CN114185194B - Geometric phase liquid crystal spatial optical complex amplitude modulator - Google Patents

Abstract

The invention relates to a geometrical phase liquid crystal space light complex amplitude modulator, and belongs to the technical field of light modulation. The modulator comprises a 1/4 wave plate I, a liquid crystal panel, a 1/4 wave plate II and a polaroid which are sequentially arranged; in the liquid crystal panel, two groups of IPS electrode pairs which are mutually perpendicular in-plane rotation are arranged in the glass layer, namely an IPS electrode pair I and an IPS electrode pair II; the first IPS electrode pair generates an electric field along the y direction, the second IPS electrode pair generates an electric field along the x direction, and Ex and Ey are overlapped to form a total electric field; and the voltage difference between the two groups of IPS electrode pairs is regulated, so that the modulation of the total electric field size E and the direction alpha which are mutually independent is realized. The total electric field magnitude E and the direction alpha determine the refractive index difference and the optical axis direction of the liquid crystal layer, and finally independent modulation of the amplitude and the phase of the incident light is realized.

Description

Geometric phase liquid crystal spatial optical complex amplitude modulator

Technical field

The invention belongs to the field of light modulation technology and relates to a geometric phase liquid crystal spatial optical complex amplitude modulator.

Background technique

In traditional phase modulation liquid crystal devices, the usual working mode of liquid crystal molecules is: under the action of an electric field, the liquid crystal orientation is continuously deflected from parallel to the device surface to perpendicular to the device surface. The linear polarization direction of the incident polarized light is the same as that of the liquid crystal when it is not energized. The direction of the director is parallel. When the liquid crystal director rotates, the effective refractive index felt by the incident polarized light gradually decreases. When the liquid crystal is parallel to the device surface, its effective refractive index is ne. When the liquid crystal is perpendicular to the device surface, its effective refractive index is no, so , the phase modulation range of the device is where k0 is the wave vector of incident light in vacuum, and d is the thickness of the liquid crystal. Since holographic displays usually require a phase modulation capability of 2π, the liquid crystal thickness needs to meet:

k0·(ne-no)·d≥2π

That is, the thickness of the liquid crystal reaches at least one complete wave plate.

In traditional amplitude modulation liquid crystal devices, the usual working mode of liquid crystal molecules is: under the action of an electric field, the liquid crystal orientation is continuously deflected from parallel to the device surface to perpendicular to the device surface. Different from the phase modulator, the incident polarized light The linear polarization direction is incident at 45° to the direction of the liquid crystal director when no power is supplied. When the power is not supplied, the linearly polarized light is rotated 90° by the liquid crystal layer and cannot pass through the second linear polarizer. When the power is supplied, the liquid crystal molecules rotate parallel to the direction of the incident light, and the linearly polarized light does not change its polarization direction after passing through. Completely transparent, this method requires the thickness of the liquid crystal to be a half-wave plate.

In order to perform complex amplitude modulation, the traditional solution is generally that the incident light passes through the amplitude modulation liquid crystal device and the phase modulation liquid crystal device in sequence, which will face the optical alignment problem between the two layers of liquid crystal panels.

Contents of the invention

In view of this, the object of the present invention is to provide a geometric phase liquid crystal spatial optical complex amplitude modulator to solve the problem that a single liquid crystal panel cannot perform amplitude modulation and phase modulation at the same time.

In order to achieve the above objects, the present invention provides the following technical solutions:

The geometric phase liquid crystal spatial optical complex amplitude modulator includes a 1/4 wave plate 1, a liquid crystal panel, a 1/4 wave plate 2 and a polarizing plate arranged in sequence;

In the liquid crystal panel, there are two sets of mutually perpendicular in-plane rotating IPS electrode pairs in the glass layer, namely IPS electrode pair one and IPS electrode pair two;

The first pair of IPS electrodes generates an electric field along the y direction, and the second pair of IPS electrodes generates an electric field along the x direction. _Ex and E _y are superimposed to form a total electric field; the magnitude of the total electric field is:

The angle between the total electric field direction and the x-axis is:

Adjust the voltage difference between the two sets of IPS electrode pairs to achieve independent modulation of the total electric field size ||E|| and direction α.

Optionally, the geometric phase is the phase delay caused by the change of polarization state when light propagates through anisotropic media. When the incident light is incident on the birefringent material along the Z-axis direction, the thickness of the birefringent material is d, the extraordinary optical axis is perpendicular to the Z-axis, and the angle with the x-axis is α, the incident light is left-handed circularly polarized or right-handed circularly polarized Polarized light, represented by |L> and |R> respectively, the emitted light will contain both |L> and |R> components;

Assume that the incident light is completely left-handed circularly polarized light, and the complex amplitudes of the outgoing lights |L> and |R> are β _L and β _R respectively, that is:

|Ex _ut >＝β _L |L>+β _R |R>

Using the Jones matrix, calculate after passing through the liquid crystal:

in, n _o is the refractive index of ordinary light propagating in the liquid crystal material, n _e is the refractive index of the extraordinary light propagating in the liquid crystal material, λ is the wavelength of the incident light, after the left-handed circularly polarized light is incident on the liquid crystal panel, the emitted right-handed light is A phase delay term of 2α, which is a geometric phase.

Optionally, the amplitude of the right-handed light component is Among them, the size of Φ _e - Φ _o is positively related to the size of the total electric field ||E||, and adjusting the size of the total electric field ||E|| modulates the size of the right-handed light component;

The phase magnitude of the right-handed light component is where e ^{i 2α} is the geometric phase,/> is the propagation phase, α is the angle between the total electric field direction and the x-axis. Adjusting α can perform 0-2π phase modulation of the right-handed light component.

||E|| and α are modulated independently of each other, the right-handed light component is subjected to complex amplitude modulation, and the final emitted linearly polarized light is subjected to complex amplitude modulation.

The beneficial effects of the present invention are:

(1) Complex amplitude modulation can be achieved with only a single LCD panel, avoiding the optical alignment problem between the two LCD panel electrodes in the traditional solution.

(2) Since the magnitude of the geometric phase modulation has nothing to do with the wavelength of the incident light, the designed device can operate in a wider wavelength range.

Other advantages, objects, and features of the present invention will, to the extent that they are set forth in the description that follows, and to the extent that they will become apparent to those skilled in the art upon examination of the following, or may be derived from This invention is taught by practicing it. The objects and other advantages of the invention may be realized and obtained by the following description.

Description of the drawings

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below in conjunction with the accompanying drawings, in which:

Figure 1 shows the refractive index ellipsoid of blue phase liquid crystal before and after applying an electric field;

Figure 2 is an elevation view of a single pixel of the LCD panel;

Figure 3 is a top view of a single pixel of the LCD panel;

Figure 4 is a superimposed electric field diagram of a single pixel of the liquid crystal panel;

Figure 5 is a diagram of the working principle of the present invention.

Reference symbols: 1-IPS electrode pair one, 2-IPS electrode pair two, 3-glass.

Detailed ways

The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. The following embodiments and the features in the embodiments can be combined with each other as long as there is no conflict.

The drawings are only for illustrative purposes, and represent only schematic diagrams rather than actual drawings, which cannot be understood as limitations of the present invention. In order to better illustrate the embodiments of the present invention, some components of the drawings will be omitted. The enlargement or reduction does not represent the size of the actual product; it is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

In the drawings of the embodiments of the present invention, the same or similar numbers correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms "upper", "lower", "left" and "right" The orientation or positional relationship indicated by "front", "rear", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must be It has a specific orientation and is constructed and operated in a specific orientation. Therefore, the terms describing the positional relationships in the drawings are only for illustrative purposes and cannot be understood as limitations of the present invention. For those of ordinary skill in the art, they can determine the specific position according to the specific orientation. Understand the specific meaning of the above terms.

The invention is a geometric phase space optical complex amplitude modulator based on blue phase liquid crystal, which can modulate amplitude and phase simultaneously.

Principle: As shown in Figure 1, the blue phase liquid crystal panel is also a special liquid crystal state. When no electric field is applied, the blue phase liquid crystal panel shows optical isotropy, with the same refractive index in each direction; when an external electric field is applied Finally, the blue phase liquid crystal panel exhibits optical anisotropy, with the optical refractive index increasing along the direction of the electric field and decreasing the optical refractive index perpendicular to the direction of the electric field. The greater the applied voltage, the greater the refractive index difference along the direction of the electric field and perpendicular to the direction of the electric field.

Compared with the propagation phase, the geometric phase does not rely on the optical path difference for phase modulation, but relies on the geometry of the device for phase modulation, so it is called the geometric phase. The principle of geometric phase modulation is as follows:

When a beam of incident light (left-hand circularly polarized light or right-hand circularly polarized light, represented by |L> and |R> respectively) is incident on a birefringent material along the Z-axis direction (the material thickness is d, the extraordinary optical axis is perpendicular to Z axis, the angle with the x-axis is α), the emitted light will contain both |L＞ and |R＞ components. Assuming that the incident light is completely left-handed circularly polarized light, the complex amplitudes of the outgoing lights |L> and |R> are β _L and β _R respectively, that is:

|E _out >＝β _L |L>+β _R |R> (1)

Using the Jones matrix, calculate after passing through the LCD panel:

In the two formulas (2) and (3), n _o is the refractive index of ordinary light propagating in the liquid crystal material, n _e is the refractive index of the extraordinary light propagating in the liquid crystal material, and λ is the wavelength of the incident light. It can be seen from equation (3) that left-handed circularly polarized light is incident on the liquid crystal wave plate, and the emitted right-handed light has a phase retardation term of 2α, which is the geometric phase.

Pixel design:

The geometric phase complex amplitude modulator designed in the present invention consists of two 1/4 wave plates, a liquid crystal panel and a polarizing plate. The single-pixel electrode design of the liquid crystal panel: there are two sets of mutually perpendicular in-plane rotations between the glasses 3 (IPS) protruding electrode. The IPS electrode pair IPS electrode pair 1 generates an electric field along the y direction, the IPS electrode pair IPS electrode pair 2 2 generates an electric field along the x direction, and Ex and Ey are superimposed to form the total electric field. The magnitude of the total electric field is:

The angle between the total electric field direction and the x-axis is:

As shown in Figures 2 to 4, by adjusting the voltage difference between the two groups of IPS protruding electrodes, independent modulation of the total electric field size ||E|| and direction α can be achieved.

The principle of complex amplitude modulation is shown in Figure 5.

After linearly polarized light enters the 1/4 wave plate along the Z direction, it is converted into left-handed circularly polarized light. When this left-handed circularly polarized light |L> is injected into the liquid crystal panel we designed along the Z direction, the emitted light contains both left-handed light , also includes right-handed light, expressed as β _L |L>+β _R |R>. According to the principle of geometric phase phase modulation, the left-handed light component is written as:

The right-handed optical component is:

in n _o is the refractive index of ordinary light propagating in liquid crystal material, n _e is the refractive index of extraordinary light propagating in liquid crystal material. After passing through the 1/4 wave plate, left-handed light and right-handed light will be converted into linearly polarized light with polarization states perpendicular to each other. The polarizing plate is used to allow the linearly polarized light converted from right-handed light to pass through completely, and the linearly polarized light converted from left-handed light component is completely reflected. .

It can be seen from formula (7) that the amplitude of the right-handed light component is Among them, the size of Φ _e - Φ _o is positively related to the size of the total electric field ||E||. Adjusting the size of the total electric field ||E|| can modulate the size of the right-handed light component. The phase size of the right-handed light component is/> where e ^{i 2α} is the geometric phase,/> It is the propagation phase. Since α can be modulated between 0 and 360°, the phase modulation effect of the 2π phase can be achieved by relying on the geometric phase. And because ||E|| and α can be modulated independently of each other, complex amplitude modulation can be performed on the right-handed light component, that is, complex amplitude modulation can be performed on the emitted linearly polarized light.

The present invention designs a single pixel electrode for a liquid crystal panel, and realizes the distribution of the electric field in the pixel area through two sets of IPS protruding electrodes.

Using a blue phase liquid crystal panel, the amplitude of the emitted light is modulated by the intensity of the external electric field, and the phase is modulated by the direction of the external electric field.

This solution is not limited to liquid crystal spatial light modulators, but also includes other optical devices applying this complex amplitude strip modulation scheme.

Use a 1/4 wave plate and a polarizing plate to select the left and right optical components.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified. Modifications or equivalent substitutions without departing from the purpose and scope of the technical solution shall be included in the scope of the claims of the present invention.

Claims (4)

1. Geometric phase liquid crystal spatial optical complex amplitude modulator, characterized by: including a 1/4 wave plate 1, a liquid crystal panel, a 1/4 wave plate 2 and a polarizing plate arranged in sequence; The material of the liquid crystal panel is blue phase liquid crystal. The electrode design of the single pixel of the liquid crystal panel: there are two sets of mutually perpendicular in-plane rotating IPS protruding electrodes between the glass layers; the IPS electrodes are arranged in contact with the upper and lower glass; In the liquid crystal panel, there are two sets of mutually perpendicular in-plane rotating IPS electrode pairs in the glass layer, namely IPS electrode pair one and IPS electrode pair two; The first pair of IPS electrodes generates an electric field along the y direction, and the second pair of IPS electrodes generates an electric field along the x direction. _Ex and E _y are superimposed to form a total electric field; the magnitude of the total electric field is: The angle between the total electric field direction and the x-axis is: Adjust the voltage difference between the two sets of IPS electrode pairs to achieve independent modulation of the total electric field size ||E|| and direction α. 2. The geometric phase liquid crystal spatial optical complex amplitude modulator according to claim 1, characterized in that: in the optical complex amplitude modulator, when the incident light is incident on the liquid crystal panel along the Z-axis direction, the thickness of the liquid crystal layer is d, which is unusual. The optical axis is perpendicular to the Z-axis, and the angle between it and the x-axis is α. The incident light is left-handed circularly polarized light or right-handed circularly polarized light, represented by |L> and |R> respectively. The emergent light will contain both |L> and |R >weight; Assume that the incident light is completely left-handed circularly polarized light, and the complex amplitudes of the outgoing lights |L> and |R> are β _L and β _R respectively, that is: |E _out >＝β _L |L>+β _R |R> Using the Jones matrix, calculate after passing through the liquid crystal: in, n _o is the refractive index of ordinary light propagating in the liquid crystal material, n _e is the refractive index of the extraordinary light propagating in the liquid crystal material, λ is the wavelength of the incident light, after the left-handed circularly polarized light is incident on the liquid crystal panel, the emitted right-handed light is A phase delay term of 2α, which is a geometric phase. 3. The geometric phase liquid crystal spatial optical complex amplitude modulator according to claim 2, characterized in that: in the optical complex amplitude modulator, after the linearly polarized light is injected into the 1/4 wave plate along the Z direction, it is converted into a left-handed circle. Polarized light, left-handed circularly polarized light |L>, is injected into the liquid crystal panel along the Z direction. The emitted light contains left-handed light and right-handed light, expressed as β _L |L> + β _R |R>. According to the principle of geometric phase modulation, The left-handed optical component is: The right-handed optical component is: After passing through the 1/4 wave plate, left-handed light and right-handed light will be converted into linearly polarized light with polarization states perpendicular to each other. The polarizing plate is used to allow the linearly polarized light converted from right-handed light to pass through completely, and the linearly polarized light converted from left-handed light component is completely reflected. . 4. The geometric phase liquid crystal spatial optical complex amplitude modulator according to claim 3, characterized in that: the amplitude of the right-handed light component is Among them, the size of Φ _e - Φ _o is positively correlated with the size of the total electric field ||E||. The size of the total electric field ||E|| is modulated to modulate the amplitude of the right-handed light component; The phase magnitude of the right-handed light component is where e ^i2α is the geometric phase,/> is the propagation phase, α is the angle between the total electric field direction and the x-axis. Adjusting α can perform 0-2π phase modulation on the right-handed light component; ||E|| and α are modulated independently of each other, the right-handed light component is subjected to complex amplitude modulation, and the final emitted linearly polarized light is subjected to complex amplitude modulation.