Three-waveguide Directional Coupler Research Articles

Efficient light transfer in coupled nonlinear triple waveguides using shortcuts to adiabaticity

We use the method of shortcuts to adiabaticity to design the variable couplings in a three-waveguide directional coupler which may contain nonlinear elements, in order to accomplish efficient light transfer between the outer waveguides for shorter device lengths, despite the presence of nonlinearity. The shortcut couplings are obtained for the ideal case where all the waveguides are linear, for which a perfect transfer is guaranteed in theory, but are tested for various combinations of linear and nonlinear waveguides in the device. We show with numerical simulations that, in most configurations, high levels of transfer efficiency can be maintained even for large values of the input power, and for shorter lengths than those of conventional adiabatic devices. We also find that efficiency is improved for shortcut couplings with less spatial extent, since in this case the nonlinearity acts during a shorter range. The present work is expected to find application in research fields like optoelectronic computing and ultrafast light switching, where the fast and controlled light transmission inside a set of waveguides is a crucial task. Additionally, the reduction in the device size may be exploited for incorporating them in integrated optical systems, where a high density of waveguides is required.

Accurate theoretical analysis of light transition in three-waveguide directional coupler based on Invariant Engineering

Accurate theoretical analysis of light transition in three-waveguide directional coupler based on Invariant Engineering

Simulation of quantum coherence dynamics in macroscopic domain using a three-waveguide directional coupler

We consider a three-waveguide (WG) directional coupler with an attempt to explore an optical analogue of the quantum coherence dynamics, which is found to be achievable in the present model at the macroscopic domain. In order to simulate the characteristics of such opto-quantum analogy, a field-coupled three-level atomic system has been undertaken in our study. Mutual correspondence between the field-induced coherence properties in the atomic system and the light transfer related optical properties in the evanescently coupled WGs has been discussed in the dissipative cases at different parameter conditions. The signature of optical impedance is highlighted in this context and the impact of these terms in visualizing the coherence dynamics inherent to a nano-photonic structure is explicitly reported.

Broadband Electro-Optical Crossbar Switches Using Low-Loss Ge2Sb2Se4Te1 Phase Change Material

This theoretical modeling and simulation paper presents designs and projected performance of non-volatile broadband on-chip 1 × 2 and 2 × 2 electro-optical switches operating in the telecommunication C -band and based on the silicon-on-insulator technological platform. These optical switches consist of an asymmetric two-waveguide directional coupler and a symmetric three-waveguide directional coupler, in which the optical phase change material Ge2Sb2Se4Te1 (GSST) is the top cladding layer for one of the silicon strip waveguides. Reversible crossbar switching is attained by the amorphous (Am) to crystalline (Cr) and Cr-to-Am phase transitions in the GSST induced by heating the GSST in contact with an indium tin oxide (ITO) microstrip through Joule heating. We examined device performance in terms of mid-band insertion loss (IL), crosstalk (CT), and 0.3-dB IL bandwidth (BW). The 2 × 2 results were IL = –0.018 dB, CT L c of 15.4 μm, and IL = 0.046 dB, CT L c of 17.4 μm. Simulations of the 1 × 2 devices at 16.7-μm L c revealed that IL = 0.083 dB and CT < 12.8 dB along with an expanded BW of 95 nm. Thermal simulations showed that a 5-V pulse train applied to 1019-cm−3 doped ITO would produce crystallization; however, the process of amorphization required a 24-V pulse of 2.9-μs duration to raise the GSST temperature above the melting temperature of 900 K.

High-extinction-ratio directional-coupler-type polarization beam splitter with a bridged silicon wire waveguide.

We demonstrate an integrated polarization beam splitter (PBS) of a simple and compact device geometry with high polarization extinction ratios (PERs). A silicon PBS based on a three-waveguide directional coupler is numerically simulated for optimum device parameters, and fabricated experimentally. The measured PER values of the fabricated PBSs are 40.74dB and 39.01dB for transverse electric and transverse magnetic modes, respectively, and their corresponding insertion losses are 0.35dB on average for a coupler length of about 29.4μm.

Broadband photonic transport between waveguides by adiabatic elimination

We propose an adiabatic method for the robust transfer of light between the two outer waveguides in a three-waveguide directional coupler. Unlike the established technique inherited from stimulated Raman adiabatic passage (STIRAP), the method proposed here is symmetric with respect to an exchange of the left and right waveguides in the structure and permits the transfer in both directions. The technique uses the adiabatic elimination of the middle waveguide together with level crossing and adiabatic passage in an effective two-state system involving only the external waveguides. It requires a strong detuning between the outer and the middle waveguide and does not rely on the adiabatic transfer state (dark state) underlying the STIRAP process. The suggested technique is generalized to an array of $N$ waveguides and verified by numerical beam propagation calculations.

Hybrid plasmonic polarization splitter using three-waveguide directional coupler in InGaAsP/InP

We investigated a polarization beam splitter based on a three-waveguides directional coupler by utilizing a hybrid plasmonic waveguide as the middle waveguide. The structure of the proposed polarization splitter is compatible to the InP based conventional waveguide. So, it has the capability of monolithic integration with InP-based active (lasers and photodetectors) and passive components. Polarization splitting is obtained by optimizing the coupling length, the InP-cladding layer thickness, and the gap between straight waveguides. Calculations show a coupling length of about 27 and 350 µm for the TM- and TE-polarization mode, respectively, an extinction ratio of 17 dB, and an insertion loss of less than 1 dB for a gap width of 30 nm and InP-cladding layer thickness of 135 nm at 1.55 µm wavelength.

Adiabatic three-waveguide coupler

We propose an adiabatic method for transfer of light in a three-waveguide directional coupler in a single mode. In our scheme the propagation coefficients of the two outer waveguides are identical, but may vary simultaneously along the propagation direction. In contrast to earlier work [E. Paspalakis, Opt. Commun. 258, 30 (2006)], where the coupling coefficients are designed to act in the counterintuitive order for an input in one of the outer waveguides, here we may have initially any light input in each of the waveguides and any order of coupling coefficients. Consequently, all three adiabatic eigenstates of the system are used in the dynamics. These solutions allow us to design some interesting waveguide devices.

Wavelength-selective switching using double-ring resonators coupled by a three-waveguide directional coupler.

A novel design of a two-bus coupled-rings 2 × 2 switch with inter-ring coupling enabled by a three-waveguide (3w) directional coupler is proposed. The device is analyzed using a theoretical model based on coupled mode theory and optical transfer formulae. We show that injected free-carriers tuning of the central waveguide in the 3w coupler affects only the bonding resonance mode while the other anti-bonding mode is transparent. This feature can be used to perform selective optical switching, and a numerical design example is given on the silicon photonics platform. The selective switch can be employed in a two-color duplex bidirectional communication system which conveniently separates the simultaneous transmitted and received signals in a single fiber-optic waveguide.

Generation of higher-dimensional modal entanglement using a three-waveguide directional coupler

In this paper, we propose a method for the generation of higher-dimensional modal entanglement through a type II spontaneous parametric down-conversion process using a three-waveguide directional coupler in a periodically poled lithium niobate substrate. We show that by a proper design, it is possible to achieve an output state of two photons occupying three different spatial modes. The advantage of using such waveguide structure is its flexibility and the design space availability to achieve desired characteristics of the photon pairs generated in the down-conversion process.

Simulation of coherently controlled population dynamics of a three-level atomic system in a three-waveguide directional coupler: An opto-quantum analogy

The optical analogue of quantum population dynamics in a three-level atom is theoretically demonstrated by employing a specially designed macroscopic photonic structure composed of three evanescently coupled straight waveguides. We have developed the theories for the two models to establish opto-quantum analogy. Various characteristics of temporal population dynamics as obtained in the quantum system have been simulated in spatial domain by computing the fractional power distribution in the three-waveguide directional coupler with specialty in configurational and coupling geometries. Both the systems exhibit exactly similar characteristics under proper parameter conditions.

All-optical switching in a symmetric three-waveguide coupler with phase-mismatched absorptive central waveguide

All-optical switching operation based on manipulation of absorption in a three-waveguide directional coupler is theoretically investigated. The proposed structure consists of one absorptive central waveguide and two identical passive side waveguides. Optically induced absorption change in the central waveguide effectively controls the coupling of light between the two side waveguides, leading to optical switching action. The proposed architecture alleviates the fabrication challenges and waveguide index matching conditions that limit previous demonstrations of similar switching schemes based on a two-waveguide directional coupler. The proposed device accommodates large modal index difference between absorptive and passive waveguides without compromising the switching extinction ratio.

Effects of nonlinearity in asymmetric adiabatic three-waveguide directional couplers

We study the effects of optical nonlinearity in asymmetric adiabatic three-waveguide directional couplers, that consist of both linear and nonlinear waveguides. We consider several combinations of linear and nonlinear waveguides and show that the different combinations have different switching characteristics. We also find that in the structure where the central waveguide is nonlinear and the two outer waveguides are linear the nonlinearity does not play a role.

Design and analysis of 2×2 half-wave waveguide couplers

Conventional couplers including the 2 x 2 directional coupler and the self-imaging multimode interference coupler always produce a 90 degrees coupling phase to yield complementary power transfer functions when the relative phase of the two input fields changes. For applications in coupled-cavity lasers, a 2 x 2 half-wave optical coupler with a 180 degrees coupling phase is required in order to produce synchronous output power for achieving high single-mode selectivity. We present the designs and optimization of 2 x 2 half-wave couplers, including a three-waveguide directional coupler and a nonimaging multimode interference coupler.

Design and analysis of 2×2 half-wave waveguide couplers

Conventional couplers including the 2×2 directional coupler and the self-imaging multimode interference coupler always produce a 90° coupling phase to yield complementary power transfer functions when the relative phase of the two input fields changes. For applications in coupled-cavity lasers, a 2×2 half-wave optical coupler with a 180° coupling phase is required in order to produce synchronous output power for achieving high single-mode selectivity. We present the designs and optimization of 2×2 half-wave couplers, including a three-waveguide directional coupler and a nonimaging multimode interference coupler.

Analysis and design of thermo-optical variable optical attenuator using three-waveguide directional couplers based on SOI

A thermo-optical variable optical attenuator (VOA), consisting of three cascaded three-waveguide directional couplers, was designed on Silicon-On-Insulator (SOI) wafer. Thermo-optical dynamic, static analysis and optical propagation characteristic simulation at the wavelength of 1550 nm were presented. The dynamic attenuation range from 0.14 dB to 50 dB was achieved by a refractive index (RI) variation: 0 to 5.55 x 10(-3), (the corresponding temperature variation: 0 to 30 degrees C). The response time was about 5 micros, which was attributed to Si/Al(2)O(3)/Si structure. The device could be easily used to fabricate multi-channel VOA as the basic unit and integrated in silicon optoelectronic circuits.

Wideband Arrayed Waveguide Grating With Three Low-Loss Maxima Per Passband

By using a novel multisection three-waveguide directional coupler, we significantly improve the performance of a passband-flattened arrayed waveguide grating router that uses a three-arm interferometer connected to the input. Each passband has three low-loss maxima. For a 16-channel demultiplexer, we achieve a 1- to 20-dB passband-width ratio of 0.62 and a fiber-to-fiber insertion loss of 2.5-3.6 dB

Optical switching in a symmetric three-waveguide nonlinear directional coupler

In this paper we study optical switching in a system of a three-waveguide nonlinear directional coupler. We consider a waveguide structure with three parallel waveguides in a linear, symmetric coupling configuration. We work in the case that the (absolute value of the) difference of the propagation constants of the outer and centre waveguides is much larger than the linear coupling constants. When one of the outer waveguides is initially excited, we show that for small values of the initial power the system behaves as a two-waveguide nonlinear directional coupler where only the two outer waveguides are involved in the switching. For larger values of the initial power, transfer of light between the initially excited waveguide and the centre waveguide is observed.

Adiabatic three-waveguide directional coupler

We propose a three-waveguide directional coupler based on adiabatic evolution of a single normal mode of the system and analyze its switching properties using coupled mode theory. In our scheme the propagation coefficients of the waveguides are constant and the coupling coefficients are variable. This device works in the case that the propagation coefficients of the two outer waveguides are identical and that the coupling coefficients are designed to act in a counterintuitive order.

Three-dimensional photonic devices fabricated in glass by use of a femtosecond laser oscillator

Three-dimensional photonic waveguide devices are fabricated in glass by use of femtosecond pulses from an extended-cavity laser oscillator. Three-dimensional devices, including a symmetric three-waveguide directional coupler and a three-dimensional microring resonator, are fabricated and tested. Waveguides can be fabricated at depths of approximately 1 mm inside a glass substrate, thus demonstrating the capability of achieving dramatic increases in device density. These results demonstrate the potential to fabricate new classes of devices that are not possible in two dimensions.