Optical Transmission Loss Research Articles

Impact of low-pressure glow-discharge-pulsed plasma polymerization on properties of polyaniline thin films

This study reports on polyaniline thin films deposited on a glass substrate using a low-pressure glow-discharge-pulsed plasma polymerization method. The polyaniline thin film obtained by pulsed plasma polymerization has been successfully demonstrated as an optical waveguide with a transmission loss of 3.93 dB cm−1, and has the potential to be employed in integrated optics. An attempt has been made to investigate the effect of plasma OFF-time on the structural, optical as well as surface properties of polyaniline thin film. The plasma ON-time has been kept constant and the plasma OFF-time has been varied throughout the work. The plasma OFF-time strongly influenced the properties of the polyaniline thin film, and a nanostructured and compact surface was revealed in the morphological studies. The plasma OFF-time was found to enhance film thickness, roughness, refractive index and optical transmission loss, whereas it reduced the optical band gap of the polyaniline thin films. Retention in the aromatic structure was confirmed by FTIR results. Optical studies revealed a π-π* electronic transition at about 317 nm as well as the formation of a branched structure. As compared with continuous wave plasma, pulsed plasma polymerization shows better properties. Pulsed plasma polymerization reduced the roughness of the film from 1.2 nm to 0.42 nm and the optical transmission loss from 6.56 dB cm−1 to 3.39 dB cm−1.

A Robust Distributed Multipoint Fiber Optic Gas Sensor System Based on AGC Amplifier Structure.

A harsh environment-oriented distributed multipoint fiber optic gas sensor system realized by automatic gain control (AGC) technology is proposed. To improve the photoelectric signal reliability, the electronic variable gain can be modified in real time by an AGC closed-loop feedback structure to compensate for optical transmission loss which is caused by the fiber bend loss or other reasons. The deviation of the system based on AGC structure is below 4.02% when photoelectric signal decays due to fiber bending loss for bending radius of 5 mm, which is 20 times lower than the ordinary differential system. In addition, the AGC circuit with the same electric parameters can keep the baseline intensity of signals in different channels of the distributed multipoint sensor system at the same level. This avoids repetitive calibrations and streamlines the installation process.

射流水波导表面轮廓特性对传输损耗的影响

射流水波导表面轮廓特性对传输损耗的影响

Investigation of optical transmission loss by using a plasmonic Au nanoparticle assembly on a tapered fiber region

The optical transmission loss in a tapered fiber fabricated by using plasmonic Au nanoparticle deposition was investigated in the tapered region of the fiber. The amount of Au nanoparticle deposition was determined as a function of time, and the transmission loss was then compared with the losses of several spatial modes. The higher-order mode was found to affect the rate of increase in the transmission loss during the initial period of deposition, and a lower-order mode was found to contribute to the process during the latter period of deposition.

Combining novel device architecture and NIR dye towards the fabrication of transparent conductive oxide-less tandem dye sensitized solar cells

Tandem solar cells with different device architectures utilizing a back contact transparent conductive oxide-less bottom electrode (TCO-less tandem DSSC) that has better control of the optical transmission losses incurred by intermediate TCO layers with flexible Pt/tin-doped indium oxide (ITO)-polyethylene terephthalate film as an intermediate layer are reported. The proposed device architecture suppresses the optical loss to a greater extent (around 30%). Sensitizers were ruthenium-based N719 dye in the top electrode, while the newly synthesized phthalocyanine dye (PC25) corresponding to photon harvesting in the near infrared (NIR) region (up to 900 nm) was used in the TCO-less bottom cell. Open circuit voltage (Voc) ≥ 1.18 V (sum of top cell and bottom cell Voc) justifies the TCO-less tandem DSSC formation.

A preliminary study of direct 10Be2+ counting in AMS using the super-halogen anion BeF3−

The key to effective 10Be measurements by AMS is to efficiently suppress the interference of the isobar 10B and at the same time optimize 10Be transmission. In this work, a new approach of measuring 10Be by AMS has been studied. It uses the super-halogen anion of beryllium, BeF3−, which inherently suppresses 10B interference by nearly 5 orders of magnitude because the accompanying BF3− anion is rarely formed. The resulting 10B suppression factor is not as high as that achieved with energy degrader foils, but the 10B and 10Be separation in the final ionization detector was found to result in sufficient total 10B suppression for 10Be2+ to be counted directly at ∼6MeV energies. Although the stripping yield from 10BeF3− to 10Be2+ is not as large as that from 10BeO−, this inefficiency is compensated by avoiding the reduction in transmission due to charge fraction splitting and optical transmission losses after the degrader foil. This paper summarizes our first observation of the direct 10Be2+ counting approach using the 3MV multi-element system at the Xi’an AMS.

Optimized design and fabrication of nanosecond response electro–optic switch based on ultraviolet-curable polymers**Project supported by the National Natural Science Foundation of China (Grant Nos. 61177027, 61107019, 61205032, and 61261130586).

A nanosecond response waveguide electro-optic (EO) switch based on ultraviolet (UV) sensitive polymers of Norland optical adhesive (NOA73) and Dispersed Red 1 (DR1) doped SU-8 (DR1/SU-8) is designed and fabricated. The absorption properties, refractive indexes, and surface morphologies of NOA73 film are characterized. The single-mode transmission condition is computed by the effective index method, and the percentage of optical field distributed in EO layer is optimized to be 93.78 %. By means of spin-coating, thermal evaporation, photolithography, and inductively coupled plasma etching, a Mach–Zehnder inverted-rib waveguide EO switch with micro-strip line electrode is fabricated on a silicon substrate. Scanning electron microscope characterization proves the physic-chemical compatibility between NOA73 cladding and DR1/SU-8 core material. The optical transmission loss of the fabricated switch is measured to be 2.5 dB/cm. The rise time and fall time of switching are 3.199 ns and 2.559 ns, respectively. These results indicate that the inverted-rib wave-guide based on UV-curable polymers can effectively reduce the optical transmission loss and improve the time response performance of an EO switch.

Low loss, long time stable sol–gel derived silica–titania waveguide films

Silica–titania waveguide films were fabricated via the sol–gel method using dip-coating technique. Chemical uniformity, surface morphology, thickness and refractive index as well as optical transmission losses were investigated. The investigations show, that fabricated silica–titania waveguide films of high refractive index (~1.8) are uniform, very smooth (rms~0.298nm) and exhibit ultra low optical transmission losses (below 0.2dB/cm), constancy through over five years.

PN-type carrier-induced filter with modulatable extinction ratio.

We demonstrate the first PN-type carrier-induced silicon waveguide Bragg grating filter on a SOI wafer. The optical extinction ratio of this kind of filter can be efficiently modulated under both reverse and forward biases. The carrier-induced Bragg grating based on a PN junction is fabricated on the silicon waveguide using litho compensation technology. The measured optical bandwidth and the extinction ratio of the filter are 0.45 nm and 19 dB, respectively. The optical extinction ratio modulation under the reverse bias is more than 11.5 dB and it is more than 10 dB under the forward bias. Only 1-dB optical transmission loss is realized in this Bragg grating under a reverse bias. The shifting rates of the central wavelength under forward and reverse biases are ~-1.25 nm/V and 0.01 nm/V, respectively. The 3-dB modulation bandwidth of this filter is 5.1 GHz at a bias of -10 V.

Selective growth and integration of silver nanoparticles on silver nanowires at room conditions for transparent nano-network electrode.

Recently, metal nanowires have received great research interests due to their potential as next-generation flexible transparent electrodes. While great efforts have been devoted to develop enabling nanowire electrodes, reduced contact resistance of the metal nanowires and improved electrical stability under continuous bias operation are key issues for practical applications. Here, we propose and demonstrate an approach through a low-cost, robust, room temperature and room atmosphere process to fabricate a conductive silver nano-network comprising silver nanowires and silver nanoparticles. To be more specific, silver nanoparticles are selectively grown and chemically integrated in situ at the junction where silver nanowires meet. The site-selective growth of silver nanoparticles is achieved by a plasmon-induced chemical reaction using a simple light source at very low optical power density. Compared to silver nanowire electrodes without chemical treatment, we observe tremendous conductivity improvement in our silver nano-networks, while the loss in optical transmission is negligible. Furthermore, the silver nano-networks exhibit superior electrical stability under continuous bias operation compared to silver nanowire electrodes formed by thermal annealing. Interestingly, our silver nano-network is readily peeled off in water, which can be easily transferred to other substrates and devices for versatile applications. We demonstrate the feasibly transferrable silver conductive nano-network as the top electrode in organic solar cells. Consequently, the transparent and conductive silver nano-networks formed by our approach would be an excellent candidate for various applications in optoelectronics and electronics.

Optimization of a polymer four-port microring optical router with three channel wavelengths

Optimization and simulation are performed for a polymer four-port microring optical router with three channel wavelengths, which contains four-group basic routing elements with two different ring radii. In terms of microring resonance theory, coupled mode theory and transfer matrix method, expressions of output power of basic routing element and optical router are derived. In order to realize single-mode propagation, low optical transmission loss and phase match between microring waveguide and channel waveguide, the device parameters are optimized. With the selected three channel wavelengths of 1550 nm, 1552 nm and 1554 nm, characteristics are calculated and analyzed, including output spectrum, insertion loss and crosstalk. Simulation results indicate that the device has 12 possible I/O routing paths, the insertion losses of three channel wavelengths along their routing paths are within the range of 0.02–0.61 dB, the maximum crosstalk between the on-port along each routing path and other off-ports is less than −39 dB, and the device footprint size is ∼0.13 mm2. Based on the proposed structure, through proper selection on ring radius, the routing structure can also be used for other channel wavelengths. Therefore, the designed structure shows wide applications in integrated optical networks-on-chip (NoC).

Ageing and vapor chopping effect on the properties of MgO thin films

Nanoscale magnesium oxide thin films have been prepared on glass substrates by thermal oxidation (in air) of vacuum evaporated magnesium films. The ageing (air exposure) effect for 1, 10, 20 and 30days on the various properties of MgO thin films was studied. The ageing effect on the optoelectronic devices i.e. optical waveguide and plasma display panel’s performance was examined by measuring their optical transmission loss and secondary electron emission yield, respectively. Vapor chopping technique was employed for thin film quality improvement followed by ageing inhibition. The firing voltage for fresh vapor chopped (VC) MgO thin films was in 125–150V range, which shifted to 140–178V after 30days, whereas in the non-chopped (NC) films it increased up to 165–210V from 140–160V. After 30days ageing, NC thin film surface morphology changed from polished to dull due to wrapped moisture like layer, whereas VC thin film morphology was unpretentious. The XPS analysis also confirmed the VC MgO thin films superior sustainability against the ageing than NC films.

Low drive voltage optical phase modulator with novel InGaAlAs/InAlAs multiple-quantum-barrier based n-i-n heterostructure

An optical phase modulator based on novel n-i-n InGaAlAs/InAlAs multiple-quantum-barrier (MQBs) is proposed to reduce the waveguide loss and enhance the modulation efficiency. Efficient bias loading with low leakage current is realized by taking advantages of the large conduction band discontinuity in InGaAlAs/InAlAs heterostructure and high electron reflection by MQBs. Low optical transmission loss of 2.3 dB/cm and improved modulation performance with a voltage length product of 1.06 V⋅cm are demonstrated for TE mode at 1550 nm. The linear and quadratic electro-optic coefficients of the fabricated device are estimated to be 1.0 pm/V and 1.4 × 10⁻¹⁹ m²/V², respectively.

Process Control of Cantilever Deflection for Sensor Application Based on Optical Waveguides

This paper reports on the fabrication of cantilever silicon-on-insulator (SOI) optical waveguides and presents solutions to the challenges of using a very thin 260-nm active silicon layer in the SOI structure to enable single-transverse-mode operation of the waveguide with minimal optical transmission losses. In particular, to ameliorate the anchor effect caused by the mean stress difference between the active silicon layer and buried oxide layer, a cantilever flattening process based on Ar plasma treatment is developed and presented. Vertical deflections of 0.5 μm for 70-μm-long cantilevers are mitigated to within few nanometers. Experimental investigations of cantilever mechanical resonance characteristics confirm the absence of significant detrimental side effects. Optical and mechanical modeling is extensively used to supplement experimental observations. This approach can satisfy the requirements for on-chip simultaneous readout of many integrated cantilever sensors in which the displacement or resonant frequency changes induced by analyte absorption are measured using an optical-waveguide-based division multiplexed system.

An Optical Actuation System and Curvature Sensor for a MR-compatible Active Needle.

A side optical actuation method is presented for a slender MR-compatible active needle. The needle includes an active region with a shape memory alloy (SMA) wire actuator, where the wire generates a contraction force when optically heated by a laser delivered though optical fibers, producing needle tip bending. A prototype, with multiple side heating spots, demonstrates twice as fast an initial response compared to fiber tip heating when 0.8 W of optical power is applied. A single-ended optical sensor with a gold reflector is also presented to measure the curvature as a function of optical transmission loss. Preliminary tests with the sensor prototype demonstrate approximately linear response and a repeatable signal, independent of the bending history.

3-D integrated heterogeneous intra-chip free-space optical interconnect

This paper presents the first chip-scale demonstration of an intra-chip free-space optical interconnect (FSOI) we recently proposed. This interconnect system provides point-to-point free-space optical links between any two communication nodes, and hence constructs an all-to-all intra-chip communication fabric, which can be extended for inter-chip communications as well. Unlike electrical and other waveguide-based optical interconnects, FSOI exhibits low latency, high energy efficiency, and large bandwidth density, and hence can significantly improve the performance of future many-core chips. In this paper, we evaluate the performance of the proposed FSOI interconnect, and compare it to a waveguide-based optical interconnect with wavelength division multiplexing (WDM). It shows that the FSOI system can achieve significantly lower loss and higher energy efficiency than the WDM system, even with optimistic assumptions for the latter. A 1×1-cm2 chip prototype is fabricated on a germanium substrate with integrated photodetectors. Commercial 850-nm GaAs vertical-cavity-surface-emitting-lasers (VCSELs) and fabricated fused silica microlenses are 3-D integrated on top of the substrate. At 1.4-cm distance, the measured optical transmission loss is 5 dB, the crosstalk is less than -20 dB, and the electrical-to-electrical bandwidth is 3.3 GHz. The latter is mainly limited by the 5-GHz VCSEL.

An optical analysis tool for avoiding dust formation in very-high frequency hydrogen diluted silane plasmas at low substrate temperatures

Control of the formation of dust particles in a silane deposition plasma is very important for avoiding electrical shunts in devices, such as thin film silicon solar cells. In this work we present a noninvasive in situ method for identification of the plasma regime, based on optical emission spectroscopy (OES), which can be applied to silane/hydrogen plasmas at low substrate temperatures. By monitoring the OES spectra as a function of the position perpendicular to the plasma electrodes we developed a method to identify the transition of a plasma from the dust free to a dusty regime, which was confirmed by TEM images of layers deposited in both regimes. Using this technique we mapped this transition as a function of applied forward very-high frequency (VHF) power and hydrogen dilution at different substrate temperatures. The advantage of this technique is that the experiment is insensitive to optical transmission loss at the viewport due to deposition of silicon films. As the transition from the dust free to the dusty regime is substrate temperature dependent and the transition from amorphous to nanocrystalline growth mainly depends on hydrogen dilution, a limited parameter window has been defined in which dust-free amorphous silicon can be deposited at low substrate temperatures. A single simple OES technique can be used for in situ monitoring of amorphous to nanocrystalline transition as well as the onset of the dusty regime in a thin film silicon cell fabrication process.

Characterization of Si nanowaveguide line edge roughness and its effect on light transmission

Abstract The manufacture of low-loss silicon-on-insulator (SOI) photonic wires for telecommunication wavelengths (∼1.55 μm) is a challenge. Side wall and line edge roughness (LER) are the dominant sources of scattering loss. In this work the characterization of Si nanowaveguide (NW) LER was performed and its effect on light transmission was theoretically analyzed and measured. NW structures with a width of 0.5 μm and height of 0.22 μm were prepared using different thickness of hard-mask and plasma etch process technologies on SOI platforms. LER determination was performed by critical-dimension scanning electron microscope (CD-SEM), conventional atomic force microscope (AFM) and 3D-AFM. The characterization of LER quality was carried out by monitoring of its RMS deviation σ , main frequencies and correlation length L c . The effect of sampling length was evaluated. The data for σ from 0.8 to 6 nm and L c from 20 to 50 nm were found to be dependent mostly on etch process technology. Theoretical simulation of scattering loss due to LER based on the 2D analytical model for planar waveguides was performed. Finally, the correlation between NW optical transmission (scattering) losses (TL) and LER was obtained and can be applied to future technology development. Especially for the case of σ ∼ 0.85 nm and L c ∼ 20 nm the lowest value of TL ∼ 1.2 dB/cm was measured at a wavelength of 1.55 μm. Good qualitative agreement between calculated and measured losses due to LER was found.

High-Order Distortion in Directly Modulated Semiconductor Lasers in High-Loss Analog Optical Links With Large RF Dynamic Range

A theoretical and experimental investigation of the effects of high-order nonlinear distortion products produced by directly modulated semiconductor lasers on the performance of high-loss analog optical communication links requiring large RF dynamic range is reported. In order to provide sufficient RF dynamic range to support radio services in links with high optical transmission loss, for example in radio over free-space optics (RoFSO), while keeping costs low, it is necessary to use directly modulated lasers. However, in these applications the lasers must be driven to high modulation depths to maximize dynamic range. Simulations show that under these unique conditions the first detectable nonlinear distortion is often the result of dynamic distortion due to the laser being driven near threshold. It is shown that this type of distortion is characterized by a sharp increase in the contribution of high-order (fourth order or greater) nonlinear terms resulting from the influence of laser relaxation oscillations. As a consequence, the third-order spurious-free dynamic range (SFDR) metric no longer accurately reflects the performance of such links as it assumes that third order effects are dominant. An alternative measure of dynamic range called dynamic-distortion-free dynamic range (DDFDR) is proposed. This differs in that the upper limit is defined as the modulating power at which the peak optical modulation index (OMI) reaches unity. At this point the error vector magnitude (EVM) measured for a range of different wireless services starts to increase rapidly due to high order distortion. This makes DDFDR a practical, service-independent metric of dynamic range. For two different wireless services it is observed experimentally that on average the DDFDR upper limit predicts the EVM knee point to within 1.1 dB, while the third-order SFDR predicts it to within 6.2 dB. The DDFDR is thus shown to be a more accurate indicator of real link performance when high-order distortion is dominant.

The Study of the Dual-Wavelength Fiber-Optic Temperature Sensor

A new dual-wavelength optic-fiber temperature sensor is introduced in this paper. Transmitted probe of this sensor system is designed. LED IR880 and LED IR940 which peak wavelength is 880nm and 950nm are used as the survey light source and the reference light source of the sensor system. So the infection from the changes of the optical fiber transmission loss, the temperature effect of the temperature probe and the optical detector excursion of the sensor can be eliminated. The accuracy and stability of the temperature sensor can be improved and the cost of temperature sensor can be reduced.