84 research outputs found
Influence Factors of an All-Optical Recovered Clock from Two-Section DFB Lasers
No full textAll-optical clock recovery by a two-section DFB laser with different injection wavelengths is demonstrated experimentally at 38.5 GHz. An optical clock with a root-mean-square timing jitter of 250 fs and an extinction ratio of 12.1 dB is obtained with 1551 nm injection. The timing jitter of the recovered clock is further investigated for various intensity ratios of the two DFB emission modes
Amplified feedback DFB laser for 40 Gb/s all-optical clock recovery
No full textA monolithic integrated amplified feedback semiconductor laser (AFL) was fabricated based on quantum well intermixing (QWI) technique. The AFL works as a self-pulsation laser. It consists of a gain-coupled multiple quantum well distribute feedback (DFB) laser diode (LD) section, a passive phase section and an amplified feedback section. The free-running repetition frequency of the AFL can be tuned from 32 GHz to 51 GHz via controlling the feedback strength. All-optical 40 Gb/s clock recovery was experimentally demonstrated using the AFL with a low timing jitter. (C) 2011 Elsevier BM. All rights reserved
NEAR-INFRARED SPECTROSCOPY WITH DFB LASERS
No full textAuthor Institution: Department of Physics, Faculty of Science and Technology, Keio UniversitySemiconductor lasers in the 1.3 to region are rapidly developed for the demand of optical communication, and a DFB (Distributed Feedback) laser which operates at a single longitudinal mode is available. It is an excellent light source not only for optical communication but for molecular spectroscopy. It has a lot of advantages over Pb-salt diode lasers widely used for infrared spectroscopy: it operates at room temperature needs no monochromator, and continuously sweeps its frequency over 50 without any gaps and jumps. The emitted power is large and smoothly varied against change of injection current and frequency. Absorption spectra of and HCN are recorded from to with two DFB lasers and the molecular constants of some excited vibrational states will be reported
The Experimental Design of Radio-over-Fibre System for 4G Long Term Evolution
No full textThe 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is the potential key to meet the exponentially increasing demand of the mobile end users. The entire LTE network architecture and signal processing is carried out at the enhanced NodeB (eNB) level, hence the increased complexity and cost. Therefore, it is not efficient to deploy eNB for the purpose of extending the network coverage. As a solution, deployment of relay node (RN), with radio-over-fibre (RoF) acting as the interface between eNB and RN is proposed. Due to the high path loss and multipath fading, wireless interface would not be the ideal channel between eNB and RN. A detailed investigation is carried out by comparing the Rayleigh multipath fading channel with the optical fibre channel, where the latter achieved a ~31 dB of signal-to-noise ratio (SNR) gain. The distributed feedback laser (DFB) is selected as the direct modulated laser (DML) source, where the modulation method introduces a positive frequency chirp (PFC). The existing mathematical expression does not precisely explain on how the rate equations contribute to PFC. Therefore, an expression for PFC is proposed and derived from the carrier and photon densities of the rate equations. Focusing on theoretical development of DML based RoF system, a varying fast Fourier transform (FFT) scheme is introduced into LTE-Advanced (LTE-A) technology as an alternative design to the carrier aggregation. A range of FFT sizes are investigated with different levels of optical launch power (OLP), the optimum OLP has been defined to be within the range of ~-6 to 0 dBm, which is known as the intermixing region. It is found that FFT size-128 provides improved average system efficiency of ~54% and ~65% in comparison to FFT size-64 and FFT size-128, respectively, within the intermixing region. While fixing FFT size to 128, the investigation is diverted to the optimisation of optical modulators. The author revealed that the performance of dual electrode-Mach Zehnder modulator (DE-MZM) is superior to both DML scheme and single electrode (SE)-MZM, where DE-MZM achieved a transmission span of 88 km and 71 km for 16-quadrature amplitude modulation (QAM) and 64-QAM, respectively. At the initial experimental link design and optimisation stage, an optimum modulation region (OMR) is proposed at the optical modulation index (OMI) of 0.38, which resulted in an average error vector magnitude (EVM) of ~1.01% for a 10 km span. The EVM of ~1.01% is further improved by introducing the optimum OLP region at –2 dBm, where the observed average EVM trimmed to ~0.96%. There is no deviation found in the intermixing region by transmitting the LTE signal through a varying transmission span of 10 to 60 km, additionally, it was also revealed that the LTE RoF nonlinear threshold falls above the OLP of 6 dBm. The proposed system was further developed to accommodate 2×2 multiple-input and multiple-output (MIMO) transmission by utilising analogue frequency division multiplexing (FDM) technique. The studies procured that the resulting output quality of signal at 2 GHz and 2.6 GHz is almost identical with a twofold gain in the peak data rate and no occurrence of intermodulation (IMD). In order to emulate the complete LTE RoF solution, an experimental design of full duplex frequency division duplex (FDD) system with dense wavelength division multiplexing (DWDM) architecture is proposed. It is found that channel spacing of 50 MHz between the downlink (DL) and uplink (UL) introduces severe IMD distortion, where an adjacent channel leakage ratio (ACLR) penalty of 14.10 dB is observed. Finally, a novel nonlinear compensation technique utilising a direct modulation based frequency dithering (DMFD) scheme is proposed. The LTE RoF system average SNR gain observed at OLP of 10 dBm for the 50 km transmission span is ~5.97 dB. External modulation based frequency dithering (EMFD) exhibits ~3 dB of average SNR gain over DMFD method
Demonstration of 80 Gbps NRZ-OOK electro-absorption modulation of InP-on-Si DFB laser diodes
No full textHigh-speed electro-absorption modulation of a heterogeneously integrated InP-on-Si DFB laser diode is used for the transmission of an 80 Gbps NRZ-OOK signal over 2 km of NZ-DSF link below the hard-decision forward-error-correction threshold. (C) 2019 The Author(s
Millimeter-wave frequency tripling based on four-wave mixing in sideband injection locking DFB lasers
No full textan approach to generating 60 GHz millimeter- (mm-) wave carrier based on four-wave mixing (FWM) effect is experimentally demonstrated. The FWM effect is generated in a slave DFB laser which is injection locked by the side band of a modulated tunable DFB laser. The optically generated mm-wave carrier has a frequency of 60 GRz with a 3 dB- bandwidth less than 30 Hz and a phase noise less than -95 dBc/Hz at 100 kHz offset.Engineering, Electrical & ElectronicPhysics, AppliedEICPCI-S(ISTP)
DFB Laser Diode Pumped Rubidium Atomic Frequency Standard
No full textWe present our recently experimental results on a DFB laser diode pumped Rubidium atomic frequency standard. Our experiment was based on a homemade lamp-pumped Rubidium frequency standard with the discharge lamp assembly removed. In the experiment, we first locked a DFB laser diode to the (87)Rb cycling transition (5S(1/2), F=2 -> 5P(3/2), F=3) by means of saturation absorption locking technique. After that, we optimized the parameters carefully related to the clock performance, such as temperature of the physical package, amplitude of the modulation signal for the laser locking. The preliminary short-term stability of our clock is measured 5.25x10(-12)tau(-1/2) (1s<tau<100s).http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000295261600046&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Engineering, Electrical & ElectronicPhysics, AppliedTelecommunicationsCPCI-S(ISTP)
DFB Fiber Laser Hydrophone With an Acoustic Low-Pass Filter
No full textA novel distributed-feedback (DFB) fiber laser hydrophone with an acoustic low-pass filter is presented. An aluminous cover with an orifice in the center is used to eliminate high-frequency acoustic components. The acoustic pressure response is theoretically analyzed based on an electro-acoustic method. Two types of hydrophones of this kind have been fabricated and tested. The experimental results over the range of 10 to 2000 Hz are in good agreement with the theoretical expectations
Single-sideband Modulation of Vector Signals Based on an Injection-locked DFB Laser in 60-GHz RoF Systems
No full textWe experimentally demonstrate vector signals transmission over 60-GHz RoF systems using single-sideband modulation based on an injection-locked DFB laser. Both 1-Gb/s QPSK and 1.2-Gb/s 16QAM transmission over 50-km SSMF are realized successfully. (C) 2010 Optical Society of Americahttp://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000290513601074&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Engineering, Electrical & ElectronicOpticsPhysics, AppliedEICPCI-S(ISTP)
Modeling of DFB surface emitting lasers and semiconductor laser arrays
No full textTheoretical modeling of novel semiconductor laser systems, i.e., distributed-feedback (DFB) surface emitting lasers and semiconductor laser arrays, is presented. The DFB surface emitting lasers can produce stable single-mode outputs even under high bit-rate direct modulation and form two-dimensional laser arrays. A simple and accurate analytical model using the coupled-mode theory is developed to describe these surface emitting lasers. Due to the simplicity of the model, the desired laser output characteristics, i.e., low threshold condition, large side mode suppression ratio, and stable and low noise Bragg-mode outputs, can be obtained by systematically optimizing the device length, optical coupling and phase shifter in the device.The nonplanar laser arrays are of much interest because of their simple fabricating procedures and very high output power. A theoretical study is performed to understand the efficiency and far-field and near-field patterns. A number of important physical mechanisms for high power semiconductor laser operations are studied using a self-consistent model. These include the two-dimensional current spreading in the cladding layers, the coupling between the carrier distribution and the photon distribution, and the carrier saturation effects at high power operation. The mesas, bends, and grooves are treated as adjacent waveguides, each described by the effective index method. The output field patterns in the nonplanar laser structures are composed of a linear combination of the individual waveguide modes. The multimode operation in practical devices can be explained by spatial hole burning effects, nonuniform current injection, and competition for available carriers in the neighboring waveguides between different optical modes. The possibility of obtaining phase-locked output by reducing the groove depth is also investigated. A finite-difference time-domain (FDTD) model is used to study the radiation losses due to the bend. A groove depth as small as 0.1 m can be used for maximum optical coupling while the bending loss is still large enough to suppress the lateral lasing operation in the nonplanar laser array.The highest semiconductor laser output powers have been achieved by the laser arrays employing optical turning mirrors. The effects of the rough turning mirrors on the laser array performance are estimated using the FDTD method. A number of steps are employed to reduce the computation time on these very large mirrors (about sixty wavelengths) to make the FDTD model a possible computer-aided design tool. The computation time is reduced by a factor of twenty.Made available in DSpace on 2011-05-07T12:55:51Z (GMT). No. of bitstreams: 2
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