We present our recent work on silicon resonance and slow-light based devices for optical signal processing. Waveguide self-coupling and mutual coupling are used to tailor the waveguide spectral and dispersion characteristics. With selfcoupling, optical resonances are generated with unique transmission performances. Electromagnetically induced transparency (EIT)-like effect appears in cascaded self-coupled waveguides. With mutual coupling between ridge and slot waveguides, group velocity experiences a big jump and optical signal can be delayed for a large range with low distortion by using thermo-optic tuning.
We present our recent work on silicon resonance and slow-light based devices for optical signal processing. Waveguide self-coupling and mutual coupling are used to tailor the waveguide spectral and dispersion characteristics. With selfcoupling, optical resonances are generated with unique transmission performances. Electromagnetically induced transparency (EIT)-like effect appears in cascaded self-coupled waveguides. With mutual coupling between ridge and slot waveguides, group velocity experiences a big jump and optical signal can be delayed for a large range with low distortion by using thermo-optic tuning.
Summary form only given. Slow light has achieved great progress in waveguide and fibers in room temperature, which could be accelerating the transition of this technique to applications. This talk will review devising methods for tailoring the dispersion of optical materials, such as electromagnetically induced transparency, photonic crystals, and nano-optic resonators over the last decade. And the potential applications of slow light for optical buffering, data synchronization, optical memories, and optical signal processing will be cataloged. Then the interaction between slow light and Sagnac effect is discussed. The concept of the Sagnac effect in a slow-light medium and resonator structure with high group dispersion is investigated. It is found that a slow-light medium can be utilized for relative motion sensing, and a slow-light resonator structure is suitable to detect absolute rotation for navigation purposes. It is noted that the high group dispersion leads to a huge enhancement of the rotation sensor's sensitivity in a resonating structure, and an approach to evaluate and design resonator devices with slow-light property is proposed. Moreover, a folded loop-lattice-based structure is numerically simulated to verify the concept.
We comprehensively simulate and experimentally demonstrate a novel approach to generate tunable electromagnetically induced transparency (EIT) in a fully integrated silicon photonics circuit. It can also generate tunable fast and slow light. The circuit is a single ring resonator with two integrated tunable reflectors inside, which form an embedded Fabry-Perot (FP) cavity inside the ring cavity. The mode of the FP cavity can be controlled by tuning the reflections using integrated thermo-optic tuners. Under correct tuning conditions, the interaction of the FP mode and the ring resonance mode will generate a Fano resonance and an EIT response. The extinction ratio and bandwidth of the EIT can be tuned by controlling the reflectors. Measured group delay proves that both fast light and slow light can be generated under different tuning conditions. A maximum group delay of 1100 ps is observed because of EIT. Pulse advance around 1200 ps is also demonstrated.
The analogue of electromagnetically induced transparency in optical methods has shown great potential in slow light and sensing applications. Here, we experimentally demonstrated a coupled resonator induced transparency system with three cascaded ring coupled resonators in a silicon chip. The structure was modeled by using the transfer matrix method. Influences of various parameters including coupling ratio of couplers, waveguide loss and additional loss of couplers on transmission characteristic and group index have been investigated theoretically and numerically in detail. The transmission character of the system was measured by the vertical grating coupling method. The enhanced quality factor reached 1.22 × 10⁵. In addition, we further test the temperature performance of the device. The results provide a new method for the manipulation of light in highly integrated optical circuits and sensing applications.
We investigate the resonance property of a self-coupled optical waveguide (SCOW) with four coupling points. Under a special condition that the two outer couplers are in weak coupling and the two inner couplers are in strong coupling, an implicit standing-wave resonance mode is formed inside the SCOW structure. As the resonance is feedback coupled via an S-shape bus waveguide, electromagnetically induced transparency (EIT)-like resonance features are observed in the output transmission spectrum. The SCOW resonator is analyzed using the coupled mode theory and finite-difference time-domain simulation. The device is experimentally demonstrated on the silicon-on-insulator platform. The measurement results overall agree well with the theoretical calculation. The EIT-like peak can be tuned by a thermo-optic phase shifter made of a NIN-type silicon resistor integrated in the feedback waveguide. The results point to new ways of creating on-chip optical analog of the EIT phenomenon that can be utilized for various optical signal processing applications.
Metamaterials, or artificial materials with optical properties not known for natural materials, have recently been used to demonstrate unusual optical phenomena, such as negative refraction, perfect lenses, subwavelength components, and electromagnetic invisibility cloaks. Most of the metamaterials designed to date are periodic structures containing a single resonating element in each unit cell, such as a split-ring resonator (SRR), a cutwire, or a slab-wire pair [1]. In this contribution, we demonstrate that a metamaterial with two coupled SRRs can exhibit an effect reminiscent of electromagnetically induced transparency (EIT), a coherent process normally observed in three-level atomic media [2]. Due to this process, a small transparency window with low absorption appears in the spectral response of the metamaterial. Simultaneously, extremely steep normal dispersion is observed in the transparency window, which is useful for slow-light applications.
Research into slow light began theoretically in 1880 with the paper [1] of H A Lorentz, who is best known for his work on relativity and the speed of light. Experimental work started some 60 years later with the work of S L McCall and E L Hahn [2] who explored non-linear self-induced transparency in ruby. This field of research has burgeoned in the last 10 years, starting with the work of L Vestergaard Hau and coworkers on slow light via electromagnetically induced transparency in a Bose–Einstein condensate [3]. Many groups are now able to slow light down to a few metres per second or even stop the motion of light entirely [4]. Today, slow light – or more often `slow and fast light' – has become its own vibrant field with a strongly increasing number of publications. In broad scope, slow light research can be categorized in terms of the sort of physical mechanism used to slow down the light. One sort of slow light makes use of material dispersion. This dispersion can be the natural dispersion of the ordinary refractive index or can be the frequency dependence of some nonlinear optical process, such as electromagnetically induced transparency, coherent population oscillations, stimulated light scattering, or four-wave mixing processes. The second sort of slow light makes use of the wavelength dependence of artificially structured materials, such as photonic crystals, optical waveguides, and collections of microresonators. Material systems in which slow light has been observed include metal vapours, rare-earth-doped materials, Raman and Brillioun gain media, photonic crystals, microresonators and, more recently, metamaterials. A common feature of all of these schemes is the presence of a sharp single resonance or multiple resonances produced by an atomic transition, a resonance in a photonic structure, or in a nonlinear optical process. Current applications of slow light include a series of attractive topics in optical information processing, such as optical data storage, optical memories, quantum information devices, and optical communication systems in which the use of slow light will allow all-optical processing with less wasted heat. To implement these applications, devices such as buffers, memories, interferometers and switches that utilize slow light need to be developed. Future challenges include the need for improved coupling of light into slow light modes, overcoming propagation losses, and mitigating the influence of large dispersion of the group velocity. The collection of papers in this special issue of Journal of Optics features a broad spectrum of articles that highlight actual developments in many of the material types and schemes described above. It represents therefore an excellent up to date snapshot of the current state of the field of slow light research. References [1] Lorentz H A 1880 Uber die Beziehung zwischen der Fortpflanzung des Lichtes und der Körperdichte Wiedemann Ann. 9 641–64 [2] McCall S L and Hahn E L 1967 Self-induced transparency by pulsed coherent light Phys. Rev. Lett. 18 908–11 [3] Vestergaard Hau L, Harris S E, Dutton Z and Behroozi C H 1999 Nature 397 594 [4] Philips D F, Fleischhauer A, Mair A, Walsworth R L and Lukin M D 2001 Storage of light in atomic vapor Phys. Rev. Lett. 86 783–6