Yuji Kotaki

High-output-power polarization-insensitive semiconductor optical amplifier

A high-output-power 1550 nm polarization-insensitive semiconductor optical amplifier (SOA) was developed for use as a compact in-line optical amplifier. A very thin tensile-strained bulk structure was used for the active layer and active width-tapered spot-size converters (SSCs) were integrated on both input and output sides. The SOA module exhibited a high saturation output power of +17 dBm together with a low noise figure of 7 dB, large gain of 19 dB, and low polarization sensitivity of 0.2 dB for optical signals of 1550 nm wavelength. For the amplification of optical signals modulated at 10 Gb/s in the nonreturn-to-zero (NRZ) format, a good eye pattern without waveform distortion due to the pattern effect was obtained at an average output power of up to +12 dBm. Additionally, good amplification characteristics were demonstrated for the signal wavelength range corresponding to the C-band.

Penalty-free 10 Gb/s NRZ transmission over 100 km of standard fiber at 1.55 μm with a blue-chirp modulator integrated DFB laser

We present transmission beyond the dispersion limit with a blue-chirp modulator integrated DFB laser for the first time. By suppressing the hole pile-up in the modulator, stable modulation characteristics were realized in negative /spl alpha/ regime. Blue-chirp operation was clearly observed by time-resolved dynamic chirp measurement. Penalty-free 10 Gb/s transmission over 100 km of standard fiber at 1.55 /spl mu/m was demonstrated with the device. This modulator integrated DFB laser is promising for use as a high-power blue-chirp transmitter in multigigabit transmission systems.

FM response of narrow-linewidth, multielectrode lambda /4 shift DFB laser

Flat FM response from 100 kHz to 15 GHz was achieved in a multielectrode distributed-feedback (DFB) laser. A lambda /4-shifted corrugation and a 1200- mu m-long cavity were very effective not only in reducing the linewidth to less than 1 MHz, but also in making FM response flat by selective current injection.<<ETX>>

Long-cavity multiple-phase-shift distributed feedback laser diode for linewidth narrowing

A long-cavity multiple-phase-shift distributed-feedback (MPS-DFB) laser diode with three phase shifts in the corrugation for linewidth narrowing is discussed. The threshold gain difference and the field uniformity along the laser cavity of the MPS-DFB laser are analyzed by varying the amount and the position of phase shifts using the coupled-wave theory. It is shown that a large threshold gain difference and a uniform field distribution are obtained in the MPS-DFB laser with some special amount and position of phase shifts. Based on the analysis, a MPS-DFB laser with a 1200- mu m-long cavity and three phase shifts was fabricated. This MPS-DFB laser exhibits stable single-mode operation and shows a very narrow linewidth of 830 kHz at an optical output power of 25 mW. >

A novel method for designing chirp characteristics in electroabsorption MQW optical modulators

We propose a novel method to control the chirp parameter characteristics in electroabsorption (EA) multiquantum-well (MQW) optical modulators. We demonstrate that a large decrease of absorption on the short wavelength side enables us to achieve a negative chirp parameter that is independent of the extinction characteristics. This is achieved by enhancing the decrease in the absorption by higher states, which can be brought about by a shallow heavy-hole band discontinuity. It is also experimentally shown that a negative chirp operation from a near-zero-bias voltage in GaInAsP MQW optical modulators is realized by applying this new concept.

Distributed feedback laser emitting at 1.3 &#181;m for gigabit communication systems

A distributed feedback (DFB) laser emitting at 1.3 μm for gigabit lightwave communication systems has been developed. The distributed feedback structure has been introduced in a newly developed buried heterostructure and designs for stable single-mode operation, high speed modulation, and low noise have been done. Threshold current of 10-15 mA, differential efficiency of around 0.28 mW/mA, low noise, small signal modulation bandwidth of 13.9 GHz, and satisfactory modulation waveform at 5-Gbit/s NRZ modulation have been attained with high single-mode operation yield.

High-efficiency wavelength conversion using FWM in an SOA integrated DFB laser

A wavelength converter that uses four-wave mixing (FWM) in an SOA-integrated distributed-feedback (DFB) laser was demonstrated. Lossless conversion up to 300-GHz detuning and a conversion efficiency of -5 dB at 1-THz detuning was achieved. The device exhibited low ASE (noise) level, and noise figure (NF) characteristics of 24 dB for 16-nm wavelength conversion was observed. This high-efficiency FWM wavelength conversion provided by a single device is promising for optical wavelength shifters in large-scale optical communication systems.

Extremely low-noise facet-reflectivity-controlled InGaAsP distributed-feedback lasers

Extremely low-noise (relative intensity noise (RIN) < - 160 dB/Hz) was attained with the facet-reflectivity-controlled 1.3-μm wavelength InGaAsP buried-heterostructure distributed-feedback lasers, Noise increase due to the optical feedback was greatly suppressed. It was interpreted as a result of counterbalanced mode competition between distributed-feedback mode and Fabry-Perot mode.

Reactively ion etched nonuniform-depth grating for advanced DFB lasers

An ethane (C/sub 2/H/sub 2/) reactive ion etching (RIE) technique that offers smooth-etched morphology, high controllability of depth, and anisotropic geometries for forming a nonuniform-depth grating on an InP substrate is discussed. The fabrication of a lambda /4-shifted multiple quantum well (MQW) distributed feedback (DFB) laser with a 900 mu m cavity and a nonuniform-depth grating is described. It is shown that the larger threshold gain difference predicted by theory is obtained despite strong hole-burning.<<ETX>>

High saturation output power polarization insensitive semiconductor optical amplifier

A 1550 nm polarization insensitive semiconductor optical amplifier with a very thin tensile-strained bulk active layer was developed. The SOA module exhibited a record high fiber-coupled saturation output power of +17 dBm.