Integrated silicon photonics is recognized as a potential candidate to achieve on-chip optical interconnects. Compared with other optical microcavities, photonic crystal nanobeam cavity (PCNC) has emerged as a promising platform for optical filtering, lasering, optical modulation/switching and sensing, due to their attractive properties of ultra-high Q/V and ultra-compact footprints. While numerous PCNCs focus on the characterizes of single air or dielectric mode, the cavity confining both air and dielectric modes has not yet been fully exploited. Here, we demonstrate experimentally the coupling characterizes of spatial modes in PCNC with two side coupling configurations. Experimental results show that arc waveguide side coupling PCNC supporting both air and dielectric modes with low insertion loss and high quality factors are achieved, compared with in-line coupling and parallel waveguide side coupling.
We present an ambient refractive index (RI) insensitive temperature sensor based on a Silicon-on-Insulator (SOI) ellipse stack major axis modulated photonic crystal (PC) nanobeam cavity (EPCNC). The PC nanobeam cavity is covered with SU-8 cladding to increase the temperature sensitivity by taking advantage of the relatively high thermooptic (TO) coefficient of SU-8 cladding. Three dimensional finite-difference time-domain (3D-FDTD) simulations are used for our analysis. The results show that the sensitivity of temperature sensing is -108.9pm/K. In particular, the proposed sensor not only achieves a competitive temperature sensitivity, but also eliminates the influence of ambient RI on sensing. Therefore, the proposed sensor is potentially a promising platform for future application of temperature sensing.
Space division multiplexing elastic optical networks (SDM-EONs) are advocated as a promising solution to cater to the significant increasing of network bandwidth demands. In this paper, a novel crosstalk-aware and flexible grouping routing, spectrum and core assignment (CaFG RSCA) algorithm based on mixed super-channel is proposed to suppress the spectrum fragments and improve the network performance in SDM-EONs. The algorithm focuses on the issues of spectrum fragmentation and allocation efficiency with consideration on the inter-core crosstalk in multi-core fiber (MCF). Simulation results confirm that the proposed algorithm gains effective reduction in spectrum fragments and performs better than other congeneric algorithms in terms of the service blocking probability and spectrum resource utilization.
Few-mode ring-core fibers (FM-RCFs) have been widely consider as promising optical fibers in the mode-division multiplexing transmission system, for reducing inter-modal crosstalk. In this paper, we present a numerical analysis on the bend property of a few-mode ring-core fiber supporting seven spatial modes for practical necessity. The factors for simulation contain the bend loss, modal effective area, spatial density, effective refractive index, propagation constant and effective index difference. The results indicate that the FM-RCF also can keep good properties under bending conditions. In order to further explore the bend property of the FM-RCF, the effect of the refractive index difference between inner core and outer core on the bend property of the FM-RCF, is also investigated. The results show that the refractive index difference also plays a significant role in mitigating the intramodal nonlinearity and benefiting the bending insensitivity.
We propose a broad FSR and high sensitivity refractive index (RI) sensor by using a composite lattice cells based photonic crystal nanobeam cavity (CLC-PCNC). Due to the special structure of the proposed CLC, cavities with free spectra ranges (FSRs) more than 90nm meanwhile with quality factor (Q) values above 5×104 are obtained. Besides, the optical overlap integrals of nearly 30% are achieved for both of the fundamental and the first order dielectric mode of the cavity, quantitatively demonstrating strong interaction between optical and matter, resulting in high sensitivities for RI sensing. Simulation results show that sensitivities of 390.9 nm/RIU and 413.6 nm/RIU, and detection limits of 7.6×10-6 RIU and 7.2×10-6 RIU, are achieved for the fundamental and the first order dielectric mode, respectively. Furthermore, ultra-compact size of only about 220 nm × 550 nm × 10 μm (height × width × length) of the cavity is realized. Therefore, due to the remarkable performances, the proposed sensor shows great potential in realizing applications such as high integration large-scale on-chip sensing and multi-function detection in the future.
Subwavelength grating (SWG) ring resonators have demonstrated better sensitivity compared to the conventional silicon strip ring resonators due to the enhanced photon-analyte interaction. As the sensors are usually used in absorptive ambient environment, it is extreme challenging to further improve the sensitivity of the SWG ring resonator without deteriorating the quality factor because the coupling strength between the bus waveguide and the circular ring resonator is not sufficient to compensate the loss. To explore the full potential of the SWG ring resonator, we experimentally demonstrate a silicon-based high quality factor and low detection limit transverse magnetic (TM) mode SWG racetrack resonator around 1550 nm. A quality factor of 9800 is achieved in aqueous environment when the coupling length and gap are equal to 6.5 μm and 140 nm, respectively. The bulk sensitivity (S) is ~429.7 nm/RIU (refractive index per unit), and the intrinsic detection limit (iDL) is 3.71×10-4 RIU reduced by 32.5% compared to the best value reported for SWG microring sensors.
In this paper influence of high-precision optical inline dispersion compensation and ideal electric domain dispersion
compensation in 100Gbit/s coherent detection polarization division multiplexing quadrature phase shift keying (PDMQPSK)
system are studied by numerical simulation. The results show that the system performance of the system without
optical inline dispersion compensation is significantly better than the system with high-precision inline dispersion
compensation, and the system with ideal electric domain dispersion compensation is more suitable for long-distance
transmission. We also try to search the optimal ratio of inline dispersion compensation in high-precision optical inline
dispersion compensation system. We discover that there is not the ratio that can make the performance of the highprecision
optical inline dispersion compensation system significantly better than the other ratio in a certain range of
inline dispersion compensation ratio. Furthermore, the performance of the high-precision inline dispersion compensation
system is obviously worse than the ideal electric domain dispersion compensation system when the ratio is optimal, and
the performance is a little better than the performance when the ratio is 100%.
An integrated model of photonic crystal (PC) demultiplexer that can be used to combine dense wavelength-division multiplexing (DWDM) and coarse wavelength-division multiplexing (CWDM) systems is first proposed. By applying the PC demultiplexer, dense channel spacing 0.8 nm and coarse channel spacing 20 nm are obtained at the same time. The transmission can be improved to nearly 90%, and the crosstalk can be decreased to less than −18 dB by enlarging the width of the bus waveguide. The total size of the device is 21×42 μm 2 . Four channels on one side of the demultiplexer can achieve DWDM in the wavelength range between 1575 and 1578 nm, and the other four channels on the other side can achieve CWDM in the wavelength range between 1490 and 1565 nm, respectively. The demonstrated demultiplexer can be applied in the future CWDM and DWDM system, and the architecture costs can be significantly reduced.
The broadband and low-power optical bright soliton propagation in a line-defect photonic crystal waveguide (PCW) is obtained. The line-defect PCW is composed by polystyrene background material and Si-rods. By adjusting the PCW structure parameters, optical bright soliton in the optimized PCW structures with a bandwidth of 2.35 nm/3.61 nm and a peak power as low as 8.1 μW/35.7 μW is achieved. For a dense wavelength division multiplexing system with 0.2 nm of channel spacing in optical fiber communications, 8 and 16 channels can be supported within the 2.35-nm and 3.61-nm bandwidths. The peak power range is within the power range of the optical fiber communication criterion.
A new method to optimize transmission of photonic crystal filter composed of coupled cavities is proposed. This method can improve transmission without changing 3 dB bandwidth and it is achieved by shifting the defect rods in two cavities centripetally to shorten the distance between energy distribution centers within two cavities. Finally, an ultra compact four-channel demultiplexer is demonstrated by using this optimization method, and this device satisfies the coarse wavelength division multiplexing standard of ITU-T G.694.2 with transmission 99% for each channel.
A microdisplacement sensor formed by a fixed and mobile hole-array based slot photonic crystal (slot-PhC) components is demonstrated. The sensing technique is based on a nanoscale cavity with a high-Q factor in photonic crystals (PhCs). The high-Q nanocavity (H0-cavity) is formed by only laterally shifting two adjacent holes outwards slightly in the opposite direction. The properties of the microdisplacement sensor are analyzed theoretically and simulated using the finite-difference time-domain method. The simulation results indicate that with a proper operating frequency, a quasilinear measurement of microdisplacement is achieved with a sensitivity of 1.0a−1 (a is the lattice constant) in the sensing range between 0.00a and 0.20a. Although other researchers such as Xu et al.1 who demonstrated a micro displacement sensor possessing an equivalent sensitivity, the Q factor is only 40. In this paper, combined with harmonic analysis, we show numerically that an intrinsic Q value of up to 6×103 is achieved. In addition, it is worth mentioning that when the parameters of the H0-cavity are determined, the resonant frequency of the H0-cavity remains approximately constant as the mobile PhC segment shifts along the common axis. It will be easier and more accurate for measurements in practical applications.
We investigate the influence of structure parameters to the band structures of one-dimensional photonic crystals
stacking of alternating positive and negative refractive index materials. The refractive index of these two materials has
the same given absolute value. We find that the layers' thickness of the photonic crystals determines the frequency and
angle of the transmission peaks, and when the thickness is given, the permittivity and permeability of the negative index
material determine the width of frequency peak and angular peak. For realizing ultra-narrow band frequency and sharp
angular filer, we add a defect layer with positive refractive index in the middle of the photonic crystals. Setting its
structure parameters satisfying some special conditions, there will be a narrow peak in the middle of the band gap.
When electromagnetic wave incident on such PC, only those portions with special frequency and special angle can pass
though, and the accuracy can be very high. Such filter will have wide applications in microwave and optical
communications.
Transmission properties of slow light in one dimensional photonic crystal coupled resonator waveguide have been
investigated. By inserting multiple half-wavelength cavities discretely to forming CROW, the slow light band in
photonic crystal bandgap can be broadened effectively. Otherwise cavities distance and refractive difference can flatten
the rough pass band. By modulating these parameters, an optimized broadened flat pass band with 20.99nm has been
obtained. Within the band, the group velocity is in the range of 0.0142c to 0.02148c. The propagation mechanism has
been investigated via analysis of the field distribution in CROW.
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