1550-nm Wavelength Research Articles

Achromatic critically coupled racetrack resonators

In this paper, we investigate the spectral response of whispering-gallery-mode (WGM) resonators coupled to their access waveguide with a view to design their constitutive waveguides to promote critical-coupling over a wide spectral range and thereby facilitate their use for high-sensitivity sensing or nonlinear frequency conversion applications. The carried-out theoretical analysis is based on the universal response functions of singlemode and unidirectional devices. A coupled-mode treatment of the coupling region enables to derive two sets of favorable designs. The identified resonator/access waveguide systems exploit waveguides with mismatched propagation constants forming a coupling section exhibiting either an achromatic beat-length or an achromatic power-transfer coefficient. This generic model is followed by a numerical case study of vertically-coupled Si3N4 racetrack resonators. The conventional (quasi-)phase-matched configuration, treated as a reference case, is shown to display a critical-coupling bandwidth of 23 nm at a wavelength of 1550nm, whereas the proposed new designs demonstrate critical bandwidths larger than 330nm, i.e. exhibit bandwidths enhanced by more than one order of magnitude.

Spectral detection of graphene and graphene oxide with SU-8 based asymmetry tripled-Arm Mach Zehnder

This paper reports the experimental application of the fabricated SU-8 based triple arm Mach-Zehnder interferometer (MZI) in the detection of graphene and graphene oxide. A standard MZI has two arms in its structure. In our design, we combine two MZIs with different dimensions together in a way that a short arm MZI replaces one longer arm of the larger MZI. The parallel connections of the two MZIs with a common arm would enhance the overall sensitivity of the sensor. The measurands graphene and graphene oxide with almost similar refractivity has been applied to sensing arms of the MZI in separate steps. The equidistance picometric spectral shifts corresponding to each measurands over the operating wavelength of 1550nm are observed and is suitable for detection of graphene and graphene oxide.

Optical gain analysis of GaAs-based InGaAs/GaAsSbBi type-II quantum wells lasers.

A novel active region design based on a type-II InGaAs/GaAsSbBi quantum wells on GaAs substrate is proposed and studied in this work. The band structures of the InGaAs/GaAsSbBi type-II quantum wells are studied based on a self-consistent 14-band k·p model. The electronic and optical properties of dilute-bismide InGaAs/GaAsSbBi type-II quantum well structures are investigated theoretically. Moreover, the room temperature gain characteristics of the laser active region are studied with different Bi composition. The theoretical results indicate that adding Bi into InGaAs/GaAsSb type-II active regions on GaAs substrate extends the laser emission wavelength beyond 1550nm without sacrificing the peak gain value. It is shown that these type-II quantum well structures are suitable for 1550nm wavelength region operation at room temperature.

Research on synthetic-grating SOI structure for simultaneous operation of 1310 and 1550 nanometer signal: A handy proposal of optical interconnect for photonic integrated circuits

A single apt photonic device is adduced in this research for operating two signals concurrently In this case the proposed device deals with synthetic grating silicon on insulator (SOI) structure, where signals are realized with the wavelengths of 1310nm and 1550nm. To accomplish the same, reflectance and transmittance characteristics are investigated using plane wave expansion (PWE) technique pertaining wavelengths. To validate the PWE method, this report compares the output f some exsiting work with present simulating result which is carried out by PWE method. Finally, this work divulges that the thickness of odd and even layer including nature, position and configuration of grating SOI structure is a paramount parameter to yield maximum output from such aforementioned proposed structure.

Investigation of third-order optical nonlinearities of copper doped germanium-gallium-sulfur chalcogenide glasses

A series of copper doped germanium‑gallium‑sulfur (GGS-Cu) chalcogenide glasses were synthesized by melt-quenching method. Raman spectra showed that the introduction of Cu could alter the main structure of GGS network, leading to modification of thermal, mechanical and optical properties of the GGS glasses, even at very low doping level. Femtosecond Z-scan measurements were employed to study the third-order optical nonlinearities (TONL) of the GGS-Cu glasses at wavelength of 1550nm. Significant improvement of TONL performance due to the Cu doping was observed, and its possible mechanism was studied.

Direct detection of fluoride ions in aquatic samples by surface-enhanced Raman scattering

Given the strong hydration propensity of fluoride ions, it is difficult to detect fluoride, especially inorganic fluoride, in aqueous samples. Resolving the issue of fluoride detection in aqueous samples is a scientific undertaking of great practical significance. Herein, we propose a new method for the sensitive and selective detection of fluoride in aqueous samples without the addition of organic solvents. The method involves surface-enhanced Raman spectroscopy using 1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP) compounds and Ag nanoparticles. The method is based on a diketopyrrolopyrrole compound linked to 1-butyl iodide (DPP1), which can sense fluoride sensitively and selectively. When DPP1 was combined with Ag NPs and reacted with tetrabutylammonium fluoride or inorganic fluoride in aqueous samples, an obvious Raman enhancement was obtained at the excitation wavelength of 633nm. This response arises because the introduction of fluoride anions into the system changes the molecular orientation of DPP1 on the Ag NP substrate from horizontal to vertical, inducing a signal enhancement in the Raman spectrum. This system can detect inorganic fluoride at concentrations as low as 1.0μmolL−1 (0.018ppm), which is far below the public health service recommended levels for drinking water (0.7–1.2ppm). Furthermore, using the proposed method, a linear response for fluoride in the concentration range of 1.0 × 10−3–1.0 × 10−6molL−1 was obtained, which makes fluoride detection possible in practical samples, such as fluoride-containing toothpaste.

Highly birefringent, highly negative dispersion compensating photonic crystal fiber.

A triangular lattice dispersion compensating photonic crystal fiber is presented in this paper. The fiber produces high birefringence and operates at fundamental mode only. The full vector finite element method with a perfectly matched absorbing layer boundary condition is applied to investigate the guiding properties of the proposed fiber. The designed fiber demonstrates that it is possible to obtain a very large negative dispersion of -9486.1 ps/(nm·km) at 1550nm wavelength with a negative dispersion more than -7000 ps/(nm·km) over the entire C-band (1530-1565nm), which is suitable for broadband dispersion compensation. The birefringence is about 4.13×10-2 at 1550nm wavelength, which is also very high. All these properties make this fiber very suitable in the area of broadband dispersion compensation and polarization-maintaining applications.

Effect of back reflectors on photon absorption in thin-film amorphous silicon solar cells

In thin-film solar cells, the photocurrent conversion productivity can be distinctly boosted-up utilizing a proper back reflector. Herein, the impact of different smooth and textured back reflectors was explored and effectuated to study the optical phenomena with interface engineering strategies and characteristics of transparent contacts. A unique type of wet-chemically textured glass-substrate 3D etching mask used in superstrate (p–i–n) amorphous silicon-based solar cell along with legitimated back reflector permits joining the standard light-trapping methodologies, which are utilized to upgrade the energy conversion efficiency (ECE). To investigate the optical and electrical properties of solar cell structure, the optical simulations in three-dimensional measurements (3D) were performed utilizing finite-difference time-domain (FDTD) technique. This design methodology allows to determine the power losses, quantum efficiencies, and short-circuit current densities of various layers in such solar cell. The short-circuit current densities for different reflectors were varied from 11.50 to 13.27 and 13.81 to 16.36 mA/cm2 for the smooth and pyramidal textured solar cells, individually. Contrasted with the comparable flat reference cell, the short-circuit current density of textured solar cell was increased by around 24%, and most extreme outer quantum efficiencies rose from 79 to 86.5%. The photon absorption was fundamentally improved in the spectral region from 600 to 800 nm with no decrease of photocurrent shorter than 600-nm wavelength. Therefore, these optimized designs will help to build the effective plans next-generation amorphous silicon-based solar cells.

Analysis of zero dispersion shift and supercontinuum generation at near IR in circular photonic crystal fibers

In this paper, we engineered a Circular PCF having a very low confinement loss and high nonlinear coefficient, from five Circular PCFs of same ring separation value. From the analysis, it is derived that the zero dispersion wavelengths can be shifted by increasing the d/R ratio. Analysis of light propagation fiber characteristics such as confinement loss, effective mode area, non linear coefficient, numerical aperture and chromatic dispersion of silica core circular photonic crystal fibers have been investigated by full vector finite element method. Simulation results show that, the magnitude of confinement loss can be reduced to a value of 5.5012×10−6dB/km at the operating wavelength 1550nm for the structure with d/R=0.8 and the corresponding effective mode area is 3.78046μm2 and nonlinear coefficient is 0.03313km−1W−1. C-PCFs with small air hole diameter show flat chromatic dispersion response over the wavelength region 1400nm to 1800nm. In addition to tight light confinement and Gaussian output over the entire operating wavelengths, we have simulated the Supercontinuum generation in the d/R=0.8 fiber for different coupled power.

N × N Reconfigurable Nonblocking Polymer/Silica Hybrid Planar Optical Switch Matrix Based on Total-Internal-Reflection Effect

We present a reconfigurable model for N × N non-blocking optical switch matrix (OSM) constituted by N(N-1)/2 2 × 2 thermo-optic polymer/silica hybrid total-internal-reflection switch elements. The number of the elements in the general model is reduced by about 50% compared to the reported all nonblocking OSM, in addition, the proposed model is more compact in footprint and more power-efficient. Each element consists of crossed multimode polymer/silica hybrid waveguides and a heater electrode at the switching node. A switching power of 53.9 mW is required at 1550-nm wavelength to drop the crosstalk below -28.0 dB. Measurements result in a rise time of 421.5/410.1 μs (O1/O2), a fall time of 534.2/464.6 μs (O1 /O2), and crosstalk of -27.6 and -29.1 dB under cross state and bar state, respectively. Subtracting coupling losses, propagation losses of the device under cross state and bar state are about 1.0 and 1.8 dB, respectively. The fabricated 3 × 3 and 4 × 4 reconfigurable non-blocking OSMs using three and six switch elements at sizes of 16.0 mm × 6.8 mm and 26.0 mm × 6.8 mm all show excellent switching performances, and the insertion losses are less than 3.6 and 7.2 dB, respectively.

Thermalization of one-dimensional photon gas and thermal lasers in erbium-doped fibers.

We demonstrate thermalization and Bose-Einstein (BE) distribution of photons in standard erbium-doped fibers (edf) in a broad spectral range up to ~200nm at the 1550nm wavelength regime. Our measurements were done at a room temperature ~300K and 77K. It is a special demonstration of thermalization of photons in fiber cavities and even in open fibers. They are one-dimensional (1D), meters-long, with low finesse, high loss and small capture fraction of the spontaneous emission. Moreover, we find in the edf cavities coexistence of thermal-equilibrium (TE) and thermal lasing without an overall inversion (T-LWI). The experimental results are supported by a theoretical analysis based on the rate equations.

Optimized design and fabrication of polymer/silica thermo-optic switch with low power consumption.

In this paper, the power-consumption characteristics of a polymeric thermo-optic (TO) switch consisting of a silica under-cladding on silicon substrate, a polymer core surrounded with polymer upper-cladding, and aluminum heating electrodes with different widths were investigated. Norland optical adhesive 73 with a larger TO coefficient was selected as the core layer, which could reduce the power consumption effectively. The silica under-cladding, with large thermal conductivity, could shorten the response time. The influences of the heating electrode width and the air trench structure on the power consumption of the device were systemically studied. A device with different widths of electrodes was fabricated by using conventional semiconductor fabrication techniques and measured with the planar optical waveguide testing system. Under 1550-nm wavelength, the power consumption of the device would be reduced from 23.27 to 4.35 mW, while the heating electrode width was decreased from 25 to 7 μm. Furthermore, it would be reduced to 1.7 mW after the air trench structure was employed. The switching time of the device was also measured, which was about 200 μs.

Optofluidic refractive index sensor based on air-suspended SU‐8 grating couplers

This work presents the design, numerical simulation, fabrication and characterization of a label-free optofluidic refractive index sensor that is based on air-suspended SU‐8 grating couplers. By exploiting a polymer-onto-polymer lamination method for thin structured SU‐8 films, waveguide grating couplers can be fabricated in a film on top of a microfluidic channel system. A capillary force valve, integrated into the microchannels, precisely positions the employed test analytes, which are different DI water based sugar solutions, below the sensing grating coupler. By performing numerical simulations, the sensing grating coupler is optimized to a center wavelength of 1550nm in the case that pure DI water (n=1.33) is applied to the microfluidic channel. When a supported mode, guided in the waveguide, reaches the sensing grating region, it is exposed to the test solution resulting in a change of the effective refractive index of the mode. Similar to the simulation results, the experimental characterization of the sensor structure demonstrates a refractive index sensitivity of approximately 400nm per refractive index unit (RIU) with respect to the wavelength shift of the grating coupler response, and 17dBRIU‐1 with respect to the intensity decrease at the individual center wavelengths for refractive index variations between n=1.33 and n=1.36. Due to the combination of microfluidic channels and air-suspended grating couplers, analytes can directly be probed in-line in an integrated microfluidic channel making the presented principle suitable for low-cost, in-line polymer optofluidic and photonic sensing applications.

Durability-reinforced electrochromic device based on surface-confined Ti-doped V2O5 and solution-phase viologen

A novel durability-reinforced electrochromic device (ECD) is described, in which the electrochromic materials remain in different physical form. Solution-phase ethyl viologen is used as the working electrochromic material, and modified Ti-doped V2O5 is utilized as counter electrochromic material. Electrochromic and spectral performances of the device are recorded here. The ECD shows good electrochromic performances in the visible and utraviolet region. Particularly, it’s worth mentioning that the ECD could work for 250,000 cycles at 60°C, with transmittance of 70% and 8% between bleached and colored states at the wavelength of 600nm, which shows remarkable long term stability. The excellent durability are mainly attributed to the reasonable choice of matching states and durability reinforced Ti-V2O5 film: the color change, charge capacity and switching speed of the viologen solution could be controlled through adjusting the concentration, and the addition of Ti provides excellent stability due to the distorted V2O5 layer structure.

Fabrication and characterization of polycrystalline Ho:CaF2 transparent ceramics for 2.0 μm laser application

In this paper, high optical quality of Ho:CaF2 (2at%) transparent ceramics based on nanopowders were fabricated by hot-pressed method successfully. Ho:CaF2 ceramics with the average size of about 500nm were obtained at 800°C for 1h. The transmittance of the sample measured to be 89% at the wavelength of 1300nm. The reduced transmittance in the near-IR range is likely due to the residual pores in the ceramics. The spectral properties of Ho:CaF2 ceramics demonstrated that there is a strong emission peak around 2030nm under the excitation of 640nm.

A SPICE Compatible Model of Graphene/Silicon Schottky Barrier Photodiode

In this work, a theoretical analysis is presented for the photo-response studies of graphene/silicon Schottky barrier type diodes. A computed 238.8 W-1 photocurrent to dark current ratio normalized by the power source (633nm wavelength and 10mW laser) is obtained. An equivalent circuit model of the graphene/silicon Schottky barrier diode compatible with SPICE simulation is developed and simulated photo-response characteristics are presented using analog behavior modeling which are in close agreement with the theoretical analysis.

Design and Simulation of Top Illuminated InGaAs PIN Photodetector for Millimeter-Wave Applications

This paper proposed a newdesign of top illuminated PIN photodetector at 1550nm wavelength for millimeter-wave applications. Device topology, structure and fabrication methods were considered in designing the photodetector. The combination material of InP/InGaAsP/InGaAs/InGaAsP was used in designing the top illuminated PIN photodetector. This PIN photodetector was targeted to produce at least 0.60A/W of responsivity with a dark current of <100nA. The design, layout, and electrical characteristics of this photodetector were carried out using SILVACO TCAD tool. The simulated results show higher responsivity value than targeted, device frequency response of -3dBm at 40GHz with targeted dark current achievable within the wavelength absorption bands specification. The results are compared with similar designs from other reported works.

Investigations on photoluminescence enhancement of poly(vinyl alcohol)-encapsulated Mn-doped ZnS quantum dots

In our work, we focused on the photoluminescence (PL) enhancement of poly(vinyl alcohol) (PVA)-encapsulated Mn2+-doped zinc sulfide quantum dots (ZnS:Mn2+ QDs) synthesized at 80°C in basic aqueous solutions. The structural, morphological and optical properties were investigated using characterization techniques such as X-ray powder diffraction (XRD), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), UV–vis absorption and photoluminescence (PL) spectroscopy. According to the results of UV–vis absorption spectra, the optical bandgap of the quantum dots was higher than that of the bulk ZnS due to the quantum confinement effect. The studied result showed that the Mn2+ 4T1 → 6A1 emission intensity at the wavelength of 600nm significantly increased with the increase of Mn2+ doping content and reached its maximum value at the Mn2+ concentration of 4.5%. In addition, the effect of PVA/Zn2+ molar ratio on the PL enhancement of PVA-encapsulated Mn2+-doped ZnS quantum dots also was systematically investigated and explained in this paper. The studied results indicated the energy transfer process from the ZnS host lattice and PVA capping molecules to Mn2+ centers is more efficient at the optimal PVA/Zn2+ molar ratio of 3 × 10−4. Furthermore, a mechanism for the formation of the PVA-encapsulated Mn2+-doped ZnS quantum has also been suggested in this study.

Negative Wigner function at telecommunication wavelength from homodyne detection

Quantum states of light having a Wigner function with negative values represent a key resource in quantum communication and quantum information processing. Here, we present the generation of such a state at the telecommunication wavelength of 1550nm. The state is generated by means of photon subtraction from a weakly squeezed vacuum state and is heralded by the `click' of a single photon counter. Balanced homodyne detection is applied to reconstruct the Wigner function, also yielding the state's photon number distribution. The heralding photons are frequency up-converted to 532nm to allow for the use of a room-temperature (silicon) avalanche photo diode. The Wigner function reads W(0,0)=-0.063 +/- 0.004 at the origin of phase space, which certifies negativity with more than 15 standard deviations.

Simulation on the dynamic flow and heat and mass transfer of a liquid column induced by the IR laser photothermal effect actuated evaporation in a microchannel

The photothermal effect induced evaporation in microchannels is a typical phenomenon in optofluidics, which greatly affects the performance of this type microdevice. In this study, the dynamic flow and heat and mass transfer characteristics of a liquid column induced by an IR laser with the wavelength of 1550nm in a microchannel is numerically studied. The results show that the Marangoni convection is caused by the non-uniform temperature distribution arising from a local heating source of the IR laser. The intensity of the Marangoni convection is weak at the beginning because the spontaneous evaporation is dominant. With the laser heating going on, the intensity of the Marangoni convection becomes strong and then weak again due to the competition between the photothermal effect and increased vapor pressure. It is also found that the heat transfer coefficient at the interface and Biot number decrease with the laser heating time because the increased vapor pressure in the gas phase resists the evaporation. Due to the same reason, although the evaporation mainly relies on the spontaneous evaporation at the beginning, the evaporation rate is the highest and then gradually decreases with the laser heating time and finally becomes relatively stable. Correspondingly, the mass transfer coefficient at the interface is also gradually decreased with the laser heating time. Besides, the effects of the laser power and air humidity are also studied. It is shown that the evaporation rate increases with increasing the laser power and decreasing the air humidity.