A butterfly-shaped SOA optical device with two input and two output fibers on the same side

Abstract

The present invention relates to a butterfly-shaped SOA optical device with two input and two output fibers on the same side. A polarization-maintaining fiber array, a heat sink, a first roof prism and a second roof prism are fixed in sequence in a tube shell in a direction away from the fiber port. The polarization-maintaining fiber array has two light-incoming polarization-maintaining fibers extending from the fiber port and two light-exiting polarization-maintaining fibers extending from the fiber port. One of the light-incoming polarization-maintaining fibers is coupled to the first roof prism via an SOA chip on the heat sink, and the other light-incoming polarization-maintaining fiber is coupled to the second roof prism via another SOA chip on the heat sink. The first roof prism and the second roof prism are respectively coupled to the two light-exiting polarization-maintaining fibers. The beneficial effect is that due to the use of a rectangular polarization-maintaining fiber array, the polarization-maintaining directions of the light-incoming polarization-maintaining fibers and the light-exiting polarization-maintaining fibers can be easily controlled to be consistent with the SOA chip, and thus the expensive cylindrical tapered lens fiber can be omitted, and the cost is greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of optical devices, and in particular to a butterfly-shaped SOA optical device with two input and two output optical fibers on the same side. Background Art

[0002] The traditional butterfly-shaped SOA optical device is a single-input single-output butterfly-shaped SOA optical device, which includes: a tube shell, the tube shell is butterfly-shaped, and two optical fiber ports are relatively opened on the tube shell, one of the optical fiber ports is inserted with a light-input polarization-maintaining optical fiber, and the other optical fiber port is inserted with a light-output polarization-maintaining optical fiber, and the area outside the tube shell where the light-input polarization-maintaining optical fiber and the light-output polarization-maintaining optical fiber are located is covered with a stress release tube, and a TEC cooler is fixed between the light-input polarization-maintaining optical fiber and the light-output polarization-maintaining optical fiber in the tube shell, one end of the light-input polarization-maintaining optical fiber in the tube shell is fixed to a heat sink through a welding bracket, and one end of the light-output polarization-maintaining optical fiber in the tube shell is fixed to a heat sink through a welding bracket, and the two heat sinks are respectively fixed on the cold surface of the TEC cooler, and an SOA chip is coupled between the light-input polarization-maintaining optical fiber and the light-output polarization-maintaining optical fiber, and the SOA chip is fixed to the cold surface of the TEC cooler through an aluminum nitride heat sink, and a thermistor is fixed on the aluminum nitride heat sink, as shown in detail. Figure 1 As shown, this type of two-input and two-output fiber same-side butterfly SOA optical device has the following defects:

[0003] 1) Since the incoming polarization-maintaining fiber and the outgoing polarization-maintaining fiber are located on both sides of the tube shell, and the bending radius of the incoming polarization-maintaining fiber and the outgoing polarization-maintaining fiber is generally greater than 15 mm, when the butterfly-shaped SOA optical device is used as a module, it takes up a lot of layout space, resulting in layout difficulties;

[0004] 2) Currently, the input polarization-maintaining fiber and the output polarization-maintaining fiber in this type of butterfly SOA optical device use cylindrical conical lens fibers, and the fiber end faces are integrated with lenses, which are costly. In addition, since it is not easy to mark the polarization-maintaining direction of cylindrical polarization-maintaining fibers, it is difficult to align the polarization direction during coupling.

[0005] 3) The incoming polarization-maintaining fiber and the outgoing polarization-maintaining fiber are located on both sides of the tube shell. The length of the polarization-maintaining fiber in the tube shell is too short. Since the polarization-maintaining fiber and the tube shell need to be sealed by brazing process, and the temperature of the polarization-maintaining fiber coupling part is controlled at 25°C, when the temperature of the tube shell is very high, such as reaching above 85°C, the temperature of the polarization-maintaining fiber and the shell brazing is very high, while the temperature of the polarization-maintaining fiber and the SOA chip coupling is very low, which will lead to large thermal stress at the brazing of the polarization-maintaining fiber and the tube shell, and the polarization-maintaining fiber is prone to slight deformation, thereby affecting the optical power stability and optical return loss;

[0006] 4) This type of butterfly SOA optical device does not have backlight monitoring, which is not conducive to the use of SOA modules;

[0007] 5) It has a single-input and single-output. For some special occasions, if you want to realize the input and output of two signals, you need to equip it with two single-input and single-output butterfly SOA optical devices, which takes up a lot of space. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a butterfly-shaped SOA optical device with two input and two output optical fibers on the same side, so as to overcome the deficiencies in the above-mentioned prior art.

[0009] The technical solution of the present invention to solve the above technical problems is as follows: a butterfly-shaped SOA optical device with two input and two output fibers on the same side, comprising: a tube shell, a fiber port is provided on the side wall of the tube shell, a polarization-maintaining fiber array, a heat sink, a first roof prism for turning light by 180 degrees, and a second roof prism for turning light by 180 degrees are fixed in sequence in the tube shell along the direction away from the fiber port, the polarization-maintaining fiber array has two light-incoming polarization-maintaining fibers extending from the fiber port and two light-exiting polarization-maintaining fibers extending from the fiber port, two SOA chips are fixed on the heat sink, one of the two light-incoming polarization-maintaining fibers is coupled to the first roof prism via an SOA chip, the other light-incoming polarization-maintaining fiber is coupled to the second roof prism via another SOA chip, and the first roof prism and the second roof prism are respectively coupled to the two light-exiting polarization-maintaining fibers.

[0010] The beneficial effects of the present invention are:

[0011] In this solution, since the incoming polarization-maintaining fiber and the outgoing polarization-maintaining fiber are output from the same side of the tube shell, half of the fiber bending space can be saved, thereby greatly reducing the difficulty of SOA module layout. In addition, the length of the incoming polarization-maintaining fiber and the outgoing polarization-maintaining fiber in the tube shell can be greatly increased. When the incoming polarization-maintaining fiber and the outgoing polarization-maintaining fiber are sealed with the fiber ports of the tube shell by the brazing process, the thermal stress is greatly reduced, thereby reducing the impact on the optical power and optical return loss.

[0012] Since the present invention has two light-input polarization-maintaining optical fibers, two SOA chips, and two light-output polarization-maintaining optical fibers, two-input and two-output are formed, which is equivalent to two traditional single-input and single-output SOA optical devices being integrated together, saving at least one tube shell, and the overall size is significantly reduced compared with two single-input and single-output SOA optical devices. In the prior art, the conical lens optical fiber is fixed by laser welding because of the small coupling tolerance. The size of the laser welding fixing bracket is very large, so it is impossible to make a double path in one tube shell;

[0013] Since a rectangular polarization-maintaining fiber array is used, it is easy to control the polarization-maintaining directions of the incoming polarization-maintaining fiber and the outgoing polarization-maintaining fiber to be consistent with the SOA chip, and coupling is very convenient. As a result, instead of using expensive cylindrical conical lens fibers, ordinary end-face polarization-maintaining fibers and ordinary lenses can be used, which greatly reduces costs.

[0014] Based on the above technical solution, the present invention can also be improved as follows.

[0015] Furthermore, a TEC cooler is fixed in the tube shell, and the polarization-maintaining optical fiber array, the heat sink, the first roof prism and the second roof prism are respectively fixed on the cold surface of the TEC cooler.

[0016] The above further beneficial effects are: the TEC cooler can dissipate heat from the devices thereon. Since the lengths of the input polarization-maintaining optical fiber and the output polarization-maintaining optical fiber in the tube shell are greatly lengthened, and the polarization-maintaining optical fiber array is fixed on the cold surface of the TEC cooler, the deformation of the optical fiber does not affect the stability of the coupled optical path and the optical return loss. In addition, the length of the TEC cooler in this solution is greatly reduced, thereby reducing the cost.

[0017] Furthermore, the polarization-maintaining optical fiber array is fixed on the cold surface of the TEC cooler by bonding.

[0018] Furthermore, the end face of the polarization-maintaining fiber array at the optical port is an 8° face, and two MPD chips are fixed on the cold surface of the TEC cooler. The two MPD chips are used to receive stray light reflected by the two light-emitting polarization-maintaining optical fibers respectively.

[0019] The above further beneficial effect is as follows: since the end face of the optical port side of the output polarization-maintaining optical fiber array can be designed as an 8° face, backlight monitoring can be achieved by adding an MPD chip to receive stray light reflected by the output polarization-maintaining optical fiber, while the tapered lens optical fiber cannot achieve this purpose. Adding backlight monitoring is conducive to the use of the SOA module (i.e., a module with an SOA driving circuit and a TEC control circuit). The SOA module monitors the optical power and can well control the optical power output range.

[0020] Furthermore, a thermistor is fixed on the heat sink.

[0021] A further beneficial effect of the above is that the thermistor is used to monitor the temperature of the SOA chip so that the TEC cooler can adjust the working power.

[0022] Furthermore, on the cold surface of the TEC cooler, a non-spherical lens and a first polarization-independent optical isolator are sequentially coupled between each light-incoming polarization-maintaining optical fiber and each SOA chip along the light propagation direction.

[0023] Furthermore, a collimating lens and a second polarization-independent optical isolator are coupled in sequence between one of the two SOA chips and the first roof prism along the light propagation direction, and a collimating lens and a second polarization-independent optical isolator are coupled in sequence between the other SOA chip and the second roof prism along the light propagation direction, the collimating lens is fixed on the cold surface of the TEC refrigerator, and the second polarization-independent optical isolator is fixed on the side of the first roof prism or the second roof prism.

[0024] Furthermore, a converging lens is coupled between the first roof prism and one of the two polarization-maintaining optical fibers, and a converging lens is coupled between the second roof prism and the other polarization-maintaining optical fiber. The converging lens is fixed on the cold surface of the TEC refrigerator.

[0025] The beneficial effects of adopting the above three steps are: due to the discrete lenses (aspherical lens, collimating lens and converging lens), the coupling tolerance is larger than that of tapered lens optical fiber, and the optical path is more stable. In addition, adding a polarization-independent optical isolator to the optical path can ensure the stability of the optical path and the optimal optical return loss performance.

[0026] Furthermore, the light-incoming polarization-maintaining optical fiber and the optical fiber port of the tube shell are sealed by a brazing process, and the light-outgoing polarization-maintaining optical fiber and the optical fiber port of the tube shell are sealed by a brazing process.

[0027] Furthermore, the heat sink is made of aluminum nitride and the tube shell is butterfly-shaped. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a top view of a butterfly-shaped SOA optical device with two input and two output optical fibers on the same side in the prior art;

[0029] Figure 2 A top view of a butterfly-shaped SOA optical device with two input and two output optical fibers on the same side of the present invention;

[0030] Figure 3 This is a structural diagram of the MPD chip involved in the present invention.

[0031] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0032] 1. Shell and tube, 2. Polarization-maintaining fiber array, 210. Light-input polarization-maintaining fiber, 220. Light-output polarization-maintaining fiber, 3. Heat sink, 4. First roof prism, 5. Second roof prism, 6. SOA chip, 7. TEC cooler, 8. MPD chip, 9. Thermistor, 10. Aspherical lens, 11. First polarization-independent optical isolator, 12. Collimating lens, 13. Second polarization-independent optical isolator, 14. Converging lens. DETAILED DESCRIPTION

[0033] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0034] Example 1

[0035] like Figure 2As shown, a butterfly-shaped SOA optical device with two input and two output fibers on the same side comprises: a tube shell 1, a fiber port is provided on the side wall of the tube shell 1, that is, in this solution, the tube shell 1 has only one fiber port, a polarization-maintaining fiber array 2, a heat sink 3, a first roof prism 4 for turning light by 180°, and a second roof prism 5 for turning light by 180° are fixed in sequence in the tube shell 1 in a direction away from the fiber port, the polarization-maintaining fiber array 2 has two light-incoming polarization-maintaining fibers 210 and two light-exiting polarization-maintaining fibers 220, the two light-incoming polarization-maintaining fibers 210 extend from the fiber port, and the two light-exiting polarization-maintaining fibers 220 extend from the fiber port, that is, the light-incoming polarization-maintaining fibers 210 and the light-exiting polarization-maintaining fibers 220 exit from the same side of the tube shell 1, and are two-incoming and two-exiting;

[0036] Two SOA chips 6 are fixed on the heat sink 3, one of the two incoming polarization-maintaining optical fibers 210 is coupled to the first roof prism 4 via one SOA chip 6, the other of the two incoming polarization-maintaining optical fibers 210 is coupled to the second roof prism 5 via another SOA chip 6, the first roof prism 4 is coupled to one of the two outgoing polarization-maintaining optical fibers 220, and the first roof prism 4 is coupled to the other of the two outgoing polarization-maintaining optical fibers 220;

[0037] For the first incoming light beam, it is incident on one of the incoming polarization-maintaining optical fibers 210 to a SOA chip 6 coupled thereto, and then incident on the first roof prism 4 from the SOA chip 6, and after the light is turned 180° by the first roof prism 4, it is incident on one of the outgoing polarization-maintaining optical fibers 220;

[0038] For the second incoming light, it is incident on an SOA chip 6 coupled with it through another incoming light polarization-maintaining fiber 210, and then incident on the second roof prism 5 through the SOA chip 6, and the light is turned 180° by the second roof prism 5 before being incident on another outgoing light polarization-maintaining fiber 220;

[0039] In this solution, since the incoming polarization-maintaining optical fiber 210 and the outgoing polarization-maintaining optical fiber 220 are output from the same side of the tube shell 1, half of the optical fiber bending space can be saved, thereby greatly reducing the difficulty of SOA module layout. In addition, the length of the incoming polarization-maintaining optical fiber 210 and the outgoing polarization-maintaining optical fiber 220 in the tube shell 1 can be greatly increased. When the incoming polarization-maintaining optical fiber 210 and the outgoing polarization-maintaining optical fiber 220 are sealed with the optical fiber port of the tube shell 1 by the brazing process, the thermal stress is greatly reduced, thereby reducing the influence on the optical power and optical return loss.

[0040] Since the present invention has two light-input polarization-maintaining optical fibers 210, two SOA chips 6, and two light-output polarization-maintaining optical fibers 220, two-input and two-output are formed, which is equivalent to two traditional single-input and single-output SOA optical devices being integrated together, saving at least one tube shell 1, and the overall size is significantly reduced compared with two single-input and single-output SOA optical devices. In the prior art, the conical lens optical fiber is fixed by laser welding because of the small coupling tolerance. The size of the laser welding fixing bracket is very large, so it is impossible to make a double path in one tube shell;

[0041] In addition, optical communication is usually in multiples of 2. If the design is three-input and three-output, the existing butterfly device shell cannot be used and needs to be re-molded. In addition, the existing shell size, especially the size of the round screw holes at the four corners, is standardized. If it is changed, many materials will have to be re-developed and designed when the user uses it.

[0042] Since a rectangular polarization-maintaining fiber array 2 is used, it is convenient to control the polarization-maintaining directions of the incoming polarization-maintaining fiber 210 and the outgoing polarization-maintaining fiber 220 to be consistent with the SOA chip 6, and coupling is very convenient. As a result, instead of using expensive cylindrical conical lens fibers, ordinary end-face polarization-maintaining fibers and ordinary lenses can be used, thereby significantly reducing costs.

[0043] Example 2

[0044] like Figure 2 As shown, this embodiment is a further improvement on the basis of embodiment 1, and the details are as follows:

[0045] A TEC cooler 7 is fixed in the tube shell 1, and the polarization-maintaining fiber array 2, the heat sink 3, the first roof prism 4 and the second roof prism 5 are respectively fixed on the cold surface of the TEC cooler 7. The polarization-maintaining fiber array 2 can be fixed on the cold surface of the TEC cooler 7 by bonding, and the TEC cooler 7 can dissipate heat from the devices thereon. Since the lengths of the incoming polarization-maintaining fiber 210 and the outgoing polarization-maintaining fiber 220 in the tube shell 1 are greatly lengthened, and the polarization-maintaining fiber array 2 is fixed on the cold surface of the TEC cooler 7, the deformation of the optical fiber does not affect the stability and optical return loss of the coupled optical path. In addition, the length of the TEC cooler 7 in this solution is greatly reduced, thereby reducing the cost.

[0046] Example 3

[0047] like Figure 3 As shown, this embodiment is a further improvement on the basis of embodiment 2, and the details are as follows:

[0048] The end face on the optical port side of the polarization-maintaining fiber array 2 is an 8° surface. Two MPD chips 8 are fixed on the cold surface of the TEC cooler 7. The two MPD chips 8 are respectively used to receive stray light reflected by the two output polarization-maintaining optical fibers 220. Since the end face on the optical port side of the output polarization-maintaining optical fiber array 2 can be designed as an 8° surface, the MPD chip 8 can be added to receive the stray light reflected by the output polarization-maintaining optical fiber 220 to achieve backlight monitoring. The conical lens optical fiber cannot achieve this purpose. Adding backlight monitoring is conducive to the use of the SOA module (i.e., a module with an SOA driving circuit and a TEC control circuit). The SOA module monitors the optical power and can well control the optical power output range.

[0049] Example 4

[0050] like Figure 2 As shown, this embodiment is a further improvement on the basis of embodiment 1, and the details are as follows:

[0051] A thermistor 9 is fixed on the heat sink 3 , and the thermistor 9 is used to monitor the temperature of the SOA chip 6 , so that the TEC cooler 7 can adjust the working power and reduce energy consumption.

[0052] Example 5

[0053] like Figure 2 As shown, this embodiment is a further improvement on any one of Embodiments 2 to 4, and the details are as follows:

[0054] On the cold surface of the TEC cooler 7, an aspheric lens 10 and a first polarization-independent optical isolator 11 are coupled in sequence along the light propagation direction between each incoming polarization-maintaining optical fiber 210 and each SOA chip 6, and the light from the incoming polarization-maintaining optical fiber 210 passes through the aspheric lens 10 and the first polarization-independent optical isolator 11 in sequence and then is incident on the SOA chip 6 coupled thereto.

[0055] In addition, a collimating lens (12) and a second polarization-independent optical isolator 13 are coupled in sequence between one of the two SOA chips 6 and the first roof prism 4 along the light propagation direction, and a collimating lens 12 and a second polarization-independent optical isolator 13 are coupled in sequence between the other of the two SOA chips 6 and the second roof prism 5 along the light propagation direction, the collimating lens 12 is fixed on the cold surface of the TEC cooler 7, and the second polarization-independent optical isolator 13 is fixed on the side of the first roof prism 4 or the second roof prism 5.

[0056] The light from one of the two SOA chips 6 passes through a collimating lens 12 and a second polarization-independent optical isolator 13 in sequence and then is incident on the first roof prism 4, while the light from the other of the two SOA chips 6 passes through a collimating lens 12 and a second polarization-independent optical isolator 13 in sequence and then is incident on the second roof prism 5.

[0057] A converging lens 14 is coupled between the first roof prism 4 and one of the two polarization-maintaining optical fibers 220, and a converging lens 14 is coupled between the second roof prism 5 and the other of the two polarization-maintaining optical fibers 220. The converging lens 14 is fixed on the cold surface of the TEC refrigerator 7. The first roof prism 4 deflects the light 180° and then injects it into one of the two polarization-maintaining optical fibers 220 through a converging lens 14. The second roof prism 5 deflects the light 180° and then injects it into the other of the two polarization-maintaining optical fibers 220 through a converging lens 14.

[0058] Because they are discrete lenses (aspherical lens, collimating lens and converging lens), the coupling tolerance is larger than that of tapered lens fiber, and the optical path is more stable. In addition, adding a polarization-independent optical isolator to the optical path can ensure the optimal stability of the optical path and optical return loss performance.

[0059] The light-incoming polarization-maintaining optical fiber 210 and the optical fiber port of the tube shell 1 are sealed by brazing, and the light-outgoing polarization-maintaining optical fiber 220 and the optical fiber port of the tube shell 1 are sealed by brazing. The heat sink 3 is preferably made of aluminum nitride, and the tube shell 1 is butterfly-shaped.

[0060] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A butterfly-shaped SOA optical device with two input and two output fibers on the same side, characterized in that: include: A tube shell (1), wherein a fiber port is provided on a side wall of the tube shell (1), wherein a rectangular polarization-maintaining fiber array (2), a heat sink (3), a first roof prism (4) for redirecting light by 180 degrees, and a second roof prism (5) for redirecting light by 180 degrees are fixed in sequence in the tube shell (1) in a direction away from the fiber port, wherein the polarization-maintaining fiber array (2) comprises two light-incoming polarization-maintaining fibers (210) extending from the fiber port and two light-outgoing polarization-maintaining fibers (220) extending from the fiber port, wherein two SOA chips (6) are fixed on the heat sink (3), and the two light-incoming polarization-maintaining fibers (210) and the two light-outgoing polarization-maintaining fibers (220) are fixed on the heat sink (3). One of the optical fibers (210) is coupled to a first roof prism (4) via an SOA chip (6), and the other optical fiber (210) is coupled to a second roof prism (5) via another SOA chip (6). The first roof prism (4) and the second roof prism (5) are respectively coupled to two light-emitting polarization-maintaining optical fibers (220). The second roof prism (5) and the first roof prism (4) are overlapped and distributed front to back. The light-incoming polarization-maintaining optical fiber (210) and the light-emitting polarization-maintaining optical fiber (220) both use polarization-maintaining optical fibers with common end faces and common lenses.

2. The two-input and two-output fiber same-side butterfly SOA optical device according to claim 1, characterized in that: A TEC cooler (7) is fixed in the tube shell (1), and the polarization-maintaining optical fiber array (2), the heat sink (3), the first roof prism (4) and the second roof prism (5) are respectively fixed on the cold surface of the TEC cooler (7).

3. The two-input and two-output fiber same-side butterfly SOA optical device according to claim 2, characterized in that: The polarization-maintaining optical fiber array (2) is fixed on the cold surface of the TEC refrigerator (7) by bonding.

4. The two-input and two-output fiber same-side butterfly SOA optical device according to claim 2, characterized in that: The end face of the polarization-maintaining optical fiber array (2) on the optical port side is an 8° face, and two MPD chips (8) are fixed on the cold surface of the TEC cooler (7), and the two MPD chips (8) are respectively used to receive stray light reflected by the two light-emitting polarization-maintaining optical fibers (220).

5. The two-input and two-output fiber same-side butterfly SOA optical device according to claim 1, characterized in that: A thermistor (9) is fixed on the heat sink (3).

6. The two-input and two-output fiber same-side butterfly SOA optical device according to claim 2, characterized in that: On the cold surface of the TEC cooler (7), an aspheric lens (10) and a first polarization-independent optical isolator (11) are sequentially coupled between each incoming polarization-maintaining optical fiber (210) and each SOA chip (6) along the light propagation direction.

7. The two-input and two-output fiber same-side butterfly SOA optical device according to claim 2, characterized in that: A collimating lens (12) and a second polarization-independent optical isolator (13) are sequentially coupled between one of the two SOA chips (6) and the first roof prism (4) along the light propagation direction, and a collimating lens (12) and a second polarization-independent optical isolator (13) are sequentially coupled between the other SOA chip (6) and the second roof prism (5) along the light propagation direction, the collimating lens (12) is fixed on the cold surface of the TEC refrigerator (7), and the second polarization-independent optical isolator (13) is fixed on the side of the first roof prism (4) or the second roof prism (5).

8. The two-input and two-output fiber same-side butterfly SOA optical device according to claim 2, characterized in that: A converging lens (14) is coupled between the first roof prism (4) and one of the two light-emitting polarization-maintaining optical fibers (220), and a converging lens (14) is coupled between the second roof prism (5) and the other light-emitting polarization-maintaining optical fiber (220), and the converging lens (14) is fixed on the cold surface of the TEC refrigerator (7).

9. The two-input and two-output fiber same-side butterfly SOA optical device according to claim 1, characterized in that: The light-incoming polarization-maintaining optical fiber (210) and the optical fiber port of the tube shell (1) are sealed by a brazing process, and the light-outgoing polarization-maintaining optical fiber (220) and the optical fiber port of the tube shell (1) are sealed by a brazing process.

10. The two-input and two-output fiber same-side butterfly SOA optical device according to claim 1, characterized in that: The heat sink (3) is made of aluminum nitride, and the tube shell (1) is butterfly-shaped.

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