Optical Code Division Multiplexing System Research Articles

Noise Suppression Using Amplitude-Shaping OCDM With 16-Chip Multi-Level Phase-Shifted En/Decoder

We propose an amplitude-shaping (AS) technique to shape an en/decoded signal in 10-Gb/s coherent time-spreading optical-code division multiplexing (OCDM) with ON– OFF keying modulation format, using 16-chip multi-level phase-shifted keying en/decoders. By employing this technique, the primary beat noise and the multiple access interference can be suppressed, and the code detection performance is improved. The bit error rate and the power penalty of the $8\times 10$ Gb/s AS-OCDM, obtained from the calculation and the simulation, are improved, in comparison with the conventional OCDM system.

Optical Code-Division Multiplexing (OCDM) Networks Adopting Code-Shift Keying/Overlapping PPM Signaling: Proposal and Performance Analysis

Optical code-division multiplexing (OCDM) systems use short pulses compared with bit-duration to achieve high transmission rate. The use of short pulses poses several problems as a result of group velocity dispersion (GVD), intersymbol interference (ISI) (due to avalanche photodiode (APD) buildup time), and receivers limited bandwidth. In this paper, an OCDM system employing code-shift keying (CSK) and overlapping pulse-position modulation (OPPM) signaling is proposed and theoretically investigated. By using CSK while maintaining same data rate, the chip duration can be increased to counteract the GVD effect in 2D OCDM systems. Moreover, by increasing the chip duration, the chip rate is decreased and the stringent requirement on receiver bandwidth is relaxed. In addition, using overlapping property in OPPM allows for further chip duration increase. We consider using correlation receivers with hard-limiters and APDs at the receiver side. The bit error probability (BEP) of the proposed system is derived taking into account the impacts of APD noise, thermal noise, GVD, ISI, and multiple-access interference (MAI). A performance comparison between OOK-, PPM-, OPPM-OCDM and the proposed system is carried out. Our results reveal that the use of CSK/OPPM-OCDM with data rate constraint allows the reduction of MAI, GVD and ISI effects with improved spectral efficiency.

Performance Analysis of Time-Diversity Atmospheric OCDM Systems and their Efficiency Enhancement of a Digital TV Signal

In this paper, we propose a new scheme of time-diversity system using optical code division multiplexing (OCDM) in free space optical (FSO) communication. Our design is a full-optical communication system without optical and electrical conversion that facilitates synthesizing the time-diversity signals. We found that employment of the proposed scheme can effectively minimize the influence of scintillation caused by atmospheric turbulence. We analyze the bit error rate (BER) performance of the time-diversity scheme through atmospheric turbulence channels and its efficiency enhancement with a digital TV signal. It not only considers the intensity scintillation of atmospheric turbulence, but also considers scintillation temporal-frequency. We present the theoretical analysis which is based on lognormal models, and validate the performance of the proposed scheme through simulations. Simulation results are further demonstrated to confirm the analytical results. They show that under some circumstances the bit error rate can be improved by a few orders of magnitude using the time-diversity scheme to compensate for the scintillation.

High-security 25 Gbps, polarization multiplexed 256-ary OCDM using a single multi-port encoder/decoder

A block-ciphered (M-ary) optical code division multiplexing (OCDM) can provide larger security than a conventional OCDM system based on bit ciphering. We propose a polarization multiplexed (POL-MUX) M-ary OCDM system and demonstrated 2.5 Gbps, POL-MUX 256 ( = 16X16)-ary OCDM transmission using a single multi-port optical encoder/decoder (E/D). We show that this architecture reduces the number of required optical codes and enhances the system confidentiality.

Grating-based 40-Gbit/s optical code-division multiplexing system incorporating a nonlinear amplifying loop mirror

Abstract. A seven-chip, 280-Gchip/s OCDM system incorporating qua-ternary phase coding and decoding is experimentally demonstrated. Theencoder and decoder, consisting of superstructured fiber Bragg gratings,are fabricated using the equivalent-phase-shift method; only ordinaryphase masks and submicrometer precision in control are required. Inter-channel interference noise is also considered and evaluated; 40-Gbit/s2-channel multiplexing is demonstrated. In addition, a nonlinear ampli-fying loop mirror NALM within the receiver is introduced to improve thesystem performance under two-channel operation. Switching is obtainedfor peak signal power less than 10 mW. We show that the NALM can actas a nonlinear processing element capable of reducing both the pedestalassociated with conventional matched filtering and the width of the as-sociated code recognition pulse. © 2007 Society of Photo-Optical InstrumentationEngineers. DOI: 10.1117/1.2424917 Subject terms: optical code-division multiplexing; superstructured fiber Bragggrating SSFBG ; all-optical encoding and decoding; equivalent phase shift; non-linear amplifying loop mirror .NALMPaper 060430R received Jun. 6, 2006; revised manuscript received Jul. 18, 2006;accepted for publication Jul. 20, 2006; published online Jan. 5, 2007.

Performance enhancement of the 2-D wavelength-hopping/time-spreading synchronous OCDM system using a heterodyne detection receiver and PPM signaling

Feature Issue on Optical Code Division Multiple AccessTwo-dimensional wavelength-hopping/time-spreading synchronous optical code-division multiplexing systems using a heterodyne detection receiver and pulse-position modulation (PPM) signaling are investigated. Prime sequences are used as signature code for both wavelength hopping and time spreading. Performance of the proposed systems is theoretically analyzed taking into account various kinds of noise and interference, including multiple access interference, optical beating interference, crosstalk, and receiver noise. We also compare the performance of the proposed systems with the conventional ones using ON-OFF keying signaling. Numerical results show the improvement in both number of users and optical power gain with a proper selection of PPM word length M.

Optical Code-division Multiplexing Systems using Extended Prime Codes with Reused Zero Codes

In this paper, the extended prime code which inherits all of the correlation properties from the modified prime code is introduced. A novel optical code-division multiplexing system which uses balance encoder with reused zero codes is also introduced. In the proposed system, the interference power is constant; hence, the receiver is simple. The performance of the proposed system is proved to be superior to that of the on-off-keying systems, which were originally proposed for optical code-division multiple access systems.

Design of strict optical orthogonal codes with nonconstant weights for use in optical code-division multiplexing multimedia systems

We report the design of a new family of strict optical orthogonal codes (SOOCs) that permit the use of nonconstant code weights in optical code-division multiplexing (OCDM) systems. Because this new code can possess any number of pulses (i.e., 1s) in each codeword while still maintaining the minimum autocorrelation and cross-correlation constraints (i.e., “1”) for incoherent optical processing, its use can flexibly support multimedia applications in an OCDM system to meet varieties of transmission performance and traffic requirements which are demanded by different types of communication services. The method of designing the proposed codes is presented, and the bound on code length is also given.

Optical code-division multiplexing systems using Manchester coded Walsh codes

The authors propose an optical code-division multiplexing (OCDM) system using a Manchester coded Walsh code (MCWC) as the spreading code. The MCWC, which is a modification of the traditional Walsh code, has some special properties that are suitable for both single-rate and multirate synchronous OCDM systems. In such systems, the multiple-access interference (MAI) is directly proportional to the number of users; therefore, as long as the number of users is determined, the MAI can be estimated and cancelled. According to the performance analysis of the proposed system, the numerical results show that the bit error rate of the proposed OCDM system is much lower than that of other OCDM systems.

Photonic encoder and decoder for optical code-division multiplexing with time-to-space converters and angle-multiplexed holograms.

A photonic encoder-decoder pair for optical code-division multiplexing (OCDM) that uses time-to-space converters and angle-multiplexed holograms is proposed. The encoder converts the pulse from each input port into a specific code and multiplexes input signals into the output port. The hologram in the decoder generates a correlation waveform between the transmitted code and the recorded code. The performance of the OCDM system with the encoder-decoder pair is estimated. The maximum spectral efficiency for 8-bit length orthogonal codes in the worst case at a bit-error rate of 10(-9) is 0.17 (bits/s)/Hz when the number of channels is 8.

Demonstration of novel optical code‐division multiplexing systems for multirate and variable‐rate data communications

We demonstrate optical code-division multiplexing (OCDM) systems using a new optical orthogonal code (OOC) to support multirate and variable-rate data communications. An important characteristic of the proposed codes is that their autocorrelation and cross-correlation operations are dependent only on each individual code word rather than a periodic pulse sequence at the input of OCDM receivers. Consequently, multirate and variable-rate data communications are offered without violating cross-correlation and autocorrelation constraints of 1. This is achieved without increasing any system complexity. Compared with conventional OOCs, our proposed codes not only can have shorter code-word lengths for multirate and variable-rate data communications, but also have high flexibility and performance. Experimental OCDM systems using the proposed code are also carried out.