10 Gb/s 120-km Bidirectional Repeaterless Transmission over Single-Mode Fiber

A successful repeaterless 10 Gb/s bidirectional transmission experiment is demonstrated at the 1550 nm wavelength through 120 km of single-mode fiber. Fiber chromatic dispersion compensation in both transmission directions is realized by insertion of the same dispersion compensating fiber in the transmission fiber span. Excellent long-term error rate performance (BER < 10-¹⁴) is achieved by suppression of the Rayleigh backscattered signal power with low loss narrow-band fiber grating reflection filters.     

Design and evaluation of fundamental-mode and polarization-stabilized VCSELs with a subwavelength surface grating

We demonstrate 850-nm oxide-confined vertical-cavity surface-emitting lasers (VCSELs) with a locally etched subwavelength surface grating that are single-mode and polarization stable from threshold up to thermal roll-over, reaching /spl sim/4 mW of output power. The side-mode suppression ratio (SMSR) is >30 dB and the orthogonal polarization suppression ratio (OPSR) is /spl sim/20 dB. Moreover, no distortion of the far-field beam profile is observed as a result of the surface grating. Our numerical calculations show that a carefully designed VCSEL can have a high simultaneous mode and polarization selectivity without a significant increase in loss for the favored fundamental mode with polarization state perpendicular to the grating lines. This indicates characteristics such as threshold current and resonance frequency will not be notably degraded. The calculations also show a low sensitivity to variations in grating etch depth and duty cycle, which relaxes fabrication tolerances. In our experimental parametric study, where the oxide aperture diameter, surface grating diameter, and grating duty cycle were varied, the combined mode and polarization selection was investigated. For an optimum combination of oxide aperture and surface grating diameters of 4.5 and 2.5 /spl mu/m, respectively, the device is found to be single-mode and polarization stable for a broad range of grating duty cycles, from 55% to 75%, with only a small variation in other laser performances, which is in line with theory.     

Very-low-threshold, highly efficient, and low-chirp 1.55-/spl mu/m complex-coupled DFB lasers with a current-blocking grating

Low-threshold current DFB lasers have been fabricated based on a complex-coupled structure with a current blocking grating. A threshold current as low as 5 mA was obtained, which enabled high temperature operation up to 105/spl deg/C. Asymmetric facet coatings were applied to obtain a high efficiency of 0.3 W/A. The strained InGaAsP MQW active region and the antiphase coupling has resulted in a low modulation chirping. By direct modulation of the device at 2.488 Gb/s and using optical amplifiers, we have demonstrated digital transmission over a 235 km-long standard single-mode fiber with a power penalty of 1.55 dB.     

1.5-µm λ/4-shifted InGaAsP/InP DFB lasers

A single wavelength light source in 1.5-μm range was developed using InGaAsP/InPlambda/4-shifted distributed feedback (DFB) semiconductor heterostructures. Superiority of thelambda/4-shifted DFB structure in terms of stability of the main mode at the Bragg wavelength was shown theoretically, in which the threshold, the output, and the polarization characteristics were taken into account. Alambda/4-shifted corrugated grating was made by a newly developed negative and positive photoresists technique. Buried heterostructure (BH) diode lasers with nonreflective window ends were fabricated and highly stable single-mode operation with a low threshold was obtained reproducibly. Direct modulation properties and life-tests results indicated that thelambda/4-shifted DFB lasers could be a reliable single-mode light source in a long span lightwave transmission system in 1.5-μm range.     

低弯曲损耗少模光纤传输特性研究

提出一种采用少模阶跃光纤与单模光纤连接的方法,实现低弯曲损耗传输的新型光纤通信系统。采用有限元法研究了在模场直径相同的情况下少模光纤纤芯半径与折射率差的关系,以及不同参数下光纤的弯曲损耗;采用光束传播法计算了少模光纤的各种模式与普通单模光纤的基模的连接损耗。证明了采用少模光纤可以利用模式间的正交性实现有效的单模传输,并具有低的弯曲损耗和连接损耗。     

高性能InAs/GaAs量子点外腔激光器

为了获得高性能的量子点外腔激光器(ECL),利用InAs/GaAs量子点Fabry-Perot(FP)腔激光器研制了光栅外腔可调谐ECL。对InAs/GaAs量子点ECL进行了一系列的性能测试,主要包括单模稳定性测试、单模调谐范围测试、阈值电流密度测试、无跳模连续调谐测试和输出功率测试。在室温条件下获得了24.6nm的连续调谐范围,覆盖波长从999.2nm到1 023.8nm,并且实现了波长无跳模连续调谐。在调谐范围内最低阈值电流密度为1 525A/cm2,而且在中心波长处获得的单模输出功率为15mW,单模边模抑制比(SMSR)高达35dB。研究结果表明,通过构建光栅外腔可以实现高性能的InAs/GaAs量子点ECL。     

A 5-$mu$m-Thick SOI Waveguide With Low Birefringence and Low Roughness and Optical Interconnection Using High Numerical Aperture Fiber

A 5-m-thick silicon-on-insulator waveguide possessing low birefringence of and 9-nm lithography roughness is investigated using arrayed waveguide grating and an atomic force microscope. Instead of complex processing using a 3-D mode size converter, the high numerical aperture fiber is utilized as the bridge between the corresponding waveguide and single-mode fiber (SMF-28) to obtain a competitive coupling loss of 0.4 dB.     

Laser-to-fiber coupling scheme by utilizing a lensed fiberintegrated with a long-period fiber grating

An optical coupling scheme between a laser diode and a single-mode fiber utilizing a lensed fiber integrated with a long-period fiber grating is experimentally demonstrated and qualitatively analyzed. A long working distance of 110 μm and a coupling of 35% are obtained for a laser diode with an ellipticity of 2.5. The longitudinal and transverse tolerances at 1-dB excess loss are 26 and 2.5 μm, respectively     

40 Gbit/s electroabsorption modulated distributed feedback laser

A 40 Gbit/s multi-quantum well (MQW) electroabsorption modulator (EAM) with a lumped electrode monolithically integrated with a distributed feedback (DFB) laser is demonstrated. Superior characteristics are exhibited for the device, such as low threshold current of 18 mA, over 40 dB side-mode suppression ratio at 1 550 nm and more than 30 dB extinction ratio when coupled into a single-mode fiber. By adopting deep ridge waveguide and planar electrode structures combined with buried benzocyclobutene (BCB), the capacitance of the EAM is reduced down to 0.18 pF and over 33 GHz modulation bandwidth at a small signal has been demonstrated. Negative chirp operation is realized when the bias voltage is beyond 1.6 V.     

External-cavity semiconductor laser with focusing grating mirror

A novel external-cavity semiconductor laser with a focusing grating mirror (FGM), which enables a single-mode oscillation at a specified wavelength, is proposed. The optical properties of the FGM, which is a computer-generated holographic grating with chirp and bend structure, are numerically analyzed. An optimally designed FGM for realizing laser oscillation at a specific wavelength of 1.30 μm is fabricated by using a computer-controlled electron-beam writing system. The fabricated FGM with grating area of 1×1 mm² is combined as an external feedback mirror with an InGaAsP-InP semiconductor laser of 1.3 μm wavelength range, and the lasing characteristics are experimentally measured. Stable and single-mode oscillations with spectral line width less than 10 MHz are observed     

40-Gb/s Low Chirp Electroabsorption Modulator Integrated With DFB Laser

A 40-Gb/s monolithically integrated transmitter containing an InGaAsP multiple-quantum-well electroabsorption modulator (EAM) with lumped electrode and a distributed-feedback semiconductor laser is demonstrated. Superior characteristics are exhibited for the device, such as low threshold current of 20 mA, over 40-dB sidemode suppression ratio at 1550 nm, and more than 30-dB dc extinction ratio when coupled into a single-mode fiber. By adopting a deep ridge waveguide and planar electrode structures combined with buried benzocyclobutene, the capacitance of the EAM is reduced to 0.18 pF and the small-signal modulation bandwidth exceeds 33 GHz. Negative chirp operation is also realized when the bias voltage is beyond 1.6 V.      

Low-loss single-mode wavelength-division multiplexing with etched fibre arrays

A 9-channel single-mode grating wavelength-division multiplexing scheme is demonstrated at 1.5 ?m with insertion losses as low as 1.5 dB. An array of fibres with core-to-core spacing of 36 ?m acts as a channel concentrator giving a channel separation of 20 ? and channel width of 2 ?.     

400 Mbit/s transmission test using A 1.53 ?m DFB laser diode and 104 km single-mode fibre

Transmission characteristics for a 400 Mbit/s signal over a 104 km single-mode fibre are reported. A DFB laser diode is restricted to a single longitudinal mode at 1.53 ?m. No degradation is observed in the error-rate performance at a low loss and a finite dispersion wavelength.     

Wavelength multiplexer based onSiO2-Ta2O5 arrayed-waveguide grating

The characteristics of a wavelength multiplexer based on an arrayed-waveguide grating are carefully investigated by using the grating theory and related experiments. A 28-channel multiplexer is designed and fabricated as SiO₂-Ta₂O₅ waveguides on a 1 cm×2 cm substrate. The designed wavelength channel spacing of 1 nm is obtained. The crosstalk to an adjacent channel is -15 dB. The measured minimum loss is 4.2 dB, which is composed of 3.4 dB excess loss and 0.8 dB grating loss     

Surface-plasmon distributed-feedback mid-infrared quantum cascade lasers based on hybrid plasmon/air-guided modes

Surface-plasmon distributed-feedback quantum cascade lasers with a first-order grating realised by the sole patterning of the top metallic contact are demonstrated. The devices have a single-mode emission with a sidemode suppression ratio greater than 20 dB. The emission wavelength at 78 K is centred at 7.3 m and has a tuning rate as a function of temperature 0.4 nm/K.     

基于衍射光栅耦合输出的一级分布反馈太赫兹量子级联激光器

对比研究了两种不同结构太赫兹波段的双金属波导一级分布反馈量子级联激光器(THz-DFB-QCL).提出并实现基于衍射光栅耦合输出的THz-DFB-QCL中,太赫兹波通过衍射光栅而非解理腔面形成出射.计算表明,优化衍射光栅的结构可实现约70%的激光输出效率和小于1%的反射率,激光发散角约为10°×50°.极低的反射率可以有效抑制反射波对腔内谐振的干扰,是获得单模激射的关键.实验上,利用衍射光栅耦合输出的激光器实现了频率约2.58 THz的稳定单模激光,边模抑制比达23 dB,光束分布与理论计算相吻合.得益于较好的衍射效率和光束准直性,相比于常规的解理腔面边发射激光器,通过衍射光栅耦合输出显著提升了激光功率.     

一种基于三芯光纤的模式复用器/解复用器的设计

提出了一种基于三芯光纤的模式复用器/解复用器,三个纤芯包括两个相同的单模纤芯和一个少模纤芯,在少模纤芯中写入长周期光纤光栅以实现单模纤芯中LP01模与少模纤芯中LP11模间的转换。同时从两个单模纤芯输入LP01模,能激发少模纤芯中两个简并的LP11,a模和LP11,b模。采用光束传播法分析了该模式复用器/解复用器的耦合特性及串扰。数值模拟结果显示,若以少模纤芯中LP11模输出能量大于-1dB的波长范围作为该模式复用器/解复用器的工作带宽,则能够达到23nm,并且少模纤芯中生成的其他模式的输出能量皆比LP11模的输出能量小-21dB以上。该模式复用器/解复用器能够实现对少模光纤的模式复用与解复用,并具有极低的串扰。     

Monolithically integrated InGaAs-AlGaAs master oscillator poweramplifier with grating outcoupler

A monolithically integrated master oscillator power amplifier with a grating outcoupler, fabricated using a simple process without regrowth and emitting a collimated output beam, is proposed and demonstrated using an InGaAs-AlGaAs strained single-quantum-well gradient-index separate-confinement-heterostructure. Stable single-mode lasing up to 124-mW output power was obtained under continuous-wave operation. An increase of the output beam divergence, due to a wavefront distortion produced in the power amplifier, was observed with increasing power amplifier injection current. The wavefront distortion can be compensated by an appropriate design of the grating outcoupler     

Widely tunable 850-nm metal-filled asymmetric cladding distributed Bragg reflector lasers

Broadly tunable distributed Bragg reflector (DBR) lasers utilizing metal-filled surface-etched diffraction gratings were fabricated on a GaAs-unstrained quantum well with AlGaAs core and cladding layers. Devices with 200- and 400-/spl mu/m gratings sections were fabricated. Single-mode devices are fabricated over a broad spectral range, exhibiting over 55 mW of single-facet output power. The optical properties of this structure are analyzed in terms of effective index step between the peak and valley of the grating and scattering loss in the DBR. Discrete devices were fabricated with lasing wavelengths between 846.6 and 862.9 nm at intervals of 1.44nm, representing a range of 16.3 nm. Wavelength tuning by current injection into the DBR section is explored, and a broad tuning range of over 18 nm is measured while single-mode performance is maintained. The spectral linewidth of these devices is measured. The temperature dependence of light versus current, threshold current values, and spectral characteristics are also examined.     

A computer controlled narrow bandpass optical tunable filter usinga Fourier diffraction grating in the range of 1.3-1.55 μm

A novel tunable filter using a Fourier grating is studied and discussed. It consists of a Fourier grating, a collimator lens, single-mode fibers, and a computer controlled rotary actuator. It has very low polarization dependence of less than 0.3 dB, an insertion loss of less than 3 dB, and a narrow bandwidth of 1.5 nm. Wavelength selection was realized by rotating the grating, which was controlled by a computer. The device is able to select the light at the desired wavelength from more than 100 WDM optical data streams with 2 nm spacing in the range of 1.3-1.55 μm