The rapid growth in data center traffic is driving the need for increased performance and overall bandwidth of networking equipment, including optical interfaces and Ethernet switches, which are based on pluggable transceivers today. But looking just a few years ahead, bandwidth scalability challenges are looming in terms of density, cost, and power; challenges that require tighter integration of optics and networking silicon. This paper reviews the motivation for integration, the enabling technology elements, and discusses how advanced packaging and Silicon Photonics enable higher density, reduced power per bit, and ultimately the continued scalability of network bandwidth and performance.
A variety of material platforms including glass, lithium niobate, and polymer are being utilized for opto-electronic components. Among these, high performance thermo-optic polymers are particularly advantageous for active telecom applications because they possess a unique suite of properties including large thermo-optic coefficient, high thermal stability, refractive index tenability, and compatibility with high-volume wafer scale processing. In this paper, we discuss our approach for material selection and its relation to device design optimization in a Si-polymer based variable optical attenuator array. We outline the key material and device design trade-offs and show that Si-polymer based devices can meet and exceed the reliability requirements for telecom components. To this end, performance, qualification testing, and key properties that are related to high reliability and device lifetime are addressed.
Silicones are known for their excellent performance in applications with harsh environmental conditions. They are very well known for their high temperature stability, resistance to moisture and other adverse conditions. This paper will overview key properties of siloxanes that make them attractive materials for numerous photonics device applications with emphasis on polymer waveguides. Both thermal-mechanical and optical properties will be reviewed. Testing of key optical properties of several siloxane materials, both before and after exposure to heat, humidity, and high optical flux will be discussed. Fabrication and processing for production of polymer waveguides, and the resulting polymer device performance will be shown. Finally, the high reliability of siloxane based waveguides is demonstrated by the Telcordia testing of a fully functional, packaged, Variable Optical Attenuator (VOA).
Scanning Kelvin microscopy (SKM) has been applied to the characterization of poled non-linear optical (NLO) polymer films, carbon black filled epoxy polymers and sulfur- passivated GaAs(100). This paper demonstrates that SKM is applicable to the detection of the magnitude and the direction of the field-induced polarization in poled NLO polymer films. We compare the response to that obtained from the scanning second-harmonic-microscopy method in which the direction of the orientation cannot be seen. A local illumination of the GaAs(100) surface during treatment in sodium sulfide solutions has significant influence on the work function distribution on the passivated surface. The image of the lateral distribution of the carbon black electrical network in epoxy resin by SKM is demonstrated.
We present experimental and theoretical details on how to analyze the polarization distribution in poled second order nonlinear optical polymers in three dimensions. The polar order can be analyzed in both the lateral and the vertical directions by scanning second harmonic microscopy (SSHM) at various wavelengths along the absorption tail of the polymer. Local thermal reorientation was accomplished using an Argon laser at a wavelength of 488nm, and the resulting change in polarization was analyzed by multi-(lambda) SSHM. We could demonstrate that the relative change in polarization is strongest at the surface that was irradiated with the Argon laser and decreases towards the opposite surface.
We present a method for analyzing the homogeneity of the (chi) (2) distribution in poled nonlinear optical polymer films. The second order nonlinear coefficient in these polymers is commonly induced by electric field poling methods which can lead to a (chi) (2) distribution with poor spatial homogeneity. In this paper, we analyze the (chi) (2) distribution using scanning Kelvin microscopy. This allows us to detect the height and the direction of the induced polarization through the probing of the counter charges that are present on the polymer surface. We compare the response to that obtained from the scanning second harmonic microscopy (SSHM) method, in which the direction of the orientation, and thus the phase of (chi) (2), can not be seen. We also propose a method to measure the (chi) $_(2)) distribution in 3D by analyzing the SSHM images obtained at various wavelengths.
We present a novel nondestructive experimental technique for the determination of the lateral distribution of the polar order in second order nonlinear optical (NLO) thin films. The sample, which consists of a poled polymer film, is scanned through the focus of an infrared laser beam in a second harmonic generation (SHG) setup and the second harmonic intensity is monitored stepwise. In combination with a conventional electrooptic (EO) characterization it is possible
to create an EO-coefficient map of the sample. The resolution of this mapping technique can be significantly increased by using high numerical aperture (NA) microscope optics for the illumination of the poled polymer. This method, for instance, allows the evaluation ofpoling inhomogeneities due to high field poling and field distortions at the edges ofpoling electrodes.
We report on electrical conduction phenomena occurring during high electric field electrode poling of side chain (chi) (2) polymers. Electric current and second harmonic intensity were measured simultaneously in poling experiments performed on samples with and without an additional inorganic poly-methyl-siloxane layer. Current densities appeared to be limited by a Bardeen-type potential barrier at the electrode/insulator interface. The field dependence of current density was found to be Schottky charge injection for medium field strengths (EPOL <EQ 100 V/micrometers ) whereas it was dominated by Fowler-Nordheim tunneling at higher poling fields. In the presence of the buffer layer, a significant suppression of tunneling was observed which leads to a reduced probability of singular breakdown events and shifted the limit of avalanche dielectric breakdown to higher internal effective poling fields.
An inorganic methyl-siloxane based buffer material has been investigated that is suitable for nonlinear optical waveguides used in integrated electro-optic devices. Slab waveguide structures were fabricated to study the influence of buffer layers on poling mechanisms. Poling currents and second harmonic intensities were measured simultaneously under various poling conditions. Maximum poling efficiency for sandwich structures was found to be close to Tg being identical to samples without buffer. Poling currents first decreased with time following a t-4 dependence and finally reached a steady-state value. Resistivities were determined from saturation currents for different temperatures and electric field strengths. An Arrhenius-like temperature dependence of the resisitivity was found for both buffer materials and NLO polymer in its glassy state. For both materials a Schottky-type dependence of the resisitivity on the elctric field strength was observed at poling tempertures. Charge injection currents into buffer were found to be one order of magnitude smaller than into the NLO polymer. Electro-optic coefficients of poled samples with and without buffer layer were measured providing that even higher degrees of chromophore orientational order can be achieved in samples with buffer due to an increased electrical breakdown limit. A low index of refraction and a high transmittance were determined for the whole visible to near infrared spectral region. Channel waveguides wer realized by photobleaching.