Wide temperature operation of 40-Gb/s 1550-nm electroabsorption modulated lasers

Electroabsorption modulated lasers (EMLs) exploiting the quantum confined Stark effect need thermoelectric coolers to achieve stable output power levels and dynamic extinction ratios. Temperature-independent operation is reported between 20/spl deg/C and 70/spl deg/C for InGaAlAs-InP-based monolithically integrated 1550-nm EMLs exploiting a shared active area at 40 Gb/s by actively controlling the electroabsorption modulator bias voltage. Dynamic extinction ratios of at least 8 dB and fiber-coupled mean modulated optical power of at least 0.85 mW are obtained over the mentioned temperature range.     

Surface-grating VCSELs with dynamically stable light output polarization

It has been shown recently that the polarization of single- and multimode vertical-cavity surface-emitting lasers (VCSELs) can be defined and stabilized very effectively with a monolithically integrated surface grating. Orthogonal polarization suppression ratios of 20 dB or more have been achieved even for transverse multimode devices. It has not been investigated in detail yet whether these lasers are also polarization stable under high-frequency modulation. We show that surface-grating VCSELs remain polarization stable for digital high-frequency modulation up to 10Gb/s, modulation amplitudes of up to 1.5 V/sub pp/, and different modulation patterns. Under modulation, neither polarization-resolved time traces nor polarization-resolved spectra nor the power ratio of the two polarizations indicate a deterioration of the polarization properties compared to the static case.     

马赫-曾德复合腔激光器泄漏功率的输出特性

基于自组织相干合成原理,在马赫-曾德复合腔中引入3dB光纤环镜为共用腔镜,低反(4.5%)布拉格光栅作为输出腔镜,获得了93.5%的相干合成效率;通过对泄漏端功率输出特性的研究,在理论和实验上研究了复合腔自组织相干的物理机制.为相干合成技术研究提供新的分析思路和更便捷的方法,并能在简单的实验设施下实现.     

Noise characterization of femtosecond fiber Raman soliton lasers

The broadband amplitude noise and phase noise (timing jitter) measured in femtosecond fiber Raman soliton lasers is discussed. For a single-pass compressor using 300 m of either standard single-mode fiber or polarization preserving fiber, white amplitude noise ⩾50 dB above shot noise at 2 mA photocurrent was measured, for frequencies higher than approximately 100 kHz. This is ≈30 dB larger than the amplitude noise observed from fiber grating pulse compressors. The timing jitter increases with pump power, and at 1.6 W pump power, 5.2 ps r.m.s. timing jitter was measured, given ≈2 ps jitter from the Nd:YAG pump. Longer fibers in the single-pass compressor do not affect the amplitude noise, but increase the timing jitter even further. A synchronously pumped ring cavity reduced the timing jitter substantially, but did not significantly improve the amplitude noise     

All-active tapered 1.55-/spl mu/m InGaAsP BH-DFB laser with continuously chirped grating

We demonstrate the first realization of all-active tapered index coupled 1.55-/spl mu/m InGaAsP buried-heterostructure distributed feedback lasers involving chirped gratings. The variation of the effective refractive index along the tapered active stripe is compensated using an optimized continuously chirped grating. The grating has been formed using a novel direct-write electron-beam lithography technique. Lasers with an antireflection/cleaved cavity show stable single-mode operation and high optical output power up to 60 mW. The yield of lasers with a sidemode suppression ration > 40 dB is more than 70%. The -3-dB farfield angles (full-width at half-maximum) amount to 14/spl deg/ and 20/spl deg/ in lateral and vertical direction, respectively.     

Complex-coupled quantum cascade distributed-feedback laser

Quantum-cascade distributed-feedback lasers (QCDFB) with a grating close to the active region are reported. Feedback is provided by the grating in a refractive index-dominated coupling scheme. Reliable single-mode emission at /spl lambda//sub cm//spl ap/5.4 /spl mu/m with a side-mode suppression ratio (SMSR) /spl ap/30 dB is observed. The laser is continuously tunable over 40 nm with a coefficient of /spl Delta//spl lambda///spl Delta/T/spl ap/0.37 nm/K in the temperature range from 200 K to 300 K. Comparison with Fabry-Perot QC lasers shows an overall improved performance of QC-DFB lasers.     

Holographic fabricated continuous wave operation of distributed feedback quantum cascade lasers atλ≈8.5μm

The fabrication and characterization of distributed feedback（DFB） quantum cascade lasers emitting atλ≈8.5μm are reported.The first-order DFB grating structure was defined using the holographic lithography technique.Reliable dynamic single-mode emission with a side-mode suppression ratio of 20 dB and a tuning coefficient of-0.277 cm^-1/K from 93 to 210 K is obtained in continuous wave mode by using high-reflectivity coating on the rear facet.The output power is over 100 mW at a temperature of 80 K.     

4$,times,$25-Gb/s 40-km PHY at 1310 nm for 100 GbE Using SOA-Based Preamplifier

We present extensive numerical simulations of an optical link deploying four electroabsorption modulated lasers (EMLs) at 25 Gb/s over up to 40 km of standard single-mode fiber. The receiver comprises a semiconductor optical amplifier (SOA) as a preamplifier. We analyze the bit error ratio (BER) along different link lengths under varying conditions such as output power and extinction ratio of the EML transmitters, the noise figure of the SOA preamplifier and the bit and word alignment of the four wavelength channels. We demonstrate that the EML transmitters require a minimum extinction ratio of 8 to 10 dB and a minimum output power of +2 to +4 dBm in order to meet the BER requirements for 100 Gigabit Ethernet (100 GbE) using 4 times 25-Gb/s physical media dependent (PMD) devices. Furthermore, we show that single-channel performance analyses can be used to estimate the behavior for multichannel amplification in the SOA preamplifier.     

Electroabsorption modulated laser for long transmission spans

Strain-compensated AlGaInAs quantum-well electroabsorption modulated lasers (EMLs) transmit at 10 Gbits/s on uncompensated transmission spans of >75 km of standard fiber and >225 km of MetroCor fiber. Details of the design, fabrication, and testing are presented. A complex-coupled distributed feedback (DFB) grating is used to enable high output power. The epitaxy and chip structure are described. The paper studies what is needed to accomplish long-span transmission in terms of minimum physical requirements for laser mode control, facet reflection, index grating strength, laser-modulator matching, laser-modulator electrical isolation, modulator extinction ratio, modulator capacitance, linewidth enhancement factor, etc. The interaction of the modulator with the laser is analyzed and a requirement for this structure is computed for the electrical isolation resistance between modulator and laser contacts. Stability of the laser source is discussed and a method is derived for determining the grating's gain-coupling coefficient at operating power. Chirp due to the modulator is analyzed. Nonzero chirp of the modulator is shown to have beneficial impact on the quality of the signal after transmission. The effect of a bias-dependent alpha parameter is analyzed. Because bit-error rate is a strong function of mean alpha parameter and not a strong function of the range of alpha during nonreturn-to-zero modulation, we determine that tuning the chirp of the EML modulator to suit different fiber types (MetroCor, SMF-28, etc.) is practical. Specific tradeoffs are also required. Experimental results verify the analysis     

Infrared Optical Fibers

A state of the art review of nonsilica based infrared fibers is presented. Two types of fiber materials have been investigated--crystals and glasses. Crystal fiber work appears to be focused on development of short haul CO/sub 2/ laser power delivering lines at 10.6 µm. The maximum delivering power of the CW CO/sub 2/ laser has reached up to about 100 W by the polycrystalline KRS-5 fiber. A number of glass fibers are being developed in fluorides, sulfides and heavy metal oxides. The best optical attenuation of each glass fiber has been respectively reduced to 21 dB/km at 2.55 µm for ZrF/sub 4/-based glass fiber with a core-clad structure, 78 dB/km at 2.4 µm for As-S unclad glass fiber, and 13 dB/km at 2.05 µm (70 dB/km at 2.40 µm) for GeO/sub 2/-Sb/sub 2/O/sub 3/ glass fiber with a core-clad structure. Recent progress of these infrared fibers offers great potential for new wavelength fiber finks operating in the 2-10 µm region which have not been realized by silica-based fiber.     

Sampled-grating DBR laser-based analog optical transmitters

Sampled-grating distributed Bragg grating (SGDBR) laser-based widely tunable optical transmitters are investigated for application in high-performance analog links. More than 45 nm tuning range, 40 dB sidemode suppression ratio, and peak relative intensity noise below -153 dB/Hz is measured. SGDBR lasers integrated with semiconductor optical amplifiers and electroabsorption modulators (EAMs) are characterized with spurious free dynamic range of 125-127 dB/spl middot/Hz/sup 4/5/ over the wavelength tuning range. It is also shown how the modulation response of the EAM is affected by the optical power to limit the performance of the analog transmitter.     

光纤光栅外腔半导体激光器的理论及实验研究

对影响光纤光栅外腔半导体激光器特性的几个重要因素(光纤光栅长度、耦合系数、内腔反射系数)进行了理论分析和数值模拟。从实验上进行了验证,实测了不同反射率情况下激光器的激射光谱,得到了带宽为0.1nm、出纤功率达417.4μW、边模抑制比高达37.9dB的激光谱线。验证的结果表明,理论分析、数值模拟、实验结果是吻合的。     

Narrow-linewidth strained-layer 1.5 mu m multiquantum well distributed feedback lasers

The performance characteristics of narrow-linewidth strained-layer 1.5 mu m multi-quantum-well distributed feedback (MQW-DFB) lasers are presented. Measured linewidth as low as 3.5 MHz has been observed for one of the 250 mu m long devices at 14.4 mW output. Under 1.7 Gbit/s 1.0, 1.0, . . . pattern signal modulation, the lasers have 20 dB down full width chirp in the range of 5-6 AA for the off state at 0.8 I/sub th/. The chirp widths are about half of those of bulk-active DFB lasers. A 1.7 Gbit/s amplitude-shift-keying transmission experiment using one of the low-chirp lasers has been demonstrated. The transmission over 60 km of standard fibre only result in a 0.8 dB dispersion power penalty and has a receiver sensitivity of -36.2 dBm at BER=10/sup -9/.<>     

基于重叠光栅和啁啾光栅的双波长光纤激光器

研究光寻址电位传感器(LAPS)的器件噪声特性 。通过对LAPS半导体场效应器件的结构分析,建 立LAPS的理论模型,并进一步分析LAPS器件噪声信号的来源、种类及特性。以 pH缓冲液中H离子 浓度为检测对象,搭建基于NI采集卡和Labview环境的LAPS测试系统,对影响LAPS信号噪声 特性的光源 波长、光源调制频率、光源强度和Si衬底厚度等因素进行了仿真和实验研究。结果表明,增 大光源波长和光源强度 是提高输出信号幅值和信噪比(SNR)的最有效方法。     

基于内嵌FBG的Sagnac环的双波长光纤激光器

提出了一种内嵌光纤Bragg光栅(FBG)对的Sagnac环结构双波长掺铒光纤(EDF)环形激光器。对内嵌FBG对的Sagnac环的滤波特性进行了理论分析,实验获得了输出波长分别为1 554.92nm和1 555.2nm的稳定双波长光纤激光,边模抑制比约为65dB,功率稳定性优于0.2dB,波长稳定性优于0.02nm。     

Vacuum-ultraviolet laser-induced refractive-index change and birefringence in standard optical fibers

Strong photosensitivity responses with the use of above-bandgap 157-nm F/sub 2/-laser radiation are reported for standard germanosilicate fiber. A large 1.3/spl times/10/sup -3/ effective index change at 1.55 /spl mu/m was inferred by trimming strong and weak Bragg gratings in hydrogen-free fiber. The F/sub 2/-laser fluence-processing window of <50 mJ/cm/sup 2/ is much lower than with traditional ultraviolet (UV) lasers. For hydrogen-soaked fiber, highly asymmetric refractive-index profiles were noted by atomic force microscopy and microreflection microscopy, yielding a peak index change of >0.01 across a small 1-/spl mu/m penetration depth at the fiber core. The index asymmetry appears to underlie the large >5/spl times/10/sup -5/ value of laser-induced birefringence.     

Efficient and tunable Er/Yb fiber grating lasers

Efficient and tunable single-frequency fiber Bragg grating (FBG) lasers are demonstrated using a novel photosensitive Er/Yb fiber design. Both sub-mW threshold pump power, and high slope efficiencies of ~31% at 1536 nm and ~26.1% at 1562 nm were achieved. Wavelength tuning could be obtained over 11 and 25 nm in 1535 and 1550 nm wavelength regions, respectively, by cavity-length tuning     

波长可切换窄线宽单频掺镱光纤激光器（特邀）

基于光纤环形激光器,设计出由三端口环形器、偏振控制器、未泵浦保偏掺镱光纤和光纤布拉格光栅组成的滤波器件作为高精度滤波器对谐振腔内的模式个数进行抑制,通过调谐偏振控制器,在保偏掺镱光纤内形成的梳状光谱和动态光栅,实现了窄线宽、单、双波长可切换单频掺镱光纤激光器。单波长运行时,在1064.37 nm处测得激光器输出线宽346 Hz,光信噪比大于50 dB,30 min内该激光器波长及功率的不稳定性均在0.01 nm和0.2 dB范围内。通过调节偏振控制器,单波长和双波长可以实现互相切换,双波长分别位于1064.156 nm和1065.236 nm。该技术为超窄线宽激光器的双波长输出提供了新的途径。     

Vertical-cavity surface-emitting lasers with monolithically integrated horizontal waveguides

We present the development of novel 980-nm Ga/sub 0.8/In/sub 0.2/As-GaAs vertical-cavity surface-emitting lasers (VCSELs) with an internal waveguide structure. The monolithic integration of a horizontal waveguide in the top distributed Bragg reflector (DBR) creates the potential for achieving VCSEL-based photonic integrated circuits. In this work, an AlGaAs-GaAs-AlGaAs waveguide designed for horizontal propagation of light was monolithically integrated as part of the upper GaAs-AlGaAs DBR of the device. VCSELs with 9-/spl mu/m apertures emitted 3-mW single-mode power with both longitudinal and lateral mode suppression ratio of 40 dB under room-temperature continuous-wave operation.     

High-Performance and Low-Cost 40-Gb/s CWDM Optical Modules

High-performance and low-cost 40-Gb/s optical modules using four different wavelength uncooled 10-Gb/s distributed-feedback (DFB) lasers are proposed and demonstrated. The 40-Gb/s optical module was integrated with coarse wavelength division multiplexing (CWDM) thin-film filters which enabled four 10-Gb/s transmission channels output through a single fiber. The 10-Gb/s DFB laser was packaged by commercialized low-cost coaxial TO-Can technology. The results of the 40-Gb/s optical module showed that the output optical power was above ${-}1$ dBm per channel and the system power budget was 12 dB. The transmission distance with a single-mode fiber reached more than 30 km at a bit-error-rate of $10^{{-}9}$. Compared with conventional 40-Gb/s optical modules, the module is easy to fabricate and is low cost. This proposed high-performance 40-Gb/s CWDM optical module demonstrates not only the feasibility of a 30 km transmission, but also shows the low-cost possibility of ensuring the application of WDM-passive optical network fiber-to-the-home systems.