Jiqiang Kang

Extended temporal cloak based on the inverse temporal Talbot effect

A temporal cloak with a significantly extended cloaking window and spatial distribution is created using the inverse temporal Talbot effect. The continuously cloaking window and the total cloaking ratio are 196 ps and 74%, respectively, which are 5.4 and 1.6 times larger than the previous record. Moreover, the cloak is maintained over 5-km of dispersion-compensating fiber (DCF), which enables cloaking temporal events at multiple positions simultaneously. To demonstrate the cloaking performance, both message-encoded and pseudo-random temporal events are successfully concealed. Last, but not least, since our configuration does not require opposite sign of dispersion, the idea can be applied analogously to the spatial domain according to the space-time duality, thus also enriching the spatial cloaking technique.

Compact and stable temporally magnified tomography using a phase-locked broadband source.

The temporally magnified tomography system is further improved in terms of resolution and imaging stability. We simplify the system configuration and improve the axial resolution simultaneously by utilizing a stabilized all-fiber broadband source. The highly stable spectrum of the source assisted by a phase-locked loop guarantees an improved imaging quality. In addition, the impact of the repetition-rate fluctuation of the source to the system stability is analyzed, which also applies to other temporal imaging systems. Achieving a 90-μm in-air resolution at 89-MHz A-scan rate and improved stability, we are taking one major step toward the practical application of this new optical tomographic modality.

Sensitivity enhancement in swept-source optical coherence tomography by parametric balanced detector and amplifier

We proposed a sensitivity enhancement method of the interference-based signal detection approach and applied it on a swept-source optical coherence tomography (SS-OCT) system through all-fiber optical parametric amplifier (FOPA) and parametric balanced detector (BD). The parametric BD was realized by combining the signal and phase conjugated idler band that was newly-generated through FOPA, and specifically by superimposing these two bands at a photodetector. The sensitivity enhancement by FOPA and parametric BD in SS-OCT were demonstrated experimentally. The results show that SS-OCT with FOPA and SS-OCT with parametric BD can provide more than 9 dB and 12 dB sensitivity improvement, respectively, when compared with the conventional SS-OCT in a spectral bandwidth spanning over 76 nm. To further verify and elaborate their sensitivity enhancement, a bio-sample imaging experiment was conducted on loach eyes by conventional SS-OCT setup, SS-OCT with FOPA and parametric BD at different illumination power levels. All these results proved that using FOPA and parametric BD could improve the sensitivity significantly in SS-OCT systems.

Tri-band spectroscopic optical coherence tomography based on optical parametric amplification for lipid and vessel visualization.

Abstract. A tri-band spectroscopic optical coherence tomography (SOCT) system has been implemented for visualization of lipid and blood vessel distribution. The tri-band swept source, which covers output spectrum in 1.3, 1.5, and 1.6  μm wavelength windows, is based on a dual-band Fourier domain mode-locked laser and a fiber optical parametric amplifier. This tri-band SOCT can further differentiate materials, e.g., lipid and artery, qualitatively by contrasting attenuation coefficients difference within any two of these bands. Furthermore, ex vivo imaging of both porcine artery with artificial lipid plaque phantom and mice with coronary artery disease were demonstrated to showcase the capability of our SOCT.

Ultrawide C- and L-band mode-locked erbium-doped fiber ring laser and its application in ultrafast microscopy

We report an ultrawide C- and L-band erbium-doped fiber ring laser with 92-nm bandwidth centered at 1550 nm and 44.5-MHz repetition rate. Furthermore, it was applied to ultrafast time-stretch microscopy.

Dissipative soliton resonance in thulium-doped fiber laser and its application for microscopy

We experimentally observe dissipative soliton resonance in a thulium-doped fiber laser operating in the anomalous dispersion regime. The laser output exhibits broad quasi-Gaussian spectra (~38 nm) centered at 1970 nm. The system is subsequently applied to spectrally encoded confocal microscopy.

Versatile laser and optical amplifier for ultrafast imaging

Photonic technologies revolutionize optical imaging, from source generation to signal detection. Here we report MHz broadband swept sources for ultrafast imaging modalities. Their performance can be enhanced by broadband and sensitive fiber optical parametric amplifier.

Pulse-spacing manipulation in a passively mode-locked multipulse fiber laser

Passively mode-locked fiber lasers have been intensively applied in various research fields. However, the passive mode-locking typically operates in free-running regime, which easily produces messy multiple pulses due to the fruitful nonlinear effects involved in optical fibers. Actively controlling those disordered pulses in a passively mode-locked laser is of great interest but rarely studied. In this work, we experimentally investigate a flexible pulse-spacing manipulation in the passively mode-locked multipulse fiber laser by both intracavity and extracavity methods. A tuning range of pulse spacing up to 1.5 ns is achieved. More importantly, continuous pulse-spacing modulation is successfully demonstrated through external optical injection. It is anticipated that the results can contribute to the understanding of laser nonlinear dynamics and pursuing the optimal performance of passively mode-locked fiber lasers for practical applications.

Optical receiver sensitivity enhancement by single- and dual-band fiber optical parametric amplifier

A semi-classical model is proposed theoretically and demonstrated experimentally on the optical receiver sensitivity enhancement by single-band (signal or idler) and dual-band (signal and idler) fiber optical parametric amplifier (FOPA). The sensitivity enhancement by single-band is determined by the gain of FOPA and the transmission loss of signal and idler, and it can be further improved by up to 3-dB using amplified signal and phase-conjugated idler together at dual-band configuration. The theoretical results are experimentally verified in both fiber communication and biomedical imaging applications. This detection sensitivity enhancement scheme can be potentially applied in the scenarios where ultrafast broadband signal at low-power level is being handled.

Fiber chirped pulse amplification of a short wavelength mode-locked thulium-doped fiber laser

Exploiting the promising third near-infrared optical window (1600–1870 nm) for deep bioimaging is largely underdeveloped, mostly because of the lack of stable femtosecond laser sources in leveraging the less scattering loss and locally reduced water absorption. In this letter, we demonstrate the fiber chirped pulse amplification of a short wavelength mode-locked thulium-doped fiber laser (TDFL) at 1785 nm. The mode-locked TDFL (via nonlinear polarization rotation) operates stably at the soliton pulsing regime with a fundamental repetition rate of 46.375 MHz. Utilizing a two-stage fiber amplifier incorporated along the pulse chirping fiber, the power of the laser pulse is boosted up to 690 mW. After dechirping with a diffraction grating pair, laser pulse with a duration of 445 fs, pulse energy of 5.7 nJ, and peak power of 12 kW is achieved. Higher power can be achieved by exploiting low-loss high power fiber components at this special wavelength range.