2012 Vol. 5, No. 5
Conventional semiconductor lasers suffer from the scale of the diffraction limit due to the light to be confined by the optical feedback systems. Therefore, the scales of the lasers cannot be miniaturized because their cavities cannot be less than the half of the lasing wavelength. However, lasers based on the Surface Plasmon Polaritons(SPPs) can operate at a deep sub-wavelength, even nanometer scale. Moreover, the development of modern nanofabrication techniques provides the fabrication conditions for micro- or even nanometer scale lasers. This paper reviews the progress in nano-lasers based on SPPs that have been demonstrated recently. It describes the basic principles of the SPPs and gives structures and characteristics for several kinds of nanometer scale lasers. Then, it points out that the major defects of the nanometer scale lasers currently are focused on higher polariton losses and the difficulties in fabrication and electronic pumping technologies mentioned above. Finally, the paper considers the research and application prospects of the nanometer scale lasers based on the SPPs.
This paper demonstrates theoretically that a Raman gain grating can be formed in an ultracold atomic medium driven by a standing wave and a probe field. Due to the spatial modulation of active Raman gain, the weak probe field propagating along the direction normal to the standing wave can be diffracted into the first-order direction effectively, and the zero-order diffracted beam is also amplified. Under manipulation by a microwave field, the first-order diffraction efficiency can be improved to be higher than that of electromagnetically induced phase grating. This system can be used as a highly efficient switch for an all-optical network.
The first-order astigmatism-free conditions in a crossed Czerny-Turner (C-T) structure spectrometer are derived in this paper and the optical parameters determined for a relative aperture of 1: 8 and a working range of 780 nm to 1 014 nm. An astigmatism-free crossed C-T spectrometer is built up with ZEMAX software, and a corresponding coma-free crossed C-T spectrometer is also built up for the comparison. The initial structures for the two types of crossed C-T optical systems are then optimized, and the performance merits are compared. It is shown that the astigmatism-free crossed C-T structure has superior optical performance with an RMS for the spot diagram only 12% to 52%, compared with that of the corresponding coma-free C-T structure over the working range. This indicates that the astigmatism-free crossed C-T structure possesses not only a better energy concentration along the slit direction, which is beneficial to spectrometers requiring larger condenser capacity, but also a smaller spot diameter along the direction perpendicular to the slit indicating that a higher spectrum resolution is achievable.
In order to maintain the dynamic stability of a Deep Ultra-Violet(DUV) lithographic projection objective, a kinematic supporting structure which is able to eliminate the effects of temperature change and external strain is designed. The lens surface deformation due to temperature variation and external strain is studied. Firstly, the theoretical formula for the compliance of a supporting seat is derived, then the radial compliance of the supporting seat is calculated by using the derived formula and is compared with the results of the whole supporting seat from a Finite Element Analysis(FEA) analysis. The lens surface profile variation due to temperature change and external strain is analyzed and the supporting structure is compared with a 3-point glue supporting structure. The calculated results indicate that the absolute difference between the radial compliance obtained from the derived formula and the FEA simulation is within 2.2%, RMS values of the optical surfaces are less than 0.36 nm with a 0.1 ℃ temperature rise, and the RMS values of the optical surfaces are less than 0.05 nm for a manufacturing tolerance is 5 m. Compared with the 3-point glue suporting method, the kinematic supporting structure can eliminate the effect of temperature change and outside strain on the lens surface.
The Liou-Brennan eye model is constructed using the optical design software ZEMAX. The Depth of Focus(DOF), extended Intraocular Lenses(IOL) that includes aspherical IOL, refractive multifocal IOL and diffractive multifocus IOL are included in the design. The optical performance of the pseudophakic eye for the designed IOLs is analyzed for both the spot diagram and visual acuity. For the pseudophakic eye with a 3 mm pupil, when the spherical aberration is fully corrected by the aspherical IOL, the best visual acuity reaches 1.2 with a DOF of only 1.4 m-1. When the spherical aberration is 0.4, the best visual acuity is 0.9 with a DOF as high as 2.2 m-1. With the implantation of refractive or diffractive multifocus IOLs, the pseudophakic eye has fairly good distant and near vision, while the intermediate vision is lower than 0.5. Diffractive multifocal IOL allows 81% input energy to image and the energy distribution is not affected by the pupil size. The energy distribution of the refractive multifocal IOL is dependent on the pupil diameter. The aspherical IOL, refractive multifocal IOL and diffractive multifocal IOL can extend DOF after surgery. However, they all have advantages and disadvantages, which should be taken into consideration under clinical conditions.
The spectra of Light Emitting Diode (LEDs) with different colors and powers are measured with a photometric, chromatic and electric characteristic analyzer, and then a new model consisted of several Gaussian distribution functions is used to represent the spectra of LED. Meanwhile, the model coefficients are calculated through the LED spectra in a rated current. It is shown that an expression with 3n Gaussian distribution functions is proper to represent the LED's spectrum of n peaks. The errors between the established model and the actual spectra of high power LEDs of red, yellow, blue, green and white color are 3.45%, 1.01%, 2.33%, 4.65% and 2.49%, respectively. For the low-power LEDs, the errors are 2.61%, 2.65%, 3.77%, 2.87% and 2.48%, respectively. Compared with the reported models, the established model has characteristics of high precision and good universality. This study is very important to design the photometric, chromatic instruments or the intelligent products of LEDs.
A lens for a Light Emitting Diode (LED) rear turn lamp of motor vehicles is designed to increase the accuracy of light distribution and energy efficiency of the lamp. According to the nonimaging optical principle and Snell's law, the lens design is obtained by an iterative solution, and the height and the diameter of the lens are 8.32 mm and 12.64 mm, respectively. By using the optical software TracePro, the LED and the lens of rear turn lamp are traced and simulated. The results show that in a rectangular range from -80? to 80? in the x direction and from -80? to 80? in the y direction, the luminous intensity is greater than 1.6 cd. Moreover, in the rectangular range from -20皌o 20癷n the x direction and from -10皌o 10癷n the y direction, the luminous intensity distribution is approximatly rectangular, and the luminous intensity of each test point meets the requirements of GB17905-2008. The lens can control the LED light precisely, which is beneficial to improve the performance of the light distribution and energy efficiency of the rear turn lamp.
To calibrate the test instrument of a Head-Mounted Display(HMD), a standard HMD optical system with a simple configuration and ascendant optical performance is proposed. In the limited space avoilable, the optical system is designed with only a spherical surface and an on-axial scheme to meet the requirements of low distortion and high resolution. By the symmetry principle of optical design, most aberrations of the standard HMD system can be corrected synthetically. The standard HMD system is used twice so that the system has a sharp exit pupil. The standard HMD system has a designed for a 0.5 inch Cathode Ray Tube (CRT) with a field of view 30? and an exit pupil distance of 75 mm. The MTF at 30 lp/mm resolution across the entire field of view is more than 0.3, and the maximum distortion is less than 0.9%. The designed standard HMD has a simple layout and compact structure, and the obtained results confirm the feasibility of the new system.
A new method to design a wavefront-guided lens is proposed based on an individual eye optical model. The individual eye model is constructed, then by regarding the eyeball and the wavefront-guided lens as a single system. For the lens-eye system, the surface profiles of the lens are determined by optimizing the lens design. In addition, the visual performance of the lens-eye system is analyzed for both ?7? field of view and ?20? rotation of the eyeball. In comparison with the results from wavefront fitting, the prescription difference in defocus, astigmatism and in the axis of astigmatism are (-0.057?0.015) m-1, (0.015?0.013) m-1, (0.100?0.316)?, respectively. Furthermore, the visual acuity of the lens-eye system is above 1.25 because of the correction of the wavefront-guided lens. The visual acuity for the eight eyes is as high as 1.5. For a field of view of 0?, the performance for the eye without rotation is better than that of eyes with a rotation of 20?. However, for a field of view of 7?, the performance for eyes without rotation is much better than that of eyes with a rotation of ?20?. Experiments show that the prescription of the wavefront-guided lens from the new method is objective and reliable and it is possible to predict the visual quality of the eye with the wavefront-guided lens.
A combined reflector for Light Emitting Diode(LED) street lamps is designed to produce a rectangular light spot and uniform lighting in the road, as well as having a simple structure and high light efficiency. Based on the principles of non-imaging optics and mechanical design software, a segmented compound parabolic reflector was designed. The reflecting beams of light from the reflector have an approximately rectangular distribution while the light efficiency can reach 96%. The analysis and simulation results show that the uniformity of illuminance can reach 0.5 over an area of 10 m?30 m when the LED lamp is installed at a height of 10 m. The reflector design when applied to shaping the LED beam into the rectangle shape has a high optical efficiency and low costs. The simulation results show that it can satisfy the current requirement for road lighting.
A chromatic corrector with two refractive-diffractive hybrid elements is designed for a wide field-of-view of 14 to correct chromatic aberrations in human eyes. The performance of the corrector based on several optical criteria is compared with a chromatic corrector with single refractive-diffractive element. Results show that both correctors can correct for Longitudinal Chromatic Aberration(LCA). However, it is demonstrated that the chromatic corrector with a single element introduces serious eccentric Transverse Chromatic Aberration (TCA) that increases from 14.61 m to 81.4 m. This deteriorates the image quality at the edge field-of-view. On the chromatic corrector with two refractive-diffractive elements, both the LCA and the TCA can be corrected and the TCA is just 1.64 m. The designed chromatic corrector can be used to improve the retinal image quality and has potential applications in the design of visual instruments.
A sensitive Z-scan measurement system using a femtosecond Nd: YAG laser(800 nm) as the excited light and based on Labview is reported. Under the control of Labview, the digital oscilloscope TDS3012 and the micro-translation stage are used to measure the light intensity, and the Z-scan function is realized. By taking a 800 nm fs laser from a Nd: YAG fs amplifier as a detecting light, the two transmittance intensities of light is measured by passing it through a thin nonlinear sample with a digital oscilloscope. Then both the nonlinear refractive index and nonlinear absorption coefficient can be obtained. The nonlinear absorption coefficient of Rhodamine 6B at 800 nm was measured. The results produced a two-photon absorption cross-section of 6.8 GM(GM=10-50 cm4 s photon-1 molecule-1). The system is shown to be reliable by comparison of our measured results with the those obtained from other different measuring methods.
According to the idea of the position-self-stabilization of a ship, this paper proposes a position calculation arithmetic for an inertia platform based on coordinate conversion. This arithmetic calculates the position value between the inertia platform and the carrier in real time by coordinate conversion, then the value is used as a position stabilization controllable input to insulate the position interferece of the carrier and to stabilize the platform. The experimental result shows that the stabilities of the outer and inner frames for the platform are 0.1 mrad, and 0.3 mrad, respectively, which satisfies the index requirement of 1 mrad. The position calculation arithmetic for the inertia platform based on coordinate conversion availability solves the stabilization problem for the inertia platform carried by the car and also improves the cost of the entire stabilization system.
The response characteristics of a Fiber Bragg Grating(FBG) irradiated by high energy laser beams are investigated both theoretically and experimentally to explore the possible applications of the FBG to High Energy Laser(HEL) parameter measurements. The thermal response characteristics of the FBG irradiated by HEL beams are obtained by solving the heat transfer equation using certain approximations. The resonance wavelength information of the FBG is recorded with an interrogator. The experimental results show that the maximum resonance wavelength shift of the FBG changes linearly with the irradiating power density within a certain range, which agrees with the results of numerical simulation.