Structure of a passively mode-locked optical fiber laser

• US 5,898,716 A
• Filed: 09/22/1997
• Issued: 04/27/1999
• Est. Priority Date: 09/23/1996
• Status: Expired due to Term

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Lee, Hack Kyu, Ahn, Joon Tae, Kim, Kyong Hon
• Primary Examiner(s): Bovernick, Rodney
• Assistant Examiner(s): Wise, Robert E.
• Application Number:
  US08/934,810
• Time in Patent Office: 582 Days
• Field of Search: 372/6, 372/11, 372/18, 372/21, 372/94, 372/703, 372/700
• US Class Current: 372/6
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06791 Fibre ring lasers fibre laser gyrometers G01C19/72
• CPC Class Codes: H01S 3/082 defining a plurality of resonators, e.g. for mode selection or suppression
• CPC Class Codes: H01S 3/105 by controlling the mutual position or the reflecting properties of the reflectors of the cavity , e.g. by controlling the cavity lengthH01S3/10076, H01S3/13 take precedence
• CPC Class Codes: H01S 3/1112 Passive mode locking
• CPC Class Codes: H01S 3/1608 erbium

Abstract

A laser structure for obtaining an optical pulse of a very short duration by using the benefit of a passive mode locking and for improving a repetition rate of an output optical pulse was described. In general, a passively mode-locked laser generates a short optical pulse than a active mode locked laser does, while it has difficulties in increasing the repetition rate of the output optical pulse because the repetition rate of the passively mode-locked laser is determined by the length of the resonator. In accordance with the present invention, a delayed optical path is added to the linear loop of a conventional figure-8 optical fiber laser. The propagation time difference ΔT between the delayed optical path and undelayed short optical path is adjusted to a divisor of the round trip time, T, of the original resonator by properly adjusting the length of the delayed optical path. Thus, the repetition rate of the output optical pulse of the mode locked laser can be increased from 1/T Hz to 1/ΔT Hz. The optical fiber laser which can fully exploit the advantages of the passive mode locking and improve the repetition rate of the output optical pulse in accordance with the present invention can be applied to a wide range of applications including an optical communication and an ultra high speed analysis of optical phenomena.

Claims

1. A passively mode-locked optical fiber laser for increasing the repetition rate of output optical pulses thereof, comprising:

a nonlinear amplifying loop mirror serving as a saturable absorber for a passive mode locking and including

a polarization controller for adjusting the birefringence of a resonator and varying a transmission rate thereof,

an erbium-doped fiber for the gain medium of the laser, a wavelength division multiplexer for coupling an output of a laser diode for optically pumping said erbium-doped fiber to the laser resonator,

a directional coupler for splitting a signal which is input or output, and

a nonlinear optical fiber for obtaining a nonlinear phase difference sufficient to cause a passive mode locking between two lights which are split from said directional coupler and propagate in the clockwise and counterclockwise directions around said nonlinear amplifying loop mirror, respectively; and

a linear loop including

an optical isolator which blocks a light reflected by said nonlinear amplifying loop mirror and allows a light transmitted from said nonlinear amplifying loop mirror to pass therethrough,

a directional coupler for splitting the transmitted signal, a delay line for receiving one of output signals from said directional coupler and for adjusting the length of a delayed optical path to improve a repetition rate of an mode-locked optical laser pulse,

a polarization controller for adjusting a polarization of the light incident through said delay line,

a undelayed short optical path for receiving the other output signals from said directional couplers,

a directional coupler for combining the two signals from said delayed optical path and said indelayed short optical path,

respectively, and also used for splitting mode-locked laser output,

an erbium-doped optical fiber for supplying a gain required in accordance with the increase of the repetition rate,

a wavelength division multiplexer for coupling an output of a laser diode for optically pumping said erbium-doped fiber to the laser resonator,

a laser diode for optically pumping said erbium-doped optical fiber, and

a polarization controller for causing an oscillation of the laser by adjusting the polarization of the light propagating through the linear loop.

2. The passive mode locking optical fiber laser according to claim 1, wherein said delay line adjusts the optical path length difference between said delayed optical path and said undelayed short optical path.

3. The passively mode-locked optical fiber laser according to claim 2, wherein said delay line adjusts the time difference delayed by the delayed optical path such that it becomes a divisor of the round trip time of the original resonator.