US-12619029-B2 - Depolarization

US12619029B2US 12619029 B2US12619029 B2US 12619029B2US-12619029-B2

Abstract

Provided herein is a depolarizer circuit having an input waveguide configured to receive light from a light source; a splitter configured to provide light from the input waveguide in a first and second polarization states; a first rotator configured to rotate the light from the first polarization state to the second polarization state; a first delay line configured to delay the light in the second polarization state; a coupler configured to couple the rotated and delayed light; a second rotator configured to rotate the coupled light back to the first polarization state; a second delay line configured to delay the coupled light in the second polarization state; and a combiner configured to combine light from second rotator and delay line as depolarized light, where the first and second delay lines provide a phase delay difference therebetween greater than or equal to a coherence of the light source.

Inventors

Ronny Bockstaele
Karsten VERHAEGEN
Thijs SPUESENS

Assignees

SENTEA NV

Dates

Publication Date: 20260505
Application Date: 20220429
Priority Date: 20210430

Claims (15)

1 . A depolarizer circuit, comprising: an input waveguide configured to receive light; a splitter connected to the input waveguide and configured to provide, at a first output of the splitter, light in a first polarization state and, at a second output of the splitter, light in a second polarization state; a first rotator connected to the first output of the splitter and configured to rotate light received therefrom from the first polarization state to the second polarization state; a first delay line connected to the second output of the splitter; a coupler comprising a first and second output and configured to couple the light received from the first rotator and the first delay line; a second rotator connected to the first output of the coupler and configured to rotate light received therefrom back to the first polarization state; a second delay line connected to the second output of the coupler; and a combiner connected to the second rotator and the second delay line and configured to combine light received from each thereof as depolarized light, wherein the first and second delay lines provide a phase delay difference there between being greater than or equal to a coherence of the light received by the input waveguide.
2 . The depolarizer circuit according to claim 1 , wherein at least one of the first and second delay line provides a phase delay being greater than the coherence of the light received by the input waveguide.
3 . The depolarizer circuit according to claim 1 , wherein one of the first and second delay lines provides a first phase delay at least twice a second phase delay provided by the other one of the first and second delay lines.
4 . The depolarizer circuit according to claim 1 , wherein the phase delay difference relates to a difference in one or more of: length, waveguide cross-sectional dimension, and waveguide material.
5 . The depolarizer circuit according to claim 1 , wherein the depolarizer circuit is an integrated optical depolarizer circuit.
6 . The depolarizer circuit according to claim 1 , wherein the coupler comprises a switch configured to switch light to a plurality of outputs of the depolarizer circuit.
7 . The depolarizer circuit according to claim 1 , further comprising an active phase modulator configured to modulate combined light.
8 . The depolarizer circuit according to claim 1 , further comprising: a further input waveguide configured to receive light; and a spectrometer configured to separate wavelengths of received light.
9 . The depolarizer circuit according to claim 8 , further comprising: a further splitter connected to the further input waveguide and configured to provide, at a first output of the third splitter, light in a first polarization state and, at a second output of the further splitter, light in a second polarization state; a third rotator connected to the first output of the further splitter and configured to rotate light received therefrom from the first polarization state to the second polarization state; a third delay line connected to the second output of the further splitter; and a coupler connected to the third rotator and the third delay line and configured to couple light received from each thereof and to provide the coupled light to the spectrometer.
10 . The depolarizer circuit according to claim 9 , wherein at least one of the second and third delay lines provides a phase delay being greater than the coherence of the light received by the input waveguide.
11 . The depolarizer circuit according to claim 9 , wherein the second and third delay lines provide a further phase delay difference there between being at least twice a phase delay provided by the other of the second and third delay lines.
12 . The depolarizer circuit according to claim 1 , further comprising: an input interface configured to couple the light source with the input waveguide; and an output interface configured to couple the output waveguide with the output of the depolarizer circuit.
13 . A system comprising a reflector and the depolarizer circuit of claim 1 , wherein the reflector is configured to receive depolarized light from an output of the depolarizer and to reflect light to an input of the depolarizer circuit.
14 . The system of claim 13 , wherein the system is an optical interrogator.
15 . A method of depolarizing light in the depolarizer circuit of claim 1 , comprising the steps of: receiving light, by the input waveguide; splitting, by the splitter, the light into a first portion having the first polarization state and a second portion having the second polarization state; rotating, by the first rotator, the polarization of the first portion, such that it has the second polarization state; delaying, by the first delay line, the second portion; coupling, by the coupler, the first portion and second portion into a third portion and a fourth portion; rotating, by the second rotator, the polarization of the third portion back to the first polarization state; delaying, by the second delay line, the fourth portion; and combining, by the combiner, the third portion and the fourth portion as depolarized light, wherein the method further comprises providing a phase delay difference between the first and second delay lines, the phase delay difference being greater than or equal to a coherence of the light received by the input waveguide.

Description

FIELD OF THE INVENTION The present invention relates, in general, to a depolarizer circuit. The present invention further relates to a system composing a depolarizer circuit. The present invention further relates to a use of a depolarizer circuit in an optical interrogator. The present invention further relates to a method for depolarizing light in a depolarizer circuit. BACKGROUND ART Depolarizers are optical devices, required to convert polarized light into a pseudo-randomly polarized light, which is then called depolarized or scrambled light. While polarized light can be very useful in many photonic applications, some specific applications require non-polarized light for effective operation and accurate measurement, like Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) spectrometry, Raman amplifier, optical imaging, and optical fiber rotation sensing. Several types of depolarizers are well known, such as Cornu depolarizer, Lyot depolarizer, Wedge depolarizer and Time-variable depolarizer. However, such depolarizers are very expensive and have very limited applications. Moreover, existing optical interrogators, e.g. including the afore-mentioned types of depolarizers, are bulky and, thus, impractical. Ragheb et al. (2015) have described an integrated slanted angle Lyot depolarizer and an integrated Mach-Zehnder optical depolarizer in “Design of an InGaAsP/InP compact integrated optical depolarizer”. However, such depolarizers require an active phase shifter and a feedback control signal for any general elliptically polarized light. Moreover, such depolarizers can entail interference effects. Therefore, there is a need in the art to provide an improved depolarizer circuit and method for depolarizing light therein. SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved depolarizer circuit, which does not show one or more of the above-mentioned disadvantages. According to the present invention, a depolarizer circuit is provided, comprising an input waveguide configured to receive light from a light source; a splitter connected to the input waveguide and configured to provide, at a first output of the splitter, light in a first polarization state and, at a second output of the splitter, light in a second polarization state; a first rotator connected to the first output of the splitter and configured to rotate light received therefrom from the first polarization state to the second polarization state; a first delay line connected to the second output of the splitter; a coupler comprising a first and second output and configured to couple the light received from the first rotator and the first delay line; a second rotator connected to the first output of the coupler and configured to rotate light received therefrom back to the first polarization state; a second delay line connected to the second output of the coupler; and a combiner connected to the second rotator and the second delay line and configured to combine light received from each thereof as depolarized light, wherein the first and second delay lines provide a phase delay difference there between being greater than or equal to a coherence of the light source. According to the present invention, a system comprising a reflector and a depolarizer circuit as described above is provided. According to the present invention, use of a depolarizer circuit as described above in an optical interrogator and/or an optical gyroscope is provided. According to the present invention, a method of depolarizing light in a depolarizer circuit, preferably the depolarizer circuit as defined above is provided. Advantageously, the present invention may ensure that interference effects on light from two light paths are minimized. Moreover, the present invention may provide improved incoherent coupling of light, which results in an effective depolarization of the light. Additional and alternative objects of the present invention may be understood from the following. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be discussed in more detail below, with reference to the attached drawings, in which: FIG. 1 depicts a schematic diagram of a system comprising a depolarizer circuit according to the present invention; FIG. 2 depicts a schematic diagram of a depolarizer circuit according to the present invention; FIG. 3 depicts a schematic diagram of a system comprising a depolarizer circuit according to the present invention; and FIGS. 4A and 4B depict schematic diagrams of depolarizer circuits according to the present invention. DESCRIPTION OF EMBODIMENTS The following descriptions depict only example embodiments and are not considered limiting in scope. Any reference herein to the disclosure is not intended to restrict or limit the disclosure to exact features of any one or more of the exemplary embodiments disclosed in the present specification. Furthermore, the terms first, second, third and the like in the descriptio