Carrier-to-sideband Ratio Research Articles

Planar array antenna coupled InGaAs/InAlAs multi-quantum well optical modulator for 60 GHz band millimeter wave signals

A Fe-InP-based planar array antenna-coupled InGaAs/InAlAs multiple quantum well (MQW) optical phase modulator is proposed and demonstrated for radio over fiber (RoF) applications with 60 GHz-band millimeter-wave wireless signals. The modulator comprises five types of five-layer asymmetric coupled quantum wells (FACQWs) and a two-element array antenna. The FACQWs are designed to have a significant electric-field-induced refractive index change with small electric fields induced in the antenna. In the fabricated modulator, a carrier-to-sideband ratio (CSR) of up to 45.9 dB was successfully obtained at a power density of 11 W/m2, corresponding to a phase shift of 10.1 mrad. Furthermore, data transmission of a 2 GHz modulated wave with a 60 GHz wireless carrier wave was demonstrated.

D-band optical modulators using electro-optic polymer waveguides and non-coplanar patch antennas.

D-band (110-170 GHz) antenna-coupled optical modulators with electro-optic (EO) polymer waveguides and non-coplanar patch antennas were fabricated using a poled EO polymer film transfer method. A carrier-to-sideband ratio (CSR) of 42.3 dB corresponding to an optical phase shift of 15.3 mrad was obtained by irradiating 150 GHz electromagnetic waves with an irradiation power density of 34.3 W/m2. Our devices and fabrication method have great potential for achieving highly efficient wireless-to-optical signal conversion in radio-over-fiber (RoF) systems.

Broadband and High-Capacity Silicon Photonics Single-Sideband Modulator

We propose a novel photonic-integrated single-sideband (SSB) modulator realized in silicon on insulator technology operating either in suppressed-carrier or full-carrier mode with continuously tunable carrier-to-sideband ratio (CSBR). Large rejection levels of the spurious sidebands and residual carrier in excess of 40&#x00A0;and 30&#x00A0;dB, respectively, with a CSBR tunability over a <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>&#x00A0;50&#x00A0;dB range, are demonstrated. By employing a single silicon photonics (SiP) phase modulator and a compact and high-performance filtering element, the proposed architecture exhibits a compact layout and tolerates high driving voltage levels, leading to large OSNR values of the modulated sideband in excess of 50&#x00A0;dB. The device supports broadband RF data signals and its operation is tested with an up to 5&#x00A0;Gbps ASK-modulated carrier at 16.5&#x00A0;GHz, limited by available RF equipment. Furthermore, the technique allows to implement a frequency-multiplication mechanism for the input RF carrier, and up to threefold effective bandwidth enhancement of the SiP modulator is obtained by generating an optical SSB signal with a modulated spectral component spaced by 49.5&#x00A0;GHz from the optical carrier. Such features are promising for implementing cost-effective optical distribution of millimeter-wave wireless data signals supporting the evolution of next-generation radio access networks.

Photodetector optic power optimization to increase the gain on sub-octave microwave photonic link / Optimização da potência óptica do fotodetector para aumentar o ganho na ligação fotónica de microondas sub-octave

An investigation of the optic spectral components beating at the photodetector to recover the RF signal at the output of a sub-octave microwave photonic link is presented, by a theoretical and experimental approach. It is demonstrated the best efficiency is achieved when the carrier to sideband ratio (CSR) is 0 dB at a low bias voltage condition on Mach-Zehnder (MZM) intensity modulator. A RF power link gain improvement of 9.7 dB is demonstrated for a same photodetector incident optic power, compared with a link operating at quadrature bias voltage condition on the MZM.

W-band optical modulators using electro-optic polymer waveguides and patch antenna arrays.

In this study, W-band (75-110 GHz) antenna-coupled optical modulators with a cyclo-olefin polymer (COP) lower cladding, an electro-optic (EO) polymer waveguide, and a gap-embedded patch antenna array were fabricated using a transfer and bonding method of a poled EO polymer film. A carrier-to-sideband ratio (CSR) of 56 dB corresponding to an optical phase shift of 3 mrad was obtained under irradiation with 100 GHz electromagnetic waves with a power of 12.8 W/m2. Our devices have the potential to achieve highly efficient wireless-optical signal conversion in radio-over-fiber (RoF) systems.

Multidimensional Optimization of a Radio-Over-Fiber Link

Nonlinear distortion and chromatic dispersion are two long-standing limiting factors of radio-over-fiber (ROF) links. Here, we proposed an ROF link with both the two problems mitigated simultaneously. Furthermore, a tunable optical carrier-to-sideband ratio (CSR) can also be implemented in this simple system to improve the gain and the noise figure (NF) of the link. All these three factors are optimized in a simple ROF link which shows increased performance of the system. The scheme is based on a single dual-polarization Mach-Zehnder modulator (DPol-MZM). One bias voltage of the Dpol-MZM is employed to mitigate the nonlinear distortion. The polarization direction and the phase relationship of the modulated polarization multiplexed signal are used to adjust the CSR and suppress the dispersion, respectively, by adjusting a polarization controller (PC). In the experiment, 3-30-GHz RF signal is transmitted without power fading. A two-tone signal with the frequencies of 12.5 and 12.505 GHz is employed to verify the optimization of three main parameters of the ROF link [link gain, NF, and spurious-free dynamic range (SFDR)] where the link gain, NF, and SFDR are improved by 11.9, 5.8, and 14.5 dB, respectively, compared with conventional quadrature biased link based on one Mach-Zehnder modulator for 50-km single-mode fiber (SMF) transmission. Meanwhile, 100-Mbaud 16 quadrature amplitude modulation (QAM) signals centered at 12.5 and 14.7 GHz are used to verify the transmission performance. After dispersion compensation, nonlinear optimization, and CSR optimization, error vector magnitude (EVM) is improved from 17.03% to 2.97%.

InGaAs/InAlAs multiple-quantum-well optical modulator integrated with a planar antenna for a millimeter-wave radio-over-fiber system.

An InGaAs/InAlAs multiple-quantum-well (MQW) optical phase modulator integrated with a planar antenna for a millimeter-wave (MMW) radio-over-fiber (RoF) system is fabricated, and its high-speed modulation under irradiation of MMW signals is experimentally demonstrated. The modulator exhibits a carrier-to-sideband ratio (CSR) of 62.7 dB, corresponding to a phase shift Δϕ of 1.46 mrad under irradiation of MMW signals with an RF power density P of ∼77 W/m2 at a frequency of 57.5 GHz. The modulator is operated over the C band in optical communications. The modulation operation was attributed to the large change in refractive index caused by the quantum-confined Stark effect in the MQW. This is the first case where the refractive index change of a semiconductor was used as an antenna-coupled optical modulator.

Analog Photonic Link With Tunable Optical Carrier to Sideband Ratio and Balanced Detection

Optical carrier to sideband ratio (CSR) optimization and balanced detection are two effective techniques to improve the performance of an analogy photonic link (APL). Here, we proposed an APL where tunable optical CSR and balanced detection can both be implemented. A single integrated polarization division multiplexing Mach–Zehnder modulator (PDM-MZM) is used to generate a polarization multiplexed signal containing an optical carrier and two radio frequency modulated sidebands, and the optical CSR can be tuned from –15 to 15 dB by simply adjusting the direct current bias of the modulator. By optimizing the optical CSR in the proposed link, the link gain and noise figure (NF) are improved by 12 and 6.8 dB compared with conventional quadrature biased link. In addition, after balanced detection in the proposed link, the link gain, NF, third-order spurious free dynamic range (SFDR), and especially the second-order SFDR are further improved.

Joint Influence of the Optical Carrier-to-Sideband Ratio and Guard Band on Direct-Detection SSB-OOFDM System

The signal-to-interference-plus-noise ratio of the noised single-sideband optical orthogonal frequency-division multiplexing (SSB-OOFDM) signal in a direct-detection OFDM system is first deduced theoretically. The relationship of the carrier-to-sideband ratio (CSR) and guard band (GB) to the signal-to-signal beat interference (SSBI) is explored. According to our theoretical analysis, the degradation caused by SSBI on the SSB-OOFDM signal becomes worse as the GB reduces, whereas the increase in the CSR can loosen this degradation. Therefore, a tradeoff between the GB and CSR balances their joint influence on system performance. The simulation for the 20-km optical link with 40-Gb/s 16-quadrature amplitude modulation (16-QAM) noised SSB-OOFDM signal is conducted to confirm our theoretical results. It shows that, without any complex device or algorithm, the GB can be reduced to 40% only by increasing the CSR to $\sim$ 8 dB, and thus, the spectral efficiency of the DDO-OFDM link is improved after optimizing the CSR and GB of the SSB-OOFDM signal. In addition, the influence of the optical signal-to-noise ratio and the electronic filter on the optimum CSR of the system is further analyzed.

Free space millimeter wave-coupled electro-optic high speed nonlinear polymer phase modulator with in-plane slotted patch antennas.

We report in-plane slotted patch antenna-coupled electro-optic phase modulators with a carrier-to-sideband ratio (CSR) of 22 dB under an RF power density of 120 W/m(2) and a figure of merit of 2.0 W(-1/2) at the millimeter wave frequencies of 36-37 GHz based on guest-host type of second-order nonlinear polymer SEO125. CSR was improved more than 20 dB by using a SiO(2) protection layer. We demonstrate detection of 3 GHz modulation of the RF carrier. We also derive closed-form expressions for the modulated phase of optical wave and carrier-to-sideband ratio. Design, simulation, fabrication, and experimental results are discussed.

Quasi-optical single-sideband modulation with continuous carrier-to-sideband ratio tunability

A quasi-optical single-sideband (quasi-OSSB) modulation approach with a tunable carrier-to-sideband ratio (CSR) is proposed and demonstrated. By simply tuning the polarizing angle, a continuously tunable CSR can be obtained. Since the upper sideband is highly suppressed during the CSR’s tuning, quasi-OSSB modulation signals with extremely small interference are generated. An experiment is undertaken for verification. It is found that the target CSR can be continuously tuned over a wide range, which can be used to improve the receiver sensitivity of the fiber links.

Performance improvement of double-sideband signals in radio-over-fiber links utilizing pre-distortion method

In this paper, we investigate the optimal carrier-to-sideband ratio (CSR) for optical double-sideband (DSB) signals in radio-over-fiber (RoF) transmission. A pre-distortion method based on spectral shaping is proposed to optimize the signal CSR and eliminate the dispersion-induced power fading. A 12 GHz RoF transmission over 29 km standard single mode fiber (SSMF) is experimentally demonstrated which reveals that pre-distorted DSB has a 4.4 dB improvement over the one without pre-distortion, and 1.2 dB sensitivity advantage over single sideband (SSB) both with optimal CSR. The pre-distortion method is also applied to multi-channel transmission. The multi-channel experiment shows that for all channels the dispersion-induced power fading effects can be simultaneously mitigated and the pre-distorted DSB signals have ~1 dB sensitivity improvement over the SSB signals.

Optical single sideband modulation radio over fiber system by using a fiber-Bragg-grating-based acousto-optic filter

An optical single sideband (OSSB) modulation radio over a fiber system, by using an acousto-optic filter (AOF), is proposed and demonstrated. In the AOF, a uniform fiber Bragg grating is etched and modulated by an axially propagating acoustic wave. Due to the acousto-optic superlattice modulation, two secondary reflection peaks, centered on the primary reflection peak, are generated. In the scheme, an optical double-sideband signal passes though the AOF to realize OSSB modulation. Because the reflect depth of the primary peak is much deeper than those of the secondary peaks, the carrier experiences higher attenuation than the upper sideband, which means the carrier-to-sideband ratio (CSR) can be optimized at the same time. We demonstrate this scheme via simulations, and successfully reduce the CSR from 9.73 to 2.9 dB. As a result, the receiving sensitivity improved from −23.43 to −31.18 dBm at BER of 10 −9 with 30 km long SMF.

Single-sideband modulated radio-over-fiber system based on long period fiber grating

We present a prototype for optical single-sideband (SSB) modulated radio-over-fiber (RoF) system by employing a long period fiber grating (LPFG). A LPFG with 13.78nm base width of transmission spectrum and 0⿿23.2dB of transmission depth was designed by using commercial software. Then it is used in RoF SSB modulation scheme. In the scheme, a Mach⿿Zehnder modulator modulates the light wave with millimeter-wave driving signals to realize optical double-sideband (ODSB) modulation, the generated ODSB modulation signals pass through a LPFG. Due to the negative slope in transmission spectrum, the lower sideband experiences higher attenuation than the upper sideband. Thus the conversion from ODSB to optical single sideband with carrier (OSSB+C) can be easily achieved by using only one LPFG. Also, the carrier to sideband ratio (CSR) can be reduced by using a LPFG, results show the CSR can be decreased from 12.49dB to 1.1dB.

Overwritten fiber Bragg grating and its application in an optical single sideband with carrier modulation radio over a fiber system

We present a prototype for optical single sideband (SSB) modulation with carrier (OSSB+C) by employing an overwritten fiber Bragg grating (FBG) is proposed and demonstrated. The grating is written using two different uniform phase masks of slight variation in the period. Then it is used in millimeter-wave SSB modulation scheme. Its operation principle can be concluded as the following two steps: (i) first, an intensity modulator double sideband (DSB) modulates the lightwave with millimeter-wave driving signals; (ii) then, the generated DSB modulation signals are reflected by the overwritten FBG. The overwritten FBG can reflect the carrier and the sideband simultaneously, resulting in two coherent subcarriers. Thus the conversion from DSB to OSSB+C can be easily achieved by using only one grating. Also, carrier-to-sideband ratio (CSR) can be optimized by using grating with different reflection depth. We demonstrate this scheme via simulation and successfully reduce signals' CSR from 14.44 to 1.25 dB.

Performances improvement in radio over fiber link through carrier suppression using Stimulated Brillouin scattering

The performances of radio-over-fiber (RoF) link with fixed incident optical power on photodetector (PD) are improved through carrier suppression method. Firstly, a precise analytical model is proposed to quantify the relationship between the improvement of link gain, noise figure (NF), spur-free dynamic range (SFDR) and the carrier suppression ratio x, in which, the modulation index m is fully considered for the first time to our knowledge. Then the optimum optical carrier-to-sideband ratio (CSR) for RoF link performances in both double-sideband and single-sideband modulation is obtained from the optimum x for the link performances. Finally the experiments with the carrier subtraction method realized by Stimulated Brillouin scattering (SBS) are carried out and the experimental results show good agreement with the simulation ones.

Simultaneous Generation of Centralized Lightwaves and Double/Single Sideband Optical Millimeter-Wave Requiring Only Low-Frequency Local Oscillator Signals for Radio-Over-Fiber Systems

We have designed and experimentally demonstrated radio-over-fiber (ROF) systems to simultaneously generate optical millimeter-wave (mm-wave) and centralized lightwaves using one low-bandwidth intensity modulator (IM) with low-frequency local oscillator (LO) signals while simplifying the transmission design and reducing the cost of the base station (BS). The techniques based on double-sideband (DSB) and single-sideband (SSB) signals for ROF systems are discussed in detail in terms of architecture efficiency, bandwidth requirement, and fiber transmission performance. The repetitive frequency of the optical mm-wave carriers are four times of that of the LO in central office (CO) by using DSB scheme. Full-duplex transmission services have been successfully realized over 20-km single-mode fiber (SMF) based on wavelength-reuse technique. In order to mitigate chromatic dispersion, the SSB technique has also been investigated in this paper. We had realized an ROF system that attained dispersion-free transmission and a negative power penalty by using SSB generation. We also quantified the optical carrier-to-sideband ratio (CSR) of downstream transmission in this ROF link and established that the performance of ROF system can be significantly improved when the optical signals are transmitted at a CSR value of 0 dB. The proposed architectures require much less bandwidth of the modulators, receiver sensitivity, system operation efficiency, and reliability.

A Novel Scheme to Generate Single-Sideband Millimeter-Wave Signals by Using Low-Frequency Local Oscillator Signal

We have proposed and experimentally demonstrated a novel scheme to generate optical millimeter-wave (mm-wave) signals by using single-sideband modulation with low-frequency local oscillator (LO) signals. In this architecture, by incorporating the proper dc bias of the modulator in central office, the optical mm-wave carriers are generated with two times frequency of the LO signal while largely reducing the bandwidth requirement of the modulator. We quantify the optical carrier-to-sideband ratio (CSR) of downstream transmission in this radio-over-fiber (ROF) link and establish that the performance of the ROF system can be significantly improved when the optical signals are transmitted at CSR equal to 0 dB.

Analysis of optical carrier-to-sideband ratio for improving transmission performance in fiber-radio links

In this paper, we investigate the optimum carrier-to-sideband ratio (CSR) for maximizing the transmission performance of an optically modulated millimeter-wave signal in a fiber-wireless system via experiment, theory, and simulation. We present a simple analytical model to assess the performance enhancement resulting from optical CSR variations. The model is capable of analyzing systems incorporating binary phase-shift keyed and quaternary phase-shift keyed modulation formats. We quantify the optical CSR of a point-to-point fiber-radio link and establish that the performance of the fiber-wireless links can be significantly improved when the optical signal is transmitted at the optimum CSR of 0 dB. The analysis further shows that the optimum optical CSR is independent of transmission bit rates.