Properties of monolithic integration of a resonant tunneling diode and a quantum well laser

An investigation of the electrical and optical characteristics of a resonant tunneling diode monolithically integrated with a quantum well laser is carried out. An analytic expression for the propagating model current is given in terms of the total spontaneous emission rate. The laser is pumped by the current emitted by the resonant tunneling diode. When the current in the laser exceeds the threshold current, laser light is produced. Since the current in the laser exhibits negative differential resistance similar in behavior to the current of a resonant tunneling diode, a bistable light output can be obtained from this new device.     

Tunable single-mode Fabry-Perot laser diode using a built-in external cavity and its modulation characteristics

A tunable single-mode laser is obtained by using a weakly coupled cavity structure involved in a coaxially packaged Fabry-Perot laser diode. The cleaved end facet of the coupling fiber becomes an optical reflector and forms an external cavity with a laser facet. The single-mode oscillation condition is controlled and stabilized by tuning the operating temperature. The tuning range is about 10 nm with the side-mode suppression ratio of more than 27 dB when the temperature changes from 11.5 degrees C to 25 degrees C. Direct modulation characteristics were investigated, and our results show that a shorter external cavity can bear deeper modulation depth.     

Demonstration of an all-optical switch by use of a multiwavelength mutual injection-locked laser diode

Error-free all-optical packet switching is demonstrated by use of a multiwavelength mutual injection-locked Fabry-Perot laser diode. A 10-Gbit/s data signal is switched on and off with an extinction ratio of 16.9 dB when an optical control signal is turned off and on with a power difference of only 3 dB.     

基于硅波导的喇曼光放大器

在硅波导上添加反向偏压的PIN结构,当波导产生受激喇曼散射时,可以将波导中双光子吸收(TPA)产生的光生自由载流子扫出波导,降低了波导的非线性损失,极大地提高了硅波导中泵浦光对信号光的喇曼增益。为了应用已经非常成熟的硅工艺,并且应用硅波导使器件小型化,根据法布里-帕罗(F-P)腔和行波放大器理论,在硅波导两端的解理面蒸镀增透膜,应用这种波导的喇曼效应设计了一种光放大器,即基于硅波导的喇曼光放大器。建立了计算放大器增益的方程,给出了不同波导长度和输入功率情况下的放大器增益,得出适当增加波导长度和泵浦光功率可以得到较高喇曼增益的结论。基于硅的光放大器有较高的饱和功率且没有泵浦源的限制,通过调整泵浦激光的波长可以放大不同波长的信号光。     

波长可调谐超短光脉冲的简便高质的生成技术

提出了一种以处于增益开关调制状态下的法布里珀罗(Fabry-Pérot)半导体激光器作为光源,采用简单的自激注入锁定方式,以生成波长可调谐的超短光脉冲的实验系统。该实验装置中,激光器的外腔包括两个串联在一起的布拉格光纤光栅,一个掺铒光纤放大器(EDFA),一个光耦合器和两个环行器,其作用是选模,以及增强并控制反馈回激光器内腔的光强。该实验系统简单而高效,在24nm的波长调谐范围内获得了边模抑制比高于40dB的单模光脉冲输出;而在1521.8nm和1550.0nm之间28.2nm的波长调谐范围内,边模抑制比高于35dB。所得到的各个单波长激光脉冲的时域半峰全宽为140~260ps,各个脉冲的光谱半峰全宽皆为0.1nm。     

Comparison of electrical characteristic between AlN/GaN and AlGaN/GaN heterostructure Schottky diodes

Ni/Au Schottky contacts on AlN/GaN and AlGaN/GaN heterostructures are fabricated.Based on the measured current–voltage and capacitance–voltage curves,the electrical characteristics of AlN/GaN Schottky diode,such as Schottky barrier height,turn-on voltage,reverse breakdown voltage,ideal factor,and the current-transport mechanism,are analyzed and then compared with those of an AlGaN/GaN diode by self-consistently solving Schrdinger’s and Poisson’s equations.It is found that the dislocation-governed tunneling is dominant for both AlN/GaN and AlGaN/GaN Schottky diodes.However,more dislocation defects and a thinner barrier layer for AlN/GaN heterostructure results in a larger tunneling probability,and causes a larger leakage current and lower reverse breakdown voltage,even though the Schottky barrier height of AlN/GaN Schottky diode is calculated to be higher that of an AlGaN/GaN diode.     

20-GHz optical pulse source based on cascaded electroabsorption modulators

A high-quality low-timing-jitter 20-GHz optical pulse train is generated by using two cascaded sinusoidally driven electroabsorption modulators (EAMs) at very low bias voltage of -0.8 V in conjunction with a tunable distributed feedback (DFB) semiconductor laser. An approximate transform-limited optical pulse,with the pulse width less than 7 ps, the spectral width of 0.3 nm, and the side-mode suppression ratio (SMSR) above 20 dB, is obtained by tuning the optical delay line.     

Voltage-controlled storage and retrieval of an infrared-light pulse in a quantum-dot molecule

Dynamic storage and retrieval of a weak infrared (IR)-light pulse are investigated theoretically with feasible parameters in an asymmetric double quantum dot system, a quantum dot molecule (QDM). It is shown that, with a voltage-controlled tunneling, we are able to store and retrieve the IR signal pulse in this three-subband QDM medium by slowly switching off and on the tunneling. The scheme proposed may open up the electrical controllability of quantum optical information storage and retrieval, which is expected to be useful in quantum information science in an asymmetric double quantum dot controlled by voltage.     

Power line monitoring system using fiber optic power supply

We propose a novel power-line-monitoring system using optical fibers for transmitting power as well as signal. The principle is experimentally confirmed with a system composed of a monitoring side with a 1.5-μm laser diode, transmission line of a single mode fiber, and a sensing side having an efficient photovoltaic (PV) cell, electrical junction sensor, and low power liquid crystal optical modulator (LCOM). The PV cell generates the electrical power in the sensing side with a conversion efficiency of 20%. The LCOM is driven with low power of less than 50 μW, modulates the laser light with a signal indicating the power line condition, and transmits the optical signal. The developed sensing unit produces an optical signal having an extinction ratio of 15 dB with low optical power of 1.8 mW. Five systems were in operation for two years, faithfully monitoring the oil pressure in electrical cables every 20 min without incident.     

Investigation of Q-switched InP-based 1550 nm semiconductor lasers

High energy picosecond pulse generation from a two contact tapered 5 quantum well (QW) InGaAlAs/InP diode laser (1550 nm) is investigated using a passive Q-switching technique. Single peak pulses with pulse energies as high as 500 pJ and durations of typically hundreds of picoseconds are obtained from the device by applying reverse bias voltages in the range of 0 V to ?18 V to the absorber section of the device. It is also demonstrated that more symmetrical Q-switched pulses are obtained by reducing the duration of electrical pulses applied to the gain section of the laser. Such an improvement is attributed to the reduced time of the population inversion in the gain section due to shorter electrical pulse. We also show comparatively the dependence of optical spectra on the reverse bias voltage for diode lasers emitting at 1550 nm and 1350 nm, and demonstrate that better spectral output is obtained from AlGaInAs lasers emitting at a wavelength of 1550 nm.     

High-resolution optical time domain reflectmetry based on a broadband continuous wave multimode laser diode

A broadband light source can be obtained by operating a multimode laser diode with a bias current below threshold. We propose an optical time domain reflectometer for high-resolution with a broadband cw multimode laser. The emission spectrum of the multimode laser diode that affects an interference signal is investigated. With this method, the spatial resolution is measured as 11.5 μm, corresponding to that of 38.3-fs pulses, and a minimum detectable reflectivity < -90 dB is achieved.     

S-shaped current bistability in a bipolar resonant tunneling diode

The bipolar tunneling transport through p–i–n double barrier structures has been studied by means of simultaneous electrical transport measurements and electroluminescence spectroscopy. An “inverted” hysteresis loop is observed at the onset of the first electronic resonance in the current–voltage characteristics with an electrical ON/OFF ratio of more than two orders of magnitude. Relating the different branches of the current–voltage characteristic to the space charges accumulated throughout the structure the inverted hysteresis loop is interpreted in terms of an S-shaped current bistability. The S-shaped current bistability is similar to the current driven negative differential resistivity as known for instance from thyristor action. This analogy between the bipolar double barrier structure with alloyed n-type emitter and the thyristor will be briefly discussed.     

Optical bistability effects in a Tm,Ho:YLF laser at room temperature

We demonstrate strong optical bistability in a 2 microm continuous-wave Tm,Ho:YLF laser pumped by a 792 nm laser diode near room temperature. The bistable region is as much as 100 mW wide at 283 K and can be controlled by the temperature of the laser crystal. The influence of crystal temperature on the characteristics of optical bistability is obtained. The influence of the pump-to-mode ratio on the bistable characteristics of the laser is also discussed. To our knowledge this is the first report of optical bistability effects in Tm,Ho:YLF lasers.     

Generation of twin beams from an optical parametric oscillator pumped by a frequency-doubled diode laser

Quantum-correlated twin beams were generated from a triply resonant optical parametric oscillator with an a-cut KTP crystal pumped by a frequency-doubled diode laser. A total output of 5.1 mW was obtained in the classical-nonclassical light-conversion system driven by a 50-mW diode laser at 1080 nm. A quantum-noise reduction of 4.3 dB (63%) in the intensity difference between the twin beams was successfully observed at the detection frequency of 3 MHz.     

Low Timing Jitter and Tunable Dual-Wavelength Picosecond Pulse Generation from a Fabry--Pérot Laser Diode with External Injection

A novel scheme to generate tunable dual-wavelength optical pulses with low timing jitter at arbitrary repetition rates is proposed and demonstrated experimentally. The pulses are generated from a gain-switched Fabry-Pérot laser diode with two external cw beams for injection seeding simultaneously. The cw light is generated by two independent distributed feedback laser diodes, and their wavelengths can be tuned independently by two temperature controllers. The dual-wavelength pulses with the pulse width of 57 ps, the timing jitter of 340 fs, are obtained. The sidemode-suppression ratio of the output pulses is better than 23dB over a 10-nm wavelength tuning range.     

Characteristics of the S/N ratio of the beat note obtained from the frequency-mixing experiments between a CO2 and an H2O laser

The S/N ratio of the beat note obtained from the frequency mixing between a 32 THz CO₂ laser, a 10.7 THz H₂O laser and a 22 GHz klystron is measured as a function of incident power of both lasers and the klystron on the W-Ni point contact diode. A maximum S/N ratio of 36 dB is obtained. It is found that the S/N ratio arises from the product of the contributions due to the incident power and the fifth coefficient of the current-voltage characteristic of the W-Ni diode. These characteristics are discussed qualitatively.     

The effects of external optical feedback on the power penalty of DFB-LD modules for 2.5Gbs−1 optical transmission systems

We report the effects of external optical feedback on the power penalty of commercial distributed feedback laser diode (DFB-LD) modules for 2.5Gbs–1 optical transmission systems. External optical feedback presented to the DFB-LD modules causes the excitation of external cavity modes, resulting in increased relative intensity noise (RIN) and intensity noise ripples at low frequency region below 500MHz. For a 10–10 bit error rate (BER), the minimum power penalty is as much as 1.25dB for a feedback ratio of –8.8dB. An excess power penalty of 0.5dB per 3dB increase in the feedback ratio was also empirically obtained. We suggest that optical isolators in 2.5Gbs–1 DFB-LD modules used in conventional optical transmission systems or WDM systems must have a peak isolation ratio of better than 54.5dB, instead of the previously recommended 30dB, for negligible power penalty induced by external optical feedback.     

用于10Gb/s传输系统的电吸收调制器与分布反馈激光器集成光源

采用超低压(22×１０^２Pa)选择区域生长(selective area growth, SAG)金属有机化学气相沉积(metal-organic chemical vapor deposition, MOCVD)技术成功制备了应变型InGaAsP/InGaAsP电吸收调制器(electroabsorption modulator, EAM)与分布反馈激光器(distribute feedback laser, DFB)单片集成光源的新型光电器件.实验结果表明，采用该技术制备的集成器件表现出了良好的性能：激射阈值为19 mA，出光功率接近7 mW，边模抑制比(side-mode suppression ratio, SMSR)大于40 dB，将该集成器件出射光耦合进普通单模光纤后进行测量，获得了16 dB的消光比，器件3 dB响应带宽达到了10 GHz以上.将该集成器件完全封装后成功进行了10 Gb/s非归零码(non-return zero, NRZ)的传输实验：在误码率为10^-10的传输条件下于普通单模光纤中传输了53.3 km，色散代价小于1.5 dB，动态消光比大于8 dB，且眼图清晰张开. 关键词： 超低压 选择区域生长 集成光电子器件 10 Gb/s     

10 Gbit/s Silicon modulator and germanium detector chip-to-chip optical link

Experimental results of a high-speed silicon optical modulator based on carrier depletion in a pipin diode and Germanium photodetectors are presented. 10 Gbit/s data transmission is obtained for both optoelectronic devices, with for the optical modulator an extinction ratio (ER) higher than 8 dB and insertion loss (IL) lower than 6 dB and for Ge photodetector, a zero-bias operating at 10 Gbit/s. Finally, a 10 Gbit/s optical link combining Si modulator and Ge photodetector is demonstrated.     

Asymmetric Fabry-Perot modulators with an InGaAs/AlGaAs active region

Strained layer superlattices have been used as the active region in asymmetric Fabry-Perot cavity optical modulators. The active layer of the Fabry-Perot modulator consisted of a 50 period In_0.15 Ga_0.85As/Al_0.30Ga_0.70As (10nm/10nm) superlattice. These quantum wells operate at typical wavelength of around 960 nm. By varying the length of the Fabry-Perot cavity in the modulator by including AlGaAs space layers of different thicknesses in the cavity, it is shown experimentally that both normally on and normally off devices can be obtained using the same stack of quantum wells. For the first type of device operation, a maximum contrast ratio of 8.3 dB could be measured for a reverse voltage of 7 V at 969 nm, while for the second type, a maximum of 8.9 dB at 957 nm was obtained for a 20 V reverse voltage. Using the same structure with an extra Bragg reflector on top of the quantum well layers to increase the surface reflection, a device with a higher finesse of the cavity was obtained. A maximum contrast ratio of 11.5 dB was measured for a reverse bias voltage of 30 V at 978 nm, with an insertion loss of –4.2dB.