TWI477843B - Terahertz phase modulator - Google Patents

Description

Megahertz phase modulator

The present invention relates to a phase modulator, and more particularly to a phase modulator for a band of megahertz waves.

Liquid crystal applications are widely used in optical applications in addition to displays, and are often used as phase modulators.

With the development of the megahertz wave field, various megahertz modulation components have been researched and invented in recent years. In the past research, phase modulation was made using nematic liquid crystal. Since the nematic liquid crystal has a large birefringence, the refractive index of the nematic liquid crystal molecules is changed by the electric field. Change as a phase modulation.

As shown in FIG. 1 , it is an invention patent of "Adjustable Megahertz Phase Shifter or Phase Delayer Using Magnetic Field to Control Liquid Crystal Birefringence", and includes a liquid crystal cell 11, a set of magnets 12, and a The mechanism 13 for controlling the angle of the magnet and the fixture for fixing the sample. The magnet 12 is rotatable along the rotating shaft 14 to provide a magnetic field 15 which can change direction, thereby changing the alignment of the liquid crystal molecules in the liquid crystal cell 11. When the direction of the magnetic field 17 and the polarization direction 18 of the megahertz wave 16 are as shown, The refractive index of the corresponding liquid crystal cell 11 will change as the angular angle of the magnetic field 15 changes, and the equivalent optical path of the megahertz wave 16 is also A change is made to provide a continuously adjustable phase delay.

However, since the modulator that uses the magnetic field to control the birefringence of the liquid crystal must use the polarization direction of the megahertz wave in use, that is, the megahertz wave must be incident at a specific polarization angle, and the phase adjustment cannot be performed at a specific polarization angle incidence. Therefore, when the nematic liquid crystal is used as the phase modulator, the polarization direction of the incident light needs to be considered, and there is still inconvenience in execution.

SUMMARY OF THE INVENTION A primary object of the present invention is to provide a megahertz phase modulator that does not require consideration of the polarization direction of the megahertz wave.

To achieve the above object, the present invention provides a megahertz phase modulator comprising a two substrate, a two electrode layer, a plurality of spacers, and a cholesteric liquid crystal.

Each substrate has an inner surface and an opposite outer surface, the substrates are spaced apart and the inner surfaces are facing each other; the electrode layers are respectively disposed on inner surfaces of the substrates; the spacers are stacked on The electrode layers together form an accommodating space; the cholesteric liquid crystal is disposed in the accommodating space.

The invention has the advantages of utilizing the non-polarization property of the cholesteric liquid crystal in the megahertz band, adjusting the chrome liquid crystal pitch and controlling the voltage, so that a phase modulation of 2π is achieved in one megahertz band, and can be used as a successful phase modulation. a transformer; that is, the phase modulator of the present invention overcomes the use of a magnetic field or The phase change of the nematic liquid crystal by the electric field is limited by the polarization angle of the megahertz wave, thereby improving the inconvenience caused by the polarization direction of the incident light when the nematic liquid crystal is used as the phase modulator.

In an embodiment of the invention, a voltage is formed between the electrode layers, the voltage exceeding a threshold voltage of the cholesteric liquid crystal, such that liquid crystal molecules of the cholesteric liquid crystal are vertically aligned.

In an embodiment of the invention, the voltage is between 200 volts and 1400 volts.

In an embodiment of the invention, the cholesteric liquid crystal penetrates a meristor liquid crystal into an optical rotatory agent.

In an embodiment of the invention, the cholesteric liquid crystal has a pitch of 4 um to 20 um.

In an embodiment of the invention, the accommodating space has a thickness of less than 5 mm.

In an embodiment of the invention, each spacer has a thickness of less than 1 mm.

The above and other objects, features and advantages of the present invention will become more <RTIgt; Furthermore, the directional terms mentioned in the present invention, such as "upper", "lower", "before", "after", "left", "right", "inside", "outside" or "side" Face, etc., only refer to the direction of the additional schema. Therefore, the directional terminology used is for the purpose of illustration and understanding of the invention.

Referring to FIG. 2, the megahertz phase modulator 1 according to an embodiment of the present invention mainly includes two substrates 2, two electrode layers 3, a plurality of spacers 4, a cholesteric liquid crystal 5, two conductive contacts 6, and two. The insulating colloid 7, the megahertz wave penetrates the phase modulator 1 according to the path 8, and the detailed structure, assembly relationship and operation principle of the above-mentioned respective components will be described in detail below.

Each of the substrates 2 has an inner surface 21 and an opposite outer surface 22. The two substrates 2 are spaced apart by a distance, and the inner surfaces 21 of the substrates 2 face each other. In this embodiment, the substrates 2 It is a transparent quartz glass (Fused Silica).

The electrode layers 3 are respectively disposed on the inner surface 21 of the substrates 2, and the electrode layers 3 of the present embodiment are formed with an electroconductive thin film (ITO) on the inner surface 21 of the substrates 2 by electroplating.

The spacers 4 are stacked in the electrode layer 3 and form an accommodating space (not shown). The cholesteric liquid crystal 5 is disposed in the accommodating space for the passage of the megahertz wave. The spacer 4 is a cover glass, and each cover wave has a thickness of 1 mm. The substrate 2, the electrode layer 3, the spacer 4, and the cholesteric liquid crystal 5 constitute a liquid crystal cell.

The two conductive contacts 6 are respectively disposed on the electrode layer 3 for electrically connecting an external power source, and the insulating glue 7 covers the electrode layer 3 and the guiding point 6 for fixing the phase modulation of the megahertz wave. The overall structure of the device 1 and the electrode layers 3 and the contact points 6 are insulated from the outside.

It should be noted that when a bias voltage is applied, the liquid crystal molecules of the cholesteric liquid crystal 5 are subjected to a bias applied by a bias, and the liquid crystal molecules are aligned in a direction in which the direction of the liquid crystal molecules is biased. If the applied bias voltage is small, the liquid crystal molecules of the cholesteric liquid crystal 5 may exhibit a fingerprint pattern with a liquid crystal spiral axis parallel to the substrates 2. If the cholesteric liquid crystal 5 is placed in a strong electric field exceeding a critical voltage, its helical structure will be untwisted, and the liquid crystal molecules of the cholesteric liquid crystal 5 will be aligned in the direction of the electric field and perpendicular to the substrates 2 to form a vertical alignment ( Homeotropic texture). When the electric field is removed, the molecular arrangement will enter a Focal conic texture, and the helical axes of the cholesteric liquid crystal 5 will be arbitrarily arranged.

According to the above configuration, the megahertz phase modulator 1 of the present invention can change the structure of the cholesteric liquid crystal 5 by applying a bias voltage to the electrode layer 3 during phase modulation, by fingerprint type arrangement ( Fingerprint texture) is converted to a homeotropic texture to adjust the refractive index of the cholesteric liquid crystal 5.

That is to say, when the electrode layers 3 have not been biased, the cholesteric liquid crystal 5 is a Focal conic texture, and since the guiding axes of the cholesteric liquid crystals 5 are randomly arranged, the megahertz waves are incident in an arbitrary polarization direction. The refractive index seen will be equivalent to the average of the refractive indices of the liquid crystal molecules. . As the bias voltage of the electrode layer 3 is increased, the liquid crystal molecules of the cholesteric liquid crystal 5 are gradually straightened, and when the electrode layer 3 is biased to exceed the threshold voltage of the cholesteric liquid crystal 5, the liquid crystal molecules become vertically aligned (Homeotropic texture At this time, the refractive index of the megahertz wave incident in any polarization direction is n = n _o , wherein the critical electric field is inversely proportional to the pitch, and the threshold voltage formula is:

Generally, the pitch of the cholesteric liquid crystal 5 can be designed to be between 4 um and 20 um, and the cholesteric liquid crystal 5 of the present embodiment is made by adding the optical s811 s811, and the pitch is 20 um, thereby reducing the straightening of the liquid crystal molecules into a vertical alignment (Homeotropic Texture) The required threshold voltage.

As shown in FIG. 3, the refractive index change dn = n - n _o of the cholesteric liquid crystal of the BL006 nematic liquid crystal is between 0.064 and 0.071. In the present embodiment, the thickness of the accommodating space is 5 mm, and the megahertz wave can be made at 1 THz. The phase modulation is more than 2 π .

Referring to FIG. 4, the megahertz phase modulator 1 of the present invention adds different voltages such as 0V, 700V, and 1400V to the electrode layer 3, and inputs megahertz waves of different polarization directions. The same bias voltage can be found in FIG. Under the rotation angle of the incident megahertz wave, the measured signal intensity is the same. This characteristic has the same situation at different voltages such as 0V, 700V, 1400V, so it can be known that the megahertz wave is incident at any polarization angle. Phase modulation is possible.

Please refer to FIG. 5 , which is the change of the frequency of the megahertz wave to the phase at different input voltages (100V~1400V) of the electrode layer 3, wherein the phase modulation at different frequencies changes linearly, and the megahertz wave 1THz is Enter a range of 800V to have a modulation of more than 2 π . As shown in Fig. 6, for the megahertz waves of various frequencies, the input voltage of the electrode layer 3 is changed by the phase.

According to the above design, since the cholesteric liquid crystal 5 has a characteristic independent of the polarization direction of the incident light due to its spiral characteristic, the refractive index seen by the megahertz wave is n _effect without an applied bias voltage; After the bias voltage is greater than the threshold voltage, the liquid crystal molecules begin to be gradually pulled by the voltage, causing the refractive index seen by the megahertz wave to change, thereby achieving the phase modulation effect. Therefore, the condensed liquid crystal 5 is placed in the accommodating space to be adjusted. Cholesterol liquid crystal pitch size and control voltage in the electrode layer 3, so that a phase modulation of 2π is achieved in one megahertz band, and thus can be used as a successful phase modulator; that is, the phase modulator of the present invention overcomes utilization. The phase modulation of the nematic liquid crystal by the magnetic field or the electric field is limited by the polarization angle of the megahertz wave, thereby improving the inconvenience caused by the polarization direction of the incident light when the nematic liquid crystal is used as the phase modulator.

1‧‧‧ phase modulator

2‧‧‧Substrate

21‧‧‧ inner surface

22‧‧‧ outer surface

3‧‧‧electrode layer

4‧‧‧shims

5‧‧‧Cholesterol LCD

6‧‧‧Contact points

7‧‧‧Insulating colloid

8‧‧‧ Path

Fig. 1 is a schematic view showing the structure of a tunable megahertz phase shifter or phase retarder using a magnetic field to control a liquid crystal birefringence phenomenon.

Figure 2 is a block diagram showing the structure of a megahertz phase modulator according to an embodiment of the present invention.

Fig. 3 is a graph showing the relationship between the frequency and refractive index of a cholesteric liquid crystal of a nematic liquid crystal according to an embodiment of the present invention.

Figure 4 is a graph showing the relationship between the bias voltage and the megahertz wave of different polarization directions in an embodiment of the present invention.

Fig. 5 is a graph showing the relationship between frequency and phase change under various bias voltages according to an embodiment of the present invention.

Figure 6 is a graph showing the relationship between voltage and phase at each frequency in an embodiment of the present invention.

1‧‧‧ phase modulator

2‧‧‧Substrate

21‧‧‧ inner surface

22‧‧‧ outer surface

3‧‧‧electrode layer

4‧‧‧shims

5‧‧‧Cholesterol LCD

6‧‧‧Contact points

7‧‧‧Insulating colloid

8‧‧‧ Path

Claims (7)

A megahertz phase modulator comprising: two substrates, each substrate having an inner surface, and an opposite outer surface, the substrates being spaced apart and the inner surfaces facing each other; the two electrode layers, the electrodes The layers are respectively disposed on the inner surface of the substrate; a plurality of spacers are stacked on the electrode layers to form an accommodating space; and a cholesteric liquid crystal is disposed in the accommodating space. The megahertz phase modulator according to claim 1, wherein a voltage is formed between the electrode layers, and the voltage exceeds a threshold voltage of the cholesteric liquid crystal, so that liquid crystal molecules of the cholesteric liquid crystal are vertically aligned. The megahertz phase modulator according to claim 2, wherein the voltage is from 200 volts to 1400 volts. The megahertz phase modulator according to claim 1, wherein the cholesteric liquid crystal penetrates a meristor liquid crystal into a light-emitting agent. The megahertz phase modulator according to claim 1, wherein the cholesteric liquid crystal has a pitch of 4 um to 20 um. The megahertz phase modulator according to claim 1, wherein the accommodating space has a thickness of less than 5 mm. The megahertz phase modulator according to claim 1, wherein each of the spacers has a thickness of less than 1 mm.