Some characteristics of an extremely-short-external-cavity laser diode realized by butt coupling a Fabry-Perot laser diode to a single-mode optical fiber

When butt coupling a Fabry-Perot laser diode to an extremely closely spaced waveguide (separation less than or equal to a few times the Rayleigh range of the laser beam), there is a trade-off between the optimal power coupling and the variation of the coupled laser diode's operational characteristics. Changes in the butt-coupling configuration parameters influence the coupling efficiency, as well as the strength of the feedback into the laser diode. Using a previously reported phenomenological model that treats the butt-coupled laser diode as an extremely short external-cavity (ESEC) device, we quantitatively describe how the butt-coupling parameters can be used to control the output power, threshold current, wavelength, and relative intensity noise of the ESEC laser diode. Our analyses are supported by experimental results. The importance of choosing the correct coordinate plane for evaluation of the overlap integrals that are used in the model is also discussed.     

Theory and optimization of lens ducts

Lens ducts are simple optical devices that have found application in the coupling of pump radiation from extended two-dimensional semiconductor laser diode arrays into solid-state laser gain media. The operation of these devices relies on the combined effects of lensing at their curved input surface and channeling by total internal reflection off their canted planar sides, to contain and couple semiconductor diode laser light efficiently to the input face of a solid-state laser crystal or glass. The lens duct provides a robust method for amplifying the irradiance of laser diode array pump sources and has made possible a scalable diode end-pumping architecture that offers the opportunity to expand significantly the number of ions and transitions that can be practically engaged in diode-pumped solid-state laser systems. An analytic model that describes the transfer efficiency of lens ducts and aids in the optimization of their design is presented.     

激光自混合变速测量的多项式相位参数提取

激光自混合能有效用于匀速运动物体的速度测量,为了加速激光自混合用于物体速度测量的实用化进程,对激光自混合用于变速运动物体的速度测量进行了探索.引入了基于多项式相位参数提取的信号处理算法;基于激光自混合的测速原理,推导了激光自混合用于变速测量时输出信号的多项式相位表示式,也即建立了激光自混合用于变速测量的仿真模型.通过仿真分析证明:在激光自混合变速测量中采用基于相位多项式参数提取的方法,可以获得物体运动的速度和加速度信息;该方法在较低信噪比的情况下仍然适用.     

Determination of the transmission coefficients for quantum structures using FDTD method

The purpose of this work is to develop a simple method to incorporate quantum effect in traditional finite-difference time-domain (FDTD) simulators. Witch could make it possible to co-simulate systems include quantum structures and traditional components. In this paper, tunneling transmission coefficient is calculated by solving time-domain Schr?dinger equation with a developed FDTD technique, called FDTD-S method. To validate the feasibility of the method, a simple resonant tunneling diode (RTD) structure model has been simulated using the proposed method. The good agreement between the numerical and analytical results proves its accuracy. The effectness and accuracy of this approach makes it a potential method for analysis and design of hybrid systems includes quantum structures and traditional components.     

Analysis of the diffractional properties of dual-period apodizing gratings: theoretical and experimental results

We present an analysis of the diffractional properties of dual-period apodizing gratings. In a previous paper we used these components to obtain single-lateral-mode and dual-longitudinal-mode emission from a broad-area diode laser. We now calculate the diffracted field for a monochromatic beam incident on the grating by using an analytical model. Predictions of the model are compared with experimental measurements made with several dual-period gratings. We also discuss the situation in which a dual-period grating is used as an external coupler of a diode laser in a two-wavelength emission regime.     

Mechanical characterization of glass/polyimide microjoints fabricated using cw fiber and diode lasers

This paper discusses the laser-irradiated microjoints between glass and polyimide for applications in neural implants. To facilitate bonding between them, a thin titanium film with a thickness of approximately 0.2 μm was deposited on glass wafers using the physical vapor deposition (PVD) process. Two sets of samples were fabricated where the bonds were created using diode and fiber lasers. The samples were subjected to tension using a microtester for bond strength measurements. The failure strengths of the bonds generated using fiber laser are quite consistent, while a wide variation of failure strengths are observed for the bonds generated with diode laser. Few untested samples were sectioned and the microstructures near the bond areas were studied using an optical microscope. The images revealed the presence of a sharp crack in the glass substrate near the bond generated with the diode laser. However, no such crack was observed in the samples made using fiber laser. To investigate the reasons behind such discrepancy in bond quality further, uncoupled three-dimensional finite element analyses (FEA) were conducted only for the samples created using diode laser. First, the transient heat diffusion-based FEA was conducted by using the laser power intensity distribution as a time dependent heat source. This model calculates the temperature distribution within the substrates as a function of time. Next, the structural model predicts the amount of residual stresses developed in the joint system as it is cooled down to room temperature. The out-of-plane normal component of residual stresses was within the failure strength range of glass that may have caused fracture initiation in the substrate.     

Effect of diode wavelength broadening in a diode end-pumped solid-state amplifier

The effect of the spectral broadening in cw diode pumping and the wavelength shift in pulsed pumping of a solid-state laser is investigated theoretically. A very simple model allowing the computation of the reduction of the absorbed pump energy is developed. The results are applied to an ytterbium-doped solid-state laser and should be fruitful for amplifier and laser design.     

Performance of a neodymium yttrium aluminum borate green laser pumped with a fiber-coupled laser diode

Using a space-dependent rate-equation model and considering the effect of pump beam quality, the optimum pump condition for a fiber-coupled diode end-pumped neodymium yttrium aluminum borate laser has been determined. Under optimum pump conditions, greater than 10% optical-to-optical conversion efficiency was obtained when the laser was pumped by a fiber-coupled laser diode with good beam quality. The influence of pump beam quality on the conversion efficiency is also discussed.     

Applications of an extremely short strong-feedback configuration of an external-cavity laser diode system fabricated with GaAs-based integration technology

A composite-cavity laser diode is used to monitor the reflectivity or the displacement of the external-cavity mirror for micromechanical photonics devices. Optical disk bits are read out in the near field from the difference in medium reflectivity with an antireflection-coated laser diode and a photodiode. Microbeam vibration is also detected in the near field from the phase difference with an uncoated laser diode and a photodiode. In both cases the carrier-to-noise ratio is very high (more than 45 dB) because of the lack of mode-hopping noise resulting from the extremely short (less than 3 μm) external-cavity length and strong light feedback. These composite-cavity laser diode microdevices are fabricated on a gallium arsenide substrate to eliminate the need for optical alignment.     

以半导体激光器为光源的准直研究

对半导体激光器的准直装置、温度变化对准直精度的影响、温度控制方法作了论述。试验表明,采用半导体激光器作准直光源,准直的稳定性可达到1×10~(-6)。     

60瓦半导体激光器光纤耦合器件

应用光纤列阵耦合方式，对大功率半导体激光器线列阵输出光束的快轴方向用一根柱透镜准直，准直后的光束耦合到光纤列阵中，实现出纤功率为60瓦的大功率半导体激光二极管线列阵光纤耦合器件，耦合效率大于80％，光纤的数值孔径NA为0．11。     

半导体激光端点测长干涉仪实验系统

半导体激光端点干涉测长法是利用半导体激光频率调制特性的一种在长度的两个端点干涉测量长度的新方法。本文介绍基于这种测长方法研制的半导体激光端点测长干涉仪实验的基本原理,构成,定标方法和测量结果。     

Interferometric ellipsometer with wavelength-modulated laser diode source

An interferometric ellipsometer, with no moving parts and an inexpensive laser diode source, is demonstrated. Temporal fringes are produced by a small modulation of the laser diode bias current and unbalanced arms in the interferometer. Fringe analysis algorithms are developed, and accurate measurements of the optical properties of a number of samples are made. Temperature tuning the laser diode center wavelength allows the frequency dependence of the optical properties to be determined over a wavelength range of approximately 1 nm.     

High-resolution random-modulation cw lidar

A high-resolution random-modulation continuous wave lidar for surface detection using a semiconductor laser diode is presented. The laser diode is intensity modulated with the pseudorandom binary sequence. Its enhanced resolution is achieved via interpolation and a novel front-end analog technique, lowering the requirement of the analog-to-digital converter sampling rate and the associated circuitry. Its mathematical model is presented, including the derivation of the signal-to-noise ratio and the distance standard deviation. Analytical and experimental results demonstrate its capability to achieve distance accuracy of less than 2?cm within 2.6?ms acquisition time, over distances ranging from 1 to 12?m. The laser diode emits 1.4?mW of optical power at a wavelength of 635?nm.     

Analysis of error yielded by scalar approximation to the properties of laser diode beams

Based on the vector Rayleigh-Sommerfeld far-field diffraction integral formula, a vector model for describing the far field of a laser diode is proposed beyond the paraxial approximation. Through the analysis of the error yielded by the scalar approximation to the properties of laser diode beams, it is found that the error is only correlative with propagation distance and the coordinate perpendicular to the junction plane, and there is a certain relationship between the error and a space angle.     

Diode-laser-to-waveguide butt coupling: extremely short external cavity

An ultrashort composite cavity (相似文献   

Extending the continuous tuning range of an external-cavity diode laser

The continuous tuning range of an external-cavity diode laser can be extended by making small corrections to the external-cavity length through an electronic feedback loop so that the cavity resonance condition is maintained as the laser wavelength is tuned. By maintaining the cavity resonance condition as the laser is tuned, the mode hops that typically limit the continuous tuning range of the external-cavity diode laser are eliminated. We present the design of a simple external-cavity diode laser based on the Littman-Metcalf external-cavity configuration that has a measured continuous tuning range of 1 GHz without an electronic feedback loop. To include the electronic feedback loop, a small sinusoidal signal is added to the drive current of the laser diode creating a small oscillation of the laser power. By comparing the phase of the modulated optical power with the phase of the sinusoidal drive signal using a lock-in amplifier, an error signal is created and used in an electronic feedback loop to control the external-cavity length. With electronic feedback, we find that the continuous tuning range can be extended to over 65 GHz. This occurs because the electronic feedback maintains the cavity resonance condition as the laser is tuned. An experimental demonstration of this extended tuning range is presented in which the external-cavity diode laser is tuned through an absorption feature of diatomic oxygen near 760 nm.     

Amplitude-stabilized frequency-modulated laser diode and its interferometric sensing applications

A direct frequency-modulated (FM) laser diode light source without light power variation is developed. The amplitude variation of the FM laser diode is compensated by means of a feedback system with use of a superluminescent diode as an external light power controller. Output power greater than 1 mW is obtained at the modulation frequency to 5 kHz with a >10 stabilization factor. By use of the amplitude-stabilized FM laser diode, we measured subfringes with high accuracy in FM continuous wave interferometry, increased the dynamic range of the displacement measurement, and improved the stabilization factor in the laser diode feedback interferometer.     

Resolution enhancement printing with a variable spot-size laser diode

We demonstrate enhanced resolution printing using a variable spot-size laser diode. The near-field spot size of the laser diode can be changed by controlling the refractive-index distribution in the laser stripe through the injected current. The ratio of the minimum-to-maximum spot size is 2.1:1. This technology provides high-resolution printing without increasing the scanning frequency. Smoother character outlines that consist of finer steps are produced with this laser diode. An effective resolution of 1200 dots /in. (dpi) can be obtained by a printer system with 600-dpi resolution.     

Design and stability analysis of a CMOS feedback laser driver

A feedback laser driver circuit has been developed to control the average optical output power of a double heterostructure CW laser diode and also to operate with a wideband amplitude modulation. The average light power monitoring is realized by measuring the photoelectric current of a photodiode integrated inside the package of the laser diode. Safety features, including transient signal suppression, protect the laser against excessive light power. To obtain responses that are not out of the absolute maximum ratings of the laser diode light power, a study of the feedback loop stability is necessary. Two transconductance structures, using inverting and noninverting circuits are compared using the dominant pole compensation method. Then, the more stable driver circuit is analyzed and integrated using CMOS technology.