JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 28, NO. 13, JULY 1, 2010 1987 Photonic Down-Conversion of Millimeter Wave Multiband Orthogonal Frequency Division Multiplexing Ultra-Wideband Using Four Wave Mixing in an Electro-Absorption Modulator Bouchaib Hraimel, Xiupu Zhang, and Ke Wu, Fellow, IEEE Abstract—We propose and demonstrate a novel and cost-effec- tive photonic down-conversion scheme for millimeter wave (mm- wave) over fiber (MoF) uplinks using an electro-absorption modu- lator (EAM) at a base station. Two wavelengths with frequency dif- ference of , used as dual wavelength, are incident to an EAM that is driven by an mm-wave signal at to obtain optical subcar- rier modulation. Due to four-wave mixing (FWM), two new wave- lengths are generated inside the EAM and used for the optical car- riers for the uplink. One of the generated two wavelengths and one of two mm-wave signal subcarriers is separated by in frequency, thus down-converted. Furthermore, down-conver- sion with tunability of optical carrier to optical subcarrier power ratio can be achieved by simply controlling the dual wavelength power into the EAM. We experimentally investigate the efficiency of the FWM versus EAM reverse bias voltage and input optical power. The performance of the proposed scheme for down-conver- sion of a 30 GHz multiband (MB) orthogonal frequency division multiplexing (OFDM) ultra-wideband (UWB) is also investigated in terms of error vector magnitude (EVM) versus RF and LO mod- ulation index, and received optical power at the photodetector. Index Terms—Electro-absorption modulator, four-wave mixing, millimeter-wave over fiber, multi-band OFDM ultra-wideband, photonic down-conversion. I. INTRODUCTION F UTURE wireless with features of high data rate and open network architecture is desired to satisfy the in- creasing demand for broadband wireless access. To achieve high capacity wireless access networks, one solution is to use IEEE 802.15.3a proposed for wideband personal local access networks, where 14 channels that occupy the frequency band from 3.1 to 10.6 GHz are divided in five groups, and each channel is 528 MHz wide and can have a variable throughput from 53.3 to 480 Mb/s [1]. On the other hand, unlicensed millimeter-wave (mm-wave) band which provides high band- width due to the high frequency carriers has been considered Manuscript received August 31, 2009; revised January 13, 2010, March 14, 2010; accepted May 17, 2010. Date of publication May 27, 2010; date of current version July 05, 2010. This work was supported in part by NSERC strategic project from the Natural Sciences and Engineering Research Council of Canada (NSERC) and Quebec-China research collaboration project. B. Hraimel and X. Zhang are with the Advanced Photonic Systems Labora- tory, Department of Electrical and Computer Engineering, Concordia Univer- sity, Montreal, QC H3G1M8, Canada, (e-mail: xzhang@ece.concordia.ca). B. Hraimel and K. Wu are with the Department of Electrical Engineering, Ecole Polytechnique de Montreal, QC, H3T1J4, Canada. Digital Object Identifier 10.1109/JLT.2010.2051140 a potential wireless radio frequency (RF) carrier band for the future wireless communications. However, ultra-wideband (UWB) signals are designed to have noise-like properties and the energy is spread over a very large bandwidth (FCC part 15:-41.3 dBm/MHz) [2]. Also, mm-wave has very high atten- uation for transmission over air. Therefore, the transmission of UWB signals at mm-wave band wirelessly is limited to a few meters and its distribution over coaxial cable is exceedingly expensive. Optical fiber provides an excellent alternative for the distribution of mm-wave UWB signals due to its low loss, low cost and wide bandwidth characteristics. However, mm-wave transmission over fiber (MoF) using conventional optical double sideband modulation technique suffers from chromatic dispersion induced power fading [3]. To overcome this power fading, optical single sideband modulation has been proposed [4] but still uses mm-wave frequency. A straight forward way to up/down-convert mm-waves is to do it electrically, but very ex- pensive and not cost-effective because many base stations (BS) are needed due to small size of the wireless pico-cell. Also, RF designers are facing difficulties in designing high-performance broadband and low-cost mixers, especially in mm-wave band [5]. Therefore, simple and cost effective techniques are needed to generate and distribute high quality mm-wave radio signals for downlinks [6], [7]. Mm-wave MB-OFDM UWB signal generation using optical frequency up-conversion and transmis- sion over fiber has been investigated [8], [9]. However, optical frequency down-conversion and transmission of mm-wave MB-OFDM UWB over fiber has not been investigated. It is also desirable to have a low cost BS with simple frequency down-conversion from a received mm-wave to an intermediate frequency (IF) for uplinks. An electro-absorption modulator (EAM) presents a low power consumption, compact size, polarization insensitivity, easy integration with other devices, and higher speed operation in photodetection, mixing and optical modulation due to the EAM inherent characteristics. It was demonstrated that an EAM could be used for frequency down-conversion from an mm-wave to an IF signal using cross-absorption modulation in an EAM [10]–[12] or frequency shifting [13]. Instead of using both transmitted CW and optical local oscillator (LO) wave- lengths [10], [11], or higher radio frequency LO at the central station [13] a simple technique [12] was proposed for mm-wave down-conversion in an EAM for optical uplink transmission with only one LO wavelength used. However, its modulation 0733-8724/$26.00 © 2010 IEEE