用法布里-珀罗干涉仪分析飞秒脉冲激光辐射

根据固体激光飞秒脉冲的锁模技术,本文论证了利用法布里——珀罗干涉仪,测量具有辐射光谱带宽少于倍频程的激光混合频率精梳实验方法。     

Mode locking of individual array modes of a gain-guidedsingle-quantum-well laser array with an external mirror

Mode locking of individual spatial lateral array modes of gain-guided GaAs single-quantum-well laser array with an external mirror is observed. The single-lobe fundamental array mode and several higher order array modes were individually selected by adjusting the external mirror. The array modes were characterized by the far-field patterns of the laser array. The corresponding spectrum consists a number of narrow longitudinal modes indicating that a single array mode was selected. These array modes were mode locked using a combination of feedback from the external mirror and sinusoidal RF modulation. The far-field patterns remained spatially constant when the RF modulation was applied. Autocorrelation pulsewidth measurements showed that the pulses have a Gaussian shape. Pulses as short as 70 ps were obtained for the lowest order array mode, where all the laser emitters were in phase, and increase with increasing array mode order     

The energy-limiting characteristics of a polarization-maintaining Sagnac interferometer with an intraloop compressively strained quantum-well saturable absorber

An experimental demonstration of an energy limiter for short pulses at 1550 nm is reported. The limiter is based on an optical fiber Sagnac loop with an intraloop dichroic saturable absorber based on an InGaAsP-based waveguide with compressively strained multiple quantum wells. The saturable absorber is placed asymmetrically in the loop and is used as a Kerr-like nonlinear phase shifter. The device is operated in a novel dual polarization scheme, which offers some unique advantages. Excellent limiting for noise reduction purposes is demonstrated with the device.     

The influence of external frequency shifted feedback on a DFB semiconductor laser

To investigate the possibility of optical isolation of a semiconductor laser using acoustooptic interaction, the influence of frequency shifted feedback on a DFB laser was studied experimentally. The isolation concept is based on a frequency shift of the laserlight by means of an acoustooptic Bragg deflection. This concept offers the opportunity of optical integration when Surface Acoustic Waves are used. In the experiments, a clear difference in laser performance between regular feedback and frequency shifted feedback was observed.     

The laser oscillator with an external signal

The problem considered is that of a laser oscillator with an externally applied signal. Calculations are made 1) to determine the conditions for quenching the natural oscillation, 2) to evaluate the frequency pulling and pushing effects, and 3) to determine the power gain at the forcing frequency.     

Coherent transmission using an external waveguide Bragg reflector laser with direct frequency modulation

Single-frequency l.5?m semiconductor lasers, formed by butt-coupling of a regular Fabry?Perot laser to an external waveguide Bragg reflector, are shown to have very uniform frequency modulation characteristics under direct current modulation. The laser's frequency modulation characteristics, together with its narrow linewidth (? 1 MHz), make coherent transmission possible without external modulators. The laser performance was evaluated in a 417Mbit/s, 102 km, frequency-shift-keying coherent transmission experiment.     

Photosensitization of standard fibers with deep UV laser radiation

A strong and permanent ultraviolet photosensitivity enhancement was locked into standard optical fiber pre-treated with above-bandgap 157-nm F/sub 2/-laser radiation. Below-bandgap 248-nm irradiation of the pre-treated fiber yielded fiber Bragg gratings (FBGs) with an index contrast of 6.5 /spl times/ 10/sup -4/, a value four-fold larger than that available in 16% Ge-doped photosensitive fiber. The F/sub 2/-laser photosensitivity locking was 300 times more effective than with KrF-laser pre-treatment in terms of the accumulated fluence required to lock in a similar refractive index change. Accelerated FBG aging tests equivalent to 25 years at 70/spl deg/C revealed a less than 2% reflectivity decay in both 157- and 248-nm pre-treated fibers, which is sufficient to eliminate the postannealing step typically required in hydrogen-loaded fibers. The large photosensitization and the superior thermal stability of both 248- and 157-nm pre-treated fibers are associated with a new Si-H bond absorption feature at 1387 nm, which appears only during the FBG formation step.     

Frequency stabilization of an external cavity laser diode usingelectrooptic effect

An external cavity laser diode, which consists of a LiNbO₃ phase modulator, was frequency-stabilized to a resonance frequency of a Fabry-Perot interferometer using the electrooptic effect. The optical frequency fluctuation was detected through a Fabry-Perot interferometer and the detected signal was negatively fed back to the phase modulator to reduce the frequency fluctuation. The rear facet of the electrooptic phase modulator was coated with gold and used as an external mirror. At feedback-off state, the peak-to-peak frequency fluctuation of the laser diode was 52 MHz in 2 min. At feedback-on state, the peak-to-peak frequency fluctuation was reduced to 1.5 MHz. This condition was maintained for the duration of the observation, 1 h and 40 min     

Mid-range coherent optical frequency domain reflectometry with aDFB laser diode coupled to an external cavity

The optical frequency of an external double cavity coupled laser diode was controlled via the phase of the feedback light. Strong linewidth and mode hopping reductions were obtained, extending coherent reflectometry with semiconductor sources to the range of hundreds of meters     

Pulsing behavior of a three-level laser with saturable absorber

A numerical study of a three-level laser model that includes a saturable absorber is presented. The theory models the laser as a lumped element. This assumption is valid as long as the laser pulses are much longer than the cavity. The model is intended to be somewhat representative of an erbium-doped fiber laser without trying to mimic the operating parameters of such a laser too closely. As expected, the presence of the saturable absorber causes the laser to be unstable under certain operating conditions. The question of stability is explored by examining small perturbations of the steady-state solutions of the rate equations. It is found that the predictions of this stability analysis are in excellent agreement with the behavior of the solutions of the full time-dependent rate equations. It is also found that under certain conditions the laser may pass from pulsed to stable operation simply by raising the pump power     

Oscillation frequency, linewidth reduction and frequency modulation characteristics for a diode laser with external grating feedback

Simple analytical expressions are given for the oscillation frequency, linewidth, FM noise spectrum and frequency modulation characteristics of a diode laser with external grating feedback. The analytical expressions are found to be in good agreement with experimental results and to be useful for quantitative predictions and optimisations of the external feedback controlled diode laser performance.     

用半导体吸收体实现陶瓷激光器被动锁模研究进展

新型陶瓷材料近年来开始作为激光增益材料,具有低成本、大尺寸、制备时间短、热导率高等优点。大功率飞秒激光器是近年来超短脉冲激光制备的一大热点。本文探讨了使用半导体可饱和吸收镜实现被动锁模大功率陶瓷飞秒激光器的可行性,研究现状以及未来趋势。     

高重频激光压制干扰与激光制导系统相互作用效应研究

在时域上分析了高重频激光压制式干扰作用时激光导引头的信息处理过程.以具有抗干扰措施的激光制导系统为干扰目标,采用二极管泵浦全固体高重频激光器为干扰源干扰激光导引头,通过外场试验从系统级角度研究了高重频压制干扰与激光制导系统相互作用效应.用所记录的目标视线和系统光轴角误差数据表征相互作用效应,说明高重频激光压制干扰与激光制导系统相互作用效应表现为激光导引头的信息处理机制被破坏,不能正常给出的水平、俯仰角度误差信息,但这种破坏在压制干扰消除后即刻消除.     

Experimental study of a ring dye laser with an external retroreflecting mirror

We have experimentally studied the forward-to-backward intracavity intensity ratios for a rhodamine 6G ring dye laser with an external retroreflecting mirror. The experiments were conducted at several wavelengths, degrees of excitation, and cavity configurations. The results indicate the large forward-to-backward ratios are only achievable near threshold and that this method is not suitable for the elimination of susceptibility gratings in the medium.     

On the stability of modes in a laser resonator with an active medium

A discussion is given on the stability of laser modes; particularly for those in active resonators having negative gain profiles.     

The stability of modes in a laser resonator which contains an active medium

The stability of the eigenmodes of a laser resonator which contains a medium with a gain profile is discussed. Some arguments given recently by different investigators are examined, and the discrepancy among them is clarified.     

外腔锁相中二极管列阵相邻单元间不同侧模的耦合系数

推导了锁相外腔中半导体激光器列阵相邻发光单元之间不同阶侧模的耦合系数,计算了耦合系数的幅度与外腔长度的关系。结果表明:幅度的极大值对应的外腔长度随侧模阶次增大而减小,不同阶次侧模耦合系数的最大幅度也随阶次降低而减小。上述结果意味着;要实现相邻单元间的基侧模耦合锁相,应该把腔长放在对应的极大值附近;同时也预示着如果腔长过短,可能会出现高阶侧模的外腔锁相。     

Stable single-mode operation of an 850-nm VCSEL with a higher ordermode absorber formed by shallow Zn diffusion

We report that an 850-nm vertical-cavity surface-emitting laser with a planar higher order mode absorber, formed by shallow Zn diffusion (<0.3 μm), operated at stable single-mode over the entire drive current range. A device with a 5×5 μm² absorber aperture and a 5×5 μm² oxide confined active region showed a ~0.8 mA threshold and a mode suppression ratio of 40 dB. The modeling indicates that the higher order modes will be suppressed strongly due to the much larger threshold gain, compared to that of the fundamental mode as long as the Zn diffusion depth outside the 5×5 μm² absorber aperture is over ~0.2 μm, which agrees well with the experimental results     

The effect of external optical feedback on timing jitter in modulated laser diodes

Laser diodes with optical feedback are numerically modeled using single-mode rate equations. The effects of the optical feedback on the pulse turn-on delay and timing jitter are examined, for gain-switching, periodic and pseudorandom modulation formats. It is shown that there is a change in turn-on delay and a considerable increase in the timing jitter due to the changes in the output power distributions as optical feedback increases. The cause of the increased jitter is found to be the additional intensity noise introduced by the optical feedback.<>