Transverse optical mode patterns for an RF excited Ar-He-Xe laser

Transverse optical modes for an RF excited Ar-He-Xe laser are studied both experimentally and theoretically. A diffraction model for a waveguide with a nonsaturable gain and refractive index gradients placed between two plane mirrors is formulated. The effects of gain and diffraction index gradients and of diffraction in free space are evaluated for typical experimental conditions. A direct comparison between theoretical mode patterns and experimentally measured ones at distances of 17 and 114 cm from the output mirror demonstrated a satisfactory agreement for various laser wavelengths and gas mixture compositions     

Extreme timing jitter reduction of a passively mode-locked laserdiode by optical pulse injection

Reduction of the timing jitter to less than that of the master laser pulses was achieved for a passively mode-locked laser diode stabilized by subharmonic-frequency optical pulse injection. Detailed investigation revealed that this phenomenon originates from the short-term stability of the mode locking frequency under passively mode-locking operation with suitable bias conditions of the saturable absorber and the gain sections     

Selective lasing of InGaAs quantum-wire array on a V-grooved GaAssubstrate by distributed optical feedback

Distributed-feedback (DFB) lasers were fabricated by using strained InGaAs quantum-wire (QWR) arrays on V-grooved GaAs substrates as an active grating. After characterizing the luminescence from the QWRs and parasitic quantum wells (QWLs), a DFB laser cavity incorporating such a QWR array with its emission wavelength matched to the Bragg wavelength was designed and fabricated. The wavelength selectivity of the DFB cavity was found to strongly support the QWR emission, and DFB lasing from QWR gain up to 145 K has been achieved under pulsed current. The emission from the parasitic QWLs was suppressed by the DFB filtering and the loss induced by coupling to radiation modes. The DFB cavity was shown to be essential for obtaining lasing from QWRs on V-grooved substrates     

The dynamic response analysis of a pyroelectric thin-film infraredsensor with thermal isolation improvement structure

Both theoretical and experimental studies of the substrate effect on the thermal behavior of a PbTiO₃ infrared (IR) sensor have been reported. With active cantilever dimensions of 200×100×5 μm³ formed by etching processes, the pyroelectric micro-electro-mechanical system (pyro/MEMS) structure exhibits a much superior performance to that of a traditional IR-sensing bulk structure under the 800-μW incident optical light with wavelength of 970 nm. Two-order improvement in current responsivity is obtained for the pyro/MEMS structure. This shows the substrate effect on the performance of a pyro/MEMS IR sensor is very significant. A simple model has also been proposed to illustrate the substrate effect more comprehensively     

钛宝石激光泵浦的1.06μm和1.34μm高效连续掺钕氟钒酸锶激光器

利用钛宝石激光作为泵浦源,实现了掺钕氟钡酸锶（ＮｄＳＶＡＰ）晶体在１．０６μｍ和１．３４μｍ的高效连续激光运转。在１．０６μｍ和１．３４μｍ处得到的最低泵浦阈值分别为２ｍＷ和２．４ｍＷ,最高斜效率分别为４９．４％和３７．４％,最大输出功率分别为３３６ｍＷ和１６５ｍＷ。     

Real-time 3-D model-based navigation system for endoscopicparanasal sinus surgery

This paper presents a three-dimensional (3-D)-model-based navigation system for endoscopic sinus surgery treating paranasal sinusitis. Endoscopic surgery is becoming more common because of its low invasiveness. Its problem with disorientation, however, is one of the toughest barriers for the novice and may lead even an expert to commit serious surgical errors, e.g., causing cerebrospinal fluid (CSF) leakage or blinding the patient. To prevent such complications and optimize training, the authors' system aids in navigation by showing a single perspective view of the patient and the endoscope models. This virtual endoscope has a viewing cone with a simulated light to indicate the viewing direction and visual field in real-time. The system's three clipping planes automatically follow the endoscope and help keep the surgeon aware of the endoscope's actual position. An experiment comparing the system to conventional navigation using a triplanar display showed that the perspective view was referenced very frequently, giving a positive impressions, while the triplanar display was almost completely ignored, apparently because it was too difficult to interpret immediately     

Dynamic channel allocation in interference-limited cellular systemswith uneven traffic distribution

Most recently proposed wireless dynamic channel allocation methods have used carrier-to-interference (C/I) information to increase the system performance. Power control is viewed as essential for interference-limited systems. However, the performance of such systems under an imbalance of load among cells, as may occur often in microcells, is largely unknown. Here, we study a typical interference-limited dynamic channel allocation policy. Calls are accepted if a channel can be assigned that will provide a minimum C/I, and power control and intracell handoffs are used to maintain this level. We focus on the relationship between system performance and the amount of imbalance in load among neighboring cells. Previous studies for systems that do not use C/I information have found that dynamic channel allocation (DCA) outperforms fixed channel allocation (FCA) in all but heavily loaded systems with little load imbalance. We present two principal new results. First, we find that with use of C/I information, the difference in performance between FCA and DCA (in terms of throughput or blocking probability) is increasing with load imbalance. DCA was found to be more effective in congestion control at the cost of a slightly lower call quality. Second, we find that use of power control to maintain a minimum C/I results in two equilibrium average power levels for both DCA and FCA, with DCA using a higher average power than FCA, and that while DCA's power is increasing with load imbalance, FCA's average power is decreasing with load imbalance     

Acoustooptic modulator using the Stark effect and stress-inducedbandgap changes

An analysis of the semiconductor multiple-quantum-well (MQW) acoustooptic modulator is performed. The strain and electric-field components generated by surface acoustic waves (SAW's) in a multilayered semiconductor piezoelectric structure are presented. The effects of a SAW propagation on the modulator optical parameters are studied. Two kinds of SAW effects in the modulator structure are taken into account: the variation of the excitonic energies of the MQW due to strain and the companion electric field generated by the SAW is determined. The hole's effective mass change induced by the SAW is analyzed and included in the Schrodinger equation. The optical absorption coefficient spectra of the modulator as a function of the SAW power is presented. Experimental results concerning optical absorption variations of quantum-well structures produced by various SAW powers are shown     

Waveguide polarization-independent optical circulator

We fabricated a new type of waveguide polarization-independent optical circulator which does not need a polarization-beam splitter. The circulator is based on a non-reciprocal Mach-Zehnder interferometer which consists of two waveguide Faraday rotators, two thin-film half-waveplates and two planar lightwave circuit-type 3-dB couplers. The fabricated circulator provides a 14.0-23.7-dB isolation and a 3.0-3.3 dB insertion loss at λ=1.55 μm. This circulator presents a new possibility for developing non-reciprocal devices in the field of integrated optics     

Transverse-junction-stripe GaAs-AlGaAs lasers for squeezed lightgeneration

We fabricated 850-nm GaAs transverse-junction-stripe (TJS) lasers by an improved metal-organic chemical vapor deposition (MOCVD) and double Zn diffusion process. The high V/III ratio used during the MOCVD growth significantly reduced the intermixing of GaAs active layer and AlGaAs cladding layers. The modified process realized good confinement for both carriers and photons and smaller saturable loss. We measured squeezing of -2.8 dB (-4.5 dB after correction for detection efficiency) at a pumping rate of I/I_th≈20 from these lasers, which is in close agreement with the theoretical limit. This squeezing remained unchanged under injection locking, indicating almost perfect conservation of the intensity noise correlation among the longitudinal modes. These TJS lasers had very small low-frequency 1/f noise