Multimode Fiber Channel Research Articles

Self-supervised dynamic learning for long-term high-fidelity image transmission through unstabilized diffusive media

Multimode fiber (MMF) which supports parallel transmission of spatially distributed information is a promising platform for remote imaging and capacity-enhanced optical communication. However, the variability of the scattering MMF channel poses a challenge for achieving long-term accurate transmission over long distances, of which static optical propagation modeling with calibrated transmission matrix or data-driven learning will inevitably degenerate. In this paper, we present a self-supervised dynamic learning approach that achieves long-term, high-fidelity transmission of arbitrary optical fields through unstabilized MMFs. Multiple networks carrying both long- and short-term memory of the propagation model variations are adaptively updated and ensembled to achieve robust image recovery. We demonstrate >99.9% accuracy in the transmission of 1024 spatial degree-of-freedom over 1 km length MMFs lasting over 1000 seconds. The long-term high-fidelity capability enables compressive encoded transfer of high-resolution video with orders of throughput enhancement, offering insights for artificial intelligence promoted diffusive spatial transmission in practical applications.

On off keying line coding based optical transmitter for various both optical fiber communication and OWC channels

Abstract This paper demonstrated the on off keying line based optical line transmitter for different fiber communication and wireless lighted channels. The max Q form and min BER values after PIN receiver based optical fiber base band channel, linear multi-mode fiber channel and OWC at optimum length is clarified. Lighted power variations after light fiber channel, linear multi-mode fiber channel and OWC versus spectral base band wavelength variations at optimum length is demonstrated. Lighted power form variations after lighted base band fiber channel, linear multi-mode fiber channel and OWC versus time variations at optimum length is indicated. Total lighted power after optical fiber base band channel, linear multi-mode fiber channel and OWC at optimum length is clarified. Total electrical power after PIN receiver based optical fiber channel, linear multi-mode fiber channel and OWC at optimum length.

Joint Pre- and Post-Equalization with Higher-Order Modulation Formats in SDM-Based Optical MIMO Systems

The multiple-input and multiple-output (MIMO) technology is a promising area of research to cope up with the demands of higher data rates and capacity. In the optical communication domain, the combination of space-division multiplexing (SDM) with higher-order modulation (HOM) formats over an optical MIMO system actively addresses these challenges. By allowing multi-level signaling with limited increment in the transmitter’s complexity, a jointly designed pre- and post-equalization (PPE) for an optical MIMO system with a multi-mode fiber (MMF) link is proposed. Cost-effectiveness of the system is incorporated by utilizing intensity modulation/direct detection (IM/DD) with HOM formats such as pulse-amplitude modulation (PAM) schemes. With the aid of a numerical optimization algorithm, the proposed joint-PPE filter coefficients are optimized with respect to the MMF channel and the transmit power constraint. In contrast to existing research on the single-mode fiber (SMF) based optical systems, the effectiveness of the proposed joint-PPE filter is analyzed on an MMF link, which is considerably degraded by the modal dispersion. In the analyzed experimental scenario, the proposed joint-PPE scheme confirms to be beneficial as compared to the post-equalization only (PE-only) in terms of bit-error rate (BER) performance. Furthermore, the required average received optical power to reach a BER 10−4 by the joint-PPE scheme is improved by 2 dB with comparison to the minimum mean-squared error (MMSE) PE-only.

Joint pre‐ and post‐equalization using optical multi‐level signaling

A joint pre- and post-equalization scheme is proposed for an optical intensity modulation and direct detection (IM/DD) system. At the transmitter, a linear feed-forward pre-equalizer with just two, three, or four filter taps is suggested to limit the transmitter's complexity and to allow the use of multi-level modulation. Finally, this concept is combined with a zero-forcing post-equalizer at the receiver. By utilizing numerical optimization to design the multi-level signals, the intersymbol-interference originating from the channel is mitigated pre-equalizer taps, a reduction of 3 % in received power compared to a conventional zero-forcing design is achieved. The equalization scheme is tailored for an optical IM/DD system. Therefore, the specific power constraints of such a setup are taken into account in the equalizer design process. In contrast to existing research, the approach is tested for a multi-mode fiber system, which is affected by increased inter-symbol interference due to modal dispersion. The simulation results show that by shifting a small portion of the equalization complexity to the transmitter side, the required optical power to reach a bit-error rate of 10 − 3 $10^{-3}$ is reduced by 7.3% for zero-forcing and 6.8% for minimum mean square error post-equalizers. the noise increase by the post-equalizer is reduced by 6.9 % when including the pre-equalizer with just two filter taps. Compared to an equalization scheme that solely relies on a zero-forcing post-equalizer, the suggested joint pre- and post-equalization scheme is able to improve the bit-error rate performance by an average of 7.15 %. A testbed experiment with a 250 m multi-mode fiber channel and a data rate of 2.5 Gbps operating at 1550 nm confirms these simulation results.

Basis expansion model for tracking and equalizing rapidly varying multimode fiber channels

In multi-mode fibers, environmental perturbations induce changes in the channel transfer matrix at rates proportional to the total length of affected segments and the number of modes; potentially reaching levels where adaptive equalizers fail in tracking the channel state. We propose a technique that tracks the channel on a frame-by-frame basis by modeling variations in mode coupling coefficients over the period of a full frame of symbols as a linear combination of discrete prolate spheroidal sequences (DPSS). In simulations of rapidly varying channel scenarios where least-mean square (LMS) and recursive least squares (RLS) fail completely, our proposed approach consistently tracks and equalizes the channel variation; yielding a symbol error rate of 10-4 at 15-dB signal-to-noise ratio. DPSS, being matched to the dynamic channel behaviour, is a key factor in minimizing the pilot resources expended in channel estimation, with losses in spectral efficiency starting from 4% up to 20% in the worst case.

Performance analysis of grating-assisted passive mode-division multiplexing device using silicon photonics for high-speed RoF/RoFSO communication

The performance of a bidirectional silicon mode-division (de)multiplexer has been analyzed in the radio over fiber passive optical network system. The device uses two grating-assisted contra-directional coupler sections to demultiplex the transmitted fundamental, first-order, and second-order quasi-transverse electric (TE) modes. A bandwidth of 791 GHz and acceptable crosstalks of −25.73 dB (TE0m), −10.30 dB (TE1m), and −11.84 dB (TE2m) have been achieved from the 2.5D finite-difference time-domain method at a wavelength of 1550 nm. The system uses parabolic index multimode fiber (MMF) and free-space optics channels alternatively. A 120-Gbps data rate has been obtained using differential quadrature phase-shift keying scheme and hybrid mode-division multiplexing techniques. The system maintains an acceptable bit error rate (≤10 − 12) over transmission distances of ≤5.3 km MMF and ≤1.9 km for free-space optics link with receiver sensitivities of ≥ − 26.2 and ≥ − 24.8 dBm, respectively.

Selective excitation in multimode fiber using elliptical few mode fiber

The endless growth of the Internet and its applications compels us to introduce new technologies and solutions for increasing data bandwidth demands. In this paper, we propose a technique for selective excitation of fifteen mode groups in a multimode fiber (MMF) using an elliptical few mode fiber (FMF). The elliptical FMF was designed using finite difference beam propagation method and inserted as a pre-compensator before a MMF channel in a numerical optical system to evaluate its modal properties and transmission quality. For performance comparison, the elliptical FMF-pre-compensated MMF optical fiber system is compared with a non-pre-compensated optical consisting of only a MMF. The obtained results show that the elliptical FMF improves the modal purity of the channels and the bit error rate (BER).

Feasibility of Space-Division-Multiplexed Transmission of IEEE 802.11 n/ac-Compliant Wireless MIMO Signals Over OM3 Multimode Fiber

In this paper, we have experimentally demonstrated the feasibility of space-division-multiplexed 3 × 3 multiple-input multiple-output (MIMO) transmission over a single OM3 multimode fiber (MMF) using commercial IEEE 802.11 n/ac access points. Throughput performance for different fiber length links under a range of fiber bending conditions was evaluated. To study the throughput improvement by MIMO technology, throughput performance of single-input single-output (SISO), 2 × 2 MIMO and 3 × 3 MIMO over separate SMF links was also measured for comparison. It is shown that, spatially-multiplexed MMF channel with 3 × 3 MIMO configuration could provide a significant throughput increase in comparison with SISO and 2 × 2 MIMO SMFs configurations, and present a comparable performance with 3 × 3 MIMO SMFs configuration. Meanwhile, the analyses of the impact of fiber bending indicate that, even under a tight fiber bending radius as low as 2 mm, the system performance could still keep at an acceptable level. With all fiber bending radii tested, within each 5-min measurement time, the fiber channel is found to be good enough to provide throughput greater than twice the average SISO value for more than 87.66% and 72.72% of the time, at the 2.4 and 5 GHz bands, respectively. These results together point out a very simple and cost-saving solution for future in-building DASs to distribute wireless MIMO signals using commercially-available MMF infrastructure by space division multiplexing technique, even though it may encounter tight bending conditions.

Single-Tap Equalization for Fast OFDM Signals Under Generic Linear Channels

Channel cannot be compensated by single-tap equalizers in fast orthogonal frequency-division multiplexing (OFDM) easily unless the channel impulse response (CIR) is symmetric. In this letter, we propose a low-complexity fast OFDM scheme, which enables efficient single-tap equalization for generic linear channels without the symmetric limitation. Simulations under both wireless multipath fading and multimode fiber channels are provided to verify the feasibility. Compared with other schemes, the proposed technique is simpler and avoids net data rate loss. It is shown that this scheme exhibits better performance than the frequency-domain-equalization-based fast OFDM scheme under the wireless frequency-selective fading channel.

MIMO Signal Processing for Mode-Division Multiplexing: An overview of channel models and signal processing architectures

We present the fundamentals of multiple-input, multiple-output (MIMO) signal processing for mode-division multiplexing (MDM) in multimode fiber (MMF). As an introduction, we review current long-haul optical transmission systems and how continued traffic growth motivates study of new methods to increase transmission capacity per fiber. We describe the key characteristics of MIMO channels in MMF, contrasting these with wireless MIMO channels. We review MMF channel models, the statistics derived from them, and their implications for MDM system performance and complexity. We show that optimizing performance and complexity requires management of channel parameters-particularly group delay (GD) spread and mode-dependent loss and gain-by design of transmission fibers and optical amplifiers, and by control of mode coupling along the link. We describe a family of fibers optimized for low GD spread, which decreases with an increasing number of modes. We compare the performance and complexity of candidate MIMO signal processing architectures in a representative long-haul system design, and show that programmable frequency-domain equalization (FDE) of chromatic dispersion (CD) and adaptive FDE of modal dispersion (MD) is an attractive combination. We review two major algorithms for adaptive FDE of MD-least mean squares (LMS) and recursive least squares (RLS)-and analyze their complexity, throughput efficiency, and convergence time. We demonstrate that, with careful physical link design and judicious choice of signal processing architectures, it is possible to overcome MIMO signal processing challenges in MDM systems.

0.18-/spl mu/m CMOS equalization techniques for 10-Gb/s fiber optical communication links

Limitations in data transmission caused by modal dispersion in fiber-optic links can be significantly improved using equalization techniques. In this paper, two different equalizer implementation approaches are proposed to extend the transmission capacities of existing fiber-optic links. The building blocks of the equalizer including a multiplier cell, a delay line, and an output buffer stage are fully integrated on a 0.18-/spl mu/m CMOS process. For the continuous-time tap-delay implementation, a passive LC delay line and an active inductance peaking delay line are compared for performance against process variation, as well as power consumption. In addition, a delay-locked loop is proposed to counter delay variations caused by changes in the process corner. A 10-Gb/s nonreturn-to-zero signal is received after transmission through a 500-m multimode-fiber channel, and the signal impairment due to the differential modal delay is successfully compensated using both feed-forward equalizers.

On the performance of the electrical equalization technique in MMF links for 10-gigabit ethernet

In this paper, the electrical equalization technique utilized in multimode fiber (MMF) links for 10-Gigabit Ethernet is reported. This paper presents and compares three kinds of equalizers: linear equalizer, decision feedback equalizer (DFE), and a nonlinear finite-impulse-response DFE (NL-FIR-DFE) based on the analysis of nonlinear operations of direct modulation and detection in MMF links. Computer simulations reveal that NL-FIR-DFE exhibits superior performance in comparison with normal DFE. The equalization performance for an MMF channel with bandwidth 500 MHz-km as well as 160 MHz-km is demonstrated. It is demonstrated that with direct modulation of cost-effective vertical-cavity surface-emitting laser (VCSEL) or Fabry-Perot laser, the transmission distance for installed MMF with a bandwidth of 500 MHz-km at 10 Gb/s can be extended to 300 m with an appropriate offset restricted mode launch condition by utilizing normal DFE and to more than 650 m for NL-FIR-DFE. Moreover, it is shown that the transmission distance for an MMF with a bandwidth of 160 MHz-km can reach 300 m with more than seven times bandwidth improvement by using NL-FIR-DFE.

Orthogonal frequency-division multiplexing in wireless communication systems with multimode fiber feeds

The feasibility of using multimode fiber as an inexpensive cell feed in broad-band indoor picocellular systems is investigated in this paper. The performance of coded orthogonal frequency-division multiplexing (OFDM) for a variety of multimode fiber profiles, including stepped index and /spl alpha/-profile graded index fibers, is assessed. In addition to its ability to perform well in a frequency-selective multipath environment, OFDM is shown to offer good protection against the frequency selectivity of a dispersive multimode fiber. Data rates in excess of 100 Mb/s (without equalization) over a multimode fiber channel are possible, whereas they may be limited to some 20-30 Mb/s using conventional ASK modulation.

Effects of relative intensity noise on a multiwavelength OOCDMA communication system

The effects of relative intensity noise (RIN) on the multiwavelength optical orthogonal code-division multiple-access (OOCDMA) communication system is investigated with two-, three-, four-, and six-wavelength cases using an erbium-doped fiber laser, a graded-index multimode (GI–MM) fiber channel, and a direct-detection (DD) receiver assuming chip synchronization between user codewords, performing Gaussian approximation analysis. It reveals that RIN affects the error performance of the system significantly, for example, with w=3, Ps=−50 dB, RIN=−120 dB/Hz, s=10,000, and M=56, Pe is 9.09×10−9 compared to 1.72×10−14 without RIN, showing more than four orders of increase in magnitude. When Ps=−65 dB, Pe increases with an increase in the number of wavelengths w with RIN and without RIN for a specified modal parameter s. On increased power, say −50 dB, Pe decreases with an increase in w without RIN, while the variation with RIN is neither increasing nor decreasing uniformly for large values of s. This result in system error performance not only depends on the received laser power and the number of wavelengths, but also on the presence of RIN and the modal parameter. ©2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 307–311, 2000.

Effects of relative intensity noise on a multiwavelength OOCDMA communication system

The effects of relative intensity noise (RIN) on the multiwavelength optical orthogonal code-division multiple-access (OOCDMA) communication system is investigated with two-, three-, four-, and six-wavelength cases using an erbium-doped fiber laser, a graded-index multimode (GI–MM) fiber channel, and a direct-detection (DD) receiver assuming chip synchronization between user codewords, performing Gaussian approximation analysis. It reveals that RIN affects the error performance of the system significantly, for example, with w=3, Ps=−50 dB, RIN=−120 dB/Hz, s=10,000, and M=56, Pe is 9.09×10−9 compared to 1.72×10−14 without RIN, showing more than four orders of increase in magnitude. When Ps=−65 dB, Pe increases with an increase in the number of wavelengths w with RIN and without RIN for a specified modal parameter s. On increased power, say −50 dB, Pe decreases with an increase in w without RIN, while the variation with RIN is neither increasing nor decreasing uniformly for large values of s. This result in system error performance not only depends on the received laser power and the number of wavelengths, but also on the presence of RIN and the modal parameter. ©2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 307–311, 2000.

A theoretical analysis of the performance of code division multiple access communications over multimode optical fiber channels .II. System performance evaluation

In this paper, we conduct a system performance evaluation of code division multiple access communications over multimode optical fiber channels. More specifically, we complete the task started in Part I of this paper. In our system evaluation, we consider a collection of independent users sharing a common multimode optical fiber channel, which obey a binomial channel access and utilization model. Under this model, the bit error probability at the ith receiver is calculated as a function of the peak receive signal-to-noise ratio; where the signal-to-noise ratio is a function of the number of active users, the bit energy over "white" noise spectral density, and the percentage time users are active. We also make a comparison of the performance of this system with that obtained for an ideal channel.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A theoretical analysis of the performance of code division multiple access communications over multimode optical fiber channels-part I: transmission and detection

This paper presents results of a theoretical investigation to evaluate the performance of code division multiple access communications over multimode optical fiber channels in an asynchronous, multiuser communication network environment. The system is evaluated using Gold sequences for spectral spreading of the baseband signal from each user employing direct-sequence biphase shift keying and intensity modulation techniques. The transmission channel model employed is a lossless linear system approximation of the field transfer function for the /spl alpha/-profile multimode optical fiber. Due to channel model complexity, a correlation receiver model employing a suboptimal receive filter was used in calculating the peak output signal at the ith receiver. The performance measures for the system, i.e., signal-to-noise ratio and bit error probability for the ith receiver, are derived as functions of channel characteristics, spectral spreading, number of active users, and the hit energy to noise (white) spectral density ratio. >

A model for the α-profile multimode optical fiber channel: a linear systems approach

In this paper, a linear systems model for the /spl alpha/-profile class of multimode optical fibers is proposed and investigated, The modeling approach is rooted in results obtained by Gloge, et al, and is augmented by the application of basic principles from linear systems theory. Propagation losses and modal mixing were not considered in the model, owing to the superior quality of current optical fiber technology. Intermodal dispersion was the major source of dispersion considered in the model; effects due to waveguide and material dispersion were minimized by imposing a narrowband transmission assumption. Both the field transfer function and the corresponding field impulse response were calculated in a small neighborhood around the optimum value of the core parameter /spl alpha/. Results from this investigation, to the extent possible, were compared to those found by Gloge et al, and were found to be in agreement.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of the characteristics of a radio signal at the output of a multimode interference-type fiber channel

An analysis is made of a theoretical model of an interference fiber channel for transmission of microwave signals. It is assumed that the channel consists of a multimode fiber waveguide with a step or graded refractive-index profile. A typical statistic of a longitudinal distribution of inhomogeneities is also assumed. Calculations are reported of the interference losses, the spectral profile of the output radio signal, the signal/noise ratio in the channel, and of the dependences of these parameters on: the type, diameter, and the length of the multimode fiber waveguide; the spectral width of the radiation source; the frequency offset between the interfering optical signals.