TW202411700A - Portable terminals and photography modules - Google Patents

Abstract

The subject of the present invention is to provide a portable terminal that can suppress the inclusion and glare of objects other than the object when shooting a variety of objects. The smart phone of the present invention is equipped with a camera module (30). The photographic module (30) has a frame that can be fixed to the frame of a smart phone, and the following components are fixed to the frame: a light source unit (40) that irradiates light to an object (100), a first polarizing plate (45) that converts the emitted light from the light source unit (40) into linear polarized light, a second polarizing plate (55) that transmits reflected light from the object (100), a camera (60) that receives reflected light from the object that passes through the second polarizing plate (55) and outputs an image signal of the object, a polarizing rotator (50) that transmits the linear polarized light that passes through the first polarizing plate (45), and a controller (70) that controls the voltage applied to the polarizing rotator (50) to convert the linear polarized light that passes through the first polarizing plate (45) into circular polarized light or elliptical polarized light.

Description

Portable terminal and camera module

The present invention relates to a portable terminal such as a smart phone or a tablet computer terminal equipped with a camera module and a camera module for irradiating light onto various objects and obtaining images resulting from the reflected light.

In recent years, portable terminals such as smartphones and tablet computers are equipped with camera modules, and images and videos taken by users are published on the Web through SNS or auction sites. When users use portable terminals such as smartphones to shoot objects, they want to shoot the objects as beautifully as possible. For example, Patent Document 1 discloses a technology that enables photographers to obtain an ideal composition when taking selfies.

Although the technology disclosed in this publication can correct composition deviation, it cannot prevent the inclusion of objects other than the photographer's image (photobombing). In other words, although photography caused by carrying a terminal can be easily performed outdoors or indoors, sometimes sunlight, fluorescent light, various objects with high reflectivity, etc. will be included during photography, resulting in unclear objects being photographed.

The patent applicant of this case proposed an optical unit for removing glare from an object when photographing the object (see patent document 2). This optical unit has a first polarizing element that converts the emitted light from the light source into linear polarized light, a second polarizing element that transmits the reflected light from the object and has a polarization axis that is 90° orthogonal to the polarization axis of the first polarizing element, a first wavelength plate superimposed on the first polarizing element, and a second wavelength plate superimposed on the second polarizing element and having the same phase difference as the first wavelength plate. Moreover, the first wavelength plate and/or the second wavelength plate are rotatably arranged with respect to the superimposed polarizing element, and glare is removed by mechanically rotating the wavelength plate. [Prior art] [Patent document]

[Patent Document 1] Japanese Patent Application No. 2016-39547 [Patent Document 2] WO2021/106244

[The problem that the invention wants to solve]

The optical unit disclosed in the aforementioned patent document 2 cannot be mounted on a portable terminal with a small frame. That is, the frame of the portable terminal is thin, and the installation space for various devices is also limited, and it is impossible to install a wavelength plate or a mechanism for mechanically rotating the wavelength plate. Therefore, in existing portable terminals, the image captured by the installed camera module sometimes captures objects other than the subject, resulting in a problem of reduced image quality. In addition, in order to suppress photobombing, a flash is sometimes used, but it cannot fully suppress photobombing, and the reflected light from the subject becomes glare (strong light), and the image quality cannot be fully improved.

The present invention is invented based on the above-mentioned problem, and its purpose is to provide a portable terminal that can suppress the inclusion and glare of objects other than the object when shooting various objects, and a photography module that can perform such photography. [Means for solving the problem]

In order to achieve the above-mentioned purpose, the portable terminal of the present invention is equipped with a photographing module for photographing an object, which is characterized in that the photographing module has a frame fixed to the frame of the portable terminal, and the following components are fixed to the frame: a light source unit for irradiating light to the object; a first polarizing plate for converting the emitted light from the light source unit into linear polarized light; a second polarizing plate for transmitting reflected light from the object; a camera for receiving reflected light from the object transmitted through the second polarizing plate and outputting an image signal of the object; a polarizing rotator for transmitting the linear polarized light transmitted through the first polarizing plate; and a controller for controlling the voltage applied to the polarizing rotator to convert the linear polarized light transmitted through the first polarizing plate into circular polarized light or elliptical polarized light.

In the aforementioned structure, the camera module installed in the portable terminal such as a smart phone or a tablet computer can make the emitted light from the light source pass through the first polarizing plate and the polarizing rotator to become circular polarized light or elliptical polarized light, and illuminate the object. The reflected light from the object becomes circular polarized light (elliptical polarized light) that is opposite to the circular polarized light (elliptical polarized light) illuminated, and is photographed by passing through the second polarizing plate. In this case, the emitted light is made into circular polarized light (elliptical polarized light) and illuminates the object, and passes through the second polarizing plate, and does not cause light shielding degradation regardless of the interference between the optical elements in the camera and the intersection angle of the polarization axes of the first polarizing plate and the second polarizing plate, so it can more effectively prevent the entry than irradiating linear polarized light. Furthermore, by adjusting the brightness (the darkest light is obtained at a 90° intersection angle) and controlling the voltage applied to the polarization rotator according to the intersection angle of the polarization axes (absorption axes) of the first and second polarization elements fixed to the object, the light irradiated to the object can be changed from circular polarization to elliptical polarization, thereby achieving the optimal polarization state according to the reflectivity, surface condition, surrounding brightness, etc. of the object.

Therefore, in a portable terminal equipped with a camera module such as the one described above, an image with reduced interference from external objects can be obtained simply by controlling the applied voltage to the polarization rotator. That is, there is no need to mechanically rotate the wavelength plate that converts the irradiated light (linear polarization) from the light source into circular polarization or elliptical polarization, so a small and lightweight camera module can be constructed and installed in a portable terminal. Furthermore, the polarization rotator here can be composed of, for example, a liquid crystal polarization rotator such as a nematic liquid crystal rotator, a crystal polarization rotator, or the like. This type of polarization rotator can rotate the transmitted light by controlling the applied voltage (including pulse voltage) of about 1V, so it can be fully driven by the internal battery of the portable terminal. Since its control speed is also fast, it can be started immediately when taking a photo.

Furthermore, the purpose of the present invention is to provide a photographic module as described above. Such a photographic module can be made small and lightweight, and can be easily installed on various external machines such as FA (factory automation).     [Effect of the invention]

According to the present invention, a portable terminal capable of suppressing the entry of objects other than the objects when photographing various objects and a photographing module capable of performing such photography are provided.

The following describes an implementation form of the portable terminal of the present invention with reference to Figures 1 to 5. Furthermore, in this implementation form, as shown in Figure 1, a smart phone is disclosed as a portable terminal, but it is not limited to any product as long as it is equipped with a camera (camera module).

The smart phone 1 of the present embodiment has a roughly rectangular-shaped frame 2, as is well known, and a camera module 30 to be described later is installed at a predetermined position in the frame 2. On the surface side of the aforementioned frame 2, a well-known touch-operated display unit (display) 3 for displaying various images and inputting operation signals is provided. On the back side of the frame 2, the structural elements of the camera module 30, namely, a light source unit 40 and a camera 60 for receiving reflected light from an object and photographing the object, are arranged side by side in the upper and lower parts. In addition, on one side of the frame 2, functional components such as a power switch 5a, a volume switch 5b (switch type), and a speaker 6 are provided, and a microphone 7 is provided on the lower side of the display unit 3. Furthermore, the configuration of these structural elements is not particularly limited.

Here, referring to the block diagram of Figure 2, the outline of the structural elements that make the smart phone shown in Figure 1 move is explained.   Inside the frame 2 of the smart phone 1, there are provided a photography module 30 for photographing an object and a control unit 10 for controlling the overall movement of the smart phone 1.

The control unit 10 includes a control unit (CPU) 12 for controlling the operation of various functional parts installed in the camera module 30 and the frame, a ROM 13 storing a control program for controlling the operation of various drive elements, a RAM 14 for temporarily storing various information, a memory unit 15 for storing acquired image data and sound data, and various program software (application software), etc., which transmit and receive signals via a bus 18. In addition, the bus 18 connects the various drive elements (display 3, switches 5a, 5b, speakers 6, microphones 7, power supplies 8, and a communication unit 9 for communicating with the outside, etc.) described above and controlled by the control unit 10.

The photographic module 30 includes a light source 40 for irradiating light to an object, a polarization rotator 50 for changing the phase of light emitted from the light source 40, and a camera 60 for transmitting the polarization rotator 50, receiving light reflected from the object, and outputting an image signal of the object.

As described above, the polarization rotator 50 is composed of, for example, a liquid crystal polarization rotator such as a nematic liquid crystal rotator, a crystal polarization rotator, etc. Such a polarization rotator can rotate the light transmitted through the polarization element by controlling an applied voltage (including a pulse voltage) of about 1V, and the applied voltage is adjusted by the control of the controller 70 installed in the camera module 30. That is, by adjusting the applied voltage, the light transmitted through the polarization rotator can be rotated at a predetermined angle to become circularly polarized light or elliptical polarized light, and irradiated to the object.

For example, when the polarizing element of the polarization rotator 50 is composed of nematic liquid crystal, the molecules in the nematic liquid crystal layer have the property of being generally oriented in a certain direction. When the voltage is applied ON/OFF, the molecular arrangement structure is quickly switched to twist the transmitted light (it can quickly switch between polarized and unpolarized photography). That is, by controlling the applied voltage to the polarization rotator 50 through the controller 70 (by changing the voltage value or changing the pulse width to control), as shown in FIG3, the transmitted light can be changed from 0° to 90°. In this case, it can be estimated that the accuracy of the twisting of the light transmitted through the polarization rotator 50 and the switching speed are different according to the number of layers of nematic liquid crystal, but in the present invention, about 50 to 150 layers are sufficient.

When the camera module 30 is mounted on the frame 2, the controller 70 is connected to the connection port 20 on the control unit 10 side through the connection port 80, and controls the applied voltage according to the control signal (trigger signal) from the control unit 20.

Next, the schematic structure of the aforementioned photographic module 30 is described with reference to FIG3 . The aforementioned light source unit 40 uses LED elements and is configured in a manner of emitting light by the LED elements. The emitted light from the light source unit 40 may be diffuse light, or may be configured as parallel light or convergent light by providing a lens 41 or the like. Furthermore, the light-emitting body of the light source is not limited to LED elements, and may be composed of an organic EL light source, a surface-emitting laser, or the like.

A first polarizing plate 45 having a function of making the light emitted from the light source 40 linearly polarized is disposed between the light source 40 and the polarization rotator 50. A second polarizing plate 55 for transmitting the reflected light from the object 100 is disposed on the front side of the camera 60. The first polarizing plate 45 and the second polarizing plate 55 can be formed, for example, by a linear polarization filter, a thin film polarizer, a nano-grid polarizer, an inorganic polarizer (a thin aluminum film is formed on a glass wafer to form fine slits), or the like.

The first polarizing plate 45 and the second polarizing plate 55 are arranged in such a manner that their respective polarization axes intersect at a predetermined angle. The light emitted from the aforementioned light source unit 40 (light in a non-polarized state) is converted into linear polarization by the first polarizing plate 45, and becomes linear polarization with a certain vibration direction of the electric field (and magnetic field). In this case, when the linearly polarized light is directly irradiated on the object 100, if the surface of the object 100 is in a mirror state, the reflected light will directly become linear polarization, but in reality, there are foreign objects such as bumps and so on, so the reflected light becomes diffuse light (non-polarized state) containing a linear polarization component. The light in this non-polarized state contains a component of regular reflected light (the incident linear polarization light is directly reflected as linear polarization). The component of the regular reflected light will become the cause of the photography, so by transmitting the second polarizer 55 whose polarization axis intersects with the polarization axis of the first polarizer 45, an image can be obtained without the reflected component that becomes the cause of the photography, and the image signal of the object sent from the camera 60 can suppress the photography.

Furthermore, the intersection angle of each polarization axis of the first polarizing plate 45 and the second polarizing plate 55 can be set in the range of 0° to 90°. However, by setting it to 90°, although the image becomes darker, it can become a state in which the light is removed the most (a state in which glare is suppressed).

In this case, the linear polarized light transmitted through the first polarizer 45 can be converted into circular polarized light or elliptical polarized light by voltage control of the polarization rotator 50, and can be irradiated to the object. Therefore, by appropriately setting the intersection angle of each polarization axis of the first polarizer 45 and the second polarizer 55, the appearance can be adjusted.

The aforementioned imaging module 30 has a polarization rotator 50 superimposed on the first polarizing plate 45. Generally speaking, when light is irradiated to an object and reflected light is obtained, if the vibration direction of the electric field of the light is correctly aligned with the polarized light, the correctly aligned polarized light will also be returned from the object. In this case, by irradiating the object with circularly polarized light or elliptically polarized light and observing the time required for the transmission of the light and the change in intensity, the difference in the molecular stereo configuration, that is, the chirality, can be obtained. Generally, the surface of an object is in various states. In such a surface, light cannot be reflected in a regular manner but is diffusely reflected. Also, depending on the color of the surface, part of the wavelength band of the irradiated light is reflected or absorbed, and the color information of the light is lost (contrast changes), and the reflected light becomes hazy (turbid).

In this way, depending on the color of the object 100, the unevenness of the surface, and other factors, the diffuse reflection of the surface changes due to the object, and since the color information of the light also changes in various ways, compared to irradiating linearly polarized light, by configuring the polarization rotator 50, the linearly polarized light is transmitted through it and becomes right-handed/left-handed circularly polarized light/elliptical polarized light (appropriate polarization state) and irradiates the object 100, which can more effectively remove the absorption caused by the surrounding reflection.

The polarization rotator 50 can freely adjust the phase angle between ±90° (adjust the twist angle of the linear polarization passing through the nematic liquid crystal layer) by changing the applied voltage (making the applied voltage of the nematic liquid crystal variable). Therefore, even if the polarization axes of the first polarizer 45 and the second polarizer 55 are not orthogonal (90°), as long as the phase angle is within the adjustment range, the polarization state (circular polarization or elliptical polarization) can be made regardless of the relative position relationship (crossing angle) of the polarization axes of the first polarizer 45 and the second polarizer 55.

Furthermore, the difference between circular polarization (elliptical polarization) and linear polarization is that the crossing angle of the polarization axes of each polarizing plate changes, and the light shielding does not deteriorate, so it is better to irradiate the object with circular polarization (elliptical polarization) from the perspective of practicality. In addition, in the case of linear polarization, there is interference with the optical elements inside the camera, so it is better to use circular polarization (elliptical polarization). In particular, the polarization axes of the first polarizer 45 and the second polarizer 55 are made orthogonal, and the linear polarization light transmitted through the first polarizer 45 is rotated 45° (-45°; 135°) by the polarization rotator 50 to be converted into circular polarization light for irradiation. Compared with the case of elliptical polarization, the polarization state is more stable, and the image obtained from the object can obtain a stable state without the introduction.

Furthermore, the appearance of the object will change depending on the background conditions and reflectivity of the object, and since the reflection angle will also change, by changing the applied voltage of the polarization rotator 50, the phase angle can be gradually deviated within the range of ±90˚ (for example: 10˚, 20˚, 30˚, etc.) to set it to the clearest state.

However, in the smart phone of the present embodiment, the first polarizing plate 45 and the second polarizing plate 55 are arranged so that their respective polarization axes are orthogonal to each other at approximately 90°, and the controller 70 controls the polarization rotator 50 by the ON/OFF input of the trigger signal from the control section 12 on the control unit 10 side, and switches between photography in a circularly polarized state that can suppress the most exposure to the object 100 and photography in a non-polarized state (a state that is neither circularly polarized nor elliptical polarized). In such a structure, the operation can be simplified as needed.

This kind of switching of photography is pre-stored in the control unit 10 in the dedicated application software, and can be performed by, for example, controlling the polarization rotator 50 through the ON/OFF input of the touch operation of the display 3 by the user. That is, the user can switch between photography in a state of less photography due to circular polarization and photography in a state of linear polarization (shutter switching action) through the touch operation of the display 3.

Next, a specific structural example of the aforementioned photographic module 30 is described with reference to FIG. 4 and FIG. 5 . The photographic module 30 of this embodiment has a frame 30A having two base plates 30a and 30b, and the aforementioned base plates 30a and 30b are arranged in a manner of being separated by connecting frames 30c to 30h to maintain a predetermined interval. The frame 30A having such a structure is installed and fixed at a predetermined position in the frame 2 of the smart phone 1. Furthermore, according to the setting structure of the side of the frame 2, the structure of the frame 30A can be appropriately deformed.

The light source unit 40, the first polarizing plate 45, the second polarizing plate 55, the camera 60 for outputting an image signal of an object, the polarizing rotator 50 for transmitting the linear polarized light transmitted through the first polarizing plate 45, and the controller 70 for controlling the voltage applied to the polarizing rotator 50 to convert the linear polarized light transmitted through the first polarizing plate 45 into circular polarized light or elliptical polarized light are fixed to the frame 30A.

In this embodiment, the light source unit 40 and the camera 60 are fixed adjacent to the base plate 30a on one side, and the substrate 40A of the light source unit 40 is mounted on the base plate 30a. In addition, the first polarizing plate 45 is fixed to the ends of the connecting frames 30d and 30e, and the polarizing rotator 50 is fixed in a state of overlapping the first polarizing plate 45. The emission side of the polarizing rotator 50 is mounted on the base plate 30b on the other side, and is fixed in a manner that the emission side of the polarizing rotator 50 is exposed from the opening 30b1 formed in the base plate 30b. That is, it is configured in a manner that circularly polarized light or elliptical polarized light is emitted from the polarizing rotator 50 through the opening 30b1.

The two base plates 30a and 30b are separated by a connecting frame (connecting wall) 30c. The base plate 30b is separated from the opening 30b1 by a predetermined interval, and an opening 30b2 is formed on the opposite side of the connecting wall 30c. The second polarizing plate 55 is exposed in the opening 30b2, and the second polarizing plate 55 is fixed to the ends of the connecting frames 30g and 30h.

The camera 60 is fixed to the aforementioned frame 30a, and its lens 61 and the second polarizing plate 55 are arranged adjacent to each other. The reflected light from the object 100 incident on the lens 61 is detected by the imaging element in the camera 60, and is sent to the aforementioned control unit 10 as an image signal and stored in the memory 15. Furthermore, when such a photographic module 30 is installed on an external device such as FA, it can also be sent to the control unit of the external device through the output terminal 65 for the camera signal.

The two base plates 30a and 30b are separated by a connecting frame (connecting wall) 30f, and a controller 70 is fixed to the base plate 30a, separated from the light source unit 40. The controller 70 is a device that allows the applied voltage of the polarization rotator 50 to be variable, and controls the applied voltage of the polarization rotator by a trigger signal from the control unit 12 on the control unit 10 side or the control unit side of an external device, and controls the phase angle between 0° and 90°.

Furthermore, in the smartphone of the present embodiment, as described above, the phase angle is switched between two modes between 0° and 45° (-45°), thereby achieving a simple switching operation. Furthermore, if nematic liquid crystal is used as a polarization rotator, the switching speed becomes faster, and it is possible to quickly switch between photography with and without circular polarization.

According to the aforementioned photographing module 30, the irradiation light to the object is electrically adjusted through the controller 70 of the polarizing rotator 50, so there is no need for a mechanism for mechanically rotating the wavelength plate and the polarizing plate as in the past, and it can be easily installed in a small portable terminal such as a smart phone. In addition, the response speed of the polarizing rotator 50 is also fast, and it does not take too much time to take a picture.

The aforementioned camera module 30 can be installed in various optical systems of machines constituting FA (factory automation). For example, scratches or dirt (foreign matter) may be attached to the surface of various industrial products, food, fresh produce, etc. (objects), and such foreign matter needs to be found and removed in the manufacturing line, processing stage, inspection stage, etc. Usually, foreign matter is detected by irradiating light in an easily visible manner and visually observing its reflected light.

However, in this inspection method of irradiating light and detecting reflected light, glare (strong light) caused by surface reflection of light may sometimes be generated. This glare will hinder the detection of foreign matter, so it is necessary to effectively remove it. In this case, the reflection angle and light absorption will vary depending on the content of the object and the foreign matter (scratches, dust, etc.), and the appearance of the reflected light will also change. Therefore, the applied voltage of the polarization rotator 50 is appropriately adjusted in the active state, and the phase angle is slightly changed each time to maintain it at the optimal position. That is, by sending to the control unit of an external machine (such as a foreign matter detection device) through the output terminal 65 of the aforementioned camera 60, the presence or absence of foreign matter is detected by a predetermined detection program, and the process of removing the object to which the foreign matter is attached from the conveyor line is executed. For example, by sending a foreign object detection signal to an external processing device (object removing device) 400 provided downstream of the object conveying path, a process such as removing the object to which the foreign object is attached from the conveying line can be performed.

As described above, the camera module 30 can be designed to be compact enough to be installed in a smartphone frame and can be installed in a variety of external devices.

The above has been described with respect to the implementation form of the present invention, but the present invention is not limited to the aforementioned implementation form and can be variously modified. The photographic module 30 can also be applied to the medical field, etc. For example, an inspection device set in the human body, or an observation device set in a surgical image, etc., can be viewed or recorded in a glare-free state.

1: Smartphone (portable terminal) 2: Frame 3: Display (display) 5a: Power switch 5b: Volume switch 6: Speaker 7: Microphone 8: Power 9: Communication 10: Control unit 12: Control unit (CPU) 13: ROM 14: RAM 15: Memory 18: Bus 20: Port 30: Camera module 30A: Frame 30a: Base plate 30b: Base plate 30b1: Opening 30b2: Opening 30c: Connection frame 30d: Connection frame 30e: Connection frame 30f: Connection frame 30g: Connection frame 30h: Connection frame 40: Light source 40A: Substrate 41: Lens 45: 1st polarizing plate 50: Polarizing rotator 55: 2nd polarizing plate 60: Camera 61: Lens 70: Controller 80: Port 100: Object

[Figure 1] A smartphone is disclosed as an example of a portable terminal of the present invention, (a) is a perspective view of the front side, and (b) is a perspective view of the back side.   　　[Figure 2] A schematic block diagram of the structural elements that enable the smartphone shown in Figure 1 to operate.   　　[Figure 3] A conceptual diagram of the camera module shown in Figure 1.   　　[Figure 4] A diagram of the camera module installed in the smartphone shown in Figure 1, (a) is a front view, (b) is a bottom view, and (c) is a side view.   　　[Figure 5] A perspective view of the camera module shown in Figure 4.

30: Photography module

40: Light source

41: Lens

45: 1st polarizing plate

50: Polarization rotator

55: Second polarizing plate

60: Camera

61: Camera lens

70: Controller

100: Object

Claims (5)

A portable terminal is a portable terminal equipped with a photographing module for photographing an object, and is characterized in that: the photographing module has a frame fixed to the frame of the portable terminal, and the following components are fixed to the frame: a light source for irradiating light to the object; a first polarizing plate for converting the light emitted from the light source into linear polarized light; a second polarizing plate for converting the light emitted from the light source into linear polarized light. The reflected light from the aforementioned object is transmitted; the camera receives the reflected light from the aforementioned object that is transmitted through the aforementioned second polarizer, and outputs an image signal of the object; the polarizer transmits the linear polarized light that is transmitted through the aforementioned first polarizer; and the controller controls the voltage applied to the polarizer to convert the linear polarized light that is transmitted through the aforementioned first polarizer into circular polarized light or elliptical polarized light. The portable terminal as recited in claim 1, wherein the controller receives a voltage supply from a power source disposed in the frame, controls the voltage supplied from the power source by a trigger signal generated by operating an operating portion of the portable terminal, and converts the linear polarization into circular polarization or elliptical polarization to irradiate the object. The portable terminal as recited in claim 2, wherein the first polarizing plate and the second polarizing plate are fixed to the frame in such a manner that their respective polarization axes are orthogonal at approximately 90°, and the controller controls the polarizing rotator by turning the input of the trigger signal ON/OFF to switch between photographing in a circularly polarized state and photographing in a non-polarized state with respect to the object. A photographic module is a photographic module having a frame that can be fixed to a frame of an external device and that obtains an image of an object, and is characterized in that:  The following components are fixed to the aforementioned frame:  A light source unit irradiates light to the aforementioned object;  A first polarizing plate converts the emitted light from the aforementioned light source unit into linear polarized light;  A second polarizing plate transmits the reflected light from the aforementioned object;  A camera receives the reflected light from the aforementioned object that is transmitted through the aforementioned second polarizing plate and outputs an image signal of the object;  A polarizing rotator transmits the linear polarized light that is transmitted through the aforementioned first polarizing plate; and  A controller controls the voltage applied to the aforementioned polarizing rotator to convert the linear polarized light that is transmitted through the aforementioned first polarizing plate into circular polarized light or elliptical polarized light. The photographic module as described in claim 4, wherein the controller receives a voltage supply from a power source of the external device, controls the applied voltage by a trigger signal from the external device, and variably controls the phase angle of the polarization rotator between 0˚ and 90˚.

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