We propose and experimentally demonstrate a voltage-controllable add–drop multiplexer with a tunable coupler based on long-period fiber gratings (LPFGs). The tunable coupler is based on cladding mode coupling between two parallel LPFGs with divided coil heaters, which controls the resonant wavelength positions of the two LPFGs. The wavelength tunability of the tunable coupler is measured to be $-0.45\mathrm{nm}∕°\mathrm{C}$ in the temperature range from $20\text{to}120°\mathrm{C}$ . The large tuning range of optical signals $(\sim 50.54\mathrm{nm})$ from $1502.32\text{to}1552.86\mathrm{nm}$ , which covers both the short (S) and the conventional (C) bands, is achieved. The channel isolation is as high as $\sim 40\mathrm{dB}$ . It has several advantages, including a broad tuning range of wavelength in both the S- and C-bands, high channel isolation, no backreflection, and so on.