60 GHz Radio over Fiber Technology for Wireless Access by employing Narrow-Angle PSK Modulation

This paper investigates two key techniques used in 60 GHz Radio over Fiber (RoF) technology for wireless access, namely, the generation of 60 GHz signals and the distribution of 60 GHz local oscillator (LO). In the proposed model, a 60 GHz PSK signal is generated by a heterodyne of two subcarriers with narrow-angle PSK (NA-PSK) modulation, whose phase shift is equal to one half that of a normal PSK signal. Then we use a 60 GHz mixer to frequency mix two PSK signals in two different bands, 60 GHz and baseband. By doing this, the modulation information can be fully eliminated, resulting in a 60 GHz LO. In the wireless terminal, coherent demodulation is realized by a self-mixing of the transmitted 60 GHz PSK signal and LO. Thus no millimeter-wave (mm-wave) band oscillator is needed in the wireless terminal.     

A novel optical mm-wave generation scheme based on three parallel Mach-Zehnder modulators

We propose a novel optical mm-wave generation scheme based on three parallel Mach-Zehnder modulators (MZMs) for the first time. First, the scheme is investigated theoretically, which suggests that it can be used for sextupling, 12-tupling, and 18-tupling mm-wave generation. Then simulation results are given, 60 GHz mm-wave is generated from 5 GHz, or 10 GHz RF oscillator based on frequency 12-tupling or sextupling, and 90 GHz mm-wave is generated from 5 GHz RF oscillator based on frequency 18-tupling. The optical sideband suppression ratio (OSSR) and the radio frequency spurious suppression ratio (RFSSR) are analyzed by simulation, in which several non-ideal factors are taken into consideration. Results indicate that all the three mm-wave generation methods are practical and very good performance can be obtained when the extinction ratio of the MZM is 30 dB, even if the extinction ratio of the MZM is 20 dB, the performance is still good, especially for the sextupling mm-wave generation method, whose performance is excellent and insensitive to the extinction ratio of MZM, the non-ideal RF driving voltage and the non-ideal DC bias. At last, we set up a RoF system by simulation to verify the transmission performance of the scheme. The BER performance and eye diagrams are given.     

A novel MI-insensitive and filterless frequency octupling scheme based on two parallel dual-parallel Mach–Zehnder modulators

A novel MI-insensitive and filterless frequency octupling scheme based on two parallel dual-parallel Mach–Zehnder modulators (DP-MZMs) is proposed. The proposed scheme is not sensitive to modulation index and relatively strong MMW signal with good radio frequency spurious suppression ratio (RFSSR) can be obtained without strict requirement on modulation index. Filterless feature makes the scheme quite suitable for wavelength division multiplexing (WDM) applications. For verification, a 60 GHz millimeter wave with 44 dB RFSSR is generated from a 7.5 GHz radio frequency wave by simulation. Performance of the proposed scheme has been characterized under different conditions including DC-bias drifts of MZMs, different amplitudes of RF inputs and different extinction ratios of MZMs.     

A full-duplex radio-over-fiber link with 12-tupling mm-wave generation and wavelength reuse for upstream signal

A full-duplex radio-over-fiber (RoF) link with a novel scheme to generate 60 GHz mm-waves from a 5 GHz RF signal source is investigated. In the RoF downlink, the required frequency of the RF oscillator is reduced greatly. Since the optical carrier is not modulated by downstream data, part of it is reused to carry upstream data and the upstream data is transmitted to the central station using optical single-sideband modulation. In this way, a single wavelength is used for both downstream and upstream transmissions. Based on this scheme, a full-duplex RoF link is built and its transmission performance is analyzed. Theoretical analysis and numerical simulation show that the downstream signal cannot only eliminate code form distortion caused by time shift of the code edges, but also reduce the influence of the fading effect as the 60 GHz DSB optical mm-wave signal is transmitted along the fiber, and the upstream signal is immune to both fading effect and time shift of the code edges.     

A novel approach for simultaneous millimeter wave generation and high bit rate data transmission for Radio over Fiber (RoF) systems

We propose a novel method for simultaneous transmission of OC-192 (9.95328 Gbps) digital data and 60 GHz RF generation in a Standard Single Mode Fiber (SSMF) link utilizing Stimulated Brillouin Scattering (SBS). The system comprises of a 1550 nm DFB Laser diode, Mach Zehnder modulator (MZM), 50 km SSMF and Optical receiver. The receiver includes laser diode for optical pump, a regenerator for data retrieval and a RF bandpass filter for RF generation. This system requires minimum number of RF and optical components for the generation of 60 GHz RF. The remotely generated 60 GHz RF signal may be used for wireless transmission of data. The entire link is simulated in Optisystem software to analyze the system performance.     

All-optical clock recovery using a ridge width varied two-section partly gain-coupled DFB self-pulsation laser

A 1.55 μm InGaAsP-InP partly gain-coupled two-section DFB self-pulsation laser (SPL) with a varied ridge width has been fabricated. The laser produces self-pulsations with a frequency tuning range of more than 135 GHz. All-optical clock recovery from 40 Gb/s degraded data streams has been demonstrated. Successful lockings of the device at frequencies of 30 GHz, 40 GHz, 50 GHz, and 60 GHz to a 10 GHz sidemode injection are also conducted, which demonstrates the capability of the device for all-optical clock recovery at different frequencies. This flexibility of the device is highly desired for practical uses.     

Simulation of DWDM signals using optimum span scheme with cascaded optimized semiconductor optical amplifiers

We numerically simulated the ten channels at 10 Gb/s dense wavelength division multiplexing (DWDM) transmission faithfully over 17,227 km using 70 km span of single mode fiber (SMF) and dispersion compensating fiber (DCF) using optimum span scheme at channel spacing 20 GHz. For this purpose, inline optimized semiconductor optical amplifiers (SOAs) and DPSK format are used. We optimized the SOA parameters for inline amplifier with minimum crosstalk and amplified spontaneous emission noise with sufficient gain at bias current 400 mA. For this bias current, constant gain 36.5 dB is obtained up to saturation power 21.35 mW. We have also optimized the optical phase modulator bandwidth for 400 mA current which is around 5.5 GHz with crosstalk −14.2 dB between two channels at spacing 20 GHz.We show the 10×10 Gb/s transmission over 70 km distance with inline amplifier has good signal power received as compared to without amplifier, even at equal quality factor. We further investigated the optimum span scheme for 5670 km transmission distance for 10×10 Gb/s with channel spacing 20 at 5.5 GHz optical phase modulator bandwidth. As we increase the transmission distance up to 17,227 km, there is increase in power penalty with reasonable quality.The impact of optical power received and Q factor at 5670 and 17,227 km transmission distance for different span schemes for all channels has been illustrated. For launched optical power less than saturation, all channels are obtained at bit error rate floor of 10⁻¹⁰.     

EAM-SOA millimeter-wave frequency up-converter for radio-over-fiber applications

We present an optical scheme for photonic frequency up-conversion at the millimeter-wave bands based on Semiconductor Optical Amplifier. The proposed scheme modulates the bias current with the Intermediate Frequency in order to achieve frequency mixing of an incoming optical signal modulated with the Local Oscillator. Theory indicates that the proposed scheme supports data bandwidths in the tens of GHz for LO values above 10 GHz. This scheme allows for photonic integration of the considered optical devices. A laboratory demonstration of the scheme for up-conversion to the 40 GHz band, using narrow-band IF signals, showed relatively low thresholds for the optical input power and bias current level to achieve error free operation: − 14.5 dBm 100 mA for a 64-QAM signal. Spurious-Free Dynamic Range showed an acceptable performance, with a linearity about 52.5 dB·Hz^2/3 for an optical input power of − 6 dBm.     

A flattop PLC polymer waveguide interleaver based on folded two-stage-cascaded Y-junction Mach-Zehnder interferometers

We demonstrate realization of a flattop Y-Junction Planar Optical Waveguide Interleaver (YJPOWI) with a channel spacing of 100 GHz through a novel scheme of folded cascaded two-stage unbalanced Mach-Zehnder interferometers (MZI) fabricated on a polymer Planar Lightwave Circuit (PLC) platform. The characteristic 0.5 dB passbands of the interleaver centered at ITU wavelength grids at its two output ports were 50 and 45 GHz, respectively. The operating bandwidth of the device spanned the entire C band of a fiber amplifier and it is compact in size (1.3 × 1.4 cm²). In addition, the device is easy to fabricate and do not require any individual heater to trim its performance.     

64 GHz optical millimeter-wave generation by octupling 8 GHz local oscillator via a nested LiNbO3 modulator

A novel scheme to generate a 64 GHz optical millimeter (mm)-wave via a nested LiNbO₃ Mach-Zehnder modulator with an 8 GHz local oscillator is proposed and simulated. Since the frequency response of the modulator and the local oscillator frequency are greatly reduced, the bandwidth requirements of the optical and electrical components in the transmitter are significantly decreased. The simulation results show that the generated optical mm-wave signal maintains good performance even after being transmitted over 20 km standard single-mode fiber.     

Optimization of electromagnetic matching of carbonyl iron/BaTiO3 composites for microwave absorption

Microwave absorbing materials filled with BaTiO₃ and carbonyl iron (CI) particles with various weight fractions (BaTiO₃/CI particles=100/0 to 0/100) are investigated. The dielectric and magnetic properties of the absorbers can be tuned by changing the weight ratio of BaTiO₃/CI particles in the frequency range of 2-18 GHz. Numerical simulations are also performed to design a single-layer and double-layer absorber. The minimum reflection loss of the composite filled with 20 wt% BaTiO₃ and 60 wt% CI particles at 2.0 mm thickness can be reached to −42 dB at 4.1 GHz. With the weight ratio of CI particles in the composite increased, the microwave absorption peak shifted to the lower frequency region. By using a double-layer absorber structure, the microwave absorption performance of the absorber is enhanced. The result shows that the total thickness of the absorber can be reduced below 1.4 mm by using a matching layer filled with 50 wt% BaTiO₃, and an absorption layer filled with 60 wt% BaTiO₃ and 20 wt% CI particles, whereas the reflection loss below −10 dB can be obtained in the frequency range of 10.8-14.8 GHz and the minimum reflection loss of −59 dB can be obtained at 12.5 GHz.     

Fabrication and electromagnetic performance of micro-tubular nanocomposites composed of monodisperse iron nanoparticles and carbon

Low density and thin thickness are essential for electromagnetic (EM) wave absorbers. In this study, we fabricated a novel micro-tubular iron nanocomposite (MTIC) that composed of carbon microtubes and monodisperse iron nanoparticles (NPs). The bulk density of MTIC is only 0.35±0.04 g cm⁻³ due to its micro-tubular structure. The presence of iron NPs increased the magnetic loss significantly and therefore enhanced the reflection loss (RL) of MTIC/paraffin composite. The optimum thickness for the composite is 1.5-1.8 mm, with maximum bandwidth of 7.6 GHz for RL<−5 dB and 3.6 GHz for RL<−10 dB. The corresponding frequency at this thickness is 10-18 GHz. Because of low density and broad bandwidth at thin thickness, MTIC is a promising light-weight absorber for EM wave absorption or microwave shielding. This study will also provide new ideas for fabricating microwave absorbers with low density and thin thickness.     

Photonic generation of 60 GHz-band vector signals for RoF systems based on optical vector signal down-conversion

A novel photonic method of 60 GHz-band vector signal generation for RoF systems based on optical vector signal down-conversion is proposed and experimentally demonstrated in this paper. In the proposed method, the target vector signals are first generated in the optical domain with the help of mature commercial optical devices and then directly distributed to the base stations (BSs) through the fiber link. The generated vector signals can be automatically down-converted to the 60 GHz band in the BSs after O/E conversion, and then directly transmitted to the users without any further processing. With the proposed method, higher spectrum efficiency and system capacity will be obtained compared with the traditional OOK RoF systems while almost no extra system complexity and cost is brought in. According to the characteristics of different types of vector signals, two particular modulation schemes are provided, which are then verified by corresponding simulations and experiments. In the experimental 60 GHz RoF system, the 622 MSym/s 60 GHz-band 8-QAM and 4-QAM signals generated with two different schemes respectively are successfully transmitted over 50 km SMF and 5 m wireless channel without any compensation, and the power penalty are both about 1.7 dB at the BER of 10^− 9.     

Tunable negative index metamaterial using yttrium iron garnet

A magnetic field tunable, broadband, low-loss, negative refractive index metamaterial is fabricated using yttrium iron garnet (YIG) and a periodic array of copper wires. The tunability is demonstrated from 18 to 23 GHz under an applied magnetic field with a figure of merit of 4.2 GHz/kOe. The tuning bandwidth is measured to be 5 GHz compared to 0.9 GHz for fixed field. We measure a minimum insertion loss of 4 dB (or 5.7 dB/cm) at 22.3 GHz. The measured negative refractive index bandwidth is 0.9 GHz compared to 0.5 GHz calculated by the transfer function matrix theory and 1 GHz calculated by finite element simulation.     

All optical arbitrary waveform generation by optical frequency comb based on cascading intensity modulation

We propose and experimentally demonstrate an all optical arbitrary waveform generation by optical frequency comb (OFC) based on cascading intensity modulation. By selecting spectral lines of interest from OFC through optical filters, 10 GHz, 20 GHz, and 60 GHz sinusoidal signals with low phase noise and more complex waveforms, including ultra-short pulse, half-wave cosine, and single frequency modulated MMW signals, are generated easily.     

Potential of the high modal bandwidth OM4 glass multimode fiber for the multi-services concept

In this paper, we report new results dealing with the wavelength multiplexing transmission scheme over the OM4 high modal bandwidth multimode fiber. Fiber bandwidth measurements both at 850 nm and 1300 nm clearly show the huge bandwidth/length product of this fiber. The simultaneous transmission of a high data rate baseband signal (10 GbE) at 850 nm and a radiofrequency MultiBand Orthogonal Frequency Division Multiplexing Ultra-Wide Band (band group 5-10 GHz) MB-OFDM UWB signal (480 Mbps) at 1300 nm is presented. The measurements - Bit Error Rate (BER) for the 10 GbE signal and Error Vector Magnitude (EVM) for the MB-OFDM UWB signal - that are hereby reported show safe results under the requirements of the corresponding communication standards; they give this architecture an affordable approach for home/office networking at high data rate in a joint fixed and wireless environment.     

An optical MEMS-based dynamic capacity allocation scheme for handoff using moving extended cells in radio-over-fiber networks

We demonstrate a Dynamic Capacity Allocation scheme for the realization of Moving Extended Cells in Radio-over-Fiber networks. Our scheme exploits a reconfigurable MEMS-based Central Office architecture for routing of and switching between six data carrying wavelengths, forming in this way cell clusters that transmit the same information content and can move with the mobile user. Error free transmission through 25 km SMF is presented for a 5-cell MEC structure, with each optical channel carrying 500 Mb/s data subcarrier-modulated at 8.5 GHz.     

A synthesis technique of single square loop frequency selective surface at terahertz frequency

In this paper, we have explored and extended the use of frequency selective surface towards the terahertz regime of the electromagnetic spectrum where interesting applications such as imaging, sensing and communication exist. We have discussed a synthesis technique to design the single square loop frequency selective surface (SSLFSS) at 150 and 300 GHz which have found suitable application in the fast analysis and fabrication of the frequency selective surface. Moreover, the analytical results have been supported by the CST Microwave Studio and Ansoft HFSS commercial simulators. We have discussed the angular insensitivity of the SSLFSS at 150 GHz as well as 300 GHz. However, the specific problems arise at terahertz frequencies as compared to the radio and microwave frequencies are the ohmic losses. The proposed analysis has been extended from 100 GHz to 350 GHz to discuss the ohmic and dielectric losses. We have also discussed the other important issues which are very much significant in the terahertz regime of the spectrum such as skin depth and surface roughness.     

Atomic and molecular spectroscopy with a continuous-wave, doubly resonant, monolithic optical parametric oscillator

Doppler-broadened atomic and molecular spectra were observed with a one octave tunable, continuous-wave, doubly resonant, monolithic optical parametric oscillator (OPO) using 5% MgO-doped LiNbO₃ as a non-linear crystal with a birefringent phase-matching configuration. By tuning the frequency of a pump laser, longitudinal mode selection over 20 successive modes, corresponding to a 60 GHz span, was possible, owing to the simple structure of the monolithic OPO. Continuous frequency tuning was achieved using an external waveguide-type electrooptic phase modulator (EOM). By changing the modulation frequency of the EOM, frequency tuning of the optical sidebands over 12 GHz was possible, which is larger than the one free spectral range of the monolithic cavity of 3 GHz. We could observe the Cs-D₁ (894 nm), Cs-D₂ (852 nm), Rb-D₁ (795 nm), acetylene R9 (1520 nm) and P9 (1530 nm) transitions with the single monolithic OPO.     

Optical beamforming networks employing phase modulation and direct detection

We propose a novel dispersion-based optical beamforming network scheme employing phase modulation and direct detection. Optical phase modulators have the advantages of simple-structure, low loss and absence of bias. Dispersion-induced phase-to-intensity conversion is utilized to facilitate direct detection. A structure of wideband dispersive device (WDD) cascaded with periodic dispersive device (PDD) is introduced to enhance the system flexibility, so that the delay adjustability and RF response can be properly designed respectively by choosing appropriate dispersions of the WDD and PDD. A concept-proof system with a wideband chirped fiber grating (CFG) as the WDD and two multiband CFGs (MCFG1 and MCFG2) as the PDD separately is built to demonstrate the basic idea. The delay tuning range is 0-1.8 ns with increment of 164.2 ps. The passband center is 30 GHz for MCFG1 and 20 GHz for MCFG2, and the fractional bandwidth is 51.8%. The shot-noise-limited spurious-free dynamic range is also analyzed and measured to be 105.7 dB ⋅ Hz^2/3 when the average photocurrent is 2.7 mA.