H. Imai

Bio: H. Imai is an academic researcher from Fujitsu. The author has contributed to research in topics: Laser & Semiconductor laser theory. The author has an hindex of 16, co-authored 37 publications receiving 942 citations.

Stability in single longitudinal mode operation in GaInAsP/InP phase-adjusted DFB lasers

Abstract: A single longitudinal mode (SLM) operating condition for phase-adjusted (PA) DFB lasers has been made clear both experimentally and theoretically. As expected, we got a high SLM operation yield of 80 percent in a moderate coupled case up to a light output power of 10 mW. However, in the strongly coupled cases, the two-mode operation with the TE0 mode and the TE + 1 mode occurred frequently. To explain the two-mode operation and to optimize the PA-DFB laser structure, we have developed a theory. Taking the spatial hole burning along the laser axis into account, we succeeded in explaining the longitudinal mode behavior. From our theory, moderate coupling ( kL = 1.25 ) was found to be optimum to maintain the large threshold gain difference above threshold.

Tunable DBR laser with wide tuning range

Abstract: Characteristics of a 1.55 mu m wavelength tunable DBR laser with three sections are described. The wavelength tuning range is investigated by changing the composition of the GaInAsP guide layer. The maximum change of the Bragg wavelength is nearly 10 nm at lambda /sub g/=1.38 mu m, and a continuous tuning range of 6.2 nm is achieved for lambda /sub g/=1.29 mu m.

1.55μ wavelength tunable FBH-DBR laser

Abstract: The fabrication and characteristics of a 1.55μm wavelength tunable FBH-DBR laser with three sections are described. This laser showed single-longitudinal-mode lasing at any wavelength throughout a range of 4.5 nm. The wavelength of the identical longitudinal mode was tuned continuously over 3.15 nm under constant output power condition.

Linewidth reduction in DFB laser by detuning effect

Abstract: The detuning effect on the spectral linewidth in the DFB laser has been investigated. When we set the lasing wavelength of the DFB laser at the shorter side of the gain peak by 10 nm, a reduction in spectral linewidth of 50% was obtained experimentally. This result agreed with the theoretical prediction.

Dependence of spectral linewidth on cavity length and coupling coefficient in DFB laser

Abstract: The dependence of the spectral linewidth of DFB lasers on cavity length and coupling coefficient has been investigated. It was shown experimentally that the long cavity was very effective at reducing the spectral linewidth of DFB lasers, whereas a large coupling coefficient was ineffective. With a corrugation depth of 15 nm and a cavity length of 1200 mu m, a narrow linewidth of 1.7 MHz was obtained at 11 mW.< >

Dense wavelength division multiplexing networks: principles and applications

Abstract: The very broad bandwidth of low-loss optical transmission in a single-mode fiber and the recent improvements in single-frequency tunable lasers have stimulated significant advances in dense wavelength division multiplexed optical networks This technology, including wavelength-sensitive optical switching and routing elements and passive optical elements, has made it possible to consider the use of wavelength as another dimension, in addition to time and space, in network and switch design The independence of optical signals at different wavelengths makes this a natural choice for multiple-access networks, for applications which benefit from shared transmission media, and for networks in which very large throughputs are required Recent progress in multiwavelength networks are reviewed, some of the limitations which affect the performance of such networks are discussed, and examples of several network and switch proposals based on these ideas are presented Discussed also are critical technologies that are essential to progress in this field >

All-optical wavelength conversion by semiconductor optical amplifiers

Abstract: Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber.

Pot economy and one-pot synthesis

Abstract: The one-pot synthesis of a target molecule in the same reaction vessel is widely considered to be an efficient approach in synthetic organic chemistry. In this review, the characteristics and limitations of various one-pot syntheses of biologically active molecules are explained, primarily involving organocatalytic methods as key tactics. Besides catalysis, the pot-economy concepts presented herein are also applicable to organometallic and organic reaction methods in general.

Linewidth broadening factor in semiconductor lasers--An overview

Abstract: The objective of this paper is to present an overview of topics related to one of the fundamental parameters for semiconductor lasers-the linewidth broadening factor α that describes the coupling between carrier-concentration-induced variations of real and imaginary parts of susceptibility. After introducing the definition of α and discussing its dependence on carrier concentration, photon energy, and temperature, we give a short historical summary on how the concept of α evolved over the past two decades. This is followed by a discussion of α dependence on device structure in gain-guided and subdimensional lasers (quantum wells and quantum wires). The bulk of the paper is devoted to a detailed review of laser properties influenced by α and of associated methods of estimating the value of α. Results of measurements reported to date are collected and the most reliable methods are indicated.