Compared with the arrayed waveguide grating (AWG) that widely used as optical wavelength multiplexers and/or demultiplexers (MUX/DMUX) in optical communication networks, AWG of low diffraction order has enormous potential of application in cases that need a large free spectrum range (FSR), to name a few, various integrated optical spectrometer, and wavelength MUX/DMUX in coarse wavelength division multiplexing (CWDM) networks. In the current paper, an investigation is conducted on S-shaped antisymmetric design scheme for low diffraction order AWG layouting. To reduce overall AWG device dimension and increase bend waveguide curvature radius uniformity, particle swarm optimization (PSO) with constrained conditions is employed to find optimized geometrical parameters which determine AWG structure. PSO algorithm could reduce by about 50.6% of the AWG dimension compared with previously reported AWG and thus PSO could be a promising optimization method when designing AWG.
An integrated high-resolution ratio-metric wavelength monitor (RMWM) is demonstrated on SOI platform. The device consists of a reconfigurable demultiplexing filter based on cascaded thermally tunable microring resonators (MRRs) and Ge-Si photodetectors integrated with each drop port of the MRRs. The MRRs are supposed to achieve specific resonant wavelength spacing to form the “X-type” spectral response between adjacent channels. The ratio of the two drop power between adjacent channels varies linearly with the wavelength in the “X-type” spectral range, thus the wavelength can be monitored by investigating the drop power ratio between two pre-configured resonant channels. The functional wavelength range and monitor resolution can be adjusted flexibly by thermally tuning the resonant wavelength spacing between adjacent rings, and an ultra-high resolution of 5 pm or higher is achieved while the resonant spacing is tuned to 1.2nm. By tuning the resonant wavelength of the two MRRs synchronously, the monitor can cover the whole 9.6nm free spectral range (FSR) with only two ring channels. The power consumption is as small as 8 mW/nm. We also demonstrate the multi-channel monitor that can measure multi-wavelength-channel simultaneously and cover the whole FSR by presetting the resonant wavelengths of every MRR without any additional power consumption. The improvements to increase the resolution are also discussed.
Two layers of buried optical waveguides are manufactured in silicate glass substrate. Using ion-exchange process, this procedure is composed of two successive cycles of buried waveguide fabrication. Characterizations of these waveguides show that the two layers have similar dimensions for both waveguide core and for mode field, and thus similar optical properties. Loss analysis indicates that coupling loss of top and bottom layer waveguide with single-mode-fiber being 0.80 dB/facet and 0.75 dB/facet, respectively.
Due to the Joule heating effect induced by the use of an assisting electric field, glass wafer temperature is experimentally found to increase synchronically with the flow of current during the process of field-assisted ion diffusion. A theoretical analysis demonstrates that the amplitude of the glass wafer temperature increase is dictated by competition between two factors, heat generation and heat dissipation. Heat generation and heat dissipation both become stronger as the glass wafer temperature increases. Studies have shown that the Joule heating effect can influence the waveguide manufacturing process profoundly, including aspects such as the stability of ion diffusion, theoretical modeling of the ion-diffusion process, and waveguide depth uniformity over the glass wafer.
A model based on the charge-density flux (CDF) is proposed for the electric-field-assisted (EFA) ion-exchange, which is suitable for various EFA ion exchanging processes. Theoretical analysis shows that the CDF model is equivalent to the voltage model when the local temperature change around the glass wafer is negligible when a constant voltage is applied to the ion exchanging process. However, our experiments show that the CDF model is more applicable than the voltage model because the constant-voltage scheme shows a positive feedback process and the local temperature rising is unavoidable in the ion exchanging process. Our further experiments also show that the EFA ion exchanging process can be conveniently characterized by the proposed CDF model with the monitored electrical current, no matter the EFA ion exchanging process is with a constant-voltage/current scheme, a mixed scheme, or even a scheme with random voltage change, while additional complicated measures will be required to characterize the EFA ion exchanging process with the traditional voltage model.
Traditional glass-waveguide-based electric-field-assisted ion-exchange model is characterized by the product of voltage
and time which is well known as the voltage model. In the voltage model, the modeling condition is mainly assumed to
be with a constant voltage (or a constant electric field) and temperature is considered to be a constant, diffuse depth is
mainly determined by voltage and time. However, our recent studies and experimental results show that there is a
thermally-induced warming effect in the ion-exchange, which leads to a change of local temperature in the glass
substrate which means the electrical current induced heating effect and the decrease of the local electrical resist with the
increase of the local temperature. In this paper, we analyze the influence of the temperature variation and introduce a
temperature-independent parameter to modify the traditional voltage model and solve the influence of ion-exchanging
temperature variation. Experiment results show that the voltage model with the temperature-independent parameter
modification is more applicable than the traditional one. We obtain a more precise result than traditional model in our
Silicon photonics can found applications in optical interconnects and optical signal processing. Recent years, silicon
photonics was developed rapidly. In this paper, we report our research work on silicon photonics. Based on the standard
CMOS foundry, we studied the silicon waveguides and related photonic components.
Optical splitter is one of most typical device heavily demanded in implementation of Fiber To The Home (FTTH) system.
Due to its compatibility with optical fibers, low propagation loss, flexibility, and most distinguishingly, potentially costeffectiveness,
glass-based integrated optical splitters made by ion-exchange technology promise to be very attractive in
application of optical communication networks. Aiming at integrated optical splitters applied in optical communication
network, glass ion-exchange waveguide process is developed, which includes two steps: thermal salts ion-exchange and
field-assisted ion-diffusion. By this process, high performance optical splitters are fabricated in specially melted glass
substrate. Main performance parameters of these splitters, including maximum insertion loss (IL), polarization
dependence loss (PDL), and IL uniformity are all in accordance with corresponding specifications in generic
requirements for optic branching components (GR-1209-CORE). In this paper, glass based integrated optical splitters
manufacturing is demonstrated, after which, engineering-oriented research work results on glass-based optical splitter are
In this paper, an accurate Fourier Optics method of designing AWG demultiplexer based on high-index-contract
Silicon-on-Insulator (SOI) materials is presented. The typical SOI photonic wire waveguide has a cross section of
400×340nm2 satisfying single-mode condition, and operating central wavelength is 1.5500μm. A three-stigmatic-points
method is also applied in order to improve the accuracy, considering the aberration theory. Furthermore, our AWG has
another important characteristic--the flat field of the output ports. In the example presented here, we design a 1×256
channel AWG with 0.1-nm channel spacing. The simulation result shows that the insert loss is almost 0dB for the central
and peripheral output ports as well, representing a good uniformity. Meanwhile, the crosstalk to the adjacent channel is
14.4dB. Free spectral region (FSR) equals to 30nm as designed.
Multimode Interference (MMI) based devices are widely used due to excellent performance. Here in this paper, a 1×2
multimode power splitter based on MMI is designed using three-dimensional beam propagation method (3D-BPM), and
then fabricated in glass using the Ag+-Na+ ion-exchange technique. The width of the input and output multimode
waveguides was 50μm and they were tapered to 75μm at the interface to the MMI region. The MMI region was also
quadratically tapered .First, Ag+-Na+ ion exchange was run in nitrate melt at 350°C.Then an electric field was applied at
300°C so that the silver ions continued their migration award. Under the wavelength of 1550nm, the measured results
showed that the propagation loss of multimode straight waveguide can be lower than 0.31dB/cm, and the insertion loss
and uniformity of the splitter were 4.28dB and 0.21dB, respectively. Parameters of the fabrication process and structure
of the device can be optimized to improve the performance of the device.
The optical waveguide switch utilizing the principle of total internal reflection (TIR) is a promising structure since its
merits such as compact size, digital response characteristic, insensitivity to wavelength and polarization, and so on. In
this paper the TIR switch is studied both in theory and in experiment. At first, we give a comprehensive analysis about
reflection mechanism in the TIR switch from the following three issues: the grazing incidence of a narrow beam in the
free space, the beam reflection in a bounded space, and the beam expansion induced by the reflection in a two-dimensional
gradient field of the refractive index decrease. Then based on the analytical works, we successfully fabricate
practical TIR switches by utilizing the thermo-optical effect of polymer and the carrier injection effect of GaAs (both the
current injection and the photon injection manners are employed). The testing results show that: the extinction ratio of
the thermo-optical TIR switch exceeds 35 dB at an power consumption of 80 mW; for the carrier injection TIR switch
utilizing the current injection manner, its operation speed is faster than 20 ns and its operation current is about 70 mA.
The properties of truly confined modes of a 2D hex horizontal photonic crystal slot slab waveguide are analyzed. Then
the dispersion of liner defect waveguide is calculated. In addition, what influence the slots with different height have
over the band structure and the group velocity dispersion of the defect mode waveguide are analyzed. Based on these
studies, an ultra-compact silicon-based Mach-Zehnder amplitude modulator is proposed. For a design with almost
negligible first order chromatic dispersion in an optical bandwidth of 1THz, we predict a modulation bandwidth of
40GHz and a length of about 80µm. This is achieved by infiltrating an electro-optic polymer into a slotted photonic
crystal waveguide, the strong field confinement in slotted waveguides and the slow light interaction enhancements
provided by the photonic crystal waveguide, where group velocity and dispersion may be controlled.
A slot waveguide structure is used in the part of arrayed waveguides in AWG instead of silicon waveguides. It is filled
with high negative thermo-optic coefficient polymer in the narrow slot. The arrayed slot structure can remarkably reduce
the center wavelength shift when the temperature changes. In this study, we use the polymer WIR30-490 and ZP49 to be
filled in the slot. The thermo-optic coefficients of WIR30-490 and ZP49 are negative, and have the same order of
magnitude with silicon. In our simulations, by adjusting several variables of the slot structure, such as the width of the
slot between the pair of silicon wires, the width of the silicon waveguide, and the height of the silicon waveguide, we can
get the athermal condition of AWG for each polymer. Even if there is an acceptable error on fabrication, temperature-dependent
center wavelength shift of AWG can still be reduced down to 1 pm/°C. It makes the fabrication of athermal
silicon AWG possible.
One kind of electro-optic polymer assisted Mach-Zehnder optical switch based on silicon slot structure is presented. By
filling electro-optic material in the void slot of the arms, direct electro-optic modulation can be introduced. Theoretical
model and detailed analysis is given in this paper.