The woman had been working at the school a year when the assault took place.
A summary of facts from police states the employee was called into Han's office to discuss renewal of her employment contract which was due to expire.
They went through the contract and when the woman got up to leave the room Han went with her to the door.
As she reached for the handle he put his arms around her from behind.
"The defendant placed his hands on the complainant's chest touching her breasts," the summary of facts stated.
"The defendant pressed his body against the complainant's from behind. She could feel his erect penis pressing against her buttocks."
The victim struggled to get away and asked Han what he was doing.
A third charge of male assaults female is detailed in the summary but it's unclear if Han was convicted on that.
The woman was so upset and ashamed she initially did not tell her boyfriend.
However with support she wrote a letter to Han 10 days later, outlining the allegations and telling him he had invaded her personal space.
"I do not want this. This behaviour constitutes sexual harassment. It is inappropriate and completely unwelcome.
"I am deeply hurt and disgusted by what you have done. I do not want you touching me, or invading my personal space ever again."
She threatened legal action against Han if he tried to touch her again. The letter, seen by the Herald on Sunday, was also signed by two colleagues.
A month later she went to police and soon after she resigned, traumatised and embarrassed.
When spoken to by police over the charges, Han said: "No, I didn't do it".
At sentencing in February this year Judge Philip Connell said the victim trusted Han not to treat her the way he did.
"That was appalling and it is appalling from a man of your age where you have gone ahead with a [young] female and done that to her.
"She was someone who was working for you on relatively low wages and was obviously committed in her work, was happy to be there and you then wrecked that."
He said Han, although somewhat remorseful, was in a state of disbelief and not able to admit the offending outright, and at one point considered an appeal to the conviction.
Han moved to New Zealand in 1997, completed a PhD at the University of Waikato and set up the language institute in 2002.
The school receives funding from the Tertiary Education Commission, according to its website.
Connell sentenced Han to 12 months' supervision which included undertaking a psychological assessment and any treatment recommended from that, and not associating with the complainant.
He was also ordered to pay emotional harm reparation of $5000 to the victim who was without work for four months after leaving the school.
The victim said giving evidence during the trial was frightening because she had to see Han.
She said she no longer goes to the central city mall below the building where the school is based in case she bumps into Han.
She hoped that by speaking out other victims of indecent assault, particularly Asian women who she said were often too scared to lay a complaint, would be encouraged to come forward.
Han did not respond to Herald on Sunday attempts to speak to him.
