Design of the pulse duty cycle of the pseudolite signal in local area augmentation systems

The short-pulse TDMA signal is an excellent solution to the near-far problem in the pseudolite augmentation systems,and the pulse duty cycle is an important element in the solution.This paper aims at designing the duty cycle of the pseudolite pulse signals with a theoretical method.At first,the scope of the duty cycle is derived theoretically with the object of ensuring the reception of both the pseudolite signals and the satellite signals,and the expression for the theoretical upper limit is given.Then bas...     

Performance evaluation method of hybrid navigation constellations with invalid satellites

The construction of a navigation system plays an important role in the development of national politics,economy and military affairs.Nowadays,the Beidou navigation system is facing a transition period from the regional navigation system to the global one.For the global constellation,the system performance will not be seriously degraded when one or two satellites are invalid,but it is out of case for the regional constellation,which usually has fewer satellites and less redundancy.This paper deals with this ...     

Electronic structure and optical property of boron doped semiconducting graphene nanoribbons

We present a system study on the electronic structure and optical property of boron doped semiconducting graphene nanoribbons using the density functional theory. Energy band structure, density of states, deformation density, Mulliken popular and optical spectra are considered to show the special electronic structure of boron doped semiconducting graphene nanoribbons. The C—B bond form is discussed in detail. From our analysis it is concluded that the Fermi energy of boron doped semiconducting graphene nano...     

1047-nm all-solid-state laser based on Nd:LuLF

A compact all-solid-state continuous-wave (CW) laser at 1047 nm is developed based on Nd:LuLF, which is grown through the Czochralski technique. From the laser system, 1.3-W laser can be obtained, which corresponds to the slope efficiencies of 20.1% and 49.5% with respect to the incident and absorbed pump powers, respectively. To the best of our knowledge, this is the highest power level achieved at 1047 nm based on the Nd:LuLF crystal.     

Highly birefringent octagonal photonic crystal fibers with two zero-dispersion wavelengths

A new highly birefringent octagonal photonic crystal fiber(Hi-Bi OPCF) with a rectangular array of four elliptical airholes in the fiber core region is proposed and analyzed using the full-vector finite element method with anisotropic perfect match layer absorbing boundaries.Numerical results show that the phase birefringence of the photonic crystal fiber(PCF) reaches 3.43×10-2 at the wavelength of 1 550 nm.Moreover,two zero-dispersion wavelengths are achieved in the visible and near infrared wavelength regions for one polarization state but not in the other.     

Compact and high-power broadband terahertz source based on femtosecond photonic crystal fiber amplifier

We present a review of the development of a compact and high-power broadband terahertz (THz) source optically excited by a femtosecond photonic crystal fiber (PCF) amplifier.The large mode area of the PCF and the stretcher-free configuration make the pump source compact and very efficient.Broadband THz pulses of 150 μW extending from 0.1 to 3.5 THz are generated from a 3-mm-thick GaP crystal through optical rectification of 12-W pump pulses with duration of 66 fs and a repetition rate of 52 MHz.A strong saturation effect is observed,which is attributed to pump pulse absorption;a Z-scan measurement shows that three-photon absorption dominates the nonlinear absorption when the crystal is pumped by femtosecond pulses at 1 040 nm.A further scale-up of the THz source power is expected to find important applications in THz nonlinear optics and nonlinear THz spectroscopy.     

Study on the saturation characteristics of high-speed uni-traveling-carrier photodiodes based on field screening analysis

A back-illuminated mesa-structure InGaAs/InP charge-compensated uni-traveling-carrier(UTC) photodiode(PD) is fabricated,and its saturation characteristics are investigated.The responsivity of the 40-μmdiameter PD is as high as 0.83 A/W,and the direct current(DC) saturation current is up to 275 mA.The 1-dB compression point at the 3-dB cutoff frequency of 9 GHz is measured to be 100 mA,corresponding to an output radio frequency(RF) power of up to 20.1 dBm.According to the calculated electric field distributions in the depleted region under both DC and alternating current(AC) conditions,the saturation of the UTC-PD is caused by complete field screening at high optical injection levels.     

Experimental study on minimum resolvable velocity for heterodyne laser Doppler vibrometry

A high spatial resolution,high velocity resolution all-fiber laser Doppler vibrometry(LDV) based on heterodyne detection for vibration measurements is reported.A linewidth of 1-kHz single-mode continuous fiber laser,polarization-preserving fiber,and a telescope with 30-mm aperture are used in this LDV.With the inphase-quadrature circuit and the digital differentiating discriminator,a high velocity resolution of 96.9 nm/s and a high displacement resolution of 2.5 pm are obtained simultaneously with a glass a...     

Image edge-enhancement in optical microscopy with a phase mismatched spiral phase plate

We present a spiral phase filtering system with a large tolerance for edge enhancement of both phase and amplitude objects in optical microscopy.The method is based on a Fourier 4-f spatial filtering system.A phase mismatched spiral phase plate (SPP) fabricated by electron beam lithography is employed as the radial Hilbert transform for image edge enhancement.Compared with holography,SPP is simple,economical,reliable,and easy to integrate.     

Property (ω′) and Its Perturbation

In this note we define the property (ω′), a variant of Weyl’s theorem, and establish for a bounded linear operator defined on a Hilbert space the necessary and sufficient conditions for which property (ω′) holds by means of the variant of the essential approximate point spectrum σ1(·) and the spectrum defined in view of the property of consistency in Fredholm and index. In addition, the perturbation of property (ω′) is discussed.