Integrated electroabsorption-modulated DFB laser by using an improved butt-joint method

An improved butt coupling method is used to fabricate an electroabsorption modulator (EAM) monolithically integrated with a distributed feedback (DFB) laser.The obtained electroabsorption-modulated laser (EML) chip with the traditional shallow ridge exhibits very low threshold current of 12 mA, output power of more than 8 mW,and static extinction ratio of-7 dB at the applied bias voltage from 0.5 to -2.0 V.     

Packaging multi-wavelength DFB laser array using REC technology

Packaging of Distributed feedback （DFB） laser array based on reconstruction=equivalent-chirp （REC） tech- nology is a bridge from chip to system, and influences the practical process of REC chip. In this letter, DFB laser arrays of 4 channel @1 310 nm and 8 channel @1 550 nm are packaged. Experimental results show that both 4 channel @1 310 nm and 8 channel @1 550 nm have uniform wavelength spacing and average side mode suppression ratio （SMSR）〉35 dB. When I=35 mA, we get the total output power 1 mW of 4 channel @1 310 nm, and 227 μW of 8 channel @1 550 nm, respectively. The high frequency characteristic of the packaged chips is also demonstrated, and the requirements of 4× 10 G or even 8× 10 G system can be reached, we demonstrate the practical and low cost performance of REC technology and indicates its potential application in the future fiber-to-the-home （FTTH）.     

Improved performance of complex gain-coupled DFB laser by using tapered grating structure

In this paper, theoretical analysis of antireflection complex gain coupled distributed feedback lasers (CGC-DFB) with tapered grating structure has been presented. Two types of gratings, convex and concave tapered grating with longitudinal variable depth, in active layer have been proposed. Evaluation of flatness parameter variation above threshold condition shows that concave tapered grating improves the stability of CGC-DFB laser against spatial hole burning (SHB) effect. The dependencies of output power, side mode suppression ratio (SMSR) and oscillation wavelength of CGC-DFB laser on convex and concave grating parameters have been studied. Both convex and concave tapered grating CGC-DFB structures have higher output power than conventional CGC-DFB lasers with uniform grating. It is found that, concave tapered grating structure with parameters p ₀?=?15?nm and a ₀?=?0.7 nm has minimum flatness parameter, stable lasing wavelength and flat SMSR profile as a function of current. Theoretical calculation model is based on the numerical solution of coupled wave equations and carrier rate equation by using transfer matrix method. In numerical calculation SHB effect has been assumed.     

Acoustic emission detection using intensity-modulated DFB fiber laser sensor

The bonded distributed feedback(DFB) fiber laser(FL) acoustic emission sensor and the intensity response of the DFB-FL to external acoustic emissions are investigated. The dynamic sensitivity of the DFB-FL is calibrated by a referenced piezoelectric receiver. In the DFB-FL we used here, the minimum detectable signal is2 × 10~(-6)m∕s at 5 kHz. Using wavelet packet technology, the collected signals are analyzed, which confirms that an intensity-modulated DFB-FL sensor can be used to detect acoustic emission signals.     

A narrowband grazing incidence pulsed dye laser improved by using an active multiregion

A novel and simple laser cavity is proposed in which the active medium is separated spatially into three regions in a single dye cell. This configuration permits to improve laser performance in spectral linewidth, purity and energy conversion. Using only one 5 cm-grazing incidence grating as a selective element, a tunable narrow band dye laser has been constructed having a simple-mode spectrum of about 750 MHz depending on dye concentration (5 x 10^-4 M-10^-3 M). Continuous scanning of a 1.3 GHz (FWHM) line over the entire lasing region of the dye is obtained with an efficiency of 6%. The advantages of using an active multiregion are discussed in relevance to possible applications.     

Fringe skeletonizing using an improved derivative sign binary method

A modified derivative sign binary method is proposed to extract fringe skeletons from interferometric fringe patterns. A fringe direction map ranging from 0° to 360° is obtained with an unambiguous relationship between the grayscale and fringe tangent direction. Using this approach, the derivative sign binary map is detected without a fringe direction jump. The dark (light) fringe intensity minimum (maximum) can be extracted automatically to define fringe skeletons. In addition, two different anisotropic one-dimensional filters are described that can be used for further improving the fringe quality. Examples are provided for a holographic interferogram and a Moiré fringe pattern to illustrate applications and benefits of the approach.     

一种改进的数字散斑相关方法用于检测人的口型变化

提出了一种基于数字散斑相关测量技术的口型变化检测技术,该技术以白光数字散斑相关测量方法为基础,根据实际应用的需要,引入重心算法并进行了改进,可以实时地检测人说话时的口型变化。通过实验表明,提出的方法是一种实用的、快速、高精度的口型变化测试方法,可为今后的唇语识别技术奠定基础。     

A double wavelength DFB laser with an identical active area for CWDM

A novel distribute feedback (DFB) laser which gave two different wavelengths under two distinct work conditions was fabricated. The laser consists of two Bragg gratings with different periods corresponding to wavelength spacing of 20 nm in an identical active area. When driving current was injected into one of the different sections separately, two different wavelengths at 1542.4 and 1562.5 nm were realized. The side mode suppression ratio (SMSR) of 45 dB or more both for the two Bragg wavelengths were achieved. The fabricating process of the laser was just the samp as that of traditional DFB laser diode. This device can be potentially used in coarse wavelength division multiplexer (CWDM) as a promising light source and the technology idea can be used to enlarge the transmission capacity in metro area network (MAN).     

A double wavelength DFB laser with an identical active area for CWDM

A novel distribute feedback (DFB) laser which gave two different wavelengths under two distinct work conditions was fabricated. The laser consists of two Bragg gratings with different periods corresponding to wavelength spacing of 20 nm in an identical active area. When driving current was injected into one of the different sections separately, two different wavelengths at 1542.4 and 1562.5 nm were realized. The side mode suppression ratio (SMSR) of 45 dB or more both for the two Bragg wavelengths were achieved. The fabricating process of the laser was just the same as that of traditional DFB laser diode. This device can be potentially used in coarse wavelength division multiplexer (CWDM) as a promising light source and the technology idea can be used to enlarge the transmission capacity in metro area network (MAN).     

High accuracy wavelength locking of a DFB laser using tunable polarization interference filter

A temperature-tunable polarization interference filter (PIF) made of YVO4 crystal has been presented and applied for wavelength locking of a distributed feedback (DFB) semiconductor laser in dense wavelength-division-multiplexing (DWDM) optical communication systems. This new design offers a flexible way to monitor and then lock an operating wavelength of DFB laser to any preselected point without dead spots. The results show that the laser wavelength can be locked with accuracy better than ±0.01 nm with much relaxed requirement on temperature stability of the filter.     

Fabrication of low threshold current monolithic DFB laser with an MMI combiner

We fabricate low threshold current monolithic distributed feedback(DFB) laser with a multi-mode interface(MMI) combiner using butt-joint metal-organic chemical vapor deposition technology with different waveguide structures. Multi-layer mask self-aligned photolithography technology is used to form different waveguides in active and passive regions, respectively. The result shows that the laser threshold current is lower than 10 m A, with 50 d B side-mode suppression ratio.     

DFB fiber laser hydrophone with band-pass response

A distributed-feedback fiber laser hydrophone with band-pass response is presented. The design of the hydrophone aims to equalize static pressure and eliminate signal aliasing of high-frequency acoustic components. Theoretical analysis is presented based on electro-acoustic theory. The experimental results agree well with the theory. The measured underwater responses show that the hydrophone has a pressure sensitivity of -170 dB re:pm/μPa over a bandwidth between 100 Hz and 500 Hz. A sensitivity reduction exceeding -35 dB is observed at 2500 Hz. The tested static pressure sensitivity of the hydrophone is -226 dB. The proposed fiber laser hydrophone of this kind is expected to have important application in deep water fiber-optic sonar systems with anti-aliasing, and the understanding gained through this work can be extended to a guide of hydrophone design for required filtering bandwidth.     

激光自外差相干测量中分布反馈半导体激光器电流调谐非线性的补偿方法

半导体激光器的电流调谐非线性对自外差相干测量的精度影响很大.研究了分布反馈半导体(DFB) 激光器的电流调谐特性,据此提出一种数学模型补偿方法.利用已知光程差下的差拍频率,建立了动态调频 系数的数学模型.以此模型对DFB激光器的电流调谐非线性进行补偿,可以将差拍信号频率预测值的相对误差 减小约3%,提高了系统的测量精度.数学模型补偿方法简化了测量系统的结构,适用于高精度的电流调谐 激光在线测量系统.     

All-optical clock recovery using a ridge width varied two-section partly gain-coupled DFB self-pulsation laser

A 1.55 μm InGaAsP-InP partly gain-coupled two-section DFB self-pulsation laser (SPL) with a varied ridge width has been fabricated. The laser produces self-pulsations with a frequency tuning range of more than 135 GHz. All-optical clock recovery from 40 Gb/s degraded data streams has been demonstrated. Successful lockings of the device at frequencies of 30 GHz, 40 GHz, 50 GHz, and 60 GHz to a 10 GHz sidemode injection are also conducted, which demonstrates the capability of the device for all-optical clock recovery at different frequencies. This flexibility of the device is highly desired for practical uses.     

Analysis of elastoplasticity problems using an improved complex variable element-free Galerkin method

In this paper, based on the conjugate of the complex basis function, a new complex variable moving least-squares approximation is discussed. Then using the new approximation to obtain the shape function, an improved complex variable element-free Galerkin(ICVEFG) method is presented for two-dimensional(2D) elastoplasticity problems. Compared with the previous complex variable moving least-squares approximation, the new approximation has greater computational precision and efficiency. Using the penalty method to apply the essential boundary conditions, and using the constrained Galerkin weak form of 2D elastoplasticity to obtain the system equations, we obtain the corresponding formulae of the ICVEFG method for 2D elastoplasticity. Three selected numerical examples are presented using the ICVEFG method to show that the ICVEFG method has the advantages such as greater precision and computational efficiency over the conventional meshless methods.     

Ultrasonic absorption constant in liquids by an improved optical method

The optical diffraction set up as originally employed byDebye andSears andLucas andBiqdard has been used with various modifications to estimate the intensity of sound fields at two or more points along the axis of an ultrasonic beam travelling in a liquid and thereby to determine the absorption coefficient of the liquid medium. Almost all these methods involve a two step operation with the attendant possibility of errors due to variation in the conditions under which the two observations are made. In the method here reported two axially parallel beams of parallel monochromatic light are made to traverse the liquid normally to the direction of propagation of the sound beam and the resulting diffraction spectra are brought to focus on a common photographic plate. Sound intensities at two points separated by a known distance are thus measured simultaneously under identical conditions. Absorption coefficients calculated for half a dozen liquids by this method are reported. The values compare very favourably with those obtained by other precision methods.     

Flow visualization by an improved double exposure method in holography

Some optical differential interferometric techniques were investigated in order to measure the density distribution in the air jet flow of a small scale flow cell while excluding the effects of the optical distortion of its glass windows. A technique using moiré fringe formation by rotating the reference wave in one exposure of the double exposure method was found to be most suitable for this purpose. High contrast and multiplication of moiré fringes can be obtained by a moiré fringe sharpening and multiplication method.     

Numerical studies of penetration problems by an improved particle method

A particle mapping transportation algorithm was proposed on the basis of the particle-in-cell method.The particles with rectangular influence domains were employed in the transportation algorithm to reduce the numerical fluctuations.Based on the error analysis in the process of particle motion computation,a prediction-correction algorithm was introduced to improve the computational accuracy.Furthermore,the performance of the particle mapping transportation method was evaluated by using the rotation,the slotted disk and the shear advection tests,and the results were compared with other interface reconstruction methods.Finally,the hemispherical projectile penetration into a steel target was numerically simulated.The results showed that the proposed method produced less numerical fluctuations and exhibited clear material interfaces,which indicated that it is accurate and effective.     

An improved method of measuring laser induced pressure transients

Such measurements require a special consideration of the electric setup which substantially affects the interpretation of the signals. In this paper we analyze these considerations and derive an algorithm that permits the correction of measured pressure transients. Received: 26 June 1996/Revised version: 30 October 1996