All-optical WDM-to-TDM conversion with total capacity of 33 Gb/sfor WDM network links

We demonstrate all-optical WDM-to-TDM conversion in a switching node with a total throughput of 33 Gb/s. This is the highest throughput ever reported using a low timing jitter monolithic mode-locked semiconductor laser and a nonlinear optical loop mirror. The NOLM serves as an N×1 wavelength converter and the node has a unified output wavelength at 1554 nm. Wavelength-to-time-domain conversion using the node is simulated by inputting two data channels each at 1 Gb/s. This scheme is proposed to serve as an interface between independent high capacity WDM networks to avoid the limitations imposed by the optical bandwidth and unequal gain of EDFAs in optical networking and to minimize the deleterious effect of fiber nonlinearities during transmissions. The switching node for multiwavelength operation based on the wavelength dependence of the switching characteristics of the NOLM is also evaluated     

Tunable optical wavelength converters with reconfigurablefunctionality

We propose novel circuits for tunable all-optical wavelength converters with reconfigurable functionality. Circuits for wavelength converters based on cross-gain modulation (XGM) and cross-phase modulation (XPM) in semiconductor optical amplifiers (SOAs) are considered, for both copropagating and counterpropagating pump and probe signals. The circuits use arrayed-waveguide grating multiplexers (AWGMs) to filter and route signals in and out of the SOAs. The AWGM's minimize the component count in the circuits and may lead to future integration of wavelength converters. We experimentally demonstrate a XGM wavelength converter with copropagating pump and probe signals and report its bit-error-rate (BER) performance at 2.5 Gb/s     

波长转换器在国网OTN骨干网络的配置问题研究

为降低系统成本,文章通过部分配置波长转换器的方法缓解国网OTN骨干网络的波长连续性限制,并保障波长的资源利用效率。对国网OTN网络中波长转换器配置问题进行了理论研究,详细阐述了子图+ADD算法及其改进算法的设计思想,对各个算法的性能进行分析,在国家电网公司大容量骨干光传输网拓扑上进行仿真,并给出波长转换设备的最佳配置方案。仿真结果表明,通过合理地部署波长转换单元,可达到与全波转换相近的性能指标。     

Oscillation wavelength shift characters of a semiconductor laser in a magnetic field: Observation by using a beat note

In papers published previously, we discussed the oscillation wavelength shift of a semiconductor laser in a magnetic field at room temperature. Observations were carried out by means of a monochromator that was able to measure the oscillation wavelength shift in a steady state only and that was subject to a certain degree of measurement error. In this work, we used the beat note between two semiconductor lasers as a means of observing the wavelength shift. This method reduces the overall measurement error to about one tenth that obtained when using the monochromator and enables us to observe the time dependence of the wavelength shift, after establishing a magnetic field. The observed wavelength shift was delayed in comparison with the square of the magnetic flux density, which is proportional to the wavelength shift in a steady state. The delay was about 0.07 s, which is much longer than we actually expected, when changing the temperature in an active layer. © 1998 Scripta Technica. Electr Eng Jpn, 122(3): 46–54, 1998     

40 Gb/s Field-Modulated Wavelength Converters for All-Optical Packet Switching

We present a high-functionality photonic integrated circuit that performs field-modulated wavelength conversion. This device incorporates an on-chip sampled grating distributed Bragg reflector laser for wide tunability. Wavelength conversion is accomplished using a preamplified semiconductor optical amplifier photodiode receiver interconnected with a traveling-wave modulator to form a high-speed optical gate. This paper discusses the design and performance of this device, as well as its potential for optical packet switching applications. Error-free wavelength conversion is demonstrated at 40 Gb/s with 1–3 dB power penalty compared with back-to-back transmission over 22 nm of input and output tuning. Output extinction in all cases is greater than 9 dB, and conversion efficiency ranges from $-$2 to $-$ 6 dB over the tuning range. This device additionally demonstrates the capability for external 10 Gb/s modulation, which can be used for optical label encoding.      

All-Optical Tb/S 3R Wavelength Conversion Using Dispersion-Managed Light Bullets

We present an all-optical wavelength converter that can operate at a very-high-switching rate with simultaneous reshaping, retiming, and regenerating (3R) capabilities based on nonlinear interactions between dispersion-managed (DM) (3+1)-dimensional optical solitons (light bullets). Numerical simulations have been performed to demonstrate the generation of the DM light bullets and the spatial dragging interaction between solitons with different colors for ultrafast wavelength conversion application. This all-optical 3R wavelength converter has a very compact size of 100 mum times 100 mum times 1 mm, and is able to convert information at an ultrahigh speed of over 1 Tb/s between wavelength channels of 50 nm apart. Such an ultrafast all-optical wavelength converter has potential applications in future optical time-division multiplexing (OTDM) and wavelength-division multiplexing (WDM) combined communication networks that require both the ultrafast switching speed due to the large bandwidth within each wavelength channel and the wavelength conversion function for exchanging information between different wavelength bands or spatial switching within the same wavelength bands.     

Tuning range extension by active mode-locking of external cavity laser including a linearly chirped fiber Bragg grating

We demonstrate electrical wavelength tuning by mode locking of an external cavity laser (ECL) with linearly chirped fiber Bragg grating (LCFBG). The configuration consists of a laser chip providing the gain coupled to an LCFBG with a large chip rate of 10 or 55 nm/cm providing the counter-reaction for laser oscillation. The laser chirp is electrically modulated by a sinusoidal signal in such a way that the ECL is mode locked. By changing the modulation frequency, a wavelength tuning range of 27 nm is achieved with the 10 nm/cm LCFBG, and a partial tuning range over 41 nm is demonstrated with the 55-nm/cm LCFBG. The output pulse stream at a specific mode-locking frequency and a corresponding wavelength is obtained for both positively and negatively chirped grating. A time bandwidth product reduction is measured in the case of negatively chirp grating when compared with positively chirp grating. A simple general law between the laser parameters is given (locking frequency, tuning range, and FBG chirp value). The parameters for a 40-nm tunable source modulated at 10 GHz are given. This simple tuning mechanism is very well adapted for a structure that requires accurate wavelength monitoring.     

Frequency plan and wavelength switching limits for widely tunablesemiconductor transmitters

As wavelength-division-multiplexing (WDM) channel spacing continues to decrease in size, and with the application of tunable lasers in dense wavelength-division-multiplexing (DWDM) systems, we demonstrate the ability of tunable semiconductor lasers to cope with demanding channel spacing and inevitable low frequency setting error. By finding the stable operating points of a single tunable laser at the desired frequencies, using advanced software a lookup table to drive the laser was generated. Once the drive currents to access 2000 channels with the laser are found, their frequency setting error and side mode suppression ratio (SMSR) were found. These results open up new possibilities for DWDM access networks as well as providing a limit of achievement for channel density in the network. Meanwhile, since the sampled-grating distributed Bragg reflector (SG-DBR) laser is among the most attractive sources for DWDM, it is important to investigate its wavelength switching characteristics. This behavior will affect wavelength routing and the capability limits for channel reallocation in future networks. We present new detailed experimental studies on a high-speed SG-DBR laser by using a Fabry-Perot interferometer technique adapted for the noncontinuous wave case. Measurements of fast intramodal (i.e., cavity mode) and intermodal (i.e., supermode) wavelength switching and insights into the device's dynamic behavior are obtained. Implications are given for transmitter design in dynamic wavelength routing and channel reallocation     

故障后半波长输电线路的稳态过电压控制措施

半波长输电技术是一项具有前瞻性和竞争力的新型输电技术。特高压半波长输电线路稳态工频过电压问题严重,须制定相关的故障后安全稳定控制措施。该文提出了通过切除送端配套机组、线路末端投并联无功补偿设备、快速直流调制等控制措施抑制半波长输电线路稳态工频过电压,同时给出了相关理论分析,并通过大电网仿真算例验证了控制措施的有效性。该文研究成果进一步丰富和完善了对特高压半波长输电线路接入系统后控制特性的认识,将为大电网新型输电技术提供理论储备和技术保障。     

A long pulse discharge excited ArF laser

An X-ray preionised, discharge excited ArF excimer laser, λ=193 nm, has been studied in the long pulse regime. The laser performance is found to be primarily dependent on the discharge stability, and therefore, on the gas composition, preionization timing and the pumping power. Using X-ray preionization and prepulse-mainpulse excitation, laser pulselengths of up to 120-ns full-width at half-maximum at 4 mJ/l are obtained by decreasing the partial pressures of the active ingredients, F₂ and Ar, and using Ne as a buffer gas. This is almost six times as long as usual for discharge excited ArF lasers     

Monolithic Wavelength Converters for High-Speed Packet-Switched Optical Networks

This paper describes the design and demonstration of advanced 40-Gb/s return-to-zero (RZ) tunable all-optical wavelength converter technologies for use in packet-switched optical networks. The device designs are based on monolithic integration of a delayed interference Mach-Zehnder interferometer (MZI) semiconductor optical amplifier (SOA) wavelength converter with a sampled-grating distributed Bragg reflector tunable laser and an on-chip waveguide delay. Experimental results are presented demonstrating error-free wavelength conversion with 1-dB power penalty at 40-Gb/s data rates. By incorporating label modulation functionality on-chip along with a fast tunable 40-Gb/s wavelength converter, fully monolithic packet-forwarding chips are realized that are capable of simultaneous error-free wavelength conversion of 40-Gb/s payloads, remodulation of 10-Gb/s packet headers, and data routing through fast wavelength switching     

Laser-damage impact on lithography system throughput

With the transition to high-power excimer laser sources for lithography systems, the impact of laser damage, particularly compaction in fused silica, on the optics life, dose at the wafer plane, and system throughput, is a major concern. This paper will develop the first-order equations for the analysis, apply the equations to a step-and-scan catadioptric system, and show that for 248-nm systems, the limitation on throughput is dose, not laser-induced damage, while at 193 nm, laser-induced damage becomes the limitation for throughput for system lifetimes in excess of ten years. The boundary conditions used in the analyses are based on design experience at SVG Lithography Systems, Inc. (SVGL), data from excimer laser manufacturers, and papers presented at SPIE Microlithography 1995     

Optical Wavelength Conversion by Cross-Phase Modulation of Data Signals up to 640 Gb/s

In this paper, all-optical wavelength conversion by cross-phase modulation in a highly nonlinear fiber is investigated. Regenerative properties of the wavelength converter are demonstrated, and the effect of adding Raman gain to enhance the performance of the wavelength converter is shown. The wavelength conversion scheme is demonstrated at the record-high bit rate of 640 Gb/s.     

Wide-band modeling of photoinduced carriers at the end of anopen-ended microstrip line

This paper presents a wide-band model describing the behavior of an open-ended microstrip line illuminated at its termination. The photoinduced carriers create a plasma at the end of the line, which modifies the complex dielectric constant and, therefore, also the field configuration. The perturbation due to the illumination is modeled by an optically controllable termination load. Its analytical expression is obtained from the integration of the conductivity predicted by the plasma theory. Measurements made on devices fabricated on a silicon substrate validate the model from 0.01 to 20 GHz for an illumination power density of 4 mW/mm² at a wavelength of 685 nm. The validation includes the extraction of the characteristic impedance, which is a complex value because of the low resistivity wafers used (≈250Ω·cm)     

Imaging of tissue microstructures using a multimodal microscope design

We investigate a microscope design that offers high signal sensitivity and hyperspectral imaging capabilities and allows for implementation of various optical imaging approaches while its operational complexity is minimized. This system uses long working distance microscope objectives that enable for off-axis illumination of the tissue, thereby allowing for excitation at any optical wavelength and nearly eliminating spectral noise from the optical elements. Preliminary studies using human and animal tissues demonstrate the feasibility of this approach for real-time imaging of intact tissue microstructures using autofluorescence and light scattering imaging methods.     

A new method to determine the absolute mode number of a mode-locked femtosecond-laser comb used for absolute optical frequency measurements

The generation of optical frequency combs, directly referenced to the SI second, can be used to make measurements of optical frequencies. This provides a supreme method for the realization of the meter. However, an approximate knowledge of the frequency of the radiation is normally needed for such measurements in order to determine the integral order of the comb component used. Such information is usually obtained by prior wavelength measurements of the radiation under study. This paper demonstrates a new method to determine the absolute mode number in optical frequency measurements using mode-locked femtosecond lasers, thus eliminating the need for complementary wavelength measurements. Measurements of the frequency of an iodine-stabilized He-Ne laser at /spl lambda/=633 nm and a Nd:YAG laser at /spl lambda/=532nm are given as examples.     

Resonant cavity enhanced Ge photodetectors for 1550 nm operation on reflecting Si substrates

We have fabricated and characterized the first resonant cavity-enhanced germanium photodetectors on double silicon-on-insulator substrates (Ge-DSOI) for operation around the 1550-nm communication wavelength and have demonstrated over four-fold improvement in quantum efficiency compared to its single-pass counterpart. The DSOI substrate is fabricated using an ion-cut process and optimized for high reflectivity (>90%) in the 1300-1600-nm wavelength range, whereas the Ge layer is grown using a novel two-step ultra-high vacuum/chemical vapor deposition direct epitaxial growth technique. We have simulated a Ge-DSOI photodetector optimized for operation at 1550 nm, exhibiting a quantum efficiency of 76% at 1550 nm given a Ge layer thickness of only 860 nm as a result of both strain-induced and resonant cavity enhancement. For this Ge thickness, we estimate a transit time-limited 3-dB bandwidth of approximately 25 GHz.     

Material Considerations for Avalanche Photodiodes

Avalanche photodiodes (APDs) are widely used to detect and amplify weak optical signals by utilizing the impact ionization process. The choice of material is critical for the detection of a particular wavelength, and it is often expedient to use a combination of different materials to optimize the overall device performance. The APDs are now capable of covering a wide spectrum from the infrared down to the ultraviolet wavelengths. This paper will review the material requirements to achieve high gain with low excess noise at the different wavelength regions.     

环境温度和驱动电流对LED的峰值波长的影响

LED作为一种节能高效的发光器件,其光学特性受驱动电流、环境温度等因素的影响。本文主要研究不同的环境温度和驱动电流模式对不同波长LED峰值波长的影响,选取了可见光波段内的13种不同的波长的LED、3种不同的环境温度、10种不同的驱动电流进行实验,并得出以下实验结论:①在相同温度情况下,415~531 nm波长区间内的LED的峰值波长随着驱动电流占空比的增加而增加,在591~740 nm波长区间的LED的峰值波长随着驱动电流占空比的增加而减小。②在相同模式电流驱动下,随着环境温度的升高,所有不同波长类型的LED的峰值波长都增加,即发生红移,且LED峰值波长的移动量与温差之间具有很好的线性关系。③环境温度的升高可以使得LED波长增大,且这种波长增大量与LED本身波长有关,温度使红光LED波长增大量Δλ红明显比蓝光LED波长增大量Δλ蓝要高。④环境温度与驱动电流共同作用下,可以使得LED峰值波长出现更大的偏移量,两种因素对LED峰值波长的影响效果可以叠加。实验结果希望可为改变LED光学特性提供参考。     

Optimal routing and wavelength assignment for survivable multifibre WDM networks

Multifibre optical networks use a bundle of fibres to realize a link between two optical nodes. Such networks can offer significant economic benefits over single-fibre networks because of their ability to relax the restrictions imposed by the wavelength continuity constraint and their potential for handling future growth. This paper introduces two new and efficient integer linear program (ILP) formulations for dynamic wavelength allocation in survivable multifibre wavelength-division multiplexing (WDM) networks, using dedicated and shared protection. Single-fibre networks, both with and without wavelength conversion, can be treated as a special case of these formulations. The new formulations have been tested on several well-known WDM networks, and the results have been compared to those for single-fibre networks. A simple heuristic for dynamic lightpath allocation is also proposed, and its performance is validated by a comparison of the results to optimal solutions generated by the ILPs. Experimental results demonstrate that the new ILPs are feasible for current networks under low-to-medium traffic. For very large or highly congested networks, the heuristic can be used.