A new type of synchronous code division multiple access (S/CDMA) scheme for optical subscriber systems is reported. Passive channel multiplexing is promising for optical subscriber systems because it realizes high system performance at low cost. Unfortunately, passive channel multiplexing suffers from phase differences among the upstream channels, and these differences prevent the usage of traditional synchronous CDMA techniques that reduce cross channel interference. This paper proposes the new technique of block-interleaving & redundancy code sequences to overcome this problem. This combination realizes S/CDMA even in the presence of phase differences and eliminates cross channel interference completely. Therefore, in an optical subscriber system using the new type S/CDMA, the bit error rate performance is independent of phase difference levels and the number of multiplexed channels.

A Wavelength division multiplexing passive optical network (WDM-PON) system that uses spectrum-sliced broadband incoherent light is attractive because it avoids the cost of operating/administering wavelengths in optical network units (ONU) at customer premises. However, it is difficult to enhance the spectrum efficiency to ensure a sufficient signal to noise ratio because it would demand broad channel width. To overcome this problem, we proposed a spectrum-interleaved duplex technique. It enables upstream and downstream communications to share one channel by using a cyclic filter. This sharing of one channel eliminates the need for a guard interval between signal lights duplexed in the channel. One residual issue regarding single band transmission is its robustness to reflection in the transmission medium. To increase the reflection robustness of the spectrum-interleaved duplex scheme, we propose a reflection remover based on an optical code division multiplexing technique. We also evaluate the extent to which capacity of the spectrum efficiency of the spectrum-interleaved duplex WDM-PON system that uses spectrum-sliced broadband incoherent light can be increased.

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.

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.

This paper describes a flexible point-to-multipoint access protocol for the fiber-optic passive double star (PDS) system. To provide various types of services, and permit flexibility in changing transport capacity, a time division multiple access (TDMA) scheme for the PDS system is considered. Dynamic time slot multiplexing based on TDMA is proposed to provide required time slots efficiently according to service changes. The effectiveness of dynamic time slot multiplexing is calculated and compared to fixed time slot multiplexing for telephony services. A TCM/TDMA frame structure and an access protocol enabling dynamic time slot multiplexing are proposed. ONU bandwidth is dynamically assigned by using a set of pointers. The ONU access protocol causes no interruption to operating ONUs on the same PDS system during the configuration or reconfiguration of an ONU. The access time is analyzed to estimate the performance of the access protocol. The probability density of access time is calculated for the number of ONUs connected. The calculation results indicate that a PDS system can accommodate up to around 60 ONUs within the maximum access time specified by ITU-T. The experimental results also agree fairly well with the theoretical values.