| dc.description.abstract | This research is aimed to produce squeezed vacuum state in single-pass optical parametric amplifier (OPA) in nonlinear optics. The process based on a single-spatial-mode periodically poled lithium niobate (PPLN) waveguide, also called on-chip squeezer. In this work, we provide more compact, robustness and scalability via integrated photonic circuits rather than conventional optical measurement scheme. According to Heisenberg ′s uncertainty principle,
there is minimum fluctuation in optical field, that is standard quantum limit (SQL). By utilizing squeezing light, we can obtain noise level below SQL in one quadrature (may in amplitude or phase), and another quadrature will be amplified higher than SQL. This characteristic can apply
in quantum sensing area providing extra precise metrology. Additionally, in order to realize large photonic quantum circuits (PQCs), we designed adiabatic coupler (AC) which has fabrication tolerant and broadband operation properties as a beam splitter to separate pump and signal wavelength.
We had developed squeezing light source and beam splitter integrated on Ti-diffused periodically poled lithium niobate (PPLN) waveguides. From stimulated Raman adiabatic passage (STIRAP) theory, we built up adiabatic coupler geometric structure and simulation through beam propagation method (BPM), to fabrication process flow with lithography, thin
film, diffusion, chemical-mechanical polishing, etch. Finally, measuring the chip characteristic (1)Extinction ratio of adiabatic coupler achieve up to 23.4dB at 1550nm. In addition, extinction ratio more than 20dB and 10dB has 18nm、68nmrespectively. (2)Nonlinear optics process second harmonic generation (SHG), the chip demonstrates normalize SHG conversion efficiency 15.8%/W/cm2. with 15mm quasi phase matching (QPM) length. (3)By balance homodyne detection (BHD) method to measure squeezing level, we estimated the squeezing and antisqueezing levels can be -0.67dB and 0.72dB, respectively.
In future work, we can design different coupler and even can change the waveguide type which enhance the nonlinear conversion efficiency, durability for high-power pump and low propagation loss. Due to above mentioned optimizations, we can fabricate more quality on-chip squeezer. The quantum light source is preliminary condition in quantum network system. By means of the thesis contribution, we can offer a stable nonclassical light which is squeezing light. In other group, they integrated directional coupler (DC) as 50:50 beam splitter (BS) on chip cascade OPA process [1]. Not only did it improve the spatial mode matching, but it minimizes optical setup. We believe that our work combine the DC can toward integrated quantum system further.
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