Khalid Anwar, 40, was found guilty of the attack following a trial at the High Court in Glasgow.
The 44-year-old victim told a jury how she was raped after earlier having consensual sex with Anwar four times that day.
Anwar, who at the time was an officer with the then Lothian and Borders force, was remanded in custody pending sentencing.
The rape took place in a property in Tillicoultry, Clackmannanshire, in October 2011.
The woman recalled how she and Anwar had sex five times that day - but that on the final occasion she had not agreed to having sex.
The court heard about text messages exchanged between the pair after the attack. One sent by her included the words: "I'm annoyed you carried on when I asked you not to." Anwar replied in which he made reference to the woman having "enjoyed it, but in a painful way".
The officer was accused of then harassing his victim, which included him sending a vile text and threatening to pin up naked pictures of her at work and on her street.
Anwar insisted in court the sex was consensual. Anwar, of Edinburgh, was asked what he would have done if she had said stop and replied: "I would have at once." He also branded his victim "volatile".
As well as the sex attack, Anwar was convicted of a charge of engaging in a course of conduct that left the woman in "fear and alarm".
Judge Lady Scott deferred sentencing for reports until October 23 at the High Court in Edinburgh.
Anwar, who shook his head repeatedly on being found guilty, was also placed on the Sex Offenders' Register.
The judge said: "It is almost inevitable you will be receiving a period of imprisonment, so I am not minded to grant bail meantime."