Micromechanical photonics is evolving in interdisciplinary research and engineering fields to merge independently developed technologies based on optics, mechanics, electronics and physical/chemical sciences. Manufacturing technologies such as semiconductor lasers, surface-micromachining, and bulk-micromachining are promoting technology fusion. New conceptual frameworks such as very short external cavity tunable laser diodes, tunable filters, optical scanners, free-space micro-optical elements, integrated optical heads, a photothermal microresonator, optical tweezers, and optical rotators are now appearing.

View full abstract

Multi-mode tapered fiber has been proposed and demonstrated for demagnifying optical spot size. A loss of less than 5-dB in the conversion of spot size in the range of 400 μm to 125 μm is achieved. The conversion loss dependence on the taper fiber length has experimentally clarified.

View full abstract

Stokes dynamics in stimulated Brillouin scattering generated in optical fibers is analyzed over a wide range of nonlinear refractive indices under a no feedback condition. The Stokes fluctuation becomes complicated as the nonlinear refractive index increases. Chaotic behavior appears without external feedback at a large nonlinear refractive index of 10^-19 m²/V² with pump power larger than 0.3 W.

View full abstract

We describe optical components and optical modules using a photofabrication technique to demonstrate applicability of the technique for optical purposes. A thick plate and a prism were fabricated to study fabric characteristics. Examples of optical modules implemented by the photofabrication technique are a beam expander and an interferometer baseplate.

View full abstract

The polarized intensity enhancement of the light backscattered multiply from a fractal aggregate of particles is numerically investigated using Monte Carlo simulations. It is confirmed only for the co-polarized intensity component that an effective mean free pathlength l_D defined for a fractal medium has the same physical meaning as a mean free pathlength l for a homogeneously random medium. Furthermore, co- and cross-polarized components of the backscattering intensity enhancement decrease in accordance with θ^2.16-1.03D and θ^4-1.8D in the far-field plane and with ξ^0.93D-3.94 and ξ^1.07D-3.98 in the boundary plane between the scattering medium and the air. Therefore, the two-dimensional Fourier transform relation is satisfied only between the co-polarized intensity distributions in the far-field and the boundary planes but not the cross-polarized ones with the accuracy of the numerical simulation. Finally, we notice the applicability of the enhanced backscattering light to estimating the dimension of the absorbent fractal medium on the basis of the result that the slope of the intensity decay of the intensity peak is directly proportional to the dimension of the medium but is independent of the absorption.

View full abstract

The concept of a binary feature tree (BFT) and the principle of its formation are described. A pattern is divided into sub-parts by comparing its similarity with other patterns. The BFT is established by sub-parts of a group of patterns and mapped into a three layered neural network which Sethi called an entropy network. The interconnection pattern between the first and hidden layers is formed according to the “AND” relationship of node feature patterns determined by BFT. The interconnection pattern between the hidden and last layers is obtained by training. The advantage of the proposed network is that the scale is small because a feature neuron is adopted and the interconnection is local instead of full; therefore, it is easily implemented by either hardware or software. Two simulation examples show the success of the entropy network for pattern recognition. A feature extraction by an optical inner product method is also described.

View full abstract

The signal-to-noise ratio (SNR) in the photochromic super-resolution readout of optical disks was theoretically analyzed. The shot noise limited SNR, such as that in magnetooptical disks, was improved only for the short recorded mark. However, the media noise limited SNR, such as that in phase change disks, was greatly improved for both short and long recorded marks.

View full abstract

The authors proposed an interlacing technique (IT) approach for the synthesis of kinoform which uses a number of subkinoforms interlaced together into a multikinoform. Using the IT approach, the reconstructed image can be improved by optimizing each subkinoform with the general error-reduction algorithm. In this paper, they show a new iterative algorithm based on the IT, namely an iterative multikinoform method (IMM). After each of the subkinoforms is generated by the IT, the error image, which is the difference between the desired image and the sum of the images reconstructed from all subkinoforms, is circulated into an individual subkinoform to optimize each subkinoform so that the reconstruction error can be reduced further. This process can be performed on all subkinoforms iteratively. Simulation results show that the reconstruction error can be reduced further for kinoforms with larger quantization levels (larger than 2⁴) and its convergence is very rapid when the IMM is used.

View full abstract

Optical crossbar switches were fabricated using multiwavelength vertical-cavity surface-emitting lasers and free-space microoptics. Four-channel optical switches with 10-nm wavelength intervals were successfully demonstrated.

View full abstract

Amplification process in an excimer laser of dense modes is studied. Rate-equations with wavelength dependence are used to reproduce its spectra. Two extreme cases are tried and in spite of the duration of the output pulse relative to the relaxation time, the short pulse limit is proved to describe well the oscillation process of individual mode.

View full abstract

A high-power, unmodulated frequency standard laser light with low running cost is a powerful tool for industrial measurement involving laser calibration and interferometry in length and shape. To obtain such a laser light, we developed an intermittent frequency offset locked laser (IFOL laser). This laser system, composed of an iodine stabilized He-Ne laser (I₂SL) and a high-powered symmetric three-mode He-Ne laser (HP-3ML, optical output=5 mW), provides two stabilization operational modes: (1) independent mode (I-mode) and (2) slave mode (S-mode). Utilizing the frequency pulling effect, HP-3ML is stabilized at the condition of symmetric three-mode oscillation, and a 3 mW single-mode light with frequency instability of 10^-12 is obtained (I-mode). When the optical frequency deviates from the allowed limit during I-mode, HP-3ML is temporarily offset-locked to I₂SL (S-mode) with frequency resettability of 10^-10 and frequency instability of 10^-12. After completion of the drift reset in S-mode, HP-3ML is stabilized in I-mode again, and then I₂SL is turned off. In a typical case of allowed drift in MHz, repetitive operation of I-mode for 10 days and S-mode for 5 min was satisfactory. Such an intermittent operation reduces the working time of I₂SL dramatically, resulting in low running cost that enables long-term use in industrial measurement.

View full abstract

When two waves are coupled in Bi₁₂SiO₂₀ crystals, the polarization states of the signal wave are affected by the self-diffraction. We have theoretically studied the influence of the self-diffraction on the polarization of the signal wave. The change of polarization states are strongly affected by the self-diffraction effect when the external field is applied. We present a new method that converts the change of polarization into an intensity signal.

View full abstract

Four wave mixing (FWM) is of considerable interest in generation of a phase conjugate beam with photorefractive crystals. The common methods of FWM are parallel polarization FWM and cross polarization FWM. In this paper, we analyze the phase matching property of the latter. First, we consider the phase matching condition, and derive equations representing the angler relationship of interacting beams. Then, we consider the phase mismatching which is caused by shift of the probe beam angle from the phase matching condition, and calculate the effect of the shift of this angle on the amount of phase mismatching. We also determine and closely examine the coupling constant.

View full abstract

A new type of underwater acoustic sensor is proposed with an optical fiber Bragg grating (FBG). Because of the photoelasticity with respect to the refractive index and the elasticity of the fiber, the sound pressure in water modulates the Bragg reflection wavelength and, in turn, the intensity of the laser light transmitted through the FBG fiber. Good linearity between the detected signal and the sound pressure is obtained in the range from 81 dB to 140 dB re 1 μPa. Since the upper and lower limits of the acoustic signal level for operation of the sensor are limited by the driving circuit and the transduction of the sound in water, the sensor is expected to operate with much larger dynamic range both at higher and lower pressure levels. Operation of the sensor is very stable with the insertion of optical isolators into the system, although without the isolators the output signal fluctuates at low frequency due to the Fabry-Perot interference effect between the FBG and the various facets.

View full abstract

Automatic lens design is viewed as a multiobjective optimization problem and is resolved by a minimization of the weighted Tchebycheff norm of objective functions. It is analytically solved using the multiplier method and a solution vector is transformed into the same form as the normal equation of the least squares method. Some numerical examples are given to show the effectiveness of the proposed method. The resultant solutions can not be obtained using the damped least squares method.

View full abstract

A method for simulating latent image formation in a photoresist illuminated by an arbitrary imaging system is presented. A variational formulation for light scattering, which does not depend on a specific configuration of the imaging system, is derived and solved using the finite-element method. The perfectly matched layer absorbing boundary condition is applied to take wave propagation in the infinite region surrounding the photoresist into account. The validity of the method is examined by comparing the results with those made by the vertical propagation model and the previous two-dimensional models.

View full abstract

Estimation of surface spectral reflectance functions and colorimetric values of object colors was carried out for the image data captured by video camera under unknown illuminations. The estimation method is based on the finite-dimensional linear model of illuminants and surfaces using a single reference reflectance with known surface spectral reflectance in a scene. Experimental results showed that recovered surface spectral reflectance functions are the almost same for different illuminations. This method is useful for the colorimetric calibration of the devices, since any set of orthonormal basis vectors to represent illuminations and any set of eigen vectors derived from principal component analysis on the data set of a color chart to express surfaces of different objects can be applied to the estimation. The recovered surface reflectances were evaluated by color differences in CIE L^*a^*b^* color space.

View full abstract