Novel compact design for 4-channel SOI-based reconfigurable optical add/drop multiplexer using microring resonators
is presented and analyzed. Microring resonators have two important attributes as a key new technology
for future optical communications, namely functionality and compactness. Functionality refers to the fact that
a wide range of desirable filter characteristics can be synthesized by coupling multiple rings. Compactness refers
the fact that ring resonators with radii about 30μm can lead to large scale integration of devices with densities on
the order of 104 - 105 devices per square centimeter. A 4-channel reconfigurable optical add/drop multiplexer
comprises a grid-like array of ridge waveguides which perpendicularly cross through each other. SOI-based resonators
consisted of multiple rings at each of the cross-grid nodes serve as the wavelength selective switch, and
they can switch an optical signal between two ports by means of tuning refractive index of one of the rings. The
thermo-optic coeffcient of silicon is 1.86×10-4/K. Thus a temperature rise of 27K will increase the refractive
index by 5×10-3, which is enough to cause the switching of our designed microring resonators. The thermo-optic
effect is used to suppress the resonator power transfer, rather than to promote loss. Thus, the input signal only
suffers small attenuation and simultaneously low crosstalk can be achieved by using multiple rings.
Two types of silicon-on-insulator thermo-optic variable optical attenuators (VOAs) based on a Mach-Zehnder interferometer and a multimode-interference coupler are fabricated, one with thermal isolating grooves to improve heating efficiency and the other without. Comparison of optical and electrical properties, such as insertion losses, the maximum attenuation levels and the corresponding power consumptions, and the response times, is carried out between the two types of VOAs. The comparison results indicate that use of thermal isolating grooves leads to better values for most characteristics and is an effective way to improve the performance of Mach-Zehnder interferometer-type thermo-optic devices.
A compact polarization-insensitive 8×8 arrayed waveguide grating with 100GHz channel spacing at 1.55µm is presented on the material of silicon on insulator (SOI). Increasing the epitaxial layer thickness can reduce the birefringence of the waveguide, but the wvaeguide's bend radius also increases at the same time. We choose the SOI wafer with 3.0μm epitaxial layer to reduce the device's size and designed the appropriate structure of rib waveguides to eliminate the polarization dependant wavelength shift. Compared to the other methods of eliminating the polarization dependant wavelength shift, the method is convenient and easy to control the polarization without additional etching process. The index differences between TE0 and TM0 of straight and bend waveguides are 1.4×10-5 and 3.9×10-5, respectively. The results showed that the polarization dependant wavelength shift is 0.1nm, and the device size is 1.5×1.0 cm2.
OADM is a key component in DWDM due to many merits such as good performance in low loss, low price, simple and flexible integration structure. One of the critical issues focused on the research of OADM is to design multiplexer/demultiplexer hoping to reduce the insertion loss and improve the propagation efficiency of the total device. In this paper, we present the design of 4×1 and 8×1 multiplexers based on SOI materials. The devices show several advantages including low insertion loss, phase-insensitiveness, polarization independence and compact size. The devices' performances are simulated under different conditions and all exhibit satisfying results. It's ideal to equip them in compact optical system.
A thermo-optic variable optical attenuator (VOA) based on a Mach-Zehnder interferometer and multimode-interference coupler is fabricated. Not a single-mode but a multimode waveguide is used as the input and output structures of the optical field, which greatly reduces the coupling loss of the VOA with a normal single-mode fiber. The insertion loss of the fabricated VOA is 2.52 to 2.82 dB at the wavelength of 1520 to 1570 nm. The polarization dependent loss is 0.28 to 0.45 dB at the same wavelength range. Its maximum attenuation range is up to 26.3 dB when its power consumption is 369 mW. The response frequency of the fabricated VOA is about 10 kHz.