Showing papers in "IEEE Photonics Journal in 2010"
TL;DR: In this article, a direct comparison between coupled resonator optical waveguides (CROWs) and photonic crystal waveguide (PhCWs), which have both been exploited as tunable delay lines, was conducted under the same silicon-on-insulator (SOI) technological platform.
Abstract: In this paper, we report a direct comparison between coupled resonator optical waveguides (CROWs) and photonic crystal waveguides (PhCWs), which have both been exploited as tunable delay lines. The two structures were fabricated on the same silicon-on-insulator (SOI) technological platform, with the same fabrication facilities and evaluated under the same signal bit-rate conditions. We compare the frequency- and time-domain response of the two structures; the physical mechanism underlying the tuning of the delay; the main limits induced by loss, dispersion, and structural disorder; and the impact of CROW and PhCW tunable delay lines on the transmission of data stream intensity and phase modulated up to 100 Gb/s. The main result of this study is that, in the considered domain of applications, CROWs and PhCWs behave much more similarly than one would expect. At data rates around 100 Gb/s, CROWs and PhCWs can be placed in competition. Lower data rates, where longer absolute delays are required and propagation loss becomes a critical issue, are the preferred domain of CROWs fabricated with large ring resonators, while at data rates in the terabit range, PhCWs remain the leading technology.
200 citations
TL;DR: An analytical model for the transmission of orthogonal frequency division multiplexing (OFDM)-based signals over freespace optics (FSO) links is introduced, taking into account the optical noises, the laser diode nonlinear distortion, and the atmospheric turbulence effect on the FSO channel modeled by the gamma-gamma distribution.
Abstract: Radio-on-free space optical (RoFSO) communication systems are rapidly gaining popularity as an efficient and cost-effective means of transferring high data rates and radio frequency (RF) signals with the same capacity as optical fiber. However, the performance of those systems depends strongly on the atmospheric conditions and the nonlinear characteristics of the optical link. In this paper, we introduce an analytical model for the transmission of orthogonal frequency division multiplexing (OFDM)-based signals over freespace optics (FSO) links. Further, we derive a closed-form bit error probability (BEP) and outage probability expressions, taking into account the optical noises, the laser diode nonlinear distortion, and the atmospheric turbulence effect on the FSO channel modeled by the gamma-gamma distribution. This paper reports the most significant parameters that degrade the transmission performance of the OFDM signal over FSO links and indicates the cases that provide the optimal operating conditions for the link. The obtained results can be useful for designing, predicting, and evaluating the RoFSO system's ability to transmit wireless services over turbulent FSO links under actual conditions.
188 citations
TL;DR: In this article, a simple configuration for the generation of tunable multiwavelength picosecond-pulse fiber ring lasers by exploiting the intracavity birefringence-induced comb filter is demonstrated.
Abstract: A simple configuration for the generation of tunable multiwavelength picosecond-pulse fiber ring lasers by exploiting the intracavity birefringence-induced comb filter is demonstrated. The fiber laser is passively mode locked by using nonlinear polarization rotation (NPR) technique. The polarization-dependent isolator combined with the intracavity birefringence acts as two functions: the tunable comb filter and the mode locker. Up to four-wavelength picosecond pulses were simultaneously obtained in the experiment. The mode competition of the multiwavelength lasing is suppressed by the use of NPR-induced intensity-dependent loss. In addition, the number of the lasing wavelengths, the lasing location, and the spacing between the lasing wavelengths could be flexibly tuned by properly rotating the polarization controllers.
167 citations
TL;DR: The progress in III-Nitride photonics research in 2009 is reviewed in this article, where several new research areas related to terahertz photonics, intersubband quantum wells, nanostructures, and other devices are discussed.
Abstract: The progress in III-Nitride photonics research in 2009 is reviewed. The III-Nitride photonics research is a very active field with many important applications in the areas of energy, biosensors, laser devices, and communications. The applications of nitride semiconductors in energy-related technologies include solid-state lighting, solar cells, thermoelectric, and power electronics. Several new research areas in III-Nitride photonics related to terahertz photonics, intersubband quantum wells, nanostructures, and other devices are discussed.
163 citations
TL;DR: This paper reviews recent work on the design, experimental implementation, and application of two fundamental all-optical analog signal processing functionalities, namely,Photonic temporal differentiation and photonic temporal integration, using customized grating devices directly written in optical fibers.
Abstract: This paper reviews recent work on the design, experimental implementation, and application of two fundamental all-optical analog signal processing functionalities, namely, photonic temporal differentiation and photonic temporal integration, using customized grating devices directly written in optical fibers.
142 citations
TL;DR: In this paper, blind and data-aided receivers are compared for coherent single-carrier optical systems in terms of complexity, tracking ability, and convergence speed for time-domain and frequency-domain-based receivers.
Abstract: Fiber-optic research in signal processing for the first generation of coherent communication systems was dominated by receivers with blind adaptation. Next-generation systems will require a scalable and modular design for higher order modulation formats. Due to the nature of the fiber channel and the required parallelization in high-speed receivers, data-aided and blind algorithms call for a general reassessment when used in coherent optic receivers employing higher order modulation formats. In this paper, blind and data-aided receivers are compared for coherent single-carrier optical systems in terms of complexity, tracking ability, and convergence speed. Methods for equalization are discussed for time-domain- and frequency-domain-based receivers covering the most important algorithms. The general superiority of data-aided frequency-domain equalization is demonstrated.
130 citations
TL;DR: In this article, the authors presented a 2D camera based on a 32 × 32 array of smart pixels, each comprising a single-photon avalanche diode detector, an analog front end, and a digital processing electronics.
Abstract: Many demanding photonic applications require the acquisition of images at very low light-level conditions and at high speed. Advanced imagers available on the market are generally not able to provide both performances in one detector. We present a 2-D imager based on a 32 × 32 array of “smart pixels,” each comprising a single-photon avalanche diode detector, an analog front end, and a digital processing electronics, which provides single-photon sensitivity, high electronic noise immunity, and high readout speed. The imager can be operated at a maximum of about 100 000 frame/s with negligible blind time between frames, provides high Photon-Detection Efficiency in the visible range and dynamic range, and low Dark-Counting Rate, even at room temperature. To easily integrate the imager into different applications, we developed a complete single-photon camera system, which fully operates the array simply through a USB 2.0 link and user-friendly software to configure camera parameters and operating modalities, as well as to perform readout.
122 citations
TL;DR: In this paper, slow-light photonic crystals were used to enhance optical switching and modulation in silicon, and an extinction ratio in excess of 15 dB was obtained over the entire 11nm bandwidth of the modulator.
Abstract: We use slow-light photonic crystals to enhance optical switching and modulation in silicon. By using dispersion-engineered designs, a switch as short as 5 ?m was achieved, in which we have demonstrated rerouting of optical pulses on a 3-ps time scale through the absorption of a femtosecond pulse. We additionally demonstrate a modulator with a Mach-Zehnder interferometer (MZI) configuration with flat-band slow-light photonic crystal phase shifters that is designed to give a large group-index-bandwidth product. An extinction ratio in excess of 15 dB is obtained over the entire 11-nm bandwidth of the modulator.
99 citations
TL;DR: In this article, an ultracompact transverse magnetic (TM)-pass polarizer based on silicon nanophotonic waveguides is proposed, which contains two tapered waveguiders sandwiching a narrow waveguide section only supporting TM-mode propagation.
Abstract: An ultracompact transverse magnetic (TM)-pass polarizer based on silicon nanophotonic waveguides is proposed, which contains two tapered waveguides sandwiching a narrow waveguide section only supporting TM-mode propagation. A full-vectorial eigenmode solver is employed to determine the appropriate cross section of the silicon nanophotonic waveguide. The device is first designed in a 2-D approximate model using a wide-angle beam propagation method, and numerical verification is carried out afterward using a parallel full-vectorial 3-D finite-difference time-domain simulation. Both approaches indicate that the finite thickness of the buried SiO2 layerand the reflection at the substrate play important roles on the extinction ratio of the device. A designed numerical example shows an extinction ratio of ~26 dB for the waveguide polarizer with a length of ~10 ?m, while the insertion loss for the TM mode is negligible.
89 citations
TL;DR: In this paper, an asymmetrical fiber Mach-Zehnder interferometer (aFMZI) consisting of a fiber taper and a lateral-shifted junction is proposed and demonstrated to realize simultaneous measurement of axial strain and temperature.
Abstract: An asymmetrical fiber Mach-Zehnder interferometer (aFMZI) consisting of a fiber taper and a lateral-shifted junction is proposed and demonstrated to realize simultaneous measurement of axial strain and temperature. The interferometer exhibits different environmental sensitivities for different device architectures. If the taper and the lateral-shifted junction locate spatially close (15 mm), the experimental results would indicate temperature sensitivities of 60.4 and 63.9 pm/°C (redshift) and axial strain sensitivities of -1.47 and -2.71pm/μe (blueshift) at the higher and lower interference orders m1 (49) and m2 (48), respectively, for the taper-junction interferometer. The junction-taper interferometer has temperature sensitivities of 60.1 and 63.3 pm/°C (redshifts) and axial strain sensitivities of -1.51 and -2.75 pm/μe (blueshifts) at the interference orders m1 and m2 , respectively.
75 citations
TL;DR: In this article, a multiband DFT-spread OFDM (MB-DFT-S-OFDM) is proposed to reduce the peak-to-average power ratio (PAPR) within each subband.
Abstract: There is a common belief that coherent optical orthogonal frequency-division multiplexing (CO-OFDM) has inferior nonlinear performance in the fiber optic channel due to its high peak-to-average power ratio (PAPR). In this paper, we show that due to the uniqueness of chromatic dispersion in the optical fiber, properly designed CO-OFDM can, in fact, possess a nonlinearity advantage over a coherent single carrier (SC) for ultrahigh-speed transport at 100 Gb/s and beyond. In particular, we propose a novel approach called multiband DFT-spread OFDM (MB-DFT-S-OFDM), by which the DFT-S-OFDM is applied to each subband of the multiband CO-OFDM to reduce the PAPR within each subband. It is found that eight-band DFT-S-OFDM surpasses the conventional OFDM and the coherent SC by 1.3 and 0.5 dB, respectively, for SSMF107-Gb/s transmission over a 1000-km standard-single-mode-fiber (SSMF).
TL;DR: In this article, a fringe visibility-enhanced extrinsic Fabry-Perot interferometer (EFPI) was proposed by fusion splicing a quarter-pitch length of a graded-index fiber (GIF) to the lead-in single mode fiber (SMF).
Abstract: We report a fringe visibility-enhanced extrinsic Fabry-Perot interferometer (EFPI) by fusion splicing a quarter-pitch length of a graded-index fiber (GIF) to the lead-in single mode fiber (SMF). The performance of the GIF collimator is theoretically analyzed using a ray matrix model and experimentally verified through beam divergence angle measurements. The fringe visibility of the GIF-collimated EFPI is measured as a function of the cavity length and compared with that of a regular SMF-EFPI. At the cavity length of 500 m, the fringe visibility of the GIF-EFPI is 0.8, while that of the SMF-EFPI is only 0.2. The visibility-enhanced GIF-EFPI may provide a better signal-to-noise ratio (SNR) for applications where a large dynamic range is desired.
TL;DR: In this article, the authors theoretically and experimentally investigated the performance of silicon-on-insulator (SOI) microring add-drop filters in the limit of extreme miniaturization for potential application in very dense integration of silicon photonic devices.
Abstract: We theoretically and experimentally investigated the performance of silicon-on-insulator (SOI) microring add-drop filters in the limit of extreme miniaturization for potential application in very dense integration of silicon photonic devices. Rigorous numerical analyses were performed to predict the theoretical limit of achievable intrinsic quality factors as the microring radius is scaled down to 1 μm. Experimental measurements of fabricated SOI microring resonators showed that ultracompact add-drop microring filters with radii as small as 1 μm can be achieved with a free spectral range exceeding 80 nm and an insertion loss of only 1 dB. These devices are also shown to exhibit intrinsic quality factors approaching the theoretically achievable limit set by the bending loss in ultracompact microring resonators.
TL;DR: It is shown that coded IPQ can achieve capacity for signal-to-noise ratios (SNRs) of up to 25 dB and increase the total propagation distance over optical transmission systems by 275 km over coded star-quadrature amplitude modulation (QAM).
Abstract: In this paper, we propose a nonuniform coded-modulation format based on iterative polar quantization (IPQ) as a scheme to enable achieving channel capacity in ultrahigh-speed optical communication systems. The proposed modulation format is coded with structured low-density parity-check (LDPC) codes optimized for Gaussian channels and, in combination with polarization-multiplexing, can achieve 800 Gb/s per wavelength aggregate rate and beyond utilizing the currently available components operating at 50 GS/s. Using coded IPQ, we show that we can achieve capacity for signal-to-noise ratios (SNRs) of up to 25 dB and increase the total propagation distance over optical transmission systems by 275 km over coded star-quadrature amplitude modulation (QAM).
TL;DR: In this article, a novel long-wavelength vertical-cavity surface-emitting laser (VCSEL) structure based on a subwavelength high-contrast grating (HCG) as the output mirror has been realized.
Abstract: A novel long-wavelength vertical-cavity surface-emitting laser (VCSEL) structure based on a subwavelength high-contrast grating (HCG) as the output mirror has been realized. By design, these devices are highly polarization stable, are single mode at large apertures, and solve the VCSEL-mirror problem at long wavelengths in an elegant way. With cost-effective mass fabrication in mind, the top HCG reflector consists of amorphous silicon on isolator (amorphous silica). The single-mode laser emission is tailored to be around 1320-nm wavelength, targeting applications in high-speed optical data transmission, particularly those for passive optical networks. We report single-mode emission for devices with apertures as large as 11 μm operating in continuous wave with output powers in excess of 0.4 mW. Pulsed operation with output powers up to 4 mW at room temperature is demonstrated as well. This is the first electrically pumped VCSEL structure realized in this wavelength regime utilizing an HCG mirror.
TL;DR: It is shown that AMOOFDM not only significantly reduces the nonlinear wavelength-division multiplexing (WDM) impairments induced by the effects of cross-phase modulation and four-wave mixing but also effectively compensates for the DML-induced frequency chirp effect.
Abstract: The transmission performance of multichannel adaptively modulated optical orthogonal frequency-division multiplexing (AMOOFDM) signals is investigated numerically, for the first time, in optical-amplification-free and chromatic-dispersion-compensation-free intensity-modulation and direct-detection systems directly incorporating modulated distributed feedback (DFB) lasers (DMLs). It is shown that AMOOFDM not only significantly reduces the nonlinear wavelength-division multiplexing (WDM) impairments induced by the effects of cross-phase modulation and four-wave mixing but also effectively compensates for the DML-induced frequency chirp effect. In comparison with conventional modulated optical orthogonal frequency-division multiplexing (OFDM), which uses an identical signal modulation format across all the subcarriers, AMOOFDM improves the maximum achievable signal transmission capacity of a central WDM channel by a factor of 1.3 and 3.6 for 40- and 80-km standard single-mode fibers, respectively, with the corresponding dynamic input optical power ranges being extended by approximately 5 dB. In addition, AMOOFDM also causes the occurrence of cross-channel complementary modulation format mapping among various WDM channels, leading to considerably improved transmission capacities for all individual WDM channels.
TL;DR: In this paper, a novel approach to achieving photonically assisted microwave frequency twelve-tupling with large frequency tunability is proposed and demonstrated, which is realized through a joint operation of polarization modulation, four-wave mixing, and stimulated-Brillouin-scattering-assisted filtering.
Abstract: A novel approach to achieving photonically assisted microwave frequency twelvetupling with large frequency tunability is proposed and demonstrated The frequency twelvetupling is realized through a joint operation of polarization modulation, four-wave mixing, and stimulated-Brillouin-scattering-assisted filtering The key significance of the technique is that the system is capable of realizing simple frequency tuning over a wide frequency range An experiment is performed An electrical signal with a frequency that is tunable from 48 to 132 GHz is generated
TL;DR: In this paper, the authors applied line-by-line pulse shaping on a phase-modulated continuous-wave frequency comb to obtain high-modulation-depth photonic millimeter-wave (MMW) waveforms.
Abstract: We report generation of high-modulation-depth photonic millimeter-wave (MMW) waveforms by applying line-by-line pulse shaping on a phase-modulated continuous-wave frequency comb. The optimized 20 and 100 GHz optical waveforms are then converted into electrical MMW signals using a near-ballistic uni-traveling-carrier photodiode (NBUTC-PD). A 7.4 dB MMW power enhancement is experimentally achieved by using 2.6 ps optimized pulses at a 100 GHz repetition rate, as compared with excitation by a conventional sinusoidal signal for the NBUTC-PD operated at the same photocurrent. This is in qualitative agreement with a theoretical analysis of spectral power enhancement by optical short pulses comprised of equi-amplitude frequency lines over sinusoidal excitation.
TL;DR: In this paper, an InP-based membrane p-i-n photodetector on a silicon-on-insulator sample containing a Si-wiring photonic circuit that is suitable for use in optical interconnections on Si integrated circuits was presented.
Abstract: We present an InP-based membrane p-i-n photodetector on a silicon-on-insulator sample containing a Si-wiring photonic circuit that is suitable for use in optical interconnections on Si integrated circuits (ICs). The detector mesa footprint is 50 μm2, which is the smallest reported to date for this kind of device, and the junction capacitance is below 10 fF, which allows for high integration density and low dynamic power consumption. The measured detector responsivity and 3-dB bandwidth are 0.45 A/W and 33 GHz, respectively. The device fabrication is compatible with wafer-scale processing steps, guaranteeing compatibility toward future-generation electronic IC processing.
TL;DR: In this paper, a nonlinear envelope equation was proposed to study the nonlinear evolution of ultrabroadband optical pulses in quadratic nonlinear media, allowing treatment of all the harmonics by means of a single equation.
Abstract: We present a comprehensive framework to study the nonlinear evolution of ultrabroadband optical pulses in quadratic nonlinear media. We employ a nonlinear envelope equation that goes beyond the traditional slowly varying approximation and allows treatment of all the harmonics by means of a single equation. We exploit this model to simulate recently observed supercontinuum phenomena such as ultrabroadband parametric downconversion and the generation of octave-spanning spectra from femtosecond pulses.
TL;DR: In this article, the authors describe the design, fabrication, and characterization of high-reflectivity broadband mirrors operating in the near-infrared (700-1000 nm) wavelength range, which consist of 1-D and 2-D subwavelength resonant gratings (SWGs) fabricated on a silicon-on-insulator (SOI) wafer.
Abstract: We describe the design, fabrication, and characterization of high-reflectivity broadband mirrors operating in the near-infrared (700-1000 nm) wavelength range. The mirrors consist of 1-D and 2-D subwavelength resonant gratings (SWGs) fabricated on a silicon-on-insulator (SOI) wafer. A very good agreement between numerical and experimental results is obtained. The mirror response can be tailored by adjusting the geometrical parameters of the gratings, with the grating period as the main parameter. The optimized mirrors reflect strongly (> 95%) over a fractional optical bandwidth Δλ/λ of about 12% and 7.5% for 1-D and 2-D gratings, respectively. The important and somewhat surprising feature of these gratings is that high reflectivities have been achieved, despite the fact that silicon exhibits significant absorption in this wavelength range.
TL;DR: In this article, the authors reviewed recent progress on photonic integrated devices for higher bit-rate and long-distance transmission technologies with advanced modulation formats, which are essential for increasing the network capacity at a low cost and with efficient power consumption.
Abstract: Photonic integration technologies, which have been developed since the deployment of optical communications, are essential for increasing the network capacity at a low cost and with efficient power consumption. This paper reviews recent progress on photonic integrated devices for higher bit-rate and long-distance transmission technologies with advanced modulation formats.
TL;DR: The novel components, architecture, and realization of UWB UROOF systems are proposed and new experimental results related to UWB signal up-conversion, photonic radio impulse generation, and digital and analog signal coexistence are presented.
Abstract: We have developed novel ultra-wideband (UWB) radio-over-optical-fiber (UROOF) concepts and technologies for a number of important in-house applications characterized by a high data rate. We propose the novel components, architecture, and realization of UWB UROOF systems. We present new experimental results related to UWB signal up-conversion, photonic radio impulse generation, and digital and analog signal coexistence. We also discuss future trends in the field of UWB UROOF technologies.
TL;DR: Two schemes to simultaneously provide an ultra-wideband (UWB) service and a wired service using a centralized light source are reported, which would greatly reduce the cost while significantly improving the spectrum efficiency of a WDM-PON network incorporating UWB-over-fiber (UWBoF) systems for broadband wireless access.
Abstract: Simultaneous provision of multiple services using a centralized light source can greatly reduce the complexity and cost of a wavelength-division multiplexing passive optical network (WDM-PON). In this paper, we report two schemes to simultaneously provide an ultra-wideband (UWB) service and a wired service using a centralized light source. In one scheme, a UWB signal and a wired signal are multiplexed and modulated on a single wavelength in the center office for wireless and wired downstream services. In the other scheme, the wavelength from a UWB downstream signal is reused in the optical network unit to provide a wired upstream service. Both schemes are experimentally demonstrated with the data-transmission performance evaluated by measuring the electrical spectra, eye diagrams, and receiver sensitivities. The proposed schemes would greatly reduce the cost while significantly improving the spectrum efficiency of a WDM-PON network incorporating UWB-over-fiber (UWBoF) systems for broadband wireless access, making the WDM-PON network more attractive for practical deployment.
TL;DR: In this article, a three-pole modulation function is derived from a 3-D set of rate equations, and a 70% 3-dB bandwidth enhancement is computed and experimentally realized in an undoped quantum-dot gain-lever laser under extreme asymmetric bias conditions.
Abstract: We investigate the small-signal modulation response of two-section, gain-lever, quantum-dot semiconductor lasers. A three-pole modulation function is derived from a 3-D set of rate equations, and a 70% 3-dB bandwidth enhancement is computed and experimentally realized in an undoped quantum-dot gain-lever laser under extreme asymmetric-bias conditions. Finally, it is demonstrated that the 3-dB bandwidth is three times the free-running relaxation oscillation frequency in these types of laser structures, as opposed to 1.55 times in the case of conventional single-section lasers.
TL;DR: In this paper, the Schottky barrier photodetector was shown to have excellent thermal stability in the annealing temperature range of 100°C to 200°C.
Abstract: This paper reports fabrication, characterization, and testing of the thermal stability of ZnO-based Schottky ultraviolet photodetectors. The ZnO thin film was grown on a p-type Si 〈100〉 substrate by the sol-gel technique. The surface morphological and the structural properties of the thin film were studied by an atomic force microscope (AFM) and a scanning electron microscope (SEM). For the investigation of the surface chemical bonding, X-ray photoelectron spectroscopy (XPS) measurements were also performed. The I-V characteristics of the Schottky barrier photodetector were studied, and the parameters such as ideality factor, leakage current, and barrier height were extracted from the measured data at room temperature. With applied bias voltages in the range from -3 to 3 V, the contrast ratio, responsivity, detectivity, and quantum efficiency of the photodetectors were measured for an incident optical power of 0.1 mW at 365-nm wavelength. The electrical and optical study revealed that the performance of the device improves with increasing post metal deposition annealing temperature up to 100°C. The device exhibited excellent thermal stability in the annealing temperature range of 100°C to 200°C. For annealing temperatures beyond 200°C, the performance of the device degrades drastically. It was also found that at under 200°C, there is a harmonious correlation between the photoresponse and electrical characteristics of the device. Above this temperature, there is no correlation between the variations of photoresponse and electrical characteristics with increasing annealing temperature. The variation of the electrical and photoresponse properties of the Schottky photodetector subjected to different post-fabrication annealing can be attributed to the combined effects of interfacial reaction and phase transition during the annealing process.
TL;DR: In this paper, the design of photonic circuits that make use of Ti:LiNbO3 diffused channel waveguides to generate photons with various combinations of modal, spectral, and polarization entanglement was considered.
Abstract: We consider the design of photonic circuits that make use of Ti:LiNbO3 diffused channel waveguides to generate photons with various combinations of modal, spectral, and polarization entanglement. Down-converted photon pairs are generated via spontaneous parametric down-conversion (SPDC) in a two-mode waveguide (TMW). We study a class of photonic circuits comprising: 1) a nonlinear periodically poled TMW structure; 2) a set of single-mode waveguide (SMW)- and TMW-based couplers arranged in such a way that they suitably separate the three photons comprising the SPDC process; and, for some applications, 3) a holographic Bragg grating that acts as a dichroic reflector. The first circuit produces two frequency-degenerate down-converted photons, each with even spatial parity, in two separate SMWs. Changing the parameters of the elements allows this same circuit to produce two nondegenerate down-converted photons that are entangled in frequency or simultaneously entangled in frequency and polarization. The second photonic circuit is designed to produce modal entanglement by distinguishing the photons on the basis of their frequencies. A modified version of this circuit can be used to generate photons that are doubly entangled in mode number and polarization. The third photonic circuit is designed to manage dispersion by converting modal, spectral, and polarization entanglement into path entanglement.
TL;DR: In this paper, p-doped and undoped quantum dot (QD) optical amplifiers (SOAs) having a similar chip gain of 22-24 dB are compared with regard to their static and dynamic characteristics.
Abstract: P-doped and undoped quantum dot (QD) semiconductor optical amplifiers (SOAs) having a similar chip gain of 22-24 dB are compared with regard to their static and dynamic characteristics. Amplified spontaneous emission (ASE) spectra reveal the influence of p-doping on the gain characteristics and the temperature stability. In contrast to QD lasers, p-doping does not significantly increase the thermal stability of QD SOAs. The static four-wave mixing efficiency is larger and more temperature stable in undoped devices, leading to a maximum chip conversion efficiency of -2 dB. Small-signal cross-gain modulation (XGM) experiments show an increase in the small-signal bandwidth from 25 GHz for the p-doped SOAs to 40 GHz for the undoped QD SOAs at the same current density. P-doped QD SOAs also achieve small-signal bandwidths beyond 40 GHz but at a larger bias. The XGM is found to be temperature stable in the range of 20°C to 40°C.
TL;DR: In this paper, the attosecond pulses are now available in many different labs with additional gating techniques which somewhat relax the requirements for the pulse duration of the intense infrared laser pulses.
Abstract: We continue to observe strong progress moving from femtosecond to attosecond optics. Attosecond pulses are now available in many different labs with additional gating techniques which somewhat relax the requirements for the pulse duration of the intense infrared laser pulses. The pulse repetition rate still sets a limit on the signal-to-noise ratio for attosecond pump-probe measurements, and therefore, other streaking techniques have resulted in time-resolved measurements with sub-10-attosecond accuracy. Recent improvements on high-power ultrafast diode-pumped solid-state and fiber lasers will offer alternative sources for megahertz attosecond pulse generation. First proof-of-principle experiments have been demonstrated.
TL;DR: The novel polarization diversity technique is proposed to improve receiving sensitivity and increase the anti-interference capacity of the wireless transmission at the in-building environment.
Abstract: This work presents our recent progress on advanced radio-over-fiber (ROF) technologies for in-building optical-wireless access networks, including multiservice, full-duplex, and polarization diversity ROF system design, as well as the experimental delivery of uncompressed high-definition television (HDTV) signals. The novel polarization diversity technique is proposed to improve receiving sensitivity and increase the anti-interference capacity of the wireless transmission at the in-building environment. Furthermore, the integration architecture of ROF and Ethernet passive optical network (EPON) is investigated, mainly focusing on polar duplex antenna for non-line-of-sight (NLOS) transmission and home gateway for different network topologies. The hybrid system distributes the multimedia services (e.g., HDTV in EPON) and other wireless data services to the terminal rooms over ROF links and thus expands the superbroadband EPON services to the subscribers for the last meters in both wired and wireless ways.