Demonstration of a chip-based optical isolator with parametric amplification

Abstract

Despite being fundamentally challenging in integrated (nano)photonics, achieving chip-based light non-reciprocity becomes increasingly urgent in signal processing and optical communications. Because of material incompatibilities in conventional approaches based on the Faraday effect, alternative solutions have resorted to nonlinear processes to obtain one-way transmission. However, dynamic reciprocity in a recent theoretical analysis has pinned down the functionalities of these nonlinear isolators. To bypass such dynamic reciprocity, we here demonstrate an optical isolator on a silicon chip enforced by phase-matched parametric amplification in four-wave mixing. Using a high-Q microtoroid resonator, we realize highly non-reciprocal transport at the 1,550 nm wavelength when waves are injected from both directions in two different operating configurations. Our design, compatible with current complementary metal-oxide-semiconductor (CMOS) techniques, yields convincing isolation performance with sufficiently low insertion loss for a wide range of input power levels. Moreover, our work demonstrates the possibility of designing chip-based magnetic-free optical isolators for information processing and laser protection.

On-Chip Optical Nonreciprocity Using an Active Microcavity

“…We notice that the pseudo-circulator37 can be used to replace a beam splitter in an otherwise all-fiber system, because it is substantially more efficient and does not rely on free-space optics. To bypass the dynamic reciprocity, in a very recent work we have successfully realized a chip-based optical isolator based on direction-sensitive momentum conservation (or phase matching) in four-wave mixing parametric amplification occurring in a high-Q silica microtoroid38 for the first time. We note that by utilizing direction-sensitive phase matching, nonreciprocal optically induced transparency has been recently demonstrated in a high-Q microsphere cavity39.…”

Realization of Directional Amplification in a Microwave Optomechanical Device

“…Instead of spatially distinct transfer paths, nonreciprocity can be obtained by a fictitious a loop, which is formed by several modes splitting signals into paths where they interfere under phase-controlled tones driving the system. These ideas have been used in the context of Josephson junction non-reciprocal devices [1][2][3][4][5][6], optical nonlinearities [7][8][9][10][11][12] or time-modulation of dielectric constants [13][14][15][16] where interfering processes generally consist in simultaneous down-and up-conversions.…”

Transmission Nonreciprocity in a Mutually Coupled Circulating Structure

“…Synthetic magneto-optical effects, such as those of spatio-temporal modulations [5][6][7][8][9][10][11][12] and optomechanics [13][14][15], were primarily considered as the replacement for Faraday effect. Numerous other methods [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] were also found for the purpose.To propagate asymmetrically, light fields should be under an effect depending on their propagation directions. For example, the momenta of photons should satisfy a phase-matching condition for interband transitions [5] or in parametric processes [26].…”

“…Numerous other methods [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] were also found for the purpose.To propagate asymmetrically, light fields should be under an effect depending on their propagation directions. For example, the momenta of photons should satisfy a phase-matching condition for interband transitions [5] or in parametric processes [26]. Or else, nonreciprocal transmissions can occur by unequal couplings of a system to the inputs from two directions.…”

“…To use the MCCS as an approximate optical isolator, a necessary condition is the highly asymmetric transmission contrast under the forward and backward drives together [26,48]. The isolation of two simultaneous inputs is measured by the logarithmic ratio 10 log 10 (3) stabilize with increased E f /E b .…”