P. C. Chui

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.

Parametric spectro-temporal analyzer (PASTA) for real-time optical spectrum observation

Real-time optical spectrum analysis is an essential tool in observing ultrafast phenomena, such as the dynamic monitoring of spectrum evolution. However, conventional method such as optical spectrum analyzers disperse the spectrum in space and allocate it in time sequence by mechanical rotation of a grating, so are incapable of operating at high speed. A more recent method all-optically stretches the spectrum in time domain, but is limited by the allowable input condition. In view of these constraints, here we present a real-time spectrum analyzer called parametric spectro-temporal analyzer (PASTA), which is based on the time-lens focusing mechanism. It achieves a frame rate as high as 100 MHz and accommodates various input conditions. As a proof of concept and also for the first time, we verify its applications in observing the dynamic spectrum of a Fourier domain mode-locked laser, and the spectrum evolution of a laser cavity during its stabilizing process.

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.

A Comprehensive Study on Crosstalk Suppression Techniques in Fiber Optical Parametric Amplifier by Modulation Format

With the presence of multiple-WDM input signals, ON-OFF keying (OOK)-modulated signals suffer from crosstalk in fiber optical parametric amplifier (OPA) due to cross-gain modulation (XGM) and four-wave mixing (FWM) effects. We demonstrated substantial crosstalk suppression in one-pump OPA by using return-zero differential phase-shift keying (RZ-DPSK) modulation format, which with its pattern-independent amplitude and subunity duty cycle would be effective in reducing the XGM and FWM effects significantly. By using the RZ-DPSK format, the power penalty was improved by at least 0.8 dB over RZ-OOK, non-RZ (NRZ)-DPSK, and NRZ-OOK formats with four 10 Gb/s channels, separated by 200 GHz spacing. With eight 10 Gb/s channels separated by 100 GHz spacing, a Q-factor penalty of the RZ-DPSK signal was reduced by 2.4 dB compared to RZ-OOK counterparts.

Speckle reduction of retinal optical coherence tomography based on contourlet shrinkage

Speckle reduction of retinal optical coherence tomography (OCT) images helps the diagnosis of ocular diseases. In this Letter, we present a speckle reduction method based on shrinkage in the contourlet domain for retinal OCT images. The algorithm overcomes the disadvantages of the wavelet shrinkage method, which lacks directionality and anisotropy. The trade-off between speckle reduction and edge preservation is controlled by a single adjustable parameter, which determines the threshold in the contourlet domain. Results show substantial reduction of speckle noise and enhanced visualization of layer structures as demonstrated in the image of the central fovea region of the human retina. It is expected to be utilized in a wide range of biomedical imaging applications.

Dual-Band Time-Multiplexing Swept-Source Optical Coherence Tomography Based on Optical Parametric Amplification

We report a high-speed time-multiplexing dual wavelength band swept laser source based on an optical parametric amplifier. A dual-band swept-source optical coherence tomography (OCT) system is implemented to demonstrate the advantage of a second wavelength band for fast spectroscopic OCT (SOCT). The innovative time-multiplexing architecture greatly reduces the complexity of the coupling and detecting configuration in comparison with the previous dual-band swept-source setup. We demonstrate the optical parametric amplification’s characteristics as a dual-band generator and applied the source to firstly achieve the SOCT around 1550 nm.

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.

High-Sensitivity Optical Preamplifier for WDM Systems Using an Optical Parametric Amplifier

We propose and demonstrate a novel preamplifier to improve receiver sensitivity for a 10-Gb/s return-to-zero on-off keying format by using a fiber optical parametric amplifier. Receiver sensitivity can reach down to -42 dBm at bit-error rate = 10-9. This sensitivity is only 1.1 dB off the quantum limit. The crosstalk issue is also investigated for this dual-end detection scheme in a wavelength-division-multiplexing system.