Showing papers on "Optical modulator published in 2012"
TL;DR: Benefited from the symmetrical band structure of graphene near Dirac point, such design eliminates the optical loss widely existing in silicon photonics and has advantages including small footprint, low energy consumption, and low insertion loss.
Abstract: Here we report a high-performance double-layer graphene optical modulator. By using two graphene layers and an oxide layer in between to form a p-oxide-n like junction, this modulator operates at 1 GHz with a high modulation depth (∼0.16 dB/μm) at a moderate drive voltage (∼5 V). Benefited from the symmetrical band structure of graphene near Dirac point, such design eliminates the optical loss widely existing in silicon photonics and has advantages including small footprint, low energy consumption, and low insertion loss.
733 citations
TL;DR: In this paper, the authors presented the first optical modulation at 50 Gb/s with a 3.1dB extinction ratio obtained from carrier depletion based phase shifter incorporated in a Mach-Zehnder interferometer.
Abstract: Optical modulators formed in silicon are the keystone to many low cost optical applications. Increasing the data rate of the modulator benefits the efficiency of channel usage and decreases power consumption per bit of data. Silicon-based modulators which operate via carrier depletion have to the present been demonstrated at data rates up to 40 Gb/s; however, here we present for the first time optical modulation at 50 Gb/s with a 3.1-dB extinction ratio obtained from carrier depletion based phase shifter incorporated in a Mach-Zehnder interferometer. A corresponding optical insertion loss of approximately 7.4 dB is measured.
413 citations
TL;DR: In this article, a planar, optical microcavity was used to control the efficiency and spectral selection of photocurrent generation in the integrated graphene device, and a twenty-fold enhancement of the photocurrent was demonstrated.
Abstract: Graphene has extraordinary electronic and optical properties and holds great promise for applications in photonics and optoelectronics. Demonstrations including high-speed photodetectors, optical modulators, plasmonic devices, and ultrafast lasers have now been reported. More advanced device concepts would involve photonic elements such as cavities to control light–matter interaction in graphene. Here we report the first monolithic integration of a graphene transistor and a planar, optical microcavity. We find that the microcavity-induced optical confinement controls the efficiency and spectral selection of photocurrent generation in the integrated graphene device. A twenty-fold enhancement of photocurrent is demonstrated. The optical cavity also determines the spectral properties of the electrically excited thermal radiation of graphene. Most interestingly, we find that the cavity confinement modifies the electrical transport characteristics of the integrated graphene transistor. Our experimental approach opens up a route towards cavity-quantum electrodynamics on the nanometre scale with graphene as a current-carrying intra-cavity medium of atomic thickness.
349 citations
TL;DR: This paper presents photonic devices with 3 dB/cm waveguide loss fabricated in an existing commercial electronic 45 nm SOI-CMOS foundry process and demonstrates an 8-channel optical microring-resonator filter bank and optical modulators, both controlled by integrated digital circuits.
Abstract: This paper presents photonic devices with 3 dB/cm waveguide loss fabricated in an existing commercial electronic 45 nm SOI-CMOS foundry process. By utilizing existing front-end fabrication processes the photonic devices are monolithically integrated with electronics in the same physical device layer as transistors achieving 4 ps logic stage delay, without degradation in transistor performance. We demonstrate an 8-channel optical microring-resonator filter bank and optical modulators, both controlled by integrated digital circuits. By developing a device design methodology that requires zero process infrastructure changes, a widely available platform for high-performance photonic-electronic integrated circuits is enabled.
235 citations
TL;DR: Though electroabsorption modulators with large reverse bias have substantial energy penalties from photocurrent dissipation, it is argued that modulator diodes with thin depletion regions and operating in small reverse and/or forward bias could have little or no photocurrent energy penalty, even conceivably being more energy-efficient than an ideal loss-less modulator.
Abstract: We analyze energy consumption in optical modulators operated in depletion and intended for low-power interconnect applications. We include dynamic dissipation from charging modulator capacitance and net energy consumption from absorption and photocurrent, both in reverse and small forward bias. We show that dynamic dissipation can be independent of static bias, though only with specific kinds of bias circuits. We derive simple expressions for the effects of photocurrent on energy consumption, valid in both reverse and small forward bias. Though electroabsorption modulators with large reverse bias have substantial energy penalties from photocurrent dissipation, we argue that modulator diodes with thin depletion regions and operating in small reverse and/or forward bias could have little or no such photocurrent energy penalty, even conceivably being more energy-efficient than an ideal loss-less modulator.
211 citations
IBM1
TL;DR: The first sub-100nm technology that allows the monolithic integration of optical modulators and germanium photodetectors as features into a current 90nm base high-performance logic technology node is demonstrated.
Abstract: The first sub-100nm technology that allows the monolithic integration of optical modulators and germanium photodetectors as features into a current 90nm base highperformance logic technology node is demonstrated. The resulting 90nm CMOS-integrated Nano-Photonics technology node is optimized for analog functionality to yield power-efficient single-die multichannel wavelength-mulitplexed 25Gbps transceivers.
198 citations
TL;DR: By combining previously reported techniques, this work can achieve complete amplitude, phase and polarization control for the diffracted light that allows the creation of arbitrary diffractive optical elements including polarization control.
Abstract: We present a method to generate complete arbitrary spatially variant polarization modulation of a light beam by means of a parallel aligned nematic liquid crystal spatial light modulator (SLM). We first analyze the polarization modulation properties in a transmission mode. We encode diffraction gratings onto the SLM and show how to achieve partial polarization control of the zero order transmitted light. We then extend the technique to a double modulation scheme, which is implemented using a single SLM divided in two areas in a reflective configuration. The polarization states of the transmitted beam from the first pass through the first area are rotated using two passes through a quarter wave plate. The beam then passes through the second area of the SLM where additional polarization information can be encoded. By combining previously reported techniques, we can achieve complete amplitude, phase and polarization control for the diffracted light that allows the creation of arbitrary diffractive optical elements including polarization control. Theoretical analysis based on the Jones matrix formalism, as well as excellent experimental results are presented.
168 citations
TL;DR: A decomposition of guided modes propagating in optical fibers is implemented and it is shown that the observed field can be reconstructed with very high fidelity.
Abstract: A procedure for the real-time analysis of laser modes using a phase-only spatial light modulator is outlined. The procedure involves encoding into digital holograms by complex amplitude modulation a set of orthonormal basis functions into which the initial field is decomposed. This approach allows any function to be encoded and refreshed in real time (60 Hz). We implement a decomposition of guided modes propagating in optical fibers and show that we can successfully reconstruct the observed field with very high fidelity.
167 citations
TL;DR: In this paper, an electro-absorption optical modulator based on a dual-graphene layer is presented, which consists of a silicon-on-insulator waveguide upon which two graphene layers reside, separated by a thin insulating region.
Abstract: An electro-absorption optical modulator concept based upon a dual-graphene layer is presented. The device consists of a silicon-on-insulator waveguide upon which two graphene layers reside, separated by a thin insulating region. The lower graphene acts as a tunable absorber, while the upper layer functions as a transparent gate electrode. Calculations based upon realistic graphene material properties show that 3-dB bandwidths over 100 GHz (30 GHz) are possible at near- (\lambda=1.55 \mu m) and mid- (\lambda=3.5\mu m) infrared bands. The effect of background doping and potential fluctuations on the bandwidth, modulation depth and insertion loss are also quantified.
153 citations
TL;DR: In this paper, an electro-absorption optical modulator concept based upon a dual-graphene layer is presented, which consists of a silicon-on-insulator waveguide upon which two graphene layers reside, separated by a thin insulating region.
Abstract: An electro-absorption optical modulator concept based upon a dual-graphene layer is presented. The device consists of a silicon-on-insulator waveguide upon which two graphene layers reside, separated by a thin insulating region. The lower graphene acts as a tunable absorber, while the upper layer functions as a transparent gate electrode. Calculations based upon realistic graphene material properties show that 3-dB bandwidths over 120 GHz (30 GHz) are achievable at near- (λ = 1.55 μm) and mid- (λ = 3.5 μm) infrared bands. The effect of background doping and potential fluctuations on the bandwidth, modulation depth, and insertion loss are also quantified.
150 citations
TL;DR: An electro-optic modulator that integrates single-layer graphene in a sub-wavelength thick, reflective modulator structure is reported on, offering solutions to a variety of high-speed amplitude modulation tasks that require optical amplitude modulation without phase distortions, a flat frequency response, or ultra-thin geometries.
Abstract: Graphene’s featureless optical absorption, ultrahigh carrier mobility, and variable optical absorption by an applied gate voltage enable a new breed of optical modulators with broad optical and electrical bandwidths. Here we report on an electro-optic modulator that integrates single-layer graphene in a sub-wavelength thick, reflective modulator structure. These modulators provide a large degree of design freedom, which allows tailoring of their optical properties to specific needs. Current devices feature an active aperture ~100 µm, and provide uniform modulation with flat frequency response from 1 Hz to >100 MHz. These novel, low insertion-loss graphene-based modulators offer solutions to a variety of high-speed amplitude modulation tasks that require optical amplitude modulation without phase distortions, a flat frequency response, or ultra-thin geometries, such as for controlling monolithic, high-repetition rate mode-locked lasers or active interferometers.
TL;DR: The interdigitated diode is shown to outperform the lateral diode in achieving a low VπLπ of 0.62 V∙cm with comparable propagation loss at the expense of a higher depletion capacitance.
Abstract: Carrier-depletion based silicon modulators with lateral and interdigitated PN junctions are compared systematically on the same fabrication platform. The interdigitated diode is shown to outperform the lateral diode in achieving a low VπLπ of 0.62 V∙cm with comparable propagation loss at the expense of a higher depletion capacitance. The low VπLπ of the interdigitated PN junction is employed to demonstrate 10 Gbit/s modulation with 7.5 dB extinction ration from a 500 µm long device whose static insertion loss is 2.8 dB. In addition, up to 40 Gbit/s modulation is demonstrated for a 3 mm long device comprising a lateral diode and a co-designed traveling wave electrode.
TL;DR: In this article, a thin ENZ film is sandwiched in a single-mode waveguide, and an ENZ-slot waveguide is formed, where the absorption can be greatly enhanced.
Abstract: We present a promising application of epsilon-near-zero (ENZ) materials in optical modulators. When a thin ENZ film is sandwiched in a single-mode waveguide, an ENZ-slot waveguide is formed, where the absorption can be greatly enhanced. We propose electroabsorption modulators based on tunable ENZ materials and slot waveguides. Transparent conducting oxides (TCOs) may be employed as the active slot, which can be tuned between ENZ (high absorption) and epsilon-far-from-zero (low absorption) by accumulation carriers. Numerical simulation shows that over 3-dB modulation depth can be achieved in a 250-nm-long TCO-slot waveguide. The modulators have the advantages of nanoscale footprints, small insertion loss, potentially ultrahigh speed, and easy fabrication.
TL;DR: A full-range complex and transmissive spatial light modulator (SLM) for simultaneous and independent amplitude and phase modulation of an input wave field of arbitrary scalar complex optical fields is demonstrated.
Abstract: We demonstrate a full-range complex and transmissive spatial light modulator (SLM) for simultaneous and independent amplitude and phase modulation of an input wave field. Arbitrary scalar complex optical fields are generated by stacking a pixelated liquid crystal display operating in phase-only (2π) modulation with passive polarization-sensitive components. The principle is based on optical combining the light fields of two neighboring phase-only modulating pixels, which were made orthogonally polarized by a structured half-wave plate, then passing through a birefringent plate to laterally shift one of the beams collinear to the other, and finally bringing to interference by a linear polarizer. Complex modulation by the proposed SLM is experimentally verified in monochrome green operation.
TL;DR: Two low-loss silicon optical modulators are demonstrated, based on the carrier depletion effect in a pipin diode, to generate a good compromise between high efficiency, speed and low optical loss.
Abstract: 40 Gbit/s low-loss silicon optical modulators are demonstrated. The devices are based on the carrier depletion effect in a pipin diode to generate a good compromise between high efficiency, speed and low optical loss. The diode is embedded in a Mach-Zehnder interferometer, and a self-aligned fabrication process was used to obtain precise localization of the active p-doped region in the middle of the waveguide. Using a 4.7 mm (resp. 0.95 mm) long phase shifter, the modulator exhibits an extinction ratio of 6.6 dB (resp. 3.2 dB), simultaneously with an optical loss of 6 dB (resp. 4.5 dB) at the same operating point.
TL;DR: An equivalent circuit model for the coplanar waveguide (CPW) which serves as the traveling wave electrode to drive carrier-depletion-based silicon modulators is proposed in this article.
Abstract: We propose an equivalent circuit model for the coplanar waveguide (CPW) which serves as the traveling wave electrode to drive carrier-depletion-based silicon modulators. Conformal mapping and partial capacitance techniques are employed to calculate each element of the circuit. The validity of the model is confirmed by the comparison with both finite-element simulation and experimental result. With the model, we calculate the modulation bandwidth for different CPW dimensions and termination impedances. A 3 dB modulation bandwidth of 15 GHz is demonstrated with a traveling wave electrode of 3 mm. The calculation indicates that, by utilizing a traveling wave electrode of 2 mm, we can obtain a 3 dB modulation bandwidth of 28 GHz.
20 Apr 2012
TL;DR: In this paper, the optical loss of graphene can be tuned by shifting its Fermi level, which can be used for high-speed optical modulator at telecommunication wavelength.
Abstract: The optical loss of graphene can be tuned by shifting its Fermi level. We demonstrated that this tuning can be used for in a high-speed optical modulator at telecommunication wavelength.
TL;DR: The first sub-100 μm silicon Mach-Zehnder modulators (MZMs) that operate at >10 Gb/s are demonstrated, by exploiting low-dispersion slow-light in lattice-shifted photonic crystal waveguides (LSPCWs) using two LSPCW-MZM structures.
Abstract: We demonstrate the first sub-100 μm silicon Mach-Zehnder modulators (MZMs) that operate at >10 Gb/s, by exploiting low-dispersion slow-light in lattice-shifted photonic crystal waveguides (LSPCWs). We use two LSPCW-MZM structures, one with LSPCWs in both arms of the MZM, and the other with an LSPCW in only one of the arms. Using the first structure we demonstrate 10 Gb/s operation with a operating bandwidth of 12.5 nm, in a device with a phase-shifter length of only 50 μm. Using the second structure, owing to a larger group index as well as lower spectral noise, we demonstrate 40 Gb/s operation with a phase-shifter length of only 90 μm, which is more than an order-of-magnitude shorter than most 40 Gb/s MZMs.
TL;DR: An 80-nm-wide intrinsic silicon gap between the p-type and n-type doped regions is designed to reduce the capacitance of the diode and prevent the diodes from working in a slow diffusion mode and can be driven with a small differential voltage of 0.5 V with no bias.
Abstract: We demonstrate a 26 Gbit/s Mach-Zehnder silicon optical modulator. The doping concentration and profile are optimized, and a modulation efficiency with the figure of merit (VπL) of 1.28 V·cm is achieved. We design an 80-nm-wide intrinsic silicon gap between the p-type and n-type doped regions to reduce the capacitance of the diode and prevent the diode from working in a slow diffusion mode. Therefore, the modulator can be driven with a small differential voltage of 0.5 V with no bias. Without the elimination of the dissipated power of the series resistors and the reflected power of the electrical signal, the maximum power consumption is 3.8 mW.
TL;DR: A high-speed silicon modulator based on cascaded double microring resonators that can provides an ultra-high-speed optical modulation with a further improvement in electrical bandwidth of the device is demonstrated.
Abstract: A high-speed silicon modulator based on cascaded double microring resonators is demonstrated in this paper. The proposed modulator experimentally achieved 40 Gbit/s modulation with an extinction ratio of 3.9 dB. Enhancement of the modulator achieves with an ultra-high optical bandwidth of 0.41 nm, corresponding to 51 GHz, was accomplished by using cascaded double ring structure. The described modulator can provides an ultra-high-speed optical modulation with a further improvement in electrical bandwidth of the device.
TL;DR: A lithium niobate electro-optic phase modulator based on a coplanar waveguide ridged structure that operates up to 300 GHz is developed, able to eliminate substrate modes and observe optical sidebands over the full millimeter-wave spectrum.
Abstract: In recent years, the development of new lithium niobate electro-optic modulator designs and material processing techniques have contributed to support the increasing need for faster optical networks by considerably extending the operational bandwidth of modulators. In an effort to provide higher bandwidths for future generations of networks, we have developed a lithium niobate electro-optic phase modulator based on a coplanar waveguide ridged structure that operates up to 300 GHz. By thinning the lithium niobate substrate down to less than 39 µm, we are able to eliminate substrate modes and observe optical sidebands over the full millimeter-wave spectrum.
TL;DR: It is shown that, in order to attain complete polarization control across a beam, two spatially resolved variable retardations need to be introduced to the light beam.
Abstract: We show that, in order to attain complete polarization control across a beam, two spatially resolved variable retardations need to be introduced to the light beam. The orientation of the fast axes of the retarders must be linearly independent on the Poincare sphere if a fixed starting polarization state is used, and one of the retardations requires a range of 2π. We also present an experimental system capable of implementing this concept using two passes on spatial light modulators (SLMs). A third SLM pass can be added to control the absolute phase of the beam. Control of the spatial polarization and phase distribution of a beam has applications in high-NA microscopy, where these properties can be used to shape the focal field in three dimensions. We present some examples of such fields, both theoretically calculated using McCutchen’s method and experimentally observed.
TL;DR: The first experimental demonstration of quadrature phase-shift keying (QPSK) modulation using compact microring modulators is reported, which may be used in miniature optical transponders for high-capacity optical data links.
Abstract: Advanced optical modulation formats are a key technology to increase the capacity of optical communication networks. Mach-Zehnder modulators are typically used to generate various modulation formats. Here, we report the first experimental demonstration of quadrature phase-shift keying (QPSK) modulation using compact microring modulators. Generation of 20 Gb/s QPSK signals is demonstrated with 30 μm radius silicon ring modulators with drive voltages of ~6 V. These compact QPSK modulators may be used in miniature optical transponders for high-capacity optical data links.
TL;DR: In this article, a traveling-wave directional coupler modulator based on electro-optic polymer is presented, which is able to provide both high linearity and broad bandwidth.
Abstract: In this paper, we present the design, fabrication, and characterization of a traveling-wave directional coupler modulator based on electro-optic polymer, which is able to provide both high linearity and broad bandwidth. The high linearity is realized by introducing Δβ -reversal technique in the two-domain directional coupler. A traveling-wave electrode is designed to function with bandwidth-length product of 302 GHz·cm , by achieving low microwave loss, excellent impedance matching, and velocity matching, as well as smooth electric-field profile transformation. The 3-dB bandwidth of the device is measured to be 10 GHz. The spurious-free dynamic range of 110 dB ±3 Hz2/3 is measured over the modulation frequency range of 2-8 GHz. To the best of our knowledge, such high linearity is first measured at the frequency up to 8 GHz. In addition, a 1 × 2 multimode interference 3-dB splitter, a photobleached refractive index taper, and a quasi-vertical taper are used to reduce the optical insertion loss of the device.
IBM1
TL;DR: The results illustrate that optical modulator design methodologies previously developed for telecom-band devices can be successfully applied to produce high-performance devices for a silicon nanophotonic mid-infrared integrated circuit platform.
Abstract: We demonstrate electrooptic modulation at a wavelength of 2165nm, using a free-carrier injection-based silicon Mach-Zehnder modulator. The modulator has a Vπ∙L figure of merit of 0.12V∙mm, and an extinction ratio of −23dB. Optical modulation experiments are performed at bitrates up to 3Gbps. Our results illustrate that optical modulator design methodologies previously developed for telecom-band devices can be successfully applied to produce high-performance devices for a silicon nanophotonic mid-infrared integrated circuit platform.
TL;DR: An optical system for synthesizing double-phase complex computer-generated holograms using a phase-only spatial light modulator and a phase grating filter to synthesize arbitrary complex optical field distributions is proposed.
Abstract: We propose an optical system for synthesizing double-phase complex computer-generated holograms using a phase-only spatial light modulator and a phase grating filter. Two separated areas of the phase-only spatial light modulator are optically superposed by 4-f configuration with an optimally designed grating filter to synthesize arbitrary complex optical field distributions. The tolerances related to misalignment factors are analyzed, and the optimal synthesis method of double-phase computer-generated holograms is described.
TL;DR: A plasmonic waveguide is presented that functions as an index modulator with Δn > 20% at λ0 = 1,550 nm (0.80 eV), by using a thin active layer to strike a balance between maximizing index contrast while mitigating attenuation.
Abstract: Actively tunable metal-insulator-metal waveguides that employ vanadium dioxide films as the active medium are analyzed numerically. Vanadium dioxide exhibits strong contrast between the optical properties of its insulating and metallic phases. In particular, the large optical absorption in the metallic phase makes it straightforward to implement broadband attenuation modulators and switches, but this strong loss can also complicate the design of other types of devices. We present a plasmonic waveguide that functions as an index modulator with Δn > 20% at λ0 = 1550nm (0.80 eV), by using a thin active layer to strike a balance between maximizing index contrast while mitigating attenuation. A second device is configured as a band-stop absorption modulator, taking advantage of symmetry to selectively suppress the TM1 and TM3 modes, with relatively minimal attenuation of the TM0 and TM2 modes.
TL;DR: This work presents a fast and easy technique for measuring the beam propagation ratio, M(2), of laser beams using a spatial light modulator, based on digitally simulating the free-space propagation of light, thus eliminating the need for the traditional scan in the propagation direction.
Abstract: We present a fast and easy technique for measuring the beam propagation ratio, M2, of laser beams using a spatial light modulator. Our technique is based on digitally simulating the free-space propagation of light, thus eliminating the need for the traditional scan in the propagation direction. We illustrate two approaches to achieving this, neither of which requires any information of the laser beam under investigation nor necessitates any moving optical components. The comparison with theoretical predictions reveals excellent agreement and proves the accuracy of the technique.
TL;DR: In this paper, a single in-phase/quadrature (I/Q) optical modulator driven by 8-level electrical waveforms from a novel high-power digital-to-analog converter (DAC) was used to achieve 400-km single-channel transmission.
Abstract: We generate a single-carrier 21.4-Gbaud polarization-division-multiplexed (PDM) 64-ary quadrature-amplitude-modulated (QAM) signal (256.8-Gb/s line rate) using a single in-phase/quadrature (I/Q) optical modulator driven by 8-level electrical waveforms from a novel high-power digital-to-analog converter (DAC). We measure a required optical signal-to-noise ratio of 29.5 dB (0.1-nm reference bandwidth; 10-3 bit-error rate), 4.6-dB off the theoretical limit. Using ultra-large-area fiber, we achieve 400-km single-channel transmission. The DAC was also used to obtain excellent results with quadrature-phase-shift-keyed and 16-QAM signals at 21.4 Gbaud.
TL;DR: This work proposes and demonstrates a novel architecture consisting of an array of photonic crystal modulators connected by a dielectric bus waveguide that features very high scalability and the modulators operate with an AC energy consumption of less than 1fJ/bit.
Abstract: Integration density, channel scalability, low switching energy and low insertion loss are the major prerequisites for on-chip WDM systems. A number of device geometries have already been demonstrated that fulfill these criteria, at least in part, but combining all of the requirements is still a difficult challenge. Here, we propose and demonstrate a novel architecture consisting of an array of photonic crystal modulators connected by a dielectric bus waveguide. The device architecture features very high scalability and the modulators operate with an AC energy consumption of less than 1fJ/bit. Furthermore, we demonstrate cascadeability and multichannel operation by using a comb laser as the source that simultaneously drives 5 channels.