Electrical Spectrum Analyzer Research Articles

Frequency noise measurements using coherent self-heterodyne detection

We demonstrate a refined way to extract the frequency noise (FN) spectrum of lasers by tailoring the delay in a conventional delayed self-heterodyne setup to sub-coherence lengths. The method achieves direct proportionality between electrical spectrum analyzer traces and the FN spectrum, which provide the intrinsic linewidth of the lasers. This proposed method is validated by comparing the FN spectrum with that obtained from a commercial frequency noise analyzer. The method provides a cost-effective alternative for FN measurements, which also requires minimal post-processing as compared to the state-of-the-art.

Measurement and multiplexing of ultra-low duty cycle Nyquist pulse sequences.

In this paper, we propose a novel, to the best of our knowledge, method to our knowledge for generating and accurately measuring Nyquist pulse sequences with an ultra-low duty cycle of only 0.037, which breaks the limitations caused by the noise and bandwidth of the optical sampling oscilloscope (OSO) by using a narrow-bandwidth real-time oscilloscope (OSC) and an electrical spectrum analyzer (ESA). By this method, it is found that the bias point drift of the dual parallel Mach-Zehnder modulator (DPMZM) is the main cause of the distortion of the waveform. In addition, we increase the repetition rate of Nyquist pulse sequences by a factor of 16 by multiplexing the unmodulated Nyquist pulse sequences.

High-speed high-resolution optical correlation-domain reflectometry without using electrical spectrum analyzer

We propose a newly configured optical correlation-domain reflectometry (OCDR) without the use of an electrical spectrum analyzer (ESA) for high-speed distributed reflectivity measurement with an enhanced spatial resolution. First, the operation of ESA-free OCDR is analyzed by numerical simulation, the results of which show the potential of the configuration to perform distributed reflectivity measurement with an improved spatial resolution. Subsequently, the simulation results are verified by comparison experiments, where distributed reflectivity measurements along a 32-m-long single-mode fiber joint with multiple connectors are performed using both conventional (with averaging) and ESA-free OCDR configurations (without averaging) at a repetition rate of 100 Hz. The widths of the reflectivity peaks experimentally obtained by the conventional and ESA-free OCDR configurations are 22.9 cm and 7.0 cm, respectively. Finally, we experimentally evaluated the performance of the ESA-free OCDR at higher repetition rates, achieving 6.3-cm spatial resolution at a repetition rate of 1 kHz. This result indicates that the ESA-free OCDR can perform a distributed reflectivity measurement with an improved spatial resolution at a higher operation speed than ever.

Total spectral power-based method for estimating Brillouin frequency shift in optical fibers

A cost-effective method for estimating the Brillouin frequency shift (BFS) of the whole sensing fiber without using an electrical spectrum analyzer is developed. The Brillouin gain spectrum is down-converted and low-pass-filtered, and its total transmitted power is used to estimate the BFS. The strain dynamic range of this method is experimentally shown to be double the value of a conventional slope-assisted method.

Compensation of noise floor distortion in long-range simplified optical correlation-domain reflectometry without the use of electrical spectrum analyzer

In simplified optical correlation-domain reflectometry (OCDR) without the use of an electrical spectrum analyzer (ESA), the noise floor of the reflectivity distribution is distorted in long-range measurement, which sometimes causes significant errors in the distributed reflectivity measurement. Herein, we experimentally analyze the distorted noise floor by high-speed ESA-free OCDR and clarify the origin of the noise floor. Then we show that this noise floor can be compensated by appropriate filtering. Consequently, distributed reflectivity measurement over a 1.1 km long sensing fiber is properly performed at a repetition rate of 100 Hz.

Comparison of Different Linewidth Measuring Methods for Narrow Linewidth Laser

We experimentally demonstrate a fiber laser with different linewidths based on self-injection locking (SIL) and the stimulated Brillouin scattering effect. Based on the homemade fiber laser, the error origin, resolution, and applicable range of delayed self-heterodyne interferometry (DSHI), self-correlation envelope linewidth detection (SCELD) and Voigt fitting are investigated numerically and experimentally. The selection of the linewidth measuring method should meet the following conclusions: an approximately Lorentzian self-heterodyne spectrum without the pedestal and high-intensity sinusoidal jitter is a prerequisite for DSHI; the SCELD needs a suitable length of delay fiber for eliminating flicker noise and dark noise of the electrical spectrum analyzer; a non-Lorentzian self-heterodyne spectrum without a pedestal is an indispensable element for Voigt fitting. According to the experimental results, the laser Lorentzian linewidth of SIL changes from 1.7 kHz to 587 Hz under different injection powers. When the Brillouin erbium fiber laser is utilized, the Lorentzian linewidth is measured to be 60 ± 5 Hz.

Research and development of 40 GHz bandwidth laser relative intensity noise measurement system using PID controller and ESA spectrum analyser

Measuring and evaluating the quality of laser sources used in optical communications and in the precision measurement system is essential. Relative intensity noise (RIN) is a parameter that directly affects the system quality. Therefore, RIN needs to be measured periodically. This study presents a high-sensitivity, broadband (40 GHz) RIN measurement system using a precisely temperature-controlled photodetector and an electrical spectrum signal analyser. RIN value is determined through indirect measurement of noise components: thermal noise, total detected noise, and the shot noise of the laser source. These noises are measured by using an Electrical spectrum analyser (ESA) and a super sensitive 61/2 digital multimeter (DMM). The experimental results of the RIN measurement of the reference Distributed feedback (DFB) laser source show the similarity between the RIN value measured by the system and the RIN value provided by the manufacturer.

Simultaneous and Unambiguous Measurement for Doppler Frequency Shift and Angle of Arrival of a Microwave Signal with High Precision

ABSTRACT A photonic scheme for simultaneously measuring both the Doppler frequency shift (DFS) and angle of arrival (AOA) of a microwave signal based on a polarization division multiplexing dual-parallel Mach-Zehnder modulator (PDM-DPMZM) is proposed. In our scheme, the single-sideband (SSB) modulated signals via PDM-DPMZM are divided into two branches, and so two ac power-phase mapping functions with higher slopes are formed by different polarization processing. Since one ac power-phase curve serves as a calibration line, the system can realize unambiguous AOA measurement with the phase range of −180°~180°. The value and direction of DFS can only be determined using an electrical spectrum analyzer (ESA). In addition, the scheme has a larger operating bandwidth because no filter is required. Simulation results show that the AOA from −83.92° to 83.92° is measured with an error of ±0.9°, and the DFS measurement within ±100 KHz is realized with an error less than ±5 × 10−3 Hz. The characteristics of low error, high precision, and wide bandwidth are important for microwave signal detection.

Photonic Frequency Down Conversion Approach to Measure Microwave Signal Angle of Arrival

This paper presents an angle-of-arrival (AOA) measurement system based on microwave photonic frequency down conversion. It has the novelty of no LO is needed for the frequency conversion process. Instead, a ramp waveform is used to shift the frequency of an optical carrier, which is phase modulated by a microwave signal in the subsequent stage. Two low-frequency IF signals are generated after photodetection. The AOA of the incoming microwave signal can be determined by measuring the phase difference of the two IF signals. Comparing with the previously reported frequency converter based AOA measurement systems, the proposed structure does not need a high-frequency tunable LO source and high-frequency electrical components. Expensive and bulky equipment such as an electrical spectrum analyser are not required in the proposed AOA measurement system. Experimental results show AOA measurement of different-frequency and different-power microwave signals, with small measurement errors.

Experimental Investigation on the Ranging Resolution of a FMCW Lidar

In some previous reports about frequency-modulated continuous-wave (FMCW) Lidar, observing the longer waveform of a de-chirped signal is considered an effective scheme for further improving the ranging resolution. In this work, the ranging resolution of a FMCW Lidar is experimentally investigated, and the feasibility of such a scheme is tested. During the experiment, a FMCW signal is generated via a Mach–Zehnder modulator in the transmitted port. In the received port, the de-chirped signal is extracted based on a homodyne detection scheme and is analyzed by an electrical spectrum analyzer. Two different methods are adopted to determine the ranging resolution. One is based on a single target, for which the ranging resolution is obtained through inspecting the shift of spectral peak position as the target moves. The other is based on two targets, for which the ranging resolution is acquired through inspecting the variation of spectrum distribution as the spacing of two targets changes. The experimental results demonstrate that extending the observed duration of the de-chirped signal cannot improve the ranging resolution, and the corresponding physical mechanism is revealed.

Performance analysis of DP-MZM radio over fiber links against fiber impairments

Abstract In this research article, the radio over fiber (RoF) Architecture using dual-parallel Mach–Zehnder modulator (DP-MZM) is analyzed and simulated. The nonlinearity is the main issues which degrade the performance of the RoF links. Using DP-MZM modulators, the nonlinearity can be reducing in the significant amount by controlling the bias voltages. The DP-MZM consists of two MZM modulators in parallel form with the variations of extinction ratio (ER). The proposed RoF link operated with single tone frequency signal at 10 GHz and the optical signal is transmitted further on Single mode optical fiber. The electrical spectrum at the output of photodetector confirms the quality of received signal while having desired and undesired terms. The proposed structure is designed using Optical Simulator simulation Software to confirm and validate the proposed results. The simulation output shows that the RF power of DP-MZM based RoF link has been found a decrement of 6.95 dB corresponding to undesired components with respect to desired RF signal for the increment in fiber length from 10 to 30 km. The digital transmission RoF link model is proposed and optimized for fiber impairments for 2–30 km, using 10 Gbps digital data string. electrical spectrum analyzer shows that very good eye openings for different fiber impairments, its shoes that proposed RoF model is optimized and having good SNR.

Transceiver Noise Characterization Based on Perturbations

In this paper, we discuss a new technique for measuring transceiver noise, skew, and for the detection of uncompensated transceiver impairments. The method consists on the introduction of frequency domain notch or notches at the transmitter, which allows to estimate of the Signal-to-Noise and Distortion Ratio (SNDR) at different stages over the transmission chain. The proposed technique requires the detection of the signal spectrum using either: a modem receiver, an Optical Spectrum Analyzer (OSA), an oscilloscope, or an Electrical Spectrum Analyzer (ESA), depending on the stage where the spectrum is measured and requiring minimal processing of the received signal. Our analysis is focused on Ciena's WaveLogic Ai commercial transceiver and a 95 Gbaud DAC. We demonstrate that symmetrically placed frequency domain notches can be used to mitiguate the influence of crosstalk on the SNDR estimates. Finally, we show how a single notch spectrum can be used to detect and compensate for impairments, and we perform skew estimation as an example.

Transceiver Noise Characterization based on Perturbations

In this paper, we discuss a new technique for measuring transceiver noise, skew, and for the detection of uncompensated transceiver impairments. The method consists on the introduction of frequency domain notch or notches at the transmitter, which allows to estimate of the Signal-to-Noise and Distortion Ratio (SNDR) at different stages over the transmission chain. The proposed technique requires the detection of the signal spectrum using either: a modem receiver, an Optical Spectrum Analyzer (OSA), an oscilloscope, or an Electrical Spectrum Analyzer (ESA), depending on the stage where the spectrum is measured and requiring minimal processing of the received signal. Our analysis is focused on Ciena's WaveLogic Ai commercial transceiver and a 95 Gbaud DAC. We demonstrate that symmetrically placed frequency domain notches can be used to mitiguate the influence of crosstalk on the SNDR estimates. Finally, we show how a single notch spectrum can be used to detect and compensate for impairments, and we perform skew estimation as an example.

Application of an aerosol electrical mobility spectrum analyzer: Charged-particle polarity ratio measurement in the Antarctic and Arctic regions

An aerosol electrical mobility spectrum analyzer (AEMSA), developed at Hanyang University, was employed to investigate the particle charge characteristics in the Antarctic and Arctic regions. The particle charge characteristics in these areas were compared with the charging state in Ansan, South Korea, located in the midlatitude, where artificial factors, such as human activity, urbanization, and traffic, might result in a higher total concentration. Furthermore, in Ansan, South Korea, the charged-particle polarity ratio was very stable and was close to 1. However, notably different particle charge characteristics were obtained in the Antarctic and Arctic regions. The imbalance between the numbers of positively and negatively charged particles was evident, resulting in more positive charges on the atmospheric particles. On average, the positively charged particle concentrations in the Antarctic and Arctic areas were 1.4 and 2.8 times higher, respectively, compared with the negatively charged particles. The developed AEMSA system and the findings of this study provide useful information on the characteristics of atmospheric aerosols in the Antarctic and Arctic regions and can be further utilized to study particle formation mechanisms.

Photonic Approach for Measuring AOA of Multiple Signals With Improved Measurement Accuracy

The objective of this paper is to present a microwave photonic system that can measure the angle of arrival (AOA) of multiple microwave signals with improved measurement accuracy. It is based on a photonic mixer approach to down convert the incoming microwave signals into IF signals, which enables a low-frequency electrical spectrum analyser to be used for measuring the power of the IF signals to determine the incoming microwave signal AOAs. AOA measurement errors can be reduced by operating the optical modulator at a different transmission point for a different range of microwave signal AOA. The system also has the ability to remove the incoming microwave signal amplitude dependence in the AOA measurement. Measured results demonstrate 0°−81.5° AOA measurement with less than ±2° errors over the 0°−30° and 30°−81.5° AOA measurement range when the optical modulator is biased at the minimum and maximum transmission point respectively. The errors remain below ±2° even when there is a ±0.1 dB change in the output IF signal power. AOA measurement of two microwave signals is also demonstrated.

Simple photonics-based system for Doppler frequency shift and angle of arrival measurement.

A novel photonic approach for simultaneously measuring both the Doppler frequency shift (DFS) and the angle of arrival (AOA) of a microwave signal in a radar system is presented. It has the same structure as a fiber optic link consisting of a laser, an optical modulator and a photodetector. The incoming microwave signal and a reference signal are applied to the optical modulator. Beating of the echo and reference signal sidebands at the photodetector generates a low-frequency electrical signal. The DFS and the AOA can be determined from the frequency and the power of the low-frequency electrical signal measured on an electrical spectrum analyzer. The system has a very simple structure and is low-cost. It has a wide operating frequency range and a robust performance. Experimental results demonstrate a DFS measurement at around 15 GHz with errors of less than ±0.2 Hz, and a 0° to 90° AOA measurement with less than ±1° errors.

Photonic Doppler frequency shift measurement without ambiguity based on cascade modulation

A novel scheme based on the cascade structure of a dual-polarization Mach–Zehnder modulator (DPol-MZM) and a phase modulator (PM) is proposed which can simultaneously identify the value and direction of Doppler frequency shift (DFS). A low frequency reference signal and an echo signal are modulated by the DPol-MZM into orthogonal polarization states. The transmitted signal is modulated onto the reference signal by the PM and then one side band of the modulated signal is suppressed after a filter. The value of DFS is obtained by mixing the echo signal and the transmitted signal and the direction is distinguished by mixing the echo signal and the modulated reference signal. The system has only one channel and DFS measurement only needs a low frequency electrical spectrum analyzer (ESA). The measurement error is less than 0.1 Hz. Because of the cascade modulation structure and the direct frequency mixing of the transmitted signal and the echo signal, the operation frequency range of the system is not limited by the carrier frequency and the scheme has high measurement accuracy.

A tunable self-mixing chaotic laser based on high frequency electro-optic modulation

A tunable self-mixing chaotic laser based on high frequency electro-optical modulation is proposed. A laser dynamics system is designed and tested for tunable chaotic laser generation and provides optical feedback and electro-optic modulation with two degrees of freedom. The chaotic laser is generated by optical feedback, and it becomes tunable by high frequency electro-optic modulation. The frequency is modulated from 10 MHz to 10 GHz to test this system, and an ultra-wide band chaotic laser from 0.8 GHz to 24 GHz is measured by an electrical spectrum analyzer (ESA). The experimental results show the generation of a tunable chaotic laser via electro-optic modulation. At the same time, this tunable chaotic laser has a highly sensitive dynamic response near the 2.0 GHz range of frequency modulation. The system is proved to be suitable for applications in high-speed broadband communication and sensing.

Calibration and stability of highly sensitive fibre based laser through relative intensity noise

This work is concerned with the characterization of the fiber based laser sensor by means of relative intensity noise (RIN). The characterization has been done by an electrical based measurement system, which has been accomplished by the implementation of an optical receiver setup. The optical receiver setup has been built by using commercially available low noise amplifier (LNA), Bias Tee, and fast photodiode (FPD). Besides the optical receiver setup designing, software in Labview has been built and implemented to enable easy and fast measurement of data from measurement instruments. Using the self assembled optical receiver and an electrical spectrum analyzer (ESA), optical fluctuation ’noise’ of the fiber based laser sensor has been measured. We have found good agreement between the measurement results taken by our measurement setup and costly Agilent RIN measurement setup. Also, average RIN over wide frequency range has been calculated and discussed for different operating states of the laser sensor. The results are applicable in the field of an optical sensor.

Brillouin-induced self-heterodyne method for low jitter measurement of laser linewidth

In this paper, we study experimentally and analytically the stimulated Brillouin-induced self-heterodyne technique for linewidth measurement of lasers having narrow spectral widths. The output of a laser under test (LUT) is modulated by a RF signal to generate the sidebands. The carrier and the sidebands co-propagate in a single-mode fiber (SMF) along with the stimulated Brillouin scattering (SBS) signal generated by a counter-propagating pump. The SBS process amplifies one of the sidebands, which beats with the LUT carrier wave. The beat signal is detected using a photodiode and analyzed using an electrical spectrum analyzer to compute the laser linewidth. We analyze the SBS-induced self-heterodyne (SISH) scheme mathematically to obtain expression of the power spectral density of the photocurrent. Experimental results show 20 dB and 3 dB linewidths of 15 kHz and 5.5 kHz, respectively, which are in excellent agreement with the estimated theoretical values, thereby validating the analysis. We also perform the conventional delayed self-heterodyne measurement and obtain 20 dB linewidth of 15 kHz, which compares well with the SISH method. However, the SISH technique reduces jitter by 10 dB. We also study the dependence on linewidth measurement of the SISH scheme on fiber length. For 2 km SMF length, the 20 dB linewidth is 23 kHz, which is higher compared to the measurement obtained by using 25 km SMF.