CN105467628A - Hybrid integrated electric-control liquid-crystal optical switch array - Google Patents

Abstract

The invention discloses a hybrid integrated electric-control liquid-crystal optical switch array. The hybrid integrated electric-control liquid-crystal optical switch array comprises a hybrid integrated electric-control liquid-crystal optically-focused microlens array and an electric-control liquid-crystal optically-diffused microlens array, and the optical axis of each liquid-crystal optically-focused microlens unit is coincident with that of each liquid-crystal optically-diffused microlens unit. When being powered up, optically-focused microlenses carry out internal-focusing optically-focused operations to a light beam under the effect of electric-control signals of different mean square amplitudes. and optically-diffused microlenses carry out controllable operations with a controllable diffusion degree to a light beam under the effect of electric-control signals of different mean square amplitudes. When being powered off, the liquid-crystal optically-focused microlenses and the optically-diffused microlenses are converted into liquid-crystal phase-shift plates which only delay light wave phases, and the liquid-crystal phase-shift plates which are formed after the liquid-crystal optically-focused microlenses and the optically-diffused microlenses are powered off form the opening state of the optical switch. The hybrid integrated electric-control liquid-crystal optical switch array can complete electric-control light beam on-off operations, and is suitable for optical fiber or optical cable systems which are wide in spectrum scope and large in wave beam intensity change scope.

Description

A Hybrid Integrated Electronically Controlled Liquid Crystal Optical Switch Array

technical field

The invention belongs to the technical field of optical communication, and more specifically relates to a hybrid integrated electronically controlled liquid crystal optical switch array.

Background technique

At present, the widely used optical fiber communication technology uses light as the information carrier and optical fiber as the transmission medium, and transmits voice, image and data information by transmitting light wave signals in the optical fiber. With the characteristics of large transmission capacity and good confidentiality, it has become the most important means of wired communication in the world. The optical switch is an important functional component in the optical fiber communication system. It has one or more optional transmission windows and channels. The optical signals in the path perform mutual switching operations. So far, optical switches have become the basic functional components in optical transmission and optical interface networks. Currently commonly used optical switches include: (1) mechanical optical switches, (2) micro-electromechanical (MEMS) optical switches, (3) functional optical modulation optical switches, etc. Key parameters characterizing optical switches include: insertion loss, optical signal return loss, optical isolation, optical crosstalk, and extinction ratio. Practical optical switches generally have the characteristics of relatively low cost and power consumption, small structural size, and as low as possible requirements for the optical transport index of optical fibers. The application shows that the insertion loss of the mechanical optical switch is relatively low, the optical isolation is high, and it is not affected by the polarization and spectral characteristics of the beam. In the communication optical network. Thanks to the rapid development of microelectronics technology in recent years, MEMS optical switches, which are still in progress, are mainly used in optical channel switching, optical connection or directional beam delivery links. Its light-controlled switching is mainly based on the insertion or directional tilting of electromagnetically actuated micromirrors to guide light beams into output waveguides or optical fibers in multidirectional discrete configurations. By densely arranging multiple independently controlled micro-mirror groups, the incident light beam is directed to a specific direction to realize link on-off. The insertion loss is relatively low, the optical isolation and extinction ratio are high, and it has high coupling efficiency and microsecond switching response time with the input and output optical fibers or waveguides. It is easy to package, but there is a certain degree of optical crosstalk. Typical optical (waveguide) modulated optical switches are mostly used in some high-end applications at present, and their switching time has the development potential of picosecond level, but insertion loss, extinction ratio, polarization loss and crosstalk cannot be optimized at the same time. In short, according to different application requirements and economic affordability, the current optical switches are still being further improved in terms of the above-mentioned performance indicators.

To sum up, the existing mainstream optical switch technology still has defects in dealing with the current high-intensity big data transmission beams, mainly in the following aspects: (1) The millisecond-level switching time of mechanical optical switches is too long, and insertion The loss is still large and the isolation is insufficient; (2) MEMS optical switches need to adjust the beam transmission through the mechanical movement of the micro-functional structure, and the switching action caused by the mechanical movement inertia is relatively slow, the cycle is long, and the insertion loss is still not ideal (3) Conventional electro-optic switches generally use the electro-optic or electro-absorption effect of materials to change their refractive index, beam phase or polarization state under the action of an electric field, based on optical interference, diffraction or polarization, etc. Changing the light intensity or bending the optical path, the modulation and curing of the optical structure and parameters are complicated, the control is relatively difficult, and the parameters of different types of switches are uneven, it is difficult to make overall plans and the cost is high; (4) Directional coupling optical switches Generally, the periodic conversion of optical power is realized by coupling waveguides, such as typical M-Z interferometric and waveguide M-Z interferometric optical switches, which have complex structures and configurations, many control and variable factors, and cost problems; (5) Polarization Modulated optical switches are mainly aimed at transmission wave fields with high polarization degrees, including conventional liquid crystal polarized light switches, etc.; (6) Typical thermo-optical switches are based on the temperature dependence of the physical properties of the medium caused by thermal effects, so that the refractive index of the transmission medium changes And delayed optical phase, with large thermal inertia, often used in steady state or slowly changing occasions; (7) Typical acousto-optic switches are based on the mechanical strain of the acoustic wave in the material to cause periodic changes in the refractive index to form a Bragg grating to diffract Specific wavelength beams are mainly used for long-wavelength beam on-off operations in view of the low-frequency characteristics of sound waves. In short, the development of an optical switch architecture suitable for stronger beam transmission power, small/miniaturized structure, low insertion loss, high optical isolation and extinction ratio, and relatively low price is still a hot and difficult issue for the further development of optical switch technology. , has received widespread attention and attention.

Contents of the invention

Aiming at the above defects of the prior art, the present invention provides a hybrid integrated electronically controlled liquid crystal optical switch array. The on-state and off-state formed with the liquid crystal phase shift plate can complete the electronically controlled opening and closing of the transmission channels of beams of different intensities. In addition, the array of the present invention has a wide applicable spectrum range and a large variable range of beam intensity, which is easy to Advantages such as coupling with optical fiber or optical cable.

In order to achieve the above object, the present invention provides a hybrid integrated electronically controlled liquid crystal optical switch array, including an electronically controlled liquid crystal concentrating microlens array and an electronically controlled liquid crystal astigmatism microlens array. Under the action of the electric drive control signal, the incident light beam can be adjusted to focus and focus. In the power-off state, it is a liquid crystal phase shift plate that delays the light wave phase; The light beam implements the astigmatism operation with controllable divergence degree. It is a liquid crystal phase shift plate that delays the light wave phase in the power-off state; the electronically controlled liquid crystal concentrating microlens array and the liquid crystal astigmatism microlens array are converted into a liquid crystal phase shifting plate after power off The plate forms the open state of the optical switch, and the liquid crystal phase shift plate converted into the liquid crystal phase shift plate after being powered off forms the closed state of the optical switch; The light-gathering and astigmatism performances of the lens array and the liquid crystal astigmatism micro-lens array complete the switching of the transmission paths of beams of different intensities on and off.

Preferably, both the electronically controlled liquid crystal focusing microlens array and the electrically controlled liquid crystal astigmatizing microlens array are M×N elements, wherein M and N are both integers greater than 1; each unit liquid crystal focusing microlens and The filling factor of the liquid crystal astigmatism microlens is lower than 40%, that is, the ratio of the area of the light acting area of each unit of the liquid crystal microlens to perform converging or diverging operations on the light beam projected around its optical axis to the light incident area of the microlens is lower than 40 %.

Preferably, the electronically controlled liquid crystal light-concentrating microlens is composed of a liquid crystal material with a micron thickness encapsulated between the top surface microhole electrode and the bottom surface common electrode, and the electronically controlled liquid crystal astigmatism microlens is composed of a top surface common electrode and a bottom surface common electrode. The micron-scale thickness liquid crystal material between the ring microhole-shaped electrodes on the bottom surface is composed, and the center vertical line of the microhole, the ring microhole and the surface electrode coincides with the optical axis of the corresponding liquid crystal concentrating microlens and liquid crystal astigmatism microlens.

Preferably, the electronically controlled liquid crystal optical switch array composed of the electronically controlled liquid crystal concentrating microlens array and the electronically controlled liquid crystal astigmatizing microlens array is also M×N elements.

Preferably, it also includes a ceramic housing, wherein the electronically controlled liquid crystal focusing microlens array is located in front of the electrically controlled liquid crystal astigmatizing microlens array and coaxially placed in the ceramic housing in sequence, and each unit of the liquid crystal focusing microlens is connected to the The optical axes of the liquid crystal astigmatism microlenses of each unit are coincident; the light incident surface of the electronically controlled liquid crystal light concentrating microlens array is exposed through the front opening of the ceramic shell, and the light exit surface of the electronically controlled liquid crystal astigmatic microlens array The opening through the back of the ceramic shell is exposed to the outside.

Preferably, the electronically controlled liquid crystal concentrating microlens array is provided with a first port and a first indicator light, and the first port is used to access the electric drive control input from an external device to the liquid crystal concentrating microlens array. signal, the first indicator light is used to indicate whether the electronically controlled liquid crystal concentrating microlens array is in a normal electric drive control signal input state;

Preferably, the electronically controlled liquid crystal astigmatism microlens array is provided with a second port and a second indicator light, and the second port is used to access an electric drive control signal input from an external device to the liquid crystal astigmatism microlens array, The second indicator light is used to indicate whether the electronically controlled liquid crystal astigmatism microlens array is in a normal electric driving control signal input state.

Preferably, a small triangular symbol is provided on the upper side of the upper right side of the ceramic housing near the light exit surface to indicate the position of the light exit surface of the optical switch.

Compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

1. Based on the electric drive control signal to control the on-off of the optical transmission path, it has the advantages of flexible and diverse electronic control methods, and is easy to couple with other optical, photoelectric or electronic structures;

2. Due to the modulation effect on both polarized and non-polarized beams, it has the characteristics of good polarization adaptability of the beam;

3. Due to the electronically controlled bending of the beam through the functionalized thin-film liquid crystal, it has the characteristics of adapting to a wide spectrum and a large range of beam intensity fluctuations;

4. The miniaturized integrated structure of the switch and the flat end face show good structural adaptability, which can be flexibly inserted into the optical path or integrated into the optical link;

5. The production cost is low and the price is relatively low.

Description of drawings

Fig. 1 is a schematic diagram of the front (light incident surface) structure of a hybrid integrated electronically controlled liquid crystal optical switch array according to an embodiment of the present invention;

Fig. 2 is a schematic diagram of the structure of the back (light exit surface) of a hybrid integrated electronically controlled liquid crystal light switch array according to an embodiment of the present invention;

Fig. 3 is a working principle diagram of a hybrid integrated electronically controlled liquid crystal optical switch array according to an embodiment of the present invention;

Fig. 4 is a schematic diagram of optical fiber bundle coupling and beam channel switching of a hybrid integrated electronically controlled liquid crystal optical switch array according to an embodiment of the present invention.

Throughout the drawings, the same reference numerals are used to designate the same elements or structures, wherein:

1-Ceramic shell, 2-First port, 3-First indicator light, 4-Second port, 5-Second indicator light, 6-Light exit surface indicator, 7-Light incident surface, 8-Light exit surface .

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

Fig. 1 is a schematic diagram of the structure of the front (light incident surface) of a hybrid integrated electronically controlled liquid crystal optical switch array according to an embodiment of the present invention, and Fig. 2 is a back side (light incident surface) of a hybrid integrated electronically controlled liquid crystal optical switch array according to an embodiment of the present invention. Schematic diagram of the exit surface). As shown in the figure, the electronically controlled liquid crystal concentrating microlens array and the electronically controlled liquid crystal astigmatism microlens array are mixed and integrated with the optical axis and placed in the ceramic housing 1, wherein the electronically controlled liquid crystal concentrating microlens array is located in the electronically controlled liquid crystal astigmatism microlens array. In front of the microlens array, the light incident surface of the electronically controlled liquid crystal concentrating microlens array is exposed through the front opening of the ceramic shell 1, and the light exit surface of the electronically controlled liquid crystal astigmatism microlens array is exposed outside through the back opening of the ceramic shell 1. .

Fig. 3 is a working principle diagram of a hybrid integrated electronically controlled liquid crystal optical switch array according to an embodiment of the present invention. As shown in the figure, the basic functional unit of the optical switch is formed by mixing and integrating the upper and lower layers of liquid crystal micro-optical structures. The upper liquid crystal micro-optical structure is composed of a micron-scale liquid crystal material encapsulated between the top surface micro-hole electrode and the bottom surface common electrode, and the lower liquid crystal micro-optic structure is composed of a micron-scale liquid crystal material encapsulated between the top surface common electrode and the bottom ring micro-hole electrode. It is made of thick liquid crystal material, and the center vertical line of the microhole and ring microhole coincides with the optical axis of the corresponding liquid crystal light-condensing microlens and liquid crystal astigmatism microlens. The electronically controlled liquid crystal concentrating microlens array implements adjustable focus and concentrating operations on the incident beam under the action of electric drive control signals of different mean square amplitudes. It is a liquid crystal phase shift plate that delays the light wave phase in the power-off state; Under the action of electric driving control signals with different mean square amplitudes, the lens array implements astigmatism operation with controllable divergence degree on the incident beam. It is a liquid crystal phase shift plate that delays the light wave phase in the power-off state; the electronically controlled liquid crystal concentrating microlens array The liquid crystal phase shift plate that is converted into a liquid crystal phase shift plate after power-off with the liquid crystal astigmatism microlens array forms an open state of the optical switch, and the electronically controlled liquid crystal astigmatism microlens array and the liquid crystal condensing microlens array are powered off and converted into a liquid crystal phase shift plate to form an optical switch. The closed state of the switch; by separately modulating the light concentrating and astigmatism performances of the electronically controlled liquid crystal concentrating microlens array and the electronically controlled liquid crystal astigmatizing microlens array, the electronically controlled on and off switching of the transmission paths of beams of different intensities is completed.

Both the electronically controlled liquid crystal concentrating microlens array and the electronically controlled liquid crystal astigmatizing microlens array are M×N elements, where M and N are both integers greater than 1. The electronically controlled liquid crystal optical switch array formed by mixing and integrating the electronically controlled liquid crystal concentrating microlens array and the electrically controlled liquid crystal astigmatizing microlens array is also M×N elements. For example, the electronically controlled liquid crystal concentrating microlens array, the electronically controlled liquid crystal astigmatizing microlens array or the electronically controlled liquid crystal optical switch array can be arrays of 3×3 elements, 4×4 elements, 3×4 elements or even larger arrays. The electronically controlled liquid crystal optical switch array is placed between two optical fibers or two optical fiber clusters to complete the on or off operation of the optical fiber pair or the beam transmission path between the optical fiber clusters; The light exit surface is coupled with the optical axis of each access fiber to complete the continuous transmission of light waves between the fibers or the cut-off of the path. In the figure, the refraction concentrating and refraction astigmatism microlenses with conventional curved surface profiles are used to equivalently display the beam bending conditions of the electronically controlled liquid crystal concentrating microlens and the electronically controlled liquid crystal astigmatizing microlens.

Fig. 4 is a schematic diagram of a hybrid integrated electronically controlled liquid crystal optical switch array coupled with an optical fiber cluster to realize the switching on and off of the optical path according to the embodiment of the present invention. As shown in the figure, the upper and lower fiber clusters of 6×6 channels are respectively coupled with the optical switches of 6×6 channels. At this time, the corresponding optical fibers in the upper and lower fiber clusters are arranged on the same optical axis as the corresponding optical switches. When the optical path is turned on, the light beam in the top fiber is guided into the bottom fiber; when the light path is closed, the light beam in the top fiber is diverged by the electronically controlled liquid crystal astigmatism microlens and cannot enter the bottom fiber.

The first port 2 and the first indicator light 3 are arranged on the electronically controlled liquid crystal light-condensing microlens array, wherein the first port 2 is used to input the electric driving control signal loaded on the liquid crystal structure, and the first indicator light 3 is used for To show whether the electric drive control signal is effectively connected, if the electric drive control signal is normally connected, the first indicator light 3 will flicker, otherwise it will go out; the electronically controlled liquid crystal astigmatism microlens array is provided with a second port 4, a second Indicator light 5, wherein the second port 4 is used to input the electric drive control signal loaded on the liquid crystal structure, the second indicator light 5 is used to display whether the electric drive control signal is effectively connected, and the electric drive control signal is normally connected Enter, then the second indicator light 5 flickers, otherwise it goes out.

The first port 2, the second port 4, the first indicator light 3, and the second indicator light 5 are all exposed outside through the = side opening of the ceramic shell 1.

The working process of a hybrid integrated electronically controlled liquid crystal optical switch array according to the embodiment of the present invention will be described below with reference to FIG. 1 , FIG. 2 and FIG. 3 .

First, connect the first port 2 and the second port 4 with a parallel signal line. The electric driving control signal of the liquid crystal structure is sent from the first port 2 and the second port 4 through the parallel signal line. At this time, the first indicator light 3 and the second indicator light 5 are turned on and flashing. After the self-test passes, the first indicator light 3 and the second indicator light 5 are extinguished, and the liquid crystal micro-optical structure in the electronically controlled liquid crystal light switch enters the working state.

The electric driving control signal is sent from the first port 2 through the signal line, and the liquid crystal micro-optical structure is driven to appear as an electronically controlled liquid crystal concentrating microlens array converging light beams. At this time, the first indicator light 3 is turned on and flashes. At the same time, The signal for driving the liquid crystal micro-optical structure loaded on the second port 4 is cut off, the liquid crystal micro-optic structure is converted into a liquid crystal phase shift plate that delays light waves, and the electronically controlled liquid crystal optical switch starts to connect the optical path between the front and rear fiber beams operate. The electric driving control signal is sent from the second port 4 through the signal line, and the liquid crystal micro-optical structure is driven to appear as an electronically controlled liquid crystal astigmatism microlens array with divergent light beams. At this time, the second indicator light 5 is turned on and flashes. At the same time, the loading The signal for controlling the liquid crystal micro-optical structure on the first port 2 is cut off, the liquid crystal micro-optic structure is converted into a liquid crystal phase shift plate that delays light waves, and the optical switch starts to close the optical path between the front and rear fiber beams.

As shown in Figure 3, the unit hybrid integrated electronically controlled liquid crystal optical switch performs the concentrating operation of the incident beam by the electronically controlled liquid crystal concentrating microlens placed on the top of the electronically controlled liquid crystal astigmatism microlens. The astigmatism microlens is converted into the liquid crystal micro-optical structure of the liquid crystal phase shift plate to complete the opening operation of the beam transmission channel of the electronically controlled liquid crystal optical switch; The concentrating microlens is converted into a liquid crystal phase shift plate. At the same time, the liquid crystal structure at the bottom is restored and converted into an electronically controlled liquid crystal astigmatism microlens; The liquid crystal astigmatism microlens is diffused and cannot enter the optical fiber core layer coupled to the light output end of the electronically controlled liquid crystal astigmatism microlens, thereby completing the closing operation of the light transmission path.

The hybrid integrated electronically controlled liquid crystal optical switch array of the present invention adopts the method of mixing and integrating the electronically controlled liquid crystal concentrating microlens array and the electronically controlled liquid crystal astigmatizing microlens array, and implements coupling connection with optical fibers or optical fiber clusters. The light beam transmission path is opened and closed by orderly powering on and powering off the liquid crystal micro-optical structure. It has the characteristics of good polarization adaptability to transmitted light waves, and is suitable for electronically controlled opening and closing between optical fibers or optical cables with a wide spectral range and a large fluctuation range of beam intensity.

Generally speaking, compared with the prior art, the above technical solutions conceived by the present invention are mixed and integrated with the electronically controlled liquid crystal concentrating microlens array and the electronically controlled liquid crystal astigmatism microlens array, and the liquid crystal microlens array is ordered Power on or off to perform optical switching operations; the liquid crystal concentrating and astigmatizing microlens arrays constructed under the excitation of the electric drive control signal are converted into liquid crystal phase shift plates in the power-off state; the electronically controlled liquid crystal microlens array and the liquid crystal The phase shift plate is coupled to form the light control actuator of the optical switch to realize the opening and cutting of the arrayed optical paths. The above switching system has the ability to perform on-off switching of the optical transmission path based on the electric driving control signal, and is suitable for optical fiber or optical cable systems with a wide spectral range and a large fluctuation range of beam intensity. The larger the scale of the liquid crystal light-condensing or astigmatic micro-lens array, the greater the number of optical fibers that the optical switch can couple.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (7)

1. A hybrid integrated electronically controlled liquid crystal optical switch array, comprising an electronically controlled liquid crystal concentrating microlens array and an electronically controlled liquid crystal astigmatism microlens array, is characterized in that, The electronically controlled liquid crystal concentrating microlens array implements an adjustable focusing operation of the incident beam under the action of electric driving control signals of different mean square amplitudes; The electronically controlled liquid crystal concentrating microlens array is converted into a liquid crystal phase shift plate that delays the light wave phase in a power-off state; The electronically controlled liquid crystal astigmatism microlens array implements the controllable divergence degree astigmatism operation of the incident light beam under the action of electric drive control signals with different mean square amplitudes; The electronically controlled liquid crystal astigmatism microlens array is converted into a liquid crystal phase shift plate that delays the light wave phase in a power-off state; The electronically controlled liquid crystal concentrating microlens and the liquid crystal phase shift plate converted into the liquid crystal astigmatism microlens after power-off form an open state of an optical switch; The electronically controlled liquid crystal astigmatism microlens and the liquid crystal phase shift plate converted to the liquid crystal concentrating microlens after power-off form an off state of the optical switch. 2. The hybrid integrated electronically controlled liquid crystal light switch array as claimed in claim 1, is characterized in that, by respectively modulating the light concentrating sum and Astigmatism performance, complete the electronically controlled on and off switching of beams of different intensities. 3. hybrid integrated electronically controlled liquid crystal optical switch array as claimed in claim 1, is characterized in that, described electronically controlled liquid crystal concentrating microlens array and described electronically controlled liquid crystal astigmatism microlens array are M * N element, wherein , M and N are both integers greater than 1, and the filling factor of the electronically controlled liquid crystal focusing microlens and the electronically controlled liquid crystal astigmatizing microlens of each unit is lower than 40%. 4. The hybrid integrated electronically controlled liquid crystal optical switch array as claimed in claim 1, characterized in that, the electronically controlled liquid crystal composed of the electronically controlled liquid crystal concentrating microlens array and the electronically controlled liquid crystal astigmatism microlens array are mixed and integrated. The optical switch array is also M×N elements. 5. The hybrid integrated electronically controlled liquid crystal light switch array according to any one of claims 1 to 4, further comprising a ceramic housing; wherein, The electronically controlled liquid crystal concentrating microlens array and the electronically controlled liquid crystal astigmatism microlens array are sequentially placed in a ceramic housing with the same optical axis, wherein the electronically controlled liquid crystal concentrating microlens array is located in the electronically controlled liquid crystal astigmatism microlens array The front of the lens array, and the optical axis of each unit of electronically controlled liquid crystal concentrating microlens coincides with the optical axis of each unit of electronically controlled liquid crystal astigmatism microlens, and the light incident surface of the electronically controlled liquid crystal concentrating microlens array passes through the front of the ceramic shell The openings are exposed, and the light exit surface of the electronically controlled liquid crystal astigmatism microlens array is exposed outside through the openings on the back of the ceramic shell. 6. The hybrid integrated electronically controlled liquid crystal optical switch array as claimed in claim 5, characterized in that, the electronically controlled liquid crystal focusing microlens array is provided with a first port and a first indicator light, and the electrically controlled liquid crystal The astigmatism microlens array is provided with a second port and a second indicator light; The first port is used to access the electric drive control signal input by external equipment to the liquid crystal concentrating microlens array; The first indicator light is used to indicate whether the liquid crystal concentrating microlens array is in a normal electric drive control signal input state; The second port is used to access the electric drive control signal input by external equipment to the liquid crystal astigmatism microlens array; The second indicator light is used to indicate whether the liquid crystal astigmatism microlens array is in a normal electric driving control signal input state. 7. The hybrid integrated electronically controlled liquid crystal optical switch array as claimed in claim 6, characterized in that a small triangle symbol is provided on the upper side of the upper side of the upper right side of the ceramic shell, which is close to the light exit surface. Indicates the light exit position of the optical switch.