  Quantum Communication (QC) represents a promising futuristic technology,
revolutionizing secure communication. Photon-based Quantum Key Distribution
(QKD) is the most widely explored area in QC research, utilizing the
polarisation degree of freedom of photons for both fibre and free-space
communication. In this work, we investigate and mitigate the challenges posed
by fibre birefringence and atmospheric effects on QKD, using a $50$-meter
free-space optical link and entanglement-based BBM92 QKD protocol. We implement
a passive polarisation correction scheme to address the critical issue of
polarisation scrambling induced by fibre birefringence and the difference in
the frame of reference between Alice and Bob. This scheme effectively mitigates
these adverse effects, ensuring reliable polarisation control over the quantum
channel. Furthermore, we conduct QKD experiments in both day and night
conditions, encountering challenges such as high background noise levels and
dynamic environmental changes. To overcome these issues, we employ various
filtering techniques to enhance signal quality and security. Our results
demonstrate the successful implementation of QKD over a free-space optical link
by producing information-theoretic secure QBER of $<11\%$ on an average and
high keyrate, even under varying lighting and weather conditions. Over one 24
hour cycle of data acquisition, we measured an average daylight keyrate and
QBER of ($3.9118\pm0.7339 KHz$ and $10.5518\pm1.3428\%$) respectively and night
time keyrate and QBER of ($4.6118\pm0.8088 KHz$ and $10.3545\pm1.2501\%$)
respectively.
