High Optical Coupling Efficiency Research Articles

Development of a compact NDIR CO2 gas sensor for harsh environments

We present a compact non-dispersive infrared (NDIR) gas sensor that can be adopted in high-moisture and low temperature environments. The NDIR gas sensor was formed by a Micro-Electro-Mechanical Systems (MEMS) emitter working at 400℃ with a broadband radiation spectrum, a MEMS thermopile detector that integrated with an optical filter, a compact gas-cell with high optical coupling efficiency of ∼ 48 %, and an imbedded miniature thermostat. The footprint of the sensor is 24 mm × 8 mm × 8 mm (length × width × height), making it just 30 % of the size of conventional NDIR gas sensors with equivalent detection resolution, and its heat capability is around 7.29 J/K that promise a cost-effective thermoregulation. The sensor is capable of accurately detecting gas, such as Carbon dioxide, within a concentration range spanning from 0.5 % to 20 % with a reading error of ± 0.1 % covering a working temperature from −20 ℃ to 60 ℃. Because the sensor is equipped with a waterproof breathable film at the air hole, the sensor can operate in the humidity range from 0 to 100 %RH, and the maximum detection reading error is 0.1 % ± 230 ppm. It is possible to be applied for both low temperature environments (e.g. food preservation cabinet, biological cabinet, etc) and high-moisture environments (e.g. greenhouse, humidity chambers, etc.).

Polymer tapered pillar grown directly from an SMF core enables high efficiency optical coupling with a silicon photonics chip.

Silicon photonics technology has attracted considerable attention because of the growing need for high-bit-rate optical interconnections. The low coupling efficiency resulting from the difference in spot size between silicon photonic chips and single-mode fibers remains a challenging issue. This study demonstrated a new, to the best of our knowledge, fabrication method for a tapered-pillar coupling device using a UV-curable resin on a single-mode optical fiber (SMF) facet. The proposed method can fabricate tapered pillars by irradiating only the side of the SMF with UV light; therefore, high-precision alignment against the SMF core end face is automatically achieved. The fabricated tapered pillar with resin cladding has a spot size of 4.46 µm and a maximum coupling efficiency of -0.28 dB with a SiPh chip.

Elaboration and optimization of microlens for high optical coupling efficiency

Elaboration and optimization of microlens for high optical coupling efficiency

Polymer tapered pillar on a fiber end fabricated by UV irradiation using a high-NA fiber

The increasing need for single-mode fibers (SMFs) and advances in silicon photonics (SiPh) devices have led to the need for an efficient method of optical coupling between them. To achieve a higher coupling between them, a polymer tapered pillar was fabricated on the end face of the SMF by applying the optical diffraction effect and a self-written waveguide technology using a high numerical aperture (HiNA) fiber. The initial 10.4 µm spot size was reduced to 4.17 µm at 1.55 µm wavelength, and the greatest coupling efficiency of –1.01 dB was reached between an SMF with a tapered pillar and uncured resin cladding and a HiNA fiber. Full Text: PDF ReferencesR. Marchetti, C. Lacava, L. Carroll, K. Gradkowski, P. Minzioni, "Coupling strategies for silicon photonics integrated chips [Invited]", Photonics Res. 7, 201 (2019). CrossRef R. Bachelot, C. Ecoffet, D. Deloeil, P. Royer, D.-J. Lougnot, "Integration of micrometer-sized polymer elements at the end of optical fibers by free-radical photopolymerization", Appl. Opt. 40, 5860 (2001). CrossRef P. Pura, M. Szymanski, M. Dudek, L.R. Jaroszewicz, P. Marc, M. Kujawinska, "Polymer Microtips at Different Types of Optical Fibers as Functional Elements for Sensing Applications", J. Lightwave Techn. 33, 2398 (2015). CrossRef O. Mikami, R. Sato, S. Suzuki, C. Fujikawa, "Polymer Microlens on Pillar Grown From Single-Mode Fiber Core for Silicon Photonics", IEEE Photonics. Technol. Lett. 32, 399 (2020). CrossRef Y. Kamiura, T. Kurisawa, C. Fujikawa, O. Mikami, "High optical coupling efficiency of polymer microlens and pillar on single mode fiber for silicon photonics", Jpn. J. Appl. Phys. 61, SK1009 (2022). CrossRef F. Tan, H. Terasawa, O. Sugihara, A. Kawasaki, T. Yamashita, D. Inoue, M. Kagami, C. Andraud, "Two-Photon Absorption Light-Induced Self-Written Waveguide for Single-Mode Optical Interconnection", J. Lightwave Tech. 36, 2478 (2018). CrossRef H. Terasawa, O. Sugihara, "Near-Infrared Self-Written Optical Waveguides for Fiber-to-Chip Self-Coupling", J. Lightwave Technol. 39, 7472 (2021). CrossRef K. Vanmol, K. Saurav, V. Panapakkam, H. Thienpont, N. Vermeulen, J. Watté, J. Van Erps, "Mode-field Matching Down-Tapers on Single-Mode Optical Fibers for Edge Coupling Towards Generic Photonic Integrated Circuit Platforms", J. Lightwave Tech. 38, 4834 (2020). CrossRef Y. Saito, K. Shikama, T. Tsuchizawa, H. Nishi, A. Aratake, N. Sato, "Tapered Self-Written Waveguide between Silicon Photonics Chip and Standard Single-Mode Fiber", Opt. Fiber Communication Conference (OFC2020), paper W1A.2, (2020). CrossRef Y. Saito, K. Shikama, T. Tsuchizawa, N. Sato, "Tapered self-written waveguide for a silicon photonic chip I/O", Opt. Lett. 47(12), 2971 (2022). CrossRef N.A. Baharudin, C. Fujikawa, O. Mitomi, A. Suzuki, S. Taguchi, O. Mikami, S. Ambran, "Tapered Spot Size Converter by Mask-Transfer Self-Written Technology for Optical Interconnection", Photon. Technol. Lett. 29, 949 (2017). CrossRef H. Nawata, K. Ohmori, Proc. International Conference on Electronics Packaging (ICEP), paper 23 (2014) DirectLink S. J. Frisken, "Light-induced optical waveguide uptapers", Opt. Lett. 18, 1035 (1993). CrossRef Y. Obata, Y. Oyama, H. Ozawa, T. Ito, O. Mikami, T. Uchida, "Multi-array Self-written Waveguides using Photo-mask for Optical Surface Mount Technology", International Conference on Electronics Packaging (ICEP), paper 225 (2005). DirectLink P. Yin, J.R. Serafini, Z. Su, R. Shiue, E. Timurdogan, M.L. Fanto, S. Preble, "Low connector-to-connector loss through silicon photonic chips using ultra-low loss splicing of SMF-28 to high numerical aperture fibers", Opt. Expr. 27, 24188 (2019). CrossRef https://coherentinc.force.com/Coherent/UHNA3?cclcl=en_US, (18/09/2022). DirectLink

Polymer Spot Size Expanders for High Efficiency Optical Coupling in Optical Interconnection

Improving the low coupling efficiency due to spot size differences remains a challenge for achieving high bit-rate optical interconnections. To solve this problem, the test spot size expander device is fabricated using UV-curable resin on the end face of a fiber with a high numerical aperture. The expanded spot size of 9.38 μm from the original 3.2 μm at a wavelength of 1.55 μm and the maximum coupling efficiency with a single mode fiber of –1.19 dB are achieved. In addition, the –3 dB tolerance of the coupling efficiency along the vertical optical axis was ±4.1 µm.

Edge coupling for hybrid mono-crystalline silicon and lithium niobate thin films

The hybridization of mono-crystalline silicon and lithium niobate thin films (Si-LNOI) combines the excellent electrical properties and mature micro-nano processing technology of Si, as well as the remarkable optical properties of LN. The Si-LNOI platform will drive new and promising integrated photonics devices. High-efficiency fiber-waveguide optical coupling is necessary to realize the full potential of devices and practical applications. In this study, a spot-size converter (SSC) was designed and demonstrated for efficient edge coupling between a Si-LNOI waveguide and lens fiber. The SSC was fabricated by standard semiconductor process, which consisted of an inverted-tapered Si and a silicon-rich nitride (SRN) waveguide overlying the inverted-tapered Si. At a wavelength of 1550 nm, the TE and TM light achieved coupling losses of 1.9 and 2.1 dB/facet, respectively. The coupling efficiency was stable in the wavelength range of 1500–1600 nm. The tolerance of alignment was also evaluated.

High optical coupling efficiency of polymer microlens and pillar on single mode fiber for silicon photonics

Silicon photonics technology has attracted considerable attention these days. However, the low coupling efficiency due to the difference in spot size between silicon photonic (SiPh) chips and single-mode fibers (SMFs) remains a challenging issue. We have already proposed a unique combination of a microlens and a pillar on the facet of SMF. However, the pillar may have difficulty in keeping a single mode for a signal beam of 1. 55 μm wavelength due to air cladding. In this study, we clarified the length of the pillar that can support the single mode through simulations and experiments. By the optimum designing, the spot size as the same level as the SiPh chip was obtained. We could show that our coupling device provides high coupling efficiency with a test sample of SiPh chip, and this device also can be applied to multi-core fibers.

III–V gain region/Si waveguide hybrid lasers with InP-based two-storied ridge structure by direct bonding technology

We have fabricated III–V gain region/Si waveguide hybrid lasers with an InP-based two-storied ridge structure using direct bonding technology. Continuous-wave operation at a temperature of 20 °C with a threshold current as low as 30 mA was obtained for a hybrid laser consisting of a Fabry–Perot cavity with facets formed on the Si waveguide, and it was achieved thanks to a high optical coupling efficiency of over 80% at the interface between the III–V gain region and the Si waveguide using a two-storied ridge structure and a taper waveguide. The wavelength tunable laser which is comprised of a Si cavity with a loop mirror and double ring filters and III–V gain regions with laser and semiconductor optical amplifier (SOA) sections was demonstrated by utilizing this hybrid structure. It exhibited a wide wavelength tuning range of 48.6 nm and an optical amplification of 10 dB by SOA.

Reducing current crowding in meander superconducting strip single-photon detectors by thickening bends

To facilitate high optical coupling efficiency and absorptance, the active area of a superconducting nano/microstrip single-photon detector (SNSPD/SMSPD) is often designed as a meander configuration with a high filling factor (e.g. ⩾0.5). However, the switching current (I sw) of SNSPD/SMSPD, at which the detector switches into the normal state, is significantly suppressed by a geometry-induced ‘current crowding effect’, where there are sharp bends in the strip. Here, we propose and experimentally verify an alternative method to reduce current crowding both in SNSPD and SMSPD by directly increasing the thickness of the bends through the deposition and lift-off of a secondary superconducting film. We measure and compare the performance of SNSPDs and SMSPDs with different filling factors and bend configurations, with or without thickened bends. Improvements for detectors were observed in detection efficiency, intrinsic dark count rate, and time jitter, owing to the enhanced I sw. Our method provides a promising way of optimizing SNSPD/SMSPD detection performance.

Optical fibre taper-enabled waveguide photoactuators

Photoactuators have attracted significant interest for soft robot and gripper applications, yet most of them rely on free-space illumination, which requires a line-of-site low-loss optical path. While waveguide photoactuators can overcome this limitation, their actuating performances are fundamentally restricted by the nature of standard optical fibres. Herein, we demonstrated miniature photoactuators by embedding optical fibre taper in a polydimethylsiloxane/Au nanorod-graphene oxide photothermal film. The special geometric features of the taper endow the designed photoactuator with microscale active layer thickness, high energy density and optical coupling efficiency. Hence, our photoactuator show large bending angles (>270°), fast response (1.8 s for 180° bending), and low energy consumption (<0.55 mW/°), significantly exceeding the performance of state-of-the-art waveguide photoactuators. As a proof-of-concept study, one-arm and two-arm photoactuator-based soft grippers are demonstrated for capturing/moving small objects, which is challenging for free-space light-driven photoactuators.

A design of an ultra-compact infrared gas sensor for respiratory quotient (qCO2) detection

We present an integrated non-dispersive infrared (NDIR) gas sensor for respiratory quotient (qCO2) detection with ultra-compact size and low-power consumption. The NDIR gas sensor consists of a MEMS emitter with broadband radiation, a special designed gas-cell with high optical coupling efficiency, and a MEMS thermopile detector. The minimum size of the sensor is 10 mm × 10 mm × 4 mm (length × width × height) which is only 10 % of the size of conventional NDIR gas sensors with the same gas detection resolution of around 65 ppm. The sensor is suitable for detecting gas (e.g. CO2) with concentrations in the range of 0.5 – 20 %. This sensor has potentials to be adopted by portable breath analyzers and indoor air quality monitoring systems, etc.

Realization of exceeding 80% external quantum efficiency in organic light-emitting diodes using high-index substrates and highly horizontal emitters

Although both high-index substrates and horizontal-dipole emitters have been shown to be facile approaches for enhancing OLED (organic light emitting diode) light extraction, the full benefits and potential of their combination for OLED optical out-coupling have not been thoroughly studied and explored. Simulation studies indicate that very high optical coupling efficiency into substrates ϕsub (and perhaps similarly high OLED external quantum efficiencies) of ~90% can be possibly obtained with both high-index substrates (refractive index >1.8–1.9) and highly horizontal-dipole emitters (horizontal dipole ratio >85%), together with adoption of low-index or index-matching carrier transport layers and optimization of organic layer and transparent electrode thicknesses. With these judicious device design conditions, all waveguided modes and surface plasmon modes in devices can be effectively suppressed for optimal optical out-coupling. Finally, combining the sapphire substrate having high index of n~1.78, the recently developed OLED emitters having high horizontal emitting dipole ratio of up to 87%, and simple external extraction lens, OLED devices having external quantum efficiency of over 80% was successfully realized.

Sensing performance improvement of resonating sensors based on knotting micro/nanofibers: A review

Compared with traditional optical fibers, optical micro/nanofibers can support the large proportion of evanescent fields, high efficiency optical coupling, low bending loss and high sensitivity, which have paved their way to all-optical transmission, environmental monitoring and life sciences. Because of the high quality factor, simple fabrication process and low cost, the microfiber knot resonator was used to explore some novel micro/nanophotonic devices, for example, micro-lasers and sensors. Where, the sensing performance was improved by elaborating the fiber surface or packaging the whole structures with the sensitive materials, enabling the sensors for determining the temperature, humidity, radiation intensity, current, gas concentration, etc. In this review, the microfiber knot resonators reported in the last decade have been reviewed, compared and analyzed. The future research has been prospected finally.

Influence of positioning errors of optical shaping components for single emitter laser diode on beam shaping effects

Beam shaping is required for semiconductor lasers to achieve high optical fiber coupling efficiency in many applications. But the positioning errors on optics may reduce beam shaping effects, and then lead to low optical fiber coupling efficiency. In this work, the positioning errors models for the single emitter laser diode beam shaping system are established. Moreover, the relationships between the errors and the beam shaping effect of each shapers are analysed. Subsequently, the relationship between the errors and the optical fiber coupling efficiency is analysed. The result shows that position errors in the Z axis direction on the fast axis collimator have the greatest influence on the shaping effect, followed by the position errors in the Z axis direction on the converging lens, which should be strictly suppressed in actual operation. Besides, the position errors have a significant influence on the optical fiber coupling efficiency and need to be avoided.

56.3: Flexible and Transparent Optical Fingerprint Capture System Based on Multilayer‐Coated Gratings of Polydimethylsiloxane

With the rapidly growing demand of wearable displays, flexible and stretchable fingerprint recognition modules are needed, as one of the crucial components in a display device. In this work, a grating coupler typed optical fingerprint capture(OFC) based on Polydimethylsiloxane(PDMS) substrate is presented in both simulation and experiment. The PDMS not only affords superior elasticity, but also facilitates the breaking of total internal reflection (TIR) of coupling lights to enhance the capture of fingerprint. Multilayer‐coated gratings are proposed to achieve high optical coupling efficiency of incident light. The proposed sensitive and flexible OFC system is of great promising in the practical applications.

Optical coupling characteristics of graded-index type photonic crystal fiber collimator depending on air hole diameter ratio to pitch

A graded-index type photonic crystal fiber (GI-PCF) has a graded effective index distribution that can be realized by an α-power air hole diameter distribution in radial direction. Since a beam diameter varies periodically along the propagation direction in the GI-PCF with Gaussian beam excitation, an appropriate length of GI-PCF should be spliced to a single-mode PCF for collimator application. It is desired that GI-PCF structures to obtain high optical coupling efficiency and good tolerance for fiber length error are designed. In this paper, we theoretically studied coupling characteristics of GI-PCF collimator for conventional single-mode PCF depending on air hole diameter ratio to pitch, where the GI-PCF had parabolic air hole diameter distribution in radial direction, and had the air hole pitch that was equal to that in the conventional single-mode PCF. It was found that the optical coupling efficiency could be higher for larger air hole diameter ratio to pitch, where the coupling efficiency almost equal to that in conventional GI-type multimode fiber (GI-MMF) collimator could be obtained. On the other hand, it was clarified that GI-PCF collimators were more tolerant for fiber length error compared with GI-MMF collimator and that the GI-PCF with smaller air hole diameter ratio to pitch exhibited a better tolerance in fiber length error. We clarified that the GI-PCF collimator had an ability to obtain better wavelength characteristics with fiber length error compared with the GI-MMF collimator.

Beam-combining scheme of high-power broad-area semiconductor lasers with Lyot-filtered reinjection: modeling, simulations, and experiments

A brightness- and power-scalable polarization beam-combining scheme for high-power, broad-area semiconductor laser diodes is investigated numerically and experimentally. To achieve the beam combining, we employ Lyot-filtered optical reinjection from an external cavity, which forces lasing of the individual diodes on interleaved frequency combs with overlapping envelopes and enables a high optical coupling efficiency. Unlike conventional spectral beam-combining schemes with diffraction gratings, the optical coupling efficiency is insensitive to thermal drifts of laser wavelengths. This scheme can be used for efficient coupling of a large number of laser diodes and paves the way toward using broad-area laser diode arrays for cost-efficient material processing, which requires high-brilliance emission and optical powers in the kW regime.

A Path to High-Efficiency Optical Coupling for HIRMES

The high-resolution mid-infrared spectrometer (HIRMES) under development for Stratospheric Observatory for Infrared Astronomy is an instrument operating in the 25–122 μm spectral range with a spectral resolution R = Δλ/λ ~ 100,000 and has two absorber-coupled transition edge sensor bolometric detector focal planes. We have developed novel NbTiN low-stress absorber coatings which have the required optical impedance across the HIRMES operating band. The low intrinsic stress of these coatings allow for a peak-to-valley corrugation amplitude < 5 μm of the 450 nm thick, 1.4 mm × 1.7 mm detector pixels. Furthermore, these coatings have a superconducting transition temperature ~ 10 K, which allows them to simultaneously serve as an absorber in the desired signal band and a rejection filter at long wavelengths. This attribute makes them especially attractive for ultrasensitive absorber-coupled bolometric detector applications, because it helps in controlling the optical loading from out-of-band radiation. We also discuss a novel method for integrating a wedged-reflective absorber termination to the detector array.

Design of compact surface optical coupler based on vertically curved silicon waveguide for high-numerical-aperture single-mode optical fiber

A surface optical coupler based on a vertically curved Si waveguide was designed for coupling with high-numerical aperture single-mode optical fibers with a mode-field diameter of 5 µm. This coupler has a quite small device size, with a height of approximately 12 µm, achieved by introducing an effective spot-size converter configured with the combination of an extremely short Si exponential-inverse taper and a dome-structured SiO2 lens formed on the coupler top. The designed coupler shows high-efficiency optical coupling, with a loss of 0.8 dB for TE polarized light, as well as broad-band coupling with a 0.5-dB-loss band of 420 nm.

Double-stage guided-mode converter for pure TM-mode guiding in pillar photonic-crystal waveguide devices.

We propose a double-stage guided-mode converter for pillar photonic-crystal (PhC) waveguide devices. The converter consists of a pillar-to-wire waveguide coupler and a transverse-magnetic-mode-selective spot-size converter. The former secures high-efficiency wide-band optical coupling of a pillar-PhC waveguide to a wire waveguide. The latter improves the coupling efficiency of the wire waveguide and an outside waveguide such as an optical fiber and also the signal-to-noise ratio of light guided in the pillar-PhC waveguide. The transmission band of a fabricated pillar-PhC waveguide having the converters on both ends was 88 nm in wavelength. The cutoff at the band edge was steep and deep with an extinction ration of 40 dB in a 4-nm wavelength range.