A transversal equalizer composed of a surface-acoustic-wave tapped delay line and PIN diode control circuits is described. In the amplitude frequency response, the change, which can be expressed in terms of a cosinusoid, can be obtained by controlling the amplitude of the echo signals.

We have recently discovered a novel phenomenon for the fabrication of nanostructures. A self-organization phenomenon of a strained InGaAs/AlGaAs system on a GaAs (311)B substrate during metal-organic vapor phase epitaxial growth is described, and nano-scale confinement lasers with self-organized InGaAs quantum disks are mentioned. Low-threshold operation of strained InGaAs quantum disk lasers is achieved under a continuous-wave condition at room temperature. The threshold current is around 20 mA, which is consider-ably lower than that of a reference double-quantum-well laser on a GaAs (100) substrate grown side-by-side. However, the light output versus the driving current exhibits a pronounced tendency towards a saturation compared to that of the (100) quantum well laser. We also discuss new methods using self-organization for nanofabrication to produce high-quality low-dimensional optical devices, considering requirements and the current status for next-generation optical devices.

A two-phase phase-shift-keyed modulator is realized utilizing a SAW delay line and diode switching circuits. Fundamental performances of the device were clarified experimentally and theoretically.

Fine adjustment of wide-bandwidth SAW filter responses by trimming the interdigital transducer finger lengths was successfully achieved. In SAW devices, second-order effects, such as end effects, diffraction and bulk mode generation, disturb the simple design performances. The slight difference in wide-bandwidth frequency responses between the theoretical and experimental responses was modified by trimming the IDT finger lengths by hand.

Frequency characteristics of SAW tapped delay lines (TDL's) with equal tap spacing and in-line array are investigated. It is found that reflected SAW echo signals in SAW TLD's cause pulse-like ripples and sharp stopband distortions periodically in the frequency passbands. Tapping design techniques are proposed to remove spurious interference distortion influences on SAW TDL frequency responses. Their applicability is confirmed experimentally. Typical features of a SAW TDL with 101 taps at a 20 MHz bit rate employing 128 rotated Y-cut and X-propagation LiNbO3 substrate are as follows: center frequency is 55.4 MHz, frequency bandwidth is 10 MHz, insertion losses are 3239 dB, and ripples in the passband are about 4 dB.

This paper reports the realization of 2 GHz surface-acoustic-wave delay line (SAW DL) oscillator, utilizing 3rd harmonic operation of double interdigital transducers (4F-IDTs). The simple design technique for the SAW DL harmonic oscillators is made clear, based on the state-of-the-art of microfabrication technique. 0.58 µm linewidth aluminum 4F-IDTs of a SAW DL filter have been successfully obtained on the rotated Y-cut quartz by conventional photolithographic contact printing without lift-off process. They consist of 618 lines and 0.4 mm overlap length. On the clarified design technique, a 2 GHz SAW DL oscillator was achieved without external filtering and matching networks. The frequency stability of the experimental 2 GHz SAW DL oscillator is also presented and discussed. The short-term stability of 2 part in 108 at 1 sec. gate time was measured and a nearly parabolic frequency variation with temperature (the turn-over temperature was near 20) was obtained. It was found that SAW DL oscillators can be small, lightweight and stable GHz oscillators in many communication systems.

Fundamentals and development of PDFAs are described. Spectroscopic data of Pr3+ in a fluoride glass are presented with a view to understanding the performance of PDFA. An amplification mechanism model which explains PDFA performance is established. On the basis of the model pump schemes which efficiently extract the potential in Pr3+-doped fluoride fiber are discussed in order to construct amplifier modules. Gain characteristics of Pr3+-doped fluoride fibers are clarified. Codoping effect on pump wavelength extension is investigated. LD-pumped PDFA construction and performance are described. PDFAs are shown to be attractive device to upgrade the performance of optical systems at 1.3µm. Furthermore future approaches to PDFA research are discussed.