Optical Beat Noise Research Articles

Analog network coding aided multiuser visible light communication networks using optical CDMA

A novel architecture of a visible light communication (VLC) network that can provide bidirectional transmission for multiple users is proposed in this paper. Multiple users can exchange data asynchronously and simultaneously thanks to the use of analog network coding (ANC) and optical code division multiple access (OCDMA) with the support of a coordinator, which plays a role as a relay node. We derive the mathematical expressions for bit error rate (BER) and network throughput of an indoor VLC network with multiple users located in a room and one coordinator mounted on the ceiling. Many physical layer impairments are considered in our analysis, including shot noise, thermal noise, multiuser interference (MUI), and optical beat noise. BER and throughput performance are investigated versus the transmitted optical power, the number of users, and the VLC transceiver’s parameters. The numerical results obtained in this paper will provide useful information for designing the indoor multiuser VLC networks.

Reducing Inter-Core Crosstalk Impact via Code-Interleaving and Bipolar 2-PPM for Core-Multiplexed SAC OCDMA PON

Inter-core crosstalk (XT), caused by closely spaced cores, is the principal challenging issue of implementing multicore fiber (MCF)-based optical networks as it limits the network performance severely. In this paper, we propose and demonstrate using bipolar M-ary pulse position modulation (PPM) signaling in conjunction with the code-interleaving (CI) technique to address the inter-core XT problem in MCF-based optical code-division multiple-access (OCDMA) passive optical networks (PONs) with spectral-amplitude coding employed as the coding scheme. The bit error rate of the proposed network is derived based on an accurate analysis for the statistics of the decision random variables, i.e., mean and variance. The analysis accounts for inter-core XT, optical beat noise, and receiver noise. In addition, a comparison between the performance of core-multiplexed OCDMA PON adopting the newly proposed techniques, namely, unipolar on-off keying (OOK) with CI and bipolar 2-PPM with CI and that adopting unipolar OOK without CI, is presented under both data rate and average photons per bit constraints. The obtained results show that bipolar 2-PPM and CI are capable of reducing the inter-core XT impact on the performance of MCF-based OCDMA PONs. Furthermore, bipolar 2-PPM with CI outperforms other schemes in terms of the number of supportable users and energy efficiency.

Performance Analysis of Core-Multiplexed Spectral Amplitude Coded OCDMA PON

Spatial division multiplexing is emerging as a promising solution to improve the optical fiber transmission capacity. In this paper, a multicore fiber (MCF)-based optical access network architecture utilizing spectral amplitude coded optical code division multiple access (SAC-OCDMA) is proposed. We numerically analyze the impact of intercore cross talk (XT) on the bit error probability (BEP) performance of the SAC-OCDMA signals where a closed-form formula for the BEP of the proposed network is derived. We also consider the effects of multiple access interference noise, optical beat noise, and receiver noise in the analysis. Through numerical simulations, we find the penalty in the required Q-factor caused by intercore XT, compared with a single-core system with no XT, for different values of mean intercore XT.

An uplink data transmission method based on wavelet packet transform coding in passive optical networks

A novel uplink data transmission method in electrical code division multiplexing passive optical networks is proposed, simulated and experimentally verified, in which each optical network unit (ONU) is assigned a special multi-level orthogonal code based on wavelet packet transform. Comparing with the normal bi-level orthogonal code by using Walsh code or Gold code, the proposed method can improve the bandwidth utilizations and reduce the optical beat noise. Simulation results show 31 ONUs, of which each data rate is 10 Gb/s and total rate is 310 Gb/s, can be transmitted 30 km. Three ONUs with each data at 622 Mb/s over 50-km single-mode fiber is experimentally demonstrated.

Sub-Tb/s Physical Random Bit Generators Based on Direct Detection of Amplified Spontaneous Emission Signals

The most common optical amplified spontaneous emission sources can become the ultimate tools for the generation of ultra-broadband truly random bit sequences (TRBS). By using a straightforward configuration we experimentally prove that the amplified spontaneous emission noise of an optical amplifier-either an Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+3</sup> -doped fiber amplifier (EDFA) or an InGaAs semiconductor optical amplifier (SOA)-is an efficient source for TRBS generation. A bit rate up to 560 Gb/s has been recorded, seeded by the direct detection of the unfiltered spontaneous-spontaneous (sp-sp) optical intensity beat noise on a broadband photoreceiver. The generation rate is practically limited only by the detection bandwidth, the electronic digitization process and the post-processing circuitry. The proposed mechanism passes the existing benchmarks of randomness.

Performance analysis of coherent bandwidth-limited time-spreading encoding OCDMA system employing pulse-position modulation

Time-spreading (TS) phase encoding optical code division multiplexing access (OCDMA) systems with pulse-position modulation (PPM) signalling are investigated, the multiple access interference, optical beat noise and bandwidth limitation of receiver are considered. The authors also compare the performance of the PPM system with that of the conventional on-off keying (OOK) system with optimum threshold detection. Numerical results show that there exists an optimum pulse-position multiplicity for the PPM OCDMA system, and the corresponding PPM scheme is superior to OOK scheme in the coherent bandwidth-limited TS OCDMA system under the chip time constraint.

Reduction of MAI and Beat Noise in OCDMA Systems Using an SA-SOA-TPA-Based Receiver

In this letter, we investigate the removal of multiple access interference and optical beat noise from a two-channel optical system that simulates the output from a time-spread optical code-division multiple access system operating at a data rate of 100 Mb/s. Both noise sources were removed using a saturable absorber semiconductor optical amplifier two-photon absorption receiver structure. Experimental results show error-free operation when all three devices are used together.

Coherence-Multiplexed Optical RF Feeder Networks

An optical RF feeding system for wireless access is proposed, in which the radio access points are distinguished by means of coherence multiplexing (CM). CM is a rather unknown and potentially inexpensive optical code division multiple access technique, which is particularly suitable for relatively short-range applications with moderate transmission bandwidth requirements. Subcarrier multiplexing (SCM) can possibly be used on top of CM, either as single-channel or multichannel SCM. The performances of the resulting distribution networks are analyzed, incorporating the effect of chromatic dispersion, optical beat noise, shot noise, thermal noise, and-in the case of multichannel SCM-intermodulation distortion. The results of the analyses are illustrated by using numerical examples, based on the IEEE 802.11b standard for wireless LAN.

Optical beat noise reduction in WDM-SCM access networks using modulated optical pulse train

We proposed a new method to suppress the optical beat interference (OBI) in wavelength-division-multiplexing/subcarrier-multiple-access network. The proposed scheme uses the modulated optical pulse train that has broad bandwidth in frequency domain. Since the OBI noise is inversely proportional to the optical bandwidth of beating optical signals, the generated OBI noise by beating of optical pulse train signals from several optical network units (ONUs) spreads over wide frequency range. In addition, the chance of optical beating is low because optical pulse trains from different ONU have different pulse timing. We have demonstrated the proposed idea experimentally. In beating experiment, the carrier-to-noise ratio was obtained over 30 dBc regardless of optical beating. In addition, 6-Ms/s 16 quadrature amplitude modulator data at 0.7 GHz was successfully transmitted up to 20 km with an average error-vector-magnitude of 4.5% in presence of optical beating.

Effect of physical layer impairments on SUM and AND detection strategies for 2-D optical CDMA

The effect of physical layer impairments on the error performance of two-dimensional wavelength hopping/time spreading optical code-division multiple-access (OCDMA) systems is investigated for SUM and AND detection strategies. Relative intensity noise of the optical source, the signal-dependent shot noise, optical beat noise, and thermal noise at the receiver, fundamental issues in the design of OCDMA systems, are included in the bit-error-rate analysis. The analysis indicates that the SUM detection scheme is more robust in a noisy environment.

Performance analysis of low-coherence interferometry, taking into consideration optical beat noise

An extensive study for the optical beat noise in low-coherence two-beam interferometry under uniform spectrum illumination is presented. A new formula for the beat noise is derived. The analytical formulas for the signal-to-noise ratio and the resolution in the detection of small phase change and absolute optical path length are given. The effects of the beat noise on the achievable sensing performances in real sensing systems are numerically evaluated and discussed. The sensing performances are improved by use of a wider optical bandwidth of the illuminating light.

Optical beat noise reduction in subcarrier multiplexed optical link using dual current modulation of master and slave lasers

A novel method to reduce optical beat noise (OBN) which is critical in subcarrier multiplexed-based optical access link is suggested. The chirped optical signal was generated by using dual current modulation through master and slave lasers. The sidelobes of the slave laser decreased up to -90 dBm close to the noise floor. The OBN was reduced by 20 dB because of the spectral broadening of the slave laser resulted from the increased chirp.

Noise waveforms generated by frequency shifted feedback lasers: application to multiple access communications

Using frequency shifted feedback lasers, noise waveforms repetitive in phase but not amplitude are generated. The time correlation function is quasiperiodic, while the power spectrum is broadband and exhibits no structure. To illustrate potential applications of this source, a multiple access communication method is described in which the noise repetition length of each transmission is part of a key used to encode and decode signals. There is no evidence of optical beat noise between two waveforms. The electrical signal-to-noise ratio is observed to decrease in proportion to the number of users.

A symmetric-structure CDMA-PON system and its implementation

A code-division multiple-access (CDMA) passive optical network is proposed as an optical access network system to satisfy the subscriber's increasing data traffic. A CDMA scheme is used not only for delivering multiple channels to as many remote units, but also for suppressing optical beat noise. In this study, a beat noise environment is analyzed and a transceiver structure to efficiently increase the reverse link rate is suggested. Fundamental experimental results are provided to show its validity.

Optical beat noise suppression and power equalization in subcarrier multiple access passive optical networks by downstream feedback

This paper describes a cost-effective method of suppressing optical beat noise in subcarrier multiple access passive optical networks. The method is based on initial power equalization followed by automatic fine tuning of laser wavelengths, via downstream feedback control of their mean powers, so that the receiver noise floor level is continuously minimized. Application and performance of the method is demonstrated for a low-cost 16-channel system with uncooled Fabry-Perot lasers, utilizing narrow-band QPSK modulated subcarrier frequencies over more than one octave. In static and dynamic temperature worst-case situations a considerable reduction in the number of transmission errors caused by optical beat noise is observed, depending on the temperature change rate.

Backreflection and loss in single-fiber loopback networks

We have studied the effects of network loss and back-reflections on single-fiber loopback transmission, in which a modulator replaces the optical source at the remote terminal. Combining a broad-band source at the host terminal with an amplified modulator at the remote terminal effectively suppresses the optical beat noise, allowing data transmission at 50 Mb/s with realistic loss budgets, even in the presence of Fresnel back-reflections as large as -15 dB.

New method for developing optical code division multiplexed access sequences using genetic algorithm

A new method for developing optical code division multi- plexed access (CDMA) address code sequences is presented. The method is based on the genetic algorithm, which has already shown success in developing two-dimensional correlation functions for pattern recognition. The algorithm is very flexible in its optimization criteria and is thus adequate for various optical CDMA applications, including coherent and noncoherent systems. Preliminary computer experimental results are presented that indicate very good discrimination ratios and very fast convergence of the search process. Important implications include synchronization-independent CDMA system design, reduction in optical beat noise, optical power budget improvement, and enhanced security. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)01901-7) Subject terms: optical CDMA; genetic algorithm; optical communication; optical coding.

Capacity of coherence-multiplexed CDMA networks

We determine the capacity and numbers of users that can be supported by CDMA networks that use coherence multiplexing. The analysis takes into account reduced optical beat noise due to differential detection of the decoder outputs. The analysis also includes the effect of fibre dispersion and shows that there is an optimum source linewidth for a given link length and user bit rate. We confirm that the capacity is severely restricted by optical beat noise. However, our calculations show that performances achievable may be adequate for certain local area and access network type applications. For example, at 40 Mb/s per user a maximum of 50 users can be supported over 12 km. We compare our calculations with the measured performance of our recent network demonstration and find good agreement.

Optical-fiber grating-based beamforming network for microwave phased arrays

A new photonic-based beamforming network that can realize a large number of simultaneous and independent beams in a wide-band phased-array antenna, and which eliminates optical beat-noise interference is presented. It is based on discrete and chirped Bragg-grating true-time delay elements and photodetector arrays at each beam port. This achieves a highly parallel delay-processing structure for signal equalization and eliminates the fundamental optical beat-noise limitation to the realization of large array sizes. Results show a very substantial reduction in the number of interconnects required of 98.4% for a 512-beam array and 99.2% for a 1024-beam array, in comparison to conventional beamforming techniques.

Increasing the transmission capacity of coherence multiplexed communication systems by using differential detection

We experimentally verify the impact of optical beat noise on a coherence-multiplexed optical communication system. We then show that optical beat noise can be significantly reduced, and transmission capacity increased, by using differential detection. We demonstrate transmission at low bit error rate of four coherence multiplexed channels, each having a capacity of 1 Gb/s, over 8 km of dispersion-shifted fiber. This is the highest capacity demonstration to date for any code-division multiplexing scheme.