Student Projects

Evanescent field probe to characterize optical micro-resonators

Micro-resonators are structures with application in the field of integrated optics, including optomechanics, sensing and telecommunication. A large variety of materials and platforms are used to fabricate such devices, and not always it is possible to create integrated waveguides and mode converting structures (e. g. grating couplers) to couple the signal from external lasers, to the device under test and finally to detectors. Conventional method of probing individual micro-resonators involve the use of tapered optical fibers moved in the proximity of the structures. The coupling between the fiber and the micro-resonator works by overlapping the evanescent field of the fiber mode with the structure. To achieve it, the fiber needs to be thinned adiabatically in order to extend the guided optical field in the air, outside the glass.

In this project, we aim to design and fabricate a new type of probe to characterize micro-resonators. The concept is shown in figure 1: two optical fibers are cleaved and aligned, mounted on a stiff support, and a thin polymer waveguide is fabricated to connect the two cores. The polymer waveguide will be designed to match the fiber optical mode and will be adiabatically thinned similarly to the conventional tapered fiber probes. The advantages of this new type of optical probe are the compactness and the mechanical stability compared to the conventional tapered fiber probes.

Figure 1 – Schematic representation of the concept for the new evanescent field probe.

 

Figure 2 : 3D Printing at the Nanoscale (www.nanoscribe.de)

The process is based on the new 3D laser lithography system (Nanoscribe Photonic Professional GT), recently installed in EPFL CMi cleanrooms, that will allow to expose 3D geometry in a polymer layer. A support structure to aid the fabrication and the handling of the final probe will be fabricated using standard silicon processes available in the clean rooms. Finally, the probe will be fabricated starting from two bare fibers and it will be characterized by measuring the optical spectrum of a microdisk or microsphere.

Project Components:

  • Design and simulation of the polymer waveguide.
  • Design of the mechanical support for the optical fibers.
  • Planning of the fabrication process flow.
  • Fabrication of the optical probe.
  • Testing by characterization of a micro-disk or micro-sphere.

 

Type of Project: Semester or Master Project
Section(s): Microengineering
Contact(s):

Teodoro Graziosi, ELG 232, Tel 37863
Niels Quack, ELG 236, Tel 37383

 

 

Innovative Diamond Micro-Lenses enabled by 3D Micro Printing

Single crystal diamond is an outstanding material for the fabrication of micro-optical components, thanks to its excellent optical, thermal and chemical properties. In this project, the goal is to develop a new fabrication method to obtain high aspect ratio, arbitrarily shaped diamond micro-lenses, with potential applications in high-power, laser or spectroscopy optics.

Usually, the fabrication of micro-lenses starts with a photolithography step to define an array of cylinders made of photoresist on the diamond surface (Figure 1). A thermal reflow step transforms these cylinders in hemispheres, and the resulting shapes are transferred in the diamond substrate by dry etching. However, this method has two major limitations: (1) The shape of the lenses can only be hemispherical or hexagonal, and (2) as the diamond etching is based on oxygen plasma, the photoresist is rapidly consumed and only allows shallow etching depths.

 

Figure 1 Conventional method for fabricating diamond micro-lenses. (Diamond & Related Materials 65 (2016) 37–41)
 

 

Figure 2 : Polymeric structures obtained by
3D laser lithography (nanoscribe.de/files/1314/7308/3021/AppNote_MicroOptics_V02_2016_web.pdf)

In this project, the strategy is to use a 3D laser lithography system (Nanoscribe Photonic Professional GT), recently installed in EPFL CMi cleanrooms to overcome the first limitation. This system offers an alternative to the photolithography/thermal reflow procedure. By precisely exposing arbitrarily defined patterns in the bulk of a polymer layer, any 3D shape can be obtained (Figure 2). To get around the second limitation, a possible approach is to deposit a layer of a material resistant to oxygen plasma, such as SiO2, between the diamond and the polymer. Next, the shape defined in the polymer is transferred to the SiO2 layer using dry etching with a He/C4F8 chemistry. Finally, the SiO2 is used as a “hard mask” to transfer the pattern in the diamond during a second etching step, with an O2 chemistry. The project is well balanced and includes a complete engineering cycle from target specification definition, design, fabrication and final testing and characterization.

Project Components:

  • Concept and Design of Micro-Lenses
  • Concept and Design of Optical Characterization Setup
  • Microfabrication Process Flow Definition
  • Microfabrication of Micro Lenses in Single Crystalline Diamond at CMi
  • Mechanical (Surface Roughness, Curvature) and Optical Characterization (Focal length, Optical Performance)
Type of Project: Semester or Master Project
Section(s): Microengineering
Contact(s):

Adrien Toros, ELG 232, Tel 37841
Niels Quack, ELG 236, Tel 37383

 

 

Diamond Diffractive Micro-Optical Component Design & Fabrication

Single crystalline diamond provides an extraordinary combination of material properties: chemically inert, extremely hard, high thermal conductivity, a high refractive index, high transparency in the uv, visible and infrared to name a few. While single crystalline diamond has become available commercially in high quality recently, microstructuring remains difficult. At the Q-LAB, we are exploring micro- and nanofabrication methods at the facilities of CMI to manufacture single crystalline diamond nanophotonic and micro-optical structures.

In this project, these techniques are being applied to design single crystalline diamond diffractive micro-optical components, including gratings (see figures). During this project, the student will design and simulate diamond diffractive optical elements and choose a design to fabricate based on performance and fabrication process. The student designs a process flow to be executed in the CMi cleanrooms and carries out the necessary fabrication steps. The resulting components are then characterized by the student using SEM and/or AFM, and optically, and compared to the design.

Figure 1 Diamond micrograting fabricated at EPFL Q-LAB.

 

Figure 2 : Diffraction pattern of the diamond micrograting fabricated at EPFL Q-LAB.

The successful optical components will allow to manufacture high quality optical components for high-power laser or spectroscopy optics. It can be expected that a successful project will spur interest in industrial collaborations.

Project Components:

  • Concept and Design of Optical Diffractive Components and/or System in Diamond
  • Design of Process Flow for Cleanroom Fabrication of Components
  • Characterization of Fabricated Components via SEM / AFM / interferometry
  • Concept and Design of Optical Characterization Setup

 

Type of Project: Semester or Master Project
Section(s): Microengineering
Contact(s):

Marcell Kiss, ELG 232, Tel 37841
Niels Quack, ELG 236, Tel 37383

 

 

Comb Drive Actuated Piston Micromirror for Tunable Optical Microsystems

Piston movement micromirrors can be used for translational movements in Micro-Optoelectromechanical Systems (MOEMS) such as Fourier Transform Infrared Spectrometers (FTIR), tunable detectors and lasers. In this project, microfabrication technologies will be combined with assembly technologies to integrate the MEMS micromirror with permanent magnets. The project will include the design and fabrication of the silicon based MEMS. While this project involves design, layout, simulation and characterization, it is also an excellent opportunity to extend your hands-on fabrication experience in a state of the art clean room at CMI..

 

 

3D View of a piston movement MEMS micromirror.

 

Project Components:
•    Study of literature
•    Design and simulation of the electrostatic comb drive actuator
•    Definition of process flow
•    Fabrication at CMI
•    Microassembly
•    Experimental characterization

Type of Project: Master Project
Section(s): Microengineering
Contact(s): Niels Quack
ELG 236
Tel 37383

 

 

Magnetically Actuated MEMS Piston Micromirror

Piston movement micromirrors can be used for translational movements in Micro-Optoelectromechanical Systems (MOEMS) such as Fourier Transform Infrared Spectrometers (FTIR), tunable detectors and lasers. In this project, microfabrication technologies will be combined with assembly technologies to integrate the MEMS micromirror with permanent magnets. The project will include the design and fabrication of the silicon based MEMS. While this project involves design, layout, simulation and characterization, it is also an excellent opportunity to extend your hands-on fabrication experience in a state of the art clean room at CMI.

 

 

Schematic example cross section of an electromagnetically actuated piston MEMS mirror.

Project Components:
•    Study of literature
•    Evaluation of permanent magnets
•    Design and simulation of the electromagnetic actuator
•    Definition of process flow
•    Fabrication at CMI
•    Microassembly
•    Experimental characterization
Type of Project: Master Project
Section(s): Microengineering
Contact(s): Niels Quack
ELG 236
Tel 37383

 

 

Diamond Refractive Micro-Optics

Single crystalline diamond provides an extraordinary combination of material properties: chemically inert, extremely hard, high thermal conductivity, a high refractive index, high transparency in the uv, visible and infrared to name a few. While single crystalline diamond has become available commercially in high quality recently, microstructuring remains difficult. At the Q-LAB, we are exploring micro- and nanofabrication methods at the facilities of CMI to manufacture single crystalline diamond nanophotonic structures. In this project, these techniques are being applied to manufacture single crystalline diamond photonic refractive micro-optical components, including concave and convex lenses (see figures). The successful optical components will allow to manufacture high quality optical components for high-power, laser or spectroscopy optics. It can be expected, that a successful project will spur interest in industrial collaborations.

Examples of microlenses fabricated in single crystalline diamond (Lee et al., Diamond and Related Materials, 15, 4-8, 725-728).
 

Project Components:
• Concept and Design of Optical Refractive Components and/or System in Diamond
• Concept and Design of Optical Characterization Setup
• Microfabrication Process Flow Definition
• Microfabrication of Micro-Optical Elements in Single Crystalline Diamond at CMI
• Mechanical Characterization (Surface Roughness, Curvature, etc.)
• Optical Characterization

Type of Project: Master Project
Section(s): Microengineering
Contact(s): Niels Quack
ELG 236
Tel 37383

 

 

MEMS Microshutter Array

This project aims at the development of a demonstrator of a MEMS Microshutter Array as an active part in a Smart Slit Assembly. While currently, an optical relay system is being investigated for the use in for space applications [1], we here propose to develop an alternative design, making use of a tightly integrated novel MEMS Microshutter Array. The project will involve the design of the Microshutter Array using finite element simulations and the development of the fabrication process and assembly approach.
 

 

 

[1] Guldimann, B., Minoglou, K., “Smart Slit Assembly for high-resolution spectrometers in space”, Proc. SPIE 9754, Photonic Instrumentation Engineering III, 97540B (March 16, 2016); doi:10.1117/12.2209336

 

 

Project Components:
• Concept and Design the Microshutter Array
• FEM Simulations of the MEMS Actuator
• Definition of Assembly Strategy for Optical Path Elements
• Microfabrication Process Flow Definition
• Microfabrication of the demonstrator MEMS at CMI
• Mechanical Characterization
• Assembly and Optical Characterization

 

Type of Project: Master Project
Section(s): Microengineering
Contact(s): Niels Quack
ELG 236
Tel 37383