Photoreceivers based on InP are becoming increasingly important for 40 Gbit/s telecommunication systems operating at the wavelength of 1.55 micrometers . Due to the monolithic integration, they are advantageous in respect of high-speed performance, small size and cost saving in high-frequency packaging. Research groups worldwide are engaged in developing such OEIC's, with varying architectures and types of the components. Our broadband photoreceiver OEIC consists of a waveguide-integrated GaInAs p-i-n photodetector and a distributed amplifier. The 5*20 micrometers sized photodetectors, with a responsivity of 0.4 A/W, reveal a 3 dB cut-off frequency of 70 GHz. The electrical distributed amplifier is made of our high-electron mobility transistors. The HEMT devices with gate lengths of 0.25 micrometers exhibit cut-off frequencies f_T and f_max of up to 100 and 250 GHz, respectively. The integrated photoreceivers are characterized on-after using a heterodyne-measurement setup and finally packaged into modules for system experiments. On recently fabricated wafers, the receivers show a bandwidth of 40 GHz, whereas the amplifiers alone even exhibit values as high as 43 GHz, with gain ripple less than 1 dB.

Optical transceivers are one of the essential systems for optical communication, especially for bi-directional transmission between one transmitter and multiple receivers. Up to now, these modules are typically realized as monolithic integrated circuits, that cause high costs. Our effort is to develop an optical transceiver by means of hybrid-technologies which enable to fabricate these modules cheaper and in high numbers.

We introduce an optoelectronic VLSI implementation of a parallel signal processor whose processing nodes receive their binary constant values by means of an optical interconnection network. The processing nodes are integrated in a fixed array raster. Each node requires its own optical inputs realized as smart-detector units. A smart-detector is a combination of an optical receiver device and a receiver circuit and transforms the optical information into electrical signals. We use integrated photo diodes as optical receivers. The photo diodes are optimized for fiber optical coupling and they can be integrated with standard mainstream CMOS/BiCMOS technology. The project is in progress and we present first results.

This paper describes the limits for the efficiency of integrated photodiode arrays in a standard CMOS-process. It shows that an efficiency of more than 60% is not possible for wideband incident light. The efficiency depends on the area of the diodes, the distance between the diodes and the depth of the diode junction. The resulting efficiency of integrated photodiodes in a 0.8 micrometers -CMOS-process is shown. For these photodiodes two ways of crosstalk reduction between photodiode arranged in a line or a 2D array are introduced. Injecting a substrate current between the diodes, the cross-talk can be reduced in a controlled way by the magnitude of the current. Another possibility is to embed every diode in a separate well. The advantages and disadvantages of both systems are discussed. Finally, an application of integrated photodiodes in an edge detector IC is presented. This 6 mm² circuit has been manufactured in a 0.8 micrometers process using embedded photodiodes for crosstalk reduction. The circuit performs a position measurement of a shade edge or contrast edge imaged onto its photodiode array. With its all-analog signal processing, even semitransparent media can be detected without precision tradeoffs.

Modulation Transfer Function (MTF) is an important figure of merit in focal plane array sensors, especially for accurate target positions such as star trackers. In-situ evaluation by MTF in different stages of imager system developments is necessary for an ideal design of different sensors and their signal processing. Understanding the tradeoff between different figures of merit will enable designers to achieve the most efficient design in specific missions. Advanced active pixel test sensors have been designed and fabricated where different pixel shapes were placed. Research on analyzing the MTF for the proper pixel shape is currently in progress for a centroidal configuration of a star. Explicit formulas for the modulation transfer function have been studied for the rectangular shaped pixel array. MTF will give us a more complete understanding of the tradeoffs opposed by the different pixel designs and by the signal processing conditions. In this paper, preliminary results of two different active pixel sensor (APS) focal plane arrays are presented in terms of crosstalk using a laser. MTF measurements of the APS arrays are achieved by applying only a single image. A rising or falling edge rather than the conventional bar target of slit scanning is needed to perform the measurement in each direction for the evaluation of the design efficiency.

Photonic links operating in the 1.55 micrometers erbium gain band are finding their way into an increasing variety of microwave applications. At present, the performance of high power photonic links is limited by the characteristics of the photodetector. For microwave links at 1.55 micrometers , the most successful photodetector architectures have been implementations of surface-illuminated, InGaAs p-i-n photodiodes. One photodetector design issue has been the tradeoff between microwave bandwidth, responsivity, and maximum average DC current. Low bandwidth photodiodes, for example, can be operated at a few GHz with average currents on the order of 50 mA, but are typically constructed with illuminated diameters on the order of 50 micrometers or more. By contrast, high-responsivity photodetectors with bandwidths on the order of 20 GHz are restricted to diameters of around 25 micrometers , and limited to 20 mA average current. It would be beneficial to extend the current capability of 20 GHz photodetectors to the 100-mA range.

Active refrigeration of optoelectronic components through the use of thin film solid state coolers based on III-V materials is proposed and investigated. Enhanced cooling power comparing to the thermoelectric effect of the bulk material is achieved through thermionic emission of hot electrons over a heterostructure barrier layer. It is shown that these heterostructures can be monolithically integrated with other devices made from similar materials. Experimental analysis of an InP p-i-n diode monolithically integrated with a heterostructure thermionic cooler is performed. Cooling performance is investigated for various device sizes and ambient temperatures. Several important non-ideal effects are determined such as contact resistance, heat generation in the wire bonds, and the finite thermal resistance of the substrate. These non-ideal effects are studied both experimentally and analytically, and the limitations induced on performance are considered. The experimental results are then used to predict the improved performance of better designed coolers. These micro- refrigerators can provide control over threshold current, power output, wavelength, and maximum operating temperature in diode lasers. Heterostructure integrated thermionic cooling is demonstrated to provide cooling power densities of several 100's W/cm².

All-optical networks that exhibit high speed, high capacity, scalability, configurability, and transparency are becoming a reality through the exploitation of the unique properties of fiber and integrated optics. An advanced polymeric waveguide technology was developed for affordable passive and active integrated optical elements that address the needs of these networks. We engineered high-performance organic polymers that can be readily made into photonic circuits of controlled numerical apertures and geometries. These materials are formed from highly-crosslinked acrylate monomers with specific linkages that determine properties such as flexibility, robustness, optical loss, thermal stability, and humidity resistance. These monomers are intermiscible, providing for precise continuous adjustment of the refractive index over a wide range. In polymer form, they exhibit state-of-the-art optical loss values, suppressed polarization effects, and exceptional environmental stability. A wide range of rigid and flexible substrates can be used. The devices we describe include demultiplexers, tunable wavelength filters, digital optical switches, and variable optical attenuators.

We have demonstrated a polymeric electro-optic modulator based on a 1 X 2 Y-fed directional waveguide coupler. The symmetric geometry of the 1 X 2 Y-fed directional coupler provided the modulator unique characteristics of intrinsic 3 dB operating point and two complementary output ends. A low switching voltage of 3.6 V and a high extinction ratio of 26 dB were obtained with the modulator operating at a wavelength of 1.34 micrometers . The modulator was fabricated with a novel electro-optic polymer that was synthesized from polyurethane crosslinking with a chromophore.

A beam deflector device has been demonstrated that used thin-film electro-optical polymeric waveguide. Prism cascade was fabricated within a planar waveguide. We report the detail of the design and fabrication of new polymer material beam deflector to operate at 1.3 micrometers .

Presented is the effect of using various cladding layers with different dielectric constants on the applied modulation voltage for nonlinear optic (NLO) polymer based integrated OE devices. The dielectric constants of the core and cladding materials used for NLOs polymer based integrated optoelectronic devices are typically very similar in magnitude. This suggests that even for low modulation rates, only 20% to 25% of the applied modulation voltage (voltage between the electrodes) is being dropped across the core region. With this small percentage of applied voltage reaching the NLO core layer, it becomes necessary to apply 4 to 5 times higher modulation voltage in order to achieve the desired (pi) phase change through the core.

We report on a low-cost monolithic integration method for fabricating semiconductor photonic integrated circuits using selective epitaxy without regrowth. To build a photonic circuit, active and passive devices are required with different energy band gaps. Selective-area growth that uses a mask of parallel SiO₂ strips on a substrate induces variations in epilayer thickness and composition that result in localized shifts of the band gap. From our photoluminescence measurements on such selectively grown InGaAsP/InP multiple quantum well-waveguide materials, a band gap shift above 100 meV has been observed. We developed a waveguide device processing technique for this kind of selective epitaxy material. A few combinations of integrated waveguide splitters, modulators, and amplifiers were designed and fabricated. To test each individual device, we designed a new measurement method which determines the insertion loss and the intrinsic waveguide loss for a device in the middle of an integrated system. Preliminary results indicate few dB gain for a 0.6 mm long amplifier and approximately 10 dB contrast for a modulator operating near 1550 nm. Based on the initial data, new quantum well layer and waveguide structures have been designed to improve the performance in our next-generation devices.

We report in this paper the architectural design and implementation of all-optical packet networks. Using photonic switches to route information, an all-optical network has the advantages of bit rate, wavelength, and signal format transparencies. Within the transparency distance, the network is capable of handling a widely heterogeneous mix of traffic. We will describe our research on the implementation of all-optical backbone switches. The switch components including frame synchronizers, frame delineation units, frame header over-writing units, wavelength converters, frame concentrators, and WDM buffers were constructed at 2.5 Gb/s. Their subsystem and device structure as well as preliminary performance are reported.

We have grown epitaxial GaN and ZnO films on sapphire and silicon substrates, and investigated the possibility of forming channel waveguides utilizing the effect of thin- film-induced index change. 2D confinement of light was clearly observed in the channel region of GaN defined by a SiN cladding layer of a stripe window pattern. The lateral confinement of light in the window region indicates that the effective guide index in the window region of GaN is higher than that in the SiN-loaded outer region. We carried out numerical analyses on the various possible effects that might contribute to the overcompensation of the negative loading effect of a SiN cladding window. This includes the photoelastic, piezoelectric, and electro-optic effects in GaN induced by a SiN window layer. The analysis result suggests that the observed phenomenon can be ascribed to a combination of both the photoelastic and electro-optic effects, and especially that the spontaneous polarization field in GaN might play an important role in forming a channel waveguide in the window region.

Optical wavelength conversion at 1.5 micrometers to four different wavelength channels with 60 GHz spacing using an integrated wavelength-tunable laser-modulator device is reported. High output extinction ratios were obtained over all channels and over input wavelengths ranging from 1530 - 1560 nm.

The electro-absorption modulated 1.55 micrometers DFB laser (EML) represents the first III-V optoelectronic integrated circuit in high volume production. The dominance of this device in dense wavelength division multiplexed telecommunications system is testimony to the advancements made in III-V fabrication technology and demonstration that OEIC's are no longer solely of academic interest. The intensed demand for higher bandwidth telecommunications systems is now pushing the EML device toward increased functionality and hence higher levels of integration. The need for wavelength selectable capability is the most prominent of these thrusts. In this talk we review the current state-of-the-art in single frequency EML technology and present design and performance results of an advanced wavelength selectable EML structure.

Monolithic multiple-wavelength arrays of vertical-cavity surface-emitting lasers (VCSEL) and resonance-enhanced photodetectors (REPD) with matching wavelengths are useful for wavelength-division multiplexed optical interconnects, in which parallelism is achieved using a single fiber. Multiple wavelength channels can be optically multiplexed and broadcast to different nodes, where they are demultiplexed (selected) by REPDs with different spectral selectivity. Alternatively, the multiplexed data can be spectrally separated and sent to different destinations. Wavelength-graded VCSEL arrays with a 57 nm wavelength span have been realized, and VCSELs have been integrated with REPD arrays for improved wavelength matching. Wavelength multiplexing and demultiplexing are demonstrated at > 1 Gb/s using quasi-planar, multi-wavelength, InGaAs (VCSEL) and REPD arrays with closely matching wavelengths, with a crosstalk of > 10 dB between channels approximately 4 nm apart. The transmission performance of a single-channel fiberoptic link with a 1 km span is characterized, and the impact of optical crosstalk from neighboring wavelength channels and the effect of thermally-induced wavelength de- tuning are studied.

We report the first technology demonstration of the use of an IR fiber cable in an IRCM system for missile jamming. The IR fiber cable contains sulphide glass fibers which possess low loss, high strength and high threshold to laser damage. The fiber cable was used to transmit the output from a laser operating in the 2 - 5 micrometers atmospheric window to a Jam Head located remote from the laser. The demonstration was successful and fiber cable performed remarkably well and without damage.

Neodymium (Nd) doped polymer based optical amplifiers have been studied. NdCl₃.6H₂O and Nd(III) hexafluoracetylacetonate were used as dopants. Photoluminescence at 0.89 micrometers , 1.06 micrometers and 1.33 micrometers from Nd ions in polyimide was detected. Phase separation with possible formation of liquid crystal polymer was observed in NdCl₃.6H₂O doped polyimide. Thin film waveguides and multimode channel waveguides were fabricated using a novel planarizing technique to reduce scattering losses. Optical gain of about 5.4 dB at 1.06 micrometers was demonstrated in a 5 cm long NdCl₃.6H₂O doped polyimide channel waveguide.

This paper reports on the viability, effectiveness, versatility, and the utility of the concept of the planar integrated optical interconnection scheme with respect to the concept of the free-space interconnection scheme in realizing multiple integration of various micro/nano- photonic devices and components for applications in optical interconnection, optical circuits, optical switching, optical communication and information processing. Several planar optics schemes to detect parallel optical packet addresses in WDM switching networks, to perform a space- variant processing such as fractional correlation, and to construct multistage interconnection networks, have been successfully demonstrated in the 3D glass blocks. Using a gradient-index (GRIN) substrate as a signal propagation medium in the planar optics is a unique advantage, when compared to the free-space optics. We have demonstrated the GRIN-substrate concept by using six 1/4-pitch GRIN rod lenses and a vertical cavity surface emitting laser (VCSEL). The GRIN planar optics can be further extended to the use of 2D array of VCSEL microlasers and modulators in making massively parallel interconnects. A critical comparison between the planar integrated optics scheme and the free- space integrated scheme is given in terms of physics, engineering and technological concept.

We report thermally- and mechanically-dependable 2D photonic band-gap lasers operating at room temperature. Our thin slab photonic band-gap laser structure is sandwiched between air and a drilled aluminum oxide layer provided by fusion techniques. In this thin slab structure, the optical confinement of photons is achieved by 2D triangular photonic lattice in horizontal plane and total internal reflection in vertical direction. Pulsed lasing action is observed at 1.54 micrometers by 10-mW optical pumping with duty cycle up to 10%.

We report the formation of high-performance polyimide waveguide arrays with 45 degree(s) micro mirror coupler fabricated at each end, which provides a high-efficiency output or input surface-normal light couple for the waveguide. This fully embedded integration provides an efficient method of optical interconnection for the board-level data communication and the multi-layer connection. We employed the Si CMOS process compatible polyimide as the fabrication material, which is relatively easy to process and has low propagation loss for light at 850 nm wavelength. A 1 X 12 waveguide array with 45 degree(s) micro mirror coupler fabricated at each end is experimentally demonstrated.

We describe CMOS pixel design and fabrication results of the time-domain correlation image sensor, which has been proposed and studied in our laboratory. This sensor can essentially be regarded as an array of demodulators--it computes temporal correlation between incident light intensity and a global reference signal every frame. The correlation detection allows sensitivity to high frequency illumination, and makes various applications possible by using this sensor together with active sensing methods such as modulated illumination and camera motion. The prototype pixel, based on a transconductance multiplier with a photodiode current source and a pair of capacitive loads, is designed as a MOS pair with its common source and drains extended to form a photodiode and capacitors, respectively. Based on this design, 64 times 64-pixel sensors were fabricated with a 1.2-micron CMOS process. Experiments under sinusoidally modulated illumination confirmed temporal correlation performance of the fabricated sensors. Application examples such as lock-in photometry and vibrometry are also presented.

This paper is to report in a collective review of our recent work that multiply interconnected GaAs/AlGaAs multiple shallow quantum wells p-i-n-i-p type diodes that we designed and fabricated have been useful in realizing novel devices such as non-biased all-optical bistable devices and all- optical oscillators. A pair of two oppositely polarized p-i- n type diode and n-i-p type diode were monolithically integrated, in which the two intrinsic regions were made of extremely shallow quantum well layers. These layers provide large electric field swing and strong light absorption even without any externally applied bias. We observed bistable contrast ratios of 2:1 and an oscillation frequency reaching several MHz. Non-biased scheme can allow high packing density and simple layout due to electrically independent nature of the devices.

Semiconductor based optical modulators offer flexibility in providing engineerable optical transfer characteristics that can target specific applications. Use of quantum well active regions provides the capability of efficient and linearized transfer characteristics that can benefit analog RF systems in terms of link gain, noise figure and spur free dynamic range. We present experimental results demonstrating the potential for improvements in modulator linearity and efficiency using quantum well based Mach-Zehnder modulators.

Semiconductor electroabsorption modulator (EAM) is a promising alternative to lithium niobate modulator for digital and analog fiber optic links due to its inherent small size, high modulation efficiency, and potential of monolithic integration with other electronic and optoelectronic components. For high-speed application, the bandwidth of the lumped element EAM is known to be RC-time limited. To achieve an ultra large bandwidth in lumped element EAM, the modulation efficiency has to be greatly sacrificed. This is especially critical in analog operation where RF link loss and noise figure must be minimized. To overcome the RC bandwidth limit and to avoid significantly compromising the modulation efficiency, the traveling wave electroabsorption modulator has been proposed and experimentally investigated by several authors.

An optical realization of the Blass matrix based on a substrate-guided wave true-time delay (TTD) module has been proposed and designed for a photonic phased-array antenna (PAA) system, which will operate from 18 to 26 GHz. It is the highest RF frequency range for system level that has been reported until now. A 3 X 8 triangular array lattice will be used and all the elements divided into 8 sub-arrays controlled optically by true-time delay signal. To avoid the squint error caused by the phase control within the subarray, we propose a new squint-free subarray steering technique, which is based on the operation of the true-time delay signals provided by our new optical TTD Blass matrix. The simulation result is given for the far-field radiation pattern of photonic PAA controlled by this technique and no squint is found. We also demonstrate an optical heterodyne system for photonic RF signals generation with conversion efficiency that approaches the theoretical limit.

We propose a method for 2D multiple beam generation without causing extraneous beams in the ASTRO architecture. By simply adding a circular light block (spatial filter) at the center of the polygon mirror on the ASTRO true time delay generator, all the extraneous beams can be removed without requiring additional hardware. Experimental results to prove the concepts will be described with related analyses.

Avalanche photodiodes with thin, sub-micron avalanching regions are found to give avalanche noise lower than predicted by conventional noise theory. Measurements of the excess noise on a range of sub-micron GaAs, InP and Si homojunction p-i-n diodes show that the noise decreases as the avalanching width decreases, even though the electron and hole ionization coefficients remain very similar at high electric fields. Simple Monte Carlo modeling of the ionization process suggests that this reduction is due to the increasing importance of the `dead-space', the minimum distance over which carriers need to travel in order to gain the ionization threshold energy. As this dead-space becomes more significant and the subsequent ionization coefficient increases, the ionization process becomes more deterministic and hence the avalanche noise decreases. Modeling also predicts that reductions in avalanche noise can be obtained in p-n junctions where the electric-field varies rapidly and this has now been observed experimentally.