A highly efficient and accurate full-vector finite-difference mode solver is developed for calculation of both guided and
leaky modes of circular symmetric optical fibers with high index contrast. To demonstrate and validate the mode solver,
several examples, such as the guided modes of a silicon wire with a large index difference, the vector properties of
guided modes in step-index fibers, as well as the quasi-guided and leaky modes in a Bragg fiber, are simulated.
A novel wavelength converter using LiNbO<sub>3</sub> waveguide ring resonator is proposed and simulated.
In the design, a new wavelength is generated by combining the second harmonic generation (SHG) and the
difference frequency generation (DFG). The quasi-phase-matched condition is achieved by periodically
domain inverted lithium niobate crystal. A waveguide ring and four 1x2 beam splitters/combiners are used
to link the SHG and SFG structures. The 1x2 beam splitter/combiners are carefully designed so that only
the SHG signal at λ=0.77μm can stay inside the ring while the pumping signal at λ=1.54μm, idler signal at
λ=1.55μm, and the converted signal at λ=1.53μm can coupled into and out of the ring. Therefore, the SHG
signal, served as intermediate pumping source for the DFG, keeps circulating inside the ring and form
resonance to gain higher power and to achieve higher conversion rate. The detail design is described and
the design concept is proved by the simulation results.
The self-image effects of the multi-port multimode couplers based on weakly guided graded Ti:LiNbO<sub>3</sub> optical waveguides are analyzed through the three dimensional (3D) full-vector beam propagation method (FVBPM). By applying the perfect matching layer (PML) boundary condition, we can efficiently calculate the various performances such as insertion loss, crosstalk, and power splitting ratio of the multimode couplers. Through this model, the effect of the design and fabrication parameters such as the thickness and width of the Ti-strip and diffusion time and temperature on performances of the multimode couplers can be easily investigated. By comparing with traditional MMI couplers based on step-index optical waveguides, some salient features are observed and the related design rules should be revised. Finally, some related issues such as the bending loss and high order modes are discussed.
As the development of the technology, fiber-to-the-home (FTTH) becomes a feasible solution to meet the increasing demand on bandwidth. Due to the massive number of end users, cheap and reliable components become the bottleneck to deploy the new technology. Triplexer is one of the key components in the FTTH and is used by every end user. Currently, the available triplexers are either based on bulk optics or fiber optics with large size and high price due to manual labor involved. Planar lightwave circuit (PLC) is a possible technology for massive production and cost reduction. However, it is very challenging to design such bi-directional triplexer on PLC. The first challenge is that three channels, at λ=1310nm, 1490nm, and 1555nm, are separated unevenly over a very large wavelength range; Secondly, the bandwidths of the three channels, Δλ=100nm, 20nm, and 10nm, are very different. In the paper, we proposed a novel design by combining both coarse WDM and dense WDM. In the design, a multi-mode interference (MMI) device is used for coarse WDM to separate the 1310nm from the other two channels. The dense WDM for the remaining two channels is performed by an array waveguide gratings (AWG). The MMI and AWG are built on the same wafer with monolithic integration. Initial simulation results show it is a very promising device.
In wavelength division multiplexing (WDM) systems, such as the fiber-to-the-home (FTTH) service (e.g., wavelength 1.31/1.55/1.49 mm in the EPON and wavelength 1.31/1.545/1.5x mm in the APON), coarse and dense WDM are two key technologies. In general, it takes two steps to accomplish this mixing (coarse/dense) WDM functions. In order to make the WDM device compact and low loss, it is necessary to integrate these two WDM functions into one step. In this paper, we propose two typical designs of the coarse/dense multiplexers, which multiplex the coarse/dense-WDM (C/D-WDM) signals simultaneously. We believe that, although their operation principle is simple, the proposed structures simplify the design of integrated photonic devices and will be needed in future WDM systems, specially for the WDM filter in the FTTH service.
The proposed devices consist of a grating-assisted symmetrical or asymmetrical Mach-Zehnder interferometer with the wideband coupler (WBC) and/or the 3dB coupler. Depending on different operation principles, the WBC coupler operates as a 3dB coupler in two wavelength bands or operates as a 3dB coupler in one wavelength band and a cross-state coupler in another one. In this paper, firstly, the operation principles of the proposed C/D-WDM Multiplexers are demonstrated though an example of multiplexing three signals (l1/l2/l3) in two wavelength bands, where l1 (e. g., 1.31mm) belongs to the first band and l2/l3 (e. g., 1.55/1.5x mm) belong to the second band. Then, the design procedure and simulation results of those C/D-WDM multiplexers and related components such as the WBC coupler and planar gratings, which are based on the silica material, are given. Finally, some related issues such as polarizatin dependence and material dispersion are discussed.
A novel design of photonic crystal fiber (PCF) for broadband dispersion compensation is proposed. By changing the radius of the air holes placed in close proximity of the guiding core, the PCF fiber can realize effective broadband dispersion compensation. Through the proper design, the PCF fiber is shown to provide large normal dispersion up to several hundred ps/nm/km. Two examples of the PCF fibers for dispersion compensation of the standard single mode fiber and "True wave-RS" fiber are given. For example, by decreasing the diameter of second ring of air holes, the proposed PCF fiber is shown to provide large normal dispersion (up to -811 ps/nm/km), nearly ten times of conventional dispersion compensating fibers, and compensate conventional single-mode fibers within ±0.05 ps/nm/km over a wavelength range of the conventional C-band.
This paper presents concepts behind the use of the beam propagation method (BPM) to model the vector nature of optical waves, and for wave propagation at wide angles off-axis. The two enhancements have been combined.
The existing computer-aided-design tools in optoelectronics are reviewed and compared. The beam propagation method, the most commonly used method in guided-wave devices, is applied to optical filter design. The simulation result is compared with the published experimental result.
A CAD tool for the optical interconnects is developed and described. It is able to trace scalar or polarized electromagnetic fields propagating through complex optical waveguiding media or free space. The scattering and radiation at index discontinuities are considered and optical beams diverging from the waveguide axis may be simulated. The intra-board and inter-board optical interconnects are simulated and discussed.
We present the design and analysis of a microfabricated silicon pressure transducer. The operating principle for this device is based on the evanescent modulation of power in an integrated optical waveguide. A silicon diaphragm attenuator is initially separated from the waveguide by a precise microfabricated gap spacing. When external pressure is applied to the sensor, the silicon attenuator is moved into closer proximity with the waveguide, and light is coupled out of the waveguide into the attenuator. Thus, by monitoring the light intensity at the output of the waveguide, one can deduce the pressure applied to the silicon diaphragm. Packaging considerations have played an important role in the development of the device and have led to the use of anti-resonant reflecting optical waveguides (ARROWs), which are etched down to form a rib in order to provide confinement in the lateral direction. These waveguides provide good spatial and index matches to single-mode optical fibers. Numerical simulations of device performance have provided information critical to the design of the sensor.
A vector beam propagation method based on finite-difference (FD-VBPM) is developed and described. The polarization property and the hybrid nature of the propagating waves are considered. The assessment and the applications of the FD-VBPM are presented.