CN115542565A - 90-degree space optical mixer insensitive to polarization - Google Patents
90-degree space optical mixer insensitive to polarization Download PDFInfo
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- CN115542565A CN115542565A CN202211366761.XA CN202211366761A CN115542565A CN 115542565 A CN115542565 A CN 115542565A CN 202211366761 A CN202211366761 A CN 202211366761A CN 115542565 A CN115542565 A CN 115542565A
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- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
- G02B27/283—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising used for beam splitting or combining
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- G—PHYSICS
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
- G02B27/286—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another
Abstract
The invention belongs to the technical field of free space optical communication equipment, and discloses a polarization insensitive 90-degree space optical mixer which comprises a first half-wave plate, a phase modifier, a second half-wave plate, a third half-wave plate, a first quarter-wave plate, a second quarter-wave plate, a first polarization beam splitting interface, a second polarization beam splitting interface, a first beam splitting interface, a second beam splitting interface, a first reflection interface and a second reflection interface; the invention is suitable for signal light in any polarization state, has simple structure and higher stability.
Description
Technical Field
The invention relates to the technical field of free space optical communication equipment, in particular to a polarization insensitive 90-degree space optical mixer.
Background
In coherent optical communication, coherent detection needs to use an optical mixer to superpose received optical signals and local oscillator optical signals, and the optical mixer formed by using the spatial optical device has the advantages of small insertion loss, high stability, low cost and the like. The optical mixer requires that the polarization state of the received optical signal is matched with the polarization state of the local oscillator light, when the polarization states of the received optical signal and the local oscillator light are consistent, the beat frequency efficiency is highest, and if the polarization states are vertical to each other, the beat frequency signal is completely offset, so that normal receiving cannot be performed. However, the polarization state of the signal light is randomly changed when the signal light is transmitted through the channel, and the polarization state of the signal light and the polarization state of the local oscillator light cannot be guaranteed to be consistent, so that stable frequency mixing is difficult to achieve. For example, patent CN103257402A (published japanese: 2013-08-21) proposes a spatial optical mixer with a simple structure, which can demodulate DP-QPSK optical signals, but requires that the polarization states of local oscillation light and signal light are the same.
In order to solve the above problems, patent CN105353520A (published: 2016-02-24) provides a spatial light 90 ° frequency mixer with high frequency mixing efficiency, and an electronically controlled polarization controller is adopted to adjust the polarization state of local oscillator light to be consistent with the polarization state of signal light, but this solution needs to allocate 10% of signal power to a feedback control circuit to adjust the polarization controller in real time, which increases the complexity of the system and cannot cope with the high-speed change of polarization caused by adverse environmental effects. The scheme of patent CN110824719A (published japanese: 2020-02-21) is similar, and the polarization state of the local oscillation light is also feedback controlled by detecting the polarization state of a part of the optical signal. Although the proposal of patent CN102142901A (published: 2011-08-03) does not need any active control module, the output optical signal reaches 16 paths, which greatly increases the number of detectors and the complexity of subsequent processing circuits.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a 90-degree spatial optical mixer insensitive to polarization.
The technical scheme of the invention is realized as follows:
a polarization insensitive 90 degree space optical mixer comprises a first half wave plate, a phase modulator, a second half wave plate, a third half wave plate, a first quarter wave plate, a second quarter wave plate, a first polarization beam splitting interface, a second polarization beam splitting interface, a first beam splitting interface, a second beam splitting interface, a first reflection interface and a second reflection interface,
the first polarization beam splitting interface and the second polarization beam splitting interface are respectively positioned on two sides of the same plane formed by the first beam splitting interface and the second beam splitting interface, the first beam splitting interface and the second beam splitting interface are respectively positioned on two sides of the other plane formed by the first polarization beam splitting interface and the second polarization beam splitting interface, and the two planes are vertically crossed;
the first polarization beam splitting interface is used for polarizing and splitting beams of the signal light to generate horizontally polarized first signal light and vertically polarized second signal light; the second polarization beam splitting interface is used for polarization beam splitting of the local oscillator light subjected to polarization rotation and phase modulation to generate horizontally polarized first local oscillator light and vertically polarized second local oscillator light;
an included angle between the main axis direction of the first half-wave plate and the horizontal direction is-22.5 degrees, and the first half-wave plate is used for converting horizontally polarized local oscillator light into linearly polarized light of-45 degrees; the phase modulator is used for modulating a phase difference alpha between a horizontal polarization component and a vertical polarization component of the-45-degree linear polarization local oscillation light;
the incident interfaces of the first half wave plate and the phase modulator are parallel to each other and form an included angle of 45 degrees with the second polarization beam splitting interface, so that the incident direction of local oscillation light is perpendicular to the incident interfaces of the first half wave plate and the phase modulator, and the included angle of the local oscillation light and the second polarization beam splitting interface is 45 degrees;
an included angle between the main shaft direction of the second half-wave plate and the horizontal direction is 22.5 degrees, the second half-wave plate is positioned between the first polarization beam splitting interface and the first beam splitting interface, and the included angles between the incident interface and the first polarization beam splitting interface are both 45 degrees, so that the first signal light of the horizontal polarization is changed into a linear polarization light of 45 degrees;
the included angle between the main shaft direction of the third half-wave plate and the horizontal direction is-22.5 degrees, the third half-wave plate is positioned between the first polarization beam splitting interface and the second polarization beam splitting interface, and the included angle between the incident interface and the second polarization beam splitting interface is 45 degrees, so that the vertically polarized second signal light is changed into linearly polarized light of-135 degrees;
the included angle between the main axis direction of the first quarter-wave plate and the horizontal direction is-45 degrees, the first quarter-wave plate is positioned between the second polarization beam splitting interface and the second beam splitting interface, and the included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, so that the first quarter-wave plate is used for changing the second local oscillation light of vertical polarization into circularly polarized light;
an included angle between the main axis direction of the second quarter-wave plate and the horizontal direction is-45 degrees, the second quarter-wave plate is positioned between the second polarization beam splitting interface and the first beam splitting interface, and included angles between an incident interface and the first polarization beam splitting interface are both 45 degrees, so that the first local oscillation light of the horizontal polarization is changed into circularly polarized light;
the first beam splitting interface is used for enabling the first signal light with 45-degree linear polarization and the first local oscillator light with circular polarization to interfere to generate first interference light and second interference light; the second beam splitting interface is used for enabling a second signal light with linear polarization of-45 degrees and a second local oscillator light with circular polarization to interfere to generate a third interference light and a fourth interference light;
the first reflection interface and the second reflection interface are positioned on two sides of a plane formed by the first polarization beam splitting interface and the second polarization beam splitting interface at equal intervals and are parallel to the plane;
the first reflecting interface is used for reflecting the first interference light and the second interference light; the second reflecting interface is used for reflecting the third interference light and the fourth interference light;
the first polarization beam splitting interface is further used for enabling the horizontal polarization component of the first interference light and the vertical polarization component of the third interference light to be subjected to polarization beam combination to generate first mixed light; the vertical polarization component of the first interference light and the horizontal polarization component of the third interference light are subjected to polarization beam combination to generate second mixed light;
the second polarization beam splitting interface is further used for enabling the horizontal polarization component of the second interference light and the vertical polarization component of the fourth interference light to be subjected to polarization beam combination to generate third mixed light; and the vertical polarization component of the second interference light and the horizontal polarization component of the fourth interference light are subjected to polarization beam combination to generate fourth mixed light.
Preferably, the first polarization beam splitting interface and the second polarization beam splitting interface are respectively and correspondingly formed by polarization beam splitting interfaces of a first polarization beam splitter and a second polarization beam splitter;
the first beam splitting interface and the second beam splitting interface are respectively and correspondingly composed of beam splitting interfaces of a first non-polarization beam splitter and a second non-polarization beam splitter.
Preferably, the first reflective interface and the second reflective interface are respectively formed by reflective surfaces of the first right-angle prism and the second right-angle prism.
Preferably, the first reflective interface and the second reflective interface are respectively formed by reflective surfaces of a first mirror and a second mirror.
Preferably, the first polarization beam splitter and the second polarization beam splitter have the same size, the length and the width are both 2L, and the height is L; the first non-polarization beam splitter and the second non-polarization beam splitter are cubes, and the length, the width and the height are both L; the width and height of the second half-wave plate, the third half-wave plate, the first quarter-wave plate and the second quarter-wave plate are all L;
the light beam incident interface and the light beam emergent interface of the second half-wave plate are respectively attached to the light beam transmission interface of the first polarization beam splitter and the first light beam incident interface of the first non-polarization beam splitter; the light beam incident interface and the light beam emergent interface of the third half-wave plate are respectively attached to the light beam reflecting interface of the first polarization beam splitter and the first light beam incident interface of the second non-polarization beam splitter;
the light beam incident interface and the light beam emergent interface of the first quarter-wave plate are respectively attached to the light beam reflecting interface of the second polarization beam splitter and the second light beam incident interface of the second non-polarization beam splitter; the light beam incident interface and the light beam emergent interface of the second quarter-wave plate are respectively attached to the light beam transmission interface of the second polarization beam splitter and the second light beam incident interface of the first non-polarization beam splitter;
and a light beam incidence interface of the phase modulator is attached to a light beam emergence interface of the first half-wave plate, and the light beam emergence interface is attached to a light beam incidence interface of the second polarization beam splitter, so that the phase modulator and the second quarter-wave plate are respectively positioned at two sides of the second polarization beam splitter.
Preferably, the first right-angle prism and the second right-angle prism have the same size, the length of each right-angle side is 2L, the height of each right-angle side is L, and a reflecting film is plated on the outer side of each inclined plane;
one right-angle surface of the first right-angle prism and the surface opposite to the light beam reflecting interface of the first polarization beam splitter are positioned on the same plane, and the other right-angle surface and the surface opposite to the light beam reflecting interface of the second polarization beam splitter are positioned on the same plane;
one right-angle surface of the second right-angle prism and the surface opposite to the light beam transmission interface of the first polarization beam splitter are positioned on the same plane, and the other right-angle surface and the surface opposite to the light beam transmission interface of the second polarization beam splitter are positioned on the same plane.
Preferably, the phase modulator dynamically modulates the phase so that the phase difference between the modulated phase and the orthogonal polarization component of the signal light is pi/2.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a polarization insensitive 90-degree space optical mixer, which mixes two polarization components of signal light with two components with equal amplitude of local oscillator light respectively by polarizing and splitting the input signal light, and can realize polarization insensitive photosensitive mixing without being influenced by the polarization change of the signal light by only phase modulating one of the local oscillator light components. The invention is suitable for signal light in any polarization state, has simple structure and higher stability.
Drawings
FIG. 1 is a schematic diagram of a polarization insensitive 90 ° spatial optical mixer of the present invention;
FIG. 2 is a schematic diagram of a 90 ° spatial optical mixer insensitive to polarization according to the present invention;
fig. 3 is a schematic diagram of the optical path of the polarization insensitive 90 ° spatial optical mixer of the present invention.
In the figure: the polarization beam splitter comprises a first half-wave plate 1, a phase modulator 2, a second half-wave plate 3, a third half-wave plate 4, a first quarter-wave plate 5, a second quarter-wave plate 6, a first polarization beam splitting interface 7, a second polarization beam splitting interface 8, a first beam splitting interface 9, a second beam splitting interface 10, a first reflection interface 11, a second reflection interface 12, a first polarization beam splitter 13, a second polarization beam splitter 14, a first non-polarization beam splitter 15, a second non-polarization beam splitter 16, a first right-angle prism 17 and a second right-angle prism 18.
Detailed Description
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown.
As shown in fig. 1, a polarization insensitive 90 ° spatial optical mixer comprises a first half wave plate 1, a phase modulator 2, a second half wave plate 3, a third half wave plate 4, a first quarter wave plate 5 and a second quarter wave plate 6, and a first polarization beam splitting interface 7, a second polarization beam splitting interface 8, a first beam splitting interface 9, a second beam splitting interface 10, a first reflective interface 11 and a second reflective interface 12,
the first polarization beam splitting interface 7 and the second polarization beam splitting interface 8 are respectively located on two sides of the same plane formed by the first beam splitting interface 9 and the second beam splitting interface 10, the first beam splitting interface 9 and the second beam splitting interface 10 are respectively located on two sides of the other plane formed by the first polarization beam splitting interface 7 and the second polarization beam splitting interface 8, and the two planes are vertically crossed;
the first polarization beam splitting interface 7 is configured to polarizedly split the signal light to generate a first signal light with horizontal polarization and a second signal light with vertical polarization; the second polarization beam splitting interface 8 is configured to polarizedly split the local oscillation light subjected to polarization rotation and phase modulation to generate a first local oscillation light of horizontal polarization and a second local oscillation light of vertical polarization;
an included angle between the main axis direction of the first half-wave plate 1 and the horizontal direction is-22.5 degrees, and the included angle is used for converting horizontally polarized local oscillator light into linearly polarized light of-45 degrees; the phase modulator is used for modulating a phase difference alpha between a horizontal polarization component and a vertical polarization component of the-45-degree linear polarization local oscillation light;
the center of the first half-wave plate 1 is aligned with the center of the phase modulator 2, the incident interfaces of the first half-wave plate 1 and the phase modulator 2 are parallel to each other, and the included angle between the incident interfaces and the second polarization beam splitting interface 8 is 45 degrees, so that the incident direction of local oscillation light is perpendicular to the incident interfaces of the first half-wave plate 1 and the phase modulator 2, and the included angle between the incident direction of local oscillation light and the second polarization beam splitting interface 8 is 45 degrees;
an included angle between the main shaft direction of the second half-wave plate 3 and the horizontal direction is 22.5 degrees, the second half-wave plate is positioned between the first polarization beam splitting interface 7 and the first beam splitting interface 9, and the included angles between the incident interface and the first polarization beam splitting interface are 45 degrees, so that the first signal light of the horizontal polarization is changed into a linear polarization light of 45 degrees;
an included angle between the main shaft direction of the third half-wave plate 4 and the horizontal direction is-22.5 degrees, the third half-wave plate is positioned between the first polarization beam splitting interface 7 and the second beam splitting interface 10, and the included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, so that the third half-wave plate is used for converting vertically polarized second signal light into linearly polarized light of-135 degrees;
an included angle between the main axis direction of the first quarter-wave plate 5 and the horizontal direction is-45 degrees, the first quarter-wave plate is positioned between the second polarization beam splitting interface 8 and the second beam splitting interface 10, and included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, and the first quarter-wave plate is used for converting vertically polarized second local oscillation light into circularly polarized light;
the included angle between the main axis direction of the second quarter-wave plate 6 and the horizontal direction is-45 degrees, the second quarter-wave plate is positioned between the second polarization beam splitting interface 8 and the first beam splitting interface 9, and the included angles between the incident interface and the first polarization beam splitting interface are both 45 degrees, so that the first local oscillation light of the horizontal polarization is changed into circular polarization light;
the first beam splitting interface 9 is configured to interfere the first signal light with linear polarization of 45 ° with the first local oscillator light with circular polarization, so as to generate first interference light and second interference light; the second beam splitting interface 10 is configured to interfere the-45 ° linearly polarized second signal light with the circularly polarized second local oscillator light to generate third interference light and fourth interference light;
the first reflecting interface 11 and the second reflecting interface 12 are positioned on two sides of a plane formed by the first polarization beam splitting interface 7 and the second polarization beam splitting interface 8 at equal intervals and are parallel to the plane, and the first reflecting interface and the second reflecting interface are perpendicular to the plane formed by the first beam splitting interface 9 and the second beam splitting interface 10;
the first reflective interface 11 is used for reflecting the first interference light and the second interference light; the second reflective interface 12 is used for reflecting the third interference light and the fourth interference light;
the first polarization beam splitting interface 7 is further configured to perform polarization beam combination on the horizontal polarization component of the first interference light and the vertical polarization component of the third interference light to generate first mixed light; the vertical polarization component of the first interference light and the horizontal polarization component of the third interference light are subjected to polarization beam combination to generate second mixed light;
the second polarization beam splitting interface 8 is further configured to perform polarization beam combination on the horizontal polarization component of the second interference light and the vertical polarization component of the fourth interference light to generate third mixed light; and the vertical polarization component of the second interference light and the horizontal polarization component of the fourth interference light are subjected to polarization beam combination to generate fourth mixed light.
The phase modulator 2 performs dynamic phase modulation so that the phase difference between the adjusted phase and the orthogonal polarization component of the signal light is pi/2.
The specific working principle is as follows:
the polarization state of the signal light can be written as
Wherein, the first and the second end of the pipe are connected with each other,
the frequency, initial phase, and phase difference between orthogonal polarization components of the signal light, respectively. The signal light is first incident on the first polarization beam splitting interface 7, and is split into the horizontally polarized first signal light and the vertically polarized second signal light.
Then, after passing through the second half-wave plate 3 and the third half-wave plate 4, the polarization states of the first signal light and the second signal light respectively become:
the horizontally polarized local oscillator light enters the first half wave plate 1, the polarization is rotated to-45 degrees and then the phase difference alpha of the orthogonal polarization components is modulated by the phase modulator 2, and the polarization state can be written as
Wherein the content of the first and second substances,
the amplitude, the frequency and the initial phase of the local oscillator light are respectively. Then the light is incident to a second polarization beam splitting interface 8, and is split into a first local oscillation light with horizontal polarization and a second local oscillation light with vertical polarization, and the polarization states of the two local oscillation lights respectively pass through a second quarter wave plate 6 and a first quarter wave plate 5 to become:
the first signal light and the first local oscillator light arrive at the first beam splitting interface 9 at the same time to interfere with each other, so as to generate first interference light and second interference light, which can be written as
The second signal light and the second local oscillator light arrive at the second beam splitting interface 10 at the same time to interfere with each other, so as to generate third interference light and fourth interference light, the polarization states of which can be written as
The first interference light is reflected by the first reflection interface 11, the third interference light is reflected by the second reflection interface 12 and then simultaneously reaches the first polarization beam splitting interface 7 for polarization beam combination, wherein the horizontal polarization component of the first interference light and the vertical polarization component of the third interference light are subjected to polarization beam combination to generate first mixed light
The vertical polarization component of the first interference light and the horizontal polarization component of the third interference light are subjected to polarization beam combination to generate second mixed light
The second interference light is reflected by the first reflection interface 11, the fourth interference light is reflected by the second reflection interface 12 and then simultaneously reaches the second polarization beam splitting interface 8 for polarization beam combination, wherein the horizontal polarization component of the second interference light and the vertical polarization component of the fourth interference light are subjected to polarization beam combination to generate third mixed light
The vertical polarization component of the second interference light and the horizontal polarization component of the fourth interference light are polarized and combined to generate fourth mixed light
Photoelectric conversion of the first mixed light and the third mixed light using a balanced detector to produce a differential current of
Photoelectric conversion of the second mixed light and the fourth mixed light using a balanced detector to produce a differential current of
Wherein R is the response coefficient of the detector,
is an intermediate frequency signal.
Since the polarization change of the signal light is a slow process,
is also slowly changed, and can dynamically adjust alpha according to the size of an output signal and by combining with a PID control algorithm
When the two differential currents are respectively
It is obvious that the polarization angle information of the signal light is converted into the phase information of the intermediate frequency signal, and the amplitude and the polarization angle of the intermediate frequency signal are output
Irrelevantly, namely, any fluctuation of the polarization state of the signal light cannot influence the amplitude demodulation of the intermediate frequency signal, and the receiving sensitivity of heterodyne detection cannot be reduced. Therefore, by adjusting the phase α of the second local oscillation light, the influence of the change in the polarization state of the signal light on the final output signal can be eliminated, and stable optical mixing can be achieved.
As shown in fig. 2, example:
the polarization insensitive space optical mixer has the following structure: the first polarization beam splitting interface 7 and the second polarization beam splitting interface 8 are respectively and correspondingly composed of polarization beam splitting interfaces of a first polarization beam splitter 13 and a second polarization beam splitter 14;
the first beam splitting interface 9 and the second beam splitting interface 10 are respectively and correspondingly composed of beam splitting interfaces of a first non-polarization beam splitter 15 and a second non-polarization beam splitter 16;
the first reflecting interface 11 and the second reflecting interface 12 are respectively formed by the reflecting surfaces of a first right-angle prism 17 and a second right-angle prism 18.
The first polarization beam splitter 13 and the second polarization beam splitter 14 have the same size, the length and the width are both 2L, and the height is L; the first non-polarization beam splitter 15 and the second non-polarization beam splitter 16 are cubes, and both the length, the width and the height are L; the width and height of the second half-wave plate 3, the third half-wave plate 4, the first quarter-wave plate 5 and the second quarter-wave plate 6 are all L;
the light beam incident interface and the light beam emergent interface of the second half-wave plate 3 are respectively attached to the light beam transmission interface of the first polarization beam splitter 13 and the first light beam incident interface of the first non-polarization beam splitter 15; the light beam incident interface and the light beam emergent interface of the third half-wave plate 4 are respectively attached to the light beam reflecting interface of the first polarization beam splitter 13 and the first light beam incident interface of the second non-polarization beam splitter 16;
the light beam incident interface and the light beam emergent interface of the first quarter-wave plate 5 are respectively attached to the light beam reflecting interface of the second polarization beam splitter 14 and the second light beam incident interface of the second non-polarization beam splitter 16; the light beam incident interface and the light beam emergent interface of the second quarter-wave plate 6 are respectively attached to the light beam transmission interface of the second polarization beam splitter 14 and the second light beam incident interface of the first non-polarization beam splitter 15;
a light beam incidence interface of the phase modulator 2 is attached to a light beam emergence interface of the first half-wave plate 1, and the light beam emergence interface is attached to a light beam incidence interface of the second polarization beam splitter 14, so that the phase modulator 2 and the second quarter-wave plate 6 are respectively positioned on two sides of the second polarization beam splitter 14;
the first right-angle prism 17 and the second right-angle prism 18 have the same size, the side lengths of the two right-angle prisms are both 2L, the height of the two right-angle prisms is L, and the outer sides of the inclined planes are plated with reflecting films;
one right-angle surface of the first right-angle prism 17 and the surface opposite to the light beam reflection interface of the first polarization beam splitter 13 are on the same plane, and the other right-angle surface and the surface opposite to the light beam reflection interface of the second polarization beam splitter 14 are on the same plane;
one right-angle surface of the second right-angle prism 18 is positioned on the same plane with the surface opposite to the light beam transmission interface of the first polarization beam splitter 13, and the other right-angle surface is positioned on the same plane with the surface opposite to the light beam transmission interface of the second polarization beam splitter 14.
The specific working principle is as follows:
the optical paths of the signal light and the local oscillator light transmitted and mixed in the spatial optical mixer are shown in fig. 3.
The polarization state of the signal light can be written as
Wherein the content of the first and second substances,
respectively, the frequency of the signal light, the initial phase, and the phase difference between the orthogonal polarization components. The signal light is first incident on the first polarization beam splitter 13, and is split into the first signal light of the horizontal polarization and the second signal light of the vertical polarization at the first interface.
Then, after passing through the second half-wave plate 3 and the third half-wave plate 4, the polarization states of the first signal light and the second signal light respectively become:
the horizontally polarized local oscillator light enters the first half wave plate 1, the polarization is rotated to-45 degrees and then the phase difference alpha of the orthogonal polarization components is modulated by the phase modulator 2, and the polarization state can be written as
Wherein the content of the first and second substances,
the amplitude, the frequency and the initial phase of the local oscillator light are respectively. Then enters the second polarization beam splitter 14, is split into a first local oscillation light of horizontal polarization and a second local oscillation light of vertical polarization at the second interface, and the polarization states of the two become after passing through the second quarter wave plate 6 and the first quarter wave plate 5, respectively:
the first signal light and the first local oscillator light reach the beam splitting interface of the first non-polarizing beam splitter 15 at the same time to interfere with each other, so as to generate first interference light and second interference light, which can be written as
The second signal light and the second local oscillator light simultaneously reach the beam splitting interface of the second non-polarization beam splitter 16 for interference to generate third interference light and fourth interference light, and the polarization states of the third interference light and the fourth interference light can be written as
The first interference light is reflected by the first reflection interface of the first right-angle prism 17, the third interference light is reflected by the second reflection interface 12 of the second right-angle prism 18 and then simultaneously reaches two sides of the beam splitting interface of the first polarization beam splitter 13, polarization beam combination is carried out at the first interface P1, wherein the horizontal polarization component of the first interference light and the vertical polarization component of the third interference light are subjected to polarization beam combination to generate first mixing light
The vertical polarization component of the first interference light and the horizontal polarization component of the third interference light are polarized and combined to generate second mixed light
The second interference light is reflected by the first inverse interface of the first right-angle prism 17, the fourth interference light is reflected by the second inverse interface of the second right-angle prism 18 and then simultaneously reaches two sides of the beam splitting interface of the second polarization beam splitter 14, polarization beam combination is carried out at the second polarization beam splitting interface 8, wherein the horizontal polarization component of the second interference light and the vertical polarization component of the fourth interference light are subjected to polarization beam combination, and third mixed-frequency light is generated
The vertical polarization component of the second interference light and the horizontal polarization component of the fourth interference light are polarized and combined to generate fourth mixed light
The first mixed light and the third mixed light are photoelectrically converted using a balanced detector to generate a differential current of
Photoelectric conversion of the second mixed light and the fourth mixed light using a balanced detector to produce a differential current of
Wherein, R is the response coefficient of the detector,
is an intermediate frequency signal.
Since the polarization change of the signal light is a gradual process,
is also slowly varied, and can dynamically adjust alpha according to the size of an output signal by combining with a PID control algorithm
When the two differential currents are respectively
It is obvious that the polarization angle information of the signal light is converted into the phase information of the intermediate frequency signal, and the amplitude and the polarization angle of the intermediate frequency signal are output
Irrelevantly, i.e. any fluctuation of the polarization state of the signal light will not affect the amplitude demodulation of the intermediate frequency signal, nor will it reduce the receiving sensitivity of heterodyne detection. Therefore, by adjusting the phase α of the second local oscillation light, the influence of the change in the polarization state of the signal light on the final output signal can be eliminated, and stable optical mixing can be achieved.
It can be known from the embodiments of the present invention that the present invention provides a polarization insensitive 90 ° spatial light mixer, which performs polarization beam splitting on input signal light, so that two polarization components of the signal light are respectively mixed with two components of local oscillator light with equal amplitude, and only one of the local oscillator light components needs to be phase-modulated, so as to implement polarization insensitive optical mixing without being affected by the polarization change of the signal light. The invention is suitable for signal light in any polarization state, has simple structure and higher stability.
Claims (7)
1. A polarization insensitive 90-degree space optical mixer is characterized by comprising a first half-wave plate (1), a phase modulator (2), a second half-wave plate (3), a third half-wave plate (4), a first quarter-wave plate (5), a second quarter-wave plate (6), a first polarization beam splitting interface (7), a second polarization beam splitting interface (8), a first beam splitting interface (9), a second beam splitting interface (10), a first reflection interface (11) and a second reflection interface (12),
the first polarization beam splitting interface (7) and the second polarization beam splitting interface (8) are respectively positioned on two sides of the same plane formed by the first beam splitting interface (9) and the second beam splitting interface (10), the first beam splitting interface (9) and the second beam splitting interface (10) are respectively positioned on two sides of the other plane formed by the first polarization beam splitting interface (7) and the second polarization beam splitting interface (8), and the two planes are vertically crossed;
the first polarization beam splitting interface (7) is used for polarization beam splitting of the signal light to generate a first signal light with horizontal polarization and a second signal light with vertical polarization; the second polarization beam splitting interface (8) is used for polarization beam splitting of the local oscillation light subjected to polarization rotation and phase modulation to generate horizontally polarized first local oscillation light and vertically polarized second local oscillation light;
the included angle between the main shaft direction of the first half-wave plate (1) and the horizontal direction is-22.5 degrees, and the first half-wave plate is used for converting horizontally polarized local oscillator light into linearly polarized light of-45 degrees; the phase modulator (2) is used for modulating a phase difference alpha between a horizontal polarization component and a vertical polarization component of the-45-degree linear polarization local oscillation light;
the incidence interfaces of the first half-wave plate (1) and the phase modulator (2) are parallel to each other, and the included angles between the incidence interfaces and the second polarization beam splitting interface (8) are 45 degrees, so that the incidence direction of local oscillation light is perpendicular to the incidence interfaces of the first half-wave plate (1) and the phase modulator (2), and the included angle between the local oscillation light and the second polarization beam splitting interface (8) is 45 degrees;
an included angle between the main shaft direction of the second half-wave plate (3) and the horizontal direction is 22.5 degrees, the second half-wave plate is positioned between the first polarization beam splitting interface (7) and the first beam splitting interface (9), and included angles between the incident interface and the first polarization beam splitting interface are both 45 degrees, so that the first horizontally polarized signal light is changed into 45-degree linearly polarized light;
an included angle between the main shaft direction of the third half-wave plate (4) and the horizontal direction is-22.5 degrees, the third half-wave plate is positioned between the first polarization beam splitting interface (7) and the second beam splitting interface (10), and the included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, so that the vertically polarized second signal light is changed into linearly polarized light of-135 degrees;
an included angle between the main axis direction of the first quarter-wave plate (5) and the horizontal direction is-45 degrees, the first quarter-wave plate is positioned between the second polarization beam splitting interface (8) and the second beam splitting interface (10), and included angles between the incident interface and the second polarization beam splitting interface are both 45 degrees, so that the first quarter-wave plate is used for changing the vertically polarized second local oscillation light into circularly polarized light;
the included angle between the main axis direction of the second quarter-wave plate (6) and the horizontal direction is-45 degrees, the second quarter-wave plate is positioned between the second polarization beam splitting interface (8) and the first beam splitting interface (9), and the included angles between the incident interface and the first polarization beam splitting interface are both 45 degrees, so that the first local oscillation light of the horizontal polarization is changed into circular polarization light;
the first beam splitting interface (9) is used for enabling the first signal light with 45-degree linear polarization and the first local oscillator light with circular polarization to interfere to generate first interference light and second interference light; the second beam splitting interface (10) is used for enabling the-45-degree linearly polarized second signal light and the circularly polarized second local oscillation light to interfere to generate third interference light and fourth interference light;
the first reflecting interface (11) and the second reflecting interface (12) are positioned on two sides of a plane formed by the first polarization beam splitting interface (7) and the second polarization beam splitting interface (8) at equal intervals and are parallel to the plane;
the first reflecting interface (11) is used for reflecting the first interference light and the second interference light; the second reflecting interface (12) is used for reflecting the third interference light and the fourth interference light;
the first polarization beam splitting interface (7) is further used for enabling the horizontal polarization component of the first interference light and the vertical polarization component of the third interference light to be subjected to polarization beam combination to generate first mixed light; the vertical polarization component of the first interference light and the horizontal polarization component of the third interference light are subjected to polarization beam combination to generate second mixed light;
the second polarization beam splitting interface (8) is further used for enabling the horizontal polarization component of the second interference light and the vertical polarization component of the fourth interference light to be subjected to polarization beam combination to generate third mixed light; and the vertical polarization component of the second interference light and the horizontal polarization component of the fourth interference light are subjected to polarization beam combination to generate fourth mixed light.
2. The polarization insensitive 90 ° spatial optical mixer according to claim 1, wherein the first polarization beam splitting interface (7) and the second polarization beam splitting interface (8) are respectively formed by polarization beam splitting interfaces of a first polarization beam splitter (13) and a second polarization beam splitter (14);
the first beam splitting interface (9) and the second beam splitting interface (10) are respectively and correspondingly composed of beam splitting interfaces of a first non-polarization beam splitter (15) and a second non-polarization beam splitter (16).
3. The polarization insensitive 90 ° spatial optical mixer according to claim 2, wherein the first and second reflective interfaces (11, 12) are constituted by reflective surfaces of a first right angle prism (17) and a second right angle prism (18), respectively.
4. The polarization insensitive 90 ° spatial optical mixer according to claim 1, wherein the first and second reflective interfaces (11, 12) are respectively formed by reflective surfaces of a first and second mirror.
5. The polarization insensitive 90 ° spatial optical mixer according to claim 3, wherein the first polarization beam splitter (13) and the second polarization beam splitter (14) are of the same size, with length and width of 2L and height of L; the first non-polarization beam splitter (15) and the second non-polarization beam splitter (16) are cubes, and the length, the width and the height are both L; the width and height of the second half-wave plate (3), the third half-wave plate (4), the first quarter-wave plate (5) and the second quarter-wave plate (6) are all L;
the light beam incidence interface and the light beam emergence interface of the second half-wave plate (3) are respectively attached to the light beam transmission interface of the first polarization beam splitter (13) and the first light beam incidence interface of the first non-polarization beam splitter (15); the light beam incidence interface and the light beam emergence interface of the third half-wave plate (4) are respectively attached to the light beam reflection interface of the first polarization beam splitter (13) and the first light beam incidence interface of the second non-polarization beam splitter (16);
the light beam incidence interface and the light beam emergence interface of the first quarter-wave plate (5) are respectively attached to the light beam reflection interface of the second polarization beam splitter (14) and the second light beam incidence interface of the second non-polarization beam splitter (16); the light beam incident interface and the light beam emergent interface of the second quarter-wave plate (6) are respectively attached to the light beam transmission interface of the second polarization beam splitter (14) and the second light beam incident interface of the first non-polarization beam splitter (15);
and a light beam incidence interface of the phase modulator (2) is attached to a light beam emergence interface of the first half wave plate (1), and the light beam emergence interface is attached to a light beam incidence interface of the second polarization beam splitter (14), so that the phase modulator (2) and the second quarter wave plate (6) are respectively positioned on two sides of the second polarization beam splitter (14).
6. The polarization insensitive 90 ° spatial optical mixer according to claim 5, wherein the first right angle prism (17) and the second right angle prism (18) have the same size, both right angle prisms have a side length of 2L and a height of L, and the outer side of the inclined plane is plated with a reflective film;
one right-angle surface of the first right-angle prism (17) and the surface opposite to the light beam reflecting interface of the first polarization beam splitter (13) are in the same plane, and the other right-angle surface and the surface opposite to the light beam reflecting interface of the second polarization beam splitter (14) are in the same plane;
one right-angle surface of the second right-angle prism (18) is positioned on the same plane with the surface opposite to the light beam transmission interface of the first polarization beam splitter (13), and the other right-angle surface is positioned on the same plane with the surface opposite to the light beam transmission interface of the second polarization beam splitter (14).
7. The polarization insensitive 90 ° spatial optical mixer according to claim 6, wherein the phase modulator (2) dynamically modulates the phase difference between the modulated phase and the orthogonal polarization component of the signal light by pi/2.
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| CN201541265U (en) * | 2009-11-18 | 2010-08-04 | 福州高意通讯有限公司 | Optical mixer |
| JP2011120030A (en) * | 2009-12-04 | 2011-06-16 | National Institute Of Information & Communication Technology | 90° optical hybrid |
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| CN103257402A (en) * | 2013-04-23 | 2013-08-21 | 青岛海信宽带多媒体技术有限公司 | Optical mixer and method for demodulating signal through optical mixer |
| CN115065417A (en) * | 2022-08-11 | 2022-09-16 | 北京中科国光量子科技有限公司 | Polarization-independent coherent receiving device |
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| JPH07190714A (en) * | 1993-12-24 | 1995-07-28 | Olympus Optical Co Ltd | Interferometer |
| CN201541265U (en) * | 2009-11-18 | 2010-08-04 | 福州高意通讯有限公司 | Optical mixer |
| JP2011120030A (en) * | 2009-12-04 | 2011-06-16 | National Institute Of Information & Communication Technology | 90° optical hybrid |
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