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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.

Thin-film lithium niobate on insulator (LNOI) is emerging as one of the promising platforms for integrated photonics due to the excellent material properties of lithium niobate, which includes a strong electro-optic effect, high second-order optical nonlinearity, a large optical transparency window, and low material loss. Although direct etching of lithium niobate has been adopted more widely in recent years, it remains to be seen if it will be adopted in foundry processes due to the incompatibility with standard CMOS fabrication processes. Thus, the scalability of the LNOI platform is currently still limited when compared with other platforms such as silicon photonics. Dielectrically loaded LNOI waveguides may present an alternative. These waveguides have been used to demonstrate a range of optical components with a simplified fabrication process while demonstrating competitive performance. In this contribution, we review the recent progress in dielectrically loaded LNOI waveguides, summarize the advantages and disadvantages of different loading materials, compare the performance of different platforms, and discuss the future of these platforms for photonic integrated circuits.

We propose and demonstrate an all-optical tunable polymer bottle micro-resonator fabricated by droplet dispensing method. A microfiber is used to excite whispering gallery mode (WGM) of the micro-resonator. Continuous wave (CW) laser is employed as pump light to tune the WGM. To illustrate tuning performance of the fabricated device, external and internal pump light methods are both employed. For external pump light method, the tuning efficiency is about 5.23 pm/mW. For internal pump light, tuning efficiency of 68.3 pm/mW is obtained. The experimental results reveal that the bottle micro-resonator (BMR) can achieve wavelength tuning more than one free spectral range (FSR), which indicates the WGM can be tuned within a transparent window covered the full wavelength range. In addition, the fabricated device has advantages of high tuning efficiency, small size, easy fabrication, and extremely low cost.

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.

Optical directed logic (DL) is a novel logic operation scheme that employs electrical signals as operands to control the working states of optical switches to perform the logic functions. This review first provides an overview of the concept and working principle of DL. The developing trends of DL computing are then discussed in detail, including the fundamental optical DL gates, combinational optical DL operations, reconfigurable logic computing, low power optical logic computing, and programmable photonic network. The concluding remarks provide an outlook on the DL future development and its impacts in optical computing. Graphical Abstract

Mode division multiplexing (MDM) technology has been well known to researchers for its ability to increase the link capacity of photonic network. While various mode processing devices were demonstrated in recent years, the reconfigurability of multi-mode processing devices, which is vital for large-scale multi-functional networks, is rarely developed. In this paper, we first propose and experimentally demonstrate a scalable mode-selective converter using asymmetrical micro-racetrack resonators (MRRs) for optical network-on-chip. The proposed device, composed of cascaded MRRs, is able to convert the input monochromatic light to an arbitrary supported mode in the output waveguide as required. Thermo-optical effect of silicon waveguides is adopted to tune the working states of the device. To test the utility, a device for proof-of-concept is fabricated and experimentally demonstrated based on silicon-on-insulator substrate. The measured spectra of the device show that the extinction ratios of MRRs are larger than 18 dB, and modal crosstalk for selected modes are all less than −16.5 dB. The switching time of the fabricated device is in the level of about 40 μs. The proposed device is believed to have potential applications in multi-functional and intelligent network-on-chip, especially in reconfigurable MDM networks.

Various mode-order converters are implemented in optical mode multiplexing and mode switching systems. Typically, such devices can only accomplish one mode-order conversion function. In this paper, we propose a multi-channel parallel mode-order converter based on inverse-design optimization method. By using a QR-code-like silicon structure, it can realize the mode-order conversions of multiple mode channels simultaneously in a compact footprint. As a proof of concept, we design and demonstrate a dual-channel silicon mode-order converter, which converts TE0 mode to TE2 mode, and TE1 mode to TE3 mode. It has a footprint of 4 μm×3 μm. Simulation results show that the insertion losses for the two mode-order conversion process are 0.8–1.0 dB and 0.9–1.2 dB, and have good tolerance to temperature variations. The inter-mode cross-talk is lower than −19.9 dB and −17.4 dB. Experimental results show that its range of insertion losses for the two process fluctuate within 2.0–3.6 dB and 1.5–5.1 dB in the wavelength range of 1525–1565 nm. The inter-mode cross-talk is lower than −10.7 dB and −13.1 dB, respectively.

Electro-optic (EO) modulators, which convert signals from the electrical to optical domain plays a key role in modern optical communication systems. Lithium niobate on insulator (LNOI) technology has emerged as a competitive solution to realize high-performance integrated EO modulators. In this Letter, we design and experimentally demonstrate a Mach–Zehnder interferometer-based modulator on a silicon nitride loaded LNOI platform, which not only takes full advantage of the excellent EO effect of L i N b O 3 , but also avoids the direct etching of L i N b O 3 thin film. The measured half-wave voltage length product of the fabricated modulator is 2.24 V·cm, and the extinction ratio is ∼ 20 d B . Moreover, the 3 dB EO bandwidth is ∼ 30 G H z , while the modulated data rate for on–off key signals can reach up to 80 Gbps.

Lithium niobate on insulator (LNOI) is a promising platform for high-speed photonic integrated circuits (PICs) that are used for communication systems due to the excellent electro-optic properties of lithium niobate (LN). In such circuits, the high-speed electro-optical modulators and switches need to be integrated with passive circuit components that are used for routing the optical signals. Polarization beam splitters (PBSs) are one of the fundamental passive circuit components for high-speed PICs that can be used to (de)multiplex two orthogonal polarization optical modes, enabling on-chip polarization division multiplexing (PDM) systems, which are suitable for enhancing the data capacity of PICs. In this Letter, we design and experimentally demonstrate a high-performance PBS constructed by a photonic crystal (PC)-assisted multimode interference (MMI) coupler. The measured polarization extinction ratio (ER) of the fabricated device is 15 dB in the wavelength range from 1525 to 1565 nm, which makes them suitable for the high-speed and large data capacity PICs required for future communication systems.

We experimentally demonstrate a compact temperature sensor using a microfiber-based Mach–Zehnder interferometer with a knot micro-ring resonator. The arm with a knot micro-ring resonator is embedded in polydimethylsiloxane (PDMS), which acts as the temperature transducer. The scattering matrix method is employed to establish the numerical model of the device. Owing to the high thermo-optic coefficient of PDMS, the response spectrum of the device will blue-shift when the ambient temperature increases. The device is characterized by changing temperature in two different environments (air and liquid), respectively. For temperature sensing operated in air, the device is tested utilizing a heating platform, which shows a sensitivity of −35.12 pm/°C when the temperature of the heating platform varies at a range of 15.5 °C. After that, a sensitivity boosting up to −41.58 pm/°C is measured when the device is immersed in a salt solution (25 ‰ in concentration) with the temperature changing from 22.2 °C to 32.9 °C.

Data exchange plays a key role in enhancing network resources utilization and optimizing network performance. In this paper, a data exchange device based on mode-division multiplexing (MDM) technology is proposed and demonstrated, which is capable of exchanging data information between a fundamental mode (TE0) signal and an arbitrary high-order mode (TE x ) signal. We experimentally demonstrate the exchange between a TE0 mode signal and a TE1 mode signal using single microring resonator. The insertion loss is about 7.5 dB, including terminal coupling loss, the extinction ratio is more than 20 dB within the C -band. The crosstalk for the TE1-to-TE0 and TE0-to-TE1 mode conversions is measured to be less than −22 and −16 dB, respectively. Clear and open-eye diagrams of two different wavelength signals at 10 Gb/s are obtained. The proposed scheme is expected to be used for on-chip MDM networks in the future due to its scalability, compact size, and low power consumption.

The manipulation of optical modes directly in a multimode waveguide without affecting the transmission of undesired signal carriers is of significance to realize a flexible and simple structured optical network-on-chip. In this Letter, an arbitrary optical mode and wavelength carrier access scheme is proposed based on a series of multimode microring resonators and one multimode bus waveguide with constant width. As a proof-of-concept, a three-mode (de)multiplexing device is designed, fabricated, and experimentally demonstrated. A new, to the best of our knowledge, phase-matching idea is employed to keep the bus waveguide width constant. The mode coupling regions and transmission regions of the microring resonators are designed carefully to selectively couple and transmit different optical modes. The extinction ratio of the microring resonators is larger than 21.0 dB. The mode and wavelength cross-talk for directly (de)multiplexing are less than −12.8 dB and −19.0 dB, respectively. It would be a good candidate for future large-scale multidimensional optical networks.

We experimentally demonstrate a compact all-optical tunable Mach–Zehnder interferometer (MZI) based on microfiber. The graphene-assisted sandwich structure (GASS) integrated on the microfiber is adopted to form the all-optical tunable structure. The effective footprint of the fabricated device is about 7 . 31 × 8 . 66 mm2 which is much more compact than other reported all-optical tunable MZIs based on fiber system. An out-fiber 1535 nm continuous-wave pump light is employed to irradiate the GASS vertically, which can produce the strong interaction of light-graphene. As a result, the device’s response spectrum occurs red-shift due to the graphene’s photothermal effect. Compared with the microfiber MZI with only the bottom graphene film, the tuning efficiency of the microfiber MZI with GASS is improved by 6 times, which is about 0.856 pm/mW. Meanwhile, the red-shift range can exceed one free spectral range (FSR) that means the resonant wavelength can be tuned to arbitrary wavelength in the range of the transparent window. This microfiber MZI with GASS featured with wavelength tunability, all-in-fiber, compact size, easy fabrication, and simple packaging is expected for the fabricated device to be used as all-optical modulator, tunable optical filter and optical switch, etc.

An on-chip biochemical sensor based on two-dimensional waveguide-integrated plasmonic crystal formed by a nanogap tile (NGT) array is realized. By using on-chip optical lenses, an ultra-wide collimated Gaussian beam is launched, coupled with surface plasmonic crystals and collected with relatively low additional insertion loss, allowing a large sensing area. The optical field enhancement and stop-band shift of the NGT device for biochemical sensing are numerically and experimentally demonstrated with sensitivity reaching up to ∼ 260 n m / R I U . Our sensor is demonstrated with monolayer thiol molecules illustrating that it can be functionalized with this class of molecule which is commonly used with bulk surface plasmon resonance sensors.

The optical parity checker plays an important role in error detection and correction for high-speed, large-capacity, complex digital optical communication networks, which can be employed to detect and correct the error bits by using a specific coding theory such as introducing error-detecting and correcting codes in communication channels. In this paper, we report an integrated silicon photonic circuit that is capable of implementing the parity checking for binary string with an arbitrary number of bits. The proposed parity checker consisting of parallel cascaded N micro-ring resonators (MRRs) is based on directed logic scheme, which means that the operands applied to MRRs to control the switching states of the MRRs are electrical signals, the operation signals are optical signals, and the final operation results are obtained at the output ports in the form of light. A 3-bit parity checker with an operation speed of 10 kbps, fabricated on a silicon-on-insulator (SOI) platform using a standard commercial complementary metal-oxide-semiconductor (CMOS) process, was experimentally and successfully demonstrated.

One of the most outstanding advantages for mode division multiplexing (MDM) technology is its compatibility with wavelength division multiplexing (WDM) to significantly increase the communication channel capacity. Consequently, researches on the basic components for complex optical networks which simultaneously use MDM as well as WDM are necessary. In this paper, we propose a reconfigurable mode converter compatible with WDM for complex optical networks, based on parallel micro-ring resonators. The proposed device can convert the input monochromatic light to an arbitrary quasi-transverse electric mode by tuning the resonant states of the micro-ring resonators. If a light with several wavelengths is launched, each wavelength can be switched to a specific mode. For proof of concept, we fabricate and demonstrate the proposed device which can convert the input light to a first-order mode or fundamental mode. The static response spectra with extinction ratios larger than 10 dB are demonstrated, which shows high-performance mode conversion. Also, the function of channel conversion is demonstrated. Finally, to demonstrate the utility of this device, clear and open eye diagrams at speed rates of 10 Gbps for mode and wavelength data transmission are demonstrated successfully.

In this paper, we propose and experimentally demonstrate an integrated optical device that can implement the logical function of priority encoding from a 4-bit electrical signal to a 2-bit optical signal. For the proof of concept, the thermo-optic modulation scheme is adopted to tune each micro-ring resonator (MRR). A monochromatic light with the working wavelength is coupled into the input port of the device through a lensed fiber, and the four input electrical logic signals regarded as pending encode signals are applied to the micro-heaters above four MRRs to control the working states of the optical switches. The encoding results are directed to the output ports in the form of light. At last, the logical function of priority encoding with an operation speed of 10 Kbps is demonstrated successfully.

We propose a novel approach to demonstrate an add-drop filter based on microfiber knot resonator (MFKR). The two coupled regions and four ports (including input port, through port, drop port, and add port) of this device are formed using the same one microfiber. By reconnecting the ends of the through and add ports with other two microfibers, this structure could serve as an add-drop filter, which is a key building block in the fields of optical networks and optical information processing system. The MFKR-based add-drop filter with the quality factor (Q-factor) of 21 000 and a diameter of 740 mu m is demonstrated successfully. The intrinsic loss and extinction ratio are about -2 and 18.5 dB for the drop port, and -4.6 and 10.7 dB for the through port, respectively. The fabrication process also shows the feasibility and simplicity of this device.

We propose and experimentally demonstrate a silicon photonic circuit that can perform the comparison operation of two-bit digital signals based on microring resonators (MRRs). Two binary electrical signals regarded as two operands of desired comparison digital signals are applied to three MRRs to modulate their resonances through the microheaters fabricated on the top of MRRs, respectively (here, one binary electrical signal is applied to two MRRs by a 1×2 electrical power splitter, which means that the two MRRs are modulated by the same binary electrical signal). The comparison results of two binary electrical signals can be obtained at two output ports in the form of light. The proposed device is fabricated on a silicon-on-insulator substrate using the complementary metal-oxide-semiconductor fabrication process, and the dynamic characterization of the device with the operation speed of 10 kbps is demonstrated successfully.

Dielectrically loaded thin-film lithium niobate (LiNbO3) on insulator (LNOI) platforms have enabled a range of photonic integrated circuit components, such as high-speed optical modulators, switches, and nonlinear devices, while avoiding the direct etching of the LiNbO3 thin film. Silicon nitride (Si3N4) is one of the most attractive dielectric loading materials as it has a similar refractive index and transparency window to LiNbO3 and can be deposited and patterned by mature fabrication processes. The patterning of Si3N4 opens the opportunity to fabricate grating couplers in the same fabrication step, providing efficient optical interfaces for wafer-scale testing. In this paper, we investigate and demonstrate single-step etched grating couplers on a Si3N4-LNOI (X-cut) platform. The grating couplers (straight and curved) are designed and fabricated for TE-polarized modes along the Y and Z crystallographic directions, considering the LiNbO3 crystal’s birefringence. The experimentally demonstrated coupling losses are as low as 4.02 and 4.24 dB along the crystallographic Y and Z directions, respectively. The corresponding peak wavelengths are 1609 and 1615 nm, respectively. The measured 3-dB bandwidths are wider than 70 nm for both crystallographic directions. We also numerically investigated the influence of fabrication variations and the fiber angle on the transmission. To the best of our knowledge, this work is the first demonstration of grating couplers with different light propagation directions on the Si3N4 loaded LNOI platform.

Optical directed logic is a novel logic operation scheme that employs electrical signals as operands to control the working states of optical switches to perform the logic operations. In this Letter, we propose and demonstrate an integrated photonic circuit which can implement five different optical logic operations by utilizing two optical modes. The proposed device is fabricated on a silicon-on-insulator substrate by using electron beam lithography and inductively coupled plasma etching processes. The static experimental results show that the fabricated device can implement five different operations correctly—XOR, XNOR, NOR, NOT, and AND—from which we can see that the signal-to-noise ratios are larger than 17.6 dB over the entire C band for all five logic functions. At last, all five logic operations with the speed of 10 Kbps are demonstrated. The proposed device with simple structure, large bandwidth, and versatility would be a promising candidate for information processing in optical mode division multiplexing networks.

Currently, the reversible logic circuit is a popular research topic in the field of information processing as it is a most effective approach to minimize power consumption, which can achieve the one-to-one mapping function to identify the input signals from its corresponding output signals. In this letter, we propose and experimentally demonstrate an optical Feynman gate for reversible logic operation using silicon micro-ring resonators (MRRs). Two electrical input signals (logic operands) are applied across the micro-heaters above MRRs to determine the switching states of MRRs, and the reversible logic operation results are directed to the output ports in the form of light, respectively. For proof of concept, the thermo-optic modulation scheme is used to achieve MRR’s optical switching function. At last, a Feynman gate for reversible logic operation with the speed of 10 kbps is demonstrated successfully.

Owing to the promising application prospect of mode division multiplexing technology, reconfigurable optical mode multiplexers/demultiplexers, which enable convenient construction of flexible and complex on-chip optical networks, have attracted increasing attention in the academic community. Here, we propose and experimentally demonstrate a reconfigurable two-mode multiplexer/demultiplexer based on novel three-waveguide-coupling structures. The fabricated device can multiplex two input signals to fundamental and first-order quasi-transverse electric modes with large operation bandwidth. 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 highspeed data transmission ability 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.

We propose and demonstrate a reconfigurable data exchange device for wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM) compatible optical networks, which is capable of exchanging data information between a fundamental mode (TE0) signal and an arbitrary high-order mode (TEx) signal with the same wavelength. We experimentally demonstrate exchange for a TE0 mode signal and a TE1 mode signal. The insertion loss is about 7.5 dB including terminal coupling loss, the extinction ratio is more than 20 dB within the C band. The crosstalk for the TE1-to- TE0 and TE0-to-TE1 mode conversions is measured to be less than -22 dB and -16 dB, respectively. Clear and open eye diagrams of two different wavelength signals at 10 Gb/s are obtained. The proposed scheme is expected to be used for on-chip WDM-MDM compatible networks in future due to its scalability, compact size and reconfigurable functionality.

We experimentally demonstrate a bow-shaped fiber structure (BFS) fabricated by a simple knotting method. Interference transmission spectra of output light is observed due to interference between the core and cladding mode. The extinction ratio (ER) of output transmission spectra can be adjusted by pulling fiber pigtail of the BFS, which indicates the device can be applied to strain or displacement sensor. The temperature sensing performance is investigated with both bare and polydimethylsiloxane (PDMS)-assisted BFS. Compared with the bare structure, the sensitivity is extremely enhanced when the microfiber region is embedded in PDMS layer, which is as large as -1.63 nm/°C when temperature changing from 21.0 °C to 25.0 °C. The PDMS-assisted BFS with excellent characteristics of good mechanical stability, high sensitivity, low cost, easy fabrication and high flexibility is believed to have promising applications in the future.

In this paper, we propose and demonstrate a 4×4 non-blocking optical router utilizing 8 mode (de)multiplexers and a 4×4 microring-based grid network, which can passively assign signals carried by optical wavelength and mode channels from an arbitrary input port to corresponding output ports without additional switch time, realizing the non-blocking property. The proposed device is fabricated on a silicon-on-insulator platform using the standard Complementary Metal-Oxide-Semiconductor (CMOS) fabrication processes. The insertion loss is lower than 5.7 dB including the loss of the auxiliary mode (de)multiplexers (AMUXs), while the crosstalk is lower than −15.6 dB for all routing states. Moreover, the transmission spectra from the input ports to the next cascading device are also measured to demonstrate the feasibility of further expanding via cascading multiple blocks, with the insertion loss and crosstalk lower than 7.1 dB (including the mode coupling loss of AMUXs) and −16.4 dB, respectively. The 12 Gbps dynamic transmission experiment is demonstrated with clear and open eye diagrams, illustrating the utility of the device. The device has high geometrical symmetry and good scalability, we exhibit all solutions to expand the 4×4 optical router to 8×8 and 16×16 optical routers with the advantages and deficiencies of each solution discussed.

In this paper, we propose a reconfigurable electro-optic logic circuit, which can perform any combinatorial logic operations using a microring resonator (MRR)-based optical switching array. The operands are represented by electrical signals, which are applied to the corresponding MRRs to control their switching status. The operation results are directed to the output port in the form of light. For proof of concept, the circuit consisting of four thermooptic MRR-based optical switches is fabricated on the silicon-on-insulator (SOI) substrate using the commercial complementary metal-oxide-semiconductor (CMOS) fabrication process. Finally, several logic operations of four operands with the operation speed of 10 kb/s are demonstrated successfully.

We propose and demonstrate a directed optical logic circuit that can perform the XOR and XNOR logic operations consisting of two cascaded microring resonators, i.e., an upper waveguide and an under waveguide. No waveguide crossings exist in the circuit, which is very useful to improve the signal quality and reduce the insertion loss of the device. As proof of principle, XOR and XNOR logic operations with the speed of 10 kb/s are successfully demonstrated. In addition, numerical simulation results indicate that the length difference between the upper waveguide and the under waveguide can change the output spectrum characteristics of the device, which acts like a Mach–Zehnder interferometer (MZI).

Microbubbles have attracted widespread attention within the academic community, owing to their great potential for applications in microsystems. Considering practical applications, it is critical to use a simple method to generate a controllable microbubble without contaminating the target environment. In this paper, we propose a convenient and controllable method to generate a vapor microbubble using a monolayer graphene-assisted microfiber (GMF). When the light beam at a wavelength of 1.55 μm is coupled to GMF immersed in liquid, light energy can be converted into heat energy due to the photothermal effect of graphene, and thus a stable and controllable microbubble can be generated due to the existence of a temperature gradient around the GMF. This microbubble is used to capture microsphere particles such as polystyrene particles by means of the Marangoni Convection around it. Compared with bare microfiber, GMF has a higher fabrication tolerance for the purposes of generating microbubbles, and a lower threshold optical power due to the strong photothermal effect of graphene. Our proposed device, which demonstrates advantages such as ease of manufacture, simple structure, and biocompatibility, is a promising candidate for future applications in the fields of directional transport of drugs, biomedicine, biochemistry, microfluidics, etc.

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.

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.

We experimentally demonstrate a reconfigurable electro-optic directed logic circuit which can perform any combinatorial logic operation using cascaded carrier-injection micro-ring resonators (MRRs), and the logic circuit is fabricated on the silicon-on-insulator (SOI) substrate with the standard commercial Complementary Metal-Oxide-Semiconductor (CMOS) fabrication process. PIN diodes embedded around MRRs are employed to achieve the carrier injection modulation. The operands are represented by electrical signals, which are applied to the corresponding MRRs to control their switching states. The operation result is directed to the output port in the form of light. For proof of principle, several logic operations of three-operand with the operation speed of 100 Mbps are demonstrated successfully.

The mode-order converter is a building block in a multimode optical transmission and switching system. It can be used for switching signals carried on different mode channels. However, such devices constructed by conventional structures can commonly accomplish one mode-order conversion process. It is because the phase-matching condition, which is utilized by a majority of designs, can usually be fulfilled between only one mode pair for specific device geometry. In this Letter, we propose a dual-polarization mode-order converter referring to the concept of a silicon planar metasurface. It can realize mode-order conversions on transverse electrical and transverse magnetic polarizations in parallel. In order to verify our concept, we design and experimentally demonstrate a prototype that can realize conversions from TE0 to TE1 and from TM0 to TM1 simultaneously. The footprint is 4 μm×1.6 μm. The measured insertion losses for both polarizations are smaller than 2.3 dB, and the crosstalk is lower than −11.5 dB within the wavelength range of 1525–1565 nm. We envision that the device can be a building block in polarization and mode multiplexed optical switching systems and endow the systems with simpler structure and a more compact footprint.

In this Letter, we first demonstrate periodically and independently tunable double Fano resonances (DFRs) using waveguide-coupled cavities consisting of two silicon microring resonators (MRRs) and a feedback-coupled waveguide. The proposed device is fabricated on the silicon-on-insulator substrate using the standard complementary metal-oxide-semiconductor fabrication process. The DFR can be tuned independently by changing the resonant wavelengths of two MRRs using the thermo-optic effect. The highest extinction ratio of the Fano resonances is measured to be as high as 29.20 dB, which enables this device to be a promising candidate for high-performance multi-wavelength optical switches and high-sensitivity biochemical sensors.

We experimentally demonstrate a tunable Fano resonance which originates from the optical interference between two different resonant cavities using silicon micro-ring resonator with feedback coupled waveguide fabricated on silicon-on-insulator (SOI) substrate. The resonance spectrum can be periodically tuned via changing the resonant wavelengths of two resonators through the thermo-optic effect. In addition to this, we can also change the transmission loss of the feedback coupled waveguide (FCW) to tune the resonance spectrum by the injection free carriers to FCW. We also build the theoretical model and we analyze the device performance by using the scattering matrix method. The simulation results are in a good agreement with the experimental results. The measurement maximum extinction ratio of the Fano resonance is as high as 30.8dB. Therefore, the proposed device is a most promising candidate for high on/off ratio optical switching/modulating, high-sensitivity biochemical sensing.