The phase-shifting mask consists of a normal transmission mask that has been coated with a transparent layer patterned to ensure that the optical phases of nearest apertures are opposite. Destructive interference between waves from adjacent apertures cancels some diffraction effects and increases the spatial resolution with which such patterns can be projected. A simple theory predicts a near doubling of resolution for illumination with partial incoherence σ < 0.3, and substantial improvements in resolution for σ < 0.7. Initial results obtained with a phase-shifting mask patterned with typical device structures by electron-beam lithography and exposed using a Mann 4800 10× tool reveals a 40-percent increase in usuable resolution with some structures printed at a resolution of 1000 lines/mm. Phase-shifting mask structures can be used to facilitate proximity printing with larger gaps between mask and wafer. Theory indicates that the increase in resolution is accompanied by a minimal decrease in depth of focus. Thus the phase-shifting mask may be the most desirable device for enhancing optical lithography resolution in the VLSI/VHSIC era.

Improving resolution in photolithography with a phase-shifting mask

A key device in all-optical networks is the optical filter. There are different types of optical filters, for example, Bragg gratings, thin film filters, arrayed waveguide gratings (AWGs). An optical filter which has emerged in the last few years in integrated optics and which is designed and investigated on the basis of GaInAsP / InP in this thesis is the ring resonator filter. Ring resonator filters do not require facets or gratings for optical feedback and are thus particularly suited for monolithic integration with other components such as lasers and photodetectors for example. A required passband shape of ring resonator filters can be custom designed by the use of multiple serial or parallel coupled resonators. REQUIREMENTS: The realization of ring resonators in integrated optics requires low loss waveguides with a strong confinement to achieve low bending radii (R ≈ 100 μm). Tuneability is essential for the system application of optical filters. In the case of periodic filters, in our case ring resonators, it is important to fit the transmission curve to the defined channel spacing (e.g. ITU-grid). The performance of passive ring resonators for filter applications is limited by internal losses. The incorporation of a semiconductor optical amplifier (SOA) enables additional functionality (e. g. switchability) including the compensation of internal losses. REALIZED DEVICES: Passive single and double ring resonators in the material system GaInAsP / InP in the form of racetracks, coupled to a multimode interference (MMI) coupler or a codirectional coupler (CC) with radii of R = 100 μm – 200 μm and free spectral ranges (FSRs) of 50 GHz and 100 GHz and on-off ratios of more than 20 dB are realized. Single and triple ring resonators with integrated SOAs (length = 100 μm – 800 μm), coupled to two input/output waveguides using codirectional couplers with radii of R = 100 μm – 800 μm are demonstrated. The ring losses are compensated by the SOA and an on-off ratio for the throughput and drop port of more than 20 dB is realized. The achieved free spectral range is 12.5 GHz, 25 GHz and 50 GHz. The tuning to a specific wavelength and the resonance matching of the double and triple ring resonators is demonstrated by using integrated Pt – resistors. The passband shape depends sensitively on the relative interactions between all resonators and the used couplers. In order to achieve a box-like filter response, a general design rule is developed for engineering definite filter shapes using double and triple coupled ring resonators. The performance of the devices is analyzed with respect to insertion loss, polarization dependence, functionality and application. Acknowledgment This work was performed at the Heinrich-Hertz-Institut fur Nachrichtentechnik Berlin GmbH. First of all I thank M. Hamacher, H. Heidrich and U. Troppenz, H. Venghaus for their valuable support and helpful discussions which have enabled the realization of this thesis. Further I would like to thank my roommates S. Fidorra, R. Stenzel and B. Huttl, F. Boczianowski and my former roommates H. Bunning and H. Stolpe for their support and fruitful discussions and for creating a wonderful working atmosphere. This work would not have been possible without the help and knowledge of my collegues at the Heinrich-Hertz-Institute and their willingness and openness for discussions, especially P. Albrecht (optical measurement), R. Kaiser (“my famous teacher”), K. Janiak (reactive ion etching), W. Rehbein (optical measurement), J. Kreisl (laser fabrication), F. Fidorra (former project leader), G. Wache (draughtswoman), T. Gaertner and R. Turck (anti reflection coating), W. Furst (CAD mask design), M. Gravert and C. M. Weinert (finite difference and waveguide modeling software), C. Weimann (SEM and AFM), R. Steingruber (electron beam writing), H. Schroeter-Janssen (SAMOVPE), F. Reier and H. Barsch (Epitaxy), I. Tiedke, Ch. Schulz, B. Reinsperger (Photolithography), K. Schweers and U. Knospe (secretary). I would like to thank E. V. K. Rao and Y. Gottesman from France Telecom for performing the OLCR measurements. Being a PhD student is not always an easy task and it is therefore important to have “fellowsufferers” not only for helpful talks, beer drinking and badminton but for everything else which helps in accomplishing the “goal”. I therefore thank T. Tekin, O. Brox, R. Hauffe, U. Siebel and L. Zei very much. I would like to take this opportunity in thanking my parents and my sister who always believed in their son and brother which is a precious gift and gives tremendous motivation. Further I would like to thank my "big brother" Wolfram and my "big sister" Gabriele for their overwhelming support. This work would not have been fulfilled without the patience, support, help and motivation of my beloved fiancee Regina. Last but not least I would like to thank Prof. Dr. K. Petermann (TU Berlin) for his valuable discussions and for supporting this thesis and Prof. Dr. H. G. Weber (HHI) for his willingness to supervise this thesis.

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Realization of optical filters using ring resonators with integrated semiconductor optical amplifiers in GaInAsP/InP

The diffraction properties of rectangular phase gratings in a schlieren optical system are analysed. Those gratings are in a good approximation produced by liquid crystal control layers especially designed for phase modulation. In a first step, the dependence of the diffraction efficiency on the geometrical parameters of the control layer is investigated and optimum parameters for good efficiency and linearity are defined. In the second step, the influence of the schlieren optical system itself is analyzed, where the extension of the light source is taken into account. The optimum values for good contrast are evaluated. The problem of the tradeoff between contrast and intensity for high resolution can be solved by subdivision of the pixels which keeps the number of active addressing elements constant but produces a higher carrier frequency. The contrast can nearly be doubled in this case without loss of intensity.

Diffraction Properties of Rectangular Phase Gratings in a Liquid Crystal Phase Modulator

We derive a set of concise formulas to characterize the temperature
sensitivity of holographic wavelength-division
multiplexers–demultiplexers (H-MUX’s–H-DMUX’s). The
normalized parameters such as dispersion abilities, central wavelength
shift rate, and variations of insertion loss hold for general
grating-based wavelength-division multiplexing–demultiplexing
(WDM–WDDM) structures. The results are applicable to both
wide-WDM–WDDM and dense ones working in 800-, 1300-, and 1550-nm
optical wavelength windows, regardless of whether their input–output
ports are single-mode or multimode fibers. Detailed analysis and
experiments are carried out on a fully packaged four-channel
H-MUX–H-DMUX. The experimental results at temperatures from 25 to
80 °C fit nicely with the theoretical prediction. We conclude
that passive grating-based H-MUX’s–H-DMUX’s are promising for
meeting the requirements on temperature sensitivity in optical data
communications and telecommunications. Most of the analysis can be
applied to other types of Bragg-grating-based WDM–WDDM.

http://chen-server.mer.utexas.edu/GroupPapers/316.pdf

Temperature sensitivity of passive holographic wavelength-division multiplexers-demultiplexers.

AbstactWe summarize field propagation techniques for fibre and integrated optics with emphasis on fast Fourier transform, finite-difference, finite-element and Lanczos methods for both paraxial and wide-angle calculations.

INVITED PAPER A guide to electric field propagation techniques for guided-wave optics

A novel, to our knowledge, integrated wavelength-division
multiplexing–passive optical net demultiplexer that uses an
arrayed-waveguide grating and diffractive optical elements is
presented. The demultiplexer is used to distribute 1.3-µm
wavelength signals and to multiplex an eight-channel
wavelength-division multiplexer spectrum at a 1.55-µm
wavelength. The device shows high functionality and good optical
performance. The measured cross talk was less than -21 dB, and the
3-dB bandwidth was determined to be 97 GHz, which is close to the
theoretical value of 93 GHz. Average losses of 4.5 and 8 dB were
measured for the 1.3- and the 1.55-µm signals,
respectively.

Fabrication of a multichannel wavelength-division multiplexing-passive optical net demultiplexer with arrayed-waveguide gratings and diffractive optical elements.

A single-lens imaging system is described that provides spatial frequency filtering to an extended incoherent light source. Two ways to calculate the modified image are considered: First, the image is derived from the filtered diffraction pattern by Fourier synthesis. Second, the convolution of the object function with a Fourier transform of the filter function has to be evaluated with regard to a phase function that corresponds to the light source position.

Spatial frequency filtering in an optical imaging system with an extended incoherent light source.

In a single light valve system, MTF curves and light efficiencies are calculated, which are only caused by the dark field method. Extended light sources in a regular arrangement with continuous spectral density in each of the three color channels-red, green, and blue-of the TV color projector are taken into account. Continuously tuned sinus modulation of the carrier gratings written into the control layer, acting as phase objects for the transmitted light, is chosen for the calculations. The results obtained are in good agreement with measurements.

Berndt Kuhlow

Papers

Fabrication of a multichannel wavelength-division multiplexing-passive optical net demultiplexer with arrayed-waveguide gratings and diffractive optical elements.

Spatial frequency filtering in an optical imaging system with an extended incoherent light source.

Calculation of the optical transfer function of a light valve system with dark field observation.