Self-heterodyne System Research Articles

Fast prediction of a high directivity antenna characterization for future wireless communication based on terahertz photonics

Fast prediction of high-directivity antenna characterization has been presented. The Cassegrain antenna working at J band frequency has been evaluated using a terahertz (THz) photonic system based on near-field measurement. The generation and detection of THz signal are based on a non-polarimetric electrooptic (EO) frequency down-conversion technique combined with a self-heterodyne system. The synthesis method is introduced to estimate far-field E and H-plane antenna characteristics. The antenna result is calculated using amplitude and phase-synthesized data based on the measured data. A near-field (NF) to far-field (FF) transformation is employed in the antenna radiation pattern. The effect of blocking objects on the antenna (supporting rods and sub-reflector) is discussed. The antenna characteristics of the measured and synthesized data are compared to the ITU F.699 recommendation. The synthesized result agrees with the measured one on the main lobe angle.

Interference dynamics of matter-waves of SU($N$) fermions

Interacting N-component fermions spatially confined in ring-shaped potentials display specific coherence properties. The orbital angular momentum per particle of such systems can be quantized to fractional values specifically depending on the particle-particle interaction. Here we demonstrate how to monitor the state of the system through homodyne (momentum distribution) and self-heterodyne system’s expansion. For homodyne protocols, the momentum distribution is affected by the particle statistics in two distinctive ways. The first effect is a purely statistical one: at zero interactions, the characteristic hole in the momentum distribution around the momentum k=0 opens up once half of the SU(N) Fermi sphere is displaced. The second effect originates from the interaction: The fractionalization in the interacting system manifests itself by an additional “delay” in the flux for the occurrence of the hole, that now becomes a characteristic minimum at k=0. We demonstrate that the angular momentum fractional quantization is reflected in the self-heterodyne interference as specific dislocations in interferograms. Our analysis demonstrates how the study of the interference fringes grants us access to both number of particles and number of components of SU(N) fermions.

Precise laser linewidth measurement by feature extraction with short-delay self-homodyne.

We propose a precision measurement method of laser linewidth based on short-delay self-homodyne, using the second peak-valley difference (SPVD) feature of the coherent power spectrum to fit laser linewidth. The SPVD model of the self-homodyne coherent envelope spectrum was established. One-to-one correspondence among the values of SPVD, the delay length, and the laser linewidth was determined theoretically and through simulations, while the reliability and stability of the method was verified experimentally. By comparing the detected results, it is found that the fitted laser linewidth obtained by the self-homodyne system is closer to its true value than that obtained by the self-heterodyne system. Hence, the simpler structure of the short-delay self-homodyne coherent envelope laser linewidth measurement method proposed is expected to substitute the previous laser linewidth measurement method, including complex short-delay self-heterodyne coherent envelope laser linewidth measurement method and traditional self-homodyne/heterodyne laser linewidth measurement method, to achieve more precise laser linewidth value.

Chirped Microwave Signals Generation Using a Distributed Feedback Laser With Alternating Structure of Active- and Passive-Cavity

We proposed a new type of distributed feedback laser with alternating active- and passive-cavities (APC DFB), which enjoys the same quantum well layer where the butt-joint re-growth process can be avoided. By utilizing the chirp characteristics of the APC DFB laser in a delayed self-heterodyne system, a chirped microwave signal with a sweep range up to 40 GHz and a sweep period of 25 μs is generated. The power fluctuation of the generated signal between 0-40 GHz within 30 minutes does not exceed 3 dB, and the scanning range fluctuates about 600 MHz. And experiment results show that the thermal efficiency of the current is always related to the working environment. In the static wavelength measurement, it is controlled by the injection current; when the chirped signal is generated, it is determined by the bias current. In particular, the waveform and the period as well as the sweep range of the generated chirped microwave signals can be accurately tuned by adjusting the modulating current, which has provided a deeper insight into the photonic generation of microwave signals.

Photonic generation and theoretical investigation of phase noise in quadrupling and 12-tupling millimeter wave Signal using optical self-heterodyne system

In this paper, photonic generation of quadrupling and twelve-tupling millimeter wave signal using single radio frequency (RF) signal is proposed. The purity of generated signal is observed by using mathematical approach which is further verified on simulation platform. Cascaded DP-DDMZM configuration is used in the proposed optical self- heterodyne system to generate millimeter-wave signals four times and twelve times the input RF source frequency. Selective sideband generation and carrier suppression techniques are utilized to generate the desired RF signal at the photodetector. Furthermore, the phase noise analysis of the generated millimeter wave signal is theoretically investigated. Expression of power spectral density for 40 GHz and 120 GHz millimeter signal is mathematically calculated to observe how the spectral quality is affected by the random phase fluctuations of input RF and optical sources. Phase noise of the millimeter-wave signal for different optical path length difference at various offset frequency is compared and discussed. System parameters such as noise figure, insertion loss, and spurious-free dynamic range (SFDR) are calculated for generated millimeter-waves/RF signals. The present proposed system uses a single RF source to generate quadrupling and 12-tupling millimeter wave and find its application in WDM systems, optical signal processing, radar system, etc. The results can be used to build an opto-electronic oscillator for a high-frequency microwave photonic communication system.

MIMO Self-Heterodyne OFDM Using Band Selection Technique.

The 5G technology is a promising technology to cope with the increasing demand for higher data rate and quality of service. In this paper, two proposed techniques are implemented for multiple input multiple output (MIMO) self-heterodyne OFDM system to enhance data rate and minimize the bit error rate (BER). In both of the two proposed techniques, Band Selection (BS) approach is used, once with Space Time Block Coded (STBC) for the first proposed technique (BS- STBC), and once again with Frequency Space Time Block Coded (FSTBC) for the second proposed technique (BS-FSTBC). The use of the BS in the proposed techniques helps to choose the sub-band with better subchannels gains for sending the information and consequently, minimize the BER. Moreover, the use of the FSTBC instead of STBC helps to use the spectral efficiently and hence increase data rate. The simulation results show that the proposed techniques BS-STBC and BS-FSTBC, for the MIMO self-heterodyne OFDM system, provide a great enhancement in the BER performance when compared to the conventional techniques. Moreover, the simulation results show that the first proposed technique BS-FSTBC outperform the second propose technique BS-STBC in term of the BER performance.

Seamless Convergence of Fiber and Wireless Systems for 5G and Beyond Networks

We propose different fronthaul systems for facilitating future mobile networks based on the seamless convergence of fiber-optic and wireless systems in the millimeter-wave (mmWave) bands. First, a flexible and high-performance wireless fronthaul system is proposed through an encapsulation of radio signals onto a converged fiber–mmWave system. A simultaneous transmission of three radio signals over the system is successfully demonstrated. Second, a high-performance optical self-heterodyne system is proposed and demonstrated for the generation and transmission of radio access signals in high-frequency bands. Third, a high-spectral-efficiency optical fronthaul system for the simultaneous transmission of multiple radio signals in different frequency bands is proposed using a subcarrier-multiplexing intermediate-frequency-over-fiber system. Satisfactory performance is experimentally confirmed for the transmission of three different radio signals in the microwave and low- and high-mmWave bands. The proposed systems can overcome the challenges and bottlenecks of the current mobile fronthaul systems and can be useful in different usage scenarios of 5G and beyond networks.

Fast and Accurate THz Permittivity Measurement Using a Self-Heterodyne Technique and Multitone Signal With Nonuniform Intervals

A permittivity measurement system operating in the terahertz waveband around 300 GHz achieves fast measurement by using a self-heterodyne technique to measure phase differences. Errors are reduced because a multitone technique with nonuniform frequency intervals enables us to apply a phase-unwrapping method to the self-heterodyne system. For multitone signal generation, just single-frequency oscillators and local oscillator leakage from a modulator are used. The system achieves a measurement time of 0.03 ms at one point, which is 1/200 compared to a conventional system using a vector network analyzer. With the same measurement time, the maximum measurement error can be reduced to less than half compared to the conventional two-tone self-heterodyne system.

Optoelectronic Feedback Loop for Phase Noise Suppression in THz Self-Heterodyne Detection

A novel terahertz (THz) self-heterodyne detection system using an optoelectronic feedback loop is proposed. Conventional THz self-heterodyne detection system is inherently vulnerable to phase noise associated with the optical path length difference between the laser sources and the photomixer. The proposed THz self-heterodyne detection system utilizes the optoelectronic feedback loop to suppress the phase noise of the intermediate frequency signal at the output of the photomixer. The optoelectronic feedback loop requires a feedback loop with a relatively small loop bandwidth and thus is implemented without using rather sophisticated integrated photonics technology. The proposed THz self-heterodyne detection system with the optoelectronic feedback loop suppresses the phase noise by more than 25 dB.

Terahertz-Wave Vibrometer Using a Phase-Noise-Compensated Self-Heterodyne System

A terahertz (THz) vibrometer based on a photomixing self-heterodyne system for measuring the vibration of an object behind an opaque barrier is reported. The proposed THz vibrometer employs a phase noise compensation technique to reduce the phase noise of the system and thereby improves the signal-to-noise ratio (SNR) of the system. In this letter, the performance of THz vibrometers with and without the phase noise compensation technique is compared. The proposed THz vibrometer employing a phase noise compensation technique shows an improved SNR and larger bandwidth compared with those of the conventional THz vibrometer using a Golay cell.

Robust terahertz self-heterodyne system using a phase noise compensation technique

We propose and demonstrate a robust terahertz self-heterodyne system using a phase noise compensation technique. Conventional terahertz self-heterodyne systems suffer from degraded phase noise performance due to phase noise of the laser sources. The proposed phase noise compensation technique uses an additional photodiode and a simple electric circuit to produce phase noise identical to that observed in the terahertz signal produced by the self-heterodyne system. The phase noise is subsequently subtracted from the terahertz signal produced by the self-heterodyne system using a lock-in amplifier. While the terahertz self-heterodyne system using a phase noise compensation technique offers improved phase noise performance, it also provides a reduced phase drift against ambient temperature variations. The terahertz self-heterodyne system using a phase noise compensation technique shows a phase noise of 0.67 degree in terms of a standard deviation value even without using overall delay balance control. It also shows a phase drift of as small as approximately 10 degrees in an open-to-air measurement condition without any strict temperature control.

All-electronic line width reduction in a semiconductor diode laser using a crystalline microresonator

This study examines the capability to significantly suppress the frequency noise of a semiconductor distributed feedback diode laser using a universally applicable approach: a combination of a high-Q crystalline whispering gallery mode microresonator reference and the Pound–Drever–Hall locking scheme using an all-electronic servo loop. An out-of-loop delayed self-heterodyne measurement system demonstrates the ability of this approach to reduce a test laser’s absolute line width by nearly a factor of 100. In addition, in-loop characterization of the laser stabilized using this method demonstrates a 1-kHz residual line width with reference to the resonator frequency. Based on these results, we propose that utilization of an all-electronic loop combined with the use of the wide transparency window of crystalline materials enable this approach to be readily applicable to diode lasers emitting in other regions of the electromagnetic spectrum, especially in the UV and mid-IR .

Visualization of the spatial–temporal evolution of continuous electromagnetic waves in the terahertz range based on photonics technology

Visualization of the field evolution of the continuous waves in the terahertz (THz) range with high phase and spatial resolution is a new approach to the study of the physical dynamics of unique beams, such as nondiffractive, self-reconstructing, and vortex beams. As near-field visualization can reveal device dynamics, it is also useful for diagnosing the THz devices. Here, we demonstrate the visualization of the spatial–temporal evolution of freely propagating continuous THz waves by adapting the nonpolarimetric electro-optic (EO) detection technique to the self-heterodyne system. The amplitude and phase of a THz wave (125 GHz, λ=2.4 mm, 650 μW) radiated from a horn antenna were simultaneously and precisely measured in the self-heterodyne system, in which two frequency-detuned free-running lasers were used both for the generation (photomixing) and EO detection of THz waves. The nonpolarimetric EO detection technique has solved an intrinsic problem of the conventional polarimetric EO detection technique, in which the sensitivity of the measurements can be changed drastically by the fluctuation of the polarization state of the optical local oscillator signal for the EO detection. As a result, field evolution could be visualized with a maximum signal-to-noise ratio of 27 dB and a phase resolution of 2π/78 rad (80 mrad), by scanning an optical fiber-mounted EO crystal (ZnTe) in a free space repeatedly.

A method to compensate the tuned nonlinearity of DFB diode laser in the laser self-heterodyne coherent measuring system

The measuring accuracy of self-heterodyne coherent measuring system can be deteriorated by the tuning nonlinearity of the diode laser with injection current. The tuning characteristics of a DFB laser were analyzed, and a mathematical model for compensating Mach-Zehnder interferometer based self-heterodyne system was presented. The dynamic frequency modulation coefficient of the model was built by prior beat frequency of foregone optical path difference. The relative error of predicted beat frequency is reduced about 3%. This method could simplify the setup of the system, and is especially suited for online tunable laser measurement system.

Improved peak power method for measuring frequency responses of photodetectors in a self-heterodyne system

An improved peak power method for measuring frequency responses of photodetectors in a self-heterodyne system consisting of a distributed Bragg reflector laser is proposed. The time-resolved spectrum technique is used to measure the peak power of the beat signal and the intrinsic linewidth of heat signal for calibration. The experimental results show that the impact of the thermal-induced frequency drift, which is the main reason for producing an error in measurement by conventional peak power method and spectrum power method, can be removed.

Self-Oscillating Harmonic Opto-Electronic Mixer Based on a CMOS-Compatible Avalanche Photodetector for Fiber-Fed 60-GHz Self-Heterodyne Systems

A self-oscillating harmonic opto-electronic mixer based on a CMOS-compatible avalanche photodetector for fiber-fed 60-GHz self-heterodyne systems is demonstrated. The mixer is composed of an avalanche photodetector fabricated with 0.18-mum standard CMOS process and an electrical feedback loop for self oscillation. It simultaneously performs photodetection and frequency up-conversion of photodetected signals into the second harmonic self-oscillation frequency band. The avalanche photodetector and the mixer are characterized and analyzed, and the RF avalanche multiplication factor is investigated. In addition, conversion efficiency as well as internal conversion gain is determined, and bias conditions are optimized for the best self-oscillating harmonic opto-electronic mixer performance. Data transmission of 5-MS/s 32 quadrature amplitude modulation signals using self-oscillating harmonic opto-electronic mixer is successfully demonstrated.

Frequency response measurement of high-speed photodetectors using the spectrum power method in a delay self-heterodyne system

An improved delay self-heterodyne system consisting of a distributed Bragg reflector (DBR) tunable laser and an optical fiber ring interferometer is used to measure the frequency responses of high-speed photodetectors. By adjusting the amplitude of the phase-tuning-voltage which is applied across the phase section of the DBR laser, the beat signals with frequencies from zero to several tens of gigahertz will be generated at the photodetectors. The peak power method (PPM) and spectrum power method (SPM) were used to measure the frequency response of photodetectors. The effects of the phase-tuning-voltage over different ranges on the measurement accuracy were experimentally investigated. Theoretical analysis indicates that the variations of optical linewidth and lineshape are the main reasons for producing a large error in the measurement by PPM, and that the fluctuation of optical power did not generate errors in the frequency response measurements by both PPM and SPM. The experimental results show that when a low phase-tuning-voltage range is used in measurement by SPM, the error of the measuring frequency response of the photodetector can be sharply reduced.

Fibre-supported 60 GHz self-heterodyne systems based on CMOS-compatible harmonic optoelectronic mixers

Fibre-supported 60 GHz self-heterodyne systems using harmonic optoelectronic mixers fabricated with the 0.18 µm standard CMOS technology are demonstrated. Down-link data transmission of 25 Mbit/s, 32 quadrature-amplitude modulation signals in 60 GHz band is successfully performed.

Millimeter-wave remote self-heterodyne system for extremely stable and low-cost broad-band signal transmission

We have developed a millimeter-wave remote self-heterodyne transmission system that enables extremely stable and low-cost broad-band transmission in the millimeter-wave band. The system was applied to a 60-GHz-band transmission system for the first time. The transmitter of the developed system transmits RF modulated signals and a local oscillation signal simultaneously, and the receiver detects these signals by using a square-law-type detection technique, thus creating a very stable and low phase-noise millimeter-wave transmission link without the use of an expensive and more advanced frequency-stabilization technology. Since the receiver no longer requires a millimeter-wave oscillator for frequency conversion, the devices used in this system can be miniaturized and the cost of the system can be reduced. This paper discusses the performance of the developed system in terms of its phase-noise degradation and carrier-to-noise power ratio (CNR). We also discuss the optimal transmitter design to obtain the maximum CNR. Using our miniaturized monolithic millimeter-wave integrated-circuit-based 60-GHz-band experimental system, we demonstrate that our millimeter-wave transmission link is completely free of phase-noise and frequency-offset degradation due to the use of a millimeterwave local oscillator. We show that equal transmission-power distribution between the RF signal and local carrier gives the maximum CNR under the transmission-power-limited conditions. Also, we demonstrate that QPSK-modulated satellite broadcast multichannel video signals with a 300-MHz bandwidth, in total, can be successfully transferred over a distance of 8 m.

60 GHz band 64 QAM/OFDM terrestrial digital broadcasting signal transmission by using millimeter-wave self-heterodyne system

This paper describes the first time experimental studies on 60-GHz band transmissions of terrestrial digital broadcasting signals (ISDB-T) with 64-QAM modulations on coded orthogonal frequency division multiplexing (COFDM) format. It has been a very difficult experiment to accomplish because it requires very stable and low phase-noise oscillators in the millimeter-wave band. The use of our proposed millimeter-wave self-heterodyne system, overcame this problem without using a stable oscillator, and provided a bit error rate (BER) of less than 10/sup -6/ without any forward error correction. We also discuss the relationship between the carrier-to-noise power ratio and the BER obtained, and demonstrate that the penalty of the required CNR for our experimental system is less than 1 dB compared to the results of a back-to-back BER test.