Rails 4 Angularjs Paperclip how to upload file

I'm novice to manipulate angularjs with Rails 4 which provide only api's. I try to create a simple angular service to upload a file. But I use Paperclip to manage file and I have some issues.

First, I don't understand how to collect properly the file of the input. I have see a lot of plugin or fat directive to do that. But i want juste a simple directive that collect my file and put in my ng-model.

And finally I want to know if it is more efficient to encode my file in Base64 ?

My Rails controller

class Api::EmployeesController < Api::BaseController
  def create
    employee = Employee.create(employee_params)
    if employee.save
      render json: employee
    else
     render :json => { :errors => employee.errors.full_messages }, :status => 406
     end
  end

  def employee_params
    params.require(:employee).permit(:first_name,:mobile_phone,:file)
  end
end

My Angularjs Service

angular.module('test').factory 'Employee', ($resource, $http) ->
 class Employee
  constructor: (errorHandler) ->
  @service = $resource('/api/employees/:id',
  {id: '@id'},
  {update: {method: 'PATCH'}})
  @errorHandler = errorHandler

  create: (attrs, $scope) ->
    new @service(employee: attrs).$save ((employee) ->
      $scope.employees.push(employee)
      $scope.success = true
      $timeout (->
        $scope.success = false
      ), 3000
    ), @errorHandler

My Angularjs Controller

angular.module('test').controller "EmployeesController", ($scope, $timeout,  $routeParams, $location, Employee) ->

$scope.init = ->
 @employeeService = new Employee(serverErrorHandler)
 $scope.employees = @employeeService.all($scope)

$scope.createEmployee = (employee) ->
  if $scope.employeeFirstName
    @employeeService.create (
      first_name: $scope.employeeFirstName
      last_name:     $scope.employeeLastName
      promotion: $scope.employeePromotion
      mobile_phone: $scope.employeeMobilePhone
      nationality: $scope.employeeNationality
      social_number: $scope.employeeSocialNumber
      born_place: $scope.employeeBornPlace
      employee_convention: $scope.employeeConvention
      employee_type: $scope.employeeType
  ), $scope
  else
    $scope.error = "fields missing"