Wavelength Division Demultiplexer Research Articles

On-Chip Multichannel Dispersion Compensation and Wavelength Division MUX/DeMUX Using Chirped-Multimode-Grating-Assisted Counter-Directional Coupler

On-chip optical dispersion compensation and wavelength division multiplexing/demultiplexing (WDM) are highly demanded functions for optical communications. In this work, we proposed a multichannel dispersion compensation structure based on chirped multimode grating within a counter-directional coupler (CMG-CDC). Simultaneous wavelength division multiplexing and demultiplexing can be realized within a compact footprint. A device design for four-channel CMG-CDC at the C/L (1530–1565 nm) band is presented with a channel spacing of 20 nm assisted by a grooved multimode waveguide structure. The average dispersion for all channels is about −2.25 ps/nm with a channel bandwidth of about 3.1 nm. The device is highly compact and highly scalable, which makes it rather convenient for increasing the group velocity dispersion (GVD) and channel number, indicating flexible applications for versatile systems, including typically coarse wavelength division multiplexer four-lane (CWDM4) transceivers.

Eight-channel C-Band demultiplexer based on one-dimensional photonic crystals defected with lithium niobate

We propose an eight-channel Dense Wavelength Division Demultiplexer (DWDM) device based on one-dimensional photonic crystal (1-D PC) structures defected with lithium niobate (LiNbO3) thin films. The demultiplexer operates in the C-band window (1460–1560 nm), which belongs to the ITU grid for DWDM applications. The desired output wavelength is achieved by applying the proper external electric field to the LiNbO3 layer at various temperatures. The transfer matrix method (TMM) is used to simulate the transmittance spectrum. Efficient output channels with transmittances of about 90% are attained. An excellent quality factor of 30919 and a very small line width of 0.05 nm are exceptional values acquired by the output channels. A very small channel spacing of 0.182 nm is attained without compromising the crosstalk, which reaches a minimum value of −34 dB. The astounding characteristics of the eight channels reveal that the proposed demultiplexer could be a potentially efficient device for DWDM networks.

High-density optical interconnects based on self-imaging in coupled waveguide arrays

Rapidly increasing demand for higher data bandwidths has motivated exploration of new communication channels based on spatially multiplexed in-fibre and on-chip coupled light guides. However, the conventionally used periodically arranged coupled waveguides display complicated light propagation patterns, ranging from quasiperiodic to nearly chaotic. Taking a different approach, we spectrally engineer interwaveguide coupling to instigate self-imaging of the input light state at the array output and thus enable construction of novel high-fidelity interconnects. Simple implementation via modulation of the interwaveguide separations makes these interconnects realizable in all fabrication platforms. Their competitive advantages are negligible crosstalk-induced information loss, high density that exceeds the current standards by an order of magnitude, and compatibility with both classical and quantum information encoding schemes. Moreover, the wavelength-dependent self-imaging opens up new possibilities for wavelength and spatial division demultiplexing. The proposed analytical designs are supported by extensive numerical simulations of silicon-on-insulator, silicon nitride and silica glass waveguide arrays, and a statistical feasibility study.

Photonic-chip-based dense entanglement distribution

The dense quantum entanglement distribution is the basis for practical quantum communication, quantum networks and distributed quantum computation. To make entanglement distribution processes stable enough for practical and large-scale applications, it is necessary to perform them with the integrated pattern. Here, we first integrate a dense wavelength-division demultiplexing system and unbalanced Mach-Zehnder interferometers on one large-scale photonic chip and demonstrate the multi-channel wavelength multiplexing entanglement distribution among distributed photonic chips. Specifically, we use one chip as a sender to produce high-performance and wideband quantum photon pairs, which are then sent to two receiver chips through 1-km standard optical fibers. The receiver chip includes a dense wavelength-division demultiplexing system and unbalanced Mach-Zehnder interferometers and realizes multi-wavelength-channel energy-time entanglement generation and analysis. High quantum interference visibilities prove the effectiveness of the multi-chip system. Our work paves the way for practical entanglement-based quantum key distribution and quantum networks.

A ‘DOMZM–Filter–BPD’-Based Microwave Photonic Link for Eliminating Even Harmonics Distortion

The ‘Mach-Zehnder modulator (MZM)–wavelength division demultiplexer (WDM)–photodetector (PD)’ structure in photonic analog-to-digital converters (PADCs) may result in residual even harmonics after photodetection. In this paper, we build the model for the ‘Dual-output MZM (DOMZM)–filter–balanced PD (BPD)’-based microwave photonic link, where the amplitude and the phase responses of the filter can be arbitrary. It is proved that this link can eliminate the aforementioned even harmonics. Theoretical analysis is verified by the simulation and experimental results. By using this structure, the spur-free dynamic range (SFDR) limited by the even harmonics can be improved and the sampling frequency range can be expanded for the PADCs. As the spectrum contains only odd harmonics, the inverse cosine transform for calibrating the nonlinearity of the MZM can be applied to further improve the SFDR.

Shock wave diagnostics with an ultra-short optical fiber probe

We report a highly localized, rapid-response pressure measurement of a shock wave front in a solid by utilizing a miniature fiber-optic-based probe. The probe used was a 100 μm-long fiber Bragg grating (FBG) inscribed on a standard silica communication fiber, 125 μm in diameter. The optical fiber was embedded within a ceramic zirconia ferrule and was shocked axially by a polycarbonate impactor fired from a gas gun. In a second ferrule, included in the same experiment, a 1 mm long FBG was embedded for comparison. Both FBGs were positioned at the front face of their respective ferrules, in order to sense the region where the shock wave is pristine, with no release waves, and where the stress conditions were expected to be constant for a few hundreds of nanoseconds. A simulation has been performed using LS-DYNA software describing the temporal dependence of the axial stress operating on the zirconia target and the embedded fiber gratings. The reflected spectra of both fiber grating probes were interrogated by an array of wavelength division demultiplexers and 200 MHz InGaAs detectors. Both probes exhibited a wavelength shift that corresponded to the pressure profile of the shock wave that traveled through the fiber, agreeing quite well with the predictions of the simulation. The wavelength blueshift was about 3.5 nm under a calculated shock pressure in the silica of 320 MPa, induced by a shock pressure of 700 MPa in the host zirconia target. Overall, the 100 μm probe demonstrated superior measurement capabilities to the 1 mm probe, both in time response and localization, as well as better agreement with the simulation. Multiple probes can be applied to provide high resolution mapping of shock phenomena in space and time, thus assisting in establishing the dynamic properties of materials under impact loading.

Investigation on Ultra-Compact 2DPC Coarse Wavelength Division Demultiplexer

A two dimensional Photonic Crystal (2DPC) based eight-channel wavelength division de-multiplexer is proposed and designed for Coarse Wavelength Division Multiplexing (CWDM) applications. The circular ring resonator, channel selector, circulator rod, L bend waveguide and linear bus waveguide are essential parts of the proposed system. The system’s functional parameters such as Transmission efficiency, resonant wavelength, spectral width, channel spacing, Quality factor and crosstalk investigated this paper. The eight different wavelengths of channels are filtered out by altering the size of channel selector rod, setting the radius of the circle shaped cavity and relative refractive index of circulator rod. Initially the Photonic Band gap (PBG) is manipulated by applying Plane Wave Expansion (PWE) method of the 2DPC structure. The functional parameters are analysed by Finite Difference Time Domain (FDTD) method in periodic and non-periodic structure of the proposed system to arrive normalized transmission spectrum. The resonant wavelengths of designed eight paths of the device are varying from 1420nm to 1460nm with average spectral width and channel spacing are 5.8nm, 5.6nm respectively. The footprint of the device is 286.84μm2. Hence, this small device can be implemented for CWDM systems in Photonic Integrated Circuits (PIC)

On-chip silicon nano-slab photodetector integrated wavelength division de-multiplexer in the 850 nm band.

We present an on-chip photodetector integrated wavelength filter on a SiN-on-silicon-on-insulator (SOI) platform in the 850 nm wavelength window. The wavelength filter is designed using an echelle grating with a distributed Bragg reflector as the grating reflectors. We present the design and experimental realization of a six-channel wavelength filter with a channel spacing of 10 nm. Experimentally, we achieve an insertion loss of 4.3 dB and an adjacent channel cross talk of 22 dB. We demonstrate a silicon nano-slab waveguide integrated metal-semiconductor-metal photodetector with a maximum responsivity of 0.56 A/W and dark current of 217 nA. Furthermore, we demonstrate the integration of the echelle grating with the detector and show the feasibility of a CMOS compatible SiN-on-SOI platform for various applications, including short-reach communication and sensing applications.

Omnidirectional narrow-band ultraviolet filtering based on one-dimensional defective photonic crystal containing hyperbolic metamaterial

As a kind of Fabry-Perot cavities, one-dimensional photonic crystals (1DPCs) with defect layers have been widely utilized for narrow-band filtering. However, according to the Bragg interference condition, photonic band gaps (PBGs) in conventional all-dielectric 1DPCs shift towards shorter wavelengths (blueshift) as the incident angle increases. Therefore, transmittance peaks in all-dielectric one-dimensional defective PCs also shift along with PBGs as the incident angle increases. Recently, the emergence of angle-insensitive PBGs in 1DPCs containing hyperbolic metamaterials (HMMs) provides us a possibility to realize omnidirectional narrow-band filtering. In this paper, we design an angle-insensitive ultraviolet PBG in a 1DPC containing HMM, where HMM layer is mimicked by a subwavelength dielectric-metal multilayer. By introducing a defect layer into the 1DPC and adjusting the dielectric thickness within the 1DPC, we achieve omnidirectional narrow-band ultraviolet filtering with angle-insensitive property. This omnidirectional narrow-band filtering might possess applications in digital display, organic solar cell and wavelength division demultiplexing.

Effects of the Nonlinearity Caused by 'MZM-WDM' Structure in Time-Wavelength Interleaved Photonic Analog-to-Digital Converters.

The effects of the nonlinearity caused by the structure of ‘Mach-Zehnder modulator (MZM) - wavelength division demultiplexer (WDM)’ in Time-Wavelength Interleaved Photonic Analog-to-Digital Converters is studied for the first time. Even if the MZM is biased at quadrature, the narrow passband width of the WDM after modulation may result in the presentation of even harmonics in the spectrum of the sampling results. As the frequency of the signal being sampled increases and the passband width of the WDM decreases, the magnitudes of the even harmonics increase. As a result, the spur-free dynamic range (SFDR) would be determined by the magnitudes of the signal and the 2nd harmonic instead of the 3rd harmonic. When the passband width of the WDM is less than 100 GHz, the variation of the SFDR can be as much as 6 dB over 0~25 GHz-frequency range of the signal being sampled. Theoretical analysis is verified by the simulation and experimental results. When the passband width of the WDM is greater than 150 GHz, the SFDR over 0~25 GHz-RF range is always dominated by the 3rd harmonic. When the passband width is 50 GHz, the SFDR is dominated by the 2nd harmonic for RF frequencies above 10 GHz, and can be as much as 20 dB higher than the 3rd harmonic term at 25 GHz-RF frequency. The requirement for the passband width of the WDM can be specified according to the frequency range of the signal being sampled to avoid the presentation of even harmonics and optimize the design of TWIPADCs.

Scan-less 3D optical sensing/Lidar scheme enabled by wavelength division demultiplexing and position-to-angle conversion of a lens.

We propose a novel scheme for 3D sensing or Lidar without the need for beam scan or 2D photo-imaging. The scheme is enabled by the combination of a lens' position-to-angle conversion and the wavelength division multiplexing/demultiplexing (WDM) commonly used in optical fiber communication systems. However, unlike in a WDM system where different wavelengths carry different data channels, here lights of different wavelengths are demultiplexed into different waveguides or fibers with their exiting ends placed in the focal plane of the lens, which converts the exiting lights into beams of different angles to form a 1D or 2D beam array according to the relative position of the fiber ends with respect to the optical axis of the lens for illuminating the targets and finally sensing the light reflected from different directions. The returned signals are then demultiplexed into different photodetectors to determine the distances of the reflections in different directions. We show that the scheme has the potential to be implemented in photonics integrated circuit (PIC) for low cost production. We successfully demonstrate the scheme with the off-the-shelf discrete fiber optic components using 4 WDM channels and time-of-flight (ToF) technique for distance measurement, although hundreds wavelength channels from a photonic integrated microcomb may be used in practice. Finally, we demonstrate that the angular resolution of the beam array of different wavelengths can be improved by dithering the fiber array or the lens. We believe this new scheme provides an attractive alternative to the MEMS and optical phased array based beam scanning and can be explored further to enable low cost and high speed 3D sensing, particularly Lidar systems.

Tunable Optical Demultiplexer for Dense Wavelength Division Multiplexing Systems Using Graphene–Silicon Microring Resonators

An ultracompact tunable optical dense wavelength division demultiplexer (DWDM) compatible with complementary metal–oxide–semiconductor technology is proposed, consisting of a central bus waveguide coupled to two drop waveguides through two ring resonators, all made of silicon (Si). Each Si ring resonator is topped by a graphene microribbon whose chemical potential can be tuned as desired. The center wavelength of each drop channel is determined by the resonant wavelength of the adjacent ring resonator, which in turn is tuned by modifying the conductivity of the graphene. Simulations show that the proposed structure with two graphene–Si ring resonators (GSRRs) having a chemical potential difference of 210 meV demultiplexes a broad optical signal into two narrow channels centered at about 1552.42 nm and 1552.85 nm (with a channel spacing of less than 0.43 nm), each emerging from one drop waveguide, with a transmission efficiency above 64%. The full-width at half-maximum values of the channels are 160 pm and 250 pm, providing quality factors of ∼ 9705 and 6209 with crosstalk of less than − 13.3 dB. By exchanging the chemical potentials of the GSRRs, the drop channels can be swapped dynamically without mechanical manipulation of the device. The proposed ultracompact graphene-based demultiplexer enables electrically tuned optical demultiplexing for DWDM systems as a potential alternative to the thermooptically tuned demultiplexers employed in long-haul optical communications.

Femtosecond synchronization of multiple mode-locked lasers and a microwave oscillator by multicolor electro-optic sampling.

Simple multicolor electro-optic sampling-based femtosecond synchronization of multiple mode-locked lasers is demonstrated. Parallel timing error detection between each laser and a common microwave is achieved by wavelength division multiplexing and demultiplexing. The parallel timing error detection enables simultaneous femtosecond synchronization of more than two mode-locked lasers to the microwave oscillator, even when the lasers have different repetition rates. The residual root-mean-square (rms) timing jitter of laser-laser synchronization measured by an optical cross correlator is 2.6 fs (integration bandwidth, 100 Hz-1 MHz), which is limited by the actuator bandwidth in the laser oscillator. The long-term rms timing drift and frequency instability of laser-microwave synchronization are 7.1 fs (over 10,000 s) and 5.5×10-18 (over 2000 s averaging time), respectively. As a versatile and reconfigurable tool for laser-laser and laser-microwave synchronization, the demonstrated method can be used for various applications ranging from ultrafast x-ray and electron science facilities to dual- and triple-comb spectroscopy.

Giant Goos-Hänchen shift with a high reflectance assisted by interface states in photonic heterostructures

We achieve interface states with a high reflectance in photonic heterostructures composed of two kinds of all-dielectric one-dimensional photonic crystals (1DPCs) with symmetric unit cells. The reflectance of interface states can be controlled flexibly by tuning the mismatch degree between the imaginary phases of the two kinds of 1DPCs. Assisted by the interface state with a high reflectance as well as a high-$Q$ factor, the Goos-H\"anchen (GH) shift can be greatly enhanced to larger than three orders of wavelengths. Our work provides a route, completely under the current experimental conditions, to design high-performance sensitive sensors, wavelength division demultiplexers, and polarization beam splitters based on this giant GH shift together with a high reflectance.

Photonic crystal ring resonator based optical MUX/DEMUX design structures: a survey and comparison study

For the past few decades, the design of photonic crystal (PC)-based optical devices and components are mainly focused by several researchers as miniaturisation becomes a crucial need in many integrated applications. In optical communication system, the PC-based wavelength division multiplexer and demultiplexer is considered as one of the most essential component as it offers high transmission rate in single optical fibre by performing multiplexing operation. Due to its major role, numerous optical MUX/DEMUX structures based on different design mechanisms like resonant cavity, super prism effect, cascading multiple channel drop filters, coupling and cascading the PC waveguide, defect waveguides and photonic crystal ring resonator (PCRR), etc., have been reported and analysed so far. However, despite the various mechanisms, the design structure based on PCRR mechanism has attracted the attention of many researchers in recent years due to its design flexibility, high quality factor and low loss which satisfies the requirements of major applications. Hence, the main aim of this paper is to discuss about the various existing design structures of optical MUX/DEMUX based on PCRR mechanism along with its respective pros and cons. Further, the comparison of their corresponding structural and performance parameters is also tabulated in detail. From the literature review and comparison study, the future design considerations are suggested for the researchers which would be helpful for them in designing better structure with improved performance.

Transmission of low-noise supercontinuum based wide-spectral carriers in a simulated atmosphere channel with tunable turbulence

We report a free space optical transmission system with low-noise wide-spectral carriers in a simulated turbulent channel with tunable turbulence intensity. The low-noise supercontinuum generation is achieved by using amplified diode-laser pulses to pump nonlinear fiber with the aid of amplified spontaneous emission seeding. Subsequent wide-spectral carriers are generated by filtering the low-noise SC with a coarse wavelength division demultiplexer. Transmission characteristics in turbulent channel, including power fluctuation, eye patterns, and bit error rate, between narrow-spectral, wide-spectral and low-noise wide-spectral carriers are compared respectively. It is experimentally verified that our methods can improve pulse-to-pulse fluctuation of wide-spectral carriers without weakening its ability of turbulence resistance, thus the transmission performance of low-noise wide-spectral carriers in turbulence channel is highly evaluated. It is feasible to apply the wide-spectral carriers transmission scheme to reduce influence of atmosphere turbulence and our further improvement make the scheme more adaptive to present FSO network.

Microwave multi-frequency measurement based on an optical frequency comb and a photonic channelized receiver.

A new method, to the best of our knowledge, to measure frequencies of received microwave signal based on an optical frequency comb (OFC) and a photonic multi-channel receiver is proposed and simulated. The measurement system mainly includes a seed laser, an OFC generator composed of two cascaded Mach-Zehnder modulators, a frequency shifter, an intensity modulator, a wavelength-division demultiplexer, photodiodes (PDs), and electrical filters. Two sets of beat signals need to be obtained in the measurement process. By analyzing the two sets of beat signals, multiple frequency components of the microwave signal can be measured at a time. The validity of the proposed scheme is verified by VPI simulation software. It is shown that microwave frequencies within dozens of gigahertz can be precisely measured, and factors affecting the frequency measurement range are also studied.

Dual wavelength Talbot self-imaging using facet patterned nonlinear crystals.

A method for functional patterning of facets of a nonlinear crystal using focused ion beam milling has been developed. The near-field diffraction on periodic gratings has been experimentally and theoretically studied. The periodicity of the structure enables Talbot self-imaging at the fundamental and second-harmonic frequencies simultaneously. Spatial interference patterns for both harmonic frequencies are individual ones, which can enable the higher-accuracy optical testing, coupling the radiation at both frequencies, and wavelength-division demultiplexing. The impact of the aperture effect on a Talbot carpet is discussed.

Compensation of dispersion-induced power fading with adjustment-free operation

A scheme for compensation of dispersion-induced power fading is proposed and experimentally demonstrated. The system transmits two modulated laser lights via a wavelength division multiplexer and a wavelength division demultiplexer. By optimizing the power ratio and the phase difference between the two modulated signals, the dispersion-induced power fading can be adequately compensated. A key significance of our approach is that no adjustments are required when the input radio frequency signal scans over a broad bandwidth of 1 to 12 GHz. We successfully demonstrate the compensation of the power fading for both 20- and 30-km fiber links. An improvement of spurious-free dynamic range is also achieved.

On-chip hybrid demultiplexer for mode and coarse wavelength division multiplexing

We propose a hybrid demultiplexer for mode and coarse wavelength division multiplexing on silicon-on-insulator (SOI) nanowires and photonic crystal (PhC) slab. First, a V-shape waveguide–cavity–waveguide filter based on PhC slab is presented. Coupling of resonant modes is introduced to the filter to suppress the crosstalk caused by connection with nanowires. Then, we cascade and optimize the filter to compose a coarse wavelength division demultiplexer. After that, a hybrid demultiplexer is constructed by combining the coarse wavelength division demultiplexer on PhC slab and mode division demultiplexer on SOI nanowires. The parameters of the hybrid demultiplexer are calculated using three-dimensional finite-difference time-domain (3D-FDTD) method. The numerical results show that the fundamental transverse electric ( $$\hbox {TE}_0$$ ) modes and the first-order TE ( $$\hbox {TE}_1$$ ) modes of 1530 nm and 1550 nm can be demultiplexed. The insertion loss is smaller than 2.0 dB, and the channel crosstalk is less than − 25 dB. The hybrid demultiplexer can be applied in a system that using mode and coarse wavelength division multiplexing simultaneously.