A High-Speed 12-Layer Two-Dimensional Bar-Code Detection System

A new photodetection amplifier configuration with an amplification-type current-to-voltage converter is presented to realize a high-gain wideband amplifier. A high-speed 12-layer two-dimensional (2D) bar-code detection system (BCDS), consisting of the new photodetection amplifier and a raster scanner combined with a complementary light emission drive method for laser diodes, has been developed to provide both a highly effective scanning speed and multi-layer bar-code detection. The 12-layer 2D BCDS has shown 1,250 scan/s, which is two and a half times the scanning speed of a conventional bar-code detection system. Comparison with experimental results verified that Li’s scan pattern theory provides an accurate model for laser scanning beam traces obtained by the raster scanner. As theoretical evaluation of bar-code configuration in the new system, an optimum bar-code height per one-layer is given by a function of detection length.     

Research on phosphor-conversion laser-based white light used as optical source of VLC and illumination

Visible light communication (VLC) based on light emitting diodes (LEDs) or laser diodes (LDs) has attracted considerable interest in recent years. Due to the advantages of laser diodes based on nitrides, such as small size, high brightness, visible light and high bandwidth, it can be applied to illumination and communication at the same time. In this paper, blue laser and yellow phosphors were employed to synthesize white light. And “efficiency droop” is not observed in the LIV characteristics of LD-based white light either. The bandwidth measurement system with high reliability was set up. The bandwidth of blue laser diode and phosphor-conversion laser-based white light was measured. The maximum of optical ?3 dB bandwidth of blue LD is around 1.8 GHz at 80 mA and maximum of optical ?3 dB bandwidth of white light is about 1.3 GHz at 60 mA. The color parameters of the synthetic white light were characterized through integrating sphere. Moreover the trends of test data with injection current were analyzed in detail. The problem of thermal degradation of yellow phosphors has been improved by a special design that can keep a certain distance between the blue laser diode and phosphors. The experiment results verified that laser diodes based on nitrides have promising applications in lighting and communications.     

High-resolution optical time domain reflectmetry based on a broadband continuous wave multimode laser diode

A broadband light source can be obtained by operating a multimode laser diode with a bias current below threshold. We propose an optical time domain reflectometer for high-resolution with a broadband cw multimode laser. The emission spectrum of the multimode laser diode that affects an interference signal is investigated. With this method, the spatial resolution is measured as 11.5 μm, corresponding to that of 38.3-fs pulses, and a minimum detectable reflectivity < -90 dB is achieved.     

Suppressed speckle contrast of blue light emission out of white lamp with phosphors excited by blue laser diodes for high-brightness lighting applications

The speckle contrast of blue light emission out of high-brightness white lamps using phosphors excited by InGaN/GaN blue laser diodes is evaluated as a measure of coherence. As a result, speckle contrast of as low as 1.7%, the same level as a blue light emitting diode, is obtained. This implies that the original blue laser light can be converted into incoherent light through lamp structures without any dynamic mechanisms. This unique speckle-free performance is considered to be realized by multiple scattering inside the lamp structure, the multi-longitudinal mode operation of the blue laser diodes, and the use of multiple laser diodes. Such almost-incoherent white lamps can be applied for general lighting without any nuisance of speckle noise and should be categorized as lamps rather than lasers in terms of laser safety regulation.     

利用半导体激光器环产生27 GHz的平坦宽带混沌激光

关键词： 激光器 混沌 宽带 环形结构     

Dual-wavelength bandwidth-narrowed output of a high-power diode laser using a simple external cavity

Using an external cavity consisting of an etalon and a mirror, dual-wavelength operation of a high-power broad-area multi-stripe diode laser is achieved. The reflection of the etalon is used as the output beam of the system. The free-running bandwidth of the laser diode is about 2.0 nm. At dual-wavelength operation, the bandwidth of each wavelength component is narrowed to about 0.07 nm, while the space between them is 1.65 nm, determined by the FSR of the etalon. We obtain an available dual-wavelength output power of 2.0 W at the drive current of 6.5 A. The power ratio of the components at two different wavelengths can be changed by changing the temperature of the diode laser. To tune the wavelength of the dual-wavelength output, the temperature of the laser diode and the tilt angle of the etalon are changed simultaneously PACS 42.55.Px; 42.60.Fc; 42.60.Da     

A broadband external cavity tunable InAs/GaAs quantum dot laser by utilizing only the ground state emission

A broadband external cavity tunable laser is realized by using a broad-emitting spectral InAs/GaAs quantum dot (QD) gain device. A tuning range of 69 nm with a central wavelength of 1056 nm, is achieved at a bias of 1.25 kA/cm2 only by utilizing the light emission from the ground state of QDs. This large tunable range only covers the QD ground-state emission and is related to the inhomogeneous size distribution of QDs. No excited state contributes to the tuning bandwidth. The application of the QD gain device to the external cavity tunable laser shows its immense potential in broadening the tuning bandwidth. By the external cavity feedback, the threshold current density can be reduced remarkably compared with the free-running QD gain device.     

An acousto-optical spectrometer with a visible laser diode source

An acousto-optical spectrometer has been constructed using a visible laser diode light source. The advantages of a visible laser diode in this application over the more prevalent infrared laser diodes are discussed. These include increased Bragg cell bandwidth and diffraction efficiency, and easier instrumental alignment, the latter allowing the attainment of much lower scattered light levels.     

Chaotic synchronization of two inverse-injection semiconductor lasers for logic gates

A round-coupling configuration of two inverse-injection semiconductor lasers is presented for logic gate applications. Two laser diodes coupled via injection from the opposite laser became chaotic. Chaotic synchronization is achieved between the two lasers. Two all-optical or two optoelectronic logic gates can be implemented by modulating the injected light or laser diode current, respectively, to synchronize or unsynchronize the two chaotic states. Numerical results show the validity and feasibility of the method.     

Diode laser frequency-noise suppression by >50dB by use of electro-optic parametric master oscillators

We demonstrate a novel frequency-stabilization scheme for laser diodes that is capable of linewidth reduction by more than 5 orders of magnitude. In this master-slave scheme the diode laser emission is frequency-offset phase locked to the emission of an electro-optic parametric oscillator (EOPO), and the laser diode is simultaneously used as the EOPO pump source. As a result the initial frequency fluctuations of the pump are reduced to the intrinsic noise level of the EOPO, which can be extremely small. We demonstrate that subhertz linewidths of the beat notes of the signals of two of these systems can be readily achieved if acoustic perturbations are suppressed.     

Broadband Light-Emitting Diodes with One-Dimensional Photonic Crystal Layer

In this article, a broadband gallium-nitride-based light-emitting diode with a one-dimensional photonic crystal layer is investigated. The broadband light-emitting diode using the proposed backside reflector has high reflectance (>95%) over a 270-nm bandwidth in visible light at an arbitrary incidence angle. A broadband light-emitting diode of high output power due to the high reflectivity is achieved. Also reported are the results for light-emitting diodes by the transistor outline can (TO-can) package. The proposed light-emitting diodes possess broadband high reflected spectra, high output power for light extraction, and a good view angle.     

Amplitude-modulation-free optoelectronic frequency control of laser diodes

A novel method is described for fast frequency modulation or frequency control of diode lasers that avoids problems associated with bias current modulation, namely, amplitude modulation and thermal phase delays. The method is based on amplitude-modulated, noninterfering control light with a wavelength near the transparency region of the laser diode, which specifically modifies the spectral gain profile to yield a constant gain but a controllable refractive index at the lasing wavelength. This permits amplitude-modulation-free frequency modulation at modulation frequencies up to the relaxation oscillation frequency. A phase lock between the emissions of two extended-cavity diode lasers that could not be achieved with bias current modulation was achieved by this method.     

基于双音外差的电光相位调制器半波电压自校准测量方法

电光相位调制器是光纤通信系统、微波光子系统和相干光通信系统中的关键器件之一. 作为器件本征参数, 电光相位调制器的半波电压通常利用光谱方法和电谱方法进行测量. 光谱方法受到光源线宽和光谱仪分辨率限制, 测量的分辨率较低; 电谱方法则需要光电检测之前将相位调制转换成强度调制, 电谱方法的主要困难在于需要对探测器的不平坦响应进行额外校准. 提出了利用双音外差实现电光相位调制器半波电压自校准测量新方法, 该方法利用双音电光相位调制的边带与移频光载波的外差拍频, 对外差拍频信号进行频谱分析, 获得电光相位调制器的半波电压; 通过设定双音调制信号的频率关系, 克服了探测器光电转换中的不平坦频率响应, 实现了自校准测量. 该方法可扩展探测器和频谱仪的测试频率两倍以上, 节省至少一半的带宽需求. 与光谱测量方法相比, 该方法测试分辨率大幅提高且避免了光源线宽的影响; 与传统电域测量方法相比, 该方法无须额外校准, 无驱动功率和工作波长限制, 且对测试仪器带宽需求降低一半以上. 实验证实了所提方法获得的电光相位调制器半波电压的测量结果与光谱分析法获得的结果一致, 且大幅度地提高了测量范围和分辨率. 该方法提供了非常简单的电光相位调制器微波特性化分析方法, 对其他光电子器件分析也提供了参考.     

Tuning high-power laser diodes with as much as 0.38 W of power and M(2) = 1.2 over a range of 32 nm with 3-GHz bandwidth

Gain-guided diode lasers usually have emission wavelengths determined by the manufacturing process, with typically 0.5-1-nm bandwidth. Furthermore, their beam quality is rather poor. We show that external cavities allow for tunable narrow-bandwidth operation of gain-guided diode lasers. At the same time the beam quality is drastically improved; almost diffraction-limited light of more than 200 mW has been achieved over the whole tuning range from 910 to 942 nm with narrow bandwidth.     

Degradation of II-VI ZnSe-Based Single Quantum Well Light-Emitting Devices

Degradation of ZnSe-based light-emitting devices (light-emitting diodes and diode lasers) are reviewed. These devices quickly degrade (i.e., show a decrease in the amount of light emitted) during continuous operation at room temperature. The best lifetimes are currently only a few hours for cw diode laser operation. Degradation of ZnSe quantum-well devices are shown to correlate with the current density necessary for operation and with the density of preexisting defects. The temperature of the quantum well during operation has been shown to be >250°C. The decrease in light emission correlates with the development of dark spot defects (DSDs) and dark line defects (DLDs) in or near the active quantum-well region of the device. It is shown that stress in the quantum well is not relaxed until late in the degradation process, and then only partially. Instead, the mechanism of degradation is shown to be the injection of point defects due to nonradiative relaxation processes, which ultimately collapse into the DSDs and DLDs. Methods to reduce the degradation of these devices are discussed.     

Simulation of quantum-well slipping effect on optical bandwidth in transistor laser

An optical bandwidth analysis of a quantum-well （16 nm） transistor laser with 150-μm cavity length using a charge control model is reported in order to modify the quantum-well location through the base region. At constant bias current, the simulation shows significant enhancement in optical bandwidth due to moving the quantum well in the direction of collector-base junction. No remarkable resonance peak, limiting factor in laser diodes, is observed during this modification in transistor laser structure. The method can be utilized for transistor laser structure design.     

Properties of monolithic integration of a resonant tunneling diode and a quantum well laser

An investigation of the electrical and optical characteristics of a resonant tunneling diode monolithically integrated with a quantum well laser is carried out. An analytic expression for the propagating model current is given in terms of the total spontaneous emission rate. The laser is pumped by the current emitted by the resonant tunneling diode. When the current in the laser exceeds the threshold current, laser light is produced. Since the current in the laser exhibits negative differential resistance similar in behavior to the current of a resonant tunneling diode, a bistable light output can be obtained from this new device.     

光注入提高半导体激光器混沌载波发射机的带宽

外光反馈下的半导体激光器可视为混沌载波发射机.数值研究发现，外部强光注入可以显著提高混沌载波发射机的带宽，带宽提高的程度在一定范围内与注入光的强度成正比.当外部光注入系数k_inj=0.39时，混沌载波的带宽由无光注入时的2.7GHz增大到14.5GHz，提高了5倍多.研究还发现，在相同的注入强度条件下，当注入光的频率比半导体激光器的中心频率高2—4GHz时，可实现最大限度的带宽增强.此外，适当提高半导体激光器的偏置电流也可以在一定程度上提高其产生的混沌载波的带宽. 关键词： 半导体激光器 混沌 带宽     

An approach of open-path gas sensor based on tunable diode laser absorption spectroscopy

Tunable diode laser absorption spectroscopy (TDLAS) is a new method to detect trace-gas qualitatively or quantificationally based on the scan characteristic of the diode laser to obtain the absorption spectroscopy in the characteristic absorption region. A time-sharing scanning open-path TDLAS system using two near infrared distributed feedback (DFB) tunable diode lasers is designed to detect CH4 and H2S in leakage of natural gas. A low-cost Fresnel lens is used in this system as receiving optics which receives the laser beam reflected by a solid corner cube reflector with a distance of up to about 60 m. High sensitivity is achieved by means of wavelength-modulation spectroscopy with second-harmonic detection. The minimum detection limits of 1.1 ppm·m for CH4 and 15 ppm·m for H2S are demonstrated with a total optical path of 120 m. The simulation monitoring experiment of nature gas leakage was carried out with this system. According to the receiving light efficiency of optical system and detectable minimum light intensity of detection, the detectable optical path of the system can achieve 1 - 2 km. The sensor is suitable for natural gas leakage monitoring application.     

Leakage current and sub-bandgap photo-response of oxygen-plasma treated GaN Schottky barrier diodes

The effect of oxygen plasma treatment on the performance of GaN Schottky barrier diodes is studied. The GaN surface is intentionally exposed to oxygen plasma generated in an inductively coupled plasma etching system before Schottky metal deposition. The reverse leakage current of the treated diodes is suppressed in low bias range with enhanced diode ideality factor and series resistance. However, in high bias range the treated diodes exhibit higher reverse leakage current and corresponding lower breakdown voltage. The X-ray photoelectron spectroscopy analysis reveals the growth of a thin GaO_x layer on GaN surface during oxygen plasma treatment. Under sub-bandgap light illumination, the plasma-treated diodes show larger photovoltaic response compared with that of untreated diodes, suggesting that additional defect states at GaN surface are induced by the oxygen plasma treatment.