Working Wavelength Range Research Articles

Waveguide Schottky photodetector with tunable barrier based on Ti3C2T x /p-Si van der Waals heterojunction

Abstract MXene, a new advanced two-dimensional material, has attracted great attention in energy storage, transparent electrodes, and electromagnetic shielding due to its high conductivity, high specific surface area, and hydrophilic surface. Given the solution-processability and tunable work function, MXene also holds great potential for wide-range photodetection and integrated optics. Here, we demonstrate a waveguide integrated Schottky photodetector based on Ti3C2T x /Si van der Waals heterojunction. Specifically, the barrier of the Schottky photodetector can be adjusted by using simple surface treatment. The work function of the Ti3C2T x is reduced from 4.66 to 4.43 eV after vacuum annealing, and the barrier height of Ti3C2T x /p-Si Schottky junction is correspondingly increased from 0.64 to 0.72 eV, leading to 215 nm working wavelength blue-shift. The photodetector exhibits working wavelength tunability in short-wavelength infrared regions due to the engineered Schottky barrier. To our best knowledge, this is the first demonstration of utilizing MXene in waveguide-integrated photodetection, showing the potential applications for various scenarios thanks to the flexible working wavelength range induced by the tunable barrier.

Minimizing surface reflectance of crystalline silicon: A simulation based study

Silicon has been a popular choice for optoelectronic devices and solar cells since its discovery mainly due to its abundance in nature. However, methods to improve light trapping and hence increase the efficiency of these devices has always been a subject of great interest. The objective of this study has been to minimize the surface reflectance of thin film silicon through use of anti-reflection coating and surface patterning. In this study, the most effective anti-reflectance coating (ARC) is determined amongst three well known materials namely, Silicon Nitride(Si3N4), Titanium Dioxide(TiO2) and Magnesium Fluoride (MgF2) by simulation through S4 software by implementing Rigorous Coupled Wave Analysis Algorithm (RCWA). The best possible combination of the substrate and ARC is determined for a working wavelength range of 300 nm to 900 nm by varying the thickness of ARC. The best possible combination of substrate and ARC has been subjected to further investigation by imparting patterns and minimum average reflectance of 0.135986 was obtained experimentally.

Low-crosstalk and fabrication-tolerant four-channel CWDM filter based on dispersion-engineered Mach-Zehnder interferometers.

The O-band coarse wavelength-division (de)multiplexing (CWDM) has been extensively used in data-center optical communications, whereas it's still challenging to reduce crosstalk and enhance fabrication tolerances for a CWDM filter. In this paper, we propose and experimentally demonstrate a low-crosstalk and fabrication-tolerant four-channel CWDM filter by utilizing dispersion-engineered Mach-Zehnder interferometers. The multi-sectional phase shifters are exploited to eliminate the phase errors induced by width deviations, leading to ultra-precise phase shifts and ultra-large width-error tolerances. The random-phase errors are also inhibited by using multi-mode waveguides as phase-shifting sections. The two-stage-coupler scheme is utilized to flatten the strong coupling-ratio dispersions for directional couplers, so that low crosstalk can be achieved over the whole O-band. The experimental results show both low insertion losses (< 1.2 dB) and low crosstalk (< -22.2 dB) over the whole working wavelength range. The measured width-error tolerance is also as large as ≈ 70 nm.

Cascaded dual-channel fiber SPR temperature sensor based on liquid and solid encapsulations* *Project supported by the National Natural Science Foundation of China (Grant No. 61705025), the Natural Science Foundation of Heilongjiang Province, China (Grant No. F2018027), partially supported by Chongqing Natural Science Foundation (Grant Nos. cstc2019jcyj-msxmX0431 and cstc2018jcyjAX0817), the Science and Technology Project Affiliated to the Education Department of Chongqing

In order to control the working wavelength range of the fiber surface plasmon resonance (SPR) temperature sensor and realize the wavelength division multiplexing type multi-channel fiber SPR temperature sensor, by comprehensively investigating the influence of liquids with different thermal-optical coefficients and solid packaging materials on the performance of fiber SPR temperature sensor, a dual-channel fiber SPR temperature sensor based on liquid–solid cascade encapsulation was designed and fabricated. The liquid temperature sensing stage encapsulated in capillary worked in 616.03 nm–639.05 nm band, the solid sensing stage coated with pouring sealant worked in 719.37 nm–825.27 nm band, and the two stages were cascaded to form a fiber dual-channel temperature sensor. The testing results indicated that when the temperature range was 35 °C–95 °C, the sensitivity of two-stage temperature detection was –0.384 nm/°C and –1.765 nm/°C respectively. The proposed fiber sensor has simple fabrication and excellent performance which can be widely used in various fields of dual-channel temperature measurement and temperature compensation.

Study on the Laser Beam Polarization Based on LabVIEW

With the wide application of laser technology in laser processing and photoelectric detection, the measurement and display of the laser beam polarization has become an extremely important prerequisite. In this paper, we realize the laser polarization measurement tool based on the virtual instrument LabVIEW software platform. The set-up is designated to measure the Stokes parameters for an arbitrarily polarized beam, using the rotating waveplate method provided by the stepper motor, drive circuit, photodetector, and computer processing of the digitized electrical signal in the PCI expansion card. The Poincare sphere is used for the interpretation of the state of polarization (SOP) and degree of polarization (DOP). The working wavelength range is declared to be 400 – 1100 nm, the accuracy of DOP, azimuth measurement, and ellipticity are ±2%, 0.4°, and 0.4°, respectively.

A High-Speed Spectral Pyrometer Based on a Kolibri-2 Spectrometer

The operating speed of commercially available spectral-ratio pyrometers and brightness pyrometers often appears insufficient for control of a fast-changing temperature (e.g., in a graphite cell of an AAS electrothermal atomizer, whose temperature increases at a rate of 104 °C/s). An advantage of spectral pyrometers is high speed and ability to measure the temperature of objects with unknown emissivity. The goal of this work is to develop a high-speed spectral pyrometer based on a Kolibri-2 spectrometer with a BLPP-2000 photodetector array that provides a working wavelength range of 400–1050 nm and a minimum basic exposure time of 0.4 ms. The temperature was calculated by plotting the emission spectrum of the object in Wien coordinates (with allowance for calibration of the spectral pyrometer using a radiation source of known temperature) and by measuring the slope angle of the obtained graph. The relative error of temperature measurements with a spectral pyrometer estimated by comparing the measurement results and the data obtained with a calibrated Termokont-TN5S1M single-channel pyrometer (Termokont company) was no more than 1.5% in a temperature range of 1000–2400°C and higher and the operating speed was up to 2500 measurements/s. The results of measuring the temperature of the graphite cell in the electrothermal atomizer using a spectral pyrometer during sample atomization at a rate of the temperature increase up to 10 000°C/s are presented.

Influence of Working Temperature on the InSb/Si Heterojunction Photodetectors Performance

Traditional silicon-based photodetectors are limited by the band gap of silicon, which results in a limited working wavelength range. In this report, due to the excellent properties of Indium Antimonide, the InSb/Si heterojunction photodetectors are fabricated. Under ambient temperature of 280K, as-prepared photodetectors show a specific detectivity of 9.31011 cm Hz1/2/W, responsivity of 54 mA/W, on/off ratio of 5104 under the laser irradiation of 635 nm. In order to explore the influence of working temperature on device performance, the photoresponse at different temperatures was tested. This report proved that as the working temperature increases, the responsivity and specific detectivity of the device decrease, and the performance of the device becomes worse.

Miniature Broadband NIR Spectrometer Based on FR4 Electromagnetic Scanning Micro-Grating.

This paper presents a miniaturized, broadband near-infrared (NIR) spectrometer with a flame-retardant 4 (FR4)-based scanning micrograte. A 90° off-axis parabolic mirror and a crossed Czerny–Turner structure were used for creating an astigmatism-free optical system design. The optical system of the spectrometer consists of a 90° off-axis parabolic mirror, an FR4-based scanning micrograte, and a two-color indium gallium arsenide (InGaAs) diode with a crossed Czerny–Turner structure optical design. We used a wide exit slit and an off-axis parabolic mirror with a short focal length to improve the signal-to-noise ratio (SNR) of the full spectrum. We enabled a miniaturized design for the spectrometer by utilizing a novel FR4 micrograte for spectral dispersion and spatial scanning. The spectrometer can detect the full near-infrared spectrum while only using a two-color InGaAs diode, and thus, the grating scanning angle of this spectrometer is small when compared to a dual-detector-based spectrometer. In addition, the angle signal can be obtained through an angle sensor, which is integrated into the scanning micrograte. The real-time angle signal is used to form a closed-loop control over the scanning micrograte and calibrate the spectral signal. Finally, a series of tests was performed. The experimental results showed that the spectrometer has a working wavelength range of 800–2500 nm. The resolution is 10 nm at a wavelength range of 800–1650 nm and 15 nm at a wavelength range of 1650–2500 nm. Similarly, the stability of these two wavelength ranges is better than ±1 nm and ±2 nm, respectively. The spectrometer’s volume is 80 × 75 × 65 mm3 and its weight is 0.5 kg. The maximum spectral fluctuation does not exceed 1.5% and the signal-to-noise ratio is 284 after only one instance of averaging.

Characterization of the ASTRONIRCAM Spectral Mode

The algorithm for the reduction of spectroscopic observations with the ASTRONIRCAM camera-spectrograph installed at the 2.5-m telescope of the Sternberg Astronomical Institute of the Moscow State University is described. The instrument allows spectra of astronomical objects with long ( $$280^{\prime\prime}$$ ) and short ( $$10^{\prime\prime}$$ ) slits to be taken in the wavelength range from 1 to 2.5 $$\mu$$ m. The measured resolution reaches $$R=1270$$ for a $$0\overset{{}^{\prime\prime}}{.}9$$ slit; the light efficiency of the system changes from 6 to $$14\%$$ in the working wavelength range in the long-slit mode and from 1 to $$2\%$$ in the cross-dispersion mode. The transmission is limited by the quality of the grisms used. We have estimated the fraction of scattered light and studied the mechanical flexures and temperature drifts of the structure.

Low-loss and broadband fiber-to-chip coupler by 3D fabrication on a silicon photonic platform

We propose and demonstrate a low-loss fiber-to-chip vertical coupler on the silicon photonic platform by using a 3D two-photon fabrication method. Such a coupler significantly reduces insertion loss, measured to be 1 dB, and provides a wide working wavelength range for both TE and TM polarizations over the entire C-band. Moreover, a large tolerance for misalignment of the coupling fiber, up to 4.5 µm for a 1 dB loss, enables the development of relaxed alignment techniques.

Photocatalytic Degradation of Rhodamine B Dye by TiO2 and Gold Nanoparticles Supported on a Floating Porous Polydimethylsiloxane Sponge under Ultraviolet and Visible Light Irradiation.

A combination of plasmonic nanoparticles (NPs) with semiconductor photocatalysts, called plasmonic photocatalysts, can be a good candidate for highly efficient photocatalysts using broadband solar light because it can greatly enhance overall photocatalytic efficiency by extending the working wavelength range of light from ultraviolet (UV) to visible. In particular, fixation of plasmonic photocatalysts on a floating porous substrate can have additional advantages for their recycling after water treatment. Here, we report on a floating porous plasmonic photocatalyst based on a polydimethylsiloxane (PDMS)–TiO2–gold (Au) composite sponge, in which TiO2 and Au NPs are simultaneously immobilized on the surface of interconnected pores in the PDMS sponge. This can be easily fabricated by a simple sugar-template method with TiO2 NPs and in situ reduction of Au NPs by the PDMS without extra chemicals. Its ability to decompose the organic pollutant rhodamine B in water was tested under UV and visible light, respectively. The results showed highly enhanced photocatalytic activity under both UV and visible light compared to the PDMS–TiO2 sponge and the PDMS–Au sponge. Furthermore, its recyclability was also demonstrated for multiple cycles. The simplicity of fabrication and high photocatalytic performance of our PDMS–TiO2–Au sponge can be promising in environmental applications to treat water pollution.

Broadband multi-wavelength optical sensing based on photothermal effect of 2D MXene films

Abstract Two-dimensional (2D) materials were widely used in sensing owing to the tunable physical or chemical properties. For years, optical sensing attracted a massive amount of attention on account of high accuracy, high security, non-invasive measurement, and strong anti-interference ability. Among the various optical sensing schemes, multi-wavelength optical sensing (MWOS) is an important branch and widely adopted in optical image, spectroscopy, or bio/chemical research. However, no spectral selectivity, limited working wavelength range, or intrinsic instability makes conventional 2D materials unsuitable for MWOS. A new class of 2D materials, known as MXene, exhibits outstanding electronic, optical, and thermal properties, leading to new applications in optical sensing. In this paper, we propose an integrated photothermal optical sensor (PHOS) using Ti3C2Tx MXene films. Thanks to the inherent spectral dependence of Ti3C2Tx MXene over a broadband range, the proposed PHOS can respond to different wavelengths from visible to short-wavelength infrared. Because of the efficient photothermal conversion, the PHOS has a control efficiency up to 0.19 π · mW−1 · mm−1 under 980-nm laser pumping and shows a higher control efficiency under red light (690 nm) irradiation. The measured response time of the proposed PHOS is 23.4 μs. This paper brings MXene into chip-integrated optical sensing fields for the first time and shows the potential applications.

Electrically tunable temporal imaging in a graphene-based waveguide

We propose an electrically tunable temporal imaging system (TIS) based on four-wave mixing in a dispersion engineered graphene-based waveguide, which could realize a magnification factor of 1000× for a signal consisting of two 100-fs-wide pulses separated by 500 fs and a large working bandwidth of about 700 nm. The TIS was analyzed by solving the couple-mode equations in detail. It was demonstrated that the working wavelength range could be tuned via a small disturbed bias voltage applied to the graphene layer without changing the geometric structure of the waveguide. These results provide attractive insights for potential applications in integrated optics and optical communications.

Aspects of the directional synthesis of carbon nanotubes to create hierarchical radio-absorbing composite materials

The conducted information review showed that there are various types of radio absorbing materials. The expansion of the working wavelength range for radio-absorbing composites is possible due to the combined use of conductive fillers, characterized by different magnetic and dielectric characteristics and the value of electrical conductivity. As a rule, the increase in the efficiency of radio absorption of materials is associated with an increase in the concentration of metal fillers in them, as a result of which the weight and size parameters increase proportionally. To avoid this, the use of carbon nanomaterials, which have the ability to create self-organizing hierarchical structures in the bulk of the composite, allows. Varying the composition of the catalytic systems of the CVD process allows directional synthesis of carbon nanomaterials with the necessary morphological characteristics. To assess the effect of the composition of the catalyst on the morphology and structure of the synthesized CNTs, 3 Ni / MgO catalyst compositions with different contents of the active component (Ni) were selected. The effectiveness of the obtained catalysts was determined by the specific yield of CNTs (gC/gkat). The morphology and structure of the catalysts and the synthesized CNTs were studied by means of scanning electron microscopy (a Hitachi H-800 transmission electron microscope). CNTs were additionally examined by transmission electron microscopy (a Hitachi H-800 transmission electron microscope). The use of a nickel-based catalyst provides the material with magnetic properties. The diameter of carbon filiform formations synthesized on Ni/0.16MgO and Ni / 0.3MgO catalysts is ~ 30 ? 60 nm. The Ni/0.5MgO system is characterized by low productivity in one-dimensional nanostructures; the sample after the CVD process contains a large number of unstructured forms of carbon and an unchanged catalyst. Structural diversity in carbon nanomaterials allows to obtain on their basis an effective hierarchical structure in the radio absorbing composite..

Laser spot image acquisition and processing based on LabVIEW

With the wide application of laser technology in various fields, how to quickly and quantitatively evaluate the characteristic parameters of laser spot becomes a hot issue in laser technology research. In this paper, based on the virtual instrument LabVIEW platform, the image is captured by USB camera, the NI-IMAQdx module is used for programming.Through image acquisition, gradation transformation, filtering processing, threshold segmentation and edge detection, the pseudo-color transformation display, centroid, long and short axis values and ellipticity of laser spot intensity are obtained, the corresponding display level is 0–256, and the working wavelength range is 400 nm–1100 nm, which satisfies the testing and analysis requirements in most current environments.

Theoretical Design of Plasmonic Refractive Index Sensor Based on the Fixed Band Detection

In this paper, we theoretically and numerically reported a simple plasmonic sensor design for the accurate detection of refractive index (RI). The sensing property was characterized by a derived theoretical model, which demonstrated the accurate sensing by measuring the intensity of a fixed narrow passband. It was found that the coupling phase modulation caused by the analyte was the main mechanism of the plasmonic sensing. The main advantage of this sensor design was that the sensing response band (or resonance wavelength) was fixed and narrow, even when the RI of analyte increases. Thus, an optical detector with certain working wavelength range can be used to detect the wide range of the RI, this was also confirmed by a two times narrower range than the common used approach in detecting the same analyte. The specific sensor design and the results may provide some guidance for the integrated plasmonic sensor design and make the sensor more flexible in the RI detecting.

High-speed spectral pyrometer based on a «Kolibri-2» spectrometer

The operation speed of commercially available spectral-ratio pyrometers and brightness pyrometers often appears insufficient for control of fast-changing temperature (e.g., in a graphite cell of an AES electrothermal atomizer, the rate temperature change is 104°C/sec). An advantage of spectral pyrometers is high speed and ability to measure the temperature of objects with unknown emissivity. The goal of this study is to develop a high-speed spectral pyrometer based on a «Kolibri-2» spectrometer with BLPP-2000 photodetector array that provides a wide working wavelength range 400 – 1050 nm, and minimum basic exposure time of 0.4 msec. The temperature was calculated by plotting the emission spectrum of the object in Wien coordinates (with allowance for calibration of the spectral pyrometer using radiation source of the known temperature) and measuring slope of the obtained graph. The relative error of temperature measurements on a spectral pyrometer estimated by comparing measurement results and data obtained with a calibrated Termokont-TN5S1M (Termokont company) single-channel pyrometer was not more than 1.5% in a temperature range of 1000 — 2400°C and higher, and rapidity up to 2500 measurements/sec. The results of measuring temperature of the graphite cell of the electrothermal atomizer using a spectral pyrometer during sample atomization at a rate of temperature change up to 10 000°C/sec are presented.

A high speed optical modulator based on graphene-on-graphene hybrid nanophotonic waveguide

Using an important feature of the hybrid graphene nanophotonic waveguide that TM and TE modes residing in two separated areas, we design a TE mode modulator and optimize its performance by tuning the ridge width and the low index layer height. Furthermore, the essential parameters including the insertion loss, the modulation depth, the bandwidth and figure of merit have been investigated. Our designed modulator demonstrates a 3-dB modulation depth with extra-small dimension (2 μm × 1.1 μm × 12.17 μm) and then a small footprint (0.5 μm × 12.17 μm) can be achieved. In addition, the modulator offers a broad working wavelength range and 80 GHz high modulation bandwidth upon the energy 108.8 fJ/bit.

Post-Integrated Dual-Core Large-End Spot-Size Converter With Si Vertical Taper for Fiber Butt-Coupling to Si-Photonics Chip

We experimentally demonstrated a post-integrated dual-core spot-size converter (SSC) that had a coupling end with a 10-μm diameter at the edge of an Si-photonics chip. Although there was an extra loss increase as a result of post-integration, it can be reduced and, thus, the SSC is a promising candidate for practical use. The large coupling end enabled the SSC to be butt-coupled to a single mode fiber (SMF) theoretically at an optical loss of less than 0.7 dB, and post-integration of the SSC allowed us to apply complementary metal-oxide-semiconductor technologies to optoelectronic circuits on wafers before the SSC forming process. We attached the SSC to a 1.5-μm-thick Si rib waveguide. The observed near field patterns of light from the SSC were close to that of an SMF independently of light polarizations. The working wavelength range spanned more than 100 nm. The excess loss caused by the post-integration process was estimated to be 1 dB.

Stability of MIR transmittance of silver and thallium halide optical fibres in ionizating β- and γ-radiation from nuclear reactors

In this paper we investigated spectral transmission of irradiated IR fibres derived from single crystals of AgCl-AgBr and AgBr-TlI solid solutions. The fibres were exposed to β- and γ-radiation. The highest absorbed dose was 500 kGy. It was found that even modest radiation doses cause a reduction in transmission in AgCl-AgBr fibres within the entire working wavelength range, while for AgBr-TlI fibres the irradiation causes an increase in transmission when compared to corresponding values of non-irradiated fibres at wavelengths of 4–6 µm. We proposed a mechanism of this radiation-induced translucence and we expect that this phenomenon may be used for improvement of optical fibres. Additionally, we investigated how the transmission of AgCl-AgBr irradiated fibres depends on time after irradiation. Summarizing, both kinds of the fibres are suitable for applications in high radiation environments, for example, as a probe in on-line remote IR spectroscopy.