JPH07234390A - Method for mounting high speed optical element - Google Patents

Abstract

PURPOSE:To provide a high speed frequency characteristic without being limited based on element capacity of an optical element by dividing an electrode pattern provided on an optical waveguide to at least two parts or above and electrically connecting respective divided electrodes in series. CONSTITUTION:Although an optical modulator 2 divides the electrode pattern on the optical waveguide to two parts, and makes them the electrode 1-1 and the electrode 1-2, capacity in respective electrodes 1-1 and 1-2 are reduced monotonically by dividing. Further, an interval between bonding pad parts 3 provided on respective electrodes of the electrode 1-1 and the electrode 1-2 is connected in series by a bonding wire 9, and one end is connected to a through hole 8 connected to a chip carrier base 5 through a terminating resistor 7, and the other end is connected to a strip line path 6 formed on a high frequency substrate 4. The frequency characteristic independent of element capacity is obtained by dividing the electrode and connecting to the line path provided with inductance matching with the divided capacity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for mounting a high-speed optical element in which the electrode structure of the optical element is improved to increase the speed.

[0002]

2. Description of the Related Art With the recent increase in the speed of optical transmission, the optical elements used are required to operate at high speed. Therefore, the present invention intends to improve the high frequency characteristics of the optical element to speed up the optical transmission. A factor for achieving a high-speed response of an optical element is a CR time constant which is a product of an operating speed of the optical element and a load resistance. In the conventional optical element, the optical element capacitance has been reduced in order to reduce the CR time constant and obtain a high speed operation. A typical example is the 1989 National Congress of Applied Physics,
27p-ZH-9, Otaka, Wakita, Mitomi, Kawamura, Asai et al., "PN Junction InGaAs / InAlAs".
"MQW high-speed optical modulator". The above-mentioned representative example is an example in which the light absorption layer of the undoped layer is thickened to reduce the device capacitance to 0.3 pF or less to improve the device operation speed, and as a result, a frequency response up to 40 GHz is realized. There is.

[0003]

In the above-mentioned prior art, in order to improve the operation speed of the optical element, the light absorption layer which is an undoped layer is made thicker for the purpose of reducing the element capacitance. An increase in drive voltage due to a decrease in electric field application effect cannot be avoided. As described above, the capacity of the optical element is generally in the relationship of being replaced by other optical element characteristics,
If one characteristic is improved, another characteristic is deteriorated, and it is difficult to achieve an essential improvement in performance only by simply reducing the element capacitance.

It is an object of the present invention to provide a high-speed optical device mounting method which can greatly improve the operating speed of the optical device without deteriorating other performances of the optical device by avoiding the speed limit due to the CR time constant. Is to get.

[0005]

The above-mentioned object is to mount a high-speed optical element having an electrode pattern on an optical waveguide in a method for mounting the electrode pattern, divide the electrode pattern into at least two, and electrically connect the divided electrodes in series. It is achieved by

Further, the electric series connection of the divided electrodes is achieved by a bonding wire or a line formed on a mounting substrate.

[0007]

As is well known, the resonance connection circuit of the capacitance C connected in parallel and the impedance L connected in series is Z = √ (L / L in the region below the LC resonance frequency.
It is approximated by a line having an impedance of C).
By setting the impedance Z equal to the impedance of the drive line, the electric signal input to the optical element is applied to the electrodes of each part of the optical element without distortion. Further, in this case, the reflection of electric signals, which is a problem when driving the capacitive element, does not occur. Therefore, it is possible to operate the device without depending on the CR time constant. The device can be operated only in the region below the LC resonance frequency, but the resonance frequency can be increased above the desired frequency by keeping the individual capacitance C small by dividing the electrodes. It can be set independently of the element capacitance. That is, the electrode of the optical element is divided into two or more, and the capacitance of each electrode portion is reduced to a predetermined design value or less. In this case, it is sufficient that the insulation resistance between the electrodes is 1 kΩ or more, so that no special isolation structure is required between the electrodes. At this time, the line for connecting the respective electrodes in series may be provided on the optical element, external to the optical element, or arranged anywhere. Since the inductance line compensates for the effect of the element capacitance, the element operation independent of the CR time constant becomes possible.

As described above, the frequency characteristic independent of the element capacitance can be realized by connecting the electrode division and the line having the inductance matched with the division capacitance.

Further, when the optical module having the optical element mounted by the high-speed optical element mounting method of the present invention as described above is used, the transmission rate is improved to increase the degree of multiplexing as compared with the conventional one. It is possible to obtain an optical transmission device having low performance and high transmission cost.

[0010]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a high-speed optical device mounting method according to the present invention, FIG. 2 is a diagram showing characteristics of an optical device calculated by an equivalent circuit of the above embodiment, and FIG. 3 is another embodiment of the present invention. FIG. 4 is a diagram showing an embodiment, and FIG. 4 is a diagram showing a configuration of an ultrahigh-speed optical transmission device using a high-speed optical element mounted by the high-speed optical element mounting method as still another embodiment of the present invention.

FIG. 1 showing an embodiment of the present invention is a diagram showing a basic element structure and its mounting state in a method of mounting a high-speed optical element. FIG. 1 (a) is a high frequency substrate formed on a chip carrier base 5. 4, the optical modulator 2 as an optical element
3A and 3B are plan views showing a state in which is mounted and connected by bonding wires 9 and mounted, FIG. 6B is a side view in the mounted state, and FIG. 6C is an equivalent circuit in the mounted state. The optical element used in this example is an electro-absorption type optical modulator 2 having a multi-quantum well (MQW) 13 as an absorption layer, and the element capacitance is a bonding pad for connecting the junction capacitance of the pin junction and the split electrode. Although represented by the sum of the stray capacitance of the portion 3, in the present embodiment, the lower portion of the bonding pad portion 3 is filled with a thick polyimide film which is a low dielectric constant material, so that the stray capacitance is at a pad diameter of 50 μm. Was also 50 fF. Since the stray capacitance is sufficiently smaller than the junction capacitance of about 0.5 pF, even if the number of bonding pad portions is increased by dividing the electrode, the total element capacitance hardly changes. In the optical modulator 2, the electrode pattern on the optical waveguide is divided into two as shown in FIG. 1A to form an electrode 1-1 and an electrode 1-2. In each of the electrodes 1-1 and 1-2, The capacity decreases monotonically by dividing.

In order to electrically separate the electrodes 1-1 and 1-2, the distance between the electrodes is 10 μm.
m, and the highly doped cap layer between the separated electrodes was removed by etching. By doing so, an electrode separation resistance of about 1 kΩ was obtained. The spacing between the bonding pad portions 3 provided on the electrodes 1-1 and 1-2 is 0.5 mm, and the gaps are connected by the bonding wires 9 and one end is connected to the chip carrier base 5. Is connected to the through hole 8 via the terminating resistor 7, and the other end is connected to the high frequency substrate 4.
It is connected to the strip line 6 formed above. Since the bonding wire 9 has an inductance of about 1 nH / mm, the bonding wire connecting the both electrodes has an inductance of about 0.5 nH.

FIG. 1C shows an equivalent circuit of the embodiment in the mounted state. In the figure, C _p is the capacitance of the bonding pad portion 3, C _j is the junction capacitance with the optical modulator 2, R _in is the series resistance of the optical modulator 2, and R _iso is the electrode 1-1 and the electrode 1-2. A resistor R between them indicates a terminating resistor 7. In addition, L _in represents the impedance between the split electrode 1-1 and the strip line 6, and L _out represents the impedance of the wire connecting between the split electrode 1-2 and the terminating resistor 7, respectively.
L _iso represents the inductance between the bonding pads 3 to which the wires are connected. In addition, Z
_o indicates the characteristic impedance of the strip line 6.

2A and 2B are diagrams showing the characteristics of the optical element calculated by using the above equivalent circuit. FIG. 2A shows changes in the small signal response coefficient with respect to changes in frequency, and FIG. 2B shows electrical characteristics with respect to changes in frequency. The change in the reflection coefficient is shown. By setting the inductance component to a predetermined value, in the change of the small signal response coefficient shown in (a), the 3 dB band in the small signal response coefficient reaches 23 GHz, which is about double from 12 GHz when the electrode is not divided. Increase to
Also, by dividing the electrode by the method of the present invention as shown in (b), the electric reflection coefficient is significantly improved,
For example, at 10 GHz, -6d when the electrode is not divided
It is reduced from B to -21 dB. When an optical modulator was actually produced and the modulation band was measured, a modulation band of 20 GHz could be obtained, and the configuration of the optical element based on the present invention and the effectiveness of its mounting method could be confirmed.

In the above embodiment, the case where the number of electrode divisions is set to 2 has been exemplified, but in the case where the number of electrode divisions is 3 or more according to the present invention, it is as effective as in the above embodiment and the modulation band. Increases according to the number of divisions.

Next, another embodiment of the high-speed optical device mounting method of the present invention is shown in FIG. 3, (a) is a plan view showing the high frequency substrate, (b) is a side view of the high frequency substrate, (c) is a rear view of the optical modulator, (d) is a side view of the optical modulator, FIG. 3E is a diagram showing a state in which the optical modulator is mounted on the high frequency substrate. This embodiment shows an example in which the optical modulator 2 which is an optical element is mounted on the surface of a high frequency substrate 4 which is a mounting substrate, and wire bonding in which the respective divided electrodes in the above embodiment are connected in series. Instead of the above, a strip line 6 formed so as to have a predetermined inductance is used on the high frequency substrate 4 to connect the split electrodes 1-1 and 1-2. In order to prevent stray capacitance from being generated between each element pattern on the high frequency substrate 4 and the optical modulator 2,
An upper surface of the high frequency substrate 4 or a lower surface of the optical modulator 2,
Alternatively, a metal thick film is provided on each of the connection surfaces facing each other by a method such as plating, and the thickness of the metal thick film is set such that the optical modulator 2 is located at the localization value of the high frequency substrate 4. At this time, they are formed so that the distance between them is about 10 μm. By doing so, the stray capacitance between the high frequency substrate 4 and the optical modulator 2 is several tens of fF.
Since it is as follows, it is possible to sufficiently reduce the influence on the device characteristics. The feature of this embodiment is that the inductance component in the pattern of the strip line 6 formed on the high frequency substrate 4 can be set with good reproducibility. Further, since the area of the portion corresponding to the bonding pad of the above-described embodiment can be reduced, the stray capacitance does not increase even when the number of divided electrodes is increased. Therefore, a greater effect can be obtained by dividing the electrodes.

FIG. 4 shows another embodiment of the present invention.
The structure of an ultrahigh-speed optical transmission device using the optical modulator module mounted by the mounting method of the high-speed optical element shown in each of the above-mentioned embodiments will be shown. The transmitter of the optical transmission device is as shown in FIG.
It is composed of a multiplexer that multiplexes an input electric signal to form an ultrahigh-speed electric signal, a drive circuit that forms an optical modulator drive signal from the ultrahigh-speed electric signal, an optical modulator module, and a laser that is a light source. ing. Further, the optical signal transmitted from the transmitter is transmitted to the receiver via an optical fiber. The receiver includes a light receiving element for converting the optical signal into an electric signal, and the electric signal is amplified to a predetermined level. Amplifier, a discriminator that converts the amplified electric signal into a digital signal of 0 or 1, a clock extraction circuit that supplies a timing signal to the discriminator, and an ultrahigh-speed signal into a plurality of electric signals at a predetermined speed. It is composed of a separator for separating. Here, by applying the optical modulator mounting method according to the present invention to the optical transmission device, the operating speed limit of the optical modulator unit, which has been a problem in the past, is solved.
It is possible to significantly improve the transmission speed in the optical transmission device. That is, the degree of multiplexing can be significantly improved as compared with the related art. Further, this effectively works not only to improve the performance of the optical transmission device but also to reduce the transmission cost per bit. Therefore, the method of mounting a high-speed optical element according to the present invention not only improves the performance of the optical element, but also improves the performance of the entire optical transmission device, and
It also effectively reduces the transmission cost.

In the above description, the optical modulator is used as the optical element, but the present invention is not limited to the optical modulator, and is widely applied to waveguide type devices represented by semiconductor lasers. Can be applied.

[0020]

As described above, according to the method of mounting a high-speed optical element according to the present invention, in the method of mounting a high-speed optical element having an electrode pattern on an optical waveguide, the electrode pattern is divided into at least two or more, and each divided By electrically connecting the electrodes in series, high-speed frequency characteristics can be realized without being limited by the element capacitance of the optical element.
Further, by using the optical modulator mounted by the mounting method described above, it is possible to obtain a high-performance optical transmission device with improved transmission speed and reduced transmission cost.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a high-speed optical device mounting method according to the present invention, in which (a) is a plan view showing a mounted state of an optical modulator,
(B) is a side view in the mounted state, and (c) is a diagram showing an equivalent circuit in the mounted state.

2A and 2B are graphs showing characteristics of an optical element calculated by the equivalent circuit of the above embodiment, FIG. 2A shows a change in small signal response coefficient with respect to frequency, and FIG. 2B shows a change in electric reflection coefficient with respect to frequency. FIG.

3A and 3B are views showing another embodiment of the high-speed optical device mounting method according to the present invention, in which FIG. 3A is a plan view showing a high-frequency substrate, FIG. 3B is a side view of the high-frequency substrate, and FIG. Rear view of the vessel,
(D) is a side view of the optical modulator, and (e) is a diagram showing a state where the optical modulator is mounted on the high-frequency substrate.

FIG. 4 is a diagram showing a configuration of an ultrahigh-speed optical transmission device using an optical modulator module mounted by the high-speed optical element mounting method of the present invention.

[Explanation of symbols]

 1-1, 1-2 Split electrode 2 Optical modulator 5 Chip carrier base 6 Strip line 9 Bonding wire

Claims (5)

[Claims] 1. A method for mounting a high-speed optical element having an electrode pattern on an optical waveguide, characterized in that the electrode pattern is divided into at least two and each divided electrode is electrically connected in series. Device mounting method. 2. The method of mounting a high-speed optical element according to claim 1, wherein the series connection of the divided electrodes is performed by a bonding wire. 3. The method for mounting a high-speed optical element according to claim 1, wherein the series connection of the divided electrodes is performed by a line formed on a mounting substrate. 4. An optical module having at least one optical element mounted therein using the method for mounting a high-speed optical element according to any one of claims 1 to 3. 5. An optical transmission device using the optical module according to claim 4.