Showing papers on "Optical modulator published in 1986"
TL;DR: In this paper, the electrooptic and dielectric properties of potassium titanyl phosphate (KTP) have been measured from dc to 1 GHz and compared with other electro-optic materials.
Abstract: The electro‐optic and dielectric properties of potassium titanyl phosphate (KTP) have been measured from dc to 1 GHz and are compared with other electro‐optic materials. KTP is shown to possess a combination of properties that make it unique for a variety of electro‐optic modulator applications.
284 citations
TL;DR: In this article, the authors describe the monolithic integration of a laser diode and an optical waveguide modulator that have the same GaAs/AlGaAs quantum well double heterostructure grown on the same substrate.
Abstract: This letter describes the monolithic integration of a laser diode and an optical waveguide modulator that have the same GaAs/AlGaAs quantum well double heterostructure grown on the same substrate. The intensity of the light emitted from the laser diode is modulated by the modulator, utilizing the effect of an electric field on exciton absorption. The absorption loss coefficient of the modulator waveguide with no applied voltage was estimated to be 60 cm−1. This value is much smaller than the previously reported corresponding value of a veguide having a conventional GaAs double heterostructure. The modulation depth achieved was 7 dB for a driving voltage of 2.3 V; the cut‐off modulation frequency was 0.88 GHz. A prospect for improving these characteristics is also presented.
79 citations
TL;DR: An experimental correlator using the Light-Mod magnetooptic spatial light modulator (SLM) devices for real-time modulation of both input images and Fourier plane filters has been constructed and demonstrated and is in good agreement with computer simulations based on the FFT.
Abstract: An experimental correlator using the Light-Mod magnetooptic spatial light modulator (SLM) devices for real-time modulation of both input images and Fourier plane filters has been constructed and demonstrated. Results are in good agreement with computer simulations based on the FFT. The experiment, results and comparison with theory are briefly described here. The optical system is diagrammed in Fig. 1. A five-lens design was used to reduce system length by a factor of ~ 4 compared with that required for a classical two-lens coherent correlator configuration. The Light-Mod devices were 48 X 48-element arrays. Polarizers following each Light-Mod, necessary for proper operation, are not shown. Proper scal ing of the Fourier transform pattern on the second (filter) device required an effective focal length of 1219 mm for the first transform lens determined by the wavelength (632.8 nm) and Light-Mod element spacing (0.127 mm). The first (input) Light-Mod was operated in the binary amplitude modulation (on-off) mode, while the second (filter) device was operated as a binary (0-180°) phase modulator. Thus the filter device comprised an electrically programmable binary phase-only filter (BPOF). Properties of this type filter have been reported recently. Both devices are con trolled by an Apple He computer, and filters or input images can be introduced into the system in a few milliseconds each. A 128X 128-point FFT model was used to predict results and to generate BPOFs to drive the filter Light-Mod. To generate filters, 128 X 128 transforms were averaged over 3 X 3 subareas, and the BPOF phase value was set according to the sign of the real part of the transform, as previously reported. Figure 2(a) shows the input pattern used in the experiments. Figure 2(b) shows predicted correlation re sults using the input of Fig. 2(a) and a BPOF calculated for the X pattern. Figure 3 shows the experimental correlation result ob tained with the input and filter patterns corresponding to the computer model result of Fig. 2(b). The figure shows video monitor photos taken at two different brightness set tings while the correlation pattern was read out with a cam era tube. Excellent agreement with theory is apparent. Figure 3(b), taken with the lower brightness setting, indi cates the two brightest peaks corresponding to the position of the two X characters in the input plane. Figure 3(a) shows the theoretically predicted cross-correlation structure (between 0 inputs and X filter) at the lower right position. Absence of such a structure at the upper left position is attributed to nonuniform input plane illumination. Experi mental results also were likely degraded by the defects pres ent in both Light-Mods comprising approximately two lines which were permanently set in one magnetic state in each device. The results reported here demonstrate the potential for useful real-time correlation systems based on the use of Fig. 1. Diagram of Light-Mod correlator system.
73 citations
TL;DR: In this article, a simple architecture for bidirectional optical fiber transmission using an MQW device as both modulator and photodetector was proposed, which achieved transmission of 50 Mbit/s and 600 M bit/s in both directions over one 3.34 km-long single-mode fiber at 860 nm wavelength.
Abstract: We demonstrate a simple architecture for bidirectional optical fibre transmission which uses an MQW device as both modulator and photodetector. We achieved transmission of 50 Mbit/s and 600 Mbit/s in both directions over one 3.34 km-long single-mode fibre at 860 nm wavelength. Coherent Rayleigh interference was found to be a limiting factor in single-source bidirectional systems.
67 citations
TL;DR: In this article, the first successful monolithic integration of InGaAsP/InP distributed feedback (DFB) lasers and MQW optical modulators using LPE (liquid phase epitaxy)/MBE (modlecular beam epitaxy) hybrid growth was reported.
Abstract: The first successful monolithic integration of InGaAsP/InP distributed feedback (DFB) lasers and InGaAs/InAlAs multiple quantum well (MQW) optical modulators using LPE (liquid phase epitaxy)/MBE (modlecular beam epitaxy) hybrid growth reported. A 14% light output modulation is observed in this integrated device.
66 citations
TL;DR: The GaAs/AlGaAs ridge waveguide phase modulators were investigated in this article, where the authors showed that the speed of the phase modulator is only limited by the RC time constant.
Abstract: The characteristics of novel reverse‐biased waveguide phase modulators are reported. These devices, which use the translation of a depletion edge, have provided the highest efficiency figure of merit (56 °/Vmm) ever reported for a reverse‐biased device. Furthermore, the speed of the device is only limited by the RC time constant. The investigated devices were GaAs/AlGaAs ridge waveguide modulators, a geometry which is well suited for integrated optoelectronics.
62 citations
TL;DR: In this paper, a Niobate traveling-wave interferometric light modulator/switch with a groove excavated at the electrode gap has been fabricated and tested at microwave frequency.
Abstract: A Ti dffused lithium niobate traveling-wave interferometric light modulator/switch with a groove excavated at the electrode gap has been fabricated and tested at microwave frequency. The groove suppresses the undesirable light coupling between the two parallel waveguides for the phase shifting section so that the drive voltage is decreased by reducing the separation of the parallel waveguides, or of the electrodes. In addition, the groove decreases the effective index for the modulating wave to reduce the velocity mismatch between light wave and microwave so that the bandwidth is broadened. The modulation experiment was carried out from dc to 15 GHz at 633 nm light wavelength. For the modulator with the electrodes 6 mm long and 10 μm apart, the half-wave or switching voltage was 3 V, the extinction ratio was 18 dB, the 3 dB bandwidth was 12 GHz and a P/\Delta f of 1.5 mW/GHz was obtained.
61 citations
24 Feb 1986
TL;DR: In this article, a phase-modulated (PM) optical wave with no amplitude modulation propagating in an optical fiber will be adversely affected by group velocity dispersion in the fiber, which causes amplitude modulation of the received signal which in turn leads to a penalty in coherent transmission systems.
Abstract: Coherent detection in lightwave transmission systems can improve receiver sensitivities by 10-20dB over direct detection sensitivities. In phase-shift-keyed (PSK) systems the information is impressed on the phase of the optical field while the amplitude is held nominally constant. A phase-modulated (PM) optical wave with no amplitude modulation propagating in an optical fiber will be adversely affected by group velocity dispersion in the fiber. In particular, the various frequency components of the PM wave will arrive at the end of the fiber at slightly different times. This causes amplitude modulation of the received signal which in turn leads to a penalty in coherent transmission systems.[1,2]
56 citations
TL;DR: In this paper, an active Q switching in a GaAs/AlGaAs multiquantum well laser with an intracavity electroabsorption monolithic loss modulator is demonstrated.
Abstract: Active Q switching in a GaAs/AlGaAs multiquantum well laser with an intracavity electroabsorption monolithic loss modulator is demonstrated. In this device, an efficient loss modulation is achieved through the quantum confined Stark effect in a modulator section and the enhanced carrier induced band shrinkage effect in an optical amplifier section. It is found that a picosecond pulse as narrow as 18.6 ps full width at half-maximum is generated and a high repetition rate of more than 3 GHz is obtained.
54 citations
Patent•
30 Sep 1986
TL;DR: In this paper, a fiber optic modulator was designed to steer the radiation beam of a phased array antenna 10 using photomixing at the output of a single-mode fiber optic interferometer, where the phase of the electrical signal is shifted over several cycles in direct proportion to a voltage applied to an optical modulator.
Abstract: A fiber optic device 50 designed to steer the radiation beam of a phased-array antenna 10 has been demonstrated. A radio frequency (RF) signal is generated via photomixing at the output of a single-mode fiber optic interferometer. The phase of the electrical signal is shifted over several cycles in direct proportion to a voltage applied to an optical modulator 34, 60. The modulator consists of a Pockels-type optical phase modulator located in one arm of the heterodyne interferometer. Rapid changes in RF phase are feasible. A miniature low-voltage version of the device 50, 72, based upon integrated optics, has been devised.
54 citations
TL;DR: A new and inexpensive holographic technique for measuring the phase errors of a two-dimensional spatial light modulator (SLM) is described, and experimental verification is provided.
Abstract: A new and inexpensive holographic technique for measuring the phase errors of a two-dimensional spatial light modulator (SLM) is described, and experimental verification is provided. A new technique to correct spatial phase errors in any SLM is then detailed and experimentally demonstrated. This technique is employed for the Radio Shack liquid-crystal television SLM, and a shift-invariant correlator is obtained. Additional low-pass filtering techniques (appropriate for any SLM with a fixed pattern of modulating cells) are discussed that provide improved contrast and achieve proper correlations.
TL;DR: InGaAs/InP monolithic integrated circuits composed of a compact carrier-injection optical switch and distributed feedback laser diodes are fabricated in this paper, which have a variety of functions, such as monolithic modulators, switches and optical amplifiers for optical communication systems.
Abstract: InGaAs/InP monolithic integrated circuits composed of a compact carrier-injection optical switch and distributed feedback laser diodes are fabricated. These integrated circuits have a variety of functions, such as monolithic modulators, switches and optical amplifiers for optical communication systems.
TL;DR: In this paper, the first measurements of large anistropic electroabsorption and modulation of long-wavelength light propagating along the plane of InGaAs/InAlAs multiple quantum well (MQW) structures grown by molecular beam epitaxy (MBE) are reported.
Abstract: The first measurements to be made of large anistropic electroabsorption and modulation of long-wavelength light propagating along the plane of InGaAs/InAlAs multiple quantum well (MQW) structures grown by molecular beam epitaxy (MBE) are reported. Photocurrent response of waveguide p-i-n diodes is studied for incident light polarization parallel and perpendicular to the MQW layers. Photocurrent increase with reverse bias throughout the entire photoresponse spectrum is observed for both polarizations. The MQW p-in optical modulator shows a capacitance-limited pulse response of 250 ps and the modulation depth is 14 percent.
TL;DR: In this paper, the first measurements of dynamic spectra of an InGaAsP/InP light modulator under high-frequency large-signal modulation were reported, and a spectral broadening factor was determined from the relative sideband strength to the carrier, and it decreased with increasing operating electric field in the modulator.
Abstract: The first measurements of dynamic spectra of an InGaAsP/InP electroabsorption light modulator under high-frequency large-signal modulation are reported. A spectral broadening factor ? was determined from the relative sideband strength to the carrier, and it decreased with increasing operating electric field in the modulator. The estimated ?-value for full modulation was |?| = 2.3, which can be reduced by designing a modulator to give a more effective change of electro-absorption.
TL;DR: An in-line polarizer has been demonstrated that uses the birefringent properties of a nematic liquid crystal placed in the evanescent field of a single-mode fiber to polarize the liquid-crystal molecules.
Abstract: An in-line polarizer has been demonstrated that uses the birefringent properties of a nematic liquid crystal placed in the evanescent field of a single-mode fiber. A polarization-extinction ratio of 45 dB was measured with an insertion loss of 1.1 dB. Amplitude modulation was also demonstrated by using an external electric field to reorient the liquid-crystal molecules.
TL;DR: The design, fabrication, measurement, and performance charcteristics of the titanium-indiffused proton-exchanged microlenses, microlens arrays, and their combinations in LiNbO3 with emphasis on the most recent results are detailed first.
Abstract: In this paper, design, fabrication, measurement, and performance charcteristics of the titanium-indiffused proton-exchanged microlenses, microlens arrays, and their combinations in LiNbO3 with emphasis on the most recent results are detailed first. Utilization of such TIPE microlenses for acoustooptic Bragg diffraction in a LiNbO3 channel–planar composite waveguide and realization of an integrated AO Bragg modulator module in a substrate size of 0.2 × 1.0 × 2.0 cm are then described. Some of the potential applications of such an integrated optic module together with the preliminary results of a simple experiment on matrix–vector multiplication are also presented.
TL;DR: In this article, a theoretical analysis of the bipolar transistor structure applied to a DH X crossing is presented, with emphasis on the switching speed, and it is shown that switching times can be as fast as 60 ps for the required ON-OFF optical switching.
Abstract: Bipolar transistor structures can be used, instead of conventional p-n (p-i-n) junctions, to realize high-speed optical modulators and switches, which are operated by free-carrier injection. Some basic results obtained by the theoretical analysis of the structure applied to a DH X crossing are presented, with emphasis on the switching speed. It is shown that switching times can be as fast as 60 ps for the required ON-OFF optical switching, which is considerably faster than those expected for a diode structure.
13 Feb 1986
TL;DR: An overview of the state of the art of two-dimensional spatial light modulator technology is provided in this article, touching on the basic operation and performance of most of the more promising electronically and optically addressed device technologies.
Abstract: An introduction and comparative overview to the state of the art of two-dimensional spatial light modulator technology is provided, touching on the basic operation and performance of most of the more promising electronically- and optically- addressed device technologies. The fundamental functional capabilities and potential applications of these light control devices are also discussed, and some projections are offered on the future directions of spatial light modulator technology.
TL;DR: In this paper, a 1×2 Ti:LiNbO3 modified directional coupler modulator is demonstrated, which has a 3 dB operating point and requires no bias voltage.
Abstract: A novel 1×2 Ti:LiNbO3 modified directional coupler modulator is demonstrated. The 3 dB operating point requires no bias voltage. The device has a lower switching voltage requirement than a conventional directional coupler.
Patent•
21 Feb 1986TL;DR: In this paper, the two branch waveguides are spaced close enough to maximize the field overlap between the applied electrical field and the optical field in the waveguide but are optically decoupled to prevent cross-coupling of light between the branches.
Abstract: A Mach-Zehnder interferometric modulator includes on a Z-cut crystal substrate of LiNbO 3 an input waveguide section (302), an input branching section (303) for dividing an optical signal on the input waveguide into two substantially equal portions, first and second branch waveguides (304, 305) each having an electrode associated therewith (309, 308), an output branching section (306) for recombining the light from each branch waveguide into a single optical signal on an output waveguide section (307). The two branch waveguides are spaced close enough to maximize the field overlap between the applied electrical field and the optical field in the waveguides but are optically decoupled to prevent cross-coupling of light between the branches. This decoupling is achieved by using structures which change the propagation constant of one of the branches with respect to the other along the modulation length.
TL;DR: This work describes the first reported electro-optic cutoff modulator that utilizes a thermally annealed single-mode proton-exchanged channel waveguide in a X-cut Y-propagating LiNbO(3) substrate and finds thermal annealing was found greatly to improve the linearity of modulation.
Abstract: We describe the first reported electro-optic cutoff modulator that utilizes a thermally annealed single-mode proton-exchanged channel waveguide in a X-cut Y-propagating LiNbO3 substrate. The large changes in extraordinary refractive index obtainable by the proton-exchange process enabled us readily to form single-mode waveguides with a channel width as small as 2 μm. As a result, the voltage required for electro-optically controlled propagation cutoff was significantly reduced. Thermal annealing was used to provide fine tuning on the refractive-index changes that was in turn used to bring the waveguide to the very edge of cutoff and thus permitted further reduction in the voltage requirement. Thermal annealing was also found greatly to improve the linearity of modulation. For example, we have measured a modulation depth of 97% at a total voltage swing of only 7 V and a high linearity. In addition, no optical damage has been observed after a 2-h continuous exposure of 632.8-nm He–Ne laser light at an intensity as high as 104 W/cm2.
TL;DR: In this paper, an analysis of phase-reversal electrode structures used for phase matching in travelling-wave integrated-optic phase modulators is given; both modulus and argument of the phase shift are obtained; both are required for applications involving broadband excitation.
Abstract: An analysis is given of phase-reversal electrode structures used for phase matching in travelling-wave integrated-optic phase modulators. Both modulus and argument of the phase shift are obtained; both are required for applications involving broadband excitation. Periodic and non-periodic lossy structures are treated and the advantage of non-periodic structures for wide-band operation is demonstrated. Optimum structure arrangements and upper bounds to phase shift and figure of merit are derived.
TL;DR: The components required for coherent optical-fiber systems are discussed and those devices that can be implemented using electrooptic waveguide technology are identified and the system performance when these components are employed summarized.
Abstract: The components required for coherent optical-fiber systems are discussed and those devices that can be implemented using electrooptic waveguide technology are identified. The current usage of integrated optic components in coherent optical-fiber systems is indicated and the system performance that has been obtained when these components are employed summarized. The design and performance of LiNbO 3 electrooptic waveguide modulators, optical combiners, frequency translators, and polarization controllers are reviewed and the benefits to be gained by employing optical-integrated circuits in coherent optical-fiber systems considered. Finally, a novel low-voltage LiNbO 3 optical-integrated circuit for use in coherent detection is presented and the various design compromises discussed.
TL;DR: In this article, a fibrepigtailed, broadband travelling-wave X-cut Ti:LiNbO3 phase modulator for λ = 1.55 μm with 1.8 dB total insertion loss and 8 V modulation voltage was presented.
Abstract: We report the design, fabrication and performance of a fibrepigtailed, broadband travelling-wave X-cut Ti:LiNbO3 phase modulator for λ = 1.55 μm with 1.8 dB total insertion loss and 8 V modulation voltage.
TL;DR: In this paper, a large on/off ratio optical modulation of long-wavelength light propagating along the plane of InGaAs/InAlAs multiple-quantum-well (MQW) structures grown by molecular beam epitaxy (MBE) is obtained for the first time.
Abstract: Large on/off ratio optical modulation of long-wavelength light propagating along the plane of InGaAs/InAlAs multiple-quantum-well (MQW) structures grown by molecular beam epitaxy (MBE) is obtained for the first time. These waveguide MQW optical modulators have a modulation on/off ratio of 30:1 (15 dB) at a driving voltage as low as 9 V, and a capacitance-limited pulse response of 280 ps (FWHM). This measurement is the first step in achieving faster and higher extinction ratio devices.
TL;DR: By using a surface acoustic-wave device, modulation depths up to 70% have been obtained and a bandwidth of 4 MHz centered at 4.5 MHz has been obtained with the device reported here.
Abstract: The two principal polarizations of birefringent optical fiber can be coupled by subjecting the fiber to stress that is spatially periodic along the length of the fiber. If the stress is temporally varied by using an acoustic wave, the coupling varies accordingly, and optical power can be transferred between polarizations dynamically. When an output polarizer is used to pass only one of the principal polarizations, this transfer of power is seen as a modulation of the intensity of the light passed by the polarizer. By using a surface acoustic-wave device, modulation depths up to 70% have been obtained. The bandwidth of such a device is limited only by the bandwidth of the transducers. A bandwidth of 4 MHz centered at 4.5 MHz has been obtained with the device reported here.
TL;DR: In this paper, the influence of the commonly used buffer layers between electrodes and waveguides in an integrated optics electrooptic device is investigated and the electric field distribution is calculated and the impact on device performance of this buffer layer is assessed.
Abstract: The influence of the commonly used buffer layers between electrodes and waveguides in an integrated optics electrooptic device is investigated. The electric field distribution is calculated and the impact on device performance of this buffer layer is assessed. It is shown that even thin (~50nm) buffer layers of low relative dielectric constant increase the required drive power in typical modulator structures.
TL;DR: In this paper, a new type of GaAs/AlGaAs charge-coupled device (CCD) was demonstrated in which the charge is confined to a quantum well channel.
Abstract: We have demonstrated a new type of GaAs/AlGaAs charge‐coupled device (CCD) in which the charge is confined to a quantum‐well channel. The MBE‐grown quantum‐well CCD (designated QWCCD) has a channel consisting of a 140 A GaAs layer clad on both sides by AlGaAs layers. This structure was grown on a multiple‐quantum‐well (MQW) structure consisting of 60 periods of GaAs and AlGaAs layers of about 100 A thickness each. Large optical modulation effects involving quantum‐confined excitons were observed in the MQW structure when a bias was applied perpendicular to the plane of the layers. The combination of QWCCD and MQW structures has promise as a high‐speed spatial light modulator for applications in optical signal processing.
TL;DR: In this article, the first all-optical power limiter based on cascaded InSb etalons was reported, where the power limiting effect is due to a dispersive nonlinearity in InSB at room temperature as a result of generation of free carriers through two-photon absorption of 10 μm radiation.
Abstract: We report the first all‐optical power limiter based on cascaded InSb etalons. The power limiting effect is due to a dispersive nonlinearity in InSb at room temperature as a result of generation of free carriers through two‐photon absorption of 10 μm radiation. The efficiency and dynamic range of this all‐optical circuit are discussed.