Enhancement of the group delay in quadratic coupling optomechanical systems subjected to an external force

We theoretically study the effect of the quadratic coupling strength on optomechanical systems subjected to a continuous external force. Quadratic coupling strength originates from strong coupling between the optical and the mechanical degrees of freedom. We show that the quadratic coupling strength reduces the amplitude of the dispersion spectra at the resonance in both blue-and red-sideband regimes. However, it increases(decreases) the amplitude of the absorption spectrum in the blue-(red-)sideband regime. Furthermore, in both sideband regimes, the effective detuning between the pump and the cavity deviates with the quadratic coupling strength. Thereby, appropriate selection of the quadratic coupling strength results in an important magnification(in absolute value) of the group delay for both slow and fast light exiting from the optomechanical cavity.

Enhanced and controllable reflected group delay based on Tamm surface plasmons with Dirac semimetals

The reflected group delay from a multilayer structure comprising a one-dimensional photonic crystal coated with a bulk Dirac semimetal(BDS)separated by a spacer layer is investigated theoretically.It is shown that the group delay of the reflected beam in this structure can be significantly negatively enhanced and switched from negative to positive.The enhanced group delay originates from the steep phase change caused by the excitation of the optical Tamm state at the interface between the BDS and spacer layer.Moreover,positive and negative group delays can be actively tuned through the Fermi energy and the relaxation time of the BDS.We believe that this enhanced and tunable delay scheme has important research significance for the fabrication of optical delay devices.

Time-domain nature of group delay

The characteristic of group delay is analyzed based on an electronic circuit, and its time-domain nature is studied with time-domain simulation and experiment. The time-domain simulations and experimental results show that group delay is the delay of the energy center of the amplitude-modulated pulse, rather than the propagation delay of the electromagnetic field. As group velocity originates from the definition of group delay and group delay is different from the propagation delay, the superluminaiity or negativity of group velocity does not mean the supeduminal or negative propagation of the electromagnetic field.

Optical soliton with group delay in microring coupled-resonator optical waveguides

This paper derives the dispersion relation of microring coupled-resonator optical waveguides （CROWs） without any approximation by using the transfer matrix method. Based on the established dispersion relation of CROWs it obtains the slow group velocity and dispersion coefficient. It finds that the effect Of dispersion on optical pulses can be adjusted to balance the effect of nonlinearity by changing coupling coefficient or loss, so optical soliton with group delay can be obtained in microring CROWs. The optical soliton with group delay is of great significance for applications of microring CROWs in delay lines and optical buffers of future all-optical communication systems.

Optical time-domain differentiation based on intensive differential group delay

An optical time-domain differentiation scheme is proposed and demonstrated based on the intensive differential group delay in a high birefringence fibre waveguide. Results show that the differentiation waveforms agree well with the mathematically calculated derivatives. Both error and efficiency will increase when the birefringence fibre becomes longer, and the error rises up more quickly while the efficiency approaches to a maximum of ~0.25. By using a 1-m birefringence fibre a lower error of ~0.26% is obtained with an efficiency of 1% for the first-order differentiation of 10-ps Gaussian optical pulses, and the high-order optical differentiation up to 4th order is achieved with an error less than 3%. Due to its compact structure being easy to integrate and cascade into photonic circuits, our scheme has great potential for ultrafast signal processing.

The generation of group delay ripple of chirped fiber gratings

The analysis of the group delay ripple (GDR) generated by chirped fiber gratings is developed based on the Fabry-Perot (F-P) resonator. It shows clearly how the GDR is generated and why the periods of GDR varies along the chirped fiber gratings. It could also explain why apodization could suppress the GDR and how apodization affects the chirp of the grating. The theory could be used to devise the apodization of fiber gratings.

Group delay and phase delay in GNSS systems

GNSS signals have previously been modulated using binary phase shift keying but this modulation scheme is being replaced by binary offset carrier(BOC)modulation.Research has considered how the BOC signals might be affected differently when passed through a surface acoustic wave(SAW)filter.The concern has been that because of the split spectrum nature of the BOC signals,the upper and lower side-lobes will be delayed significantly differently.This was suggested because SAW filters have nonlinear phase characteristics and therefore different frequencies are delayed differently.It was suggested that this difference in delay will result in greater distortion of the correlation triangle.A delay magnification effect was also mentioned when analyzing the delay of a BOC signal.It was not understood why the theoretical delay calculations did not match up with the actual results in both hardware and simulation.This paper clarifies some of the confusion and explains why the“delay magnification”applies to phase delay but not group delay.This paper also takes a look at how the code phase delay can vary with frequency and correlator spacing as a result of the SAW filter properties.

Prediction of Group Delay Distribution Around Receiving Point Using Modified IRI Model and IGRF Model

The international reference ionosphere （IRI） model is generally accepted standard ionosphere model. It describes the ionosphere environment in quiet state and predicts the ionosphere parameters within a certain precision. In this paper, we have made a breakthrough in the application of the IRI model by modifying the model for regions of China. The main objectives of this modification are to construct the ionosphere parameters foF2 and M （3000） F2 by using the Chinese reference ionosphere （CRI） coefficients, appropriately increase hmE and hmF2 height, reduce the thickness of F layer, validate the parameter by the measured values, and solve the electron concentration distribution with quasi-parabolic segment （QPS）. In this paper, 3D ray tracing algorithm is constructed based on the modified IRI model and international geomagnetic reference field （IGRF） model. In short-wave propagation, it can be used to predict the electromagnetic parameters of the receiving point, such as the receiving area, maximum useable frequency （MUF） and the distribution of the group delay etc., which can help to determine the suitability of the communication. As an example, we estimate the group delay distributions around Changchun in the detection from Qingdao to Changchun using the modified IRI model and IGRF model, and provide technical support for the short-wave communication between the two cities.

A 3-5GHz CMOS UWB power amplifier with±8ps group delay ripple

A differential power amplifier （PA）, designed using the linear-phase filter model, for a BPSK modulated ultra-wideband （UWB） system operating in the 3-5 GHz frequency range is presented. The proposed PA was fabricated using 0.18μm SMIC CMOS technology. To achieve sufficient linearity and efficiency, this PA operates in the class-AB region, delivering an output power of 8.5 dBm at an input-1 dB compression point of-0.5 dBm. It consumes 28.8 mW, realizing a fiat gain of 9.11± 0.39 dB and a very low group delay ripple of ±8 ps across the whole band of operation.

Relationships among group delay,energy storage,and loss in dispersive dielectric mirrors

We show that absorbed and stored electromagnetic energy are proportional to the reflection group delay in highly reflective dispersive dielectric mirrors over the high-reflectivity band. Our theoretical considerations are verified by numerical simulations performed on different dielectric mirror structures. The revealed pro- portionality between group delay and absorbed energy sets constraint on the application of ultrabroadband and/or dispersive dielectric mirrors in broadband or widely tunable, high-power laser systems.

A large bandwidth photonic delay line using passive cascaded silicon-on-insulator microring resonators

This paper investigated the design and the characterization of a photonic delay line based on passive cascaded silicon-on-insulator （SOI） microrings. We considered the compromise of group delay, bandwidth and insertion loss. A 3-stage double channel side-coupled integrated spaced sequence of resonator （SCISSOR） device was optimized by shifting the resonance of each microring and fabricated with electron beam lithography and dry etching. The group delay was measured to be 17 ps for non-return-to-zero signals at different bit rates and the bandwidth of 78 GHz was achieved. The experiment result agreed well with our simulation.

基于MEMS开关的可调实时延时器设计

为了有效解决相控阵雷达/天线瞬时带宽小、孔径效应严重、功耗大等问题,将射频MEMS开关引入实时可调延时器结构中,设计了一种基于射频MEMS开关的实时可调延时器。通过MEMS双掷开关选择具有不同电长度的延时路径,在DC~20 GHz内实现了5位的射频信号延时。利用HFSS三维电磁仿真软件对延时单元的几何参数进行仿真优化,得到5个可切换延时状态的延时量,分别为64.76 ps,101.46 ps,137.97 ps,174.61 ps,210.98 ps,延时步进为36.5 ps,整体面积约为5 mm^(2)。与其他实时可调延时器相比,该实时可调延时器具有多可控位数、大延时带宽积、高集成度等优点。

Investigation of Helical Pulse Forming Line

To investigate the feasibility for a helical line to be used as a pulse forming line （PFL）, the transmission characteristics of the helical transmission line is studied both theoretically and experimentally. The results indicate that it is feasible to employ a helical line as a long-pulse PFL, and the influence of its dispersion is negligible. Compared with a conventional coaxial PFL, the helical PFL with the same size can produce a longer pulse.

Novel uncertainty relations associated with fractional Fourier transform

In this paper the relations between two spreads, between two group delays, and between one spread and one group delay in fractional Fourier transform （FRFT） domains, are presented and three theorems on the uncertainty principle in FRFT domains are also developed. Theorem 1 gives the bounds of two spreads in two FRFT domains. Theorem 2 shows the uncertainty relation between two group delays in two FRFT domains. Theorem 3 presents the crossed uncertainty relation between one group delay and one spread in two FRFT domains. The novelty of their results lies in connecting the products of different physical measures and giving their physical interpretations. The existing uncertainty principle in the FRFT domain is only a special ease of theorem 1, and the conventional uncertainty principle in time-frequency domains is a special case of their results. Therefore, three theorems develop the relations of two spreads in time-frequency domains into the relations between two spreads, between two group delays, and between one spread and one group delay in FRFT domains.

An optical rotation sensor based on dispersive slow-light medium

Slow light supported by electromagnetically induced transparency effect in dispersive medium is extremely susceptible with respect to Doppler detuning. In this paper, the Doppler effect induced by rotating dispersive medium was considered and the effect of the velocity of rotating dispersive medium on the group velocity was studied. Based on a dispersive slow-light medium, a high sensitive optical rotation sensor for measuring absolute rotation is proposed and analysed. The sensitivity of the rotation sensor is the group delay between the counterpropagationed wave packets in the device, and scales directly with square of the group index which can reach 102-10s orders of magnitude by selecting a proper dispersive medium.

Precise relative rotation sensing using slow light

A novel relative rotation sensor based on slow light is proposed and analysed. A theoretical analysis shows that the high sensitivity of the proposed rotation sensor is achieved through an electromagneticaIly-induced-transparency medium. Unlike the tradition detection method, the idea of rotation sensing is to detect group delay between counterpropagating wave packets. It can be used to realize an ultra-precise rotation sensor.

Anisotropy Characteristics of Magnetostatic Surface Wave Propagating in YIG/Dielectric/Metal Layered Structure

The anisotropy of magnetostatic surface wave （MSSW） propagating in finite width YIG /dielectric/metal layered structure is analyzed. This problem is solved by finding the rigorous solution of each layer from Maxwell equation and the appropriate transmission Green＇s function matrix G. From the relationship of Green＇s function matrixes of dielectric layer and ferrite layer, the dispersion equation is obtained. The MSSW filter is designed to verify the dispersion characteristics. The experiment results are in good agreement with the calculating data from the model.

Frequency correlation and group time delay of ambient noise and ship radiated-noise in the sea

The characteristics of frequency correlation and group time delay of ambient noise and ship radiated-noise in the sea are studied. The theoretical and experimental results show that the frequency correlation of ship radiated-noise is much greater than that of ambient noise,and the frequency correlation of ship radiated-noise at long distance has obvious group time delay

HTS filter subsystem for future mobile communication system

A high-temperature superconducting （HTS） filter subsystem consisting of a 10-pole HTS filter with group delay self-equalization, a cryogenic low noise amplifier （LNA）, and a cooling device is presented in this paper. The HTS filter has a 0.51% fractional bandwidth at 1955 MHz, simulated in Sonnet, and is fabricated using double-sided TI2Ba2CaCu208 films on 0.5 mm thick LaAIO3 substrate. Measured responses show that the minimum insertion loss of the filter is 0.16 dB, and the out-of-band rejection is better than 75 dB. The slope is 27 dB MHz^-1 at the low band edge and 22 dB MHz-1 at the upper band edge. The HTS filter subsystem has a gain of 19.3 dB and a noise figure （NF） of 0.8 dB. Furthermore, the phase distortion of HTS filters is considered, and an efficient design approach for self-equalized HTS filters is proposed.

An eighth order channel selection filter for low-IF and zero-IF DVB tuner applications

An eighth order active-RC filter for low-IF and zero-IF DVB tuner applications is presented, which is implemented in Butterworth biquad structure. An automatic frequency tuning circuit is introduced to compensate the cut-off frequency variation using a 6-bit switched-capacitor array. Switched-resistor arrays are adopted to cover different cut-off frequencies in low-IF and zero-IF modes. Measurement results show that precise cut-off frequencies at 2.5, 3, 3.5 and 4 MHz in zero-IF mode, 5, 6, 7 and 8 MHz in low-IF mode can be achieved, 60 dB frequency attenuation can be obtained at 20 MHz, and the in-band group delay agrees well with the simulation. Two-tone testing shows the in-band IM3 achieves -52 dB and the out-band IM3 achieves -55 dB with -11 dBm input power. This proposed filter circuit, fabricated in a SMIC 0.18μm CMOS process, consumes 4 mA current with 1.8 V power supply.