Search

Optical frequency combs can potentially provide an efficient light source for multi-terabit-per-second optical superchannels. However, as the bandwidth of these multi-wavelength light sources is increased, it can result in low per-line power. Optical amplifiers can be used to overcome power limitations, but the accompanying spontaneous optical noise can degrade performance in optical systems. To overcome this, we demonstrate wideband noise reduction for comb lines using a high-Q microring resonator whose resonances align with the comb lines, providing tight optical filtering of multiple combs lines at the same time. By distilling an optical frequency comb in this way, we are able to reduce the required comb line OSNR when these lines are used in a coherent optical communications system. Through performance tests on a 19.45-GHz-spaced comb generating 71 lines, using 18 Gbaud, 64-QAM sub-channels at a spectral efficiency of 10.6 b/s/Hz, we find that noise-corrupted comb lines can reduce the optical signal-to-noise ratio required for the comb by ∼9 dB when used as optical carriers at the transmitter side, and by ∼12 dB when used as a local oscillator at the receiver side. This demonstration provides a method to enable low power optical frequency combs to be able to support high bandwidth and high-capacity communications. [ABSTRACT FROM AUTHOR]

Microbottle resonators (MBR) have attracted research interest for studying nonlinear optical interactions in last two decades, due to the ultra-tight optical confinement in spaces of three dimensions. In this paper, silica MBRs exhibiting rich resonant modes with ultra-high quality factor up to $3.73 \times {10^8}$ are demonstrated, based on which a portable and robust packaged platform with a tapered fiber coupling is established. Such a packaged platform effectively avoids external perturbations such as air flow and tiny mechanical vibrations, which supports our experimental demonstration of nonlinear scattering effects including four-wave mixing (FWM), simulated Raman scattering, and simulated Brillouin scattering. As a result, Raman-assisted FWM and Brillouin-assisted FWM are observed due to the strong field enhancement in the MBR. In a further investigation, a Kerr frequency comb with broad bandwidth of ∼200 nm and a Raman-assisted comb with a bandwidth up to ∼50 nm is achieved, correspondingly. Our works show the versatility of MBR for fundamental research and may open a new route to the development of practical applications in frequency conversion, spectroscopy and communications. [ABSTRACT FROM AUTHOR]

Single dissipative Kerr soliton (DKS) formed in microresonator shows few-cycle femtosecond pulses along with smooth and phase-coherent comb spectra that easily reaching an octave spanning. Such unique characteristics lead to revolutionary breakthrough in advanced communications, spectroscopy, metrology, etc. However, as hidden deepest inside the multistable states of driven-damped microresonator, the single DKS state remains challenging to generate deterministically and straightforwardly. Here, we theoretically show that a train of energetic pulse trigger imposed on an external continuous-wave driving pump can quickly kick start the cavity to deterministically evolve into a single DKS state. Neither the pump frequency nor the cavity resonance frequency requires to be scanned, thus possessing the potential for turnkey soliton microcombs generation. The additional degrees of freedom given by the combined pump enables the manipulation of multi-DKS and even perfect soliton crystals generation in the same microresonator. The proposed pulse train triggering method can also be harnessed for ultrahigh speed all-optical clock recovery with a potential rate up to terahertz. Our results open up a new path for manipulating single and multi-DKS in microesonators and a robust optical clock recovery module simultaneously possessing ultrahigh speed, on-chip integration, and cost-efficiency. [ABSTRACT FROM AUTHOR]

The coupling mechanism of a system in which two identical microresonators with slot are coupled through a tapered fiber is theoretically investigated and its transmission rate is numerically calculated. Physical parameters are evaluated for their impacts on the transmission spectra. Fano-like lineshape is observed under certain condition (γc > 2κ) and optimization of dominant parameters (κ1/κ0, kL, γc/κ0 and Q0) is applied to make the lineshape more steepened and sharper. This structure is promising for application in optical switch, sensing and research on Fano resonance. [ABSTRACT FROM AUTHOR]

In this letter, we report an optical frequency comb (OFC) generated in a whispering-gallery-mode microbottle resonator, and present a convenient and simple method for adjustment of the zero dispersion wavelength (ZDW). The ZDW tunability of the microbottle resonator realized by exciting modes with different axial mode numbers is predicted theoretically and demonstrated experimentally by changing the coupling position of a tapered fiber. Cascaded four-wave mixing (FWM)-based frequency combs are investigated by pumping the resonator in different dispersion regimes. The results show that the OFC based on degenerated FWM could be generated under the anomalous dispersion, while Raman or Raman-assisted OFC are obtained in the normal dispersion regime. [ABSTRACT FROM AUTHOR]

The single soliton propagating in a microresonator (MRR) is characterized by a smooth spectrum. However, the number of solitons that propagate in an MRR in the anomalous dispersion regime is usually stochastic and gives rise to a complex spectrum. In this paper, we introduce a new passive mechanism based on third-harmonic-induced nonlinear coupling for the formation of a single deterministic soliton in an MRR. We show that with appropriate fundamental and third harmonic mode coupling strength and a slight phase mismatch, deterministic single soliton generation can be realized by simply scanning the detuning of a continuous wave serving as a pump. Under strong mode coupling strength, a relatively smaller wave vector mismatch within suitable range can be used for single soliton generation. Our work provides a potential approach for on-chip generation of coherent optical Kerr combs and efficient THG conversion. [ABSTRACT FROM AUTHOR]

Microwave phased array antennas (PAAs) are very attractive to defense applications and high-speed wireless communications for their abilities of fast beam scanning and complex beam pattern control. However, traditional PAAs based on phase shifters suffer from the beam-squint problem and have limited bandwidths. True-time-delay (TTD) beamforming based on low-loss photonic delay lines can solve this problem. But it is still quite challenging to build large-scale photonic TTD beamformers due to their high hardware complexity. In this paper, we demonstrate a photonic TTD beamforming network based on a miniature microresonator frequency comb (microcomb) source and dispersive time delay. A method incorporating optical phase modulation and programmable spectral shaping is proposed for positive and negative apodization weighting to achieve arbitrary microwave beam pattern control. The experimentally demonstrated TTD beamforming network can support a PAA with 21 elements. The microwave frequency range is 8–20 GHz; and the beam scanning range is $\pm \text{60.2}^\circ$. Detailed measurements of the microwave amplitudes and phases are performed. The beamforming performances of Gaussian, rectangular beams, and beam notch steering are evaluated through simulations by assuming a uniform radiating antenna array. The scheme can potentially support larger PAAs with hundreds of elements by increasing the number of comb lines with broadband microcomb generation. [ABSTRACT FROM AUTHOR]

Software-defined servers provide high flexibility and customizablility with low power consumption. To satisfy the ultrahigh bandwidth requirement of the interconnection of these servers, integrated optical switch networks, based on the recent development of silicon photonics, are promising candidates. In this study, we present a family of floorplan optimized delta optical networks (FODONs) with the proposed stage switches. Both the analytical approximation and the loss model based on the exhaustive search approach are developed to evaluate the loss parameters in the networks. The optimization of the stage switch radix is conducted as well. Results show that when 32 WDM channels are employed, the worst-case loss of the $ 1024\times 1024$ FODON with $ 4\times 4$ stage switches is only 26 dB, which is 95, 63, 37 dB less than Beneš, Fat-tree, and Baseline networks of the same size, respectively. Furthermore, the average loss and the cost of hardware resources of FODONs are much lower than other networks. [ABSTRACT FROM PUBLISHER]

We fabricated and theoretically investigated an add–drop filter (ADF) using an on-chip whispering gallery mode (WGM) microtoroid resonator with ultrahigh-quality factor (Q) side coupled to two taper fibers, forming the bus and drop waveguides. The new device design incorporates silica side walls close to the microresonators which not only enable placing the coupling fibers on the same plane with respect to the microtoroid resonator but also provides mechanical stability, leading to an ADF with high drop efficiency and improved robustness to environmental perturbations. We show that this new device can be thermally tuned to drop desired wavelengths from the bus without significantly affecting the drop efficiency, which is around 57%. [ABSTRACT FROM PUBLISHER]

Microring resonators can be exploited for biochemical sensing applications. To gain a better understanding of the design and optimization of microring sensors, the authors analytically derive the detection limit and the sensitivity. Other important parameters, including the ON-OFF contrast ratio and the signal-to-noise ratio (SNR), are also considered. In this paper, the combination of two sensing mechanisms and two sensing schemes are analyzed. These calculations provide a guideline for determining the microring geometry to satisfy the desired sensing requirements. In addition, the results can provide insights on how to enhance the sensitivity and lower the detection limit [ABSTRACT FROM PUBLISHER]

This paper presents an analysis of optical buffers based on slow-light optical delay lines. The focus of this paper is on slow-light delay lines in which the group velocity is reduced using linear processes, including electromagnetically induced transparency (EIT), population oscillations (POs), and microresonator-based photonic-crystal (PC) filters. We also consider slow-light delay lines in which the group velocity is reduced by an adiabatic process of bandwidth compression. A framework is developed for comparing these techniques and identifying fundamental physical limitations of linear slow-light technologies. It is shown that slow-light delay lines have limited capacity and delay-bandwidth product. In principle, the group velocity in slow-light delay lines can be made to approach zero. But very slow group velocity always comes at the cost of very low bandwidth or throughput. In many applications, miniaturization of the delay line is an important consideration. For all delay-line buffers, the minimum physical size of the buffer for a given number of buffered data bits is ultimately limited by the physical size of each stored bit. We show that in slow-light optical buffers, the minimum achievable size of 1 b is approximately equal to the wavelength of light in the buffer. We also compare the capabilities and limitations of a range of delay-line buffers, investigate the impact of waveguide losses on the buffer capacity, and look at the applicability of slow-light delay lines in a number of applications. [ABSTRACT FROM PUBLISHER]

An analytical method for the calculation of the coupling between a microdisk and a waveguide is presented. The theoretical analysis is based on the perturbation theory well known in integrated optics. Only whispering-gallery modes with high quality factor are considered to be propagating in this study when the microresonator is used as a laser structure. The influence of the distance disk/waveguide is investigated. These results are compared with calculations obtained with a two-dimensional finite-difference time domain needing more computational requirements. A good agreement between both methods is shown. [ABSTRACT FROM PUBLISHER]