Sui F. Lim

Modulation of a vertical-cavity surface-emitting laser using an intracavity quantum-well absorber

We demonstrate a novel modulation technique with a vertical cavity surface-emitting laser (VCSEL) using an intracavity embedded voltage-biased quantum well absorber. We achieved a -3-dB small-signal bandwidth of 9 GHz and a response of 7 GHz//spl radic/(mA) by modulation of the absorber. Our calculations show that this technique introduces significantly less chirp at higher frequencies than direct current modulation.

Vertical-cavity lasers with an intracavity resonant detector

We demonstrate the first intracavity quantum-well photodetector within an InGaAs DBR QW VCSEL for top- and bottom-emitting structures. Minimal spontaneous emission is detected by the internal detector. Dark current is on the order of picoamperes, limited by our instrument noise floor. The internal detector demonstrates high insensitivity to external ambient light as compared to an external detector. Combining various measurement techniques, we gain an understanding of such an integration and discuss the various ramifications of the issues surrounding the design, fabrication, and performance of these integrated VCSEL-detectors. This configuration facilitates flexible tailoring of the laser efficiency and the integrated detector responsivity.

The physics of negative differential resistance of an intracavity voltage-controlled absorber in a vertical-cavity surface-emitting laser

We have constructed a vertical-cavity, surface-emitting laser with a voltage-controlled quantum well absorber in the upper mirror stack. If the lasing wavelength of this device is designed to be slightly longer than the absorber band edge, sharp negative differential resistance can be obtained in the absorber under lasing conditions. We present strong experimental evidence that this behavior arises from redshifting of the absorption excitonic peak due to the quantum confined Stark effect. Design criteria are proposed for applications including high speed modulation and self-pulsation.

Compact, integrated optical disk readout head using a novel bistable vertical-cavity surface-emitting laser

We demonstrate a novel integrated optical disk readout head using a vertical-cavity surface-emitting laser (VCSEL) with an intracavity quantum-well absorber. Optical pickup detection is performed by measuring the change in the absorber voltage as optical feedback into the VCSEL cavity is varied. We obtain a 0.22-V peak-to-peak response with a RC time constant of 20 /spl mu/s, indicating a rolloff frequency of 50 kHz. The unique design flexibility of this device allows amplification of the detection signal by operating the device in a bistable regime.

Dynamic behavior and applications of a three-contact vertical-cavity surface-emitting laser

We have developed a novel three-contact vertical-cavity surface-emitting laser (VCSEL) with an intracavity absorber for use in high-speed data communications. We demonstrate two distinct designs for our VCSEL and discuss the device physics underlying the behaviors of the two designs. Furthermore, we demonstrate a wide range of applications for these VCSELs, including optical intensity modulation, phase and amplitude modulation of a microwave optical subcarrier, optical bistability, self-pulsation, and optical disk readout.

Independent phase and magnitude control of an optically carried microwave signal with a three-terminal vertical-cavity surface-emitting laser

We demonstrate a compact integrated method for phase and magnitude control of an optically carried microwave signal with no external high-frequency circuitry. Our device consists of a novel three contact VCSEL, which permits external control of both the cavity loss and gain. Independent control of the phase and magnitude of the optically carried signal is demonstrated. With reference to the small-signal rate equations, we show that such independent control is only possible given the extra degree of freedom offered by the three contact design.

Comparative study of the analog performance of a vertical-cavity surface-emitting laser under gain and cavity loss modulation

The analog performance of a vertical-cavity surface-emitting laser is compared for gain and cavity loss modulation. Direct gain modulation consistently results in a larger spur free dynamic range (SFDR) than does cavity loss modulation; the maximum SFDR achieved is 96.5 dB Hz2/3. Analysis of the physical origins of variations in the measured SFDR with applied electrical bias indicates potential strategies for improving the analog response of these lasers.

Frequency tuning of self-pulsations in a VCSEL with a voltage-controlled saturable absorber

Summary form only given. Self-pulsating lasers are extremely useful in a variety of applications, including multimode fiber systems and optical disk readout. It is desirable to attain self-pulsating vertical-cavity surface-emitting lasers (VCSELs) because the surface-normal geometry facilitates two-dimensional array configurations and wafer-scale fabrication. We previously demonstrated on-off control of GHz-range self-pulsations in a VCSEL. In this work, we believe we demonstrate for the first time 700 MHz frequency tuning of self-pulsations in a VCSEL by using an active quantum well absorber integrated in the mirror stack. These pulsations have a 700 kHz relative frequency linewidth. We present theoretical and experimental demonstrations of a novel design criterion, whereby the absorber wavelength is slightly shorter than the lasing wavelength, leading to the negative differential resistance, which is essential to obtaining self-pulsation. By careful device design, the VCSEL can be made to self-pulsate at low absorber biases, GHz-range frequencies, and potentially at high output powers.

Self-pulsations, bistability, and intracavity quantum-well absorber modulation of VCSELs

We have constructed a novel VCSEL structure in which a voltage biased quantum well absorber is embedded in the mirror stack. Several applications for these devices are demonstrated. The devices exhibit regimes of negative differential resistance in the absorber under varying laser bias conditions. By choosing the absorber bias conditions such that the operating load line intersects the absorber IV trace three times, the laser can be made to exhibit optical bistability. The magnitude of the bistability and consequent hysteresis loop can be controlled by adjusting the absorber bias. If the bias conditions are adjusted so that the load line is tangential to the portion of the absorber IV exhibiting negative differential resistance, then the device can be made to self-pulsate. Self-pulsations at frequencies as high as 2 GHz with 700 kHz rf linewidth FWHM (full-width at half-maximum) have been obtained using these devices. Furthermore, the self-pulsation frequency can be tuned over 700 MHz by adjusting the bias conditions, representing a substantial advance over existing self- pulsating VCSELs. We have also demonstrated a novel modulation scheme using these devices, in which the drive signal is applied to the bias voltage across the absorber. Theoretical analysis of the chirping mechanism leads us to expect that this technique will minimize the chirp at high modulation frequencies, while still providing substantial modulation depth and high speeds. We achieved a minus 3 dB bandwidth of 9 GHz; the bandwidth increases with the laser bias current at a rate of 7 GHz/(root)mA.

Optimization of VCSEL with an integrated resonant photodetector

We show that the intracavity detector-VCSEL performance depends critically on the relative alignment of the Fabry-Perot wavelength and the quantum-well absorber band edge. By strategic design, we obtain well-matched behavior of the internal and external detectors-up to 5 times threshold. Comprehensive modeling agrees with experimental results.