Optical Review

Published by Springer Verlag
Online ISSN: 1349-9432
Print ISSN: 1340-6000
Publications
Log relative sensitivity (quanta delivered to the cornea) is plotted as a function of age for mechanisms dominated by either S-(unfilled squares), M-(filled circles), or L-(unfilled circles) cone mechanisms. The data are normalized arbitrarily along the sensitivity axis for each cone mechanism. Least-squares linear regression lines are shown for each cone type. [Data from Werner and Steele 19 ].  
Wavelengths of the spectral unique hues plotted as a function of age for 0.95° diameter, foveally-viewed stimuli (7.1 cd·m −2 ). Solid lines are based on a least-squares linear regression equation. [Data from Schefrin and Werner 38 ].  
Proportion of blue (filled symbols) and green (unfilled symbols) responses to 40 simulated Munsell chips presented on a computer screen are plotted as a function of ocular media density. The slopes of the least-squares linear regression lines did not differ significantly from zero. The range shown here spans the lowest values typically found in an adult population to values typically diagnosed as early-stage cataract. [Data from Hardy, Frederick, Kay and Werner 49 ].  
Locus of the achromatic point for one observer as a function of time before and after cataract extraction plotted in CIE x,y coordinates. The dashed lines cross at equal-energy white. [Data from Delahunt, Webster, Ma and Werner 50 ].  
The human visual system undergoes continuous anatomical, physiological and functional changes throughout the life span. There is also continuous change in the spectral distribution and intensity of light reaching the retina from infancy through senescence, primarily due to changes in the absorption of short-wave light by the lens. Despite these changes in the retinal stimulus and the signals leaving the retina for perceptual analysis, color appearance is relatively stable during aging as measured by broadband reflective or self-luminous samples, the wavelengths of unique blue and yellow, and the achromatic locus. Measures of ocular media density for younger and older observers show, indeed, that color appearance is independent of ocular media density. This may be explained by a renormalization process that was demonstrated by measuring the chromaticity of the achromatic point before and after cataract surgery. There was a shift following cataract surgery (removal of a brunescent lens) that was initially toward yellow in color space, but over the course of months, drifted back in the direction of the achromatic point before surgery. The spatial characteristics of color mechanisms were quantified for younger and older observers in terms of chromatic perceptive fields and the chromatic contrast sensitivity functions. Younger and older observers differed with small spots or with chromatic spatial gratings near threshold, but there were no significant differences with larger spots or suprathreshold spatial gratings.
 
We present a simple model of the pulse-frequency-modulation (PFM) photosensor that provides explicit relationships between circuit parameters and output characteristics. The model treats the PFM photosensor with a feedback loop as an open loop circuit. Several characteristics such as output pulse frequency for light intensity and photosensitivity are expressed by device parameters of a photodiode, reset transistor, and chain of inverters. The relationships derived from the proposed model help us to comprehend the results by simulation program with integrated circuit emphasis (SPICE) or experiments. We design and fabricate a 128 x 128-pixel PFM image sensor with photosensitivity of 0.15 Hz/lux. As a demonstration, a figure of a dinosaur is captured using the fabricated image sensor to discuss its operation. Characteristics of a normal pixel and white and black defect pixels are measured and discussed based on the results of formulations.
 
We propose a dual focus optical head with a holographic optical element (HOE) which corrects spherical aberrations in order to read both 0.6 mm disks and 1.2 mm disks. The thin disks are read using transmitted light and the thick disks are read using +1st order diffracted light of the blazed HOE. The good quality of the focused spots and the focusing error signals was experimentally confirmed. No influence of unnecessary diffracted light was observed.
 
Sony and Philips have recently developed the basic technology for a 22.5 GB optical recording system, based on a blue laser (#x03BB; = 405 nm) and high numerical aperture (NA = 0.85) objective lens. This system is referred to by the acronym DVR (for Digital Video Recording). In this paper we describe the relization of a compact optical pickup unit capable of writing and reading data on disc according to the DVR format.
 
Phase holograms processed with a reversal bleaching is considered to have lower diffraction efficiency than those processed with other bleaching methods. The high diffraction efficiency could also be obtained in the reversal bleach under the adjustment of developer component. This paper shows that must have been optimized the type and the concentration of developer component in order to obtain the high diffraction efficiency. Experiments were carried out with Slavich PFG-01 plates on the processing of transmission holograms and the four types developer used with reversal bleach. The developer is composed of 1-ascorbic acid, metol, phenidone, and sodium carbonate contained with different amounts. The maximum diffraction efficiency of 89% was obtained.
 
In this paper we present the design of a modified hexagonal photonic crystal fiber (PCF) having high birefringence and a near-zero flattened dispersion. Using the finite-difference method (FDM), it is shown that the proposed multiple Gedoped core hexagonal PCF exhibits a high birefringence of order 10−3 and a nearly zero flattened dispersion in the optical coherence tomography (OCT) waveband. In addition, the proposed PCF has a confinement loss of less than 10−8 dB/m at 1.06 μm. PCFs with such properties are considered suitable for both endoscopic OCT and other experimental setups employing 1.06 μm lasers. Keywordsphotonic crystal fiber (PCF)-birefringence (B)-dispersion (D)-confinement loss (L C )-optical coherence tomography (OCT)-finite difference method (FDM)
 
To eliminate the temperature dependence of narrow-band filter, a three-dimensional athermal waveguide of which optical path length is independent of temperature was developed at 1.3 μm wavelength. The temperature coefficient of the refractive index of films made of glass materials was measured at this wavelength, and a strip-loaded athermal waveguide was designed using a scalar finite element method. The temperature coefficient of optical path length was successfully decreased to 9.65X10-9[/K] (0.1% of the conventional waveguide).
 
Temperature stability of the threshold current and the lasing wavelength is investigated in a 1.3-μm GaInNAs/ GaAs single quantum-well laser. The measured characteristic-temperature was 88 K. The small wavelength shift per change in temperature of 0.35 nm/C was obtained, indicating the superior lasing-wavelength stability. Therefore, it is shown experimentally that GaInNAs is very promising material for the fabrication of light source with excellent high-temperature performance for optical fiber communications.
 
Less than 100ps, polarization-independent switching operation of an active birefringent optical fiber loop filter using 1.3 μm control optical pulses as well as a 1.3 μm semiconductor optical amplifier (SOA) has been demonstrated. In the proposed SOA-based active birefringent filter operating at 1.55 μm wavelength, 1.3 μm SOA is employed to control the polarization-mode dispersion in the loop part. By injecting 1.3 μm ps gain-switched optical control pulses into the SOA, 1.5 μm input signals can be switched from the transmission port to the reflection port with less than 100 ps rise time.
 
A multi-quantum-well (MQW) active layer has been introduced to 1.3-μm GaInAsP/InP surface-emitting (SE) lasers. Room temperature pulsed operation of a 1.3-μm MQW SE laser was obtained for the first time and its threshold current was 15 mA. CW (continuous wave) operation up to 7C (threshold current 1th=7.6 mA at 7C) was achieved.
 
Temperature sensing using 1.54 μm fluorescence at the transition between the energy levels4I15/2 (ground state) and4I13/2 generated in an erbium-doped fiber with 1.48 μm pumping is proposed. The fluorescence has a peculiar spectral profile that possesses two peaks around 1.530 μm and 1.552 μm wavelengths. The temperature-dependent fluorescence is investigated in the temperature range between -50°C and 90°C. The power ratio between the two peaks increases with an increase in temperature. The sensitivity of the ratio is 0.007/°C on average in the measured temperature range. The total fluorescence power and the absorption loss at λ = 1480 nm in the fiber decrease as the temperature increases. Optical fiber temperature sensing immune from the fluctuation in pumping power can be performed using the peak power ratio and/or the absorption loss.
 
Characterization of an ultra-low loss and high finesse Fabry-Perot cavity at 1064 nm is reported. The characteristics are obtained from measurements of cavity decay time, frequency response and transmission efficiency. The results show that the mirrors have the loss of 1.5 ppm including absorption and scattering losses and the reflectance of 99.9873% which corresponds to a cavity finesse of 2.48×104. Fabry-Perot cavity, mirror, finesse, scattering loss, absorption loss, reflectance, transmission efficiency.
 
A Mie hdar system with an eye-safe wavelength of 1.54 m was developed and its performance characteristics were experimentally discussed. The wavelength was generated by a Nd:YAG based methane-shifted Raman laser. The collected backscattering light was detected by an InGaAs avalanche photodiode working in photon counting mode at that wavelength. Results of atmospheric observation showed clearly the dynamics of multi-layered cluds up to an altitude of 7 km. The systems performance was confirmed on the point of signal to noise ratio in both the observation and the simulation. Advantages of the eye-safe 1.54 m wavelength in lidar atmospheric research and system limitations were discussed. 2004 The Optical Society of Japan
 
We have calculated the characteristics of reflected near infrared light, which is incident on the skin surface, scattered in the skin tissue and detected, in the wavelength range from 1000 nm to 1900 nm. We have used a Monte Carlo method to calculate the propagation path, the average photon visit depth, the average photon path length, etc. for the cases of short source-detector distances, to which the isotropic scattering approximation cannot be applied. An experiment to validate the simulation results was also conducted using a liquid phantom.
 
In today's digital age, digital projectors and their application are gaining in significance, especially in the home theater area where the projected area is more than hundred inches. More attention has to be paid to the design of these than of ordinary data projectors due to the enhancement of both definition and contrast for home theater projectors. This complicates the optical design of the projector, especially in 1080 P flat plane panel resolution requirements with strong offset of 130%, whose semi-image height (18.6 mm) is very close to that of 35 mm film (20 to 21 mm). In this paper the lens design samples focus on the application of a projector with a 1080 P digital micromirror device (DMD) system with 10.68 μm per pitch. Such lenses have the telecentric design on the image side because of the total internal reflection (TIR) prism. The complicated design is the reason for this: firstly, there must be a very long back focal length due to the huge TIR prism and zoom mechanical system; secondly, there is an extremely relative luminance requirement (70% minimum) at semi-image height (18.6 mm); thirdly, there are difficulties in the elimination of lateral aberration due to the limited choice of glass and, fourthly, there is a 2 × zoom ratio with modulation transfer function requirement of 40% at 501p/mm at a semi-image height of 18.6 mm minimum and, most important, limited total overall length. The lens design with 2 × zoom ratio for 1080 P resolution was presented with great success; the optimal calculation of lateral chromatic aberration via genetic algorithm (GA) was introduced in this research and then a local minimum of lateral color aberration was identified.
 
A high-power singlemode Raman fiber laser (RFL) with maximum output power of 4.11 W and maximum power conversion efficiency of 47.40% at 1239 nm is realized using continuous wave 8.4 W Yb-doped double-clad fiber laser as a pump, 700 m phosphosilicate fiber, and a Raman cavity formed by a pair of fiber Bragg grating mirrors at 1239 nm. The output characteristics of the RFL at 1239 nm for different fiber lengths and output mirror reflectance are reported. Theoretical simulation is done to numerically optimize for fiber length and output coupler reflectivity to obtain maximum first Stokes power.
 
In this paper, a vision chip for edge detection based on the structure of biological retina is introduced. The key advantage of retinal structure is speed of operation. However, bio-inspired vision chips have suffered from low resolution which is caused by their complex circuit structure. To sufficiently improve the resolution for real application, the circuits for analog processing were separated from circuits for image capturing. In addition, we compensated the low speed problem of operation which is caused by bottleneck of data transfer between photo-sensors and analog processing circuit by adding a reset decoder. The vision chip was fabricated using 0.35 μm 2-poly 4-metal complementary metal---oxide---semiconductor technology. Using the vision chip, we could obtain a contrast-enhanced image without any other cost-increase for fabrication of chips. Then, the edge image was easily achieved by thresholding the previous contrast-enhanced image.
 
A complementary metal oxide semiconductor (CMOS) image sensor for the detection of modulated light under background illumination has been developed. When an object is illuminated by a modulated light source under background illumination the sensor enables the object alone to be captured. This paper describes improvements in pixel architecture for reducing fixed pattern noise (FPN) and improving the sensitivity of the image sensor. The improved 128 × 128 pixel CMOS image sensor with a column parallel analog-to-digital converter (ADC) circuit was fabricated using 0.35-mm CMOS technology. The resulting captured images are shown and the properties of improved pixel architecture are described. The image sensor has FPN of 1/28 that of the previous image sensor and an improved pixel architecture comprising a common in-pixel amp and a correlated double sampling (CDS) circuit. The use of a split photogate increases the sensitivity of the image sensor to 1.3 times that of the previous image sensor.
 
An experimental and theoretical study of adaptive processing of non-stationary speckled waves by a dynamic reflection holographic grating formed in photorefractive (100) cut BTO crystal without applying external electrical field is presented.
 
Holographic properties of a 13-demethyl retinal bacteriorhodopsin (13-demethyl BR) film in gelatin matrix were investigated and compared to those of a native bacteriorhodopsin (BRWT) film. A two-wave mixing experiment was performed to study the self-diffraction efficiency of the samples. The rise and the decay of the grating in the 13-demethyl BR film was measured. The film is relatively slow enabling the recording of simultaneous gratings. Phase conjugate reflectivity was measured by a four-wave mixing experiment. Diffraction efficiency and phase conjugate reflectivity of the 13-demethyl BR film were observed to be comparable to those of the BRWT film.
 
A continuous wave (CW) high-power Raman fiber laser (RFL) with maximum output power of 2.24 W and slope efficiency of 32.8% at 1484 nm is obtained using a CW 8.4 W/ 1064 nm Yb-doped double-clad fiber laser as a pump, 700 m phosphosilicate fiber, and cascaded cavities with two pairs of fiber Bragg grating mirrors for the first and the second Stokes orders. Theoretical simulation of the RFL using a very efficient and rapidly converging collocation method is done to understand and optimize the fiber length to obtain maximum second Stokes power. RFL performance for the 300, 700 and 1150 m phosphosilicate fiber lengths was experimentally investigated by observing maximum output power, slope efficiency, threshold power, and full-width at half maximum at the second Stokes wavelength.
 
We constructed a polarization spectrometer based on a laminar grating applied with a Mo/B4C multilayer coating. The multilayer-coated grating had been previously evaluated to have high polarizance at around 6.7 nm (184 eV) due to the Brewster reflection. In this study the polarization spectrometer was found to be usable in a range from 150 to 190 eV. Using it, σ and π emission spectra in the B 1s emission from a CrB2 single crystal were separately recorded for the first time in the soft x-ray region. The spectral feature of the emission was reasonably well reproduced by the band calculation.
 
Nonlinear optical materials of the type Znx Cd1-x Te single crystals, where x = 0.0, 0.2, 0.4, 0.6, 0.7, 0.8, and 1.0, have been grown by the Bridgman method, using a vertical furnace. We have investigated the electro-optic (E-O) coefficient and refractive index of Znx Cd1-x Te single crystals at optical communication wavelength (1550 nm). In the case of CdTe crystal, the E-O coefficient was 15.5 × 10-12 m/V, which is the biggest among the E-O coefficients of Znx Cd1-x Te crystals. The E-O modulation signal was very big in low frequency range (DC-100kHz), but the signal amplitude became smaller as we increased frequency above 100 kHz. We also found the acousto-optic modulation at CdTe single crystals.
 
We made a parallel aligned liquid crystal spatial light modulator (PAL-SLM) respond within 6 ms to meet requirements for a single-SLM color projection system. This was done by adjusting thicknesses of its optical addressing layer and its light modulating layer.
 
180° mode phased array lasers with multiple stripes were systematically investigated for high-power, single lateral mode operation. Phased array lasers with a conventional loss guide structure were fabricated for 180° mode operation because the structure allowed the threshold gain of 180° mode to become smallest by introducing optical loss between stripes and outside the stripe region. It showed complete single lateral mode operation under pulsed condition. However, under continuous wave operation, phase-uncoupling occurred at the edge emitters as a result of the temperature distribution inside the stripe region. This was confirmed both experimentally and theoretically. To minimise the temperature distribution, dummy stripes were introduced outside the stripe region. The current in the dummy stripes did not cause lasing, but did increase the temperature of the edge stripes, which improved the thermal distribution inside the stripe region. As a result, complete single lateral 180° mode operation under continuous wave operation was attained.
 
This paper presents a high performance fiber-optic sensing system for analyzing the isozymes reaction of cytochrome P450 (CYP). In the inherent biological system of lifeguard against chemical toxicants, the enzymes metabolize such chemical species to safer formulae. As is well known, some particular types of CYP, such as CYP-1A, however, often trigger the cancer development process by selective activation of carcinogen. A new technique for medical diagnosis of cancer development at very early or even predictive stage may be achievable based on the evaluation of the activity of the enzymes related to the cancer development by using the present system. In order to demonstrate the potential of the system, CYP-1A induced in liver of living rats by medication using 2,3,7,8-tetrachloro-dibenzofuran (2,3,7,8-TCDF) is measured and curves revealing the fluorescent power transition for each concentration of toxicants are successfully observed with good sensitivity.
 
We propose a grating interferometer for step-profile altitude difference measurement. There are two main characteristics in this interferometer. The first is that the intensity distribution of the interference pattern is independent of the wavelength of the laser-diode used. No change of the intensity distribution occurs when the wavelength fluctuates. The second is that the measuring range is much larger than the wavelength of the light source because the spatial period of the grating is much larger than the wavelength. Sinusoidal phase modulating interferometry is easily applied to detect the phase variation of the interference pattern by vibrating the grating sinusoidally. The thickness of a 3.5-inch disk is measured with an accuracy of less than 0.5 μm.
 
An investigation was carried out on decay time of the 2.09 eV emission of S2–vacancy pair centers in NaCl crystals. When the crystal was excited by a pulsed 337 nm light from an N2 laser, the 2.09 eV yellow luminescence principally decayed with the lifetime of 14.2 μs at low temperatures, and exhibited a weak thermal quenching with an activation energy of 51.3 meV above about 150 K. Such S2--vacancy pair centers responsible for the 2.09 eV luminescence were thermally stable at room temperature, and not bleached even when exposed to ultraviolet lights below about 5 eV. Thus, the 2.09 eV emission center possibly can be used as a solid-state laser active center working at room temperature.
 
Optical components and systems with dimensions between 10 and 200 mm are discussed with specific examples of testing, simulation, and assembly methods. This size regime, which is conventionally classified with micro-optics, offers attractive possibilities for next-generation micro-optics packaging. However, optics in this regime suffer from few available testing and simulation tools. Several theoretical application examples are described, including a high-index solid immersion lens and a pickup for optical data storage. Challenges and solutions for design and simulation, testing, and assembly of such systems are also discussed.
 
Al0.25In0.04Ga0.71N 310 nm near solar blind ultraviolet (UV) metal-insulator-semiconductor (MIS) sensors with different SiO2 cap layer thickness were successfully fabricated. With appropriate SiO2 layer thickness, the dark current of AlInGaN sensors was notably suppressed from 1.88 × 10−6 to 1.91 × 10−9 A, and the photo-generated carriers still could reach the electrodes by tunneling through the thin SiO2 layer under the illumination. It could be clearly seen that cut-off occurred at around 300/310 nm while the responses above the bandgap were flat. KeywordsAlGaN-MIS-sensor-ultraviolet
 
Computer-generated image holograms are particularly useful for 3D-display applications. We discuss the properties of the reconstructions obtained with this hologram type. Conditions are given which must be fulfilled to ensure a disturbance free reconstruction. A new efficient algorithm is presented which implements the hidden surface effect for synthetic image holograms.
 
We propose an active triangulation based range-finding system that, besides its simplicity, has two advantages over similar existing systems. First, the system can acquire range data for large-depth objects since it generates an illumination pattern with large-depth of focus using Fresnel diffraction from a Ronchi grating projected over the entire object surface. Secondly, the system does not need preliminary recording of reference fringes since it displays simultaneously, on a single image, both reference and object deformed fringes. This system offers other properties: it is mechanically simple, uses everyday optical components, is low cost, can be operated via a PC and uses relatively simple image analysis software. Three dimensional reconstructions are illustrated for various objects having 10 cm maximum depth variations. The depth accuracy (typically 0.5 mm for an object located at 350 mm from the camera) is comparable with other systems, but a certain compromise has to be accepted in acquisition time (typically 1 minute). This system can find applications in research laboratories as a tool to provide range data with relatively good depth accuracy.
 
The frequency of a SHG of a high power laser diode has been stabilized to the 5s2S1/2#x2212;5p2P1/2 transition of 88Sr#x002B; at 421.671 nm using the differential detection of the absorption signal of a hollow-cathode lamp. The frequency fluctuation never exceeded 10 MHz. The fluorescence signal of 88Sr#x002B; ions was detected.
 
(Color online) Laser output power as a function of input pump power.
(Color online) Laser output spectrum as a function of pump power variation.
(Color online) (a) Output pulse width and (b) output spectrum at modulation frequency of 2.5 GHz in active mode- locking regime. 
By the use of installed fibers inside the city we demonstrated a 48.8 km ultralong Erbium-doped fiber laser in modelocking regime with repetition rate varying from 1–10 GHz. The shortest pulse duration of 42 ps at 2.5 GHz was obtained by optimization of intracavity dispersion. Keywordslasers-ultralong erbium fiber lasers-mode-locked lasers
 
Line-mixing coefficients of the NO-N2 system are calculated within the infinite-order sudden (IOS) and energy-corrected sudden (ECS) approximations. The so-called sum rule between the line width and the line-mixing coefficients is used for line-mixing calculation. Line widths calculated from the ECS model are in good agreement with experimental data for the 5.3 μm NO band. The band-correction function of NO, which characterizes the deviations from the superposition of Lorentz profiles, is also calculated. The ECS results as well as experimental data indicate strong sub-Lorentzian behavior in the wing of the R branch of the 5.3 μm NO band.
 
The shape of the spectral lines in the 5.3 μm fundamental band of NO perturbed by N2 was studied by means of an infrared spectrometer. Sub-Lorentzian line profile was observed in the wing of the R -branch. These deviations from the Lorentz shape can be mainly interpreted in terms of line mixing. To calculate line-coupling coefficients, the exponential gap law and the statistical exponential power gap law (SEPG) were used. In the case of the SEPG model the degeneracy factor dependence on the inelastic rate is also discussed. The influence of the slit width on the observed band-correction function was found to be small in the R -branch wing of NO.
 
Intracavity frequency doubling of a single-mode Nd:YAG laser using a nonplanar ring cavity is demonstrated. The nonplanar ring cavity consists of a Brewster-angled Nd: YAG crystal placed in a magnetic field, a KTP crystal, and two spherical mirrors. In this design the Nd:YAG crystal acts as both a nonreciprocal polarization rotator and a partial polarizer, and the nonplanar portion of the ring cavity, which is formed by a relative twist angle between the Brewster-angled end surfaces of the crystal, serves as a reciprocal polarization rotator. Eigenpolarization theory for the cavity configuration is presented and a suitable value of the relative twist angle for unidirectional operation is estimated. A single-mode output power of 22 mW at 532 nm is obtained with a 1.2-W diode laser at 809 nm and a laser linewidth of less than 100 kHz is inferred from a beat note frequency spectrum between two identical laser systems.
 
With recent advances in technology, diffractive lenses can be used for a variety of applications. In this paper, the diffractive lenses are treated on an athermal chart which is developed for refractive lenses. An athermalized hybrid single lens designed with the chart, operating in the 3-5 μm wavelength band is presented.
 
We developed a simple method of continuous wavelength sweep using a commercial laser diode (LD) without antireflection (AR) coating. A 630 nm AlGalnP LD was installed in a Littrow-type external cavity. In this cavity, the LD has the same effect as an etalon, and its free spectral range can be controlled easily by the LD drive current. By scanning the grating angle of the external cavity and LD drive current simultaneously, we obtained single-mode oscillation and continuous wavelength sweep of over 22 GHz without mode hopping. This technique is simple and inexpensive because it does not need AR coating on its output facet, and does not use a servo system which requires apparatuses such as a lock-in amplifier and local oscillator.
 
A CMOS image sensor that focuses on very low illumination applications is described. The sensor uses a 0.35 m 2-poly 4-metal standard CMOS process and is realized as a 64 64 array of 7.8 7.4 m2 active pixels with a fill factor of 33%. The unit pixel contains 3 NMOSFETs and a gate-body tied PMOSFET photodetector. The image sensor features highly sensitive characteristics because of the photodetector which has a maximum photo-responsivity of 2.5 102 A/W, and a pixel configuration with a voltage gain of about 1.3 and a pixel sensitivity of 1.2 10 V/lxs. Furthermore, this sensor has a well-defined output voltage at a very low illumination level of sub-10 lx, such as with a photo-sensitivity of 35mV/lx without adjusting gain and integration time.
 
AlGaInP laser diode structures with different ridge designs. 
Theoretical analysis for InGaP/AlGaInP laser diodes with different ridge waveguide structures is performed to investigate the lateral mode behavior using advanced device simulation. The internal physical mechanisms including temperature-induced changes in the refractive index profile, spatial hole burning effect, lateral carrier distribution, and gain profile variation with increasing input current are discussed by theoretical calculation to analyze the effects of different ridge structures on the lateral mode behavior of 660-nm AlGaInP laser diodes. The simulation results show that the use of narrow and shallow ridge geometry is the approach to obtaining single mode operation. Furthermore, it is found that the different values of the ridge height cause the lateral carrier distribution within the active region to be varied, which is also an important factor in determining the emergence of the first order lateral mode in addition to the geometry-dependent waveguide cutoff condition. Keywordssemiconductor lasers-optical properties-III–V semiconductors-numerical simulation
 
Stretched silver island multilayers have been investigated for patterned optical polarizers for the wavelength of 800 nm. Submicrometer-thick optical polarizing films are fabricated by stretching periodic multilayers consisting of silver island layers and Pyrex layers at the temperature of 660C. As the optical anisotropy of the optical polarizing film is lost by heating at a temperature higher than the stretching temperature, the fine non-polarizing areas can be deliberately and easily formed on the optical polarizing film by laser irradiation with high power density. We have successfully formed various non-polarizing areas on the optical polarizing film with a 1 W-class carbon dioxide laser. The demonstrated fabricating techniques of deliberately patterned optical polarizing films should be useful for novel optical computing and sensing devices.
 
We demonstrate an extension of forming a photorefractive volume grating in an Fe:LiNbO3 crystal by chirped intense femtosecond laser pulses generated from a Ti:Al2O3 regenerative amplifier at 1 kHz. We confirm that one-photon absorption is still dominant in the Fe:LiNbO3 crystal up to 70 GW/cm2. To generate a photorefractive grating at such a low laser repetition rate within a practical writing time, the laser pulse intensity is increased to >30 GW/cm2. Furthermore, we demonstrate the amplification of femtosecond laser pulses by the chirped volume grating that is written in the Fe:LiNbO3 by two-wave mixing. Keywordsultrashort laser pulse–photorefractive effect–holographic volume grating–two-wave mixing
 
Microlens-integrated 980 nm vertical-cavity surface-emitting lasers (VCSELs) were fabricated and their mode-stabilized operations investigated. A stable single fundamental transverse mode operation in the microlens-integrated VCSEL was observed. Numerical modal calculations accurately explain the effects of the microlens on mode stabilization.
 
Thin-film 850-nm vertical-cavity surface-emitting lasers (VCSELs) were improved in light output power by designing both the reflectivity of the distributed Bragg reflector on the light-emitting side and also the degree of de-tuning between the photoluminescence peak and the etalon wavelength. Thin-film VCSELs, which were fabricated on A1N substrates by a functional layer transfer technique, are attractive components for the hybrid integration of optoelectronic devices. Their maximum output power was 2.8 mW and their slope efficiency was 0.40 W/A for the 15μm diameter VCSEL devices that we studied. Uniform spontaneous emission over the entire mesa area, and a single transverse laser mode up to 1.3 times the threshold current were confirmed by observing the near-field images.
 
We propose a high-speed and parallel method to determine lens aberrations from its confocal axial response. This method analyzes the intensity confocal response including the aberration information of the objective lens by means of neural network algorithm. This method is designed to work parallely for many microlenses, and simultaneously determines aberrations of each element of a microlens array. A prototype system can determine spherical aberration coefficients of a microlens in the range from −0.7λ to 0.3λ with less than 1% RMS error.
 
To increase recording density in an optical disk system, a two-lens system which enlarge its numerical aperture (NA) has been developed. When NA becomes larger, however, the spherical aberration due to disk thickness error increases. We propose an optical pickup with a spherical aberration compensator using nematic liquid crystal (LC). Our LC device is composed of two LC cells each of which has X and Y stripe electrodes, respectively. We discussed how the spherical aberration due to the disk thickness error can be compensated by combination of two crossed cylindrical phase distributions induced by the LC cells, and confirmed the compensation effect in a design example by simulation. We have also fabricated the crossed stripe LC device actually, and have obtained the experimental result which shows that amount sufficient to compensate the aberration is achieved.
 
Experimental images from standard incoherent imaging system (a, b, & c,) and from focus-invariant optical/digital system (d, e, & f). (a,d) Geometrically in-focus, (b, e) small mis-focus, and (c,f) large mis-focus. Even at large misfocus, the focus-invariant system images are as clear as the standard system when infocus. 
We have developed a fundamental technique for control of important known and unknown lens aberrations. Control of lens aberrations through traditional means is very difficult in high-performance optical systems. Minimizing aberrations caused by deterministic design errors as well as statistical fabrication errors has often led to costly systems and fabrication techniques. By employing a special-purpose optical phase mask and digital signal processing we can form imaging systems that are invariant, or substantially insensitive, to a number of important lens aberrations.
 
The three-beam interference technique with high coherent illumination is considered promising for application to the measurement of lens aberrations due to its ease of use and convertibility of the results to Zernike coefficients. The coefficients widely describing the characteristics of aberrations are crucially important for the prediction of aberration impacts on a specific pattern, and are expected to minimize the impacts. Furthermore, intensive study of the three-beam interference technique is necessary for highly accurate prediction. This paper discusses the expected characteristics of three-beam interference based on theoretical considerations and experimental results. In one experiment, a krypton fluoride excimer laser scanner with a numerical aperture of 0.68 was used. Having practicable highly coherent illumination affects sensitivity in detecting aberrations, and makes results independent of exposure dose and focus. Such characteristics improve repeatability under realistic conditions that the exposure dose is not uniform and the wafer surface is not flat.
 
The measurement of human ocular aberration is now frequently performed because of the increase in refractive surgery on the human cornea. The Hartmann-Shack (H-S) wavefront sensor is considered to be the most useful wavefront sensor, and a calculation method for wavefront aberration has been established. New methods of measuring wavefront aberrations of human eyes, using the Talbot image of a two-dimensional grating as a wavefront sensor and local shift of the Talbot image to calculate tilt of the wavefront are shown. The shift of the Talbot image was determined by comparing the phases of fundamental spatial frequency between the grating and the local patch of the Talbot image by Fourier transformation. The actual experiment was performed using a modified commercially available wavefront analyzer. Using these methods, Talbot images were obtained from model eyes and a human eye, and wavefront shapes were successfully reconstructed. Wavefront aberrations can be measured even when the obtained image is degraded by defocusing or scattering.
 
Top-cited authors
Dinesh Narayana Naik
  • Indian Institute of Space Science and Technology
Rakesh kumar Singh
  • Indian Institute of Technology (Banaras Hindu University) Varanasi
Wei Wang
  • Heriot-Watt University
Pavel Zemanek
  • The Czech Academy of Sciences
Lukas Chvatal
  • The Czech Academy of Sciences