Hyperband electro-optic modulator based on a two-pulley coupled lithium niobate racetrack resonator.

Integrated optical modulators (IOMs) are crucial components of on-chip photonic circuits. However, most conventional IOMs are restricted to specific spectral bands. Here, we leveraged the wide transparency window of lithium niobate in conjunction with the two-pulley coupled resonator method. This approach led to the development of a hyperband electro-optic (EO) modulator that operates over an expansive spectral range from 775 to 1550 nm on a single device. The demonstrated EO modulator exhibits half-wave voltage-length products of 0.25, 0.93, and 0.68 V·cm at wavelengths of 1539.50, 969.70, and 775.17 nm, respectively.

Spontaneous soliton mode-locking of a microcomb assisted by Raman scattering.

We successfully control the interaction dynamics between optical parametric oscillation (OPO) and stimulated Raman scattering, leading to the generation of distinct frequency comb states in a microresonator. Through Raman-scattered photons, a Raman comb with a sech2 envelope is demonstrated having a broad RF beat note linewidth of several hundred kHz. Moreover, under a specific coupling regime, we successfully generate self-locked Raman single-solitons which is confirmed by a narrow RF beat note of 25 Hz. Remarkably, this spontaneous Raman soliton is deterministically generated through adiabatic pump frequency detuning without the requirement of external locking mechanisms. Additionally, we identify a frequency comb with an unconventional envelope that can be fitted with a Lorentzian × sech2 function, generated via an anti-Stokes process with respect to the Raman comb.

Quantitative gas pressure measurement by molecular spectroscopy using chip-based supercontinuum in the mid-infrared.

We demonstrate the quantitative pressure measurement of gas molecules in the mid-infrared using chip-based supercontinuum and cepstrum analysis without additional measurements for baseline normalization. A supercontinuum generated in an on-chip waveguide made of chalcogenide glass having high nonlinearity passes through CO gas and provides a transmission spectrum. The gas absorption information is deconvoluted from the original supercontinuum spectral information containing temporal fluctuation by cepstrum analysis and extracted simply by applying a bandpass filter in the temporal domain. The gas pressure estimated from the extracted absorption information is consistent with the value measured by a pressure gauge within a difference of 1.25%, despite spectral fluctuations in the supercontinuum baseline comparable to the spectral depth of the gas absorption lines.

Two-point coupling method to independently control coupling efficiency at different wavelengths.

To efficiently access light waves confined in a high-quality-factor (Q) microcavity over a wide spectral range, it is necessary to independently control coupling efficiency at different wavelengths. Here we suggest an approach to add a degree of freedom to control the coupling efficiency based on a two-point coupling geometry. By changing the phase difference between two paths connecting two coupling points, various combinations of coupling efficiencies at multiple wavelengths can be achieved. An analytic model describing the coupling property is derived and confirmed by experimental results. It is also shown that the coupling property can be modified by adjusting the effective refractive index difference between a waveguide and a resonator.

Electro-optic control of the external coupling strength of a high-quality-factor lithium niobate micro-resonator.

Controlling the optical coupling between a micro-resonator and waveguide plays a key role in on-chip photonic circuits. Here, we demonstrate a two-point coupled lithium niobate (LN) racetrack micro-resonator that enables us to electro-optically traverse a full set of the zero-, under-, critical-, and over-coupling regimes with minimized disturbance of the intrinsic properties of the resonant mode. The modulation between the zero- and critical-coupling conditions cost a resonant frequency shift of only ∼344.2 MHz and rarely changed the intrinsic quality (Q) factor of 4.6 × 105. Our device is a promising element in on-chip coherent photon storage/retrieval and its applications.

Fabrication of Al2O3 coated 2D TiO2 nanoparticle photonic crystal layers by reverse nano-imprint lithography and plasma enhanced atomic layer deposition.

This paper reports simple process to enhance the extraction efficiency of photoluminescence (PL) from Eu-doped yttrium oxide (Y2O3:Eu3+) thin-film phosphor (TFP). Two-dimensional (2D) photonic crystal layer (PCL) was fabricated on Y2O3:Eu3+ phosphor films by reverse nano-imprint method using TiO2 nanoparticle solution as a nano-imprint resin and a 2D hole-patterned PDMS stamp. Atomic scale controlled Al2O3 deposition was performed onto this 2D nanoparticle PCL for the optimization of the photonic crystal pattern size and stabilization of TiO2 nanoparticle column structure. As a result, the light extraction efficiency of the Y2O3:Eu3+ phosphor film was improved by 2.0 times compared to the conventional Y2O3:Eu3+ phosphor film.

The variation of the enhanced photoluminescence efficiency of Y2O3:Eu3+ films with the thickness to the photonic crystal layer.

This study examined the effects of the thickness of Y(2)O(3):Eu(3+) phosphor films on quartz substrates coated with two-dimensional (2D) SiO(2) square-lattice nanorod photonic crystal layers (PCL) at identical heights on their extraction and absorption efficiency. The photoluminescence (PL) efficiency enhancement ratio decreased exponentially with increasing Y(2)O(3):Eu(3+) film thickness. The 2D PCL-assisted Y(2)O(3):Eu(3+) film with a thickness (t) = 400 nm showed enhancement in the upward and downward PL emission by factors of 6.2 and 8.6, respectively, with respect to those of a conventional flat film. This observation was attributed to diffraction scattering of the excitation and emission light.