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The field of diamond photonics is reviewed, with a focus on recent experimental demonstrations of photonic integrated devices in a single crystal diamond. This field leverages the outstanding material properties of diamond with the aim to establish large-scale integrated photonics for applications in sensing, information and communication technologies, and optomechanics. Accordingly, this review introduces recent progress in scalable micro- and nano-fabrication techniques for single crystal diamond photonic integrated devices, and provides quantitative comparative evaluation of the performance of the state of the art devices. The review concludes with an outlook of the potential of photonic integrated circuits in single crystal diamond.

A tunable high-order sideband spectra generation scheme is presented by using a photonic molecule optomechanical system coupled to a waveguide beyond the perturbation regime. The system is coherently driven by a two-tone laser consisting of a continuous-wave control field and a pulsed driving field which propagates through the waveguide. The frequency spectral feature of the output field is analyzed via numerical simulations, and we confirm that under the condition of intense and nanosecond pulse driving, the output spectrum exhibits the properties of high-order sideband frequency spectra. In the experimentally available parameter range, the output spectrum can be efficiently tuned by the system parameters, including the power of the driving pulse and the coupling rate between the cavities. In addition, analysis of the carrier-envelop phase-dependent effect of high-order sideband generation indicates that the system may present dependence upon the phase of the pulse. This may provide a further insight of the properties of cavity optomechanics in the nonlinear and non-perturbative regime, and may have potential applications in optical frequency comb and communication based on the optomechanical platform. Cavity optomechanics1,2 describes the interaction between the electromagnetic radiation and nanomechanical or micromechanical motion, which has been developing rapidly. During the past decades, it leads to various important applications, such as gravitational-wave detection 3 , cooling of mechanical oscillators to the ground-state of motion 4-11 , optomechanically induced transparency (OMIT) and slow light [12][13][14][15][16][17][18] , precision measurements 19,20 , squeezing of light 21 , quantum information processing [22][23][24] , and so on. Most of the recent developments in cavity optomechanics are based on the perturbative interaction between the driving light fields and the optomechanical system. For example, in the context of OMIT, the optomechanical system is coherently driven by both a control field and a probe field. If the strength of the probe field is far less than that of the control field, the perturbation method can be used and the OMIT can be properly described by the linearization of the Heisenberg-Langevin equations. Aside from OMIT, the linearization of optomechanical interaction has also been adopted in many other studies, such as optomechanical dark state 25 and normal mode splitting 26 . One key aspect is that if the strength of the probe field becomes comparable with that of the control field, the perturbative description breaks down, and some novel nonlinear and non-perturbative effects come to appear 27,28 . Therefore, extending the studies of cavity optomechanics from the linear and perturbation regime to the nonlinear and non-perturbative regime is of great interest. On the other hand, as a natural extension of the generic optomechanical system, the composite optomechanical system which consists of two directly coupled whispering-gallery-mode microcavities (called a photonic molecul...

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As the interaction between the photons and the environment which will make the entangled photon pairs in less entangled states or even in mixed states, the security and the efficiency of quantum communication will decrease. We present an efficient hyperentanglement purification protocol that distills nonlocal high-fidelity hyper-entangled Bell states in both polarization and spatial-mode degrees of freedom from ensembles of two-photon system in mixed states using linear optics. Here, we consider the influence of the photon loss in the channel which generally is ignored in the conventional entanglement purification and hyperentanglement purification (HEP) schemes. Compared with previous HEP schemes, our HEP scheme decreases the requirement for nonlocal resources by employing high-dimensional mode-check measurement, and leads to a higher fidelity, especially in the range where the conventional HEP schemes become invalid but our scheme still can work.