As a service

$ocLazyLoad.load({
    name: 'TestModule',
    files: ['testModule.js']
}).then(function(data) {
    // do what you want
});

With your router

$stateProvider.state('index', {
    url: "/",
    controller: 'AppCtrl'

    resolve: {
        loadMyCtrl: ['$ocLazyLoad', function($ocLazyLoad) {
            // you can lazy load files for an existing module
             return $ocLazyLoad.load({
                name: 'app',
                files: ['js/AppCtrl.js']
             });
        }]
    }
});

As a directive

<div oc-lazy-load="{name: 'TestModule', files: ['js/testModule.js']}">
    <!-- Use a directive from TestModule -->
    <test-directive></test-directive>
</div>

Bonus: DI

angular.module('MyModule', [{
        name: 'pascalprecht.translate',
        files: ['vendor/angular-translate.js']
    }]
).controller('MyCtrl', function($translate) {
    this.love = $translate.instant('<3');
});