The essential functions of the passive double star (PDS) system are clarified by comparing them to the functions of the single star (SS) and the active double star (ADS) system. A layered structure describing the functional characteristics of the PDS system is proposed for flexible transport capability. The functions of the optical network unit (ONU) on the customer premises are systematically partitioned into four layers. The functions of the optical subscriber unit (OSU) in the central office are described using five layers. Call by call activation and deactivation techniques are described on the basis of a layered architecture. The reduction of ONU power consumption by adopting activation and deactivation control is also discussed.

We propose a novel architecture (Switched Access Star: SAS) using an optical switch for access networks and prove its operating principle experimentally. In this architecture, the multiple optical network units (ONUs) in subscriber premises are connected to one optical subscriber unit (OSU) in a central office through an optical switch. SAS can increase the number of accommodated ONUs, the transmission line length, and the capacity per ONU. Moreover, this architecture does not need encryption or ID/passwords. SAS can reduce system cost and yield flexible transmission capacities and realize easy management and maintenance of optical transmission lines.

A hybrid integrated optical module composed of a silica-based planar lightwave circuit (PLC), a laser diode with an integrated monitor-photodiode, and a pin-photodiode is fabricated for use in high-performance, compact and cost-effective fiber optic subscriber systems. Its applicability to a wavelength-division-multiplex (WDM) system with a 1.3-µm bi-directional signal and a 1.5-µm one-way signal is demonstrated. The PLC was fabricated by a combination of flame hydrolysis deposition (FHD) and reactive ion etching (RIE), and it simultaneously achieved 1.3-µm/1.5-µm multi/demultiplexing and 1.3-µm Y-branching functions. The optical module exhibited insertion losses of 4.1dB at 1.31µm (including a Y-branch circuit loss of 3dB) and 0.5dB at 1.53µm. An optical output power of more than -4dBm was obtained from the optical module and the crosstalk was sufficiently low at less than -20dB between wavelengths of 1.3µm and 1.5µm. Temperature cycle tests on the optical module showed reliable and stable operation with an optical power fluctuation of less than 0.3dB for 500 cycles.