Yoshihisa Warashina

MEMS based miniature FT-IR engine with built-in photodetector

A MEMS-FTIR engine has been developed as a key device for the Fourier-Transform Infrared Spectrometer, which consists of a Michelson interferometer including an electro-static actuator to control a moving mirror, an optical fiber groove for incident light and a photodetector. All these elements except for the photodetector are monolithically fabricated in Silicon using MEMS technology. The optical elements such as a beam splitter, a fixed mirror and a moving mirror are formed and aligned simultaneously with high degree of precision by Deep Reactive Ion Etching (DRIE). The vertical side walls are utilized as optical planes so that the incident light path is located in parallel with the Silicon substrate. The moving mirror is driven by an electro-static MEMS actuator. The photodetector is placed above an angled mirror, which is formed by alkaline wet etching exposing the Silicon crystal plane at the end position of light path. All the elements including the photodetector are hermetically covered by a lid of Silicon in the vacuum chamber by using a surface activate bonding technology. In order to reduce the cost, wafer level process and separation of each chip by a laser dicer after all assembly processes are introduced. The realized MEMS-FTIR is 10×17×1 mm in size and a signal noise ratio (SNR) of better than 35dB, which comes from a good verticality of less than 0.2 degree in the vertical side walls as optical planes by managing the DRIE etching conditions.

Streak-camera-based long-distance range finder with 10(-7) resolution.

A novel optical distance meter with a pulsed yttrium aluminum garnet laser and a pair of streak cameras is developed. To minimize timing errors, the time scale is marked by an optical-registration-clock pulse. This assures an intrinsic resolution of 3 mm. For field applications, comparison of multiwavelength and single-wavelength methods confirms that the latter method is much better if carefully corrected. By use of the equipotential temperature criterion for correction of the atmospheric parameters, such as the atmospheric boundary layer effect and the temperature along the ray trajectory, a resolution of better than 1 cm is achieved over a range of 30 km. This result corresponds to a relative resolution of 3 × 10(-7). Typical ranging results in a geophysical application are shown for monitoring of the relative translational shift of the Asian (Eurasian) and the Philippine plates; the predicted shift is found to be absent.

Single-mode fiber-compatible plastic-molded surface-contact receptacles

A single-mode fiber-compatible surface-contact (SC) receptacle is fabricated by insert-molding technology with a zirconia sleeve in the mold patterns. The zirconia sleeve, lens holder, and a plastic case consist of the same mold pattern for precise coincidence of the optical axes. Almost all of the case structures are fundamentally cylindrical to disable temperature modifications due to mechanical expansion or deformation. For the same reason, the grade of liquid crystalline polymer is selected carefully. Furthermore, the roof mirror array lens used in the facsimile machine is selected as a graded-index (GRIN) rod lens to reduce costs. The fabrication results show that in this structure, the mechanical removal strength in the zirconia sleeve attained over 50 kg f, and mechanical tolerance is also maintained after more than 1000 plug coupling tests. The fabrication methods are successively suitable for mass production and contributed to the cost effective SC receptacle. This receptacle is compatible not only with multimode fiber but also with single-mode fiber. The total coupling loss in this receptacle equipped with a 1.3-µm multi-quantum-well laser diode is —6 dB with the singlemode fiber. The contribution due to the GRIN rod lens is —5.5 dB and the excess coupling loss due to the assembly is within —0.5 dB.

Plastic-molded SC module consisting of a single-mode fiber

A single-mode-fiber-compatible SC-type optical module (SC module) is developed. This module realizes low optical coupling loss and low cost by means of plastic molding technology and the developemnt of automatic fabrication equipment. The SC module consist of a plastic adapter to be compatible with a SC-mode-fiber connector and a plastic housing for optical components: a GRIN rod lens and an optical transmitting/receiving device. The housing is made from a plastic with an extremely low thermal expansion coefficient, and is designed as acylindrical structure for thermal stability. It has a mount for an optical device, a lens holder, and a fiber connection. A zirconia ceramic sleeve, installed in the housing by insert molding technology, is employed to obtain a high plug coupling strength and the optimum optical power coupling. The optical axis between the zirconia sleeve and GRIN rod lens is adjusted automatically and accurately by insert molding technology: the lens holder is formed by the same plastic mold that holds the zirconia sleeve along it. In order to lower the cost, the optical module is fabricated using automatic fabrication equipment, which carried out the processes from supplying the optical device to fixing it with UV-cured resin. The following characteristics of the SC module are obtained from experimental results where total optical loss was 6dB. The portion of 5.5dB of the total loss is contributed by the GRIN rod lens. The remainder is the excess loss of 0.5dB due to assembly. The thermal stability is found to be within 0.1dB in the temperature range from -10 degrees to 65 degrees C.