Takeshi Yamatoya

High Power GaInAsP/InP Strained Quantum Well Superluminescent Diode with Tapered Active Region

High-power broadband superluminescent diodes (SLDs) have been studied for spectrum-sliced multiwavelength light sources for use in wavelength division multiplexing systems. We present the design and fabrication of high-power broadband GaInAsP/InP strained quantum well SLDs with a tapered active region emitting in a 1.55 µm wavelength band. The fabricated device exhibited the high-power operation of over 1 W. Also, the spectral width has been increased to over 60 nm by using chirped multiquantum wells which have different well thicknesses.

Optical preamplifier using optical modulation of amplified spontaneous emission in saturated semiconductor optical amplifier

This paper demonstrates a novel optical preamplifier using optical modulation of amplified spontaneous emission (ASE) emitted from a saturated semiconductor optical amplifier (SOA). Requirements on optical alignments and antireflection coating for SOAs can be relaxed and the elimination of an optical filter gives us a large tolerance of an input light wavelength in the proposed optical preamplifier. A small-signal gain of a fabricated preamplifier was over 13.5 dB for an input power of below -20 dBm. An optical gain bandwidth was over 60 nm. We measured the small-signal response of the optically modulated ASE. The 3 dB bandwidths at SOA bias currents of 200, 300, and 400 mA were 5.8, 12.6, and 16.5 GHz, respectively. We also investigated improvements in receiver sensitivities with the proposed optical preamplifier. Our calculation shows a possibility of 10 dB improvement in receiver sensitivities by using the optical preamplifier at 10 Gb/s. The measured receiver sensitivity was -22.7 dBm at 10 Gb/s with the optical preamplifier, which is corresponding to an improvement of 2.5 dB in the receiver sensitivity. Further improvements of the receiver sensitivity can be expected by optimizing the structure of SOAs for saturating ASE.

High-Power CW Operation of GaInAsP/InP Superluminescent Light-Emitting Diode with Tapered Active Region.

We have developed a 1.55 µm superluminescent light-emitting diode (SLD) with a tapered active region. We achieved high power and broadband operation demonstrating an output power of 330 mW under cw operation at 7°C. We examined the beam profile of output light by measuring its near field and far field patterns. It was found that the output light shows a fundamental transversal mode profile in both horizontal and vertical directions. This device will be applicable to spectrum-sliced multiwavelength light sources for use in wavelength division multiplexing optical communication systems as well as in lightwave sensing.

Highly gain-saturated GaInAsP/InP SOA modulator for incoherent spectrum-sliced light source

We proposed and demonstrated a highly gain-saturated semiconductor optical amplifier (SOA) modulator for spectrum-sliced multi-wavelength light sources. The saturation in gain enables us to reduce the spontaneous emission beat noise in spectrum-sliced incoherent light, which is a main problem in incoherent spectrum slicing. The intensity modulation of spectrum-sliced incoherent light using a GaInAsP/InP SOA modulator was carried out with a bit rate of 600 Mb/s. An error rate floor was removed with a help of highly saturated gain. Expected performances of this proposed SOA modulator including efficiency and noise reduction capabilities will also be discussed for use in high-capacity WDM local area networks.

Novel optical preamplifier with inverted ASE signal of semiconductor optical amplifier

We propose and demonstrate a novel optical preamplifier using an inverted signal of amplified spontaneous emission (ASE) of a semiconductor optical amplifier (SOA). The input signal is converted to the modulation of the ASE because of saturation characteristics. The proposed device can not only amplify optical signal but can also suppress the intensity noise of the input signal under the saturation regime. The receiver sensitivity was improved by 10 dB at 1 Gbit/s using the proposed preamplifier. Also, the intensity noise of a 1 Gbit/s spectrum-sliced light was significantly suppressed using the nonlinear characteristics of the preamplifier. A larger gain and a higher speed can be expected simultaneously at a lower input signal power by increasing the length of SOA. The proposed device will be useful in low cost access and metro networks.

Noise Suppression and Intensity Modulation in Gain-Saturated Semiconductor Optical Amplifiers and Its Application to Spectrum-Sliced Light Sources

We present a quantitative estimation of noise reduction in a gain-saturated semiconductor optical amplifier (SOA) for spectrum-sliced incoherent light sources. A noise reduction of 10 dB over a bandwidth of a few GHz was experimentally demonstrated. In addition, the intensity modulation of spectrum-sliced incoherent light using a GaInAsP/InP SOA modulator was carried out with a bit rate of 600 Mb/s. An error rate floor in bit error rate vs received optical power characteristics was removed with the help of this technique.

High-speed operation of optical preamplifier using inverted amplified spontaneous emission signal of saturated semiconductor optical amplifier

We investigate the dynamics of an optical preamplifier using an inverted amplified spontaneous emission (ASE) signal of a saturated semiconductor optical amplifier (SOA). The small-signal response of the converted ASE was measured and its 3 dB bandwidth was over 9 GHz when the injection current of the SOA was increased to more than 200 mA. The rise and fall times of the converted output ASE were also evaluated. In addition, we achieved 10 Gbit/s operation of the proposed preamplifier. The minimum receiver sensitivity was improved by 7 dB using the preamplifier for the 10 Gbit/s signal.

10 Gb/s operation of optical preamplifier using inverted ASE signal of saturated semiconductor optical amplifier

Summary form only given. Semiconductor optical amplifiers (SOAs) are attractive for use in metro optical networks as well as in access networks. We proposed an optical preamplifier using the optical modulation of ASE in a saturated SOA. The proposed preamplifier only needs a single connection between a fiber and the SOA, which relaxes requirements on AR coating and assembling with a single mode fiber. In addition, this preamplifier can potentially avoid using a narrow-band optical filter. In this paper, we investigate the high-speed response of the preamplifier and demonstrate 10 Gb/s operation. In our proposed preamplifier, an input signal is converted to the modulation of the ASE due to the saturation characteristic in an SOA, resulting in the amplification of the signal. We investigated the high-speed response of the optical preamplifier. We used a polarization insensitive GaInAsP bulk SOA. We also investigated the improvement in receiver sensitivity of the optical preamplifier. We measured bit error rate (BER) curves with and without the optical preamplifier. The minimum receiver sensitivity was improved by about 10, 8 and 7 dB for 2.5, 5 and 10 Gb/s signal, respectively.

Design and fabrication of high power and broad-band GaInAsP/InP strained quantum well superluminescent diodes with tapered active region

High power and broadband superluminescent diodes (SLDs) would be useful for various optical sensing applications and for spectrum-sliced multi-wavelength light sources. We proposed and developed SLDs with a tapered active region. We present the design and fabrication of GaInAsP-InP strained QW SLDs with an optimized taper structure. Also, broad-band emission has been obtained by using chirped QW structures.

Modulation dynamics of amplified spontaneous emission in saturated GaInAsP/InP semiconductor optical amplifiers

We investigate modulation dynamics of amplified spontaneous emission (ASE) of saturated semiconductor optical amplifiers (SOAs) with various device lengths. We measured the optical intensity modulation of ASE of GaInAsP/InP SOAs. In a long SOA, a large input-signal-wavelength dependence of the ASE response was observed, which was relaxed in a large-signal measurement in comparison with a small-signal measurement. Faster responses in ASE were obtained under higher bias current density and in longer SOAs even with the same injection current density. We demonstrated a high speed response beyond 20 GHz with an long SOA. In addition, we demonstrated 10 Gbit/s operation of the optical preamplifier using inverted ASE signal of a saturated SOA with a receiver sensitivity of -22.7 dBm.