Comodulation masking release (CMR) as a function of masker bandwidth, modulator bandwidth, and signal duration

These experiments examine how comodulation masking release (CMR) varies with masker bandwidth, modulator bandwidth, and signal duration. In experiment 1, thresholds were measured for a 400-ms, 2000-Hz signal masked by continuous noise varying in bandwidth from 50-3200 Hz in 1-oct steps. In one condition, using random noise maskers, thresholds increased with increasing bandwidth up to 400 Hz and then remained approximately constant. In another set of conditions, the masker was multiplied (amplitude modulated) by a low-pass noise (bandwidth varied from 12.5-400 Hz in 1-oct steps). This produced correlated envelope fluctuations across frequency. Thresholds were generally lower than for random noise maskers with the same bandwidth. For maskers less than one critical band wide, the release from masking was largest (about 5 dB) for maskers with low rates of modulation (12.5-Hz-wide low-pass modulator). It is argued that this release from masking is not a "true" CMR but results from a within-channel cue. For broadband maskers (greater than 400 Hz), the release from masking increased with increasing masker bandwidth and decreasing modulator bandwidth, reaching an asymptote of 12 dB for a masker bandwidth of 800 Hz and a modulator bandwidth of 50 Hz. Most of this release from masking can be attributed to a CMR. In experiment 2, the modulator bandwidth was fixed at 12.5 Hz and the signal duration was varied. For masker bandwidths greater than 400 Hz, the CMR decreased from 12 to 5 dB as the signal duration was decreased from 400 to 25 ms.(ABSTRACT TRUNCATED AT 250 WORDS)     

Si2N2O基体铌酸锂调制器有限元法研究

提出一种新型基于Si2N2O基体的LiNbO3行波调制器,利用有限元方法对该调制器进行数值分析并获得调制器的优化结构尺寸.该新型调制器带宽达到120 GHz,半波电压为3.5 V,特性阻抗为50.2 Ω.结果表明该调制器具有大的调制带宽和良好的阻抗匹配,在未来光通信中具有很好的应用前景.     

Compact optical microfiber phase modulator

A compact optical microfiber phase modulator with MHz bandwidth is presented. A micrometer-diameter microfiber is wound on a millimeter-diameter piezoelectric ceramic rod with two electrodes. When a voltage is applied to the piezoelectric ceramic, the rod is strained, leading to a phase change along the microfiber; because of the small size, the optical microfiber phase modulator can have as high as a few MHz bandwidth response.     

新型结构超宽带LiNbO3电光调制器的优化设计

采用有限元软件对新型结构的铌酸锂电光调制器进行了优化设计.分析表明,采用脊波导和T型电极相结合的方式,能在保持高的特征阻抗的同时有效的实现相速匹配和有效降低电极损耗,从而较好的提高器件性能,是一种比较有潜力的调制器.利用优化结果,给出一种带宽达153 GHz,半波电压为8.55 V,特征阻抗为44 Ω的调制器的设计例子.     

Electro-optical modulator using SiO2 waveguides with thermal poling on a Si substrate

A novel optical modulator using SiO₂ waveguides on a silicon substrate is proposed. The modulator is analyzed and designed with the finite element method. The numerical results have shown that an optimally designed modulator can give a broad bandwidth, good impedance match, and low cost. The proposed modulator can be fabricated easily using Si-based very large-scale integrated technology, and it is very suitable for opto-electronic integrated circuits.     

InP基矩形马赫-曾德高速电光调制器行波电极设计与测试

提出了一种由新型沟槽耦合器和90°弯曲波导构成的InGaAsP/InP基矩形马赫-曾德电光调制器,对该调制器的L型波导相移臂设计了T型类微带行波电极.首先利用电极的等效电路估算带宽上限,进而在考虑阻抗匹配、回波损耗以及带宽等性能的基础上,使用有限元方法对电极的传输、输入/输出以及过渡区的结构参量进行优化.仿真结果表明由于受到电极输入及过渡区的性能限制,设计的整体行波电极匹配阻抗大于42Ω,回波损耗小于-15dB,带宽可达65GHz.测试制备的Ti/Au行波电极,得到回波损耗为-12dB和带宽为20GHz的最优性能.     

Ultra-Broad-Band LiNbO_3 Electro-Optic Modulators with Novel Complex Electrode

1 IntroductionFOr LiNbO3 modulators, the bandwidth is mainly restricted by the microwaveattenuation of the travelling--wave electrode and the phase velocity ndsmatch betWeenmicrowave and optical wave in the devices. When the phase velocity matching issatisfied it is very i~rtant to decrease the microwave attenuation for expandingbandwidth. The thecrowave propagating lOSS is the main source Of the microwaveattenuation in the interactive region. The larger the cross-sectional area or the lOn…     

Ultra-Broad-Band LiNbO3 Electro-Optic Modulators with Novel Complex Electrode

The characteristics of Z- cut LiNbO3 optical modulators with novel complex electrode are discussed by using the finite element method (FEM) and studied experimentally in this paper. The travelling wave electrode consists of upper and lower parts. It can easily realize phase velocity matching between microwave and optical wave and drastically reduce microwave electrode loss. An electrooptic modulator with larger than 100 GHz bandwidth and half wave voltage 6 V is designed, fabricated and measured. Vπ is 5.1 V and the attenuation coefficient a0 is 0.3 dB/(cm· GHz1/2 ). The experimental results show that the modulator has great potentiality for expanding bandwidth.     

Characteristic of a broadband Ti:LiNbO3 optical modulator with buried electrodes and etched grooves in the buffer layer

Traveling wave Ti:LiNbO₃ Mach-Zehnder optical modulators with buried electrodes and etched grooves in the SiO₂ buffer layer are analyzed by the finite element method. The tradeoff between the bandwidth BW and the half-wave voltage Vπ is discussed. The value of BW/Vπ is used to weight the total performance of the modulator. Taking a thick buffer layer and etching deep grooves in the buffer layer are demonstrated as two effective methods to improve the performance of the modulator. A 3-dB optical bandwidth of 18 GHz with half-wave voltage 5V at a wavelength of 1.55 pm could be obtained even though the electrode is not very thick. When the requirement of half-wave voltage is not very critical, a bandwidth of more than 100 GHz can be obtained.     

Hybrid silicon modulators Invited Paper

A number of active elements have been demonstrated using the hybrid silicon evanescent platform, includ- ing lasers, amplifiers, and detectors. In this letter, two types of hybrid silicon modulators, fulfilling the building blocks in optical communication on this platform, are presented. A hybrid silicon electroabsorp-tion modulator, suitable for high speed interconnects, with 10-dB extinction ratio at -5 V and 16-GHz modulation bandwidth is demonstrated. In addition, a hybrid silicon Mach-Zehnder modulator utilizing carrier depletion in multiple quantum wells is proved with 2 V.mm voltage-length product, 150-nm optical bandwidth, and a large signal modulation up to 10 Gb/s.     

Asymptotic formalism for ultraflat optical frequency comb generation using a Mach-Zehnder modulator

We theoretically prove that a conventional Mach-Zehnder modulator can generate an optical frequency comb with excellent spectral flatness. The modulator is asymmetrically dual driven by large amplitude sinusoidal signals with different amplitudes. The driving condition to obtain spectral flatness is analytically derived and optimized, yielding a simple formula. This formula also predicts the conversion efficiency and bandwidth of the generated frequency comb.     

Free-space optical interconnection: A technology comparison of vertical-cavity surface-emitting lasers and multiple-quantum-well modulators

We evaluate current vertical-cavity surface-emitting laser (VCSEL) and multiple-quantum-well (MQW) modulator technologies for low-fanout system applications. Si-CMOS transimpedance receiver circuits are used in the comparison. The aggregate bandwidth per unit area is calculated from the bandwidth and the total on-chip power dissipation. The results indicate that the electrical power dissipation in the receiver circuits dominates at low operating frequencies. At high operating frequencies the receiver gain drops significantly, thus more electrical power is dissipated in the transmitter to provide more optical power to the receiver to satisfy the voltage requirement at the receiver output. In VCSEL based systems, the optical power is generated entirely on-chip. Thus, only VCSELs with low threshold current and low series resistance would be able to provide the same aggregate bandwidth as the MQW modulator based systems.     

Flexible quadrature amplitude modulation with semiconductor optical amplifier and electroabsorption modulator

Optical quadrature amplitude modulation (QAM) is experimentally demonstrated with a low-complexity modulator based on a semiconductor optical amplifier and electroabsorption modulator. Flexible amplitude/phase format transmission is achieved. The applicability of octary QAM for coherent optical access networks with sustainable 3 Gb/s per-user bandwidth is investigated for a long reach of 100 km, and its compatibility with a potentially high split is verified.     

基于强度调制的新型偏振光谱仪调制器优化设计

强度调制是一种高光谱偏振信息获取新方法,可有效地解决现有测量法存在的不足。调制器是其中的关键硬件模块之一。从调制器实现偏振、光谱信息调制的基本原理入手,结合偏振、光谱信息的解调理论,提出了调制器参数优化设计方法,并对该方法进行了计算机数值模拟。结果表明:经过优化设计的调制器产生的各个载波信号的频率在光谱仪的采样带宽内均匀分布,有效地拓展了可测Stokes矢量元素谱的带宽范围,也为后续的偏振、光谱信息的高保真解调奠定了基础。     

Switchable down-, up- and dual-chirped microwave waveform generation with improved time-bandwidth product based on polarization modulation and phase encoding

A switchable down-, up- and dual-chirped microwave waveform generation technique with improved time-bandwidth product (TBWP) is proposed and demonstrated based on a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM) cascaded with a polarization modulator (PolM). By properly controlling the phase shifts of the radio frequency signals applied to the DP-DPMZM, switchable down-, up- and dual-chirped waveforms with simultaneous frequency and bandwidth doubling can be generated. To enlarge the TBWP further, splitting parabolic signal and phase-encoding splitting parabolic signal are used to drive the PolM for the enhancement of bandwidth and time duration. Numerical results demonstrate the generation of down-, up- and dual-chirped microwave waveform with TBWP of 8, 160 and 10240. The proposed method may find applications in future multifunction radar systems due to the high performance and flexibility.     

Terahertz modulator using photonic crystals

In this letter, a novel terahertz wave modulator based on a silicon oxide/polyaniline photonic crystal is proposed. The modulation mechanism of the novel modulator is based on a dynamic shift of the photonic band gap by the applied external electric field. Its performances were investigated with the finite-difference time-domain method. The novel modulator has 3 dB modulation bandwidth of 10 kHz, a size as small as 20 mm and its extinction ratio larger than 30 dB at the frequency of 1 THz.     

Within-channel cues in comodulation masking release (CMR): experiments and model predictions using a modulation-filterbank model

Experiments and model calculations were performed to study the influence of within-channel cues versus across-channel cues in comodulation masking release (CMR). A class of CMR experiments is considered that are characterized by a single (unmodulated or modulated) bandpass noise masker with variable bandwidth centered at the signal frequency. A modulation-filterbank model suggested by Dau et al. [J. Acoust. Soc. Am. 102, 2892-2905 (1997)] was employed to quantitatively predict the experimental data. Effects of varying masker bandwidth, center frequency, modulator bandwidth, modulator type, and signal duration on CMR were examined. In addition, the effect of band limiting the noise before or after modulation was shown to influence the CMR in the same way as a systematic variation of the modulation depth. It is demonstrated that a single-channel analysis, which analyzes only the information from one peripheral channel, quantitatively accounts for the CMR in most cases, indicating that an across-channel process is generally not necessary for simulating results from this class of CMR experiments. True across-channel processes may be found in another class of CMR experiments.     

Broadband optical frequency comb generation with a phase-modulated parametric oscillator

We introduce a novel broadband optical frequency comb generator consisting of a parametric oscillator with an intracavity electro-optic phase modulator. The parametric oscillator is pumped by 532-nm light and produces near-degenerate signal and idler fields. The modulator generates a comb structure about both the signal and the idler. Coupling between the two families of modes results in a dispersion-limited comb that spans 20 nm (5.3 THz). A signal-to-noise ratio of >30 dB in a 300-kHz bandwidth is observed in the beat frequency between individual comb elements and a reference laser.     

GaAs／GaAlAs定向耦合器型行波调制器：1.设计

从理论上重点分析和研究了器件行波电极的微波特性，在半绝缘ＧａＡｓ衬底上设计了具有ｎ＾＋重掺杂外延层和共平面电极的ＧａＡｓ／ＧａＡｌＡｓ定向耦合器型行波调制器，针对实验中发现的行波电极上微波的高传输损耗问题。分析了起因并提出了器件的改进设计方案，从而设计出可达到３５ＧＨｚ带宽的高速调制效应的光波导调制器。     

Wideband versatile radio-frequency spectrum analyzer

Operation of a wideband, versatile optical spectrum analyzer for radio-frequency (RF) signals is demonstrated. The device is based on spectral hole burning (SHB). The demonstration features 2.3-GHz instantaneous bandwidth, 500-kHz resolution, and a 32-dB dynamic range. A true RF signal, transferred to the optical carrier with the help of a Mach-Zehnder modulator, is analyzed with optical carrier suppression and zooming capabilities. This is to the authors' knowledge the largest instantaneous bandwidth ever demonstrated for a SHB-based processor in rare-earth-doped crystals.