Free-space cavity optomechanical systems on a chip with III-V heterostructures
Doctoral thesis, 2023

Cavity optomechanics examines the mutual interaction between light and mechanical motion for controlling mechanical resonators down to the quantum regime. A major challenge in the field of cavity optomechanics remains accessing a strong interaction between the light field and mechanics on the level of single quanta. Optomechanical systems with small mode volumes show considerable enhancement in the interaction strength. However, in a majority of these systems the increase in the interaction strength comes at the cost of additional optical losses. Therefore, one cannot exploit the novel capabilities of such systems often.

This thesis is about the development of a monolithic cavity optomechanical platform using III-V materials which demonstrates a pathway to combine a free-space optical cavity with an integrated mechanical system. To this end, we showcase the design, fabrication and characterization of optomechanical microresonators in AlGaAs/InGaP heterostructures. We demonstrate the enhancement of the out-of-plane reflectivity by reflectance engineering using photonic crystals. We utilize the features of III-V heterostructures by realizing monolithic fully-suspended micromechanical resonator arrays with sub-┬Ám gap in GaAs. This would enable the possibility of enhancing the optomechanical interaction using the concept of multi-element optomechanics. We explore integrated cavity optomechanical systems formed by two photonic crystals reflectors and by a photonic crystal reflector with an integrated distributed Bragg reflector mirror. Furthermore, we propose the use of highly-frequency dependent photonic crystal reflectors in the optomechanical system for realizing photonic bound states in a continuum, which decouple the otherwise coupled cavity loss rates and coupling strength.

The quality factor of the mechanical resonator can be increased by using tensile-strained InGaP which is compatible with AlGaAs heterostructures growth. We determine the material properties of InGaP relevant for mechanical resonators. We demonstrate quality factors of 10^7 in trampoline resonators in InGaP at room temperature. The quality factor is pressure limited and can be enhanced using strain engineering. Free-space integrated multi-element cavity optomechanical systems in III-V heterostructures have the potential to enter the quantum optomechanics regime at room temperature.


Micromechanical resonators

Cavity Optomechanics

III-V materials

Photonic crystals

Kollektorn, lecture room, MC2-huset, Campus Johanneberg
Opponent: Assoc. Prof. Dr. Aurelien Dantan, Aarhus University, Denmark


Sushanth Kini

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Technology

Cavity optomechanics with photonic bound states in the continuum


Journal article

S. K. Manjeshwar, A. Ciers, F. Hellman, J. Bläsing, A. Strittmater, and W. Wieczorek, "Micromechanical high-Q trampoline resonators from strained crystalline InGaP for integrated free-space optomechanics", DOI: 10.48550/ARXIV.2211.12469. 48

S. K. Manjeshwar, A. Ciers, J. Monsel, C. Peralle, S. Wang, P. Tassinand W. Wieczorek, "Cavity optomechanics with a chip-based microcavity using a suspended frequency-dependent photonic crystal mirror"

Integrated free-space optomechanics with AlGaAs heterostructures

2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021,; (2021)

Paper in proceeding

Nanophotonic Structures for Cavity Optomechanics

2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021,; Vol. June 2021(2021)

Paper in proceeding

Newton's third law of motion states `Every action has an equal and opposite reaction'. But does this law hold true for an interaction between a photon and a macroscopic object? Why does the tail of a comet always point away from the sun? How does a solar sail propel itself? The answers to these questions can be found in the field of optomechanics.

The field of optomechanics studies the mutual interaction between light and mechanical motion. The interaction between light and mechanics is enhanced placing the mechanical element inside an optical cavity. Cavity optomechanical devices can measure small displacements and forces with high sensitivity. They are used to measure gravitational waves in LIGO, to cool mechanical systems to their ground state using light and to create hybrid quantum systems that are useful for quantum technology.

This thesis covers experiments showcasing free-space monolithic integrated cavity optomechanical devices in III-V heterostructures. A key advantages of III-V heterostructures is the ability to grow tensile strained layers with precise thickness in a bottom-up grow and conducive for top-down fabrication. This enables the realization of sub-micrometer spaced mechanical resonators and an array of mechanical resonators of high mechanical quality in AlGaAs and InGaP heterostructures. The mechanical resonators can be patterned with a photonic crystal to increase their out-of-plane reflectance. We demonstrate modifications to the canonical optical spring effect due to the presence of the frequency-dependent photonic crystal.

The enhancement of the interaction strength between the light field and mechanical resonator remains a major challenge in optomechanics. In a system with the optomechanical coupling on the level of a single quanta larger than its losses, the interaction between light and mechanics becomes nonlinear. The nonlinear regime is key to explore novel quantum phenomena. The free-space multi-element optomechanical systems developed in this thesis are a promising approach towards the nonlinear regime.

Nonlinear interaction between light and mechanical motion for quantum optics and quantum sensing experiments

Swedish Research Council (VR) (2019-04946), 2020-01-01 -- 2023-12-31.

Continuously Monitored Quantum Sensors: Smart Tools and Applications

Swedish Research Council (VR) (2019-00390), 2020-01-01 -- 2022-12-31.

Areas of Advance

Nanoscience and Nanotechnology


Basic sciences

Subject Categories

Nano Technology


Chalmers Materials Analysis Laboratory

Nanofabrication Laboratory



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5258



Kollektorn, lecture room, MC2-huset, Campus Johanneberg


Opponent: Assoc. Prof. Dr. Aurelien Dantan, Aarhus University, Denmark

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