40 Gbps With Electrically Parallel Triple and Septuple 980 nm VCSEL Arrays

Abstract

Electrically parallel and optically uncoupled triple and septuple oxide confined vertical-cavity surface-emitting laser (VCSEL) arrays emitting at about 980 nm where each VCSEL has an oxide aperture diameter (φ) of ∼7.5 μm transmit data at 40 Gbps at room temperature (RT) in a back-to-back test configuration using standard two-level non-return-to-zero pulse amplitude modulation at bias current densities (J) of 17.4 and 10.3 kA/cm 2 , respectively. Reference single VCSELs processed with the VCSEL arrays on the same wafer pieces with φ ∼7.5, 13.5, and 19.5 μm transmit data at up to 45, 40, and 35 Gbps at RT at J of 20.4, 13.3, and 10.7 kA/cm 2 , respectively, where the latter two single VCSELs have total emitting areas nearly equal to the total additive emitting areas of the triple and septuple VCSEL arrays, respectively. The RT optical output power at J ∼10 and 15 kA/cm 2 is 11.4 and 17.2 mW for the triple arrays and 31.1 and 45.9 mW for the septuple arrays, respectively. By increasing the number of emitters in an array for a fixed φ per VCSEL from 3 to 7 we increase the total optical output power and simultaneously we decrease the J required for error free digital data transmission at 40 Gbps.

Electrically Parallel Three-Element 980 nm VCSEL Arrays with Ternary and Binary Bottom DBR Mirror Layers

“…As an example, in Figure 8 , we plot, after correcting the data for the frequency response of the New Focus 25 GHz bandwidth photoreceiver, the measured |S21| (absolute value magnitudes) versus frequency of a 980 nm triple VCSEL array with ϕ ~6 μm at DC bias currents of I = 4, 8.5, and 18.5 mA (corresponding to bias current densities of about 4.7, 10.0, and 21.8 kA/cm 2 ). We fit the measured |S21| data to the following equation [ 18 ]: where c (in dB) is a constant we use to set the fitted frequency response to the reference level 0 dB at the frequency f = 0 Hz, f R is the relaxation oscillation resonance frequency (in GHz), γ is the damping (in GHz or equivalently in ns), and f p is the parasitic frequency (in GHz). In Table 1 , we list the fitting parameters and measured bandwidths for the 6 μm triple VCSEL array corresponding to the measured data in Figure 8 .…”

“…We constructed electrically parallel, optically uncoupled triple (three-element) 980 nm VCSEL arrays with variable oxide aperture diameters and variable inter-VCSEL pitch (separation distance) as follows [ 17 , 18 ]. The top mesas (mesa 1) consisted of three circles with identical diameters, each centered on one of the three imaginary vertices of an equilateral triangle.…”

“…We measured the triple VCSEL array characteristics using the methods and test equipment we described in [ 17 , 18 , 19 , 20 ]. Herein, we performed all measurements at ambient room temperature (RT ~23 °C) on three separate test stations in our university laboratory.…”

“…Lastly, for data transmission measurements using two-level pulse amplitude modulation at 25 to 40 Gb/s (see [ 18 ] for a schematic of the test setup), we placed the fabricated wafers onto a third test station and made electrical contact with a GSG probe on one array at a time. Via an SHF 12100B (Berlin, Germany) bit pattern generator (which received a clocking signal from an Agilent E8257D (Santa Clara, CA, USA) signal generator) and a bias-tee, we excited the VCSEL array with a DC bias current plus (as a large signal peak-to-peak voltage (typically ~610 mV) on top of the DC bias), a standard pseudorandom bit (or binary) sequence (PRBS) of word length 2 7 − 1.…”

“…In [ 18 ], we reported the static and dynamic characteristics of a three-element electrically parallel, optically uncoupled 980 nm VCSEL array with ϕ ~7.5 μm. We achieved a maximum f 3dB of ~24 GHz, WPE max of ~36%, and L max of ~27 mW.…”