Adrian Keating

Long wavelength vertical-cavity semiconductor optical amplifiers

This paper overviews the properties and possible applications of long wavelength vertical-cavity semiconductor optical amplifiers (VCSOAs). A VCSOA operating in the 1.3-/spl mu/m wavelength region is presented. The device was fabricated using wafer bonding; it was optically pumped and operated in reflection mode. The reflectivity of the VCSOA top mirror was varied in the characterization of the device. Results are presented for 13 and 12 top mirror periods. By reducing the top mirror reflectivity, the amplifier gain, optical bandwidth, and saturation output power were simultaneously improved. For the case of 12 top mirror periods, rye demonstrate 13-dB fiber-to-fiber gain, 0.6 nm (100 GHz) optical bandwidth, a saturation output power of -3.5 dBm and a noise figure of 8.3 dB. The switching properties of the VCSOA are also briefly investigated. By modulating the pump laser, we have obtained a 46-dB extinction ratio in the output power, with the maximum output power corresponding to 7-dB fiber-to-fiber gain. All results are for continuous wave operation at room temperature.

1.3-μm vertical-cavity amplifier

We demonstrate the first 1.3-/spl mu/m vertical-cavity optical amplifier. The amplifier was optically pumped and operated in reflection mode. Optimization of the top mirror reflectivity resulted in a 9.4-dB continuous wave fiber-to-fiber gain, a gain-bandwidth product of 220 GHz, and a saturation output power of -6.1 dBm, all at room temperature. By modulating the pump source, an extinction ratio of 27 dB in the output signal power was obtained.

High-temperature optically pumped 1.55-μm VCSEL operating at 6 Gb/s

Vertical cavity lasers operating at a wavelength of 1547 nm were optically pumped by a 980-nm diode laser. Continuous-wave fiber-coupled output powers of 2 mW at room temperature and 140 nW at 105/spl deg/C were observed. Fiber optic transmission over 25 km at 6 Gbit/s with a power penalty of 0.3 dB was demonstrated.

Photocurrent-assisted wavelength (PAW) conversion with electrical monitoring capability using a traveling-wave electroabsorption modulator

A new mechanism of cross-absorption modulation is proposed and experimentally demonstrated to assist wavelength conversion using a traveling-wave electroabsorption modulator (TW-EAM). The photocurrent signal generated by the pump propagates along the TW electrodes and changes the absorption of the waveguide, which imprints data to the probe. The photocurrent signal can also be received by an external electronic circuit to provide monitoring capability. This photocurrent-assisted mechanism does not rely on the saturation of absorption and has the potential to reduce the high pumping power required by EAM-based wavelength converters. Using 2.5-Gb/s nonreturn-to-zero data, the conversion range can cover 30 nm in C-band and the lowest power penalty is 0.5 dB.

Long wavelength vertical cavity lasers

The need for low cost, high speed telecommunication sources demands the maturation of long wavelength vertical cavity lasers (VCLs). Both long haul fiber optic systems and gigabit ethernet links are potential markets for 1.3 and 1.55 micron VCLs. This past year has seen much progress to this end, but the emerging technology has yet to be determined. This paper overviews critical issues in long wavelength VCL design, and discusses the most recent technological advances in the field.

Analog modulation of 1.55-μm vertical-cavity lasers

We analyze the performance of InP/GaAs fused 1.55 micrometers vertical-cavity lasers (VCLs) under analog modulation. Our VCLs employ a strain-compensated InGaAsP/InP multi-quantum well (MQW) active region sandwiched between two AlGaAs/GaAs distributed Bragg reflectors. The first AlGaAs layer of the p-doped top mirror is laterally oxidized for optical and electrical confinement. These devices exhibit the lowest threshold current as well as the highest temperature of continuous-wave operation of any electrically pumped long- wavelength VCL. Two different device designs are investigated and compared. Reduction of the MQW barrier strain and enhancement of the optical index guiding by the oxide layer lead to an improvement of VCL performance. However, parasitic effects limit the modulation bandwidth. Higher order harmonic distortion is measured and simulated using a rate equation model. The model includes a non-linear gain function, gain compression, spontaneous emission and Auger recombination as well as carrier density dependent absorption in the quantum wells which reduces the differential gain. The good agreement between measurement and simulation indicates that electron-photon interaction within the quantum wells dominates the non-linear distortion. Multiple higher order response peaks are measured and reproduced by the model.

30 Gbit/s operation of a traveling-wave electroabsorption modulator

Electroabsorption modulators with traveling-wave electrodes have been designed and fabricated using MOCVD grown InGaAsP-InGaAsP quantum wells. 30-Gbit/s transmission was demonstrated with a 2-/spl mu/m-wide 300-/spl mu/m-long device.

1.3 /spl mu/m vertical cavity amplifier

We report the first optically pumped 1.3 micron vertical cavity amplifier with a gain of 13.7 dB in reflection mode. Optimization of the output mirror reflectivity revealed a gain bandwidth of 31 GHz and a saturation power of /spl sim/5 dBm.

8-Gb/s free space transmission over 150 meters using a 980 nm laser diode

Optical free space transmission for terrestrial, inter- and intra-satellite communications offers the wireless advantages of RF systems, but with greater directivity, less crosstalk, and higher data rates. Semiconductor lasers used in these applications allow direct modulation which reduces optical components and overall transmitter size. We directly modulated a 980 nm laser diode and transmitted over 150 meters at a bit rate of 8 Gb/s. This represents the highest bit rate transmitted over such a free space distance.

High temperature, optically pumped, 1.55 /spl mu/m VCSEL operating at 6 Gb/s

In this paper, we use a 980 nm laser to optically pump 1.55 /spl mu/m vertical cavity surface emitting lasers (VCSELs) and demonstrate record output power of 2 mW at 25/spl deg/C and a record operating temperature of 105/spl deg/C with 140 /spl mu/W output power. Single mode operation with a side mode suppression ratio (SMSR) of 61 dB was achieved and transmission over 25 km of fiber at a bit rate of 6 Gb/s was demonstrated.