M. Azadeh

Smart pixels with smart illumination

Smart pixels with smart illumination is a new concept in sensor array technology based on structured built-in illumination and optoelectronic feedback. It offers many new possibilities and potential advantages over more-traditional sensor arrays. We discuss an edge-detection system as an example of how smart illumination can advantageously be used to achieve a variety of functions. We also present initial experimental results from a fabricated chip based on this concept. The chip includes an integrated array of photodetectors and LEDs. The output of each pixel can be controlled based on the feedback received by its dual detectors.

A model for optoelectronically interconnected smart pixel arrays

Theoretical results for modeling source-based smart pixel arrays are presented. Attention is focused on modeling the nonlinearities in sources, as well as electrical and optical couplings and interactions within a single pixel. A matrix formalism is used to generalize the theory to include the behavior of an entire smart pixel array consisting of interacting pixels with arbitrary optical and electrical interconnections. A vertical cavity surface emitting laser (VCSEL)-based smart pixel array is used for experimental demonstration of the application of the theory in the design and implementation of an optoelectronic flip-flop, where the nonlinear characteristics of the VCSELs are utilized in a positive feedback scheme to achieve bistability.

Efficient waveform recall in absorbing media

We have found that highly efficient waveform recall is possible in coherent transient systems in which the storage is optically thick. Coherent transients may be used in a variety of information storage and processing applications with advantages over traditional electronic methods. However, it is believed that a serious problem in application of photon echoes in practical systems is the relatively low efficiency of the process. We show in our numerical studies that waveform recall efficiencies greater than unity can be achieved in absorbing media with appropriate choice of absorption length and brief pulse area, even for very weak data pulses. We also present our preliminary experimental results in Barium vapor in which efficiencies of 50% were obtained for both the stimulated and two-pulse photon echoes.

Characteristics of optoelectronic feedback for smart pixels with smart illumination

The application of optoelectronic feedback in addressing various problems in smart pixel arrays is considered. Special attention is paid to issues associated with light sources such as device nonlinearity and nonuniformity. Moreover, new classes of smart pixel applications taking advantage of the useful properties of optoelectronic feedback are discussed. Experimental results from a demonstration chip based on monolithic integration of optoelectronic devices on GaAs substrate are presented.

Smart pixel optical sensor based on positive optical feedback

A smart pixel optical sensor based on positive optical feedback is described and demonstrated. The scheme uses the reflectance of an external scene as part of the positive feedback loop and uses the nonlinear characteristics of a vertical-cavity surface-emitting laser to obtain bistability and hysteresis. As a result, the continuous reflectance variation of the scene is mapped to a digital output with increased noise immunity for each pixel of the array.

Field solutions for bidirectional high-gain laser amplifiers and oscillators

General analytical solutions are obtained for the amplitude, phase, and intensity of the electromagnetic waves in bidirectional homogeneously broadened high-gain laser amplifiers and oscillators. These solutions are important as increasingly high-gain lasers are being employed in practical systems. Expressions are derived relating the output power to the input, including the effects of arbitrary mirror reflectivities and frequency detunings from the line center. For negligible reflectivities, these regenerative amplifier results reduce to earlier expressions for single-pass high-gain amplifiers. Multivalued outputs also occur, and in the limit of low gain per pass the results are consistent with earlier studies of single-frequency laser oscillators.

Power control of VCSEL arrays using monolithically integrated focal plane detectors

Accurate optical power control of a vertical-cavity surface-emitting laser (VCSEL) array is achieved through the use of monolithically integrated photodetectors, which lie within the focal plane of the array and are interconnected into optoelectronic feedback loops. Piecewise linear device models, which also account for crosstalk and optoelectronic device variations, are developed to provide design guidelines. Direct digital control of the individual VCSEL output powers is then achieved through a custom CMOS driver chip based on programmable current-mode digital-to-analog converters. Experimental results verify the power control scheme and the developed models. The performance of this power control method in the presence of crosstalk and noise is also presented.

Accurate CMOS current mode control and processing for a VCSEL array

Summary form only given. Application specific integrated circuits (ASICs) based on CMOS can perform a variety of signal processing tasks and act as an efficient interface between optoelectronic chips and the more traditional electronic circuits. This paper deals with the design of a CMOS chip that includes several basic blocks for demonstration of analog current mode processing functionalities with digital accuracy. The chip was fabricated through the MOSIS service with the AMI 1.2 technology and was tested with an optoelectronic array chip consisting of 16 VCSELs and 16 metal-semiconductor-metal (MSM) detectors to implement an optoelectronic feedback loop.

Smart pixel sensor arrays based on optoelectronic feedback

Summary form only given. Smart pixels present the possibility of integrating an array of light detectors and an array of light sources on a single chip. The demonstration chip used for experiments was based on monolithic integration of LEDs and optical detectors and was fabricated as part of MITs OPTOCHIP project. Each pixel in our design included a LED in the middle, and a pair of MSM and OPFET detectors. These results demonstrate the validity of the model for integrated LED sources and provide a base for implementation of more advanced sensor systems.

Smart pixels with built-in illumination and optical feedback

Summary form only given. We have designed a demonstration chip based on monolithic integration of GaAs electronics, MSM and OPFET detectors, and LEDs in the form of a seven-pixel array. The chip was fabricated by a group at MIT as part of their OPTOCHIP process. Our chip allows us to perform proof-of-concept demonstrations of several of the proposed applications. Characterization and performance of the system in an edge detection application will be presented.