K.Y. Lau

Dynamic range requirements for optical transmitters in fiber-fed microcellular networks

Analog fiber-optic links can be used for antenna remoting in microcellular networks. Using a statistical model of user access in a wireless network, it is shown that by accepting a modest (<0.5%) percentage of blocked calls, a modest optical link dynamic range of 91 dB (1 Hz) is required. By using multiple fiber-fed antennas per cell and proper network protocol, the required dynamic range is dramatically reduced to <80 dB for the same blocking probability.<<ETX>>

High single-transverse-mode output from external-cavity surface-emitting laser diodes

Room‐temperature cw electrically pumped external‐cavity surface‐emitting laser diodes are reported. The external cavity provides a way to control the transverse modes of the surface‐emitting laser diodes. Powers greater than 100 mW pulsed and 2.4 mW cw in the lowest order (TEM00) transverse mode are reported. The surface‐emitting laser diode was grown on a p‐doped substrate, resulting in uniform current injection in devices as large as 100 μm in diameter. To our knowledge, this is also the first report of a working surface‐emitting laser diode grown on a p‐type substrate.

Micromachined polysilicon microscanners for barcode readers

We describe the design and fabrication of micromachined resonant scanners that have large scan angles at fast scan speeds. Driven by an electrostatic combdrive actuator, these 200 /spl mu/m/spl times/250 /spl mu/m micromirrors have a maximum scan angle of 28/spl deg/ (optical) at a resonant frequency of 3 kHz when driven by a sinusoidal voltage of 9.5 V (amplitude) superimposed on a 30-V dc bias. Fabricated with a four-layer polysilicon-surface-micromachining process, these resonant scanners are compact, extremely light in weight, potentially very low in cost, and operate at very low power levels. Using the scanner as a laser-beam deflector, we have demonstrated a barcode reader system.

Techniques for improving in-building radio coverage using fiber-fed distributed antenna networks

The characteristics of an in-building fiber-fed distributed antenna network are addressed by simulation of an indoor non-shadowed radio environment at 900 MHz, 1.8 and 1.9 GHz. The performance of the network is discussed in terms of the number and placement of antennas, and the method of diversity combination used. Statistical analysis of the radio environment shows that the arbitrary placement of two fiber-fed antennas in the room is as good as conventional half-wave diversity. Furthermore, the performance of multiple distributed antennas (>3) is typically superior to non-distributed architectures.

Stretched-film micromirrors for improved optical flatness

We have developed a new tensile optical-surface (TOS) process to produce optically flat micromirrors capable of scanning at high frequencies. A polysilicon membrane is stretched across a stiff, single-crystal silicon-rib structure. This structure increases the stiffness of the mirror without significantly increasing its mass. The low mass makes possible high operating frequencies without deformation that could significantly compromise the optical performance of the mirror. Electrostatic comb drives, made of thick single-crystal silicon, provide large forces that enable mirror operation at tens of kHz.

Silicon-micromachined micromirrors with integrated high-precision actuators for external-cavity semiconductor lasers

We present an actuated silicon-micromachined micromirror with continuous and highly accurate position adjustment designed to be used in the construction of external-cavity semiconductor-laser modules. In our initial design, a positioning accuracy better than /spl plusmn/0.2 /spl mu/m for the actuated micromirrors is obtained. The mechanical robustness, small size, and fine-positional precision of the actuated micromirrors are sufficient for external-cavity-laser applications. In production, the cost of these miniature external-cavity-laser systems should be low because they are batch-processed.

High single‐mode output power from compact external microcavity surface‐emitting laser diode

Transverse mode control is demonstrated in an electrically pumped surface‐emitting laser diode coupled to an external microcavity with room‐temperature single‐mode powers reaching 2.0 mW continuous wave and 36.7 mW pulsed. The wavelength chirp is less than 0.044 nm for the pulsed results. The external microcavity is formed with a flat dielectric mirror placed less than 700 μm from the wafer surface. Diffraction and spatial filtering in the external cavity provide high‐order mode suppression and produce a large fundamental mode of width 36 μm. This external cavity geometry readily lends itself to integration.

Gain compression in tensile‐strained 1.55 μm quantum well lasers operating at first and second quantized states

Gain compression coefficients in tensile‐strained 1.55 μm single quantum well lasers are measured using an optical injection method. Lasers operating in the first and second quantized states are used. An explicit linear dependence of nonlinear gain on the differential gain is obtained from these measurements. These results are quantitatively compared to a recently proposed model involving carrier transport in and out of the quantum well.

A novel all-optical self-routed wavelength-addressable network (SWANET)

A novel all-optical self-routed wavelength-addressable network based on a new multiwavelength routing protocol is proposed. A distributed switching network that uses a low-speed routing header provides a transparent path for the high-speed data while utilizing low-speed electronic processing of the routing header. Each data packet is preceded by a routing header composed of a serial combination of wavelengths. The number of destination addresses is dramatically increased over conventional wavelength-division multiplexing or conventional photonic packet switching networks for the same number of wavelengths or header digits, respectively. A 1/spl times/4 switching node is implemented demonstrating the switching and transmission capabilities of this wavelength-addressable network.<<ETX>>

Stroboscopic interferometer with variable magnification to measure dynamics in an adaptive-optics micromirror

Interferometry has proven a powerful tool to measure out-of-plane movements in MEMS with high accuracy, In this paper, we demonstrate a setup for stroboscopic interferometry that combines the precise data registration obtained by combining phase-shifting techniques with the high spatial resolution and aperture that are characteristic for an optical microscope.