Waveguide Wavelength Research Articles

Multipoint temperature measurement system composed of fiber-optic Fabry–Perot interference sensors and a wavelength-division multiplexing filter

A multipoint optical-fiber remote temperature measurement system was developed using reflection-type sensors consisting of a Fabry–Perot interference (FPI) structure with good temperature characteristics combined with a wavelength-division multiplexing (WDM) filter. The FPI sensor was fabricated using a short temperature-sensing region sandwiched between single-mode fibers. FPI optical fibers and a WDM filter functioned as the temperature sensors and wavelength-selective optical source using an amplified spontaneous emission light source, respectively. This system was operated in a dense WDM configuration using an arrayed waveguide wavelength filter.

Computer-aided design of quadra-ridged waveguide transformers for full-band matching of half-height rectangular waveguides

A quadra-ridged waveguide transformer (QRWT) is proposed for full-band matching between a standard waveguide and a half-height waveguide, which meets the need for compact waveguide components and the need for multiple sections of irregular transmission lines for better matching in wider operation bands. Unlike conventional matching circuits with monotonically changing impedances, QRWTs form abrupt cross-section changes between transmission line steps. The initial configuration of QRWT is built by CST MICROWAVE STUDIO, a system-level electromagnetic compatibility and general high frequency passive device simulation software, according to the basic electromagnetic (EM) concept and then is optimized by optimization functions from an advanced EM simulator, during the optimization, releasing restrictions as many as possible. To explain the concept, a sample QRWT is designed to match a standard rectangular waveguide WR34 to a half-height waveguide. The reflection coefficient is less than −24 dB in the full operation bandwidth, from 21.7 to 33 GHz. The optimized QRWT has a length of 3.088 mm, 0.218 times the waveguide wavelength at its center operation frequency of 27.35 GHz. For comparison, a two-stage quarter-wave transformer matching circuit is optimized. For similar reflection coefficients in the same bandwidth, the QRWT has a length 57% shorter than the conventional one, and it has an easier manufacturing method using wire-electrode cutting. To verify the design, a back-to-back matching circuit was fabricated using brass material without extra dielectric material. Its measured reflections are less than −16.6 dB, and the insertion loss is less than 0.2 dB.

Low-loss silicon nitride photonic ICs for near-infrared wavelength bandwidth.

Low-loss photonic integrated circuits (PICs) are the key elements in future quantum technologies, nonlinear photonics and neural networks. The low-loss photonic circuits technology targeting C-band application is well established across multi-project wafer (MPW) fabs, whereas near-infrared (NIR) PICs suitable for the state-of-the-art single-photon sources are still underdeveloped. Here, we report the labs-scale process optimization and optical characterization of low-loss tunable photonic integrated circuits for single-photon applications. We demonstrate the lowest propagation losses to the date (as low as 0.55 dB/cm at 925 nm wavelength) in single-mode silicon nitride submicron waveguides (220×550 nm). This performance is achieved due to advanced e-beam lithography and inductively coupled plasma reactive ion etching steps which yields waveguides vertical sidewalls with down to 0.85 nm sidewall roughness. These results provide a chip-scale low-loss PIC platform that could be even further improved with high quality SiO2 cladding, chemical-mechanical polishing and multistep annealing for extra-strict single-photon applications.

Highly Sensitive Micro-Opto-Electromechanical Systems Accelerometer Based on MIM Waveguide Wavelength Modulation

In this article, a novel micro-opto-electro- mechanical system (MOEMS) accelerometer sensor based on metal–insulator–metal (MIM) waveguide wavelength modulation is proposed. The device senses the vibration signal of external acceleration by the mechanical sensing system and uses the MIM waveguide in the optical sensing system to sense the displacement of the mechanical vibration component to cause the change of the light wavelength. The characteristics of the optical sensing system and the mechanical sensing system of the MOEMS accelerometer are analyzed by the finite-difference time-domain (FDTD) and finite-element analysis (FEA) methods, respectively. The simulation results show that the proposed accelerometer sensor has an optical system sensitivity of up to 7.827 in the wavelength modulation range of 1– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12~\mu \text{m}$ </tex-math></inline-formula> , a mechanical sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.292963~\mu \text{m}$ </tex-math></inline-formula> /g, a natural frequency of 939.28 Hz, and a linear measurement range of ±4.4 g. Surprisingly, we obtained accelerometer sensitivity up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.293~\mu \text{m}$ </tex-math></inline-formula> /g and resolution up to 436.1 ng ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta \lambda ={1}$ </tex-math></inline-formula> pm). We also show the performance advantages of this accelerometer with high sensitivity and high resolution over the measurement range by comparing this MOEMS accelerometer sensor with previously reported work. Based on these performance characteristics, we expect this work to be widely used in high-precision measurements for inertial navigation.

High-sensitivity multipoint refractive index measurement system composed of multimode interference sensors and arrayed waveguide wavelength filters

A multipoint sensing measurement system with high sensitivity was developed by combining multimode interference (MMI) sensors and a wavelength selection configuration. MMI optical fibers and an arrayed waveguide (AWG) wavelength filter work as refractive index sensors and wavelength selector, respectively. They were operated with a fine calibration technique using dual AWG wavelength filters and defined wavelength light from a tunable laser source. By employing narrow-core single-mode fibers for the input and output ports of the MMI, the optical fiber improved the average sensitivity up to 820 dB/RIU under multipoint sensing conditions.

Electromagnetic modeling and simulation of the biophoton propagation in myelinated axon waveguide.

Biophotons in the nervous system are a potential carrier of neural signals. Previous experiments and studies indicated that biophotons are closely related to the neuronal activity and can propagate along myelinated axons. We establish a multilayer electromagnetic simulation model and demonstrate that the myelinated axon waveguide has low attenuation and low dispersion and operates in a narrow bandwidth on the order of 10 nm. We also find that the operating wavelength of the waveguide is almost linearly related to the axon diameter and the number of myelin layers. Each additional layer of the myelin sheath causes the operating wavelength of the myelinated axon waveguide to shift 52.3 nm to the long-wave direction, while an increase in the axon diameter of 1.0 µm causes the operating wavelength to shift 94.5 nm to the short-wave direction. These findings well explain the tendency of the spectral redshift among different species and the spectral blueshift during the aging process of mice. Via the analysis method in this paper, we can predict the wavelength of the propagating biophotons based on the neural structure.

Low-Sidelobe-Level Circularly Polarized Short Leaky-Wave Antenna With A-Shaped Element Based on Substrate Integrated Image Guide

In this letter, a low-sidelobe-level (SLL) circularly polarized (CP) leaky-wave antenna with A-shaped elements is proposed based on substrate integrated image guide (SIIG). The A-shaped CP radiating element consists of a horizontal linearly polarized (LP) structure and a vertical LP structure. The horizontal LP wave and the vertical LP wave can be excited by a pair of inclined transversal metal strip patches and a longitudinal metal strip patch, respectively. Their phases are orthogonal and amplitudes can be controlled to be equal by adjusting the tilted angle of the horizontal LP structure and the length of the vertical LP structure. Moreover, the longitudinal metal strip patch is modified to the V-shaped strip patch, which can realize the field cancellation, thereby achieving the boresight radiation for such a leaky-wave antenna. Furthermore, a low SLL is realized by controlling the aperture-field distribution to obtain the desired amplitude distribution and the relatively small axial ratio. In addition, because of the short waveguide wavelength of the SIIG, this feedline can be used to achieve the small interelement spacing and element size, thereby realizing the short length of the array. The measured peak gain of this antenna is 12.3 dBic, the SLL is &#x2013;19.1 dB and the efficiency is 92.3&#x0025; at the center frequency of 14 GHz.

Efficient and tunable blue light generation using lithium niobate nonlinear photonics

Thin-film lithium niobate (LN) has recently emerged as a playground for chip-scale nonlinear optics and leads to efficient frequency conversions from near-infrared to near-visible bands. For many nonlinear and quantum photonics applications, it is desirable to operate deep into the visible band within LN's transparency window. However, the strong material dispersion at short wavelengths makes phase-matching difficult, necessitating sub-micrometer scale control of domain structures for efficient phase-matching. Here, we report the operation of thin film LN in the blue wavelength and high fidelity poling of the thin-film LN waveguide to this regime. As a result, quasi-phase matching is realized between IR (871 nm) and blue (435.5 nm) wavelengths in a straight waveguide and prompts strong blue light generation with a conversion efficiency (1040% ± 140%/W). This blue second harmonic generator exhibits stable temperature tunability, which is important for applications that require precise frequency alignment, such as atomic clocks.

Critical Wavelength in the Metal Waveguide Partially Filled with Nonlinear Crystal

Critical Wavelength in the Metal Waveguide Partially Filled with Nonlinear Crystal

Design and Simulation of Butterfly-Shaped Filtenna with Dual Band Notch for Portable UWB Applications

A compact and low cost butterfly shaped UWB filtenna with a pair of parasitic elements and a pair of slits is proposed in this work. The filtenna is supposed to be designed on a common and low-cost FR4 substrate with overall dimensions of 26mm*20mm*1.6mm .By inserting a pair of 𝝀𝒈 /2( where𝝀𝒈 is waveguide wavelength ) D-shaped parasitic elements around the antenna feed line, the radiation of the 5 GHz WLAN applications is canceled to eliminated the interference . Furthermore, the rejection of the X-band satellite downlink is achieved by engraving a pair of 𝝀𝒈 /4 J-shaped slits on the ground plane. The simulation results exhibits the perfect coverage of the proposed filtenna for the UWB frequency band as well as the elimination of the undesired radiation within the filtenna operating band

Mosquito method based polymer tapered waveguide as a spot size converter.

We create a compact low-loss spot-size converter (SSC) which utilizes a tapered core polymer optical waveguide with circular cross-sectional graded-index (GI) core using the Mosquito method we developed. First, we theoretically analyze the mutual diffusion between the core and cladding monomers, which is a feature unique to the Mosquito method when forming GI cores. The monomer diffusion effect depends on the initial core diameter that is dispensed by a microdispenser and the diffusion time before UV curing: in a small core the monomer diffuses more rapidly than in a large core. Using this diffusion dependence on the initially dispensed core diameter, it is theoretically found that a tapered polymer waveguide based SSC can adiabatically convert the mode-field diameter between 4.0 and 8.6 μm at a 1550-nm wavelength waveguide as short as 4 mm. Next, the tapered waveguide based SSC with the designed structure is experimentally fabricated using the Mosquito method, and we confirm an 8-mm long tapered waveguide with an insertion loss of 1.83dB functions as a SSC that converts the MFD from 4.7 μm to 7.5 μm at 1550-nm wavelength.

Characterization of GeSbSe Based Slot Optical Waveguides

Background: Among various chalcogenides, GeSbSe shows a good transmittance in the visible, NIR and, midIR spectrum from 1-20 μm and also demonstrates excellent moldability. Objective: In current work, we have characterized GeSbSe glass for use in sensor mechanism and for adaptive polarization control. Methods: After analysing an earlier work regarding GeSbSe based Silicon on insulator optical waveguide, we implemented GeSbSe in a low refractive index slot region of SOI slot optical waveguide. Change in waveguide geometry can cause a shift in the dispersion profile, but a relatively distinct pattern has been observed. T-slot waveguide structure has also been analysed, where GeSbSe has been implemented in low refractive index slot regions with the Graphene layer beneath the horizontal slot region for enhancement in tailoring ability of the birefringence parameters. Results: Literature review led to the presence of absorption resonance wavelength in SOI slot optical waveguide with our proposed composition, which is attributed to the single average harmonic oscillator property of the chalcogenides. In the T-slot waveguide structure, it was found that a shift in Fermi energy and Mobility values can bring a change in birefringence, even with constant waveguide geometry and operating wavelength. Conclusion: Absorption resonance wavelength in GeSbSe slot optical waveguide has been exploited for proposing the refractive index dispersion sensor. Our design approach regarding T-slot waveguide may lead to the provision of automated polarization management sources for the light on chip circuits.

IRRADIATOR WITH MINIMAL LOSSES OF PARABOLIC ANTENNA FOR RADIO MONITORING SYSTEMS OF INFORMATION CHANNELS OF RADIO RELAY COMMUNICATION LINES

Analysis of the experience of modern struggle shows that the success of combat missions to sone extent depends on the timely detection of information from communication channels, in particular, radio relay communication lines. Increasing the detection range of the radio monitoring station can be achieved by using a mirror parabolic antenna with a radiation in the form of a conical horn with low losses due to the use of a matching device. The constructive decisions of matching devices are analysed and it is determined that most of them are resonant. The substantiation and selection of the design of the dielectric transformer with the length ( – wavelength in a round waveguide, m) for coordination of the conical horn irradiator in the whole band of its operating frequencies for the wave type is carried out. To achieve the goal, the methods of antenna theories and electrodynamics were used, in particular the theory of long lines. A mathematical apparatus has been developed for calculating the parameters of a dielectric transformer (the length ). It is stated that its impedance must be equal to the modulus of load resistance. The calculation of the value of the active transformed resistance according to the formula (10) always gives a positive value of the input resistance, the value of which is greater the greater the reactive load reactance. The reliability of the obtained formulas is confirmed by the convergence of units and graphs of dependences of the changes of the outer radius of the coaxial power line (its impedance), as well as the thickness and place of inclusion on the matching dielectric transformer . The practical significance of the research results lies in the possibility of improving the matching of a horn antenna based on a circular waveguide in the range of its operating frequencies for a certain type of wave.

Polarization insensitive silicon waveguide wavelength filter using polarization rotator and mode conversion Bragg grating with resonator cavity

We demonstrate a polarization insensitive silicon waveguide wavelength filter using a polarization rotator and Bragg grating which exchanges TE0 and TE1 modes. A resonator cavity structure is used to obtain a narrow filter peak width. Two cascaded resonator cavities are used to attain a flat top transmission wavelength peak.

Mode hybridization analysis in thin film lithium niobate strip multimode waveguides

Mode hybridization phenomenon in air-cladded X-cut Y-propagating and Z-propagating thin film lithium niobate strip multimode waveguides is numerically studied and a mathematical relation between structural parameters leading to hybrid modes is formulated. Dependence of hybrid modes on waveguide dimensions, sidewall angles and wavelength is also analyzed. The results obtained are used to design lithium niobate on insulator (LNOI) taper for converting fundamental TM mode to higher order TE mode, and an optimum length for achieving a high conversion efficiency of 99.5% is evaluated. Birefringent Y-propagating LN and isotropic Z-propagating LN tapers are compared in terms of length, figures of merit, and fabrication tolerance. Tapers exhibit a broad bandwidth of 200 nm with an extinction ratio less than − 18 dB. The results of mode hybridization analysis are useful in design optimization of adiabatic tapers, tunable time delays, optical interconnects, mode converters and demultiplexers for mode division multiplexing (MDM) applications.

Broadband high-efficiency triple-tip spot size converter for edge coupling with improved polarization insensitivity

Fiber-to-chip couplers are an essential part of the interfaces to integrated photonic devices, and high coupling efficiency over a broad wavelength range is preferred for most applications. Furthermore, couplers with low polarization dependence are also of great practical significance. While tapered waveguide couplers have been applied to overcome the mode mismatch between waveguides and fibers, the inherent geometric asymmetry of high-index-contrast waveguides, especially for those with a thick core layer, leads to polarization dependence in their performance. Here a triple-tip spot size converter as an edge coupler is proposed to improve the polarization insensitivity and coupling efficiency over a broadband range for either thick or thin waveguides. For both TE and TM polarization, it is shown that our design can have below 1 dB coupling loss over a 600 nm window around 1550 nm wavelength for Si3N4 waveguides of typical core thicknesses. Meanwhile, this kind of coupler also shows better fabrication and assembly tolerance than the traditional single-tip spot size converter (inverse taper coupler). Our proposed device can be easily fabricated in simple fabrication processes compared to other designs and have good compatibility with the standard complementary metal-oxide–semiconductor processes.

Thermo-Optic Tunable Silicon Arrayed Waveguide Grating at 2-μm Wavelength Band

The transparent window in optical fiber at 2-μm waveband enables a huge potential for fiber optical communications. Intensive efforts have been devoted to pursuit of photonic devices in this new band. The arrayed waveguide grating (AWG) is one of the key components for various functionalities like wavelength multiplexer, optical filter, spectrometer and so forth. However, the integrated and wavelength tunable AWG has not been realized in the 2-μm wavelength range yet. Here, we demonstrate an 8-channel thermo-optic tunable AWG at 2 μm via silicon photonic multi-project wafer shuttle run. The device is fully compatible with standard foundry fabrication process without customization. The TiN heater is designed for uniform waveguide heating and wavelength detuning. Experiments show that the fabricated AWG has a dense channel spacing of 1.6 nm and a minimum insertion loss of 6.1 dB. The wavelength tuning efficiency is measured to be 6.4 nm/W.

Compact four‐way quasi‐rectangular cavity power combiner with high isolation and high power‐combining efficiency

AbstractA compact four‐way quasi‐rectangular cavity power combiner with high isolation and high power‐combining efficiency is presented. The quasi‐rectangular cavity is employed to realize both impedance transformation and mode conversion. The isolation circuit based on microstrip line technique is utilized to realize high isolation. Besides, a T‐junction is established as a transition from coaxial to microstrip to realize the energy transmission between the cavity and the isolation circuit. The presented power combiner is designed, fabricated, and measured. The actual assembled device is 0.74λ × 0.74λ × 0.28λ (λ is waveguide wavelength). The measured results show the return loss of the power‐combining port is greater than 20 dB from 7.84 to 10.88 GHz (36% fractional bandwidth). The measured insertion loss is about 0.4 dB, and the power‐combining efficiency is about 90%. The measured isolation of adjacent and opposite ports is greater than 20 dB in operating frequency band.

Self-similar picosecond pulse compression for supercontinuum generation at mid-infrared wavelength in silicon strip waveguides

Self-similar pulse compression has important application in highly coherent supercontinuum (SC) generation. In this paper, we numerically present the mid-infrared self-similar picosecond pulse compression in a tapered suspended silicon strip waveguide, which is designed with exponentially decreasing dispersion profile along the direction of propagation. When the variation of the Kerr nonlinear coefficient γ(z), linear and nonlinear losses, higher-order nonlinearity, and higher-order dispersion are taken into consideration, the simulation result shows that a 1 ps input pulse centered at wavelength 2.8μm could be self-similarly compressed to 47.06 fs in a 3.9-cm waveguide taper, along with a compression factor Fc of 21.25, quality factor Qc of 0.78, and negligible pedestal. After that, the compressed pulse is launched into a uniform silicon strip waveguide, which is used for the generation of SC. We numerically demonstrate that the coherence of the generated SC by the compressed pulse can be significantly improved when compared to that generated directly by the picosecond pulse. The simulation results can be used to realize on-chip mid-infrared femtosecond light source and highly coherent supercontinuum, which can promote the development of on-chip nonlinear optics.

Reducing leakage current during periodic poling of ion-sliced x-cut MgO doped lithium niobate thin films

Ion-sliced lithium niobate thin films offer high optical confinement over their bulk counter parts, enabling compact and efficient nonlinear optics. Quasi-phase matching by periodic poling of thin film lithium niobate remains challenging, however, due to large leakage currents, especially in magnesium oxide doped lithium niobate, which is used in bulk to reduce photorefractive damage. Here we present fabrication and poling details of 700 nm thick x-cut magnesium oxide doped lithium niobate thin films using electric field poling. We introduce a silicon dioxide insulation layer under co-planar electrodes to reduce leakage current. Rounded tips are utilized to encourage nucleation at the center of the electrodes. Uniform domains with 7.5 µm period and 50% duty cycle are achieved. The poling characteristics are compared to bulk lithium niobate, with and without the silicon dioxide insulation layer. The domains are characterized by piezoresponse force microscopy, hydrofluoric etching, and waveguide second harmonic generation at 1550 nm wavelength in a thin film lithium niobate waveguide loaded with a silicon nitride strip.