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EP-4741914-A1 - A DEVICE AND A METHOD FOR CONTROLLING A THERMO-OPTICAL PHASE SHIFTER

EP4741914A1EP 4741914 A1EP4741914 A1EP 4741914A1EP-4741914-A1

Abstract

A device (100) for controlling a thermo-optical phase shifter, TOPS, (202; 302) is provided, said device (100) comprising: a driving circuit (110) providing power to the TOPS (202; 302) by toggling between an on state outputting maximum power and an off state outputting minimum power, wherein a toggling scheme controls an effective power; and a controller (120) generating a modulation signal for controlling the toggling scheme and comprising a pre-distortion module (122) for determining an initial portion of the modulation signal for bringing the temperature of the TOPS (202; 302) from a first level corresponding to a first effective power of the driving circuit (110) to a second level corresponding to a second effective power of the driving circuit (110), wherein the pre-distortion module (122) determines the initial portion based on a non-linear function of the first effective power, the second effective power, and the maximum or minimum power.

Inventors

  • ROMME, JAC

Assignees

  • Stichting IMEC Nederland

Dates

Publication Date
20260513
Application Date
20241111

Claims (15)

  1. A device (100) for controlling a thermo-optical phase shifter, TOPS, (202; 302) for affecting an optical waveguide (204; 304) based on temperature of the TOPS (202; 302), said device (100) comprising: a driving circuit (110) configured to provide power to the TOPS (202; 302), wherein the driving circuit (110) is configured to toggle between an on state for outputting a maximum power and an off state for outputting a minimum power, wherein a toggling scheme of the driving circuit (110) controls an effective power output by the driving circuit (110), and wherein the effective power output by the driving circuit (110) corresponds to a temperature of the TOPS (202; 302); and a controller (120) configured to generate a modulation signal and provide the modulation signal to the driving circuit (110) for controlling the toggling scheme of the driving circuit (110), wherein the controller (120) comprises a pre-distortion module (122) for determining an initial portion of the modulation signal for bringing the temperature of the TOPS (202; 302) from a first level corresponding to a first effective power of the driving circuit (110) to a second level corresponding to a second effective power of the driving circuit (110), wherein, in case the second effective power is larger than the first effective power, the pre-distortion module (122) is configured to determine the initial portion of the modulation signal based on a non-linear function of the first effective power, the second effective power, and the maximum power of the driving circuit (110), and in case the second effective power is smaller than the first effective power, the pre-distortion module (122) is configured to determine the initial portion of the modulation signal based on a non-linear function of the first effective power, the second effective power, and the minimum power of the driving circuit (110).
  2. The device according to claim 1, wherein the pre-distortion module (122) is configured to determine the initial portion as an initial duration period, wherein the pre-distortion module (122) is configured to determine the initial duration period in relation to a period of a clock cycle for controlling the driving circuit (110).
  3. The device according to claim 2, wherein the controller (120) is configured to set the initial duration period to or an integer number of clock cycles based on the determined relation between the initial period and the period of the clock cycle.
  4. The device according to any one of the preceding claims, wherein the controller (120) further comprises a digital modulator (124) for determining a steady-state portion of the modulation signal following the initial portion.
  5. The device according to claim 4, wherein the digital modulator (124) is a delta-sigma modulator or a pulse width modulator.
  6. The device according to claim 4 or 5 when dependent on claim 3, wherein the digital modulator (124) is configured to receive input of a fractional part from the pre-distortion module (122) corresponding to a remaining fraction of clock cycles in a relation between the initial period and the period of the clock cycle, wherein the digital modulator (124) uses the fractional part for determining the modulation signal.
  7. The device according to any one of the preceding claims, wherein the pre-distortion module (122) is configured to determine the initial portion of the modulation signal based on a look-up table.
  8. The device according to any one of the preceding claims, wherein the pre-distortion module (122) is configured to determine the initial portion of the modulation signal based on the non-linear function being formed by a first order model of thermal response of the TOPS (202; 302).
  9. The device according to any one of the preceding claims, wherein the device (100) is configured to control a plurality of TOPSs (302), wherein the driving circuit (110) is configured to be cyclically sequentially connected to the TOPSs (302) of the plurality of TOPSs for providing power to the TOPSs (302), wherein the controller (120) is configured to generate the modulation signal for each of the TOPSs (302) in relation to a fraction of time during which the driving circuit (110) is connected to each of the TOPSs (302).
  10. An optical switch (200), comprising: a waveguide (204) being configured to propagate a light signal; a thermo-optical phase shifter, TOPS, (202) associated with the waveguide (204) and configured to control a refractive index of the waveguide (204) for controlling a direction of light at an output of the waveguide (204); and a device (100) according to any one of the preceding claims for controlling the temperature of the TOPS (202).
  11. An optical device (300), comprising: a plurality of waveguides (304), each waveguide (304) being configured to propagate a light signal; a plurality of thermo-optical phase shifters, TOPSs, (302), wherein each TOPS (302) is associated with a respective waveguide (304) of the plurality of waveguides and wherein each TOPS (302) is configured to control a refractive index of the respective waveguide (304); and one or more devices (100) according to any of claims 1-9 for controlling the temperature of the plurality of TOPSs (302).
  12. The optical device according to claim 11, wherein the one or more devices (100) are configured to control the temperature of the TOPSs (302) within a range of temperatures corresponding to a range of phase shifts of the light signal extending over at least 500 degrees, such as over at least 720 degrees.
  13. The optical device according to any one of claims 11-12, further comprising a plurality of light output elements (306), wherein each of the plurality of waveguides (304) is connected to a respective light output element (306) of the plurality of light output elements and wherein the optical device (300) is configured to control relative phase shifts of the light signals in the waveguides (304) for forming an optical phased array providing beam steering of an output light beam.
  14. The optical device according to claim 13, wherein the optical device (300) is configured to scan a direction of the output light beams by changing the relative phase shifts of the light signals.
  15. A method for controlling a thermo-optical phase shifter, TOPS, for affecting an optical waveguide based on temperature of the TOPS, said method comprising: generating (402) a modulation signal for controlling a driving circuit providing power to the TOPS, wherein generating the modulation signal comprises determining an initial portion of the modulation signal for bringing a temperature of the TOPS from a first level corresponding to a first effective power of the driving circuit to a second level corresponding to a second effective power of the driving circuit, wherein, in case the second effective power is larger than the first effective power, the initial portion of the modulation signal is based on a non-linear function of the first effective power, the second effective power, and a maximum power of the driving circuit, and in case the second effective power is smaller than the first effective power, the initial portion of the modulation signal is based on a non-linear function of the first effective power, the second effective power, and the minimum power of the driving circuit; providing (404) the modulation signal to the driving circuit; and outputting (406) power from the driving circuit to the TOPS, wherein outputting of power comprises toggling between an on state of the driving circuit for outputting a maximum power and an off state of the driving circuit for outputting a minimum power, wherein the modulation signal controls the toggling scheme of the driving circuit for bringing the temperature of the TOPS to the second level and for maintaining the temperature of the TOPS at the second level based on the second effective power output by the driving circuit corresponding to the second level of temperature of the TOPS.

Description

Technical field The present description relates to controlling of a thermo-optical phase shifter. The present description also relates to an optical switch and an optical device comprising one or more thermo-optical phase shifters being accurately controlled. Background Optical phase shifters are used in many applications. The optical phase shifter may control phase of a light signal, which may for instance be used for controlling a direction of the light signal, such as in an optical switching network, or for controlling beam steering, such as in an optical phased array (OPA). Several alternatives with different advantages exist for implementing an optical phase shifter. For instance, a thermo-optical phase shifter (TOPS) may be used, wherein the TOPS uses a heater for heating a waveguide. By controlling the temperature of the waveguide, a refractive index of the waveguide is slightly changed, which in turn implies that a phase shift of a light signal propagating through a length of the waveguide will be affected. The TOPS is an attractive solution in applications where low loss in the light signals is needed. However, the TOPS may require relatively high-power consumption for heating the heater and also in driving electronics for providing a control signal to the heater. For instance, driving electronics may use an amplifier that may be controlled to provide a necessary power output to the heater for controlling the temperature of the waveguide. However, there may be losses in the amplifier such that the control of the TOPS is not power efficient. In addition, heat dissipated in the driving electronics may affect the phase shift provided by the TOPSs making accurate control of the temperature of the waveguide more difficult. Further, the TOPS provides a fairly slow response such that changing the TOPS from providing a first phase shift at a first level to a second phase shift at a second level may require a time in order of a few or even hundreds of microseconds. In addition, if a fast response is desired, a higher power consumption may be needed. Thus, there is a need of providing an improved control of a TOPS for providing low power consumption and fast changes to the phase shift provided by the TOPS. Summary An objective of the present description is to provide controlling of a thermo-optical phase shifter in a power efficient and fast manner. This and other objectives are at least partly met by the invention as defined in the independent claims. Preferred embodiments are set out in the dependent claims. According to a first aspect, there is provided a device for controlling a thermo-optical phase shifter (TOPS) for affecting an optical waveguide based on temperature of the TOPS, said device comprising: a driving circuit configured to provide power to the TOPS, wherein the driving circuit is configured to toggle between an on state for outputting a maximum power and an off state for outputting a minimum power, wherein a toggling scheme of the driving circuit controls an effective power output by the driving circuit, and wherein the effective power output by the driving circuit corresponds to a temperature of the TOPS; and a controller configured to generate a modulation signal and provide the modulation signal to the driving circuit for controlling the toggling scheme of the driving circuit, wherein the controller comprises a pre-distortion module for determining an initial portion of the modulation signal for bringing the temperature of the TOPS from a first level corresponding to a first effective power of the driving circuit to a second level corresponding to a second effective power of the driving circuit, wherein, in case the second effective power is larger than the first effective power, the pre-distortion module is configured to determine the initial portion of the modulation signal based on a non-linear function of the first effective power, the second effective power, and the maximum power of the driving circuit, and in case the second effective power is smaller than the first effective power, the pre-distortion module is configured to determine the initial portion of the modulation signal based on a non-linear function of the first effective power, the second effective power, and the minimum power of the driving circuit. The driving circuit is configured to toggle between an off state and an on state. This implies that the driving circuit may be controlled based only on a switch for toggling between the on state and the off state. The effective power output by the driving circuit may thus be dependent on a percentage of time that the driving circuit is in the on state compared to the driving circuit being in the off state, which may also be referred to as a duty cycle of the driving circuit. Hence, the effective power output by the driving circuit may be controlled between the minimum power and the maximum power based on the duty cycle used. The duty cycle is a short-term duty cycle during w