InP-based Waveguide Research Articles

High Responsivity and Reliability of InP-Based Waveguide Avalanche Photodiodes with Butt-Joint Coupled Structure

High Responsivity and Reliability of InP-Based Waveguide Avalanche Photodiodes with Butt-Joint Coupled Structure

Robust InP/InGaAsP Polarization Rotator Based on Mode Evolution

InP-based polarization manipulating devices are attracting continuous interest to realize compact polarization multiplexed transceivers with monolithically integrated active components. Here, we propose and experimentally demonstrate a novel type of monolithic InP polarization rotator (PR) based on a tapered half-ridge structure. Owing to the principle of mode-evolution-based adiabatic rotation of the polarization axis along propagation, the demonstrated device inherently exhibits excellent robustness against fabrication errors. Error-tolerant conversion with an efficiency over 97&#x0025; is obtained experimentally across the entire <i>C</i>-band. With the simple self-aligned process and a thick InP upper cladding, the demonstrated device would be suitable for low-loss integration with other InP-based active waveguide components, such as lasers, amplifiers, and modulators.

Anti-reflection subwavelength gratings for InP-based waveguide facets

We demonstrate the anti-reflection properties of lithographically defined subwavelength gratings applied to the facets of integrated waveguides realized in the InP membrane-on-silicon platform. The subwavelength gratings are based on the gradient index effect to create a smooth index transition between the core material and air, making it possible to obtain reflections below -30dB at a wavelength of 1550 nm for both TE and TM polarized modes, as shown by 3D finite-difference time-domain simulations. Characterizations performed using Mach-Zehnder interferometers as test structures show relative reflections as low as -25dB, confirming the effectiveness of the technique.

InP-based waveguide frequency doubler for subterahertz-range radiation sources

Our work studies the possibility of frequency doubling in InP:Fe pumped with subterahertz radiation. The attainable power of a second harmonic is calculated for an InP:Fe wafer placed in a parallel plate waveguide. It is shown that although phase matching may be compromised when the waveguide plates are introduced, there is an optimal configuration providing conversion efficiency up to 4.5% under a moderate power of 1 kW at the fundamental frequency. A zero-frequency part of nonlinear polarization is also considered in regard to diagnosis of the power at the fundamental frequency via “optical detection.”

Design of Si-rich nitride interposer waveguides for efficient light coupling from InP-based QD-emitters to Si3N4 waveguides on a silicon substrate.

In this paper, we present a systematic analysis for the design of Si-rich-nitride (SRN) based interposer waveguide layers interfacing InP-based devices and Si3N4 waveguides, towards monolithic co-integration of active and passive elements through a Back-End-Of-Line process. The investigation is performed via extensive 2D-eigenvalue and 3D-FDTD electromagnetic simulations and focuses on three different interposer designs, where performance in terms of coupling loss and back reflections is exchanged for fabrication complexity. In addition, a tolerance analysis is performed for the demonstration of the proposed coupling scheme's resilience to fabrication misalignments. The calculations use for the refractive index of the SRN interposer, real values extracted from ellipsometry measurements of a novel ultra-Si-rich-nitride material developed and engineered for this purpose. This new material provides tunability in the real part of the refractive index with low-stress crack free samples grown up to 500nm thickness. Test structures with cutbacks featuring waveguides of 500 × 500nm2 cross section formed via e-beam lithography reveal 15dB/cm propagation losses in line with similar amorphous silicon-rich nitride (aSi:N) materials. The proposed coupling concept although assumes an InP active medium, can be applied also with GaAs based lasers and dual facet devices such as Semiconductor Optical Amplifiers (SOAs) and electroabsorption modulators. In addition, all proposed designs are compatible in terms of critical dimensions with low cost 248nm DUV lithography targeting to maximize the low-cost advantage of the Si3N4 platform with very high coupling performance. Our results are expected to pave the way for the generation of a versatile, low cost, high performance monolithic InP-Quantum-Dot (QD)/Si3N4 platform on a common Si substrate.

Effect of etching depth on the performance of InP-based hybrid plasmonic waveguides

Hybrid plasmonic (HP) waveguides have attracted a lot of attention in recent years for its ability to provide long propagation length along with subwavelength confinement. In this study, the effect of InGaAsP(Q) layer etch depth on an InP-based HP-waveguide was investigated. Then, the layer thicknesses were optimized to achieve a maximum propagation length of 80 µm and the minimum effective area of 0.03 µm2 indicating a significant improvement compared to previous studies. Meanwhile, the coupling length of a directional coupler for various etch depth was calculated. Finally, the effect of the etch depth on the optical power transmission of the 90° curved waveguide and coupling between the curved and straight waveguides were determined.

Hybrid III-V-on-SOI optical spot size converter by self-aligned selective undercut dry etching of Si.

A technology called self-aligned selective undercut dry etching processing has been demonstrated for fabricating a highly efficient hybrid optical spot size converter (SSC) on a Si-on-insulator (SOI) template. The process was based on a bonded wafer between the upper InP-based multiple quantum well heterostructure and the lower SOI substrate. After defining the mask on the upper InP-based ridge waveguide, CF4/O2 dry reactive ion etching was then used for selective undercut etching of the Si material from the surrounding materials, forming a vertical waveguide coupler of the optical SSC. The lower waveguide, whose dimension is even smaller than the upper one, can thus be vertically self-aligned to the top ridge via an independent processing step. A laterally tapered waveguide ranging from 0.3 to 3 µm in width on the upper InP waveguide was fabricated. The phase-matching condition of the vertical coupler leads to a length of 45 µm and extracts 88% conversion efficiency. The selective undercut etching processing in III-V/SOI material provides a vertical self-alignment scheme for realizing compact and submicron scale heterogeneous integration in a Si photonics template.

An investigation on shallow-etched InP-based hybrid nanoplasmonic waveguides for nonlinear applications

Hybrid plasmonic waveguides (HPWs) can provide a good compromise between loss and confinement. The Kerr nonlinear effect is potentially useful for designing new optical devices such as optical switches. In this study, a new shallow-etched nonlinear hybrid plasmonic waveguide (NLHPW) on an InP substrate is proposed. Nonlinear analysis is carried out using numerical methods to verify the properties of various parameters, including the propagation length (Lp), effective mode area (Aeff), nonlinear coefficient (γ), and figure of merit (FoM). A maximum nonlinear coefficient of γ = 6.4 × 105 W−1 km−1 is obtained for the proposed NLHPW. Finally, the results obtained for various parameters such as the propagation length, nonlinear coefficient, and FoM of the proposed NLHPW are compared with two other NLHPWs, viz. silicon-on-insulator (SOI)-based and deeply etched InP-based designs, at a wavelength of 1550 nm.

Steady-State Analysis of the Effects of Residual Amplitude Modulation of InP-Based Integrated Phase Modulators in Pound–Drever–Hall Frequency Stabilization

Residual amplitude modulation of the phase modulator deployed in Pound-Drever-Hall frequency stabilization is an effect known to cause instabilities to the absolute wavelength of the stabilized laser. We present measurements and analysis of the residual amplitude modulation in an InP-based waveguide electro-optic phase modulator. The modulator is monolithically integrated in the output waveguide of a tuneable laser. The effects on the frequency stabilization of such a laser system to a reference etalon using a Pound-Drever-Hall frequency stabilization scheme are quantified. Frequency offset values in the stabilization point from the reference Fabry-Perot etalon resonance caused by the amplitude modulation are predicted and optimum operating points to minimize residual amplitude modulation are discussed. By operating an electro-refractive phase modulator at the proper bias point we show that frequency offsets corresponding to less than 3×10 ^{-3}$ of the reference cavity full-width half-maximum can be achieved.

InP-Based Coupled Ridge Waveguide Laser Arrays Emitting at 2.1 μm

InP-Based Coupled Ridge Waveguide Laser Arrays Emitting at 2.1 <i>μ</i>m

High structural and optical quality of III-V-on-Si 1.2 nm-thick oxide-bonded hybrid interface

In order to be compatible with CMOS processing, hybrid bonding of III-V materials on Silicon should be operated at 300°C, which requires an interface layer. The thinnest layer could be obtained when surfaces are prepared oxide-free and activated. We have investigated several activation processes of de-oxidized surfaces and measured their activation efficiency by X-ray Photoelectron Spectroscopy. We report here on the high structural and optical quality of a hybrid III-V on Silicon interface obtained by bonding under vacuum at 300°C de-oxidized surfaces activated by ozone. The resulting oxide interface layer is 1.2-nm thick the thinnest already reported. Structural characterization of this interface shows no defect in both crystalline lattices. Hybrid shallow ridge waveguides supporting an optical mode overlapping such an interface show 5cm−1 propagation losses comparable to the value measured for monolithic InP-based waveguides or SOI waveguides produced with the same technology, evidencing the high optical quality of the hybrid interface. Such a thin layer is favorable for an accurate control of the optical performances within hybrid devices and offers a large versatility for their design.

InP-based photonic integrated circuit platform on SiC wafer.

We have numerically investigated the properties of an InP-on-SiC wafer as a photonic integrated circuit (PIC) platform. By bonding a thin InP-based semiconductor on a SiC wafer, SiC can be used as waveguide cladding, a heat sink, and a support substrate simultaneously. Since the refractive index of SiC is sufficiently low, PICs can be fabricated using InP-based strip and rib waveguides with a minimum bend radius of approximately 7 μm. High-thermal-conductivity SiC underneath an InP-based waveguide core markedly improves heat dissipation, resulting in superior thermal properties of active devices such as laser diodes. The InP-on-SiC wafer has significantly smaller thermal stress than InP-on-SiO2/Si wafer, which prevents the thermal degradation of InP-based devices during high-temperature processes. Thus, InP on SiC provides an ideal platform for high-performance PICs.

Optical Kerr nonlinear effect in InP-based hybrid plasmonic waveguides

This paper presents a novel nonlinear hybrid plasmonic waveguide structure on the InP-substrate. The proposed hybrid plasmonic waveguide consists of a thin layer of nonlinear polymer of DDMEBT on a conventional InP-based waveguide layer caped with a metal layer, which can be monolithically integrated with a laser and a photodetector. By using the Kerr effect at an optical communication wavelength of 1550 nm, this layer stack shows a useful all-optical switching.

Sub-Micron Anisotropic InP-based III-V Semiconductor Material Deep Etching for On-Chip Laser Photonics Devices

Two InP-based III–V semiconductor etching recipes are presented for fabrication of on-chip laser photonic devices. Using inductively coupled plasma system with a methane free gas chemistry of chlorine and nitrogen at a high substrate temperature of 250 °C, high aspect ratio, anisotropic InP-based nano-structures are etched. Scanning electron microscopy images show vertical sidewall profile of 90° ± 3°, with aspect ratio as high as 10. Atomic Force microscopy measures a smooth sidewall roughness root-mean-square of 2.60 nm over a 3 × 3 μm scan area. The smallest feature size etched in this work is a nano-ring with inner diameter of 240 nm. The etching recipe and critical factors such as chamber pressure and the carrier plate effect are discussed. The second recipe is of low temperature (−10 °C) using Cl2 and BCl3 chemistry. This recipe is useful for etching large areas of III–V to reveal the underlying substrate. The availability of these two recipes has created a flexible III–V etching platform for fabrication of on-chip laser photonic devices. As an application example, anisotropic InP-based waveguides of 3 μm width are fabricated using the Cl2 and N2 etch recipe and waveguide loss of 4.5 dB mm−1 is obtained.

Multimode Interference Power-Splitter Using InP-Based Deeply Etched Hybrid Plasmonic Waveguide

The present study proposes a novel nanoscale multimode interference (MMI) power splitter utilizing an InP-based hybrid plasmonic waveguide at an optical communication wavelength. The layer stack has the potential to realize monolithic integrated hybrid plasmonic passive and active components. The 1 × 2, 1 × 3, and 2 × 2 MMI power splitters were simulated and optimized using a three-dimensional finite difference time domain method. The effect of MMI length, width, and wavelength on optical power transmission was investigated. Transmission was higher than 90% at 1.55 μm wavelengths. This study also presents an ultracompact shallow to deep transition between shallow-etched conventional waveguide and a hybrid plasmonic waveguide on an InP-substrate. It was shown that shallow to deep transition with a length of 2 μm has a coupling efficiency of 87.5%.

High-Power InP-Based Waveguide Integrated Modified Uni-Traveling-Carrier Photodiodes

We demonstrate monolithic InP-based high-power high-speed waveguide integrated single and balanced modified UTC photodetectors. The single PD chip generates maximum RF output power levels of 8.9 dBm to 5.1 dBm in the frequency range between 60 GHz and 120 GHz. The balanced PD chip has a 3 dB-bandwidth of 80 GHz and generates 2 dBm RF output power at this frequency.

Ultra-compact III‒V-on-Si photonic crystal memory for flip-flop operation at 5 Gb/s.

We report on a photonic crystal (PhC) nanolaser based on the heterogeneous integration of a III-V PhC nanocavity on SOI, configured to operate as a Set-Reset Flip-Flop (SR-FF). The active layer is a nanobeam cavity made of a 650 nm × 285 nm InP-based wire waveguide evanescently coupled to 500 nm × 220 nm SOI wire waveguides, demonstrating a record-low footprint of only 6.2 μm2. Injection locking enables optical bistability allowing for memory operation with only 6.4 fJ/bit switching energies and <50 ps response times. Bit-level SR-FF memory operation was evaluated at 5 Gb/s with PRBS-resembling data patterns, revealing error free operation with a negative power penalty.

InP-Based Waveguide Triple Transit Region Photodiodes for Hybrid Integration with Passive Optical Silica Waveguides

We report on a novel InP-based 1.55 μm waveguide triple transit region photodiode (TTR-PD) structure for hybrid integration with passive optical silica waveguides. Using the beam propagation method, numerical analyses reveal that, for evanescent optical coupling between a passive silica waveguide and the InP-based waveguide TTR-PD, a coupling efficiency of about 90% can be obtained. In addition to that, an absorption of about 50% is simulated within a TTR-PD length of 30 µm. For fabricated TTR-PD chips, a polarization dependent loss (PDL) of less than 0.9 dB is achieved within the complete optical C-band. At the operational wavelength of 1.55 µm, a reasonable PDL of 0.73 dB is measured. The DC responsivity and the RF responsivity are achieved on the order of 0.52 A/W and 0.24 A/W, respectively. Further, a 3 dB bandwidth of 132 GHz is experimentally demonstrated and high output-power levels exceeding 0 dBm are obtained. Even at the 3 dB cut-off frequency, no saturation effects occur at a photocurrent of 15.5 mA and an RF output power of −4.6 dBm is achieved. In addition to the numerical and experimental achievements, we propose a scheme for a hybrid-integrated InP/silicon-based photonic millimeter wave transmitter.

III-V/Ge Device Engineering for CMOS Photonics

Heterogeneous integration of III-V compound semiconductors and Ge on the Si platform is one of the promising technologies for enhancing the performance of metal-oxide-semiconductor field effect transistors (MOSFETs) beyond the 10-nm technology node because of their high carrier mobilities. In addition, the III-Vs and Ge are also promising materials for photonic devices. Thus, we have investigated III-V/Ge device engineering for CMOS photonics, enabling monolithic integration of high-performance III-V/Ge CMOS transistors and III-V/Ge photonics on Si. The direct wafer bonding of III-V on Si has been investigated to form III-V on Insulator for III-V CMOS photonics. Extremely-thin-body InGaAs MOSFETs with the gate length of approximately 55 nm have successfully been demonstrated by using the wafer bonding. InP-based photonic-wire waveguide devices including micro bends, arrayed waveguide gratings, grating couplers, optical switches, and InGaAs photodetectors have also been demonstrated on the III-V-OI wafer. The gate stack formation on Ge is one of the critical issues for Ge MOSFETs. Recently, we have successfully demonstrated high-quality GeOx/Ge MOS interfaces formed by thermal oxidation and plasma oxidation. High-performance Ge pMOSFET and nMOSFET with thin EOT have been obtained using the GeOx/Ge MOS interfaces. We have also demonstrated that GeOx surface passivation is effective to reduce the dark current of Ge photodetectors in conjunction with gas-phase doped junction. We have also investigated strained SiGe optical modulators. We expect that compressive strain in SiGe enhances modulation efficiency, and an extremely small VπL of 0.033 V-cm is predicted. III-V/Ge heterogeneous integration is one of the promising ways for achieving ultrahigh performance electronic-photonic integrated circuits.

InP-based waveguide photodiodes heterogeneously integrated on silicon-on-insulator for photonic microwave generation

High-linearity modified uni-traveling carrier photodiodes on silicon-on-insulator with low AM-to-PM conversion factor are demonstrated. The devices deliver more than 2.5 dBm RF output power up to 40 GHz and have an output third order intercept point of 30 dBm at 20 GHz. Photodiode arrays exceed a saturation current-bandwidth-product of 630 mA · GHz and reach unsaturated RF output power levels of 10 dBm at 20 GHz.