High-Power Distributed Feedback Laser Diodes Emitting at 820nm

By etching a second-order grating directly into the Al-free optical waveguide region of a ridgewaveguide（RW） AlGaInAs/AlGaAs distributed feedback（DFB） laser diode,a front facet output power of 30mW is obtained at about 820nm with a single longitudinal mode. The Al-free grating surface permits the re-growth of a high-quality cladding layer that yields excellent device performance. The threshold current of these laser diodes is 57mA,and the slope efficiency is about 0.32mW/mA.

Switchable dual-wavelength erbium-doped fiber laser with a tilted fiber grating

A dual-wavelength erbium doped fiber laser with a tilted fiber Bragg grating and photonic crystal fiber is proposed and demonstrated. In the laser, a 2W EDFA provides gain for all the laser lines; the highly nonlinear photonic crystal fiber introduces dynamic energy transfer between the two wavelengths caused by four wave mixing effect, so that a stable dual- wavelength oscillation at room temperature is implemented. Different switching modes can be achieved by adjusting the lateral offset between the fiber grating and the guiding single mode fiber or by varying the state of polarization in the laser cavity. The maximum of output power of the laser has reached 314mW.

Multi-wavelength fiber laser based on broadband fiber grating and HiBi fiber loop mirror

A fiber laser based on broadband C-band fiber grating (CFG) and high birefringence (HiBi) fiber loop mirror (FLM) is demonstrated, which uses the comb-like reflection performance of the HiBi FLM. Under different polarization states, different output lasers are gained by choosing the polarization states of the light in the cavity using the polarization controller. By this method, a single wavelength or dual wavelength laser beam can be output, and multi-wavelength oscillates can be achieved.

High sensitivity micro-displacement sensor based on fiber Bragg grating and amplification substrate

A micro-displacement sensor based on fiber Bragg grating(FBG) is proposed. The device consists of a pair of FBGs with different central wavelengths fabricated by femtosecond laser phase mask method and a metal substrate with lever structure. The displacement is amplified by lever structure and it converts into axial tension of FBG, which has a high displacement sensitivity. The amplification factors obtained by theoretical analysis and finite element simulation are 2.67 and 2.50, respectively. The experimental results show that in the range of 0-50 μm the shift of FBG center wavelength is linearly related to the displacement of measured object and displacement sensitivity reaches 121 pm/μm. In addition, the cascaded FBG is used to compensate the temperature.

Dynamic Equations and Nonlinear Dynamics of Cascade Two-Photon Laser

We derive equations and study nonlinear dynamics of cascade two-photon laser, in which the electromagnetic field in the cavity is driven by coherently prepared three-level atoms and classical field injected into the cavity. The, dynamic equations of such a system are derived by using the technique of quantum Laugevin opera.tots, and then arre studied numerically under different driving＂ conditions, The results show that trader certain conditions the cascade twophoton laser can generate chaotic, period doubling, periodic populations, atomic coherences, and injected classical field, stable and bistable states. Chaos can be inhibited by atomic In ,addition, no chaos occurs in optical bista.bility.

Maximum and Continuous Wavelength Tuning Ranges of a Grating External- cavity Laser Diode

The wavelength tuning ranges of a grating external-cavity laser diode (ECLD) have been studied by the equivalent cavity method. The maximum tuning range (MTR) and the continuous tuning range (CTR), which are related to the maximum and the minimum threshold carrier densities, are deduced from the threshold condition. We define a ratio of the CTR to the MTR. This ratio is only determined by the reflectivities of the external and internal facets of the ECLD. The analysis shows that there is an appropriate combination of the external and internal-cavity reflectivities to obtain a given CTR in the design of an ECLD.

All-fiber Based Er^(3+)∶Yb^(3+) Co-doped Fiber Laser

An all-fiber based Er~ 3+ ∶Yb~ 3+ co-doped double clad fiber laser operating at 1550nm is demonstrated. By using 9m long Er~ 3+ ∶Yb~ 3+ co-doped fiber(EYDF) as the gain medium, and using a pair of fiber Bragg gratings as wavelength filters, the line-width of the output laser is as narrow as 0.2nm and the output power is more than 6mW. The fluorescent effect of the laser before its emission is also studied. And it is found that the Er~ 3+ ∶Yb~ 3+ co-doped double-clad fiber laser also exhibits a high gain for Yb~ 3+ transition near 1080nm.

A method of beam combination of high-power incoherent fiber laser

Diffraction efficiency of grating plays an important role in output power of incoherent fiber laser beam combination. Through theoretic analysis and numerical simulations it has been proved that the diffraction efficiency would increase with the decrease of grating frequency and wavelength bandwidth. On the condition that the width of a fiber array is fixed at W=I 0 cm, an optimum grating frequency were numerically simulated as f=230 mm^-1. Also an unequal interval method was proposed to improve the system efficiency of diffraction into 0.4293, which is higher than 0.3824 under the equal interval condition.

Diffraction Properties of Blazed Gratings Illuminated with Broad-bandwidth and Divergent Beam

Far-field intensity and diffraction efficiency of the blazed reflection gratings illuminated with broad-bandwidth and divergent beam are investigated.When the spectral width and divergence of the incident beam with a constant energy increase,the maximum intensity decreases,and the half width at e-2 of the maximum intensity becomes wider.Diffraction efficiency has no deterioration for the blazed grating with a proper groove shape even when the incident light contains a broad range of wavelengths and comes from a wide range of angles.

Multiwavelength Actively Mode-locked Fiber Laser with a Double-ring Configuration and Integrated Cascaded Sampled Fiber Bragg Gratings

A modified multiwavelength actively mode-locked fiber ring laser is proposed and experimentally demonstrated. In this kind of laser, stable multiwavelengths lasing is achieved by integrating cascaded sampled fiber Bragg gratings(SFBGs) into the laser cavity. To implement actively mode-locking technique, a double-ring cavity configuration is used to assure that the cavity lengths for all wavelengths lasing are identical. Thus, simultaneous mode locking of all wavelengths has been successfully achieved by using the same mode-locking signal.

Optical diffraction gratings embedded in BK-7 glass by low-density plasma formation using femtosecond laser

The optical embedded diffraction gratings with the internal refractive index modification in BK-7 glass plates were demonstrated using low-density plasma formation excited by a high-intensity femtosecond （130 fs） Ti： sapphire laser （λp=790 rim）. The refractive index modifications with diameters ranging from 400 nm to 4 gm were photoinduced after plasma formation occurred upon irradiation with peak intensities of more than 1 ×10^13 W/cm2. The graded refractive index profile was fabricated to be a symmetric around the center of the point at which low-density plasma occurred. The maximum refractive index change （An） was estimated to be 1.5x10 2. Several optical embedded gratings in BK-7 glass plate were demonstrated with refractive index modification induced by the scanning of low-density plasma formation.

冲击拉伸载荷下材料大变形的测量方法

由于橡胶基复合材料在冲击拉伸载荷下瞬时变形大 ,利用应变片等传统测量方法很难准确测得其应力一应变关系 .针对橡胶基复合材料 ,利用应变片等传统测量方法准确测得应力 -应变关系 ,提出在冲击拉伸载荷下橡胶复合材料大变形测量方法 .这种方法的原理是利用激光 -光栅将材料的大变形转换成相应的光脉冲数 ,通过确定脉冲数可测量变形值 .实验表明 :这种方法原理可行 ,测量范围宽、精度高、速度快、实现简单 ,且易于信号自动纪录和数据处理 .

Modified Holographic Exposure to Fabricate Varied Bragg Grating in an Identical Chip

A new fabricating method is demonstrated to realize two different Bragg gratings in an identical chip using traditional holographic exposure. Polyimide is used to protect one Bragg grating during the first period. The technical process of this method is as simple as that of standard holographic exposure.

Laser Doppler Vibrometer Without Directional Ambiguity Using Rectangular Phase Grating

The two-phase detection method for directional discrimination in laser Doppler measurements is discussed.The diffraction efficiency of a sin- gle period rectangular phase grating is analysed and a kind of back-scattered laser Doppler vibrometer without directional ambiguity using the single peri- od rectangular phase grating as the beam-combiner described.The principles of this kind of vibrometer are explained in detail,and some experimental re- sults are given.In this kind of vibrometer,the rectangular phase grating, without the zero diffracted order and even orders,is used to eliminate use- less stray light and to combine the useful signal light.Differential electronics is employed to reject signal noise.Therefore,the signal-to-noise ratio of Doppler signals and the measurement accuracy of the instrument are im- proved and the range of application is expanded.

A temperature sensor based on switchable dual- wavelength fiber Bragg grating laser with a semiconductor saturable absorber mirror

A temperature sensor based on a switchable dual-wavelength fiber Bragg grating （FBG） laser with a semiconductor saturable absorber mirror （SESAM） is presented and demonstrated experimentally. The repetition rate of Q-switched pulses is -17 kHz. The results demonstrate that the measured temperature has good linearity to the wavelength spacing of the two lasing wavelengths and has a temperature sensitivity of 21 pm/℃ covering a range of-10--22 ℃. The ex- perimental results prove the feasibility of the proposed temperature sensor.

Fiber Laser Sensor Based on a Phase-Shifted Chirped Grating for Acoustic Sensing of Partial Discharges

Acoustic emission monitoring is often used in the diagnosis of electrical and mechanical incipient faults in the high voltage apparatus. Partial discharges are a major source of insulation failure in electric power transformers, and the differentiation from other sources of acoustic emission is of the utmost importance. This paper reports the development of a new sensor concept - a fiber laser sensor based on a phase-shifted chirped fiber grating - for the acoustic emission detection of incipient faults in oil-filled power transformers. These sensors can be placed in the inner surface of the transformer tank wall, not affecting the insulation integrity of the structure and improving fault detection and location. The performance of the sensing head is characterized and compared for different surrounding media： air, water, and oil. The results obtained indicate the feasibility of this sensing approach for the industrial development of practical solutions.

Multi-type sensor placement and response reconstruction for structural health monitoring of long-span suspension bridges

This study is devoted to the experimental validation of the multi-type sensor placement and response reconstruction method for structural health monitoring of long-span suspension bridges. The method for multi-type sensor placement and response reconstruction is briefly described. A test bed, comprising of a physical model and an updated finite element （P-E） model of a long-span suspension bridge is also concisely introduced. The proposed method is then applied to the test bed; the equation of motion of the test bed subject to ground motion, the objective function for sensor location optimization, the principles for mode selection and multi-type response reconstruction are established. A numerical study using the updated FE model is performed to select the sensor types, numbers, and locations. Subsequently, with the identified sensor locations and some practical considerations, fiber Bragg grating （FBG） sensors, laser displacement transducers, and accelerometers are installed on the physical bridge model. Finally, experimental investigations are conducted to validate the proposed method. The experimental results show that the reconstructed responses using the measured responses from the limited number of multitype sensors agree well with the actual bridge responses. The proposed method is validated to be feasible and effective for the monitoring of structural behavior of longspan suspension bridges.

A widely tunable fiber ring laser with closed loop control based on high-precision stepper motor

A tunable single-longitudinal mode erbium-doped fiber ring laser based on stepper motor and closed loop control is proposed and demonstrated. The system consists of an erbium-doped fiber （EDF）, a tunable fiber Bragg grating （FBG） filter and a wavelength detector. The characteristics of output laser, such as output power, power stability and 3-dB linewidth, are investigated in the operation range of I 531-1 569 nm. The repeated experimental results of the fiber laser show that the 3-dB linewidth is less than 17 ps, the side-mode suppression ratio （SMSR） is up to 60 dB, the outout Dower is up to 1.37 dBm. and the Dower variation is less than 0.61 dR

Single-row laser beam with energy strengthened ends for continuous scanning laser surface hardening of large metal components

For laser surface hardening of metal components with large superficies,a binary grating is proposed to generate single-row laser beam with proportional-intensity diffractive orders.To obtain a uniform hardened band distribution and improve the wear resistance of the sample surface,the binary grating is designed to produce single-row laser beam with energy strengthened at the two ends.The profile of the laser beam spot was designed to be strip with high length-width ratio to improve the machining efficiency of the hardening of large surfaces.A new advantage is suggested to obtain proportional intensity spots with evenness.The design results show that the diffractive efficiency of the binary grating is more than 70%,and the uniformity is less than 3%.The surface profile of the grating fabricated was measured,which shows that the fabrication error is less than 2%.The application of the binary grating in the laser surface hardening of metal components with large superficies is experimentally investigated,and the results show that the hardness distribution of the modified layer is more uniform than that hardened by Gaussian laser beam or array spots with equal intensity distribution.

Nanostrain Measurement Using Chirped Bragg Grating Fabry-Perot Interferometer

A simple nanostrain direct current （DC） measurement system based on a chirped Bragg grating Fabry-Perot （FP） structure is presented. The FP cavity, formed between the chirped fiber Bragg grating （CFBG） and the fiber end face, presents an aperiodic behavior due to the CFBG. A laser located in the fringe pattern slope is used to interrogate the sensing head. The optical power parameter is analyzed when strain is applied, for long and short period fringe pattern wavelengths, and sensitivities of-2.87 μW/με and-5.48μW/με are respectively obtained. This configuration presents a resolution of 70 ε.