Alan R. Johnston

Holographic Optical Interconnects For VLSI

This paper introduces new applications and design trade-offs anticipated for free-space optical interconnections of VLSI chips. New implementations of VLSI functions are described that use the capability of making optical inputs at any point on a chip and take advantage of greater flexibility in on-chip signal routing. These include n-port addressable memories, CPU clock phase distribution, hardware multipliers, and dynamic memory refresh, as well as enhanced testability. Fault tolerance and production yields may be improved by reprogramming the optical imaging system to circumvent defective elements. These attributes, as well as those related to performance alone, will affect the design methodology of future VLSI ICs. This paper focuses on identifying the design issues, their possible solutions, and their impact on VLSI design tech-niques and, finally, presents some preliminary measurements on various sys-tem components.

THE STRAIN‐FREE ELECTRO‐OPTIC EFFECT IN SINGLE‐CRYSTAL BARIUM TITANATE

Strain-free electro-optic effect in single crystal barium titanate as function of temperature between 10 and 120 degrees C

Dispersion of Electro‐Optic Effect in BaTiO3

The dispersion of both the quadratic and linear electro‐optic effects in flux‐grown crystals of BaTiO3 has been measured polarimetrically between 0.4 and 1.0 μ yielding (g11 ‐ g12) and rc =r33 ‐ (na/nc)3 r13. A strong dispersion was found: (g11 ‐ g12) increases to double its long‐wavelength limit at 0.4 μ. Both unclamped (low frequency) and clamped measurements were made. Birefringence and the principal indices were also determined. A two‐oscillator Sellmeier model, in which one oscillator frequency is polarization dependent, was shown to represent closely all the data. The unclampled polarization potential, which specifies the magnitude of the oscillator frequency shift, was 3.9 eV m4 C−2, while its clamped value was one‐third as large. Ultraviolet reflectivity calculated from the model assuming reasonable values of empirical damping agrees with the observations of Cardona and Gahwiller.

Sensitive Automatic Torque Balance for Thin Magnetic Films

An automatic torque balance has been constructed for use in studying the magnetic properties of thin ferro‐magnetic films. The automatic servo force balancing technique using a photoelectric pickoff has been applied to a fused‐silica torsion fiber suspension. A sample up to 600 mg in weight can be handled. The data are automatically recorded by an X‐Y plotter. Sensitivity of 10−6 dyn‐cm and a response time of a fraction of a second have been obtained, providing a significant improvement over similar instruments previously used. An appropriate set of coils provides the magnetic field H. Since the torque on a sample is given by M×H=L, measurement of torque affords a means of studying the behavior of the magnetization M. Provision is made for observing torque either parallel or perpendicular to the film surface. The sensitivity available will permit the study of 1‐cm‐diam films as thin as one‐half an atomic layer under ideal conditions. Examples are given of the measurement of the saturation magnetization, r...

dc electric field meter with fiber-optic readout

The design of a dc electric field meter capable of measuring the magnitude and direction of the electric field at an arbitrary location above the ground plane is described. The meter is based on measuring induced charge on a split cylindrical electrode pair which is rotated around its axis of symmetry. Data readout is by fiber-optic cable using pulse frequency encoding. The sensing head is electrically isolated. Initial results are reported from a series of tests at General Electrics High Voltage Transmission Research Facility, Pittsfield, MA. The electric field was measured in a large test cage and under a dc test line. Measurement of field magnitude and direction around a human subject standing under the conductor was demonstrated.

Picosecond pulse generation from a synchronously pumped mode‐locked semiconductor laser diode

A semiconductor laser diode was mode locked in an external cavity when synchronously pumped with 90-ps current pulses. Transform-limited optical pulses with a 10-ps pulse width and a peak power of 160 mW were produced. Operating characteristics of such a system are described.

Kerr response of nematic liquids.

The Kerr response of seven nematic substances has been measured just above their nematic‐isotropic transition temperature, in their isotropic state. If the reciprocal of the Kerr constant B is plotted against temperature, a linear relationship analogous to the Curie‐Weiss dielectric relationship in ferroelectrics is found in all cases. The transient Kerr response—that is, the variation of induced birefringence with time in response to a field step—was also measured in three of the compounds. In p‐(p‐ethoxybenzylidene) amino benzonitrile (EBAB), a maximum Kerr constant of 175×10−10 cm2 V−1 was observed, together with a response time of 13 nsec. The extremely short response time indicates that molecular association does not take place. On the other hand, n‐(p‐methoxybenzylidene)‐p‐butylaniline (MBBA) under similar conditions showed a response time of 3 μsec, indicating that a high degree of association does take place in the isotropic phase.

Optically powered data link for power system applications

The practicability of an optically powered data link has been demonstrated. The link has moderate bandwidth (1 kHz), accuracy (1%) and dynamic range (>60 dB) over a useful range of ambient temperatures. The link uses commercially available components, including a photodiode array fabricated using the dielectric isolation process in silicon. An application to the measurement of current in a high voltage line by means of a linear coupler is described, and experimental results are presented. Power transmission efficiency is presently low, at about 0.3% overall (electrical-to-electrical) and 5% optical-to-electrical. >

Stark‐Effect Modulation of a CO2 Laser by NH2 D

The molecular Stark effect in NH2D was used to modulate the 10. 6‐μ P(20) line of a CO2 laser yielding a modulation depth of 40% from a 200‐V cm−1 rms signal applied to a 19. 7‐cm gas cell external to the laser. NH2D was prepared by mixing ND3 and NH3. The absorption coefficient of the M=4 Stark‐split line was measured as a function of mixing ratio and pressure. The observed pressure‐broadening coefficient was 32. 5 MHz/Torr.

Effect of temperature on optical fiber transmission

Results are presented concerning the effects of temperature on the transmission properties of various optical fibers including a silicone plastic clad, an acrylic plastic clad, and CVD step-index fibers both with and without polyurethane jackets. Results are presented for the normalized transmitted power vs temperature, the index of refraction vs temperature, and induced attenuation coefficients vs temperature. The data show that the intrinsic transmission of a CVD fiber is independent of temperature over the -110 to +150 C range. Plastic clad fused silica fibers are subject to transmission losses at lower temperatures due to changes in the optical index of the cladding polymer. Acrylic-clad and plastic-clad silica fibers also show transmission losses at lower temperatures, but to lesser extents.