Research

The interaction between light and mechanical modes of vibration has drawn great interest in recent years with applications in microwave photonic (MWP) subsystems and quantum information processing. Acoustic wavelengths are well-suited to chip-scale patterning at RF frequencies and provide an excellent conduit for such systems, as a means of bridging the frequency gap to the optical domain. Traditionally, modulation in bulk materials has been implemented at the expense of large mode sizes and optical circuits with limited modulation efficiency. Our work has focused on developing integrated acousto-optic devices in thin film aluminum nitride, resulting in demonstrations of displacement and strain based acousto-optic modulation. We are interested in extending the application of such devices as well as leverage emerging material platforms such as thin film lithium niobate and scandium-doped AlN.

S. Ghosh and G. Piazza, APL Photonics 1, 036101 (2016).

S. Ghosh and G. Piazza, Opt. Express 23, 15477 (2015).

Implementing simultaneous transmit and receive (STAR) capabilities in communication systems is an important problem to which delay line based non-reciprocal networks are a potential solution. Acoustic wave devices are excellent candidates for such delay lines, finding applications in correlators and other signal processing devices. One interesting property of propagating acoustic waves in a piezoelectric material that are allowed to interact with the drifting carriers of a semiconductor is the acoustoelectric (AE) effect. Under the proper conditions, this effect can demonstrate non-reciprocal behavior, generating acoustic wave amplification in one direction and concurrent attenuation in the other. We have demonstrated appreciable non-reciprocities in material systems including thin film silicon on lithium niobate and gallium nitride on sapphire. By making use of acoustic modes with high electromechanical coupling we seek to extend the performance of these platforms and enable co-integration of most of the key pieces for an RF front end with interference rejection on a single platform.

S. Ghosh, J. Micromech. Microeng. 32, 114001 (2022).

S. Ghosh, et al., Appl. Phys. Lett. 114, 063502 (2019).

We are interested in developing optical and acoustic wave microsystems for higher performance by investigating heterogeneous material integration, novel device designs and emerging materials. Recently thin film lithium niobate photonics has generated tremendous interest, but enabling large scale integration remains a challenge. An appealing approach thus includes the ability to bond lithium niobate (or similar strongly piezoelectric material) on the top surface of a silicon nitride photonics platform. Using wafer-bonding processes previously developed for acoustoelectric microdevices with atomic-layer deposition, we have developed similar processes for isolating thin film lithium niobate on silicon nitride photonic integrated circuits. Likewise, we have pursued photonic integration directly in piezoelectric materials such as AlN, thus enabling co-integration of photonic devices with existing libraries of RF resonators, sensors and actuators.

S. Ghosh, et al., Opt. Express 31, 12005 (2023).

S. Ghosh and G. Piazza, J. Appl. Phys. 113, 016101 (2013).

As the progress of digital CMOS technologies begin to plateau, there is a desire to find alternative computing approaches to address certain classes of problems in the category of combinatorial optimization (CO). To this end, one promising approach is the use of physical systems that perform energy minimization. This is linked to the well-studied Ising model, which has been proven to directly map to various CO problems. We have demonstrated a 4-node Ising machine with coupled LC oscillators made entirely from standard electronic components. All components in this design are largely compatible with integrated circuit technologies. We are interested in exploring such approaches and more generally, mixed-domain oscillator systems. Past work has focused on opto-acoustic oscillators (an analog of the well-developed optoelectronic oscillator), where piezoelectric actuation is used to drive an oscillator loop and analyze phase noise performance. 

J. Chou, et al., Sci. Reports 9, 14786 (2019).

S. Ghosh and G. Piazza, IEEE Trans. Electron Dev. 65, 1391 (2018).