Quasi-transverse Electric Modes Research Articles

On-chip Optical Phase Monitoring in Multi-Transverse-Mode Integrated Silicon-based Optical Processors

We design a Multi-Transverse-Mode Optical Processor (MTMOP) on 220 nm thick Silicon Photonics exploiting the first two quasi-transverse electric modes (TE0 and TE1). The objective is to measure the optical phase, required for programming the optical processor, without use of conventional optical phase detection techniques (e.g., coherent detection). In the proposed design, we use a novel but simple building block that converts the optical phase to optical power. Mode TE0 carries the main optical signal while mode TE1 is for programming purposes. The MTMOP operation relies on the fact that the group velocity of TE0 and TE1 propagating through a mode-sensitive phase shifter are different. An unbalanced Mach-Zehnder interferometer (MZI) consists of a mode-sensitive and mode-insensitive phase shifters in the two arms. We set the bias of the phase shifters so that TE0 propagating in the two arms constructively interfere while this will not be the case for TE1. Hence, we detect the phase shift applied to TE0 by measuring the variation in the optical power of TE1. To the best of our knowledge, this design is the first attempt towards realizing a programmable optical processor with fully integrated programming unit exploiting multimode silicon photonics.

On-Chip Non-Blocking Optical Mode Exchanger for Mode-Division Multiplexing Interconnection Networks

Optical mode exchange is an important technology for advanced mode-division multiplexing (MDM) interconnection networks, which provides enhanced flexibility by swapping signals between different mode channels. However, the available dual-mode exchange devices cannot fully meet the demands of MDM systems applying multiple orthogonal guided modes for parallel transmission. In this paper, an on-chip non-blocking mode exchanger is proposed based on a mesh network of interconnected Mach-Zehnder interferometers with demonstrated reconfigurability and scalability, and thus, the device is capable of swapping signals among arbitrary multiple optical modes at will. As a proof of concept, the non-blocking mode exchange among the first three order quasi-transverse electric modes is successfully demonstrated on a silicon-on-insulator platform. The device shows a large bandwidth covering the whole C band (1525–1565 nm), low insertion loss (less than 7.6 dB including the auxiliary mode coupling loss) and low inter-modal crosstalk (less than −14.3 dB) for all mode conversions. In order to demonstrate the data processing capabilities of this device, 40 Gbps data transmission experiment at the wavelength of 1550 nm is successfully carried out, and the obtained clear and wide-open eye diagrams indicate its good performance.

On-chip silicon photonic controllable 2\u2009\xd7\u20092 four-mode waveguide switch

Multimode optical switch is a key component of mode division multiplexing in modern high-speed optical signal processing. In this paper, we introduce for the first time a novel 2 × 2 multimode switch design and demonstrate in the proof-of-concept. The device composes of four Y-multijunctions and 2 × 2 multimode interference coupler using silicon-on-insulator material with four controllable phase shifters. The shifters operate using thermo-optic effects utilizing Ti heaters enabling simultaneous switching of the optical signal between the output ports on four quasi-transverse electric modes with the electric power consumption is in order of 22.5 mW and the switching time is 5.4 µs. The multimode switch exhibits a low insertion loss and a low crosstalk below − 3 dB and − 19 dB, respectively, in 50 nm bandwidth in the third telecom window from 1525 to 1575 nm. With a compact footprint of 10 µm × 960 µm, this device exhibits a relatively large width tolerance of ± 20 nm and a height tolerance of ± 10 nm. Furthermore, the conceptual principle of the proposed multimode switch can be reconfigurable and scalable in multifunctional on-chip mode-division multiplexing optical interconnects.

Compact, Highly Efficient, and Controllable Simultaneous 2 × 2 Three-Mode Silicon Photonic Switch in the Continuum Band

Multimode switch (MMS) allows realizing multimode optical communication enabling high-speed communication. However, to develop such an ultrafast switch for simultaneous multimode with a compact size is very challenging. In this paper, we design and demonstrate a compact multimode 2×2 MMS based on numerical simulation methods using silicon Ψ-junctions and multimode interference (MMI) couplers. The switch is controlled by thermal-optic phase shifters which is able to switch simultaneously states of the optical signal between three quasi-transverse electric modes. The MMS exhibits a low insertion loss from -1.5 dB to -3 dB, low crosstalk below -22 dB, and high extinction ratio larger than 22 dB in 40-nm bandwidth in the third telecom window from 1520 to 1560 nm, respectively. With a compact footprint of 12 μm ×1300 μm, the MMS exhibits relatively large dimensional tolerances. Besides, the MMS provides total electric power consumption levels smaller than 103 mW at an ultrafast switching time of 4.4 μs without the impact of the plasmonic effect. Furthermore, the conceptual principle of the proposed MMS can be reconfigurable and scalable in dimensional multifunctional on-chip mode-division multiplexing optical interconnects and promising potential for photonic large scale integration circuits in the continuum band.

A Flexible and Reconfigurable Optical Add-Drop Multiplexer for Mode Division Multiplexing Systems

Reconfigurable optical add-drop multiplexer (ROADM) is one of the key building blocks for on-chip optical networks, which can download the desired signals from the bus waveguide to the corresponding drop port and upload the local signals from the add port to the bus waveguide to achieve the signals dropping/adding between the local and the bus waveguide. In this letter, we propose a ROADM based on a Benes network for mode-division multiplexing systems. As a proof of the concept, a ROADM with three quasi-transverse electric modes (TE0-TE2) is fabricated and experimentally demonstrated, which can download signals from TEi (i = 0, 1, 2) mode channel in the bus waveguide to an arbitrary local drop port or upload local signals to TEi mode channel via an arbitrary add port. The excess loss of the fabricated device is less than 10.7 dB, and the crosstalk among different space or mode channels is lower than -13.7 dB. Finally, a 12 Gbps data transmission experiment is carried out to verify the performance of the device. The proposed device is reconfigurable and scalable, and thus, it is expected to be used for optical data processing in the mode-division multiplexing systems.

On-chip switchable and reconfigurable optical mode exchange device using cascaded three-waveguide-coupling switches.

Data exchange between different data channels can offer more flexible and advanced functions for many optical networks. In this paper, we propose a switchable and reconfigurable data exchange device for arbitrary two optical mode channels based on three-waveguide-coupling (TWC) switches in mode-division multiplexing (MDM) networks. The working principle of the TWC switches is numerically analyzed using the coupled supermode theory. As a proof of concept, switchable data exchange between arbitrary two mode channels among the first three-order quasi-transverse electric modes is experimentally demonstrated successfully. The insertion losses of the device are less than 5.6 dB, including the coupling loss of the multiplexer and demultiplexer, while the mode crosstalk is less than -13.0 dB for all functions. The proposed device is expected to offer more flexibility to on-chip MDM networks due to its low loss, low crosstalk and good scalability.

On-chip reconfigurable and scalable optical mode multiplexer/demultiplexer based on three-waveguide-coupling structure.

Reconfigurable optical mode multiplexers/demultiplexers have attracted increasing attention in the academic community, because they enable convenient construction of flexible and complex on-chip optical networks. Here, we propose and demonstrate a scheme of reconfigurable and scalable optical mode multiplexer/demultiplexer with large operation bandwidth, based on three-waveguide-coupling structures. As proof of concept, a reconfigurable device that can multiplex input signals to the fundamental and first-order quasi-transverse electric mode is fully fabricated and demonstrated successfully. Static response spectra show that the optical crosstalk at the output ports of the device are less than -14.3 dB and -13.7 dB over the entire C band (> 40 nm), respectively. The dynamic performance with data transmission speeds of 40 Gbps for each multiplexing channel are also demonstrated successfully. The presented device is believed to be a potential candidate for future on-chip optical network with large-scale integration, flexible functionality, and low cost.

Highly efficient graphene-on-gap modulator by employing the hybrid plasmonic effect.

We propose a highly efficient graphene-on-gap modulator (GOGM) by employing the hybrid plasmonic effect, whose modulation efficiency (up to 1.23dB/μm after optimization) is ∼12-fold larger than that of the present graphene-on-silicon modulator (∼0.1 dB/μm). The proposed modulator has the advantage of a short modulation length of ∼3.6 μm, a relatively low insertion loss of ∼0.32 dB, and a larger modulation bandwidth of ∼0.48 THz. The physical insight is investigated, showing that both the slow light effect and the overlap between graphene and the mode field contribute. Moreover, an efficient taper coupler has been designed to convert the quasi-transverse electric mode of conventional silicon waveguide to the hybrid plasmonic mode of GOGM, with a high coupling efficiency of 91%. This Letter may promote the design of high-performance on-chip electro-optical modulators.

Low-loss planar and stripe waveguides in Nd3+-doped silicate glass produced by oxygen-ion implantation

We report on the fabrication and characterization of low-loss planar and stripe waveguides in a Nd3+-doped glass by 6MeV oxygen-ion implantation at a dose of 1×1015ions∕cm2. The dark mode spectroscopy of the planar waveguide was measured using a prism coupling arrangement. The refractive index profile of the planar waveguide was reconstructed from a code based on the reflectivity calculation method. The results indicate that a refractive index enhanced region as well as an optical barrier have been created after the ion beam processing. The near-field mode profiles of the stripe waveguide were obtained by an end-fire coupling arrangement, by which three quasitransverse electric modes were observed. After annealing, the propagation losses of the planar and stripe waveguides were reduced to be ∼0.5 and ∼1.8dB∕cm, respectively.

Microstrip resonator for GHz measurements of microscale magnetic objects (abstract)

The integration of thin ferromagnetic films for applications above 1 GHz is expected to require micron scale, thin film objects (∼100 μm×100 μm×0.1 μm) with volumes less than ∼10−15 m3. With maximum relative susceptibilities of ∼100, the measurement of these micro-objects by small perturbative techniques is experimentally challenging. Here, we describe the design, calibration, and performance of a microstrip resonator with a cavity volume of <10−6 m3 and a cross-sectional area <1 mm2. We have designed and built a gap-coupled, transmission-type, linear microstrip resonator. At even (odd) harmonics of the fundamental resonance, maxima of the electric (magnetic) field are established at the midpoint of the linear resonator. This resonator was designed to measure the magnetic responses of ensembles of micron scale ferromagnetic objects in the 0.4–10 GHz frequency range. The lowest resonant frequency (400 MHz) intentionally overlapped the upper operating frequency range of our lower frequency measurement systems, to permit comparison and calibration. The center conductor of the microstrip was photolithographically patterned in a 6 μm thick gold film electroplated on a high quality microwave alumina substrate. A quasi transverse electric mode (TEM) was launched on the microstrip from a well-matched transition to a 3.5 mm coaxial connector. The microstrip resonator was excited by coupling to the microstrip transmission line through two 50 μm capacitive gaps (∼0.07 pF) in the center conductor. The measurements were performed with HP 8510 network analyzer. The equivalent circuit of the microstrip transmission resonator and coupling capacitors were used to compute the 22 transmission resonances expected in the 0.4–10 GHz range. The results compare well with the measured resonances indicating the applicability of the quasi static approximation to 6 GHz. A perturbation theory for calculating the permeability from the measured cavity parameters was formulated for the microstrip resonator. Initial measurements on microscale magnetic objects are in good agreement with those obtained from other measurements.

The propagation of mixed polarization VLF (f ≤5 kHz) radio waves in the Antarctic Earth‐ionosphere waveguide

During 1986, a series of special VLF transmissions at ∼3 kHz and ∼5 kHz were made from the crossed dipole antenna at Siple Station, Antarctica, which simulated transmissions from a single horizontal dipole at a number of different orientations. The subionospheric signals thus excited were recorded at four Antarctic stations: Faraday, Halley, South Pole and Arrival Heights (McMurdo Sound). The signals excited broadside to the dipole were seen to exhibit characteristics notably different from those of signals excited along the axis of the antenna, showing a minimum in received power (the depth of the minimum decreasing for the more highly attenuating paths) and increases in apparent arrival azimuth error and elevation angle. A simple computer model for mode propagation close to 5 kHz in the Antarctic Earth‐ionosphere waveguide showed that these variations were the consequence of two effects: the preferential excitation of quasi‐transverse magnetic (QTM) modes along the axis of the antenna and the lower attenuation of quasi‐transverse electric (QTE) modes (with respect to QTM modes) over the Antarctic ice sheet. These results have important implications for studies involving the subionospheric propagation of signals with frequencies at the lower end of the VLF band and over highly attenuating surfaces, showing that QTE modes play a significant and sometimes dominant role. The propagation characteristics derived from the model may be applied to studies of the effect of burst energetic electron precipitation on subionospheric VLF signals (the Trimpi effect). Furthermore, the mode structure of subionospheric VLF signals radiated from the Siple transmitter, or a similar facility in Antarctica, may be controlled through the appropriate choice of signal frequency and antenna arrangement.

Propagation of tweek atmospherics

In order to investigate the propagation mechanism of tweek atmospherics near mode cut-off frequencies, the attenuation coefficient and excitation factor of the Earth-ionosphere waveguide are calculated for both quasitransverse magnetic (QTM) and quasitransverse electric (QTE) modes. Computations are presented for propagation under a homogeneous anisotropic ionosphere, assuming the QL approximation, in the frequency range 1.5 to 10 kHz. It is shown that the QTE modes (here numbered 1, 3, 5, …) are efficiently excited by a vertical dipole source, especially just above the mode cut-off frequency where they exhibit very low attenuation constants (typically < 1 dB Mm ), and it is suggested that these modes play an important role in the propagation of tweek atmospherics.