John Schlafer

Measurement of hole velocity in n‐type InGaAs

Hole drift velocities in n‐type In0.53Ga0.47As have been determined experimentally for the first time. Measured values of the frequency response of transit‐time‐limited InGaAs p‐i‐n photodiodes were fit with the theoretical response using hole velocity as the only free parameter. Measurements over field strengths from 54 to 108 kV/cm showed the drift velocity to be relatively constant at (4.8±0.2) 106 cm/s, indicating that velocity saturation has occurred at field levels below 54 kV/cm.

Anomalously high damping in strained InGaAs-GaAs single quantum well lasers

Measurements of the relative intensity noise spectra of strained, single-quantum-well, separate-confinement-heterostructure (SCH) InGaAs-GaAs lasers indicate that their frequency response is strongly damped. The ratio of the damping rate to the square of the resonance frequency is k=2.4 ns. This intrinsically limits the 3-dB modulation bandwidths of these lasers to about 4 GHz, negating the predicted increase in modulation bandwidth due to the large differential gain often associated with quantum-well devices. The damping behavior of these lasers is inconsistent with previous predictions of damping in bulk lasers due to spectral hole burning. A structure-dependent damping mechanism is proposed for quantum-well lasers.<<ETX>>

Wide-bandwidth receiver photodetector frequency response measurements using amplified spontaneous emission from a semiconductor optical amplifier

The white optical noise (spontaneous-spontaneous beat noise) generated by amplified spontaneous emission from a semiconductor-optical amplifier is used to measure the frequency response of over-wide-bandwidth photodetectors and optical receivers. This technique can be used to characterize optoelectronic components of arbitrarily wide bandwidths. >

Reduction of relative intensity noise in 1.3 μm InGaAsP semiconductor lasers

Relative intensity noise (RIN) from 1.3 μm InGaAsP vapor phase regrown buried heterostructure diode lasers with cavity lengths of 100–300 μm and resonant frequencies exceeding 15 GHz is measured for the first time over the 2.5–18 GHz frequency range. We show that the RIN decreases by nearly 8 dB as the cavity length increases from 100 to 300 μm, and that the RIN is also reduced by lowering the active p‐doping concentration. The measured RIN is in excellent agreement with the expression derived from the laser rate equations.

Relative intensity noise in semiconductor optical amplifiers

The spontaneous noise spectrum of high-gain semiconductor optical amplifiers is normally assumed to be dominated by spontaneous-spontaneous and signal-spontaneous beat noise, which is white over the frequency range important to fiber-optic systems. Recent measurements have shown that a strong resonance peak in the spontaneous noise spectrum appears well below the threshold current, indicating the existence of relative intensity noise. This noise term has important implications for system design, and its effect on several transmission systems is described. Relative intensity noise in semiconductor optical amplifiers is compared to the similar relative intensity noise found in semiconductor lasers.<<ETX>>

Selective regrowth of a wide-bandwidth 1.3 mu m integrated lossless tap and optical preamplifier

The authors report the first monolithically integrated wide-bandwidth lossless tap-that is, an optical semiconductor amplifier followed by a colinear reverse-biased waveguiding photodetector with fiber-coupled input and output. The integration was achieved by using off-axis selective epitaxial growth of ridge waveguides on a patterned dielectric layer. The tilted facets produced by the off-axis growth, along with photodetector absorption, serve to reduce the effective facet reflectivity to -36 dB without any antireflection coating. By adjusting the length of the absorbing photodetector section, part or all of the amplified light may be absorbed, allowing the device to function respectively as a lossless tap or an optical preamplifier. A lossless tap with an electrical bandwidth of 7 GHz, a responsivity of 26 A/W, and a fiber-to-fiber gain of 3 dB is shown to have a receiver sensitivity of -22 dB at 3 Gb/s.<<ETX>>

A hermetic fiber-coupled p-i-n photodetector package for use in fiber-optic preamplifier circuits

A fiber-coupled photodetector package has been developed that provides a true hermetic environment. Fiber coupling is accomplished using expanded-beam connector elements to image the fiber core onto the photodetector through the package window. This particular package concept has important applications in printed-circuit-board implementations of fiber-optic receiver preamplifiers.

Wide-bandwidth 1.3-um integrated lossless tap and optical preamplifier

A high-sensitivity, wide-bandwidth, optical preamplifier is demonstrated in the form of a monolithically integrated semiconductor optical amplifier and waveguide photodetector. By fabricating the same device with a shorter photodetector section, part of the signal is passed through to an output fiber, forming an optical tap. Amplifier gains are sufficient to overcome the fiber-coupling and detector loss, and exhibit zero-insertion-loss operation. A lossless tap with an electrical bandwidth of 7 GHz, a responsivity of 26 A/W, and a fiber-to-fiber gain of 3 dB is shown to have a receiver sensitivity of -22 dBm at 3 Gb/s.

Dynamic and spectral properties of quantum-well lasers with nonlinear gain

The homogeneously broadened, linear gain model of semiconductor lasers does not predict many of the observed dynamic and spectral properties of these devices. We begin by phenomenologically introducing the simplest form of nonlinear gain compression into the single-mode rate equations and review its effect on the lasers dynamic response. A recently developed rate-equation model of quantum-well lasers is then introduced to explain how carrier transport, in conjunction with single-mode nonlinear gain, determines the intrinsic structure-dependent frequency response of quantum-well lasers. The need for a two-mode, nonlinear gain model to describe the low-frequency relative intensity noise (RIN) spectra of semiconductor lasers is briefly reviewed. Finally, recent experimental measurements of the longitudinal mode spectra and the beat spectra between adjacent modes of nearly single-mode lasers are presented. It is shown that understanding of three-mode coupling is required for a proper description of these measurements.

Integrated optical preamplifier technology for optical signal processing and optical communication systems

Optical preamplification has been shown to significantly improve the sensitivity of receivers for wideband lightwave systems when compared with conventional electronic postamplification. However, the large size and relatively fragile nature of optical preamplifiers assembled from discrete optoelectronic components (i.e., hybrid assemblies) has discouraged the use of optical preamplifiers for system applications. This paper discusses the technology required for integrating a semiconductor optical amplifier with a high-speed photodetector on the same chip, [1] and the expected performance of such a device. The monolithically Integrated Optical Preamplifier (lOP) is expected to combine the performance of hybrid receivers with the functionality of a single optoelectronic component. In addition, this integrated device can be used as a lossless optical tap for network monitoring and/or system reconfiguration, functions that are highly desirable for advanced network architectures.