Optical pulling provides a new degree of freedom in optical manipulation. It is generally believed that long-range optical pulling forces cannot be generated by the gradient of the incident field. Here, we theoretically propose and numerically demonstrate the realization of a long-range optical pulling force stemming from a self-induced gradient field in the manipulated object. In analogy to potential barriers in quantum tunnelling, we use a photonic band gap design in order to obtain the intensity gradients inside a manipulated object placed in a photonic crystal waveguide, thereby achieving a pulling force. Unlike the usual scattering-type optical pulling forces, the proposed gradient-field approach does not require precise elimination of the reflection from the manipulated objects. In particular, the Einstein-Laub formalism is applied to design this unconventional gradient force. The magnitude of the force can be enhanced by a factor of up to 50 at the optical resonance of the manipulated object in the waveguide, making it insensitive to absorption. The developed approach helps to break the limitation of scattering forces to obtain long-range optical pulling for manipulation and sorting of nanoparticles and other nano-objects. The developed principle of using the band gap to obtain a pulling force may also be applied to other types of waves, such as acoustic or water waves, which are important for numerous applications.

光牵引为光学操纵提供了新的自由度。一般认为，长程光学拉力不能由入射场梯度产生。在这里，我们从理论上提出并在数值上证明了由操纵对象中自感梯度场产生的长程光学拉力的实现。与量子隧道中的势垒类似，我们使用光子带隙设计来获得放置在光子晶体波导中的被操纵物体内部的强度梯度，从而获得拉力。与通常的散射型光学拉力不同，所提出的梯度场方法不需要精确消除被操纵物体的反射。特别是，应用爱因斯坦-劳布形式主义来设计这种非常规的梯度力。在波导中被操纵物体的光学谐振处，力的大小可以增强高达 50 倍，从而使其对吸收不敏感。所开发的方法有助于打破散射力的限制，以获得用于纳米粒子和其他纳米物体的操纵和分类的长程光学拉力。使用带隙获得拉力的开发原理也可以应用于其他类型的波，例如声波或水波，这对于许多应用都很重要。