Optical Code Division Multiplexing Research Articles

Asynchronous OCDM-Based 10 G-PON Using Cascaded Multiport E/Ds to Suppress MAI Noise

We propose and experiment a novel asynchronous 10G-passive optical network (PON) system based on optical code division multiplexing (OCDM), where a set of cascaded multiport encoder/decoders (E/Ds) are used in the remote node to suppress multiple access interference (MAI) noise. We demonstrate that the proposed configuration drastically suppresses both MAI and coherent beat noises in a fully asynchronous 160 Gb/s (10 Gb/s × 16 optical network units) PON. We also demonstrate the transmission of an OCDM signal with spectral efficiency 12.5 GHz/code, over a 50-km link without dispersion compensation.

Inter-BSs virtual private network for privacy and security enhanced 60 GHz radio-over-fiber system

A novel inter-basestations (inter-BSs) based virtual private network (VPN) for the privacy and security enhanced 60GHz radio-over-fiber (RoF) system using optical code-division multiplexing (OCDM) is proposed and demonstrated experimentally. By establishing inter-BSs VPN overlaying the network structure of a 60GHz RoF system, the express and private paths for the communication of end-users under different BSs can be offered. In order to effectively establish the inter-BSs VPN, the OCDM encoding/decoding technology is employed in the RoF system. In each BS, a 58GHz millimeter-wave (MMW) is used as the inter-BSs VPN channel, while a 60GHz MMW is used as the common central station (CS)–BSs communication channel. The optical carriers used for the downlink, uplink and VPN link transmissions are all simultaneously generated in a lightwave-centralized CS, by utilizing four-wave mixing (FWM) effect in a semiconductor optical amplifier (SOA). The obtained results properly verify the feasibility of our proposed configuration of the inter-BSs VPN in the 60GHz RoF system.

Performance of OCDM/WDM Optical Packet Switches with DPSK-OCDM modulation system

The performance of a Differential-Phase-Shift-Keying Optical Code-Division Multiplexing (DPSK-OCDM) system with balanced detection is investigated in the case in which Gold codes are used. Allowing more optical codes to be supported, the performance in Packet Loss Probability of a DPSK-OCDM Optical Packet Switch, using both code and wavelength domains to solve output packet contentions, may be increased. In the proposed case study the increase is of three orders of magnitude when the offered traffic is 0.7.

Simultaneous detection of 10-Gbit/s QPSK × 2-ch Fourier-encoded synchronous OCDM signals with digital coherent receiver

We experimentally demonstrate the simultaneous detection of 10-Gbit/s quadrature phase shift keying (QPSK) × 2-channel Fourier-encoded synchronous optical code division multiplexing (FE-SOCDM) signals using a digital coherent receiver, for the first time. First, we analytically verify that simultaneous detection can be achieved with an N-point discrete Fourier transform (DFT) using digital signal processing (DSP) because the N-channel Fourier encoding corresponds to an N × N inverse DFT, then the operation is experimentally confirmed. Simultaneous detection of 10-Gbit/s QPSK × 2-channel FE-SOCDM signals is evaluated. The proposed scheme dramatically expands the capability of OCDM systems.

Scaling the System Capacity and Reach of a 10G-TDM–OCDM-PON System Without an En/Decoder at an ONU

To realize high scaling of a 10-Gbps-class optical access system, we propose and demonstrate two different long-reach hybrid multiplexing passive optical network (PON) systems. First, we demonstrate good scalability in the ultimate transmission distance over 100 km single-mode fiber without dispersion compensation of a 10G wavelength division multiplexing (WDM)-time division multiplexing (TDM)-optical code division multiplexing (OCDM) PON system. Second, we also demonstrate a 100 km 10G/1G-TDM-OCDM-PON system for the purpose of the scalability of the current mixed GE-PON and 10G-EPON system.

Full-Duplex, Extended-Reach 10G-TDM-OCDM-PON System Without En/Decoder at ONU

In this paper, we propose a novel long-reach 10.3 Gb/s time division multiplexing (TDM) and optical code division multiplexing (OCDM) hybrid passive optical network (PON) system without en/decoder at optical network unit (ONU), which can realize the aggregation and the extended reach of 10 Gb/s-class TDM-PON systems. Full-duplex transmission, including 4 packets × 4 optical codes (OCs) burst uplink, over single mode fiber (SMF) 65 km without dispersion compensation is experimentally demonstrated by adapting key components such as multi-level phase-shift-keying (PSK) multi-port optical en/decoder, narrow-band optical band pass filter and 10.3 Gb/s burst-mode 3R receiver.

Noise suppression using optimum filtering of OCs generated by a multiport encoder/decoder

We propose a novel receiver configuration using an extreme narrow band-optical band pass filter (ENB-OBPF) to reduce the multiple access interference (MAI) and beat noises in an optical code division multiplexing (OCDM) transmission. We numerically and experimentally demonstrate an enhancement of the code detectability, that allows us to increase the number of users in a passive optical network (PON) from 4 to 8 without any forward error correction (FEC).

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.

Inter-Band Crosstalk Reduction Using Sinc Apodization of Super-Structured Fiber Bragg Gratings for Hybrid WDM/OCDM Add/Drop Filters

Here, we propose a newly developed hybrid system of wavelength-division multiplexing (WDM) and optical code-division multiplexing (OCDM) with phase-shifted coherent time-spreading for the future metro-access integrated network. In order to suppress the inter-band crosstalk from the WDM interfering channels, the sinc-apodizing technique is proposed for the super-structured fiber Bragg gratings (SSFBGs) as the add/drop filters. The suppression of crosstalk is demonstrated by two-channel WDM and OCDM experiments, compared with conventional SSFBGs with uniform index profile. The proposed method suppresses the crosstalk and shows the feasibility of the 160 (10 WDM 16 OCDM)-channel system.

Cost Analysis in Optical Burst Switching Networks with Optical Label Processing

The aim of this work is the analysis of optical burst switching (OBS) networks with optical label processing based on optical code division multiplexing (OCDM) technology. An architecture of resource reservation based on just-in-time (JIT) was proposed and the blocking probability of burst loss considering the number of wavelength and traffic characteristics. Also, a cost model to compare the traditional electronic processing and optical processing was developed. The main results have showed the decrease of burst loss and economy of network resources when optical processing is utilized.

4096-Ary OCDM/OCDMA System Using Multidimensional PSK Codes Generated by a Single Multiport En/Decoder

We experimentally demonstrate a record 4096 (=16 × 16 × 16)-ary optical code division multiplexing (OCDM) system at 2.5 Gbps using multidimensional phase shift keying (PSK) codes generated/processed by a single multiport optical encoder/decoder (E/D). To analyze the system performance, we evaluate the power margin and the data confidentiality. For application to access networks, we propose and numerically evaluate the performance of 10 Gbps, 4096-ary optical code division multiple access (OCDMA)-based passive optical network (PON).

Evaluation of Optimum Threshold in OCDM/WDM Optical Packet Switches

In this paper we illustrate a procedure to evaluate the optimum receiver threshold in Optical Code Division Multiplexing (OCDM) systems using Gold Codes. The use of the optimum threshold allows for a higher number of optical codes carried on each wavelength. The increase in OCDM/WDM Optical Packet Switch performance is also evaluated when the threshold optimization is performed. We show that when the offered traffic is equal to p=0,7, the packet loss probability of the OCDM/WDM switch in saturation conditions, equals 1,28*10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> in the case in which the optimal receiver threshold is used. On the contrary the performance reaches only 3,91*10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> if a traditional threshold is chosen.

Transparent Transmission of a Secure Time Domain Spectral Phase Encoding/Decoding DPSK–OCDM Signal Over a DWDM Network

We propose and experimentally demonstrate a transparent optical-code-division multiplexing (OCDM) overlay public dense wavelength-division multiplexing (DWDM) network architecture enabled by a passive spectral notch filter for extracting and detecting a secure OCDM signal, which employs a time domain spectral phase encoding/decoding scheme that can simultaneously generate differential-phase-shift-keying (DPSK) data and optical code patterns using only a single phase modulator. The time domain encoded OCDM signal has been scrambled bit-by-bit by a prime hopping pattern and concealed in the public DWDM channels to significantly improve the OCDM channel security. The effect of optical code patterns, the channel number, and bandwidth of the spectral notch filters on the system performance has been theoretically simulated and experimentally validated. In the experiment, error-free transmission of a 2.5-Gb/s time domain spectral phase encoded DPSK–OCDM signal with three 8-chip, 20-Gchip/s optical codes and a scrambled code pattern in the transparent OCDM overlay two-channel 10-Gb/s DWDM network has been successfully demonstrated.

Demonstration of OCDM Coder and Variable Bandwidth Filter Using Parallel Topology of Quadruple Series Coupled Microring Resonators

The quadruple series coupled microring resonator (MRR) can realize a boxlike spectral response and lower adjacent channel crosstalk. Utilizing these features, we demonstrated the element of Optical Code Division Multiplexing (OCDM) coding circuit using two wavelength selective switches (WSSs) consisting of quadruple series coupled MRRs laid out in parallel topology and a phase shifter incorporated in the one arm between them. In addition, a digitally variable bandwidth filter was successfully demonstrated using the same circuit as the OCDM coder.

Spectrally Efficient Frequency-Domain Optical CDM Employing QAM Based on Electrical Spatial Code Spreading

We propose frequency-domain optical code-division- multiplexing (CDM) employing quadrature-amplitude-modulation (QAM) using two of multi-level (M-ary) data generated based on electrical-domain spatial code spreading. Its spectral efficiency is enhanced compared to the conventional scheme with amplitude-shift-keying (ASK) using only one of M-ary data. Although it demands the recovery of amplitude and optical phase information, the practicality of the receiver is retained with self-homodyne detection using a phase-shift-keying (PSK) pilot light. Performance is theoretically evaluated and the optimal parameters are derived. Finally, the feasibility of the proposed technique is experimentally confirmed.

Experimental demonstration and analysis of security-improved optical code division multiple-access networks using multiple-group optical orthogonal codes

Conventional single-group optical orthogonal codes (OOC)-based optical code division multiplexing (OCDM) networks have been introduced and analyzed in some literature. To overcome the security restriction of single-group OOC-based OCDM networks, a new method for security improvement of OCDM networks is proposed, theoretically analyzed, and experimentally demonstrated for the first time in this work. A family of multiple-group OOC (MGOOC) is presented, and an example of a changing principle of the MGOOC is then considered in OCDM networks. Optical encoders and decoders for the MGOOC are designed and experimentally demonstrated successfully, and an OOC of the MGOOC is also selected randomly for any single user in this experiment. These results indicate that the new method for MGOOC-based OCDM networks is effective to enhance security performance.

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.

Fiber fault PON monitoring using optical coding: Effects of customer geographic distribution

We analyze the performance of fiber fault monitoring of a PON using a centralized, passive optical coding (OC) system. We develop an expression for the detected monitoring signal, study its statistics, and contrast our OC monitoring system with standard optical code division multiplexing (OCDM) data communication. We derive a new closed form lower bound expression for the interference probability, and use this to find the signal-to-interference ratio (SIR). A service provider cannot control the physical layout of homes in a coverage area; measuring performance for one network layout would be insufficient to test our proposed monitoring system. Client geographic distribution has a significant impact on the SIR. We consider five different PON geographical distributions and study their effect on OC monitoring performance. Our results show that SIR is sufficient to successfully monitor the network. In addition, we find that the uniform radial (UR) distribution, an analytically tractable distribution, gives good performance estimation and can therefore be a useful tool in characterizing performance in terms of both SIR and signal-to-noise ratio (SNR).

Optical Code-Labeled Router Based on OCDM

An optical code-labeled router that performs packet forwarding through optical code label swapping (OCLS) based on code division multiplexing technology is proposed. It can enhance the processing speed of packets that can adapt to the growth of data and the aggregation of data service. The throughput of the router increases obviously since the optical code division multiplexing (OCDM) paths on the same wavelength can be processed in parallel. Moreover, it is attractive for its traffic control, bandwidth efficiency, protocol transparency, channel granularity, and so on.

Future Optical Access Network and Spectral M-Ary ASK OCDM as Its Key Technology

This paper presents spectral multi-level (M-ary) amplitude shift keying (ASK) optical code-division-multiplexing (OCDM) as a key technology for future optical access network. A novel transmitter configuration to achieve flexible scalability that is required in future optical access network is proposed. The transmitter employs pre-biasing circuits and dummy data input. Pre-biasing circuits enable us to achieve high tolerance to multiple access interference by compensating for the nonlinearity of the M-ary ASK and increase the number of multiplexed binary data streams. By inputting the dummy data into the transmitter so that the total number of multiplexed binary data streams including those that actually accommodate users/services and the dummy streams remains constant, the number of users/services can be increased up to the total number of data streams without changing the parameters for pre-biasing. Therefore, the proposed transmitter can flexibly enhance the scalability of the spectral M-ary ASK OCDM. The formulas for calculating the bit error rate characteristics are described when using the conventional and proposed transmitters. The feasibility of the proposed transmitter is verified theoretically using the established formulas.