Complete Optical Isolation Research Articles

Multi-frequency complete optical isolation based on indirect interband transition

Indirect interband photonic transition is an important approach to achieve on-chip complete optical signal isolation. We demonstrate that the operational isolation bandwidth based on this effect can be increased by utilizing non-interfering transition channels obtained from the process of transition channel engineering. Multiple optical modes can be excited through non-interfering channels and be absorbed by matched filters without interfering with each other, thus achieving multi-frequency complete optical isolation. With two non-interfering transition channels, an optical isolator design that achieves complete isolation at two frequencies is proposed as an example. The potential design of multi-frequency isolator is also discussed. All the results are verified with finite-difference time-domain simulation.

Nonreciprocal Photonics Without Magneto-Optics

Optical isolators, which break the Lorentz reciprocity, are fundamental building blocks for regulating the flow of light. Here, we provide a brief perspective on the developments in nonmagnetic approaches to constructing optical isolators. We show that nonlinear optical isolators are fundamentally constrained by dynamic reciprocity and cannot completely reproduce functionalities of standard magneto-optical devices. We also show that complete optical isolation is achievable with dynamic modulation of refractive index. Moreover, the reciprocity-breaking in modulated systems is closely related to the concept of an effective gauge potential for photons. The use of such gauge potential points to a route toward novel nonreciprocal topological photonics physics as well as new capabilities for controlling the propagation of electromagnetic waves.

Complete All-Optical Silica Fiber Isolator via Stimulated Brillouin Scattering

This study demonstrates the theoretical operation of an all-optical silica fiber isolator using stimulated Brillouin scattering. Two pump sources that copropagate through a double-mode fiber generate acoustic waves through electrostriction. These acoustic waves then induce unidirectional interband optical transitions between a separate pair of signal sources. With 1 W of total input pump power, complete optical isolation is achieved with a silica rod waveguide of radius 0.67 μm over a length of approximately 12 m, with pumps operating at a wavelength of 1.55 μm and signals at 1.50 μm.

Tunable broadband isolator based on electro-optically induced linear gratings in a nonlinear photonic crystal

We theoretically propose a broadband optical isolator based on second-harmonic generation in a one-dimensional quadratic nonlinear photonic crystal (NPC) with an embedded defect. An external electric field along the z axis is applied to modulate the NPC refractive index periodically. Complete optical isolation always could be reached with the help of an external field. Influences of the defect position and thickness are discussed. The spectral and power tolerances of the isolator also have been investigated and show high contrast within a wide wavelength range at different power levels.

Erratum: Complete optical isolation created by indirect interband photonic transitions

Nature Photonics 3, 91–94 (2009); published online: 11 January 2009; corrected online 15 April 2009. The authors wish to correct equation (4) of the above Letter; it should have appeared as shown below. This also affects the final sentence in the third paragraph from the end of page 92, which shouldnow read: For this device, our calculation indicates that over a frequency bandwidth of 1.

Complete optical isolation created by indirect interband photonic transitions

Achieving on-chip optical signal isolation is a fundamental difficulty in integrated photonics1. The need to overcome this difficulty is becoming increasingly urgent, especially with the emergence of silicon nano-photonics2,3,4, which promises to create on-chip optical systems at an unprecedented scale of integration. Until now, there have been no techniques that provide complete on-chip signal isolation using materials or processes that are fundamentally compatible with silicon CMOS processes. Based on the effects of photonic transitions5,6, we show here that a linear, broadband and non-reciprocal isolation can be accomplished by spatial–temporal refractive index modulations that simultaneously impart frequency and wavevector shifts during the photonic transition process. We further show that a non-reciprocal effect can be accomplished in dynamically modulated micrometre-scale ring-resonator structures. This work demonstrates that on-chip isolation can be accomplished with dynamic photonic structures in standard material systems that are widely used for integrated optoelectronic applications. The realization of a chip-based, broadband optical isolator is of considerable interest for integrated photonics. To date, no technique has been shown to be able to do this using materials and processes that are CMOS-compatible. Now, scientists propose that the use of direction-dependent photonic mode transitions in silicon nanophotonic structures could be the solution.

Thermal links for the implementation of an optical refrigerator

Optical refrigeration has been demonstrated by several groups of researchers, but the cooling elements have not been thermally linked to realistic heat loads in ways that achieve the desired temperatures. The ideal thermal link will have minimal surface area, provide complete optical isolation for the load, and possess high thermal conductivity. We have designed thermal links that minimize the absorption of fluoresced photons by the heat load using multiple mirrors and geometric shapes including a hemisphere, a kinked waveguide, and a tapered waveguide. While total link performance is dependent on additional factors, we have observed net transmission of photons with the tapered link as low as 0.04%. Our optical tests have been performed with a surrogate source that operates at 625 nm and mimics the angular distribution of light emitted from the cooling element of the Los Alamos solid state optical refrigerator. We have confirmed the optical performance of our various link geometries with computer simulations using CODE V optical modeling software. In addition we have used the thermal modeling tool in COMSOL MULTIPHYSICS to investigate other heating factors that affect the thermal performance of the optical refrigerator. Assuming an ideal cooling element and a nonabsorptive dielectric trapping mirror, the three dominant heating factors are (1) absorption of fluoresced photons transmitted through the thermal link, (2) blackbody radiation from the surrounding environment, and (3) conductive heat transfer through mechanical supports. Modeling results show that a 1 cm3 load can be chilled to 107 K with a 100 W pump laser. We have used the simulated steady-state cooling temperatures of the heat load to compare link designs and system configurations.

A noise-immune cesium magnetometer

A high-sensitivity (∼1 fT at a 100-s measurement time) self-generating magnetometer based on the optical orientation of cesium atoms and intended for measurements of absolute values of weak (∼2 × 10−6 T) magnetic fields is described. Its distinctive feature is the complete optical isolation of the magnetic sensor from the electronic units, allowing one to perform magnetic measurements under conditions of high electromagnetic noise. It is proposed that the magnetometer be used as part of the multichannel system for stabilizing the neutron magnetic resonance in the search for the electrical dipole moment of a neutron.