In this paper, a spread-spectrum clock generator (SSCG) with triangular modulation is presented. The proposed SSCG with a third-order sigma-delta modulator can generate clocks with center spread ratios of 0.25%, 1%, 1.75%, 2.5%, 3.5%, 5% and down spread ratios of 0.5%, 2%, 3.5%, 5%, 7%, 10%. The SSCG is implemented on a chip using SMIC 0.13 um CMOS process. Measurements show that 11.31 dB attenuation of the EMI at 80 MHz with down spread ratio of 10% and 12.98 dB attenuation at 133.3 M with center spread ratio of 5% can be achieved which have a good agreement with the theoretical calculations.
In recent years, researchers have discovered the phenomena of slow light and superluminal light in many mediums and structures. Coupled Resonator Induced Transparency (CRIT) is used to explain this phenomena and resonators which are capable of inducing CRIT can be widely used in fields like optical sensor, feedback cavity of laser, optical filter and so on. In coupled resonant cavity, mutually independent resonant states interact by weak coupling effect between different cavities, thus changing the characteristics of the whole resonant system and generating CRIT. Generally, this transparency can be produced in single mode fiber (SMF) coupled resonant cavity in both dual-ring and multi-ring coupled structure. Based on these two fundamental structures, in this paper we put forward two new structures which can also generate CRIT: multimode fiber (MMF) ring resonator and polarization maintaining fiber (PMF) ring resonator. Substantially, we change tandem resonant cavities into parallel resonant cavities and they have the same resonant effect. A section of PMF or MMF equals to dual-ring coupled structure or multi-ring structure respectively. Our proposal is verified theoretically and experimentally. Both simulation and experimental results show that the PMF ring resonator can induce more stable and symmetric transparency than the MMF ring resonator. This phenomenon can be explained from three aspects: modal energy coupling efficiency, initial phase of coupling modes and modal polarization states. Additionally, we connect several sections of PMFs and MMFs in serial with a rotation angle of 45°between each other's ends. This improvement is equivalent to increase the number of parallel resonant cavities in an exponential extent and the interference effect of light from different cavities can change the characteristics of the output transparency. We also verify this structure theoretically and experimentally.
We investigate the formation of photonic bound states in the continuum (BICs) in photonic crystal slabs from an analytical perspective. Unlike the stationary at-$\mathrm{\ensuremath{\Gamma}}$ BICs which originate from the geometric symmetry, the tunable off-$\mathrm{\ensuremath{\Gamma}}$ BICs are due to the weighted destructive via the continuum interference in the vicinity of accidental symmetry when the majority of the radiation is precanceled. The symmetric compatible nature of the off-$\mathrm{\ensuremath{\Gamma}}$ BICs leads to a trapping of light that can be tuned through continuously varying the wave vector. With the analytical approach, we explain a reported experiment and predict the existence of a new BIC at an unrevealed symmetry.
Polarization reciprocity is studied both theoretically and experimentally in an optically compensated configuration of interferometric fiber optic gyroscope (IFOG). In conventional IFOGs based on the minimal scheme, the output port of the coil coupler cannot be used mainly because of its polarization nonreciprocity (PN), and thus it is usually called the "nonreciprocal port". We show that the PN errors at the nonreciprocal port are effectively eliminated by optical compensation. With this unique property, the optically compensated IFOG can possess two low-PN ports for rotation sensing at the same time. From another perspective, one port IFOGs are possible to be constructed with less structural complexity.
We demonstrate a novel nanoscale torsion-free photonic crystal pressure sensor array. The proposed sensor array consists of piston-type resonator array side-coupled to photonic crystal waveguide. The pressure sensitivity as high as 0.50nm/nN is observed.
In high-contrast (HC) photonic crystals (PC) slabs, the high-order coupling is so intense that it is indispensable for analyzing the guided mode resonance (GMR) effect. In this paper, a semi-analytical approach is proposed for analyzing GMR in HC PC slabs with TE-like polarization. The intense high-order coupling is included by using a convergent recursive procedure. The reflection of radiative waves at high-index-contrast interfaces is also considered by adopting a strict Green's function for multi-layer structures. Modal properties of interest like band structure, radiation constant, field profile are calculated, agreeing well with numerical finite-difference time-domain simulations. This analysis is promising for the design and optimization of various HC PC devices.
In traditional fiber-optic gyroscopes (FOG), the polarization state of counter propagating waves is critically controlled, and only the mode polarized along one particular direction survives. This is important for a traditional single mode fiber gyroscope as the requirement of reciprocity. However, there are some fatal defects such as low accuracy and poor bias stability in traditional structures. In this paper, based on the idea of polarization multiplexing, a double-polarization structure is put forward and experimentally studied. In highly birefringent fibers or standard single mode fibers with induced anisotropy, two orthogonal polarization modes can be used at the same time. Therefore, in polarization maintaining fibers (PMF), each pair of counter propagating beams preserve reciprocity within their own polarization state. Two series of sensing results are gotten in the fast and slow axes in PMF. The two sensing results have their own systematic drifts and the correlation of random noise in them is approximately zero. So, beams in fast and slow axes work as two independent and orthogonal gyroscopes. In this way, amount of information is doubled, providing opportunity to eliminate noise and improve sensitivity. Theoretically, this double-polarization structure can achieve a sensitivity of 10-18 deg/h. Computer simulation demonstrates that random noise and systematic drifts are largely reduced in this novel structure. In experiment, a forty-hour stability test targeting the earth's rotation velocity is carried out. Experiment result shows that the orthogonal fiber-optic structure has two big advantages compared with traditional ones. Firstly, the structure gets true value without any bias correction in any axis and even time-varying bias does not affect the acquisition of true value. The unbiasedness makes the structure very attractive when sudden disturbances or temperature drifts existing in working environment. Secondly, the structure lowers bias for more than two orders and enhances bias stability for an order higher (compared with single axis result), achieving a bias stability of 0.01 deg/h. The evidences from all aspects convincingly show that the orthogonal fiber-optic structure is robust against environmental disturbance and material defects, achieving high stability and sensitivity.
Optical compensation is studied for suppressing polarization nonreciprocity (PN) induced errors in interferometric fiber-optic gyroscopes (IFOG). In convention IFOGs, a polarizer is necessarily used, and only one polarization is used for interference in order to achieve low PN error. Differently, we propose a new approach for using two polarizations simultaneously in the IFOG. PN error can be effectively suppressing by optical compensation between the two detected signals. Both simulation and experiment are presented, which shows that PN errors are effectively reduced by optical compensation. This new approach paves the way for low drift IFOGs with no polarizer.
Interference Fiber Optic Gyroscope (IFOG) is the mainstream Interferometric Fiber Optic Gyroscope (IFOG) is the mainstream optic inertial sensor products of rotation measurement in nowadays. However, short time migration as well as long time bias had been impacting IFOG for the first day it invented. For a better operation of orthogonal demodulation algorithm, which we proposed before had demonstrated an ability of suppressing the noise in IFOG. This article firstly concerning about the initial phase in the orthogonal demodulation of IFOG. Through posteriori estimation we achieved the balance orthogonal demodulation. Secondly, we place the 2 orthogonal channel data obtained from the IFOG, as reference signal for each other into an adaptive filter module, based on the LMS principle, obtaining a real-time improvement of short time migration and long time stability.
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