Efficiency and optical feedback of traveling-wave semiconductor laser amplifier to single-mode fiber coupling: Theory and experiment

This paper analyzes the coupling efficiency and optical feedback of the tapered fiber end with a high-index hemiellipsoidal microlens. Such a device has been used as a coupler of traveling-wave semiconductor laser amplifier (TW-SLA) to single mode fiber (SMF).

A theory of the calculation of coupling efficiency and optical feedback is presented including the effects of spherical aberration and Fresnel reflection of thick lens. In consideration of the large beam divergency of the TW-SLA chip, the finite transmission aperture is introduced.

The calculations are in agreement with experiment results and a group of optimum structure parameters of the coupler are given.     

Estimation of maximum measurable distance in optical time domain reflectometry

The dependence of the maximum measurable distance (MMD) in optical time domain reflectormetry (OTDR) upon fiber and receiver parameters, number of averaging times, signal pulse width, and input power launched into the fiber has been investigated for both 1.3- and 1.5-μm wavelengths.

The calculations have been performed for both Ge- and InGaAs/InP-APD receivers. As a result it is found that (1) the (MMD) is larger for the InGaAs/InP-APD receiver and (2) a further increase in the MMD can be achieved by cooling the InGaAs/InP-APD receiver.     

Development of proposed federal standard 1070: 62.5/125-μm graded-index, multimode optical fiber waveguides for on-premises applications

This paper describes a process that has been successful in generating a specification to guide the user community in the procurement of single-size, multimode optical fiber for on-premises applications. This process began with an attempt to adopt an industry standard as a federal standard that would eliminate a multiplicity of choices available from the marketplace. The initial EIA-458-A Standard contained four “preferred” sizes. Discussions both in a government standards committee and in an applications-oriented industry (EIA) working group indicated the desirability of recommending a single fiber size. The process by which the industry committee selected the 62.5-μm core diameter/125-μm cladding diameter multimode fiber is presented.

The next element of the process was that of selecting the appropriate standard performance measures and attributes that would assure minimum performance of graded parameters such as attenuation and bandwidth, as well as a uniform specification of the product. The vehicle selected for this specification was the EIA 492-Series Generic, Sectional, and Blank Detail Specifications. Inputs were solicited from all of the identified U.S. manufacturers of this fiber size. Those inputs were coordinated and integrated into a detail specification, which is now being circulated by the EIA on a standards proposal ballot. After ballot approval, it will be published as an ANSIIEIA standard specification. Similar work has been initiated to develop a detail specification for fiber optic cables based on a related set (472-Series) of EIA specifications.

The process of developing a detail specification that assures conformance of the product to dimensional and strength tolerances as well as performance measures requires considerable coordination and iteration. No proprietary information or processes are contained in the specification so that the industry participants are free to compete on price and performance as long as compliance with the specification can be demonstrated.     

Worldwide activities and fiber optic market trends: Part I—markets

This paper reviews the recent progress of fiber optics applications worldwide and assesses the potential market growth. Market growth will occur at the expense of existing or planned technologies, such as the circular waveguide, and hence, the potential market growth must be considered in light of these existing markets.

Although the application of fiber optics technology is developing rapidly, there are certain countries which are progressing more rapidly than others. Each of the major countries or groups will be discussed, and the reasons for the activity or lack thereof will be given. The impact of fiber optics on the third world is yet to be felt; however, this may be one of the areas of future potential growth.

In order to give the reader an indication of the extent of applications that have occurred in the telephone, data, power, CATV, and military sectors, a complete listing and review of over 100 experimental systems is provided in Part II of this paper.     

Minimization of Cross-Gain Saturation in Wavelength Division Multiplexing by Optimizing Differential Gain in Semiconductor Optical Amplifiers

We successfully simulated the 10 × 40 Gbit/s soliton RZ-DPSK WDM signals over 1050 km with spectral efficiency approaching 0.4 bit/s/Hz using semiconductor optical amplifiers (SOAs) as in-line amplifier. The cross-gain saturation of SOA can be minimized by settling crosstalk at a lower level by decreasing the differential gain. This decrease in differential gain is in such a way that we get nil power penalty. The maximum transmission distance of 1050 km is possible with differential gain 210 atto cm² of SOA.

The impact of amplification factor, ASE noise power, crosstalk, quality factor and bit error rate for different differential gain has been investigated. It has been shown that with the increase in differential gain of SOA, the transmission distance goes on decreasing. At high value of differential gain 2.5 × 10^-16 cm² for the transmission distance 1050 km, all channels produce inter channel crosstalk with bit error rate greater than 10^-6. But for lower differential gain 190 atto cm², the quality of all channel increases at the cost of large power penalty.

With slight increase in differential gain 200 atto cm², the maximum transmission distance observed is 4550 km with quality of received signal more than 15 dB and having nil power penalty. We observed clear eye diagrams and optical power spectra for received signal with transmission distance 1050 km and 4550 km using soliton RZ-DPSK system. The bit error rate for all channels increase more than 10^-10 with the increase in launched input power that is due to power saturation.     

Integrated optical fiber data link transmitter/receiver for local area network application

Optical fiber data link transmitters and receivers have been developed for local area network applications. The features are of wide-bit-rate range and wide dynamic range as well as compact and of highly reliable construction. State-of-the-art LSI technology has been applied for the circuit electronics integration. Design emphasis was also placed on the optical connector development for ease of operation as well as reliable connection and compact size.

The data link transmitter and receiver developed utilize an AlGaAs light-emitting diode and a Si PIN photodiode as the light source and detector, respectively. Performance data were obtained for a bit rate range of dc to 35 Mbps and an 18-dB dynamic range.     

高非线性微结构光纤中基于受激布里渊散射的慢光延迟

全光连续可调的慢光技术在全光网络和光信息处理等领域具有重要的应用前景. 利用自行设计并拉制的高非线性微结构光纤, 实验研究了基于受激布里渊散射的可调谐慢光延迟. 采用单抽运光和单级延迟方案, 当抽运光功率为162.6 mW时, 在长度为120 m的高非线性微结构光纤中获得了最大76 ns的延迟量, 相当于0.76个脉冲宽度. 通过调节抽运光功率的大小, 可以实现对慢光延迟量的可调谐.该慢光延迟方案具有延迟量大、 全光可调谐及与现有光通信系统兼容等优势. 关键词： 慢光 微结构光纤 受激布里渊散射     

New plastic optical fiber using polycarbonate core and fluorescence-doped fiber for high temperature use

This article describes the development of a plastic optical fiber composed of a polycarbonate core with a glass transition temperature of 150°C, and a cladding of newly developed poly-4-methyl penten-1, which softens at 173°C. This cladding is suitable for use at temperatures up to 130°C. The minimum optical attenuation is 0.8 dB/m at 765 nm in the near-infrared region. The cause of the attenuation of the PC-core fiber was analyzed and the intrinsic loss limit was estimated to be 0.4 dB/m at 765 nm. The fiber has excellent characteristics, including thermal stability up to 125°C, high flexibility, high strength, and self-extinguishing properties.

The polycarbonate core fiber, doped organic fluorescing materials, has also been developed for automotive uses such as light guide and illuminator. Light can be transmitted through this fiber with incident optical beam perpendicular to the fiber as well as the beam parallel to the fiber.     

Channel reduction schemes for fiber-optic angle encoders

Three fiber-optic sensor systems designed to remotely determine angular position that achieve high angular resolution with fewer channels than comparable Gray code encoders are described. Two of the Systems use a sheet polarizer affixed to a “codewheel” and the third system uses a two-channel digital shaft encoder style “codewheel.”

The first polarization scheme uses four optical channels, two of which are analog and two digital. The ratio of the two analog channel intensities yields tan²θ. The fourfold quadrant ambiguity is resolved by the two digital channels that are transected by two semicircular masks on the polarizer codewheel (Ref. U.S. Patent No. 4,577,414, 25 Mar 1986). The second polarization scheme again uses quadrant ambiguity masks but employs only one analog channel that simulates a polarization vector that oscillates through 90°. The oscillating vector is produced by the superposition of two sine-wave-modulated beams at the polarizer codewheel. The modulations of the two beams have a phase difference that is created by time delaying one of the beams in a fiber delay loop. The phase difference between the generated composite signal and a reference signal then determines the angle of the codewheel. We have demonstrated experimentally that this type of split analog-digital scheme has a resolution equivalent to a 10-bit digital system (i.e., ±0.35°) independent of codewheel diameter.

The serial digital shaft encoder scheme uses only two digital channels and a codewheel that has two concentric masks with 48 equally spaced windows offset with respect to each other by one-half window width. At 0° there is a unique mask that initializes an up/down decoder chip (Hewlett-Packard HCTL-2000). This system has a resolution better than 7 bits using a 5-cm diameter code wheel and 1-mm Selfoc^TM lenses.

The supporting electro-optical systems including sources, fibers, lenses, mirrors, couplers, WDMs, polarizers, detectors, and signal processing for all schemes are described and the relative merits of each are compared.     

20-Gb/s and Higher Bit Rate Optical Wavelength Conversion for RZ-DPSK Signal Based on Four-Wave Mixing in Semiconductor Optical Amplifier

We investigate 20 Gb/s wavelength conversion for return-to-zero differential phase-shift keying (RZ-DPSK) signal using four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). We show that the 10-Gb/s RZ-DPSK signal-to-pump ratio increases up to -0.286 dB with Q factor improvement of 1.663 dB for increasing the cascadeability of optical networks. The effect of variation in bandwidth for an ideal dual-arm Mach-Zehnder interferometer (MZI) is illustrated. For different bit rates, the converted power signal is investigated with increase in signal input power. We show that the quality of converted signal is best before the saturation of SOA. The dependence of four-wave mixing (FWM) efficiency and converted signal power with signal input power is also studied, and it is found that FWM efficiency decreases with increase in signal input power.

The impact of signal-to-pump power ratio, unsaturated amplifier gain, and pump power is further optimized with minimum Q factor penalty for 10-Gb/s and 20-Gb/s bit rate. We show that converted signal power increases up to power saturation level and then starts decreasing. We also show that with higher bit rate, we have a wide range of choices for pump power signal. We further investigate the quality of converted signal at 10 Gb/s, which shows an improvement over signal input power. Finally, the increase in transmission distance after wavelength conversion is investigated.     

Secure Fiberoptic Communications

At the heart of our current information explosion is the communication network. Networks are now an intrinsic part of our daily activities, whether they are for Internet business transactions or military communications in Future Combat Systems. Protection of this communication infrastructure is a must.

In this article, we discuss two approaches for securing all-optical networks. The first is an optical encryption technique that denies the information to intruders. The second is an authentication scheme capable of detecting and identifying unauthorized users.     

Numerical Analysis of the Crosstalk on an Integrated Acousto-Optic Tunable Filter (AOTF) for Network Applications

In this article, we did a study of the crosstalk level (Xtalk) and extinction ratio (Xratio) of an acousto-optic tunable filter (AOTF) operating with ultra-short light pulses (2 ps). It is clear that the transmission bandwidth decreases as the length of the device increases. The compression factor was studied for the switched pulse in an AOTF without loss considering five nonlinearity profiles. One can observe that there is always an optimum value for β (final value of the nonlinearity) that one can obtain a switched pulse with the same time duration of the input pulse. The study of the crosstalk level, of this device, considering the optimum values of β obtained from the compression studies, as a function of the pump power (P₀) was done. For the soliton profile at 1 W of pump power one can notice that the Gaussian profile presents the lower Xtalk value (-13 dB), and the constant profile presents the worst value (-9.8 dB). However, if one is looking for a specific Xtalk value, one can conclude that with the constant profile one can obtain this value with a lower power. For the quasi-soliton profile of the same device, with low pump power (1 W), one can notice again that the Gaussian profile presents the lower Xtalk value (-13 dB) and the constant profile presents the worst value (-9.87 dB). This fact can be explained because, with pump power at 1 W, soliton and quasi-soliton profiles lead equivalent input pulses and under the same conditions produce equal results. The Xtalk level, considering all the profiles as a function of the β value, was studied. For all the profiles one has a strong increase of the Xtalk level with the increase of the final β value of the nonlinearity profile. Comparing all the profiles one can conclude that the Gaussian profile presents the lower Xtalk value in the range of β values in use. At the same time the value of the Xtalk for this profile does not change much with the change in the β value, presenting values in interval (-13 dB; -11.7 dB).

The studies of the Xratio of the same device operating with the input pulses with the soliton and quasi-soliton profiles reveal that for all the nonlinearity profiles the Xratio increases with an increase in pump power. For the quasi-soliton profile one can notice that there is a minimum of the Xratio as a function of the pump power. The Xratio considering all the profiles as a function of the β value shows that for all the profiles one has a strong increase of the Xratio level with the increase of the final β value of the nonlinearity profile. Comparing all the profiles one can conclude that the Gaussian profile presents the lower Xratio value in the range of β values in use. One can conclude that the operation of the AOTF in a switching configuration is worse for high pump power as observed for Xtalk.

The study of the crosstalk level and the extinction ratio on the AOTF operating with ultra-short optical solitons provides possibilities for achieving high efficiency in ultra fast all-optical signal processing, especially for optical switches, filters, and optical transistors. The acoustic-optic tunable filter (AOTF) has attracted great attention in recent years, in part because it appears to be a suitable basis for multi-wavelength optical cross-connects. It is probably the only known tunable filter that is capable of selecting several wavelengths simultaneously. This capability can be used to construct a multi-wavelength router.     

Optical performance models for FDDI links

A loss budget model has been developed to predict optical perjormnce of the fiber distributed-data interjace (FDDI) type of networks in the premises-distribution environment. This model tailors existing statistical loss budget models to the FDDI standard. It is expected that as FDDI becomes popular, fiber-based distribution systems will become common. When designing a fiber-distribution system, it is important to understand the constraints placed on link perjormance by the cable plant. To determine these constraints, the model is examined numerically using a large range of initial conditions. The total link length is used as the dependent variable. This set of initial conditions corresponds to an ensemble ofpossible link configurations, and these link configurations are studied in the context of the premises-distribution environment.

The model is extended to include the use of optical bypass switches. Laboratory measurement data are presented to verify the accuracy of the bypass switch model. The extended model, including the bypass switch, is examined numerically for a similar set of initial conditions. These constraints are applied to the use of bypass switches in wiring closets, between Jlaors, and at the work location. Distance limitations are determined for FDDI links utilizing optical bypass switches.     

Electromagnetic properties of random material

This work addresses the relationship between grain properties and the permeability and permittivity spectra of non-crystalline materials or aerosols.

The scattered multipolar fields about a single sphere are related to the polarizability of a random collection of such spheres. Using the Clausius-Mossotti relation the effective permeability and permittivity spectra of an amorphous material is determined for arbitrary permittivity and permeability of the individual spheres, packing density, and sphere size. Although the author considers the spectra over a range where the product of the external wavevector and sphere radius is kept small, typically less than one-tenth, the product of the internal wavevector and sphere radius is unconstrained and seen to have a large effect on predicted spectra.

The result is a variety of possible spectral types which include resonances, relaxations and certain complex. conglomerate spectra that have been measured and far which no direct explanation is otherwise available.     

An acoustic shadowgraph trial to detect convection in the Arctic

The EU Framework 5 project CONVECTION aims to understand convection processes in the Greenland Sea. By studying water motion close to the surface we hope to determine how convection is linked to atmospheric conditions and local surface features.

The usual methods of studying such processes in the ocean are by taking multiple soundings of conductivity, temperature and pressure or towing a large chain measuring temperature and salinity through a cross-section of ocean. These have the disadvantage of yielding information only while the research vessel is in the area. We have employed an alternative acoustic method that can provide data for long periods using semi-permanent moorings.

The acoustic shadowgraph method relies on the fact that when an acoustic signal propagates through a region containing convective irregularities the temperature variations along the path cause the signal amplitude to fluctuate. Unlike tomography, the shadowgraph does not require travel times to be measured and so the equipment can be much cheaper.

This paper describes the experimental apparatus, its testing and deployment on Vesteris Bank in the Greenland Sea in October 2001 and its recovery in April 2002. It also gives an overview of some of the acoustic intensity results and shows how they can be interpreted to yield estimates of sub-surface convection velocities.     

Form factor for large quantum graphs: evaluating orbits with time reversal

It has been shown that for a certain special type of quantum graphs the random-matrix form factor can be recovered to at least third order in the scaled time τ using periodic-orbit theory. Two types of contributing pairs of orbits were identified: those which require time-reversal symmetry and those which do not. We present a new technique of dealing with contributions from the former type of orbits.

The technique allows us to derive the third-order term of the expansion for general graphs. Although the derivation is rather technical, the advantages of the technique are obvious: it makes the derivation tractable, it identifies explicitly the orbit configurations which give the correct contribution and it is more algorithmic and more system-independent, making possible future applications of the technique to systems other than quantum graphs.

(Some figures in this article are in colour only in the electronic version)     

160 km all-optical OFDM transmission system with inline chromatic dispersion compensation

An experimental demonstration of an all-optical sampling orthogonal frequency division multiplexing (AOS-OFDM) transmission system with inline chromatic dispersion (CD) compensation is carried out to test the nonlinear influence. With five subcarriers non-return-to-zero (NRZ) modulated, the total bit rate is 50 Gb/s without polarization multiplexing. The receiver end is highly simplified with direct detection using optical Fourier transform filter. After transmission in 160-km standard single-mode fiber (SSMF) link with 130-ps/nm residual CD, an optimum input optical power for the system performance is achieved.     

半导体光放大器的稳态增益饱和特性

高速全光逻辑门是实现光分组交换、光计算和未来高速大容量光传输的关键器件,近年来受到广泛的关注。半导体光放大器（SOA）因为具备体积小、工作波长范围宽、响应时间短及良好的非线性特性等优点,成为研制高速全光逻辑器件的首选。采用分段模型分析了SOA的稳态增益饱和特性,通过数值求解载流子速率方程和光传输方程对其特性进行了仿真实现。结果表明,SOA在入射光功率不同时会表现出明显的非线性;在一定范围内增加光功率,SOA增益持续增加,继续增加入射光功率,SOA逐渐进入饱和吸收状态,增益反而降低。     

Implication of very wide fiber bandwidth for network architecture

The basic premise of this article is that at some point in the future all the transmission facilities of the public (telephone) network will be fiberoptic, i.e., end-to-end fiber connectivity will be provided to each subscriber. With the advent of coherent transmission systems the available bandwidth will become enormous, and thus the question we address is: given the availability of “infinite” bandwidth to every subscriber in the relatively near future, what does this imply for the network architecture? In particular, which switching technology is best suited to providing all foreseeable voice, data, and video services? Having discussed advantages and disadvantages of architectures based on different switching technologies, we conclude that an architecture based on circuit-switched, fixed-bandwidth channels for the transport of user information is the most appropriate for a network in which there are no constraints on the transmission bandwidth. The standard channel capacity should be determined by the service having the greatest bandwidth requirement.