KEYWORDS: Polarization, Radio optics, Laser optics, Radio over Fiber, Signal detection, Digital signal processing, Hybrid fiber radio, Interference (communication), Modulation, Single mode fibers, Sensors, Light sources
One of polarization diversity techniques in offset-frequency-spaced two-tone optical coherent transmission of radio-over-fiber signal is investigated. As the polarization diversity, successful combination of quadrature-phase-shift-keying constellations recovered from two orthogonal polarization components after a 20-km fiber-optic transmission is experimentally demonstrated.
The millimeter-wave (MMW) radar is a promising candidate for high-precision imaging because of its short wavelength and broad range of available bandwidths. In particular in the frequency range of 92-100 GHz, which is regulated for radiolocation, an atmospheric attenuation coefficient less than 1 dB/km limits the imaging range. Therefore, a combination of MMW radar and distributed antenna system directly connected to optical fiber networks can realize both high-precision imaging and large-area surveillance. In this paper, we demonstrate a multi-channel MMW frequency-modulated continuous-wave distributed radar system connected to an analog radio-over-fiber network.
KEYWORDS: Radio over Fiber, Modulation, Digital signal processing, Laser optics, Radio optics, Signal detection, Single mode fibers, Interference (communication), Sensors, Signal generators
We have proposed a laser-phase-fluctuation-insensitive optical coherent detection scheme assisted by a digital signal processing (DSP) technique for radio-over-fiber (RoF) systems. In this system, a “two-tone” local light is used for an individual optical coherent detection of both the carrier and the modulated components of RoF signal, where a frequency separation of two-tone local light is the same as that of RoF signal. To distinguish the carrier and the modulated components in the process of optical coherent detection, they have to be separated in the optical domain. In this paper, we proposed a new optical coherent detection scheme with an “offset-frequency-spaced two-tone” local light, which is also in principle insensitive to the laser phase fluctuation and is assisted by the DSP technique. In the proposed scheme, it is not required to separate the carrier and the modulated components in the optical domain because they can be easily separated in the electrical domain after the photodetection. Therefore, the system configuration is expected to be simpler than that in the previous scheme. First, we explain the principle of our new proposal and experimentally demonstrate the data recovery. Then, the influence of the frequency detuning between photo-detected modulated and unmodulated signals is discussed. Moreover, the transmission performance with an error vector magnitude (EVM) is also evaluated for the optical coherent detection of a 10-Gbaud quadrature-phase-shift-keying RoF signal after a 20-km-long standard single-mode fiber transmission. As a result, it is shown that the EVM of less than 12.4 %rms is achieved.
KEYWORDS: Radio optics, Radio over Fiber, Digital signal processing, Modulation, Modulators, Networks, Signal generators, Terahertz radiation, Frequency conversion, Signal to noise ratio
In this paper, we describe seamless networks based on millimeter and terahertz wave radio links using waveform transfer over optical fibers. Coherent optical transceivers with digital signal processing provide transmission impairment compensation in both optical and radio sections, where devices for the signal processing are implemented at edges of the links. Waveforms, which include the modulation formats, the symbol rates, etc., are maintained in the entire links, to reduce transmission latency and energy consumption in the network.
KEYWORDS: Radio over Fiber, Standards development, Telecommunications, Modulation, Analog electronics, Radio optics, Transceivers, Optical networks, Modulators, Networks
The Radio on Fiber (RoF) technologies are unique transmission means of radio analog signals through optical fiber cables. These technologies are currently discussed at international standard organizations such as ITU-T, IEC, APT and IEEE802. This invited paper summarizes RoF standardization activities at those standard organizations.
KEYWORDS: Radio over Fiber, Radio optics, Digital signal processing, Frequency combs, Optical amplifiers, Forward error correction, Telecommunications, Signal detection, Antennas, Signal generators
Millimeter-wave and sub-millimeter-wave radio-over-fiber (RoF) technology with digital-signal-processing aided coherent detection can be a promising candidate for high-speed radio transmission links with a capacity of greater than 10 Gb/s if the energy consumption does not increase drastically. We demonstrate 100-GHz and 300-GHz-band simultaneous RoF signal generation using an optical frequency comb source comprising an optical frequency shifter in an amplified optical fiber loop, and its radio transmission over the air. 10-Gbaud quadrature-phase-shift-keying provides a capacity of 18.6 Gb /s with a 7% forward error correction overhead in single carrier signal transmission as well as in multi-carrier transmission.
The first bi-directional laser communication demonstration between an optical ground station and the Optical Inter-orbit
Communication Engineering Test Satellite (OICETS) was successfully conducted in March, May, and September, 2006,
with an uplink of 2 Mbps and a downlink of 50 Mbps. The optical ground station, located in Koganei, Tokyo, Japan, is
operated by the National Institute of Information and Communications Technology (NICT), Japan. Four laser beams
were transmitted from the optical ground station to the OICETS satellite in order to reduce the optical signal's intensity
fluctuation due to atmospheric turbulence. The optical scintillation as a function of the number of beams and the
frequency response were measured, and the uplink and downlink laser transmission results were obtained.
Ground-to-satellite laser communication experiments between the optical ground station located in Koganei of downtown Tokyo and a low earth orbit (LEO) satellite, the Optical Inter-orbit Communications Engineering Test Satellite (OICETS) called "Kirari", were successfully performed in March and May, 2006. The optical communication demonstration experiment at the optical ground station was conducted in cooperation between the Japan Aerospace Exploration Agency (JAXA) and the National Institute of Information and Communications Technology (NICT). Ten trials over the course of two months were conducted during the test campaign. Acquisition and tracking of the satellite were successful on seven days out of the assigned test days. The tests were unsuccessful during three out of the four days when it was cloudy or rainy, but they were successful on all six of the days when partly clear skies were predominant. For the uplink, the fluctuation of the received signal power was well minimized by using multi-beam laser transmissions. The bit error ratio (BER) on the downlink was measured to be as low as 10-5. The applicability of the onboard optical terminal was demonstrated, aiming not only for geostationary earth orbit (GEO)-LEO links but also for ground-to-LEO optical links.
We describe some of our recent results on DWDM mm-wave radio-on-fiber (RoF) technology for future broadband wireless systems. A supercontinuum (SC) light source is a promising multiwavelength light source for the system with photonic up-conversion. Multiplexing and demultiplexing schemes for optical frequency interleaving in order to extend the number of antenna base stations can be constructed using a properly designed arrayed-waveguide grating (AWG). We demonstrate a full-duplex WDM mm-wave RoF system using a SC light source. The periodic nature of AWG, where the period is free spectral range (FSR), is used for utilizing the full bandwidth of the SC light source. Half of the SC output modes are used for downlink transmission with photonic upconversion. Another half of the SC output modes are used for uplink transmission with photonic downconversion. These techniques are effective to use a wealth of optical frequency resources from the SC light source. Two-channel downlink and one-channel uplink 60- GHz band RoF signals were simultaneously transmitted over 25-km standard single-mode fiber with error-free and no noticeable power penalty.
We investigated the frequency spectra and two-dimensional (2-D) distributions of the beam-centroid fluctuation created by spot dancing, which are needed to optimize the design of the tracking system, by using a novel spot-dancing measurement method to suppress the effect of building and/or transmitter vibration. In this method, two laser beams are propagated apart from each other and observed simultaneously using high-speed cameras. The position of each beam centroid is obtained using an image processing system. The effect of transmitter vibration is suppressed by taking the difference between the 2-D coordinate data of the beam-centroid positions. The frequency spectra are calculated using the fast Fourier transform. The beam spots of two HeNe lasers propagated 100 m (indoor) and 750 m (open-air) were observed using a high-speed camera of 10,000 frame/sec. Frequency spectra of the beam-centroid variance of up to 5 kHz could be observed. We also measured the variations of spot dancing in two days when the rates of sunshine were 100% and 0%.
We experimentally demonstrate a demultiplexing scheme for the frequency-interleaved dense wavelength division multiplexing (DWDM) radio-on-fiber system using an arrayed-waveguide grating (AWG). We first show the principle of the frequency-interleaved DWDM radio-on-fiber and possible configurations of multiplexing and demultiplexing (DEMUX) schemes using an AWG. In the experiment, 25-GHz separated 2-channel optical double sideband signals modulated by a 60-GHz millimeter-wave carrying a 156 Mbps data are optically multiplexed by frequency interleaving. The power penalty after DEMUX, which was due to interchannel interference, was less than 0.5 dB. We also made a transmission experiment in 25-km standard single mode fiber (SMF). No noticeable power penalty in the received data due to transmission was observed. This is because carrier and only one of the sidebands are detected in the proposed DEMUX scheme.
This paper reviews some recent developments of high-speed millimeter-wave photonic components and their application in millimeter-wave fiber-wireless systems. In particular, this paper is concerned with waveguide transceiver elements designed for simultaneous modulation and photodetection at mm-wave frequencies, where the transceiver concept is based upon electroabsorption in multiple-quantum wells. The fabrication procedure of such 1.55 micrometers electroabsorption transceivers (EAT) on InP substrates in briefly reported and the successful employment of mm-wave EATs in a 60-GHZ fiber- wireless network is demonstrated. Furthermore, a 60-GHz mm- wave band point-to-point fiber-wireless link architecture employing an EAT is presented and full-duplex broadband transmission within the 60-GHz band is experimentally achieved.
Recently, lightwave systems have attracted great interest not only for digital optical communication but also for the distribution of microwave and mm-wave signals in wireless applications. Future wireless communication networks are expected to offer broadband multimedia services to a large number of subscribers. As a consequence, the radio frequency is expected to be within the mm-wave band where a sufficient bandwidth for the large number of broadband channels is available. Since the electrical transmission of the mm-wave radio signals over long distances is not feasible, fiber-wireless systems have attracted great interest. They are considered to form the backbone of future broadband mm-wave wireless communication systems. Obviously, the successful implementation of mm-wave wireless communication networks in mass-market applications strongly depends on the costs of the infrastructure. In that respect, specially the cost of each single base station (BS) is a very critical factor since future wireless networks are expected to support a large number of remote BSs. Consequently, it is of great interest to reduce the base station complexity and cost. In this paper, we present a novel photonic transceiver component and discuss its application in mm-wave fiber-wireless systems. In detail, an InP-based 1 .55im waveguide electroabsorption transceiver (EATs) is presented that serves as a modulator and a photodetector simultaneously. Besides the basic device concept and its properties, the employment of high-speed EAT in 60GHz millimeter-wave (mm-wave) fiber-wireless applications is experimentally demonstrated. For the first time, full-duplex broadband (155.52Mbit/s) fiber-optic transmission in the 60GHz band has been achieved in a point-to-point link. Furthermore, a point-to-multipoint fiber-ring network architecture employing EAT is presented and in a first experiment full-duplex point-to-multipoint operation in the 60GHz band is experimentally demonstrated.
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