Dispersion-induced Power Penalty Research Articles

Frequency Octupling Radio over Fiber System with Multiple Remote Antenna Units

Bidirectional radio over fiber (RoF) transmission to multiple remote antenna units (RAUs) with frequency octupling is proposed in this paper. The proposed RoF system uses a dual-port Mach-Zehnder modulator (DP-MZM) and an arrayed waveguide grating (AWG) to generate millimeter-wave (mm-wave) to four different RAUs. Bit Error Rate (BER) and received optical power are key parameters used to measure the performance of the system. From the simulation results, it is shown that the proposed system achieves an acceptable performance a fiber distance of 50 km with a BER of 10-12. Furthermore, the results indicate that the dispersion-induced power penalties for both uplink and downlink transmission of all RAUs are less than 1 dB. In summary, the proposed system simplifies the RoF system by reusing wavelengths and utilizing low RoF frequency through the frequency-octupling technique.

Optical Channel Selection Avoiding DIPP in DSB-RFoF Fronthaul Interface.

The paper presents a method of selecting an optical channel for transporting the double-sideband radio-frequency-over-fiber (DSB-RFoF) radio signal over the optical fronthaul path, avoiding the dispersion-induced power penalty (DIPP) phenomenon. The presented method complements the possibilities of a short-range optical network working in the flexible dense wavelength division multiplexing (DWDM) format, where chromatic dispersion compensation is not applied. As part of the study, calculations were made that indicate the limitations of the proposed method and allow for the development of an algorithm for effective optical channel selection in the presence of the DIPP phenomenon experienced in the optical link working in the intensity modulation–direct detection (IM-DD) technique. Calculations were made for three types of single-mode optical fibers and for selected microwave radio carriers that are used in current systems or will be used in next-generation wireless communication systems. In order to verify the calculations and theoretical considerations, a computer simulation was performed for two types of optical fibers and for two selected radio carriers. In the modulated radio signal, the cyclic-prefix orthogonal frequency division multiplexing (CP-OFDM) format and the 5G numerology were used.

DSP enabled next generation 50G TDM-PON

With 10G time division multiplexed passive optical network (TDM-PON) systems ready for massive deployment worldwide, the next generation PON standards are being intensively discussed in both IEEE and ITU-T. Compared with the IEEE’s wavelength stacked 2 ∗ 25 G solution, the ITU-T’s single carrier non-return-to-zero-based 50G TDM-PON has the advantages of low cost, easy operation, and convenient management. However, the 50G TDM-PON will also have to face great challenges in real-world operating conditions. In this paper, we will illustrate the unique role for digital signal processing (DSP) in solving the challenges for the next generation 50G TDM-PON systems, such as device bandwidth limitation, dispersion induced power penalty, and high link budget. To analyze DSP’s feasibility in this application, potential issues such as cost and interoperability are analyzed. Through offline experiments and prototype demonstrations, DSP’s role in enabling next generation single carrier 50G TDM-PON is highlighted.

Chirp-adjustable optical intensity modulator with tunable OCSR based on Sagnac interferometer

Abstract In this paper a novel optical intensity modulator with tunable optical carrier-to-sideband ratio (OCSR) and adjustable chirp parameter is proposed and theoretically investigated. It is based on a bidirectional phase modulator (PM) and a tunable nonreciprocal optical phase shifter in a Sagnac interferometer (SI). Because no bias is necessary for a PM, the bias-drift problems are automatically removed. Besides, clockwise (CW) and counter clockwise (CCW) propagating lights travel in the same path so enhances robustness against environmental perturbations. In this modulator two radio frequency (RF) signals with opposite phases and tunable power ratio are applied to the bidirectional PM. Chirp parameter and OCSR of the modulator can be tuned by tuning the phase shift of the optical phase shifter and RF power ratio. Besides, this modulator can have two complementary balanced outputs. So common-mode noises such as relative intensity noise (RIN) of the laser can be suppressed in a microwave photonic link (MWPL) based on this modulator and using a balanced receiver. This novel modulator can also operate bidirectionally. An intensity modulated optical signal with tunable OCSR and chirp parameter is achieved by adjusting the optical phase shifter and the RF power ratio. The effect of the lossy SI and finite optical extinction ratio on the performance of the proposed modulator is theoretically investigated. In addition applications of the proposed chirp-adjustable modulator to overcome fiber dispersion-induced power penalty in a MWPL is investigated It is shown that by adjusting the chirp parameter, link distance for a given frequency (or bandwidth for a given link distance) doubles.

Experimental demonstration of PAM-DWMT for passive optical network

We experimentally demonstrate a discrete wavelet multitone (DWMT) modulation scheme based on pulse amplitude modulation (PAM) for next generation passive optical network (PON), which offers high tolerance against chromatic dispersion, high spectral efficiency, low peak to average power ratio (PAPR) and low side lobes. The experimental results show the chromatic dispersion induced power penalties are negligible after 20km fiber transmission. Compared with orthogonal frequency division multiplexing (OFDM), DWMT offers a better receiver sensitivity.

A Photonic Technique for Instantaneous Microwave Frequency Measurement Utilizing a Phase Modulator

We propose a simple microwave frequency measurement approach utilizing a phase modulator. After properly adjusting the polarization controllers in the proposed system, two dispersion-induced power penalty functions with different variation trends are obtained. A distinct relationship between the power ratio and the microwave frequency can be constructed by comparing the two power penalty functions. Thus, the microwave frequency can be determined by the power ratio value. Since only a bias drift free phase modulator and a single laser source are needed, the measurement system is significantly simplified. In the experiment, a frequency measurement over the range of 1.6–24.6 GHz with measurement errors within ±0.3 GHz is achieved.

Bidirectional MM-Wave Radio over Fiber transmission through frequency dual 16-tupling of RF local oscillator

In this paper for the first time, a 60 GHz bidirectional Millimeter Wave (MM-Wave) Radio over Fiber (RoF) transmission through a new frequency dual 16-tupling of 3.75 GHz local oscillator (LO) is demonstrated. The proposed system is constructed with parallel combination of two cascaded stages of MZMs. The upper cascaded stage and the Lower cascaded stages are biased at the Maximum Transmission Point (MATP). By suitable adjustments of LO phase and amplitude, optical sidebands with spacing of 8 times the input LO frequency is generated. These sidebands are then separated using filters to achieve dual 16-tupling. A good agreement between numerical derivations and the simulation results are achieved. Further, a simulation is performed to access the dual bidirectional transmission performance for the double and single tone modulation with 2.5 Gbps data transmission. The transmission distance is limited to 25 km for the double tone modulation due to bit walk of effect. A 60 km link distance is achieved with single tone modulation. The dispersion induced power penalties less than 0. 5 dB at 10−9 BER is observed for both up and down streams.

Dispersion-Tolerant DDO-OFDM System and Simplified Adaptive Modulation Scheme Using CAZAC Precoding

We apply the signal- and channel-independent constant amplitude zero autocorrelation sequence (CAZAC) precoding technique to a bandwidth-limited longer-reach DDO-OFDM system, and propose a simplified adaptive modulation scheme according to the equalized SNR per subcarrier after CAZAC precoding. Simulation results show that with the optimized modulation index, conventional 8.23-Gb/s double sideband (DSB) modulated QPSK-OFDM signal cannot realize 100 km standard single-mode fiber (SSMF) transmission at the given received optical power, while CAZAC precoding can enable 100 km SSMF transmission with dispersion-induced power penalty as low as 2.7 dB. The advantage becomes more obvious when CAZAC precoding is employed to 16.46-Gb/s 16QAM-OFDM systems. Thanks to the frequency diversity, OFDM system with CAZAC is proved to be more dispersion tolerant with improved receiver sensitivity. We also analyze the signal-to-noise ratio (SNR) of each individual subcarrier and its flatness is confirmed to be much improved independent of modulation formats and transmission distances when precoding is used. Based on the priori knowledge of flat SNR curve, we further propose a simplified adaptive modulation scheme using only three steps where bit loading can be applied with power loading omitted. Simulation and experimental results demonstrate that the BER performance can be further improved with negligible data rate reduction and system complexity aggravation using our proposed simplified adaptive modulation method.

Multichannel Up-Conversion Based on Polarization-Modulated Optoelectronic Oscillator

Photonic microwave multichannel up-conversion based on a polarization-modulated optoelectronic oscillator is proposed and demonstrated. The scheme produces a high-quality local oscillation signal, implements photonic microwave multichannel up-conversion at arbitrary optical wavelengths, and realizes dispersion penalty compensation for multichannel radio over fiber links with different transmission distances in different channels simultaneously. An experiment is carried out. The 50-Mb/s 16 QAM signals at 3.5 and 7.5 GHz are successfully up-converted to 13.436 and 17.436 GHz, and transmitted over 20- and 15-km fibers with dispersion-induced power penalty removed in two independent channels, respectively. The phase noise curves with or without IF signals applied are superimposed, with the value being lower than -110 dBc/Hz at 10-kHz offset.

Broadband Phase-to-Intensity Modulation Conversion for Microwave Photonics Processing Using Brillouin-Assisted Carrier Phase Shift

We theoretically and experimentally demonstrate a novel broadband phase-to-intensity modulation conversion technique for microwave photonics processing system. The technique is based on optical carrier phase shift of a phase modulated signal using stimulated Brillouin scattering. More than 360 ° carrier phase shift can be achieved. By simply adjusting the carrier phase shift while preserving its amplitude unchanged, the phase modulation can be fully or partially converted to intensity modulation. The main advantage of the proposed method lies in its broadband nature since the SBS is only imparted on the optical carrier and the phase modulated sidebands are not affected as long as the modulating frequency is higher than the Brillouin bandwidth. In addition, as a microwave photonics processing application, we demonstrate the dispersion induced power penalty control in radio-over-fiber systems using the proposed technique. Experimental results match well with the theoretical prediction.

Carrier generation and IF signal up-conversion using optical injection locking and stimulated Brillouin scattering

We theoretically investigate the intermediate frequency (IF) signal up-conversion with dual modes modulation (DMM) and single-mode modulation (SMM) of two single sideband (SSB) modulation modes for radio-over-fiber (RoF) systems. The simulation results indicate that the SMM can overcome the dispersion-induced power penalties of the generated carrier and up-converted IF signals. Then, we experimentally demonstrate an approach for RF carrier generation with SSB modulation and IF signal up-conversion with SMM using a combination of direct modulation in an injection-locked distributed feedback (DFB) laser and stimulated Brillouin scattering (SBS). The experimental results are compared with the predictions of the numerical simulation in SMM condition, and both are in good agreement with each other. The advantages and limits of the proposed method are discussed.

Instantaneous Microwave Frequency Measurement With Improved Measurement Range and Resolution Based on Simultaneous Phase Modulation and Intensity Modulation

A novel approach to implementing instantaneous microwave frequency measurement based on simultaneous optical phase modulation and intensity modulation with improved measurement range and resolution is proposed and experimentally demonstrated. The simultaneous optical phase modulation and intensity modulation are implemented using a polarization modulator (PolM) in conjunction with an optical polarizer. The phase- and intensity-modulated optical signals are then sent to a dispersive element, to introduce chromatic dispersions, which results in two complementary dispersion-induced power penalty functions. The ratio between the two power penalty functions has a unique relationship with the microwave frequency. Therefore, by measuring the microwave powers and calculating the power ratio, the microwave frequency can be estimated. Thanks to the complementary nature of the power penalty functions, a power ratio having a faster change rate versus the input frequency, i.e., a greater first-order derivative, is resulted, which ensures an improved measurement range and resolution. The proposed approach for microwave frequency measurement of a continuous-wave and a pulsed microwave signal is experimentally investigated. A frequency measurement range as large as 17 GHz with a measurement resolution of plusmn 0.2 GHz for a continuous-wave microwave signal and plusmn0.5 GHz for a pulsed microwave signal is achieved.

Time-bandwidth product of the photonic time-stretched analog-to-digital converter

The time-bandwidth product of the photonic time-stretched system is modeled in terms of physical system parameters. Using the time-bandwidth product as figure-of-merit, the performances of optical double-sideband and single-sideband (SSB) intensity modulation are compared, and optical SSB intensity modulation is identified as a potential solution to extend the system's time-bandwidth product. An SSB-modulated time-stretched system is theoretically analyzed and experimentally demonstrated. As an important practical consideration, the analytical model relating the system performance to the phase and amplitude mismatches in the SSB modulator is presented. The results show that the system is tolerant to such unavoidable mismatches. Experiments using commercially available components suggest that the dispersion-induced power penalty can be kept below 2.5 dB over 4 - 20 GHz bandwidth for any stretch factor. Additional experiments demonstrating 120-GSamples/s real-time digitization of a 20-GHz SSB-modulated signal are also reported.

Design and performance of the bidirectional optical single-sideband modulator

We present a detailed study of the design and performance of the bidirectional optical single-sideband modulator (BOSSM). This is a new scheme to achieve optical single-sideband modulation (OSSB) that uses a standard single-electrode Mach-Zehnder modulator (MZ-EOM) and passive fiber-optic components. The design is based on a novel technique to operate electrooptic modulators in which the radio frequency (RF) electrode is bidirectionally driven. The fundamentals of this bidirectional operation are analyzed thoroughly and it is found that it requires the use of a wide-bandwidth MZ-EOM with an electrode design that provides good velocity match between the optical and microwave modes. Deriving the expressions for the optical field and power at the output of the BOSSM, the OSSB operation is shown to be independent of the MZ-EOM bias. Therefore, the optical modulation depth at the output of the device can be enhanced using minimum transmission biasing to provide suppression of the optical carrier. Moreover, it is found that the second-order distortion is unaffected by the MZ-EOM bias; hence the technique can be applied to multi-octave bandwidth systems. Finally, the performance of the BOSSM is evaluated using a prototype based on a commercial 10 Gb/s MZ-EOM. The experimental characterization of the electrooptical parameters of this device reveals that the RF electrode design is not optimized for bidirectional operation. Therefore, the performance of the prototype is limited by the particular MZ-EOM deployed. However, sideband suppression over 10 dB is measured for most frequencies up to millimeter-waves, with peaks in the 20 dB to 30 dB range for narrow bands. This performance has enabled the demonstration of a 22-km fiber link transmitting a 29-GHz subcarrier conveying binary phase-shift keying modulated data at 622 Mb/s. The BOSSM reduces the dispersion-induced power penalty in the link to less than 1.5 dB. Furthermore, the bit error rate of the link is increased by five orders of magnitude using the carrier suppression technique.

Dispersion-induced power penalties in millimeter-wave signal transmission using multisection DBR semiconductor laser

In this paper, we present a simple analytical model to characterize the effect of fiber chromatic dispersion when using a multisection distributed-Bragg reflector (DBR) semiconductor laser as a millimeter-wave optical transmitter in a millimeter-wave fiber-radio system. We characterize the dispersion penalty of the laser as a function of the laser operating conditions and establish that the penalty is dependent on the distribution of optical power among the modes in the laser output. This, in turn, is dependent on the spectrum-filtering property of the laser DBR section and the gain profile of the laser. In addition to the dispersion penalty, the stability of the generated millimeter-wave carrier from the multisection laser is investigated, including the detected RF power and resulting phase noise. We establish that a compromise must be made when finding the optimum bias condition of the laser which provides minimum dispersion penalty, maximum received RF power, and minimum phase noise of the generated millimeter-wave carrier.

Dispersion-induced power penalty in fiber-Bragg-grating WDM filter cascades using optically preamplified and nonpreamplified receivers

In wavelength-division-multiplexed optical networks, signals pass through cascades of multiplexing/demultiplexing channel filters present in the network access nodes. We describe experimental measurements and numerical simulations of the signal power penalty at 10 Gbps due to dispersion slope in such a cascade of fiber-Bragg-grating filters. The dispersion penalty of the cascade limits the allowed frequency detunings of the signal laser and channel filters. We observe that optically-preamplified receivers show a significantly larger dispersion penalty than nonpreamplified receivers, with a simple relation between the two penalties. This penalty difference should exist for any signal impairment that degrades optical signal extinction such as dispersive filter or fiber transmission and optical channel bandwidth narrowing.

Tailoring Chirped MoirÉ Fiber Bragg Gratings for Wavelength-Division-Multiplexing and Optical Code-Division Multiple-Access Applications

The design and fabrication of chirped Moiré fiber Bragg gratings (CMGs) are presented, which can be used in either (1) transmission as passband filters for providing wavelength selectivity in wavelength-division-multiplexed (WDM) systems or (2) reflection as encoding/decoding elements to decompose short broadband pulses in both wavelength and time in order to implement an optical code-division multiple-access (OCDMA) system. In transmission, the fabricated CMGs have single or multiple flattened passbands (< 0.5 dB ripple) and exhibit > 12 dB isolation and near constant in-band group delay. It is shown that these filters do not produce any measurable dispersion-induced power penalties when used to provide wavelength selectivity in 2.5 Gbit/s systems. It is also demonstrated how CMGs can be used in reflection to encode/decode short pulses from a wavelength-tunable mode-locked Er-doped fiber laser.

Generalized study of dispersion-induced power penalty mitigation techniques in millimeter-wave fiber-optic links

The authors present a comprehensive analysis of the chromatic dispersion effects in harmonic upconverted millimeter-wave (mm-wave) fiber-optic links. The optical upconversion is performed through a photonic mixer based on a Mach-Zehnder electrooptical modulator. It is shown that by biasing the electrooptical modulator either at the maximum or at the minimum transmission bias points, the dispersion-induced power penalty effect on the upconverted signal may be sharply mitigated, which results in increasing the frequency-length product of the fiber-optic link. Experimental results are provided for the three different types of bias.

Analysis of hybrid modulation techniques in MZ-EOM-based photonic mixers to overcome dispersion-induced power penalty in up-converting millimeter-wave fiber-optic links

In this letter, we investigate the combination of single-sideband (SSB) and double-sideband (DSB) modulation techniques in up-converting millimeter-wave fiber-optic links. It is shown that the dispersion-induced power penalty due to fiber chromatic dispersion may be mitigated and eventually overcome by employing MZ-EOM SSB modulation over the local oscillator signal and/or the intermediate frequency signal. Experimental results are provided for the hybrid modulation scheme which combines both SSB and DSB. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 127–129, 1999.

Analysis of hybrid modulation techniques in MZ‐EOM‐based photonic mixers to overcome dispersion‐induced power penalty in up‐converting millimeter‐wave fiber‐optic links

In this letter, we investigate the combination of single-sideband (SSB) and double-sideband (DSB) modulation techniques in up-converting millimeter-wave fiber-optic links. It is shown that the dispersion-induced power penalty due to fiber chromatic dispersion may be mitigated and eventually overcome by employing MZ-EOM SSB modulation over the local oscillator signal and/or the intermediate frequency signal. Experimental results are provided for the hybrid modulation scheme which combines both SSB and DSB. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 127–129, 1999.