Optical Beam Path Research Articles

Micro-block Stacking 방법으로 제작한 집적형 Triplexer 제작 및 특성 측정

본 논문에서는 정밀 세라믹 부품을 이용한 MBS(Micro-Block Stacking) 방법으로 1550 nm 파장의 아날로그 신호 수신과 1310nm/1490nm 파장의 디지털 신호 송, 수신이 가능한 8 pin mini DIL 형태의 집적형 Triplexer를 제작하였다. 제작된 전체 어셈블리는 <TEX>$5.40mm{\times}2.15mm{\times}1.05mm$</TEX> 크기로 통신용 광모듈 국제 표준인 MSA(Multi Source Agreement) 규격의 SFP(Small Form Pluggable) 광모듈 제작이 가능하다. 자동 능동 광정렬 장비를 사용하여 제작된 집적형 Triplexer를 단일모드 광섬유에 광정렬하였을 때, 1310 nm 송신부 최대 광출력이 -14.5 dBm이었고, 송신부에 의하여 위치가 자동 정렬된 1550 nm와 1490 nm 수신부 수신감도는 각각 0.83 A/W, 0.73 A/W로 단거리 통신에 적용 가능한 값을 얻었다. In this paper, we have fabricated by means of the "Micro-Block Stacking (MBS)" method the 8 pin mini DIL integrated Triplexer, which can transmit CATV and voice/data at the same time in a single fiber. Our MBS technique is a novel scheme of compact optical module packaging which secures precision positioning of the components on the optical beam path by prefixed stacks of ceramic blocks. The subassembly in which a laser diode, two receiver photodiodes, two WDM filters, and four micro lenses are integrated is only <TEX>$5.40mm{\times}2.15mm{\times}1.05mm$</TEX> in size. As the Triplexer is aligned to the single mode fiber, the transmitter power of -14.5 dBm and the receiver sensitivities of 0.83 A/W, 0.73 A/W for 1550 nm, 1490 nm, respectively are obtained.

Laser schlieren deflectometry for temperature analysis of filamentary non-thermal atmospheric pressure plasma

The heat convection generated by micro filaments of a self-organized non-thermal atmospheric pressure plasma jet in Ar is characterized by employing laser schlieren deflectometry (LSD). It is demonstrated as a proof of principle, that the spatial and temporal changes of the refractive index n in the optical beam path related to the neutral gas temperature of the plasma jet can be monitored and evaluated simultaneously. The refraction of a laser beam in a high gradient field of n(r) with cylindrical symmetry is given for a general real refraction index profile. However, the usually applied Abel approach represents an ill-posed problem and in particular for this plasma configuration. A simple analytical model is proposed in order to minimize the statistical error. Based on that, the temperature profile, specifically the absolute temperature in the filament core, the FWHM, and the frequencies of the collective filament dynamics are obtained for non-stationary conditions. For a gas temperature of 700 K inside the filament, the presented model predicts maximum deflection angles of the laser beam of 0.3 mrad which is in accordance to the experimental results obtained with LSD. Furthermore, the experimentally obtained FWHM of the temperature profile produced by the filament at the end of capillary is (1.5 ± 0.2) mm, which is about 10 times wider than the visual radius of the filament. The obtained maximum temperature in the effluent is (450 ± 30) K and is in consistence with results of other techniques. The study demonstrates that LSD represents a useful low-cost method for monitoring the spatiotemporal behaviour of microdischarges and allows to uncover their dynamic characteristics, e.g., the temperature profile even for challenging diagnostic conditions such as moving thin discharge filaments. The method is not restricted to the miniaturized and self-organized plasma studied here. Instead, it can be readily applied to other configurations that produce measurable gradients of refractive index by local gas heating and opens new diagnostics prospects particularly for microplasmas.

Mirror design for piezo-driven mechanical devices: Modeling and simulations

The principal operation of a ring laser gyroscope depends on the phase difference for the counter-propagating waves within a closed path. The reflection mirrors mounted on the resonator block form the traveling waves. Thus, the dimension accuracy of resonator block influences the traveling path of beam. In order to maintain the stable optical beam path in the ring resonator, the piezo-driven moveable mirror is adopted for the path length control under the thermal expansion or mechanical strain of resonator block. This paper presents the mathematical description of the elastic behavior of piezo-driven mirror. This description can be applied for the concept design of piezo-driven mirror. For the beam path control due to a piezo-driven mirror, this paper presents a theory of deflection of piezo-driven mirror as a function of the geometries and material properties of mirror components. In comparison with the simulation of finite element model, the theoretical result has the feasible error tolerance. If the effective geometries on the base of deformation can be taken into account, the more precise result can be calculated. But through the comparison, the presented theoretical approaches are known to be available.

Stabilized hot electron bolometer heterodyne receiver at 2.5 THz

We report on a method to stabilize a hot electron bolometer (HEB) mixer at 2.5 THz. The technique utilizes feedback control of the local oscillator (LO) laser power by means of a swing-arm actuator placed in the optical beam path. We demonstrate that this technique yields a factor of 50 improvement in the spectroscopic Allan variance time which is shown to be over 30 s in a 12 MHz noise fluctuation bandwidth. Furthermore, broadband signal direct detection effects may be minimized by this technique. The technique is versatile and can be applied to practically any local oscillator at any frequency.

Lensless digital holography with diffuse illumination through a pseudo-random phase mask

Microscopic imaging with a setup consisting of a pseudo-random phase mask, and an open CMOS camera, without an imaging objective, is demonstrated. The pseudo random phase mask acts as a diffuser for an incoming laser beam, scattering a speckle pattern to a CMOS chip, which is recorded once as a reference. A sample which is afterwards inserted somewhere in the optical beam path changes the speckle pattern. A single (non-iterative) image processing step, comparing the modified speckle pattern with the previously recorded one, generates a sharp image of the sample. After a first calibration the method works in real-time and allows quantitative imaging of complex (amplitude and phase) samples in an extended three-dimensional volume. Since no lenses are used, the method is free from lens abberations. Compared to standard inline holography the diffuse sample illumination improves the axial sectioning capability by increasing the effective numerical aperture in the illumination path, and it suppresses the undesired so-called twin images. For demonstration, a high resolution spatial light modulator (SLM) is programmed to act as the pseudo-random phase mask. We show experimental results, imaging microscopic biological samples, e.g. insects, within an extended volume at a distance of 15 cm with a transverse and longitudinal resolution of about 60 μm and 400 μm, respectively.

Columnar shaped microresonators for mass detection and gas analysis

In this paper miniaturized silicon columns mounted perpendicular to a surface are presented as microresonators for the detection of an exceedingly small mass. In a first sensor design the column resides on a rigid silicon substrate and is forced to oscillate in the first flexural eigenmode. Mass sensitivity was investigated loading a single latex sphere on the top surface of the column and detecting the frequency shift of the resonant frequency. Oscillation was monitored using the optical beam deflection method, focusing a laser beam at the same surface. However, optical readout was substantially hampered by scattering of the laser beam at the loaded particles and diffraction at the column surface. In a second optimized design a silicon column was mounted on a flexible silicon nitride membrane. In this way the optical readout was applied from the flip side of the membrane completely separating the load area and the optical beam path. A proof of principal is given for the optimized sensor design investigating the influence of pure gases on the extrinsic damping behavior of the membrane columnar oscillator.

링 공명기의 경로치 제어를 위한 피에조 구동 거울의 설계

링 레이저 자이로스콥의 주 동작은 폐경로 내의 상대 전파에 대한 위상 차에 의존한다. 공명 블록위에 설치 된 반사경들이 순항 파를 형성한다. 따라서, 공명 블록의 차원 정확도가 빔의 순항 경로에 영향을 미친다. 링의 공진 내에서 안정된 광학 빔 경로를 유지하기 위해서 피에조로 구동되는 이동거울이 공명 블록의 열팽창이나 기계적 변형하에서 경로치 제어를 하고자 선택되었다. 이 논문에서는 피에조 구동 거울의 탄성거동에 대한 수학적 설명을 제시하였다. 이 설명은 피에조 구동 거울의 개념 설계에도 적용될 수 있다. The principal operation of a ring laser gyroscope depends on the phase difference for the counter-propagating waves within a closed path. The reflection mirrors mounted on the resonator block form the traveling waves. Thus, the dimension accuracy of resonator block influences the traveling path of beam. In order to maintain the stable optical beam path in the ring resonator, the piezo-driven moveable mirror is adopted for the path length control under the thermal expansion or mechanical strain of resonator block. This paper presents the mathematical description of the elastic behavior of piezo-driven mirror. This description can be applied for the concept design of piezo-driven mirror.

Fabrication of Tunable Band Pass Filters for CWDM Applications

AbstractThe paper describes a method to fabricate tunable band pass filters. The thin film optical filters are based on a Fabry‐Perot structure with laterally varying layer thickness. This leads to a variation of the transmission band along the substrate. The filter can be tuned by lateral translation of the filters through an optical beam path. A linear variation of the layer thickness and, therefore, of the transmission band along a 75 mm long substrate could be achieved by choosing proper geometries in the coating chamber. Filters are designed for a centre wavelength of 1300 nm with a −3 dB transmission bandwidth of 2.0 nm. A tuning range of more than 150 nm could be achieved with constant filter losses of ≈0.9 dB. So, the filters are well suited for side band suppression in CWDM applications.

Calibrating excitation light fluxes for quantitative light microscopy in cell biology

Power output of light bulbs changes over time and the total energy delivered will depend on the optical beam path of the microscope, filter sets and objectives used, thus making comparison between experiments performed on different microscopes complicated. Using a thermocoupled power meter, it is possible to measure the exact amount of light applied to a specimen in fluorescence microscopy, regardless of the light source, as the light power measured can be translated into a power density at the sample. This widely used and simple tool forms the basis of a new degree of calibration precision and comparability of results among experiments and setups. Here we describe an easy-to-follow protocol that allows researchers to precisely estimate excitation intensities in the object plane, using commercially available opto-mechanical components. The total duration of this protocol for one objective and six filter cubes is 75 min including start-up time for the lamp.

A laser ablation system for the analysis of radioactive samples using inductively coupled plasma mass spectrometry

This work describes the design and function of an α-box integrated laser ablation system coupled to an inductively coupled plasma mass spectrometer, designed and built at the hotlaboratory of the Paul Scherrer Institut, for the analysis of highly radioactive samples. A 266 nm Nd:YAG laser based ablation system was separated into beam generation and ablation and sample handling to avoid radiation induced defects of the hardware. The optical beam path is delivered through a window within the α-box. The focusing optics and the ablation cell suitable for handling highly radioactive samples are described in detail. The laser ablation system was coupled to a multi-collector ICP-MS and evaluated by applying various laser parameters to ablate uranium dioxide reference materials. Isotope ratios were measured with a precision of 0.3% and a spatial resolution down to 10 μm. The optimized parameters were applied to spent nuclear fuel samples.

Vector-component isolation of an arbitrary modulating electric field in zincblende electro-optic probes

Analysis of the field-induced linear birefringence in zincblende crystals shows that one can obtain complete isolation of a single vector component of an arbitrary modulating electric field. For an optical probe beam path aligned parallel to the [110] direction and an optical probe beam polarization aligned parallel to the [110] direction, the field-induced birefringence occurs only for the component of the modulating electric field aligned parallel to the [110] direction. Measurements using a modulating electric field with known polarization and electro-optic probes machined from (110) gallium arsenide wafers demonstrate an alignment-limited isolation between orthogonal modulating electric field components of 17 dB.

THE CHALLENGE OF QUALITY ASSURANCE FOR EMISSION FLUX MEASUREMENTS OF LARGE AREA SOURCES BY OPTICAL REMOTE SENSING

Monitoring the emissions flux of contaminant gases from large area sources requires measurement of concentrations from an optical remote sensing device and reconstruction of the plume. Path integrated concentrations are determined using multiple optical beam paths. The spatial distribution of concentrations is generated for a plane perpendicular to the direction of the wind. Estimates of the emission flux are determined by integrating the product of the calculated concentrations and wind speeds over the plane. No standard method exists for the complete process, defensible estimates of the uncertainty of the final emission flux have not yet been developed, and a data validation procedure is needed. Auditors are challenged to configure an adequate performance evaluation standard that is representative of a large area source.

Electro-optical measurements of ultrashort 45 MeV electron beam bunch

We have made an observation of 45 MeV electron beam bunches using the nondestructive electro-optical (EO) technique. The amplitude of the EO modulation was found to increase linearly with electron beam charge and decrease inversely with the optical beam path distance from the electron beam. The risetime of the signal was bandwidth limited by our detection system to ~ 70 ps. An EO signal due to ionization caused by the electrons traversing the EO crystal was also observed. The EO technique may be ideal for the measurement of bunch structure with femtosecond resolution of relativistic charged particle beam bunches.

Combined ultrasound and near infrared diffused light imaging in a test object

We have investigated the use of combining near infrared (NIR) diffuse light and ultrasound imaging methods to increase the detection sensitivity and to reduce the false alarm rate in small target detection. A line-of-sight optical projection through a test object is identified from an amplitude null and a sharp phase transition produced by diffusive waves originating from two in-phase (initial phase 0 degrees ) and out-of-phase (initial phase 180 degrees ) light emitting diode sources. This line-of-sight is scanned across a scattering phantom. A complete ultrasound B-scan image is recorded at each projected line in the optical scan. Each acoustic image plane is bisected by the optical beam path and lies in the optical scan plane. The scattering phantom simulates acoustic and optical properties of homogeneous tissue. A single small cylinder-like object simulating some acoustic and optical breast tumor properties is inserted at various places in the scattering phantom. With this single object, the optical scanning identifies the line-of-sight passing through the simulated tumor quite well. Most of these simulated tumors were at or below the threshold for acoustic detection and were not seen consistently with unguided ultrasound. For tests in which a target was apparently detected optically, the selected line-of-sight was indicated in each of three adjacent ultrasound images. Two radiologist observers were statistically more accurate (83%) in identifying the target location on the optically-selected ultrasound images than in the unmarked images (52%). That is, in these single-targets of homogeneous scattering background, the optical technique usually provided the correct line-of-sight, and ultrasound generally showed the location along that line.

A peristaltic injection nozzle for collinear laser and molecular beams

A novel gas nozzle design that allows for collinear laser and molecular beams is described. Unlike conventional nozzles that open and close to limit the gas flow into a vacuum chamber, this nozzle opens to release a small volume of gas into the chamber. Gas pulses of 300 μs duration and 65±5 μs opening times have been obtained. When room-temperature H2 is used as the source gas, the rotational temperature was found to be 175±12 K, whereas when room-temperature D2 was used, the rotational temperature was found to be 104±7 K. The collinear optical and molecular beam path provided in this design may be useful in photodissociation experiments, the study of atomic and molecular collisions, Rydberg state lifetime measurements, and vacuum ultraviolet generation by nonlinear mixing in gases.

Quasi-phase-matched second-harmonic generation by use of a total-internal-reflection phase shift in gallium arsenide and zinc selenide plates

We fabricated a novel quasi-phase-matched frequency converter, using a zigzag optical beam path in a thin, polished parallel plate. Second-harmonic generation experiments demonstrated angle-tuned output at 4.6 to 5.3mum in GaAs and 1.7 to 2.0mum in ZnSe crystals when pulsed infrared laser sources were used.

Studies on formation mechanisms of self-pumped phase conjugation in BaTiO_3:Ce crystals at wavelengths from 570 to 680 nm

Formation mechanisms of self-pumped phase conjugation (SPPC) in two BaTiO3:Ce crystals with different doping concentrations have been experimentally studied. The pump beam was from dye lasers, with an overall tunable wavelength region lying between 570 and 680 nm. Variations of the optical beam path patterns as well as reflectivity of the phase conjugators with respect to the incident angle, the incident position, and the wavelength of the pump were investigated in two configurations. One configuration corresponds to that in which the pump enters an a face of the crystal; the other to that in which the pump enters the +c face of the crystal. It was found that SPPC is sometimes established in a way similar to that of a cat phase conjugator, but usually without the formation of a clear beam path loop. Sometimes SPPC is established by a stimulated photorefractive backscattering and four-wave mixing mechanism. In these cases, however, the crystal corners as well as the scattering centers on the crystal faces usually play an important role by seeding the stimulated photorefractive backscattering processes. In other cases SPPC is established by both the cat and the stimulated photorefractive backscattering and four-wave mixing mechanisms.

Mechanism transformation with wavelength of self-pumped phase conjugation in BaTiO_3:Ce

We report what is to our knowledge the first observation of mechanism transformation with wavelength of self-pumped phase conjugation (SPPC) in BaTiO(3):Ce crystals in the near infrared. It was found that the SPPC mechanism changed from a backscattering and four-wave-mixing mechanism to a cat mechanism when the pump wavelength was varied from 706 to 770 nm. In addition, SPPC was obtained when the pump beam entered the crystal by the +c face, and a variation with wavelength of optical beam paths in the crystal was also observed.

Elimination of phase noise of pulsed laser diodes in electrooptic sampling systems

The multimode operation of pulsed laser diode sources is converted into excess noise in electrooptic probing systems for electrical waveforms and prevents measurements with shot-noise-limited sensitivity. The transfer function of the sampling system is determined and analyzed in terms of the wavelength and electric field dependence. It is shown that by proper orientation of the polarizing components within the optical beam path, points of operation can by found which have both a vanishing wavelength dependence of the transfer function and maximum sensitivity to the electric fields to be measured. Excess noise sources due to wavelength fluctuations of the laser are thus eliminated, and shot-noise-limited voltage resolution is obtained. The system has been optimized to yield a voltage sensitivity of 2.3 mV/ square root Hz for a longitudinal LiNbO/sub 3/ probe crystal. >

Generation and cancellation of second-order harmonic distortion in analog optical systems by interferometric FM-AM conversion

The generation of strong harmonic distortion from interferometric FM-AM conversion in analog lightwave systems is demonstrated both theoretically and experimentally. The effect results from the combined effects of wavelength chirping of the laser coupled with the nonlinear transmission characteristics of a dispersive element in the optical beam path. It is shown that reflections as small as 2-10/sup -4/ will result in second-order distortion as large as -65 dBc. The effect can also be used to cancel any laser- or detector-induced harmonic distortion. In one example, the -36 dBc second-order distortion in a distributed-feedback (DFB) laser is improved to better than -70 dBc.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>