Alistair Leiper, of Tooting, had a series of online video chats with two teenagers between December 2013 and April 2014, the court heard.
The 37 year old admitted three counts of attempting to engage in sexual activity in the presence of a child and one of causing or inciting a child to engage in sexual activity.
He was jailed for two years.
Judge Alistair McCreath said Leiper's actions had "stained" his otherwise "exemplary" reputation.
Southwark Crown Court heard the former police constable pretended to be a teenager and asked his victim her age, whether she liked "older boys" and if she "was a virgin".
Defending, Edmund Gritt said there was "no grooming of these victims" and there was "no building of an apparent false friendship or trust".
He was sentenced to two years' imprisonment for inciting a child to engage in sexual activity and 12 months, to run concurrently, for attempting to engage in sexual activity in the presence of a child.
He was also given a Sexual Harm Prevention Order for five years and placed on the sexual offenders register for 10 years.
Leiper has been dismissed from the Met.
A former Met police officer has been jailed for asking a 14-year-old girl to perform a sex act during a Skype call.