Andrew Turner, 51, continued with the attack even after the woman pretended to be unconscious, a court was told.
Turner, of Sapley Road, Hartford, who launched the assault on August 31 last year, was jailed for 12 years and put on the sex offenders' register for life. He was also given an indefinite restraining order preventing him from contacting his victim when he appeared at Peterborough Crown Court on January 7.
The court was told that the woman made it clear she did not consent to sex and even pretended to be unconscious, but Turner continued his assault.
Police were called a few months later after the victim confided in a friend, Turner was arrested and officers searched both his home and car, where they found the same knife used in the rape.
In police interview Turner initially denied the offences, but he later admitted rape and possession of a knife.
DC Luke Ephgrave, who investigated, said: "I would like to commend the victim for her bravery and for supporting a conviction in this case.
"She has understandably been affected by this incident and I hope this sentencing brings her some closure and allows her to move forward from what happened to her.
"Reporting a sexual assault or rape can be extremely difficult for a victim. We want to ensure people that we take all reports seriously, no matter when they occurred, and have trained staff who will support you through the process."
Anyone who is concerned someone may have been convicted of a sex offence, and could be posing a risk to someone, can apply for disclosure information through Clare's Law and Sarah's Law.