ionicPopup does not show the content

I'm trying to use $ionicPopup in my project. Following is my code

$scope.showPopup = function(){
    $ionicPopup.prompt({
      title: 'Enter a new TODO item',
      inputType: 'text'
    })
    .then(function(result){

    })
  };

But the problem is I dont see the prompt, all I see is the dark overlay. Please refer the screen shot enter image description here

What could I be doing wrong, thanks in advance

PS: I tried the example in the ionicframeworkdocs and still the same result