We describe a cost-effective new packaging platform for CWDM passives. The Compact CWDM (CCWDM) devices use free-space beam cascading schemes and offer far better size, performance and reliability measures than traditional counterparts built by cascading 3-port thin-film filters.
In order to reduce size and cost, and at the same time increase overall performance, we designed a compact 8-ch CWDM MUX/DeMUX scheme based on free space optics. The device offers the following competitive performance specifications: IL < 0.8dB, IL ripple < 0.2dB, PDL < 0.1dB, PMD < 0.15ps, CD < 3ps/nm, IL uniformity < 0.3dB, adjacent channel isolation > 40dB, return loss > 50dB and pass-band bandwidth > 14nm. Such a device can operate in the temperature range of -10C° to 70C° with a TDL ~0.002dB/C°. In this paper, we will discuss the following three critical aspects of its design and implementation: (I) Design considerations and tolerance simulation. Here we discuss optimization of a set of critical design parameters: angle of incidence (AOI), beam size (BS), working distance (WD), filter aperture, filter orientation and filter-to-filter distance. (II) Build-in tolerance and critical alignment control. We have done extensive simulations to identify the critical variables and tolerance range for each variable. Based on this analysis, we then built in the alignment guidance and tolerances control into mechanical design. (III) Process control, material selection and surface preparation: Here we discuss the proper usage of the adhesives including the types of dual-effect adhesives, use of silica filler and coupling agent, surface preparation to achieve proper surface energy, tension and porosity, the optimum combination of the substrate and adhesive material for best shear and peel strength, and balancing temperature compensation and stress absorption.
Reconfigurable Add/drop Multiplexer (ROADM) is a broad definition of a functionally reconfigurable filtering device for dynamic networking. We focus on a class of ROADM architecture that allows scalability of wavelength channels, add/drop port counts as well as functional capability of integrating variable attenuation and monitoring elements. We demonstrate the proposed concepts of integrating a ROADM with a variable optical attenuator and a performance monitor array.
We discuss recent surge of interests in coarse DWM (CWDM) applications and implied challenges for low cost and compact devices. We show that for further cost-reduction and performance enhancements, an old WDM packaging architecture can be revitalized to address the new compact CWDM (CCWDM) filter challenges. In particular, we demonstrate a CCWDM filter platform and show its use in both an 8-channel Mux/DeMux and a 4-channel OADM applications.
The beam propagation method (BPM) is one of the most popular approaches in modeling electromagnetic field propagation. The conventional BPM is established on scalar Helmholtz equation using paraxial approximation. There are limits in the analysis of the vector properties of electromagnetic field and wide-angle propagation. This paper presents the techniques of removing these limits. A full-vectorial BPM bases on finite-difference technique is described from vector wave equations, called finite-difference vectorial beam propagation method (FD-VBPM). The main disadvantage of FD-VBPM is the calculation inefficiency, especially in three dimensional modeling. To obtain two dimensional equivalent structures, a precise optimization approach is adopted. Propagation constant and field of fundamental mode best match those of the original waveguide. The method has very high accuracy. The decoupled
semi-vectorial BPM is also derived. The full-vectorial method is extended to wide-angle BPM removing paraxial limit. The method bases on Pade approximant. Simulations are made on rib waveguide.
A radial finite-difference beam propagation method is proposed systematically with circular cylindrical coordinates, which is more accurate for simulation of some radiated waveguide structures. Theoretical design and simulation of low insertion loss arrayed waveguide gratings with couplers of tapered arrayed waveguides are presented using this full-vectorial beam propagation method.
A low-aberration planar concave grating is discussed to design N by N wavelength interconnector in this paper. First a special linear system model is built based on the scalar diffraction theory. With the derived model some transmission characteristics of the planar grating are studied, including dispersion value, channel spacing, FSR, and spectral response. Numerical simulation focuses on the geometrical aberration and spectral resolution of the grating.
In this paper a flat-field micro-spectrometer is designed by using varied-pitch gratings. The geometrical parameters which affect the focal curve, i.e. the radius of curvature, pitch variation, incidence angle, and the position of the focal plane, are analyzed. Then a planar concave grating is optimized by the Simulated Annealing Algorithm. The spectral region covers 400 - 800 nm and the linear dispersion is about 6 micrometers /nm. The obtained linearity of the focal curve is better than 98%. Furthermore, to get better aberration, the concave grating with arbitrary grating profile is also discussed.
Traditional Rowland-circle concave gratings suffer large aberrations especially in the case of flat-field receiving. With the development of vertical photolithography, the fabrication of gratings with arbitrary profile and groove distribution comes into practice. To overcome the restrictions existing in the traditional geometries, a general iterative design geometry based on the optical path function is developed in this paper. The structure of a grating is determined by two explicit of implied constraint equations containing the grating profile and the groove function. Constraints in some typical cases are studied. Finally some numerical examples of flat-field concave gratings for micro-spectrometer are shown by the proposed equations. The aberration of the device based on stigmatic points can be lower than λ/4.
A method of designing a flat-field planar concave grating for a miniature spectrometer is studied based on the second- order aberration is defocusing. To obtain low defocusing, two steps are applied: first tune the detecting plane, then adjust the groove distribution.
A method for collimation test by utilizing various binary spiral gratings is developed in this paper. Detailed discussion has been focused on the means to improve sensitivity and the optimum tuning mode giving the extremum resolution is proposed. Experimental results indicate that this method is a feasible and promising one.