旋流二氧化碳激光器腔内增益分布的改进

常用的工业二氧化碳激光器,主要为横流、纵流和扩散冷却三种.文章对作者提出的新型旋流二氧化碳激光器进行了简要介绍,重点研究了腔单元结构和电极结构变化对腔内增益分布状态的改进.依托该研究结果,发展出新型转流二氧化碳激光器实验样机,实现了基模700W输出,并进行了板材样品的精密切割实验.     

Control of vertical-cavity laser polarization with anisotropictransverse cavity geometries

We show the two-fold polarization degeneracy of etched air-post vertical-cavity surface emitting laser diodes can be lifted and a dominant polarization state selected through use of anisotropic transverse laser cavity geometries. For lasers with rhombus-shaped cavities, fundamental mode lasing emission linearly polarized along one specified crystal axis is obtained up to twice the threshold current. For dumbbell-shaped lasers, fundamental mode lasing emission linearly polarized along one specified crystal axis is maintained over the entire operating range of the device producing a maximum orthogonal polarization suppression ratio of 14 dB     

Dynamic, polarization, and transverse mode characteristics ofvertical cavity surface emitting lasers

The dynamic, polarization, and transverse mode characteristics of strained InGaAs-GaAs quantum well vertical cavity surface emitting lasers (VCSELs) emitting at 0.98 μm are investigated. The dynamic behavior of VCSELs with high and low operating voltages and series resistances is compared. A large wavelength chirp in the lasing spectrum was observed for the lasers with high voltage/resistance, even under low-duty-cycle pulse operation. This is thought to be due to resistive heating close to the laser junction. It is observed that the transverse mode structure of VCSELs and their dependence on laser dimensions and drive current are highly analogous to those of edge emitting lasers, whereas the polarization characteristics of the two types of lasers are significantly different     

Calculated spontaneous emission factor for double-heterostructure injection lasers with gain-induced waveguiding

The fraction of spontaneous emission going into an oscillating laser mode has been calculated. It is shown that this fraction strongly depends on the strength of astigmatism in the laser output beam. Therefore the spontaneous emission factor in planar stripe lasers with narrow stripe is in the order of 10^-4and by one order of magnitude larger than in injection lasers with a comparable active layer volume and with a built-in index waveguide. It is shown that the spontaneous emission factor is approximately proportional to the solid angle of laser radiation and nearly independent of the transverse active layer dimensions. Owing to the large spontaneous emission factor, the spectral width of narrow planar stripe lasers is significantly broader compared to narrow stripe lasers with a built-in index waveguide. In addition the large spontaneous emission coefficient also yields a much stronger damping of relaxation oscillations.     

Comparison of wavelength splitting for selectively oxidized, ion implanted, and hybrid vertical-cavity surface-emitting lasers

The wavelength splitting between the LP/sub 01/ and LP/sub 11/ modes of selectively oxidized, ion implanted, and hybrid ion implanted/selectively oxidized vertical-cavity surface-emitting lasers is studied by experiment and theory. Measured splittings at threshold show marked differences between the different laser structures due to the effects of index guiding and thermal lensing. Theoretical results were obtained using a vector optical mode solver and show good agreement with experimental results. The hybrid lasers exhibited behavior intermediate between the ion implanted and selectively oxidized lasers and could be optimized for high power single transverse mode emission.     

High-radiance room-temperature GaAs laser with controlled radiation in a single transverse mode

A GaAs laser for room-temperature operation is reported with high radiance and short delay times. For high radiance, the radiation of a 200-μ-wide GaAs laser diode is confined to the lowest order transverse mode. This is accomplished by operating the laser diode with an optical cavity in which the transverse mode is controlled by aperture-limiting slits. In the cavity, built of spherical lenses and plane mirrors, the mode width and height coincide with the width and height of the active region of the injection laser. The diffraction losses of the higher order transverse modes introduced by the apertures are sufficiently high to yield controlled radiation in the TEM00mode ; this control was not always assured in the earlier design of the GaAs laser with the external resonator [1]. For short delays of the onset of stimulated emission, GaAs lasers are used for which the transition from short to long delays occurs above room temperature. Also, the external cavity is coupled closer to the active region of the semiconductor diode than reported previously [1] to minimize losses that would increase the delay times. Test results on the radiance, room-temperature delay times, and mode structure of the GaAs laser with the optical cavity are presented and the observed spiking pattern is discussed.     

A stabilized zinc diffused-proton bombarded (GaAl)As laser

A new (GaAl)As stripe laser in which a refractive index step is created by a zinc diffusion on both sides of a conventional proton stripe structure, called a diffused bombarded stripe (DBS) laser, is presented. This diffusion provides passive transverse guiding with a relatively simple technology. The index step can be adjusted by controlling the diffused zinc concentration in relation to the active region doping level. A self-alignment technique for the diffused and bombarded stripes reduces the current leakage through the diffused regions. Lasing threshold currents as low as those of conventional proton stripe lasers are obtained. A significant improvement of light-current linearity, transverse mode stability and longitudinal mode structure are observed with the DBS lasers.     

Polarization characteristics of fiber DFB lasers related to sensingapplications

An experimental and theoretical investigation of how the polarization mode competition and beat frequency of Er-doped fiber distributed-feedback lasers depend on perturbations such as localized transverse forces, back reflections, or changes in pump polarization is reported. Good agreement between the experiments and a comprehensive theoretical model is obtained. Use of a dual-polarization laser as a transverse force sensor with a resolution on the order of 1-100 nN/√Hz above 20 Hz is also discussed     

New stripe-geometry laser with simplified fabrication process

A new type of GaAs-GaAlAs stripe-geometry laser with an appreciably simplified fabrication process is described. Owing to the excellent lateral current confinement of this structure, low threshold current densities are achieved even for very narrow stripe widths. In addition, the built-in passive wave-guiding stabilises the fundamental horizontal transverse mode, thereby avoiding nonlinearities in the light output against current characteristic. For 3?m wide and 175 ?m long lasers, threshold currents of 30?35 mA are achieved and stable transverse and longitudinal monomode emission has been observed up to more than 5 mW light power output.     

Adjustable modules for high-power (over 7.5-mW CS) coupling of diode lasers to single-mode fibers

Single-mode (SM) fiber output power of over 7.5-mW CW has been obtained in unique adjustable coupling modules. These are the highest powers ever reported coupled between diode lasers and single-mode fibers. Coupling efficiencies over 30 percent were obtained in simple butt-coupling by taking advantage of the large mode size available from RCA constricted-double-heterojunction large-optical cavity (CDH-LOC) lasers. We also observed peak fiber power of over 9 mW with 100-ns 50-percent duty cycle pulses. The minature modules provide relative transverse and lateral motion between fiber and laser with 2000-Å resolution, allowing fine tuning against long-term drifts. The coupling, while adjustable, is still stable against moderate acceleration of module and motion of fiber pigtail. The adjustments may be adapted to servo control.     

Polarization state of the emission of external grating diode lasers

The laser emission of transverse electric (TE) and transverse magnetic (TM) polarization, in alternating successive spectral ranges, that can occur when external grating diode lasers are wavelength tuned, is theoretically and experimentally investigated. The modulated threshold gain curves of the external cavity for the two polarizations can be made to intersect with each other if a grating is used in such a way as to practically eliminate the difference between the laser diode losses and confinement factors for TE and TM polarization. The result is a sequence of wavelength ranges where the threshold gain is alternately lower for the TE resp. TM polarization. Within each range, a wavelength tunable single mode laser emission is obtained. The phenomenon is described, taking into account the characteristics of the key components of the external cavity, i.e., laser diode structure, antireflective (AR) coating, and grating efficiency. Design tools are proposed for the characteristics of the components necessary for the development of such an external cavity. The theoretical and design concepts are experimentally confirmed in a number of external cavities, using diode lasers emitting around 1.5 μm, with different types of antireflective coatings, as well as different grating configurations     

The role of axially nonuniform carrier density in altering theTE-TE gain margin in InGaAsP-InP DFB lasers

Axial nonuniformities in the carrier density profile of 1.55 μm capped-mesa-buried-heterostructure distributed-feedback (CMBH-DFB) InGaAsP-InP diode lasers are discussed. This is accomplished by directly measuring the spontaneous emission at various locations in the laser optical cavity. The authors observe that the highly asymmetric optical field, inherent in DFB lasers, produces a strong longitudinal nonuniformity in the carrier density. This promotes degradation of the lasing gain margin between the dominant TE Bragg modes, which is verified through measurements of the relative shift of the lasing mode in the stopband. The reduction of gain margin is shown to cause multimode operation in devices with large optical field asymmetries. In devices with modest optical field asymmetries, the reduction of the gain margin saturates, and single mode behavior is maintained. Measurements are consistent in many respects with the predicted consequences of spatial hole burning     

Global excess spontaneous emission factor of semiconductor laserswith axially varying characteristics

An expression of the excess spontaneous emission factor of semiconductor lasers having axially varying characteristics has been derived, using a classical treatment for the contribution of spontaneous emission to the laser's noise figure. Although the analysis is focused on semiconductor laser structures, including DFB lasers, the expression obtained can be applied with minor changes to other standing-wave laser geometries. This global excess spontaneous emission factor, accounting for transverse as well as longitudinal effects, is relevant even for laser structures wherein the longitudinal and lateral field distributions are mutually coupled. In this situation, this factor is not equivalent to the product of Petermann's excess noise factor and a longitudinal correction factor accounting for outcoupling losses     

Axial profile of grating coupled radiation from second-order DFBlasers with phase shifts

Axial profiles of the grating-coupled radiation field emitted in a direction normal to the surface of distributed-feedback (DFB) lasers with phase-shifted second-order corrugation are theoretically analyzed. The profiles are calculated for nonreflecting DFB lasers with the following phase shifts: λ/4 shift, two λ/8 shifts, and two 3λ/8 shifts. It is demonstrated that the radiation field can be controlled by changing the phase shifts. This result suggests a new method for modulating the surface emission of a DFB laser     

Transverse mode control of vertical-cavity top-surface-emittinglasers

Transverse mode characteristics and control for vertical-cavity top-surface-emitting lasers (VCSELs) are discussed. A spatial filtering concept for the control of VCSEL transverse modes that allows over 1.5-mW single TEM₀₀ transverse mode emission to be routinely achieved from continuous-wave electrically excited VCSELs is introduced. Without spatial filtering, L-I and V-I kinks are observed     

Electroluminescence properties of a whispering-gallery-mode laser with coupled disk cavities

Whispering-gallery-mode (WGM) lasers (emission wavelength λ = 2.1–2.4 μm) with coupled disk cavities connected by a bridge are developed on the basis of a GaInAsSb/GaAlAsSb quantum-well nano-heterostructure and their emission spectra and optical far-field patterns are studied. Almost single-mode lasing in one spatial mode is observed in a wide range of supply currents. The emission wavelength grows with increasing current due to heating of the laser, and this phenomenon can be used in diode-laser spectroscopy. An assumption is made that the flux of generated emission can pass in lasers of this kind from one cavity to the other and back along the cavity-connecting bridge. It is found that strong narrowing of the laser emission pattern occurs with increasing current near the plane separating the coupled cavities.     

Device characteristics of GaAlAs buried-multiquantum-well lasers fabricated by Zn-diffusion-induced disordering

A new transverse mode controlled buried-multiquantum-well (BMQW) laser has been fabricated using the simple and reliable Zn-diffusion-induced disordering process. BMQW lasers are characterized by low threshold current (20 mA) and single transverse and longitudinal mode oscillation. It is observed that the threshold current is proportional to the stripe width and the transverse mode is controlled by controlling the stripe width. From these results, it is confirmed that the BMQW structure provides good optical confinement as well as current confinement.     

Measurements of the polarization dependence of the gain of strained multiple quantum well InGaAs-InP lasers

The polarization-dependent gain spectra of both tensile and compressive strain multiple-quantum-well (MQW) In/sub x/Ga/sub 1-x/As-InP lasers in a relatively large strain regime are presented. The results show that MQW lasers with tensile strain and an In concentration as low as 43% in the wells lase in a pure transverse magnetic (TM) mode rather than a transverse electric (TE) mode with a gain difference of 60-70 cm/sup -1/ at all the injection currents investigated. The peak gain for the TE mode is shifted toward shorter wavelengths from that of the TM mode, indicating that the emission is principally due to light hole-electron transition. The differential gain of the TM mode is about 1.5 times higher than that of the TE mode operation. Opposite phenomena were observed in the compressive strained MQW lasers.<>     

5000小时室温连续激射GaAs/AlGaAs双异质结激光器

一、引言 半导体激光器采用双异质结构(DH),对有源层内的注入载流子及辐射光场进行限域,使得阈电流密度迅速下降为～1×10~3安培/厘米~2,1970年实现了室温连续激射。双异质结激光器是光纤通讯和精密测距的较理想光源,但急待解决稳定性和可靠性问题。自从对DH激光器退化机理有了比较清楚了解之后,激光器寿命基本上每年提高半个至一个数量级。到1976年美国Bell公司通过升温加速老化试验推断激光器寿命可望达到100万小时。也已采用多种方式制作各