Robert R. Hayes

Nonlinearity of p-i-n photodetectors

At higher operating frequencies, the field dependence of the carrier velocity in p-i-n photodetectors generates harmonics and intermodulation products that can degrade the dynamic range of RF fiber-optic links. The authors present both a perturbational theory and measured harmonic data for a p-i-n photodiode operated at very high power densities which show that this and other detector nonlinear effects need not seriously compromise link performance. In particular, neither transit-time nor static nonlinearities in p-i-n photodiodes need limit the dynamic range of fiber-optic links operating below 5 GHz. The fact that the theoretical bandwidth of the photodiode, with all parasitic capacitance and inductance ideally removed, is 17 GHz, suggests that comparable spur-free performance should be achievable at X and Ku-band frequencies, once packaging parasitics are reduced.<<ETX>>

GaAs spiral optical waveguides for delay-line applications

Spiral optical waveguides can be used to provide moderately long delays for a variety of microwave applications. A brief analysis of the performance limitations of spiral delay lines is presented, together with loss measurement data for spirals having air-equivalent lengths as long as 46 cm. It is shown that the present limitation to longer delay lengths is the straight-guide loss of GaAs/AlGaAs waveguides, and not bending or intersectional losses. >

GaAs and silica-based integrated optical time-shift network for phased arrays

We compare the GaAs and Silica-based approaches for realizing integrated time-shift networks. The performance of a fully functional 2-cm X 2-cm monolithic GaAs circuit is reviewed in detail. In addition, we describe the design of an optoelectronic- switched network that uses Silica-based star-couplers and waveguide arrays.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High-efficiency waveguide-coupled lambda =1.3 mu m In/sub x/Ga/sub 1-x/As/GaAs MSM detector exhibiting large extinction ratios at L and X band

The design and fabrication of a 1.3- mu m waveguide-coupled strained-layer In/sub x/Ga/sub 1-x/As/GaAs MSM detector with an optimized active layer thickness is reported. For 100- mu m-long devices, a responsivity of 0.58 mA/mW is observed. Using the detector as an optoelectronic switch, on/off ratios better than 40 dB were achieved at L and X band.<<ETX>>

Analog intersatellite communication with frequency-modulated light. Part 1. Noise theory

A detailed analysis of the noise properties of wideband optical FM systems is presented. The equations, which are extensions of the results derived by Middleton [Q. Appl. Math. 7, 129 (1949)] and Rice [Bell Syst. Tech. J. 27, 109 (1948)] over 50 years ago, can be used to determine the final noise spectral density for all degrees of limiting, with and without sinusoidal frequency modulation. These results are perfectly general and can be used for any FM system (radio, microwave, or optical) having the particular type of limiter described herein.

GaAs optical time-shift network for steering a dual-band microwave phased-array antenna

A monolithic optical time-shift network is described which is designed to steer a dual-band microwave phased array antenna at 2 and 10 GHz. The advantages of using cascade type network architectures to achieve the desired resolution are demonstrated. The implementation of different delay times in this optical time-shifter via bias control of detectors integrated monolithically on a GaAs wafer is described.

Fading statistics for intersatellite optical communication

The narrow beam widths associated with intersatellite optical communication links make such links susceptible to signal fading because of pointing jitter. Such fading can be aggravated by stationary offsets in pointing. We calculated the fade rates for the case of two spaceborne telescopes having Gaussian beam profiles, a pointing offset, and pointing jitter that can be described by Gaussian statistics. An integral solution is derived for the general case of a nonsymmetrical system, with and without pointing bias, and closed-form solutions are presented for the case of a symmetrical system (identical platforms and optics). These results show that, for a system with 3-dB margin, the rms pointing jitter must be held to less than 7% of the full beam width to keep the fade rate below once per year.

Broadband microwave fiber optic link with a compact transmitter

A microwave fiber optic link is developed for operation from 8 to 18 GHz. Modulation of a 1.3-μm wavelength optical carrier is accomplished using a lithium niobate Mach-Zehnder interferometer modulator that was designed for broadband operation up to 19 GHz. The link transmitter components, which consist of a high-power semiconductor laser, an optical isolator, and a modulator with polarization-preserving fiber pigtails, are spliced together to fit into a 10.16- x 5.08- x 2.54-cm3 (4- x 2- x 1-in.) box for applications where space is critical. The average link electrical gain is 45 dB, the frequency response is flat to within ±4 dB across the 10-GHz band, and the spur-free dynamic range of the link is 84 dB.