Mingshan Zhao

Athermal Silicon-on-insulator ring resonators by overlaying a polymer cladding on narrowed waveguides

Athermal silicon ring resonators are experimentally demonstrated by overlaying a polymer cladding on narrowed silicon wires. The ideal width to achieve athermal condition for the TE mode of 220 nm-height SOI waveguides is found to be around 350 nm. After overlaying a polymer layer, the wavelength temperature dependence of the silicon ring resonator is reduced to less than 5 pm/degrees C, almost eleven times less than that of normal silicon waveguides. The optical loss of a 350-nm bent waveguide (with a radius of 15 microm) is extracted from the ring transmission spectrum. The scattering loss is reduced to an acceptable level of about 50 dB/cm after overlaying a polymer cladding.

Analysis and optimization of intensity noise reduction in spectrum-sliced WDM systems using a saturated semiconductor optical amplifier

Theoretical and experimental results on the reduction of the intensity noise in spectrum-sliced wavelength-division-multiplexing systems using a saturated semiconductor optical amplifier (SOA) are presented. The influence of the injected current and the input power to the saturated SOA on the noise reduction and its bandwidth are studied. The optimum condition for a high noise suppression ratio and a large bandwidth is derived. For the optimum operation of the SOA, an increase of 13.5 dB in the intensity-noise-limited signal-to-noise ratio for a bitrate of 2.488 Gb/s and of 17.5 dB for a bitrate of 622 Mb/s are obtained experimentally in a single-stage SOA.

A Label-Free Optical Biosensor Built on a Low-Cost Polymer Platform

Planar integrated optical biosensors are becoming more and more important as they facilitate label-free and real-time monitoring with high sensitivity. In this paper, the systematic work on the development of this kind of optical biosensor built on a novel polymer platform named PSQ-Ls will be presented. The material itself is of very low cost, and the optical devices with high performances are fabricated through a simple UV-based soft imprint lithography technique. Especially for ring resonator, Q value as high as 5 × 104 and 2.7 × 104 are achieved in air and water condition. These optical chips are functionalized efficiently with protein A molecules through physical immobilization, after careful investigation of the physicochemical and chemical properties of their surface. Both bulk sensing and surface sensing are performed. The proposed optical biosensor exhibits good response not only to its surrounding environments change but also to the small amount of targeted molecules appearing in the buffered solution, which is human-IgG in our study.

A Study on Liquid Hybrid Material for Waveguides—Synthesis and Property of PSQ‐Ls for Waveguides

Silicate‐based inorganic‐organic hybrid polymer systems have many unique properties including thermal stability and photo‐stability, chemical resistance with the combination of tunable optical properties. Two kinds of new UV‐patternable hybrid materials PSQ‐Ls were synthesized by a sol‐gel process at room temperature, which can be used for low cost fabrication of optical waveguides. Thick films (up to 8.31 µm) can be coated by a single spin‐coating process without any cracking and the average surface roughness (Ra), detected by atomic force microscopy (AFM), is below 0.5 nm. The optical properties (refractive index, birefringence, and optical loss at 1310 nm and 1550 nm, respectively) of the PSQ‐Ls films are investigated by a prism coupler. The refractive index of PSQ‐Ls can be exactly tuned from 1.4483 to 1.5212 by blending PSQ‐LH (nTE=1.5212 @ 1310 nm) and PSQ‐LL (nTE=1.4483 @ 1310 nm). The maximum refractive index contrast is about 4.8%. After post‐baking, birefringences of the films are below 0.0005 and optical losses are about 0.2 dB · cm−1 at 1310 nm, 0.7 dB · cm−1 at 1550 nm, respectively. Furthermore, the PSQ‐Ls films also show outstanding thermal stability in air atmospheres.

Athermal arrayed waveguide gratings in silicon-on- insulator by overlaying a polymer cladding on narrowed arrayed waveguides

Athermal arrayed waveguide gratings (AWGs) in silicon-on-insulator (SOI) are experimentally demonstrated for the first time to our knowledge. By using narrowed arrayed waveguides, and then overlaying a polymer layer, the wavelength temperature dependence of the AWGs is successfully reduced to -1.5 pm/°C, which is more than 1 order of magnitude less than that of normal SOI AWGs. The athermal behavior of the AWGs is obtained with little degradation of their performance. For the central channel, the cross talk is less than -15 dB and the insertion loss is around 2.6 dB. Good characteristics can be maintained with temperatures up to 75 °C. The total size of the device is 350 μm × 250 μm.

Experimental demonstration of an all-optical 2R regenerator with adjustable decision threshold and "true" regeneration characteristics

Experimental 2R regeneration characteristics of an optical decision circuit based on a Mach-Zehnder interferometer with gain clamped semiconductor optical amplifiers in both arms are reported for the first time. The decision circuit gives a true regeneration, i.e., a digital characteristic on a linear instead of a logarithmic (or dB) scale for the input and/or output power.

A PSQ-L Polymer Microring Resonator Fabricated by a Simple UV-Based Soft-Lithography Process

Photonic integrated circuits based on polymer waveguides have great potential as low-cost optical devices. A novel inorganic-organic hybrid polymer polysiloxane-liquid (PSQ-L) is introduced for defining the waveguides and for use as both core and cladding layer for the waveguides. The waveguide circuits are replicated by a simple ultraviolet-based soft lithography method consisting of two steps. All-polymer microring resonators are fabricated by this approach and characterized. About 6-dB extinction ratio at the through port and 18-dB extinction ratio at the drop port is demonstrated. A Q-factor of 4.2 times 104 is obtained. Extracted from the measured spectrum, the scattering loss of the ring waveguides is estimated to be about 1.6 dB/cm. This easy fabrication technique can be easily extended to fabricate other devices.

All-optical 2R regeneration based on polarization rotation in a linear optical amplifier

All-optical 2R-regeneration based on polarization rotation in a single semiconductor linear optical amplifier is experimentally demonstrated. An extinction ratio (ER) improvement of 15 dB has been obtained for an input ER of 5 dB under static operation. With a degraded input signal, a receiver-sensitivity improvement of >3 dB at a bit error rate of 10/sup -9/ was found for 2.5 Gb/s. Regenerative capability for 10 Gb/s has also been verified.

Organic silicone sol-gel polymer as a noncovalent carrier of receptor proteins for label-free optical biosensor application.

Optical biosensing techniques have become of key importance for label-free monitoring of biomolecular interactions in the current proteomics era. Together with an increasing emphasis on high-throughput applications in functional proteomics and drug discovery, there has been demand for facile and generally applicable methods for the immobilization of a wide range of receptor proteins. Here, we developed a polymer platform for microring resonator biosensors, which allows the immobilization of receptor proteins on the surface of waveguide directly without any additional modification. A sol-gel process based on a mixture of three precursors was employed to prepare a liquid hybrid polysiloxane, which was photopatternable for the photocuring process and UV imprint. Waveguide films were prepared on silicon substrates by spin coating and characterized by atomic force microscopy for roughness, and protein adsorption. The results showed that the surface of the polymer film was smooth (rms = 0.658 nm), and exhibited a moderate hydrophobicity with the water contact angle of 97°. Such a hydrophobic extent could provide a necessary binding strength for stable immobilization of proteins on the material surface in various sensing conditions. Biological activity of the immobilized Staphylococcal protein A and its corresponding biosensing performance were demonstrated by its specific recognition of human Immunoglobulin G. This study showed the potential of preparing dense, homogeneous, specific, and stable biosensing surfaces by immobilizing receptor proteins on polymer-based optical devices through the direct physical adsorption method. We expect that such polymer waveguide could be of special interest in developing low-cost and robust optical biosensing platform for multidimensional arrays.

Dynamic birefringence of the linear optical amplifier and application in optical regeneration

Dynamic birefringence of the linear optical amplifier (LOA) is theoretically and experimentally investigated. Significant nonlinear variations of the state of polarization with the input power and bias current of the LOA have been found. Based on this nonlinear change of the state of polarization, an all-optical 2R regenerator is demonstrated. Under static operation, an extinction ratio (ER) improvement of 15 dB has been obtained for an input ER of 5 dB. With a degraded input signal, a receiver sensitivity improvement of over 3 dB at a bit-error rate (BER) of 10/sup -9/ has been found for 2.5 Gb/s. For 10 Gb/s, zero power penalty is observed. Significant improvements of ER for both 2.5 and 10 Gb/s are obtained.