A tunable nonreciprocal device is presented based on PT symmetry. This device structure is composed of two pairs PT symmetry ring. Signal λ1 is only transmitted in the forward direction, while another signal λ2 is transmitted in the backward direction. The signal channel spacing can also be controlled.
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 modal expansion method is utilized to study the reflection mechanism in the total-internal-reflection (TIR) switch. Due to the confinement of the waveguide, the beam reflection within the TIR switch is completely different from that in the free space. Its essence is the degeneracy between the even and odd modes in the waveguide of the reflection region.
We propose a compact variable optical attenuator (VOA) based on the W type five-layer symmetric slab waveguide. Simulation result shows that: for the attenuator based on GaAlAs/GaAs epitaxial layers, with a refractive index change of -0.01 in the current injection region of 1000 &mgr;m long (corresponding to injected current of about 80mA), an attenuation of more than 30dB is achieved. The attenuation range can be scaled to fit the requirements by varying the electrode length.
Generally, in the section of photonic crystal fiber, all air holes are arranged to a triangular regulation, when the size of air holes, the pitch of between neighboring air holes, and refractive index of background material are mapped optimally, one missing air hole in the central of section can localize optical field and form a single mode fiber. Here, each air hole is replaced by twin air holes with fixed distance and axis direction. Accordingly, we can think the central of
section where twin air holes missing is the core of fiber, and optical field is guided in here. In the novel photonic crystal
fiber, all twin air holes arranged according to identical axis direction in the cladding of PCF bring an asymmetry structure of section, and birefringence can come into being in this novel PCFs. After some parameters are selected optimally, the effective refractive index difference between two orthogonal directions Δneff can reach the magnitude of 10-4. From the result of numerical calculation, we also can see that the birefringence parameter Δneff can increase
slightly when the distance between twin air holes is shortened a little but keeping each air holes size and the pitch of
neighboring cell composed by twin air holes.
We propose an analytical reflection model for the waveguide switch with total-internal-reflection structure, which is the grazing reflection of beam with narrow beamwaist. For such incidence condition, the output optical field is the superposition of incident and reflected fields, we deduce the effective reflection coefficient together with angular spectrum of the output field.
An ultra compact, highly integrated photonic switch with 2×3 configuration was designed and fabricated using the thermo-optical effect of polymer materials. By exerting voltage to proper compartment of the electrode, the input light can be switched freely among three output ports. The experiment results show: for the "insufficient reflection" state, the extinction ratio is 16.64dB for the middle output port; for the "bar" state, the extinction ratio for the reflection port is 26.8 dB. The power consumption is on the scale of 100 mW, and varies with different function mode.
In this paper, the beam-propagation characteristics of the total internal reflection induced by the thermo-optic effect are investigated. Based on the Fourier heat transmission principle and variable separation method, we derive the analytical transient expression of thermal field for general thermo-optic (TO) devices. Based on the analytical expression, time response and steady-state temperature distribution of thermal-optic devices are presented. The expansion rule of total internal reflection (TIR) in the thermal field is developed mathematically, and quantitative calculation is given about specific expansion value. As an illustration and application of this rule, a X-junction 2×2 TIR switch is designed to accomplish the object of high reflection efficiency. The computer simulation results show the structure presents a high reflection coefficient indeed, the reflection loss is only -0.76dB. The computer simulation results agree with the calculation well.