D.A. Louderback

Parallel free-space optical interconnect based on arrays of vertical-cavity lasers and detectors with monolithic microlenses.

We investigate the use of low-threshold 980-nm vertical-cavity surface-emitting lasers for free-space optical interconnects. The vertical-cavity surface-emitting lasers and backilluminated detectors are monolithically integrated with microlenses on the back sides of the growth substrates to eliminate the necessity of external optics. With a channel pitch of 250 mum, an interconnect length between boards of the order of 5 to 10 mm with a ?50-mum lateral alignment tolerance can be achieved without external relay optics. The complete link is modeled to predict the systems efficiency and maximum bit rate. Data transmission at 500 Mbits/s per channel is demonstrated. The data rate was limited by parasitics, not the inherent bandwidth of the laser diodes.

Technique for integration of vertical cavity lasers and resonant photodetectors

We demonstrate a design that allows fabrication of substrate input/output resonant-cavity photodetectors and vertical cavity lasers (VCLs) on the same substrate without regrowth. By selectively oxidizing a few layers in the bottom mirror the as-grown 80% reflectivity mirror, used as the input mirror for the detector, is converted to a 99.3% reflectivity mirror allowing fabrication of VCLs from the same epitaxial material. Since these two reflectivities are uncorrelated, the detectors and VCLs can be individually designed. Despite the change in refractive index from ∼3 to ∼1.6 in the oxidized layers, the structure can be designed to have nearly the same resonance wavelength for both the detectors and VCLs. Using this design strategy, we have successfully fabricated high-performance resonant photodetectors and VCLs from the same epitaxial material. The photodetectors have an absorption of 56% and an optical bandwidth of 5.9 nm, in good agreement with theory. Small diameter, single-mode VCLs have threshold c...

Flip-chip bonded arrays of monolithically integrated, microlensed vertical cavity lasers and resonant photodetectors

We present flip-chip bonded arrays of novel, monolithically integrated, microlensed vertical-cavity lasers (VCLs) and resonant photodetectors. The bottom emitting VCLs exhibit ∼300 μA threshold currents, while adjacent detectors have the same operating wavelength and responsivities of ∼0.4 A/W. Only a single epitaxial growth is required.

Modulation and free-space link characteristics of monolithically integrated vertical-cavity lasers and photodetectors with microlenses

We present temperature, modulation, and free-space link characteristics of monolithically integrated vertical-cavity lasers (VCLs) and resonant photodetectors. The devices have been integrated using a novel structure that makes it possible to fabricate devices with through-the-substrate emission and detection. Taking advantage of the substrate emitting/detecting architecture, we monolithically integrate microlenses on the substrate side of the devices and flip-chip bond arrays without via processes or substrate removal. Low-threshold high-efficiency VCLs exhibit maximum small-signal modulation bandwidths, which are limited by parasitics, of /spl sim/9.5 GHz at 20/spl deg/C and /spl sim/8.4 GHz at 70/spl deg/C. The VCLs have the lowest reported bias currents required to reach bandwidths of up to /spl sim/8 GHz. A free-space optical link is demonstrated with flip-chip-bonded arrays of microlensed, monolithically integrated VCLs and detectors. The link is found to be tolerant to temperature differences of /spl plusmn/75/spl deg/C between the VCL and detector, with error free (BER<10/sup -12/) data transmission demonstrated in each case.

Temperature Dependence of 980-nm Oxide-Confined VCSEL Dynamics

Temperature dependence of 980-nm vertical-cavity surface-emitting laser (VCSEL) dynamics is reported. Resonance frequency and damping factor of a 7-m active diameter laser have been measured using noise spectra. The primary cause of reduced bandwidth with increasing temperature was reduced photon density. Differential gain is relatively constant for temperatures from 10 C to 70 C, and damping analysis showed there was also no significant change in -factor as a function of temperature.

Flip-chip bonded arrays of monolithically integrated, microlensed vertical-cavity lasers and resonant photodetectors

We present flip-chip bonded arrays of monolithically integrated vertical-cavity lasers (VCLs) and resonant photodetectors. The VCLs and photodetectors are integrated using a novel structure that allows through-the-substrate emission and detection without compromising device performance. Substrate-side microlenses have been integrated to take advantage of the through-the-substrate architecture. Flip-chip bonded VCLs exhibit threshold currents as low as 135 /spl mu/A with differential efficiencies of /spl sim/53%. The detectors have the same operating wavelength as the VCLs and responsivities of 0.48 A/W, corresponding to 60% absorption, with optical bandwidths of 7 nm.

Flip-chip bonded, back-emitting, microlensed arrays of monolithic vertical cavity lasers and resonant photodetectors

We present flip-chip bonded arrays of monolithically integrated vertical-cavity lasers (VCLs) and resonant photodetectors. The VCLs and photodetectors are integrated using a novel structure that allows through-the-substrate emission and detection without compromising device performance. Substrate-side microlenses have been integrated to take advantage of the through-the-substrate architecture. Flip-chip bonded VCLs exhibit threshold currents as low as 135 /spl mu/A with differential efficiencies of 53%. The detectors have the same operating wavelength as the VCLs and responsivities of 0.48 A/W, corresponding to 60% absorption, with optical bandwidths of 7 nm. The VCLs exhibit maximum small-signal modulation bandwidths, which are limited by parasitics, of /spl sim/9.5 GHz at 20/spl deg/C and /spl sim/8.4 GHz at 70/spl deg/C. The VCLs have the lowest reported bias currents required to reach bandwidths of up to /spl sim/8 GHz. A free-space optical link is demonstrated with these flip-chip bonded arrays of microlensed, monolithically integrated VCLs and detectors. The link is found to be tolerant to temperature differences of /spl plusmn/75/spl deg/C between the VCL and detector, with error free (BER<10/sup -12/) data transmission demonstrated in each case.

Densely packed pie shaped vertical-cavity surface-emitting laser array incorporating a tapered one-dimensional wet oxidation

Wavelength-division-multiplexing (WDM) photonic integrated emitter (PIE) vertical-cavity surface-emitting laser (VCSEL) arrays are fabricated using a post growth wet oxidation technique. High-density integration of WDM VCSEL arrays is possible by combining the technique of one-dimensional oxidation and large-scale tapered oxidation. Eight channels are integrated into a circle of 60 /spl mu/m in diameter. Seven channels are found to operate as lasers. The lasing wavelengths range from 823 to 836 nm corresponding with the distance between the VCSEL mesa and the tuning trench. The successful demonstration of incorporating wet oxidation into the wavelength control of the PIE VCSEL array opens a new way of fabricating mask-defined densely packed WDM VCSEL arrays.

Vertical-cavity surface-emitting lasers with monolithically integrated horizontal waveguides

We present the development of novel 980-nm Ga/sub 0.8/In/sub 0.2/As-GaAs vertical-cavity surface-emitting lasers (VCSELs) with an internal waveguide structure. The monolithic integration of a horizontal waveguide in the top distributed Bragg reflector (DBR) creates the potential for achieving VCSEL-based photonic integrated circuits. In this work, an AlGaAs-GaAs-AlGaAs waveguide designed for horizontal propagation of light was monolithically integrated as part of the upper GaAs-AlGaAs DBR of the device. VCSELs with 9-/spl mu/m apertures emitted 3-mW single-mode power with both longitudinal and lateral mode suppression ratio of 40 dB under room-temperature continuous-wave operation.

Individually optimized bottom-emitting vertical-cavity lasers and bottom-illuminated resonant photodetectors sharing the same epitaxial structure

We demonstrate a novel design that allows fabrication of substrate input/output photodetectors and lasers on the same substrate by selective oxidation of the bottom mirror.