Hyuk-Kee Sung

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.

Optical Single Sideband Modulation Using Strong Optical Injection-Locked Semiconductor Lasers

We report on the experimental demonstration of optical single sideband (SSB) modulation using a directly modulated semiconductor laser under strong optical injection-locking. Modulation sidebands with 15-dB power ratio between the lower and upper sidebands have been achieved. The longer wavelength sideband is resonantly amplified by the injection-locked laser cavity mode. The radio-frequency performance of the optical SSB after 80-km fiber transmission is significantly improved compared with a typical symmetric sideband modulation of a free-running laser. A 622-Mb/s data transmission on a 20-GHz subcarrier is demonstrated over an 80-km fiber link.

Frequency Response Enhancement of Optical Injection-Locked Lasers

The modulation response of injection-locked lasers has been carefully analyzed, theoretically and experimentally, with a focus on the strong optical injection regime. We derive closed-form solutions to the relaxation oscillation (resonance) frequency and damping term, as well as the low-frequency damping term, and discuss design rules for maximizing resonance frequency and broadband performance. A phasor model is described in order to better explain the enhancement of the resonance frequency. Experimental curves match closely to theory. Record resonance frequency of 72 GHz and broadband results are shown.

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.

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.

Optical Properties and Modulation Characteristics of Ultra-Strong Injection-Locked Distributed Feedback Lasers

The optical properties and the frequency responses of ultrastrong (injection ratio > 10 dB) injection-locked distributed feedback lasers are investigated experimentally and theoretically. We have observed three distinctive modulation regimes under different frequency detuning between the master and the slave lasers. At large negative frequency detuning, the laser exhibits enhanced modulation efficiency at low frequencies. At intermediate frequency detuning, a flat frequency response with large 3 dB bandwidth is observed. At large positive frequency detuning, the modulation response shows a pronounced resonance peak at high frequencies. These phenomena can be explained by the resonance enhancement of the slave laser cavity mode, with the resonance frequency equal to the difference between the injection-locked frequency and the cavity mode. The experimental results agree well with theoretical calculations based on three coupled rate equations. Depending on the applications, the injection locking conditions can be optimized to achieve high RF link gain, broadband, or high resonance frequency operations.

Ultra-high, 72 GHz resonance frequency and 44 GHz bandwidth of injection-locked 1.55-/spl mu/m DFB lasers

We demonstrate record high resonance frequency (72 GHz) and record broadband performance (44 GHz) for 1.55-mum direct-modulated distributed-feedback (DFB) lasers under strong optical injection locking. The frequency response above 50 GHz is measured directly using optical heterodyne detection

Modulation bandwidth enhancement and nonlinear distortion suppression in directly modulated monolithic injection-locked DFB lasers

We have experimentally investigated the dynamic performance and the suppression of nonlinear distortions of a monolithic optical injection-locked distributed feedback (DFB) laser. The master and the slave lasers are monolithically integrated in a single strip of strongly coupled DFB laser. Optical injection locking is achieved by current tuning. The resonant frequency of the laser is increased from 11 GHz to 23 GHz, and nonlinear distortions are suppressed by more than 15 dB.

Scaling of resonance frequency for strong injection-locked lasers

It has been shown that strong optical injection locking can significantly enhance the resonance frequency of semiconductor lasers. In this Letter, we describe the trade-off between the maximum resonance frequency enhancement and the quality factor (Q) of the lossless laser cavity and show that the time-bandwidth product (product of photon lifetime and maximum resonance frequency) is equal to one half the square root of the external power injection ratio. The theoretical model agrees well with our experimental data.

Optical injection-locked gain-lever distributed Bragg reflector lasers with enhanced RF performance

Directly modulated fiber-optic links offers significant advantages in system cost and complexity. However, they often suffer from high link loss and inferior RF performance compared with externally modulated links. In this paper, we have experimentally investigated the amplitude modulation (AM) efficiency, modulation bandwidth, and the nonlinear distortions of a directly-modulated gain-lever distributed Bragg reflector (DBR) laser under external light injection for the first time. By combining gain-lever modulation with optical injection locking, increased modulation efficiency (10 dB) and bandwidth (3 times) as well as suppressed third-order intermodulation distortion (15 dB) have been achieved simultaneously.