Optical modulator and optical transmitting device using the optical modulator

Abstract

The present invention provides an optical modulator that reduces transmission losses from the driving circuit element to the modulation substrate. The optical modulator houses a modulation substrate (1) and a driving circuit element (2) within a housing (3). The modulation substrate (1) has an optical waveguide (200) and a modulation electrode (10) for modulating light waves propagating in the optical waveguide. The driving circuit element (2) generates a modulation signal applied to the modulation electrode (10). The optical modulator is characterized in that an output terminal (20') for outputting the modulation signal is provided on the upper surface side of the driving circuit element (2), and a wiring board (4) is arranged across the upper sides of the driving circuit element (2) and the modulation substrate (1). The wiring board (4) has wiring that electrically connects the output terminal (20') to the modulation electrode (10).

Description

Technical Field

[0001] The present invention relates to an optical modulator and an optical transmitting apparatus using the optical modulator, and particularly to an optical modulator having a modulation substrate and a driving circuit element housed within a housing, the modulation substrate having an optical waveguide and a modulation electrode for modulating an optical wave propagating in the optical waveguide, and the driving circuit element generating a modulation signal applied to the modulation electrode. Background Technology

[0002] In the fields of optical communication and optical measurement, optical modulators utilizing a modulation substrate are widely used. This modulation substrate has an optical waveguide and a modulation electrode, which modulates the light wave propagating in the optical waveguide. Recent advancements in the miniaturization and low-power consumption of optical modulators, such as those shown in Patent Document 1, have led to continuous progress in the development of optical modulators that integrate an InP semiconductor power / optical conversion element chip (modulation substrate) and a driver IC (driver circuit element) within the same housing.

[0003] Furthermore, due to the requirement for broadband, the modulation signal has become microwave above 60 GHz. When the driving circuit elements are connected to the modulation substrate by existing wire bonding, the high-frequency characteristics deteriorate due to the increase in inductive component.

[0004] Previously, the modulation signals used to drive optical modulators were differential signals and single-ended signals. While differential signals are noise-resistant and effective for long wiring, they tend to suffer from significant transmission losses due to wiring design limitations. On the other hand, while single-ended signals are more susceptible to external noise, they offer advantages such as ease of design, shorter wiring lengths, and reduced transmission losses.

[0005] Due to advancements in digital signal processing technology in recent years, digital signal processors (DSPs) are increasingly used in optical transmission devices. Because DSPs operate with small signals, they require improved tolerance to noise from other devices, and differential signals are frequently used for modulation.

[0006] The modulated signal output from the DSP is routed using a differential signal to a drive circuit element housed within the optical modulator housing. This drive circuit element is configured to combine signal amplifiers into multiple stages, and the output signal utilizes a high-quality differential signal when the transmission line wiring length is long. Therefore, because multiple signals are routed from the drive circuit element to the modulation substrate, the wiring length also increases. This results in a deterioration in the transmission loss of the modulated signal.

[0007] On the other hand, due to the widening of bandwidth, it is necessary to wire the modulated signal amplified by the driving circuit elements to the electro-optical conversion element (modulation substrate) with very little transmission loss (shortest wiring). Moreover, the wiring of the modulation substrate to the modulation electrodes is also constrained by the miniaturization / integration of the modulation substrate, so wiring based on single-ended signals is desired.

[0008] Prior art literature

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2014-164243 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] The problem to be solved by the present invention is to provide an optical modulator that solves the aforementioned problems and suppresses the degradation of high-frequency characteristics from the driving circuit elements to the modulation substrate. Furthermore, an optical modulator is provided that can effectively apply the differential signal output from the driving circuit elements as a single-ended signal to the modulation electrode. Moreover, an optical transmission device using the above-described optical modulator is provided.

[0013] Solution for solving the problem

[0014] In order to solve the above-mentioned problems, the optical modulator and optical transmission device of the present invention have the following technical features.

[0015] (1) An optical modulator, comprising a modulation substrate and a driving circuit element housed within a housing, the modulation substrate having an optical waveguide and a modulation electrode for modulating an optical wave propagating in the optical waveguide, the driving circuit element generating a modulation signal applied to the modulation electrode, the optical modulator being characterized in that an output terminal for outputting the modulation signal is provided on the upper surface side of the driving circuit element, and a wiring board is disposed across the upper side of the driving circuit element and the modulation substrate, the wiring board having wiring for electrically connecting the output terminal to the modulation electrode.

[0016] (2) In the optical modulator described in (1) above, the wiring of the wiring board is electrically connected to the output terminal and the modulation electrode by flip bonding.

[0017] (3) In the optical modulator described in (1) or (2) above, the wiring board is configured to receive a differential signal from the driving circuit element and output only one of the differential signals to the modulation electrode.

[0018] (4) In the optical modulator described in (3) above, the characteristic is that another signal in the differential signal is set to the terminator of the wiring board.

[0019] (5) In the optical modulator described in (4) above, the terminator is provided on the back side of the surface opposite to the modulator substrate relative to the wiring substrate.

[0020] (6) In the optical modulator described in (4) or (5) above, the characteristic is that a heat dissipation unit is provided on the wiring board, which releases the heat generated by the terminal.

[0021] (7) An optical transmitting apparatus, characterized in that it comprises: an optical modulator as described in any one of (1) to (6) above; and a signal generator for generating a modulation signal input to the driving circuit element.

[0022] Invention Effects

[0023] According to the present invention, an optical modulator houses a modulation substrate and a driving circuit element within a housing. The modulation substrate has an optical waveguide and a modulation electrode for modulating light waves propagating in the optical waveguide. The driving circuit element generates a modulation signal applied to the modulation electrode. An output terminal for outputting the modulation signal is provided on the upper surface of the driving circuit element. A wiring board is disposed across the upper surface of the driving circuit element and the modulation substrate, and the wiring board has wiring for electrically connecting the output terminal to the modulation electrode. Therefore, an optical modulator with reduced transmission loss from the driving circuit element to the modulation substrate can be provided.

[0024] Furthermore, the wiring board is configured to receive a differential signal from the driving circuit element and output only one of the differential signals to the modulation electrode, thus providing an optical modulator that can effectively apply the differential signal output from the driving circuit element as a single-ended signal to the modulation electrode. Attached Figure Description

[0025] Figure 1 This is a top view illustrating an example of the optical modulator of the present invention.

[0026] Figure 2 yes Figure 1 A side view of an optical modulator.

[0027] Figure 3 It means Figure 2 A side view of the connection structure between the driving circuit elements and the modulation substrate in an optical modulator.

[0028] Figure 4 This is a side view showing another example of the optical modulator of the present invention.

[0029] Figure 5 It means Figure 4A side view of the connection structure between the driving circuit elements and the modulation substrate in an optical modulator.

[0030] Figure 6 It means Figure 5 A top view of a portion of the optical modulator.

[0031] Figure 7 This is a top view showing an example of a modulation substrate used in the optical modulator of the present invention.

[0032] Figure 8 This is a diagram illustrating an example of a wiring substrate in the optical modulator of the present invention.

[0033] Figure 9 This is a diagram illustrating another example of a wiring substrate in the optical modulator of the present invention.

[0034] Figure 10 It is a diagram illustrating the layout of electrical wiring and terminals on the wiring board.

[0035] Figure 11 This diagram illustrates an example in which a heat dissipation unit is provided on the wiring board in the optical modulator of the present invention.

[0036] Figure 12 This is another example of a wiring board in the optical modulator of the present invention having a heat dissipation unit. Detailed Implementation

[0037] Hereinafter, the present invention will be described in detail using preferred embodiments.

[0038] like Figures 1 to 3 or Figures 4 to 6 As shown, the present invention relates to an optical modulator, wherein a modulation substrate 1 and a driving circuit element 2 are housed in a housing (3). The modulation substrate 1 has an optical waveguide 200 and a modulation electrode 10. The modulation electrode 10 is used to modulate the light wave propagating in the optical waveguide. The driving circuit element 2 generates a modulation signal applied to the modulation electrode. The optical modulator is characterized in that an output terminal for outputting the modulation signal is provided on the upper surface side of the driving circuit element, and a wiring substrate 4 is arranged across the upper side of the driving circuit element and the modulation substrate. The wiring substrate 4 has wiring that electrically connects the output terminal to the modulation electrode.

[0039] As a modulation substrate, a strong dielectric substrate with electro-optic effect, such as lithium niobate (LN) or lithium tantalate (LT), PLZT (lead lanthanum zirconate titanate), can be used, or a structure in which a vapor-phase grown film based on these materials is formed on a reinforcing substrate.

[0040] Alternatively, substrates made of various materials such as semiconductor materials like InP or organic materials can be used.

[0041] As a method for forming an optical waveguide, one can use etching on the surface of a substrate other than the waveguide or forming grooves on both sides of the waveguide to make the portion of the substrate corresponding to the waveguide convex, forming a ridge-shaped optical waveguide. Alternatively, a high-refractive-index portion can be formed on the substrate surface using methods such as thermal diffusion or proton exchange to form an optical waveguide. Furthermore, a composite optical waveguide can be formed by diffusing a high-refractive-index material into the ridge-shaped waveguide portion.

[0042] To achieve velocity matching between the microwave and light waves in the modulation substrate where the optical waveguide is formed, the thickness can be made of a thin plate of 10 μm or less, more preferably 5 μm or less. Furthermore, the height of the ridge-shaped optical waveguide is set to 2 μm or less, more preferably 1 μm or less. Additionally, a vapor-grown film can be formed on the reinforcing substrate and then processed into the shape of an optical waveguide.

[0043] To improve mechanical strength, the modulation substrate, which is made of a thin plate, is bonded to a reinforcing substrate by direct bonding or by bonding through an adhesive layer such as resin. For direct bonding, a material with a lower refractive index than the optical waveguide and the substrate on which the optical waveguide is formed, and a thermal expansion coefficient close to that of the optical waveguide, such as quartz, is preferred as the reinforcing substrate. Furthermore, when bonding to the reinforcing substrate via an adhesive layer, a material similar to the thin plate, such as an LN substrate, can also be used as the reinforcing substrate.

[0044] Modulation electrodes and bias electrodes are formed along the optical waveguide. As a method of forming the electrodes, Au can be deposited onto a substrate metal such as Au or Ti using a plating method.

[0045] like Figure 1 and 2 ,or Figure 4 As shown, a drive circuit element 2 is disposed adjacent to the modulation substrate 1. The drive circuit element 2 has a structure that connects signal amplifiers in multiple stages, taking a differential signal as the modulation signal as input and outputting an amplified differential signal. For example, the modulation signal S is generated by a digital signal processor (DSP) or the like disposed outside the housing. The modulation signal S is transmitted via... Figure 1 , 2 The electrical signal input unit 6, as shown in Figure 4, is inserted into the housing 3. Various wiring units, such as flexible wiring, pins, or connector terminals, can be used for the electrical signal input unit. The following description focuses on flexible wiring, but is not limited to it.

[0046] The flexible wiring 6, serving as an electrical signal input unit, is connected to the relay substrate 5 within the housing. For example... Figure 3 As shown in Figure 5, electrical wiring 60 is formed on flexible wiring 6, and electrical wiring 50 is formed on relay substrate 5. This ensures the path for external electrical signals to reach the input terminals of drive circuit element 2.

[0047] like Figure 1 As shown, light wave L1 is input from the outside via an optical fiber to the optical waveguide of the modulation substrate 1 disposed inside the housing 3. Furthermore, light wave output from the modulation substrate 1 is emitted to the outside as output light L2 via an optical fiber. Reference numerals 7 and 70 are collimators incorporating lenses, etc. Figure 2 The number 30 indicates the cover portion of the housing 3.

[0048] like Figure 4 As shown, the connection between the modulation substrate 1 and the light waves of the collimators 7 and 70 is achieved using a spatial optical system based on lenses or prisms. In particular, when polarizing the two output beams, a portion of the optical components, such as a polarizing beam splitter, is housed within the housing. Furthermore, lens blocks or similar components can be attached to the end face of the modulation substrate 1, reducing the need for alignment and adjustment of the optical components.

[0049] Figure 3 This is a more detailed explanation of what it includes. Figure 1 and 2 A diagram showing the structure of the modulation substrate 1 and the driving circuit element 2. Furthermore, Figure 5 and 6 This is a more detailed explanation of what it includes. Figure 4 A diagram showing the structure of the modulation substrate 1 and the driving circuit element 2. Figure 6 yes Figure 5 A top-down view, but even Figure 3 Top view, Figure 6 The diagram on the right side, starting from drive circuit element 2, is also the same as the attached diagram.

[0050] like Figure 3 In the case of using flexible wiring 6, wiring 60 is formed on flexible substrate, and vias 50 are provided on relay substrate 5, through which wiring 60 is electrically connected to pad portion 51. The input terminal of drive circuit element 2, i.e., pad portion 20, is connected to the pad portion 51 via wire bonding 8.

[0051] In use Figure 4 In the case of the electrical signal input unit 6 (which can use a flexible or rigid substrate), such as Figure 5 As shown, the wiring 60 from the electrical signal input unit 6 is electrically connected to the input terminal (pad portion) 20 of the drive circuit element via the wiring 50 of the relay board 5. The connection between the terminals utilizes wire bonding 8. Furthermore, as... Figure 5 Top view Figure 6 As shown, input terminals 52 and output terminals 53 can be separately configured on the relay board 5, and the terminals of the two can be connected by wiring 50.

[0052] The wiring board 4, which connects the driving circuit element 2 to the modulation electrode 10 of the modulation board 1, uses an insulating substrate made of alumina or aluminum nitride ceramic. Figure 3 or Figure 5 Electrical wiring is formed on the upper or lower surface of the wiring board 4. Figure 6 In this case, wiring 40 and terminal 41 are arranged on the upper surface of wiring board 4.

[0053] exist Figure 3 or Figure 5 In the wiring board 4, a through hole 43 is formed to electrically connect the pad portion 42 provided on the lower surface of the wiring board 4 to the electrical wiring 40 provided on the upper surface. The connection between the wiring board (pad portion 42) and the output terminal (20') of the drive circuit element 2, or the connection between the wiring board (pad portion 42') and the pad portion 100 of the modulation electrode of the modulation board 1, is performed by flip bonding. Specifically, there are methods such as forming the pad portions of both by Au electrode pads and connecting them by pressure bonding based on heat / vibration application, or bump connection based on conductive adhesive 9 (9').

[0054] Figure 7 It means Figure 3 or Figure 5 ( Figure 6 A top view of an example of the modulation substrate 1 used in (e.g.) Figure 7 As shown, an optical waveguide 200 is formed on the modulation substrate 1, and a modulation electrode 10 is formed in the active portion of the optical waveguide 200. The modulation electrode consists of a signal electrode and a ground electrode. Figure 7 The example shown only represents a portion of the signal electrodes. Furthermore, bias electrodes can also be provided to control the DC bias voltage of an interferometric optical modulator using a Mach-Zehnder type optical waveguide.

[0055] The modulation electrode 10 is electrically connected to the input terminal (pad portion) 100 of the input modulation signal via wiring 101. Figure 7 In this configuration, the optical waveguide is arranged to allow light waves to enter and exit from the same end face of the modulation substrate. However, it is not limited to this configuration; it can also be configured to bend the optical waveguide into a right angle, so that light incident from one side of the modulation substrate exits from an adjacent side. Furthermore, it can also be configured to... Figure 7 The branch waveguides of the Mach-Zehnder type optical waveguide are formed to be long, bending the branch waveguides by 180 degrees.

[0056] Figure 8 This diagram shows an example of wiring board 4. For simplicity, only one wiring related to the differential signal is shown.

[0057] Towards Figure 8The output signal of the drive circuit element is introduced into the left side of the wiring board 4, and a differential signal (S) is set on the wiring board 4. + ,S - The wiring 40 corresponds to the differential signal and ground (G). The configuration and number of wirings for the differential signal and ground are set according to the output terminals of the drive circuit elements. Furthermore, as... Figure 6 In the case where multiple modulation signals are output using four differential signals, the wiring board 4 also has the same wiring pattern arranged side by side corresponding to the number of modulation signals. It should be noted that the grounding wiring G may also be shared between adjacent wirings.

[0058] exist Figure 8 In the middle, one of the differential signals (S) + One signal is output to the modulation electrode as a single-ended signal, and the other signal (S) is output to the modulation electrode. - The signal line is terminated by a terminator. The terminator can be configured by placing a terminating resistor 41R between the signal line and the ground line. Furthermore, in order to absorb the signal line (S) from the terminated signal line... - The microwave emitted from the end of the signal wiring can be configured to connect the ground wiring in a manner that surrounds the signal wiring. Furthermore, the terminating resistor 41R is configured to prevent S... - Unnecessary reflections in signal wiring can be minimized by placing it as close as possible to the electrodes of the drive circuit elements. Figure 8 (Left side).

[0059] The structure of the terminal can not only be like Figure 8 The resistive film configured as a terminating resistor 41R as shown can also be constructed as a chip-shaped electrical component in which resistors or the like are incorporated. In the case of such a chip-shaped terminating device, the wiring 40 is electrically connected and fixed to the wiring board 4 by a conductive adhesive.

[0060] Figure 9 It is formed on the lower surface of the wiring substrate 4. Figure 9 The wiring of (a), and as Figure 9 The diagram shows only the terminal 41 positioned on the upper surface of the wiring substrate 4, as shown in (b). Corresponding to the position of the terminal 41, wiring guide holes are formed in the wiring substrate 4. If this wiring substrate is shown in a side view, it becomes... Figure 10 The structure of (b) Figure 10 (a) is with Figure 3 or Figure 5 With the same structure, wiring 40 is formed on the upper surface of the wiring substrate, and a terminator 41 is also disposed on the upper surface. Figure 10 In the arrangement of (b), it is also possible to... Figure 10As in (c), the wiring 40 and the terminator 41 are arranged together on the lower surface of the wiring substrate. Furthermore, in Figure 10 In arrangement (a), the wiring 40 may be arranged on the upper surface of the wiring board and the terminator 41 may be arranged on the lower surface. In this case, the wiring 40 and the terminator 41 are connected by a via 43".

[0061] like Figure 10 (a) and Figure 10 The reason for placing the terminator on the upper surface of the wiring board 4 (the side facing away from the modulation board relative to the wiring board) as in (b) is to ensure the signal wiring (S - In the terminating resistor (terminating part) of the modulation board, the electrical signal is converted into heat. Therefore, in order to protect the modulation board which is not resistant to heat and to suppress the drift phenomenon caused by heat, the terminating resistor is provided at a position that is further separated from the modulation board 1.

[0062] In addition, to improve the heat dissipation of the wiring board 4, it is possible to... Figure 11 The heat dissipation unit is obtained by providing through holes around the terminal or by arranging conductive components in the through holes, or as shown. Figure 12 As shown, through-holes are provided in a portion of the grounding wiring to serve as heat dissipation units. These through-holes (especially those with conductive components) or through-holes also help suppress the propagation of terminated microwaves to the modulation substrate side.

[0063] By incorporating the aforementioned optical modulator and a signal generator (DSP, etc.) that generates a modulation signal input to the drive circuit elements within the optical modulator, an optical transmission device with the same effect can also be provided.

[0064] Industrial applicability

[0065] As described above, according to the present invention, it is possible to provide an optical modulator that reduces transmission losses from the driving circuit elements to the modulation substrate. Furthermore, it is also possible to provide an optical modulator that can effectively apply the differential signal output from the driving circuit elements as a single-ended signal to the modulation electrode. Moreover, it is possible to provide an optical transmission device using the aforementioned optical modulator.

[0066] Label Explanation

[0067] 1. Modulation substrate

[0068] 2. Drive circuit components

[0069] 3. Shell

[0070] 4 Wiring board

Claims

1. An optical modulator in which a modulation substrate and a drive circuit element are housed in a housing, the modulation substrate having an optical waveguide and a modulation electrode for modulating an optical wave propagating in the optical waveguide, the drive circuit element generating a modulation signal to be applied to the modulation electrode, characterized in that an output terminal outputting the modulation signal is provided on a top surface side of the drive circuit element, a wiring substrate is disposed straddling the drive circuit element and the modulation substrate on a top side thereof, the wiring substrate having a wiring electrically connecting the output terminal and the modulation electrode, the wiring substrate is configured to accept a differential signal from the drive circuit element and output only one of the differential signals to the modulation electrode, the other of the differential signals is terminated by a terminator provided to the wiring substrate, a heat dissipation unit that releases heat generated from the terminator is provided to the wiring substrate, the heat dissipation unit is provided to a periphery of the terminator, and the heat dissipation unit is composed of a through-hole in which an electrically conductive member is disposed.

2. The optical modulator according to claim 1, characterized in that the wiring of the wiring substrate is electrically connected to the output terminal and the modulation electrode by flip-chip bonding.

3. The optical modulator according to claim 1 or 2, characterized in that the terminator is provided to a surface on a back surface side with respect to a surface of the wiring substrate opposite to the modulation substrate.

4. An optical modulator system comprising the optical modulator according to any one of claims 1 to 3 and a signal generator that generates a modulation signal to be input to the drive circuit element. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 4. An optical transmitting apparatus, characterized by comprising: ​

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