A 127-element adaptive optical system has been developed and integrated into a 1.8-m astronomical telescope in September 2009. In addition, the first light on a high-resolution imaging for stars has been achieved (September 23, 2009). In this letter, a 127-element adaptive optical system for 1.8-m telescope is described briefly. Moreover, star observation results in the first run are reported. Results show that the angular resolution of the system after adaptive optics correction can attain 0.1 arcsec, which approaches the diffraction limit of 1.8-m telescope at 700–900 nm band.

A qualitative method to analyze wavefront aberrations is presented. Aberrations of the primary type, expressed in their matrix forms, are used to write the generalized ray transfer matrix of an optical component. The aberrations were treated collectively by examining the pseudospectra of an augmented matrix constructed from the aberration matrices. Results show that aberrations can be distinguished and relative strengths pronounced using this qualitative method.

Turbo-coded 1.25-Gb/s orthogonal frequency-division multiplexing (OFDM) signals in 60-GHz radio-overfiber system are demonstrated. It can overcome impairments in fibers and extend transmission distance. Experimental results show that the transmission distance of turbo-coded OFDM signals at 1.25 Gb/s with coding (pure bit rate of 830 Mb/s) can be extended by over 30%.

We propose an improved design of photonic crystal fiber (PCF) with ultra broadband-flattened dispersion and ultra-low confinement loss in the telecommunication window. The design is considerably suitable for the generation of wideband supercontinuum spectrum. Numerical results reveal that the proposed PCF structure possesses a low dispersion of 0+-1.5 ps/(nm.km) in the wavelengths ranging from 1.134 to 1.805 \mum (approximately 700-nm bandwidth) with a confinement loss of less than 10?8 dB/km. In addition, a nonlinear coefficient greater than 11.47 (W.km)?1 and a dispersion slope of as low as 0.005694 ps/(nm2.km) are obtained at 1.55-μm wavelength. Moreover, a symmetric flat supercontinuum spectrum with a 10-dB bandwidth of 190 nm is achieved in a 3-m-long fiber, verifying the excellent optical features of the innovative PCF.

The novel characteristics of guided modes in the chiral negative refractive index fiber are investigated theoretically in this letter. We derive the characteristic equation of guided modes. Based on two types of chiral metamaterial parameters, we present the dispersion curves, energy flux, and power of guided modes. Some abnormal features, such as the existence of surface mode and dispersion curves with different shapes, intersection of dispersion curves of different guided modes, negative energy flux in the achiral cladding, and zero power at some normalized frequencies, are found in the chiral negative refractive index fiber.

We propose and demonstrate experimentally a novel scheme to realize all-optical up-conversion and wavelength-conversion based on the bi-directional-pump four-wave mixing (FWM) effect in high nonlinear fibers (HNLFs). The pump is generated with optical carrier suppression in a Mach-Zehnder modulator. The two pumps are always parallel and phase-locked. A balance-detection photo-detector for optical signal detection is employed with 3-dB improvement in power penalty. The 2.5-Gb/s signals are transmitted successfully over the 25-km single-mode fiber in 30-GHz radio over fiber (ROF) systems.

A 60-GHz bidirectional radio-over-fiber (RoF) system using two-carrier-injected distributed feedback (DFB) laser is proposed and demonstrated to realize optical single sideband (SSB) modulation for downlink. An injection-locked Fabry-P′erot laser is also carried out to realize wavelength reuse in uplink. Transmission of 2.5 Gb/s on a 60-GHz carrier for downlink and 622-Mb/s baseband signal for uplink are both successfully demonstrated over 50-km single mode fiber without chromatic dispersion compensation.

To improve the restoration performance of a multicast service of multi-protocol label switching transport profile (MPLS-TP) enabled optical network, this letter proposes a local-node initiated fast restoration (LNIFR) scheme for MPLS-TP optical multicast service. The proposed scheme allows the local node to establish a segment of fast loopback label switch path by the local node along the upstream of the failed node or link to the nearest downstream node. The fast restoration of optical multicast trees is realized through this part restoration, which focuses on failed node or link. Simulation analysis and results demonstrate that the new scheme outperforms the other schemes in terms of restoration time and success rate.

In three-dimensional displays, large vertical parallax in parallax images is disadvantageous to stereo vision due to the presence of visual fatigue. Based on the principle that homologous points in different parallax images correspond to the same object point, a method is proposed to eliminate the vertical parallax in multi-view parallax images. The coordinate mapping relationship between a standard parallax image and an awaiting rectification parallax image is established according to the coordinates of the image points of the rectangular calibration board vertices. Experiments are conducted, and results prove that the proposed method is reliable.

A hyperspectral imaging system is developed to detect dichlorvos residue on the surface of navel orange. After acquiring hyperspectral images of 400 navel oranges, the actual content of dichlorvos residue is measured by gas chromatography. Optimal wavelengths are extracted using the regression coefficients of partial least squares (PLS), and a PLS model with 12 factors is established. In the prediction set of 0.2282?11.652-mg/kg pesticide residue, the correlation coefficient and the root mean standard error are 0.8320 and 1.3416, respectively. The hyperspectral imaging technology can meet the requirement of online fast nondestructive detection.

We study and experimentally demonstrate a sensitive single-shot correlation system in which only a diffraction grating is used to produce a transverse time delay (TTD) in the reference pulse. The mechanism of the TTD introduced by the grating and the formation of the relative time delay (RTD) in the noncollinear correlation system are analyzed in detail. By using our system, we successfully measured the temporal duration of picosecond laser pulses, and a time resolution of ～0.047 ps is obtained at 1047 nm. The impact of the grating dispersion and the second harmonic beam walk-off effect on the measurement are considered.

Conventional analytical methods in the wavelet domain are used to present an analysis of terahertz (THz) waveguide modes. To obtain THz radiation pulses passing through a waveguide, we build a simple experimental system with a 5-mm-long, 230-\mum-inner-diameter stainless steel waveguide. The single-mode guided signal from the experiments and the multi-mode signal of a similar THz waveguide reported in the literature are analyzed using the continuous wavelet transform (CWT). The results demonstrate that analyzing THz waveguide modes in the wavelet domain not only possesses all the functionality of the traditional THz time-domain spectroscopy (TDS) data processing but also has the ability to unscramble quantitatively and intuitively detailed information about the target samples, such as mode type, cut-off frequency, amplitude distinction, and group velocity.

The theoretical analysis and experimental results of the wavelength tunability of a tandem optical parametric oscillator (TOPO) based on a single nonlinear crystal are presented. TOPO is a configuration wherein the signal laser is used as a pump laser to generate secondary optical parametric oscillator (OPO). The cascaded parametric interactions are achieved synchronously in a single-grating-period MgO doped periodically poled lithium niobate (PPMgOLN). Tunable multiple-wavelength mid-infrared (mid-IR) lasers are obtained by changing the temperature of the crystal. When the PPMgOLN crystal with a grating period of 31.2 μm is operated at 148 oC, the dual OPOs generate an identical mid-IR laser of 2.83 \mum. The secondary OPO transforms into an optical parametric amplifier, in which different frequency mixing from the signal laser results in the amplification of the idler laser in the first OPO. TOPO is a useful configuration for multiple laser output, broad tuning range, and high-efficiency mid-IR lasers.

A new approach to realize high-energy and high-power stimulated Brillouin scattering phase conjugation mirrors (SBS-PCMs) is described. The reflectivity of SBS-PCM is investigated under a 10-Hz repetition rate and a high energy load. The relationship between reflectivity and input energy is examined experimentally with different PCM structures, focus lengths, and medium cell structures. A medium cell with a circulating structure is designed, and its advantage is demonstrated through an experimental comparison with traditional PCM structures. The 30-cm focus lens and 150-cm collimation lens are optimized when the input energy reaches 1010 mJ at 10-Hz repetition rate. Therefore, a reflectivity of 84.7% and a higher energy load using the circulating two-cell structure are achieved.

A new concept to realize negative refractive index in non-resonance spectrum using chiral metamaterial is proposed. A low-index metamaterial is added to diminish the effective refractive index of the combined structure. Simulation and material parameter retrieval procedures are carried out to determine material performances. Results show evidence of negative refractive index and strong optical activity in the new chiral metamaterial.

Using LiF and YF3 as starting materials, we prepare feed material from fluorides according to the molar ratio of LiF:YF3 = 51.5:48.5. The anhydrous LiYF4 polycrystalline material is synthesized via the fluoridation process with a dried HF flow at elevated temperature. By charging the feed material and adding a small amount of active carbon powder in a sealed platinum crucible, the crystal can be grown via the vertical Bridgman method in a nonvacuum atmosphere. This is possible because the oxidization and volatilization of the melt is avoided. Using optimum conditions, that is, a growth rate of 0.5–0.6 mm/h and a temperature gradient of 25–30 oC/cm across the solid-liquid interface under a furnace temperature of 920–930 oC, the colorless crystal LiYF4 with the size of \phi 25 \times 50 (mm) is successfully grown. The optical transmittance of the crystal is as high as 85% above the absorption edge at 190 nm. The induced absorption bands are observed below 700 nm in the transmission spectrum after the crystal is subjected to a high dose of \gamma-ray irradiation.

A fluorescence molecular tomography system for in vivo tumor imaging is developed using a 748-nm continuous wave diode laser as an excitation source. A high sensitivity cooled charge-coupled device (CCD) camera with excitation and emission filters is utilized to obtain the excitation and fluorescence images. The laser beam performs fast raster scanning using a dual-axis galvanometric scanner. The accuracy of the laser spot position at the source window is within +-200 \mum. Based on the phantom experimental results, the spatial resolution is less than 1.7 mm, and the relative quantitation error is about 10%. In vivo imaging of a tumor-bearing nude mouse tagged with near-infrared dye demonstrates the feasibility of the system.

A new method for characterizing living tissue cells is demonstrated using both phase and amplitude information derived from the spectrally resolved interferogram in a single measurement. The effect of the light source spectral distribution can be cancelled out with the help of the zero order spectrum of the Fourier transform of the interferogram. The ratio of amplitudes between the two interference beams is acquired without this effect. The group delay, the first and second order dispersions, and the absorption, etc., for the full wavelength range can be measured. The results of the culture medium and the HeLa living cells are given. In addition, the measured values of d2n/d \lambda 2 and absorption of the distilled water are also provided for comparison.

All-reflective optical systems, due to their material absorption and low refractive index, are used to create the most suitable devices in extreme ultraviolet lithography (EUVL). In this letter, we present a design for an all-reflective lithographic projection lens. We also discuss its design idea and structural system. After analysis of the four-mirror optical system, the initial structural parameters are determined, the optical system is optimized, and the tolerances of the system are analyzed. We also show the implementation of optimal layout and desired imaging performance.

Steering accuracy is limited by the quantized phase modulation values and the number of phase pixels for spatial light modulators (SLMs). Conventional methods of beam steering lack optimum precision. In this letter, a beam steering approach based on horizontally moving phase steps is proposed. Compared with the conventional methods, this novel method is able to reduce the maximum normalized steering error in SLM significantly by a factor proportional to the number of pixels. In addition, steering errors of high steering angles can be drastically reduced by a factor proportional to the product of the number of pixels and the quantized phase levels; the number of high-precision steering angles increases with the number of pixels or the quantized phase levels increasing.

A mathematical model for the spectra of monocolor light-emitting diodes (LEDs) and phosphor-coated white LEDs at different drive currents is established. The simulation program of the color rendering of a white light LED cluster is developed based on this model. The program can predict not only the spectral power distribution and color rendering index (CRI), but also the number of LEDs, drive currents, input power, and luminous efficacy of a white light LED cluster at a given color temperature according to the requirement of the luminous flux. The experimental results show that the relative spectral power distributions (SPDs) and chromaticity coordinates of the model LED are very close to that of the real LED at different drive currents. Moreover, the correlated color temperature (CCT), CRI, special color rendering index (R9) luminous flux, input power, and luminous efficacy of the white light LED cluster predicted by simulation are also very close to the measured values. Furthermore, a white/red cluster with high rendering (CCT = 2903 K, CRI = 91.3, R9 = 85) and a color temperature tunable warm-white/red/green/blule LED cluster with high rendering (CCT = 2700?6500 K, CRI > 90, R9 > 96) are created.

The interaction between polychromatic fields and atoms is an important subject in quantum optics. Frequency locking for small frequency interval multi-field is usually required in some experiments. In this letter, we experimentally demonstrate a holistic scheme for bichromatic laser frequency stabilization. Compared with traditional saturation absorption methods and complicated frequency shift schemes, offset locking for bichromatic fields is simply achieved using polarization spectroscopy and Doppler effect. Frequency locking with a wide-range asymmetry of the detuning is also shown. Our scheme makes laser spectroscopy experiments with polychromatic fields more convenient.

We establish a single diode laser sensor system to obtain temperature and water concentration in CH4/air premixed flame. Line-of-sight properties are analyzed, but line-of-sight results are not path average values for temperature measurements. The measurements are performed on a flat burner based on scannedwavelength direct absorption spectroscopy using two adjacent water lines at 7153.75 and 7154.35 cm?1. Real-time results are acquired using a data acquisition card with a Labview data processing program. The standard uncertainties of the temperature and water concentration measurements are 2.3% and 5.1%, respectively.

Reflection filters have various applications in optical communication and other systems. In this letter, we propose a narrowband high-reflection filter composed of dielectric and metallic layers, in which an optimized filter combined with an admittance-matching layer with broad stop band is achieved. The structure can be expressed as Sub j (HL)13H2L(HL)313Cr0.84H j air, with full-width at half-maximum (FWHM) bandwidth of 2.5 nm. Based on this structure, reflection filters with multi-peaks are presented, and the law of distribution of peak positions is drawn.

The cellular Yule-Nielson spectral Neugebauer (CYNSN) model to characterize a typical CMYK (i.e., cyan, magenta, yellow, and black) 4-ink color printer is presented. By reconstructing spectral reflectance, models with high accuracy of spectral and colorimetric predictions are built. A novel cell-searching algorithm is proposed and used together with the iteration method to invert the cellular Neugebauer model efficiently. Large numbers of high quality hardcopy samples are produced to evaluate model performance and prove the feasibility of the algorithm. The spectral-based model performs better compared with the usual model based on CIE1931 XYZ tristimulus values.

Some mathematical and conceptual errors contained in a recent letter [Chin. Opt. Lett. 7, 938 (2009)] are pointed out.

This is a reply to the recent comment by Lifeng Li on the paper "Focusing of high polarization order axially-symmetric polarized beams [Chin. Opt. Lett. 7, 938 (2009)]". We analyze the errors pointed out by the comment, further perfect the mathematical expressions, and present a numerical simulation at last.