KR100439479B1 - Photonic crystal waveguide devices - Google Patents

Abstract

A photonic crystal optical device and its application are disclosed. The photonic crystal optical device according to the present invention is pressed against one or more air layers (holes) formed in the waveguide direction around the center of the waveguide by externally deforming the waveguide along any of the regions along the waveguide to depress the presence or absence of a compression. And the light loss, the waveguide direction, and the transmission spectral characteristics of the waveguide vary according to the pressing size. According to the present invention, when the pressure is adjusted to a certain portion of the photonic crystal optical device, since various characteristics such as waveguide characteristics and dispersion characteristics can be easily adjusted, it can contribute a lot to the optical communication and optoelectronic fields.

Description

Photonic crystal waveguide devices and application thereof

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to photonic crystal optical devices and their applications, and in particular, by applying a photonic crystal optical waveguide to a suitable position from outside to easily change the transmission spectrum, light loss, waveguide characteristics, dispersion characteristics and mode patterns. A photonic crystal optical device capable of implementing an attenuator, an optical filter, an optical sensor, a dispersion compensator, and the like, and an application thereof.

The photonic crystal optical waveguide is a waveguide having one or more air layers around the waveguide. The photonic crystal optical waveguide is divided into a photonic crystal optical fiber (PCF) having a cylindrical shape like an optical fiber according to the structure of the waveguide. . These photonic crystal waveguides have attracted much attention in the field of optical communication because they have waveguides and dispersion characteristics different from the conventional waveguides, and there are many air layers or air holes uniformly aligned in the longitudinal direction in the cladding region. It is characterized by.

Among the photonic crystal optical waveguides, in particular, the characteristics of the photonic crystal optical fiber (PCF) can be summarized to operate in a single mode over a wide wavelength range, and have anomalous GVD characteristics in the visible and near infrared regions. Because of these new features, PCFs are being tried worldwide for many applications, including optical soliton communications, high power fiber lasers, optical measurements and clinical diagnostics. At present, the level of research on PCF at home and abroad is in the basic research stage, and it is expected that the research and development of photonic crystal optical devices based on PCF will be greatly activated in the future.

As such, the prospects for photonic crystal optical devices based on photonic crystal waveguides including PCFs are bright, but in order to commercialize them into various devices including optical attenuators, optical filters, and optical sensors, technology for making devices using photonic crystal waveguides has been developed. Should be developed. Currently, the optical attenuator made of the existing optical waveguide is mainly based on micro bending, and the optical filter mainly makes an optical waveguide grating such as an optical waveguide grating by irradiating UV light to the optical waveguide. However, since the internal structure of the photonic crystal waveguide is different from that of the conventional waveguide, it is difficult to manufacture the photonic crystal waveguide device by the same method, and it is difficult to expect the same performance even if it is manufactured.

Accordingly, an object of the present invention is to implement the functions of various optical elements including optical attenuation and optical filters by modifying the thickness of the air layer by applying pressure from the outside to the optical waveguide with the air layer.

The present invention for achieving the above object of the present invention is a photon consisting of a waveguide core for transmitting the incident light and a waveguide having at least one hole in the waveguide propagation direction of light between the cladding which is a peripheral region of the core It is applied to a crystalline optical device, wherein the photonic crystal optical device of the present invention is formed by reducing the diameter of the hole to close the core and the cladding in an arbitrary area so that the light may experience FTIR exiting through the hole from the core to the cladding. It is characterized by. In addition, while allowing the light to experience FTIR exiting the hole from the core to the cladding, at the same time, some of the light waves exiting the cladding while undergoing the FTIR are selectively recombined back to the core to provide attenuation, transmission spectrum including transmission spectrum. In order to be able to change the characteristics of, the diameter of the hole is reduced by any interval, characterized in that made by close proximity between the core and the cladding.

On the other hand, depending on the compression size and the compression position, the size of the FTIR exiting through the hole from the core to the cladding is changed, and at the same time, some of the light waves exiting the cladding undergoing the FTIR are selectively returned to the core according to the compression position interval. Combining means is formed along the waveguide to press the waveguide to change the characteristics of the waveguide including the degree of attenuation, transmission spectrum coupled to the waveguide, the pressing means is formed of the upper pressing plate and the lower pressing plate Preferably, the upper pressing plate or the lower pressing plate may be selectively formed irregularities. The irregularities may be formed in the valleys and valleys at regular intervals, or the hills and valleys at non-periodic intervals.

This theory can be applied to optical attenuators, pressure sensors, optical filters, optical switches, and the like.

The waveguide includes both an optical fiber or a planar waveguide.

1A is a cross-sectional view of a photonic crystal optical waveguide having air holes or air layers (holes) of the same size and shape when no deformation due to pressure is applied;

1B is a cross-sectional view of a photonic crystal optical waveguide having no air holes or air layers of the same size and shape when no deformation due to pressure is applied;

FIG. 2A is a cross-sectional view of a photonic crystal waveguide when the shape and size of the air layer of the photonic crystal waveguide are modified by applying pressure or a force to the waveguide direction from the outside with respect to FIG. 1A;

FIG. 2B is a cross-sectional view of the photonic crystal optical waveguide when the shape and size of the air layer of the photonic crystal waveguide are modified by applying a greater pressure or force than in FIG. 2A perpendicularly to the waveguide direction from the outside with respect to FIG.

3A is a view showing a concept of applying a force to a photonic crystal waveguide perpendicular to the direction of the waveguide from the outside;

FIG. 3B illustrates the concept that light waves are transmitted without loss through TIR (Total Internal Reflection) through the optical fiber core when no external force is applied to the photonic crystal optical waveguide perpendicularly to the waveguide direction (Z axis). drawing,

3C and 3D show that the TIR is partially broken due to thinning of the air layer outside the core when the photonic crystal optical waveguide is applied to the photonic crystal optical waveguide perpendicularly to the waveguide direction (Z axis) from the outside, as shown in FIG. 3A. Drawing showing the concept that some of the exit to the outer layer,

4A is a view illustrating a concept of applying a force to a plurality of regions on a photonic crystal optical waveguide perpendicular to the direction of the waveguide from the outside;

FIG. 4B shows that when a force is applied to the photonic crystal waveguide from outside to the direction of the waveguide as shown in FIG. 4A, the air layer outside the core becomes thinner, so that part of the TIR is broken and some of the light waves transmitted into the core fall into the outer layer. Drawing showing the process of joining the core back out

Figure 5 is an embodiment of the pressure plate to change the thickness of the air layer of the waveguide by applying pressure or force from the outside.

Explanation of symbols on the main parts of the drawings

10 photonic crystal optical waveguide

12: cladding or peripheral region of the photonic crystal waveguide

14: core or waveguide region of the photonic crystal waveguide

20: Air layer (hole) or air hole opened in waveguide direction

22, 24: Air layers or air holes having different sizes and shapes of holes drilled in the waveguide direction

26, 28: deformed air hole 20 by the pressure or force

30, 32, 34: pressure or force applied from the outside

36: photonic crystal waveguide core Light waves traveling at an angle

38: Light waves traveling through the core while the light waves 36 undergo TIR

40: beam incident on the core

44: Light wave leaking into cladding as TIR breaks due to thinning of air layer by pressure

42, 48: some of the remaining light waves due to compression

50: light waves recombined into the core among the light waves exiting the core from the cladding

52: light waves traveling to the core after recombination with light waves proceeding to the cladding

60: pressure plate

62: uneven portion

Hereinafter, with reference to the accompanying drawings will be described the principle and preferred embodiment of the present invention.

First, when an air layer or air hole is formed in the waveguide direction in order to form an optical waveguide such as an optical fiber or a planar waveguide, light is guided through the core 14 as shown in FIGS. 3 and 4. The waveguide thus formed is called a photonic crystal optical waveguide, and the optical fiber structure is called a photonic crystal fiber. The present invention will be described with respect to the operation principle of the present invention as an invention for a photonic crystal optical waveguide device that can be easily made with such a photonic crystal optical waveguide.

The operation principle of the optical waveguide device according to the present invention is to press the air layer 20 around the core 14 of the photonic crystal waveguide from the outside, so that the thickness of the air layer is sufficiently thin and the internal reflection is broken inside the core, so that the cladding 12 is the peripheral layer. It is based on the principle that part of the beam guiding with) leaks out. The degree of escape from the core to the cladding increases as the thickness of the air layer is thinner and as the length of the thin layer is longer, so when controlling the degree of external compressive force and the length of the compression site, the size of the beam exiting to the outer layer is controlled. Can be. However, since the beam leaking to the outer layer or cladding layer has a large loss, it is possible to implement a tunable photonic crystal waveguide attenuator that can control the loss by adjusting the magnitude of the externally applied force and the length of the applied portion. .

In the same principle, the photonic crystal waveguide device can detect the amount of compression or pressure or external force due to the loss because the amount of beam leaking into the lossy outer layer or cladding layer depends on the external compression. Photonic crystal waveguide pressure sensors may be implemented.

In addition, the beams that escaped into the cladding by this compression are able to reenter the core and recombine with the beams that have traveled back to the core when this compression is again along the optical waveguide. This recombination process continues if this pressure is repeated along the optical waveguide. In this case, the amount of beam coupling depends on various parameters such as the refractive index of the optical waveguide, the radius, and the thickness of the air layer. In particular, the amount of beam coupling varies greatly depending on the wavelength of the beam. It can also be implemented. In particular, since the degree of compression and the length of the compression region can be easily adjusted, a tunable photonic crystal waveguide filter is possible.

As described above, both the photonic crystal optical fiber element and the photonic crystal planar waveguide element belong to the present nickname, but as an example, the waveguide is described as an optical fiber for convenience. In addition, in the description of the drawings, reference numerals are indicated not only in terms of apparatuses but also in operation states and changes thereof, so that changes in operations are clearly distinguished and described.

Among the photonic crystal planar waveguides and photonic crystal optical fibers, which are types of photonic crystal optical waveguides, FIGS. 1A and 1B show cross-sectional views of a photonic crystal optical fiber (PCF), and FIG. 1A shows air layers or air holes having the same size and shape in an optical waveguide or FIG. 1B is a cross-sectional view of a photonic crystal optical fiber PCF having holes 22 and 24 of different sizes and shapes in the optical waveguide. Referring to FIGS. 1A and 1B, reference numeral 10 denotes a photonic crystal waveguide, 12 a cladding or peripheral region of the photonic crystal waveguide, 14 a core or waveguide region of the photonic crystal waveguide, and 20 an air layer bored in the waveguide direction. (Holes) or air holes (hereinafter referred to as holes), 22 and 24 denote air layers or air holes having different sizes and shapes of holes drilled in the waveguide direction, respectively.

The cladding or peripheral region 12 of the photonic crystal optical waveguide and the core or waveguide region 14 of the photonic crystal optical waveguide correspond to the core and cladding of the general optical fiber, respectively. PCF is mainly made of materials that are transparent to light such as silica, plastic, and glass.

The waveguide characteristics, dispersion characteristics, transmission spectrum characteristics, and mode patterns of the photonic crystal optical waveguide or the PCF optical fiber are different depending on the size and shape of the holes 20, 22, and 24 of the PCF. Accordingly, it is intended to achieve each characteristic change of the above mode by using the following method.

FIG. 2 is a cross-sectional view of a PCF expected when a pressure or a force is applied to a photonic crystal waveguide (FIG. 1A) in a direction perpendicular to the waveguide direction from the outside, and the thickness of the air layer and the shape of the air layer are deformed according to the magnitude of the pressure. It is a conceptual diagram showing that it can be. The long radius of the air layer 28 of FIG. 2B is much thinner than the long radius of the air layer 26 of FIG. 2A because of the greater pressure in FIG. 2B. As shown in FIG. 2, the PCF may be externally pressurized at one or two places perpendicular to the waveguide length direction, or may be periodically pressurized with pressure, pressure, and pressure in the waveguide length direction for each length. It can also give the PCF a periodic deformation. At this time, as the thickness of the hole is severely reduced or greatly crushed due to sufficient press, the inside of the frosted surface is clad with the photonic crystal waveguide 14 or the cladding or peripheral region 12 of the photonic crystal waveguide. Due to the leakage of light waves by the totally reflected TIR (FTIR) and the significant change in the effective refractive index of the waveguide mode, the waveguide characteristics, loss characteristics, dispersion characteristics, mode patterns, and transmission spectrum characteristics of the PCF change more and more. Here, the degree of change of these characteristics due to the pressing is better to make much larger than the general optical fiber.

FIG. 3 is a diagram to show how FTIR occurs when a pressure is applied to the photonic crystal optical fiber, and thus the loss increases. 3B is along the core 14 when no stress is applied to the photonic crystal optical fiber. It shows that the light wave 38 is waveguided without loss due to TIR because the light wave or beam 36 guiding at an angle is larger than the critical angle (sin ⁻¹ (n 2 / n 1), where n 1 = refractive index of the core, n 2 = 1). . 3C and 3D are diagrams showing that the light wave 36 leaks to the cladding layer 12 through the thin air layer by FTIR when pressed 30 to the PCF as shown in FIG. 3A. As the TIR breaks, the amount of light waves 44 leaking into the cladding increases. Alternatively, the amount of light waves 44 exiting may be greater than the amount of light waves 48 being guided. However, since the beam leaking to the outer layer or the cladding layer has a large loss, it is possible to implement a tunable photonic crystal waveguide attenuator that can control the loss by adjusting the magnitude of the externally applied force and the length of the applied portion. In addition, since the amount of beams leaking into the lossy outer layer or cladding layer depends on the degree of external compression, a photonic crystal waveguide pressure sensor that can sense the degree of compression or pressure or external force may be implemented. Reference numeral 40 is a beam incident on the core.

FIG. 4A is a view showing the force applied to the photonic crystal optical waveguide in several places perpendicularly to the direction of the waveguide from the outside, where the force 32 may be periodic or aperiodic. FIG. 4B shows that when a force is applied to the photonic crystal waveguide from outside to the direction of the waveguide as shown in FIG. 4A, the air layer outside the core becomes thinner, so that the TIR is partially broken, and thus, some of the light waves transmitted into the core are lost to the outer layer. Next, a portion of the light waves exiting the cladding from the core, that is, the light wave 50 that is combined back to the core is coupled to the core again. In this case, the amount of coupling depends on various parameters such as the refractive index of the optical waveguide, the radius, the thickness of the air layer, and the compression spacing. In particular, the amount of coupling varies greatly depending on the wavelength of the beam. The photonic crystal waveguide filter may be implemented. In particular, the degree of compression and the length of the compression region can be easily adjusted, enabling a tunable photonic crystal waveguide filter. Reference numeral 42 denotes an optical fiber remaining after some loss due to compression, and reference numeral 52 denotes a light wave traveling to the core after recombination with the light waves proceeding to the cladding.

5 is an embodiment in which the pressure or force 34 is applied to the pressure plate 60 from the outside to change the thickness of the air layer of the waveguide. Reference numeral 60 denotes a pressing plate 60 for pressing a predetermined portion of the photonic crystal optical waveguide, and 62 formed in the pressing plate 60 is an uneven portion 62 that actually presses the waveguide when the pressing plate is pressed. The uneven portion 62 may be rounded or flat as shown in FIG. 5, or of course, may have a V shape. The spacing between the uneven parts 62 and the number of the uneven parts 62 in the pressing plate 60 may vary depending on the function of the photonic crystal element. For example, when implementing an optical filter, it is preferable to use a pressure plate 60 having more than one uneven portion 62 periodically. When implementing a pressure sensor or attenuator, it is preferable to have two or more uneven portions 62. You can adjust various parameters according to the pressure to be attenuated or the attenuation to be attenuated. The shape of the pressure plate 60 may be various in addition to FIG. That is, pressurization may be performed at each of the upper and lower portions, or may be at only one side.

Although the description of the present invention mainly described only the optical fiber as the waveguide, it is well known that the above-mentioned pressure can be equally applied to the photonic crystal optical device having the planar waveguide instead of the optical fiber.

As described above, the photonic crystal optical device and its application according to the present invention, compared with the conventional optical waveguide, the photonic crystal optical waveguide is waveguided due to external pressure because there are a plurality of holes in the optical waveguide longitudinal direction around the optical waveguide center Since the characteristics, attenuation characteristics, and transmission spectrum characteristics are large, optical devices such as an optical attenuator, a tunable optical filter, and a pressure sensor, which can vary the degree of attenuation, can be realized in the case of pressing a certain compression portion of the photonic crystal optical waveguide. . Since the present invention can easily adjust various characteristics by applying force or pressure to the photonic crystal waveguide aperiodically or periodically from the outside, the present invention can be easily implemented and easily commercialized, thereby contributing much to the optical communication and optical sensor fields.

The present invention is not limited to the above-described embodiment, and it will be apparent that many modifications are possible by those skilled in the art within the technical spirit of the present invention.

Claims (19)

A photonic crystal optical element comprising a waveguide having at least one hole in a waveguide propagation direction of light between a core which is a waveguide region for transmitting incident light and a cladding, which is a peripheral region of the core, And reducing the diameter of the hole to approximate the core and cladding in an arbitrary region so that the light may experience FTIR exiting the hole from the core to the cladding. A photonic crystal optical element comprising a waveguide having at least one hole in a waveguide propagation direction of light between a core which is a waveguide region for transmitting incident light and a cladding, which is a peripheral region of the core, While allowing the light to experience FTIR exiting the hole from the core to the cladding, at the same time, some of the light waves exiting the cladding while undergoing the FTIR are selectively recombined back into the core to provide attenuation, transmission spectrum characteristics including transmission spectrum. The photonic crystal optical element, characterized in that the diameter of the hole at any interval to reduce the proximity between the core and the cladding so as to change. delete delete delete delete delete A photonic crystal optical element comprising a waveguide having at least one hole in a waveguide propagation direction of light between a core which is a waveguide region for transmitting incident light and a cladding, which is a peripheral region of the core, Depending on the compression size and the compression position, the size of the FTIR exiting through the hole from the core to the cladding is changed, and at the same time, some of the light waves exiting the cladding through the FTIR are selectively recombined to the core according to the compression position interval. A compression means is formed along the waveguide to press the waveguide to deform the hole so as to change the attenuation degree and the characteristics of the waveguide including the transmission spectrum. The pressing means is a photonic crystal optical element, characterized in that formed by the upper pressing plate and the lower pressing plate. 9. The photonic crystal optical element of claim 8, wherein the upper and lower press plates are formed by selectively forming irregularities. 10. The photonic crystal optical element of claim 9, wherein the unevenness is formed with a peak and a valley at periodic intervals. 10. The photonic crystal optical device of claim 9, wherein the unevenness is formed with a peak and a valley at aperiodic intervals. For a waveguide having at least one hole in a waveguide propagation direction of light between a core, which is a waveguide region for transmitting incident light and a cladding, which is a peripheral region of the core, the hole from the core to the cladding according to the pressing size and the pressing position. Compressing the waveguide by deforming the hole to change the magnitude of the light wave exiting the cladding while undergoing the FTIR by changing the size of the FTIR exiting through to change the characteristics of the waveguide including the optical waveguide optical loss. An optical attenuator, wherein the pressing means is formed along the waveguide. For a waveguide having at least one hole in a waveguide propagation direction of light between a core, which is a waveguide region for transmitting incident light and a cladding, which is a peripheral region of the core, the hole from the core to the cladding according to the pressing size and the pressing position. Pressing the waveguide so as to change the size of the FTIR exiting through the FTIR and at the same time some of the light waves exiting the cladding undergoing the FTIR can be selectively recombined back to the core according to the compression position interval to change the waveguide characteristics. And a pressing means for deforming the hole along the waveguide. For a waveguide having at least one hole in a waveguide propagation direction of light between a core, which is a waveguide region for transmitting incident light and a cladding, which is a peripheral region of the core, the hole from the core to the cladding according to the pressing size and the pressing position. Compressing the waveguide by pressing the waveguide to change the magnitude of the light wave exiting the cladding while undergoing the FTIR by varying the size of the FTIR exiting through to change the characteristics of the waveguide, including the optical loss of the optical waveguide. Pressure sensor characterized in that formed by the pressing means along the waveguide. For a waveguide having at least one hole in a waveguide propagation direction of light between a core, which is a waveguide region for transmitting incident light and a cladding, which is a peripheral region of the core, the hole from the core to the cladding according to the pressing size and the pressing position. While changing the size of the FTIR exiting through the FTIR, some of the light waves exiting the cladding during the FTIR are selectively recombined to the core at intervals of the compression position, and thus the characteristics of the waveguide including the optical loss depending on the pressure level. Pressure sensor characterized in that it is formed by forming a pressing means along the waveguide to deform the hole by pressing the waveguide so as to change. For a waveguide having at least one hole in a waveguide propagation direction of light between a core, which is a waveguide region for transmitting incident light and a cladding, which is a peripheral region of the core, the hole from the core to the cladding according to the pressing size and the pressing position. In addition to changing the size of the FTIR exiting through a portion of the optical wave exiting the cladding while undergoing the FTIR is selectively re-combined back to the core in accordance with the compression position interval to undergo a change in the transmission spectrum characteristics corresponding to the wavelength of the beam And a pressing means for pressing the waveguide to deform the hole so as to change the characteristics of the waveguide along the waveguide. For a waveguide having at least one hole in the waveguide propagation direction between the core, which is a waveguide region for transmitting the incident light and the cladding, which is a peripheral region of the core, the FTIR is generated at a constant compression magnitude in the core. And a pressing means along the waveguide for pressing the waveguide to deform the hole so that the light wave passes through the core to block the light wave from passing through the core. The method according to any one of claims 1 or 2 or 8, 12 to 17, The waveguide is a photonic crystal optical element, characterized in that the optical fiber. The method according to any one of claims 1 or 2 or 8, 12 to 17, And the waveguide is a planar waveguide.