1. Field of the Invention
The present invention relates to an apparatus for forming an optical aperture. In particular, the present invention relates to an apparatus for forming an optical aperture utilized in a near field device that radiates and/or detects near field light.
2. Description of the Related Art
In order to observe microregions of the sample surface on the order of nanometers, scanning probe microscopes (SPM) such as scanning tunneling microscopes (STM) and atomic force microscopes (AFM) are used. SPM scans a sharpened probe on the sample surface, observes the interaction between the probe and the sample surface such as tunneling current or atomic force, and is able to obtain images with a resolution that depends on the probe tip shape. However, there are relatively severe restrictions on the sample.
Interest has been focused on scanning near field optical microscopes (SNOM) that observe the interaction between the near field generated on the sample surface and the probe, thud enabling the observation of microregions of the sample surface.
In SNOM, near field is irradiated to the sample surface from the aperture formed at the sharpened tip of an optical fiber. The aperture has a size smaller than the diffraction limit of the light introduced into the optical fiber, for example, about 100 nm in diameter. The separation between the aperture formed at the probe tip and the sample is controlled by SPM technology, and is smaller than the aperture size. The spot size of the near field on the sample is approximately the aperture size. Therefore, by scanning the near field that is irradiated on the sample surface, it is possible to observe the optical properties of microregions of the sample.
Not only for microscopes, but also for high density optical data recording is it applicable by introducing light of relatively high intensity through the optical fiber probe towards the sample. Near field with high energy density is generated at the optical fiber probe aperture, and it modifies either the structures or the properties locally of the sample surface. In order to obtain near field of high intensity, efforts have been made to increase the vertical angle.
In these devices utilizing near field, aperture forming is the most important. As one apparatus for forming an aperture, an apparatus disclosed in Japanese Patent Publication No.21201/1993 is known. In the manner of forming the aperture with this apparatus, a pointed light waveguide on which an opaque film is deposited is used as the object for forming the aperture. The method of forming the aperture is that the pointed light waveguide with an opaque film on the point is plastically deformed by pressing the pointed light waveguide against a hard flat plate with a very small amount of pressing, which is well-controlled by a piezoelectric actuator.
Another apparatus for forming an aperture is disclosed in Japanese Patent Laid-Open No.265520/1999. In the aperture forming apparatus disclosed in Japanese Patent Laid-Open No.265520/1999, the object which is to have an aperture is the point of a projection which is formed on a plate by FIB (Focused Ion Beam). The method of forming the aperture is that FIB is irradiated on the side of the opaque film on the projection point removing the opaque film on the point.
However, according to the method of Japanese Patent Publication No. 21201/1993, the aperture can be formed on the light waveguide only one by one. Additionally, a piezoelectric actuator having a moving resolution of a few nano meters is needed to control the amount of pressing and thus an aperture forming apparatus has to be placed in an environment which is little influenced by vibration of other devices or air. Furthermore, it takes much time to adjust a waveguide rod to vertically abut on the flat plate. Moreover, in addition to the piezoelectric actuator having a small moving amount, a mechanical translation platform having a large moving amount is needed. Besides, when the pressing amount is controlled by using the piezoelectric actuator having a small moving resolution, a control unit is required and it takes a few minutes to control and form the aperture. Therefore, for aperture formation, a large-scale apparatus such as a high voltage power supply or a feedback circuit is needed. In addition, a problem has arisen that costs for aperture formation are increased.
Additionally, according to the method of Japanese Patent Laid-Open No. 265520/1999, the fabrication object is the projection on the flat plate. However, since the aperture is formed by using the FIB, the time required to form one aperture is as long as ten minutes. Furthermore, because of using the FIB, a sample needs to be placed in vacuum. Thus, a problem has arisen that fabrication costs for aperture fabrication are increased.