Phase Ripple Research Articles

Phase ripple correction: theory and application

Spectral phase ripple associated with novel dispersive devices can distort broadband optical signals. We present a digital postprocessing algorithm to correct for this distortion by exploiting the static deterministic nature of the ripple. This algorithm is demonstrated with empirical data for several systems employing chirped fiber Bragg gratings (CFBGs). We employ this technique in a photonic time-stretch system incorporating CFBGs, improving the signal fidelity by 9 dB. Simulations and experiments show that this algorithm, which can be reduced to a simple interpolation and matrix multiplication, also mitigates additive noise. We see that the act of distortion correction yields signal fidelity superior to that of an ideal dispersive element.

콤팩트 안테나 테스트 레인지용 경면수정 오프셋 복반사경 시스템의 설계

경면수정 오프셋 그레고리안 반사경 안테나는 고이득, 저 사이드로브 특성 때문에 위성 통신 시스템에 널리 사용되고 있다. 그러나 본 논문에서는 CATR(Compact Antenna Test Region)을 위한 반사경 시스템으로 설계하고 그 근접 전계 특성을 조사하였다. CATR은 시험 영역에 진폭과 위상 리플이 작고 교차 편파가 낮은 균일 평면파를 제공하여야 한다. 따라서 근접 전계를 개구면의 전력 분포, 급전 혼의 복사 패턴, 개구면과 시험 영역까지의 거리 변화에 따라 계산하여 나타냈다. 또한, 30 GHz에서 동작하는 경면수정 오프셋 복반사경을 제작하고 근접전계를 측정하였다. 그 결과, 측정치와 계산치가 비슷하게 나타났다. 이로서 본 논문에서 설계된 경면수정 오프셋 복반사경은 콤팩트 안테나 테스트 레인지로 사용될 수 있을 것으로 생각된다. Gregorian offset dual-shaped reflector antennas have been widely used in the satellite communication systems for their high gain and low sidelobe characteristics. However, in this paper, it is designed as the CATR(Compact Antenna Test Range) reflector system, and its near-field characteristics are investigated. The CATR facility needs to provide an uniform plane wave with the minimum amplitude and phase ripple and the low cross polarization to the test region. Therefore, the reflector near-field patterns are calculated and presented with the variations of the aperture power distribution, the feed horn pattern, and the distance from the aperture to the test zone. Also, the offset dual-shaped reflector is fabricated at 30 GHz, and its near-field patterns are measured. The measured results are in good agreement with the calculated results. From theses results, we confirm that the designed offset dual-shaped reflector can be used as the reflector system for the compact antenna test range.

Figure-of-Merit of Dispersion Compensating Devices Based on Chirped Bragg Gratings

A promising technology for chromatic dispersion compensation in fiber communication networks are modules based on chirped Bragg gratings (DCM). Imperfections in the Bragg grating, however, give rise to a noise-like ripple in the phase characteristics of the DCM, which causes extra system penalty. In this paper, we derive an analytic formula that calculates an upper bound of the eye-opening penalty caused by a DCM in a transmission link with no optical amplifiers and with a chirp free NRZ optical signal. The primary use of this formula is as a quickly calculated quality measure (figure-of-merit) of the phase ripple characteristics of DCMs. It is shown that the difference in as given by the formula and obtained from simulation calculations is considerable smaller than given by other formulas found in the literature.

CPTR용 카세그레인 오프셋 복 반사경의 해석

일반적으로 카세그레 인 오프셋 복 반사경(Cassegrain Dual Offset Reflector)은 위성 통신용 안테나로 사용되지만, 여기서는 CPTR(Compact Payload Test Range)을 위한 반사경 시스템으로 해석하였다. 시험 영역의 근접 전계는 물리 광학법(Physical Optics)을 적용하여 계산하였다. CPTR은 균일한 평면파 제공을 목적으로 하며, 이를 위해 최소한의 진폭과 위상 리플(ripple)을 가져야 하며, 교차 편파 또한 작아야 한다. 따라서 본 논문에서는 반사경 구조 및 시험 영역의 위치에 따른 근접 전계 패턴을 구하여 전계의 리플, 테이퍼와 교차 편파를 고찰하였다. 특히 통신용 반사경 안테나에서는 나타나지 않는 안테나 축방향의 교차 편파 성분을 고찰하였다. In general, the cassegrain dual offset reflector is used for the satellite communication antenna, but is analyzed as the reflector system for the CPTR(Compact Payload Test Range) facility in here. The near-field at the test zone of the CPTR is obtained by using the physical optics approximation. The CPTR has to provide a uniform plane wave with the minimum amplitude and phase ripple and the low cross polarization. Therefore, in this paper, the near-field pattern are calculated, and the ripple and taper of the field and the cross polarization are investigated with the variation of the reflector geometry and the position of the test region. Especially, the cross polarization of the antenna axis direction which is not found in the satellite reflector antennas is investigated.

Robust flat waves with a uniform feed using a randomized local search

AbstractPlacement of radar emitters in non‐uniformly spaced radar arrays typically involves optimizing the placement of a fixed number of emitter elements across the array. This paper explores optimizing for a flat wave under uniform feed where the number of emitter elements is not fixed. A randomized local search algorithm is used to generate an emitter design, and a greedy search is used to find the optimal solution in that neighborhood. This technique results in a near‐field wave with less than 1 dB of amplitude ripple and less than 8 degrees of phase ripple across a width of 50λ. The designs chosen are robust in the sense that solutions with neighboring pixels on are also of high quality. Furthermore, the proposed algorithm can also find array designs that generate flat waves that are not parallel to the emitter array. Copyright © 2007 John Wiley & Sons, Ltd.

42.8-Gb/s RZ-DQPSK Transmission With FBG-Based In-Line Dispersion Compensation

Phase ripple impairments induced through cascaded fiber Bragg gratings (FBGs) are discussed for 42.8-Gb/s transmission. We show the feasibility of transmission over 1140 km (12 times 95 km) using return-to-zero differential quadrature phase-shift keying modulation and FBG-only dispersion compensation. We further compare FBGs with dispersion-compensating fiber for dispersion compensation and analyze the influence of wavelength detuning.

Serrodyne frequency translation of continuous optical signals using ultrawide-band electrical sawtooth waveforms

Serrodyne frequency translation of continuous optical signals by /spl plusmn/1.28 GHz is reported, significantly exceeding the highest previously published serrodyne shifts. To achieve these shifts, an ultrawide-band high-power electrical sawtooth created by spectral modulation of dispersed optical pulses was used. Its amplification involved a novel predistortion technique to compensate for the gain and phase ripple in the amplifier bandwidth.

Dual reflector feed system for hologram-based compact antenna test range

Manufacturing of large computer-generated submillimeter wave holograms with high pattern accuracy has been the main challenge in the development of hologram based compact antenna test ranges (CATRs). Illumination of the hologram with a shaped beam produced by a dual reflector feed system (DRFS) simplifies the hologram manufacturing by eliminating the narrow slots in the hologram pattern. In this paper, the design of a shaped dual reflector feed for a hologram CATR is described. The simulated and measured illumination field amplitude and phase at 310 GHz are presented and compared to the desired hologram illumination. The measured amplitude is within /spl plusmn/0.5 dB from the design objective in the most significant central region of the illuminating beam. Measurement results of the quiet-zone field of a demonstration CATR illuminated by the DRFS are presented and compared to the measured quiet-zone amplitude and phase of a hologram fed directly with a corrugated horn. The quiet-zone diameters of the both holograms are over 0.25 meters and the measured root mean squared (rms) amplitude and phase ripples are below /spl plusmn/0.4 dB and /spl plusmn/5/spl deg/, respectively. Further improvements to the hologram CATR, such as greater tolerance to manufacturing errors, are also discussed.

Experimental study on a hologram-based compact antenna test range at 650 GHz

This paper studies the feasibility of a hologram-based compact antenna test range (CATR) for submillimeter-wave frequencies. In the CATR, a hologram is used as a collimating element to form a plane wave for antenna testing. The hologram is a computer-generated interference pattern etched on a thin metal-plated dielectric film. Two demonstration holograms of approximately 1 m in diameter were designed for 650 GHz, and they were manufactured on two different Mylar films. The holograms were illuminated with a horn, and the plane-wave field was probed at 644 GHz. The measured amplitude and phase ripples were 2 dB and 15/spl deg/ peak-to-peak for one of the holograms. A higher quiet-zone field quality can be achieved by increasing the manufacturing accuracy by further manufacturing tests. After this, the hologram-based CATR should have a potential for high-quality antenna tests at frequencies up to 650 GHz.

Wavelength-controlled photonic true time delay for wide-band applications

A radio frequency subcarrier modulated wavelength-controlled dense wavelength-division-multiplexing-based photonic true time delay module, with very low phase (/spl plusmn/4/spl deg/) and magnitude (/spl plusmn/0.5 dB) ripples over a bandwidth of several gigahertz, is demonstrated to achieve wide-band linear frequency modulation transmission (600 MHz) with -37-dB sidelobe suppression and signal-to-noise exceeding 80 dB/MHz.

Performance effect in optical-communication systems caused by phase ripples of dispersive components.

We develop a simple theory that relates the performance of an optical component to the variance of the amplitude of its phase ripple that has been weighted by the incoming signal spectrum. Comparisons of model predictions for chirped fiber gratings with 10-Gbit/s test-bed simulations and measurements agree.

Implementation of Photonic True Time Delay Using High-Order-Mode Dispersion Compensating Fibers

We demonstrate the advantageous use of highly dispersive (>450 ps/nm/spl middot/km), high-order-mode (HOM) fiber modules for true time delay applications. Along with their low insertion loss, very low phase ripple (root mean square <0.3/spl deg/ over 0-20 GHz), and high immunity to nonlinear effects, the high dispersion values facilitate the construction of devices with relatively short fibers, resulting in improved tolerance of the radio frequency delay to thermal changes. The implications of multiple path interference effects in HOM modules are also studied and shown to be very small.

Polarization mode dispersion in chirped fiber Bragg gratings

We clarify the relationship between group delay ripple and differential group delay in birefringent, chirped fiber Bragg gratings and relate this information to polarization mode dispersion. We illustrate that a grating can be characterized completely by measuring the grating phase ripple and fiber birefringence with careful selection of measurement system parameters. The impact of these imperfections on device performance as dispersion compensators in optical communications systems is explored with system testbed simulations and measurements.

Dispersion oscillations in ultrafast phase-correction devices

Dispersion compensation is one of the most important tools for the generation of ultrashort optical pulses. Chirped mirrors have significantly increased the possibilities of compensation for arbitrarily shaped high-order dispersion. However, all design methods and manufacturing attempts reported so far have shown a spectral ripple on the phase characteristics of the mirror. We investigate the origin of this dispersion ripple and its consequences on pulse shaping. Recently, similar effects have also been reported in telecommunication applications of short pulses in devices such as fiber Bragg gratings and arrayed waveguide gratings. This calls for a systematic analysis of the phase ripple artifacts, which will be addressed both by numerical simulations and approximate analytical expressions. The results allow for an estimation of the severity of phase distortions in mode-locked lasers, external compression schemes, and telecommunication applications.

Generating a plane wave with a linear array of line sources

Creating a plane wave across an antenna under test is important for accurate antenna measurements. This paper optimizes the location and weightings of an array of line sources in order to approximate a plane wave at a given location in space. The amplitude and phase ripples across a desired test aperture are optimized to be much less than that of a uniform array with the same number of elements. Results are presented for a nine-element array with optimized amplitude and phase weights, with optimized weights and spacing in the x-direction, and with optimized weights and spacing in the x and z directions. The optimized approximate plane wave is a significant improvement over a uniform array or a single line source.

Intersymbol interference investigations using a 3-D time-dependent traveling wave tube model

For the first time, a physics based computational model has been used to provide a direct description of the effects of the traveling wave tube (TWT) on modulated digital signals. The TWT model comprehensively takes into account the effects of frequency dependent AM/AM and AM/PM conversion, gain and phase ripple, drive-induced oscillations, harmonic generation, intermodulation products, and backward waves. Thus, signal integrity can be investigated in the presence of these sources of potential distortion as a function of the physical geometry of the high-power amplifier and the operational digital signal. This method promises superior predictive fidelity compared to methods using TWT models based on swept-amplitude and/or swept-frequency data. The fully three-dimensional (3-D) time-dependent, TWT interaction model using the electromagnetic code MAFIA is presented. This model is used to investigate assumptions made in conventional TWT black-box models used in communication system level simulations. To quantitatively demonstrate the effects these approximations have on digital signal performance predictions, including intersymbol interference, direct digital data input into the MAFIA model is compared to the system level analysis tool, SPW, which incorporates these approximations.

Modeling of gyroklystrons with MAGY

The self-consistent time dependent code MAGY is presently being used for designing and modeling gyrodevices. In this paper, the code's self-consistent capability is used to investigate three different issues relating to the operation of gyroklystron amplifiers. These are the effect of window reflection on the properties of the output waves, higher order mode excitation in nonlinear output tapers, and excitation in cutoff drift sections. The first two effects can potentially have major impacts on the gyroklystron output radio frequency (RF) in terms of bandwidth power ripple, phase ripple across the band, and mode purity. In fact, strong correlation between simulation results and experimental data indicates that the observed bandwidth ripple in a recently tested W-band gyroklystron can be attributed to a small (-20-dB) window reflection. The last effect, excitation in cutoff drift sections, is found to result in a high level of RF fields at the drive frequency in drift sections. This effect impacts the design and use of lossy ceramics in the drift section because of thermal considerations, particularly in high average power devices.

Spectral characterization of fiber gratings with high resolution

We demonstrate a high-resolution technique to measure the optical magnitude and phase responses of fiber gratings. The technique employs single-sideband modulation of an optical source and has spectral resolution in the hertz regime. The technique is demonstrated by measurement of the phase ripples of unapodized and apodized chirped gratings as well as the transmission spectrum of a pi-phase-shifted grating. Although it is demonstrated on fiber gratings, the technique is applicable to any optical device.

Perturbation theory for electric-field amplitude and phase ripple transfer in frequency doubling and tripling

A theory is presented for the transfer of a perturbation of the electric field from the input to the output of a frequency converter. The transfer relationship for the field ripple is shown to depend on the plane-wave operating parameters of the converter. Predictions of the theory are shown to be in excellent agreement with full numerical simulations of doubling and tripling and experiments measuring ripple transfer in frequency doubling.

Dual-reflector system with a spherical main reflector and shaped subreflector for compact range

For many years, the compact range has successfully been used to evaluate antenna electromagnetic radiation and target scattering. Single offset paraboloidal reflectors, dual parabolic–cylindrical reflectors, and dual shaped reflectors exist for the compact-range reflector systems. A dual-reflector compact-range system with a spherical main reflector and a shaped subreflector is described with this this design, an arbitrary position of the feed is permissible for the anechoic-chamber size and existing chamber-fitting considerations. A spherical surface is adopted to reduce manufacturing cost. A Gregorian-type dual-reflector system with a 1.83 m-diameter truncated spherical main reflector has been evaluated and manufactured. The test results, for frequencies from 8 to 39.5 GHz, showed that the performance of quiet zone is within ±0.4 dB amplitude ripple and ±5° phase ripple over a 70% area of the main reflector projected in the quiet-zone direction.