Composite-resonator Vertical-cavity Laser Research Articles

Circuit Modeling of Carrier–Photon Dynamics in Composite-Resonator Vertical-Cavity Lasers

We present a circuit model for composite-resonator vertical-cavity lasers (CRVCLs) based on the standard rate equations. This model is compatible with general-purpose circuit analysis program (SPICE), and it can accurately produce the dc and modulation characteristics of the CRVCL, which is verified by comparing the calculated results with the measured experimental data. In addition, using this model we verify that CRVCL has unique abilities to engineer its modulation characteristics by varying cavity asymmetries as well as to produce multilevel amplitude modulation, both of which are consistent with our previous experimental results. We also discuss some advantages and limitations of this model.

Analog and Digital Functionalities of Composite-Resonator Vertical-Cavity Lasers

Different modulation approaches for the composite-resonator vertical-cavity laser are described, with an emphasis on direct modulation using either one or both cavities. It is also observed that the unique properties of this device form the basis for analog and digital functionalities. Experimental demonstrations are also shown of multilevel amplitude modulation, preemphasis for direct modulation, microwave signal mixing, and synchronous electrical and optical signaling, none of which can be achieved using a conventional vertical-cavity surface-emitting laser.

Multilevel Amplitude Modulation Using A Composite-Resonator Vertical-Cavity Laser

Modulation characteristics of a composite-resonator vertical-cavity laser (CRVCL) can be engineered by modulating the carrier and photon densities in the two optically coupled cavities simultaneously. The total modulation response is a superposition of the individual modulation response from each cavity, when direct modulation is applied to both cavities. This property enables the CRVCL to produce multilevel signaling for optical communication. A demonstration of four-level amplitude modulation at 2.5 Gb/s is shown.

High-speed electroabsorption modulation of composite-resonator vertical-cavity lasers

The high-speed characteristics of a composite-resonator vertical-cavity laser (CRVCL) under both small- and large-signal electroabsorption modulation are investigated. The maximum -3 dB modulation bandwidth of 12.5 GHz is measured. The theoretical modulation response of the CRVCL is derived from the standard rate equations, and the qualitative form is in agreement with the measured results. The CRVCL under electroabsorption modulation exhibits a promising potential to extend the modulation bandwidth beyond that of a conventional VCSEL. However, the CRVCL under large-signal electroabsorption modulation is limited to low data rates, and the large relaxation oscillation resonance must be suppressed for higher-speed digital-optical link applications.

High slope efficiency measured from a composite-resonator vertical-cavity laser

We report high differential slope of the light versus current (L-I) characteristic in excess of 400% external quantum efficiency from a monolithic dual resonator vertical-cavity surface-emitting laser. The additional optical cavity of the composite resonator can provide gain or loss to the distributed laser mode, depending on the bias conditions. We describe the factors contributing to the internal optical loss, and present a qualitative model for the L-I characteristic. With sufficient current injected into the top cavity, the composite-resonator vertical-cavity laser achieves over 6 W/A of differential slope efficiency from threshold to greater than 1 mW of output power, which may be applicable for analog optical data links.

Threshold gain temperature dependence of composite resonator vertical-cavity lasers

Vertical-cavity surface-emitting lasers (VCSELs) with two optically coupled but electrically isolated cavities form composite resonator vertical-cavity lasers (CRVCLs). These devices may lase at one of two wavelengths depending on the bias conditions to the two cavities and temperature. A model of the modal gain is presented, which explains the lasing wavelength at threshold based on the spatial and spectral overlap of the microcavity optical modes with the two gain regions.

Polarization switching in composite-resonator vertical-cavity lasers

We report polarization switching in a monolithic dual-resonator vertical-cavity laser. The light output from the top ion-implanted cavity under forward bias above threshold is partitioned into two orthogonal polarizations of the fundamental transverse mode. A reverse bias of sufficient magnitude applied to the bottom oxide-confined cavity causes the abrupt suppression of the dominant polarization and simultaneous emergence of the orthogonal polarization. We find that the electro-optic birefringence of the two polarizations increases with increasing reverse bias. We show that the mechanism of the polarization switch is consistent with wavelength-dependent loss from electroabsorption in the reverse-biased quantum wells of the oxide-confined cavity.

Threshold and modal characteristics of composite-resonator vertical-cavity lasers

We report the operation of a vertical-cavity surface-emitting laser (VCSEL) with two active, coupled optical cavities. In contrast to a conventional single-cavity VCSEL, the coupling between the two electrically independent active regions produces emission into two longitudinal modes. The light output versus current characteristics are presented under various biasing conditions in each cavity. Laser operation is achieved with current injection into only one cavity, and additional current injected into the other cavity changes the effective threshold current measured. The longitudinal and transverse modes are characterized, and it is found that the modal evolution of the laser can be modified by current injection into each cavity.