Optical Fiber Delay Lines Research Articles

Quasi-distributed recirculation fiber-optic temperature sensor

The new structure of the quasi-distributed fiber-optic temperature sensor is offered, based on recirculation frequency registration a single pulse with its periodic regeneration on different wavelengths and allowing simultaneously to spend measurements to ten points. Fiber-roptic sensor was constructed as a closed optoelectronic contour formed by a source of radiation, an optical fiber delay line, spectral reflective elements, photoreceiver and regeneration block. The sensitive element of this device was the optical fiber. The error of temperature measurements does not exceed 0.2°C at measurement time 1 s, thus the maximum length of the fiber-optic measuring converter reaches 15 km at use multimode gradient optical fiber.

A new family of 2D wavelength/time codes with large cardinality for incoherent spectral amplitude coding OCDMA networks and analysis of its performance

A new family of two-dimensional wavelength/time codes (2D-W/T-MQC/MQCs) and its system structure of encoder/decoder are proposed, which is based on tunable optical fiber delay lines (TOFDLs) and fiber Bragg gratings (FBGs). Multiple-access interference (MAI) can fully be eliminated by using a wavelength/time balanced detector structure at the receivers. Furthermore, the performance of the system is also analyzed by taking into account the phase-induced intensity noise (PIIN), shot noise, and thermal noise. The simulation results reveal that the new code family possesses higher signal-to-noise ratio (SNR) and lower bit-error rate (BER) than the family of one-dimensional spectral amplitude coding modified quadratic congruence codes (1D-SAC-MQCs) and that of the two-dimensional wavelength/spatial M-matrices codes (2D-W/S-M-Matrices) so that a larger number of subscribers can be supported simultaneously. Additionally, the 2D-W/T-MQC/MQC system requires less signal power for each light source under the same error-free condition. As a result, the network based on the new code family will support more active users and utilize the frequency bandwidth more efficiently.

The impact of synchronization on the performance of FDL buffers

Circumventing the speed bottleneck of electronic switching, novel switching approaches like optical burst switching (OBS) and optical packet switching (OPS) handle the switching of bursts (or packets) in backbone nodes optically, and include a set of fiber delay lines (FDLs) for optical buffering. While previous work acknowledges the performance difference between optical FDL buffers and electronic RAM buffers, the important role of synchronization herein has received little attention to date. Addressing this, we developed a single-wavelength FDL model that allows to capture the interplay between FDL buffer performance, burst size distribution and synchronization. Relying on generating functions, we constructed a discrete-time queueing model with batch arrivals that is valid for general burst and batch size distribution, and allows to quantify how synchronization impacts performance. This paper presents our model and compares its output for different synchronization levels. Whether or not buffer performance benefits from synchronization, turns out to depend strongly on the burst size distribution.

A 5 bit fiber delay line based on magneto-optic switch

In order to fulfill the reliability requirements in field application, the high reliability magneto-optic (MO) switches are used to realize an optical true time delay (OTTD) line. This paper first analyzes the characteristics of MO switch, then the topologies of OTTD are analyzed. Latter, two key supporting aspects are put forward, including measuring method and integrated structure design. In this article, we present and demonstrate a 5 bit optical fiber delay line (FDL) based on MO switches and fiber. The FDL exhibits the maximal delay error of 2.98 ps in 32 states.

Elimination of residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy using an optical fiber delay line

A new fiber-optic technique to eliminate residual amplitude modulation in tunable diode laser wavelength modulation spectroscopy is presented. The modulated laser output is split to pass in parallel through the gas measurement cell and an optical fiber delay line, with the modulation frequency / delay chosen to introduce a relative phase shift of pi between them. The two signals are balanced using a variable attenuator and recombined through a fiber coupler. In the absence of gas, the direct laser intensity modulation cancels, thereby eliminating the high background. The presence of gas induces a concentration-dependent imbalance at the coupler's output from which the absolute absorption profile is directly recovered with high accuracy using 1f detection.

A Two-Dimensional Optical True Time-Delay Beamformer Consisting of a Fiber Bragg Grating Prism and Switch-Based Fiber-Optic Delay Lines

A two-dimensional optical true time-delay (TTD) beamforming system for a planar phased array antenna (PAA) is proposed and demonstrated. The optical beamforming system consists of a fiber-Bragg-grating-prism-based wavelength-dependent TTD (WD-TTD) unit for azimuth beam steering and a microelectromechanical-system-switch-based wavelength-independent TTD (WI-TTD) unit for elevation beam steering. The time delays generated by the WD-TTD and WI-TTD are measured. The results show that the proposed system can achieve the required time delays with the time-delay errors for the WD-TTD and the WI-TTD at 1 GHz less than 11.8 and 3.6 ps, which correspond to radiation direction errors of less than 1.5deg and 0.4deg for a planar PAA with the adjacent array elements spaced by a half radio-frequency wavelength.

Optimal constructions of fault tolerant optical linear compressors and linear decompressors

The constructions of optical queues is one of the most critically sought after optical technologies in all-optical packet-switched networks, and constructing optical queues directly via optical switches and fiber delay lines (SDL) has received a lot of attention recently in the literature. A practical and challenging issue in the constructions of optical queues is on the fault tolerant capability of such constructions. In this paper, we focus on the constructions of fault tolerant optical linear compressors and linear decompressors. The basic network element for our constructions is scaled optical memory cell, which is constructed by a 2X2 optical crossbar switch and a fiber delay line. We first obtain a fundamental result on the minimum construction complexity of a linear compressor by using fiber delay lines as the storage devices for the packets queued in the linear compressor. This result shows that one of our previous constructions of a linear compressor by a concatenation of scaled optical memory cells is an optimal construction in the sense of minimizing the construction complexity. However, such an optimal construction lacks the fault tolerant capability. To construct a linear compressor with fault tolerant capability, we give a multistage construction of a self-routing linear compressor by a concatenation of scaled optical memory cells, and show that if the delays, say d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , . . . , d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> , of the fibers in the scaled optical memory cells satisfy a certain condition (specifically, the condition in (A2) given in Section IV-A), then our multistage construction can be operated as a self-routing linear compressor with maximum delay Sigma <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i=1</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M-F</sup> d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> in the worst case even after up to F of the M scaled optical memory cells fail to function properly, where 0 les Fles M - 1. Furthermore, we prove that our multistage construction with the fiber delays d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , . . . , d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> given by the generalized Fibonacci sequence of order F is the best among all of the constructions of a linear compressor that can tolerate up to F faulty scaled optical memory cells by using M scaled optical memory cells. Similar results are also obtained for the constructions of fault tolerant linear decompressors.

Optical compression for samples with different bit patterns and scaling degrees

An optical packet compression for data samples with different bit patterns and scaling degrees is proposed and demonstrated. The compression stages are composed of optical modulators, 3-dB couplers and fiber delay lines. Erbium-doped fiber amplifiers are applied only between pairs of compression stages. An experiment of 16-bit packet size with compression from 150 MHz to 2.5 GHz is also reported. The proposed scheme achieved low costs in terms of optical components while preserving the signal pattern and scaling degree integrity. It is also shown that the scaling monitoring is an important performance issue for optical communications systems.

一种改进的基于反馈光缓存和反馈波长变换器的光分组交换(OPS)节点结构

The performance of an optical switching network is mainly determined by its core node structure. An improved optical packet switching (OPS) node structure based on recirculation optical fiber delay line (FDL) and feedback tunable wavelength converter (TWC), and a specific scheduling algorithm for the node structure are presented. This switching structure supports both point-to-point and point-to-multi-points broadcasting transmission with superior capacity expansion performance. Its superiority in packet loss probability is proved by simulation.

Constructions of Optical 2-to-1 FIFO Multiplexers With a Limited Number of Recirculations

Recently, there has been a lot of attention in the literature on a less well-known aspect of queueing theory, the theory of the constructions of queues. Such an interest originates mainly from optical packet switching due to the lack of optical buffers. These constructions of optical queues are based on optical switches and fiber delay lines (SDL). Theoretical studies in the SDL constructions have been recently reported for the constructions of various types of optical queues, including output-buffered switches, first-in-first-out (FIFO) multiplexers, FIFO queues, last-in-first-out (LIFO) queues, priority queues, linear compressors, nonovertaking delay lines, and flexible delay lines. In this paper, we consider the constructions of optical 2-to-1 FIFO multiplexers with a limited number of recirculations through the fibers, which is a very important practical feasibility issue on the constructions of optical queues that has not been theoretically addressed before. Specifically, we consider the constructions of optical 2-to-1 FIFO multiplexers with buffer size at least 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sup> -1 by using a feedback system consisting of an (M+2)times(M+2) optical crossbar switch and M fiber delay lines under a simple packet routing policy and under the limitation that each packet can be recirculated through the M fibers at most k times. In one of our previous works, we have shown that this can be done by using n fibers with delays 1, 2, 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ,..., 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n-1</sup> if there is no limitation on the number of recirculations through the fibers. The main idea in our constructions in this paper is to use extra fibers (other than the n fibers with delays 1, 2, 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ,..., 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n-1</sup> ) with appropriately chosen delays to emulate the effective delays of the concatenations of some of the n fibers with delays 1, 2, 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ,..., 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n-1</sup> so that the number of recirculations is reduced by so doing. It turns out that the number of fibers needed and their delays are determined based on a dynamic programming formulation obtained through a divide-and-conquer approach. We obtain a closed-form expression for the number of fibers needed in our constructions, and show that there are ( <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sup> ) possible choices for the delays of the required fibers, where r is the remainder of n divided by k. Furthermore, we give the optimal choice of the fiber delays that achieves the maximum buffer size among the ( <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sup> ) possible choices. Finally, we show that when n=k or nges2k, such an optimal choice also requires the minimum total fiber length among the ( <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sup> ) possible choices.

Dual-Frequency Laser at 1.5 $\mu$m for Optical Distribution and Generation of High-Purity Microwave Signals

We describe the stabilization of the beatnote of an Er,Yb:glass dual-frequency laser at 1.5 mum with and without an external microwave reference. In the first case, a classical optical phase-locked loop (OPLL) is used, and absolute phase noise levels as low as -117 dBrad <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Hz at 10 kHz from the carrier are reported. In the second case one or two fiber-optic delay lines are used to lock the frequency of the beatnote. Absolute phase noise levels as low as -107 dBrad <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Hz at 10 kHz from the carrier are measured, fairly independant of the beatnote frequency varying from 2 to 6 GHz. An analysis of the phase noise level limitation is presented in the linear servo-loop theory framework. The expected phase noise level calculated from the measurement of the different noise sources fits well with the predictions.

Optically Beamformed Wideband Array Performance

Optical beamforming networks (OBFNs) are an interesting alternative for the design of wideband antenna arrays, mainly due to their low losses and weight, their high parallel processing capabilities and their electromagnetic immunity. Nevertheless, for a practical implementation, different technological and architectural tradeoffs need to be assessed. In this paper, the performance of an OBFN system is analytically studied and experimentally demonstrated. The study forms part of the optical beamforming network project, a multigroup research project supported by the European Space Agency (ESA). Differently from bulky free-space geometries, the architecture is based on fiber-optic delay lines for the time delays generation and on a spatial light modulator for the phase shifts generation. Experimental results for an X-band prototype are provided, showing beam steering accuracy, multibeam capability, amplitude distribution weighting and wideband operation.

High-rate data buffering in silicon nanophotonic devices

Buffers represent one of the most important components in a communications router. The device must be able to store data packets for a substantial period of time and release the data within an acceptable delay when the switch is clear. Optical buffers—devices that store optically transmitted data—are considered key elements to achieve synchronized and contention-free traffic in the design of all-light-based communication networks. Conventional buffers use optical fiber delay lines, but since the delay is for a fixed amount of time, they are unable to guarantee contention-free connections in the switch or through a network. Hence, research on tunable optical delay lines is generating significant interest, especially with optical communications now gearing up for large-scale integration. Advances in silicon technology are making this material a choice candidate for future integrated photonics. On-chip delay lines based on silicon-on-insulator (SOI) photonic wire waveguides were recently demonstrated, consisting of up to 100 microring resonators cascaded in either coupled-resonator or all-pass filter (APF) configurations with error-free operation up to 5Gbps.1 This demonstration was a major milestone in the development of all-optical buffers for interconnects. Tunable delays in an SOI planar waveguide based on slow light induced by stimulated Raman scattering (SRS) have also been reported,2 as well as intensity-tunable group delays in siliconmicroresonators enhanced by SRS.3 The functional mechanism of a ring resonator-based optical delay line can be described as follows: When a probe beam is injected into a ring with a frequency matching the resonance of the ring, light is forced to circle multiple times, lengthening the delay. If beam frequency deviates from resonance, it will bypass the ring and no delay will occur. When a pump light, whose frequency is of a different resonance, is injected into the microring resonator, the absorbed energy is eventually converted to therFigure 1. (a) Scanning electron microscope image of a microring resonator and (b) its resonance spectrum.

Contention avoidance and resolution schemes in bufferless all-optical packet-switched networks: a survey

Optical Packet Switching (OPS) is the promising switching technique to utilize the huge bandwidth offered by all-optical networks using the DWDM (Dense Wavelength Division Multiplexing) technology. However, optical packet contention is the major problem in an OPS network. Resolution and avoidance are two schemes to deal with the contention problem. A resolution scheme resolves collisions, while an avoidance scheme tries to reduce the number of potential collision events. Many OPS architectures rely on optical buffers to resolve contention. Unfortunately, optical buffering technology is still immature as it relies on bulky optical fiber delay lines. Furthermore, it requires a complex control. Therefore, a bufferless OPS network could still be the most straightforward implementation in the near future. In this article, we survey the contention resolution and avoidance schemes proposed for bufferless OPS networks. We also review the resolution and avoidance schemes that can handle the Quality of Service (QoS) issue in a QoS-capable bufferless OPS network.

A simple proof for the constructions of optical priority queues

Constructions of optical queues by optical Switches and fiber Delay Lines (SDL) have received a lot of attention lately. In this short paper, we provide a simple proof for the construction of a priority queue with a switch and fiber delay lines in Sarwate and Anantharam (Queueing Syst. Theory Appl. 53, 115---125, 2006). Our proof not only gives the insights needed to understand why such a construction works, but also leads to a more general result that recovers the result in Sarwate and Anantharam (Queueing Syst. Theory Appl. 53, 115---125, 2006) as a special case.

Optical True Time-Delay for Two-Dimensional $X$-Band Phased Array Antennas

An optical true time-delay (TTD) scheme for two-dimensional (2-D) X-band phased array antennas (PAAs) has been proposed. It is composed of a multiwavelength optical source and a delay line matrix consisting of 2times2 optical microelectromechanical system (MEMS) switches with fiber-optic delay lines connected between cross ports. A 2-bit times 4-bit optical TTD for 10-GHz 2-D PAAs has been implemented by cascading a wavelength-dependent TTD (WD-TTD) with a unit time delay of 12 ps in the x-direction and a wavelength-independent TTD (WI-TTD) with that of 6 ps in the y-direction. The time delay error for WD-TTD was measured to be less than 2.8 ps, mainly due to jitter incurred from gain-switching. On the other hand, the error for WI-TTD was less than 0.8 ps, which is within the equipment resolution. Insertion loss of both delay line matrices was less than 1 dB due to the column-wise control of the MEMS switches. This prevents the feed current applied to each antenna element from fluctuating at any radiation angles so that antenna gain and sidelobe level do not deteriorate in this scheme

Generation of arbitrary frequency chirps with a fiber-based phase modulator and self-injection-locked diode laser

We present a technique for producing pulses of laser light whose frequency is arbitrarily chirped. The output from a diode laser is sent through a fiber-optical delay line containing a fiber-based electro-optical phase modulator. Upon emerging from the fiber, the phase-modulated pulse is used to injection-lock the laser, and the process is repeated. Large phase modulations are realized by multiple passes through the loop, while the high optical power is maintained by self-injection locking after each pass. Arbitrary chirps are produced by driving the modulator with an arbitrary waveform generator. We obtain improved performance, in both chirp rate and chirp range, relative to a diode laser that is injection-locked to a modulated source.

X-밴드 위상 배열 안테나를 위한 WDM 광 실시간 지연선로

본 논문에서는 여러 개의 DFB LD로 구성된 다파장 광원을 이용하여 선형 위상 배열 안테나(Phased Array Antenna; PAA)를 위한 WDM 광 실시간 지연선로(Optical True Time-Delay; OTTD) 빔 성형기를 제안하였다. X-밴드용 3-비트 선형 PAA 구동을 위해, 4개의 DFB LD로 이루어진 다파장 광원과 단위 시간 지연이 12 ps인 광섬유 지연선로 행렬로 구성된 WDM-OTTD를 구현하여 모든 방사각에서 시간 지연을 측정하였다. 최대 시간지연 오차는 인접 안테나 소자간 시간지연이 36 ps인 경우에 -1.74 ps와 +1.14 ps로 나타나, 방사각 오차는 주 빔의 방향이 <TEX>$46.05^{\circ}$</TEX>일 때 <TEX>$-2.87^{\circ}\sim+1.88^{\circ}$</TEX>이내가 될 것으로 예상된다. 5-GHz부터 10-GHz까지 6개의 서로 다른 RF 주파수에 대하여 시간지연 특성을 조사한 결과, 모든 주파수에서 동일한 시간 지연이 발생되는 것을 확인하였다. In this paper, we propose a WDM optical true time-delay (OTTD) beam former for phased way antenna (PAA) systems. It is composed of a delay lines matrix and a multiwavelength source with discrete DFB laser diodes. The building block of a delay lines matrix is a <TEX>$2\times2$</TEX> optical MEMS switch with proper fiber-optic delay line connected between cross ports. A <TEX>$4\times3$</TEX> matrix using four DFB lasers has been fabricated with unit time-delay difference of 12 ps. Maximum time-delay error was measured to be -1.74 ps and +1.14 ps at a radiation angle of <TEX>$46.05^{\circ}$</TEX>, corresponding to error range of <TEX>$-2.87^{\circ}\sim+1.88^{\circ}$</TEX>. By measuring time-delays at six different RF frequencies from 5- to 10-GHz, we verified the true time-delay characteristic of our OTTD.

A measurement of propagation delay

A measurement method and associated uncertainty analysis have been developed for the measurement of propagation or group delay in electrical transmission lines and optical fibres. The measurement method and uncertainty analysis were applied to measurements of optical fibre delay lines that introduce tens of microseconds of delay (1 km, 2 km and 4 km fibre lengths) and trombone lines that introduce sub-nanosecond delays. For the measurement method described here, uncertainties in the measured delay are as low as 90 fs (95% confidence interval) for a propagation delay of 660 ps and less than 200 ps (95% confidence interval) for a propagation delay of 20 µs.

Recursive optical fiber delay line filter as a frequency discrimator for RF and microwave signal processing with incoherent light

Recursive optical fiber delay line filter as a frequency discrimator for RF and microwave signal processing with incoherent light