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Polydimethylsiloxane (PDMS) is one of the important materials for microfluidic chips. The pattern of micro channels on the PDMS plate is usually fabricated through the photolithography and micro molding process. However, the photolithographic method requires multi chemical and mechanical processes and resultant long process time. The micro milling process is a feasible method for rapid fabrication of various patterns of micro channels .However, micromachininghas not yet been applied to soft polymer materials. It is difficult to machine elastic materials such as PDMS because of their low toughness. In order to machine a micro grooves on soft polymer materials, the cutting process applying cryogenic cooling is proposed because the elastic properties of soft polymer materials remarkably change from rubbery state to glassy state below the glass transition temperature. In this study, the freezing milling method using liquid nitrogen is applied to the micro grooving of PDMS. The result of a cutting test shows that micro grooves can be shaped easily and machined accurately in PDMS by the proposed method.

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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 µm to mid-infrared wavelengths with a single and compact device.Phase-matched four-wave mixing (FWM) in a whispering gallery mode (WGM) microresonator driven by a continuous wave (CW) laser have been studied for decades [1]. In particular, a microresonator frequency comb (Kerr comb) realized via a cascade FWM process makes it possible to achieve broadband optical frequency comb sources characterized as having high repetition rates, compactness and low-energy consumption [2]. They provide fascinating applications including precise spectroscopy [3] and coherent data transmission [4]. A Kerr comb, and particularly a dissipative Kerr soliton (DKS), which is a stable low noise state, features a coherent broad comb spectrum with a smooth envelope [5]. However, spectral broadening over one octave remains a challenge mainly because of the limitation imposed by group velocity dispersion (GVD). Spectral broadening utilizing dispersion engineering has been achieved with Cherenkov radiation, which can be understood in terms of the coherent dispersive wave in the frequency domain emitted from a soliton propagating along a resonator [6]. A dispersive wave induces asymmetrical spectral profiles and occurs at the point where a simple phase-matching condition is satisfied, and it is determined by the signs and values of higher-order (i.e., third-, fourth-and fifthorder) dispersion parameters.Higher-order dispersion plays important roles not only as regards a Kerr soliton in an anomalous GVD regime, but also in a weak normal GVD regime. Since a normal dispersion usually does not allow modulation instability (MI) near the pump, phase-matched FWM may be considered to occur only in an anomalous dispersion resonator. However, higher-order dispersion, particularly even orders of dispersion, enables a resonant MI process, called clustered frequency combs, to occur far from the pump mode [7][8][9]. Clustered combs, characterized by FWM generation with parametric sidebands that have a * takasumi@elec.keio.ac.jp large-frequency shift, have been reported using an MgF 2 microresonator [7,9] and silica microtoroids [8]. The fact that clustered combs have the potential to utilize microcomb source emitting in the 1.0 to 3.5 µm wavelength region with just a near-infrared pump indicates interesting potential applications, for example laser processing and optical communication. In particular,...

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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.

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