Volume Bragg Grating Modulation for Frequency-Modulated Laser Source

Doctoral Candidate Name: 
Nguyen Hai Vy Tran
Program: 
Optical Science and Engineering
Abstract: 

As the demand for stabilized and fast-tuning laser sources continues to grow in metrology applications, there is a corresponding need for innovative laser sources that satisfies this need. This dissertation aims to create a novel stabilized and frequency-modulated (FM) laser source utilizing Volume Bragg Grating (VBG) as a wavelength selection method. In order to produce this source, six subsystem components need to be integrated. These include: 1) selecting the proper laser source, 2) implementing a PID control to maintain temperature and source current, 3) laser source fast and slow axis collimation, 4) optimizing the bonding between components of the mechanical frequency-based modulator, 5) opto-mechanical design of a fixture for the modulator to enhance adjustment, and 6) interferometric measurement of the modulation depth using a Michelson configuration.
The periodic refractive index written within the bulk VBG provides a feedback mechanism to act as a wavelength selective mirror as an external cavity to the laser diode. Two piezoelectric (PZT) actuators bonded at each end of the VBG generate the oscillatory force to create a mechanical modulation of the diffraction wavelength in traditional external cavity frequency modulation techniques. This novel approach requires bonding of the actuators. To minimize damping by adhesive layers, it is necessary to choose an appropriate adhesive. Among the adhesives studied, E60HP has proven to give the best result in terms of amplitude. A mechanism that provides 6 degrees-of-freedom adjustment of the oscillator to align VBG diffraction grating to the wavefront of the laser beam is developed and tested. The VBG alignment results gave a spectrometer limited linewidth of 0.27 nm. Modulation depth study still needs to be investigated. The final system is comprised of a 775 nm external cavity laser diode, a 3033-layer VBG at replay wavelength at 778.17 nm, and with frequency modulation at 530.7 kHz.

Defense Date and Time: 
Monday, October 28, 2024 - 6:30pm
Defense Location: 
Duke Centennial Hall 106A
Committee Chair's Name: 
Dr. Stuart Smith
Committee Members: 
Dr. Tsing-Hua Her, Dr. Glenn Boreman, Dr. Jimmy Miller, Dr. Stanislav Molchanov