Spurious Sidebands Research Articles

Photonic Integrated Frequency Shifter Based on Double Side Band Modulation: Performance Analysis

In this research, we present an analysis of a photonic integrated frequency shifter as a stage for a THz dual comb generator. We studied the performance of the PIC by simulating it with standard building blocks, and aimed toward an improvement of the output signal quality. We revised two approaches of the PIC by simulating two modes of generating a double side band modulation suppressed carrier (DSB-SC) with a Mach Zehnder modulator structure (MZM). One approach was using a single Electro-Optic Phase Modulator (EOPM) on an MZM structure (SE-MZM), and the other one was using Double EOPM (DE-MZM). We found a cleaner spectrum with the DE-MZM, since this structure is usually applied to reduce the chirp effect in optical communication systems. We obtained 23 dB of side mode suppression ratio SMSR with one filter, and 44 dB of SMSR with a two-stage filter. In the case of DE-MZM, we obtained a clean tone on intermediate frequency (IF) free of spurious sidebands and comb in IF frequency with 10 dB more power compared to SE-MZM.

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.

Optical SSB modulator/frequency shifter with ultralow spurious sidebands.

In this paper, we report and theoretically investigate an optical single-sideband suppressed-carrier (OSSB-SC) modulator/frequency shifter with ultralow spurious sidebands. The novel, to the best of our knowledge, structure is based on three Sagnac interferometers (SIs) and two bidirectional phase modulators (PMs). The two bidirectional PMs are driven by four radio frequency (RF) signals with equal powers and appropriate phases. An OSSB-SC signal with only (4n+1)th-order sidebands, where n is an integer number, is generated. Besides, by applying appropriate RF phase shifts, an OSSB with carrier (OSSB+C) modulator can be obtained whose optical carrier-to-sideband ratio (OCSR) can be tuned by controlling the PMs modulation indices. Also, by using the proposed OSSB-SC modulator in another SI, its OCSR can be tuned by controlling the state of polarization in addition to the modulation indices of the PMs. Since the proposed structure is based on SI and no direct current (DC) bias is required for the PMs, it is robust against environmental perturbations and decreases problems associated with DC bias-drift. In addition, performance of the proposed structure under the power and phase imbalances due to the external non-ideal RF hybrid couplers and the phase imbalance of practical non-ideal nonreciprocal optical phase shifters are investigated. Simulation results using commercial software are also presented which are in good agreement with analytical results.

Optical single sideband polarization modulator with tunable optical carrier-to-sideband ratio and its applications in microwave photonic phase shifter and optical frequency shifter.

In this paper, a novel scheme to implement an optical single sideband (OSSB) polarization modulator (PolM) is proposed and theoretically investigated. The proposed structure contains two dual-drive Mach-Zehnder modulators inside a Mach-Zehnder interferometer whose input/output optical Y-couplers are replaced by two optical polarization beam splitters/polarization beam combiners. It is shown that by applying four equal power radio-frequency signals with appropriate phases, an OSSB polarization-modulated signal is generated. In addition, $(4n+3)$(4n+3)th-order sidebands, where ${n}$n is an integer, are suppressed without the need for an optical filter. The proposed OSSB PolM can find many applications in microwave photonic (MWP) systems. For instance, by using the proposed OSSB PolM, an OSSB modulator with tunable optical carrier-to-sideband ratio (OCSR), an OSSB-suppressed carrier modulator/optical frequency shifter with ultralow spurious sidebands, and an MWP phase shifter with 360° tunable phase shifts, are proposed and theoretically investigated. Simulation results using commercial software are also presented, which are in good agreement with analytical results.

1-bit photon cross-correlation-based phase-modulation fluorometer using an OFDM signal-modulated excitation light source

We propose a phase-modulation fluorometer, which is a combination of a 1-bit photon cross-correlator constructed using a field-programmable gate array and an excitation light source modulated by an orthogonal frequency-division multiplexing signal. Such multiplexing allows us to use multiple modulation frequencies efficiently and selectively within a given baseband. Defined as the inverse of its fundamental frequency, the symbol length of the multiplexing is set equal to the width of the time window of the cross-correlator. Therefore, all temporal waveforms of the subcarriers in the baseband are connected smoothly at both ends of the symbol interval; hence, no spurious sidebands appear in the frequency domain of the subcarriers. The 1-bit cross-correlator brings about fluorescence lifetimes in the photon-counting realm. From a phase difference spectrum between the fluorescence and the reference signal, fluorescence lifetimes for each frequency may be obtained with precision simultaneously. The resolution time and the width of the time window of the cross-correlator are 2.0 ns and 256 ns, respectively. As a proof-of-principle experiment, we measured the fluorescence lifetimes of some standard samples.

Hyperfine Intrinsic Magnitude and Phase Response Measurement of Optical Filters Based on Electro-Optical Harmonics Heterodyne and Wiener–Lee Transformation

An electro-optical heterodyne scheme is proposed and demonstrated for magnitude- and phase-frequency response measurement of optical filters based on harmonics heterodyne and Wiener–Lee transformation. The method consists of an acousto-optic frequency shifter and a phase modulator located in a frequency-shifted heterodyne interferometer. The minimum phase-frequency response is simultaneously extracted from the measured magnitude–frequency response with the help of Kramers–Kronig relations and the Wiener–Lee transformation. As compared with the single-sideband-based or double-sideband-based methods, our method eliminates small-signal assumption and features an immunity to undesired spurious sidebands, enabling harmonic sideband sweeping with even-folded measuring frequency range. Prior to the conventional frequency-shifted heterodyne methods, the method enables simultaneous extraction of intrinsic magnitude and phase frequency responses for most optical filters by introducing the Wiener–Lee transformation. A phase-shifted fiber Bragg grating is measured for extracting the frequency responses in the proof-of-concept experiment with the frequency resolution up to 50 kHz and frequency range of 80 GHz by using a frequency-swept modulation of 20 GHz.

High performance photonic microwave frequency down-conversion using a dual-drive dual-parallel Mach-Zehnder modulator

ABSTRACTPhotonic microwave frequency down-conversion based on carrier suppression single sideband (CS-SSB) modulation via an integrated dual-drive dual-parallel Mach-Zehnder modulator (DP-MZM) is proposed. The MZM on the up path of the DP-MZM is used to generate SSB modulation signal, while the MZM on the bottom path of the DP-MZM is unmodulated. By adjusting the amplitude and phase of the unmodulated optical carrier, two optical carriers are cancelled out, which improves the performance of the system with reduced local oscillator (LO) power and large suppression of mixing spurious sidebands. The frequency down-conversion approach is theoretically analyzed and verified by simulation. Simulation results show that the power of frequency down-conversion signal is at least 39 dB higher than that of the mixing spurious sidebands. Besides, 9.5 dB gain, 2.8 dB noise figure (NF) and 1.9 dB spurious-free dynamic range (SFDR) improvements can be obtained compared with the previous OCS modulation frequency down-conversion scheme while the required LO power is 10 dB, 5 dB and 5 dB lower than that of the OCS modulation scheme, respectively.

An Algorithm to Compensate the Effects of Spurious PLL Tones in Spectrum Sensing Architectures

In a nonideal PLL circuit, leakage of the reference signal into the control line produces spurious tones. When the distorted PLL signal is used as a sampling clock to an analog-to-digital converter (ADC), it creates spurious sidebands in the sampled data as well. In spectrum sensing applications, the presence of spurious sidebands can lead to false detection of signals in otherwise empty channels. To remove the spurious sidebands, we first estimate the distortions to the sampled data and then compensate the data in the digital domain. To reduce hardware complexity and computation cost, we propose an algorithm that uses a Fourier Transform block (a typical component in spectrum sensing architectures) to estimate the sampling errors from the spurious sidebands. We also analyze the effects of the spurious sidebands on spectrum sensing. Computer simulations are included to show that the proposed solution can remove the spurious sidebands and improve the detection performance.

Poly-Harmonic Modeling and Predistortion Linearization for Software-Defined Radio Upconverters

This paper presents a new predistortion linearization scheme for single-sideband mixers to be used for removing unwanted harmonics and intermodulation products of the digital IF in an heterodyne transmitter. The proposed algorithm, called poly-harmonic predistortion linearization, relies on an orthogonal expansion in the frequency domain of the nonlinearities for the mixer modeling. It takes into account memory effects that are piece-wise quasi-memoryless and enables the independent cancellation of unwanted spurious sidebands of the digital IF harmonics. The poly-harmonic predistortion linearization scheme for the weak-nonlinear regime was implemented in a field-programmable gate array and experimentally investigated for the linearization of a four-path polyphase single-sideband upconverter. The ability of the poly-harmonic predistortion algorithm to linearize the four-path polyphase mixer for input signals with high envelope fluctuation is demonstrated. -70-dBc/-62-dBc/-60-dBc spurious rejection and 18-dB/10-dB/8-dB linearization improvement of the third-order distortions are achieved for a two-tone RF signal, a 64-tone 10-MHz bandwidth multisine signal and orthogonal frequency-division multiplexing signal, respectively. The combination of the polyphase multipath technique and the poly-harmonic predistortion linearization technique offers an attractive filterless approach for the development of multimode broadband software-defined radio.

Impact of low-frequency substrate disturbances on a 4.5 GHz VCO

This paper presents the impact of low-frequency substrate disturbances on a fully integrated voltage-controlled oscillator (VCO) spectrum. A 4.5GHz VCO test-chip is presented; two substrate taps are placed inside the VCO core to measure or to inject disturbances into the substrate. The VCO carrier frequency sensitivity function of the tuning voltage and the bias current are measured. Then, the VCO spurious side-bands caused by harmonic substrate noise disturbances are analyzed to find a relation between the substrate noise characteristics and spur magnitudes. Theoretically the impulse sensitivity function (ISF) approach is used to analyze device sensitivity to substrate noise. Finally, a significant link between device sensitivity functions, low-frequency substrate disturbances and the VCO side-band spectral power, is demonstrated. According to this study, we conclude that a global approach which only considers power supply bounces in mixed IC's is not sufficient to analyze the sensitivity of RF integrated oscillators to low frequency substrate noise.

Eliminating spurious lipid sidebands in 1H MRS of breast lesions.

Detecting metabolites in breast lesions by in vivo (1)H MR spectroscopy can be difficult due to the abundance of mobile lipids in the breast which can produce spurious sidebands that interfere with the metabolite signals. Two-dimensional J-resolved spectroscopy has been demonstrated in the brain as a means to eliminate these artifacts from a large water signal; coherent sidebands are resolved at their natural frequencies, leaving the noncoupled metabolite resonances in the zero-frequency trace of the 2D spectrum. This work demonstrates that using the zero-frequency trace-or equivalently the average of spectra acquired with different echo times-can be used to separate noncoupled metabolite signals from the lipid-induced sidebands. This technique is demonstrated with simulations, phantom studies, and in several breast lesions. Compared to the conventional approach using a single echo time, echo time averaging provides increased sensitivity for the study of small and irregularly shaped lesions.

A CMOS frequency synthesizer with an injection-locked frequency divider for a 5-GHz wireless LAN receiver

A fully integrated 5-GHz phase-locked loop (PLL) based frequency synthesizer is designed in a 0.24 /spl mu/m CMOS technology. The power consumption of the synthesizer is significantly reduced by using a tracking injection-locked frequency divider (ILFD) as the first frequency divider in the PLL feedback loop. On-chip spiral inductors with patterned ground shields are also optimized to reduce the VCO and ILFD power consumption and to maximize the locking range of the ILFD. The synthesizer consumes 25 mW of power of which only 3.8 mW is consumed by the VCO and the ILFD combined. The PLL has a bandwidth of 280 kHz and a phase noise of -101 dBc/Hz at 1 MHz offset frequency. The spurious sidebands at the center of adjacent channels are less than -54 dBc.

Continuous wave multiquantum electron paramagnetic resonance spectroscopy. II. Spin-system generated intermodulation sidebands

Irradiation of a single homogeneous electron paramagnetic resonance (EPR) transition by two microwave sources separated by Δf, where Δf≪ the linewidth, results in the production of intermodulation sidebands at f0±(k+1/2)Δf, where f0 is the mean of the two irradiating frequencies and k is an integer ≥1. These sidebands can be seen directly with a microwave spectrum analyzer. Any one of the sidebands can be observed by suitable phase sensitive detection and displayed as a function of the polarizing magnetic field H0, resulting in a multiquantum EPR spectrum. The widths of the EPR lines decrease as k increases, resulting in improved resolution. The two k=1 transitions can be superimposed, resulting in a signal of double intensity. At saturating microwave power, this double-intensity line is two times less intense than an ordinary EPR line. No magnetic field modulation needs to be used when detecting multiquantum transitions, and pure absorption or pure dispersion signals are obtained with good baseline stability. Considerable attention is paid to the technical problem of irradiating the sample with just two microwave frequencies. In the apparatus described, spurious instrumental sidebands are reduced by 60 dB or more.

Amplitude noise reduction of 50 dB in colliding-pulse mode-locking dye lasers

Spurious sidebands observed in the noise spectrum of colliding-pulse mode-locking dye lasers result from coupling of the longitudinal mode beating modulations of the (argon-ion) pump laser with the dye laser. We achieve a 50-dB amplitude noise reduction at the mixing frequencies by inserting a single-frequency étalon in the argon-laser cavity. Furthermore, we find the amplitude noise of the colliding-pulse mode-locking laser to be entirely dominated by the (plasma discharge) noise of the argon laser.

Improved electrode geometry for electrooptic frequency translation in a channel waveguide

The technique of optical frequency translation by a rotating electric field in a trigonal electrooptic crystal has been adapted to a buried channel waveguide structure. To implement the field rotation under the constraints of a planar geometry, an electrode configuration was adopted consisting of three coplanar, collinear metal strips driven in phase quadrature, with the light guide under the central strip. Elimination of a cyclic modulation of field amplitude, characterizing the results of a previous study by the author, was achieved by appropriately widening the outer electrodes relative to the central one and by choosing a suitable channel depth. Spurious sidebands previously generated by an effective counter-rotating field component are thus removed. It is shown that with a residual modal birefringence equivalent to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda/20</tex> -differential phase retardation, the device here described can achieve 98 percent translation into the single first-order sideband with less than 0.5 percent combined spurious carrier and second-order upper sideband.

The continuous wave flash photolysis electron spin resonance spectra of spin-polarized (CIDEP) radicals using time-integration spectroscopy

Spurious sidebands in the E.S.R. spectra of spin-polarized radicals produced on laser flash photolysis can be suppressed using a time-integration method. This technique is analysed using a Bloch equation approach to yield analytical expressions for the lineshape for a range of experimental conditions. These are combined with theoretical stick spectra corrected for CIDEP effects to yield theoretical spectra for comparison with observed ones. The digital nature of the data from the experiment allows convenient use of numerical resolution-enhancement methods.

Analysis, Design and Performance of a Frequency-Synthesizer Loop Using Sample-Hold-Delay-Sample-Hold Phase-Detector

A new method of design for a synthesizer-loop using sample-hold-delay-sample-hold phase-detector is given. It makes the design of such loops straightforward and easy. The method is utilised in the design of a typical synthesizerloop having frequency range of 8 to 9 MHz (in steps of 250 Hz), settling time of 40 ms and greater than 110 dB suppression of unwanted spurious sidebands at its output.

Performance and Operation of the NRC Primary Cesium Clock, CsV

Since May 1, 1975, the NRC primary cesium beam frequency standard, CsV, has operated as a primary clock, generating directly a new time scale, PT(NRC CsV). Steps in the development of CsV from a frequency standard to a clock, and new error evaluations using the two NRC auto-tuned atomic hydrogen masers as stable frequency references are outlined. Details of both mechanical and electronic construction leading to successful clock operation are also discussed. The design of a new 12.632 MHz frequency synthesizer and modulator with very low spurious sidebands is outlined. Methods of partial re-evaluation of systematic errors and frequency offsets during clock operation, a procedure necessary in order to maintain primary standard accuracy, are described. The accuracy of PT(NRC CsV) is estimated to be about ±9 ns per day if all systematic errors are additive, and about ±5 ns per day if they act independently in a random manner. The frequency stability of PT(NRC CsV) is about 1 to 2 × 10-14 for periods greater than 4 hours, the short term stability being determined by the low cesium beam resonance amplitude of 1.6 to 2.0 pA normally employed for clock operation. Replenishment of the two cesium ovens is expected to be necessary at intervals of several years.

A Broad-Band Frequency Translator with 30-dB Suppression of Spurious Sidebands (Correspondence)

The theory and design of a broad-band microwave frequency translator using diode-switched coupled-line phase shifters is discussed. Results indicate spurious sideband suppression greater than 30 dB out to the 30th harmonic of the translation frequency.

Spurious Sidebands of a Linear Signal

For interference evaluation studies, the voltage or power spectrum of transmitting systems must be known. This paper evaluates the magnitude of the sideband power levels for linear FM carriers. Carriers of this type are encountered in FM-CW and FM pulsed radars. Analytical expressions are derived and spectral amplitudes are plotted which permit rapid evaluation of spurious sideband powers as a function of a normalized frequency deviation about the carrier.