Shigeki Kitajima

Tunable DFB laser with a striped thin-film heater

The authors propose a very simple tunable laser with a striped thin-film heater. The wavelength of this laser changes with a sensitivity of 3.2 nm/W to the input heating power. This laser can be continuously tuned over a range of 4 nm while maintaining an optical power of 20 mW and with a linewidth of less than 2.5 MHz. When this laser is mounted on a module, its 90% response time is 6 ms, which is fast enough for use as a local oscillator in several applications.<<ETX>>

1.244-Gb/s 32-channel transmission using a shelf-mounted continuous-phase FSK optical heterodyne system

A total capacity of 40 Gb/s is achieved using a shelf-mounted continuous-phase frequency-shift-keying (CPFSK) optical heterodyne frequency-division-multiplexing (FDM) transmission system with 32 optical channels and a bit-rate of 1.244-Gb/s per channel. For achieving a stable bit-error-rate (BER) characteristics with high-sensitivity, narrow-linewidth laser diodes, a channel-spacing stabilization circuit, and an optical tuner are developed. The obtained sensitivity at a BER of 10/sup -9/ for fiber transmission over 121 km ranges from -45.1 to -44.2 dBm, which is 9.8-10.7 dB lower than the shot-noise-limited sensitivity. The crosstalk penalty is suppressed to within 0.1 dB. The developed system has feasibility achieving a distribution system which can distribute more than 250 HDTV (high definition television) signals or 1250 current-standard TV signals to about 8000 subscribers 10 km from the office, or a 40-Gb/s trunk-line system with a fiber span of more than 50 km. >

Optical cross-connect systems for restoration of backbone fiber networks

Summary form only given. As the capacity of backbone networks is becoming larger, restoration against fiber/cable failures must become faster, because large amounts of data would be lost during the failure. The optical cross-connect (OXC) technology is an attractive alternative for fast restoration, and has the potential to provide bandwidth-management capability in future wavelength-division multiplexing (WDM) networks. This paper describes newly developed OXC systems with a low insertion loss of 1.16 dB and a high-speed restoration of <150 ms.

Properties of bit-rate-independent pulse timing measurement technique using optical heterodyne cross correlation

A novel technique for detection of the time delay between optical input signal data and a clock, suitable for applications to phase-locked loops, is investigated. This pulse timing measurement scheme, which is based on heterodyne cross correlation employing passive optical mixing, does not rely on any characteristic time associated with an optical nonlinearity, and is virtually independent of the bit rate. Experimental results on self-heterodyne correlation of mode-locked laser pulses as well as detailed theoretical analysis indicate that the timing measurement method investigated is characterized by high sensitivity.

Linear measurement of weak 1.57 μm optical pulse train by heterodyne autocorrelation

A technique for measuring optical pulses, using heterodyne autocorrelation rather than a nonlinear process, is proposed. This method gives not only the pulse width, but also information about optical phase in a simple way. Practical measurement is demonstrated with linearly chirped weak optical pulse train from an actively model‐locked external‐cavity semiconductor laser. Pulse width and chirp are quantified.

Heterodyne autocorrelation method for characterizing 1.55 /spl mu/m optical pulse train and for measuring dispersion and nonlinearity in optical fibers

Heterodyne autocorrelation measurement of 1.55 /spl mu/m optical pulses from an actively mode-locked external cavity diode laser is performed before and after transmission through an optical fiber. In heterodyne autocorrelation, optical spectrum is resolved electronically. This method is suitable for measurement of optical pulses with a spectral width of less than 100 GHz, and it gives not only the pulse width and chirp of the pulses, but also it is useful for determining the dispersion and optical Kerr constant of an optical fiber. Analytical formalism for deducing these quantities is given for Gaussian pulses. Principal measurement is performed using a mode-locked diode laser. Dispersion is measured for a conventional-dispersion fiber of 35 km. Also, self-phase modulation (SPM) is measured for a dispersion-shifted fiber of 15.83 km.

Dynamic range of bit-rate-independent pulse timing measurement technique

A novel technique for detection of the time delay between optical input signal data and a clock, suitable for applications to phase-locked loops, is investigated with respect to its sensitivity. This pulse timing measurement scheme, which is based on heterodyne cross correlation employing passive optical mixing, is virtually independent of the bit rate. Experimental results in good agreement with theoretical predictions reveal some characteristic properties of the dynamic range of the present timing measurement technique.