Optical modulating and amplifying apparatus capable of achieving modulation with high signal-to-noise ratio

摘要

An optical modulating and amplifying apparatus includes an optical amplifier 3 and a modulator 4. In the apparatus, an input optical signal S1 and an excited light SP are combined with each other by an optical mixer 31 to produce an output light signal. The excited light SP from a laser diode 40 is sensed by a photodiode 41. A bias and an amplitude of the sense signal are respectively sensed by a means value sensor 51 and a modulation signal sensor 52. A modulation degree of the excited light SP is computed by a divider 54. A control signal to develop a predetermined modulation degree is delivered from a control signal generator 45 to a variable gain amplifier 43. In response to the control signal, the amplifier 43 controls the amplitude of the oscillation signal from an oscillator 44. A laser diode driver 42 adds a bias to the oscillation signal to drive the laser diode 40. The modulation degree is kept unchanged regardless of variation in an output level of the excited light so as to achieve the modulation with a high signal-to-noise ratio. IMAGE