A novel technique is demonstrated for suppressing the relative intensity noise (RIN) and enhancing the high-speed transmission performance of 850 nm vertical-cavity surface emitting lasers (VCSELs). The orthogonal polarization suppression ratio (OPSR) of top-emitting high-speed 850 nm VCSELs with rectangular shaped mesas can be greatly enhanced by electroplating a copper substrate onto the backside, without any degradation in slope efficiency (output power). The enhancement of the OPSR results in a significant reduction of the RIN (around -130 vs. -145 dB/Hz) over a wide frequency range (near DC to 20 GHz) in comparison to the reference device without the additional copper substrate. Moreover, the structure of the demonstrated device can not only flatten the electrical-to-optical (E-O) responses but also narrow the spectral width due to the strain induced by the copper substrate. Overall, the lower RIN and flatter E-O frequency responses in turn lead to a significant improvement in the 25 Gbit/sec eye-opening and lower timing jitter in our demonstrated device.