Katsuyuki Fujito

Correlation between intensity noise and longitudinal modes of a semiconductor laser coupled to an external cavity

Correlation between intensity noise and fine structures of longitudinal modes in a semiconductor laser coupled to an external cavity has been investigated. It is experimentally shown that the intensity noise is perfectly suppressed when the laser oscillates in ‘‘pure’’ single frequency oscillation even with strong optical feedback. Intensity noise, which arises only when several external cavity modes exist, is interpreted in terms of the time‐dependent refractive index in the semiconductor cavity caused by the light beatings among the lasing modes.

Increasing acceptable number of signals in subcarrier multiple access optical networks in the presence of high optical beat interference

This paper theoretically and experimentally demonstrates that our proposed method improves the carrier-to-noise ratio (CNR) of subcarriers and significantly increases the number of acceptable optical signals in subcarrier multiple access (SCMA) systems using distributed feedback laser diodes (DFB-LDs) with the same center optical frequency. This method reduces optical beat interference by using the multiplied product of the subcarriers and a low-frequency signal. From the experimental results using 1.3 /spl mu/m DFB-LDs, the CNR sufficiently satisfies the required level even if the number of optical signals is three. Theoretically, the number of acceptable optical signals increases as LDs with wider optical line-width or with greater chirp coefficient are used. For example, assuming a laser chirp coefficient of 540 MHz/mA, the maximum number of LDs that can be used while still meeting the minimal CNR requirement is 12. This number corresponds to 66 optical beat interferences. Thus, this proposed beat-interference reduction technique is very effective in SCMA systems using DFB-LDs without optical frequency control.

Optical access links suppressing optical beat interference with FP-LDs for microwave transmission

Uncooled Fabry-Perot laser diodes (FP-LDs) without isolators realize cost-effective optical access links for microwave transmission. The optical spectrum broadening using low-frequency intensity-modulation can effectively suppress optical beat interference in the up link and make FP-LD performance stable.

Low distortion 1.3 /spl mu/m strained-layer MQW-DFB laser for AM-SCM transmission systems with large channel capacity

1.3-/spl mu/m strained-layer multiquantum-well distributed-feedback (SL-MQW-DFB) lasers with extremely low distortion and low noise characteristics up to high output-power as well as over wide frequency range were successfully fabricated. This was achieved by both the high relaxation oscillation frequency (f/sub r/) characteristics of the laser with the optimized SL-MQW active structure and the suppression of nonradiative current with relatively long laser cavity length. By using the SL-MQW laser with a 400-/spl mu/m long cavity as a light source for CATV transmission system, high quality AM-SCM transmissions with the largest channel capacity (151 channel) was demonstrated due to low distortion characteristics at high output power. Also, for the laser with 300 /spl mu/m long cavity, extremely low bias-current operation (17 mA above threshold) is realized in high quality 100 channel AMSCM transmissions, due to high f/sub r/ at low bias-current.

Ultrahigh channel capacity optical CATV systems

Summary form only given. It is widely recognized that future CATV systems will require more channels to incorporate new services such as video on demand (VOD). Various CATV systems employing subcarrier multiplexing (SCM) techniques have been proposed, however these systems do not seem to have sufficient capacity for the VOD. In this paper, we show new approaches to ultrahigh channel capacity optical CATV systems using SCM technique and discuss performances of each.

Holographic memory system for Kanji character generation.

A Fourier transform holographic memory has been developed and used for generating and storing sixteen thousand Kanji characters. The memory consists of four groups of holograms of 63 pages, recording 64 Kanji characters in each page, and has a packing density of 1.34 x 10(7) bits/cm (2). Digitized characters of sixteen sizes can be generated with natural letter faces and good image quality. This paper focuses on the recording and reconstruction of holographic Kanji memory using a pseudorandom diffuser and systematic solutions consistent with optical, mechanical, and digital systems.

High-performance long-distance fiber-optic transmission using unisolated Fabry-Perot laser for mobile radio systems

We demonstrate that spectrum broadening with low-frequency intensity modulation (LFM) is very effective in stabilizing the characteristics of unisolated Fabry Perot laser diodes in long-distance transmission, and that the system performance is enough for cellular phone systems in 20 km transmission.

Error statistic of QAM channel in AM/QAM hybrid optical transmission

The error statistic of the QAM channel in an AM/QAM hybrid optical transmission system is measured. Errors occur randomly in optical transmission without clipping. However, errors are found to occur in bursts when the impulsive noise due to clipping degrades the QAM signals BER. The error statistic is critical to properly designing the error correction employed in the hybrid system.

KANJI CHARACTER GENERATION BY A HOLOGRAPHIC MEMORY SYSTEM

ABSTRACT A selfconsistent holographic memory system for generating high quality Kanji ideograms is presented. Attainment of storage capacity corresponding to the order of 107 bits was possible by the use of a pseudorandom diffuser and Fourier transform lens systems of high performances. Random access to specified characters is effected through (i) a page address by means of driving a X-Y deflector, and (ii) a character address on a camera tube. Accurate image reconstruction of 8 × 8 characters from respective 44 pages were gained on the basis of exact Fourier transform optics, whereby the degrees of freedom in designing the total system were considerably increased and the implementation of the Kanji generator could be facilitated.

Improvement of carrier-to-noise ratio in subcarrier multiple access optical networks in the presence of multiple optical beat interference

Summary form only given. Summary form only given. The subcarrier multiple access (SCMA) systems using distributed feedback laser diodes (DFB-LDs) without wavelength control are very suitable for the upstream in passive optical networks (PON) from the point of view of realizing cost-effective and high-performance systems. However, it is well known that optical beat interference (OBI) is one of the serious problems. We have already proposed a method to greatly reduce the OBI which we have named the LSM method. This method employs multiplying the subcarrier signals and an additional signal. We experimentally and theoretically investigated the carrier-to-noise ratio (CNR) characteristics of frequency-modulated (FM) video signals by using the LSM method in the worst case that all of the OBI between any two LDs appeared in the subcarrier band. In this paper, the experimental result shows that the CNR values of the FM video signals can reach the available level by using the LSM method even if three OBIs exist in the subcarrier band, and the theoretical result shows that the acceptable number of OBI increases to ten by using DFB-LDs with an optical linewidth of 100 MHz.