CN100424550C - Photonic crystal terahertz wave modulator device and method - Google Patents

Abstract

The invention discloses a photonic crystal terahertz wave modulator device and a method thereof. The photonic crystal terahertz wave modulator device has silicon photonic crystals with line defects, electrodes, liquid crystals, and silicon dioxide substrates. Silicon photonic crystals with line defects are arranged on the silicon dioxide substrate, and silicon photonic crystals with line defects Liquid crystal is injected into the crystal hole, and electrodes are arranged on both sides of the upper end of the silicon photonic crystal with line defects. The photonic crystal terahertz wave modulation method is a method of modulating a terahertz wave signal by using the photonic band gap edge of the photonic crystal. The invention has the advantages that the photonic crystal terahertz modulator has small loss, large modulation bandwidth, fast response speed, high extinction ratio, small size, compact structure, easy integration, and meets the requirements of terahertz wave communication.

Description

Photonic crystal terahertz wave modulator device and method

technical field

The invention belongs to the technical field of terahertz wave application, and in particular relates to a photonic crystal terahertz wave modulator device and a method thereof.

Background technique

Terahertz (THz, 1THz=10E+12Hz) radiation usually refers to electromagnetic radiation waves with a frequency range from 0.1THz to 10THz. This band is located at the junction of electronics and optics. It occupies a very special position in the electromagnetic spectrum. , has a series of special properties and important academic and application value. Terahertz communication has the advantages of rich frequency band resources, large bandwidth, good confidentiality, transmission rate can reach 1-10Gb/s, etc., and terahertz communication does not require the approval of radio management department, so terahertz wave has unique advantages in the application of communication field.

At present, the terahertz wave sources used for terahertz wave communication mainly include: (1) continuous THz waves emitted by Gunns diodes. The output power of Gunns diode is high, but the frequency of Gunns diode is not adjustable, so it can be used for fixed frequency terahertz wave communication. (2) Quantum cascade lasers. Quantum cascade lasers may play an important role in future THz wave communications, but their operation currently requires cryogenic cooling (liquid helium or liquid nitrogen), and low-frequency output (<2THz) is extremely difficult, and the frequency adjustable range is small. (3) Return Wave Oscillator (BWO). The advantage of BWO is that it can realize tuning and use different return wave tubes or use frequency multiplication to select different output frequencies. Its output frequency can currently cover 0.1-1.5THz, and the spatial quality of the output wave is good, which can be used for terahertz waves. communication. At present, the application of BWO is either for spectrum analysis or imaging detection, but there is no such technology at home and abroad to apply BWO to THz wave communication.

Contents of the invention

The object of the present invention is to provide a photonic crystal terahertz wave modulator device and a method thereof.

The photonic crystal terahertz wave modulator device has silicon photonic crystals with line defects, electrodes, liquid crystals, and silicon dioxide substrates. Silicon photonic crystals with line defects are arranged on the silicon dioxide substrates, and silicon photonic crystals with line defects are provided. Liquid crystal is injected into the crystal hole, and electrodes are arranged on both sides of the upper end of the silicon photonic crystal with line defects.

The photonic crystal terahertz wave modulation method is a method of modulating the terahertz wave signal by using the forbidden band edge of the photonic band gap translation of the photonic crystal, and modulating the intensity of the terahertz wave; when the electrode has no external voltage, the photonic crystal has a photonic band gap ; When the electrode has an external voltage, due to the change of the refractive index of the liquid crystal, the photonic band gap of the photonic crystal is shifted, and the edge of the band gap is changed, so that the signal is loaded on the terahertz wave.

The invention has the advantages that the photonic crystal terahertz modulator has small loss, large modulation bandwidth, fast response speed, high extinction ratio, small size, compact structure, easy integration, and meets the requirements of terahertz wave communication.

Description of drawings

Figure 1(a) is a schematic diagram of the structure of a silicon photonic crystal terahertz wave modulator;

Figure 1(b) Cross-sectional view of silicon photonic crystal terahertz wave modulator;

Fig. 2 (a) is the photonic band gap diagram of the photonic crystal when the electrode has no external voltage;

Fig. 2 (b) is when the electrode has applied voltage, the photonic band gap diagram of photonic crystal;

Fig. 3 is a guided mode diagram of a silicon photonic crystal structure with line defects;

Figure 4(a) is a schematic diagram of the steady-state transmission of terahertz waves in the photonic crystal modulator structure when there is no external voltage applied to the electrodes;

Figure 4(b) is a schematic diagram of the steady-state transmission of terahertz waves in the photonic crystal modulator structure when the electrodes have an applied voltage;

In the figure: a silicon photonic crystal with line defects 2, an electrode 4, a liquid crystal injected into a hole 3, a silicon dioxide substrate 1.

Detailed ways

As shown in Figure 1, the photonic crystal terahertz wave modulator device has a silicon photonic crystal 2 with a line defect, an electrode 4, a liquid crystal 3, and a silicon dioxide substrate 1, and a silicon dioxide substrate with a line defect is arranged on the silicon dioxide substrate. The photonic crystal injects liquid crystal into the silicon photonic crystal hole with line defects, and electrodes are arranged on both sides of the upper end of the silicon photonic crystal with line defects.

The invention mainly uses the tunable BWO as a high-quality THz source, the terahertz wave is input from one end of the silicon photonic crystal with line defects, and the modulated terahertz wave is output from the other end of the silicon photonic crystal. When there is no applied voltage to the electrode, the photonic crystal has a photonic band gap; when the electrode is applied with an applied voltage, due to the change of the refractive index of the liquid crystal, the photonic band gap of the photonic crystal is shifted, and the band gap edge changes.

The present invention analyzes the photonic band gap translation generated by the photonic crystal under the action of the applied voltage, and by selecting a suitable guided mode (terahertz frequency), the band gap edge of the photonic crystal is used to modulate the terahertz wave, so as to load the signal onto the terahertz wave .

The working principle and process are as follows: select a suitable guided mode (terahertz frequency), the frequency falls outside the forbidden band of the photonic crystal when there is no external voltage applied to the electrode, only close to the edge of the photonic forbidden band, the terahertz wave The transmission loss passes through the structure of the photonic crystal modulator; when the electrode has an applied voltage, due to the translation of the photonic band gap of the photonic crystal, the frequency falls in the forbidden band of the photonic crystal, because the photonic band gap of the photonic crystal prohibits any frequency electromagnetic wave from being in the photonic crystal Transmission within the forbidden band, the terahertz wave at this time cannot pass through the photonic crystal modulator structure. Therefore, the intensity of the terahertz wave changes with the applied electric field, and the intensity modulation of the terahertz wave is realized.

Example 1

Terahertz wave modulation at 0.6THz frequency:

Choose the BWOs sold by Microtech, where the return wave tube model is selected as QS-400ov81 (the frequency is tunable in the 0.6-0.9THz frequency band). The designed silicon photonic crystal period a=133 μm, the silicon photonic crystal refractive index is 3.4, the photonic crystal hole radius r=53.2 μm, the width of the line defect of the silicon photonic crystal is to remove a row of holes (width is 2a), select the nanoscale In the 5CB liquid crystal injection hole, the terahertz wave frequency for terahertz communication is 0.6THz. When the obtained electrode has no external voltage, the steady-state transmission of the terahertz wave in the photonic crystal modulator structure is shown in Figure 4(a); when the electrode has an applied voltage (0.71V), the terahertz wave in the photonic crystal modulator structure The steady-state transmission of is shown in Figure 4(b). The extinction ratio of the modulator is 30dB, and the overall size of the modulator is 3.9mm.

Claims (2)

1. A photonic crystal terahertz wave modulator device is characterized in that: it comprises silicon photonic crystal (2), electrode (4), liquid crystal (3), silicon dioxide substrate (1) with line defect, in A silicon photonic crystal with line defects is arranged on a silicon dioxide substrate, liquid crystal is injected into holes of the silicon photonic crystal with line defects, and electrodes are arranged on both sides of the upper end of the silicon photonic crystal with line defects. 2. Utilize the photonic crystal terahertz wave modulation method of device as claimed in claim 1, it is characterized in that, it is the method that utilizes the photonic band gap edge of photonic crystal to modulate terahertz wave signal, carries out intensity to terahertz wave Modulation; when the electrode has no external voltage, the photonic crystal has a photonic band gap; when the electrode has an external voltage, due to the change of the refractive index of the liquid crystal, the photonic band gap of the photonic crystal is shifted, and the edge of the forbidden band is changed to realize the signal loading to terahertz waves.

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