JP2011186170A - Optical component - Google Patents

Abstract

In an optical module for housing an optical element chip configured by associating and connecting a PLC and another waveguide type optical element in a package, it is possible to suppress a decrease in optical and mechanical reliability due to thermal stress. .
An optical module includes an optical element chip in which first and second PLCs are connected to both ends of a GaN optical modulator, and a convex portion in which the GaN optical modulator is fixed. And a package 320 having 320A. The material of the package 320 can be selected so that the thermal expansion coefficient is suitable for both the GaN-based optical modulator and the PLC. In such a case, in addition to the GaN-based optical modulator 311, the first and second The second PLCs 312 and 313 can also be fixed to the convex portion 320 </ b> A of the package 320. For example, as a material of the package 320, Kovar having a thermal expansion coefficient of about 5.3 × 10 ⁻⁶ / K can be used.
[Selection] Figure 3

Description

  The present invention relates to an optical component, and more particularly to an optical component in which an optical element chip configured by associating and connecting a PLC and another waveguide type optical element is housed in a package.

An LN modulator in which an optical waveguide is formed on a lithium niobate (LN) substrate using titanium (Ti) diffusion is an important device of an optical communication system. For example, a DQPSK modulator for 40 Gbit / s and a 100 Gbit / s Development of a polarization multiplexed QPSK modulator for use is underway. However, the LN modulator has a drawback that the propagation loss and the allowable bending radius are larger than those of the PLC, and is unsuitable for the configuration of a complicated optical circuit such as a variable coupler, folding, and polarization combining circuit. Here, “PLC” refers to a quartz lightwave circuit in which an optical waveguide mainly composed of SiO ₂ glass is formed on a Si substrate.

  In order to compensate for the disadvantages of the LN modulator, a conventional example in which an optical modulator (hereinafter referred to as “PLC-LN modulator”) combining an LN modulator and a PLC as shown in FIG. (See Patent Documents 1 and 2). In FIG. 1, the LN modulator 120 is used only for the phase shifter portion, and the first and second PLCs 110 and 130 connected to both ends of the LN modulator 120 are used for the optical waveguide for routing. For this reason, the characteristics of the passive circuit excellent in PLC can be utilized while maintaining the excellent characteristics of the LN modulator. For example, the entire circuit can be reduced in size or the overall loss can be reduced.

  The mounting technology for hermetically sealing the modulator in a casing (package) has a great influence on the reliability of the PLC-LN modulator, and research for higher reliability is underway. FIG. 2 shows an optical module (optical component) in which a conventional PLC-LN modulator is housed in a package. The optical module 200 includes a PLC-LN modulator 210 in which the first and second PLCs 212 and 213 are butt-connected (butt jointed) to both ends of the LN modulator 211, and a convex portion 220A to which the LN modulator 211 is fixed. And a fiber 231 connected to the first PLC 212 via the first fiber block 214 and a fiber 232 connected to the second PLC 213 via the second fiber block 215.

  The material of the package 220 is stainless steel, such as SUS303, to reduce the difference in thermal expansion coefficient from that of LN. Although there is a large difference in thermal expansion coefficient between the PLC and the SUS 303, the first and second PLCs 212 and 213 are floating from the package 220, and thermal stress due to the difference in thermal expansion is suppressed. As a result, the stress on the LN modulator 211 itself, the connection between the LN modulator 211 and the first and second PLCs 212 and 213, and the like are suppressed, and the optical and mechanical reliability is improved. Table 1 shows the thermal expansion coefficients of the components of the optical module 200.

JP 2003-195239 A JP 2003-121806 A

  However, in the structure of FIG. 2, the first and second PLCs 212 and 213 are not fixed to the package 220. Therefore, when mechanical vibration or impact is applied in the direction perpendicular to the light beam direction, the first and second PLCs 212 and 213 are not fixed. 2 PLCs 212 and 213 may fluctuate in the vertical direction, possibly causing destruction. Also, this direction is the direction that most affects the coupling loss at the connection between the LN modulator and the PLC, and vertical fluctuations cause deterioration of optical characteristics. In addition, in the case of a TO effect device in which a heater is attached to the first or second PLC 212, 213, heat dissipation is poor, and the temperature between each waveguide is low for the TO effect device using the refractive index difference between optical waveguides. There is a problem that the difference cannot be obtained and the device characteristics are adversely affected. In addition, the temperature rising / falling speed is also limited, and high-speed response becomes difficult.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical element chip in which an optical element chip formed by connecting a PLC and another waveguide type optical element in a package is housed in a package. In the module, it is intended to suppress a decrease in optical and mechanical reliability due to thermal stress.

  In order to achieve such an object, according to a first aspect of the present invention, there is provided an optical element chip in which first and second PLCs are butt-connected to both ends of a GaN-based waveguide optical element, and the GaN-based waveguide. And a package having a convex portion to which the first or second PLC is at least partially fixed. A thermal expansion coefficient of the material of the package is the GaN-based waveguide. The optical element is selected so as to fit both the first optical element and the first and second PLCs.

  According to a second aspect of the present invention, in the first aspect, the material of the package is any one of Kovar, copper tungsten alloy, alumina, and aluminum nitride.

  According to a third aspect of the present invention, in the second aspect, the GaN-based waveguide optical element is formed on a GaN substrate.

  According to a fourth aspect of the present invention, in the second aspect, the GaN-based waveguide optical element is formed on a sapphire substrate.

  According to the present invention, in an optical module in which an optical element chip configured by associating and connecting a PLC and a GaN-based waveguide optical element is housed in a package, the thermal expansion coefficient of the material of the package is expressed as a GaN-based waveguide. Optical and mechanical reliability due to thermal stress by selecting to fit both the optic waveguide and PLC, and by fixing the PLC at least partially on the convex part of the package in addition to the GaN-based waveguide optic Deterioration can be suppressed.

It is a figure which shows the conventional PLC-LN modulator. It is a figure which shows the optical module with which the conventional PLC-LN modulator was accommodated in the package. It is a figure which shows the optical module which concerns on this invention. It is a figure which shows the Example at the time of connecting the GaN-type modulator formed on the sapphire substrate with PLC. It is a figure which shows the Example at the time of connecting the GaN-type modulator formed on the GaN substrate with PLC.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 3 shows an optical module according to the present invention. The optical module 300 is a package having an optical element chip 310 in which the first and second PLCs 312 and 313 are butt-connected to both ends of the GaN-based optical modulator 311 and a convex portion 320A to which the GaN-based optical modulator 311 is fixed. 320 and a first fiber 331 connected to the first PLC 312 via the first fiber block 314 and a second fiber 332 connected to the second PLC 313 via the second fiber block 315. Prepare. Here, the “GaN-based optical modulator” refers to an optical modulator using a group III nitride semiconductor AlN, GaN, InN and a ternary or quaternary mixed crystal thereof as a material. The group III nitride semiconductor has a wurtzite structure as the most stable crystal structure, and is known as a direct transition type wide gap semiconductor. A device using a difference in refractive index and band gap is manufactured by combining mixed crystals such as AlGaN and InGaN with GaN at the center. Therefore, here, an optical modulator composed of these group III nitride semiconductors is referred to as “ It is called a “GaN-based light modulator”.

The GaN optical modulator has almost the same refractive index as that of the LN modulator and has little connection loss with the PLC. In addition, the difference in thermal expansion coefficient from the PLC regardless of whether the sapphire substrate is used or the GaN substrate is LN modulated. It is much smaller than the case of the vessel. Therefore, unlike the conventional example of FIG. 2, it is possible to select the material of the package 320 so that the thermal expansion coefficient matches both the GaN-based optical modulator and the PLC, and when such a material is selected. In addition to the GaN-based optical modulator 311, the first and second PLCs 312 and 313 can also be fixed to the convex portion 320 </ b> A of the package 320. For example, as a material of the package 320, Kovar having a thermal expansion coefficient of about 5.3 × 10 ⁻⁶ / K can be used. Since the difference in thermal expansion coefficient between the package 320 and the optical element chip 310 is small, the characteristic fluctuation due to strain is small, and the possibility of mechanical destruction is small. Furthermore, in the case of a TO effect device in which a heater is attached to the first or second PLC 312, 313, the heat dissipation is improved. Table 2 shows the thermal expansion coefficient and refractive index of the components of the optical module 300 according to the present invention. The value of LN is also shown for reference.

Note that the thermal expansion coefficient of the GaN-based optical modulator is sufficiently thick compared to the thickness of the various nitride semiconductor layers that make up the optical modulator. It becomes dominant and can be approximated by the value of the material. PLC have also been similarly configured by depositing SiO ₂ based glass on a Si substrate, since there is sufficient thickness of the thicker Si substrate compared to the SiO ₂ glass can be approximated by the thermal expansion coefficient of the Si substrate.

In addition to Kovar as a package material, for example, the thermal conductivity is as high as about 180 W / (m · K) (Kovar thermal conductivity: 17 W / (m · K)), and a copper tungsten alloy (Cu ₁₀ W ₉₀ : thermal expansion coefficient of 6.5 × 10 ⁻⁶ / K) can be used. When using a device that generates heat, such as introducing a TO effect device into the PLC, a material with high heat dissipation can improve characteristics such as speeding up and stabilizing the response. A ceramic material such as alumina (thermal expansion coefficient: 6.7 × 10 ⁻⁶ / K) or aluminum nitride (thermal expansion coefficient: 4.5 × 10 ⁻⁶ / K) can also be used for the package material. Alumina is used for semiconductor laser packages, etc. by applying electrical wiring to the laminated ceramic, and a low-cost package can be realized. Furthermore, by making the electrical wiring suitable for high-frequency signal propagation, a small high-frequency package that does not use a high-frequency connector and can be mounted at high density can be manufactured. Aluminum nitride has the same high thermal conductivity as copper tungsten (aluminum nitride thermal conductivity:> 200 W / (m · K), alumina thermal conductivity: 17 W / (m · K)), and when using devices that generate heat In addition, it is possible to improve characteristics such as speeding up and stabilizing the response.

In addition, since GaN has a stronger crystal than semiconductor optical devices such as InP and GaAs, the device is not destroyed even if it is batted with PLC or fiber. When aligning a butt connection with a PLC, a semiconductor optical device such as InP or GaAs is easily damaged due to a difference in hardness from Si or SiO ₂ glass constituting the PLC and cannot be connected. .

  In the above description, the GaN-based optical modulator has mainly been considered as a waveguide-type optical element that is butt-connected to the PLC. However, the present invention is not limited to the optical modulator, and the GaN-based waveguide-type optical element is used. Note that it is applicable to devices.

  FIG. 3 shows that the first and second PLCs 312 and 313 are both fixed to the convex portion 320A. However, the effect of the present invention is that of the first and second PLCs 312 and 313. Such a mode is also encompassed by the present invention since it can be obtained if is fixed at least partially. When connecting a strain-sensitive PLC, the PLC portion may be loosely fixed or left unfixed.

  FIG. 4 is a diagram showing an embodiment in which a GaN-based modulator formed on a sapphire substrate is connected to a PLC. Although the GaN-based optical modulator can have a bending radius smaller than that of the PLC, it has a disadvantage that it has a large propagation loss and is unsuitable for a complicated optical circuit configuration such as an optical coupling / branching unit, a variable coupler, and a polarization beam combining circuit. In FIG. 4, a GaN-based optical modulator is used only for the phase shifter, and first and second PLCs connected to both ends of the GaN-based optical modulator are used for the optical waveguide for routing. For this reason, the characteristics of the excellent passive circuit of the PLC can be utilized while maintaining the excellent characteristics of the GaN-based optical modulator. For example, the entire circuit can be reduced in size or the overall loss can be reduced.

  The optical modulator 400 includes an optical element chip 410, a package 420 surrounding the optical element chip 410, a radio frequency (RF) connector 421 provided in the package 420, and a GaN-based light that constitutes the RF connector 421 and the optical element chip 410. High-frequency electrical wiring 430 between the high-frequency electrode 411A of the modulator 411 is provided. 4 further shows a DC connector 422 provided in the package 420, and a DC electrode wiring 440 between the DC connector 422 and the DC electrode 411B of the optical element chip 410.

  A high-frequency voltage signal is applied to the high-frequency electrode 411A on the GaN-based optical modulator 411 through the high-frequency electrical wiring 430 and the RF connector 421. As the applied voltage changes, the refractive index of the optical waveguide on the GaN-based optical modulator 411 changes and the phase of the light changes. By controlling the phase of the light, the light from the two optical waveguides is interfered to modulate the light intensity, or the phase of the light is changed by 0 and π to operate as an optical modulator that performs phase modulation. be able to. At this time, since the high-frequency voltage signal applied to the light propagating through the optical waveguide on the GaN-based optical modulator 411 needs to match the phases of the light and the electric signal, the high-frequency electric wiring 430 is connected from the RF connector 421. The length to reach the high-frequency electrode 411A through is necessary to be precisely controlled.

  FIG. 5 is a diagram showing an embodiment when a GaN-based modulator formed on a GaN substrate is connected to a PLC. The difference from FIG. 4 is that the substrate is made of GaN instead of sapphire, and the GaN substrate can be used as a cladding layer of the GaN-based optical modulator 511. In a GaN-based optical modulator using a GaN substrate as a cladding layer, the mode field can be easily expanded by making the core layer InGaN having a refractive index higher than that of GaN.

  When a GaN-based modulator is manufactured on a sapphire substrate, the light does not spread in the sapphire substrate having a large refractive index difference from GaN, so that the mode field is limited to the epitaxial thickness of the semiconductor crystal. Epitaxial growth of a GaN-based semiconductor material on a sapphire substrate is difficult to grow thick due to a difference in lattice constant, and has a thickness of about 4 to 5 μm. For this reason, the mode field diameter also expands only to about 4 to 5 μm. In order to perform low-loss optical coupling with an optical fiber or PLC, it is desirable to expand the mode field diameter to about 8 μm, which is the same as that of the fiber, and the GaN-based optical modulator formed on the sapphire substrate cannot reduce the coupling loss. It becomes a problem.

  On the other hand, a GaN-based optical modulator formed on a GaN substrate can spread light to the substrate by using InGaN having a higher refractive index than GaN as a core layer and GaN as a cladding layer. For this reason, the mode field diameter of light can be enlarged without being limited by the epitaxial thickness. Furthermore, epitaxial growth of a GaN-based semiconductor material on a GaN substrate has less difference in lattice constant than growth on a sapphire substrate, and high-quality and thick crystal growth can be performed.

  Therefore, in the GaN-based optical modulator formed on the GaN substrate, the mode field diameter can be expanded to about 8 μm, which is the same as that of the optical fiber or the PLC, and the optical coupling loss due to the mismatch of the mode field diameter is extremely small. It becomes possible to suppress.

300 Optical module (corresponding to “optical components”)
310 optical element chip 311 GaN optical modulator (corresponding to “GaN waveguide optical element”)
312 First PLC
313 Second PLC
314 1st fiber block 315 2nd fiber block 320 Package 320A Convex part 331 1st fiber 332 2nd fiber 400 Optical module (corresponding to “optical component”)
410 optical element chip 411 GaN optical modulator (corresponding to “GaN waveguide optical element”)
411A High frequency electrode 411B DC electrode 412 First PLC
413 Second PLC
420 Package 420A RF Connector 420B DC Connector 430 High Frequency Electrical Wiring 440 DC Electrical Wiring

Claims (4)

An optical element chip in which first and second PLCs are butt-connected to both ends of a GaN-based waveguide optical element;
A package having a convex portion to which the GaN-based waveguide type optical element is fixed and the first or second PLC is at least partially fixed;
An optical component characterized in that a thermal expansion coefficient of the material of the package is selected so as to match both the GaN-based waveguide type optical element and the first and second PLCs.   The optical component according to claim 1, wherein a material of the package is any one of Kovar, copper tungsten alloy, alumina, and aluminum nitride.   The optical component according to claim 2, wherein the GaN-based waveguide type optical element is formed on a GaN substrate.   The optical component according to claim 2, wherein the GaN-based waveguide type optical element is formed on a sapphire substrate.

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