Naoki Shimosaka

Photonic wavelength-division and time-division hybrid switching system utilizing coherent optical detection

The application of coherent optical detection to a photonic wavelength-division (WD) and time-division (TD) hybrid switching system for a large-capacity switching is studied. Wavelength switching time is 1.8 ns, and the wavelength is stable after wavelength switching as wide as 3-4 AA. The results suggest the feasibility of switching over 20 channels (TD 4 channels, WD approximately 6 channels) for 100-Mb/s signals. This channel number can be increased to 256 channels (WD 64 channels) in view of the maximum wavelength sweep range (40 AA) of wavelength tunable laser diodes obtained so far.<<ETX>>

A coherent optical FDM CATV distribution system

A coherent optical frequency-division-multiplexing (FDM) experimental system for an optical CATV distribution service has been developed. This system employs a channel frequency spacing locked optical FDM transmitter and a random access optical heterodyne receiver. In the transmitter, ten 1.54- mu m wavelength tunable distributed-Bragg-reflector laser-diode (DBR LD) modules were FSK modulated with a 400-Mb/s PN pattern. A reference pulse method is used for channel space control. Individual channel spacings for ten LDs are stabilized to 8 GHz. The random access optical heterodyne receiver is realized with a wavelength tunable local DBR LD, polarization diversity reception technique, and random access automatic frequency controller. A current address method realizes the random access function. The results of a ten-channel FDM transmission experiment carried out to evaluate these techniques are presented. It is estimated that over 80 channel high-definition TV signals can be distributed to 2000 subscribers with 500-GHz frequency tunable DBR LD. The feasibility of expanding the subscriber number to over 10000 was confirmed by an experiment with a traveling-wave optical amplifier. >

A coherent photonic wavelength-division switching system for broad-band networks

A coherent photonic wavelength-division (WD) switching system, utilizing a coherent wavelength switch ( lambda switch), is proposed. In the proposed coherent lambda switch, the tunable wavelength filter function is accomplished using coherent optical detection with a wavelength tunable local oscillator. The coherent photonic WD switching system has the following features; (1) low crosstalk switching for dense WDM signal, and (2) large line capacity capability. Design considerations show that 32 wavelength division channels can be available with a coherent lambda switch. It is also shown that a broadband metropolitan-area-network with over 1000 line capacity is possible, using a multistage connection in the coherent lambda switches. The switching function of the coherent lambda switch is demonstrated in a two-channel wavelength-synchronized switching experiment, using 8-GHz-spaced, 280-Mb/s optical FSK signals. >

Frequency separation locking and synchronization for FDM optical sources using widely frequency tunable laser diodes

A laser diode (LD) frequency separation locking method (called the reference pulse method) is proposed. This method has advantageous features for frequency division multiplexing (FDM) networks from the viewpoint of frequency separation stability with a strict frequency separation standard, modulation format independence, controllability over a large number of LDs, and frequency synchronization capability. Frequency locking experiments, using four and ten controlled LDs, confirmed that the control system using the method can stabilize frequency spacing for more than 100 LDs. The frequency fluctuation is suppressed to less than 10 MHz. Frequency synchronization, utilizing the reference pulse method, is proposed and demonstrated experimentally for two controlled LD groups, each consisting of three LDs. Frequency discrepancy between two LD groups was only 2.7% of the frequency separation. Required frequency-swept light power and controlled LD power at the detector input for frequency synchronization indicate that more than 50000 LD groups within a 10 km area, each having 100 LDs, can be synchronized simultaneously. >

A photonic wavelength-division switching system using tunable laser diode filters

A photonic wavelength-division switching system using semiconductor tunable wavelength filters is proposed. Wavelength switches and multistage switching networks are used. The potential of 100 wavelength-division channel achievement in switching systems is estimated, based on InP optical integrated circuits. A wavelength network synchronization method is proposed, which will enable the network to utilize such a large number of wavelength-division channels without wavelength misalignment and drift. An eight-channel wavelength-division switching experiment, using phase-shift controlled distributed-feedback laser diodes as tunable wavelength filters, is reported.<<ETX>>

A 10 channel coherent optical FDM broadcasting system

The first demonstration results of a coherent optical frequency-division-multiplexing (FDM) system with a random-access channel selection scheme for CATV distribution application are reported. Indispensable technologies for the FDM coherent transmission such as channel separation locking, random-access channel selection, and polarization diversity were developed and applied to the system. The developed system has suitable features for use as an optical digital CATV, especially for CATV distribution system applications. It is estimated from a 400-Mb/s 10-channel FDM experiment with an 8-GHz frequency separation that 64 channel HDTV signals can be distributed to more than 2000 subscribers without repeaters.<<ETX>>