Showing papers by "David A. B. Miller published in 2001"

Spatiotemporal control of ultrashort optical pulses by refractive-diffractive-dispersive structured optical elements.

Abstract: Structured optical elements that control the spatial and temporal characteristics of femtosecond light pulses are analyzed and synthesized. We show that unique spatiotemporal effects can be attained based on the diffraction, refraction, and dispersive effects that appear in the femtosecond regime. We argue that the design requirements for ultrafast optics are beyond the achromatization considerations that are usually applied to incoherent illumination because of the need to consider coherent effects. Despite fundamental limitations in the space–time control of ultrashort pulses, we show the potential of this technique to improve simultaneously the spatial and the temporal resolution of a lens and to generate ultrafast pulse sequences.

Transform spectrometer based on measuring the periodicity of Talbot self-images

Abstract: We demonstrate a compact transform spectrometer based on measuring the periodicity of Talbot self-images. The system has no moving parts; it contains only a tilted absorption grating that is imaged onto a CCD camera. The linear architecture of the system makes it possible to use this design in imaging arrays of spectrometers. Unlike other transform spectrometers, its resolution is independent of wavelength.

Ultrafast differential sample and hold using low-temperature-grown GaAs MSM for photonic A/D conversion

Abstract: This letter demonstrates an ultrafast sample and hold circuit using optically triggered metal-semiconductor-metal switches made of low-temperature-grown GaAs for use in a photonic analog-to-digital conversion system. A differential configuration is incorporated to reduce feedthrough noise.

Methods for adapative spectral, spatial and temporal sensing for imaging applications

Abstract: A method for adaptive spectral sensing developed for a two-dimensional image made up of picture elements. The method calls for illuminating at least one of the picture elements with an input light and deriving a time-varying spectral signal from the input light for that picture element. The time-varying spectral signal is processed with a time-varying reference signal by using a mathematical function such as convolution, multiplication, averaging, integrating, forming an inner product, matched filtering, addition, subtraction or division to obtain a processed output value for the picture element and this output value is then used in determining a spectral characteristic of the input light. The time-varying spectral signal is conveniently derived by optical filtering of the input light yielding an optical time-varying spectral signal. This method can be used by itself or in combination with at least one other adaptive technique such as adaptive spatial sensing and/or adaptive temporal sensing.

Optically controlled optical gate with an optoelectronic dual diode structure – theory and experiment

Abstract: A low-power, surface-normal optically controlled optical gate that incorporates two stacked AlGaAs diodes has been tested using both picosecond and femtosecond pulses. The device opens and closes within 20 ps with a 30% reflectivity change. Repeated gating with 20 ps periods has been demonstrated – a repetition period significantly faster than the external RC time constant. A theory of the dynamics of optically induced voltage across multiple-layered structures is presented and has been incorporated into simulations, matching experimental results well. This theory also provides insight into both the form and possible improvement of the device recovery using multiple layers.

Method for dispersing light using multilayered structures

Abstract: A novel method and device for separating light of differing wavelengths (wavelength demultiplexing) uses a very simple and compact multilayer dielectric structure having high angular dispersion at certain wavelengths and angles of incidence. The structure is composed of alternating layers of dielectric materials of different refractive indices, and is designed to operate just outside the main reflection region rather than within the main reflection region. In this region just outside the main reflection region there is strong group velocity dispersion, causing different wavelengths of light to travel at different angles through the dielectric stack. As a consequence, different wavelength components of a polychromatic beam are separated as they pass through the device. The dielectric stack is preferably fabricated upon one or both sides of a transparent substrate so that the device can operate with light entering and/or exiting the substrate, eliminating the need for complicated antireflective coatings interfaced with the stack. Preferably, the device also comprises anti-reflective and reflective coatings to attain high optical efficiency and to increase spatial separation of the wavelengths of light, further reducing the size of the device. The device can also operate as a multiplexer by simply reversing the direction of the light. The device may be used for optical demultiplexing a polychromatic beam into spatially separated wavelength component beams by coupling the polychromatic beam into the multilayer dielectric stack, separating the polychromatic beam into component beams having distinct component wavelengths as the polychromatic beam passes through the multilayer dielectric stack, and coupling the component beams out of the multilayer dielectric stack. By reflecting the component beams from one or more mirrors in contact with the multilayer dielectric stack and/or substrate, further separation of the component beams may be produced as the component beams again pass through the multilayer dielectric stack. The method may also include transmitting the component beams and/or the polychromatic beam through antireflective material layers in contact with the multilayer dielectric stack and/or the substrate.

Miniaturized talbot spectrometer

Abstract: A transform spectrometer determines the spectrum of light based on the Talbot effect. Light to be analyzed is passed through a spatially periodic object, thereby generating a series of Talbot images. The intensities of these Talbot images at different optical distances from the spatially periodic object are then detected, and Fourier transformed to determine the spectrum of the light. Preferably, the detector comprises a spatial masking pattern such that the intensities detected are maximized at Talbot planes or at the midpoints between Talbot planes. In one embodiment, the optical distance between the spatially periodic object and the detector is changed in order to detect image intensities at different Talbot planes. In another embodiment, the detector and the spatially periodic object are positioned along a common optical axis at relative angle θ such that different detector rows detect intensities at different Talbot planes. In yet another embodiment, the spatially periodic object is both a grating and a detector, and the Talbot images generated by the grating are reflected off a mirror back to the detector.

Latency in short pulse based optical interconnects

Abstract: We analyze the latency in three optical receiver circuit architectures intended for short optical interconnects. We compare the latency for interconnects using (i) non-return to zero (NRZ) modulation format, and (ii) modulation of short optical pulses ( 1ps). We find that the use of short optical pulses in modulator based interconnects offers the potential of a significant reduction in latency. In this paper we assume that the GaAs p-i-n modulators and diodes are hybrid integrated on 0.25 /spl mu/m CMOS circuits.

Compact transform spectrometer based on sampling a standing wave

Abstract: A spectrometer (10) for determining a spectrum of a light by using a mirror (16) to reflect the light so that the light forms an intensity standing wave pattern (26) through superposition of an incident portion of the light and a reflected portion of the light The spectrometer is equipped with an intensity detector (18) whose thickness is less than a shortest wavelength of the light being examined and which is semitransparent over the spectrum The spectrometer has a mechanism (24) to provide relative movement between the mirror and the intensity detector such that the intensity detector registers a variation of the intensity standing wave pattern An analyzer (22), such as a Fourier transform analyzer, is employed to determine the spectrum of the light from that variation of the intensity standing wave pattern

High-speed sample and hold using low temperature grown GaAs MSM switches for photonic A/D conversion

Abstract: Summary form only given. With the evergrowing demand for bandwidth, the need for high-speed A/D converters operating at GSa/s sampling rates has emerged in the areas of radar and microwave communications. As a solution, the idea of combining the low jitter and high speed advantages of photonics with electrical A/D converters has spawned a number of photonic A/D conversion systems. In our system, we utilize a sample and hold scheme with LT grown GaAs MSM switches. The short recombination lifetime and high mobility of LT GaAs allow high-speed operation with good sensitivity. Optically triggered by a short-pulse laser, the switches would be attached to a transmission line and would sample the input electrical signal onto a hold capacitor.

Adaptive imaging spectrometer in a time-domain filtering architecture

Abstract: Collecting a spectrum for each pixel in an image can give much useful information about a scene, such as chemical content, but generates a vast amount of data. Optical filters can select specific spectral features in advance, but are difficult to adapt in real time to different desired spectra. We have constructed an imaging spectrometer using a time-domain filtering architecture, capable of real-time spectral feature extraction and adaptation to different desired spectra. We demonstrate in real-time the abilities both to (i) recognize multiple specific colors in an image, and (ii) recognize individual colors while suppressing combinations of the same colors, an example of a sophisticated signal processing function that can be performed in this architecture.

Low temperature grown optical detector

Abstract: A high efficiency optical interconnect (OI) deposited directly on a silicon based IC by a low temperature process that utilizes a heterogeneous crystalline structure of a III-V compound material to convert light pulse into electrical signals. The high efficiency is established by pulsing the light beams with a shorter duration than the life time of the generated carriers and by reducing the structural volume and consequently the internal capacitance of the III-V compound to a functional height of approximately 1 micron. The analog MSM characteristic of the OI is bypassed by differential two-beam signal processing, wherein the intensity difference of two synchronous light beams is transformed in two parallel OI's into two electrical signals that compensate in a central node. The resulting polarity in the node switches either a PMOS or a NMOS transistor, which connect either a positive or negative voltage to the output node.

Real-time discrimination of spectra by time-domain adaptive filtering in a Fourier transform interferometer

Abstract: We present a programmable spectral discrimination system with minimal data extraction and processing, insensitive to scan nonlinearities. We demonstrate real-time discrimination of monochromatic sources 30 nm apart, employing a spectrometer with a nominal resolution of 200 nm. ©2001 Optical Society of America OCIS codes: (300.6300) Spectroscopy, Fourier transforms; (120.6200) Spectrometers and spectroscopic instrumentation

Optical Pump-Probe Latency Measurements of Silicon CMOS Optical Interconnects

Abstract: We present the first measurements of O/E/O conversion latency in a hybridly-integrated optoelectronic/CMOS chip designed for chip-to-chip optical interconnection. Using an optical pump-probe technique, we perform precise measurements with picosecond resolution that closely match our simulations.

Observation of wavelength-converting optical switching at 2.5 GHz in a surface-normal illuminated waveguide

Abstract: We demonstrate proof-of-principle switching of a continuous wave (CW) signal that propagates in a p-i-n multiple quantum well waveguide illuminated from above with a modulated control beam. We observe modulation of the CW signal at 2.5 GHz using /spl sim/ 1 mW control beam powers. The planar waveguide-surface normal control architecture lends itself to 2D scalability, making this a promising device for future optically switched networks.

Optical interconnects to silicon CMOS

Abstract: There are even greater problems for off-chip interconnects than on-chip ones. It is possible to break long on-chip interconnects up using on-chip repeater amplifiers, but that approach is very inconvenient off of the chip. Consequently, off-chip interconnects are a particularly attractive first implementation of optical interconnects to silicon chips. Optical interconnects are interesting for many reasons other than this scaling argument. They are immune to electromagnetic interference and crosstalk, they provide voltage isolation, they can have very low loss, and. they allow use of free-space optics, imaging many light beams from one chip to another. Historically a great impediment to integrating optical interconnects with CMOS was the absence of suitable optical output devices. Fortunately there are now two devices that may be able to fill this role - quantum-well modulator diodes, and vertical cavity surface emitting lasers (VCSELs).

Procede de dispersion de la lumiere au moyen de structures multicouches

Abstract: L'invention concerne des nouveaux procede et dispositif de separation de la lumiere de differentes longueurs d'onde (demultiplexage longueur d'onde), dans lesquels est utilisee une structure dielectrique multicouche compacte et tres simple, presentant une dispersion angulaire elevee a certaines longueurs d'onde et angles d'incidence. Ladite structure se compose de couches alternees de materiaux dielectriques a indices de refraction differents et est concue pour fonctionner juste hors de la zone de reflexion principale plutot que dans celle-ci. Dans ladite zone juste a l'exterieur de la zone de reflexion principale, une dispersion de vitesse de groupe elevee se produit, ce qui induit le deplacement de differentes longueurs d'onde selon des angles differents a travers la pile dielectrique. Ainsi, les composantes des differentes longueurs d'onde d'un faisceau polychromatique sont separees lorsqu'elles passent a travers le dispositif. La pile dielectrique est, de preference, fabriquee sur un des cotes du substrat transparent ou les deux, de maniere que le dispositif fonctionne lorsque de la lumiere entre dans le substrat et/ou en sort, ce qui elimine la necessite d'utiliser des revetement antireflechissants complexes en interface avec la pile. Le dispositif comprend egalement, de preference, des revetements antireflechissants et reflechissants, permettant une efficacite optique elevee, l'augmentation de la separation spatiale des longueurs d'onde de lumiere et la reduction de la taille du dispositif. Ledit dispositif peut fonctionner comme un multiplexeur, simplement par l'inversion du sens de la lumiere. Ledit dispositif peut etre utilise pour le demultiplexage optique d'un faisceau polychromatique en faisceaux a longueurs d'onde spatialement separees, par le couplage du faisceau polychromatique dans la pile dielectrique multicouche, par la separation du faisceau polychromatique en faisceaux a composantes possedant des longueurs d'onde de composantes differentes, lorsque le faisceau polychromatique passe a travers la pile dielectrique multicouche, et le couplage des faisceaux a composantes hors de la pile dielectrique multicouche. Par la reflexion des faisceaux a composantes par un ou plusieurs miroirs en contact avec la pile dielectrique multicouche et/ou le substrat, la separation supplementaire des faisceaux a composantes peut etre assuree lorsque lesdits faisceaux repassent a travers la pile dielectrique multicouche. Le procede de l'invention peut egalement consister a transmettre les faisceaux a composantes et/ou le faisceau polychromatique a travers les couches de materiau antireflechissant en contact avec la pile dielectrique multicouche et/ou le substrat.

Photonic analog to digital converter using ultrafast photoconductors

Abstract: There are many difficulties associated with such high sampling rates. One difficulty is in making sure that the sampling window is sufficiently precise in time, independent of the signal level or of other factors. Optical solutions may be able to improve this sampling precision. Our approach to this problem is to use photoconductive gates to sample electrical signals on a picosecond timescale. Achieving precisely timed delivery of optical pulses to trigger the sampling gates is expected to be relatively straightforward with optics without substantial degradation of the short pulse shape or variation in its arrival time. We are using low-temperature-grown GaAs photoconductive switches integrated with very small capacitors.