Measured Wavelength Range Research Articles

Ultra-broadband and high extinction ratio silicon TM-pass polarizer based on grating-assisted antisymmetric multimode waveguide

We propose an all-silicon TM-pass polarizer using a grating-assisted antisymmetric multimode waveguide (GAMW). The GAMW design facilitates the conversion of the undesired TE0 mode into the back-reflected TE1 mode, enabling efficient transmission of the desired TM0 mode with low insertion loss (IL) and high extinction ratio (ER). Furthermore, by cascading multiple GAMW structures, the device can filter TE0 mode over a broader spectral range effectively. The simulation results indicate that the single-GAMW-based polarizer achieves IL < 0.17 dB and ER > 40 dB in the wavelength range from 1480 nm to 1620 nm. When cascaded, the device expands the bandwidth to 275 nm (1435 nm–1710 nm), maintaining IL < 1 dB and ER > 40 dB simultaneously. The bandwidth can be further improved by cascading more GAMW structures working at different central Bragg wavelength. Limited by the measuring equipment, the measured wavelength range is between [1470 nm, 1630 nm]. The results of experiment demonstrate that the fabricated single-GAMW-based polarizer achieves IL < 0.65 dB and ER > 28.4 dB in 144 nm bandwidth ranging from 1470 nm to 1614 nm. For the cascaded-GAMW-based polarizer, IL < 0.83 dB and ER > 28.8 dB is achieved throughout the entire measuring wavelength range.

Ultra-high extinction ratio polarization beam splitter using an antisymmetric grating-assisted multimode waveguide

We have proposed and demonstrated a polarization beam splitter (PBS) with an ultra-high extinction ratio (ER) utilizing an antisymmetric grating-assisted multimode waveguide (AGMW) and an asymmetric directional coupler (ADC) on a silicon-on-insulator (SOI) platform. The AGMW structure is designed to facilitate the conversion of the forward TE0 mode into the backward TE1 mode. Upon injection of the TE0 mode, it transforms into the backward TE1 mode, subsequently undergoing conversion back to a TE0 mode through the ADC and ultimately dropping out from the designated port. In contrast, the injected TM0 mode traverses the device with minimal impact. The simulation results indicate that, for the TE0 mode, a bandwidth of 70 nm with an insertion loss (IL) below 0.65 dB and an ER over 40 dB is achieved. Similarly, for the TM0 mode, the bandwidth with the IL below 0.13 dB and an ER over 40 dB is 90 nm. Experimental validation confirms that, within the measured wavelength range from 1500 to 1580 nm, the bandwidth with an ER exceeding 30 dB is 61 nm for the TE0 mode and 78 nm for the TM0 mode.

Taking into account the distribution of the noise level along the wavelength during broadband control of the deposition process of optical coatings

The paper presents numerical results of simulations of the deposition process of a complex optical coating using broadband monitoring of this process in the case when the noise level in the measured transmittance coefficient has an uneven distribution along the wavelength. The influence on the accuracy of data control at the edges of the measured wavelength range, where the error in the transmittance coefficient is maximum, is investigated. It is shown that when a part of the data is removed at the edges of the range, the self-compensation coefficient of the deposition process errors almost does not change, while the average norm of the error vector of layer thicknesses significantly decreases. Thus, it is shown for the first time that taking into account the effect of self-compensation of errors in broadband control opens up the possibility of a reasonable choice of the optimal spectral range of optical control for practice.

Ultra-broadband absorber based on photonic topological transition with large-[formula omitted] metals

We propose and experimentally demonstrate an ultra-broadband metamaterial absorber based on photonic topological transition by using metals with large real part of permittivity (ε′). The simulation results show that the absorptivity is larger than 0.9 in the wavelength range from 400 nm to 2832 nm. The simulation results also show that the absorption effect is insensitive to the incident angle and polarization. According to the effective medium theory, the ultra-broad bandwidth is originated from the photonic topological transition. In addition, the analyses reveal that the absorption bandwidths can be extended by manipulating the wavelengths of photonic topological transition (PTT) points with large-ε′ metals. Furthermore, an ultra-broadband metamaterial absorber with multilayer films is fabricated by using standard film deposition techniques. The measured results show that the absorptivity is larger than 0.9 under normal incidence over the measured wavelength range of 400–2500 nm. This metamaterial absorber is expected to be potential candidate for various applications, such as thermal photovoltaic energy conversion, detectors, and solar cells.

Prospects for detecting alternariose in potato plantings using hyperspectral measurements

The harmfulness of Alternaria leaf blight on potatoes has increased significantly in recent years in the North-West of Russia. For effective protection of potato plantings from the disease it is extremely important to detect it promptly. For that purpose the ground-based portable spectroradiometer PSR-1100 with a measurement range from 320 to 1100 nm was used. The study was conducted at the experimental station of Menkovo branch of Agrophysical research institute located in Gatchina district of Leningrad region. The result of the study revealed that even in case with a slight damage of potato plants with Alternaria leaf blight (less than 10% of the leaf surface) there were significant changes in the values of the reflectivity of potato leaves were recorded by the device in the near infrared part of the spectrum especially with severe damage to the leaf surface (25-50% of the leaf surface). At the same time there were no significant differences in the entire measured wavelength range (320-1100 nm) in plants with Alternaria leaf blight damage to 25% of the leaf surface. Thus, the detection of Alternaria leaf blight in potato plantings is practicable by means of ground-based hyperspectral measurements.

Complete characterization of RNA biomarker fingerprints using a multi-modal ATR-FTIR and SERS approach for label-free early breast cancer diagnosis.

Breast cancer is a prevalent form of cancer worldwide, and the current standard screening method, mammography, often requires invasive biopsy procedures for further assessment. Recent research has explored microRNAs (miRNAs) in circulating blood as potential biomarkers for early breast cancer diagnosis. In this study, we employed a multi-modal spectroscopy approach, combining attenuated total reflection Fourier transform infrared (ATR-FTIR) and surface-enhanced Raman scattering (SERS) to comprehensively characterize the full-spectrum fingerprints of RNA biomarkers in the blood serum of breast cancer patients. The sensitivity of conventional FTIR and Raman spectroscopy was enhanced by ATR-FTIR and SERS through the utilization of a diamond ATR crystal and silver-coated silicon nanopillars, respectively. Moreover, a wider measurement wavelength range was achieved with the multi-modal approach than with a single spectroscopic method alone. We have shown the results on 91 clinical samples, which comprised 44 malignant and 47 benign cases. Principal component analysis (PCA) was performed on the ATR-FTIR, SERS, and multi-modal data. From the peak analysis, we gained insights into biomolecular absorption and scattering-related features, which aid in the differentiation of malignant and benign samples. Applying 32 machine learning algorithms to the PCA results, we identified key molecular fingerprints and demonstrated that the multi-modal approach outperforms individual techniques, achieving higher average validation accuracy (95.1%), blind test accuracy (91.6%), specificity (94.7%), sensitivity (95.5%), and F-score (94.8%). The support vector machine (SVM) model showed the best area under the curve (AUC) characterization value of 0.9979, indicating excellent performance. These findings highlight the potential of the multi-modal spectroscopy approach as an accurate, reliable, and rapid method for distinguishing between malignant and benign breast tumors in women. Such a label-free approach holds promise for improving early breast cancer diagnosis and patient outcomes.

Inverse design of asymmetric Y-junctions for ultra-compact, broadband, and low crosstalk mode (de)multiplexers.

Asymmetric Y-junctions, compared with mode coupling-based devices, possess considerably smaller wavelength dependence and thus are more promising for ultra-broadband mode (de)multiplexing in integrated optics. However, these devices also feature relatively high mode crosstalk and insertion loss. Here, we show that the mode crosstalk and loss of an asymmetric Y-junction can be significantly reduced by optimizing the waveguide shape of the Y-junction using an adjoint-based inverse design. Based on such inverse-designed asymmetric Y-junctions, we realize ultra-compact, broadband, and low crosstalk silicon photonic TE00 & TE1 and TE0 & TE2 mode (de)multiplexers with sizes of only 4.5 × 1.2 µm2 and 6 × 1.4 µm2, respectively. From simulations it is shown that the TE0 & TE1 and TE0 & TE2 mode (de)multiplexers contain wide bandwidths of 160 nm (1460-1620 nm) and 140 nm (1460-1600 nm), respectively, over which the mode crosstalks are below about -20 dB, and the losses are <0.41 dB and <0.88 dB, respectively. The experimental results show that in the corresponding TE0 & TE1 and TE0 & TE2 mode division multiplexing systems, the crosstalks are less than -15.5 dB and -15 dB over the spectral ranges of 1453-1580 nm and 1460-1566 nm, respectively, and the losses are <1.7 dB at 1520 nm and <8.24 dB over the entire measured wavelength range.

High Accuracy Solar Diffuser BRDF Measurement for On-Board Calibration in the Solar Reflective Band

In the solar reflective band, an on-board calibration method based on a solar diffuser (SD) can realize full aperture, full field of view, and end-to-end absolute radiometric calibration of optical remote sensors. The SD’s bidirectional reflectance distribution function (BRDF) is a key parameter that affects the accuracy of the on-board calibration. High-accuracy measurement of the SD BRDF is required in the laboratory before launch. Due to the uncertainty of the goniometer system, polarization effects, and other factors, the measurement uncertainty of the SD BRDF at large incident angles is much higher than that at a 0° incident zenith angle and 45° reflection zenith angle. In this paper, an absolute BRDF measurement facility is reported. The goniometric system consists of a high-brightness integrating sphere as a radiation source, a six-axis robot arm, and a large rotation stage. The measurement wavelength range was from 350 nm to 2400 nm. An improved data processing method based on the reciprocity theorem was proposed to reduce the measurement uncertainty of the SD BRDF at large incident angles. At an incident zenith angle of 75°, the improved data processing method reduced the measurement uncertainty of the SD BRDF by 52% at 410 nm to 480 nm, by 70% at 480 nm to 1000 nm, and by 20% at other bands compared to the absolute measurement method. The influence of the radiation source, goniometer system, detection system, and other factors on the measurement uncertainty are analyzed in this paper. The results show that the measurement uncertainty (coverage factor k = 2) of the SD BRDF was better than 1.04% at 350 nm to 410 nm, 0.60% at 410 nm to 480 nm, 0.43% at 480 nm to 1000 nm, and 0.86% at 1000 nm to 2400 nm.

Weak reflectivity measurements of large-mode-area FBGs by a scale composed of a fiber Fabry-Perot interferometer.

In a previous study, we proposed a measuring method for the reflectivity of weak-reflection large-mode-area fiber Bragg gratings by using scale gratings. We experimentally found that the interference between two scale fiber Bragg gratings (FBGs) is beneficial for increasing reflectivity scales, which can improve the measurement accuracy. Therefore, in this study, we designed and fabricated FBG-based Fabry-Perot cavities (FBG-FP) in single-mode fibers by two inscription methods, namely ultraviolet (UV) laser exposure and femtosecond-laser direct writing. Then, a large-mode-area double-clad (LMA-DC) FBG of weak reflectivity was measured by these two scales, and the experimental results show that the Bragg resonance reflectivity is less than 4.28% and 1.14% ∼ 2.28%, respectively. This method of measuring the weak grating reflectivity based on FBG-FP scales is convenient, efficient, and accurate. It is also worth mentioning that the method of femtosecond-laser direct writing eliminates the period limitation of the phase mask, thereby expanding the measurement wavelength range of FBGs. In the future, with the improvement of fiber grating fabrication technology, it is expected that more accurate results can be obtained.

Ultra-compact and broadband all-silicon TM-pass power splitter using subwavelength holey-structured metamaterial waveguides.

Power splitters with polarization management features are highly desired to construct high-density silicon photonic integrated circuits. However, few attempts have been made to design a single device that can act as both a power splitter and a TE- or TM-pass polarizer. In this paper, for the first time, we experimentally demonstrate an ultra-compact and broadband all-silicon TM-pass power splitter, where a triple-guide directional coupler (TGDC) composed of three parallel subwavelength holey-structured metamaterial waveguides (SHMWs) is located at central coupling region and three regular strip waveguides are connected at the input/output ports. Such a SHMW can enhance the reflection to realize a wide stop-band for the undesired TE polarized light, while achieving the low loss transmission for the TM polarized light. Besides, the TM dispersion can be significantly flattened by the designed SHMWs, leading to a broadband power splitting for TM polarization. Simulated results show that an ultra-compact device of 1.7 × 4 µm2 in size is obtained with an insertion loss (IL) of 0.34 dB and an extinction ratio (ER) of 36 dB at 1550 nm, and its working bandwidth can be extended to ∼240 nm by keeping IL < 0.9 dB and ER > 16 dB. The measurements of the fabricated devices show low IL (<1 dB) and high ER (>15 dB) over the measured wavelength range of 1460 to 1580 nm, which is consistent with the simulation results.

A Near-Infrared pin Photodetector of Strain-Enhanced Ge Layer Epitaxially Grown on a Bonded Si-on-Quartz Wafer

In Si photonics, photodetectors (PDs) of a Ge epitaxial layer on Si have been widely used, which show a high photodetection efficiency, or a high responsivity in the O (1.260–1.360 µm) and C (1.530–1.565 µm) bands. However, an issue lies in a low responsivity in the longer wavelength range of L band (1.565–1.625 µm). In this regard, we have proposed a method using a Ge layer epitaxially grown on a Si-on-quartz (SOQ) wafer [1]. The tensile in-plane lattice strain, derived from the thermal expansion mismatch between the Ge layer and base substrate, is enhanced more than 0.3% in Ge on SOQ, despite ~0.2% on Si (or Si-on-insulator). The enhanced strain in Ge on SOQ extends the fundamental optical absorption edge to about 1.65 µm, leading to a potential increase in the L-band responsivity. In this study, a vertical pin PD is fabricated using a Ge layer on SOQ, showing an increased responsivity in the L band.A bonded SQQ wafer was used as the starting substrate, fabricated by Shin-Etsu Chemical Co. Ltd. The top Si (001) layer was 200 nm in thickness, and was heavily doped p-type by B implantation. An undoped Ge epitaxial layer (500 nm) was grown by chemical vapor deposition using GeH4 as the source gas, followed by a growth of Si cap layer (50 nm) using Si2H6. In the top region of Ge layer as well as in the Si cap layer, a heavily n-type doping was carried out by P implantation, forming a vertical pin junction. Finally, a Ti/TiN electrode was formed. Responsivity spectra were measured in the wavelength range of 1.46–1.64 µm at a normal incidence. A reference pin PD was also fabricated using a Ge layer on a standard bulk Si wafer. According to x-ray diffraction measurements, the Ge layer on SOQ showed a tensile strain of 0.33%, despite 0.14% for the reference Ge on Si.Figure 1(a) shows typical current–voltage curves for a pin diode of Ge on SOQ measured under dark and under an illumination of 1.55-µm light (1.1 mW). The diode showed a good rectifying property under dark, while under the illumination, the current in the reverse bias significantly increased, showing a reasonable PD operation. Figure 1(b) shows typical responsivity spectra at a reverse bias of 1 V for PDs of Ge on SOQ and reference Ge on Si. Circles and lines correspond to experimental data points and theoretical curves, respectively. The responsivity for Ge on SOQ was larger in the measured wavelength range of 1.46–1.64 µm, including the L band. The increased responsivity is ascribed to the enhanced tensile strain. However, the increase in the L band was found to be suppressed by a high reflectance because of the multiple reflections at the interfaces. An optimized Si cap thickness as well as an anti-reflection coating with SiO2 can increase the normal-incidence responsivity as high as 0.3 (0.1) A/W up to 1.60 (1.64) µm without an increase in the Ge thickness.[1] Noguchi et al., J. Appl. Phys. 128, 133107 (2020). Figure 1

Monitoring and Condition Assessment of Insulation Paper of Distribution Transformers With Novel Oil Spectroscopy Method

Measuring the furan concentration in transformer oil is one of the most common methods of monitoring and evaluating insulation paper and estimating its degree of polymerization (DP). Here, methods for measuring furan concentration, especially ultraviolet-visible (UV-Vis) spectroscopy method, are reviewed on the old transformers oil. The results show that the excessive turbidity of old oils and noise at low wavelengths are the main disadvantages of this method, which reduce the measurements accuracy. The following solutions are proposed to overcome these disadvantages: 1) diluting insulation oil with hexane to reduce absorption intensity and 2) using average absorption at a given wavelength to reduce noise impact. These solutions are applied to the oil samples of ten old distribution transformer. It is observed that the correlation between 2-furaldehyde (2-FAL) concentration and average absorption intensity in 190–600 nm wavelength range is equal to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{{2}} =0.98$ </tex-math></inline-formula> . A mathematical equation for calculating 2-FAL concentration based on average absorption is presented. It has been shown that to reduce the test time, a 190–400 nm range is the optimal measurement wavelength range. The results show that the average difference between the values of DP in the proposed method and the direct measurement method is equal to 77.5.

Imaging Mueller matrix ellipsometry with sub-micron resolution based on back focal plane scanning.

The development of nanotechnology and nanomaterials has put forward higher requirements and challenges for precision measurement or nanometer measurement technology. In order to cope with this situation, a new type of imaging Mueller matrix ellipsometer (IMME) has been developed. A back focal plane scanning method is designed to make the IMME have the ability to measure multiple incident angles. A two-step calibration method is proposed to ensure the measurement accuracy of IMME. After calibration, the IMME can achieve measurement with wavelengths from 410 nm to 700 nm and incident angles from 0° to 65°. The lateral resolution of the IMME is demonstrated to be 0.8 μm over the entire measurement wavelength range. In addition, a Hadamard imaging mode is proposed to significantly improve the imaging contrast compared with the Mueller matrix imaging mode. Subsequently, the IMME is applied for the measurement of isotropic and anisotropic samples. Experimental results have demonstrated that the proposed IMME has the ability to characterize materials with complex features of lateral micron-distribution, vertical nano-thickness, optical anisotropy, etc., by virtue of its advantages of high lateral resolution and high precision ellipsometric measurement.

Characterisation of SiPM Photon Emission in the Dark.

In this paper, we report on the photon emission of Silicon Photomultipliers (SiPMs) from avalanche pulses generated in dark conditions, with the main objective of better understanding the associated systematics for next-generation, large area, SiPM-based physics experiments. A new apparatus for spectral and imaging analysis was developed at TRIUMF and used to measure the light emitted by the two SiPMs considered as photo-sensor candidates for the nEXO neutrinoless double-beta decay experiment: one Fondazione Bruno Kessler (FBK) VUV-HD Low Field (LF) Low After Pulse (Low AP) (VUV-HD3) SiPM and one Hamamatsu Photonics K.K. (HPK) VUV4 Multi-Pixel Photon Counter (MPPC). Spectral measurements of their light emissions were taken with varying over-voltage in the wavelength range of 450–1020 nm. For the FBK VUV-HD3, at an over-voltage of V, we measured a secondary photon yield (number of photons () emitted per charge carrier ()) of . The emission spectrum of the FBK VUV-HD3 contains an interference pattern consistent with thin-film interference. Additionally, emission microscopy images (EMMIs) of the FBK VUV-HD3 show a small number of highly localized regions with increased light intensity (hotspots) randomly distributed over the SiPM surface area. For the HPK VUV4 MPPC, at an over-voltage of V, we measured a secondary photon yield of . In contrast to the FBK VUV-HD3, the emission spectra of the HPK VUV4 did not show an interference pattern—likely due to a thinner surface coating. The EMMIs of the HPK VUV4 also revealed a larger number of hotspots compared to the FBK VUV-HD3, especially in one of the corners of the device. The photon yield reported in this paper may be limited if compared with the one reported in previous studies due to the measurement wavelength range, which is only up to 1020 nm.

Low-loss and ultra-broadband silicon nitride angled MMI polarization splitter/combiner.

The property of self-imaging combined with the polarization birefringence of the angled multimode waveguide is used to design a silicon nitride (SiN) polarization splitter (PS) at λ ∼ 1550 nm. The demonstrated PS on a 450 nm thick SiN device layer (with 2.5 µm cladding oxide) has a footprint of 80 µm×13 µm and exhibits nearly wavelength independent performance over the C+L bands. Also, the device can be configured as a polarization combiner (PC) in reverse direction with similar bandwidth and performance. The measured crosstalk (CT) and insertion loss (IL) are respectively <-18 dB (<-20 dB) and ∼0.7 dB (∼0.8 dB) for TE (TM) polarization over the measurement wavelength range of 1525 nm ≤λ ≤ 1625 nm. The measured device parameter variations suggest some tolerance to fabrication variations. Such a device is a good candidate for a photonics integrated chip (PIC) foundry-compatible, SiN PS.

Random Fiber Grating Characterization Based on OFDR and Transfer Matrix Method.

Random fiber gratings (RFGs) have shown great potential applications in fiber sensing and random fiber lasers. However, a quantitative relationship between the degree of randomness of the RFG and its spectral response has never been analyzed. In this paper, two RFGs with different degrees of randomness are first characterized experimentally by optical frequency domain reflectometry (OFDR). Experimental results show that the high degree of randomness leads to low backscattering strength of the grating and strong strength fluctuations in the spatial domain. The local spectral response of the grating exhibits multiple peaks and a large peak wavelength variation range when its degree of randomness is high. The linewidth of its fine spectrum structures shows scaling behavior with the grating length. In order to find a quantitative relationship between the degree of randomness and spectrum property of RFG, entropy was introduced to describe the degree of randomness induced by period variation of the sub-grating. Simulation results showed that the average reflectivity of the RFG in dB scale decreased linearly with increased sub-grating entropy, when the measured wavelength range was smaller than the peak wavelength variation range of the sub-grating. The peak reflectivity of the RFG was determined by (where is the coupling coefficient, is the grating length, is period variation range of the sub-grating) rather than when is larger than 8 nm in the spatial domain. The experimental results agree well with the simulation results, which helps to optimize the RFG manufacturing processes for future applications in random fiber lasers and sensors.

Determination and analysis of linear and nonlinear optical properties and electrical conductivity of amorphous PbxGe42−xSe48Te10 thin films

Thin films of amorphous PbxGe42−xSe48Te10 (6 ≤ x ≤ 18) have been synthesized by thermal evaporation method on glass substrate. From XRD analysis, it was found that films have an amorphous nature. Different constants (absorption coefficient, α, refractive index, n, extinction coefficient, k, optical energy band gap, Eg, real and imaginary parts of dielectric constants, er and ei, as well as energy band tail, Eu) depending on composition were determined by spectrophotometric measurements in wavelength range 200 ≤ λ ≤ 2500 nm. It is found that Eg1 and Eg2 increase with increasing Pb content, but Eu decreases with the increase in Pb content. By using Wemple–DiDomenico model, dispersion energy, Ed, energy of effective dispersion oscillator, Eo, dielectric constant at infinite wavelength, e∞, and first and third order of moments, (M−1) and (M−3), can be calculated. In addition, N/m* values increase with the increase in Pb concentration. Moreover, optical (σopt) and electrical (σele) conductivity can be derived from optical measurements. Electrical conductivity, σ, was investigated at room temperature. σ decreases with rising Pb concentration and then rises. Electrical properties can be discussed on the basis of Kolobov’s proposal of modulation in defect states with the addition of Pb.

Low-cost and high-efficiency single-mode-fiber interfaces to silicon photonic circuits

A high-efficiency and large-alignment-tolerance fiber interface to silicon-on-insulator wire waveguides is introduced. A spot-size converter is built through a full three-dimensional polymer waveguide and a silicon inverse taper is employed to expand the optical mode field from a silicon sub-micro waveguide to a normal cleaved single-mode fiber with a mode size of about 10μm. The fabrication for the three-dimensional structure relies on simple spin-coating processes. The coupling loss from the fiber to the silicon waveguide through the proposed structure reaches -1.0dB for both transverse electrical and transverse magnetic modes, respectively. The polarization-dependent loss for the best coupling case is kept within -0.6dB in the whole measured wavelength range. The coupling facet of the proposed fiber interface structure is polishable and facilitates an easy package procedure with standard fiber arrays.

Polyethylene glycol: Optical constants from 191 to 1688 nm (0.735–6.491 eV) by spectroscopic ellipsometry

Polyethylene glycol (PEG) is an important polymer with numerous industrial and therapeutic applications. Accordingly, the optical constants of PEG should be a useful resource to other scientists and engineers. Herein, we report the optical functions of PEG as determined from reflection spectroscopic ellipsometry (SE) and transmission ultraviolet-visible spectroscopy. These functions were obtained from a commercial liquid sample of PEG that had a molecular weight of 285–315 g/mol. Since this sample is a liquid, the reflection and transmission measurements required special experimental considerations. The reflection SE measurements necessitated roughening (frosting) the inside of the vessel (Petri dish) that contained PEG and leveling the instrument instead of the liquid sample. The transmission measurements were obtained via a dual-cuvette approach that removed the effects of the cuvettes and their interfaces. From these measurements, the extinction coefficient of the PEG was determined between 205 and 1700 nm. Since PEG has very low absorption over the measured wavelength range, and because of the relatively wide wavelength range considered here, the refractive index was fit with a Sellmeier model for wavelengths from 191 to 1688 nm. The interface at the liquid surface was modeled with a Bruggeman effective medium approximation. The optical functions obtained in this work agree well with previously reported values. For example, we obtained the following nx values for the material, where x is the wavelength in nanometers: n300 = 1.493, n500 = 1.459, and n1000 = 1.443.

Optical function of atomic layer deposited alumina (0.5–41.0 nm) from 191 to 1688 nm by spectroscopic ellipsometry with brief literature review

Atomic layer deposition (ALD) is widely used in the semiconductor industry to provide atomic level control over film thicknesses and layer conformality. Here, the authors report the thermal (332 °C) ALD of thin amorphous alumina films (0.5–41.0 nm) deposited using water and trimethylaluminum precursors. Alumina deposition was optimized by varying the dose and purge times for both precursors with an eye toward obtaining uniform film thicknesses and constant growth per cycle. Films were characterized by x-ray photoelectron spectroscopy and spectroscopic ellipsometry (from 191 to 1688 nm). The subsequent workup of the SE data was based on a multisample analysis. It considered Cauchy and Sellmeier functions and accounted for surface roughness. This modeling yielded an optical function for ALD alumina over the measured wavelength range. The authors recommend the optical function determined from the Sellmeier model.