Shinwook Lee

1.4kW high peak power generation from an all semiconductor mode-locked master oscillator power amplifier system based on eXtreme Chirped Pulse Amplification(X-CPA)

The concept of eXtreme Chirped Pulse Amplification (X-CPA) is introduced as a novel method to overcome the energy storage limit of semiconductor optical amplifiers in ultrashort pulse amplification. A colliding pulse mode-locked semiconductor laser is developed as a master oscillator and generates 600fs pulses with 6nm bandwidth at 975nm. Using a highly dispersive chirped fiber Bragg grating (1600ps/nm) as an extreme pulse stretcher and compressor, we demonstrate ~16,000 times extreme chirped pulse amplification and recompression generating optical pulses of 590fs with 1.4kW of peak power. These pulses represent, to our knowledge, the highest peak power generated from an all semiconductor ultrafast laser system.

eXtreme Chirped Pulse Oscillator Operating in the Nanosecond Stretched Pulse Regime

An eXtreme Chirped Pulse Oscillator (XCPO) implemented with a Theta cavity and based on a semiconductor optical amplifier (SOA) is presented for generating 10 ns frequency-swept pulses and 3.6 ps compressed pulses directly from the oscillator. In this experiment, we show the two distinct characteristics of the XCPO which are the scalability of the output energy and the mode-locked spectrum. By using these characteristics, we obtain a pulse energy of 58.4 pJ from the stretched pulse and a mode-locked optical bandwidth of 14.6 nm (10 dB) directly from the oscillator. The laser cavity design allows for low repetition rate operation <100 MHz, as well. The cavity, significantly, reduces nonlinear carrier dynamics, integrated self phase modulation (SPM), and fast gain recovery in an SOA. Due to the lasers ability to generate directly frequency-swept pulses from the oscillator, this oscillator can be used for high speed frequency-swept optical coherence tomography (OCT) and time-stretched photonic analog to digital converters (P-ADC).

Extreme chirped pulse oscillator (XCPO) using a theta cavity design

We demonstrate an extreme chirped pulse mode-locked laser, simultaneously generating near-transform-limited 3.9-ps optical pulses and /spl sim/510-ps linearly chirped output from the oscillator. The design overcomes fundamental limitations of energy extraction and nonlinearities induced by gain dynamics so that we can increase the dc current of the semiconductor optical amplifier up to 600 mA without distortion of the pulse characteristics. The maximum average power of the stretched pulses from the 1.95-GHz harmonically mode-locked semiconductor laser is measured to be 13.4 mW at 600 mA.

33MHz repetition rate semiconductor mode-locked laser using eXtreme Chirped Pulse Oscillator

An XCPO generates stretched pulses > 10 ns at a 33 MHz repetition rate from semiconductor mode-locked laser. The spectral bandwidth is scalable depending on the group delay of CFBG and the pulse repetition rate.

Ultrafast modelocked semiconductor laser - techniques and applications in networking, instrumentation and signal processing

This presentation will report our recent results for ultrashort pulse generation, low timing jitter pulses for sampling and metrology, optical frequency combs for coherent communications, and the use of ultrafast semiconductor diode lasers for potential applications in nonthermal ablation and machining.

Pulse-amplitude equalization by negative impulse modulation for rational harmonic mode locking

We propose a novel technique based on negative impulse modulation for pulse repetition rate multiplication by rational harmonic mode locking with pulse-amplitude-equalized pulses directly from the laser cavity. We have generated a pulse train of 15 GHz with more than 16 dB suppression of unwanted amplitude modulation spurs by using a 1 GHz RF signal. This is the highest suppression ratio for a repetition rate multiplication factor of 15 to our knowledge.

Picosecond pulse generation using a saturable absorber section of grating-coupled surface-emitting laser

We report on a passively and hybridly mode-locked grating-coupled surface-emitting laser (GCSEL) using the unpumped section of the GCSEL as a saturable absorber. We obtain 8.8-ps full-width at half-maximum (FWHM) autocorrelation pulses in passive mode-locked operation and an FWHM pulse duration of 3.4 ps in hybrid mode-locked operation, which are the shortest pulses from a GCSEL external cavity. With hybrid mode-locking, a peak power of 0.26 W and a spectral bandwidth of 0.6 nm are obtained. These results demonstrate the potential of multisegment GCSELs in ultrashort pulse generation.

Extreme chirped pulse modelocked diode laser ring oscillator using a theta cavity design

We demonstrate an extreme chirped pulse modelocked laser, simultaneously generating near-transform-limited 3.6 psec optical pulses and a 510 psec linearly chirped output. The design overcomes fundamental limitations of energy extraction and nonlinearities induced by gain dynamics

Precision laser ranging using extremely chirped pulses from chirped fiber Bragg gratings

Spectrally resolved interferometry combining up-chirped and down-chirped pulses allows for millimeter range resolution in laser ranging applications. Key in our approach is the use of temporally stretched optical pulses of 5 nanoseconds in duration. These stretched pulses were obtained from a femtosecond semiconductor mode-locked laser and were up-chirped and down-chirped using a chirped fiber Bragg grating and recombined to realize spectral interferometry. This approach provides a means to achieve the high pulse energies required for a laser radar application which are easy to achieve using nanosecond pulses but maintains the high spatial resolution associated with femtosecond optical pulses.

External-cavity actively mode-locked GCSEL (grating coupled surface emitting laser) and amplification characteristics of GCSOA (grating coupled surface emitting semiconductor optical amplifier)

We demonstrate an external cavity, active mode-locked GCSEL. The optical pulse duration from the actively mode-locked oscillator is 22.6ps and a 3 dB optical spectrum bandwidth is 0.07nm at 976nm. The average power from the oscillator is 0.72mW and its peak power is 108mW. The amplification characteristics of a GCSOA, optically injected with a continuously operated external cavity GCSEL, are also demonstrated. Despite the observation of lasing from the device, injection locking can be performed using an external source. At 4A peak current injection, 375mW output is achieved with 12mW injection.