Micro-assembly of integrated photonic devices using a high accuracy transfer printing process

This thesis was previously held under moratorium from 03/12/19 to 03/12/21The overall objective of this thesis is the development and implementation of a high accuracy transfer printing (TP) technique for the micro-assembly of integrated photonic devices. The method has particular relevance for the integration of hybrid photonic waveguides, and enables the production of passive/active photonic circuit technologies in a parallel and scalable manner. The initial work involves the design of an optical microscopy based absolute crosscorrelation alignment technique utilised within a custom-built TP system. Following this, the statistical characterisation of the method, with the measured absolute positional accuracy of fully fabricated devices integrated across multiple substrates is achieved. An absolute lateral alignment accuracy of ±385 nm (3σ) and rotational accuracy of ±4.8 mrad (3σ) are demonstrated. This is reported as the highest lateral alignment accuracy to date for transfer printing, lending itself a significant advantage for the micro-assembly of optical waveguiding components. Utilising the high alignment TP system, the micro-assembly of fully fabricated single-mode Si membrane micro-ring resonators on a target silicon-on-insulator (SOI) substrate is presented. The ultra-thin membrane resonators are vertically integrated with Si bus waveguides situated on a receiver SOI chip in a highly controllable manner, demonstrating variation in resonant coupling conditions with respect to the lateral coupling offset. Further to this, the TP method provides a means to produce 3D device architectures without any limiting multi-step full wafer bonding methods. By vertical assembling 3D stacked membrane devices, a 100 µm2 SOI distributed Bragg reflector (DBR) is produced taking advantage of high lateral and rotation placement accuracy. The structure exhibits a visible wavelength reflectance band in agreement with theoretical simulations. The micro-assembly of hybrid AlGaAs-on-SOI micro-disk resonators is also presented, demonstrating the highly controlled integration of pre-fabricated waveguide devices across multiple material platforms. Control over the integrated resonator's vertical and lateral coupling to the bus waveguides enables the precise and selective excitation of different mode families within the resonator cavity. By using the high accuracy TP method, the vertical micro-assembly of hybrid micro-disk resonators also allows selective mode coupling, with loaded Q-factors reaching ~40,000. The unique advantage of the assembled devices however come from the ability to perform (3) nonlinear processes on SOI without being limited by two-photon absorption and free-carrier losses. Four-wave mixing is shown with efficiency levels of -25 dB at a low input power of 2.5 mW, with a nonlinear coeffcient of 325 (Wm)-1 demonstrated. The measured nonlinearity is comparable to its monolithic silicon counterpart, whilst also detailing a clear reduction in the nonlinear losses inherent to this material platform.The overall objective of this thesis is the development and implementation of a high accuracy transfer printing (TP) technique for the micro-assembly of integrated photonic devices. The method has particular relevance for the integration of hybrid photonic waveguides, and enables the production of passive/active photonic circuit technologies in a parallel and scalable manner. The initial work involves the design of an optical microscopy based absolute crosscorrelation alignment technique utilised within a custom-built TP system. Following this, the statistical characterisation of the method, with the measured absolute positional accuracy of fully fabricated devices integrated across multiple substrates is achieved. An absolute lateral alignment accuracy of ±385 nm (3σ) and rotational accuracy of ±4.8 mrad (3σ) are demonstrated. This is reported as the highest lateral alignment accuracy to date for transfer printing, lending itself a significant advantage for the micro-assembly of optical waveguiding components. Utilising the high alignment TP system, the micro-assembly of fully fabricated single-mode Si membrane micro-ring resonators on a target silicon-on-insulator (SOI) substrate is presented. The ultra-thin membrane resonators are vertically integrated with Si bus waveguides situated on a receiver SOI chip in a highly controllable manner, demonstrating variation in resonant coupling conditions with respect to the lateral coupling offset. Further to this, the TP method provides a means to produce 3D device architectures without any limiting multi-step full wafer bonding methods. By vertical assembling 3D stacked membrane devices, a 100 µm2 SOI distributed Bragg reflector (DBR) is produced taking advantage of high lateral and rotation placement accuracy. The structure exhibits a visible wavelength reflectance band in agreement with theoretical simulations. The micro-assembly of hybrid AlGaAs-on-SOI micro-disk resonators is also presented, demonstrating the highly controlled integration of pre-fabricated waveguide devices across multiple material platforms. Control over the integrated resonator's vertical and lateral coupling to the bus waveguides enables the precise and selective excitation of different mode families within the resonator cavity. By using the high accuracy TP method, the vertical micro-assembly of hybrid micro-disk resonators also allows selective mode coupling, with loaded Q-factors reaching ~40,000. The unique advantage of the assembled devices however come from the ability to perform (3) nonlinear processes on SOI without being limited by two-photon absorption and free-carrier losses. Four-wave mixing is shown with efficiency levels of -25 dB at a low input power of 2.5 mW, with a nonlinear coeffcient of 325 (Wm)-1 demonstrated. The measured nonlinearity is comparable to its monolithic silicon counterpart, whilst also detailing a clear reduction in the nonlinear losses inherent to this material platform

Transfer Printing of Photonic Nanostructures to Silicon Integrated Circuits

Optical systems require the integration of technologies fabricated on different materials. We use a transfer printing technique to integrate pre-processed III-V, polymer and silicon membrane devices onto passive optical circuits with nano-metric positional accuracy

High accuracy transfer printing of single-mode membrane silicon photonic devices

A transfer printing (TP) method is presented for the micro-assembly of integrated photonic devices from suspended membrane components. Ultra thin membranes with thickness of 150nm are directly printed without the use of mechanical support and adhesion layers. By using a correlation alignment scheme vertical integration of single-mode silicon waveguides is achieved with an average placement accuracy of 100±70nm. Silicon (Si) μ-ring resonators are also fabricated and show controllable optical coupling by varying the lateral absolute position to an underlying Si bus waveguide

Characterization, selection and micro-assembly of nanowire laser systems

Semiconductor nanowire (NW) lasers are a promising technology for the realization of coherent optical sources with ultrasmall footprint. To fully realize their potential in on-chip photonic systems, scalable methods are required for dealing with large populations of inhomogeneous devices that are typically randomly distributed on host substrates. In this work two complementary, high-throughput techniques are combined: the characterization of nanowire laser populations using automated optical microscopy, and a high-accuracy transfer-printing process with automatic device spatial registration and transfer. Here, a population of NW lasers is characterized, binned by threshold energy density, and subsequently printed in arrays onto a secondary substrate. Statistical analysis of the transferred and control devices shows that the transfer process does not incur measurable laser damage, and the threshold binning can be maintained. Analysis on the threshold and mode spectra of the device populations proves the potential for using NW lasers for integrated systems fabrication

Transfer printing of AlGaAs-on-SOI microdisk resonators for selective mode coupling and low-power nonlinear processes

The transfer printing of aluminum gallium arsenide (AlGaAs) microdisk resonators onto a silicon-on-insulator (SOI) waveguide platform is demonstrated. The integrated resonators exhibit loade

High precision transfer printing for hybrid integration of multi-material waveguide devices

We present a transfer printing technique with sub-100nm absolute placement accuracy. Hybrid integration of pre-processed membrane waveguide devices is achieved across a range of materials, including silicon, polymer and III-V devices

Transfer-printing enables multi-material assembly of integrated photonic systems

Hybrid integration of photonic membrane and nanowire devices from multiple material platforms is demonstrated using high-accuracy transfer printing. The deterministic assembly technique enables serially printed devices with separations as low as 100 nm

Integration of semiconductor nanowire lasers with polymeric waveguide devices on a mechanically flexible substrate

Nanowire lasers are integrated with planar waveguide devices using a high positional accuracy micro-transfer printing technique. Direct nanowire to waveguide coupling is demonstrated, with coupling losses as low as -17 dB, dominated by mode mismatch between the structures. Coupling is achieved using both end-fire coupling into a waveguide facet, and from nanowire lasers printed directly onto the top surface of the waveguide. In-waveguide peak powers up to 11.8 μW are demonstrated. Basic photonic integrated circuit functions such as power splitting and wavelength multiplexing are presented. Finally, devices are fabricated on a mechanically flexible substrate to demonstrate robust coupling between the on-chip laser source and waveguides under significant deformation of the system

Spatially dense integration of micron-scale devices from multiple materials on a single chip via transfer-printing

The heterogeneous integration of devices from multiple material platforms onto a single chip is demonstrated using a transfer-printing (TP) technique. Serial printing of devices in spatially dense arrangements requires that subsequent processes do not disturb previously printed components, even in the case where the print head is in contact with those devices. In this manuscript we show the deterministic integration of components within a footprint of the order of the device size, including AlGaAs, diamond and GaN waveguide resonators integrated onto a single chip. Serial integration of semiconductor nanowire (NW) using GaAs/AlGaAs and InP lasers is also demonstrated with device to device spacing in the 1 μm range

Waveguide-integrated colloidal nanocrystal supraparticle lasers

Supraparticle (SP) microlasers fabricated by the self-assembly of colloidal nanocrystals have great potential as coherent optical sources for integrated photonics. However, their deterministic placement for integration with other photonic elements remains an unsolved challenge. In this work, we demonstrate the manipulation and printing of individual SP microlasers, laying the foundation for their use in more complex photonic integrated circuits. We fabricate CdSxSe1−x/ZnS colloidal quantum dot (CQD) SPs with diameters from 4 to 20 μm and Q-factors of approximately 300 via an oil-in-water self-assembly process. Under a subnanosecond-pulse optical excitation at 532 nm, the laser threshold is reached at an average number of excitons per CQD of 2.6, with modes oscillating between 625 and 655 nm. Microtransfer printing is used to pick up individual CQD SPs from an initial substrate and move them to a different one without affecting their capability for lasing. As a proof of concept, a CQD SP is printed on the side of an SU-8 waveguide, and its modes are successfully coupled to the waveguide