Fiber Delay Lines Research Articles

A parity-time-symmetric optoelectronic oscillator with polarization multiplexed channels

In this manuscript, we experimentally demonstrate a parity-time-symmetric optoelectronic oscillator (OEO) with polarization multiplexed channels. We obtained a microwave single-mode oscillation at 9.5 GHz with phase noise values of −116.2 and −122.3 dBc Hz−1 at 10 kHz offset frequencies, and side mode suppression values below −68 and −75 dBc Hz−1, by utilizing a 1 km long and 5 km long single mode fiber delay lines, respectively. Our experimental results suggest that parity-time-symmetric OEOs with polarization multiplexed channels are simple and cost-efficient alternatives to their more complex counterparts.

Design, modeling and optimization using hybrid virtual topology for QoS provision over all-optical switched networks

All-optical switched networks (AOSN), mainly optical label switching (OLS), guaranteed fast data transfer QoS support and network resource supervision. However, the emergence of new applications and services, having variable and various requirements, are produced new demands, notably in terms of QoS support and resource control. To meet these demands, a hybrid virtual topology (HVT), with multiple core node architectures employing wavelength converters (WC), fiber delay line (FDL), and deflection path (DP), is proposed. This HVT enables various node architectures to manage the availability and usage of the components, covering fixed, limited, and full range converters (FXWC, LRWC, and FRWC) also FDL. An advanced DP improves signaling and switching to supervise the potential HVT and AOSN resources while assuring QoS support. A lightpath cost is formulated to determine the potential lightpaths utilized to build the HVT guaranteeing AOSN resources and advanced traffic management. The obtained results of the conducted simulation and comparative study show that the optimized (O-HVT) approach performed better than the enhanced (E-HVT) and initial (I-HVT) approaches. Moreover, the O-HVT method optimizes AOSN resources, mainly core node architecture range, while providing QoS support for high load traffic with variable demands.

Performance analysis comparison of optical burst switching networks' contention resolution techniques

<p><span>Optical burst switching (OBS) is a transporting network for the optical internet in the years ahead vision. As OBS depends on statistical multiplexing, the effect of contention resolution is the main issue to achieve a low probability losing of burst. Basically, there are different ways to resolve contentions in the OBS networks like wavelength conversion, deflection routing, burst segmentation and optical buffering using fiber delay lines. Burst segmentation and deflection routing as well as fiber delay lines technologies, are discussed among the various accessible conflict resolution techniques in this study. However, the main aim of this study is to demonstrate that, the performance of fiber delay line (FDL) is better than other techniques to resolve contention by comparing the performance of these different schemes based on burst losing probabilities and the data handling capability. To evaluate the performance, appropriate mathematical formulae were used. Under the MATLAB environment, the performance was measured based on the probability of burst loss versus incoming traffic (load). The outcomes suggest that deflection routing outperforms fiber delay lines and burst segmentation in the OBS network in terms of resolve the contention. </span></p>

Fiber-delay-line-referenced optical frequency combs: three stabilization schemes

We demonstrate the stabilization of an optical frequency comb (OFC) using a segment of fiber delay line as a reference. A mode-locked Er-doped fiber laser is phase locked to a kilometer-long fiber delay line using three different schemes. The short-term stability of the comb modes in the OFC stabilized by these schemes is obviously enhanced, down to the 10-12 level at millisecond average time. Among these three schemes, phase locking two bunches of comb modes in the OFC to the same fiber delay line exhibits the lowest residual phase noise. Fiber-delay-line-referenced OFCs can provide reliable laser sources in precise metrology owing to the advances of low cost, compactness, and high integration.

Efficient Predictable Probe of Optical Burst Switched For Wireless Feeler Bond

Optical Burst Switching (OBS) is a promising paradigm for high speed transmission of data. In OBS, a key problem is to schedule bursts with minimum loss. Single method is not sufficient to improve performance. So, our performance model includes some feasible methods to improve OBS performance without significantly increasing the implementation complexity. The methods are addition of simple fiber delay lines (FDLs), increasing random extra offset time, window based channel scheduling (WBS) and Burst Delay Feedback scheduling (BDFS). Additional FDLs can only eliminate the negative impact caused by the variation of the offset time between control packets and data bursts. The random extra offset time approach does not require any additional hardware in the nodes. WBS provides better throughput improvement when FDLs are used in the nodes to compensate the processing time. Finally Burst Delay Feedback Scheduling in addition with these methods can significantly improve OBS throughput and reduce transmission delay.

Design of optical packet switch in presence of dispersion compensation and amplifier noise

Abstract Optical communication gained popularity in past few years. Optical communication has many distinct advantages over copper cable based electronic communication. Optical switches are integral part of optical networks which are used for rerouting of packets and also plays important role in contention resolution of the packets. These switch uses fiber delay lines (FDLs) act as optical memory. In past analysis of the switch is done by considering loss, power and noise and finally bit error rate (BER); however dispersion was neglected which is an important parameter in high speed communication. In this paper, design analysis is done by considering dispersion compensation along with optical amplifier noise.

Optical frequency comb stabilized to a fiber delay line

We have developed a simple and practical optical frequency comb (OFC) stabilization method for comb linewidth reduction in this Letter. Two comb modes of an Er-fiber optical frequency comb (OFC) have been phase-locked to a kilometer-long fiber delay line, while narrow linewidth lasers are not required as optical references. The fractional frequency stability of the 1542-nm comb mode in the Er-fiber OFC reaches 9.13 × 10−13 at 12.8 ms average time, and its short-term linewidth is 580 Hz, which is compressed by a factor of ∼170 compared to the free-running condition. The whole stabilization scheme gets rid of nonlinear progress, which can be an alternative approach for OFC stabilization, especially in ultra-high repetition-rate combs, e.g., electro-optic combs, quantum cascade laser combs, and micro-combs with low pulse energy.

Source Location and Suppression of Phase Induced Intensity Noise in Fiber-Based Continuous-Wave Coherent Doppler Lidar

The phase induced intensity noise (PIIN) may seriously reduce the signal-to-noise ratio (SNR) of continuous-wave coherent Doppler lidar (CW-CDL), thereby limiting its performance in practical applications. In this paper, we propose to use optical frequency domain reflectometry (OFDR) technique to locate the PIIN sources and evaluate their intensities. According to the OFDR information, we demonstrate that the PIIN in our CW-CDL system is mainly induced by the crosstalk of polarization beam splitter. Then, the PIIN is reduced by setting fiber delay line, polarization control, and AR-coating. Finally, a wind Doppler signal at a distance of 80 meters is obtained on a clear day, and a typical SNR of 19.4 dB is achieved.

DbOBS: dual buffered switch for variable optical bursts in future datacenters

Modern data-driven applications pose stringent requirements of high bandwidth, ultra-low-latency, low-powered, and scalable interconnections among switches and routers in data-centers. To address these demands, electronic switching is not a viable choice due to bandwidth and computing bottlenecks. Thus, researchers explored effective optical switch design principles for next-generation data-centers. In optical switches, data aggregates in the form of optical bursts (OB) at ultra-high speeds. In the case of OB contention, solutions are proposed by researchers to store OB as recirculating patterns in fiber delay lines (FDL) with induced optical delay. However, due to variable burst length, it is not possible to measure slot delay length, thus storage of contending bursts is not possible at intermediate core switches. Motivated from the aforementioned discussions, in this paper, we propose a switch design DbOBS, that is capable to store variable OB during contention slots. DbOBS estimates mean burst length, and possible deviation from mean length to minimize burst loss. The considered switch design is validated through parameters like-burst length estimation, over-reservation, and waiting time. For network-layer simulations, poison arrivals of data bursts are considered as packetized units. The packets are sent through Monte-Carlo arrivals and burst loss probability (BLP) is estimated at various input load conditions and buffer sizes. DbOBS achieves a BLP in order of $$10^{-4}$$ at load $$\approx$$ 0.8, and buffer-size of 50, and burst length of $$L=5$$ , that outperforms the traditional switch designs.

Optical Fiber Delay Lines in Microwave Photonics: Sensitivity to Temperature and Means to Reduce it

One of the key functionalities in microwave photonics is to be able to define controllable time delays during the signal processing. Optical fibers are often used to achieve this functionality, especially when a long delay or a widely-tunable delay is needed. However, the stability of this delay in the presence of environmental changes (e.g., temperature) has not, to the best of our knowledge, been reviewed yet. Here, we firstly discuss the impact of temperature-induced variations on the signal propagation time in optical fibers and its implications in microwave photonics. We compare the impact of the thermal sensitivity of various delay lines for applications in which the signal is transported from point A to point B, as well as for applications in which the propagation time through a fiber or the fiber dispersion is used to create a fixed or tunable delay. In the second part of the article we show the impact of fiber thermal sensitivity on a narrow-band microwave photonics filter made of standard single mode fiber (SSMF) and a hollow core fiber (HCF), which has significantly lower thermal sensitivity of propagation time to temperature. The central frequency of the band-pass filter changes almost 16 times more in the filter made of SSMF as compared to that of HCF, dictating very tight (0.05 °C) temperature stabilization for SSMF-based filters. On the basis of our thermal sensitivity analysis we conclude that HCFs are very promising for environmentally stable microwave photonics applications.

Research on Coherent Light detection Method Based on Phase Control of Fiber Delay Line

With the system modeling and simulation, analyzed the mechanisms of signal transmission and storage, and phase-controlling, and researched the relationship between time-delay and phase-delay. The effect of optical path difference on optical phase-matching is investigated in time domain and frequency domain. The results shows that, the signal power will obtain maximum after coherent mixing when the phase between signal light and reference light is 2nπ(n=0, 1, 2……); the signal power will obtain minimum when it is (2n+1)π(n=0, 1, 2……), and the mixing signal of other phase relationship will vary in this range. And it is proved that the time delay of optical fiber delay line could effectively compensate the phase delay which generated in the transmission and a phase controlling of the signal transmission could be achieved.

Searching for Dark Matter with an Optical Cavity and an Unequal-Delay Interferometer.

We propose a new type of experiment that compares the frequency of a clock (an ultrastable optical cavity in this case) at time t to its own frequency some time t-T earlier, by "storing" the output signal (photons) in a fiber delay line. In ultralight oscillating dark matter (DM) models, such an experiment is sensitive to coupling of DM to the standard model fields, through oscillations of the cavity and fiber lengths and of the fiber refractive index. Additionally, the sensitivity is significantly enhanced around the mechanical resonances of the cavity. We present experimental results of such an experiment and report no evidence of DM for masses in the [4.1×10^{-11}, 8.3×10^{-10}] eV region. In addition, we improve constraints on the involved coupling constants by one order of magnitude in a standard galactic DM model, at the mass corresponding to the resonant frequency of our cavity. Furthermore, in the model of relaxion DM, we improve on existing constraints over the whole DM mass range by about one order of magnitude, and up to 6 orders of magnitude at resonance.

Faraday Michelson Interferometers for Signal Demodulation of Fiber-Optic Sensors

We developed an all-fiber-based optical demodulator for the signal interrogation of low-coherence fiber-optic Fabry-Perot interferometric sensors. The optical demodulator consists of a Michelson interferometer implemented by using a 3 × 3 fiber coupler and two fiber-coupled Faraday reflectors with tunable fiber delay lines. The demodulator's output contains two optical interference signals with a constant phase shift and the output shows no sensitivity to the polarization variation in the light source or fibers. A digital phase recovery algorithm is used to extract the measurand information from the phase-shifted signals at high accuracy, high dynamic range, and high stability. The optical demodulator has been applied to the measurement of high-frequency vibrations and strains using fiber-optic sensors.

Joint Hybrid Wavelength Conversion and Fiber Delay Line for All-Optical Core Node Modeling and Optimization Using Dynamic QoS Support

All-optical networks (AON) assured a large bandwidth, high-speed switching, and QoS (Quality of Service) support. But due to the development of applications and services, new requirements are created in terms of, specifically resource utilization and QoS provision. To meet these demands, AON enabled core node architecture with multiple wavelength converters’ types involving full range wavelength converter (FRWC) having a significant cost. To reduce the cost, a hybrid AON with composite node architecture combining wavelength converters (WC), Fiber delay line (FDL), and wavelength range (WR) are introduced. In this architecture, fixed and limited wavelength converters (FXWC, LRWC) are utilized while the FRWC converter is replaced by FDL. The proposed architecture decreased the presence and usage of WC, FDL, and WR while assuring QoS support. A lightpath cost formulation is computed based on WR, WC, and FDL enabled in the proposed node architecture to decrease converter and FDL numbers. The cost also managed the wavelength availability to ensure lightpath control and QoS support using real-time requirements, especially loss and blocking delay. The obtained results in the comparative study, conducted in the simulation work, showed that the novel approach performed better than the existing approaches. Moreover, our proposal optimized AON resources, particularly node architecture design, while providing QoS support according to the traffic parameters and requirements.

4D encoding scheme for OCDMA system based on multi-diagonal code

This study represents four dimensions (polarization/spectral/temporal/spatial) encoding scheme for the multi-diagonal (MD) code implementation in an incoherent system, using a direct detection technique. In the proposed scheme, the spectral/temporal/spatial encoding is incorporated with polarization encoding as a fourth-dimension signature of MD code. The coder and decoder are based on polarization beam splitters, fiber bragg gratings, delay lines and star couplers. Spectral/temporal/spatial MD code is employed as the signature allocated to an individual horizontal or vertical state of polarization. The results indicate that the proposed scheme can be used for the high-speed transmission. Also, its performance capacity overpasses the existing codes. Hence, the proposed system enhances 1.5, 2, 2.16, 2.63 and 5.7 times the number of users of the systems based on three dimensional dynamic cyclic/ multi-diagonal (3D-DCS/MD), three-dimensional multi-diagonal (3D-MD), three dimensional perfect difference/multi-diagonal (3D-PD/MD), three dimensional perfect difference (3D-PD) and two dimensional multi-diagonal (2D-MD) systems, respectively.

Nonlinear dynamics in an optoelectronic feedback delay oscillator with piecewise linear transfer functions from the laser diode and photodiode.

We investigate the nonlinear dynamics of a recent architecture of an optoelectronic oscillator, where the emitting laser and the receiving diode are connected in a head-to-tail configuration via an optical fiber delay line. The resulting nonlinear transfer function is a piecewise linear profile, and its interplay with the delay leads to many complex behaviors such as relaxation oscillations and deterministic chaos. This system belongs to a recent class of optoelectronic oscillators where the nonlinearity does not originate from the sinusoidal transfer function of an imbalanced interferometer, and, in particular, it is a simple optoelectronic oscillator configuration that is capable of displaying a chaotic behavior. The results of the analytic study are confirmed by numerical simulations and experimental measurements.

Nonlinear dynamics of miniature optoelectronic oscillators based on whispering-gallery mode electrooptical modulators.

We propose a time-domain model to analyze the dynamical behavior of miniature optoelectronic oscillators (OEOs) based on whispering-gallery mode resonators. In these systems, the whispering-gallery mode resonator features a quadratic nonlinearity and operates as an electrooptical modulator, thereby eliminating the need for an integrated Mach-Zehnder modulator. The narrow optical resonances also eliminate the need for both an optical fiber delay line and an electric bandpass filter in the optoelectronic feedback loop. The architecture of miniature OEOs therefore appears as significantly simpler than the one of their traditional counterparts and permits us to achieve competitive metrics in terms of size, weight, and power. Our theoretical approach is based on the closed-loop coupling between the optical intracavity modes and the microwave signal generated via the photodetection of the output electrooptical comb. The resulting nonlinear oscillator model involves the slowly-varying envelopes of the microwave and optical fields, and its stability analysis permits the analytical determination the critical value of the feedback gain needed to trigger self-sustained oscillations. This stability analysis also allows us to understand how key parameters of the system such as cavity detuning or coupling efficiency influence the onset of the radiofrequency oscillation. Our study is complemented by time-domain simulations for the microwave and optical signals, which are in excellent agreement with the analytical predictions.

Hybrid buffer‐based optical packet switch with negative acknowledgment for multilevel data centers

Abstract In the present scenario, data centers serve many functionalities like storage, transfer of data, supporting web applications, etc. In data centers, various levels of hierarchy different types of switches are required; therefore, multifunctional data centers are desired. This paper discusses a novel design for optical switch which can be placed at various levels of hierarchy. In the proposed design, multifunctionality contention resolution schemes which consider electronic and optical buffering and all-optical negative acknowledgment (AO-NACK) are considered. In buffering technologies, contending packets are stored in either in electronic RAM or in fiber delay lines. In case of the AO-NACK scheme, contending packets are blocked, and a negative acknowledgment is sent back to the transmitting node and blocked packets are retransmitted. For various considered schemes, Monte Carlo simulation have been performed, results in terms of packet loss probability are presented, and it has been found that the performance of optical buffering is much superior to electronic buffering and AO-NACK schemes. It is found that, in the AO-NACK scheme, the numbers of retransmitted packets due to contention blocking are 33,304 which can be reduced to 7, by using a small amount of buffer at each node.

A controlled deflection routing and wavelength assignment based scheme in Optical Burst Switched (OBS) networks

Abstract Heterogeneous IoT-enabled networks generally accommodate both jitter tolerant and intolerant traffic. Optical Burst Switched (OBS) backbone networks handle the resultant volumes of such traffic by transmitting it in huge size chunks called bursts. Because of the lack of or limited buffering capabilities within the core network, burst contentions may frequently occur and thus affect overall supportable quality of service (QoS). Burst contention(s) in the core network is generally characterized by frequent burst losses as well as differential delays especially when traffic levels surge. Burst contention can be resolved in the core network by way of partial buffering using fiber delay lines (FDLs), wavelength conversion using wavelength converters (WCs) or deflection routing. In this paper, we assume that burst contention is resolved by way of deflecting contending bursts to other less congested paths even though this may lead to differential delays incurred by bursts as they traverse the network. This will contribute to undesirable jitter that may ultimately compromise overall QoS. Noting that jitter is mostly caused by deflection routing which itself is a result of poor wavelength and routing assigning, the paper proposes a controlled deflection routing (CDR) and wavelength assignment based scheme that allows the deflection of bursts to alternate paths only after controller buffer preset thresholds are surpassed. In this way, bursts (or burst fragments) intended for a common destination are always most likely to be routed on the same or least cost path end-to-end. We describe the scheme as well as compare its performance to other existing approaches. Overall, both analytical and simulation results show that the proposed scheme does lower both congestion (on deflection routes) as well as jitter, thus also improving throughput as well as avoiding congestion on deflection paths.

Optical frequency comb noise spectra analysis using an asymmetric fiber delay line interferometer.

A simple and practical apparatus enabling repetition rate (frep) noise, carrier-envelope frequency (fceo) noise and nth optical comb mode (νn) noise spectra measurements with high precision is established. The frep and νn noise spectra are measured by a fiber delay line interferometer, while fceo noise spectrum is measured by an f-2f interferometer. We utilize this apparatus to characterize the noise performance of an Er-fiber optical frequency comb (OFC) and analyze the origin of dominant noise sources. Moreover, this apparatus provides a powerful tool for diagnosing noise dynamics intrinsic in mode-locked lasers and OFCs. To this end, we uncover the anti-correlation between frep and fceo noise as well as the impact of servo loops on noise characteristics in the stabilized OFC.