DE19634893A1 - Mechanical stabilisation and tuning method for photon crystal filter used in optical fibre communications - Google Patents

Abstract

The method involves filling the hollow spaces in the filter, e.g. which is structured as a photon crystal, with optically transparent material of adjustable refractive index. The filled filter is subjected to an electrical field of variable field strength. The optical characteristics, e.g. the refractive index for transmitted and reflected light in the crystal's hollow chamber, fine tuning of the transmitter amplitude and fine tuning of the light phase shift are adjusted by varying the field strength of the electric field.

Description

Tunable filters for optical communications and telecommunications are e.g. Z. realized in the form of long optical fibers, which get their filtering effect through Bragg diffraction gratings inscribed with UV light in special fibers. Please refer
R. Kashyap, "Photosensitive Optical Fibers: Devices and Applications", Opt. Fibers Techn. 1, 17-34, (1994).

It is a considerable technological requirement to produce these diffraction gratings with great accuracy over great lengths from a few mm to cm. Special techniques improving electron beam lithography in its "stitching" are used to reduce this error. Please refer
HWP Koops, J. Kretz, M. Weber, "Combined Lithograpies for the reduction of stitching errors in Lithography", Proc. EIPB 94, J. Vac. Sci Technol B 12 (6) (1994) 3265-3269, and
VV Wong, J. Ferrera, JN Damask, TE Murphy, HA Haus and HI Smith, "Distributed Bragg greating integrated-optical Filters: Synthesis and fabrication" J. Vac. Sci. technol. B 13 (6) Nov / Dec 1995 pp. 2859-2864.

Fiber filters must always be plug-in or Splice connections in a hybrid technique in one Macroscopic optical arrangement can be inserted. A  Miniaturization of the assemblies is therefore not allowed to reach.

Using the process of additive lithography by computer-guided electron beam-induced deposition, photon crystals are miniaturized as 2- and 3-dimensional arrangements of long miniaturized needles made of dielectric materials with nanometer precision. Please refer
HWP Koops, R. Weiel, DP Kern, TH Baum, "High Resolution Electron Beam Induced Deposition", Proc. 31. Int. Symp. On Electron, Ion, and Photon Beams, J. Vac. Sci. Technol. B 6 (1) (1988) 477.

These can be built directly into the optical path. Due to the high-precision that is customary in the process Computer control of the electron beam in place, time and Direction of movement it is possible to almost all required Geometries of the crystals and their for the desired one optical purpose to produce targeted deformation. Thereby can create a customized optical behavior of the structure be generated.

With M. Eich, H. Looser, DY Yoon, R. Twieg, GC Bjorklund, "Second harmonic generation in poled organic monomeric glasses", J. Opt. Soc. At the. B, 6, 8 (1989) and M. Eich, A. Sen, H. Looser, GC Björklund, JD Swalen, R. Twieg, DY Yoon, "Corona Poling and Real Time Second Harmonic Generation Study of a Novel Oovalently Functionalized Amorphous Nonlinear Optical Polymer ", J. Appl. Phys., 66, 6 (1989) describes the use of nonlinear optical material. By applying a strong electric field to the nonlinear optical material, the optical path in the crystal and thus its properties can be adjusted electrically. The same effect is achieved when an electric field is applied to a liquid crystal structure. Please refer
M. Stalder, P. Ehbets, "Electrically switchable diffractive optical element for image processing", Optics Letters 19, 1 (1994). By varying the electric field, the optical transmission characteristic can be shifted in fine steps both in the case of nonlinear optical material and in the case of liquid crystals. Furthermore, a variation of the optical mirror effect, the direction of reflection and possibly the strength is possible.

Furthermore, a solution for the production of photon crystals using multibeam writing instruments is known. With this solution, the photon crystals are produced in a very economical manner by means of corpuscular rays and with the aid of additive lithography. Please refer
H. Koops, 1974, patent application P 2446 789.8-33 "Corpus Kularstrahl-Optical device for the corpuscle irradiation of a preparation", USA Patent No. 4021674,
H. Koops, 1974, patent application DE-PS 24 60 716.7 "corpuscular beam optical device for corpuscle irradiation of a preparation",
H. Koops, 1974, patent application DE-PS P 2460 715.6 "corpuscular beam optical device for corpuscle irradiation of a preparation in the form of a surface pattern with several surface elements that are identical to one another",
H. Koops, 1975, patent application DE-PS P 2515 550.4 "corpuscular beam optical device for imaging a mask onto a preparation to be irradiated",
M. Rüb, HWP Koops, T. Tschudi "Electron beam induced deposition in a reducing image projector", Microelectronic Engineering 9 (1989) 251-254 and
H. Elsner, H.-J. Döring, H. Schacke, G. Dahm, HWP Koops, "Advanced Multiple Beam-shaping Diaphragm for Efficient Exposure", Microelectronic Engineering 23 (1994) 85-88.

Band gap photon crystals are 2- and 3- dimensional dielectric structures in which the  Propagation of electromagnetic waves, depending on or regardless of their direction of propagation. Calculations and microwave measurements showed that a face centered cubic or also a 2-dimensional cubic arrangement of holes in a dielectric Matrix or of dielectric rods such photonic Show band gaps. 6 levels are sufficient to achieve a high quality of the elements. Such 2- and 3-dimensional structures are often "photonic Called crystals ".

The solution according to the invention should make it possible tunable filter based on photon crystals to manufacture.

The tunable filter should be mechanically stable. At the same time, a high variability in properties of the filter can be achieved.

The basic building block of the filter according to the invention is with the known method of additive lithography Computer-aided electron beam-induced deposition as a 2 and 3-dimensional arrangement of long miniaturi based needles made of dielectric materials. This is because of the needle-shaped crystal structure generated basic building block of the filter according to the invention mechanically less resilient.

According to the invention, the spaces between the needle-shaped Crystal structure with optically transparent material with adjustable refractive index filled so that a tunable filter is created. For the filling that the desired mechanical stability of the component causes nonlinear optical materials are particularly suitable or liquid crystals. The tuning of the filter will by the action of an electric field on the filter and especially on the transparent material of the filling achieved. The electric field is preferably through  Field plates arranged around the filter are generated. The electric field is caused by the linear optical material coefficients a change in Refractive index in the filled crystal cavity. Through the Changes in the refractive index change the Properties and thus the filter effect of the filter. Changing the field strength can have the following effects be achieved:

• - Fine-tuning the wavelength range of the transmission the filter,
• - fine-tuning the phase shift of the light,
• - fine-tuning the transmitting amplitude of the light,
• - Changing the refractive index and thus changing the Direction of reflection for the continuous and the reflected light.

In the manufacture of the basic element of the filter by means of the known methods of additive lithography Computer-aided electron beam-induced deposition can also have a targeted influence on the Take the desired filter structure.

By programmed modulation, which when building the Crystal cells are superimposed, can be optical Properties such as focusing or pre-distraction are targeted influence.

If several are sequentially also possibly different tunable photon crystals on specially in waveguide Patterned recesses built, so one high miniaturization of filters and optical resonators for laser applications. This will make one high packing density possible.

With the method according to the invention finely tunable and widely tunable narrow-band filter elements of small dimensions manufacture and integrated in high packing density realize. A variety of components and circuits  The integrated optics can be improved and new miniaturized. That applies, for example tunable electromagnetic micro-resonators for single-mode, light-emitting diodes, these Structures the spontaneous emission in a now adjustable suppress broad wavelength range and so the Reduce performance requirements and reliability of light emitters, especially optical arrays. Furthermore, an increased spontaneous emission of fine-tunable light emitters possible. This will make one faster modulation speed for optical Connections and switches possible. It can be optical High quality mirror with tailor-made finely adjustable Reflective and transmittance with geometric preset wavelengths and pass bandwidths miniaturized and built up in high packing density will. It can also be compact electrically tunable narrowband filters (0.5-1 nm), polarizers and the polarization-selecting tunable bandpass Make filters. A targeted pumping of optoelectronic elements in adjustable Wavelength range is possible. Fine-tuned directed coupling of light into predetermined and variable direction can be reached. There can be waveguides and Y-couplers with almost every adjustable shape and ultra small adjustable radii of curvature, as well as very effective fine tunable microwave antennas getting produced.

Claims (4)

1. A method for mechanical stabilization and tuning a filter structured as a photon crystal, which was produced with the method of additive lithography by computer-guided electron beam induced deposition, characterized in that the cavities of the filter structured as a photon crystal with optically transparent material adjustable refractive index, that the filled filter, structured as a photon crystal, is exposed to an electric field which can be varied in its field strength, and that by specifically changing the field strength of the electric field, optical properties such as refractive index for the continuous and the reflected light in the crystal Cavity, fine-tuning the transmitted amplitude of the light and fine-tuning the phase shift of the light. 2. The method according to claim 1, characterized in that the cavities of the structured as a photon crystal Filters filled with nonlinear optical material will. 3. The method according to claim 1, characterized in that the cavities of the structured as a photon crystal Filters are filled with liquid crystals.   4. The method according to claim 1, characterized in that the setting and variability of the field strength of the structured as a photon crystal filter Dependence on the desired optical Properties determined by calculation and is programmed.