Wangkuen Lee

Optical frequency combs from semiconductor lasers and applications in ultrawideband signal processing and communications

Modelocked semiconductor lasers are used to generate a set of phase-locked optical frequencies on a periodic grid. The periodic and phase coherent nature of the optical frequency combs makes it possible for the realization of high-performance optical and RF arbitrary-waveform synthesis. In addition, the resulting optical frequency components can be used for communication applications relying on direct detection, dense wavelength division multiplexing (WDM), coherent-detection WDM, optical time-division multiplexing, and optical code division multiple access. This paper highlights the recent results in the use of optical frequency combs generated from semiconductors for ultrawideband signal processing and communication applications.

Ultrashort, high-power pulse generation from a master oscillator power amplifier based on external cavity mode locking of a quantum-dot two-section diode laser

We investigate an external cavity curved two-section mode-locked diode laser system based on quantum-dot (QD) gain media near 1.3μm. Pulses are generated from the external laser cavity at a 5‐GHz repetition rate and amplified using a multilayer quantum-dot semiconductor optical amplifier. The pulses are compressed with a dual-grating dispersion compensator. The shortest, near transform-limited pulses are obtained when the mode-locked pulses are positive (up) chirped. The compressed pulses are 1.2ps in duration, with a pulse energy of 1.46pJ, implying a peak power of 1.22W.

Subgigahertz channel filtering by optical heterodyne detection using a single axial mode from an injection-locked passively mode-locked semiconductor laser

We report experimental results of fine (subgigahertz) channel filtering via optical heterodyne detection based on an optical injection locking technique. A passively mode-locked semiconductor laser injection locked to a master oscillator forms a comb of discrete frequency probes, and a single axial mode is used as a local oscillator (LO). The injection-locked LO carrier showed 42-dB phase noise suppression at 100-kHz offset. One of two analog radio frequency signals detuned by only 200 MHz showed a signal-to-noise ratio over 65 dB/Hz through demultiplexing with a commercially available microwave bandpass filter. The single sideband noise of the heterodyne beat tone at 13.160 GHz was measured to be -123 dBc/Hz at 100 kHz offset from the carrier under injection-locked state.

Synchronized Mode-Locked Semiconductor Lasers and Applications in Coherent Communications

The general features and characteristics of two different external-cavity mode-locked semiconductor lasers (MSLs) were studied. Coherent optical frequency combs and short pulses from the MSLs were used to develop a synchronized MSL system. Exploiting the synchronized MSLs as a phase-locked transmitter and a local oscillator, various heterodyne and homodyne coherent detection techniques were experimentally demonstrated. The experimental results have shown that the phase-coherent optical frequency combs and short pulses from the synchronized MSLs are very promising optical sources for many future coherent photonic systems, especially for spectrally phase-encoded optical code-division multiple access (SPE-OCDMA).

Ultralow noise optical pulse generation in an actively mode-locked quantum-dot semiconductor laser

We report excellent noise performance of an external-cavity actively mode-locked laser based on quantum-dot gain medium. Optical pulse trains with less than 7.5fs residual timing jitter (1Hzto10MHz) for a 12.8GHz harmonically mode-locked ring laser were obtained. This result represents, to our knowledge, the lowest residual jitter reported from actively mode-locked semiconductor lasers, and shows that quantum-dot mode-locked lasers are promising as sources of ultralow noise optical pulse trains.

Coherent pulse detection and multi-channel coherent detection based on a single balanced homodyne receiver.

The performance of coherent pulse detection (CPD) and multichannel coherent detection (MCCD) based on a single dual-balanced homodyne receiver was experimentally demonstrated using a gratingcoupled hybridly mode-locked semiconductor laser. Compared with direct detection, a high coherent gain of over 10 dB, as well as an SNR improvement of over 5 dB, was obtained in both detection schemes. Our experimental results have confirmed that the coherent detection processes in CPD and MCCD are nearly the same based on a square-root LO power dependence. Nevertheless, the MCCD scheme has shown an advantage in a path-length error over the CPD scheme, revealing 2~3 dB improvement in sensitivities.

Wavelength tunable mode-locked quantum-dot laser

We study the characteristics of wavelength tunable quantum-dot mode-locked lasers using a curved two-section device, external grating, and optical bandpass filter. Wide wavelength tunability is demonstrated due to the fact that the center wavelength of mode-locking is extended to excited state transitions as well as ground state transitions of the quantum-dot gain media.

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.

Modelocked diode lasers for ultra-wideband communications and signal processing

Modelocked semiconductor lasers are used to generate a set of phase locked optical frequencies on a periodic grid. The resulting optical frequency components can be used for communication applications relying on direct detection, dense WDM, coherent detection WDM, OTDM, and OCDMA. In addition, the periodic and phase coherent nature of the optical frequency combs make it possible for the realization of high performance optical and RF arbitrary waveform synthesis. This paper highlights recent results in the use of optical frequency combs for ultrawideband communication and signal processing applications.

Stabilized Optical Frequency Combs from Diode Lasers - Applications in Optical Communications, Signal Processing and Instrumentation

The development of compact sources of stabilized optical frequency combs from semiconductor diode lasers will be reviewed. Applications in coherent communications and signal processing will be suggested and highlighted.