This paper reports the feasibility of optical coherence tomography (OCT) technology for inspection of bonding quality of microfluidic devices in manufacturing environments. A compact optical-fiber-based OCT is developed and its measurement performance is characterized. A series of microfluidic devices respectively bonded by adhesive tape, thermal method, and oxygen plasma, are inspected. The defects of geometry deformation and sealing completeness are emphasized during measurements. Based on the inspection results, some discoveries related to the production of microfluidic devices are discussed.
Current approaches to control critical dimensions (CD) uniformity during lithography is primarily based on run-to-
run (R2R) methods where the CD is measured at the end of the process and correction is done on the next
wafer (or batch of wafers) by adjusting the parameter set-points. In this work, we proposed a method to monitor the various photoresist parameters (e.g. photoresist thickness, photoactive compound) and CD in-situ and in real-time. Through modeling and real-time identification, we develop new in-situ measurement techniques for the various parameters of interest in the lithography sequence using existing available data in the manufacturing process.
The misalignment of a particular optic in lens assembly will induce aberrations and deteriorate the performance. For the
purpose of failure analysis, there are requirements from optic manufactures for the development of measurement tool to
address the misaligned element. This paper presents a method for the quantitative measurement and analysis of
misalignment in lens assembly, which may figure out the misaligned element and its misalignment factors. Since there
are several optical elements in lens assembly, and there are different misalignments, such as decenter, tilt etc, a multiparameter
tool need to be employed in the analysis. Wavefront can be expressed with Zernike polynomials, which are
selected for the analysis. We choose a positive lens assembly with four elements for the study. A point light source is
placed in the front focus point of lens assembly; the collimated emergent wavefront is analyzed with Zernike
polynomials. We use Zeemax to simulate the propagation of wavefront, calculate Zernike coefficients correspondent to
various misalignment. The results show there is a group of Zernike polynomials correspond to each misalignment. Each
polynomial increase/decrease progressively against the magnitude of misalignment. It is difficult to tell the misalignment
only by the analysis of Zernike coefficients. To further address the misaligned elements, we present a concept - the
contrast value of Zernike coefficients, which is a series of constant even though the magnitude of misalignment changes.
The method and procedure is presented to measure the contrast value with the employment of dual directional wavefront
sensing.
When wavefront is reflected by a surface, the information of the surface profile is carried by the reflected wavefront.
Measure the wavefront can extract the profile information. There are different kinds of pre-defined surface profile with
various dimensions. While the size of particular wavefront sensor is fixed, the measurement range is limited. The design
of optical system to bridge the work piece and wavefront sensor is critical. This paper presents a platform for the
guidance of optical system design. The parameters of commercial available optical components are input to the platforms
and the propagation of reflected wavefront is simulated. The relationship of part profile and the measurement wavefront
is provided. The discussion is focused on the 2f+2f system for surface flatness measurement. The measurement of
aspherical surface is also presented. Shack-Hartmann wavefront sensor (SHWS) is selected due to its simple structure,
insensitivity to vibration etc, which is suitable for in-line application. Optical system is designed with the guidance of
simulation platform. The experimental results shows the 2f+2f system is compatible to misalignments, can be used to
monitor the deformations of parts. The measurement of aspherical surface is also presented with the comparison of
simulation results.
Microfluidic devices play a crucial role in biology, life sciences and many other fields. Three aspects have to be
considered in production of microfluidic devices: (i) material properties before and after processing, (ii) tooling and
processing methodologies, and (iii) measurements for process control. This paper presents a review of these three areas.
The key properties of materials are reviewed from both the production and device performance point of views in this
paper. The tooling and processing methodologies considered include both the direct tooling methods and the mold based
processing methods. The response of material on the production parameters during hot embossing process are simulated
for process control and product quality prediction purpose. Finally, the measurements for process control aspect discuss
different measurement approaches, especially the defect inspection, critical dimensional measurements, bonding quality
characterization and checking functionality. Simulation and experimental results are used throughout the paper to
illustrate the effectiveness of such approaches.
Shack-Hartmann Wavefront Sensor (SHWS) recently has been extensively researched for optical surface metrology due
to its extendable dynamic range compared with the interferometry technique. In our institute, we have developed a
digital SHWS by adopting a programmable Spatial Light Modulator (SLM) to function as a microlens array and replace
the physical one in the traditional configuration of this sensing system. In this paper, we proposed to use the developed
system for the relative measurement of toroidal surfaces, which are widely used in many optical systems due to their
unique optical features of different curvatures in X and Y directions. An innovative idea to design the diffractive
microlens array implemented by SLM was presented to tackle the measurement challenge. This unconventional design
approach has a great advantage to provide different optical powers in X and Y directions so that focusing spots can be
formed and captured on the detector plane for accurate centroid finding and precise wavefront evaluation for 3D shape
reconstruction of the toroidal surface. A digital Shack-Hartmann Wavefront Sensing system with this unique microlens
array was built to verify the design concept, and the experimental results were presented and analyzed.
Since its emergence in the early 1970s, Shack-Hartmann Wavefront Sensing technology has been investigated and
explored world-widely by the researchers and engineers. However, there are few papers or reports to study the system
performance and key factors to affect the performance of a Shack-Hartmann Wavefront Sensor (SHWS), in this paper,
through experimental study of the system stability of a SHWS, it is found that the image sensor and detector, normally a
CCD, should be placed exactly at the focal plane of the lenslet array, otherwise it will bring in significant wavefront
measurement error. In order to improve the system performance, a special lenslet array with long focal range is designed,
and it is functioned by a spatial light modulator for sampling wavefront in a SHWS. Diffractive lenses with long focal
length range can provide pseudo-nondiffracting beams, and a long range of focusing plane. The performances and effects
of the modified SHWS with such a special lenslet array generated by a programmable SLM, are investigated, and the
experimental results show that the system stability and measurement repeatability are not sensitive to the sensing
distance, and can keep at a good level in a long range.
Transparent toughened glass panels are widely installed in high-rise buildings. There is a growing need for inspection to detect the presence of detrimental inclusions of Nickel Sulfide. These inclusions can cause toughened glass to shatter, possibly causing property damage or injury. Optical equipment has been developed which can detect the inclusions in-situ. Light is coupled into a glass panel and propagates along the glass by total internal reflection. An inclusion in the glass will cause the light to scatter. Once an inclusion is found, it will be observed at higher magnification and the detailed image will be processed. By the analysis of its key features, the inclusion type can be identified. The coupling medium is made of a transparent, soft and deformable material. The equipment can be attached to a glass panel by vacuum suction. The optical system can scan the whole glass panel with a constant force spring as anti-weight structure. The whole system is fast, convenient and highly effective. A patent has been filed for this apparatus.
The application of an optical interferometric system using a Mirau objective to the measurement of the surface profile of micro-components is described. The proposed system produces a uniform monochromatic illumination over the test area and introduces an interference fringe pattern localized near the test surface. Both the interference fringes and the 2D images of the test surface can be focused by an infinity microscope system consisting of a Mirau objective and a tube lens. A piezoelectric transducer (PZT) attached to the Mirau objective can move precisely along the optical axis of the objective. This enables the implementation of phase-shifting interferometry without changing the focus of a CCD sensor as the combination of the Mirau objective and the tube lens provides a depth of focus which is deep in comparison to the phase-shifting step. Experimental results from surface profilometry of the protrutsion/undercut of a polished fiber within an optical connector and of the curved surface of a micro-mirror demonstrate that features in the order of nanometers are measurable. Measurements on standard blocks also show that the accuracy of the proposed system is comparable to an existing commercial white light interferometer and a stylus profilometer.
Grip strength is an easy measure of skeletal muscle function as well as a powerful predictor of disability, morbidity and mortality. In order to measure the grip strength, a novel fiber optic approach is proposed and demonstrated. Strain dependent wavelength response of fiber Bragg gratings (FBGs) has been utilized to obtain the strength of individual fingers. Five FBGs are written at different center wavelengths on a single photosensitive fiber. Each FBG is used to get the response from each individual finger. The fiber containing the gratings is attached to a suitable grip holder, which can effectively transfer the grip force to the FBGs. An additional reference FBG is also provided to make the device temperature insensitive. Experimental results show that the wavelength shifts of the order of 0.2-0.5 nm can be achieved for individual fingers. The device is calibrated in terms of load to convert the wavelength shift to the strength of the grip. The time dependent wavelength fluctuations was also studied and presented in this paper.
Lateral-pressure tuning of a coaxially embedded fiber Bragg grating in a cylindrical polymeric package is demonstrated. The polymeric coating, having very low stiffness and high Poisson's ratio, enables effective transfer of the applied radial load to the axial direction. Such a transfer enhances the tuning range and reduces birefringence. A tuning range more than 1 nm, with negligible bandpass broadening and peak splitting, could be demonstrated. A lateral pressure sensitivity of 0.3 nm/(N/mm), which is almost 7 times as high as that of bare FBG, could be obtained.
Polymeric coatings are often used to develop various thermally tunable FBG based devices. Coatings on FBGs can be intended for protection, improvement of thermal sensitivities, special spectral shaping etc., and the quality of the coating on the FBG deserves special attention. For example, the adhesion of the polymeric coatings to the silica based optical fiber plays an important role in the wavelength response characteristics of fiber Bragg gratings during thermal tuning. In this paper, we theoretically investigate the effect of adhesion and the non-uniformity of the coating thickness on the thermal tuning process of FBGs. Experiments were done to qualitatively analyze the influence of adhesion. However practically it is very difficult to quantify the percentage adhesion and quality of coatings for experimental verification. Therefore a methodology based on finite element analysis has been utilized for theoretical investigation of the effect of adhesion of polymeric coating on the performance of FBG based thermally tuned devices. Three-dimensional finite element simulations were carried out. Spring elements are used to inter connect the nodes of the meshed models of optical fiber and coating. The effect of adhesion is studied as a function of spring stiffness. The effect of non-uniformity in the coating thickness in the circumferential direction was also studied.
MOEMS packing architecture has been a major driving force for miniaturization of fiber optical components and optical communication devices. By using of bulk micromachining technology, V-grooves and micro-pits can be fabricated on a silicon wafer for coupling micro laser diode to fiber or fiber to fiber, and finally integrating into the small modules on chip packages. Because many factors, such as photolithography, material property, wet chemical etching process and operator's skills will influence the geometric accuracy, a precision measurement instrument is needed for in-situ inspection of V-grooves suitable for the critical passive optical alignments. This paper reported a novel 3D confocal profile measurement system for in-situ inspection of the depth of multi-channel V-grooves.
Bragg grating devices are widely used in the field of optical sensing and communication. Thermally tunable devices utilize the effect of temperature on the wavelength response characteristics of the fiber Bragg grating. But the low sensitivity of a Bragg grating device to temperature limits its usage to many applications. The wavelength sensitivity of a bare FBG is only 1.3 nm for a temperature change of 100°C. In order to enhance the temperature sensitivity of a fiber Bragg grating, we propose modification of the cladding of the FBG through etching and put another coating layer outside the cladding. The cladding is etched to a certain depth around the grating and the etched portion is coated with a suitable polymer. Theoretical analysis has been done to find the relationship between the wavelength shifts and the etching depths and coating thickness of the polymer. A finite element model of the cladding etched FBG coated with polymer has also been developed and the wavelength shift due to thermal expansion is analyzed under various etching depths and coating thickness. The high thermal expansion coefficient of the polymer enables to enhance the thermal sensitivity by improving the wavelength shift due to thermal expansion. Also the polymer coating on the etched fiber reduces the susceptibility of fracture and improves the reliability. It is found that that temperature sensitivity increases with increase in etching depth. But there is maximum limit to which the cladding can be etched without affecting the performance. Also it is found that increasing the coating thickness of the polymer increases the wavelength shift due to temperature change.
This paper presents a new three-wavelength ring laser using one erbium-doped fiber amplifier. The simultaneous output of three lasing wavelengths is achieved by controlling the gains of different filters through utilizing a cascaded fiber Mach-Zender interferometer (MZI) with the triangular-shaped interference transmission spectrum. The key advantage of the proposed system over existing technologies is that the output is channel-wavelength selectable. Each channel can be tuned individually from one channel wavelength to the other. The channel wavelengths are selectable over the range of 1522-1665nm.
This paper describes a multispectral liquid drop analyzer for liquid chemical and physical properties analysis. Liquid drops formed at the tip of a liquid head are measured in parallel by a fiber sensor and a capacitive sensor. The fiber sensor works as follows: multispectral light sources are injected into the drop through an optical fiber and the total internal reflections and absorptions are detected by a photodetector. By combining fiber and capacitive sensor outputs, a drop speed independent one-dimensional waveform (liquid fingerprint) is generated. Liquid surface tension, refractive index and di-electric constant can be estimated from the fingerprint. To compare two fingerprints, the sensor outputs are normalized to have the same unit of measurement and drop starting position. After that, a reference liquid based calibration is applied to correct of fingerprint distortion due to variations in environment conditions, such as changes in temperature and humidity. Finally, a normalized correlation algorithm analyses the fingerprint difference. The repeatability and sensitivity of the system are demonstrated using different liquid samples. On-line applications show that the analyzer is able to detect 2% change in alcohol density.
Confocal 3-D imaging technique is a newly developed technique and widely used in many fields of research and development. It is to utilize light intensity sensitive measuring technique. Confocal 3-D profile measurement system is widely used in high resolution inspection. For high precision 3-D imaging inspection in confocal measuring system, light source acts a very important role in system resolution and accuracy. In order to improve measuring repeatability and stability, to reduce measurement error, and to lower the light source stability requirement and cost, this paper studied light source fluctuation effect to confocal imaging measurement; deduced depth response model function; analyzed system error caused by light source fluctuation; and presented a new scheme to reduce the affection of light source fluctuation. Theoretical analysis and experiment result verified that light source fluctuation should be considered and eliminated in very high resolution confocal 3-D shape measurement system.
3-D profile confocal optical microscopy is a newly developed 3-D profile metrology and has widely applied in many kinds of 3-D shape inspection fields. Present 3-D shape measurement system used in confocal optical microscopy is single point measurement. Point by point detection to finish a 3-D profile inspection is considered a time consuming method and isn't suitable for large area measurement especially for high resolution measurement. This paper elaborated on a fiber-array confocal 3-D imaging system to improve measuring speed. In confocal measurement system, light source acts an important effect on system accuracy and repeatability. Light source fluctuation can cause a large error for high resolution 3-D shape measurement. This paper presents a novel system construction to solve the problem of light source fluctuation. The system design is compact and the construction is reasonable.
With the increasing demand for micro-products and bioengineering research, resolutions of profiles with micrometer or even nanometer scale are becoming commonplace. In addition development of large integrated manufacturing systems and the real time life science growth and adaptation need high-speed display and real-time inspection. Single point measurement is time consuming method with large area profile and micrometer resolution. Thus there is a need for a fast 3-D measurement system with high resolution. This paper presents a short overview among optical 3-D shape measurement techniques, and concentrates on the confocal method. Based on the properties analysis, a novel multi-channel 3-D topography measurement system was proposed. The feasibility and the construction of system were described A unique new structure of fiber coupled confocal system is put forth to solve present problems confronted in confocal system. This system can meet the current demand of high resolution and fast 3-D measurement.
Based on optical non-contact sensing and machine vision technology, an optical non-contact measurement instrument for measuring blind holes, as well as through holes, has been developed. By projecting a precision optical target on the internal wall of hole and sensing its reflected image, the instrument can be used to measure the hole's diameter, ovality and cylindricity. An optical selective amplification system was developed that greatly increases the sensitivity of CCD camera. Experimental test shows that the sensitivity of the laboratory apparatus is about 3 micrometers /pixel and the measurement accuracy is about 10 micrometers .
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