Showing papers on "Optical modulator published in 1993"

InGaAs/InGaAsP MQW electroabsorption modulator integrated with a DFB laser fabricated by band-gap energy control selective area MOCVD

Abstract: The fabrication and basic characteristics of a InGaAs/InGaAsP multi-quantum-well (MQW) electroabsorption modulator with a novel structure integrated with a distributed-feedback (DFB) laser are presented. A fundamental study was performed on the applicability of the InGaAs/InGaAsP MQW structure to an electroabsorption-type modulator. Efficient attenuation small hole pileup and small chirp characteristics of a discrete modulator based on this MQW structure were demonstrated experimentally. A study of the controllability of in-plane band-gap energy by the use of selective-area metal-organic chemical vapor deposition (MOCVD) was also demonstrated. The modulator was monolithically integrated with a MQW DFB laser of the same material. Using a low-capacitance semi-insulating buried heterostructure, over 14 GHz modulation under high-light-output operations up to +10 dBm was achieved. Modulation at 10 Gb/s with a modulation voltage swing of only 1 V/sub pp/ demonstrates the potential value of this system for 1.55- mu m lightwave communications. >

Microwave-optical mixing in LiNbO/sub 3/ modulators

Abstract: An investigation study of microwave-optical mixing in different configurations of LiNbO/sub 3/ Mach-Zehnder interferometric modulators is presented. In each case, models that describe mixer performance are developed and are shown to be in good agreement with measurements. For antenna remoting applications, a technique to down-convert RF signals is demonstrated by cascading in series a pair of Mach-Zehnder interferometric modulators. In general, it is shown that by virtue of their truly broadband characteristics, interferometric modulators can also by employed as microwave mixers at frequencies up to 40 GHz. >

Smart spatial light modulators using liquid crystals on silicon

Abstract: Smart pixels are discussed in terms of the following neurally inspired functions: memory, sensors, intrapixel circuitry, interpixel communication, and optical outputs. The types of liquid crystals and electronic circuits used in VLSI/liquid crystal arrays, and their electrooptic properties are reviewed. Examples of electrically addressed and optically addressed liquid crystal smart pixels, and results from a 128*128 VLSI/FLC SLM are presented. This device has a response time of 150 mu s, a contrast ratio of 8:1 measured on a row containing more than 50 pixels, and a frame rate of 4.7 kHz. Improvements of these devices are discussed in terms of what the silicon technology can yield in the future. A few examples in which the liquid crystal on silicon technology has been applied are presented. >

Liquid-crystal phase modulator for unpolarized light.

Abstract: A simple method for phase modulating unpolarized light with a double pass through a nematic liquid crystal retarder is described.

10 Gbit/s, 1.56 mu m multiquantum well InP/InGaAsP Mach-Zehnder optical modulator

Abstract: 10 Gbit/s modulation using a III-V semiconductor Mach-Zehnder interferometer is reported for the first time. The modulator has a -3 dB bandwidth in excess of 15 GHz and is operated in a push-pull drive configuration with only 2 V peak to peak. 10 Gbit/s nonreturn to zero format eye diagrams with an extinction ratio>10 dB are demonstrated.

Transform-limited optical pulse generation up to 20-GHz repetition rate by a sinusoidally driven InGaAsP electroabsorption modulator

Abstract: The authors propose and demonstrate a simple technique for generating a transform-limited optical short pulse with variable repetition rates by using a sinusoidally driven InGaAsP electroabsorption modulator without any optical resonators. Using the pulse compression effect due to nonlinear attenuation characteristics of the modulator, a transform-limited optical pulse can be generated just with sinusoidal modulation. Theoretical calculations and experimental results show that the pulse shape is very close to the sech/sup 2/ shape, and the pulse width can be easily varied by varying the bias and modulation voltages. Transform-limited optical pulse generation with a minimum pulse width of 11 ps was achieved up to 20-GHz repetition rate. The time-bandwidth product was as small as 0.32. >

Batch fabrication and operation of GaAs-Al/sub x/Ga/sub 1-x/As field-effect transistor-self-electrooptic effect device (FET-SEED) smart pixel arrays

Abstract: The structure, processing, and performance of arrays of integrated field-effect transistor-self-electrooptic effects devices (FET-SEEDs) consisting of doped-channel field-effect transistors, multiple quantum-well (MQW) modulators, and p-i-n MQW detectors are discussed. The performance of the FETs and SEEDs such as g/sub m/ and contrast, is equivalent to that obtained when they are made separately. Typical values are g/sub m/=80 mS/mm and contrast of 3. The largest arrays contain 128 circuits. The circuits operate at speeds as fast as 500 Mb/s, with optical input switching energy of approximately=400 fJ. At 170 Mb/s, the required optical input switching energy is approximately=70 fJ. This optical energy is at least a factor of 20 less than for symmetric SEEDs (S-SEEDs) with the same optical window sizes. Hence, FET-SEEDs provide superior performance compared to conventional S-SEEDs. >

20 Gbit/s operation of a high-efficiency InGaAsP/InGaAsP MQW electroabsorption modulator with 1.2-V drive voltage

Abstract: The authors have fabricated a ridge waveguide electroabsorption modulator based on the quantum-confined Stark effect in InGaAsP/InGaAsP multiple quantum wells. The drive voltage for 12-dB extinction ratio is 1.2 V, and the frequency response is flat within 2 dB from DC to 20 GHz. Operation at 20 Gb/s is reported. Extensive data concerning the parasitic phase modulation (chirping) are obtained as a function of applied bias acid operating wavelength. >

Spatial light modulator system

Abstract: A display projection apparatus comprising a light source, means for splitting light from the source into different color component beams, and a plurality of deformable mirror device spatial light modulators, characterised in that the light paths to said splitting means and modulators are provided as a single prism assembly to which said modulators are mounted.

Optical intensity modulation in a vertically stacked coupler incorporating electro‐optic polymer

Abstract: A vertically stacked directional coupler incorporating electro‐optic poled polymer was fabricated by spin coating, photolithography, and reactive ion etching processes, based on the fabrication technique used for polymeric single‐mode channel waveguides. Vertically coupled operation at 1.3 μm have been achieved between two stacked channels which were kept 3.5–5 μm apart by a narrow cladding layer. The intensity modulation has been clearly demonstrated in the coupler with electrodes when a voltage is applied at 10 kHz between them.

Integrated optical receiver/transmitter

Abstract: An integrated optical receiver/transmitter (transceiver) 8 has continuous wave (cw) light 16 that enters a Mach-Zehnder optical modulator 10 controlled by a modulator control circuit 12 that provides modulated light 30 along a waveguide 32 to an optical coupler 34 which couples a predetermined portion of the light 30 to a waveguide 44 as light 42 which then exits the transceiver from a port 46. Receive light 90 is accepted at the port 46 and travels along the waveguide 44 to the coupler 34 which couples a predetermined amount of the light 90 to a waveguide 70 as light 92 which is detected by a waveguide-integrated photodetector 72. The photodetector 72 provides a current signal on a line 74 to a receiver circuit 76 which provides a voltage signal indicative of the light 92. Alternatively, the coupler may be passive, thereby not requiring the coupler control circuit, or no coupler at all may be employed and two fibers used for communications with the transceiver 8.

Highly efficient 40-GHz bandwidth Ti:LiNbO/sub 3/ optical modulator employing ridge structure

Abstract: The design and fabrication of a Ti:LiNbO/sub 3/ optical modulator employing a ridge structure with a shielding plane are described. The ridge structure offers a relatively low microwave propagation loss and large interaction between the microwave and optical wave under the condition of a 50 Omega characteristic impedance system, resulting in a large modulation bandwidth and low driving voltage. As a result, a 3-dB optical bandwidth of 40 GHz with a driving voltage of 3.6 V is achieved at 1.5 mu m. >

Optical intensity and phase modulators in an optical transmitter apparatus

Abstract: An optical transmitter apparatus comprises a light source for optical signal transmission, an intensity modulator, a transmit signal generator and a signal generator. A transmit signal to be transmitted is supplied from the transmit signal generator to the intensity modulator, while a signal generated by the signal generator is supplied to the phase modulator. A light beam emitted from the light source passes through the intensity modulator and the phase modulator to be subsequently sent out as an optical signal for transmission with intensity thereof being modulated upon passing through the intensity modulator while spectrum thereof being spread by phase modulation which the optical signal undergoes upon passing through the phase modulator.

Multichannel optical waveguide page scanner with individually addressable electro-optic modulators

Abstract: A mulitchannel optical waveguide page scanner has a diode laser and a primary optical channel waveguide. Light is coupled from the diode into the primary channel waveguide. Multiple secondary side channels each have a thin-film electro-optic waveguide modulator. A series of T-branch connectors distribute light from the primary channel to the secondary side channels. Each of the electro-optic waveguide modulators is addressable individually.

Intermodulation distortion in high dynamic range microwave fiber-optic links with linearized modulators

Abstract: Linearization of integrated optic intensity modulators significantly reduces the two-tone intermodulation distortion. The resulting intermodulation distortion produced by these modulators then varies as the input power to the fifth-order link system, the overall intermodulation product is a combination of third-order and higher-order terms. The authors determine the dynamic range of a cascaded microwave network consisting of a preamplifier, a high-dynamic-range fiber-optic link with a highly linear modulator, and a postamplifier. An expression is found that relates the intermodulation power at the output to the relative suppression from the signal level. As an example, a hypothetical 10-GHz low-distortion fiber-optic link that has a dynamic range of 125 dB in a bandwidth of 1 Hz is cascaded with various preamplifiers, and it is shown that the dynamic range of the system is reduced by as much as 20 dB, depending on the third-order intercept of the amplifier.

Chemically enhanced bacteriorhodopsin thin film spatial light modulator

Abstract: An optically addressed spatial light modulator based on a thin film of chemically enhanced bacteriorhodopsin is demonstrated. Incoherent-to-coherent light conversion is achieved by exploitation of both the large shift in absorption maxima accompanying the bR → M phototransformation and the extended M-intermediate lifetime resulting from the chemical enhancement of the protein at high pH. The device exhibits a linear dynamic range of 120:1 at 514 nm and a resolution of ~100 line pairs/mm.

Optical pulse generator

Abstract: The short optical pulse generator is provided with a semiconductor laser which oscillates continuously at a single wavelength, a semiconductor electro-absorption type optical modulator which performs the intensity modulation of the output light from the laser, and a sinusoidal voltage generator and a DC voltage generator for driving the electro-absorption type optical modulator A DC voltage is applied to the electro-absorption type optical modulator so that the output light from the laser is sufficiently extinguished By applying a sinusoidal voltage to the optical modulator, short optical pulses are generated

Strongly non-linear optical ferroelectric liquid crystals for frequency doubling

Abstract: From our research for novel non-linear optical (NLO) materials for frequency doublers and optical modulators we report on new ferroelectric liquid crystals, which for the first time, exhibit second order NLO coefficients (for example d 22 = 5 pm V−1, which are comparable to those of state of the art inorganic NLO materials. The novel compounds contain 5-amino-2-nitrophenyl groups attached close to the chiral centres. The switching behaviour of the new compounds, their spontaneous polarization, as well as their frequency doubling of Nd:YAG laser pulses in the S*c and in the glass state, are reported. Moreover their waveguiding properties are presented.

All-optical spatial light modulator with surface plasmon resonance.

Abstract: An all-optical photoaddressed spatial light modulator has been demonstrated. The device consists of a prism of high refractive index coated with a thin silver film and a dye-doped polymer film. The writing beam photothermally changes the distribution of the refractive index of the dye-doped film. The reading beam, of a different wavelength, which is incident upon the prism near an angle for surface plasmon resonance at the metal–dye-doped-film interface, undergoes modulation on reflection. Both positive and negative modulation is possible when suitable angles of incidence are chosen for the reading beam. We obtained a resolution of 15 line pairs/mm, an ∼10-s rise time, a 2-s fall time.

Wave-front control using liquid-crystal devices.

Abstract: We report on complete wave-front control with amplitude- and phase-modulation liquid-crystal devices (LCD’s) A twisted nematic device is used for amplitude modulation, and an electrically controlled birefringent device is used for phase modulation Because the LCD’s are optically coupled with afocal optics and are driven by individual LCD driver circuits, the amplitude and the phase can be controlled two dimensionally and independently Complex amplitude data are calculated, and on-axis computer-generated holograms are directly recorded Furthermore, we discuss LCD performance requirements for high-quality reconstruction

Optical pickup apparatus and method for adjusting optical axis thereof

Abstract: A method for the optical axis of an optical pickup apparatus includes the step of adjusting the optical axis of a beam expander for enlarging the diameter of a light beam outgoing from a laser light beam radiating device into coincidence with the optical axis of the light beam radiated from the laser light beam radiating device. The laser light beam radiating device includes a non-linear optical crystal element and is adapted for radiating a second harmonic laser light beam. The method also includes the step of mounting the beam expander having adjusted its optical axis, and a step of adjusting, with the beam expander mounted on the laser light radiating device, the optical axis of an optical system converging the laser light beam radiated from the laser light beam radiating device so that the optical axis is brought into coincidence with the optical axis of the laser beam radiated from the laser light beam radiating device.

Optical clock recovery

Abstract: A system for recovering a clock from an optically encoded signal uses a mode-locked laser. A modulator is connected in common with the laser cavity of the laser and a transmission path applies the input optically encoded signal to the modulator. The modulator in response to the optically encoded signal modulates the phase and/or amplitude of light in the laser cavity thereby locking the phase and frequency of an output pulse stream to the timing wave of the optically encoded signal. In a preferred example, the modulator is a non-linear optical modulator used for cross-phase modulation (XPM) of the light in the laser cavity.

Strained-InGaAsP MQW electroabsorption modulator integrated DFB laser

Abstract: The monolithic integration of a strained-InGaAsP MQW electroabsorption modulator and a DFB laser using only two-step MOVPE growth is described. The extinction ratio is 20 dB with a low-driving voltage of 1.4 V for an optical power density of 102 kW/cm2.

Time‐lens producing 1.9 ps optical pulses

Abstract: A resonant microwave optical phase modulator in LiNbO3 with multiple passes, based on an off‐axis path in a stable optical resonator, is demonstrated as a time‐lens. With 1 W of cw microwave power at 5.2 GHz, 45 ps pulses at 1.06 μm were temporally focused to 6.7 ps (FWHM). Increasing the drive power to 13 W, at 10% duty cycle, produced 1.9 ps pulses. The aperture of the time‐lens is about 31 ps. This is the first demonstration of a useful time‐lens.

Application of phase conjugate optics to optical systems

Abstract: PROBLEM TO BE SOLVED: To apply phase conjugate optics to various fields such as optical communication, optical measurement, optical information processing and others and to provide a new apparatus applicable for the above usage. SOLUTION: The optical modulator of the optics is equipped with: a light source; an excitation light source; a nonlinear optical medium; a probe light/excitation light supply means to supply probe light from a probe light source together with the excitation light from the excitation light source to a nonlinear optical medium; and a modulating means operationally connected to the excitation light source and modulating the excitation light according to the information signal. Modulated phase conjugate light exits from the nonlinear optical medium. COPYRIGHT: (C)2004,JPO

Simulation and analysis of silicon electro‐optic modulators utilizing the carrier‐dispersion effect and impact‐ionization mechanism

Abstract: A new type of Si guided‐wave electro‐optic modulator is proposed and analyzed. The modulator makes use of the impact‐ionization mechanism for carrier generation, and the carrier‐dispersion effect for electro‐optic conversion. Both electrical and wave propagation properties of the modulator were examined by a two‐dimensional device simulator and a three‐dimensional waveguide simulator, respectively. Numerical estimates of phase modulation due to refractive‐index change and intensity modulation due to optical absorption and radiation loss were obtained. One of important features of the prospected modulator is speed. The simulated turn‐on and turn‐off time of the modulator was less than 1 ns. GHz modulation is, therefore, possible for this class of modulators with device structure and doping profiles optimized for fiber coupling.

Quadrature amplitude modulator including a digital amplitude modulator as a component thereof

Abstract: The invention provides various embodiments of a balanced modulator, each of which involves one or more individual amplitude modulators which, individually, do not provide suppressed-carrier outputs. A first embodiment employs a single amplitude modulator whose carrier input is selectively delayed by a half wavelength, depending on the polarity of the input modulating signal, and whose amplitude input receives the absolute value of the modulating input signal. A second embodiment involves summation of the outputs of two amplitude modulators whose carrier inputs are responsive to carrier signals offset by a half carrier wavelength and whose modulating signal inputs are responsive only to signals of respectively opposite polarity. Further, quadrature amplitude modulation (QAM) modulators are provided by a combination of the above-described modulators. Moreover, another embodiment of the QAM modulator involves use of an amplitude modulator operating on polar coordinate representations of the input modulating signal. The invention is useful in single sideband modulation, up-conversion, down-conversion, synchronous detection, product detection, and the like.

Integrated optical package for coupling optical fibers to devices with asymmetric light beams

Abstract: This invention embodies an integrated optical package including an optical component having an asymmetric modal output, and a lens integrated with the component for coupling to another component having a large modal area. The coupling is achieved by the use a tapered waveguide section (12). This section may be referred to as Polymeric Elongated Waveguide Emulating (PEWE) lens. In the exemplary embodiment the first optical component is a modulator (11), and the other optical component is an optical fiber (13). A facet of the modulator is etched by reactive ion etching (RIE) which allows integration of the PEWE lens on a common substrate (14). The lens is manufactured using a polymer film on a dielectric cladding layer. The fabrication relies on the remelt and reflow properties of polymer films to provide a smooth adiabatic mode contraction from a circular (optical fiber) mode (≈6µm in diameter) to a semiconductor mode (≈1µm) over a length of 250 µm. The PEWE lens permits coupling with an insertion loss of 0.5 dB and 80 percent coupling efficiency, even though the lens is butt-coupled to a fiber without any external lens. The PEWE lens allows the realization of better than 80 percent direct fiber butt-coupling efficiencies to semiconductor lasers, photodetectors, optical modulators, switches and amplifiers with a simultaneous order of magnitude relaxation of the alignment tolerances typically needed for the coupling of semiconductor devices with single-mode fibers.

Theoretical design optimization of multiple-quantum-well electroabsorption waveguide modulators

Abstract: Optical on-off modulators require low insertion loss, high contrast ratio (CR), small drive power and large bandwidth or bit-rate. A systematic approach to optimize the total performance of these modulators based on the quantum-confined Stark effect is presented here. The approach consists of minimizing the power/bandwidth ratio while satisfying a given CR and insertion loss. Our design consists of a large-core multimode passive waveguide with a thin buried active layer. The passive waveguide is designed to yield a high coupling efficiency to conventional single-mode fibers. The quantum well material structure is designed to maximize Delta alpha / Delta F/sup 2/, while maintaining a sufficiently large Delta alpha / alpha /sub 0/, where Delta alpha is the absorption change, alpha /sub 0/ is the residual absorption at zero bias, and Delta F is the swing of the applied electric field. Our theoretical model shows that i) wider quantum wells give larger Delta alpha / Delta F/sup 2/, and ii) the bandwidth/power ratio as high as 4 GHz/mW can be achieved simultaneously with small insertion loss, For example, with a drive voltage of 3 V, an RC limited bandwidth as high as 60 GHz is predicted, while a contrast ratio of 20 dB and a total insertion loss of 4.5 dB may also be obtained. >

Electroabsorption of InAsP/InP strained multiple quantum wells for 1.3 μm waveguide modulators

Abstract: We report the electroabsorption property of InAsP/InP strained multiple quantum wells (MQWs), grown by gas‐source molecular beam epitaxy, for 1.3 μm modulator applications. Very sharp excitonic absorption at room temperature was observed. Electroabsorption measurements performed for a ring‐shaped p‐i‐n diode, consisting of 10‐period InAs0.41P0.59(100 A)/InP(150 A) strained MQWs, reveal a significant red shift of the absorption peak with increasing reverse biases due to the quantum‐confined Stark effect. This large energy shift (e.g., ∼18 meV at an external field of 57 kV/cm) is well accounted for in the ‘‘effective well‐width’’ model. The change of the absorption coefficient at a 22 meV detuning is as large as 3510 cm−1 with a small residual absorption, which can be very useful for 1.3 μm waveguide modulators.