Characteristics of Gbit/s optical receiver sensitivity and long-span single-mode fiber transmission at 1.3 µm

Sensitivity of a 1.3 μm Ge APD receiver was measured at data rates ranging from 100 Mbits/s to 2 Gbits/s, using a high-speed GaAs FET RZ driver, low-noise Si bipolar transistor (BIT) receiver amplifier, and a highly sensitive TD comparator. The required received optical level at a 10^-9error rate was -31.9 dBm for 2 Gbits/s with a Ge APD/Si BIT front end having a 50 Ω input impedance. A Ge APD/ GaAs FET front end, with a 500 Ω input impedance, brought about 2 dB improvement at 100 Mbits/s, as compared with a Ge APD/Si BIT (50 Ω) front end. A coupling loss of 4 dB, achieved by a hemispherical microlens tipped on a single-mode fiber, and a low fiber loss of 0.57 dB/km, including splice loss, enabled 44.3 km single-mode fiber transmission at 2 Gbits/s. The 1.3 μm transmission system has a data rate repeater-spacing product of 88.6 (Gbit/s)km. Prospects of Gbit/s receiver sensitivity and the 2 Gbit/s transmission system, with more than 50 km repeater spacing, are also discussed.     

Gigabit/s optical receiver sensitivity and zero-dispersion single-mode fiber transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 μm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p+nn- Ge APD. The p+nn- Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55μm and a 10^-9error rate, which was 4 dB better than the receiving level with a p+n Ge APD. Detector performance at 1.3μm was also studied for comparison with performance at 1.55μm. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55μm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) . km at 1.55μm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3μm dispersion-free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.     

Gigabit/s Optical Receiver Sensitivity and Zero-Dispersion Single-Mode Fiber Transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 µm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p/sup +/nn/sup -/ Ge APD. The p/sup +/nn/sup -/ Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55 µm and a 10/sup -9/ error rate, which was 4 dB better than the receiving level with a p/sup +/n Ge APD. Detector performance at 1.3 µm was also studied for comparison with performance at 1.55 um. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55 µm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) /spl dot/ km at 1.55 µm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3 µm dispersion free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.     

基于LTCC的超宽带巴伦滤波器小型化设计

该文设计了一种基于低温共烧陶瓷(LTCC)技术的小型化超宽带巴伦(Balun)滤波器。该巴伦滤波器由一个五阶带通滤波器和基于Marchand巴伦改进型巴伦级联组成,带通滤波器采用耦合谐振式的设计方法,设计成宽带高抑制巴伦滤波器,在二阶、三阶和四阶谐振之间创新采用电感级联的拓扑结构,使相对带宽在48%以上。巴伦输入与输出之间的耦合采用一种并联堆叠式耦合螺旋传输线,增强了传输线之间的耦合,并拓宽了巴伦的带宽。结果表明,该巴伦滤波器通带为1.71～2.76 GHz,插损均小于2.3 dB;在50～669 MHz,抑制大于35 dB;在669～1 245 MHz,抑制大于17 dB;在3 205～3 400 MHz,抑制大于27 dB;在3 400～6 000 MHz,抑制均大于30 dB。两个输出端口信号的相位差和幅度差分别为180°±15°(1 710～2 340 MHz)、180°±10°(2 500～2 760 MHz)和±1.0 dB,具有较高的通用性和良好的应用市场。     

Ge-laminated polarizer for 790-850-nm applications with extinctionratios larger than 50 dB and insertion losses below 0.4 dB

A laminated structure composed of alternating layers of Ge and SiO ₂ (Ge-LAMIPOL) is usable as a miniaturized polarizer at 790-850 nm in fiber optic gyroscopes, for instance. However, peeling of the sputter deposited layers, due to the weak binding strength between Ge and SiO₂, is a serious problem during the slicing process in preparation for assembly in the fiber. In order to improve the adhesive strength, the 1-nm-thick Si layers are inserted between Ge and SiO₂ layers. The Si layer functions as the adhesive layer via the Si-O bonding formation in place of the weaker Ge-O bond. The new Ge-LAMIPOL, including 125 layers of (1-nm Si)/(4.5-nm Ge)/(1-nm Si)/ (800-nm SiO₂) is successfully prepared without any fracture. The extinction ratio and the insertion loss were 51 and 0.33 dB at 850 nm, respectively, corresponding to 59.6 and 0.36 dB as the designed values     

Modeling of photonic crystal fiber Raman amplifiers

An accurate model has been developed to study photonic crystal fiber Raman amplifiers. The proposed approach calculates the Raman gain efficiency starting from the knowledge of the fiber cross-sectional characteristics, i.e., the geometric parameters and the germania concentration in the doped area. The model allows the study of the Raman amplification process in a photonic crystal fiber with any air-hole dimension and disposition, with or without a central doped area, as well as in standard single-mode fibers with an arbitrary refractive-index profile. This flexibility allows identification of the optimum values of the physical and geometrical photonic crystal fiber parameters, and thus it guarantees an efficient design for Raman amplifiers. For example, a Raman gain of 13.7 dB at 1554.8 nm has been obtained with a 6-km-long low-loss germania-doped triangular photonic crystal fiber with d//spl Lambda/=0.44 and /spl Lambda/=4.2 /spl mu/m.     

掺Ge/B光纤紫外光敏性研究

本文分析了掺Ｇｅ／Ｂ比掺Ｇｅ光纤具有较高紫外光敏性的原因,并通过实验研究了氢载对掺Ｇｅ／Ｇ光纤紫外光敏性的影响。研究结果表明氢载可以提高掺杂Ｇｅ／Ｂ光纤的光敏性,而且它在氢载前后都存在曝光饱和点。     

Noise modeling and SiGe profile design tradeoffs for RFapplications [HBTs]

This paper investigates SiGe profile design tradeoffs for low-noise RF applications at a given technology generation (i.e., fixed minimum feature size and thermal cycle). An intuitive model relating structural parameters and biases to noise parameters is used to identify the noise limiting factors in a given technology. The noise performance can be improved by pushing more Ge into the base and creating a larger Ge gradient in the base. To maintain the SiGe film stability, the retrograding of the Ge into the collector has to be reduced, leading to a stronger f_T-I_C roll-off at high injection. Two low-noise profiles were designed and fabricated explicitly for improving minimum noise figure (NF_min) without sacrificing gain, linearity, frequency response, or the stability of the SiGe strained layer. A 0.2 dB NF_min was achieved at 2.0 GHz with an associated gain (G_assoc) of 13 dB     

A 100-km-long single-mode optical-fiber fault location

A Raman OTDR (ROTDR) fault location for a 100-km-long single-mode optical fiber has been tested. A Ge p-i-n photodiode cooled by liquid nitrogen has been used as a backscattered light receiver. The signal-to-noise ration (SNR) improvement of the cooled Ge p-i-n photodiode from a Ge avalanche photodiode (Ge APD), which operates at room temperature, is 14 dB. Spectral Stokes light power distributions, which have been emitted from a long single-mode fiber, have been measured to estimate the maximum locatable length for a single-mode fiber. It has been shown, from the measurements and calculations, that a 100- km-long and a 30-dB total attenuation at a 1.55-μm wavelength single-mode fiber fault location can be achieved with the aid of an averaging technique. On the basis of these results, a 102-km-long single-mode fiber fault location experiment has been successfully carried out.     

Spectral filtering criteria for U-band test light for in-service line monitoring in optical fiber networks

In the fiber-to-the-home era, thousands of optical fibers will have to be accommodated in the central offices of optical access networks. To reduce maintenance costs and improve the service reliability of optical fiber networks, the authors must develop an optical fiber line testing system with a function for in-service line monitoring that uses a test light with a wavelength different from the communication light wavelength. To monitor an in-service line in an optical network, the effective rejection ratio of the test light must be taken into account. This ratio depends on the spectrum of the test light from the optical time-domain reflectometer and the rejection band of the filter in front of the optical network unit. The dependence of the effective rejection ratio as a function of the sideband suppression ratio (SBSR) and of the ratio of the rejection band to the bandwidth of the sideband noise d/D is clarified. When d/D=0.1 and the target effective rejection ratio of the filter is -40 dB, the SBSR and the filter loss of the termination cable must be -70 and -43 dB, respectively, or the SBSR must be -80 dB. When d/D<0.5 and the target effective rejection ratio of the filter is -40 dB, the SBSR is also required to be -80 dB. In-service line monitoring for a 10-Gb/s transmission using a 1650-nm test light with an SBSR of -80 dB is also demonstrated.     

低损耗芯包结构Ge-Sb-Se 硫系玻璃光纤的制备与性能研究

为解决锗(Ge)基硫系玻璃光纤损耗相对较高等问题,采用物理和化学除杂相结合的工艺,制备出了高纯Ge28Sb12Se60硫系玻璃,显著降低了红外波段C、H、O 杂质吸收。应用真空高速旋转法,制备出了壁厚均匀、光学质量优异的Ge28Sb12Se58S2 硫系玻璃皮管。采用棒管法拉制出外径501.5 um、具有芯包结构的Ge-Sb-Se 硫系玻璃光纤,光纤弯曲半径为5 mm,红外波段吸收基线为2.2 dB/m(2.87 um和4.5 um 处除外)。     

基于非对称形变的全光纤宽阻滞滤波器的制作

本文提出的基于长周期光纤光栅（LPFG）的全光纤宽阻带滤波器的制做方法，基本原理是在光纤纤芯中引入周期性的非对称形变，从而使光纤纤芯的折射率发生周期性变化；提出了两种实现光纤纤芯非对称形变的方法，进而制做出阻带中心波长分别为1310nm和1550nm的全光纤宽阻带滤波器插入损耗分别小于0.8dB和1.4dB，后向反射损耗小于-70dB。这样的器件可用于提高WDM系统的隔离度。     

A wide-bandwidth Si/SiGe HBT direct conversion sub-harmonicmixer/downconverter

A wideband sub-harmonic mixer/direct-conversion downconverter is implemented in a Si/SiGe HBT technology, with improved rejection of the local oscillator (LO), high input intercept point, and low current requirements. The circuit utilizes a combination of phase shifters operating at 45° and 90° to achieve better than 33-dB input-referred rejection of the LO. The measured third-order input intercept point (IIP3) was approximately -3 dBm and the second-order input intercept point (IIP2) was roughly 35 dBm, with a measured double sideband (DSB) noise figure of 7.8 dB. A comparison was made between devices of differing germanium concentration in the base, and the devices with higher Ge content exhibited improved noise figure and gain. Each mixer required approximately 2.8 mA from a 3.3 V supply     

Connection loss reduction by thermally-diffused expanded core fiber

Connection loss reduction in ten fiber connectors prepared by the thermally diffused expanded core (TEC) method has been confirmed. The mode field diameters (MFDs) of conventional single mode (SM) fibers were expanded from 9.8 to 13 mu m by thermal treatment considering the influence of loss increase due to fiber axis misalignment. An average connection loss of 0.15 dB for 4-SM-fiber connectors was realized, which was improved by 0.22 dB compared with previous value of 0.37 dB without thermal treatment. The TEC method promises to reduce the coupling loss, which is caused by lateral offset of multifiber connectors, fiber/LD modules, and fiber/waveguide device modules.<>     

光纤光栅退火特性的研究

获得性能稳定的光纤光栅具有重要的意义,文章介绍了氢载光纤、B／Ge光纤两种光敏光纤的退火特性。经比较,B／Ge光纤经比氢载光纤具有更好的热稳定性。     

基于色散光纤环级联结构的可调谐带通微波光子滤波器

提出并验证了一种宽调谐带宽的带通微波光子滤波器设计方案。该滤波器借助可调谐光纤光栅Sagnac环对宽带光源进行均匀切割,产生波长间隔可调的连续光载波作为滤波器的抽头,结合色散光纤环级联结构,实现滤波器的可重构性。研究结果表明,在光电调制器和光电探测器的频率带宽足够大的情况下,当光纤光栅Sagnac环的臂长差在0.50~8.28mm内变化、可调谐光纤延迟线的最小变化步长为0.01mm时,该方案能够实现滤波器中心频率在8.0506~1333.2000GHz内调谐,调谐步长为161.01MHz,边瓣抑制比达到27dB。     

Dispersion and noise of 1.3 μm multimode lasers in microwavedigital systems

The intensity noise and the performance in a 1.7 Gb/s digital system of 1.3 μm InGaAsP multilongitudinal mode lasers is discussed. The total intensity noise, mode partitioning, and the impact of dispersion on optical noise are measured. It is found that under CW conditions the total simulated emission from unpackaged lasers is inherently quiet, with an integrated optical signal-to-noise ratio (SNR) of 26.8±1.5 dB over a bandwidth of 1.5 GHz and 5 mW/facet. The optical SNR decreased as a function of increasing reflection. Intense mode partitioning decreased the SNR of the main mode by ~20 dB and reduced the effective coherence length to ~2 cm in glass fiber. At 1.7 Gb/s, the power penalities associated with laser bias and fiber dispersion are reported. The best receiver sensitivity is obtained when the laser is biased 1.3 mA below threshold. In general, it is found that as the bit rate increases, the optimum transmitter design becomes progressively more restrictive     

A Highly Sensitive Fiber-Optic Refractive Index Sensor Based on an Edge-Written Long-Period Fiber Grating

A novel long-period fiber grating (LPFG) is edge-written without any destructive damage on the fiber based on the thermal shock and rapid cooling effects of the high-frequency CO₂ laser pulses exposure method in this letter. The refractive index disturbance induced by high-frequency CO₂ laser pulses mainly occurs in the edge region of the fiber cladding rather than in the fiber core. An edge-written LPFG with a resonant peak of ~18 dB is obtained using a standard telecommunication fiber. The experimental results show that such a novel LPFG structure has much higher refractive index sensitivity over conventional LPFGs side-written, which can be used as a refractive index sensor, or a tunable filter and modulator by controlling the refractive index sensitive film which is coated on the cladding of such an LPFG.     

All optical wavelength conversion schemes for increased input powerdynamic range

Schemes for increasing the input power dynamic range of interferometric wavelength converters are presented with experiments at 10 Gb/s showing large improvements. A simple conversion scheme that uses current control of the interferometer improves the dynamic range from ~3-~8 dB. A simpler method of inserting an Er-doped fiber amplifier (EDFA) before the converter results in more than 40 dB of dynamic range while a method of using a semiconductor optical amplifier (SOA) for power control gives ~28-dB dynamic range     

高灵敏度加速度抵消型分布反馈有源光纤光栅水听器研究

研究了高灵敏度抗加速度型分布反馈(DFB)有源光纤光栅水听器。采用λ/4相移型掺铒光纤光栅构成DFB激光器,输出窄线宽激光,利用弹性膜片增敏方法封装有源光纤布拉格光栅,构成了高灵敏度有源光纤光栅水听器,并以两边对称的弹性膜片构成封装结构来抵消轴向加速度干扰,提高水听器在运动情况下的检测能力,并通过对结构的优化大大提高了光纤光栅水听器的耐静水压能力。研究结果表明水听器在100～1000Hz频率范围内声-相位灵敏度达到-132.7±0.7dB(0dB=1rad/μPa),加速度灵敏度可做到-20dB(0dB=1rad/g)以下,耐静水压可达2MPa。