Colocar el foco en un elemento AngularJS

HTML

<link rel="stylesheet" href="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.2/css/bootstrap-combined.min.css">
<div ng-app="demo">
    <div ng-controller="FocusSampleCtrl" class="container">
        <label class="control-label">Campo 1:</label>
        <input type="text" id="campo1" />
        <label class="control-label">Campo 2:</label>
        <input type="text" id="campo2" demo-focus />
        <label class="control-label">Campo 3:</label>
        <input type="text" demo-focus="foco()" id="campo3" />
    </div>
</div>

JavaScript

angular
    .module("demo", [])
    .controller('FocusSampleCtrl', function() {
    foco(){
    alert('aa');
    }
    })
    .directive('demoFocus', function() {
        return {
            link: function(scope, element, attrs) {
                element[0].focus(); 
            }
        };
    });