A novelle concept for miniaturized multimode fiber optical switches is presented, which can be applied for the whole spectrum of fiber core diameter and numerical aperture. It is particularly useful for large core high numerical aperture fibers used for applications in illumination systems, sensing and optical spectrometers.
Because of relaxed positioning tolerances - compared to singlemode setups - most existing solutions are based on moving fibers or fiber collimators leading to devices with excellent optical parameters. Due to the mechanical properties of the fibers it is difficult to use these switching principles for fibers with large diameter. The system we present is based on fixed fibers, each having a collimating lens. A following imaging system projects the incoming optical beam to a tilting high-reflectivity micromirror placed in the focal plane. The reflected beam travels back through the imaging system targeting an output fiber which is addressed by the angle position of the mirror. Due to the folded optics design both input and output channels are located on the same side of the device. Special emphasis was taken on the chromatic dispersion behaviour of the setup leading to a broad spectral range.
We present the optical and mechanical design considerations and experimental results obtained with first realized prototypes of 1×4 and 1×8 style switches for 400μm core diameter multimode fibers.
A novel design of a microoptical fiberoptic 2 x 2 and 1 x 2 switch is presented. The fiber input and output ports are realized with the use of silicon V-grove fiber arrays. The input beams are collimated by a microlens array consisting of two lenslets, separated by the same pitch as the fibers. These two collimated beams which are extremely parallel to each other, are focused into one spot by a simple plano-convex lens. The focal length of the microlenses and this plano-convex lens determine the magnification of the mode field diameter of the fiber. Switching is performed by using a special two-sided high reflectivity mirror placed in the focal plane of the plano-convex lens, with the use of a high speed piezoelectric actuator. For the microlens array - fiber array mounting process a special setup has been built up, allowing for semi-automatic alignment. The assembly technology for all the single components and modules is described, gluing is used as the main fixing techniques. First prototypes show excellent optical parameters (1.5 dB insertion loss, -70 dB crosstalk) and very short switching time of 0.3 ms.
We present a novel design of a microoptical fiberoptic 2 x 2 and 1 x 2 switch. The fiber input and output ports are realized with the use of silicon V-grove fiber arrays. The input beams are collimated by a microlens array consisting of two lenslets, separated by the same pitch as the fibers. These two collimated beams which are extremely parallel to each other, are focused into one spot by a simple plan- convex lens. The focal length of the microlenses and this plano-convex lens determine the magnification of the mode field diameter of the fiber. Switching is performed by using a special two-sided high reflectivity mirror placed in the focal plane of the plano-convex lens, with the use of a high speed piezoelectric actuator. For the microlens array- fiber array mounting process a special setup has been built up, allowing for semi-automatic alignment. The assembly technology for all the single components and modules is described, gluing is used as the main fixing techniques. First prototypes show excellent optical parameters (1.5 dB insertion loss, -70 dB crosstalk) and very short switching time of 0.3 ms.
We have developed a novel concept for miniaturized fiber optic switches. It is base don microprisms moved into the path of one or several input beams which are de3flected hereby and directed to the output fibers. Coupling of the deflected light beams into the output fibers is achieved by microlens arrays. The overall optical system has been designed properly in order to minimize the switch dimensions and to obtain excellent optical parameters of the switches. Piezoelectric bending actuators with a characteristic translation range of > 0.5 mm have been sued for the microprism movement. First switch prototypes are characterized by excellent optical parameters and short switching time. Several methods for system integration have been developed and applied to prototype fabrication. The first important process is the integration of fiber arrays with microlens arrays. A special mounting procedure has been developed for this. The second critical integration process is the mounting procedure of the prisms to the bending actuators. For this purpose a special vacuum gripper has been built. With the help of this gripper all microprisms can be mounted in one step.
A novel concept has been developed for a fiber optic switch. It is based on miniaturized prisms deflecting the nearly collimated beam from the input fiber. These prisms are moved by the use of piezoelectric bending actuators. The deflected beam is directed to the output fiber, there is one prism for each output fiber. Coupling of the deflected light beam into the output fibers is achieved by microlenses. In order to simplify the integration process regular arrays of both the output fibers and the coupling microlenses have been used. A special technique and setup has been developed for fast and accurate adjustment of the lens array with respect to the fiber array. Both arrays are subsequently fixe to each other by gluing. The second critical integration process is the mounting procedure of the prisms to the bending actuators. For this purpose a special vacuum gripper has been built. With the help of this gripper all microprism can be mounted in one step. Using the developed integration processes, fiber switch prototypes have been built up with excellent optical parameters.
We have developed different concepts of fiber optic switches based on hybrid transmittive micro-optical system, where switching is achieved by piezoelectrical movement of one of the micro-optical components. The input fiber beam is either collimated and deflected by a piezoelectrically driven short focal length microlens or refocussed onto a microprism structure, which is also piezoelectrically driven and deflects the beam in a number of discrete directions. In all of our configurations after deflection the beam is redirected and coupled into one of N output fibers by the use of a microlens array. The output fibers are also arranged in regular array. The switch configuration with continuous deflection is ideally suited for a large number of output channels, however, the problem still unsolved is to achieve high output channel stability and reproducibility. At the opposite, the discrete beam deflection approach ensures high stability and reproducibility by the optical arrangement and does not require position sensing for the actuators. The latter concept, of course requires special microprism elements, which are not available commercially. They have been fabricated with sufficient high quality by gray-tone lithography. For both concepts switch prototypes have been built up, yielding excellent optical parameters with respect to insertion loss and cross-talk. Typical switching times of 1 ms have been achieved. Special experimental setups have been built up for system integration.
A novel technique, the so-called skew ray imaging concept, has been developed for beam transformation of high power diode laser bars. It leads to beam circularization with optimum brightness conservation. This concept uses two key microoptical components: a fast axis collimator microlens (FAC) of high isoplanatism and a special array of beam deflecting elements, the number of which corresponds to the single emitter number of the diode laser. Using this concept of skew ray imaging in a modified form, prototypes of pumping sources for visible fiber laser have been developed and built up. Several watts of optical power have been focused into a small spot of 25 micrometers with a numerical aperture of 0.35. GRIN cylindrical microlenses with 0.1 mm focal length and diffractive blazed gratings as redirector have been used. The grating periods of the redirector sections have been between 8 and 100 (mu) M. They have been produced by e-beam direct writing in resist. After optimization of the fabrication process the diffraction efficiencies of al sections have been beyond 86 percent with good reproducibility. Special techniques have been sued for system integration. The FAC microlenses have been attached to a copper lens holder with a subsequent gluing process of the holder to the laser diode heatsink. A UV-curable adhesive with extremely low shrinkage has been selected. The redirector element has been integrated with an additional possibility for lateral adjustment in order to compensate minor residual walk-off effects of the microlens when the laser power is varied from zero to maximum. A very compact pumping source of 3 inches X 1 inch X 1 inch dimensions has been realized with 5 W optical power in the desired spot. First diode pumped fiber laser operation in the visible has been demonstrated with this source.
Novel concepts have been developed for miniaturized fiber optic switches. They are based on transmittive microoptical components. Here, beam deflection is achieved by moving microprisms or microlenses with the use of miniaturized actuators, mainly piezoelectric actuators. The deflected beam is directed to a microlens array where each of the lenslets couples the beam into one of the output fibers. The latter are also used as a regular array. Such miniaturized switches can be realized with quite good optical parameters, and also short switching time in the order of 1 ms. For prototype fabrication and future production of such switches integration methods of the microoptical components and the actuators play an important role. In the case that all components are adjusted and fixed separately a rather complex procedure and equipment is required and a special optomechanical design must be used to ensure sufficient system stability. In order to decrease considerably the effort for system integration we tested several approaches for building at first certain subassemblies. This was especially successful for the lens array/fiber array integration as the most critical in the switch configuration. By using a lens array substrate thickness slightly smaller than the lenslet focal length we were able to fix the fiber array by gluing directly to the substrate surface. We also started to integrate other optical functions, such as deflection and collimation into one quasimonolithic component by replication techniques. Here, both microprism and microlens structures have been replicated onto SELFOC microlenses. 5
Fiber-optic switches become more and more appealing components not only in the field of optical communication, but also in measurement systems, sensors and data storage. We have developed a number of concepts for fiber optic switches, all based on different types of special microoptical components, actuated by miniaturized mechanical systems, primarily piezoelectric actuators. We present microoptical configurations and discuss their potential for the creation of different types of miniaturized switches.
Using technologies such as replication or batch-fabrication, a number of micro-optical elements can be fabricated with low costs. However, as the realization of complex optical functions, for instance beam shaping and beam deflection, often requires several optical components, the mounting effort increases dramatically. It makes sense to emphasize the system aspects already in the design work. With the help of some examples for micro-optical fiber switches and modulators driven by piezoelectric actuators, we demonstrate that the combination of gradient-index optics with planar surfaces and replicated optical elements like micro-prisms, lens arrays on these surfaces can be an important step in the system integration.
Microprisms play an important role in a number of micro- optical systems for beam shaping and beam deflection. The task of the prisms is to deflect a beam selectively in order to bring it into an other optical channel of the system or to redirect a beam in the way that the redirected beam propagates parallel with respect to the optical axis of subsequent optical elements. We derive general requirements for microprisms for these applications and discuss some experimental results.
The utilization of micro-optical components in systems for optical beam deflection and modulation offers the possibility for realization of miniaturized switches and scanners. As the required displacement of the micro-optical components for efficient beam manipulation is quite small, high speed actuators with small electrical power consumption can be used. We present micro-optical configurations and discuss their potential for the creation of different types of miniaturized switches. The combination of micro-optical components already available and semiclassical piezoelectric actuators leads to new types of switching and modulation systems for a very broad spectrum of applications.
Fiber-optic switches become more and more appealing components not only in the field of optical communication, but also in measurements systems, sensors and data storage. We have developed a number of concepts for fiber-optic switches, all based on different types of special micro-optical components, actuated by miniaturized mechanical systems, primarily piezoelectric actuators. We present micro-optical configurations and discuss their potential for the creation of different-types of miniaturized switches. Keywords: micro-optics, micro-optical switches, piezoelectric actuators
The utilization of micro-optical components in systems for optical beam deflection and modulation offers the possibility for realization switches and scanners. As the required displacement of the micro-optical components for efficient beam manipulation is quite small, high speed actuators with small electrical power consumption can be used. We present a variety of micro-optical configurations and discuss their potential for the creation of different types of miniaturized scanners and switches. The combination of micro-optical components already available and semiclassical piezoelectric actuators leads to new types of switching and modulation systems for a very broad spectrum of applications.
Most of the potential applications of high power laser diode bars and stacks need special beam transformation systems in order to create a much more symmetric output beam. We present a novel concept for single emitted beam reconfiguration of high power laser diode bars, which uses different types of microoptical components. A very compact and efficient beam shaping system has been built upon the base of this concept, forming a nearly circular output beam with minimum brightness reduction compared to the laser diode output radiation.
External modulators and switches for multimode fiber transmission systems are required for aplenty of applications in optical metrology and communication systems. We show that a confocal arrangement of microlens arrays with certain filter elements in the common focal plane of the arrays, which are moved with the help of piezoelectrical actuators, is a very simple and flexible concept to meet the needs of a number of very different applications. The focal length, lens pitch and width of the arrays have to be chosen properly. We discuss which optical elements are required for certain applications. We present experiments for an intensity modulator.
The utilization of micro-optical components in systems for optical beam deflection and modulation offers the possibility for realization of miniaturized switches and scanners. As the required displacement of the micro-optical components for efficient beam manipulation is quite small, high speed actuators with small electrical power consumption can be used. We present a variety of micro-optical configurations and discuss their potential for the creation of different types of miniaturized scanners, switches and modulators. First experimental results and even prototypes of modulators and switches have been achieved, indicating that the combination of micro-optical components already available and semiclassical piezoelectric actuators leads to new types of switching and modulation systems for a very broad spectrum of applications.
Collimating and diverging cylindrical micro lenses with N.A. up to 0.60 fabricated by thermal silver ion exchange in a special designed glass type are reported. Cylindrical microlens arrays are fabricated by field assisted ion-exchange. Applications to fiber coupling as well as to diode bar collimation are discussed.
Using the silver-sodium ion exchange process in a special optical glass, different types of gradient-index cylindrical microlenses and microlens arrays have been fabricated. High numerical aperture single cylindrical lenses are produced in thin glass slabs without any diffusion masks. Depending on the desired index profile accuracy, a two- or three-step ion exchange process is used, the maximum numerical aperture which can be achieved is about 0.6. Contrary to other lens fabrication techniques, lenses of different focal length can be produced very easily, and both focussing and diverging lenses are possible. A series of systems, combining different lenses, have been realized for anamorphotic single-mode laser diode beam transformation and high-brightness laser diode beam forming. Arrays of cylindrical lenses of moderate numerical aperture (about 0.2) have been realized by electrical field assisted ion exchange through 1D mask structures. These lens arrays have been successfully applied to multiple-stripe pulsed laser diodes for efficient reduction of the output beam divergency, thus enabling a more efficient coupling of the output power to multimode fibers.
Using the principle of focussing an incoming beam onto a plane with special optical microstructures, novel miniaturized switching elements can be built up for different applications. As switching is achieved by a lateral movement of the microstructures, only small displacements (about 10 micrometers ) are sufficient for efficient beam manipulation. In this paper, we present the results of both theoretical and experimental investigations on a concept of multichannel beam deflection by microprisms located in the focal plane of an incoming beam. This concept is suitable for singlemode fiber switches. It is shown that nearly aberration free operation can be achieved by choosing the right substrate thickness and the axial focal position with respect to the microprisms for the cases of placing them on the front or rear substrate surface. A trade-off must be made between the numerical aperture of the focussed beam, the prism angles and the number of output channels of the deflecting element in order to achieve sufficient angular separation of the deflected beams. Two different techniques have been tested for microprism fabrication: wet anisotropic etching in silicon and a new method of mask projection onto scanned photoresist layers. Microprisms with sufficient optical quality have been fabricated with both methods. In experimental investigations, we showed that for a singlemode fiber 1 X 9-switch low insertion loss (< 1 dB) and low cross-talk between the output channels (-50 dB) can be obtained.
Werner Frank, Bengt Knoedler, Alexander Schoesser, Torsten Strempel, Theo Tschudi, Frank Linke, D. Muschert, Angelika Stelmaszyk, Hans Strack, Andreas Braeuer, Peter Dannberg, Rolf Goering
Samples of PMMA (Poly-(Methyl-Meth-Acrylate)) in combination with various substrates have been modified by ionizing radiation in order generate regions of increased refractive index. These waveguiding structures were used to build passive devices such as Y-branches, couplers and Mach-Zehnder-interferometers. The refractive index and beam profil and the attenuation at different wavelengths of the generated waveguides were measured.
A new configuration of three micro-optical elements has been proposed for the realization of miniaturized optical beam deflection and modulation modules: One element with a special surface corrugation profile is placed in the focal plane of two microlenses or microlens arrays, one for focussing the incoming beam(s) and the second for output beam collimation. When the middle element is moved in lateral direction with respect to the optical axis, the parameters of the optical beam(s) is/are influenced depending on the real micro-optic structure. The results of first experiments on optical beam deflection and phase modulation are demonstrated.
Using the Ag+-Na+ exchange in a special optical glass one- and two- dimensional refractive index profiles of definite shape have been realized. It is shown that good quality one-dimensional parabolic profiles can be used for micro-cylindrical lens fabrication with high possible numerical aperture N.A. <EQ 0.46. Two-dimensional refractive index gradients of stripe waveguide geometry generated by field assisted ion exchange through a linear mask window form single cylindrical lenses as well as cylindrical lens arrays with comparable low N.A. <EQ 0.15 which can be used for the transformation of the weakly divergent direction of a laser diode or laser diode bars. Two crossed lenses of different numerical aperture are applicable for high power laser diode collimation.
Optical phase drifts of guided waves in LiNbO3 waveguides can be caused by two different physical effects: light-induced refractive index changes (photorefractive effect) and so-called DC drift effects. Both phenomena have been investigated experimentally by a special interferometric technique on simple channel waveguides with very high accuracy. Light- induced refractive index changes were measured at 633 nm wavelength and in the 800 nm region. These index changes in annealed proton exchanged (APE) waveguides are about one order of magnitude smaller compared to titanium indiffused (TI). This can be explained by an increased photoconductivity of the APE material. DC drift effects in APE waveguides, however, are quite large and cannot be reduced in the same way as for TI waveguides. This is due to an ionic charge transport process. MgO doping of the waveguide substrates leads to a considerable reduction of both the photorefractive effect and the DC drifts of APE waveguides. The influence of both drift effects on the stability of a three-beam interferometric displacement sensor was demonstrated.
Two modifications of fiber-optic temperature sensors which utilize the temperature-dependent birefringence of optical crystals have been investigated. In a first approach, an additional compensator crystal has been introduced into the customary birefringent filter. The thickness of this crystal was chosen to compensate almost completely the birefringence of the sensor crystal, but the temperature dependence of its birefringence must be negligible. For this purpose the authors used (alpha) -quartz. With this sensor they obtained a high modulation depth of the output signal even for LED light sources. In a second approach the bulk birefringent filter has been completely replaced by a titanium-indiffused waveguide in LiNbO3. Polarization maintaining fibers have been coupled directly to the waveguide ends with appropriate orientation, so that collimating and focusing lenses as well as the two polarizers can be omitted from the sensor head, and thus the compactness is considerably increased.
Proton exchanged LiNbO3 devices are used advantageously for fiber optical sensors because of the high optical damage threshold, extremely high polarization maintenance, and flexibility of waveguide parameters as a consequence of different annealing procedures. For a fiber optical gyroscope operating at a wavelength of 850 nm, a device has been developed integrating the functions of space filter, polarizer, splitter, and modulators on a single chip. This device has been fabricated by annealed proton exchange (LiNbO3:APE); the fabrication technique is described. The optical parameters of the chip and the results
Proton-exchanged LiNbO3 electrooptic waveguide devices are applicable to communications components employing phase and intensity modulation, in virtue of their (1) high optical damage threshold, (2) extremely high polarization maintenance, and (3) flexibility as to waveguide parameters, due to different annealing procedures. Attention is presently given to two examples of such devices, an LiNbO3 phase modulator and an LiNbO3 Mach-Zehnder interferometer modulator operating at 1300 nm.
A novel interferometric technique for measurements of optical phase
changes in channel waveguides is described. It is based on a simultaneous
excitation of two neighbouring channel waveguides with adjustable
intensity ratio. Phase changes are deduced from the shift of an interference
pattern formed by the superposition of the two collimated output
beams. This technique has been applied to measurements of lightinduced
refractive index changes (photorefractive effect) in LiNbO3
optical channel waveguides. Systematic investigations on LiNbO3:Ti
waveguides show that both the magnitude and the time constant of lightinduced
index changes depend characteristically on guided wave power.
Light-induced waveguide losses become significant only, when the
guided-wave power leads to waveguide cut off. The light-induced processes
of index changes can be reduced considerably after the Ti-indiffusion
by simple thermal treatments. In channel waveguides, produced
by proton exchange (PE) followed by an annealing process, light-induced
index changes are smaller, but develope faster than in Ti indiffused
waveguides, thus indicating an increased photoconductivity inside the
proton exchanged material. At A=B3O nm photorefractive effects are
reduced by about one order of magnitude compared to ?=633 nm.
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