Paul K. L. Yu

System Issues Relating To Laser Diode Requirements For VLSI Holographic Optical Interconnects

Laser requirements and limitations for VLSI optical interconnect networks employing computer-generated holograms are discussed from a system point of view. For architectures with a collimating lens at the laser and a collector lens at the detector, the restrictions on laser wave-length stability are typically ± 10 A (thus requiring the lasers temperature to be regulated to approximately ± 5°C to 10°C). Diffraction limitations are shown to restrict the density of interconnects to the 104/cm2 range from many architectures (in particular, space variant architectures), rather than the 107/cm2 to 108/cm2 range frequently cited for space invariant architectures. Architectures with a mixture of space variance and invariance can lead to intermediate densities. Some architectures require low threshold, high efficiency lasers, whereas others require very high output power with much less concern for threshold and efficiency. A network with 3000 point-to-point interconnects per square centimeter, each transmitting at a 500 Mbit rate with a 10-11 bit-error rate, is analyzed. The best system performance is obtained if wavelength stabilized high power (10 W) laser arrays are available. Monolithic integration is discussed, and the need for uniform and/or tunable emission wavelength may be the greatest challenge in this area.

Efficient, low parasitics 1.3 mu m InGaAsP electroabsorption waveguide modulators on semi-insulating substrate

The high-speed operation of waveguide modulators is limited by the RC time constant, where the capacitance is primarily due to the parasitics. As part of an effort to reduce the parasitic capacitance, the authors have demonstrated a 1.3 mu m InGaAsP electroabsorption waveguide modulator on semi-insulating InP substrate. A parasitic capacitance smaller than 10 fF was achieved by fabricating the bonding pad on an isolated mesa and by making use of an air bridge. For a 400 mu m long waveguide modulator, an operating voltage as small as 2 V at an on-off ratio of 10 dB was obtained by optimizing InGaAsP bandgap for the operating laser wavelength. The device consists of a five-layer structure on semi-insulating substrate grown by liquid-phase epitaxy. These layers are undoped-InP buffer layer, undoped-InGaAsP waveguide layer, undoped-InP spacer layer, p-InP cladding layer, and p-InGaAsP contact layer.<<ETX>>

Laser Diode Requirements And Limitations For VLSI Holographic Optical Interconnects

Laser requirements and limitations for VLSI optical interconnect networks employing CGHs are discussed from a system point of view. For architectures with a collimating lens at the laser and a collector lens at the (on-chip) detector, the restrictions on laser wavelength stability are typically ± 10 A (thus requiring the lasers temperature to be regulated to approximately ± 5 - 10°C). Dif-fraction limitations are shown to restrict the density of interconnects to the 104 /cm2 range for many architectures (in particular, space variant architectures), rather than the 107 /cm2 to 108 /cm2 range frequently quoted for space invariant architectures. Archi-tectures with a mixture of space variance and invariance can lead to intermediate densities. Some architectures require low threshold, high efficiency lasers, whereas others require very high output power with much less concern for threshold and efficiency. A network with 3000 point-to-point interconnects/cm2, each transmitting at a 500 Mbit rate with a 10-11 Bit-Error-Rate is analyzed and the best system performance is obtained if very high power laser arrays (5 - 10 W) are available. Laser output pattern control is also con-sidered.

Chirping Of Electroabsorption Modulation

Chirping characteristics due to the electroabsorption modulation in bulk InGaAsP, InGaAs/GaAs multiple quantum wells, and InGaAs/GaAs superlattice is accessed in terms of the measured electroabsorption spectra and the corresponding electrorefraction spectra calculated from the Kramers-Kronig transform. The optimal designs for intensity modulation and phase modulation of laser light are discussed.

Transient Behaviors Of Picosecond Photoconductive Switches

We report the development of theoretical and experimental study of the transient behaviors of picosecond photoconductivity. A simple photoconductor with conventional neutrality analysis is described and stripline electrodes are used for high speed operation1. The carrier transport mechanism in a photodiode is modeled, which is in a non-neutrality condition2. This leads into the analysis of the high field, high speed transient behaviors of picosecond photoconductivity by solving the transport equation in its original form without neutrality approximation. Indeed, the photogenerated carrier are found to travel in opposite directions. Future analysis will be emphasized on interaction of this behavior with external circuits.