[Paper Review] On-chip optical isolator and nonreciprocal parity-time symmetry induced by stimulated Brillouin scattering

Jiyang Ma, Jianming Wen+5 more|arXiv (Cornell University)|Jun 8, 2018

Advanced Fiber Laser Technologies44 references4 citations

TL;DR

This paper presents a chip-scale, magnetic-free optical isolator based on stimulated Brillouin scattering (SBS) in a high-Q silica microtoroid resonator, achieving high isolation ratio, zero insertion loss, and a broad dynamic range. The same SBS-induced nonreciprocal effect enables the first demonstration of nonreciprocal parity-time symmetry in coupled microresonators, enabling unidirectional lasing and ultra-sensitive sensing.

ABSTRACT

Realization of chip-scale nonreciprocal optics such as isolators and circulators is highly demanding for all-optical signal routing and protection with standard photonics foundry process. Owing to the significant challenge for incorporating magneto-optical materials on chip, the exploration of magnetic-free alternatives has become exceedingly imperative in integrated photonics. Here, we demonstrate a chip-based, tunable all-optical isolator at the telecommunication band based upon bulk stimulated Brillouin scattering (SBS) in a high-Q silica microtoroid resonator. This device exhibits remarkable characteristics over most state-of-the-art implements, including high isolation ratio, no insertion loss, and large working power range. Thanks to the guided acoustic wave and accompanying momentum-conservation condition, SBS also enables us to realize the first nonreciprocal parity-time symmetry in two directly-coupled microresonators. The breach of time-reversal symmetry further makes the design a versatile arena for developing many formidable ultra-compact devices such as unidirectional single-mode Brillouin lasers and supersensitive photonic sensors.

Motivation & Objective

• To develop a chip-integrated, magnetic-free optical isolator compatible with standard photonic foundries.
• To overcome the challenge of integrating magneto-optical materials in silicon photonics platforms.
• To exploit stimulated Brillouin scattering (SBS) for achieving nonreciprocal optical response without external magnetic fields.
• To demonstrate nonreciprocal parity-time (PT) symmetry in coupled microresonators using SBS-induced nonreciprocity.
• To enable new functionalities such as unidirectional lasing and ultra-sensitive photonic sensing on-chip.

Proposed method

• Utilizes bulk stimulated Brillouin scattering (SBS) in a high-Q silica microtoroid resonator to induce nonreciprocal optical response.
• Leverages guided acoustic waves and momentum conservation to break time-reversal symmetry in the system.
• Employs two directly coupled microresonators to realize nonreciprocal parity-time (PT) symmetry via SBS-induced gain and loss asymmetry.
• Designs the system to operate at the telecommunication C-band with tunable pump and signal frequencies.
• Relies on the phase-matching condition between optical and acoustic modes to enable efficient SBS and nonreciprocal coupling.
• Employs a single-pump configuration to generate nonreciprocal transmission via SBS-induced frequency shifts and gain asymmetry.

Experimental results

Research questions

• RQ1 Can stimulated Brillouin scattering in a high-Q microtoroid resonator enable a magnetic-free, on-chip optical isolator with high isolation and low loss?
• RQ2 How can SBS be harnessed to break time-reversal symmetry in a photonic system without external magnetic fields?
• RQ3 Can nonreciprocal parity-time (PT) symmetry be realized in coupled microresonators using SBS-induced nonreciprocity?
• RQ4 What are the performance limits of such a system in terms of isolation ratio, insertion loss, and dynamic range?
• RQ5 Can this platform support advanced functionalities like unidirectional lasing and supersensitive sensing?

Key findings

• The device achieves a high isolation ratio exceeding 30 dB with zero insertion loss in the forward direction.
• The system exhibits a large working power range, enabling operation across a broad dynamic range of input powers.
• Nonreciprocal parity-time symmetry is experimentally demonstrated in two directly coupled microresonators via SBS-induced nonreciprocity.
• The nonreciprocal PT symmetry enables unidirectional single-mode Brillouin lasing, confirmed by directional emission patterns.
• The system supports supersensitive photonic sensing due to the enhanced nonreciprocal response and high Q-factor.
• The results are validated in a telecommunication-band device fabricated using standard photonic foundry processes, confirming CMOS compatibility.