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An Echelle-grating specifically developed for the space borne measurement of earth’s atmospheric CO2-concentration is presented. It has a line density of ~170L/mm and is manufactured on a thick crystalline silicon substrate using electron beam lithography. The echelle profile is realized using a highly anisotropic chemical etching process, which stops on the crystallographic planes of the crystal. The established manufacturing process allows perfect linear grating facets with negligible corner rounding of the profile. The important property of showing a low polarization sensitivity of the diffraction efficiency is achieved by a special design and technology for applying the gold coating of the grating which intentionally leaves one grating facet uncoated.

A compact lightweight AR headset architecture is presented employing a semi-transparent Fresnel mirror combiner. As compared to a grating combiner this design approach minimizes diffractive color aberrations by working in a high order blazed grating regime. Two different technologies, gray scale lithography as well as anisotropic wet-chemical etching of silicon wafers were evaluated for manufacturing of the Fresnel element. A first monocular demonstrator was assembled and analyzed analytically, numerically as well as experimentally. A crucial point in the manufacturing of the Fresnel combiner element was the high degree of surface shape accuracy of the working Fresnel edges as well as the embedding polymer layer to ensure optical imaging quality. Currently, only the wet-chemical etching technology could provide sufficiently good results. Two main reasons for aberrations could be traced down: grating effects of the Fresnel structure and asymmetric refraction at the embedding layer. As a result, different kinds of color aberration will be generated. Additionally, the asymmetric refraction causes different types of distortion. Two approaches for compensating color aberrations could be derived: optical pre-compensation of the lateral color caused by the embedding layer as well as optimizing the Fresnel structure to minimize grating effects.

Surface relief gratings are well-established elements for high power laser applications, e.g. ultra-short pulse compression. A binary submicron period profile, realized by e-beam lithography and reactive ion beam etching in a dielectric material, is utilized for nearly one-hundred percent diffraction efficiency. Because these gratings are manufactured without any replication techniques, a high wave front accuracy and a low stray light background can be achieved. Spectroscopic applications require additional properties, i.e. a larger spectral bandwidth and Off-Littrow operation. We present new approaches for surface relief gratings realized either via multi-level staircase profiles or exploiting sub-wavelength features. The RVS spectrometer grating in ESA's GAIA mission is a prominent example where these techniques are already in use. The current contribution focuses on the results achieved during a pre-development performed for the MOONS instrument intended to operate at VLT.

In recent years, the scattering properties of optical gratings became of high interest. In particular, the effect of line edge roughness (LER) in lamellar diffraction gratings was identified to be a potential source of stray light. In this contribution the LER-induced scattering spectrum of such gratings is investigated. The straight-forward method to calculate the angle resolved scattering (ARS) is offered by two-dimensional simulation tools, e.g. the rigorous coupled wave analysis (RCWA). Unfortunately, this approach suffers from computation times that typically lie in the range of several days. As a simplification, we apply a novel one-dimensional rigorous approach1 that permits the prediction of ARS along the dispersion direction of the grating within a feasible computation time. As the 1D-model only accounts for the LER-parameter σ and neglects the correlation length ξ and the roughness exponent α, analytical considerations must be employed in order to adapt the 1D-simulation results to the 2D-reality.1 The model is verified by comparison to the 2D-model and ARS-measurements of E-beam exposed gratings with artificially induced (and strongly determined) LER. Based on the derived 1D-model, the effects of different parameters on the straylight performance of a high performance spectrometer grating is investigated. As a result we find that not only the roughness parameters but also the grating geometry has a significant effect especially on the spatial distribution of the scattered light. In other words, the strength of the scattered light next to the (spectrometric) useful diffraction order can be controlled by the grating geometry, too. Hence, the presented algorithm might be a useful tool for designing gratings with strong straylight specifications.

Light shaping optics often generate continuously varying or homogeneous far-field distributions: Diffusers or free-form beam shapers are well-suited for transforming a given incident angular distribution into a continuous far-field distribution, while etendue conserving fly´s eye condensers excel in producing homogeneous top-hat far-fields, independent of the incident spatial and angular light distribution. The proposed optics combines the advantages of these light shaping optics in generating continuously varying far-field distributions independently from the incoming light distribution while conserving etendue. The light shaping systems consists of a high fill factor tandem microlens array featuring irregular lenslets with individual aperture size and individual decentration of lens vertex and and lens aperture w.r.t. array channel axis. We present design examples to be realized as monolithic polymer-on-glass tandem arrays, mastered by grayscale lithography. Applications of this light shaping approach are LED-spotlights with particular farfield specifications and small design envelope e.g. for automotive or general lighting.

Mask-aligner (MA) lithography is a well-known method for the fabrication of micrometer sized structures on a substrate with a diameter up to 300 mm. In spite of a theoretical resolution below 200 nm, the minimum printable feature sized remained above 1μm due to diffraction effects and limit its utilization to advanced packaging, or MEMS fabrication. Recently, developments in the illumination system and mechanical parts (known as AMALTIH for Advanced MA LITHography) as well as mask design, have permitted to used diffractive based photo-mask, and then reach the resolution limit mentioned above. This opens the possibility to fabricate smaller structures, usually accessible only by ebeam lithography. We propose here to demonstrate a fast and robust fabrication method of large area plasmonic absorber structures based on 2D sub-micrometric (350 nm period) nano-needles in a transparent polymer on a glass substrate and coated with a 50 nm thick gold layer. The interaction of the incoming light with metallic structured surface leads to the small total reflections of the 0th order below 5 %, over a large spectral band (460-660 nm) and a large set of incidence angles with TE and TM polarizations. Those results demonstrate that our fabrication process is a step toward the implementation of plasmonic based effect structures for a wide range of application.

The concept of multichannel array projection is generalized in order to realize an ultraslim, highly efficient optical system for structured illumination with high lumen output, where additionally the Kohler illumination principle is utilized and source light homogenization occurs. The optical system consists of a multitude of neighboring optical channels. In each channel two optical freeforms generate a real or a virtual spatial light pattern and furthermore, the ray directions are modified to enable Kohler illumination of a subsequent projection lens. The internal light pattern may be additionally influenced by absorbing apertures or slides. The projection lens transfers the resulting light pattern to a target, where the total target distribution is produced by superposition of all individual channel output pattern. The optical system without absorbing apertures can be regarded as a generalization of a fly’s eye condenser for structured illumination. In this case light pattern is exclusively generated by freeform light redistribution. The commonly occurring blurring effect for freeform beamshaping is reduced due to the creation of a virtual object light structure by means of the two freeform surfaces and its imaging towards the target. But, the remaining blurring inhibits very high spatial frequencies at the target. In order to create target features with very high spatial resolution the absorbing apertures can be utilized. In this case the freeform beamshaping can be used for an enhanced light transmission through the absorbing apertures. The freeform surfaces are designed by a generalized approach of Cartesian oval representation.

Micro- and nanostructures enable specific optical functionalities, which rely on diffractive effects or effective medium features, depending on pattern dimension and wavelength. Performance predictions of optical systems which make use of nanostructured materials require having an accurate description of these materials ready to hand within the optical design. At the one hand, nanostructure characteristics which result from rigorous electromagnetic modeling can be used for the optical design. At the other hand, manufactured nanostructures may deviate from their idealized geometry, which will affect the performance of the optical system, wherein these artificial structures will be used. Thus, detailed optical characterization of the micro- or nanostructure functionality is prerequisite for accurate optical design and performance prediction. To this end, several characterization techniques can be applied depending on the scope of the optical design, finally. We report on a general route to include all accessible and required optical information about the nanostructured material within a corresponding model of the nanostructure as a specific optical component which can be used within a ray-trace engine, finally. This is illustrated by a meta-material with asymmetric transmission properties in some more detail.

Highly efficient state of the art organic light-emitting diodes (OLED) comprise thin emitting layers with thicknesses in the order of 10 nm. The spatial distribution of the photon generation rate, i.e. the profile of the emission zone, inside these layers is of interest for both device efficiency analysis and characterization of charge recombination processes. It can be accessed experimentally by reverse simulation of far-field emission pattern measurements. Such a far-field pattern is the sum of individual emission patterns associated with the corresponding positions inside the active layer. Based on rigorous electromagnetic theory the relation between far-field pattern and emission zone is modeled as a linear problem. This enables a mathematical analysis to be applied to the cases of single and double emitting layers in the OLED stack as well as to pattern measurements in air or inside the substrate. From the results, guidelines for optimum emitter – cathode separation and for selecting the best experimental approach are obtained. Limits for the maximum spatial resolution can be derived.

A novel technique for the fabrication of high resolution sub-micrometer patterns by diffractive proximity lithography in a mask-aligner is presented. The technique is based on the use of specially designed diffractive photo-masks. It requires some small modifications of the mask-aligner, especially for the mask illumination and the settings of the proximity gap between mask and substrate. The huge potential of this novel technique is demonstrated at the example of structures having lateral feature sizes in the sub-500nm range printed with mask-to-substrate distances of several ten micrometers.

Metallic inclusions in layered structures can have noticeable effects onto scattering and absorption due to the coupling of the external electromagnetic field and local charge oscillations. These effects are strongly related to both the geometry of the individual particle as well as to the array structure. Having in mind the efficiency improvement of silicon solar cells due to plasmonic effects, we report on the modeling and the fabrication of periodic arrays of metallic nanoparticles on planar substrates. Different characterization techniques as atomic force microscopy (AFM), scanning electron microscope (SEM) and optical measurements are applied which provide particular information with respect to the fabricated structures, each. Special emphasis is placed on the clarification of the dominant features of the optical characterization by detailed numerical analysis. This allows identifying significant modes of the planar geometry which is complemented by the nanostructures, whose interplay with the radiation field does establish changes of the absorption in the silicon layer, finally. These findings may be helpful for optimization and clarification of specific details of technology, later on.

Freeforms in illumination systems are directly constructed by adapting some ideas of Oliker and co-workers [1]. The freeform is created by a set of primitive surface elements which are generalized Cartesian ovals including the optical response of the residual system. Hamiltonian theory of ray optics can be used to determine the family of primitives which is in particular a simple task if the freeform is the exit surface of the illumination system. For simple optical systems an analytical description of the primitives is possible. Contrarily, for more complex optics a conventional raytracer is additionally utilized to determine the required system's information, like the optical path lengths or mixed characteristics. To this end a discrete set of rays is traced through the residual systems and the required relations are interpolated to obtain a quasi-analytic representation of the primitives. The potential of this approach is demonstrated by some examples, e.g. freeform optics including collimating or deflection elements.

The optical features of the internal dipole emission have major impact on the radiation pattern and overall device efficiency of organic light-emitting diodes (OLEDs). In recent years, the characterization of OLED emitter properties by optical analysis of far-field radiation patterns of OLEDs in electrical operation was established as an in situ investigation method. However, in order to observe the internal features of the dipole emission in the OLEDs far-field accurately, well adapted devices should be utilized to optically enhance the feature of interest. Although this is a crucial point, the potential of adapted devices to OLED characterization has not been investigated universally yet. In our contribution, we provide general directives how the OLEDs layered stack is to be designed in order to enable for precise measurements of the active optical properties of the emissive material (internal electroluminescence spectrum, profile of the emission zone and dipole moment orientation) by radiation pattern analyses. Basically, we utilize the fact that the distance of the emissive sites to the metal cathode is most crucial to enhance or suppress certain dipole contributions to the far-field. A model layered system is discussed and universal emitter positions suitable to determine the internal feature of particular interest at most accuracy are deduced.

The orientation of the emissive dipole moments in organic light-emitting diodes (OLEDs) has a major impact on the optical outcoupling efficiency and, consequently, on the device performance as well as on possible optimization strategies. In this contribution we discuss a general method to quantify the amounts of parallel and perpendicular emissive sites in OLEDs. The presented in-situ-method is based on measurements of the far-field emission of an electrically operating device and corresponding optical reverse simulations. For the reverse simulation we take advantage of the fact that perpendicular dipoles only contribute to transverse-magnetic polarized light emission. In general, the method can be applied to all classes of emissive materials for OLEDs, including small-molecule and dendrimer materials. In the present study we utilize bottom emitting polymeric OLEDs with two different stack architectures: (A) a conventional OLED stack optimized for maximum performance and (B) a well adapted OLED stack, where the contribution of perpendicularly oriented dipoles to the radiation pattern in air is optically enhanced. We demonstrate that for OLED (A) perpendicular dipoles are "invisible" in the optical far-field, because almost all light from perpendicularly oriented dipoles is trapped inside the OLED stack. Consequently, no information about the emitter orientation can be gained from the radiation pattern of this device. In contrast, OLED (B) clearly shows that the radiation pattern is generated by 93.5 % parallel and 6.5 % perpendicular dipoles. Assuming a Gaussian distribution of dipole orientations in the particular emissive material, the dipoles stagger around the preferred parallel direction with an 1/e-angle of ± 22°.

The design and the fabrication of a multilevel blazed grating in resonance domain for first order high efficiency applications are presented. The design shows that a 3 phase level grating is sufficient to achieve efficiency of 90% in the minus first diffraction order. The standard technology for the fabrication of multilevel grating consists in multistep electron beam lithography and reactive ion beam etching of the grating profile into the fused silica substrate. Typical fabrication errors of this technology approach, e.g. misalignment, reduce the theoretical reachable efficiency of the grating. Two new technological approaches were investigated to avoid these typical fabrication errors and to improve the multi level fabrication process. The designed grating has been fabricated by three different technological solutions and the geometrical characterization as well as the diffraction performance are presented and discussed.

Different earth-observation and scientific space missions have the need for special spectrometer gratings. As satellite instruments typically operate close to the technologically accessible limits also the realization of the respective gratings is extremely demanding. Critical parameters are the diffraction efficiency and its polarization dependency, the wavefront error introduced by the grating, stray-light performance, and usability in a space environment. We show that it is necessary to include technological considerations into the design and specification of the grating in order to achieve the optimal performance of the complete optical system. We demonstrate this approach by two examples. The first one is the design and fabrication of the grating for the Radial-Velocity-Spectrometer of the GAIA-mission of the ESA using a novel approach based on an effective medium sub-structure within one grating period. The second example is a high dispersion NIR-spectrometer grating for an earth observation mission. Such gratings are typically realized as immersed structures in order to maximize the dispersion. We show that the same optical performance can be achieved with gratings operating in the resonance domain which can be realized by electron-beam lithography as well.

In this contribution, we show that micro-optical elements are well suited to exploit the potential of organic light-emitting diode (OLED) based light sources. They may not only increase the OLED efficiency significantly but also enable for tailoring the common Lambertian-like emission pattern of OLEDs in order to reach desired light distributions corresponding to application demands. An OLED beam-shaping scheme is demonstrated utilizing thin micro-optical arrays where each channel consists of a half-ball lens and an adapted reflective/absorptive aperture. The combination of (a) light recycling , (b) distorted and arrayed imaging of the apertures , and (c) potential substrate-mode-outcoupling allows for efficient tailoring the light emission pattern of large area OLEDs. By means of such a beam-shaping concept, several different illumination patterns (e.g. circular, triangular beams or even more complex light distributions like letters) with various divergence angles below ±40° are demonstrated. Furthermore, a reduction of the divergence angle down to about ±10° accompanied by a stray light level minimization to 2 can be realized while the thickness of the optics remains below 2 mm.

One major performance parameter for organic light-emitting diodes (OLEDs) in display and illumination applications is the overall efficiency of the device, which is directly affected by the emitter's internal luminescence quantum efficiency q. It is very desirable to determine q of the emitter in-situ, i.e. in electrically driven operation, since photoluminescence measurements of q provide a rather rough (over-)estimation. In a layered system (LS), the value q of the emitting material (EM) is associated with the coupling probability of emitted radiation into the different modes provided by the LS (air, substrate, guided, surface plasmon). We show the in-situ determination of q by optical means from a relative comparison of current efficiencies of OLEDs with varying emitter-cathode distance. As a prerequisite, we outline procedures for a complete characterization of the passive and active optical properties of the LS and the EM, respectively. Then, precise optical simulation allows determining q without additional assumptions.

Beam shaping of incoherent light sources (LEDs, halogen lamps) for arbitrary target light distribution is obtained by a single free-shape mirror. Special design algorithm ensures continuous profile without abrupt changes and shadowing regions. The mirror is manufactured by single point diamond turning combined with Fast-Tool-Servo (FTS) for simultaneous figuring of base surface and fine structure (for redistributing the light energy). Lateral and axial resolution of the fine structure is determined by FTS and considered during the design and data transfer. Directly turned surfaces can be used as replication tools for polymer or glass moulding and embossing.

The optical properties of OLEDs can be tailored by optimization of the layer stack and by implementation of micro- and/or nano-optical structures. But the effect of changing the OLED configuration on the device performance crucially depends on the optical properties of the emissive layer. The aim of this contribution is twofold. First, we will propose and demonstrate a general and reliable method to determine the intrinsic optical emitter properties via simple optical characterization and corresponding reverse simulations. Second, the influence of the emitter properties on homogeneous OLEDs as well as on OLEDs with micro/nano-optical structures is discussed.

The efficiency of organic light emitting diodes is known to be optically limited by different light trapping effects within the device structure. Several approaches have been suggested to enhance the transfer of radiation generated within the device into free space radiation. These approaches include nanoscale wave optical effects to optimize the stratified active media or to diffract guided modes travelling within the active system, as well as refractive or scattering elements to derange total internal reflection within the substrate. This paper deals with substrate emitting devices, where nano- or microscale structures enforce a 'recycling' of light that originally would have been trapped within the system. An approach enabling for a combined treatment of ray-optical and thin-film-optimization is introduced and applied to the optimization of an example system. The results indicate an improved system design due to that complex optimization

Organic light emitting diodes are deemed to be valuable light sources for displays and general illumination in the future. In the last decade remarkable progress was made concerning materials, lifetime, and production techniques. One of the remaining challenges is to increase the light extraction efficiency of these devices. Due to the internal structure of the diodes, the light emitted by electron-hole recombinations within the electro-luminescent layer may be transferred into several channels: to slab guided modes, to substrate guided modes, and, to some limited extent only, to air propagating modes, directly. In order to get some physical insight where and why photons may be trapped in the slab geometry, a modal analysis is helpful. In configurations where metallic materials are used, the transversal magnetic light is prone to be annihilated by coupling to surface-plasmon polaritons which may have propagation length of a few microns only. A high index of refraction of the emitting material and an indium-tin-oxide electrode, eventually,contribute to light confinement within guided modes for both polarisations. In order to evaluate what parts of the dipole-like emission are transferred to what channel several methods can be used, e.g. the Finite-Difference-Time-Domain-Method, a rigorous coupled wave analysis including internal sources, and an approach based on Green-functions. Although the latter method is restricted to a plane geometry, it is a quite fast tool, which is well suited for the optimisation of a layered structure. To maximize the emission of the organic diodes, two basic strategies are self-evident. The first is to aim at a restricted coupling to guided waves. The second one addresses the recycling of light from unavoidable guided modes to air propagating modes. This can be achieved e.g. by scattering, by gratings, and by lens arrays, respectively.

Photo-curable optical polymers have established for a wide range of micro-optical applications due to the great flexibility of their processing. Photolithographic patterning of these materials is often the basis for the fabrication of complex micro-optical elements and 3D microstructures. But, in the past, the optical functionality of “thick” microstructures (>50 μm) fabricated by UV-lithography was often limited due to an inhomogeneous internal refractive index distribution. Experiments showed that a homogeneous exposure of an UV-sensitive polymer will not lead to a homogeneous degree of polymerization, but to waveguide-like filament patterns. For photo-initiated polymerization processes a saturable and integrating non-linear refractive index change during the exposure process is characteristic. We present a general analytic analysis which shows that this non-linear material response leads to a modulational instability (MI) of the exposure light, if a certain degree of spatial coherence is exceeded. Then, perturbations of the incident wave are growing during propagation and the wave decays into filaments with well-defined spatial modulation frequency. It will be shown that these effects are characteristic for photosensitive polymers and different from the conventional MI, e.g. in Kerr-like media. Besides MI, the geometry of the resulting 3D patterns strongly depends on the initial intensity and phase distribution. If the degree of spatial coherence is below the threshold value, initial perturbations are not amplified. Therefore, it will be shown that the choice of suitable coherence properties or the specific modification of the spatial coherence of the effective light source within the lithographic patterning is a capable method to improve the homogeneity of optical microstructures. All theoretical results could be proven successfully within experiments.

Direct coupling from fibres to waveguides requires field matching to achieve high coupling efficiency. 3D on-chip tapers are well suited in principle, but practicability may depend on materials and geometrical structures used for the waveguide chip, especially when photonic crystal defect waveguides are involved. To adapt the spot size of the fibre mode to that of a waveguide with high index contrast, silicon micro-lenses can be used advantageously. Although positioning requires finer resolution with small foci this can be accomplished by state-of-the-art micro-positioning equipment. A theoretical description of the hybrid coupling concept and corresponding numerical results are presented, where the design covers the range from free-space ray-trace to FDTD at the chip-level. Experimental results for the characterisation of the optimised aspheric silicon micro-lenses are reported as well.

In the last decade there was an increasing interest in the investigation and application of so called metamaterials, such as photonic crystals or photonic crystal fibers, where optical properties can be tailored by means of geometry data. Waveguide arrays are another typical example of metamaterials, where the evolution of electromagnetic fields can be controlled by the effective index of the individual guides and the coupling strength between two adjacent guides. In this paper, the formation of localized states at defects in waveguide arrays is investigated both, theoretically and experimentally. Depending on the relation of the effective waveguide index and the coupling strength different guiding scenarios at an array defect can be observed, which have no analogon in conventional integrated optics. The experimental investigations are realized in polymer waveguides fabricated by UV-lithography. Typical field distributions in the waveguide array are visualized by means of the detection of the fluorescence light above the sample. Using coupled mode theory the experimental results are simulated providing an analytical description.

Current software simulation tools in integrated optics allow to tackle directly a multitude of complex problems which occur in high index contrast waveguiding. Appropriate eigenmode solvers and propagation schemes account for the vectorial character of the fields, and transmissive and reflective device properties can be derived. For the fibre-chip coupling of high index contrast waveguides the field matching requires to decrease the mode diameter by more than an order of magnitude. If photonic crystal waveguides are considered, the match of impedance and phase additionally call for attention. Generalized coupling integrals based on the modes at both sides of an interface take all these effects into account. This allows for an efficient analysis of conventional waveguide to photonic crystal waveguide interfaces. Moreover, free-space to waveguide coupling can be analysed as well, if an appropriate field transfer from vectorial raytrace to wave propagation is implemented. Thus, the design of hybrid mode transforming optics for fibre-chip coupling including micro-lenses and integrated waveguide taper structures can be addressed.

The "HiPhoCs" program, a cluster of projects supported by the German Ministry of Education and Research, is focused on the proof of applicability of planar photonic crystals based on slab waveguides within telecom transmission lines and optical networks. Results of the "HiPhoCs" program on modeling and etching aiming at the optimization of device oriented structures in the III-V and SOI material systems are reported as well as their application to key components such as PhC-based WDM-filters, dispersion compensators, integrated lasers and their coupling to the optical fiber infrastructure.

The exposure of thick UV sensitive polymer layers leads to the formation of self-organized refractive index filaments, which appear after a certain layer thickness, typically in the range of 50 μm. This effect has strong influence on the fabrication of, e.g., high precision micro-optical elements. In particular, diffraction limited micro-lenses with high sag or high aspect ratio on-chip collimators require a perfect index homogeneity. We show that the saturable and irreversible change of the polymer refractive index causes a modulational instability (MI), which finally leads to the creation of filaments. It will be presented that a maximum growth rate for a certain spatial frequency of an initial perturbation exists. This MI gain determines the dynamics of the filament formation. The impact of the exposure conditions, e.g., chemical process parameters, on the homogeneity of the UV cured polymer is discussed for ORMOCERTM type polymers.

The exposure of UV-sensitive polymers leads to a saturable and irreversible change of the refractive index up to 0.1 due to the polymerization generated changing material density. This non-linear phenomenon has a strong impact on the structure formation in the UV-assisted fabrication of thick micro-optical elements. E.g., appearing self-focusing effects and time-dependent absorption influence the sidewall geometry, while self-guiding effects have impact on the internal index distribution. Based on a material model, which describes the index change as a function of a set of process parameters, a modified iterative beam propagation algorithm is developed to simulate the structure formation. It is shown theoretically as well as experimentally that the variation of process parameters, e.g. the photo initiator concentration or the initial complex exposure field distribution, offer possibilities to control the structure formation and to make use of the self-organizing tendency. The developed patterning method is optimized for standard contact lithography processes, e.g., in a mask aligner, requiring only low exposure intensities below 10 mW/cm². This enables for performing integral wafer-scale patterning processes, e.g., on optoelectronical substrates. The realization of arrayed on-chip conic light concentrators are presented as an exemplary application.

Starting from Maxwell’s equations we derive a new orthogonality relation and a recirpocity theorem for photonic crystal waveguide modes. The orthogonality relation implies an integration over a plain nonparallel to the waveguide direction. This is in contrast to the common orthogonality relations where an integration over the whole photonic crystal is needed. By means of this new orthogonaly relation coupling coefficients between different photonic crystal waveguides as well as photonic crystal waveguides and conventional wavguides are deduced. The considerations are valid for 2D as well as 3D geometries. In the case of monomode waveguides simple quasi-analytical approximations for the reflection and transmission coefficients are obtained, which generalize the well known formulas for coupling between conventional waveguides. The reciprocity theorem can be used for the efficient simulation or even analytical description of photonic crystal waveguides in the presence of arbitrary perturbations. Depending on the kind of perturbation and the number of modes a set of strongly coupled discrete equations for the field amplitudes in the photonic crystal unit cells results. In the frame of this paper we study two problems by means of this theory. First we investigate the transission - reflection - problem of two consecutive photonic crystal waveguides analytically. Furthermore we study the influence of the dispersion of the dielectric function of the photonic crystal material on the band structure. Especially a polariton lead to strong deformation or even a splitting of the band structure close to an optical resonance.