Masuduzzaman Bakaul

Fiber-Wireless Networks and Subsystem Technologies

Hybrid fiber-wireless networks incorporating WDM technology for fixed wireless access operating in the sub-millimeter-wave and millimeter-wave (mm-wave) frequency regions are being actively pursued to provide untethered connectivity for ultrahigh bandwidth communications. The architecture of such radio networks requires a large number of antenna base-stations with high throughput to be deployed to maximize the geographical coverage with the main switching and routing functionalities located in a centralized location. The transportation of mm-wave wireless signals within the hybrid network is subject to several impairments including low opto-electronic conversion efficiency, fiber chromatic dispersion and also degradation due to nonlinearities along the link. One of the major technical challenges in implementing such networks lies in the mitigation of these various optical impairments that the wireless signals experience within the hybrid network. In this paper, we present an overview of different techniques to optically transport mm-wave wireless signals and to overcome impairments associated with the transport of the wireless signals. We also review the different designs of subsystems for integrating fiber-wireless technology onto existing optical infrastructure.

Efficient multiplexing scheme for wavelength-interleaved DWDM millimeter-wave fiber-radio systems

A simple multiplexing scheme is proposed and demonstrated with the capability to interleave optically modulated 37.5-GHz radio channels in a dense-wavelength-division-multiplexed fiber-radio system with 25-GHz wavelength spacing, and also enable a carrier subtraction technique that improves the overall link performance by reducing the carrier-to-sideband ratio of the multiplexed channels. The proposed scheme is realized by the use of an arrayed waveguide grating having multiple optical loop-backs between the input and the output ports.

Multifunctional WDM optical interface for Millimeter-wave fiber-radio antenna base station

A wavelength-division-multiplexed (WDM) optical interface has been proposed and demonstrated with the capacity of adding and dropping wavelength interleaved fiber-radio WDM channels spaced at 25 GHz and also enabling wavelength reuse, which eliminates the need for a light source at the base station. The proposed WDM optical interface is realized by the use of a multiport optical circulator in conjunction with multinotch fiber Bragg grating (FBG) filters. Its functionality is demonstrated both by experiment and simulation. The effects of optical impairments on the transmission performance of WDM channels were studied in detail through simulation for single and cascaded configurations of the interface.

Simultaneous multiplexing and demultiplexing of wavelength-interleaved channels in DWDM millimeter-wave fiber-radio networks

A simultaneous multiplexing and demultiplexing (MUX/DEMUX) scheme for wavelength-interleaved millimeter-wave 37.5-GHz-band fiber-radio channels spaced at 25 GHz has been proposed. The proposed MUX/DEMUX technique potentially realizes simple, compact, and low-cost central office and remote nodes by avoiding the use of wavelength-selective pre- and postprocessing hardware. The novel scheme incorporates an arrayed-waveguide grating with multiple loop-backs between the input and the output ports, in addition to multiple optical circulators and optical isolators. The multiplexing functionality of the proposed technology enables a carrier subtraction technique and consequently reduces the carrier-to-sideband ratios of the multiplexed channels. Multiplexing of the uplink channels generated via several methods is demonstrated experimentally. These techniques include generation of the channels by using the optical carriers that correspond to wavelengths spaced at the free spectral range (FSR) or multiples of the FSR from the downlink (DL) optical carriers and reuse of the DL optical carriers that are recovered by applying a wavelength reuse technique (lambdaUL =lambdaDLplusmnntimesFSR, where n=0,1,2,3,...). The demultiplexing functionality of the proposed scheme that separates the 37.5-GHz-band wavelength-interleaved DL channels spaced at 25 GHz is also demonstrated. In addition, the effect of optical crosstalk on the transmission performance of the demultiplexed channels is also characterized experimentally

Mitigation strategy for transmission impairments in millimeter-wave radio-over-fiber networks [Invited]

Hybrid fiber-wireless networks for fixed wireless access operating in the millimeter-wave (mm-wave) frequency region have been actively pursued to provide ultrahigh bandwidth for untethered connectivity. Moving the radio operating frequency into the mm-wave region overcomes the spectral congestion in the lower microwave region and is also capable of providing high-capacity broadband wireless services in a picocellular or microcellular architecture. Optical fiber backhaul provides the broadband interconnectivity between a centralized location and a large number of high-throughput antenna base stations necessary in such an architecture. The transportation of mm-wave wireless signals within the hybrid network is subject to numerous impairments ranging from low conversion efficiency to fiber chromatic dispersion and also to signal degradation due to nonlinearity along the link. One of the major technical challenges in implementing these networks lies in the mitigation of these impairments that the wireless signals experience while traversing the links. In this paper, we present an overview of the different techniques and schemes to overcome some of the impairments for transporting mm-wave signals over optical fibers.

Simplification of millimeter-wave radio-over-fiber system employing heterodyning of uncorrelated optical carriers and self-homodyning of RF signal at the receiver

A simplified millimeter-wave (mm-wave) radio-over-fiber (RoF) system employing a combination of optical heterodyning in signal generation and radio frequency (RF) self-homodyning in data recovery process is proposed and demonstrated. Three variants of the system are considered in which two independent uncorrelated lasers with a frequency offset equal to the desired mm-wave carrier frequency are used to generate the transmitted signal. Uncorrelated phase noise in the resulting mm-wave signal after photodetection was overcome by using RF self-homodyning in the data recovery process. Theoretical analyses followed by experimental results and simulated characterizations confirm the systems performance. A key advantage of the system is that it avoids the need for high-speed electro-optic and electronic devices operating at the RF carrier frequency at both the central station and base stations.

Robust, Low Cost, In-Band Optical Signal to Noise Monitoring Using Polarization Diversity

We demonstrate a robust in-band OSNR monitor using polarization diversity and low-cost opto-electronics. The proposed technique offers relaxed manufacturing tolerances and is insensitive to extinction ratio, bit rate, chromatic dispersion and first order PMD.

Millimeter-Wave Radio-Over-Fiber System Based on Heterodyned Unlocked Light Sources and Self-Homodyned RF Receiver

A millimeter-wave (mm-wave) radio-over-fiber (RoF) system based on unlocked heterodyned light sources and self-homodyned RF receiver is proposed and demonstrated. Since the mm-wave signal is generated through the beating of two independent optical signals at the photodetector, complexities of the generation and distribution of mm-wave signal in the optical domain are avoided. Also, as RF self-homodyning is used as the means of recovering the baseband signal, phase-noise effects due to unlocking of the light sources are avoided. Experimental results confirm that the combination of these legacy solutions can successfully avoid most of the high-speed electrooptic and RF devices both from the central station (CS) and base stations (BSs).

Low-Cost PMD-Insensitive and Dispersion Tolerant In-Band OSNR Monitor Based on Uncorrelated Beat Noise Measurement

A polarization-mode-dispersion-insensitive and dispersion tolerant in-band optical signal-to-noise-ratio monitor based on uncorrelated beat noise measurement is proposed and demonstrated. The proposed technique uses an optical delay line interferometer in recovering symmetrical signal samples and exploits the benefits of low-speed balanced receivers and digital signal processing in measuring the uncorrelated beat noise.

Efficient Transmission Scheme for AWG-Based DWDM Millimeter-Wave Fiber-Radio Systems

We propose and demonstrate an upstream transmission scheme using a semiconductor optical amplifier (SOA) for arrayed waveguide grating (AWG)-based dense wavelength-division-multiplexed (DWDM) millimeter-wave fiber-radio systems and show improved link performance. In our scheme, unused optical carriers from the cyclic AWG in the downlink (DL) are tapped for uplink (UL) transmission. An SOA in conjunction with the AWG simultaneously amplifies the DL RF subcarriers and UL optical carrier, thus improving carrier-to-sideband ratio in the DL while also yielding an improved power budget for the UL. Our experimental results show that the proposed scheme can be a practical solution for future bidirectional wavelength interleaved DWDM transmission systems