Microwave Carrier Research Articles

Demonstration of InP-on-Si Self-Pulsating DFB Laser Diodes for Optical Microwave Generation

We demonstrate self-pulsating heterogeneously integrated III-V-on-SOI two-section distributed feedback laser diodes, with a wide range of self-pulsation frequencies between (but not limited to) 12 and 40 GHz. The spectral width of the free-running pulsations is 40 MHz. The dependence of the self-pulsation frequency on the injected current combination and the temperature is investigated. Finally, locking the self-pulsation to an electrical RF signal with power as low as –17 dBm is demonstrated, which can be used for the generation of an optical microwave carrier with a spectral width less than 10 Hz. Such laser could be beneficial for radio-over-fiber applications.

Photonic microwave carrier recovery using period-one nonlinear dynamics of semiconductor lasers for OFDM-RoF coherent detection.

This study investigates an all-optical scheme based on period-one (P1) nonlinear dynamics of semiconductor lasers, which regenerates the microwave carrier of an orthogonal frequency division multiplexing radio-over-fiber (OFDM-RoF) signal and uses it as a microwave local oscillator for coherent detection. Through the injection locking established between the OFDM-RoF signal and the P1 dynamics, frequency synchronization with highly preserved phase quality is inherently achieved between the recovered microwave carrier and the microwave carrier of the OFDM-RoF signal. A bit-error ratio down to 1.9×10^-9 is achieved accordingly using the proposed scheme for coherent detection of a 32-GHz OFDM-RoF signal carrying 4 Gb/s 16-quadrature amplitude modulation data. No electronic microwave generators or electronic phase-locked loops are thus required. The proposed system can be operated up to at least 100GHz and can be self-adapted to certain changes in the operating microwave frequency.

Optimization of Close-In Phase Noise for Microwaves Generated With Kerr Combs Using Brillouin-Assisted Pump Depletion

We report a method to improve the close-in phase noise performance of microwave signals generated using Kerr optical frequency combs. We propose a technique based on Brillouin-assisted pump depletion, and we show that the resulting phase noise close to the microwave carrier can be significantly lowered. We consider microwaves with 18 and 30 GHz frequency and achieve phase noise improvements up to 10 dB for close-in phase noise (offset $ kHz). This technique targets applications where particularly high spectral purity is required at sub-kHz offset from the carrier frequency.

Practical application of a bidirectional microwave photonic filter: simultaneous transmission of analog TV signals

A practical application of a bidirectional microwave photonic filter (MPF) to transmit simultaneous analog TV signals coded on microwave carriers is experimentally demonstrated. The frequency response of the bidirectional MPF is obtained by the interaction of an externally modulated multimode laser diode emitting at 1.55 μm associated to the free-spectral range of the optical source, the chromatic dispersion parameter of the optical fiber, as well as the length of the optical link. The filtered microwave bandpass window generated around 2 GHz is used as electrical carrier in order to simultaneously transmit TV signals of 67.25 and 61.25 MHz in both directions. The obtained signal-to-noise ratios for the transmitted signals of 67.25 and 61.25 MHz are 37.62 and 44.77 dB, respectively.

Frequency tuning of an active microwave bandpass filter by a monotone microwave carrier

ABSTRACTIn this article, we have demonstrated experimentally the frequency tuning effect of an active microwave bandpass filter (BPF) operating at 9.506 GHz produced by a monotone microwave carrier. Typical frequency tuning of 24 MHz has been achieved with a monotone microwave carrier power of 1.7 mW and frequency of 9.674 GHz at the input of the BPF. The BPF response shifts as a whole towards the monotone carrier which can be on either side of the centre frequency of the BPF. The amount of tuning depends upon both the power and detuning of the monotone carrier from the centre frequency of the BPF. In another experiment, the frequency tuning achieved is 320 MHz with CW carrier power of 6.75 mW and a carrier frequency of 9.44 GHz.

An experimental distribution of analog and digital information in a hybrid wireless visible light communication system based on acousto-optic modulation and sinusoidal gratings

In this paper we propose a photonic architecture as an alternative tool to distribute point to multipoint analog and digital information over a hybrid wireless visible optical communication system. The experimental set-up is composed of a red laser pointer, an acousto-optic modulator, a sinusoidal grating and a photo-detector array. By using a simple and variable interferometric system, diffraction gratings with different spatial frequencies are generated and recorded on a photoemulsion which is composed of vanilla with dichromate gelatin. Analog video and digital information are first transmitted and recovered over a wireless communication system using a microwave carrier at 4.52 GHz which is generated by distributed feedback lasers operating in the low laser threshold current region. Separately, the recovered video information and digital data are combined with a radio frequency signal of 80 MHz, obtaining a subcarrier of information that is imposed on the optical carrier of the pointer laser using an acousto-optic modulator which is operated with an angle of incident light that satisfies the Bragg condition. The modulated optical carrier is sent to a sinusoidal grating, the diffraction pattern is photo-detected using an array of PIN photo-detectors. The use of sinusoidal gratings with acousto-optic modulators allows that number of channels to be increased when both components are placed in cascade.

DUAL-CHIRP ARBITRARY MICROWAVE WAVEFORM GENERATION BY USING A DUAL PARALLEL MACH-ZEHNDER MODULATOR FEEDING WITH RF CHIRP SIGNAL

In this paper, dual-chirped arbitrary microwave waveform has been generated through photonics, incorporated with single dual parallel mach-zehnder modulator (DPMZM) inbuilt mach zehnder interferometer (MZI) structure. We have taken two cases of chirping, i.e., linear and nonlinear chirps. A case of linear chirping has been explored previously. However, to the best of the authors' knowledge effect of nonlinear chirping in this paper is evaluated for the first time. Other photonics approaches are also available, such as spectra shaping and wavelength to time mapping. But due to fixed spectral response of spectral shaper, center frequency of linear chirp generated waveform is fixed. To get large center frequency again we have to use large number of spectral shapers which will increase the system complexity. DPMZM avoids such difficulties. These MZMs are biased at the minimum transmission point to get carrier suppressed modulation. Product modulator (PM) is cascaded to the lower arm of DPMZM. Here by using DPMZM we get two advantages. First we have two complimentarily chirped microwave waveforms and second up conversion of the frequency of microwave carrier. A dual-chirped microwave waveform with centre frequency 6 GHz with bandwidth 200 MHz and 2 GHz is generated. The paper gives specific details about various performance parameters such as input signal frequency and power, output signal parameters viz output frequency, chirp rate, chirp bandwidth, time bandwidth product (TBW), etc. The overall model and its performance parameters are computed through MATLAB simulation.

Vector Signal Generation Using a Polarization and a Phase Modulator in a Sagnac Loop

A novel technique to generate a microwave vector signal based on a bidirectional use of a polarization modulator (PolM) and a phase modulator (PM) in a Sagnac loop is proposed and experimentally demonstrated. The $I$/$Q$ data streams of a vector signal are mixed with a microwave carrier and then applied to the PolM and the PM, respectively. A microwave vector signal is generated by combining two microwave signals with one obtained by beating the optical carrier and the $+ 1^{\mathrm {st}}$ order sideband of a phase-modulated signal and the other obtained by beating the optical carrier and the $+ 1^{\mathrm {st}}$ order sideband of an intensity-modulated signal. A quadrature phase is introduced due to the inherent $\pi/2$ phase shift between the optical carrier and the $+ 1^{\mathrm {st}}$ order sideband of the phase-modulated signal. The generation of a 4.5 GHz microwave signal at 625 Msym/s with quadrature phase-shift-keying (QPSK) modulation and the transmission of the signal over a 25-km single-mode fiber are evaluated. An error-free transmission is achieved at a received optical power of 6 dBm. By incorporating $I/Q$ imbalance compensation, an error-free transmission is achieved at a lower received power of 2 dBm.

Dual-Chirp Microwave Waveform Generation Using a Dual-Parallel Mach-Zehnder Modulator

A photonic approach to generating a dual-chirp microwave waveform using a single dual-parallel Mach-Zehnder modulator (DPMZM) is proposed and experimentally demonstrated. A dual-chirp microwave waveform can be used in a radar system to improve its range-Doppler resolution. In the proposed approach, a baseband single-chirp waveform is applied to one sub-Mach-Zehnder modulator (sub-MZM) in the DPMZM and a microwave carrier is applied to the other sub-MZM. By biasing the two sub-MZMs at the minimum transmission point to suppress the optical carrier, a dual-chirp microwave waveform with a central frequency upconverted to the frequency of the microwave carrier is generated. A theoretical analysis is performed, which is then verified by a proof-of-concept experiment. A dual-chirp microwave waveform at 6 GHz with a tunable bandwidth at 200 MHz and 2 GHz is generated.

A High Spectral Efficiency Coherent Microwave Photonic Link Employing Both Amplitude and Phase Modulation With Digital Phase Noise Cancellation

A high spectral efficiency coherent microwave photonic link (MPL) supporting amplitude and phase modulation incorporating a digital phase noise cancellation is proposed and experimentally demonstrated. At the transmitter, a continuous-wave light wave is amplitude- and phase-modulated by two microwave vector signals carried by a microwave carrier at an identical frequency. The modulated optical signal is polarization multiplexed with an unmodulated optical carrier and transmitted over a length of a single-mode fiber (SMF). At the receiver, the optical signal is detected coherently by a coherent receiver to which a local oscillator (LO) laser source is also applied. Through advanced digital signal processing, the microwave vector signals are recovered, and the phase noise introduced by both the transmitter laser source and LO laser source is cancelled. An experiment is performed. The transmission of a 2.5-Gb/s 16-QAM and a 1.25-Gb/s QPSK microwave vector signals both at 2.5 GHz over a 25-km SMF is implemented. The total bit rate of the MPL is 3.75 Gb/s. The transmission performance of the MPL in terms of error vector magnitudes and bit error rates is evaluated.

Sulfur Dioxide Was Carried out by Activated Carbon Adsorption in Combination with Microwave Desorption in Scene

The desulfurization of low-concentration sulfur dioxide in laboratory simulated flue gas and on-site metallurgical flue gas was carried out by activated carbon adsorption in combination with microwave desorption. In comparison with the results of desulfurization, the effect of gas impurities in on-site metallurgical flue gas on the performance of activated carbon adsorption and microwave desorption, as well as the consumption of activated carbon during the desorption process, was also studied. The results show that the gas impurities decrease the unit adsorption capacity by 28.73mg/g and increase the consumption of activated carbon by 0.25g, thus go against the adsorption of activated carbon. Moreover, the use of on-site flue gas as microwave carrier gas in the desorption process can benefit the accumulation of medium-or high-concentration SO2 from the desorption process which can be used to produce acids.

Photonic generation of binary and quaternary phase-coded microwave waveforms with an ultra-wide frequency tunable range.

A novel photonic approach to generating binary and quaternary phase-coded microwave waveforms with an ultra-wide frequency tunable range is proposed and experimentally demonstrated. In the proposed system, a dual-parallel Mach-Zehnder modulator (DP-MZM) is used as an optical wavelength shifter. To generate a phase-coded microwave waveform, the coding signal is modulated on the original wavelength using a phase modulator (PM). Combining the shifted wavelength and the original wavelength, two wavelengths with a frequency space determined by the input microwave signal are obtained. Applying them to a photodetector (PD), a phase-coded microwave waveform is generated. The key significance of the approach is that both binary and quaternary phase-coded microwave waveforms can be generated with an ultra-wide frequency tunable range. An experiment is performed. The generation of binary and quaternary microwave waveforms with a microwave carrier frequency at 10 and 20 GHz is demonstrated.

Cyclic additional optical true time delay for microwave beam steering with spectral filtering.

Optical true time delay (OTTD) is an attractive way to realize microwave beam steering (MBS) due to its inherent features of broadband, low-loss, and compactness. In this Letter, we propose a novel OTTD approach named cyclic additional optical true time delay (CAO-TTD). It applies additional integer delays of the microwave carrier frequency to achieve spectral filtering but without disturbing the spatial filtering (beam steering). Based on such concept, a broadband MBS scheme for high-capacity wireless communication is proposed, which allows the tuning of both spectral filtering and spatial filtering. The experimental results match well with the theoretical analysis.

Spatial Filtering in a Broadband In-Home OFDM Radio-Over-Fiber Network

The spatial filtering in an orthogonal frequency division multiplexing (OFDM) radio-over-fiber network is proposed to boost its capacity using broadband optical true time delay enabled microwave beam steering. The observed suppression ratio of the spatial filtering is 19.4 dB. The optical delivery and directional wireless transmission of 3.975 Gb/s OFDM data on a 19-GHz microwave carrier is studied. The observed beam directing-induced bit error ratio improvement is more than four orders of magnitude.

Arbitrary Microwave Waveform Generation Based on a Tunable Optoelectronic Oscillator

Photonic generation of a phase-coded or frequency-chirped microwave waveform with a tunable microwave carrier frequency using a frequency-tunable optoelectronic oscillator (OEO) is proposed and experimentally demonstrated, for the first time to the best of our knowledge. In the proposed system, the tunable OEO has functions to generate a frequency-tunable microwave signal and to output an optical sideband. The optical sideband and a portion of the light wave from the OEO laser source are sent to a polarization modulator (PolM), with their polarization directions aligned with the two principal axes of the PolM. An electrical signal is applied to the PolM, and two complementary phase-coded or frequency-chirped light waves are generated which are converted to an electrical signal by beating the light waves at a high-speed photodetector. The key significance of the technique is that a phase-coded or frequency-chirped microwave waveform with a tunable microwave carrier frequency and a reconfigurable phase-coding or frequency-chirping pattern can be generated without using a separate microwave source. The technique is experimentally verified. The generation of a binary- and a polyphase-coded microwave waveform with a microwave carrier frequency at 10 and 15 GHz is demonstrated. The generation of a linearly frequency-chirped microwave waveform with a chip rate of 20.98 GHz/ns at a 10-GHz carrier frequency and 22.5 GHz/ns at a 15-GHz carrier frequency is also achieved.

Modeling of sheet carrier density and microwave frequency characteristics in Spacer based AlGaN/AlN/GaN HEMT devices

In this paper, we present a physics-based model for two-dimensional electron gas (2DEG) sheet carrier density ns and various microwave characteristics such as transconductance, cut-off frequency (ft) of the proposed Spacer layer based AlxGa1−xN/AlN/GaN High Electron Mobility Transistors (HEMTs) is modeled by considering the quasi-triangular quantum well. To obtain charge density ns, the variation of Fermi level with supply voltage and the formation of various energy sub-bands E0, E1 are considered. The obtained results are simple and easy to analyze the sheet carrier density, DC model and microwave frequency performance analysis for nanoscale Spacer layer based AlxGa1−xN/AlN/GaN HEMT power devices. The Spacer layer based AlGaN/AlN/GaN heterostructure HEMTs shows excellent promise as one of the candidates to substitute present AlGaN/GaN HEMTs for future high speed and high power applications. Derived model results for drain current, transconductance, current-gain cutoff frequency for different short and long gate length device are calibrated and verified with experimental data over a full range for gate and drain applied voltages and is useful for nanoscale and microwave analysis for circuit design.

Single Phase Modulator for Binary Phase-Coded Microwave Signals Generation

We report a new approach to photonic generation of binary phase-coded microwave signals based on the asymmetric phase modulation indexes of a phase modulator in the TE and TM polarization states. The proposed system is extremely simplified compared with any other techniques reported in the previous literature since we only use one phase modulator. The microwave carrier frequency is widely tunable, and the π phase shift of the microwave signal is independent of the amplitude of the electrical driving signal. The proposed technique is theoretically analyzed and experimentally verified at carrier frequencies of 10 and 25 GHz, respectively.

Ultra-Wideband and 60-GHz Generation and Transmission Over a Wavelength Division Multiplexing-Passive Optical Network

A novel scheme to simultaneously generate an on-off keying (OOK) impulse radio ultra-wideband (IR-UWB) signal, a 60-GHz millimeter-wave (mmW) signal, and a baseband signal in the optical domain using a Sagnac loop is proposed and demonstrated. In the proposed system, a polarization beam splitter (PBS), a fiber Bragg grating (FBG), and two back-to-back connected polarization modulators (PolMs) are incorporated in the Sagnac loop. An OOK Gaussian pulse signal is modulated on a clockwise transmitted optical carrier by the first PolM and then converted to an OOK UWB impulse signal at the FBG serving as an edge filter, and the counterclockwise transmitted optical carrier is simultaneously modulated by a baseband signal and a 30-GHz mmW signal at the second PolM. By introducing a ? phase shift between the clockwise and counterclockwise optical carriers, the optical carrier of the 30-GHz signal is suppressed when applied to a polarizer. As a result, a frequency-doubled mmW signal at 60 GHz is generated by beating the two first order sidebands at a photodetector. Due to the velocity mismatch between the counterclockwise light wave and the clockwise microwave carrier, the OOK signal and the baseband signal can travel through the other PolM with negligible modulation; thus no interference from another signal would be introduced. Error-free transmission of a UWB signal at 2.5 Gbps and a wired baseband signal at 2.5 and 5 Gbps over a 25-km single-mode fiber is achieved. A frequency-doubled mmW signal at 60 GHz is also obtained.

Analysis of shot noise in the detection of ultrashort optical pulse trains

We present a frequency domain model of shot noise in the photodetection of ultrashort optical pulse trains using a time-varying analysis. Shot-noise-limited photocurrent power spectral densities, signal-to-noise expressions, and shot-noise spectral correlations are derived that explicitly include the finite response of the photodetector. It is shown that the strength of the spectral correlations in the shot noise depends on the optical pulsewidth, and that these correlations can create orders-of-magnitude imbalance between the shot-noise-limited amplitude and phase noise of photonically generated microwave carriers. It is also shown that only by accounting for spectral correlations can shot noise be equated with the fundamental quantum limit in the detection of optical pulse-to-pulse timing jitter.

A dispersive nanoSQUID magnetometer for ultra-low noise, high bandwidth flux detection

We describe a dispersive nanoSQUID (nanoscale superconducting quantum interference device) magnetometer comprised of two variable thickness aluminum weak-link Josephson junctions shunted in parallel with an on-chip capacitor. This arrangement forms a nonlinear oscillator with a tunable 4–8 GHz resonant frequency with a quality factor Q = 30 when coupled directly to a 50 Ω transmission line. In the presence of a near-resonant microwave carrier signal, a low frequency flux input generates sidebands that are readily detected using microwave reflectometry. If the carrier excitation is sufficiently strong, then the magnetometer also exhibits parametric gain, resulting in a minimum effective flux noise of 30 nΦ0 Hz−1/2 with 20 MHz of instantaneous bandwidth. If the magnetometer is followed with a near-quantum-noise-limited Josephson parametric amplifier, we can increase the bandwidth to 60 MHz without compromising sensitivity. This combination of high sensitivity and wide bandwidth with no on-chip dissipation makes this device ideal for local sensing of spin dynamics, both classical and quantum.