Showing papers on "Optical modulator published in 2009"

Device Requirements for Optical Interconnects to Silicon Chips

Abstract: We examine the current performance and future demands of interconnects to and on silicon chips. We compare electrical and optical interconnects and project the requirements for optoelectronic and optical devices if optics is to solve the major problems of interconnects for future high-performance silicon chips. Optics has potential benefits in interconnect density, energy, and timing. The necessity of low interconnect energy imposes low limits especially on the energy of the optical output devices, with a ~ 10 fJ/bit device energy target emerging. Some optical modulators and radical laser approaches may meet this requirement. Low (e.g., a few femtofarads or less) photodetector capacitance is important. Very compact wavelength splitters are essential for connecting the information to fibers. Dense waveguides are necessary on-chip or on boards for guided wave optical approaches, especially if very high clock rates or dense wavelength-division multiplexing (WDM) is to be avoided. Free-space optics potentially can handle the necessary bandwidths even without fast clocks or WDM. With such technology, however, optics may enable the continued scaling of interconnect capacity required by future chips.

Low V_pp, ultralow-energy, compact, high-speed silicon electro-optic modulator

Abstract: We present a high-speed silicon optical modulator with a low Vpp (peak-to-peak driving voltage) and ultralow energy consumption based on a microring resonator, with the refractive index modulation achieved by electric-field-induced carrier depletion in a reverse-biased lateral pn diode embedded in the ring structure. With a Vpp of 2 V, we demonstrate a silicon modulator with a 3 dB bandwidth of 11 GHz, a modulation depth of 6.5 dB together with an insertion loss of 2 dB, ultralow energy consumption of 50 fJ per bit, and a small device active area of ~1000 µm2.

Optical I/O technology for tera-scale computing

Abstract: This paper describes both a near term and a long term optical interconnect solution, the first based on a packaging architecture and the second based on a monolithic photonic CMOS architecture. The packaging-based optical I/O architecture implemented with 90 nm CMOS transceiver circuits, 1 × 12 VCSEL/detector arrays and polymer waveguides achieves 10 Gb/s/channel at 11 pJ/b. A simple TX pre-emphasis technique enables a potential 18 Gb/s at 9.6 pJ/b link efficiency. Analysis predicts this architecture to reach less than 1 pJ/b at the 16 nm CMOS technology node. A photonic CMOS process enables higher bandwidth and lower energy-per-bit for chip-to-chip optical I/O through integration of electro-optical polymer based modulators, silicon nitride waveguides and polycrystalline germanium (Ge) detectors into a CMOS logic process. Experimental results for the photonic CMOS ring resonator modulators and Ge detectors demonstrate performance above 20 Gb/s and analysis predicts that photonic CMOS will eventually enable energy efficiency better than 0.3 pJ/b with 16 nm CMOS. Optical interconnect technologies such as these using multi-lane communication or wavelength division multiplexing have the potential to achieve TB/s interconnect and enable platforms suitable for the tera-scale computing era.

Multi-Level, Multi-Dimensional Coding for High-Speed and High-Spectral-Efficiency Optical Transmission

Abstract: We review and study several single carrier based multi-level and multi-dimensional coding (ML-MDC) technologies recently demonstrated for spectrally-efficient 100-Gb/s transmission. These include 16-ary PDM-QPSK, 64-ary PDM-8PSK, 64-ary PDM-8QAM as well as 256-ary PDM-16 QAM. We show that high-speed QPSK, 8PSK, 8QAM, and 16QAM can all be generated using commercially available optical modulators using only binary electrical drive signals through novel synthesis methods, and that all of these modulation formats can be detected using a universal receiver front-end and digital coherent detection. We show that the constant modulus algorithm (CMA), which is highly effective for blind polarization recovery of PDM-QPSK and PDM-8PSK signals, is much less effective for PDM-8QAM and PDM-16 QAM. We then present a recently proposed, cascaded multi-modulus algorithm for these cases. In addition to the DSP algorithms used for constellation recovery, we also describe a DSP algorithm to improve the performance of a coherent receiver using single-ended photo-detection. The system impact of ASE noise, laser phase noise, narrowband optical filtering and fiber nonlinear effects has been investigated. For high-level modulation formats using full receiver-side digital compensation, it is shown that the requirement on LO phase noise is more stringent than the signal laser. We also show that RZ pulse shaping significantly improves filter- and fiber-nonlinear tolerance. Finally we present three high-spectral-efficiency and high-speed DWDM transmission experiments implementing these ML-MDC technologies.

Silicon waveguide modulator based on carrier depletion in periodically interleaved PN junctions

Abstract: We present the design and numerical simulation results for a silicon waveguide modulator based on carrier depletion in a linear array of periodically interleaved PN junctions that are oriented perpendicular to the light propagation direction. In this geometry the overlap of the optical waveguide mode with the depletion region is much larger than in designs using a single PN junction aligned parallel to the waveguide propagation direction. Simulations predict that an optimized modulator will have a high modulation efficiency of 0.56 V.cm for a 3V bias, with a 3 dB frequency bandwidth of over 40 GHz. This device has a length of 1.86 mm with a maximum intrinsic loss of 4.3 dB at 0V bias, due to free carrier absorption. (C) 2009 Optical Society of America

Recent Progress in High-Speed Silicon-Based Optical Modulators

Abstract: The evolution of silicon optical modulators is recalled, from the first effect demonstrations to the characterization of high-performance devices integrated in optical waveguides. Among possibilities to achieve optical modulation in silicon-based materials, the carrier depletion effect has demonstrated good capacities. Carrier depletion in Si and SiGe/Si structures has been theoretically and experimentally investigated. Large phase modulation efficiency, low optical loss, and large cutoff frequency are obtained by considering simultaneously optical and electrical structure performances. Integrated Mach-Zehnder interferometers and resonators are compared to convert phase modulation into intensity modulation. Finally, recent results on high-speed and low-loss silicon optical modulator using an asymmetric Mach-Zehnder interferometer are presented. It is based on a p-doped slit embedded in the intrinsic region of a lateral pin diode integrated in a silicon-on-insulator waveguide. This design allows a good overlap between the optical mode and carrier density variations. An insertion loss of 5 dB has been measured with a -3 dB bandwidth of 15 GHz.

Digital spatial light modulators

Abstract: Spatial control of the phase and amplitude of a laser beam is useful for applications ranging from imaging and holography to interferometry and optical tweezers, reports Neil Savage.

Instantaneous Microwave Frequency Measurement Using an Optical Phase Modulator

Abstract: A novel technique for instantaneous microwave frequency measurement using an optical phase modulator is proposed and demonstrated. In the proposed system, a microwave signal with its frequency to be measured is modulated on two optical wavelengths at the phase modulator, with the phase-modulated optical signals sent to a dispersive element, and detected at two photo-detectors. Due to the chromatic dispersion of the dispersive element, the two microwave signals will experience different power fading, leading to different power versus frequency functions. A fixed relationship between the microwave frequency and the microwave powers is established. By measuring the microwave powers, the microwave frequency is estimated. Compared with the techniques using an intensity modulator, the proposed approach is simpler with less loss. Since no bias is needed the system has a better stability, which is highly expected for defense applications. Experimental verification is presented.

Enhanced Spurious-Free Dynamic Range Using Mixed Polarization in Optical Single Sideband Mach–Zehnder Modulator

Abstract: We analyze in theory, simulation, and experiment the spurious-free dynamic range (SFDR) for a radio-over-fiber system using an optical single sideband (OSSB) Mach-Zehnder modulator (MZM) that is linearized using mixed polarization. The mixed polarization OSSB MZM makes use of a dual-electrode z-cut LiNbO3 MZM, where a linear polarizer is placed in front and in behind the optical modulator, respectively. It is found that intermodulation distortion can be suppressed significantly regardless of modulation index. Thus intermodulation induced power fading and crosstalk via fiber chromatic dispersion for a given RF carrier is reduced compared to using the conventional OSSB MZM. Improvements of ~ 13 dB in SDFR is predicted in theory, simulation, and demonstrated experimentally.

Electro-optical modulator in a polymerinfiltrated silicon slotted photonic crystal waveguide heterostructure resonator.

Abstract: We present a novel concept of a compact, ultra fast electro-optic modulator, based on photonic crystal resonator structures that can be realized in two dimensional photonic crystal slabs of silicon as core material employing a nonlinear optical polymer as infiltration and cladding material. The novel concept is to combine a photonic crystal heterostructure cavity with a slotted defect waveguide. The photonic crystal lattice can be used as a distributed electrode for the application of a modulation signal. An electrical contact is hence provided while the optical wave is kept isolated from the lossy metal electrodes. Thereby, well known disadvantages of segmented electrode designs such as excessive scattering are avoided. The optical field enhancement in the slotted region increases the nonlinear interaction with an external electric field resulting in an envisaged switching voltage of approximately 1 V at modulation speeds up to 100 GHz.

Multicarrier Light Source With Flattened Spectrum Using Phase Modulators and Dispersion Medium

Abstract: This paper describes a phase-locked multicarrier light source that employs a continuous wave (CW) light source, two phase modulators, and a dispersion medium. A sinusoidal phase modulation (PM) with a modulation index of ?/4 and a group velocity dispersion of ±1/(4?fm 2), where fm is the modulation frequency, are applied to a CW light followed by a large sinusoidal PM. This configuration provides a multicarrier light with a flattened optical power spectrum for any modulation index of the second PM. By adopting a chirped fiber Bragg grating (FBG) as a dispersion medium instead of a long normal dispersion fiber, we can increase the stability of the optical output spectrum and reduce the size of the multicarrier light generator. We have built a prototype with this configuration that generates a 61-carrier light with a 25 GHz interval and a power deviation of less than 8 dB.

Serial modulation display having binary light modulation stage

Abstract: A display has first and second spatial light modulators for modulating light from a light source. The first spatial light modulator has a plurality of elements switchable between ON and OFF states according to a pattern having a spatially-varying density. Transfer optics blur and carry light modulated by the first spatial light modulator to the second spatial light modulator to yield a light field at the second spatial light modulator. The second spatial light modulator has a plurality of elements switchable between ON and OFF states to perform temporal dithering of the light field to provide a reconstruction of the image.

Tunable optical single-sideband modulator with complete sideband suppression.

Abstract: We report on the development of a new class of widely tunable resonant single-sideband electro-optical modulators based on interaction of different mode families of a crystalline whispering gallery mode resonator with an externally applied rf field. The tunability comes from the different response of mode families to either the temperature change or the voltage applied to the resonator.

1.5% root-mean-square flat-intensity laser beam formed using a binary-amplitude spatial light modulator

Abstract: We demonstrate a digital micromirror device (DMD)-based optical system that converts a spatially noisy quasi-Gaussian to an eighth-order super-Lorentzian flat-top beam. We use an error-diffusion algorithm to design the binary pattern for the Texas Instruments DLP device. Following the DMD, a telescope with a pinhole low-pass filters the beam and scales it to the desired sized image. Experimental measurements show a 1% root-mean-square (RMS) flatness over a diameter of 0.28 mm in the center of the flat-top beam and better than 1.5% RMS flatness over its entire 1.43 mm diameter. The power conversion efficiency is 37%. We develop an alignment technique to ensure that the DMD pattern is correctly positioned on the incident beam. An interferometric measurement of the DMD surface flatness shows that phase uniformity is maintained in the output beam. Our approach is highly flexible and is able to produce not only flat-top beams with different parameters, but also any slowly varying target beam shape. It can be used to generate the homogeneous optical lattice required for Bose-Einstein condensate cold atom experiments.

Laser illuminated micro-mirror projector

Abstract: A digital image projector includes a plurality of light modulation assemblies and a dichroic combiner. Each light modulation assembly includes at least one laser light source configured to provide an illumination beam, an optional a coated surface, and a spatial light modulator. If the coated surface is present, the respective laser light source is configured to direct the illumination beam to the coated surface, which directs the illumination beam toward the respective spatial light modulator. Otherwise, the respective laser light source is configured to direct the illumination beam directly toward the respective spatial light modulator. The spatial light modulator redirects output modulated light back to the coated surface, if present, and out of the corresponding light modulation assembly. The dichroic combiner directs the output modulated light from each of the plurality of light modulation assemblies toward a projection lens for projection onto a display surface.

Dynamic manipulation of a laser beam using a liquid crystal spatial light modulator

Abstract: This article describes a graduate level optics laboratory experiment on the manipulation of the wavefront of a laser beam using a spatial light modulator. A computer generated holography technique is employed to generate a custom defined wavefront, realized in the +1 diffraction order when a collimated laser beam is diffracted by a binary transmission hologram. The hologram is written on a liquid crystal spatial light modulator and can be updated at a video rate using a personal computer interface.

Projection-type display and control thereof

Abstract: A projection display device that includes a set of light source units (eg, lasers or LEDs) and a control mechanism that monitors performance of each of the units, as well as external factors, eg, time, ambient temperature, etc is provided The control mechanism may dynamically adjust each light source unit, for example, to maximize longevity In operation, an optical modulator is configured to selectively transmit light produced by a subset of the light source units according to video data included in a video signal provided to the projection-type display device A projection lens system is configured to project light transmitted by the optical modulator along a projection path A sensor detects real time readings related to the performance of the set of light source units In accordance with the readings, a control circuitry dynamically controls the laser set to dynamically vary the luminance of the set of light source units

POLICRYPS: a liquid crystal composed nano/microstructure with a wide range of optical and electro-optical applications

Abstract: POLICRYPS (an acronym of polymer liquid crystal polymer slices) is a nano/microcomposite structure made of slices of almost pure polymer alternated with films of well aligned nematic liquid crystal (NLC). The structure is obtained by irradiating a homogeneous syrup of NLC, monomer and curing agent molecules with an interference pattern of UV/visible light under suitable experimental and geometrical conditions; the spatial periodicity can be easily varied from an almost nanometric (200 nm) to a micrometric (15 µm) scale. Where the effect on an impinging reading light beam is concerned, the POLICRYPS can be utilized either in a transmission or a reflection configuration (depending on the geometry and substrate used) with negligible scattering losses, while the effect of spatial modulation of the refractive index (from polymer to NLC values) can be switched on and off by applying an external electric field of the order of few V µm−1. In this paper, we start by reviewing the general features of the POLICRYPS structure, that is the 'recipe' to fabricate it, along with a chemical–diffusive model that indicates the right physical and chemical conditions to make samples exhibiting good morphological, optical and electro-optical properties. We then show some possible utilizations of POLICRYPS with a light beam impinging almost perpendicularly to the structure: a switchable diffraction grating and a switchable optical phase modulator. Furthermore, we put into evidence that POLICRYPS channels can become an array of mirrorless optical micro-resonators for lasing effects. Finally, we report about utilization of POLICRYPS with a light beam impinging parallel to the structure and perpendicular to the channels, demonstrating that, in this case, the structure becomes a tuneable Bragg filter. Performances exhibited in all above applications put the POLICRYPS structure at the top level of the state of art of application oriented research in optics of liquid crystalline composite materials.

Optical System and Assembly Method

Abstract: An optical system which includes some or all of the following parts: a laser light source which illuminates a spatial light modulator such that optical characteristics are preserved; a stereoscopic display which has a polarization-switching light source; a stereoscopic display which includes two infrared lasers, two optical parametric oscillators, and six second harmonic generators; two light sources processed by two parts of the same spatial light modulator; a method of assembly using an alignment plate to align kinematic rollers on a holding plate; an optical support structure which includes stacked, compartmented layers; a collimated optical beam between an optical parametric oscillator and a second harmonic generator; a laser gain module with two retroreflective mirrors; an optical tap which keeps the monitored beam co-linear; an optical coupler which includes an optical fiber and a rotating diffuser; and an optical fiber that has a core with at least one flat side.

Broadband wavelength-tunable ultrashort pulse source using a Mach-Zehnder modulator and dispersion-flattened dispersion-decreasing fiber

Abstract: The broadband wavelength tunability of femtosecond pulse generation using a Mach-Zehnder-modulator-based flat-comb generator (MZ-FCG) and a dispersion-flattened dispersion-decreasing fiber (DF-DDF) was demonstrated. Near-Fourier-transform-limit picosecond pulses generated from the MZ-FCG were compressed into femtosecond pulses by adiabatic soliton compression. By tuning the wavelength of the input cw light, 200 fs, 10 GHz pulses were generated in the wavelength range of 1,535 to 1,570 nm. Such wide-range wavelength tunability was realized by both the independence of a comb-flattening condition from the inputted wavelength and the dispersion flatness of the DF-DDF.

Characterization of a spatial light modulator and its application in phase retrieval

Abstract: Recently a phase retrieval method using a movable phase plate as modulator has been proposed [Phys. Rev. A75, 043805 (2007)]. This method is applicable to general complex-valued fields and exhibits rapid convergence and high robustness to noise. In this paper, we demonstrate how to use this technique to characterize the phase shifting properties of a liquid-crystal modulator, and in turn we use the characterized modulator as the modulation device in the presented phase retrieval method. The adoption of a dynamic modulator gives a much more robust and flexible setup.

Short‐pulse‐width and high‐peak‐power Q‐switched YVO4/Nd:YVO4 laser with an acousto‐optical modulator

Abstract: A diode-end-pumped AO Q-switched YVO4/ Nd:YVO4 composite crystal laser is demonstrated in this paper. With a comparative simple cavity, the laser can generate short pulse duration and high peak power by optimum design. The shortest pulse width of 9.5 ns and the maximum average output power of 10.12 W are obtained at the repetition rate of 90 kHz, corresponding to an optical conversion efficiency of 37.5%. A 4.2-ns pulse with 2.9-mJ pulse energy and 691.4-kW peak power has been achieved under 20 W incident pump power at 1 kHz.

O-Router: an optical routing framework for low power on-chip silicon nano-photonic integration

Abstract: In this work, we present a new optical routing framework, O-Router for future low-power on-chip optical interconnect integration utilizing silicon compatible nano-photonic devices. We formulate the optical layer routing problem as the minimization of total on-chip optical modulator cost (laser power consumption) with Integer Linear Programming technique under various detection constraints. Key techniques for variable number reduction and routing speed-up are also explored and utilized. O-Router is tested on optical netlist benchmarks modified from top global nets of ISPD98/08 routing benchmarks. O-Router experimental results are compared with conventional minimum spanning tree algorithm, demonstrating an average of over 50% improvement in terms of total on-chip optical layer power reduction.

Method And System For Encoding Multi-Level Pulse Amplitude Modulated Signals Using Integrated Optoelectronic Devices

Abstract: Methods and systems for encoding multi-level pulse amplitude modulated signals using integrated optoelectronics are disclosed and may include generating a multi-level, amplitude-modulated optical signal utilizing an optical modulator driven by two or more electrical input signals. The optical modulator may include optical modulator elements coupled in series and configured into groups. The number of optical modular elements and groups may configure the number of levels in the multi-level amplitude modulated optical signal. Unit drivers may be coupled to each of the groups. The electrical input signals may be synchronized before communicating them to the unit drivers utilizing flip-flops. Phase addition may be synchronized utilizing one or more electrical delay lines. The optical modulator may be integrated on a single substrate, which may include one of: silicon, gallium arsenide, germanium, indium gallium arsenide, polymers, or indium phosphide. The optical modulator may include a Mach-Zehnder interferometer or one or more ring modulators.

Combining multiple laser beams to form high repetition rate, high average power polarized laser beam

Abstract: Two pulsed lasers (14) or sets of lasers propagate beams of pulses (20) having orthogonally related polarization states. A beam combiner (24) combines the orthogonal beams to form a combined beam propagating along a common beam path (16) to intersect an optical modulator (30) that selectively changes the polarization state of selected pulses of either beam to provide a composite beam (18) including similarly polarized pulses from the orthogonal beams. The composite polarized beam has a composite average power and a composite repetition rate that are greater than those provided by either laser. The optical modulator can also selectively control the polarization states of pulses from either laser to pass through or be blocked by a downstream polarizer (32). Additional modulators may facilitate pulse shaping of the pulses. The system is scalable by addition of sets of single lasers or pairs of lasers with beam combiners and modulators.

Spectral Efficiency and Receiver Sensitivity in Direct Detection Optical-OFDM

Abstract: We show by analysis and simulation that by proper biasing of the optical modulator, the intermodulation distortion is minimized. Thus the spectral efficiency can be improved and receiver sensitivity can be exchanged against spectral width.

High-modulation efficiency silicon Mach-Zehnder optical modulator based on carrier depletion in a PN Diode.

Abstract: We present a high phase-shift efficienct Mach-Zehnder silicon optical modulator based on the carrier-depletion effect in a highly-doped PN diode with a small waveguide cross-sectional area. The fabricated modulator show a VπLπ of 1.8V·cm and phase shifter loss of 4.4dB/mm. A device using a 750 μm-long phase-shifter exhibits an eye opening at 12.5Gbps with an extinction ratio of 3 dB. Also, an extinction ratio of 7 dB is achieved at 4 Gbps for a device with a 2 mm-long phase shifter. Further enhancement of the extinction ratio at higher operating speed can be achieved using a travelling-wave electrode design and the optimal doping.

N-modulation displays and related methods

Abstract: A display has a light source, a spatial light modulator and an intermediate spatial light modulator. The display may be a front projection display or a rear-projection display. The spatial light modulator is illuminated with light from a light source. The intermediate spatial light modulator is located in a light path between the light source and the spatial light modulator. The light source may comprise an array of controllable light-emitters. The display may provide a high dynamic range.

Modulation of coherence and polarization using liquid crystal spatial light modulators.

Abstract: We propose a method for modulation of coherence and polarization of electromagnetic fields, employing two crossed zero-twisted nematic liquid crystal spatial light modulators. In contrast to a similar technique analyzed by Shirai and Wolf [J. Opt. Soc. Am A, 21, 1907, (2004)] our method provides a wide range simultaneous modulation of coherence and polarization. The dependence of the obtained results on different definitions of electromagnetic coherence is considered.

Methods for measurement and characterization of interferometric modulators

Abstract: Various methods are described to characterize interferometric modulators or similar devices. Measured voltages across interferometric modulators may be used to characterize transition voltages of the interferometric modulators. Measured currents may be analyzed by integration of measured current to provide an indication of a dynamic response of the interferometric modulator. Frequency analysis may be used to provide an indication of a hysteresis window of the interferometric modulator or mechanical properties of the interferometric modulator. Capacitance may be determined through signal correlation, and spread-spectrum analysis may be used to minimize the effect of noise or interference on measurements of various interferometric modulator parameters.