JPS6425588A - Integrated semiconductor laser - Google Patents

Abstract

PURPOSE:To detect oscillation frequency fluctuation in a simple composition and to obtain stable laser oscillation beams of a small spectral line width by integrating a semiconductor laser, optical wave guides and a pin photo diode on one and the same substrate. CONSTITUTION:The laser is composed of an n-type InP substrate 1, a semiconductor laser section 2 including an n-type InGaAsP active layer, the first and second optical wave guides 3 and 4 including an n-type InGaAsP optical wavelayer, a pin photo diode 5 including an n-type InGaAsP active layer, the second terminal 6 of the first optical wave guide and the first terminal 7 of the second optical wave guide. Each of them is provided with a reflecting film on the cleavage plane. As for laser oscillation beams of the semiconductor laser 2, laser beams 10 and 11 interfere with a sensitive surface of the pin photo diode 5 and sensitive power output is acquired corresponding to the phase difference of the optical pass difference. The oscillation frequency fluctuation of the semiconductor laser becomes the phase difference fluctuation and, therefore, is converted to the sensitive power fluctuation. Because the sensitive power output is amplified in a control circuit 9 and high-pass and low-pass thereof are negatively fed back to the semiconductor laser after cut, the frequency fluctuation is thereby suppressed and a small spectral line width can be acquired.