In this study, we investigate the laser spectra of the InGaAs/GaAs/InGaP quantum well lasers. Single-mode operation characteristics can be observed in the Fabry-Perot (FP) cavity laser, which exist in a large operating current range (36-68 mA). Mode-hop free wavelength tuning can be observed at a current of 14 mA. The maximum side-mode suppression ratio (SMSR) under single-mode operation of the laser is 29.8 dB at 20 ℃ with an injection current of 62 mA, while SMSR values are generally greater than 20 dB under other injection currents. Furthermore, the maximum output power (single side) of the laser under single-mode operation reaches 12.5 mW. Accordingly, the aforementioned single-mode operation characteristics can be observed for the FP cavity lasers fabricated with similar structures and materials in devices exhibiting different strip widths and cavity lengths. This unique feature results in considerable application potential in applications requiring a single-frequency laser source.