Search

Optical microcavity, which can localize light at a certain spot for a short period of time, has a wide range of applications, such as optical signal processing and optical frequency combs. Single crystal CaF2 has excellent optical properties and many research on the manufacturing process to create a microcavity has been done. However, due to its unstable thermal conditions, stable oscillation of Kerr comb could not be done. Single crystal MgF2, which also has excellent optical properties, has stable thermal conditions suitable to create a microcavity. Like CaF2, MgF2 microcavity can only be manufactured by ultra-precision cylindrical turning, yet its appropriate processing conditions is not known. In this study, a method to derive the critical depth of cut theoretically in ductile mode machining was proposed in consideration of specific cutting energy, mechanical properties and slip system of workpiece, and tool geometry. The critical depth of cut calculated by the proposed method roughly agreed with the experimental value on the MgF2 plane. Unlike CaF2, MgF2 has an optical anisotropy; therefore, in order to create a microcavity where the refractive angle is constant, the resonance part needs to be made on a cylinder with (001) plane as end face. Therefore, a microcavity was fabricated according to the critical depth of cut on a cylinder with (001) as end face derived from the proposed method, and the surface integrity was evaluated from the viewpoint of microcavity performance.

New energy saving methods are required in the industrial sector to address global climate change and resource depletion. Carbon fiber reinforced plastic (CFRP) has attracted considerable attention as a structural material that can improve energy efficiency by weight reduction. The application of CFRP to machine tools has already been realized; however, the dynamic characteristics of the position control system for CFRP machine tools have not been investigated. In this study, the mechanical properties affecting the positioning performance were experimentally evaluated using a rotary stage that could be switched to different structural materials. This study can be useful as a guideline for position control systems and the mechanical design of a CFRP stage and contribute toward achieving higher energy efficiency.

The joining of dissimilar materials is an important process to produce a large production. In other words, the reliability of such a production is determined by the joining technique because the joint interface often becomes the weakest point against stress. In case of metals, welding and riveting are popular approaches for joining dissimilar materials. However, these techniques generally involve manual and complex operations; therefore, the production quality cannot be maintained, because the accuracy and efficiency of these operations strongly depend on the worker’s skill. From this viewpoint, additive manufacturing (AM) can be useful to produce parts using a combination of dissimilar metals. Metal AM has attracted considerable attention from aerospace and automobile industries recently because of its flexibility and applicability in the production of various complex-shaped parts. Directed energy deposition (DED), one such metal AM method, forms a deposit of powder material and simultaneously irradiates a laser beam on the baseplate. DED can be applied to cladding and repairs as it can be conducted on the surface of the part. In particular, a combined part of dissimilar metals can be easily and directly produced from scratch by changing the powder material of the process. A graded material can also be produced by blending different powders and changing their ratios appropriately. In order to realize such applications of DED, the mechanical properties of the produced part must be evaluated in detail. In this study, a part combining a nickel-based superalloy (Inconel 625) and a stainless steel alloy (SUS316L) is produced using DED; the produced part is evaluated through a tensile strength test, Vickers hardness measurement, metal structure observation, and element distribution analysis. In addition, a graded material is also produced to evaluate the basic characteristics of the joint produced using DED. The experimental results show that the produced joint is sufficiently stiff against tensile stress and its hardness is increased because of the solid solution of niobium in the stainless steel area. The results of the elemental distribution analysis and the Vickers hardness test indicate that a graded joint of Inconel 625 and SUS316L can certainly be produced using DED.

Directed energy deposition (DED), an additive manufacturing process, is a suitable approach for freeform production with metallic materials. By generating a melt pool with a high-power laser beam, injected material powder is contentiously laminated on a baseplate by melting and solidifying. Although all supplied powder should be molten and solidified in order to reduce the material waste, powder distribution is difficult to converge owing to turbulence around the melt pool. Furthermore, an inappropriate powder supply easily leads to sputter generation, which also increases the material waste. In this study, the gas flow under a powder nozzle was analyzed by a computational fluid dynamics (CFD) simulation in order to achieve a high convergence in the powder supply. By measuring the powder distribution with a laser light sheet system and conducting deposition tests, the powder distribution and supply efficiency were experimentally evaluated. According to a gas-solid multiphase-flow simulation, the convergence distance of the powder flow should be shorter than the laser beam focus distance to improve the powder convergence with a lower gas-flow rate. Moreover, the powder nozzles were redesigned by taking the simulation results into consideration, and deposition tests were conducted to evaluate the powder supply efficiency, porosity rate, and penetration rate. The experimental result of the designed nozzle shows a clear improvement in the powder supply efficiency from 50.2 to 66.0%.

We demonstrate the all-precision-machining fabrication of ultrahigh-quality-factor (Q) crystalline optical microresonators. The obtained Q exceeds 100 million for both magnesium fluoride (MgF2) and calcium fluoride (CaF2) materials. This constitutes the highest Q factor obtained for whispering gallery mode crystalline microresonators fabricated solely by ultra-precision machining. We also achieve octave-wide optical parametric oscillation using an MgF2 resonator fabricated with a computer-controlled machining process. This method readily enables advanced dispersion engineering for optical parametric oscillation and makes it possible to explore microcavity nonlinear optics and quantum optics without the need for skilled manual polishing techniques.

Optical microcavity, which can localize light at a certain spot for a short period of time, have a wide range of applications, such as optical signal processing and optical frequency combs. Single crystal calcium fluoride is one of the most suitable material for fabricating optical microcavity due to its excellent optical properties; however, it cannot be manufactured by chemical processes such as etching due to its crystal anisotropy. Currently, high performance optical microcavities are fabricated by ultra-precision turning followed by a hand polishing process because it has complex shape with a size of micro order. However, hand polishing deteriorates the shape made by ultra-precision turning and has a low reproductivity. Therefore, a development of a soft mechanical polishing method to replace hand polishing is strongly desired. Electrically controlled slurry technique is a promising approach in polishing of microparts, where AC electric field is applied to the slurry in order to control the distribution of abrasives to improve the polishing properties in free abrasive polishing. In this study, polishing by applying electrically controlled slurry was conducted for microcavity and the influence of frequency and applied voltage were investigated. From the experimental results, clear differences in the surface quality of microcavity were shown according to amplitude of AC voltage and its frequency.

It is widely known that the spindle speed variation (SSV) is an effective technology for chatter suppression, especially in the turning or boring process. Its simple optimal design, however, is not a simple task. In the past, certain research works considered the chatter onset from the perspective of process energy balance in a vibration cycle. The phase shift between previous (i.e., outer modulation) and present vibrations (i.e., inner modulation) of chatter is a key factor in the process energy balance. The SSV can be conceptually interpreted as a technique that continuously perturbs the phase shift between the inner and outer modulations, thereby changing the process energy balance. Simply put, the chatter energy can be controlled by applying the SSV to suppress the chatter. This study investigates the correlation between the process energy balance and phase shift behavior in the sinusoidal SSV through numerical energy simulation. The results indicate that the phase shift at the maximum spindle speed is an important factor to minimize the total energy balance (i.e., to dissipate the chatter energy) in the SSV cycle. This probably corresponds to the fact that the beat vibration tends to occur near the maximum spindle speed in the SSV. The insights gained from this study are anticipated to serve as a guideline for shaping the phase shift profile in the SSV to effectively suppress chatter vibration.

Directed energy deposition (DED), which is one of additive manufacturing processes applicable to metals, is suitable to produce a large-scale complex-shaped part in aerospace and automobile industries. However, mechanical characteristics in a DED-produced part often varies according to the thermal conduction at each deposition point. To ensure quality uniformity in a DED-produced part, a cooling process also should be actively performed to control the thermal condition. This study evaluates variation in crystal structure in parts produced with DED applying a coolant system. By performing the cooling process at certain intervals during deposition, the variations in Vickers hardness and crystal structure are effectively suppressed in DED of Inconel 625.

A resolved stress model is presented to re-discuss the anisotropic deformation mechanism of single-crystal calcium fluoride in plunge-cut tests. The authors have investigated the machinability of CaF2 in ultra-precision cutting. However, the influence of crystal anisotropy on the brittle–ductile transition was discussed in a qualitative manner using optical microscopy and white light interferometer. Moreover, only the primary {100} slip system and { 111 } cleavage were considered as deformation mechanisms. In this study, the ductility and brittleness of CaF2 is semi-quantitatively re-discussed on the basis of computation of the resolved stresses, by considering a secondary slip system and cleavage. The surface morphologies of the machined surface were characterized using field-emission scanning electron microscopy. The primary {100} slip system is assumed to be dominant for the ductility. The brittle fracture initiated by the { 111 } cleavages was observed in a different manner in dependency rwith cutting directions.

Although the applicability of additive manufacturing (AM) to the production of complex shapes has attracted attention from the automobile and aerospace industries, companies hesitate to introduce AM processes because of their low reliability, which is due to pores inside the produced parts. Consequently, many researchers have experimentally evaluated the relation between the pore evolution and production conditions in AM processes. On the other hand, several studies have focused on finishing processes in order to enhance the quality of AM production, considering that production quality cannot be improved enough only by modifying the production conditions in AM processes. To reduce pores in a metal product, hot isostatic pressing (HIP), which applies high pressure and heat energy to metal AM products and enhances production density, has proven to be an efficient approach. However, special equipment is required to produce a high-temperature and high-pressure environment, leading to high cost and low productivity. From the view point of practicability, a simple finishing process would be a fundamental solution to make metal AM processes highly reliable. This paper therefore proposes a method of reducing pores through a remelting process in the direct energy deposition of Inconel 625. Furthermore, a method of doing a graphical analysis to evaluate the bias of pore distribution in the deposited object is proposed. The pore reduction effect in remelting is experimentally evaluated by irradiating the low density area with a laser beam, and a graphical evaluation clarifies that the concentration of residual pores occurs in the top layer of a deposited object. As a result, residual pores are eliminated with certainty through the remelting process. The density of the deposit can be enhanced easily and without any complicated finishing systems with just the laser system originally introduced in a DED machine.

The subsurface quality of single-crystal calcium fluoride (CaF2) is examined by ultra-precision cutting experiments using a boron-doped nano-polycrystalline diamond (B-NPD) tool and compared with that of CaF2 machined with a single-crystalline diamond tool (SCD). The critical depth of cut, surface morphologies, and process force did not change significantly in the plunge-cut tests. In the ultra-precision cylindrical turning tests, the surface roughness was almost the same, whereas the subsurface damage depth (SSD) changed remarkably, from ten to several hundred nanometers. The SSD depth was reduced by the use of B-NPD. Additionally, shear deformation and rotational deformation of the subsurface layer were observed. The lowering of friction coefficient at the interface between the cutting tool and the machined surface is assumed to affect the subsurface layer.

Direct energy deposition (DED) is one of additive manufacturing processes, which achieves high production efficiency by supplying material powder and irradiating high-power laser beam to a baseplate at the same time. Furthermore, the DED has a potential to produce a functional material by blending various material powders. Although a metal foam structure is well-known because of its beneficial functionality such as light-weight, the complicated foaming process requires a special equipment and long processing time. This paper proposes a simple fabrication method for metal foam structure by applying a blowing agent into DED. Metal foam structure can be produced by foaming the meltpool with titanium hydride which releases hydrogen in a high temperature environment. The proposed method certainly produces a foam structure in stainless steel by blending titanium hydride powder into stainless powder for DED.

Directed energy deposition is an additive manufacturing process which produces deposits by irradiating laser beam on the baseplate and supplying material powder to the meltpool. Although the material powder is generally conveyed with carrier-gas flow, the powders diffuse and some of them do not reach to the meltpool. In order to suppress the waste of materials, the particle movement should be analyzed and modified not only from the viewpoint of deposition conditions but also the nozzle design. Against this background, this paper presents analytical and measurement results of powder distribution under the nozzle and proposes a nozzle design to reduce the waste of material powder based on a gas-solid multiphase-flow simulation. The experimental result of designed nozzle certainly shows high powder supply efficiency of 74.8%, whereas that of the conventional nozzle is 52.6%.

Generally, manufacturing process of optical glass lenses, which are used for single lens reflex cameras, is classified into grinding and polishing for removing cracks generated by grinding. Thus, it is desired not to generate the cracks in grinding as much as possible. Because grinding condition with cracks differs depending on the material properties of the workpiece, suitable grinding condition needs to be selected based on a lot of experimental verifications. In addition, the controller’s gain of the tool spindle with grinding wheel may be intentionally set to low value in ultra-precision grinding. Thus, the spindle speed may decrease even under servo control because of grinding load. In this study, the influence of servo characteristics on crack generation is evaluated in ultra-precision grinding of optical glass lenses. Concretely, an optical glass lens was machined using an ultra-precision 5-axis grinding machine and servo information of tool spindle was monitored during the process. Comparison of the obtained servo information and the surface observation of the workpiece revealed that the spindle speed decreased and the number of the cracks increased at the outside of the workpiece. The experimental results suggested the possibility of estimating the grinding load and predicting the surface quality by monitoring the variation in the spindle speed.

An optical microcavity, which stores light at a certain spot, is an essential component to realize all-optical signal processing. Single-crystal calcium fluoride (CaF2) theoretically shows a high Q-factor which is a desirable optical property. The CaF2 microcavity can only be manufactured by ultra-precision cylindrical turning (UPCT). The authors have studied UPCT of CaF2 and shown the influence of crystal anisotropy and tool geometry on surface roughness and subsurface damage. The study indicated that a smaller nose radius of the cutting tool led to shallower subsurface damage. Thus, it is inferred that a smaller nose radius compared to the previous nose radius (0.05 mm) can further reduce subsurface damage. Nevertheless, the mechanism that causes a difference in subsurface damage due to crystal anisotropy is not sufficiently clear. The influence of subsurface damage on microcavity performance is still unclear. In this study, the UPCT of CaF2 was conducted using a tool with a nose radius of 0.01 mm. The subsurface damage was investigated by transmission electron microscope (TEM) observation from the viewpoint of the change in crystal lattice arrangement. In our previous study, fast Fourier transfer (FFT) analysis was used for confirmation of change of crystal structure. In this study, FFT analysis was also used to quantitatively evaluate the depth of subsurface damage. In addition, inverse fast Fourier transfer (IFFT) was used to analyze change of crystal lattice arrangement clearly, which enables discussion of the influence of slip systems. Finally, optical microcavities are manufactured without any crack, and the influence of subsurface damage on microcavity performance is experimentally evaluated using a wavelength tunable laser and power meter.

The use of a patterned electrode on one side only is expected to be a suitable solution for omitting the wiring to the movable electrode using electrorheological gel. Electrorheological gel is a fu...

Ultrahigh-Q crystalline microresonators have various potential applications including as microresonator frequency combs [1] and low-noise radio frequency oscillators [2]. Since crystalline materials are transparent in the visible to mid-infrared wavelength region, magnesium fluoride (MgF 2 ) and calcium fluoride (CaF 2 ) microresonators have been expected to achieve broad bandwidth Kerr comb generation. The demand for precise geometrical dispersion control to compensate for material dispersion has recently been increasing because material dispersion in the visible or mid-infrared region is not feasible for obtaining a Kerr comb [3,4]. However, the dispersion engineering of crystalline microresonators remains a major challenge since hand polishing is generally needed after diamond turning to obtain a high Q [5]. This restricts the possibility of tailoring the resonator dispersion because it degrades the controllability of the cross-sectional shape.

Sapphire has received increasing attention as an engineering material even though its machinability is still an issue. In this study, the influence of the milling process parameters on the surface quality of single-crystal sapphire is investigated. Due to the hardness and brittleness of the sapphire substrate, crack initiation becomes the main concern with respect to up- and down-milling, feed rate, tool inclination angle and tool wear. With an inclined ball-end mill cutter in feed direction various cutting tests were performed to find optimal parameters for machining microchannel. It was observed that the feed rate and depth of cut are dominant factors for the surface quality. The tool inclination angle shows a parabolic relation to the quality of the machined surface. After tool wear events, such as peeling-off of the tool coating, an increased surface roughness is observed.

In this study, plunge-cut tests are conducted on single-crystal sapphire to investigate the brittle and ductile deformation mechanisms from the viewpoint of crystal anisotropy. The anisotropic deformation behaviour of the machined sapphire substrate manifests itself in the critical depth of cut and the diverse crack morphologies. Based on a resolved stress model that is adapted to the experimental procedure, weighted resolved stresses are computed, and the tendency of brittle–ductile transition depending on the peculiarities of the low-symmetry hexagonal crystal structure is discussed. Rhombohedral twinning is assumed to dominate the brittle–ductile transition.

Large aperture lenses with high surface quality are demanded for professional imaging products such as single-lens reflex cameras and astronomical telescopes. Large aperture optical lenses are shaped by ultra-precision grinding and finished by prolonged polishing. However, the prolonged polishing process leads to deterioration of the form accuracy. In order to reduce the amount of polishing, ductile-mode ultra-precision grinding is demanded. In this study, a rubber bonded wheel, which has a low elastic modulus, is used for grinding of spherical glass BK7, and influence of the hardness of the rubber bonded wheel and abrasive chip thickness on brittle fracture and surface roughness are experimentally investigated.

Sapphire is an attractive engineering material for the cover glass of smartphones and wristwatches because of its high hardness and resistance to corrosion, wear, and heat. However, the high rate of tool wear and brittle chippings around the holes are serious problems associated with drilling sapphire. To enhance the accuracy and efficiency of the drilling process on sapphire, this paper presents a novel tool-path strategy using helical milling along with various tool path patterns. Experimental results show that the proposed method successfully reduces brittle chippings around the holes.

In recent years, many composite materials have been used in industry. Among such materials, the demand for carbon fiber-reinforced plastic (CFRP) is increasing. Although CRFP is used in various fields such as the aerospace industry, automotive industry, and sports equipment because of its light weight and high strength, it has poor production efficiency. Thus, carbon fiber-reinforced thermoplastic (CFRTP), with characteristics similar to CFRP but higher in production efficiency, has attracted attention in areas such as the automotive industry. Because CFRTP is used as a structural element, it is usually drilled to allow connection to other parts. However, it is a difficult-to-cut material requiring the development of a high-accuracy, high-efficiency processing method. This study proposes high-feed-speed processing as a method that achieves high-quality drilling at low cost. The cutting temperature was estimated to verify the effect of the high-feed-speed processing method, and processing conditions that prevented delamination and burring were identified.

The development of ultrahigh-quality-factor ( Q ) microresonators has been driving such technologies as cavity quantum electrodynamics (QED), high-precision sensing, optomechanics, and optical frequency comb generation. Here we report ultrahigh Q crystalline microresonator fabrication with a Q exceeding 10 8 , for the first time to our knowledge, achieved solely by computer-controlled ultraprecision machining. Our machining fabrication method readily achieves the dispersion engineering and size control of manufactured devices via programmed machine motion, both of which were not possible with the conventional manual polishing method. We can achieve an ultrahigh Q without the need for subsequent careful polishing that is generally required to ensure that surface integrity is maintained. We carefully addressed the cutting condition and crystal anisotropy to overcome the large surface roughness that has thus far been the primary cause of the low Q in the machining process. Our result paves the way for a reliable fabrication with a view to various photonic applications utilizing ultrahigh- Q crystalline microresonators.

This erratum presents the corrections to the Letter published in Opt. Lett. 44, 3146 (2019)OPLEDP0146-959210.1364/OL.44.003146.

We demonstrated the dispersion engineering of high-Q crystalline microresonators fabricated with computer-controlled machining enabling precise structure control. In addition, we investigated the ideal resonator structure for 100 GHz microresonator frequency comb generation in a MgF2 crystalline microresonator.

Additive manufacturing (AM) for metals has attracted attention from industry because of its great potential to enhance production efficiency and reduce production costs. Directed energy deposition (DED) is a metal AM process suitable to produce large-scale freeform metal products. DED entails irradiating the baseplate with a laser beam and launching the metal powder onto the molten spot to produce a metal part on the baseplate. Because the process enables powder from different materials to be used, DED is widely applicable to valuable production work such as for a dissimilar material joint, a graded material, or a part with a special structure. With regard to parts with a special structure, directional solidification can prospectively be used in the power plant and aerospace industries because it can enhance the stiffness in a specific direction via only a simple process. However, conventional approaches for directional solidification require a special mold in order to realize a long-lasting thermal gradient in the part. On the other hand, from the viewpoint of thermal distribution in a produced part, DED is able to control the gradient by controlling the position of the molten pool, i.e., the position of the laser spot. Moreover, unlike casting, the thermal gradient can be precisely oriented in the expected direction, because the laser supplies heat energy on the regulated spot. In this study, the applicability of DED to directional solidification in Inconel® 625 is theoretically and experimentally evaluated through metal structure observation and Vickers hardness measurements. Furthermore, the effect of two different cooling processes on directional solidification is also considered with the aim of improving the mechanical stiffness of a part produced by DED. The observations and experimental results show that both the cooling methods (baseplate cooling and intermittent treatment with coolant) are able to enhance the hardness while retaining the anisotropy.

Electro Adhesive Gel (EAG) has the unique characteristic of changing its surface adhesive property with the intensity of the electrical field applied. This property makes EAG useful in applications to fixing devices and mechanical brakes. Although its adhesion performance depends on the distribution of the electro-rheological particles in the EAG, it is difficult to arrange the particle distribution uniformly in a wide area from the perspective of production process. In this study, a novel functional elastomer that has the same function as EAG is developed, Electro Adhesive Surface (EAS). In EAS, micro photolithography is used to fabricate strut pyramids distributed uniformly on a substrate, and then silicone gel is poured into the structure. When an electrical field is applied, the silicone gel rises to the tops of the pyramids formed by the struts, and adhesion occurs to an object on EAS. To determine a micro structure design for EAS, the fixing force was measured with various struts diameter and gaps. Experimental result shows that the larger struts diameter and the narrower gaps enhance the fixing force of EAS.

Large-aperture lens used for single-lens reflex cameras is generally produced by both ultra-precision grinding and polishing because a mass-produced lens by molding process can hardly achieve the required form accuracy and surface quality. Recently, grinding process of an optical glass should make surface quality as high as possible in order to reduce removal amount in polishing process. Accordingly, evaluation of subsurface damage induced under various grinding conditions has been required because subsurface damage leads to crack initiation or deterioration of the performance. However, evaluation method of subsurface damage on the spherical glass lens after grinding has not yet been established.In this study, the quantitative evaluation method by applying wet-etching of hydrofluoric acid (HF) is proposed, then its validity is verified. From the experimental results, we clarify to evaluate the subsurface damage by examining the surface transition according to etching time.

Directed energy deposition (DED) for producing a complex shaped metal part has attracted attention in the aerospace industry. However, DED easily causes structural defects such as voids and compositional changes, which results in the deterioration of the mechanical strength of the product. Hence, reducing such defects is essential. In this study, the influence of the powder characteristics of Inconel 625 was focused upon, and the void density and compositional change inside the deposited part were analyzed. The results indicated that a slight amount of carbon in the particle caused void generation and a carbon layer was formed at the surface.

Direct energy deposition (DED) process attracts attention from industries because of its applicability to production of complex shape parts. However, technical challenges still remain in DED, such as void evolution inside of the produced object. This paper provides a new graphical evaluation method of void distribution. Binarizing a cross-sectional image of the cladded object and applying a 2-dimensional Gaussian window, the void distribution rate is separately evaluated in each local area on the cross section. To clarify the relation between void evolution and deposition condition in Inconel 625, the void distribution is experimentally evaluated through the various tests.

Optical micro-resonators attract interests as essential components to develop optical signal processing circuits which can reduce energy loss. Single-crystal calcium fluoride (CaF2) could be the most suitable material from a viewpoint of optical property. To satisfy high form accuracy and surface roughness, ultra-precision cylindrical turning (UPCT) is a feasible fabrication process. In previous research, it was indicated that the tool with sharper nose radius could make UPCT more stable and reduce subsurface damage. In this study, the tool with much smaller nose radius 0.01mm was applied, then, the influence on surface integrity was investigated by TEM observation.

To realize ultimately efficient signal processing, it is necessary to replace electrical signal processing circuits with optical ones. The optical micro-resonator, which localizes light at a certain spot, is an essential component in optical signal processing. Single-crystal calcium fluoride (CaF2) is the most suitable material for a highly efficient optical micro-resonator. The CaF2 resonator can only be manufactured by ultra-precision machining processes, because its crystal anisotropy does not allow the application of chemical etching. However, the optical micro-resonator's performance depends definitely on the surface integrity. This study investigated the relationship between surface quality after ultra-precision machining and crystal anisotropy. Firstly, crack initiation was investigated on the (1 0 0), (1 1 0), and (1 1 1) planes using the micro-Vickers hardness test. Secondly, brittle-ductile transition was investigated by orthogonal cutting tests. Finally, cutting performance of cylindrical turning was evaluated, which could be a suitable method for manufacturing the CaF2 resonator. The most difficult point in cylindrical turning of CaF2 is that the crystalline plane and cutting direction vary continuously. In order to manufacture the CaF2 optical micro-resonator more efficiently, analysis was conducted on crack initiation and surface quality of all crystallographic orientations from the perspective of slip system and cleavage.

The optical micro-resonator, which stores light at a certain spot, is essential in next-generation optical signal processing. Single-crystal calcium fluoride (CaF2) is the most suitable material for this element. Ultra-precision turning is a feasible fabrication process for CaF2 optical micro-resonators. In this study, the influence of subsurface damage on the resonator's Q factor is investigated. TEM observation shows that the subsurface layer of up to several tens of nanometers thickness changed from single-crystal to polycrystalline morphology due to ultra-precision turning. A diamond tool with 0° rake angle results in lower damage than one with negative rake angle, which enhances the resonator's performance.

The generation of an optical Kerr comb in whispering gallery mode (WGM) microcavities has been investigated for applications in frequency metrology, precise spectroscopy, and signal processing. Optical Kerr combs are generated via parametric frequency conversion, thus a high quality factor (Q) is essential for lowering the threshold power, and this can be achieved with crystalline microcavities in, for example, calcium fluoride (CaF 2 ) because of the low absorption coefficient of this material. An optical Kerr comb with a wide span is needed to obtain frequency stabilization with the f-2f self-referencing method, which requires an anomalous dispersion [1]. We used a computer controlled precise cutting machine to fabricate a dispersion controlled CaF 2 microcavity with an anomalous dispersion to obtain exactly the same dispersion as we obtained in the numerical simulation.

The demand for large aperture lenses with high surface quality and form accuracy used for single-lens reflex cameras has been increasing. Generally, large aperture glass lenses are produced by ultra-precision grinding. Considering the increasing global competition, the grinding process has to be improved. However, highly efficient grinding causes worse surface quality, which leads to much polishing and ultimately results in lower form accuracy. Thus in this study, aiming at the realization of highly efficient and precise grinding of glass lenses, cross grinding of optical glass BK7 is carried out. As a first step of the study, the influence of grinding conditions on the surface quality is investigated experimentally.

In this Letter, we report phase-matched four-wave mixing separated by over one-octave in a dispersion engineered crystalline microresonator. Experimental and numerical results presented here confirm that primary sidebands were generated with a frequency shift up to 140 THz, and that secondary sidebands formed a localized comb structure, known as a clustered comb in the vicinity of the primary sidebands. A theoretical analysis of the phase-matching condition validated our experimental observations, and our results good agree well with numerical simulations. These results offer the potential to realize a frequency tunable comb cluster generator operating from 1 um to mid-infrared wavelengths with a single and compact device., Comment: 5 pages, 5 figures

Electro-adhesive gel (EAG) is a functional material that exhibits an electrically controllable adhesive force. The adhesive characteristic of EAG highlights potential applications in fixing or handling devices. However, the EAG adhesive area under an applied electric field is often irregular due to particle distribution at the surface, which therefore leads to a large variance in the adhesive force of each sample. This paper proposes the development of an electro-adhesive pillar array (EAPA) to stabilize and improve the performance of the electro-adhesive force regardless of the sample. Electro-hydrodynamic patterning, which is a novel technique to fabricate micro-/nanostructures in a polymer film, is introduced to fabricate the pillar array. The proposed fabrication method and process are first discussed, and a preferred template design is verified. Furthermore, the fabrication process is improved with a UV-curing polymer and surface treatment of the template. The experimental results show that the improved EAPA successfully achieves a higher fixing force with a uniform adhesive area. The proposed EAPA clearly shows a better electro-adhesion performance than conventional EAG.

To achieve maximally efficient signal processing, an electrical signal processing circuit needs to be replaced with an optical one. Optical micro-resonators, storing light at certain spots, are essential for optical signal processing. Single-crystal Calcium Fluoride (CaF2) is the most suitable material for highly efficient optical micro-resonators, and a resonator made of CaF2 can be manufactured by ultra-precision machining. However, the performance of such optical micro-resonators depends on its surface integrity. In this study, the relation between the crystal anisotropy and surface integrity after ultra-precision cutting was investigated. The most difficult point in the cylindrical turning of a crystalline material is that the crystalline plane and the cutting direction constantly vary. We analyzed crack initiation and surface integrity of the entire machined surface from the perspective of slip system and cleavage. Subsurface damage was also observed by using the TEM and X-ray analyzers for more efficient manufacturing of optical micro-resonators.

Carbon fiber reinforced plastics (CFRP) have been used for various applications such as aerospace, automobiles, and sporting goods due to their superior properties, and the demand for through-hole drilling of CFRP is increasing. A novel hybrid helical milling technique applying ultrasonic vibration and cryogenic tool cooling method is proposed in this paper, as an effective machining method for CFRP. To investigate the effects of ultrasonic-vibration-assisted machining and cryogenic tool cooling method, cutting performance evaluations based on thrust force, machining accuracy, and tool wear were conducted in this study. The results of the cutting tests clearly indicated that the proposed cutting method provides reductions in thrust force, and suppresses delamination at the machined surface.