Method of and device for modulating directly a semiconductor laser

Claim 1

A device for directly modulating a semiconductor laser comprising: a semiconductor injection laser diode having a PN junction, said PN junction emitting a laser beam of one mode-order in response to the injection of a bias current of a level above the laser threshold level; a bias source connected with said laser diode to inject said bias current thereto; a modulating source connected with said laser diode and said bias source to inject and superpose a signal current pulsed on and off according to an information signal to cause said laser beam to hop from one mode order to another mode order; and an optical waveguide, disposed in the path of said emitted laser beam, said optical waveguide being able to transmit only one of said two mode orders, said optical waveguide including a pair of separate portions, said separate portions being arranged in a symmetrical manner on opposite sides of the center of the field distribution of said emitted laser beam correspondinG to one of said two mode orders, and being formed in such a manner that laser beams passing through said separate portions are joined together thereafter, whereby the amplitude of the laser beam emitted from said optical waveguide is an optical signal representative of the information signal pulses imparted to said modulating source and has the odd symmetry field distribution cancelled by said optical waveguide.

Claim 2

A device for directly modulating a semiconductor laser comprising: a semiconductor injection laser diode having a PN junction, said PN junction emitting a laser beam of one mode-order in response to the injection of a bias current of a level above the laser threshold level; a bias source connected with said laser diode to inject said bias current thereto; a modulating source connected with said laser diode and said bias source to inject and superpose a signal current pulsed on and off according to an information signal to cause said laser beam to hop from one mode order to another mode order; and an optical waveguide, disposed in the path of said emitted laser beam, said optical waveguide being able to transmit only one of said two mode orders, said optical waveguide including a pair of separate portions, said separate portions being arranged in a symmetrical manner on opposite sides of the center of the field distribution of said emitted laser beam correspondinG to one of said two mode orders, and being formed in such a manner that laser beams passing through said separate portions are joined together thereafter, whereby the amplitude of the laser beam emitted from said optical waveguide is an optical signal representative of the information signal pulses imparted to said modulating source and has the odd symmetry field distribution cancelled by said optical waveguide.

Claim 6

A device for directly modulating a semiconductor laser comprising: a semiconductor injection laser diode having a PN junction said PN junction emitting a laser beam of one mode-order in response to the injection of a bias current of a level above the laser threshold level; a bias source connected with said laser diode to inject said bias current thereto; a modulating source connected with said laser diode and said bias source to inject and superpose a signal current pulsed on and off according to an information signal to cause said laser beam to hop from one mode-order to another mode-order; and an optical waveguide, disposed in the path of said emitted laser beam, said optical waveguide being able to transmit only one of said two mode-orders, said optical waveguide including a pair of separate portions, said separate portions being arranged in a symmetrical manner on opposite sides of the center of the field distribution of said emitted laser beam corresponding to one of said two mode-orders, and being formed in such a manner that laser beams passing through said separate portions are joined together thereafter, whereby the amplitude of the laser beam emitted from said optical waveguide is an optical signal representative of the information signal pulses imparted to said modulating source; and further comprising means, coupled with said optical waveguide, for producing an optical path difference, so as to cancel the emitted laser beam having an even symmetry field distribution.

Claim 7

A device for directly modulating a semiconductor laser comprising: a semiconductor injection laser diode having a PN junction said PN junction emitting a laser beam of one mode-order in response to the injection of a bias current of a level above the laser threshold level; a bias source connected with said laser diode to inject said bias current thereto; a modulating source connected with said laser diode and said bias source to inject and superpose a signal current pulsed on and off according to an information signal to cause said laser beam to hop from one mode-order to another mode-order; and an optical waveguide, disposed in the path of said emitted laser beam, said optical waveguide being able to transmit only one of said two mode-orders, said optical waveguide including a pair of separate portions, said separate portions being arranged in a symmetrical manner on opposite sides of the center of the field distribution of said emitted laser beam corresponding to one of said two mode-orders, and being formed in such a manner that laser beams passing through said separate portions are joined together thereafter, whereby the amplitude of the laser beam emitted from said optical waveguide is an optical signal representative of the information signal pulses imparted to said modulating source; and further comprising means, coupled with said optical waveguide, for producing an optical path difference, so as to cancel the emitted laser beam having an even symmetry field distribution.

Claim 11

A method for directly modulating a semiconductor injection laser diode comprising the steps of: a. supplying a bias current to said diode to inject a bias current of a level above the laser threshold level, so that the PN junction of said laser diode emits a laser beam of one mode-order; b. superposing a signal current, which is pulsed on and off according to an information signal, on said bias current to cause said laser beam to hop from one mode-order to another mode-order; and c. passing said emitted laser beam through an optical waveguide which is able to transmit only one of said two mode-orders, said optical waveguide having a pair of separate portions, said separate portions being arranged in a syMmetrical manner on opposite sides of the center of the field distribution of said emitted laser beam corresponding to one of said two mode-orders, and being formed in such a manner that laser beams passing through separate portions are joined together thereafter, whereby the amplitude of the emitted laser beam from said optical waveguide is an optical signal representation of the information signal pulses forming said superimposed signal current, and has an odd symmetry field distribution cancelled by said optical waveguide.

Claim 12

A method for directly modulating a semiconductor injection laser diode comprising the steps of: a. supplying a bias current to said diode to inject a bias current of a level above the laser threshold level, so that the PN junction of said laser diode emits a laser beam of one mode-order; b. superposing a signal current, which is pulsed on and off according to an information signal, on said bias current to cause said laser beam to hop from one mode-order to another mode-order; and c. passing said emitted laser beam through an optical waveguide which is able to transmit only one of said two mode-orders, said optical waveguide having a pair of separate portions, said separate portions being arranged in a syMmetrical manner on opposite sides of the center of the field distribution of said emitted laser beam corresponding to one of said two mode-orders, and being formed in such a manner that laser beams passing through separate portions are joined together thereafter, whereby the amplitude of the emitted laser beam from said optical waveguide is an optical signal representation of the information signal pulses forming said superimposed signal current, and has an odd symmetry field distribution cancelled by said optical waveguide.

Claim 16

A method for directly modulating a semiconductor injection laser diode comprising the steps of: a. supplying a bias current to said diode to inject a bias current of a level above the laser threshold level, so that the PN junction of said laser diode emits a laser beam of one mode-order; b. superimposing a signal current, which is pulsed on and off according to an information signal, on said bias current to cause said laser beam to hop from one mode-order to another mode-order; and c. passing said emitted laser beam through an optical waveguide which is able to transmit only one of said two mode-orders, said optical waveguide having a pair of separate portions, said separate portions being arranged in a symmetrical manner on opposite sides of the center of the field distribution of said emitted laser beam corresponding to one of said two mode-orders, and being formed in such a manner that laser beams passing through separate portions are joined together thereafter, whereby the amplitude of the emitted laser beam from said optical waveguide is an optical signal representation of the information signal pulses forming said superimposed signal current; and further including the step of d. disposing means for producing an optical path difference in the path of the emitted laser beam, so as to cancel the emitted laser beam having an even symmetry field distribution.

Claim 17

A method for directly modulating a semiconductor injection laser diode comprising the steps of: a. supplying a bias current to said diode to inject a bias current of a level above the laser threshold level, so that the PN junction of said laser diode emits a laser beam of one mode-order; b. superimposing a signal current, which is pulsed on and off according to an information signal, on said bias current to cause said laser beam to hop from one mode-order to another mode-order; and c. passing said emitted laser beam through an optical waveguide which is able to transmit only one of said two mode-orders, said optical waveguide having a pair of separate portions, said separate portions being arranged in a symmetrical manner on opposite sides of the center of the field distribution of said emitted laser beam corresponding to one of said two mode-orders, and being formed in such a manner that laser beams passing through separate portions are joined together thereafter, whereby the amplitude of the emitted laser beam from said optical waveguide is an optical signal representation of the information signal pulses forming said superimposed signal current; and further including the step of d. disposing means for producing an optical path difference in the path of the emitted laser beam, so as to cancel the emitted laser beam having an even symmetry field distribution.