Using　transfer　matrix　method　and　TFcalc　thin　film　design　software,　the　reflectance　spectrum　of　distributed　Bragg　reflector　(DBR)　and　vertical　cavity　surface　emitting　laser　(VCSEL)　are　simulated.　The　reflectance　spectra　from　the　cavity　and　surface　are　compared　with　each　other,　thus　providing　the　basis　for　white　light　source　(WLS)　optical　reflectance　spectrum　of　the　VCSEL　epitaxial　wafer.　When　using　WLS　to　characterize　VCSEL　wafer,　it　is　necessary　to　combine　the　simulation　results　and　the　shape　of　optical　reflectance　spectrum　to　speculate　the　reflectance　seen　from　the　cavity.　The　influences　of　different　cap　layers　on　the　reflectance　of　DBRs　are　discussed　theoretically　and　experimentally.　With　a　1/4　lambda　GaAs　cap　layer,　the　reflectance　reaches　up　to　97.8%　seen　from　the　cavity.　This　design　can　make　the　wavelength　of　the　VCSEL　etalon　picked　easily　because　of　avoiding　the　influence　of　test　noise.　The　active　region　has　higher　heat　accumulation　due　to　the　small　area　and　poor　thermal　conductivity.　The　characteristics　of　the　gain　spectrum　of　InGaAs/AlGaAs　strained　quantum　well　(QW)　under　different　temperatures　and　the　temperature　distribution　in　VCSEL　are　simulated　by　Crosslight　software.　The　gain-to-cavity　wavelength　detuning　is　used　to　improve　the　slope　efficiency　and　the　temperature　stability.　The　temperature　in　active　region　ranges　from　360　K　to　370　K.　The　gain　peak　wavelength　and　the　Fabry-Perot　cavity　wavelength　are　designed　in　the　ranges　of　829-832　nm　and　845-847　nm,　respectively.　Epitaxial　wafer　with　top-emitting　VCSEL　structure　grown　by　metal-organic　chemical　vapor　deposition　is　characterized.　The　room　temperature　photoluminescence　peak　is　at　827.5　nm　and　the　etalon　cavity　wavelength　measured　by　optical　reflectance　is　847.7　nm,　which　are　consistent　with　designed　values.　The　oxide　restricted　VCSELs　with　7.5　mu　m　oxide　aperture　are　fabricated.　The　image　of　the　infrared　light　source　CCD　shows　that　the　oxide　aperture　is　circular.　A　passivation　layer　of　120　nm　SiO2　is　finally　deposited　to　insulate　water　vapor.　The　threshold　current　is　0.8　mA,　and　the　maximum　output　power　reaches　up　to　9　mW　at　13.5　mA.　The　optical　spectrum　at　6.0　mA　reveals　multiple　transverse　modes.　The　center　wavelength　is　852.3　nm　and　the　root　mean　square　(RMS)　spectrum　width　is　0.6　nm,　meeting　the　high-speed　Datacom　standards.　Shannon　theory　indicates　that　the　maximum　data　rate　is　not　only　proportional　to　bandwidth　but　also　related　to　signal-to-noise　ratio　(SNR).　It　is　effective　to　reduce　relative　intensity　noise　and　enhance　the　SNR　by　increasing　output　power.　From　the　eye　diagram　of　25　Gbit/s　on-off　key　VCSEL,　it　is　demonstrated　that　fall　time　is　38.66　ps,　rise　time　is　41.54　ps,　SNR　is　5.6,　and　jitter　RMS　is　1.57　ps.　Clear　eye　opening　is　observed　from　eye　diagram　of　25GBaud/s　PAM-4　VCSEL,　which　indicates　the　qualified　50　Gbit/s　high　speed　performance.