A low-loss LNOI edge coupler fabricated on 4-inch wafer with deep ultraviolet lithography was demonstrated. The coupler was fabricated on LNOI with 600 nm thin-film lithium-niobate by 180nm lithography and ICP etch process. The 600nm thin-film lithium-niobate was etched for three times to achieve the coupler with tri-layer structure and narrow taper tips of below 150 nm. The fiber to chip coupling loss is 0.84 dB and 1.3 dB per facet for TE light at 1550 nm, when coupled with lensed fibers, which have 4 μm and 3.5 μm mode field diameter, respectively. Furthermore, the coupling loss is less than 1 dB per facet in the wavelength range between 1520 to 1560 nm.
Photonic nanostructures have achieved nanoscale optical field modulation and ultra-low refractive index effects that traditional thin film materials cannot reach, providing a new direction for optical management and carrier management of photovoltaic devices. Dielectric nanostructures can reduce the surface light reflection of photovoltaic devices, similar to traditional antireflection films. Therefore, dielectric nanostructures are usually equivalent to the equivalent refractive index theory at the macro level. However, the macroscopic refractive index equivalent cannot reflect the manipulation ability of nanoscale light fields, and the influence of the nanoscale light field distribution on the photo-carrier generation and transport is usually ignored. Here, we introduce the self-assembly process of dielectric nanostructures on photovoltaic devices, which may lead to the controllable assembly of the density and number of layers on polycrystalline silicon solar cells. Based on this strategy, we investigate the enhancement effect of SiO2 nanosphere coating on textured silicon solar cells by systematically changing assembly conditions. Research has found that tightly packed SiO2 nanosphere monolayers generate a maximum relative efficiency improvement of 9.35%. This efficiency increase is attributed to the simultaneous enhancement of short-circuit current density and fill factor, which is different from the antireflection effect reported previously. Further, through semiconductor simulations, we theoretically analyzed the impact of nanoscale light focusing on the performance of photovoltaic devices. We explored the reasons for the changes in photocurrent, fill factor, and efficiency, providing ideas for more efficient nanoscale light focusing design and improving the performance of photovoltaic devices in the future.
Interface plays an important role in photovoltaic devices, due to the existence of surface defects and surface dangling bonds of semiconductor materials. For photovoltaic devices, defects on the surface of semiconductor materials can lead to the recombination of charge carriers at the interface and hinder the transport of carriers in the device, resulting in the degradation of device performance. We presented a simple and efficient method of interface treatment by oxygen plasma for PEDOT:PSS/silicon hybrid solar cell. Compared to the cell without oxygen plasma treatment, the cell with oxygen plasma treatment revealed a significant increase in power conversion efficiency (PCE), which resulted in interface control by oxygen plasma control can be able to effectively optimize the performance of organic-silicon hybrid solar cell.
Displacement sensor is one of the most important measuring instruments in many automated systems. We demonstrated an integrated optical displacement sensor based on an asymmetric Mach–Zehnder interferometer chip on a flexible substrate. The sensing chip was made of polymer materials and fabricated by lithography and lift-off techniques. Measured results show that the device has a loss of less than 5 dB and a potential sensitivity of about 0.105 rad/μm with quite a large space for promotion. The sensor has advantages of antielectromagnetic interference, high reliability and stability, simple preparing process, and low cost; it will occupy an important place in displacement sensors.
We proposed and theoretically investigated a ring resonator-based traveling-wave electro-optic modulator integrated with asymmetric Mach–Zehnder interferometer (AMZI). The AMZI improved the modulation sensitivity and response of the modulator. A 2.93-fold increase in modulation sensitivity was achieved when compared with conventional Mach–Zehnder (MZ) modulators. A traveling-wave analysis of this modulator was presented for the first time. The simulation results showed that the modulator had superior performance compared to conventional ring modulators and MZ modulators. A modulation up to 275 GHz was achieved in the presence of both microwave loss and velocity mismatch.
The tunable and amazing properties of plasmonic nanostructures have received significant attentions in the fields of solar energy conversion. Plasmonic nanostructures provide pathways to directly convert solar energy into electric energy by hot-carrier generation. They can also serve as economical electrodes for high-efficient carrier collection. Both have promising potential for manufacturing new generation solar cells. Here, we review recent advances in plasmonic nanostructures for electronic designs of photovoltaic devices and specially focus on plasmonic hot-carrier photovoltaic architectures and plasmonic electrode structures. Technical challenges toward low-cost and high-performance plasmonics-based solar cells are also discussed.
In this paper, Polyurethane-imide (PUI) which has the advantages of polyurethane and polyimide is synthesized and
introduced to apply in the slab optical waveguide devices. The PUI is characterized by infrared spectrum (FT-IR),
differential scanning calorimeter (DSC) and thermal gravimetric analysis (TGA). Slab optical waveguide is prepared via
spin coating the cyclopentanone solution of PUI on top of K9 glass and cured at 140 °C for 20 minutes to complete
removal of the solvent from the film. The film-formability of PUI is characterized by atomic force microscope (AFM).
The results of DSC and TGA indicate that the PUI exhibits high thermal stability up to its glass-transition temperature
(Tg) of 206 °C and 10% heat loss temperature of 310°C. Optical properties of absorption behavior and propagation loss
are investigated in slab waveguides, and propagation loss of 1.782 dB/cm at 1310nm in TE (transverse electric field)
mode has been achieved by using prism-coupler method. The results show that polyurethane-imide has distinct merits:
good processability, high thermal stability and moderate glass-transition temperature, excellent film-formability, and low
propagation loss. These advantages of polyurethane-imides make them suitable as electro-optic polymeric materials in
integrated optics.
A novel polycarbonate (PC) was introduced to apply in the optical waveguide devices. PC has following distinct merits
than common polycarbonate: good processability, high thermal stability up to 293 C°; and high optical transparency.
Optical properties of absorption behavior and propagation loss were investigated in slab waveguides, and low
propagation losses of 0.335 dB/cm (@1550nm) and 0.197 dB/cm @632.8nm) have been achieved by using prismcoupler.
Additionally, straight optical waveguide and MMI coupler of ring resonator were fabricated using ultraviolet
(UV) cured resin Norland optical adhesive 61 (NOA61) as under or upper cladding layer and polycarbonate as
waveguide core-layer material through conventional methods such as spin coating, photolithography and reactive ion
etching (RIE). The process was studied in detail and the experimental results were given.
Waveguide ring resonators are key elemental devices for wavelength filters, optical switches, lasers and optical sensors.
In order to control the finesse and notch depth of the resonator, the coupling ratio needs to be varied widely and
accurately. A novel thermooptic polymer ring resonator integrated with a tunable directional coupler was theoretical
analyzed. Polymer materials with different thermooptic coefficients were chosen as the core and cladding layers of
waveguides. The structure of the directional coupler was optimized to achieve large tuning range of coupling ratio. The
finesse, notch depth and the resonant frequency peak of the resonator can be controlled precisely by temperature. The
coupled-mode theory (CMD) and beam propagation method (BPM) were used to simulate the characteristics of the
tunable directional coupler. The transmission spectra and loss characteristic of the resonator are also discussed in detail.
This device can be used to improve the performance of integrated optical gyroscope (IOG) and other resonator-based
photonic integrated circuits.
A series of novel fluorinated polyimides second-order nonlinear optical (NLO) materials were synthesized from poly(hydroxy-imide)s, followed by the Mitsunobu reaction with NLO thiazolylazo chromophores. The polyimides prepared were characterized by IR, UV-vis, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetric analysis (DSC) and X-ray diffraction (XRD). These NLO polyimides possess high glass transition temperature (Tg) in the range of 193-200 °C with thermal stability up to 288 °C. The electro-optic coefficients (r33) at the wavelength of 1550nm for polymer thin films poled were measured by the attenuated total reflection (ATR) method. The r33 values of the polyimides 1a and 2a containing thiazolylazoaniline chromophore are better than that of the polyimides 1b and 2b attached thiazolylazopyrimidine chromophore, due to the thiazolylazoaniline chromophore having large hyperpolarizability in contrast to the thiazolylazopyrimidine chromophore. Low optical losses (1.8-2.1 dB/cm at 1.55 μm), which were measured via an immersion technique have been observed for these polymers. The polyimides demonstrate an excellent combination of thermal stability, electrooptic (EO) coefficients and optical loss, and therefore they are suitable for EO applications.
Analytical method for curved optical waveguides plays an important role in dealing with integrated optical devices based on curved optical waveguides. It helps us not only in understanding physical mechanism of waveguides deeply but also in improving performance of existing integrated devices and designing novel elements. Bend loss of curved optical waveguides is always a problem to be focused on. In order to reduce bend loss of curved optical waveguides, a number of strategies have been used. In this paper, we proposed a new method to analyze curved optical waveguides, which combined the conformal transformation method with ray optical method. An intuitionistic physical image of bend loss in optical waveguides was founded from this point of view, then the reason of bend loss was clearly shown. Accordingly, a new strategy to reduce bend loss in curved optical waveguides was given. Compared with general strategies of modifying the refractive indices whatever in core or cladding, the present strategy is totally deferent. This strategy is beneficial to decrease the radiation of propagation modes in curved optical waveguides by increasing the thickness of curved waveguides. Especially, it is more effective in situations that the radius of curvature of the waveguides and the refractive indices of materials were set beforehand. Software simulation based on BPM was used simultaneously as supplemental verification of this new strategy. Moreover, as an example with this strategy, a special design of ring waveguides structure was given.
Ring resonator is a key unit of integrated optical waveguide gyroscope. Generally the Finite Difference Time Domain (FDTD) method is used to analyze the microscopic ring resonator, but this method can not be used to deal with the ring resonator in optical waveguide gyroscope, because the size of the model is too large (the radius of ring resonator is 10 mm). In this paper, an accurate method was demonstrated to design the ring resonator, in which the model was analyzed by together with the Beam Propagation Method (BPM), guided-wave optics and the theory of multiple-beam interference. In this method, the ring resonator was divided into two parts, the coupler and the bend waveguide, and the phase condition of optimum resonance was updated, the phase shift caused by the length of bend waveguide was added upon the propagation phase shift of the coupler. Parameters such as insertion loss y; coupler coefficient k; phase shift of the coupler; the propagation constant β, and the bending radiation loss of bend waveguide were obtained accurately by this method. Through the vector analysis, the intensity of resonance of the ring resonator was calculated, and the characteristics of ring resonator were shown. At the end of this paper, the optimization fabrication of optical waveguide resonator was discussed.
Solid state optical gyrometer is a novel integrated optical gyrometer which consists of a waveguide coil fully integrated on a substrate. The planar coil design implies waveguide crossings, so called X-junction. X-junctions are loss generating. In this paper, the power loss of X-junction is simulated by beam propagation method. The relationship between the power loss and the intersection angle is illustrated, and the power coupling corresponded with the intersection angle is given. The simulation shows the power loss due to the X-junction could be neglected by increasing the intersection angle properly.
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