CN105204115B - A kind of middle infrared band adjustable light delay based on symmetric metal cladding waveguide - Google Patents

Abstract

The invention discloses a mid-infrared band adjustable optical delay device based on a symmetrical metal clad waveguide. Two identical metal-clad waveguides are placed facing each other, and the mid-infrared gain medium is filled between the two cladding layers. The infrared incident light enters the mid-infrared gain medium from the infrared laser in the air, and then passes through the middle of the two symmetrical waveguides. A series of reflections by which the outgoing infrared light returns to the air. The invention introduces the displacement enhancement effect of the high-order mode into the mid-infrared band, increases the displacement magnitude to the centimeter level, and produces a reverse displacement that does not exist in the visible light and near-infrared bands; uses Cr ²⁺ doped zinc chalcogenide materials As a mid-infrared gain medium, the loss of a reflection cycle can be reduced from 3.1dB to 2.7dB; the waveguide layer is chalcogenide infrared glass, which has high transmittance in the 2-10μm band and stable refractive index properties; simple structure and adjustable delay The range reaches 0~52.89ns, and the relative delay is large.

Description

A mid-infrared band tunable optical delayer based on a symmetrical metal-clad waveguide

technical field

The invention relates to a mid-infrared band optical delayer, in particular to a mid-infrared band adjustable optical delayer based on a symmetrical metal-clad waveguide.

Background technique

Since the Goos-Hanchen shift was discovered in 1947, how to enhance the Goos-Hanchen shift has been a research focus of scientists. Since the 21st century, the development of integrated optical devices has been very rapid, and various new optical devices have been reported continuously, so optical devices based on enhanced Goos-Hanchen shifts have also emerged as the times require. Existing studies have shown that the high-order modes excited by the metal-clad waveguide can greatly increase the skin depth of light, thereby generating a large displacement on the reflective surface, which can increase the Gus-Hanchen shift from tens of wavelengths to hundreds of wavelengths in the past. . When the incident light is visible light, the displacement can reach the order of millimeters. This structure is simple and can be combined with the circuit system to form a multifunctional photoelectric hybrid module and system, which will be used in many fields such as filtering, sensing, and biology. It is widely used and has a very bright prospect.

The mid-infrared band (2μm ~ 20μm) is an important band of sunlight radiation, which has very important applications in various scientific and technological fields, including sensing, environmental monitoring, biomedical applications, thermal imaging, etc. At present, the research on the higher-order mode theory of metal-clad waveguides is limited to the visible and near-infrared bands, which is affected by factors such as the large loss of infrared light to metals, the invisibility, and the difficulty of experimental operations. However, the size of mid-infrared devices is larger than that of near-infrared devices, and the process is relatively more convenient, and applying the Gus-Hanshin displacement enhancement effect to the mid-infrared band can further extend the displacement to the order of centimeters, and at the same time introduce mid-infrared gain material, compensating for losses due to mode coupling as well as the metal itself.

The existing research on the dimmable delayer mainly uses the following schemes:

1. The method of free space, the method of changing the optical path difference to obtain adjustable time delay, which is also the method mainly used in the present invention.

2. The fiber grating method, in cooperation with the circulator, realizes the reflection of light at different positions by changing the local central wavelength of the Bragg grating, and achieves the purpose of adjustable delay.

3. Utilize the temperature characteristics of the optical fiber, control the temperature of the optical fiber to change the refractive index of the optical fiber, and linearly change the optical path.

Contents of the invention

The object of the present invention is to provide a mid-infrared band adjustable optical delay device based on a symmetrical metal-clad waveguide. Based on the Goos-Hanchen shift enhancement effect of the high-order mode of the metal-clad waveguide, an adjustable negative Goose Hanxin displacement, using the "8"-shaped light trajectory to increase the traveling optical path of the actual beam, and controlling the optical path difference by changing the thickness of the metal film and fine-tuning the incident angle, realizing the optical delay function and controllability, and introducing the middle Infrared gain medium to compensate for mode coupling losses.

The technical scheme that the present invention adopts is as follows:

In the present invention, two identical metal-clad waveguides are placed facing each other, and a mid-infrared gain medium is filled between the two cladding layers. Infrared incident light enters the mid-infrared gain medium from an infrared laser in the air, and then passes through the two symmetrical waveguides. After a series of reflections in the middle, the infrared light returns to the air.

The two identical metal clad waveguides are composed of a three-layer structure; the cladding layer is a silver film with a thickness of 10-50nm, the waveguide layer is a chalcogenide infrared glass with a thickness of 3-5mm, and the substrate layer is a silver film with a thickness of 200nm.

The mid-infrared gain medium is a Cr ²⁺ doped zinc chalcogenide material.

The beneficial effects that the present invention has are:

1. The displacement enhancement effect of the high-order mode is introduced into the mid-infrared band, the displacement magnitude is increased to the centimeter level, and a reverse displacement that is not found in the visible and near-infrared bands is produced, which provides the possibility to realize optical delay.

2. Using Cr ²⁺ doped zinc chalcogenide material as the mid-infrared gain medium has a good gain effect at 2.5~4μm. After theoretical verification, the loss of a reflection cycle can be reduced from 3.1dB to 2.7dB.

3. The waveguide layer used in the present invention is chalcogenide infrared glass, which has high transmittance in the 2-10 μm band and stable properties such as refractive index. The metal film evaporation process is carried out by electron beam evaporation, and the precision is high.

4. Compared with the conventional delayer, the present invention has a simpler structure, and the adjustable delay range can reach 0~52.89ns, which is relatively large in delay.

Description of drawings

Figure 1 is a schematic diagram of the structure of a metal-clad waveguide in the mid-infrared band.

Fig. 2 is a schematic diagram of the structure of a dimmable delayer in the mid-infrared band and a figure-eight light trajectory.

Fig. 3 is a graph showing the relationship between the displacement of the reflection point and the thickness of the metal film.

In the figure: In the figure: 1. Substrate layer, 2. Waveguide layer, 3. Cladding layer, 4. Mid-infrared gain medium, 5. Air, 6. Infrared laser, 7. Infrared primary incident light, 8. Infrared outgoing light , 9. Infrared primary reflected light, 10, infrared secondary incident light, 11, infrared secondary reflected light, 12, light transverse propagation direction.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 2, the present invention adopts two identical metal-clad waveguides (MCW) to be placed facing each other, the mid-infrared gain medium 4 is filled between the two cladding layers, and the infrared incident light 7 is incident from the infrared laser 6 in the air 5 to the mid-infrared gain medium 4, and then undergoes a series of reflections in the middle of two symmetrical waveguides, and returns to the air 5 from the infrared outgoing light 8.

As shown in Figure 1, the two identical metal-clad waveguides are composed of three-layer structures; the cladding layer 3 is a silver film with a thickness of 10-50nm, and the waveguide layer 2 is a chalcogenide infrared glass with a thickness of 3-5mm. The bottom layer 1 is a 200nm silver thin film. When the thickness of the waveguide layer 2 is on the order of millimeters, the metal structure of the cladding layer 3 and the substrate layer 1 enables the mode order of the guided mode to reach several thousand.

The mid-infrared gain medium 4 is a medium with gain in the mid-infrared band, a Cr2+ doped zinc chalcogenide material.

Due to the complex refractive index of the substrate layer 1 and the cladding layer 3, infrared light can be directly coupled from the mid-infrared gain medium 4 into the waveguide to excite high-order modes, and produce a reverse displacement on the incident point, making the optical path along the "8" The glyph advances, greatly increasing the optical path difference.

Changing the thickness of the silver thin film of the cladding layer 3 or adjusting the incident angle can change the magnitude of the negative displacement, thereby changing the optical path difference and achieving the purpose of controlling the amount of time delay.

The working principle of the present invention is as follows:

As shown in Figure 2, the infrared primary incident light 7 is incident on the upper surface of the lower MCW structure through the mid-infrared gain medium 4, and reverse displacement occurs, and the infrared primary reflected light 9 is reflected from the upper surface of the lower MCW structure to the lower surface of the upper MCW structure surface. The infrared primary incident light 7 and the infrared primary reflected light 9 are regarded as one reflection cycle. Similarly, the reverse displacement occurs on the lower surface of the upper MCW structure, and the infrared secondary incident light 10 is incident on the upper surface of the lower MCW structure from the lower surface of the upper MCW structure. The infrared secondary incident light 10 and the infrared secondary reflected light 11 are regarded as secondary reflection cycles. Because the lateral displacement of each reflection cycle is greater than the reverse displacement, the light propagates to the right along the light transverse propagation direction 12 until the infrared outgoing light 8 returns to the air 5 .

The waveguide layer 2 is made of 3mm chalcogenide infrared glass material, which can hold more than 5000 modes at most. The cladding layer 3 adopts silver metal film within 50nm. Two MCW structures with the same structure are placed facing each other. The light exits from the infrared laser 6 of the air 5, enters the Cr ²⁺ doped mid-infrared gain medium 4, refracts to the upper surface of the lower MCW structure, and penetrates the metal film , when the waveguide layer 2 satisfies the oscillation condition, an oscillation field is formed, that is, a high-order mode, and a phase change peak will be generated at the incident point, which also explains the increased displacement between the incident point and the reflection point. Bottom 1 is thicker and impenetrable. Due to the influence of higher-order modes near the incident point on the cladding layer 3, a reverse displacement occurs, and the reflection point is in the opposite direction of the incident point propagation direction, so the light propagates along the "8"-shaped light path to the right and along the direction of the arrow, and finally at The rightmost end of the MCW structure is returned to the air by the infrared outgoing light 8 . As shown in Figure 3, one incident and one reflection are regarded as a reflection cycle, and the relationship between S _n and Z _s is controlled by changing the thickness of the cladding silver film, and the number of cycles required for light in the reflection process is also Change accordingly, so the delay time is adjusted. In Figure 3, the wavelength is 3 μm, and 0.86° and 2.95° are the coupling angles of the highest-order mode and the second-highest-order mode, respectively.

The manufacturing method of the device structure of the present invention:

First cut the original glass sheet into 3mm thick cuboid sheets with a glass cutting machine, and polish the smoothness on both sides. After the sheet is cleaned by ultrasonic waves, metal films of different thicknesses are evaporated on the two surfaces of the glass by an electron beam evaporator. Protect one surface with tape while evaporating the other to ensure thickness accuracy. After the two MCW structures are completed, zinc-sulfur materials are filled in the middle, placed on an optical indexing platform in free space, and the incident angle is adjusted to meet the coupling conditions.

Claims (2)

1. A mid-infrared band adjustable optical delay device based on a symmetrical metal-clad waveguide, characterized in that: two identical metal-clad waveguides are placed opposite each other, and a mid-infrared gain medium is filled between the two cladding layers (4 ), the infrared incident light (7) enters the mid-infrared gain medium (4) from the infrared laser (6) in the air (5), and then undergoes a series of reflections in the middle of two symmetrical waveguides, and the infrared outgoing light (8) return air(5); The two identical metal-clad waveguides are composed of a three-layer structure; the cladding layer (3) is a silver film with a thickness of 10-50 nm, the waveguide layer (2) is a chalcogenide infrared glass with a thickness of 3-5 mm, and the substrate layer ( 1) 200nm silver thin film. 2. A mid-infrared band adjustable optical delay device based on a symmetrical metal-clad waveguide according to claim 1, characterized in that: the mid-infrared gain medium (4) is Cr ²⁺ doped zinc chalcogen Material.