A former police officer who had sex with a teenager he met while volunteering at a Blue Light Disco has been jailed for three years.

Dale Martin Knoote-Parke, who was 51 at the time of the offending in 2014, pleaded guilty in February to four counts of unlawful sexual intercourse relating to his relationship with the then 16-year-old girl.

Blue Light Discos are police-organised events for youths in a safe, alcohol and drug-free environment, designed to improve relationships between police and youth.

Dale Martin Knoote-Parke pleaded guilty to four counts of unlawful sexual intercourse relating to his relationship with a then 16-year-old girl.

In the South Australian District Court on Monday, Judge Peter Brebner said the Redwood Park man's previous good character had been 'simply swept away' by his offending.

Judge Brebner described the offences as 'serious, exploitative and corruptive', the ABC reported.

He had been a senior constable working in an administrative role, but resigned after charges were laid against him, according to the ABC.

The offending took place during July and August 2014 in Adelaide.

He jailed the former officer for three years and two months and set a non-parole period of 21 months.