J. S. Weiner

Combined shear force and near‐field scanning optical microscopy

A distance regulation method has been developed to enhance the reliability, versatility, and ease of use of near‐field scanning optical microscopy (NSOM). The method relies on the detection of shear forces between the end of a near‐field probe and the sample of interest. The system can be used solely for distance regulation in NSOM, for simultaneous shear force and near‐field imaging, or for shear force microscopy alone. In the latter case, uncoated optical fiber probes are found to yield images with consistently high resolution.

Electric-field dependence of linear optical properties in quantum well structures: Waveguide electroabsorption and sum rules

We summarize the electric-field dependence of absorption and luminescence in quantum wells for fields perpendicular to the layers, present extended discussion of electroabsorption spectra and devices in waveguide samples, and derive sum rules for electroabsorption. Optical bistability, self-linearized modulation, and optical level shifting are demonstrated in self-electrooptic effect device configurations, with good modulation contrast and polarization-dependent properties. The electroabsorption spectra enable quantitative comparison of theory and experiment for absorption strengths in quantum wells with field. The sum rules enable excitonic effects to be included in the comparison, and good agreement is seen. One sum rule is also more generally applicable to electroabsorption in semiconductors.

Quadratic electro‐optic effect due to the quantum‐confined Stark effect in quantum wells

We have performed a semi‐empirical calculation of the refractive index changes induced by a perpendicular electric field in quantum wells. This calculation is based on experimental electroabsorption data, together with absorption sum rules that have recently been developed. We find good agreement with published experimental results. Our results are important to the development of electro‐optic and high‐speed electroabsorption quantum well devices.

Room‐temperature excitons in 1.6‐μm band‐gap GaInAs/AlInAs quantum wells

The first observation of strong and well‐resolved exciton peaks in the room‐temperature absorption spectra of infrared band‐gap multiple quantum well structures (MQW’s) is reported. Assignment of the optical resonances in the absorption spectra of GaInAs/AlInAs MQW’s yields the material parameters of this new heterojunction. The discontinuities of the conduction and valence bands are found to be ΔEc=0.44 eV and ΔEv=0.29 eV, respectively.

Highly anisotropic optical properties of single quantum well waveguides

The first measurements of the linear and nonlinear anisotropic absorption of light propagating along the plane of a single quantum well are reported and discussed in terms of the structure of the valence band in ultrathin semiconductor layers. Nonlinear optical effects are compared to those of multiple layer structures and to recent theory.

Strong polarization‐sensitive electroabsorption in GaAs/AlGaAs quantum well waveguides

We report the first measurements of perpendicular field electroabsorption (quantum confined Stark effect) in GaAs/AlGaAs quantum wells for light propagating parallel to the plane of the layers. This geometry is well suited for integrated optics. The absorption edge shifts to longer wavelengths with increasing field by as much as 40 meV, giving a modulation depth>10 dB. The strong dichroism present in this geometry is retained even at high fields, making polarization‐sensitive electro‐optical devices possible. We also demonstrate in the waveguide geometry optical bistability due to the self‐electro‐optic effect with 20:1 on/off ratio.

Image contrast in near-field optics

The resolution of optical microscopy can be extended beyond the diffraction limit by placing a source or detector of visible light having dimensions much smaller than the wavelength, λ, in the near‐field of the sample (<λ/10). This technique, near‐field scanning optical microscopy, is sensitive to a variety of important sample properties including optical density, refractive index, luminescence, and birefringence. Although image contrast based on certain sample characteristics is similar to that observed in traditional optical microscopy, strong coupling between the probe and sample often produces contrast unique to the near‐field.

InP D-HBT IC's for 40 Gb/s and higher bitrate lightwave transceivers

The combination of device speed (f/sub T/, f/sub max/>150 GHz) and breakdown voltage (V/sup bcco/ of about 10 V), makes the double heterojunction InP-based HBT (D-HBT), a very attractive technology to implement the most demanding analog functions of 40 Gb/s transceivers. This is illustrated by the performance of a number of InP D-HBT circuits including millimeter-wave low phase-noise VCOs up to 146 GHz, low jitter 40 Gb/s limiting amplifiers, a 40 Gb/s driver amplifier with 4.5 V differential output swing and distributed pre-amplifiers with up to 1.4 THz gain-bandwidth.

Monolithic silicon coherent receiver

We realized a monolithic polarization-diversity dual-quadrature coherent receiver with on-chip balanced detection in a silicon photonic integrated circuit with integrated germanium detectors. We tested it using a polarization-division multiplexed quadrature phase-shift keyed signal at 112-Gb/s.

Fiber laser probe for near‐field scanning optical microscopy

A hybrid near‐field/fiber laser probe has been developed for high flux, reflection mode optical imaging of surfaces on a subwavelength scale. Spatial resolution of ∼100 nm (i.e., ∼λ/10 at λ=1060 nm) has been achieved simultaneously with signals of ∼1014–1015 photons/s, an improvement of ∼103–104 over earlier designs. The probe thus represents an important step in the development of advanced near‐field transducers for high bandwidth applications such as high density data storage.