# 4-dB quadrature squeezing with fiber-coupled PPLN ridge waveguide module

## TL;DR

This paper reports the development of a fiber-coupled PPLN ridge waveguide module that achieves -4 dB of quadrature squeezing at 1553.3 nm, demonstrating a compact, alignment-free source for quantum optics applications.

## Contribution

The work introduces a novel fiber-coupled PPLN ridge waveguide module capable of generating significant quadrature squeezing with high durability and efficient fiber coupling, advancing integrated quantum optics technology.

## Key findings

- Achieved -4.0 dB noise reduction for vacuum state at 1553.3 nm.
- Estimated intrinsic loss of the squeezed vacuum is 25%.
- Output fiber squeezing level is approximately -5.7 dB after accounting for losses.

## Abstract

We have developed an optical parametric amplification module for quadrature squeezing with input and output ports coupled with optical fibers for both fundamental and second harmonic. The module consists of a periodically poled LiNbO${}_{3}$ ridge waveguide fabricated with dry etching, dichroic beamsplitters, lenses and four optical fiber pigtales. The high durability of the waveguide and the good separation of squeezed light from a pump beam by the dichroic beamsplitter enable us to inject intense continuous-wave pump light with the power of over 300 mW. We perform $-$4.0${\pm}$0.1 dB of noise reduction for a vacuum state at 1553.3 nm by using a fiber-optics-based measurement setup, which consists of a fiber-optic beamsplitter and a homemade fiber-receptacle balanced detector. The intrinsic loss of the squeezed vacuum in the module is estimated to be 25%. Excluding the extrinsic loss of the measuremental system, the squeezing level in the output fiber of the module is estimated to be $-$5.7${\pm}$0.1 dB. A modularized alignment-free fiber-coupled quadrature squeezer could help to realize quantum information processing with fiber optics.