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Pump sources for optical fiber amplifiers, e.g., Erbium-doped fiber amplifiers or Raman amplifiers, are reviewed. Higher optical power is required for the optical fiber amplifiers in DWDM transmission. Recently published results regarding improvements of the optical power are introduced.

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.

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.

Receiver optoelectronic integrated circuits (OEICs) have been successfully designed on a three-inch diameter InP substrate. Epitaxial layers grown by OMVPE on three-inch diameter InP substrates showed good uniformity of electrical and optical properties. By using the epitaxial layers, transimpedance-type receiver OEICs were fabricated. the receiver OEICs over a three-inch diameter InP substrate showed an average bandwidth of 2.78 GHz with a standard deviation of 280 MHz. the receiver also exhibited a transimpedance of 61.1 dB and a sensitivity of -24.9 dBm for 2.4 Gb/s input signals. These results indicate that the receiver OEICs designed on a three-inch diameter InP substrate are ready for practical use in Gb/s lightwave systems.

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.

Summary form only given. The photonic band structure (PBS) has been drawing much attention to control light emission and/or propagation. To realize the PBS in the optical wavelength region, we have proposed utilizing a wafer fusion technique between submicron-order patterned wafers. Furthermore, by this technique, the integration of PBS with a light-emitting layer is also possible, and the realization of novel opto-electronic devices is expected. Recently, we have developed a light-emitting device with two-dimensional (2D) triangular-lattice structure (TLS) embedded by the wafer fusion technique and have shown the very unique surface-emission pattern, which reflects the 2D photonic band nature of TLS. In the work, we demonstrate for the first time a room temperature (RT) lasing oscillation of the surface-emitting laser with 2D PBS embedded by the wafer fusion technique.

A long-wavelength receiver OEIC (optoelectronic integrated circuit) comprising an InAlAs-InGaAs MSM (metal-semiconductor-metal) detector and a InAlAs-InGaAs HEMT (high-electron mobility transistor) high-impedance preamplifier has been demonstrated. The layer structure was grown by LP-OMCVD (low-pressure organometallic chemical vapor deposition) on patterned InP substrates, which allowed independent optimization of the MSM detector and the HEMT preamplifier. The MSM detector showed the lowest leakage current (1 nA) ever reported with a 0.42 A/W responsivity, and the HEMT exhibited an external transconductance of 260 mS/mm. The bandwidth of the MSM-HEMT receiver was about 2 GHz. An excellent receiver response to 1.7 Gb/s NRZ random input signals has been obtained. The results reported strongly suggest that MSM-HEMT receivers have great potential for high-bit-rate optical-fiber communication systems. >

An 8-channel optical interconnection laser diode (LD) array module, which is a receptacle type with an multi-fibre push-on (MPO) adapter, was successfully fabricated. In consequence of adapting a receptacle type, mounting of this module on a board was facilitated. Furthermore reliability of this LD array module is guaranteed because the LD array is hermetically sealed. A variation of optical output power in each channel was obtained within 0.3 dB, and a fluctuation of coupling losses caused by reconnecting was obtained at less than 0.5 dB, respectively. Digital output at 300 Mbit/s/ch was demonstrated.

In conclusion, we have developed 1.3-/spl mu/m uncooled coaxial analog DFB MQW laser modules. They operate over the wide temperature range from -40-85/spl deg/C with low distortion and low noise, which are quite suitable for light sources of a return path in bidirectional optical CATV network systems.

In summary, a pin photodiode, a transimpedance-type preamplifier, and a comparator have been monolithically integrated on an InP substrate with pin/HBT integration technology. The receiver OEIC with a comparator showed a sensitivity of -36.0 dBm at a bit error rate of 1/spl times/10/sup -9/ for 125 Mb/s optical signals. The successful integration of digital circuits with analog circuits and optical components promises a realization of high-performance parallel optical interconnections in the near future.

Distributed Raman amplification in the transmission fiber is an attractive technique to increase the transmission capacity and to extend the reach of long-haul WDM optical system [1]. The next generation WDM system is expected to offer transmission in the wide range of S, C, and L band. A single Raman pump wavelength provides flat gain in the limited wavelength range of approximately 15nm. However, multi-wavelength pumping at 12 different pump wavelengths allows to offer high gain and very good gain flatness over the wavelength range of up to 100nm [2].

We describe the silver coating of 1.3-m secondary nirror being used for infrared observations at Subaru Telescope. This was the first successful in-house runof silve coating on thelarge moern astronimical mirror. Silver was desposited over the chromium bondange layer, using a 1.6-m vacuum coating chamber at the Advanced technology Center of the National Astronomical Obervatoryof Japan in March 1998. The reflectnc eand scatter performnce are measured by micrScan at 670 nm and 1300 nm. Monitor over 17 month shows the silve coated mirror continues to maintain high refleciton.

After the initial coating of the 8.3-m primary mirror of the Subaru Telescope in November 1998, we have conducted the first re-aluminization in August 1999. The primary mirror washing fixture worked efficiently for stripping the old coating and for washing the surface. Dry process is still to be improved. Suite of secondary and tertiary mirrors are being tested at the telescope, two of which were coated in- house, one in silver for the infrared observations and the other in aluminum for the optical observations, respectively. Evaluation of the coating film is conducted in two methods. Using a portable microScan, the reflectivity and the BRDF numbers of the primary mirror is monitored. Reflectivity over a wide range of the wavelength is measured in the witness mirrors. The preliminary data shows reasonably good number for the telescope optics. The in-situ cleaning of the primary mirror with solid and gaseous CO2 sprinkle arms is operating once every month. Next step for the coating chamber commissioning is to improve the heating capacity for silver coating of the infrared secondary and tertiary mirrors, and the experiment for silver coating is going.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A high-performance metal-semiconductor-metal high-electron-mobility transistor (MSM-HEMT) transimpedance photoreceiver fabricated using OMCVD-grown InAlAs/InGaAs heterostructures on an InP substrate is discussed. This is the first demonstration of a monolithically integrated receiver amplifier that incorporates a cascode amplifier stage and a Schottky diode level-shifting stage implemented on InP-based optoelectronic integrated circuit (OEIC) photoreceivers. The transimpedance amplifier has an open-loop gain of 5.7 and a bandwidth of 3.0 GHz, which represent the highest gain and the highest speed performance reported for 1.3-1.55- mu m-wavelength OEIC receivers. >

We have conducted a series of coating experiments using the newly installed 1.6 m evaporation chamber at the Advanced Technology Center (ATC) of the National Astronomical Observatory of Japan. The main task of this chamber is to re-aluminize the 1.6 m mirror of the Infrared Simulator at the ATC. The design concept of the 1.6 m chamber is basically the same with the 8.3 m coating facility for Subaru Telescope. Therefore, we could utilize this chamber to evaluate the fundamental performance of the larger chamber. The extensive coating experiments were done in the spring, autumn of 1996, and autumn of 1997. Reduction of the number of the filaments has lead to the increase in their size, which caused difficulty in the annealing process. Attempts are focused on securing the sufficient metal loads on the filaments. Then the filaments are fired to measure the spray pattern of a single filament exposure, or the uniformity pattern resulted from the full setup of filament arrays. Using small slide glasses, the important parameters of the resultant reflecting film that are the thickness, the uniformity of the thickness, and the spectroscopic reflectance are measured. The absolute value of the reflectivity is estimated to be around 91% immediately after opening the chamber. In order to cover a wide range of observing wavelengths for the Infrared Simulator, and eventually for the optical-IR Subaru Telescope, it is necessary to seek after a higher evaporation rate with these chambers.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Wafer fusion technique has been drawing much attention, since it can be applied to the integration of different materials and can offer new types of integrated devices. Recently, we have demonstrated a low threshold-current-density operation of MQW DFB laser with air/semiconductor gratings embedded by wafer fusion technique, where the additional phenomenon of mass-transport has been found to occur and improve the electrical characteristics at the fused interface. The fabrication of such air/semiconductor structures with submicron order inside the device without any crystal growth process is very useful to increase device designability. Moreover, the air/semiconductor gratings have potentially larger coupling coefficient, since the difference of refractive index between air and semiconductor is very large. In this work, we demonstrate for the first time the continuous-wave oscillation of the MQW DFB laser with the fused air/semiconductor gratings.

Metal-semiconductor-metal (MSM) photodetectors monolithically integrated with metal-semiconductor FET (MESFET) or a high electron mobility transistor (HEMT) on GaAs is an established technology for realizing high speed optoelectronic integrated circuits (OEICs) receivers for short wavelength fiber optic systems.1 Using this technology, transimpedance receivers have been demonstrated to exhibit a wide bandwidth and wide dynamic range for front end applications. To take advantage of the MSM-FET combination for 1.3-1.55-μm lightwave receiver systems, one has to overcome the problem of the low Schottky barrier height of metals on InGaAs. Since high leakage currents from the InGaAs MSM detectors and FETs greatly degrade the receiver performance, thin wide bandgap InAlAs semiconductor regions have been incorporated to reduce the leakage currents.2 We report here the first demonstration of a MSM-HEMT transimpedance receiver fabricated from OMCVD grown InAlAs/InGaAs heterostructures.

The optoelectronic integrated circuit (OEIC) attracts much attention because of its potential for high speed and low noise operation. As for the receivers of long wavelength optical communications, a PIN photodiode and field effect transistors (FETs), such as junction FETs and high electron mobility transistors (HEMTs), have been integrated using various growth and fabrication techniques.1-3 Although operation of receiver OEICs at Gbit/s data rate has been reported, most of the receivers need an external buffer stage and external equalizer to achieve high sensitivity and good responsivity. The first (to our knowledge) successful fabrication of a receiver OEIC with internal equalizer and buffer stage is demonstrated.

A GaInAs pin PD, a GaInAs/InP HBT transimpedance-type preamplifier, and a GaInAs/InP HBT comparator have been monolithically integrated on an InP substrate with pin/HBT integration technology. The receiver OEIC with a comparator showed a sensitivity of –36.0 dBm at a bit error rate of 1 × 10-9 for 125 Mbit/s signals.

An optical receiver, in which a GaInAs pin photodiode, an AlInAs/GaInAs HEMT high impedance amplifier and even an equaliser were integrated monolithically on an InP substrate, has been fabricated. An optical sensitivity of −30.4 dBm was obtained at 1.2 Gbit/s and 1.3 μm wavelength.

The dependence of capacitance of chemically vapor‐deposited (CVD) amorphous SiN0.2 metal–insulator–semiconductor (MIS) diodes on frequency and temperature is measured and discussed. The results show that the MIS diode includes slow states and fast states. The response time of slow states is 2.4×10−9 exp(−0.6 eV/kBT) s above 130 °C. The fast states fully respond to 95 Hz at 130 °C. It cannot be distinguished whether these states originate from the interface states or the a‐SiN0.2 gap states. The densities are evaluated to be 6×1017 cm−3 eV−1 (fast states) and 6×1018 to 2×1019 cm−3 eV−1 (slow states) as the CVD a‐SiN0.2 gap states, or 6.9×1011 cm−2 eV−1 (fast states) and 6.2×1012 to 1.2×1013 cm−3 eV−1 (slow states) as the interface states.

Measurement techniques of gap-state density in amorphous silicon (a-Si) are briefly reviewed and discussed. Especially, their applicability to a-Si which possesses rather high densities of states in the gap, when, e.g., deposited by chemical vapor deposition (CVD), is discussed. The a-Si produced by CVD is pure and thus exhibits properties relating only to positional disorder, in contrast with hydrogenated a-Si produced by glow discharge. When a-Si involves high gap-state density, hopping conduction through the gap states usually predominates and must be taken into account in the analysis of gap-state density. In this paper, two ways to measure gap-state density in CVD a-Si are described. One of them is basically an improvement of the field-effect method, and the other is the high-frequency capacitance-voltage method. Results of such measurements of the gap-state density in CVD a-Si are presented.

We report two-dimensional electron gas (2DEG) transport in InP/n-AlInAs Heterostructures. This is the first demonstration of forming 2DEG in an InP with semiconductor heterojunctions. Temperature and electron density dependences of the 2DEG mobility are presented. This 2DEG system can be utilized for high speed and high power FETs. Hot electron gas transport in an InP is simulated with including electron-electron scattering and screening by high density electrons.

Amorphous Si:N:H alloys were deposited by glow discharge of SiH 4 , N 2 , and H 2 gases, and the dependence of their properties on the deposition conditions was investigated. The deposition rate is increased by N 2 gas incorporation. Nitrogen incorporation increases the number of bonded hydrogen, which widens the optical gap. Their electrical properties are also described.

Thermal annealing and post‐hydrogenation effects on the electrical properties of chemically vapor‐deposited (CVD) amorphous silicon‐nitrogen (a‐SiNx ) alloys are studied. Annealing of CVD a‐Si and a‐SiNx films causes the increases in the ESR centers, the hopping conduction, and the gap‐state density evaluated by the field‐effect method. The nitrogen incorporation reduces the number of ESR centers in a film. The Fermi level of CVD a‐SiNx films is shifted by post‐hydrogenation, which suggests that the films include donors. The ημτ products of CVD a‐Si and a‐SiNx films are increased by post‐hydrogenation, exceeding two orders of the magnitude. Post‐hydrogenated CVD a‐SiNx films show larger ημτ product than post‐hydrogenated CVD a‐Si.

New techniques to determined the localized-state density in chemically vapour deposited amorphous silicon over a wide energy range by the field-effect method are presented. The density is measured for the first time as 10 18 ∼ 10 20 cm −3 eV −1 in the range ±0.4∼±0.5 eV around the Fermi level. From the results it is suggested that the silicon atom network of CVD a-Si has a similar randomness to that of glow discharge a-Si, providing a density of tail states of about 10 19 ∼ 10 20 cm −3 eV −1 and native defect states of about 10 18 cm −3 eV −1 .

A high‐frequency (1 MHz) capacitance‐voltage method is proposed to measure the gap‐state density in a chemically vapor‐deposited (CVD) amorphous (a‐)Si. The density is derived from the analysis of high‐frequency capacitance‐voltage characteristics of a CVD a‐Si and n‐type crystalline (c‐)Si junction. The density near the Fermi level in the CVD a‐Si deposited at 550 °C is obtained of the order of 1017∼1018 cm−3 eV−1. Further, the energy band diagram of CVD a‐Si and c‐Si junction is described, and the electron affinity of CVD a‐Si is derived to be less than 3.75 eV.

The monolithic integrated ion of a p-i-n photodiode and a high-electron mobility transistor (HEMT) amplifier on an InP substrate by organometallic vapor-phase epitaxy is discussed. The receiver operated with up to 1.6 Gb/s nonreturn-to-zero optical signals. The responsivity was 1 kV/W and the minimum optical power at a bit error rate of 10/sup -9/ was -24 dBm for 400 Mb/s nonreturn-to-zero optical signals. >

The frequency dependence of the flat‐band capacitance of a metal/insulator/semiconductor diode where the semiconductor film is glow‐discharge deposited amorphous Si:H (a‐Si:H) was measured at various temperatures. The response time and trap density at the insulator/a‐Si:H interface or a‐Si:H space‐charge region could be evaluated by a simple model.

We have monolithically integrated a GaInAs pin-photodiode and an n-AlInAs/GaInAs HEMT amplifier on an InP substrate by OMVPE for long-wavelength fibre optic communications. The response of the pin-HEMT amplifiers for 1.6 Gbit/s (NRZ) signals has been obtained.

We report the first demonstration of a new long-wavelength receiver OEIC comprising an AlInAs/GaInAs MSM detector and an AlInAs/GalnAs HEMT preamplifier. The layer structure was grown by LP-MOCVD on patterned InP substrates, which allowed independent optimisation of the MSM detector and HEMT preamplifier. The MSM detector showed the lowest leakage current yet reported and the HEMT exhibited a transconductance of 260mS/mm. An excellent receiver response to l.7Gbit/s NRZ signals has been obtained.

Temperature dependence of dark conductivity and field in a chemically vapor-deposited amorphous SiN x (x≃0.2) alloy are presented. The a-SiN x film exhibits little hopping conduction and large field effect as compared with undoped CVD a-Si. The gap-state density near the Fermi level in the CVD a-SiN x film is evaluated as 2×1018 cm-3 eV-1 which is one-fifth of that in an undoped film.

Amorphous SIN x (x≦0.6) 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.