Uwe Hollenbach

Direct fabrication of PDMS waveguides via low-cost DUV irradiation for optical sensing

We demonstrate the fabrication of single mode optical waveguides by irradiating polydimethylsiloxane (PDMS) with a low cost Hg lamp through a conventional quartz mask. By increasing the refractive index of the irradiated areas, waveguiding is achieved with an attenuation of 0.47 dB/cm at a wavelength of 635 nm. The refractive index change is stable in ambient air and water for time periods of more than 3 months. The excitation of water-dispersed fluorescent nanoparticles in the evanescent field of the waveguide is demonstrated.

Differential Rayleigh scattering method for measurement of polarization and intermodal beat length in optical waveguides and fibers

We propose a modification of the Rayleigh scattering method, which allows for measurement of polarization and intermodal beat length in single-mode and few-mode channel waveguides and optical fibers. A significant sensitivity increase is achieved by taking two high-resolution photographs in oblique scattered light of π-shifted intensity distributions produced by interference of polarization or spatial modes and applying Fourier analysis to the differential image. In the case of polarization beat length measurements, the π-phase shift is obtained by switching the polarization state at the fiber input, while in intermodal measurements, the π-phase shifting is realized by changing the excitation conditions. The usefulness of the method for characterization of channel waveguides and optical fibers is demonstrated in several examples. Moreover, we show that the combination of the spectral interferometry method with the proposed method allows for broadband measurements of differential phase and group effective indices.

Investigation of birefringence in PMMA channel waveguides inscribed with DUV radiation

We studied both experimentally and numerically the spectral behavior of modal birefringence in channel waveguides inscribed in PMMA by DUV illumination. The measurements of birefringence were carried out using a spectral interference method for different waveguide widths, respectively 2, 3, 4, 5, 6 µm, which were inscribed using 2 J cm−2 and 3 J cm−2 irradiation doses. We have also modeled the spectral dependence of birefringence related only to waveguide geometry using the finite element method. High discrepancy was observed between measured and calculated birefringence. This is related to the fact that numerical analysis accounts only for the so-called geometrical birefringence induced by an asymmetry of the waveguide, while in measurements the overall modal birefringence relates to both the geometrical and the material effect. Our measurement results indicate that the contribution of the material birefringence in the analyzed waveguides may reach up to 3 × 10−4 in a short wavelength range.

A modular fabrication concept for microoptical systems

A modular fabrication concept is used to build microoptical systems for commercial application. The concept is based on the fact that microoptical systems can be divided into two functional units, the optical and the electrooptical base plate, which covers active optical elements. In the case of defined interfaces, highly specialized manufacturers can fabricate both components separately. A third company will use these components to build the electrooptical subsystem, which is sold as an OEM system to the system manufacturer. Especially for the component fabrication, the equipment costs can be shared among different applications, which makes the component for each application cheaper. A microoptical distance sensor and a microspectrometer for the near-infrared have demonstrated the concept.

Magnetic comb drive actuator

We present the first electromagnetic comb drive actuator which allows for large, linear actuator motion at large air gap widths of 25 mum and a structural height of 400 mum. Previously reported designs require very narrow air gaps of 3 mum at structural heights of up to 1 mm [1] which makes them sensitive to operate, and challenging to fabricate. The new design reduces the reluctance by a parallel connection of several pole shoes as is well known for electrostatic actuators, which reduces the current consumption and linearizes the current - displacement characteristic. Magnetic and mechanical material properties are measured for an accurate simulation of the system behavior. Experimental results verify the theoretical predictions.

Freeform three-dimensional embedded polymer waveguides enabled by external-diffusion assisted two-photon lithography

This paper introduces a unique method to fabricate free-form symmetrical three-dimensional single-mode waveguides embedded in a newly developed photopolymer. The fabrication process requires only one layer of a single material by combining two-photon lithography and external monomer diffusion resulting in a high refractive index contrast of 0.013. The cured material exhibits high chemical and thermal stability. Transmission loss of 0.37  dB/cm at 850 nm is achieved. Due to the fact that waveguide arrays are produced with high density, this technique could pave the way for three-dimensional optical interconnects at the board level with high complexity and bandwidth density.

Low-loss single mode light waveguides in polymer

We report on the development of a UV-lithography manufacturing process for low loss single mode light waveguides in a novel polymer and the characterization of the fabricated components in a broad wavelength range from 808 nm to 1550 nm. The main focus of this work lies in providing a quick and cost efficient production technique for single mode waveguides and low loss integrated optical circuits. To achieve this goal we chose a novel photo-structurable polymer host-guest-system consisting of SU8 and a low refractive dopant monomer. Near and far-field measurements at different wavelengths show that the mode propagating within a well designed integrated waveguide structure and the mode of a standard fiber can exhibit a mode overlap value of approximately 1 and suffer only very low coupling losses. We demonstrate excess loss of 0.14 dB/cm for 808 nm, 0.33 dB/cm for 1310 nm and 2.86 dB/cm for 1550 nm. Typical insertion loss values of straight waveguides with a length of 36 mm are 0.9 dB for 808 nm, 1.5 dB for 1310 nm and 10.4 dB for 1550 nm. Polarization dependent loss was found to be less than 0.2 dB on sets of test structures of 36 mm length. We measured material attenuation in the novel polymer material before cross-linking of approximately 0.04 dB/cm for 808 nm and around 0.20 dB/cm for 1310 nm respectively. The presented production technique is suitable to provide low loss and low cost integrated optical circuits for sensor and communication applications in a broad wavelength range.

Combdrive Configuration for an Electromagnetic Reluctance Actuator

This paper presents a novel combdrive configuration of a linear magnetic microactuator. We discuss in detail the influence of the air-gap geometry on the plunger motion and give design rules to avoid pull-in behavior. This analysis results in a new configuration, which is, so far, only known for electrostatic actuators. The magnetic flux is guided over several interdigitating comb structures with moderate large gap width of 25 mum instead of one single plunger, as reported for earlier designs. This results in larger forces, scaling with the number of comb fingers, until the material reaches saturation. The new configuration linearizes the characteristics and saves driving power without sacrificing fabrication stability, which would arise from small air-gap widths. Several combdrive actuators featuring one, two, and eight comb fingers were fabricated in LIGA technology, simulated, and tested. For a driving current of 40 mA, the achievable stroke is measured to increase by 800% for eight comb fingers in comparison to one finger. Alternatively, for a given stroke, a reduction of the driving current of more than 50% is measured.

Polymer technologies: a way to low-cost micro-optical components and systems

The need for low cost micro optical devices is increasing thru all application fields like tele- and data-communication, industrial automation, displays, automobile, sensor applications etc. Polymer technologies can follow this demand due to the possibility of mass fabrication by replication techniques. Various technologies have been developed in the past to fulfill the demanding requests given by the use of micro structures in optical applications. Part of them are already used in industrial manufacturing. Also demanding products are introduced into the market. In the paper we will give an overview of the relevant techniques and demonstrate their possibilities by a few product examples.

Characterization of a micro optical distance sensor

A micro optical distance sensor with a PSD receiver built in a modular set-up using two planar chips has been characterized. Results from spot size, measurement range, linearity, resolution, and repeatability are described.