering measurement are less than ±1 dB. This is the best data yet obtained with a diode-pumped fiber amplifier. The diagnosis of fiber-optic attenuators is successfully demonstrated using the OLCR     

Improvement in signal-to-noise ratio of Rayleigh backscatteringmeasurement using optical low coherence reflectometry

I have calculated the signal-to-noise ratio (S/N) of fluctuations remaining in Rayleigh backscattered signal distributions obtained after performing moving and frequency averaging with an optical low coherence reflectometer (OLCR). From the calculation, I obtained the number of measurements needed for each averaging that achieves the required S/N with the minimum sampling data. Specifically, I derived the numbers of measurements numerically for Gaussian and Lorentzian light spectra, respectively. The result was successfully applied to diagnosis on long silica-based waveguides by using an OLCR with a high-power narrow-band light source     

Bragg gratings in multimode and few-mode optical fibers

Bragg gratings in optical fibers in multimode propagation are investigated experimentally and theoretically. Bragg gratings formed in optical fibers in multimode propagation show multiple reflection peaks or multiple transmission dips in the reflection or transmission spectra, respectively. For standard graded-index multimode fiber, the number of reflection peaks of a Bragg grating depends on excitation condition of propagating modes. The number of reflection peaks of a Bragg grating at around 1.55 μm is 19 for highly multimode excitation and 3-4 for lower order mode excitation. We analyze the phase-matching conditions of the propagating modes and identify half of the reflection peaks as the reflection to the same mode and the rest as the reflection to the neighboring modes. In dispersion-shifted fiber, a Bragg grating at around 0.8 μm in three-mode propagation shows three reflection peaks in the reflection spectrum. The temperature dependence of each reflection peak is similar to that of a conventional Bragg grating in single-mode fiber. Polarization dependence measured on a Bragg grating in multimode graded-index fiber is negligible. An advantage of Bragg gratings in multimode fiber (MMF) and the applications are discussed     

Loss distribution measurement of silica-based waveguides by using ajaggedness-free optical low coherence reflectometer

The loss distributions in silica-based waveguides are successfully measured using a jaggedness-free optical reflectometer (OLCR). The OLCR reduces jagged fluctuations which appear in Rayleigh backscattering measurements undertaken with conventional OLCRs to within ±1 dB by averaging the wavelength-dependent Rayleigh backscatter signals. Constant loss distributions and a step-like loss increase in the waveguides were clearly observed     

低相干光干涉法测量光子晶体光纤延时

对相位敏感型低相干光干涉(OLCR)法延时测量系统进行了理论分析,建立了相关数学模型,搭建了基于非平衡迈克尔逊干涉仪的OLCR测量装置,以掺铒光纤放大器(EDFA)自发宽谱光作光源,对光子晶体光纤(PCF)延时(1540～1560nm)进行测量,取得0.14ps左右的测量精度。利用该系统测量光学元件参数,多采用元件末端面反射光与参考光干涉,但对光纤等器件的延时参数进行测量时,利用透射光会更加方便。     

微波静磁波模式特性分析

全面分析了磁光薄膜波导中磁化方向对微波静磁波传播模式的影响。给出了不同模式的静磁波色散方程和带宽的一般表达式,首次完整地展现了静磁波的模式分布图。所得结论可用于分析倾斜磁场在改善基于静磁波的新型磁光B ragg器件衍射性能方面所起的作用。     

Wavelength stabilization of a DBR laser using an in-fiber Braggfilter

A control loop that stabilizes the wavelength of a tunable distributed-Bragg-reflector (DBR) laser is discussed. An in-fiber Bragg grating is used as the wavelength reference. Over a 25-hour period, this control loop held the laser wavelength constant to within 0.022 nm. This variation is traced to the temperature dependence of the in-fiber Bragg grating and can be reduced by controlling the grating's temperature     

Transverse Bragg-resonant enhancement of Modulation and switching

We demonstrate theoretically that the electrooptic phase retardation, hence, modulation, can be enhanced very substantially in transverse Bragg resonance (TBR) waveguides. This enhancement is due fundamentally to the strong dependence of the dispersion of the TBR waveguide on the Bragg condition. Both theoretical and numerical analysis show that this enhancement can be used to improve the performance of directional coupler switches and electroabsorption modulators, leading potentially to major reductions in the device size or the switching voltage/current.     

线性啁啾光纤布喇格光栅反射谱的数值模拟

为了研究线性啁啾光纤布喇格光栅的特性,并进一步把它用于光纤激光器上,介绍了线性啁啾光纤布喇格光栅的耦合模理论,采用4阶Runge-Kutta法和传输矩阵法结合控制变量法,对线性啁啾光纤布喇格光栅反射率与啁啾系数、半峰全宽与光栅长度、反射率与直流纤芯折射率改变量之间的关系进行了数值模拟。结果表明,线性啁啾光纤布喇格光纤可以展宽带宽。基于这个结论,提出了利用线性啁啾光纤布喇格光栅作为光纤激光器腔镜,使输出谱线展宽,从而可作为宽带光源使用的方案。     

Simultaneous strain and temperature measurement using a singlefibre Bragg grating

A new scheme for simultaneous strain and temperature measurement using a single fibre Bragg grating is proposed. The Bragg grating was written on the splice joint between two fibres and has two Bragg wavelengths, which show the same strain dependence but different temperature response and hence can be used for strain/temperature discrimination     

Dependence of threshold current and linearity on Bragg wavelengthfor grating-surface-emitting lasers

We report on a systematic experimental study of the dependence of the threshold current and power-current linearity on the detuning of the Bragg wavelength from the gain peak for grating-surface-emitting lasers. Minimum threshold currents were obtained for lasers emitting at wavelengths 2 to 9 nm on the long wavelength side of the gain peak, depending on the cavity length. Threshold currents as low as 98 A/cm² were obtained at the optimum Bragg wavelength. A strong dependence of the linearity on the detuning was found and the lasers showed good linearity at the wavelengths yielding optimum low threshold currents     

Temperature and polarisation insensitive Bragg gratings realised onsilica waveguide on silicon

A new technique based on the use of polymer to drastically decrease the temperature sensitivity of Bragg gratings realised on planar silica waveguides deposited on silicon is proposed. Moreover, this technique suppresses the polarisation dependence of the Bragg filters     

GaxIn1-xAsyP1-y/InP injection laser partially loaded with first-order distributed Bragg reflector

GaInAsP/InP distributed Bragg reflector (DBR) lasers with a first-order grating were demonstrated experimentally for the first time at a wavelength of 1.3 μm. Single longitudinal mode oscillation was obtained at low temperature, and the temperature dependence of the lasing wavelength was 0.7-0.8 Å/deg. The equivalent refractive index of GaInAsP at the lasing wavelength of 1.3 μm was 3.50 at 186 K.     

啁啾光栅解调的准分布式光纤Bragg光栅传感器

为了提高光纤Bragg光栅(FBG)的应用范围.提出一种线性啁啾光栅(CFBG)解调的准分布式FBG传感系统.利用波导理论分析了CFBG特性;利用传输矩阵法推导了CFBG反射谱模型及波长与相位延迟的关系,并给出了相位延迟曲线.实验表明:所设计的系统应变测量范围为0～2000 με,温度测最范围为0～80℃;相位变化与被...     

Features of the dependence of the diffraction efficiency of an acousto-optic Bragg cell with multielement traveling wave transformer on its geometric parameters

An equation for calculation of the diffraction efficiency of an acousto-optic Bragg cell with multielement traveling wave transformer taking into account the exponential distribution of the acoustic field along of the transformer is obtained. The results of theoretical and experimental studies of the dependence of the diffraction efficiency of the Bragg cell on the number of radiating elements in the piezoelectric traveling wave transformer are given. Nonlinear behavior of the dependence of the diffraction efficiency on the number of radiators in the considered transformer is analyzed.     

CW operation of 1.5 ~ 1.6 ?m wavelength GaInAsP/InP buried-heterostructure integrated twin-guide laser with distributed Bragg reflector

A 1.5 ~ 1.6 ?m GaInAsP/InP buried-heterostructure integrated twin-guide laser with distributed Bragg reflector (BH-DBR-ITG laser) was realised, for the first time, and CW operation was achieved up to 255 K. Single-wavelength operation was obtained at temperatures between 228 K and 245 K with the temperature dependence of lasing wavelength of 10 ?/deg. At 233 K, the threshold current, the output power and the differential quantum efficiency were 110 mA, 2.2 mW and 4.8%/facet, respectively.     

A tunable wavelength-conversion laser

A wavelength-conversion laser was fabricated using monolithic integration of a bistable laser diode and a wavelength-tunable distributed Bragg reflector (DBR) laser. This device converts an input light signal with a certain wavelength to output light with a tunable wavelength over 3.5 nm. Input power required for switching is investigated, and its resonant dependence on input wavelength is revealed. Input polarization is also discussed, and suppression of crosstalk is demonstrated. This device's turn-off switching response is greatly influenced by the light power of the input signal as well as bias current, and the first 1 Gb/s operation is achieved in optimum conditions for fast turn-off and stable turn-on