Smoothly wavelength-tunable picosecond pulse generation using a harmonically mode-locked fiber ring laser

A simple design of a stable, smoothly wavelength-tunable picosecond pulse generator has been demonstrated using a dispersion-tuned, harmonically mode-locked fiber ring laser with a directly modulated semiconductor optical amplifier (SOA). The SOA functions as both a polarization-insensitive mode locker and a supermode noise suppressor. Near-linearly chirped pulses are generated and compressed to less than 4 ps when the intracavity dispersion is anomalous while 11-ps, near-transform-limited pulses are generated without compression when the dispersion is normal. Smooth wavelength tuning is achieved over more than 11 nm by only tuning the modulation frequency and pulse characteristics are stable over the entire tuning span. A simple numerical model successively simulates the operation principle of the system. The tuning range is determined by both the gain profile and the total intracavity dispersion. The dispersion and the SOA ensure the long-term stability of the system.     

Wavelength tunable source of subpicosecond pulses from CW passivelymode-locked two-section multiple-quantum-well laser

A wavelength-tunable passively-mode-locked semiconductor laser source of subpicosecond pulses is demonstrated. The system includes a two-section multiple-quantum-well laser which is coupled to an external grating for tuning and is followed by an external grating pair for pulse compression. A tuning range of 16 nm round 846 nm is obtained, resulting in compressed pulse widths as short as 260 fs and pulse widths shorter than 600 fs for all wavelength values within this tuning range. Time-bandwidth products are one to two times the transform limit     

Tuning characteristics of monolithic passively mode-lockeddistributed Bragg reflector semiconductor lasers

Tuning characteristics of multicontact passively mode-locked distributed Bragg reflector (DBR) semiconductor lasers are investigated in terms of center wavelengths and pulse repetition frequencies. It is shown that the center wavelength of the pulses can be tuned over a wide range by changing the refractive index of the Bragg reflector section either by means of carrier injection or by thermal effects while maintaining the pulses to be nearly transform-limited. Tuning of the pulse repetition rates is realized by using four different approaches, i.e., current injection to a passive phase-control section, varying of the reverse bias to the absorber, varying of the injection current to the gain region, and thermal effects. Injecting current into the phase-control region results in a tuning range of more than 400 MHz while maintaining the pulses at transform-limited condition. Varying the reverse bias voltage to the absorber is shown to be an alternative to achieve large repetition rate tuning, by which a tuning range of 600 MHz is obtained. By combining these tuning schemes, a total tuning range of more than 1 GHz is realized     

半导体光纤环形腔激光器调谐特性的实验研究

采用国产半导体器件,组建了半导体光纤环形腔激光器(FRSLs)的实验装置及相应的测试系统,系统地研究了FRSLs的输出和调谐特性.结果表明,已实现高速调制情况下的动态单纵模调谐,并获得波长调谐范围大于36nm的稳定光脉冲输出.确立了FRSLs的阈值特性、输出功率等物理参量与振荡波长之间的关系,提出通过控制分光比来优化和兼顾FRSLs的调谐范围及输出功率.实验结果较好地与理论模拟结果相吻合,为进一步改善FRSLs的性能指标提供了实验依据.同时,这些分析与结论对于相关结构类型的激光器设计也具有一定的参考价值.     

Fourier-limited 1.6-ps pulses with variable repetition rate from 1to 26 GHz by passive mode-locking of a semiconductor laser in anexternal cavity

By passive mode-locking of a semiconductor laser (λ=1.3 μm) in an external cavity, 1.6 ps sech²-shaped pulses are generated with variable repetition rates from 1 to 26 GHz, presently limited only by the geometry of the set-up. The time-bandwidth product is between 0% and 40% over the theoretical limit. Wavelength tuning up to 50 nm is possible     

Mode-Locking in a Semiconductor Fiber Laser Using Cross-Absorption Modulation in an Electroabsorption Modulator and Application to All-Optical Clock Recovery

We demonstrate the use of cross-absorption modulation in an electroabsorption modulator to actively mode-lock a semiconductor fiber laser at 10 GHz. The laser cavity also comprises a linearly chirped fiber Bragg grating to obtain wavelength tunable operation based on the dispersion tuning approach. The laser exhibits uniform output pulse characteristics throughout the tuning range. We also investigate the impact of using different types of optical pump signals on the output pulses. Finally, we demonstrate the application of the mode-locked laser for all-optical clock recovery.     

Continuously wavelength-tunable MQW fabry-perot laser diode pulse source with a fiber-based external cavity

A simple continuously wavelength-tunable fiber ring laser pulse source is demonstrated. Such a source employs a gain-switched multiple quantum-well Fabry-Perot laser diode in a self-seeding scheme and the output pulse wavelength can be tuned continuously via a tunable optical filter. The optical pulses generated exhibit a pulsewidth of 92 ps at the frequency of 2.6 GHz. Within a wide wavelength tuning range of 46 nm, the side-mode suppression ratio and the average power of the output optical pulses obtained are higher than 50.1 dB and 3.3 dBm, respectively, and the pulse spectral stability can be maintained in the whole wavelength tuning range.     

Generation of transform-limited optical pulses using a combinationof a gain-switched diode laser and a semiconductor opticalamplifier

We introduce a novel method for generating nearly transform-limited picosecond optical pulses at multi-gigahertz repetition rates. Frequency-chirped optical pulses are first produced using a gain-switched semiconductor diode laser, and they are subsequently amplified by a semiconductor optical amplifier. The red frequency chirp in the gain-switched pulses is compensated for almost completely as a result of gain-saturation-induced self-phase modulation occurring in the amplification process. Experimentally, we have successfully generated nearly transform-limited 28-ps optical pulses at a 5-GHz repetition rate using a distributed feedback diode laser and a traveling wave semiconductor optical amplifier     

Efficient generation of wavelength-tunable single-mode pulses at 1.3 and 1.55 /spl mu/m by a simplified approach of self-injection seeding

A simple configuration to generate tunable single-mode pulses by self-injection seeding of a gain-switched semiconductor laser is demonstrated. The key part of the setup consists of a highly dispersive fiber and a fiber mirror. The configuration shows improved stability and promise to operate at both 1.3 and 1.55 /spl mu/m. The lasers at the respective wavelengths have been successively tuned over 13.43 and 12.81 nm with a side-mode suppression ratio >15 dB. Continuous access of wavelength with an enhanced tuning range is also achieved by combining both electrical and thermal control on the laser.     

外腔半导体激光器设计与高次谐波稳频

研究了利特罗(Littrow)结构外腔半导体激光器的结构参量对激光连续可调范围的影响。给出了反射镜转轴等处的机械加工误差对激光波长连续可调范围所造成的影响的数值计算结果。介绍了半导体激光器外腔结构设计的具体细节要点。利用该设计制作的外腔只需要配合商用半导体激光管便可以得到优质的780nm激光输出,经测量其线宽小于1MHz,连续可调谐范围大于3GHz。利用腔外Rb饱和吸收谱的三、五次谐波稳频方法对半导体激光器进行了稳频。其中提出了优化激光频率短期稳定度的方法,并对调制深度的选择给出了详细的理论解释。根据该优化方法设计出稳频系统对半导体激光器进行稳频,得到了稳定度达到10-12量级的半导体激光输出。     

On the locking range of hybridly mode-locked semiconductor lasers

We theoretically investigate the locking range of hybridly mode-locked semiconductor lasers with a DBR section as a reflector. The DBR coupling constant and length are crucial in determining the locking range. At constant pulse width, the tuning range of the repetition frequency can be increased by a factor of 3 by using a strongly coupled, long DBR rather than a short and weakly coupled DBR. For a 30 GHz cavity and a pulse width of 5 ps, a locking range of 2.5% is predicted after optimization. We explain the increase in the locking range as a consequence of the dispersion inherent to a DBR. In addition, the pulses are found to be asymmetric, depending on the DBR parameters.     

双波长可调谐TEA CO2激光器的脉冲输出特性

为了获得两束波长不同的可调谐CO2激光脉冲,采用了双光栅与输出镜构成双谐振腔的结构没计。实验中,对影响激光器脉冲输出能量和调谐范围的参量作了具体分析。结果表明,两个谐振腔可以独立振荡输出不同波长的两束激光,二者之间不存在竞争影响,并且均可在大范围内调谐输出;通过对两个光栅做小幅度失谐调整,可以实现两束激光脉冲同步输出。     

Generation of 185 fs pedestal-free pulses using a 1.55 μmdistributed feedback semiconductor laser

The authors report the generation of 185 fs pulses from a 1.55 μm distributed feedback semiconductor laser, the shortest pedestal-free pulses ever generated from semiconductor lasers. This has been realised by simultaneously performing soliton-effect compression and intensity discrimination for pedestal removal in a single fibre     

Optical signal generation at millimeter-wave repetition rates usingsemiconductor lasers with pulsed subharmonic optical injection

A new technique is presented and investigated systematically which generates optical signals at millimeter-wave repetition rates from a semiconductor laser, without the need for an intracavity saturable absorber. Optical pulses are generated from a long-cavity semiconductor laser with a repetition rate equal to its cavity resonant frequency by injecting short optical pulses at one of the cavity resonance subharmonics. A rate-equation model is proposed to explain the mechanism of this subharmonic optical injection method. Optical pulses with repetition rates of 35 and 56 GHz are generated using the proposed scheme from a semiconductor laser with a distributed Bragg reflector and a Fabry-Perot laser diode, respectively. The performance of the generated pulses is also evaluated in terms of detected RF power at the repetition frequencies, the subharmonic suppression ratio, phase noise, and timing jitter as a function of frequency detuning, injected optical power, laser bias current, and, finally, the subharmonic number. It is found that the generated optical pulses exhibit large subharmonic suppression ratio (>17 dB), large locking ranges >400 MHz, low levels of phase noise (~-93 dBc/Hz@10 kHz) and timing jitter (<0.41 ps over 100 Hz to 10 MHz), and large tolerance to variations in operating parameters     

Low threshold tunable soliton source

An actively mode-locked erbium-fiber laser with continuous wavelength tuning over the range 1528-1565 nm has been demonstrated. A gain-saturated InGaAsP NTW semiconductor optical amplifier (SOA) is used as the active mode locking element, functioning as an amplitude modulator which provides gain and has <1 dB polarization dependence. The fiber laser is diode pumped at 1480 nm with a threshold of 6 mW, and provides pulses of 25 ps (FWHM) with a transform product of 0.4 and >12 dBm peak power     

Self-seeding of Fabry-Perot laser diode for generating wavelength-tunable chirp-compensated single-mode pulses with high-sidemode suppression ratio

We report an effective technique for generating wavelength-tunable chirp-compensated single-mode pulses with a high sidemode suppression ratio (SMSR) based on self-seeding a Fabry-Perot laser diode. This technique relies on the use of a tunable linearly-chirped fiber Bragg grating to provide wavelength-selective feedback, output filtering, and chirp compensation. With this technique, we have generated chirp-compensated picosecond pulses with a SMSR higher than 40 dB over a tuning range of 11.5 nm.     

实现外腔半导体激光器连续调谐的两个基本要求

定量讨论了实现外腔式半导体激光器连续调谐的两个基本要求:同时改变外腔长度及光栅反射波长,半导体激光器(LD)端面镀减反膜。分析表明:前人给出外腔的可调整范围并非是实现最大调谐范围的必要条件,而是实现调谐连续性的一种可行选择。针对具体的减反射膜,对在ECLD上可能实现的连续调谐范围进行了研究。     

Miniature packaged actively mode-locked semiconductor laser with tunable 20 ps transform limited pulses

Miniature, fibre tailed and packaged, wavelength tunable actively mode locked semiconductor lasers have been developed for use as sources of approximately 20 ps transform limited pulses. Continuous stable operation with >40 nm tuning ranges centred either at 1.3 mu m or 1.55 mu m have been demonstrated. The package has an adjustable cavity length enabling the repetition frequency to be selected between 2 GHz and 8 GHz. Mean output powers in the monomode fibre tail are in the range -10 dBm to -5 dBm.<>     

一种新的互注入锁定产生单/双波长光脉冲的方案

本文提出了使用两个F-P半导体激光器互注入锁定来产生单/双波长光脉冲的方法.其中一个FP做增益开关调制,另一个给定直流偏置.通过简单调节一个可调光滤波器,可以输出所需波长,且重复频率保持不变.对于单波长输出,在19nm范围内其边模抑制比超过30dB;对于双波长输出,在12.1nm范围内其边模抑制比超过25dB.该系统具有简单,成本低的优点.     

Stable optical picosecond pulses from actively mode-lockedtwin-section diode lasers

Stable, repetitive pulses with durations as short as 8 ps and peak powers in excess of 400 mW are generated with actively mode-locked twin-section semiconductor lasers operating at 0.898 μm with a locking range of ±1 MHz around 496 MHz