Goro Sasaki

Coherent two-dimensional lasing action in surface-emitting laser with triangular-lattice photonic crystal structure

Lasing action of a surface-emitting laser with a two-dimensional photonic crystal structure is investigated. The photonic crystal has a triangular-lattice structure composed of InP and air holes, which is integrated with an InGaAsP/InP multiple-quantum-well active layer by a wafer fusion technique. Uniform two-dimensional lasing oscillation based on the coupling of light propagating in six equivalent Γ−X directions is successfully observed, where the wavelength of the active layer is designed to match the folded (second-order) Γ point of the Γ−X direction. The very narrow divergence angle of far field pattern and/or the lasing spectrum, which is considered to reflect the two-dimensional stop band, also indicate that the lasing oscillation occurs coherently.

Fiber-Bragg-grating external cavity semiconductor laser (FGL) module for DWDM transmission

We report on the use of butterfly-type fiber-Bragg-grating external cavity semiconductor laser (FGL) modules in dense wavelength-division multiplexing (DWDM) applications. In a dense wavelength-multiplexing experiment, we demonstrated that successive four-channel multiplexing with 25-GHz spacing and with almost the same peak power was realized by using the FGLs. The lasing wavelength of each channel was tuned to the corresponding wavelength grids with an accuracy of /spl plusmn/1 pm. In the DWDM transmission with 25-GHz channel spacing and 2.5-Gb/s direct modulation using a standard single mode fiber (SMF), a good bit-error ratio (BER) performance without floor phenomenon was achieved up to 300 km. There was no degradation of transmission characteristics caused by the optical crosstalk from adjacent channel. Even in the DWDM transmission where channel spacing was 12.5 GHz, good transmission characteristics were maintained up to 300 km and little degradation of BER performance occurred at 300 km compared with the single-channel transmission. In addition, we investigated the influence of external temperature change on the FGL reliability using temperature-cycling test. As a result, we clarified that the characteristic degradation of FGL after this test was sufficiently small and that this device had a high tolerance to the severe external temperature variation.

Properties of Chemically Vapor-Deposited Amorphous SiNx Alloys

Amorphous SINx (x0.6) alloys were deposited by thermal decomposition of Ar/SiH4/NH3 mixtures at 550°C, and their optical and electrical properties were investigated. The optical gap energy increased quadratically from 1.5 eV to 2.0 eV with the incorporated nitrogen atom concentration. The nitrogen incorporation caused a remarkable reduction in the hopping conduction, whereas it had little effect on the extended-state conduction. The products of quantum efficiency, mobility, and lifetime were little influenced by the nitrogen incorporation.

An ultra-high-speed optoelectronic integrated receiver for fiber-optic communications

An ultra-high-speed optoelectronic integrated receiver consisting of a GaInAs p-i-n photodiode and a transimpedance AlInAs-GaInAs high-electron-mobility-transistor amplifier was successfully fabricated on an InP substrate. A 3-dB bandwidth of 6 GHz with a transimpedance of 50 dB Omega was achieved for the receiver with a feedback resistance of 750 Omega . Measured noise currents of the receiver were analyzed and found to be dominated by the low-frequency noise and the induced gate noise. A sensitivity of -21.2 dBm for 8.0-Gb/s NRZ signals was deduced from the noise current characteristics. >

A high-speed eight-channel optoelectronic integrated receiver array comprising GaInAs p-i-n PD's and AlInAs/GaInAs HEMTs

The successful fabrication of an eight-channel optoelectronic integrated receiver array on an InP substrate, which comprises eighty elements including GaInAs p-i-n photodiodes (PDs) and AlInAs/GaInAs HEMTs, is reported. An average bandwidth of 1.2 GHz with a standard deviation of 190 MHz over the whole channel was obtained. An average responsivity was 546 V/W with a standard deviation of only 19.2 V/W. A crosstalk was less than -30 dB at frequencies between 3 and 900 MHz and as small as -28 dB even at 1 GHz. The yield of chips available for 1.0 Gb/s operation was as high as 62.5% over 2-in-diameter wafer. >

Eight-channel wavelength multiplexing with 200-GHz spacing using uncooled coaxial fiber Bragg grating external-cavity semiconductor laser module

As a low-cost light source for wavelength-division-multiplexing networks, the authors develop an uncooled coaxial fiber Bragg grating external-cavity semiconductor laser (FGL). To realize high-wavelength stability, an FGL structure is adopted, and to reduce the cost of light source itself, a coaxial pigtail module structure is selected. High-wavelength stabilities of 2 pm/mA and 12 pm/K against current and ambient temperature variation are realized. Using the FGLs, successive eight-channel wavelength multiplexing with 200-GHz spacing and with almost the same peak power is realized between -30/spl deg/C to 70/spl deg/C. For each channel, the wavelength difference from the corresponding ITU grid is only within /spl plusmn/0.1 nm at 25/spl deg/C.

Distributed feedback surface-emitting laser with air/semiconductor gratings embedded by mass-transport assisted wafer fusion technique

We report on a distributed feedback InGaAsP MQW laser with air/semiconductor gratings embedded by wafer-fusion technique with the assistance of mass-transport phenomenon for the first time. The air/semiconductor gratings with 0.4-/spl mu/m period and 0.2-/spl mu/m depth are successfully fabricated inside the device, and a single longitudinal mode oscillation at about 1.28 /spl mu/m is demonstrated under pulsed condition at room temperature. The threshold current density is estimated to be about 1.4 kA/cm/sup 2/. It is also shown that the device has a surface-emitting function since it has a low loss multiquantum-well waveguide with grating output coupler.

Characterization of a distributed feedback laser with air/semiconductor gratings embedded by the wafer fusion technique

Wafer fusion between patterned or structured wafers is very useful in the construction of new optical materials and/or devices that have submicrometer-order structures inside semiconductors. In order to investigate the feasibility of wafer fusion for this purpose, a distributed feedback (DFB) laser wafer developed which has air/semiconductor gratings that are embedded using the wafer fusion technique. In this paper, the characteristics of the newly developed DFB laser and the coupling coefficient are investigated. Single-longitudinal-mode oscillation at 1.28 /spl mu/m is achieved under pulsed conditions at room temperature with a low threshold current density of 1.3 kA/cm/sup 2/, and the coupling coefficient is estimated to he approximately 100 cm/sup -1/. In addition, high-power surface emission (over 6 mW) is demonstrated due to the large difference between the refractive index of air and that of InP. These results indicate the feasibility of applying wafer fusion techniques to form submicrometer structures in semiconductors, and several other applications are expected.

Semiconductor lasers with one- and two-dimensional air/semiconductor gratings embedded by wafer fusion technique

This paper describes the use of wafer fusion technique between submicrometer-order patterned wafers to realize novel optoelectronic devices. First, to demonstrate the feasibility of applying the technique to optoelectronic devices, we demonstrate a continuous wave oscillation of a one-dimensional distributed feedback laser with air/semiconductor gratings embedded by the wafer fusion technique. Next, we fabricate a device with two-dimensional triangular-lattice structure and obtain a very unique hexagonal symmetric surface-emitting pattern. From the calculated photonic band diagram of the device, the surface-emitting pattern is considered to reflect the photonic band nature of triangular-lattice structure. The room temperature lasing oscillation of the device with two-dimensional triangular-lattice structure is also achieved. These results indicate that the air/semiconductor gratings formed by wafer fusion technique can be applied to develop various optoelectronic devices, and the realization of novel devices is expected.

A four-channel multiwavelength fiber-grating external-cavity-laser array

A fiber-grating external-cavity-laser (FG-ECL) is expected as a useful light source in optical fiber communication systems. Its oscillation wavelength is determined by a reflection peak wavelength of the fiber grating. The wavelength controllability of fiber gratings is in the order of subnanometers, so the FG-ECL could be especially useful in dense wavelength-division multiplexing (WDM) systems where precise wavelength control of lasers is required. Utilizing a four-channel fiber grating array, we obtained a four-channel multiwavelength oscillation with 1-nm spacing, which demonstrated the feasibility of the FG-ECL as the WDM light source.