Extinction Ratio Enhancement Research Articles

Analysis on dual Fano resonance in a coupled-resonator waveguide

Dual Fano resonance was demonstrated in a compact coupling system without additional large footprint tunable devices consisting of a grating-coupled waveguide and a micro-racetrack resonator on thin film lithium niobate. A multimode interference model was proposed for the dual Fano resonance system. The inverse design method was used to realize model fitting, validate our model, and analyze our model. Based on the parameters obtained by the inverse design, we further analyzed the influence of different parameters. Our research also shows that through the interaction of two Fano resonance modes, tunable line shape and enhanced extinction ratio can be realized in the transmission spectrum, which has potential applications in optical sensing.

P‐11.17: Research of extinction ratio enhancement of linear polarized micro‐LED

P‐11.17: Research of extinction ratio enhancement of linear polarized micro‐LED

40 Gb/s multimode all-optical regenerator based on the low-loss silicon-based nanowaveguide.

With the increasing demand for communication capacity, all-optical regeneration of multimode signals is a helpful technology of network nodes and optical signal processors. However, the difficulty of regenerating signal in higher-order modes hinders the practical application of multimode all-optical regenerators. In this study, we experimentally demonstrate the 40 Gb/s all-optical regeneration of NRZ-OOK signal in TE0 and TE1 modes via four-wave mixing (FWM) in the low-loss silicon-based nanowaveguide. By optimizing the parameters of waveguide section to enhance FWM conversion efficiency of two modes, and introducing Euler bending to reduce crosstalk between modes, the transmission loss of the silicon waveguide is 0.3 dB/cm, and the FWM conversion efficiency of the multimode regenerator is as high as -9.6 dB (TE0) and -13.0 dB (TE1). Both modes achieve extinction ratio enhancement of about 6 dB after regeneration. This silicon-based all-optical regenerator has great application potential in all-optical signal processing systems.

Modal analysis of the quasi-resonant extinction ratio enhancement in the amorphous silicon wire grid polarizer

The previously discovered effect of quasi-resonant enhancement of the extinction ratio in an amorphous silicon wire polarizer is investigated using the Bloch wave approach and the modal method. Effective indices of grating modes, modal fields and transmission coefficients were numerically evaluated and our prior hypothesis of destructive interference of lower order grating modes as a mechanism for the enhancement of the extinction ratio was confirmed. Using the numerical optimization, we showed that the quasi-resonance wavelength can be tuned by changing the parameters of the grating structure.

Local laser oxidation of titanium film for the post-fabrication trimming of photonic integrated circuits

Local laser oxidation of a thin titanium film is considered as a means of a precise adjustment of losses and effective refractive index of dielectric optical waveguides. A fine phase control of an operating point and extinction ratio enhancement up to 57 dB were demonstrated using an integrated optical Ti:LiNbO3 Mach-Zehnder modulator. This technique only slightly affects the dielectric waveguide material and is very promising for a high precision permanent trimming of photonic devices based on dielectric waveguides of different material platforms and fabrication technologies.

Ultrafast dynamic switching of optical response based on nonlinear hyperbolic metamaterial platform

The pursuit of high-speed and on-chip optical communication systems has promoted extensive exploration of all-optical control of light-matter interactions via nonlinear optical processes. Here, we have numerically investigated the ultrafast dynamic switching of optical response using tunable hyperbolic metamaterial (HMM) which consists of five pairs of alternating layers of indium tin oxide (ITO) and SiO2. The nonlinearity of the HMM is analyzed by the ultrafast dynamics of the hot electrons in the epsilon-near-zero (ENZ) ITO. Our approach allows large and broad all-optical modulation of the effective permittivity and topology of the HMM on the femtosecond time-scale. Based on the proposed HMM platform, we have shown considerable tunability in the extinction ratio and Purcell enhancement under various pump fluence. In addition, we have achieved all-optical control of the coupling strength through depositing plasmonic resonators on the HMM platform. A significant tuning of the coupled resonance is observed by changing pump fluence, which leads to a switching time within 213 fs at a specific wavelength with a relative modulation depth more than 15 dB.

Performance optimization of a metasurface incorporating non-volatile phase change material.

Optical metasurface is a combination of manufactured periodic patterns of many artificial nanostructured unit cells, which can provide unique and attractive optical and electrical properties. Additionally, the function of the metasurface can be altered by adjusting the metasurface's size and configuration to satisfy a particular required property. However, once it is fabricated, such specific property is fixed and cannot be changed. Here, phase change material (PCM) can play an important role due to its two distinct states during the phase transition, referred to as amorphous and crystalline states, which exhibit significantly different refractive indices, particularly in the infrared wavelength. Therefore, a combination of metasurface with a phase change material may be attractive for achieving agile and tunable functions. In this paper, we numerically investigate an array of silicon cylinders with a thin PCM layer at their centers. The GST and GSST are the most well-known PCMs and were chosen for this study due to their non-volatile properties. This structure produces two resonant modes, magnetic dipole and electric dipole, at two different resonating wavelengths. We have numerically simulated the effect of cylinder's height and diameter on the reflecting profile, including the effect of thickness of the phase change material. Additionally, it is shown here that a superior performance can be achieved towards reduced insertion loss, enhanced extinction ratio, and increased figure of merit when a GST layer is replaced by a GSST layer.

Design of Hybrid Plasmonic Multi-Quantum-Well Electro-Reflective Modulators Towards <100 fJ/bit Photonic Links

Realization of on-board and inter-chip optical interconnects requires a photonic data link with power consumption well below their electrical counterparts (i.e., 50 Gb/s requires 2–4 pJ/bit/channel. External reverse-biased modulators could drastically reduce this power consumption. Here we design ultralow power GaAs/AlGaAs multi quantum well electro-reflective modulators operating at 1 V for facile integration with polymer “optical bridges”, utilizing coupled quantum confined Stark effect between adjacent quantum wells and optical coupling to hybrid surface plasmon-slab modes for significantly enhanced extinction ratio and spectral bandwidth. Distinctive from conventional electro-optical or electro-absorption modulators, this new design synergistically leverages ultra-large changes in both refractive index (|Δn|∼0.05) and absorption coefficient (Δα∼104 cm−1), achieving 35-50 dB extinction ratio at 1 V reverse bias with a low insertion loss of 1–3 dB, an incident angle tolerance of ∼5°, and a spectral bandwidth of 7–10 nm. The modulator power consumption is ∼1.9 fJ/bit without the need of thermal tuning, and the RC-limited bandwidth well exceeds 100 GHz. This new modulator enables high bandwidth and ultralow power optical interconnect networks at >100 Gb/s/channel and <100 fJ/bit/channel compatible with ever-scaling CMOS technologies.

LiTaO3 Directional Coupler Switch with Enhanced Extinction Ratio and Low Insertion Loss

A novel design of optical directional coupler switch with S-bend waveguides on LiTaO3 platform has been designed with R-Soft CAD tool and the same is simulated by Beam propagation method (BPM) for light propagation analysis. The simulation results of the optical directional coupler (ODC) switch is reported. We observed that the directional coupler (DC) switch has lower insertion losses and higher extinction ratios for a certain values that are discussed in the paper. This was studied by variation in waveguide parameters such as, wavelength, waveguide gap, and length of the device. Simulation results designate that the switching efficiency for TE and TM modes with extinction ratio about 3dB when the waveguide gap is 3.5μm for both the polarization modes and insertion loss is 13dB with same waveguide gap in TE mode and 16dB in TM mode at 1550nm wavelength.

Integrated structure of polarization detection in the visible spectrum based on double wire grids

We introduce an integrated polarization detection structure consisting of a photoelectric conversion material, silicon (Si), in the form of a wire grid and an aluminum (Al) wire grid polarizer layer. This structure provides transverse magnetic (TM) polarization absorptivity and an enhanced extinction ratio in the visible spectrum. Finite difference time domain simulations were used to examine the influences of different periods and thicknesses of the Si and Al grid components. The results showed that the absorptivity of TM polarization exceeded 70% in the visible spectrum (a 20% improvement), the absorptivity of transverse electric polarization was reduced by >90 % , and the extinction ratio improved by a factor of 33. When the incidence angle is over the range of 0 deg to 30 deg, the absorptivity of TM polarization and the extinction ratio perform well, exceeded 60% and 75.

Hybrid III-V on Silicon Integrated Distributed Feedback Laser and Ring Resonator for 25 Gb/s Future Access Networks

We report on a fully integrated hybrid III-V on a silicon distributed feedback laser integrated with a ring resonator. We demonstrate an enhanced extinction ratio up to 5 dB at 25 Gb/s of the distributed feedback laser when the ring-resonator is finely tuned. We validated the transmitter with a 20-km transmission with only 2.5-dB penalty and 20-dB power budget.

Metamaterial-enhanced terahertz vibrational spectroscopy for thin film detection

We present metamaterial-enhanced terahertz vibrational spectroscopy to solve the low sensitivity problem of the THz ray absorption detection in molecular and biomolecular thin film. In a proof-of-principle experiment, we demonstrate the system in split ring resonators (SRRs) metamaterial that is strongly coupled to L-tartaric acid molecular under a low-temperature condition. The experimental results show that the extinction ratio of the detected signal can be significantly improved from 1.75 dB to 4.5 dB. The numerical calculations confirm and explain the experimental observations. By detuning the resonance of metamaterial, the behavior of the spectral signal is modified. When the SRRs and molecular vibrational resonance frequencies are closely aligned, a clear mode splitting is observed resulting in a transparency transmission with enhanced extinction ratio. This method shows great potential for application in thin film sensing by detecting molecular vibrations in the lower-energy terahertz region.

Raman-Assisted Phase-Sensitive Amplification Enabled Optical Add-Drop Filter

We present a novel reconfigurable optical add-drop filter based on phase-sensitive amplifiers (PSAs). By manipulating the relative phase among an optical pump, signals, and idlers, spectral selectivity can be achieved along with low noise amplification. The use of backward Raman amplification enhances the phase-sensitive operation of the parametric process, enabling higher stopband isolation and lower intra-band crosstalk. A Raman-assisted phase-sensitive amplifier (RA-PSA) is characterized in detail, showing a 7.8-dB combined gain extinction ratio enhancement and 10.85-dB gain improvement. For the first time, we demonstrate an RA-PSA enabled optical add-drop filter with less than 0.4-dB penalty using three-channel QPSK signals. The novel scheme provides a simple way to enhance the extinction ratio of the PSA enabled add-drop filter, which can be an essential subsystem in optical links based on phase-sensitive amplification.

Extinction ratio enhancement by sinusoidal phase modulation and nonlinear spectral focusing

We propose a new approach to enhance the extinction ratio of a pulse impaired by a coherent continuous-wave background. Taking advantage of a sinusoidal phase modulation followed by a nonlinear spectral focusing and an optical bandpass filtering, we are able to significantly decrease the level of the unwanted background. The principle of the method is experimentally validated at telecommunication wavelengths.

Integrated Hybrid III-V/SOI Directly Modulated DFB Laser and Ring Resonator at 10 Gbit/s

This letter reports on a directly-modulated hybrid III-V/SOI DFB laser and a ring resonator integrated on a single chip. The ring resonator filter provides extinction ratio enhancement. A trade-off between power losses and performance improvement is found. Error free and penalty free transmission at 10 Gb/s over 50-km single mode fiber is demonstrated.

Fast Extinction Ratio Enhancement With a Graphene-Based Device on $1.5~\mu \text{m}$ Optical Signals

Ability of fast intensity discrimination provided by a graphene-based saturable absorber device is demonstrated in the perspective of all-optical signal processing in $1.5~\mu \text{m}$ wavelength range. The dynamic extinction ratio enhancement is measured as more than 3 dB. It is argued that, the device performances are promising enough to be tested further in an efficient all-optical module to reduce crosstalk or intensity noise in high rate signals.

Enhancement of the static extinction ratio by using a dual-section distributed feedback laser integrated with an electro-absorption modulator

We report on the enhancement of the static extinction ratio by using a dual-section distributed feedback laser diode integrated with an electro-absorption modulator. A directly- modulated dual-section laser can provide improved modulation performance under a low bias level (i.e., below the threshold level) compared with a standard directly-modulated laser. By combining the extinction ratio from a dual-section laser with that from an electro-absorption modulator section, a total extinction ratio of 49.6. dB are successfully achieved.

Visible Light Communication Using Receivers of Camera Image Sensor and Solar Cell

We propose an electronic label and sensor system using visible light communication (VLC). The downlink signal is transmitted by a white-light light-emitting diode (LED) lamp that can provide lighting, VLC, and energy harvesting for mobile devices. The downlink is received by a solar cell. The uplink can be captured by a surveillance camera image sensor. However, using the camera image sensor as a VLC receiver (Rx) is challenging since the data rate is limited by the frame rate and due to uneven light exposure. The rolling shutter effect of the image sensor can be used to increase the data rate. In this paper, we propose and demonstrate how to demodulate the obtained rolling shutter pattern using a second-order polynomial (SOP) extinction ratio (ER) enhancement scheme, together with iterative and modified quick adaptive thresholding schemes. The ER enhancement scheme can significantly reduce the large ER fluctuation. Experimental results show that by using the proposed SOP ER enhancement scheme, the bit error rate (BER) improvement can be up to two orders of magnitude. We also believe that the proposed electronic label and sensor system may be applicable to Internet-of-Things sensing networks for connecting a number of mobile devices.

110 GHz hybrid mode-locked fiber laser with enhanced extinction ratio based on nonlinear silicon-on-insulator micro-ring-resonator (SOI MRR)

We propose and experimentally demonstrate a new 110 GHz high-repetition-rate hybrid mode-locked fiber laser using a silicon-on-insulator microring-resonator (SOI MRR) acting as the optical nonlinear element and optical comb filter simultaneously. By incorporating a phase modulator (PM) that is electrically driven at a fraction of the harmonic frequency, an enhanced extinction ratio (ER) of the optical pulses can be produced. The ER of the optical pulse train increases from 3 dB to 10 dB. As the PM is only electrically driven by the signal at a fraction of the harmonic frequency, in this case 22 GHz (110 GHz/5 GHz), a low bandwidth PM and driving circuit can be used. The mode-locked pulse width and the 3 dB spectral bandwidth of the proposed mode-locked fiber laser are measured, showing that the optical pulses are nearly transform limited. Moreover, stability evaluation for an hour is performed, showing that the proposed laser can achieve stable mode-locking without the need for optical feedback or any other stabilization mechanism.

Reflective all-fiber magnetic field sensor based on microfiber and magnetic fluid.

A kind of reflective all-fiber magnetic field sensor based on a non-adiabatically tapered microfiber with magnetic fluid is proposed and experimentally demonstrated. The modal interference effect is caused by the abrupt tapers, which result in an approximately sinusoidal spectral response. The reflection spectra of the proposed sensor under different magnetic field strengths have been measured and theoretically analyzed. The maximum sensitivity of 174.4 pm/Oe is achieved at wavelength of around 1511 nm. Besides, an intensity tunability of -0.02 dB/Oe is also achieved. Comparing with the traditional sensors operating at transmission mode, the presented sensor in this work owns the advantages of smaller size and higher sensitivity and resolution due to the enhanced extinction ratio. The proposed structure is also promising for designing other tunable all-in-fiber photonic devices.