Asymmetric Y-junction Research Articles

Mode-insensitive and mode-selective optical switch based on asymmetric Y-junctions and MMI couplers

Driven by the large volume demands of data in transmission systems, the number of spatial modes supported by mode-division multiplexing (MDM) systems is being increased to take full advantage of the parallelism of the signals in different spatial modes. As a key element for photonic integrated circuits, the multimode waveguide optical switch (MWOS) is playing an important role for data exchange and signal switching. However, the function of the traditional MWOS is simple, which could only implement the mode-insensitive or mode-selective switching function; it is also difficult to scale to accommodate more spatial modes because of the limitation of the device structure. Therefore, it is still challenging to realize a multifunctional and scalable MWOS that could support multiple modes with low power consumption and high flexibility. Here, we propose and experimentally demonstrate a multifunctional MWOS based on asymmetric Y-junctions and multimode interference (MMI) couplers fabricated on a polymer waveguide platform. Both mode-insensitive and mode-selective switching functions can be achieved via selectively heating different electrode heaters. The fabricated device with the total length of ∼0.8 cm shows an insertion loss of less than 12.1 dB, and an extinction ratio of larger than 8.4 dB with a power consumption of ∼32 mW for both mode-insensitive and mode-selective switching functions, at 1550 nm wavelength. The proposed MWOS can also be scaled to accommodate more spatial modes flexibly and easily, which can serve as an important building block for MDM systems.

On the Design of Broadband Asymmetric Y-Junction Ferrite Circulator for 60-GHz Inter-Satellite Communication

On the Design of Broadband Asymmetric Y-Junction Ferrite Circulator for 60-GHz Inter-Satellite Communication

Compact, Broadband, and Efficient LP01-LP11a Mode Converter Based on Cascaded Asymmetric Y-Junction

Compact, Broadband, and Efficient LP01-LP11a Mode Converter Based on Cascaded Asymmetric Y-Junction

Inverse design of asymmetric Y-junctions for ultra-compact, broadband, and low crosstalk mode (de)multiplexers.

Asymmetric Y-junctions, compared with mode coupling-based devices, possess considerably smaller wavelength dependence and thus are more promising for ultra-broadband mode (de)multiplexing in integrated optics. However, these devices also feature relatively high mode crosstalk and insertion loss. Here, we show that the mode crosstalk and loss of an asymmetric Y-junction can be significantly reduced by optimizing the waveguide shape of the Y-junction using an adjoint-based inverse design. Based on such inverse-designed asymmetric Y-junctions, we realize ultra-compact, broadband, and low crosstalk silicon photonic TE00 & TE1 and TE0 & TE2 mode (de)multiplexers with sizes of only 4.5 × 1.2 µm2 and 6 × 1.4 µm2, respectively. From simulations it is shown that the TE0 & TE1 and TE0 & TE2 mode (de)multiplexers contain wide bandwidths of 160 nm (1460-1620 nm) and 140 nm (1460-1600 nm), respectively, over which the mode crosstalks are below about -20 dB, and the losses are <0.41 dB and <0.88 dB, respectively. The experimental results show that in the corresponding TE0 & TE1 and TE0 & TE2 mode division multiplexing systems, the crosstalks are less than -15.5 dB and -15 dB over the spectral ranges of 1453-1580 nm and 1460-1566 nm, respectively, and the losses are <1.7 dB at 1520 nm and <8.24 dB over the entire measured wavelength range.

Integrated lithium niobate optical mode (de)interleaver based on an asymmetric Y-junction.

Lithium niobate on insulator (LNOI) platforms promise unique advantages in realizing high-speed, large-capacity, and large-scale photonic integrated circuits (PICs) by leveraging lithium niobate's attractive material properties, which include electro-optic and nonlinear optic properties, low material loss, and a wide transparency window. Optical mode interleavers can increase the functionality of future PICs in LNOI by enabling optical mode division multiplexing (MDM) systems, allowing variable mode assignment while maintaining high channel utilization and capacity. In this Letter, we experimentally demonstrate an optical mode interleaver based on an asymmetric Y-junction on the LNOI platform, which exhibits an insertion loss of below 0.46 dB and modal cross talk of below -13.0 dB over a wavelength range of 1500-1600 nm. The demonstrated mode interleaver will be an attractive circuit component in future high-speed and large-capacity PICs due to its simple structure, scalability, and capacity for efficient and flexible mode manipulation on the LNOI platform.

Numerical study of droplet sorting in an asymmetric Y-junction microfluidic by BEM and LS method

Numerical study of droplet sorting in an asymmetric Y-junction microfluidic by BEM and LS method

Dynamics of droplet breakup in unilateral Y-junctions with different angles

Dynamic behaviors of droplets in asymmetric unilateral Y-junctions are experimentally studied. Three breakup regimes are categorized, namely no breakup, breakup with gaps and breakup with obstruction, and regime diagrams are constructed by the capillary number and the normalized droplet length. Influences of the bifurcation angle and the viscosity ratio on the two critical conditions between neighboring regimes are revealed. In particular, necking processes in the obstructed breakup regime are discussed and they are divided into three stages according to the evolution of the thinning rate. At the two previous stages driven by the two-phase flow, the necking processes show distinct characteristics under the influences of four different parameters, including capillary number, droplet length, viscosity ratio, and bifurcation angle, and the corresponding reasons are provided in detail. By contrast, the final pinch-off stage is driven by two different mechanisms depending merely on the physical properties of liquid systems. The neck collapsing of the low-viscosity droplet is driven by the potential flow while that of the high-viscosity droplet is driven by the two-fluid Stokes flow. Quantitative relations between the minimum neck width and the remaining time are built in the two situations and are found to coincide with the theoretical predictions, respectively.

Design and simulation of asymmetric Y-junction beam splitter with controllable splitting based on adjusted air-hole defect

Design and simulation of asymmetric Y-junction beam splitter with controllable splitting based on adjusted air-hole defect

Metered reagent injection into microfluidic continuous flow sampling for conductimetric ocean dissolved inorganic carbon sensing

Continuous autonomous measurement of total dissolved inorganic carbon (TCO2) in the oceans is critical for climate change modelling and ocean acidification measurement. A microfluidic conductivity-based approach will permit integration of miniaturised chemical analysis systems into Argo ocean floats, for long-term, high-accuracy depth profiling of dissolved CO2 with minimal reagent payload. Precise metering, suitable for sample acidification and CO2 liberation, is addressed. Laser etched microfluidic snake channel restrictors and asymmetric Y-meters were fabricated, with channel dimensions down to ∼75 μm, to adjust metering ratios between seawater and acid simulants. Hydrodynamic resistances, from flow versus pressure measurements, were compared with finite element simulations for various cross-section profiles and areas. Microfluidic metering circuits were constructed from various resistance snake channels and Y-junction components. Sample to acid volume ratios (meter ratio) up to 100:1 have been achieved with 300 μm wide snake channels for lengths >m. At highest resolution, the footprint would be >600 mm2. Circuits based solely on asymmetric Y-junctions gave maximum meter ratios of 16:1 with a footprint of <40 mm2 and ∼0.2% precision. Further refinement is required to ensure the integrity of such small channels in integration of metering units into full TCO2 analysis microfluidic circuits.

The Research Progress in On-Chip Mode (De)multiplexer

With the increasing integration of communication devices and the demand for communication capacity, the methods to increase bandwidth and transmission capacity have attracted lots of attentions. As a new multiplexing dimension, mode division multiplexing (MDM) can effectively improve transmission capacity, in which different modes are utilized for data transmission. In this paper, we investigate the recent progress in on-chip mode (de)multiplexer, which is the key technology to realize mode (de)multiplexing. Firstly, several traditional on-chip mode (de)multiplexers are introduced, including mode (de)multiplexers based on Multi-Mode Interference (MMI), Adiabatic Coupler, Asymmetric Y-Junction, Asymmetry Directional Coupler (ADC) and Micro-ring Resonator (MMR), respectively. Secondly, hybrid (de)multiplexers combining MDM with Polarization Division Multiplexing (PDM) or Wavelength Division Multiplexing (WDM) are discussed. Finally, this paper looks forward to the development prospects of on-chip mode multiplexing technology.

Compact six-mode (de)multiplexer based on cascaded asymmetric Y-junctions with mode rotators

A silicon waveguide mode (de)multiplexer is theoretically proposed for compact on-chip mode (de)multiplexing (MDM). The (de)multiplexing of E11y, E21y, E31y, E12y, E22y and E32y modes is realized by cascading asymmetric Y-junctions and the E21y∕E12y mode rotators. Beam propagation method is adopted in the design and optimization. For a 124 μm-long device, the mode crosstalk among all channels is less than -24 dB. The insertion loss can be lowered to 0.96 dB at optical wavelength of 1550 nm. This proposed design method can be extended to the construction of higher-order mode (de)MUX.

Tubing-Free Microfluidic Microtissue Culture System Featuring Gradual, in vivo-Like Substance Exposure Profiles.

In vitro screening methods for compound efficacy and toxicity to date mostly include cell or tissue exposure to preset constant compound concentrations over a defined testing period. Such concentration profiles, however, do not represent realistic in vivo situations after substance uptake. Absorption, distribution, metabolism and excretion of administered substances in an organism or human body entail gradually changing pharmacokinetic concentration profiles. As concentration profile dynamics can influence drug effects on the target tissues, it is important to be able to reproduce realistic concentration profiles in in vitro systems. We present a novel design that can be integrated in tubing-free, microfluidic culture chips. These chips are actuated by tilting so that gravity-driven flow and perfusion of culture chambers can be established between reservoirs at both ends of a microfluidic channel. The design enables the realization of in vivo-like substance exposure scenarios. Compound gradients are generated through an asymmetric Y-junction of channels with different hydrodynamic resistances. Six microtissues (MTs) can be cultured and exposed in compartments along the channel. Changes of the chip design or operation parameters enable to alter the dosing profile over a large range. Modulation of, e.g., the tilting angle, changes the slope of the dosing curves, so that concentration curves can be attained that resemble the pharmacokinetic characteristics of common substances in a human body. Human colorectal cancer (HCT 116) MTs were exposed to both, gradually decreasing and constant concentrations of Staurosporine. Measurements of apoptosis induction and viability after 5 h and 24 h showed different short- and long-term responses of the MTs to dynamic and linear dosing regimes

Scalable compact mode (de)multiplexer based on asymmetric Y-junctions

A scalable asymmetric Y-junctions waveguide mode (de)multiplexer ((de)MUX) is theoretically proposed. The high-order mode in the stem is designed to be separated from the lower-order mode and evolves into the fundamental mode in the narrow arm, through waveguide widths optimization by effective index matching and beam propagation method. Within the wavelength range from 1450 to 1630 nm, the four modes (de)MUX with small footprint of 23 × 3.2μm2 demonstrates the insertion loss and crosstalk of less than 0.14 dB and -16 dB, respectively. This scheme may be expanded to handle more modes in (de)MUX design.

Highly efficient integrated mode de/multiplexing based on modified asymmetric Y-junctions (Erratum)

Highly efficient integrated mode de/multiplexing based on modified asymmetric Y-junctions (Erratum)

An Ultracompact Multimode Waveguide Crossing Based on Subwavelength Asymmetric Y-Junction

We propose and experimentally demonstrate a novel ultracompact multimode waveguide crossing. The compact asymmetric subwavelength Y-junction is introduced to convert the high-order modes into fundamental ones, enabling one to implement three or more modes simultaneously in the subsequent processing. Our proposed device occupied only a compact footprint of 34 × 34 μm 2 . The measured results indicate our fabricated device exhibited a high performance with the insertion loss less than 0.9 dB, crosstalk lower than -24 dB from 1.52 to 1.60 μm for all the three modes. Moreover, our scheme could be easily expended to implement more modes and will show great potential in dense and large-scale on-chip photonic integration.

Highly efficient Y-junctions with arc-bend branch structures of sunlight guiding systems for indoor illumination

ABSTRACTThis paper proposes both symmetrical and asymmetric Y-junctions with arc-bend branch structures for auxiliary indoor-illumination applications. These arc-bend branch structures can be used as a concave-mirror-like light guide, to change the direction of beam propagation and also to converge the beam spread angle. Optical simulation results show that the proposed arc-bend Y-junctions can achieve an inner coupling efficiency, not including plastic/air interfaces, above 90% in both usages: beam combiner and splitter. Particularly, when the applied branch opening angle becomes large, this high optical efficiency becomes more significant than those of linear straight Y-junctions. Moreover, it is also confirmed that the coupling efficiency of the symmetric arc-bend junction can be as high as 90.0%, and the asymmetric coupling efficiency is 93.4%, even if the branch opening angle is quite large.

Reconfigurable broadband mode (de)multiplexer based on an integrated thermally induced long-period grating and asymmetric Y-junction.

We propose a reconfigurable broadband mode (de)multiplexer based on a thermally induced long-period grating integrated with an asymmetric Y-junction. Either of the two spatial modes of a two-mode waveguide launched into the grating end of the device can be switched into either of the two output ports of the Y-junction by controlling the electric power applied to the electrode heater that induces the grating. Our typical device fabricated with polymer material that has a length of ∼14 mm shows a mode selectivity higher than 12dB over the C+L band at a switching power of 198mW. The device could find applications in reconfigurable mode-division-multiplexing systems.

Highly efficient integrated mode de/multiplexing based on modified asymmetric Y-junctions

Asymmetric Y-junctions at which a wide waveguide is divided into several waveguides with different widths are commonly employed as mode de/multiplexers. These structures are inherently wide-band and simple in design and fabrication. However, the cross talk between modes increases rapidly as the number of modes increases, limiting the application of these structures to four modes and below. The design methodology of low cross talk-integrated mode de/multiplexers based on asymmetric Y-junctions is presented. It is shown that the difference between mode-effective indices plays a crucial role in determining the cross talk. A modified asymmetric Y-junction structure is presented to minimize the cross talk and based on this structure, six- and eight-mode de/multiplexers are designed utilizing a silicon-on-insulator platform. Finite-difference time-domain (FDTD) simulations are performed for the presented structures, and it is shown that the maximum cross talk is as low as −8 and −7 dB for six- and eight-mode de/multiplexers, respectively. The design of a low cross talk 10-mode de/multiplexer based on the proposed method is also discussed.

Ultra-compact mode (de) multiplexer based on subwavelength asymmetric Y-junction.

We propose and experimentally demonstrate a novel multimode ultra-compact mode (de)multiplexer for highly integrated on-chip mode-division multiplexing systems. This device is composed of a wide divergence angle asymmetric Y-junction based on subwavelength structure and optimized using an inverse design method. The proposed device occupied a footprint of only 2.4 × 3 µm2. The measured insertion loss and crosstalk were less than 1dB and -24 dB from 1530 nm to 1590 nm for both TE0 mode and TE1 mode, respectively. Likewise, a three mode multiplexer is also designed and fabricated with a compact footprint of 3.6 × 4.8 µm2. Furthermore, our scheme could also be expanded to include more modes.

Experimental demonstration of a broadband two-mode multi/demultiplexer based on asymmetric Y-junctions

A broadband two-mode multi/demultiplexer using asymmetric Y-junctions is designed and experimentally demonstrated on a silicon-on-insulator platform for on-chip mode-division multiplexing applications. Within a bandwidth from 1513 to 1619 nm, the fabricated device, which consists of a two-mode multiplexer, a multimode straight waveguide, and a two-mode demultiplexer, exhibits demultiplexing crosstalk of less than −9.1 dB. The demultiplexing crosstalk as low as −42.1 dB, lower than −12.8 dB over the C band can be obtained. The measured insertion loss varies from 0.40 to 0.56 dB at a wavelength of 1550 nm. A transmission experiment of 10 Gbit/s electrical signals carried on TE0 and TE1 modes is successfully achieved with open and clear eye diagrams.