how to get a coupon code in magento 2.right now i am getting name i want a coupon code

public function __construct(

        \Magento\Framework\View\Element\Template\Context $context,

        \Magento\Framework\Registry $registry,

        \Magento\SalesRule\Model\ResourceModel\Rule\CollectionFactory  $collection,
        \Magento\Framework\Stdlib\DateTime\Timezone $_stdTimezone,
        array $data = []
    ) {
        $this->_coreRegistry = $registry;
        $this->collection = $collection;
        $this->coupon = $coupon;
        $this->_stdTimezone = $_stdTimezone;
        parent::__construct($context, $data, $collection, $coupon);
    }

public function getDiscountCoupon()

    {

        $currentTime = $this->_stdTimezone->date()->format('Y-m-d');
        $rules = $this->collection->create()
                        ->addFieldToFilter('is_active', 1)
                        ->addFieldToFilter('to_date', ['gteq' => $currentTime]);
            //echo $rules->getSelect()->__toString(); die();
        $product = $this->_coreRegistry->registry('product');

        foreach ($rules as $rule) {
            try {
                if ($rule->getActions()->validate($product)) {
                        $activeRules[] = $rule;
                }
            } catch (\Magento\Framework\Exception\NoSuchEntityException $e) {
                continue;
            }
        }
        $rulesApplied = "<h3>Applicable Offers:</h3>";
        foreach ($rules as $rule) {
                $rulesApplied .= $rule->getName()."</br>";
        }
        return $rulesApplied;
    }