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Coherence multiplexing (CM) is a specific form of CDMA that is particularly suitable for optical communication systems for medium data rates and small distances. By virtue of its potentially simple implementation, it is particularly useful for "bridging the last mile" to the subscribers, which is an issue that is receiving considerable attention in...
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... The optical spectrum of the XP mode of drive light is presented by the black solid line in Fig. 2(a). Its 3 dB spectral linewidth is around 0.32 nm, and coherence length is calculated to be 0.5 cm [29]. The polarization-resolved optical spectra are plotted in Fig. 2(a). ...
We propose and numerically demonstrate chaos synchronization of two vertical-cavity surface-emitting lasers (VCSELs) induced by common injection of constant-amplitude random-polarization light for physical key distribution. Results show that synchronization is sensitive to polarization rotation of injection light, and synchronization coefficients larger than 0.9 can be achieved as the rotation-degree mismatch is smaller than ±10°. Therefore, polarization rotation degree can serve as a hardware key parameter. Furthermore, each laser’s output has no correlation to the constant amplitude of the injected light. Their components with identical polarization state, e.g. x or y polarization of VCSEL, also have low correlation coefficient smaller than 0.2. It is therefore believed that this synchronization scheme can provide a security-enhanced method of physical key distribution.
... We consider the simplified scenario with identical polarizations of the scattered fields. The complex amplitudes at the output ports of the optical hybrid (3 × 3 coupler) are related to the complex amplitudes at the input ports via transfer matrix H 3 of the 120° hybrid[8,10]: ...
The interferometer of scattered radiation is employed for the detection of the external acoustic action upon an optical fiber. A method for the demodulation of the scattered field using the phase diversity procedure is proposed. The possibility of the fading regions in the demodulated signal is demonstrated, the reasons for such an effect are analyzed, and the methods for its elimination are proposed.
... Each coherence modulator i is illuminated by a separate optical source signal, which will be described by the normalized scalar wave representation of the optical field [15], [18], with (complex) preenvelope x i (t). The random behavior of x i (t) will be described by the thermal light model, which implies that x i (t) is considered as a circular complex Gaussian bandpass process [6], [14], [15], [18]. In the particular case of LEDs or superluminescent diodes, the spectrum is approximately Gaussian, so that the autocorrelation function of x i (t) is ...
... The outputs of the MZI are detected by a balanced receiver, consisting of linear photodiodes with identical responsivities R pd . The photonelectron conversion process is modeled as an inhomogeneous doubly stochastic Poisson process [14], [15]. The output current is amplified by a transimpedance amplifier (TIA) with transimpedance Z TIA and equivalent input noise current with power spectral density S th . ...
... It can be proven [14], [15] that the expected value of the output voltage of the low-pass filter is related to the autocorrelation function of y(t) as ...
Coherence multiplexing is a potentially inexpensive form of optical code-division multiple access, which is particularly suitable for short-range applications with moderate bandwidth requirements, such as access networks, LANs, or interconnects. Various topologies are known for constructing an optical transmission system in which several channels are coherence-multiplexed in one optical fiber. In this paper, the parallel array, the intrinsic reference ladder (IRL), and the discontinuous series system topologies will be further considered and compared with respect to code orthogonality requirements, theoretical performance, and some practical implementation aspects. A modification to the IRL system is proposed, resulting in a significant improvement in the theoretical performance.
... Coherence multiplexing (CM) [1] is a form of optical code division multiple access (OCDMA) that enables distributed users to transmit through a common optical fiber, using broadband optical sources (like LEDs) and Mach-Zehnder interferometers with very large path length differences. This is illustrated inFigure 1. ...
... For a network with a given (fixed) bit rate R b , packet length D L and number of users (transmitter-receiver pairs) N, the bit error rate (BER) and hence packet error rate (PER) increase when the number of active users M increases, because the power of the beat noise increases approximately proportionally to M 2 [1]. For some network parameter values this will cause the network to become unusable when all the users are simultaneously active (so when M=N). ...
... The relation between the BER and the other network parameters is given by [1] ...
Coherence multiplexing (CM) is a relatively unknown form of optical CDMA, which is particulary suitable in medium bit rate, short-range optical networks like LANs. The main purpose of the technique is to allow multiple users to transmit through a common optical fiber simultaneously. When this number is too large, however, the BER will become unacceptably high. Therefore a protocol is needed to control the traffic. In this paper several protocols are presented. An adapted version of synchronous TDMA, two new protocols and a central control unit will be proposed and discussed. Finally, the protocols will be compared with respect to performance and practical implementation aspects.
... Its bandwidth can be made very large and the peak-to-average ratio is reasonable. Noise as information bearer has been applied in optical communications, where it is known as Coherence Multiplexing [2]. Recently, it has been proposed for use in radio communications [3]. ...
A new RF modulation scheme based on a frequency-offset technique is presented. Instead of using sinusoidal carriers, pure noise is applied as information bearer. The transmitted signal is a combination of modulated noise and unmodulated noise acting as a reference. The reference and modulated signals are separated by a frequency offset Δf which is much smaller than the transmission bandwidth. When using the technique, very large processing gains can be obtained which provides robustness in interference-prone environments. In addition, very simple transceiver implementations result. The paper shows both analytical and experimental results.
... The system as described in Section II-C shows many similarities with a system applied in optical communications. The optical technique is called Coherence Multiplexing [9]. The performance of the Coherence Multiplexing (CM) system is limited by the self-interference-also called beat noise. ...
... The analysis for the ULPG system described in this paper largely follows the analysis of the CM system [9]. In a radio environment, in addition to the self-interference, the thermal noise introduced at the receiver input (i.e. ...
In this paper, a new RF modulation technique is presented. Instead of using sinusoidal carriers as information bearer, pure noise is applied. This allows very simple radio architectures to be used. Spread-spectrum based technology is applied to modulate the noise bearer. Since the transmission bandwidth of the noise bearer can be made very wide, up to ultra-wideband regions, extremely large processing gains can be obtained. This will provide robustness in interference-prone environments. To avoid the local regeneration of the noise reference at the receiver, the Transmit-Reference (TR) concept is applied. In this concept, both the reference noise signal and the modulated noise signal are transmitted, together forming the bearer. The reference and modulated signals are separated by applying a time offset. By applying different delay times for different channels (users) a new multiple access scheme results based on delay: Delay Division Multiple Access (DDMA). A theoretical analysis is given for the link performance of a single-user and a multi-user system. A testbed has been built to demonstrate the concept. The demonstrator operates in a 50 MHz bandwidth centered at 2.4 GHz. Processing gains ranging from 10–30 dB have been tested. The testbed confirms the basic behavior as predicted by the theory.
We propose an adaptive phase-diversity method for optical M-ary differential phase-shift keying (MDPSK) homodyne receivers, to achieve coherent optical communication. This method involves eliminating the random fluctuations in the phase differences between the signal light and local oscillator and the in-plane and quadrature signal (IQ) imbalance compensation. For the former, a phase-diversity method, which can theoretically eliminate all phase-related noise, is proposed. The gain and phase imbalances between the I and Q channels can be compensated completely by using automatic phase- and gain-control systems. The core idea is the adaptability of the receiver to the local phase shift of the local oscillator. The performance of the receiver is not sensitive to environmental factors such as temperature and vibrations. Our simulation results show that the imbalances between the IQ channels can be completely compensated over a wide imbalance range, and the baseband signals can be accurately recovered using the proposed scheme.
A novel tri-detector structure and signal processing method to suppress the local oscillator noise for optical heterodyne receiver is proposed. The tri-detector receiver adds a negative feedback loop and a photodetector compared with the traditional dual-detector receiver. Theoretical analysis shows: By use of proper signal processing technique the intensity noise of the local oscillator, which is not only in the direct current component but also in the intermediate frequency component, has been canceled completely.
Fiber-optic coherence multiplexing of 10-Gsymbol/s BPSK and QPSK signals was experimentally demonstrated for the first time. Spectrum-sliced amplified spontaneous emission (ASE) was used as a light source, and two-channel signals were multiplexed. The reference signal was polarization-multiplexed with the modulated signals and transmitted through an optical fiber. At the receiver side, we successfully retrieved the channels by properly adjusting the time shift between the reference signal and the multiplexed signals using a DGD generator. BER performances of < 10-4 for BPSK and < 10-3 for QPSK were obtained without using error correction.
The results of a study of a scattered-light interferometer for detecting external acoustic impacts on optical fiber are presented. A method of scattered field demodulation using the phase diversity technique is proposed. The demodulated signal is shown to contain regions of fading, the causes of which are analyzed.
