All-optical Isolator Research Articles

Passive magnetic-free broadband optical isolator based on unidirectional self-induced transparency.

Achieving a broadband nonreciprocal device without gain and any external bias is very challenging and highly desirable for modern photonic technologies and quantum networks. Here we theoretically propose a passive and magnetic-free all-optical isolator for a femtosecond laser pulse by exploiting a new mechanism of unidirectional self-induced transparency, obtained with a nonlinear medium followed by a normal absorbing medium at one side. The transmission contrast between the forward and backward directions can reach 14.3dB for a 2π - 5 fs laser pulse. The 20dB bandwidth is about 56 nm, already comparable with a magneto-optical isolator. This work provides a new mechanism which may benefit non-magnetic isolation of ultrashort laser pulses.

Noiseless single-photon isolator at room temperature

Nonreciprocal devices, such as isolators, are of great importance for optical communication and optical information processing. To bypass the limitation of a strong magnetic field imposed by the traditional Faraday magneto-optic effect, many alternative mechanisms have been proposed to demonstrate magnetic-free nonreciprocity. However, limited by the drive-induced noise, the noiseless isolator capable of working in the quantum regime has yet to be realized in the experiment. Here, we show a noiseless all-optical isolator with genuine single photons in hot atoms. We experimentally study this mechanism using an open V-type level scheme and demonstrate a low insertion loss of 0.6 dB and high isolation of 30.3 dB with bandwidth up to hundreds of megahertz. Furthermore, the nonreciprocal direction can be truly reversed only by tuning the frequency of the pump laser with the same setup. Our scheme relies on widely used optical technology and is thus universal and robust.

Design and analysis of passive and phase insensitive all-optical isolator in linear optical platform

In this work a very simple all-optical isolator, based on 2D holes in slab Photonic Crystal (PhC) waveguide, has been proposed and its performance has been investigated by Finite-Difference Time-Domain (FDTD) method. The unidirectional characteristic of the waveguide is phase independent in nature and no extra bias signal has been used. The structure is basically a ‘W1’ pyramid shaped waveguide having a 120° -bend in it and the unidirectional property has been achieved by making some structural modification in the bend region. This design is capable of providing a high forward transmittance of 72%, very low backward transmission of 10% and high contrast ratio 8.57 dB. Due to its simple structure, small footprint (416μm2), high forward transmission and high contrast ratio altogether make the isolator suitable for upcoming photonic integrated circuits.

Design and Analysis of All-Optical Isolator Based on Linear Photonic Crystal

Design and Analysis of All-Optical Isolator Based on Linear Photonic Crystal

Sensing and Induced Transparency with a Synthetic Anti-PT Symmetric Optical Resonator.

Synthetic dimensions and anti-parity-time (anti-PT) symmetry have been recently proposed and experimentally demonstrated in a single optical resonator. Here, we present the effect of the rotation-induced frequency shift in a synthetic anti-PT symmetric resonator, which enables the realization of a directional rotation sensor with improved sensitivity at an exceptional point (EP) and transparency assisted optical nonreciprocity (TAON) in the symmetry-broken region. The orthogonal rotation of this system results in the direction-independent frequency shift and maintenance of the EP condition even with rotation. Tunable transparency at the EP can thus be fulfilled. Hopefully, the proposed mechanisms will contribute to the development of high-precision rotation sensors and all-optical isolators and make the study of the synthetic anti-PT symmetric EP with rotation possible.

Optical Time Reversal from Time-Dependent Epsilon-Near-Zero Media.

Materials with a spatially uniform but temporally varying optical response have applications ranging from magnetic field-free optical isolators to fundamental studies of quantum field theories. However, these effects typically become relevant only for time variations oscillating at optical frequencies, thus presenting a significant hurdle that severely limits the realization of such conditions. Here we present a thin-film material with a permittivity that pulsates (uniformly in space) at optical frequencies and realizes a time-reversing medium of the form originally proposed by Pendry [Science 322, 71 (2008)SCIEAS0036-807510.1126/science.1162087]. We use an optically pumped, 500nm thick film of epsilon-near-zero (ENZ) material based on Al-doped zinc oxide. An incident probe beam is both negatively refracted and time reversed through a reflected phase-conjugated beam. As a result of the high nonlinearity and the refractive index that is close to zero, the ENZ film leads to time reversed beams (simultaneous negative refraction and phase conjugation) with near-unit efficiency and greater-than-unit internal conversion efficiency. The ENZ platform therefore presents the time-reversal features required, e.g., for efficient subwavelength imaging, all-optical isolators and fundamental quantum field theory studies.

Broadband all-optical isolator based on all-passive graded index

We propose an all optical isolator based on a passive nonlinear graded refractive index. The proposed optical isolator is fully passive and also cavity-less based structure which causes the suggested isolator to operate in a wide frequency rang. The transmission contrast between the forward and backward directions is 81.9 dB and also the transmission intensity is large at the desirable ports. Moreover, the proposed isolator can simultaneously support two incident ports without altering the structure in the forward direction and works as a 2 × 1 optical isolator. Furthermore, the graded waveguide can be easily realized and fabricated by GaAs-based waveguide in the infrared optical frequency regime.

All-optical isolator under arbitrary linearly polarized fundamental wave in an optical superlattice

We theoretically investigate an all-optical isolator under arbitrary linearly polarized fundamental wave (FW) input in an optical superlattice (OSL). The scheme is based on simultaneously phase matching the first-order Type I (oo-e) quasi-phase-matching (QPM) second-harmonic generation (SHG) process and higher-order Type 0 (ee-e) QPM SHG process in an OSL with a defect inserted in an asymmetrical position. Simulation results show that the contrast ratio of the all-optical isolator can maintain close to 1 under arbitrary linearly polarized FW. Thus, an all-optical isolator based on an OSL that is not sensitive to the direction of linear polarization can be realized. We also show that, with the defect in a strong asymmetry position, the length of the defect can be designed flexibly to maintain a high contrast ratio. Additionally, if the length of the OSL is longer, the nonreciprocal response can be realized for low optical intensities.

A non-magnetic approach

Going beyond the conventional approach based on the Faraday effect, scientists have now used acoustic modes optically excited in the core of a photonic crystal fibre to realize a reconfigurable all-optical isolator.

Reconfigurable light-driven opto-acoustic isolators in photonic crystal fibre

Scientists experimentally demonstrate a reconfigurable all-optical isolator based on the optical excitation of a gigahertz guided acoustic mode in a micrometre-sized photonic crystal fibre core. The work is expected to benefit advanced optical communications and all-optical signal-processing systems.