Sidewall Gratings Research Articles

Monolithic Dual Wavelength DFB Lasers Based on Sidewall Gratings for THz/MMW Signal Generation

Monolithic Dual Wavelength DFB Lasers Based on Sidewall Gratings for THz/MMW Signal Generation

Influence of sidewall grating etching depth on GaN-based distributed feedback laser diodes

Conventional sidewall gratings in GaN-based distributed feedback (DFB) laser diodes (LD) have a thick p-type layer, which may cause current spreading and carrier-induced anti-guiding effects, severely deteriorating the lasers performance. In this study, we report a novel fabrication technology to not only reduce the remaining p-type layer in the sidewall gratings but also realize close-coupled sidewall gratings. Afterwards, we further investigate the influence of the sidewall gratings etching depth on GaN-based DFB LDs. The results show an almost unchanged current injection efficiency, nearly coincided I–V curve and a near-field emission width for shallow etched structures, which indicate that the current spreading is neglectable in GaN-based ridge structure LDs. Based on this analysis, GaN-on-Si DFB LDs with an emission wavelength of 414 nm, full width at half maxima of 22 pm, and side mode suppression ratio of 19.1 dB were realized.

1.55-μm Sidewall Grating DFB Lasers Integrated With a Waveguide Crossing for an Optical Beam Forming Network

By using asymmetric twin-waveguide technology, a 1.55-μm sidewall grating distributed feedback laser monolithically integrated with a passive waveguide crossing was for the first time demonstrated for an optical beam forming network, which needs only one metalorganic vapor-phase epitaxy step. The distributed feedback laser with uncoated facets presents a side-mode suppression ratio of >44 dB and a low 3-dB linewidth of 68 kHz. An elliptical parabolic taper waveguide crossing had a theoretical crosstalk suppression ratio of 40 dB, while the measured cross-talk suppression ratio was at least 20 dB.

Dual-wavelength DFB Laser Array Based on Sidewall Grating and Lateral Modulation of the Grating Coupling Coefficient

A monolithic dual-wavelength DFB laser array based on sidewall gratings and a novel modulation of the grating coupling coefficient is proposed and demonstrated experimentally. The grating coupling coefficient distribution along the cavity is modulated by changing the alignment between the gratings on the two sidewalls. The frequency difference between the two lasing modes can be modulated by changing the cavity length and grating recess depth. A series of microwave signals in the range of 50 GHz to 59 GHz is observed after beating the two optical lines in a photodetector. The measured optical linewidths are 250 kHz and 850 kHz when the cavity length is 1200 μm and 1000 μm, respectively.

DFB laser array based on four phase-shifted sampled Bragg gratings with precise wavelength control.

A four-laser array based on sampled Bragg grating distributed feedback (DFB) lasers in which each sampled period contains four phase-shift sections is proposed, fabricated, and experimentally demonstrated. The wavelength spacing between adjacent lasers is accurately controlled to 0.8 nm ± 0.026 nm and the lasers have single mode suppression ratios larger than 50 dB. Using an integrated semiconductor optical amplifier, the output power can reach 33 mW and the optical linewidth of the DFB lasers can be as narrow as 64 kHz. This laser array uses a ridge waveguide with sidewall gratings and needs only one metalorganic vapor-phase epitaxy (MOVPE) step and one III-V material etching process, simplifying the whole device fabrication process, and meeting the requirements of dense wavelength division multiplexing systems.

Simulation of an AlGaInAs/InP Electro-Absorption Modulator Monolithically Integrated with Sidewall Grating Distributed Feedback Laser by Quantum Well Intermixing

A novel AlGaInAs/InP electro-absorption modulated laser (EML) with a simple fabrication process is proposed, in which the electro-absorption modulator (EAM) has a 10 nm blueshift induced by quantum well intermixing (QWI) and is monolithically integrated with a sidewall grating distributed-feedback (DFB) laser working at 1.55 μm wavelength. The extent of the QWI process is characterized by a diffusion length. The quantum confined Stark effect (QCSE) is simulated in terms of extinction ratio (ER) and chirp for bias electric fields from 0 kV/cm to 200 kV/cm and for different amounts of intermixing. The results indicate that for a 150 µm-long EAM with a 10 nm blueshift induced by QWI, an ER of 40 dB is obtained at 2.5 V reverse bias with no penalty in chirp compared to an as-grown quantum well (QW) and the insertion loss at 0 V bias is 0.11 dB for 1.55 µm operation wavelength. The simulated –3 dB bandwidth of the electrical to optical power response is 22 GHz.

EML Based on Identical Epitaxial Layer, Side-Wall Grating and HSQ Planarization

We present an electroabsorption modulated laser based on an identical epitaxial scheme, side-wall grating, on- chip microwave probe interface, and a new low-permittivity planarization method. The modulation speed is significantly increased by reducing the electrode capacitance by planarizing with a 5-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>-thick HSQ layer. Furthermore, implementing the electrode with a direct ground-signal-ground probe interface provides a straightforward interconnection that obviates the need for an external circuit and bonding wires. The device operates at 1565 nm wavelength with stable single-mode lasing, no mode-hopping, and a side mode suppression ratio above 35 dB. An extinction ratio of 19.5 dB was recorded at the maximum modulator bias of &#x2212;4 V. The electrical to optical power response of the modulated signal at&#x2013;3-dBo demonstrated a 19 GHz bandwidth at an extinction ratio of 7 dB, which supports error-free data transmission up to 27 Gbit/s.

GaN-based distributed feedback laser diodes grown on Si

This letter reports on the results of room-temperature electrically injected GaN-based distributed feed-back laser diodes (LDs) grown on Si. A hundred pairs of high-order sidewall gratings were prepared by dry-etching along the ridge to select only single mode, and tetramethyl ammonium hydroxide polishing technology was adopted to remove the etching damage and make the sidewall smooth and steep. As a result, we have successfully fabricated GaN-based distributed feedback LDs grown on Si with a side-mode suppression ratio of ∼10 dB. Further analysis revealed that the fabrication of gratings reduced the injection efficiency and increased the optical loss, which deteriorated the device performance. Further improvements of the laser material quality and device fabrication are underway.

Miniaturized integrated spectrometer using a silicon ring-grating design.

We introduce and experimentally demonstrate a miniaturized integrated spectrometer operating over a broad bandwidth in the short-wavelength infrared (SWIR) spectrum that combines an add-drop ring resonator narrow band filter with a distributed Bragg reflector (DBR) based broadband filter realized in a silicon photonic platform. The contra-directional coupling DBR filter in this design consists of a pair of waveguide sidewall gratings that act as a broadband filter (i.e., 3.9 nm). The re-directed beam is then fed into the ring resonator which functions as a narrowband filter (i.e., 0.121 nm). In this scheme the free spectral range (FSR) limitation of the ring resonator is overcome by using the DBR as a filter to isolate a single ring resonance line. The overall design of the spectrometer is further simplified by simultaneously tuning both components through the thermo-optic effect. Moreover, several ring-grating spectrometer cells with different central wavelengths can be stacked in cascade in order to cover a broader spectrum bandwidth. This can be done by centering each unit cell on a different center wavelength such that the maximum range of one-unit cell corresponds to the minimum range of the next unit cell. This configuration enables high spectral resolution over a large spectral bandwidth and high extinction ratio (ER), making it suitable for a wide variety of applications.

Dynamic Device Characteristics and Linewidth Measurement of InGaN/GaN Laser Diodes

We report on the characterization and analysis of a GaN-based distributed feedback laser diode (DFB-LD) with 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -order laterally etched sidewall gratings centered at a wavelength of 420 nm. We also compare the device parameters with two commonly used Fabry-Perot (FP) devices operating at 450 nm and 520 nm. Intrinsic properties of the devices were extracted, including damping factor, carrier and photon lifetimes, modulation efficiency, differential gain, and parasitic capacitance. These parameters showed that the DFB exhibits a lower damping rate and parasitic capacitance while demonstrating a higher modulation efficiency, indicating that the DFB shows good potential for communications applications. Additionally, spectral linewidth of a GaN DFB is reported. To the authors' knowledge, this is the first demonstration of parameter extraction and spectral linewidth measurement for GaN-based DFB-LDs.

Numerical investigation of a small footprint plasmonic Bragg grating structure with a high extinction ratio

In this paper, miniaturized design of a plasmonic Bragg grating filter is investigated via the finite element method (FEM). The filter is based on a plasmonic metal-insulator-metal waveguide deposited on a quartz substrate. The corrugated Bragg grating designed for near-infrared wavelength range is structured on both sides of the waveguide. The spectral characteristics of the filter are studied by varying the geometric parameters of the filter design. As a result, the maximum ER and bandwidth of 36.2 dB and 173 nm is obtained at λBragg=976 nm with a filter footprint of as small as 1.0 x 8.75 µm2, respectively. The ER and bandwidth can be further improved by increasing the number of grating periods and the strength of the grating, respectively. Moreover, the Bragg grating structure is quite receptive to the refractive index of the medium. These features allow the employment of materials such as polymers in the metal-insulator-metal waveguide which can be externally tuned or it can be used for refractive index sensing applications. The sensitivity of the proposed Bragg grating structure can offer a sensitivity of 950 nm/RIU. We believe that the study presented in this paper provides a guideline for the realization of small footprint plasmonic Bragg grating structures which can be employed in filter and refractive index sensing applications. Full Text: PDF ReferencesJ. W. Field et al., "Miniaturised, Planar, Integrated Bragg Grating Spectrometer", 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference (CLEO/Europe-EQEC), Munich, Germany, 2019, CrossRef L. Cheng, S. Mao, Z. Li, Y. Han, H.Y. Fu, "Grating Couplers on Silicon Photonics: Design Principles, Emerging Trends and Practical Issues", Micromachines, 11, 666 (2020). CrossRef J. Missinne, N. T. Beneitez, M-A. Mattelin, A. Lamberti, G. Luyckx, W. V. Paepegem, G. V. Steenberge, "Bragg-Grating-Based Photonic Strain and Temperature Sensor Foils Realized Using Imprinting and Operating at Very Near Infrared Wavelengths", Sensors, 18, 2717 (2018). CrossRef M. A. Butt, S.N. Khonina, N.L. Kazanskiy, "Numerical analysis of a miniaturized design of a Fabry–Perot resonator based on silicon strip and slot waveguides for bio-sensing applications", Journal of Modern Optics, 66, 1172-1178 (2019). CrossRef H. Qiu, J. Jiang, P. Yu, T. Dai, J. Yang, H. Yu, X. Jiang, "Silicon band-rejection and band-pass filter based on asymmetric Bragg sidewall gratings in a multimode waveguide", Optics Letters, 41, 2450 (2016). CrossRef M. A. Butt, S.N. Khonina, N.L. Kazanskiy, "Optical elements based on silicon photonics", Computer Optics, 43, 1079-1083 (2019). CrossRef N. L. Kazanskiy, S.N. Khonina, M.A. Butt, "Plasmonic sensors based on Metal-insulator-metal waveguides for refractive index sensing applications: A brief review", Physica E, 117, 113798 (2020). CrossRef L. Lu et al, "Mode-Selective Hybrid Plasmonic Bragg Grating Reflector", IEEE Photonics Technology Letters, 22, 1765-1767 (2012). CrossRef R. Negahdari, E. Rafiee, F. Emami, "Design and simulation of a novel nano-plasmonic split-ring resonator filter", Journal of Electromagnetic Waves and Applications, 32, 1925-1938 (2018). CrossRef M. Janfaza, M. A. Mansouri-Birjandi, "Tunable plasmonic band-pass filter based on Fabry–Perot graphene nanoribbons", Applied Physics B, 123, 262 (2017). CrossRef C. Wu, G. Song, L. Yu, J.H. Xiao, "Tunable narrow band filter based on a surface plasmon polaritons Bragg grating with a metal–insulator–metal waveguide", Journal of Modern Optics, 60, 1217-1222 (2013). CrossRef J. Zhu, G. Wang, "Sense high refractive index sensitivity with bragg grating and MIM nanocavity", Results in Physics, 15, 102763 (2019). CrossRef Y. Binfeng, H. Guohua, C. Yiping, "Design of a compact and high sensitive refractive index sensor base on metal-insulator-metal plasmonic Bragg grating", Optics Express, 22, 28662-28670 (2014). CrossRef A.D. Simard, Y. Painchaud, S. Larochelle, "Small-footprint integrated Bragg gratings in SOI spiral waveguides", International Quantum Electronics Conference Lasers and Electro-Optics Europe, IEEE, Munich, Germany (2013). CrossRef C. Klitis, G. Cantarella, M. J. Strain, M. Sorel, "High-extinction-ratio TE/TM selective Bragg grating filters on silicon-on-insulator", Optics Letters, 42, 3040 (2017). CrossRef J. Ctyroky et al., "Design of narrowband Bragg spectral filters in subwavelength grating metamaterial waveguides", Optics Express, 26, 179 (2018). CrossRef M.A. Butt, N.L. Kazanskiy, S.N. Khonina, "Hybrid plasmonic waveguide race-track µ-ring resonator: Analysis of dielectric and hybrid mode for refractive index sensing applications", Laser Phys., 30, 016202 (2020). CrossRef M. A. Butt, N.L. Kazanskiy, S.N. Khonina, "Label-free detection of ambient refractive index based on plasmonic Bragg gratings embedded resonator cavity sensor", Journal of Modern Optics, 66, 1920-1925 (2019). CrossRef N. L. Kazanskiy, M.A. Butt, Photonics Letters of Poland, 12, 1-3 (2020). CrossRef Z. Guo, K. Wen, Q. Hu, W. Lai, J. Lin, Y. Fang, "Plasmonic Multichannel Refractive Index Sensor Based on Subwavelength Tangent-Ring Metal–Insulator–Metal Waveguide", Sensors, 18, 1348 (2018). CrossRef

Design and analysis of refractive index sensors based on slotted photonic crystal nanobeam cavities with sidewall gratings.

We propose and numerically investigate a refractive index sensor based on a one-dimensional slotted photonic crystal nanobeam cavity with sidewall gratings for refractive index sensing in a gaseous environment. By using the three-dimensional finite-difference time-domain method, we demonstrate that our proposed sensor simultaneously possesses a high quality factor of $ 3.71 \times {10^6} $3.71×106 and a high sensitivity of 508 nm/RIU (refractive index unit) at the resonant wavelength near 1583 nm, yielding a detection limit as low as $ 1.97 \times {10^{ - 6}} $1.97×10-6 RIU. Moreover, the mode volume of the cavity's fundamental resonant mode is found to be as small as $ 0.022(\lambda /n)^3 $0.022(λ/n)3, resulting in a very compact effective sensing area. We finally study and assess the effect of fabrication disorder on the performances of our proposed sensor. We believe our proposed sensor will be a promising candidate for applications not only in multiplexed biochemical sensing and multielement mixture detection, but also in optical trapping of single biomolecules or nanoparticles.

InGaN/GaN Distributed Feedback Laser Diodes with Surface Gratings and Sidewall Gratings.

A variety of potential applications such as visible light communications require laser sources with a narrow linewidth and a single wavelength emission in the blue light region. The gallium nitride (GaN)-based distributed feedback laser diode (DFB-LD) is a promising light source that meets these requirements. Here, we present GaN DFB-LDs that share growth and fabrication processes and have surface gratings and sidewall gratings on the same epitaxial substrate, which makes LDs with different structures comparable. By electrical pulse pumping, single-peak emissions at 398.5 and 399.95 nm with a full width at half maximum (FWHM) of 0.32 and 0.23 nm were achieved, respectively. The surface and sidewall gratings were fabricated alongside the p-contact metal stripe by electrical beam lithography and inductively coupled plasma etching. DFB LDs with 2.5 μm ridge width exhibit a smaller FWHM than those with 5 and 10 μm ridge widths, indicating that the narrow ridge width is favorable for the narrowing of the line width of the DFB LD. The slope efficiency of the DFB LD with sidewall gratings is higher than that of surface grating DFB LDs with the same ridge width and period of gratings. Our experiment may provide a reliable and simple approach for optimizing gratings and GaN DFB-LDs.

High-Q and temperature stable photonic biosensor based on grating waveguides

In this work, analytical modeling and parameter evaluation of a photonic biosensor using cascaded silicon grating waveguides is illustrated. The sensor design consists of two cascaded waveguides with symmetric sidewall gratings to broaden the stop band region of the transmission spectra. In the work, the structure is first analyzed using the transfer matrix method. The parameter values are then optimized to obtain a sharper resonant peak in the center of the stop band. Notably, the resonant band of this structure provides a high Q factor (of 1.544 × 105), which significantly improves the limits of detection. The sensor has been designed to detect the presence of biomaterial material (seen corresponding to a change in refractive index) on its surface by changing the change in device resonant wavelength. In this study, the effect of temperature on the detection of such biomaterials has also been evaluated, as has the temperature sensitivity of the device which is − 0.0075 nm/°C, over a temperature range of 18–34 °C.

Broad bandwidth and large fabrication tolerance polarization beam splitter based on multimode anti-symmetric Bragg sidewall gratings.

A novel polarization beam splitter based on an anti-symmetric sidewall Bragg grating in a multimode silicon-on-insulator strip waveguide is demonstrated. Anti-symmetric spatially periodic refractive-index perturbations are designed for strong coupling between the fundamental (TE0) and the first-order transverse electric modes (TE1), while not for transfer magnetic modes. An adiabatic coupler is cascaded at the input-port, so as to drop the TE1 reflection. The Bragg grating has a compact length of ∼20 μm (55 periods). The polarization isolations of the through- and drop-ports at the wavelength of 1557nm are 34 and 31dB, respectively. A broad bandwidth of 64nm and a large fabrication tolerance of 80nm for polarization isolation over 20dB are also achieved.

Refractive index biosensor using sidewall gratings in dual-slot waveguide

This paper presents an optical biosensor using sidewall grating in dual slot waveguide, modeled on silicon-on-insulator (SOI) platform. By optimizing the geometric parameters of the device, the spectral response is tailored to obtain a sharp resonant peak with high transmissivity that also enhances the limit-of-detection. The device detects the shift in resonant wavelength on a variation of the biomaterial refractive index. The simulation study has performed using the transfer matrix method. The obtained characteristics of the sensors include linear response to a change in refractive index of biomaterial, limit of detection of the order of 10−6 and ease of fabrication. The device performance has also compared with other SOI resonator structures like photonic crystal waveguide, sub-wavelength grating, ring resonator and grating resonator.

Ultra-broadband mode converters based on length-apodized long-period waveguide gratings.

We propose an ultra-broadband mode converter based on the structure of a length-apodized long-period grating, where π-phase shifts are introduced at strategic locations of the grating profile. Using a 3-section length-apodized grating structure, we design and fabricate an LP01-LP11a and an LP01-LP11b mode converter with a sidewall grating and a surface grating formed along a polymer channel waveguide, respectively. The fabricated LP01-LP11a and LP01-LP11b mode converters provide a conversion efficiency higher than 99% over a bandwidth of ~120 nm and ~150 nm, respectively, or a conversion efficiency higher than 90% over a bandwidth of ~180 nm and ~300 nm, respectively. The transmission characteristics of these devices are weakly sensitive to polarization and temperature variations. These mode converters can find applications in ultra-broadband mode-division-multiplexing transmission systems based on few-mode fibers and the design principle can be applied to general grating-based mode-coupling devices for a wide range of applications.

Silicon Add-Drop Filter Based on Multimode Bragg Sidewall Gratings and Adiabatic Couplers

A silicon photonic add-drop filter is demonstrated with sidewall Bragg gratings in a multimode strip waveguide. The operating principle is based on the contradirectional coupling between the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> mode and different higher-order modes inside the multimode waveguide, which depends on the symmetry property of the periodic refractive-index perturbations. In order to relax the fabrication tolerance, a pair of adiabatic couplers is used to add/drop the optical signal at the output/input ports of the multimode waveguide. Experimental results show that the functionality of add/drop filtering is successfully achieved with a low insertion loss of 0.6 dB. We also show that by sweeping the multimode waveguide width from 700 to 1400 nm, the bandwidth can be flexibly tuned from 16 to 2 nm.

InGaN/GaN Distributed Feedback Laser Diodes With Deeply Etched Sidewall Gratings

We report on the design, fabrication, and characterization of InGaN/GaN distributed feedback laser diodes emitting at a single wavelength around 430 nm. Third-order sidewall-etched gratings were used which have the advantage of a simple fabrication route with no need for overgrowth. We carried out waveguide modeling to find the effective modal indices of the grating and calculate the coupling coefficient. The laser ridge and the grating were formed by electron beam lithography followed by inductively coupled plasma etching. The as-cleaved lasers emitted in the pulsed regime with an SMSR of 22 dB and a peak single-mode output power of 40 mW. Slope efficiency was similar for both Fabry–Perot and DFB chips demonstrating that performance is not compromised by the addition of the grating.

Integrated Optical Rectangular-Edge Filter Devices in SOI

An integrated optical design of a rectangular-edge filter device in 250-nm silicon-on-insulator platform is proposed and demonstrated experimentally. The device is designed with a multimode waveguide (supporting at least two modes) with asymmetric side-wall grating, which is adiabatically interfaced with input/output single-mode waveguides. The input/output access waveguides are terminated with grating couplers for optical characterizations. Design parameters are optimized for a sharp-edge or nearly rectangular-edge filter response in optical C-band (1530 nm $\leq \lambda _{\text{edge}} \leq $ 1565 nm). The submicron features and the entire footprint of the devices were defined with a single-step e-beam lithography process by using negative-tone resist and subsequent dry etching of $\sim$ 100 nm by using an inductively coupled reactive ion etching system. All the fabricated devices exhibit a rectangular-edge filter response at $\lambda _{\text{edge}} \sim $ 1560 nm with an edge-extinction of $>$ 40 dB at the rate of 118 dB/nm. The rectangular-edge is followed by a broad pass-band of $\sim $ 40 nm till the first-order Bragg reflected wavelength of $\lambda _B^{00} \sim $ 1600 nm in the transmission characteristics obtained for 1520 nm $\leq \lambda \leq$ 1620 nm. Tunability of a rectangular-edge filter is verified with cladding refractive index change and the observed refractive index sensitivity of the edge is $\sim$ 18 nm/RIU. The limit of detection for 1-dB transmitted power extinction at $\lambda _{\text{edge}}$ of a typical fabricated device is estimated to be 5.3 $\times\, \text{10}^{-4}$ RIU.