Fiber-based optical modulator

Patent metadata

Field	Value
Publication number	US-12537359-B2
Application number	US-202017633198-A
Country	US
Kind code	B2
Filing date	Aug 5, 2020
Priority date	Aug 6, 2019
Publication date	Jan 27, 2026
Grant date	Jan 27, 2026

Abstract

Systems and methods for temporal amplitude modulation of an optical beam. An exemplary system may include a birefringent fiber positioned between two polarizers, or between a polarized input light source and an output polarizer. Light may enter the birefringent fiber as linearly polarized. Depending on birefringence and orientation of the birefringent fiber, the polarization state changes as the light propagates through the birefringent fiber. This changed polarization state then enters the output polarizer, for which transmission is a function of the polarization state and the relative orientation of the polarization axis. The polarization state emerging from the birefringent fiber may be changed by modulating the fiber birefringence, for example through application of an external stress. Net transmittance of the system may be varied according to a magnitude of an external force (e.g., pressure) to some or all of the birefringent fiber.

First claim

What is claimed is:

1 . An optical modulator, comprising:
an optical input to receive a beam of light having a first polarization state and an optical power; an optical output having a predetermined polarization orientation relative to the first polarization state; a length of birefringent fiber between the optical input and the optical output, wherein the length of birefringent fiber is oriented to couple some of the optical power into both fast and slow birefringence axes; a perturbation device to modulate, through action upon at least a portion of the length of birefringent fiber, a polarization state of the beam that enters the optical output; and a controller input coupled to the perturbation device, wherein the perturbation device is to act upon the length of birefringent fiber in response to a control signal received through the controller input to vary a transmittance of the beam through the optical modulator from a first transmittance level at a first time instance to a second transmittance level at a second time instance, wherein the action comprises application of a compressive stress along at least one of the fast and slow birefringence axes, wherein the perturbation device is to modulate a magnitude of the compressive stress, and wherein the application of the compressive stress alters a phase delay between the fast and the slow birefringence axes, wherein the first transmittance level is associated with a first phase delay between the fast and the slow birefringence axes, and the second level of transmittance is associated with a second phase delay between the fast and slow birefringence axes, and wherein at the optical input the beam of light has a same optical power at the first and second time instances, and wherein an optical power transmitted from the optical output at the first time instance is to be at least 10% greater than an optical power transmitted through the optical output at the second time instance.

2 . The optical modulator of claim 1 , wherein:
the first polarization state is a first linear polarization state; and the fast and slow birefringence axes are oriented to between 0° and 90° of the first linear polarization state.

3 . The optical modulator of claim 2 , wherein:
the fast and slow birefringence axes are oriented at approximately 45° of the first linear polarization state; and the optical output has a polarization orientation substantially aligned with the first linear polarization state.

4 . The optical modulator of claim 1 , wherein the perturbation device comprises at least one of a mechanical clamp or a piezoelectric material.

5 . The optical modulator of claim 1 , wherein the compressive stress is to be applied substantially parallel to one of the fast or slow birefringence axes.

6 . The optical modulator of claim 1 , wherein:
the optical input comprises a first polarizing fiber having a higher polarization extinction ratio (PER) than the length of birefringent fiber, and wherein the first polarization fiber is oriented to propagate the optical beam with the first polarization state into the length of birefringent fiber; and the optical output comprises a second polarizing fiber having a higher PER than the length of birefringent fiber, wherein the second polarization fiber is oriented relative to the first polarizing fiber to propagate the optical beam with the first polarization state.

7 . The optical modulator of claim 1 , wherein the length of birefringent fiber comprises a cladding surrounding a core, wherein the core has an elliptical cross-section or the cladding comprises a stress rod.

8 . The optical modulator of claim 1 , wherein the perturbation device is to transition between first and second states according to an analog waveform with the transmittance to vary according to a continuous function that includes the first and second levels of transmittance.

9 . An optical system, comprising:
a laser; and the optical modulator of claim 1 , wherein the optical input is coupled to an output coupler of the laser and wherein the optical input comprises a polarizing fiber to define the first polarization state.

10 . The system of claim 9 , further comprising a fiber amplifier coupled to an output of the optical modulator.

11 . A laser, comprising:
a resonant optical cavity comprising an optical gain medium, and an optical modulator; a means to energize the optical gain medium; and an output coupler to couple at least a portion of an optical beam out of the cavity, wherein the optical modulator further comprises:
a first length of polarizing fiber, a second length of polarizing fiber, and a length of birefringent fiber therebetween, wherein the first and second lengths of polarizing fiber have higher polarization extinction ratios than the length of birefringent fiber, and wherein the first and second lengths of polarizing fiber are oriented to pass a beam of light having a first polarization state; and
a perturbation device to temporally vary optical loss, in response to a control signal, within the cavity through action upon the length of birefringent fiber that modulates a phase delay between fast and slow birefringence axes in the length of birefringent fiber,
wherein a first level of optical loss is associated with a first phase delay between the fast and slow birefringence axes and a second level of optical loss is associated with a second phase delay between the fast and slow birefringence axes, and wherein a power of the optical beam coupled out of the cavity at a first time corresponding the first phase delay is to be at least 10% greater than a power of the optical beam coupled out of the cavity at a second time corresponding to the second phase delay.

12 . The laser of claim 11 , wherein:
the gain medium comprises optical fiber; and the means to energize comprises a pump laser.

13 . The laser of claim 11 , wherein the perturbation device is to modulate transmittance of the optical beam between a first transmittance level and a second transmittance level to induce pulsed operation of the laser.

14 . The laser of claim 13 , wherein the perturbation device is to temporally modulate the transmittance of the optical beam between the first and second transmittance levels at a repetition rate to actively mode-lock the laser.

15 . The laser of claim 13 , wherein a difference between the first and second transmittance levels is of a sufficient magnitude to Q-switch the laser.

16 . An optical system, comprising:
a resonant optical cavity comprising an optical gain medium; a means to energize the optical gain medium; an output coupler to couple at least a portion of an optical beam out of the cavity; and a fiber optical modulator with an input coupled to the output coupler, wherein the fiber optical modulator further comprises:
a first length of polarizing fiber, a second length of polarizing fiber, and a length of birefringent fiber therebetween, wherein the first and second lengths of polarizing fiber have higher polarization extinction ratios than the length of birefringent fiber, and wherein the first and second lengths of polarizing fiber are oriented to pass the optical beam in a first polarization state; and
a perturbation device to modulate, through action upon the length of birefringent fiber, a transmittance of the beam through the optical modulator from a first transmittance level at a first time instance corresponding to a first phase delay between the fast and slow birefringence axes of the birefringent fiber to a second transmittance level at a second time instance corre

Assignees

• Nlight Inc

Inventors

• Kliner Dahv A V

Classifications

• H01S3/06712

  Polarising fibre; Polariser · CPC title

• G02F1/0136

  for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation (G02F1/0353 takes precedence) · CPC title

• G02F1/0134

  in optical waveguides · CPC title

• H01S3/1067 Primary

  using pressure or deformation · CPC title

• H01S3/121

  using intracavity mechanical devices · CPC title