W. K. Chang

Self-suspended micro-resonators patterned in Z-cut lithium niobate membranes

We report on self-suspended micro-resonators patterned in Z-cut lithium niobate on insulator substrates. The fabrication technique consists of two single steps, focused ion beam milling for the micro- and nano-structuring and subsequent SiO2 etching for the realization of thin self-suspended membranes. The fabrication process of a free-standing photonic crystal cavity and a suspended micro-disk is described and the linear and nonlinear optical properties of the micro-resonators are investigated at telecommunication wavelengths. The whispering gallery modes of the micro-disk are measured experimentally and compared to an analytical model. The fundamental transverse-electric polarized mode of the photonic crystal cavity is measured and compared to three dimensional finite difference time domain simulations. Second harmonic generation enhancement due to the field confinement in the cavity mode is demonstrated. These results are promising for the use of Z-cut lithium niobate self-suspended membranes as platforms for highly efficient miniaturized photonic devices for telecommunication applications.

Spectral narrowing and manipulation in an optical parametric oscillator using periodically poled lithium niobate electro-optic polarization-mode converters.

We report a unique spectral narrowing and manipulation technique in an optical parametric oscillator (OPO) realized by an integrated periodically poled lithium niobate comprising an optical parametric gain medium sandwiched by two electro-optic polarization-mode converters (EO PMCs). We achieved a manipulation of the gain spectrum of the OPO via EO and/or temperature control of the EO PMCs, in which we obtained single to multiple signal spectral peaks from the OPO with a spectral width reduced by up to 10 times and peak intensity increased by up to 6 times in comparison with the original signal. Fast EO tuning of the narrowed signal spectral peak has also been demonstrated.

Adiabatic light transfer in titanium diffused lithium niobate waveguides.

Ultra-broadband adiabatic light transfer was demonstrated for the first time in lithium niobate. Coupling bandwidths and efficiencies of ~540 nm and >0.96, respectively, were obtained with 5-cm long Ti:LiNbO3 adiabatic couplers for both polarization modes.

Narrow-line, cw orange light generation in a diode-pumped Nd:YVO 4 laser using volume Bragg gratings

We report on the demonstration of a narrow-line, cw orange 593-nm laser achieved via intracavity sum-frequency generation (SFG) of a diode-pumped dual-wavelength (1064 and 1342 nm) Nd:YVO(4) laser using two volume Bragg grating (VBG) reflectors. At diode pump power of up to 3.6 W, the 593-nm intracavity SFG laser radiates at the single longitudinal mode of spectral linewidth as narrow as approximately 15 MHz. More than 23-mW single-longitudinal-mode or 40-mW, <8.5-GHz (10-pm) linewidth (at 4.2-W diode pump power) 593-nm orange lights can be obtained from this compact laser system. Spectral tuning of the orange light was performed via the temperature tuning of the two VBGs in this system, achieving an effective tuning rate of ~5 pm/degrees C.

Single aperiodically poled lithium niobate for simultaneous laser Q switching and second-harmonic generation in a 1342 nm Nd:YVO 4 laser

We report the design and experimental demonstration of an electro-optically Q-switched intracavity second-harmonic generator (ISHG) based on a single aperiodically poled lithium niobate (APLN) in a 1,342 nm Nd:YVO(4) laser. This intracavity APLN, designed using the aperiodic optical superlattice technique, can perform simultaneously as a laser Q switch and a second-harmonic generator. At approximately 200 VQ-switching voltage and a 5 kHz switching rate, we measured a pulse energy of approximately 5.7 microJ and a peak power of approximately 700 W at 671 nm from the constructed ISHG with a 5.2 W diode power based on 51% fundamental energy depletion.

Electro-optically spectrum tailorable intracavity optical parametric oscillator

We report a unique, pulsed intracavity optical parametric oscillator (IOPO) whose output spectrum is electro-optically (EO) tailorable based on an aperiodically poled lithium niobate (APPLN) working simultaneously as an optical parametric gain medium and an active gain spectrum filter in the system. We have successfully obtained from the IOPO the emission of single to multiple narrow-line signal spectral peaks in a near-infrared (1531 nm) band simply by electro-optic control. The power spectral density of the EO tailored signal can be enhanced by up to 10 times over the original (nontailored) signal.

Surface domain engineering in bulk and thin film lithium niobate: A systematic experimental study

Lithium niobate (LN) is widely used and established in nonlinear and integrated optics. Efficient nonlinear frequency conversion is enabled by quasi-phase matching of the interacting waves through periodic poling of the crystal domains. For realizing miniaturized optical devices, the application of lithium niobate on insulator (LNOI) substrates becomes increasingly important. LNOI consists of a LN thin film on top of a silica layer [1]. Using the common electric field poling [2] through an LNOI wafer is impeded by the insulating silica layer. Therefore, only surface poling techniques can be employed [3-5]. Here, the electric field is applied parallel to the substrate surface along the in-plane z-axis of the x-cut LN film. In this work, we present a systematic study of the surface domain engineering of bulk LN and LNOI, aiming to optimize the quality of the domain patterns.

Electro-optically spectrum narrowed, multiline intracavity optical parametric oscillators

We report on the first building of an active spectral narrowing mechanism in a pulsed, multiline optical parametric oscillator (OPO) based on a novel aperiodically poled lithium niobate (APPLN) device constructed using the aperiodic optical superlattice technique. The APPLN device functions simultaneously in the system as a multi-channel optical parametric down converter (OPDC) and an electro-optic (EO) gain spectral filter working on the corresponding (multiple) signal bands. When the APPLN OPO was installed in a diode pumped Nd:YVO4 laser system, highly narrowed dual-wavelength signal lines (at 1540 and 1550 nm) were observed at the output of the system through EO control of the APPLN. Correspondingly, an enhancement of the power spectral density of the source by a factor of ~7.8 with respect to the system operated in passive mode was found.

Electro-optically spectrum tailorable, aperiodically poled lithium niobate optical parametric oscillators

An electro-optically spectrum tailorable intracavity optical parametric oscillator (IOPO) was built based on a novel integrated aperiodically poled lithium niobate. Spectral narrowing and manipulation of the IOPO signal was demonstrated simply by electro-optic control.

Double-Prism Domain PPLN as Simultaneously a Laser Q-Switch and an Optical Parametric Down Converter in a Nd:YVO4 Laser

We report a tunable pulsed optical parametric oscillator using a double-prism domain PPLN as simultaneously an electro-optic Q-switch and a parametric generator in a Nd:YVO4 laser. >2.3-kW peak-power eye-safe light was obtained with this system.