Jim-Wein Lin

Photonic Generation of Few-Cycle Millimeter-Wave Pulse Using a Waveguide-Based Photonic-Transmitter-Mixer

We demonstrate a novel technique for photonic generation of few-cycle millimeter-wave (MMW) pulse using a WR-10 waveguide and near-ballistic unitraveling carrier photodiode (NBUTC-PD)-based photonic-transmitter-mixer (PTM). A 2.5-cycle MMW pulse is generated by simultaneously exciting the PTM optical port with ~100-GHz optical MMW sinusoidal signal and the intermediate-frequency (IF) port with a 25-ps electrical short pulse, respectively. Compared to results using femtosecond optical short pulses to directly excite the PTM (without E-O signal mixing), our approach is capable of providing much less signal distortion, eliminating the ringing oscillation in the tail of response, a much shorter pulse duration, and a higher peak power.

Photonic Generation and Detection of W-Band Chirped Millimeter-Wave Pulses for Radar

Based on the frequency-to-time mapping approach, we generate frequency-modulated millimeter-wave (MMW) pulses with central frequencies up to the W-band by a shaped optical pulse excitation of an MMW photonic transmitter with an ultrawide band photodiode as its key component. A coherent detection is achieved via a terahertz time-domain spectroscopic setup. Two different kinds of chirped MMW waveforms are generated; one is a linearly chirped sinusoidal pulse and the other is produced by a frequency-stepped modulation. Through appropriate optical spectral design, the frequency-chirped MMW pulses with instantaneous frequencies sweeping from 120 to 60 GHz, and a time-bandwidth product of ~ 25 is experimentally demonstrated.

Enhanced Performance of Narrowband Millimeter-Wave Generation Using Shaped-Pulse-Excited Photonic Transmitters

We demonstrate a novel method to greatly enhance the narrowband millimeter-wave (MMW) power generation by use of a near-ballistic uni-traveling-carrier photodiode-based photonic transmitter (PT) excited by shaped optical pulses. The spectrum of the best tailored optical pulses is centered at 1545 nm and spread among 16 main frequency components (channels), each with a spectral width of 15.5 GHz and a spacing of 93 GHz. Compared with quasi-sinusoidal optical modulation, we achieve an enhancement in the spectral power density by ~25 times. The power-enhanced narrowband MMW signal can be tuned over ~80 GHz (60-142 GHz). In addition, we observe significant enhancement of MMW peak power with an increase of the reverse bias voltage.

Wavelength-Tunable Er

We demonstrate a wavelength-tunable Er3+-doped femtosecond mode-locked soliton fiber laser by incorporating a short-pass edge filter into a ring cavity. When the filter is thermo-optically tuned toward shorter wavelengths to strongly attenuate the wavelengths longer than the cutoff, the constituting wavelengths of the mode-locked fiber laser move to shorter wavelengths and the laser center wavelength can be tuned over 1539.7 ~ 1560 nm. The cavity dispersion is preset in the deep soliton region to keep small fluctuations of laser pulsewidth when the laser wavelength is tuned.

^{3+}

We report progress on all-optical generation and switching of few-cycle sub-THz or (millimeter wave) MMW pulses, which is demonstrated by femtosecond (fs) optical pulse pumped photonic-transmitter-mixer (PTM) based on a high-power and ultra-wide-band near-ballistic uni-traveling carrier photodiode (NBUTC-PD). Irradiated by the 100 GHz optical local-oscillator (LO) signal and all-optical ultra-fast bias modulation (switching) of the PTM, a <; 2-cycle short MMW pulse with central frequency at 93 GHz is demonstrated. Our approach yields the shortest such pulses with much less signal distortion.

-Doped fs Mode-Locked Fiber Laser Using Short-Pass Edge Filters

By using optimized shaped optical pulses, we demonstrate a factor-of-~25 enhancement in the spectral power density of sub-THz wave at 93 GHz compared with that for quasi-sinusoidal optical modulation.

Toward single-cycle MMW pulse generation by optoelectronic switching of a high-speed photonic-transmitter-mixer

We demonstrate highly efficient pulse stretching in Er(3+)-doped femtosecond mode-locked fiber lasers by tailoring cavity dispersion using an intracavity short-pass edge filter. The cavity dispersion is preset at around zero to obtain the shortest pulsewidth. When the cutoff wavelength of the short-pass edge filter is thermo-optically tuned to overlap the constituting spectral components of mode-locked pulses, large negative waveguide dispersion is introduced by the steep cutoff slope and the total cavity dispersion is moved to normal dispersion regime to broaden the pulsewidth. The time-bandwidth product of the mode-locked pulse increases with the decreasing temperature at the optical liquid surrounding the short-pass edge filter. Pulse stretch ratio of 3.53 (623.8 fs/176.8 fs) can be efficiently achieved under a temperature variation of 4 °C.

Power-enhanced narrow-band Sub-THz generation by use of a photonic transmitter and shaped optical pulses

We demonstrate a wavelength-tunable Er3+-doped femtosecond mode-locked soliton fiber laser by incorporating a short-pass edge-filter into ring cavity. When the filter is thermo-optically tuned toward shorter wavelengths, the laser center wavelength can be tuned over 1539.7∼1560-nm.