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).     

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.     

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.     

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.     

Two-dimensional DFB laser fabricated on dye-doped hybrid zirconia film by soft lithography

A two-dimensional(2D) distributed feedback(DFB) structure is fabricated on dye-doped sol-gel derived hybrid zirconia films by soft lithography.The Q-switched Nd:YAG laser(λ = 532 nm) is used to pump these structures.The lasing emissions of the gain medium doped with Rhodamine 6G(Rh6G) in two perpendicular directions are shown,and the threshold pump energy is measured.     

A fiber bragg grating acceleration sensor interrogated by a DFB laser diode

A fiber Bragg grating (FBG) acceleration sensor interrogated by a DFB laser diode is demonstrated; the sensor is fabricated by packaging a FBG on to a cantilever; the interrogation scheme takes advantage of the intensity modulation of the narrow spectral bandwidth light of a distributed feedback laser diode, when the reflection spectrum curve of a FBG moves due to the strain which is applied on the sensor. The sensor’s response to the frequency and acceleration is measured by the experiment, and the factors which have an impact on the sensor’s sensitivity are also discussed.     

All organic DFB laser enhanced by intermediate high refractive index polymer layer

Performances of a distributed feedback (DFB) organic dye laser were enhanced by introducing an intermediate high refractive index layer of poly(N-vinylcarbazole) (PVCz) laminated between a glass substrate and a laser dye doped active polymer layer. The active layer is consisted of rhodamine 6G and cellulose acetate (CA). Introduction of an intermediate layer allows a single mode lasing. Slope efficiencies of 2.2 and 4.7% and thresholds of 0.3 and 0.14 mJ/cm²/pulse were measured for the waveguides with 1.7 and 3.4 μm active layers, respectively. Furthermore, permanent relief grating on an intermediate layer gave rise to the reduction of the threshold. With increasing in amplitude of the relief grating from 20 to 45 nm, lasing threshold was reduced from 0.18 to 0.04 mJ/cm²/pulse for the waveguide with 1.7 μm active layer. The slope efficiency increased from 3.5 to 4.2%.     

Stabilized DFB laser system with large tuning range

We propose, design, and realize a compact stabilized laser system that can be tuned within 24 GHz automatically.This laser system consists of two distributed feedback(DFB) lasers, one of which is reference and locked to the D2 line of ~(87)Rb, the other laser is a slave that is locked to the reference laser via a loop servo. We measured the frequency of the beating signal of the two lasers and generated an error signal, which controlled the frequency of the slave laser to close the loop. We compressed the fluctuation of the beating signal's frequency to less than 1 MHz.Furthermore, the system can also automatically determine and control whether the slave is red detuned or blue detuned to the reference. The dimensions of our laser system are about 15 cm × 20 cm × 10 cm. This kind of laser system can be applied in many important applications, such as atomic interferometer and cold atomic clock.