Semiconductor light modulator

Abstract

The semiconductor optical modulator (5) modulates light according to a high-frequency signal (11). The terminal matching circuit (12) is connected in parallel with the semiconductor optical modulator (5). The terminal matching circuit (12) has a resistor (8) and a capacitor (9) of 0.1 pF or less connected in parallel with the resistor (8).

Description

Technical Field

[0001] The present disclosure relates to a semiconductor light modulation device in which a terminal matching circuit is connected in parallel to a semiconductor light modulator. Background Art

[0002] In the optical communication system between the relay station and the user, i.e. the access system, directly modulated semiconductor laser transmitters (DML: Directly Modulated Laser) suitable for low-speed modulation are mostly used. On the other hand, in the case of high-speed communication of 10Gb / s or above, a semiconductor integrated device that integrates an electro-absorption semiconductor optical modulator (EAM: Electro-absorption Modulator) suitable for high-speed modulation and a distributed feedback semiconductor laser, i.e. EAM-LD (Electro-absorption Modulator integrated Laser Diode), is suitable.

[0003] The laser passing through the EAM is modulated by applying a signal to the EAM that repeatedly turns on and off at the frequency of the modulated light. In high-speed communication, a high-frequency signal with a DC voltage offset is applied. Since the high-frequency signal is a high frequency of more than 10 GHz, a line such as a coaxial line that takes high-frequency characteristics into consideration is used as the power supply line.

[0004] In the case of EAM-LD, due to the parasitic capacitance and resistance of the semiconductor optical modulator, the inductance of the bonding wire, etc., as the frequency of the input signal increases, the impedance becomes unmatched, causing bandwidth degradation. For this reason, impedance matching is performed by a terminal matching circuit connected in parallel with the semiconductor optical modulator to improve the frequency characteristics (for example, refer to Patent Document 1).

[0005] Patent Document 1: International Publication No. 2019 / 229825

[0006] However, in the conventional technology, it is impossible to obtain good frequency characteristics while ensuring a desired frequency band. Summary of the invention

[0007] The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to obtain a semiconductor light modulator that can obtain good frequency characteristics while ensuring a desired frequency band.

[0008] The semiconductor optical modulator device involved in the present disclosure is characterized in that it comprises: a semiconductor optical modulator that modulates light according to a high-frequency signal; and a terminal matching circuit connected in parallel with the above-mentioned semiconductor optical modulator, and the above-mentioned terminal matching circuit has a resistor and a capacitor of less than 0.1pF connected in parallel with the above-mentioned resistor.

[0009] In the present disclosure, the terminal matching circuit connected in parallel with the semiconductor optical modulator is formed by connecting a resistor in parallel with a capacitor of 0.1 pF or less. Thus, the gain fluctuation can be suppressed at low frequencies before reaching the cutoff frequency, and the gain reduction and the degradation of the frequency band can be suppressed at high frequencies. As a result, good frequency characteristics can be obtained while ensuring the desired frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a plan view showing the semiconductor light modulator according to the first embodiment.

[0011] Figure 2 This is a circuit diagram showing a semiconductor light modulator according to the first embodiment.

[0012] Figure 3 1 is a cross-sectional view showing a capacitor of the semiconductor light modulator according to the first embodiment.

[0013] Figure 4 is a circuit diagram showing a semiconductor light modulator according to a comparative example.

[0014] Figure 5 This is a diagram showing simulation results of the frequency characteristics of the semiconductor light modulator according to the first embodiment.

[0015] Figure 6 This is a diagram showing simulation results of frequency characteristics of semiconductor light modulators according to the first and second embodiments.

[0016] Figure 7 This is a diagram showing simulation results of frequency characteristics of semiconductor light modulators according to the first and second embodiments.

[0017] Figure 8 This is a diagram showing simulation results of frequency characteristics of semiconductor light modulators according to the first and second embodiments.

[0018] Fig. 9 This is a diagram showing simulation results of frequency characteristics of semiconductor light modulators according to the first and second embodiments.

[0019] Fig.10 This is a diagram showing simulation results of frequency characteristics of semiconductor light modulators according to the first and second embodiments.

[0020] Fig.11 This is a diagram showing simulation results of frequency characteristics of semiconductor light modulators according to the first and second embodiments.

[0021] Fig.12 This is a plan view showing a semiconductor light modulator according to the second embodiment.

[0022] Fig.13 This is a circuit diagram showing a semiconductor light modulator according to the second embodiment.

[0023] Fig.14 This is a diagram showing simulation results of the frequency characteristics of the semiconductor light modulator according to the second embodiment. DETAILED DESCRIPTION

[0024] The semiconductor light modulator according to the embodiment will be described with reference to the drawings. The same reference numerals may be used to designate the same or corresponding components, and duplicate descriptions may be omitted.

[0025] Implementation Method 1

[0026] Figure 1 1 is a top view showing a semiconductor light modulator according to Embodiment 1. Signal conductors 2 and 3 are formed on the surface of a dielectric substrate 1, and an electrically connected ground conductor 4 is formed on a part of the surface, the side surface, and the back surface of the dielectric substrate 1. A semiconductor light modulator 5 is mounted on the ground conductor 4 on the surface of the dielectric substrate 1. The lower surface electrode of the semiconductor light modulator 5 is connected to the ground conductor 4.

[0027] The upper surface electrode of the semiconductor optical modulator 5 is connected to the signal conductor 2 via a bonding wire 6 and to the signal conductor 3 via a bonding wire 7. A resistor 8 is connected between the signal conductor 3 and the ground conductor 4. A tiny capacitor 9 of 0.1 pF or less is connected to the signal conductor 3 via a bonding wire 10.

[0028] Figure 2 1 is a circuit diagram showing a semiconductor light modulator according to Embodiment 1. A high-frequency signal 11 is supplied from a signal conductor 2 to a semiconductor light modulator 5 via a bonding wire 6. The semiconductor light modulator 5 modulates light according to the high-frequency signal 11. A terminal matching circuit 12 is connected in parallel to the semiconductor light modulator 5. The terminal matching circuit 12 includes a resistor 8, a capacitor 9 of 0.1 pF or less connected in parallel to the resistor 8, and a bonding wire 10 connecting the resistor 8 and the capacitor 9.

[0029] Figure 3 1 is a cross-sectional view showing a capacitor of the semiconductor light modulator according to Embodiment 1. The capacitor 9 includes a dielectric material 13 , a signal conductor 14 and a ground conductor 15 sandwiching the dielectric material 13 . The dielectric material 13 is a separate component from the dielectric substrate 1 .

[0030] Next, the effects of the present embodiment will be described by comparison with a comparative example. Figure 42 is a circuit diagram showing a semiconductor light modulator according to a comparative example. In the comparative example, the capacitor 9 and the bonding wire 10 are omitted from the terminal matching circuit 12 , and the terminal matching circuit 12 includes only the resistor 8 .

[0031] Figures 5 to 11 This is a diagram showing the simulation results of the frequency characteristics of the semiconductor light modulator involved in Embodiments 1 and 2. The frequency characteristics of S21 (transmitted component) in the S parameter are shown. The resistance value of resistor 8 is set to 40Ω. The "no capacitor" in the figure corresponds to the case of the comparative example, and the "no lead" corresponds to the case of Embodiment 2 described later.

[0032] exist Figure 5 In the embodiment, the capacitance value of the capacitor 9 is set to 0.014 to 0.14 pF, and the inductance of the bonding wire 10 is set to 0.392 nH. In the present embodiment, it can be seen that by making the terminal matching circuit 12 have a small capacitor 9, the gain near 20 to 30 GHz is improved compared with the case of the comparative example without a capacitor, and the gain variation at 0 to 30 GHz is suppressed, thereby improving the frequency characteristics.

[0033] exist Figures 6 to 11 In the simulation, the capacitance value of capacitor 9 was changed from 0.014 to 0.14 pF, and the inductance of bonding wire 10 was changed from 0.166 to 1.078 nH. The minimum inductance of 0.166 nH is equivalent to a lead length of 0.3 mm. A lead length shorter than this cannot be installed in the simulation model that reproduces the first embodiment, and is also difficult to install in actual production.

[0034] The capacitance value of capacitor 9 is Figure 6 In the Figure 7 The inductance of the bonding wire 10 was changed by setting the inductance to 0.12 pF. In this case, the gain variation was larger than that of the comparative example without capacitance under any inductance condition, and almost no improvement effect was obtained.

[0035] exist Figure 8 In the example, the capacitance value of capacitor 9 is set to 0.1 pF, and the inductance of bonding wire 10 is changed. In this case, it can be seen that under the condition that the lead is short and the inductance is as small as 0.166 nH, the gain fluctuation is suppressed compared with the comparative example without capacitor, and an improvement effect is obtained. Therefore, it is considered necessary to set capacitor 9 to 0.1 pF or less.

[0036] When the capacitor 9 is greater than 0.1pF, the inductance change has a great impact on the gain variation from 0 to 30GHz, so it can be seen that the inductance is preferably as small as possible. Therefore, as is generally known, the bonding wire 10 needs to be as short as possible. However, it is known that the smaller the capacitor 9 is, the more improvement effect of the frequency characteristics can be obtained, and the effect of the inductance change of the bonding wire 10 on the gain variation from 0 to 30GHz is small. The inductance of 0.166 to 1.078nH corresponds to the length of the bonding wire of 0.3 to 1.2mm. Therefore, by using a capacitor 9 with a capacitance value of less than 0.1pF, the frequency characteristics can be improved, and the bonding wire 10 connected to the capacitor 9 can be extended. In addition, as Fig.10 As shown, when the capacitor 9 is set to 0.056 pF and the inductance of the bonding wire 10 is set to 0.392 nH, the gain variation is minimized and a flat frequency characteristic can be obtained.

[0037] As described above, in this embodiment, the terminal matching circuit 12 connected in parallel with the semiconductor optical modulator 5 is formed by connecting the resistor 8 and the capacitor 9 of 0.1 pF or less in parallel. As a result, the gain fluctuation can be suppressed at low frequencies before reaching the cutoff frequency, and the gain reduction and the degradation of the frequency band can be suppressed at high frequencies. As a result, good frequency characteristics can be obtained while ensuring the desired frequency band.

[0038] Furthermore, by setting the capacitance value of the capacitor 9 to 0.1 pF or less, the frequency characteristic can be improved without shortening the bonding wire 10 connected to the capacitor 9. Therefore, the degree of freedom in the structural design of the semiconductor light modulator can be increased.

[0039] In addition, the minimum capacitance value of the capacitor sold as a product of the structure that can be used as capacitor 9 is 0.1pF. However, the tolerance (capacitance tolerance) of the capacitance value guaranteed in the catalog is 0.1pF. Therefore, the lower limit of the capacitance value of the capacitor sold on the market is exactly 0.1±0.1pF. Therefore, the capacitance value below 0.1pF cannot be reliably obtained in the capacitor sold on the market.

[0040] The relative dielectric constant of the dielectric material of a 0.1pF capacitor sold on the market is calculated to be 63.3. For this reason, the relative dielectric constant of the dielectric material 13 of the capacitor 9 is set to be less than 63.3. Thus, even with the same capacitance tolerance, the size tolerance of the dielectric material 13 can be eased. In addition, as the capacitor 9, a capacitance of less than 0.1pF can be achieved in a size that can be mounted on a semiconductor light modulator.

[0041] As the dielectric material 13, an aluminum nitride ceramic substrate having a relative dielectric constant of 8.8 can be applied. In addition, as the dielectric material 13, an alumina ceramic substrate having a relative dielectric constant of 8.5 to 10 can also be applied. By using a ceramic substrate having a simple structure, the capacitor 9 can be produced at a low cost. In addition, due to the low dielectric constant, a capacitor of 0.1 pF or less can be mounted with high precision.

[0042] Implementation Method 2

[0043] Fig.12 This is a plan view showing a semiconductor light modulator according to the second embodiment. Fig.13 1 is a circuit diagram showing a semiconductor light modulator according to Embodiment 2. The dielectric substrate 1 according to this embodiment is obtained by integrating the dielectric substrate 1 according to Embodiment 1 and a dielectric material 13 .

[0044] The capacitor 9 is formed by sandwiching the dielectric substrate 1 on which the semiconductor optical modulator 5 is mounted between the signal conductor 16 formed on the front surface of the dielectric substrate 1 and the ground conductor 4 formed on the back surface of the dielectric substrate 1. The capacitor 9 is connected to the resistor 8 via the signal conductor 17.

[0045] The signal conductor 16 constituting the capacitor 9 and the signal conductor 17 connecting the capacitor 9 and the resistor 8 can be integrated. Therefore, the bonding wire 10 of the first embodiment can be omitted. In addition, the capacitance value of the capacitor 9 can be adjusted by adjusting the size of the signal conductor 16 .

[0046] Fig.14 : is a diagram showing the simulation results of the frequency characteristics of the semiconductor light modulator involved in Embodiment 2. Fig.14 In the example, the resistance value of the resistor 8 is set to 40Ω, and the capacitance value of the capacitor 9 is set to 0.014 to 0.1 pF. Figure 5 In comparison, it can be seen that when the capacitance is small, such as 0.014 pF or 0.056 pF, the difference is small, but the cutoff frequency can be improved and the gain variation can be further suppressed.

[0047] Figures 6 to 11 The "No Leads" in FIG. 1 represent simulation results of Embodiment 2 corresponding to each capacitance value of capacitor 9. As can be seen from these figures, by omitting the bonding wire 10 according to this embodiment, an extension effect of making the inductance of the bonding wire 10 of Embodiment 1 smaller can be obtained. In addition, in this embodiment, when the capacitance value of capacitor 9 is 0.14 pF, the gain variation is also large compared to the comparative example without capacitor, and no improvement effect can be obtained. When the capacitance value of capacitor 9 is 0.12 pF, a slight improvement effect can be obtained compared to the comparative example.

[0048] In the present embodiment, the dielectric substrate 1 is made of a dielectric material having a relative dielectric constant of 63.3 or less. For example, an aluminum nitride ceramic substrate having a relative dielectric constant of 8.8 or an alumina ceramic substrate having a relative dielectric constant of 8.5 to 10 is used as the dielectric material.

[0049] Although various illustrative embodiments and examples are described in this application, the various features, forms and functions described in one or more embodiments are not limited to the application of a specific embodiment, and can also be applied to the embodiments alone or in various combinations. Therefore, countless unillustrated variations can be imagined within the scope of the technology disclosed in the specification of this application. For example, it includes the case where at least one constituent element is deformed, added or omitted, and also includes the case where at least one constituent element is extracted and combined with constituent elements of other embodiments.

[0050] Description of Reference Numerals

[0051] 1... dielectric substrate; 4... ground conductor; 5... semiconductor optical modulator; 8... resistor; 9... capacitor; 10... bonding wire; 11... high frequency signal; 12... terminal matching circuit; 13... dielectric material; 14, 16... signal conductor; 15... ground conductor.

Claims

1. A semiconductor light modulation device, characterized in that: have: A semiconductor optical modulator that modulates light according to a high-frequency signal; and a terminal matching circuit connected in parallel with the semiconductor optical modulator, The terminal matching circuit includes a resistor, a capacitor connected in parallel with the resistor, and a bonding wire connecting the resistor and the capacitor. The capacitance value of the capacitor is 0.1pF or less and the inductance of the bonding wire is 0.166nH or less, or the capacitance value is 0.076pF or less and the inductance is 0.392nH or less, or the capacitance value is 0.056pF or less and the inductance is 0.693nH or less, or the capacitance value is 0.014pF or less and the inductance is 1.078nH or less.

2. The semiconductor light modulator according to claim 1, wherein: The capacitor includes a dielectric material having a relative dielectric constant lower than 63.3 and a conductor sandwiching the dielectric material.

3. The semiconductor light modulator according to claim 2, wherein: The dielectric material is an aluminum nitride ceramic substrate.

4. The semiconductor light modulator according to claim 2, wherein: The dielectric material is an alumina ceramic substrate with a relative dielectric constant of 8.5-10.

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