Quantum-well laser with integrated passive waveguide fabricated byneutral impurity disordering

Double quantum-well lasers have been fabricated with an integrated low-loss waveguide in which the quantum wells have been intermixed by neutral impurity disordering. Threshold currents of devices with integrated 600-μm passive guides show an increase of less than 10% over normal Fabry-Perot lasers of the same active length, confirming that the propagation loss in the passive wavelength is significantly reduced by disordering to 4.5±2 cm^-1. Comparison with unimplanted devices suggests that the implanted dopant also passivates the waveguide electrically     

Rigorous analysis of coupling between laser and passive waveguidein multilayer slab waveguide

An approach that combines the finite-element and boundary-element methods (FEM/BEM) is extended to the analysis of arbitrarily shaped discontinuities in a multilayer slab waveguide. Here all the eigenmodes, namely, guided modes, substrate radiation modes, and substrate-cover radiation modes, are taken into account and are constructed by an extended matrix method. Computed results are given for the rigorous analysis of the coupling between a five-or six-layer laser and a four-layer passive waveguide in a monolithically integrated circuit. Some of the results are for multimode incidence. Since the coupling is one of the most important discontinuity problems in practice, this result confirms the usefulness of the approach     

Spectral characteristics of distributed feedback laser diodes withdistributed coupling coefficient

A comprehensive investigation of the spectral characteristics of distributed feedback (DPB) laser diodes (LD's) with a distributed coupling coefficient (DCC) is presented. With a proper selection of both the coupling ratio (r) and a corrugation position (CP), the performance of the DCC laser structure is enhanced with an improved single-mode stability as well as a uniform field distribution. In the analysis, the above threshold characteristics and the influence of non-lasing side modes have been investigated using the transfer matrix method (TMM). Based on a DCC laser structure with r=1/3 and CP=0.46, a normalized gain margin (ΔαL)=0.81 and a side mode suppression ratio (SMSR) of 45 dB have been achieved for a DCC LD at biasing current of 4I_th . The introduction of the DCC laser structure opens a new way of stabilizing the single-mode oscillation in DFB LD's     

Total integrated reflection loss in a laser diode to single-mode fibre coupling system

A geometrical optics approach is used to analyse the reflection of a divergent beam falling onto a concave or convex surface. The polarisation state of a ray in the incident beam depends on the position where the ray impinges upon the surface. The distribution of transmittance over the surface for different polarisation states is determined. An integration of the transmittance distribution determines the total reflection loss of a coupling lens used in a laser diode to single-mode fibre coupling system.     

DFB lasers with monolithically integrated passive waveguide

Novel MQW integrated passive waveguide (IPW) DFB lasers have been fabricated using a selective area MOVPE growth technique. Detailed measurements of the absorption loss of the passive waveguide in the structure as well as its influences on the laser linewidth are reported for the first time. A linewidth reduction factor of more than 3 is observed as compared to a simple DFB laser despite the high absorption loss     

Design and performance of asymmetric waveguide nitride laser diodes

We describe the design and performance characteristics of an asymmetric waveguide nitride laser diode structure, in which the p-cladding layer is placed immediately over the multiple-quantum-well (MQW) active region. Its close proximity to the active region enables it to serve not only as a cladding layer, but also as a potential barrier that confines injected electrons. This structure represents a departure from conventional nitride laser diode structures, where electron confinement is provided by a separate high-aluminum-content AlGaN tunnel barrier layer placed over the MQW active region. The optical confinement factor (Γ) remains: comparable to that of the conventional structure, in spite of the QW's displacement from the center of the waveguide. Room-temperature CW operation was achieved with this structure     

Measurements of mode partition noise of laser diodes

Mode partition noise may become the dominant performance limitation for single-mode fiber systems. We define the mode partition coefficientkfor laser diodes which can be used as a universal index, like threshold current and spectral width, to characterize laser diodes. Thekvalue varies between 1 and 0, and for largerk, the mode partition noise will be higher. We also demonstrate two simple techniques for measuringk: the low-pass filter method and the sampling method. We discuss thekvalues measured under different operating conditions (pulse width, dc bias) for several types of laser diodes,kvalues are around 0.4-0.6 with short pulse width (1.5-5ns), and decreases to 0.14 pulse width of 50 ns. The largestkvalues were obtained for a laser exhibiting strong relaxation oscillation. For that laser,kdid not depend on the pulse width. Thekvalue is an important factor for system and fiber design as well as laser diode design.     

Optical coupling characteristics of laser diodes to thermally diffused expanded core fiber coupling using an aspheric lens

A discussion is presented of the optical coupling characteristics of a 1.3 mu m laser diode to a thermally diffused expanded core (TEC) single-mode fiber coupling using an aspheric lens. The misalignment tolerance width for a 0.5 dB loss increment of the expanded core fiber was enlarged to 8.4 mu m from 1.9 mu m of a nonexpanded core fiber without a remarkable coupling-loss increase. The TEC fibers will make the LD module assembly easier, and reduce the assembly cost.<>     

单片集成可调谐半导体激光器研究进展

单片集成可调谐半导体激光器的使用为光纤通信系统和智能光网络带来极大的灵活性、可扩展性以及经济性.文章综述了单片集成可调谐半导体激光器的调谐机制、结构特点以及性能比较,概要介绍了最新研究进展情况,分析了相关发展趋势和市场应用前景.     

全内反射型光波导开关反射特性的分析

本文详细分析了全内反射型光波导开关的反射特性,指出反射模存在位相变化及其相对位相差。数值计算结果表明,反射TE模和反射TM模强度反射率、反射损耗,它们的位相变化及其相对位相差都与光波导开关区介质折射率改变量、损耗以及传播角有密切关系。     

High-efficiency coupling of laser diodes in tapered proton-exchanged waveguides

Low-loss coupling between a laser diode and a tapered waveguide fabricated by selective area proton-exchange in LiNbO/sub 3/ is reported. The effectiveness of this waveguide is demonstrated by generating 12.3 mW of second harmonic blue light pulse by Cerenkov radiation.<>     

Lens coupling of laser diodes to single-mode fibers

This paper studied the effect of lens aberration on coupling efficiency and loss penalty due to misalignment for a laser diode to single-mode fiber couplers. The theoretical results were in very good agreement with experimental values and the validity of the present analysis was confirmed. The paper made clear that coupling loss is dominated by aberration and proposed some basic approaches to improving coupling efficiency.     

Phase-amplitude coupling factor of single-mode gain-switchedInGaAsP laser diodes

The phase amplitude coupling factor (α-factor) of gain-switched InGaAsP laser diodes is deduced from chirp measurements. A tunable laser scheme makes it possible to obtain the wavelength dependence of α over ~40 nm. The α-values are found to be higher than those deduced from spontaneous emission spectra below threshold. It is shown that the difference is explained by the dependence of α with carrier density. Time-resolved measurements of spontaneous emission during pulse buildup reveal that the carrier density at maximum can be 1.5 times higher than the threshold carrier density. Experimental evolutions of α are well reproduced by calculations     

Realization of novel low-loss monolithically integrated passive waveguide mode converters

The novel design and fabrication of monolithically integrated passive waveguide mode converters (WMCs), realized through the utilization of the reactive ion-etch lag (RIE Lag) phenomenon, is reported. The low-loss GaAs-AlGaAs WMCs have been characterized over a wavelength range of 900-940 nm, resulting in TE-TM (TM-TE) mode conversion with efficiencies of greater than 96% and low-loss devices with conversion lengths as short as 150 /spl mu/m. The properties and characteristics of the fully integrated WMCs, fabricated with a single masking and etch process, are in agreement with theoretical predictions.     

Guided-wave and leakage characteristics of substrate integrated waveguide

The substrate integrated waveguide (SIW) technique makes it possible that a complete circuit including planar circuitry, transitions, and rectangular waveguides are fabricated in planar form using a standard printed circuit board or other planar processing techniques. In this paper, guided wave and modes characteristics of such an SIW periodic structure are studied in detail for the first time. A numerical multimode calibration procedure is proposed and developed with a commercial software package on the basis of a full-wave finite-element method for the accurate extraction of complex propagation constants of the SIW structure. Two different lengths of the SIW are numerically simulated under multimode excitation. By means of our proposed technique, the complex propagation constant of each SIW mode can accurately be extracted and the electromagnetic bandstop phenomena of periodic structures are also investigated. Experiments are made to validate our proposed technique. Simple design rules are provided and discussed.     

Simple and low-loss fibre-to-chip coupling by integrated field-matching waveguide in InP

A nested taper structure in InGaAsP/InP, using only horizontally tapered waveguides, transforms the fundamental mode of an integrated waveguide to the mode profile of a singlemode fibre. Taper tips below 300 nm width have been achieved with standard technology. Very first measurement results show an insertion loss of only 4 dB for a 1 mm long device without any antireflective coating or immersion fluid.<>     

Transform-limited picosecond optical pulses from a mode-lockedInGaAs/AlGaAs QW laser with integrated passive waveguide cavity and QWmodulator

Using a novel single-top molecular beam epitaxy growth technology on nonplanar substrates, an InGaAs/AlGaAs laser amplifier has been integrated with a 4-mm-long passive waveguide cavity and a QW modulator. Lasing action of the entire structure was achieved by a current of 60 mA flowing through the amplifier section. Mode-locking experiments in which an RF signal was applied to the modulator segment led to nearly-transform-limited pulses with a duration of 4.4 ps and a time-bandwidth product of 0.43     

基片集成脊波导传输特性的研究

将构成基片集成脊波导脊的一排金属针等效成实金属脊。基于基片集成波导等效宽度计算公式推导了基片集成脊波导等效脊宽的计算公式。运用横向谐振法推导了TE_m0模基片集成脊波导截止频率的计算公式,同时运用这些公式分别计算了TE₁₀模、TE₂₀模和TE₃₀模基片集成脊波导的截止频率,并与仿真软件计算的结果和参考文献所给结果进行了比较。结果显示:利用所给公式计算的结果具有较高的精度,且使用方便。此外,还研究了截止频率与脊宽和脊隙之间的关系,对一种适合宽带应用的宽脊结构进行了讨论。     

Dispersion characteristics of substrate integrated rectangular waveguide

Dispersion properties of the substrate integrated rectangular waveguide (SIRW) are rigorously obtained using the BI-RME method combined with the Floquet's theorem. Our analysis shows that the SIRW basically has the same guided-wave characteristics as the conventional rectangular waveguide. Empirical equations are derived from the calculated dispersion curves in order to estimate the cutoff frequency of the first two dominant modes of the SIRW To validate the analysis results, an SIRW guide was designed and measured. Very good agreements between the experimental and theoretical results were obtained.     

Novel fabrication-tolerant twin-guide laser structure with anexternal passive waveguide

The authors propose a novel quasi-symmetrical twin-guide GaAs/AlGaAs laser structure (QSTGL) with a low-loss external passive waveguide. The device is tolerant to fabrication misalignment and therefore well suited for monolithic integration. Threshold current densities of less than 1.1 kA/cm² and a coupling efficiency between 70 and 80% into the low-loss passive waveguide are achieved