Showing papers on "Optical modulator published in 2006"

Optical millimeter-wave generation or up-conversion using external modulators

Abstract: We have experimentally compared the performances of optical millimeter-wave generation or up-conversion using external modulators based on different modulation schemes. The generated or up-converted optical millimeter wave using the optical carrier suppression (OCS) modulation scheme shows the highest receiver sensitivity, highest spectral efficiency, and smallest power penalty over long-distance delivery. Moreover, the OCS modulation scheme has a simple configuration and low-frequency bandwidth requirement for both electrical and optical components. Employing an OCS modulation scheme, 16-channel dense wavelength-division multiplexing signals at 2.5-Gb/s per channel have been up-converted to a 40-GHz carrier simultaneously.

Terahertz all-optical modulation in a silicon–polymer hybrid system

Abstract: Although gigahertz-scale free-carrier modulators have been demonstrated in silicon, intensity modulators operating at terahertz speeds have not been reported because of silicon's weak ultrafast nonlinearity. We have demonstrated intensity modulation of light with light in a silicon–polymer waveguide device, based on the all-optical Kerr effect—the ultrafast effect used in four-wave mixing. Direct measurements of time-domain intensity modulation are made at speeds of 10 GHz. We showed experimentally that the mechanism of this modulation is ultrafast through spectral measurements, and that intensity modulation at frequencies in excess of 1 THz can be obtained. By integrating optical polymers through evanescent coupling to silicon waveguides, we greatly increase the effective nonlinearity of the waveguide, allowing operation at continuous-wave power levels compatible with telecommunication systems. These devices are a first step in the development of large-scale integrated ultrafast optical logic in silicon, and are two orders of magnitude faster than previously reported silicon devices.

Tissue imaging system

Abstract: A tissue imaging system (200) for examining the medical condition of tissue (290) has an illumination optical system (205), which comprises a light source (220), having one or more light emitters, beam shaping optics, and polarizing optics. An optical beamsplitter (260) directs illumination light to an imaging sub-system, containing a spatial light modulator array (300). An objective lens (325) images illumination light from the spatial light modulator array to the tissue. An optical detection system (210) images the spatial light modulator to an optical detector array. A controller (360) drives the spatial light modulator to provide time variable arrangements of on-state pixels. The objective lens operates in a nominally telecentric manner relative to both the spatial light modulator and the tissue. The polarizing optics are independently and iteratively rotated to define variable polarization states relative to the tissue. The modulator pixels optically function like pinholes relative to the illumination light and the image light.

Terahertz All-Optical Modulation in a Silicon-Polymer Hybrid System

Abstract: Although Gigahertz-scale free-carrier modulators have been previously demonstrated in silicon, intensity modulators operating at Terahertz speeds have not been reported because of silicon's weak ultrafast optical nonlinearity. We have demonstrated intensity modulation of light with light in a silicon-polymer integrated waveguide device, based on the all-optical Kerr effect - the same ultrafast effect used in four-wave mixing. Direct measurements of time-domain intensity modulation are made at speeds of 10 GHz. We showed experimentally that the ultrafast mechanism of this modulation functions at the optical frequency through spectral measurements, and that intensity modulation at frequencies in excess of 1 THz can be obtained in this device. By integrating optical polymers through evanescent coupling to high-mode-confinement silicon waveguides, we greatly increase the effective nonlinearity of the waveguide for cross-phase modulation. The combination of high mode confinement, multiple integrated optical components, and high nonlinearities produces all-optical ultrafast devices operating at continuous-wave power levels compatible with telecommunication systems. Although far from commercial radio frequency optical modulator standards in terms of extinction, these devices are a first step in development of large-scale integrated ultrafast optical logic in silicon, and are two orders of magnitude faster than previously reported silicon devices.

Quantum-Confined Stark Effect in Ge/SiGe Quantum Wells on Si for Optical Modulators

Abstract: We present observations of quantum confinement and quantum-confined Stark effect (QCSE) electroabsorption in Ge quantum wells with SiGe barriers grown on Si substrates, in good agreement with theoretical calculations. Though Ge is an indirect gap semiconductor, the resulting effects are at least as clear and strong as seen in typical III-V quantum well structures at similar wavelengths. We also demonstrate that the effect can be seen over the C-band around 1.55-mum wavelength in structures heated to 90degC, similar to the operating temperature of silicon electronic chips. The physics of the effects are discussed, including the effects of strain, electron and hole confinement, and exciton binding, and the reasons why the effects should be observable at all in such an indirect gap material. This effect is very promising for practical high-speed, low-power optical modulators fabricated compatible with mainstream silicon electronic integrated circuits

Femtosecond pulse shaping directly in the mid-IR using acousto-optic modulation

Abstract: Pulse shaping directly in the mid-IR is accomplished by using a germanium acousto-optic modulator (Ge AOM) capable of programmable phase and amplitude modulation for IR light between 2 and 18 μm. Shaped waveforms centered at 4.9 μm are demonstrated in both the frequency and the time domains. With a 50% throughput efficiency, the Ge AOM can generate much more intense pulses with higher resolution than can indirect shaping methods. Furthermore, the phase stability of the shaped pulse proved sufficient for cross correlation with unshaped mid-IR pulses. Thus, phase- and amplitude-tailored pulses can now be readily incorporated into phase-sensitive experiments, such as heterodyned 2D IR spectroscopy.

Dynamic manipulation of Bose-Einstein condensates with a spatial light modulator

Abstract: We manipulate a Bose-Einstein condensate using the optical trap created by the diffraction of a laser beam on a fast ferroelectric liquid crystal spatial light modulator. The modulator acts as a phase grating which can generate arbitrary diffraction patterns and be rapidly reconfigured at rates up to 1 kHz to create smooth, time-varying optical potentials. The flexibility of the device is demonstrated with our experimental results for splitting a Bose-Einstein condensate and independently transporting the separate parts of the atomic cloud.

Optical tomography apparatus

Abstract: Low coherence light having a central wavelength λc of 1.1 μm and a full width at half maximum spectrum Δλ of 90 nm is emitted. The low coherence light has wavelength properties suited for the light absorbing properties, the diffusion properties, and the dispersion properties of living tissue. A light dividing means divides the low coherence light into a measuring light beam, which is irradiated onto a measurement target via an optical probe, and a reference light beam that propagates toward an optical path length adjusting means. A multiplexing means multiplexes a reflected light beam, which is the measuring light beam reflected at a predetermined depth of the measurement target, and the reference light beam, to form coherent light. A coherent light detecting means detects the optical intensity of the multiplexed coherent light. An image obtaining means performs image processes, and displays an optical tomographic image on a display apparatus.

All-optical silicon modulators based on carrier injection by two-photon absorption

Abstract: This paper presents a theoretical analysis of a silicon all-optical modulator based on free-carrier injection by two-photon absorption (TPA) in a highly light-confining structure. In spite of the weak optoelectronic properties of silicon, strong light confinement allows high modulation depths in very compact devices requiring low-energy pump pulses. This analysis is applied to 1-5 mum radius silicon ring resonators with the pump pulse coupled on-chip and including in the model the scattering loss due to sidewall roughness originating from the fabrication process. The calculations show that using this scheme, modulation depths greater than 80% can be achieved, with no more than 3 pJ of pump pulse energy, at speeds on the order of 10 GHz

Impact of backreflection on upstream transmission in WDM single-fiber loopback access networks

Abstract: This paper investigates the impact of backreflection lights on upstream transmission in wavelength division multiplexing (WDM) single-fiber loopback access networks, where a WDM light source is located at the central office (CO) and each optical network unit (ONU) includes an optical modulator with optical amplifiers. This study considers backreflection lights from two sources, the continuous wave (CW) light at the CO (Reflection-I) and the modulated signal at the ONU (Reflection-II). It is confirmed, for the first time, that the impact of Reflection-II increases strongly with ONU gain. To estimate the impact of these backreflection lights, a simple intensity noise estimation scheme is presented. This scheme clarifies that the acceptable transmission line losses is 10 dB for 1.25 Gb/s under the optical return loss (ORL) of -32 dB.

Optimally tuned spatial light modulators for digital holography

Abstract: Digital holography and comparative digital holography are applications that require computer-addressable modulators for the optical reconstruction of digital holograms. The quality of the reconstructed holograms depends on the modulator's properties. Therefore a characterization of the modulators is required. We show the result of a modulator characterization and the modulator's influence on the quality of the reconstructed hologram. We then compare qualitatively and quantitatively the optical reconstruction of phase and amplitude holograms by considering their level of detail and their diffraction efficiency.

Optical modulation by carrier depletion in a silicon PIN diode.

Abstract: Experimental results for refractive index variation induced by depletion in a silicon structure integrated in a PIN diode are reported. Thermal effect has been dissociated from the electrical contribution due to carrier density variation induced by a reverse bias voltage. A figure of merit VπLπ of 3.1 V.cm has been obtained at 1.55μm. Numerical simulations show a good agreement between experimental and theoretical index variations.

Waveform-controllable optical pulse generation using an optical pulse synthesizer

Abstract: We have proposed an optical pulse synthesizer comprising of optical modulators and an arrayed waveguide grating. This system can generate arbitrary waveform pulses in combination with a broad-band optical frequency comb. We achieved the generation of the Gaussian pulses with a width of 4.7 ps, double-Gaussian pulses, and rectangular-shaped pulses by arbitrary waveform pulse synthesis, at the high repetition rate of 10 GHz.

2-dimensional image display device, illumination light source and exposure illumination device

Abstract: A 2-dimensional beam scan unit (2) reflects emission beams from a red laser light source (1a), a green laser light source (1b), and a blue laser light source (1c) and scans in the 2-dimensional direction. Diffusion plates (3a, 3b, 3c) diffuses each of light beams scanned in the 2-dimensional direction to introduce them to the respective spatial light modulation elements (5a, 5b, 5c). The respective spatial light modulation elements (5a, 5b, 5c) modulate the respective lights according to the video signals of the respective colors. A dichroic prism (6) multiplexes the lights of the three colors after the modulation and introduce the multiplexed lights to a projection lens (7) so that a color image is displayed on a screen (8). Since the 2-dimensional light emitted from the beam scan unit is diffused to illuminate the spatial light modulation element, it is possible to change the optical axis of the beam emitted from the light diffusion member for irradiating the spatial light modulation element from time to time, there by effectively suppressing the speckle noise.

Polarization sensitive Fourier domain optical coherence tomography with continuous polarization modulation

Abstract: Polarization sensitive Fourier domain optical coherence tomography (PS-FD-OCT) using fiber components with continuous polarization modulation is demonstrated. The incident polarized light is modulated by electro-optic modulator (EO modulator) synchronized with lateral B-scanning. By the incident polarization modulation and the polarization sensitive spectrometer, the depth-resolved Jones matrix image of biological sample can be measured. This method uses both polarization modulation method and Fourier transform method. In this paper, the algorithm is described and the phase retardation image of chicken breast muscle is measured.

Phase-Noise Analysis of Optically Generated Millimeter-Wave Signals With External Optical Modulation Techniques

Abstract: In this paper, the phase-noise performance of optically generated electrical signals based on external optical modulation techniques is investigated theoretically and experimentally. Mathematical models are developed to represent perturbations on the transmitted optical signal caused by the phase fluctuations of the electrical drive signal applied to the external modulator and the optical carrier that feeds the external modulator. Closed-form expressions of the power spectral density (PSD) for the electrical signals, generated both locally and remotely, are derived. The calculated PSD of the locally generated electrical signal indicates that its phase noise is determined only by the phase noise of the electrical drive signal. The PSD of the remotely generated signal shows that its spectral quality is also affected by the chromatic dispersion of the fiber and the optical carrier linewidth. An experimental setup that can generate a millimeter-wave (mm-wave) signal, continuously tunable from 32 to 60 GHz using an electrical drive signal tunable from 8 to 15 GHz, is built. The spectra of the generated millimeter-wave signal are measured for both locally and remotely generated electrical signals, with optical carriers of different linewidths. The theoretical results agree with the experimental measurements

Surface and subsurface detection sensor

Abstract: A sensor comprises an optical modulator that generates a modulation signal, an interferometer that mixes an acoustic signal evoked by a pulsed laser with the modulation signal to down-convert the acoustic signal to lower frequencies, and a photodetector that detects the down-converted signal.

Projector and optical device

Abstract: To provide a projector or the like, which use a solid-state light-emitting element as light source and which provides a bright, stable, and uniform projection image, the present invention includes: a light source to emit light; a spatial light modulator to modulate the light from the light source in accordance with an image signal; and a projector lens to project the light modulated by the spatial light modulator. The spatial light modulator is a tilt mirror device including a movable mirror element that reflects the light from the light source in the direction of the projector lens or in the direction other than that of the projector lens. The invention may further include a light-intensity measuring section provided in an imaging position of the light source or in the vicinity of the imaging position to measure the light intensity of the light reflected in the direction other than that of the projector lens; and a light-source controller to control the light source in accordance with the signal from the light-intensity measuring section.

Optical transmitter apparatus

Abstract: An optical DQPSK modulator comprises a pair of phase modulators. Each of the pair of the phase modulators is provided with first and second driving signals. The first and second driving signals are amplified by first and second amplifiers, respectively. An RZ intensity modulator generates an optical RZ-DQPSK signal from an optical DQPSK signal output from the optical DQPSK modulator. A photodetector generates a monitor signal from the optical RZ-DQPSK signal. A gain adjuster unit adjusts the gains of the first and second amplifiers so as to minimize the power of the monitor signal.

Optoelectronic oscillator using a LiNbO3 phase modulator for self-oscillating frequency comb generation

Abstract: Optical frequency comb generation by using a novel optoelectronic oscillator (OEO) is proposed and demonstrated with the emphasis placed on self-oscillating operation. In the OEO, a wideband LiNbO3 phase modulator is driven with a large-amplitude radio-frequency (RF) feedback signal to generate a deeply phase-modulated light wave; accordingly, an optical frequency comb with a bandwidth greater than the RF signal is generated by self-oscillation. Although it generates multifrequency components, the OEO exhibits characteristics of a single-mode oscillator. Its operation is stable and self-starting. An optical frequency comb with a 120 GHz bandwidth and 9.95 GHz frequency spacing was successfully generated by self-oscillation at a single frequency.

Analysis of ring resonator-based traveling-wave modulators

Abstract: We analyze ring resonator-based traveling-wave modulators that show high modulation efficiency at frequencies around multiples of the free spectral range. The modulators have better tolerance for the optical/microwave velocity mismatch and the loss of the microwave transmission line than traveling-wave Mach-Zehnder modulators.

Observation of quantum entanglement using spatial light modulators.

Abstract: We use spatial light modulators to observe the quantum entanglement of down-converted photon pairs. Acting as diffractive optical elements within one of the beams, they can be reconfigured in real time to set the spatial profile of the measured mode. Such configurations are highly applicable to the measurement of orbital angular momentum states or other spatial modes, such as those associated with quantum imaging.

Advanced LiNbO/sub 3/ optical modulators for broadband optical communications

Abstract: This paper describes advanced lithium niobate (LiNbO3) optical modulators for broadband optical communications. It includes 40-Gb/s ultralow voltage modulators, compact modulators and modulators for frequency comb generator and short pulse generation

Laser image display, and optical integrator and laser light source package used in such laser image display

Abstract: A laser image display comprising a laser light source emitting laser light, a beam deflector element for receiving laser light and deflecting its advancing direction, a beam deflecting element control section for controlling the degree of deflection performed by the beam deflector element, an optical integrator for receiving and guiding the deflected laser light to output from its outputting end face, a false surface light source element for scattering the deflected laser light, and a modulation element for receiving and modulating the laser light scattered by the false surface light source element.

High-speed optical DQPSK and FSK modulation using integrated Mach-Zehnder interferometers.

Abstract: We investigated an integrated optical modulator consisting of two Mach-Zehnder interferometers. The modulator can generate optical signals in various types of modulation formats, which have advantages for long-haul transmission, optical labeling, etc. By using a fabricated versatile optical modulator having traveling-wave electrodes designed for high-speed signals, we demonstrated generation of optical 40Gb/s frequency-shift-keying signals, which can be demodulated by an optical filter. 80Gb/s optical differential quadrature-shift-keying modulation was also demonstrated, where 40Gb/s in-phase and quadrature data were, simultaneously, fed to the modulator.

Diffraction-based determination of the phase modulation for general spatial light modulators

Abstract: We describe a characterization method based on diffraction for obtaining the phase response of spatial light modulators (SLMs), which in general exhibit both amplitude and phase modulation. Compared with the conventional interferometer-based approach, the method is characterized by a simple setup that enables in situ measurements, allows for substantial mechanical vibration, and permits the use of a light source with a fairly low temporal coherence. The phase determination is possible even for a SLM with a full amplitude modulation depth, i.e., even if there are nulls in the amplitude transmission characteristic of the SLM. The method successfully determines phase modulation values in the full 2pi rad range with high accuracy. The experimental work includes comparisons with interferometer measurements as well as a SLM characterization with a light-emitting diode (LED).

Cold atom guidance using a binary spatial light modulator.

Abstract: We have guided cold (85)Rb atoms in a blue-detuned, high-order hollow laser beam generated by a binary spatial light modulator. The binary holograms written to the modulator produce smooth hollow laser beams with steep intensity walls that can be updated with a 1.6 kHz refresh rate. We analyze the guiding laser beams numerically and experimentally, and show that the atoms are exposed to an average intensity that is ~2% of the maximum intensity of the guide at a laser detuning of 1 GHz and 2 mW of optical power.

High Speed Metal–Oxide–Semiconductor Capacitor-Based Silicon Optical Modulators

Abstract: Silicon photonics has recently attracted a great deal of attention because it offers an opportunity for low cost opto-electronic solutions for applications ranging from telecommunications down to chip-to-chip interconnect. One area of silicon photonics research that has seen an exceptional increase in activity and advancement is high speed silicon optical modulation. Within three years, modulation bandwidth has increased nearly three orders of magnitude from MHz range to 10 GHz range. This paper reviews two high speed silicon optical modulators with GHz bandwidth. It discusses in detail their design, performance, and limitations; and it outlines a path that can enable realization of further device improvements.