Fernando D. Alvarez

Optical electroabsorption modulators for wideband, linear, low-insertion-loss photonic links

We describe the characterization and development of semiconductor quantum well electroabsorption modulators (EAMs) for insertion into high-performance photonic links intended for analog applications. Limitations of existing approaches are described, motivating the potential of EAMs for exploiting the flexibility of semiconductor bandgap engineering. Relationships are established between basic modulator device characteristics and the RF system performance measures of link gain (insertion loss), bandwidth, noise figure, and dynamic range; results are then presented that have established the viability of EAMs for wideband, low-loss, linear analog photonic links.

Simultaneous optical amplification and splitting for lower-noise and higher-gain microwave signal distribution

Semiconductor optical amplifiers are investigated for use in large optical signal distributions systems requiring high dynamic range. The impact of amplifier length on the gain and noise figure of the microwave signal is illustrated experimentally. The performance of a device which simultaneously splits and amplifies the optical signal using the principle of multimode interference will be discussed, and it will be shown that this device has potentially higher performance that the previous generation Y-branch/amplifier combination.

High-power, high-duty-cycle operation of monolithic two-dimensional surface-emitting diode laser arrays in the junction-down configuration

High-power, high-duty cycle and continuous wave operation of large-area monolithic 2D surface-emitting GaAlAs laser diode arrays mounted junction-down on microchannel heat exchangers have been demonstrated. Devices mounted don 2-mm-thick Cu heat spreaders were operated to peak output power densities of > 100 W/cm2 at 35% duty cycles,a nd exhibited high power conversion efficiencies, and full width emission spectra of < 4nm. Arrays mounted on 1-mm-thick heat spreaders were operated under continuous wave operating condition to approximately equals 50 W/cm2 power density levels. Silicon microchannel heat exchangers with a measured thermal resistance per unit are of 0.0324 degree(s)C cm2/W were used to removed up to 550 W/cm2 of excess heat generated by the arrays.

Analog Signal Splitting and Amplification for Optically-Controlled Phased-Array Antennas

In this work, multimode interference in a semiconductor optical amplifier is used to simultaneously split (× 10) and amplify a RF signal on an optical carrier.

High power, high-frequency waveguide photodetectors

Optical RF analog applications are generating great interest for a number of reasons including the flexibility of fiber optic systems and the enormous RF signal processing capability offered by photonics. A limitation to the insertion of RF photonics has been the availability of high performance photonic components that can deliver on the advantages offered by photonic systems. In this paper we will discuss test results of InGaAsP-InP based waveguide photodetectors targeting optical RF analog applications.

Microwave optical splitter/amplifier integrated chip (MOSAIC) using semiconductor optical amplifiers

Microwave optical splitter/amplifier integrated chip devices using semiconductor optical amplifiers are investigated for use in large optical signal distribution systems requiring high dynamic range. After demonstrating the need for optical amplification in large optical distribution systems, we show that the amplifier length should be minimized in order to minimize the noise figure, and that the optical power level should be well below the saturation power. We have demonstrated 11 dB fiber-to-fiber RF gain in a 1 X 4 device, and 15 dB single-pass optical gain in an active 1 X 10 multimode splitter.

Broadband high-power photodetector arrays for photonically implemented phased-array antenna architectures

The authors present a monolithically integrated photodetector array combiner approach that operates over an extremely wide RF bandwidth. These arrays are suitable for coherent RF signal combining applications such as optically controlled phased array radar. The approach consisted of a monolithically integrated array of high-power, wideband photodetectors distributed along an RF transmission line resulting in a low power consumption, broadband, high power handling optical-to-RF combiner, The authors demonstrated a 4-element photodetector array with a small-signal 3dB bandwidth of 34 GHz. RF models were developed and calibrated to the measured results to predict the performance of larger arrays. The models predict than an 8-, 16-, and 48-element array would have a small-signal 3dB bandwidth of 25 Ghz, 15.7GHz, and 5.8GHz respectively. These arrays showed a reasonable amount of robustness to variations and/or errors in the time delays of the input optical feed network suggesting that implementation outside the laboratory should be practical.

Electroabsorption modulator packaging for greater than 20-GHz link applications

Efficient, linear, broadband optical modulators are an essential component in wide bandwidth optical links for high fidelity distribution and processing of wideband signals. We discuss the packaging issues and remedies for the packaging of electroabsorption modulators for greater than 20 GHz link applications. The EAM is a waveguide semiconductor quantum well device which we have demonstrated to have a excellent linearity and electrical to optical conversion efficiency. Several important issues require resolution in order to produce a high bandwidth, packaged product. These include temperature control, EAM back-side metallization, attachment of EAM to submount, Product hermeticity, alignment and attachment of input and output fibers to the device at sub- micron tolerances, retaining this alignment over operational temperatures and anticipated vibration environments, and elimination of outgassing materials that may serve as failure initiators to optical facets. This paper addresses these issues.

Q-band monolithic rf optical photoreceiver using InP-based PIN-HEMT MBE selective epitaxy

We report an RF optical InP-based PIN-HEMT photoreceiver operating across a measured 36-46 GHz frequency band fabricated on the same wafer using selective area regrowth with molecular beam epitaxy. The photoreceiver design consists of a 20 micron circular InGaAs/InP photodiode integrated with a wide band 0.15 micron gate length InGaAs/InAlAs/InP low noise amplifier optimized for 44 GHz operation. The heterodyne technique of beating the frequency of two lasers was used to generate an RF modulated light signal at 1.3 micron wavelength. The output of the photoreceiver was measured on a spectrum analyzer and was found to be -24 to -27 dBm across a 36-46 GHz band.

Diode pumped Nd:YVO/sub 4/ microlaser 2D array

Summary form only given. A 2D microchannel cooled, monolithic surface emitting array operating at 808 nm, has been used to pump a 400 /spl mu/m thick wafer of Nd:YVO/sub 4/. The 12 by 8 diode array is collimated with fiber lenses to pump 80 /spl mu/m diameter spots. The array area has a cross-section of approximately 0.5 cm/sup 2/. Thermal lensing, produced by pump light absorption, provides cavity stability for each microlaser cell in the array. The Nd:YVO/sub 4/ wafer was AR coated on the pumped side at 808 nm and HR coated at 1.064 /spl mu/m.<<ETX>>