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Lightwave Technology, Journal of

Issue 15 • Date Aug.1, 2008

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Displaying Results 1 - 25 of 66
  • Table of contents

    Page(s): 2333 - 2335
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    Freely Available from IEEE
  • Guest Editorial Special Issue on Microwave Photonics

    Page(s): 2336 - 2337
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    Freely Available from IEEE
  • Transmission Characteristics of 120-GHz-Band Wireless Link Using Radio-on-Fiber Technologies

    Page(s): 2338 - 2344
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1609 KB) |  | HTML iconHTML  

    The transmission characteristics of a 120-GHz-band millimeter-wave wireless link are described. The wireless link uses photonic technologies for generation, modulation, and transmission of millimeter-wave signals. This configuration enables set up of the photonic millimeter-wave generator and transmitter core separately; therefore, the wireless link can be used as a kind of radio-over-fiber system. The effects of transmitting 120-GHz-band optical subcarrier signals through single-mode fibers were theoretically and experimentally investigated. It was confirmed that the time shift of the code edges, because of chromatic dispersion, limits the transmission distance. A data stream at 10-Gbit/s was successfully transmitted over the 120-GHz-band millimeter-wave wireless link, with a bit error rate (BER) below 10-12 over a distance of 250 m. The results also demonstrated the stability of the wireless link, which satisfied the 10-Gb Ethernet standard under clear weather conditions. View full abstract»

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  • Advances in Organic Materials for Optical Modulation

    Page(s): 2345 - 2354
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    Theory-inspired design of organic electro-optic materials is explored for three classes of materials: (1) chromophore/polymer composites; (2) chromophores covalently incorporated into polymers, dendrimers, and dendronized polymers; and (3) chromophores doped into chromophore-containing host materials. Correlated quantum/statistical mechanical calculations are used to quantitatively simulate electro-optic activity for a variety of materials falling into these three classes, elucidating the dependence of electro-optic activity on chromophore dipole moment, chromophore shape, covalent bond potentials, and dielectric permittivity. The practical consequence has been the production of materials exhibiting femtosecond response electro-optic activity approaching 600 pm/V at telecommunication wavelengths. Theory also provides insight into minimizing optical loss and maximizing stability. View full abstract»

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  • Phase-Only Matched Filtering of Ultrawideband Arbitrary Microwave Waveforms via Optical Pulse Shaping

    Page(s): 2355 - 2363
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    We demonstrate compression of ultrawideband (UWB) microwave arbitrary waveforms via phase-only matched filtering implemented in a programmable hyperfine resolution optical pulse shaper. We synthesize spread-time UWB electrical waveforms and utilize programmable microwave photonic phase filters to impose the opposite of a waveform's spectral phase on its spectrum. This enables us to compress an UWB microwave waveform to its corresponding bandwidth-limited pulse duration via phase filtering. As an example, we present compression of a linear frequency-modulated electrical waveform with > 15 GHz frequency content with almost 200% fractional bandwidth with ~ 733 ps temporal window to a 40-ps duration pulse with more than 14-dB gain in peak power. Our technique is programmable and we believe it is applicable to a wide range of arbitrary spectral phase modulated UWB radio frequency (RF) waveforms. View full abstract»

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  • Ultra-Broadband Wireless Home Network Based on 60-GHz WPAN Cells Interconnected via RoF

    Page(s): 2364 - 2372
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    In this paper, we first identify the key requirements for the deployment of a 1-Gb/s ultra-broadband home area network (UBB-HAN). Second, we propose an architecture based on a transparent optical backbone feeding local access points. Third, we underline the role of the IEEE802.15.3c pre-standard to provide a suitable radio interface for the UBB-HAN and demonstrate the technical feasibility of the concept using radio over fiber (RoF). More than 1-Gb/s transmission is demonstrated for 50-m optical antenna remoting using radio-over-fiber plus 15-m radio transmission. View full abstract»

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  • Linearity of Modified Uni-Traveling Carrier Photodiodes

    Page(s): 2373 - 2378
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    The third-order intermodulation distortions of an InGaAs/InP charge compensated modified uni-traveling carrier (UTC) photodiode are characterized using a two-tone setup. At 0.3-GHz modulation frequency and photocurrents above 40 mA, the third-order local intercept point (IP3) reaches a record-high of 52 dBm and remains above 35 dBm up to the photodiode's 3-dB bandwidth. A simple equivalent circuit model with a voltage-dependent responsivity and a voltage- and photocurrent-dependent junction capacitance is used to explain the frequency characteristics of the intermodulation distortions. View full abstract»

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  • 60-GHz System-on-Packaging Transmitter for Radio-Over-Fiber Applications

    Page(s): 2379 - 2387
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    Using ultra-high-speed electroabsorption modulator (EAM) devices for RF/optic conversion, we fabricated system-on-packaging (SOP) transmitter (Tx) modules and characterized their performance in 60-GHz RF/radio-over-fiber (ROF) applications. Both an EAM and low-noise amplifiers (LNAs) were co-packaged with internal bias circuits into a butterfly-type metal housing. At the EAM temperature,T~ 25degC and the EAM reverse bias, VR~1.6 V was the largest RF gain obtained that was very susceptible to the change of T . The impedance matching in the 60-GHz band was accomplished with both a microstrip-line bandpass filter and a 500- Omega shunt resistor, which defined the 2-GHz passband of the SOP transmitter. In 60-GHz two-tone experiments, we observed that the spurious free dynamic range of an SOP module with two LNAs was 78 dB middot Hz2/3 while that of the narrowband EAM module showed 82 dB middot Hz2/3. In contrast, the noise figure exhibited a large reduction of up to 30 dB for the SOP module compared with the narrowband EAM module. Using the SOP Tx module, we achieved successful transmission of commercial high-definition digital CATV signals in 64-quadrature amplitude modulation (QAM) format through the 60-GHz RF/ROF link. The total throughput of the link was estimated to be 6.5 Gb/s. View full abstract»

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  • Radio-Over-MMF Techniques—Part I: RF to Microwave Frequency Systems

    Page(s): 2388 - 2395
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    Recent work on radio-over-multimode-fiber (MMF) transmission, for the support of wireless LANs and current cellular systems operating at below 6 GHz, has shown that excellent performance (e.g., spur-free dynamic range well in excess of 100 dB.Hz2/3) can be achieved. However, it is shown here that for multisystem operation, spurious emissions may be more of a restriction than meeting good signal quality requirements (such as low error vector magnitude). Initial results are reported for error vector magnitude and adjacent channel leakage for UMTS transmission over a radio-over-MMF link with a multisystem remote antenna unit with conformance to standards being demonstrated. View full abstract»

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  • Radio-Over-MMF Techniques—Part II: Microwave to Millimeter-Wave Systems

    Page(s): 2396 - 2408
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    Microwave to mm-wave radio carriers are commonly employed for creating high-capacity picocell wireless networks. Advanced radio-over-fiber (RoF) techniques can efficiently generate and transport such carriers, and deliver them to simplified antenna stations. As in in-building networks multimode fiber is predominantly used, adequate radio-over-multimode fiber (RoMMF) techniques are required to overcome the modal dispersion in multimode fiber links. The optical frequency multiplying technique is introduced; it is relatively simple to implement, yet it is shown to be robust against the modal dispersion, and it is able to generate very pure microwave carriers while requiring only moderate speed electronics. Thus, it can convey high data rates in comprehensive modulation formats on multiple-GHz carriers in MMF networks. It offers simultaneous operation at multiple radio standards, and capabilities for dynamic adaptation of the radio link parameters such as carrier frequency, transmit power, and other antenna site functions by means of an embedded control channel. Moreover, in combination with optical routing it enables dynamically adjustable network configurations for flexible wireless service delivery. View full abstract»

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  • Terahertz Photonics: Optoelectronic Techniques for Generation and Detection of Terahertz Waves

    Page(s): 2409 - 2423
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    Optoelectronic techniques for generation and detection of terahertz (THz) signals have been reviewed. The operation principles of THz photomixer sources and THz parametric sources have been studied and recent developments in these areas have been presented. The performances of developed THz optoelectronic sources have been discussed and compared. View full abstract»

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  • 60-GHz Photonic Millimeter-Wave Link for Short- to Medium-Range Wireless Transmission Up to 12.5 Gb/s

    Page(s): 2424 - 2429
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    In this paper, a 60-GHz photonic millimeter-wave link system for short- to medium-range broadband wireless data transmission is investigated. The system employs advanced mm-wave photonic components and radio-over-fiber (RoF) techniques for the generation of a DSB-SC optical mm-wave carrier and its subsequent on-off-keying modulation and transmission. For short-range applications, we have constructed a compact wireless RoF transmitter consisting of a high-frequency photodiode and a mm-wave antenna only. This system achieved error-free (BER=10-9, 231-1 PRBS, NRZ) in-door transmission of 12.5-Gb/s signals over wireless distances up to 3.1 m with a receiver sensitivity as low as - 45.4 dBm . For fixed wireless access (FWA) requiring a bit error rate of 10-4, the maximum transmission distance for 12.5 Gb/s is increased up to 5.8 m. For medium-range broadband wireless transmission an electrical radio-frequency (RF) amplifier was employed in the RoF transmitter. Here we achieved 7.5-Gb/s error-free transmission in out-door line-of-sight experiments over wireless distances of up to 36 m. Based upon the experimental results, we expect that the maximum wireless distance the system could accommodate for 12.5 Gb/s is in the kilometer range when using high-gain antennas and an RF transmitter amplifier with a sufficient bandwidth. View full abstract»

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  • High-Power Microwave Generation With Photoconductors

    Page(s): 2430 - 2440
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    This paper describes an unconventional method for the generation of high-power microwave (HPM) with orders of magnitude higher in power and energy than competing concepts. The method brings together several synergistic concepts. First, microwaves are synthesized cycle by cycle (digital synthesis) by the discharge of charged transmission lines. The method presented here generates a bipolar pulse with substantial impedance transformation. Second, photonic on switching via photoconductors is used to provide coherent timing. Third, the generation of HPM at extremely low impedance takes advantage of a fortuitous match between the peak Poynting power associated with thin films and high current density related to very high carrier concentration in photoconductors. Finally, unique HPM circuitry, termed a Switch Bypass Source circuit, is presented that affords multiple cycle generation and high pulse energy which avoids cascading switch losses. The combination of these techniques transforms HPM technology from the present level of gigawatts and hundreds of joules per pulse to levels that are orders of magnitude higher. View full abstract»

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  • RF-Over-Fiber Links With Very Low Noise Figure

    Page(s): 2441 - 2448
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    Previously published analytical models for the noise figure of an amplifierless fiber-optic link fail to predict the measured performance, with a discrepancy of 1.1 dB at 1 GHz that increases to 2.3 dB by 12 GHz. We use an equivalent circuit to derive the effect of an additional source of noise not accounted for in earlier models: thermal noise arising from loss in the modulator's traveling-wave electrodes. The electrode thermal noise has a frequency dependence matching that of the link's noise figure, such that predictions using the improved model match the measured 1-12 GHz performance of a link with record low noise figure to within ~ 0.4 dB across this band. View full abstract»

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  • Impact of Nonlinear Transfer Function and Imperfect Splitting Ratio of MZM on Optical Up-Conversion Employing Double Sideband With Carrier Suppression Modulation

    Page(s): 2449 - 2459
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    Generation of optical millimeter-wave (mm-wave) signal using a Mach-Zehnder modulator (MZM) based on double-sideband (DSB), single-sideband (SSB), and double-sideband with carrier suppression (DSBCS) modulation schemes have been demonstrated for various applications, such as broadband wireless signals or optical up-conversion for wavelength-division-multiplexing (WDM) radio-over-fiber (RoF) network, wideband surveillance, spread spectrum, and software-defined radio. Among these schemes, DSBCS modulation offers the best receiver sensitivity, lowest spectral occupancy, the least stringent requirement of electrical bandwidth, and the smallest receiving power penalty after long transmission distance. Nonetheless, the inherent nonlinear E/O (electrical/optical) conversion response of a MZM is such that the signal quality of the optical mm-wave suffers. Fabrication tolerances make a balanced 50/50 splitting ratio of the MZM's y-splitter particularly difficult to achieve. As a result, imbalanced MZMs have a finite extinction ratio (ER) and degrade the optical carrier suppression ratio (OCSR) using DSBCS modulation. In this paper, the effect of the MZM nonlinearity and imbalanced y-splitter on optical mm-wave generation by DSBCS modulation is theoretically and experimentally investigated. A novel approach with better performance and greater cost-effectiveness than dual-electrode MZM (DD-MZM) is presented to realize a DSBCS modulation scheme based on a single-electrode MZM (SD-MZM). View full abstract»

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  • Phase-Locked Coherent Demodulator With Feedback and Sampling for Optically Phase-Modulated Microwave Links

    Page(s): 2460 - 2475
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    A novel phase-locked coherent optical phase demodulator with feedback and sampling is presented and investigated for high-linearity microwave photonic links. The overall receiver concept is novel in terms that we use feedback loop for linear phase demodulation and optical sampling to achieve operation at high RF signal frequencies. The phase-locked demodulator is to be used for RF signal demodulation of optically phase-modulated analog links. We aim at operating the demodulator for short-range applications since the demodulator only recovers the phase. A new time-domain numerical model is developed and the calculated results are in good agreement with measurements. The effect of amplitude and timing jitter associated with the optical pulse source is also taken into account. Stochastic Euler scheme is used to solve stochastic differential equations associated with amplitude and timing jitter. Using the model, we investigate how loop gain, tracking phase-modulator nonlinearities and amplitude modulation influence the signal-to-intermodulation ratio (SIR) of the demodulated signal. Furthermore, in order to alleviate nonlinearities associated with the tracking phase modulator, we report on a novel cancellation technique. The proposed cancellation technique is input RF signal power and frequency independent leading to a significant increase in dynamic range of the coherent demodulator. This technique demonstrates that large values of the signal-to-intermodulation ratio of the demodulated signal can be obtained even though the tracking phase modulator is fairly nonlinear, and thereby relaxing the linearity requirements for the tracking phase modulator. The demodulator is capable of operating at high frequencies, by using optical sampling to downconvert the high-frequency input RF signal to the frequency range of the baseband loop. Using the model the effect of optical sampling on the signal demodulation is investigated. The simulation results show that the operation of th- - e sampling demodulator resembles the operation of the baseband demodulator for very short optical pulses (<2 ps). We also investigate how signal-to-noise-ratio of the demodulator is affected by timing and amplitude jitter of the pulsed optical source. Finally, experimental demonstration of the sampling loop using the phase-locked demodulator is presented. We show that an improvement of 14.1 dB in spur-free-dynamic-range is obtained using the proposed phase-locked coherent demodulator compared to the open loop sampling. View full abstract»

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  • Reconfigurable RF-Waveform Generation Based on Incoherent-Filter Design

    Page(s): 2476 - 2483
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1002 KB) |  | HTML iconHTML  

    Radio-frequency (RF) waveform generators are key devices for a variety of applications, including radar, ultra-wideband communications, and electronic test measurements. Following advances in broadband coherent pulsed sources and pulse-shaping technologies, reconfigurable RF waveform generators operating at bandwidths >1 GHz have become a reality. In this work, we demonstrate reconfigurable RF waveform generation using broadband spectrally incoherent optical sources. This is achieved in two steps. First, we implement an RF incoherent filter. The energy spectrum of the optical source is conveniently apodized using a commercially available computer-controlled D-WDM channel selector with 100-GHz resolution. The channel controller provides high flexibility for shaping the optical source energy spectrum and, hence, high reconfigurability capabilities in terms of the RF filter. Second, we show that by applying a short baseband electrical waveform to the input of the RF filter, the output RF spectrum of the electrical signal is a mapped version of the designed RF filter transfer function. Specifically, we illustrate the capabilities of our technique by generating RF signals with ~ 10 GHz bandwidth and tunable repetition rate. Finally, we discuss how this method can be scaled up to the millimeter-wave range with current technology. View full abstract»

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  • Optically Powered Remote Units for Radio-Over-Fiber Systems

    Page(s): 2484 - 2491
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    Optically powered radio-over-fiber remote units have been designed and constructed for distributed antenna system applications using separate fibers for power and signal transmission. The feasibility of this approach has been investigated through a series of transmission measurements, based on the IEEE 802.11g wireless local area networking standard at a frequency of 2.5 GHz using 64-QAM OFDM modulation at 54 Mb/s. These measurements show that high-quality multilevel signal transmission is possible with modest levels of optical power at the central unit. For example, an EVM of around 3% has been achieved for an RF output power of 0 dBm using a central unit optical power of 250 mW over a link length of 300 m. View full abstract»

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  • Methods for Ultra-Wideband Pulse Generation Based on Optical Cross-Polarization Modulation

    Page(s): 2492 - 2499
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    Optical methods for different type ultra-wideband (UWB) pulse generation based on cross-polarization modulation (CPM) are proposed and demonstrated in this paper. Two polarity-reverse pulses can be obtained by CPM and birefringence time delay to form a monocycle pulse. A semiconductor optical amplifier (SOA) is placed after the monocycle pulse process for doublet pulse generation. These two kinds of pulses can be employed in single-band impulse radio UWB (IR-UWB) systems. Two kinds of multi-band UWB pulses can be generated based on monocycle pulse train with proper apodization profiles, realized by hybrid photonic microwave filter and synchronous polarization modulation respectively. Experimental results show that these pulses can be used in multi-band UWB (MB-UWB) over fiber systems. View full abstract»

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  • High-Speed High-Isolation 2 , \times , 2 Fiber-Optic Switch for Wideband Radar Photonic Beamforming Controls

    Page(s): 2500 - 2505
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    A new high-performance 2 x 2 fiber-optic switch is designed and demonstrated for wideband radar photonic beamforming controls. The switch deploys two bulk acoustooptic deflectors (AODs) in an imaging free-space symmetric optical design that exploits image inversion control via a Dove prism to form a 2 X 2 fully reversible low crosstalk noise high-speed switching structure. Experiments at the 1550-nm test wavelength show the switch to handle 0.5-W level optical input powers, < 2.2-mus switching time, <2.6-dB fiber-to-fiber optical loss, better than 56-dB optical crosstalk levels, and <0.2-dB polarization-dependent loss (PDL).and <0.2-dB polarization-dependent loss (PDL). Index terms-delay lines, optical switches, phased-array radar. View full abstract»

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  • Reconfigurable 2.5-Gb/s Baseband and 60-GHz (155-Mb/s) Millimeter-Waveband Radio-Over-Fiber (Interleaving) Access Network

    Page(s): 2506 - 2512
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    In this paper, we propose a dynamic reconfigurable wavelength division multiplexed (WDM) millimeter-waveband radio-over-fiber (RoF) and baseband access network. We also demonstrate dynamic channel allocation capability of millimeter-waveband optical RoF and baseband signals in WDM access network using a supercontinuum (SC) light source, arrayed-waveguide gratings, and a reconfigurable optical crossconnect switch. The dynamic reconfigurable RoF and baseband network architecture is presented and its features are described. Two 155-Mb/s RoF channels and two 2.5-Gb/s baseband channels are effectively generated, transmitted through 25 km of fiber, switched, and then transmitted again through 2 km of fiber and detected with error-free operation (bit error rate< 10-9). The proposed architecture allows the RoF and baseband to coexist and is highly scalable, both in terms of channel counts and access point (AP) counts. View full abstract»

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  • Optical Generation of Binary Phase-Coded Direct-Sequence UWB Signals Using a Multichannel Chirped Fiber Bragg Grating

    Page(s): 2513 - 2520
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1067 KB) |  | HTML iconHTML  

    A novel technique to generate binary phase-coded, direct-sequence ultra-wideband (DS-UWB) signals in the optical domain is proposed and demonstrated. In the proposed system, the wavelengths from a laser array are modulated by a Gaussian pulse, which is sent to a multichannel optical frequency discriminator, to generate a UWB monocycle or doublet pulse sequence with a predetermined phase-code pattern. By tuning the wavelengths of the laser array, or by tuning the states of polarization of the wavelengths, the generated pulse shape and code pattern can be changed. The key device in the system is the multichannel dispersive chirped fiber Bragg grating (FBG), which functions, in combination with a dispersive fiber, as a multichannel frequency discriminator with a step-increased group-delay response, to ensure the generated UWB sequence to have uniform time spacing among the chips and to compensate for the fiber-induced chromatic dispersion. The proposed scheme is experimentally demonstrated. A multichannel chirped FBG is designed and fabricated. Binary phase-coded DS-UWB signals with different code patterns are experimentally generated. View full abstract»

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  • Broadband-Frequency-Tunable Sub-Terahertz Wave Generation Using an Optical Comb, AWGs, Optical Switches, and a Uni-Traveling Carrier Photodiode for Spectroscopic Applications

    Page(s): 2521 - 2530
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1639 KB) |  | HTML iconHTML  

    We present a monochromatic sub-terahertz signal generation technique using an optical comb signal, arrayed waveguide gratings (AWGs), and a uni-traveling carrier photodiode (UTC-PD) for spectroscopic applications. This scheme offers random or continuous frequency tuning in the range between 100 GHz and up to 1 THz. In addition, since a RF synthesizer is employed as a reference signal source of the photonic frequency multiplier, frequency locking with external instruments and reliable operation are offered. Highly coherent optical comb signal for the photonic frequency multiplication provides a narrow linewidth and very low phase noise in the generated sub-terahertz signal. For 125 GHz, the phase noise is approximately -92 dBc/Hz at the offset frequency of 10 kHz. This is larger than that of the 25-GHz RF source by about 13 dB and agrees well with the theory regarding phase noise multiplications due to frequency multiplication. For generating monochromatic signals, unwanted spurious signals are suppressed in the optical domain over a wide range with two AWGs, and the suppression ratio is expected to be better than 46 dBc. Utilizing the implemented sub-terahertz signal generator with a J-band UTC-PD module, absorption lines of N2O were measured in the frequency range between 240 and 360 GHz and compared with theoretical calculations. View full abstract»

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  • Analysis of the Request to Send/Clear to Send Exchange in WLAN Over Fiber Networks

    Page(s): 2531 - 2539
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (515 KB) |  | HTML iconHTML  

    A study of the effect of the optical path delay on the effectiveness of the request to send/clear to send (RTS/CTS) exchange in high-speed IEEE 802.11 wireless LAN (WLAN) over fiber networks has been carried out. It is shown that although the fiber delay might violate some of the timing boundaries of the medium access control (MAC) protocol, with a careful choice of the RTS threshold parameter, which determines when the RTS/CTS is used, these networks can benefit significantly from the four-way handshake even without the need for modifying the existing protocol. View full abstract»

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  • Performance Impairments in Single-Mode Radio-Over-Fiber Systems Due to MAC Constraints

    Page(s): 2540 - 2548
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1228 KB) |  | HTML iconHTML  

    This paper investigates performance impairments due to constraints imposed by the MAC layer when single-mode fiber (SMF) is used to extend the reach of an IEEE 802.11 network. It is shown that data throughput decreases as fiber length increases. It is also noted that the network fails long before physical layer limitations set in due to the timeout values defined within the MAC protocol. This study is based on both variants of the IEEE 802.11 Distributed Coordination Function. Moreover, both UDP and TCP packet transmissions are taken into account. An experimental enquiry is initially developed to provide a set of validation points before extending these results by simulations using the OPNET platform. Finally, an analytical approximation is presented to these results that allows designers of Radio-over-fiber (RoF) systems to quickly and accurately predict the data throughput given the specific parameters of their network. To our knowledge, this is the first analysis of this kind for a long reach fiber system. View full abstract»

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Aims & Scope

The Journal of Lightwave Technology contains articles on current research, applications and methods used in lightwave technology and fiber optics.

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Meet Our Editors

Editor-in-Chief
Peter J. Winzer
Alcatel-Lucent Bell Labs