Xiaoxue Zhao

Strong optical injection-locked semiconductor lasers demonstrating >100-GHz resonance frequencies and 80-GHz intrinsic bandwidths

By using strong optical injection locking, we report resonance frequency enhancement in excess of 100 GHz in semiconductor lasers. We demonstrate this enhancement in both distributed feedback (DFB) lasers and vertical-cavity surface-emitting lasers (VCSELs), showing the broad applicability of the technique and that the coupling Q is the figure-of-merit for resonance frequency enhancement. We have also identified the key factors that cause low-frequency roll-off in injection-locked lasers. By increasing the slave lasers DC current bias, we have achieved a record intrinsic 3-dB bandwidth of 80 GHz in VCSELs.

Microwave performance of optically injection-locked VCSELs

The optical injection-locking technique has been demonstrated to enhance the microwave performance of fiber-optic links based on vertical-cavity surface-emitting lasers (VCSELs). We report recent advances of a comprehensive study on VCSELs under ultrahigh injection-locking conditions. The performance improvements include /spl sim/20-dB increase of both spur-free dynamic range and RF link gain, a factor of 5-10 increase in resonance frequency, as well as /spl sim/20-dB reduction in laser noise.

50-GHz optically injection-locked 1.55-/spl mu/m VCSELs

High-speed directly modulated diode lasers are important for optical communications and optical interconnects. In this work, we demonstrate greatly enhanced resonance frequency for vertical-cavity surface-emitting lasers, from 7 to 50 GHz, under ultrahigh injection-locking conditions. In addition, a 20-dB gain is achieved for small signal modulation below resonance frequency.

Tunable ultraslow light in vertical-cavity surface-emitting laser amplifier

We report the experimental demonstration of tunable ultraslow light using a 1.55 um vertical-cavity surface-emitting laser (VCSEL) at room temperature. By varying the bias current around lasing threshold, we achieve tunable delay of an intensity modulated signal input. Delays up to 100 ps are measured for a broadband signal with modulation frequency of 2.8 GHz. With a VCSEL design optimized for amplification and leveraging the scalability of VCSEL arrays, delays of multiple modulation periods are feasible.

Novel cascaded injection-locked 1.55-μm VCSELs with 66 GHz modulation bandwidth

We demonstrate a novel cascaded configuration of optically injection-locked (COIL) VCSELs, which enables a wide and tailorable direct modulation bandwidth. Up to 66 GHz bandwidth is achieved using VCSELs with an original, free-running 10 GHz bandwidth. Different configurations of cascading are discussed in detail with the focus on optimizing the modulation bandwidth. We also discuss scaling capability of this technique to achieve tailorable modulation response.

THz-bandwidth tunable slow light in semiconductor optical amplifiers

We report tunable fractional delays of 250% for 700 fs pulses propagating in a 1.55 mum semiconductor optical amplifier at room temperature. This large fractional delay is attributed to a spectral hole created by the propagating pulses for pulses with duration shorter than the carrier heating relaxation time. Delay can be tuned electrically by adjusting the current with low amplitude variation across the tuning range.

Optoelectronic Oscillators Using Direct-Modulated Semiconductor Lasers Under Strong Optical Injection

In this paper, optoelectronic oscillators (OEOs) are demonstrated by using direct-modulated edge-emitting lasers under strong optical injection. The optically injection-locked OEO (OIL-OEO) enables a stable optoelectronic oscillation by converting an optical signal to an electrical signal through a long optical fiber loop. Low RF threshold gain of 7 dB for loop oscillation is attained by utilizing the cavity resonance amplification of an injection-locked semiconductor laser. We investigated both the open- and closed-loop characteristics of the OIL-OEO link by varying the injection locking parameters. Using this novel technique with optimized locking parameters, a 20-GHz RF signal with a phase noise of -123 dBc/Hz is successfully achieved without sophisticated frequency or temperature stabilization.

Reconfigurable Multifunctional Operation Using Optical Injection-Locked Vertical-Cavity Surface-Emitting Lasers

In this paper, we extend the system application of optical injection-locked (OIL) vertical-cavity surface-emitting lasers (VCSELs) to future optical networks by realizing multifunctional operation using a filter-assisted OIL-VCSEL scheme that can be reconfigured. By using a single chirp-adjustable injection-locked VCSEL (either single mode or multimode) followed by a tunable delay line interferometer, we experimentally demonstrate three functions, showing ultra-wide band (UWB) monocycle generation, nonreturn-to-zero (NRZ) to pseudoreturn-to-zero (PRZ) data format conversion, and NRZ-data clock recovery at 10 Gb/s.

Optically Injection-Locked 1.55-

The wavelength-division-multiplexed passive optical network is actively being developed to meet the ever-increasing bandwidth demands of end users in a cost-effective and future-proof manner. In this work, we propose a novel scheme that utilizes injection-locked 1.55-mum vertical-cavity surface-emitting lasers (VCSELs) for operation as low-cost, stable, directly modulated, and potentially uncooled upstream transmitters, whereby the injection-locking master source is furnished by modulated downstream signals. Our scheme eliminates the need for external injection-locking optical sources, external modulators, and wavelength stabilization circuitry. We show through experiments that the injection-locked VCSEL favors low injection powers and responds only strongly to the carrier but not the modulated data of the downstream signal, with good upstream transmission performance obtained over 25-km fiber

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In normal injection-locked semiconductor lasers, the modulation signals are applied to the slave laser. In this paper, we show that modulating the master light before injection exhibits distinctive modulation dynamics and frequency response. We first present a detailed theoretical model and simulation results. Experimentally, we have successfully demonstrated both master amplitude and master phase modulation. The resulting 3-dB bandwidths have been enhanced by up to three times, exceeding 50 GHz. The resonance frequency of the combined lasers is greater than 100 GHz.