1.3 µm wavelength InGaAsP/InP laterally coupled distributed feedback (LC-DFB) ridge laser without epitaxial re-growth process has been fabricated with reactive ion etching (RIE), electron beam (EB) lithography, and other semiconductor processes.
The threshold current density of around 1.3 kA/cm2 and side-mode-suppression-ratio of above 22 dB have been observed in room temperature under the pulsed current injection. The results of coupling coefficient calculation for optimizing device structure have also been shown. The improved LC-DFB laser will be useful in the future applications of optical CATV system and other optical access networks.
Potassium niobate (KNbO3) thin films have been deposited on silicon (Si) and strontium titanate (SrTiO3) substrates by metalorganic chemical vapor deposition.
Stoichiometric KNbO3 films were obtained by adjusting the partial pressure of precursors. The crystallinity was examined by x-ray diffraction and reflection high-energy electron diffraction (RHEED). Single-crystal (010)KNbO3 films with smooth surface were heteroepitaxially grown on (110)SrTiO3 substrate at 850 °C.
KNbO3 thin film waveguides were also successfully fabricated on (110)MgO substrates. SHG light emission was observed from the waveguide by using a YAG-laser as a fundamental light source.
LSI for VSB demodulation was developed. On the chip, a lot of functions such as nyquist filter, carrier recovery, timing recovery, AGC, Equalizer, RS decoder and so on, are integrated. VSB demodulator with high performance can be easily realized using the chip.
We have developed LSI chips for DVD players. A data processing LSI contains a Viterbi decoder, an 8/16 demodulator, an error correction circuit, and a variable bit rate control circuit. A video processing LSI contains a subtitle image processing circuit, a GUI(Graphical User Interface)image processing circuit, an NTSC/PAL encoder, and a D/A converter.
And we have developed DVD players employing these two LSIs, an MPEG2 video decoder, and an AC-3 audio decoder. The DVD players were released to the market on December 1996.
The draft of the standard book(ver. 0.9) for DVD-R; a write once type media being compatible with DVD read only disc; was established in April. The authors developed the Pick-Up for this media, "DVD-R".
Using a high power laser diode of 635 nm central wave length, a optical design to obtain the maximum power of 13mW(pulse), the Peltier device to cool the laser diode down for added life and reliability, a beam spot size suitability on the disc, and the laser modulation characteristic for the read and write characteristic improvement were researched and developed.
As a result, the read and write characteristics for a density of 3.9 Gbyte user data capacity on a 120 mm diameter disc (@ the minimum pit length of 0.44 µm, the track pitch of 0.8 µm) was confirmed and obtained.
In the recording system for the write once media called &puot;DVD-R&puot; which is fully compatible with DVD-ROM disc, we have developed the LSI for encoding to DVD physical format.
We made the real time encoding to DVD physical format possible by using the signal processing system which is composed of this LSI, DRAM for buffers, input/output interface device, and CPU for system control.
The authors have developed aprototype recording system using a write once type media called 'DVD-R' which is fully compatible with DVD-ROM.
The prototype model has the capability of real time encoding to the DVD physical format and recording.
We have confirmed that the recorded disc can not only be played DVD-ROM drive, but also a DVD-Video player.
To make DVD/CD and DVD/CD/LD compatible player,
we exploited the technique to make tracking error by one-beam, and the technique of focus jump to play dual layer disc.We also exploited the way to judge the type of disc by focus error, which is necessary for DVD player.
In the occasion of continuously decreasing consumer audio market and just before DVD-Audio Disc introduction, there arise need to reexamine what is music record. Music record is a kind of art which can only appeal to human auditory sense. Moreover, there are many steps in the production process of the music record as follows: composer
--- music performer --- concert hall --- record engineer --- recording equipment --- media --- reproduction equipment listening room --- user. We should realize that we are hearing the music record which was produced through these many steps. If there is only step which distort the music signal, emotion which composer had thought to listener by his music will not be transmitted.
The region which audio technology can improve is the process after concert hall. The important portion is the medeia and reproduction process matching with the media. There is an anticipation that if the DVD technology will be used for audio only disc, a superb sound quality will be realized. The destiny of audio industry in 21st century will depend on consequence of DVD-Audio Disc.
The authors quantified the differences of the subjective impressions experienced between (A) the wide-range sound materials whose frequency components extend to 48 kHz and (B) the high-cut sound materials which eliminate frequency components higher than 24 kHz made from wide-range sound materials. The subjects were people with normal hearing. The authors found statistically significant differences in the subjective impressions (p<0.05) between the two frequency ranges in some sound source materials used.
A Voice recognition system is used in various environments such as in a car where the noise is time-varying. It is desirable that the voice recognition system work well regardless of the conditions. The authors developed an algorithm effective for not only stationary noise but also non-stationary noise. Because the algorithm needs only a signal amount of calculation, it can be applied to car-use products such as a car navigation system.
The algorithm consists of a simple pre-processing that trains the system under a noisy environment. The experiment showed that the recognition rate with this algorithm was two times higher than that of the algorithm without the pre-processing.
A sound field analysis program using the Boundary Element Method has been developed. This program helps predict certain characteristics of audio devices that the conventional analytical methods have not been able to predict.
Another function was also developed with which we can analyze the sound field radiated from the speaker system to the outside of the cabinet and the sound field created inside the cabinet, taking into consideration the mutual influences.
It has become possible to calculate the sound field inside the passenger compartment of a car in the audio frequency bandwidth by an up-to-date high performance engineering workstation in practical time.
A thin loudspeaker system for Plasma Display Panel(PDP) has been developed. Even in a small enclosure, it can produce a powerful bass and wide range tones. The authors introduced the modal analysis to improve the response and designed an oblong shaped diaphragm to which a voice coil is attached. The voice coil is shorter than the diaphragm in the longitudinal axis. The diaphragm consists of inner and outer parts. The outer diaphragm was made to resonate at the frequency lower than the lowest resonance of the system. This resulted in increasing the amplitude in the low frequency range. In addition, the authors improved the flatness of the frequency response by optimizing the diaphragm mass distribution and dispersing a diaphragm's normal model of vibration which produced a strong peak and dip in the middle range.
With the downsizing approach in the recent loudspeaker system design, obtaining sufficient and/or massive bass sounds has become difficult. It may be due to the increase of the resonance frequency, the decrease of the radiation resistance and the decrease of the volume velocity to name a few factors. To get enough sound pressure level(SPL) in the low frequency range with a small loudspeaker unit, a volume velocity equivalent to a large loudspeaker unit is required. However, this has been difficult in that the surround of a conventional loudspeaker design does not exhibit linear relation as a function of the replacement of a diaphragm. The report describes a newly developed surround-less structure and the driving mechanism to achieve sufficient volume velocity, i.e. +_ 15 mm excursion and 100 dBSPL at 50 Hz from a 15 cm diameter unit.
The authors have developed a high-accuracy sampling rate converter that can cope with the sampling rate (fs) of 96 kHz and 24 bit resolution for professional audio applications. The converter uses a general purpose DSP chip set and realized a highly transparent up-conversion. Some of the salient features include:
MPEG-2 AAC is one of the most efficient coding schemes for multi-channel audio signals. It has been proven that the sound quality of reproduced signal encoded by the AAC with the bit rate of 64 kbps/ch is virtually transparent compared with the original one. AAC evolved into the international standard in April 1997. Alternatively, great efforts are now being performed within MPEG activities to promote the standardization procedure of the MPEG-4 aimed at the future use in broadcasting and/or communication applications.
In this report, the chronological history of the MPEG Audio is presented in order to clarify the background of the AAC and the MPEG-4 Audio. This is followed by an overview of the AAC and the technical description of each component tool. As this might interest the reader, an in-depth explanation is given. Finally the outline of the MPEG-4 Audio activities is presented briefly.