Kim K. Y. Cheung

Manipulating supercontinuum generation by minute continuous wave

We report a simple triggering mechanism that greatly enhances and stabilizes supercontinuum generation by using an extremely weak cw light (~200,000 times weaker than the pump light). Such an active manipulation scheme can be enabled by a wide range of input conditions and circumvents complex techniques such as precise time delay tuning and dedicated feedback control. It thus offers a handy and versatile approach to control and optimize supercontinuum generation, expanding its range of applications, including ultrafast all-optical signal processing, spectroscopy, and imaging. The utility of the present technique for improving signal integrity in chirped pump optical parametric amplification is also demonstrated.

Widely tunable picosecond optical parametric oscillator using highly nonlinear fiber.

We demonstrated a fully fiber-integrated widely tunable picosecond optical parametric oscillator based on highly nonlinear fiber. The ring cavity with a 50 m highly nonlinear fiber was synchronously pumped with a picosecond mode-locked fiber laser. The tuning range was from 1413 to 1543 nm and from 1573 to 1695 nm, which was as wide as 250 nm. A high-quality pulse was generated with a pulse width narrower than that of the pump.

Fast and wide tuning wavelength-swept source based on dispersion-tuned fiber optical parametric oscillator

We demonstrate a dispersion-tuned fiber optical parametric oscillator (FOPO)-based swept source with a sweep rate of 40 kHz and a wavelength tuning range of 109 nm around 1550 nm. The cumulative speed exceeds 4,000,000 nm/s. The FOPO is pumped by a sinusoidally modulated pump, which is driven by a clock sweeping linearly from 1 to 1.0006 GHz. A spool of dispersion-compensating fiber is added inside the cavity to perform dispersion tuning. The instantaneous linewidth is 0.8 nm without the use of any wavelength selective element inside the cavity. 1 GHz pulses with pulse width of 150 ps are generated.

All-Fiber-Based Ultrashort Pulse Generation and Chirped Pulse Amplification Through Parametric Processes

We experimentally demonstrate, for the first time to the best of our knowledge, the use of optical fiber for optical parametric chirped pulse amplification to amplify subpicosecond pulses. We use this system to amplify a subpicosecond signal at 1595 nm generated by a fiber-optical parametric oscillator. The 750-fs signal from the oscillator output is stretched to 40 ps, amplified by an all-fiber optical parametric amplifier and then compressed to 808 fs. The peak power of the signal is amplified from 93 mW to 10 W.

Tunable single-longitudinal-mode fiber optical parametric oscillator

A tunable single-longitudinal-mode (SLM) fiber optical parametric oscillator is demonstrated by using a subring cavity and a fiber loop mirror incorporated with a saturable absorber. It can provide dual-wavelength SLM output.

Wavelength-swept spectral and pulse shaping utilizing hybrid Fourier domain modelocking by fiber optical parametric and erbium-doped fiber amplifiers

We report the first Fourier domain modelocked (FDML) laser constructed using optical parametric amplifier (OPA) in conjunction with an erbium-doped fiber amplifier (EDFA), centered at approximately 1555 nm, to the best of our knowledge. We utilize a one-pump OPA and a C-band EDFA in serial configuration with a tunable Fabry-Perot interferometer to generate a hybrid FDML spectrum. Results demonstrate a substantially better spectral shape, output power and stability than individual configurations, with decreased sensitivity to polarization changes. We believe this technique has the potential to enable several amplifiers to complement individual deficiencies resulting in improved spectral shapes and power generation for imaging applications such as optical coherence tomography (OCT).

Fiber-Optical Parametric Amplifier With High-Speed Swept Pump

We experimentally demonstrate and characterize a high-speed frequency-swept pump in a fiber-optical parametric amplifier (FOPA). The high-speed swept pump is achieved with the swept rate as high as 78 MHz by a technique called dispersive Fourier transformation (DFT), which circumvents the fundamental speed limitation shown in the conventional swept-sources based on the cavity configurations. Based on such swept pump FOPA, the idler can be generated with a wavelength range twice the pump bandwidth. Such an all-optical approach offers an order-of-magnitude higher swept rate and thus lends itself to many applications such as high-speed signal processing and optical imaging.

Wide-Band Generation of Picosecond Pulse Using Fiber Optical Parametric Amplifier and Oscillator

We first demonstrate a wideband generation of picosecond pulse using fiber optical parametric amplifier (FOPA). High quality pulse is generated at 85 nm away from the pump with pulsewidth narrower than that of the pump. We then explore fiber optical parametric oscillator (FOPO) configuration which has the advantage of eliminating the need of seeding laser, leading to a potentially wider wavelength tunability and flexibility. The tuning range of the FOPO is from 1511 nm to 1541 nm and from 1583 nm to 1613 nm, which is as wide as 60 nm, with wavelength span of over 100 nm. Nearly-transform-limited sub-picosecond pulses are generated by this technique.

A Time-Dispersion-Tuned Picosecond Fiber-Optical Parametric Oscillator

A synchronously pumped picosecond fiber-optical parametric oscillator was demonstrated with fixed pump wavelength and with a 50-m highly nonlinear dispersion-shifted fiber as parametric gain medium. Time-dispersion-tuning offered a continuously wavelength tuning range as wide as 150 nm from 1413 to 1478 nm and from 1610 to 1695 nm with a pulsewidth of 10 ps.

Dispersion-Tuned Harmonically Mode-Locked Fiber-Optical Parametric Oscillator

The stable operation of a high-repetition-rate dispersion-tuned harmonically mode-locked fiber-optical parametric oscillator (FOPO) is demonstrated for the first time to the best of our knowledge. The experimental results match well with the theory. By introducing large cavity dispersion, the round-trip delay can vary with wavelength. Thus the cavity can be synchronized with the modulation frequency of an external clock passively. The FOPO can be tuned simply by adjusting the modulation frequency. A stable 10-GHz pulse train is obtained over 6-nm tuning range for each of the signal and idler.