JP2003315754A - Light modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light modulator of an arrayed EA modulator module which presents a favorable high frequency characteristic in a wide-band area, and does not make its package process complex with increase in the number of channels, and further eliminates the need for an optical circulator causing cost increase. <P>SOLUTION: In the light modulator, the light incident plane and the light emitting plane are formed on the side faces of an EA modulator array facing each other, and the light modulator has parallel electric wiring films wired with GCPW on a linear IPF carrier, and is electrically connected to the EA modulator array where the optical modulation elements are arranged at positions with different distances from the light incident plane on the optical axes. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulator used in optical information communication and the like, and more particularly to a multi-channel optical modulator for multiplex communication. .

[0002]

2. Description of the Related Art In recent years, research and development have been actively conducted on optical fiber communication using a wavelength division multiplexing (WDM) transmission system for expanding transmission capacity. Since the monolithic integrated optical semiconductor device can form elements having different functions on the same semiconductor substrate, it is very effective as an optical component that realizes an optical signal processing function in such a WDM network. The electro-absorption optical modulator (hereinafter abbreviated as EA modulator) can obtain high-speed signal light at a low driving voltage and also has a function as a high-speed gate switch and a wavelength conversion function, which is essential for a WDM network. It is considered to be an optical semiconductor device.

On the other hand, in order to cope with an increase in the number of wavelength division multiplexes, there is an increasing demand for an arrayed element in which a plurality of optical semiconductor elements having the same function are arranged on the same substrate. For example, when the EA modulator is formed into an array, a multi-wavelength optical modulator array or a high-speed optical gate switch array can be realized with one chip, which is advantageous for device miniaturization and cost reduction. Furthermore, since the optical semiconductor element and the optical fiber have greatly different light spot sizes, there has been a problem that the coupling loss at the optical connection point increases. Therefore, an optical semiconductor element and a passive waveguide type spot size converter are integrated on the same substrate to reduce the coupling loss with the optical fiber. Further, the passive waveguide having a high-mesa structure has the same structure as a passive waveguide functional device having a multiplexing / demultiplexing function such as an arrayed waveguide diffraction grating (AWG) and a multimode interferometer (MMI). In this way, the integration of the active element (for example, a laser diode or an optical semiconductor amplifier) and the passive waveguide can improve the functionality of the optical semiconductor integrated circuit, and thus realizes an optical component for a WDM network. Very promising above.

By the way, the EA modulator can convert continuous light into intermittent signal light by utilizing the physical phenomenon that the absorption edge wavelength shifts to the long wavelength side when a voltage is applied. In order to generate a high-speed signal light, it is necessary to feed a high frequency electric signal to the EA modulator. Therefore, a high-frequency voltage is supplied to the EA modulator module by a coaxial cable, and the microstrip line (MSL) is connected to the immediate vicinity of the element inside the module, and the MSL is connected to the electrode pad on the upper surface of the element by wire bonding. At this time, if the wire length is increased, the parasitic inductance of the bonding wire is increased and the high frequency characteristics are deteriorated. Therefore, the wire length to the EA modulator needs to be as short as possible.

Therefore, as an electrical connection method instead of wire bonding, the IPF (Impe) developed by Tomomi et al.
Dance-matched Fi1m) carriers are considered to be very effective (Fujimuro et al., JP-A-2-
34948). The IPF carrier is an impedance matching type electrical wiring film (film carrier).
It has a ground coplanar (GCPW) structure in which a coplanar (CPW) wiring pattern of a metal conductor and a ground surface are formed on both surfaces of an insulating flexible substrate, and is used immediately above a semiconductor element. At the end of the wiring pattern of the IPF carrier, a short lead having an Au bump formed in an opening for terminal connection is arranged, and is connected to an electrode pad of a semiconductor element by thermosonic bonding. Therefore, since it is possible to perform electrical wiring with impedance matching up to the immediate vicinity of the semiconductor element, it is possible to obtain good frequency characteristics in a very wide band. Tsuneji et al. Evaluated the S parameter as the frequency band characteristic of the IPF carrier (Kenji et al., The Institute of Electronics, Information and Communication Engineers, Vol.
84, No. 6, pp. 390-398, June 20
01). As a result, in the case of a linear wiring pattern, DC
S ₂₁ <-0.8d in a wide band range up to 50 GHz
Excellent high frequency characteristics of B and S ₁₁ <−20 dB are achieved.

On the other hand, the structure of an arrayed multi-channel EA modulator is shown in FIG. FIG. 5 shows an example of a 4-channel EA modulator array element.
Four passive waveguides 4 are formed in the optical waveguide, and an antireflection film 13 is formed on the light incident surface and the light emitting surface.
An optical fiber array 5 for each passive waveguide 4.
Are optically coupled to each other, and in each passive waveguide 4, an electrode pad 6 for an EA modulator for connecting a bonding wire 8 for wiring is formed, and in each channel of the EA modulator array element 3. It has a structure for applying a signal voltage. The electrode pad 6 and the MSL 14 or the terminating resistor 7 forming the circuit portion are wired by a bonding wire 8 by thermosonic bonding or the like.
Therefore, the EA modulation element (FIG.
The wire length to the passive waveguides b, c) at the device end (Fig.
Therefore, it is necessary to make the length longer than that in the case where the passive waveguides a and d) are arranged. When arranged at the end of the element, the wire length can be almost equal to that in the case of the conventional EA modulator alone, but when arranged at the center, the wire length becomes long, which causes an increase in parasitic inductance. Degradation of high frequency characteristics has been an important issue. Further, when the wires come into contact with each other, a short circuit occurs, and it becomes impossible to modulate each channel with an independent electric signal. Therefore, since it is necessary to pay close attention to the wire routing process, the mounting process becomes complicated as the number of channels increases, and the yield is reduced.

In order to solve the above-mentioned problems, Yamada et al. Developed the reflection type multi-channel modulator shown in FIG. 6 (K. Yamada et al., IEICE).
Trans. Electron. , Vol. E81
-C, No. 8, August 1998, pp. 124
5-1250). In the optical modulator having this structure, all connection points with the circuit are brought close to the same end face of the semiconductor substrate, that is, the electrode pads 6 are arranged on the high reflection film 1 of the modulator array element 3.
5 is arranged, and the circuit portion 16 is arranged on the high reflection film 15 side. As a result, all the channels of the circuit portion 16 and the EA modulator array element 3 can be bonded at the same shortest distance. In this case, since light is input and output from the side where the same antireflection film 13 is formed, the optical circulator 17 for separating the input light and the output light for each channel is required. For this reason,
Regardless of the position of the EA modulator, since it is possible to connect to any channel almost the same as the wire length in the case of the conventional EA modulator alone, good high frequency characteristics can be obtained even when arrayed. Also, in the wire routing process, since the MSL 14 is close to the electrode pad 6 of each EA modulation element, the possibility of contact with the wires of other channels is low, so that the mounting process becomes complicated even if the number of channels increases. There is a merit that there is no such thing.
However, since the optical modulator having this structure inputs and outputs light through the same optical fiber, it is necessary to use the optical circulators 17 for the number of channels. for that reason,
There was a serious problem that cost reduction would be difficult.

[0008]

As described above, in the various array type optical modulators that have been proposed hitherto, the problems in frequency characteristics, manufacturing process, and cost have been sufficiently solved. However, it was a problem in practical use. The present invention has been made in view of the above circumstances, and in an arrayed EA modulator module, shows good high-frequency characteristics in a wide band region and does not complicate the mounting process as the number of channels increases. ,
Another object is to provide an optical modulator that does not require the optical circulator 11 which causes an increase in cost.

[0009]

In order to achieve the above object, in the present invention, an electrical wiring constituted by an impedance matching type line, a plurality of optical modulators and passive waveguides on both sides of these optical modulators are provided. In an array type optical modulation device which is electrically connected to an integrated optical semiconductor element, optical waveguides are respectively connected to an optical input end and an optical output end, and an optical input end and an optical output end of each optical waveguide are connected. Are installed on the end faces facing each other, and the distance from the above-mentioned light input end along the propagation direction of light is a portion that becomes each light modulation element,
They are arranged in different positions for each channel,
It defines an optical modulation device characterized in that an electric wiring port for inputting a drive electric signal is formed on an end face different from the light input / output end of these optical waveguides.

According to a second aspect of the present invention, an input port for feeding a high frequency signal to the electric wiring formed by the impedance matching type line of the optical modulator according to the first aspect is provided on the opposite side alternately for each adjacent channel. It stipulates the structure of the optical modulator characterized by being installed on the end face.

[0011]

FIG. 1 is a top view showing the structure of an optical semiconductor device according to the first embodiment of the present invention. The semiconductor element is an element having an EA modulator array element 3 and a passive waveguide 4 having optical input / output terminals at both ends thereof.
It is a monolithic integrated multi-channel modulator array element 3 that is integrated. Although not shown, a horizontal taper structure is used at the light input / output end of the passive waveguide 4 to widen the spot size and reduce the coupling loss with the optical fiber. Multi-channel optical modulator array element 3
In order to directly optically couple the optical fiber array 5 with the optical fiber array 5 and to reduce the size of the multi-channel modulator array element 3 by setting the pitch between the channels to 500 μm, the optical coupling with the multi-channel modulator array element 3 is performed first. A spherical fiber was used. The element size is 2.5 mm x 2.5 mm,
It is a very small device.

Continuous light incident from the optical fiber array 5 on the input side enters the EA modulator array element 3 via the input side of the passive waveguide 4. The signal light converted by the EA modulator array element 3 is emitted to the optical fiber array 5 arranged on the output side from the output end of the passive waveguide 4. As described above, since the waveguide having the light input / output terminals separately configured is used, the optical circulator is not required.

By the way, it is known that the bent portion of the high-frequency electric wiring pattern causes reflection points and resonance points and therefore deteriorates high-frequency characteristics. Therefore, by disposing the four EA modulators in this embodiment at different positions on the waveguide for each channel from the light incident surface, the GC is arranged on the IPF carrier 21.
The wiring pattern 9 of PW is formed by a straight line having no bent portion in all channels, and is terminated by a 50Ω resistor 7. Thereby, since the bonding wires 8 having different lengths in FIG. 5 are not spatially arranged and connected, a good high frequency characteristic can be obtained in a wide band.

Further, the inter-channel electrical crosstalk is reduced by filling and separating the inter-channel pitch of the wiring pattern with 500 μm. GCP on the IPF carrier 21
If drive signals are input to the W wiring pattern 9 from all four channels in the same direction, a high-frequency connector such as a coaxial connector is arranged on only one side of the module, which is not shown, but the module becomes large. for that reason,
As shown in FIG. 1, drive electric signals are input alternately from both sides for each channel.

In this embodiment, the 4-channel modulator is shown, but even if the number of channels is 4 or more,
Only by increasing the number of connection points by thermosonic bonding, one IPF carrier 21 can be electrically wired. Therefore, the number of channels does not increase the complexity of the mounting process and the yield does not decrease.

A simulation was conducted to analyze the high frequency characteristics of the linear GCPW wiring pattern 9 shown in FIG. The analytical model used for the simulation is shown in FIG. 2 shows a top view of one channel, and FIG. 3 shows a cross-sectional view taken along the line AA ′ in FIG.
In FIG. 2, 1 is an input port for the high frequency drive voltage, and 2 is an output port connected to the 50Ω termination resistor 7. The line length of the signal line 10 is 2.5 mm, which is the same as the lateral width of the element,
As shown in FIG. 3, ground lines 1 are provided on both sides of the signal line 10.
1 is wired, and the surface opposite to the wiring surface, that is, the back surface opposite to the upper surface shown in FIG.

Further, in FIG. 3, the thickness of the Cu wiring pattern 19 was ignored, and the analysis was performed as a lossless line. Actually, the signal line 10 and the ground line 11 of the wiring pattern on the front surface and the ground 12 on the back surface are electrically connected by vias to strengthen the ground, but for simplicity, vias are not taken into consideration in this simulation. Further, in order to insulate the EA modulator and the IPF carrier 21, both surfaces of the IPF carrier 21 are coated with an insulating polyimide 20, but this is not taken into consideration in this simulation for simplicity. FIG. 4 shows the analysis result (S ₁₁ ). It can be seen from FIG. 4 that good characteristics of S ₁₁ <−20 dB are achieved in a wide frequency range of 1 to 40 GHz.

Although the EA modulator array in which four elements are integrated has been described as an example in the above-described embodiment, it is applied to an optical semiconductor array in which less than four elements or five or more elements are integrated. Of course, you can do it.

Further, in the above-mentioned embodiment, the voltage-driven EA modulator has been described as an example, but the present invention can be applied to other optical semiconductor elements such as a laser diode which directly modulates by current driving. Further, in the above-described embodiment, the insulating flexible wiring has been described as an example. However, a flip-chip mounting type in which a CPW wiring board formed on a ceramic substrate and an optical semiconductor element are connected by solder bumps It can also be applied to an optical semiconductor element incorporated in the optical semiconductor module of.

[0020]

The array type optical modulator according to the present invention is provided with an electric wiring formed by a parallel high frequency electric wiring film composed of impedance matching type lines, a plurality of electroabsorption type optical modulators, and passive elements at both ends of the optical modulator. In an optical modulator that electrically connects an optical semiconductor element in which a waveguide is integrated,
By arranging the modulators at different positions along the light propagation direction, it is possible to obtain a linear wiring pattern having no bending portion in the electric wiring film for supplying a driving electric signal to the modulator according to the present invention. So that you can
Good high frequency characteristics can be obtained over a wide band,
In addition, the high-speed array device required for the WDM network is realized without complicating the mounting process as the number of channels increases.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical modulator according to the present invention.

FIG. 2 is a top view of a model for high frequency characteristic simulation of a GCPW wiring pattern.

FIG. 3 is a sectional view of a wiring pattern in the model.

FIG. 4 is a characteristic diagram of the simulation result.

FIG. 5 is a configuration diagram of a conventional multi-channel EA modulator.

FIG. 6 is a configuration diagram of a conventional reflective multi-channel EA modulator.

[Explanation of symbols]

1: Input port 2: Output port 3: EA modulator array element 4: Passive waveguide 5: Optical fiber array 6: EA modulator electrode pad 7: Termination resistor 8: Bonding wire 9: GCPW wiring pattern 10: Signal line 11 : Ground line 12: Ground 13: Antireflection film 14: Macro strip line 15: Highly reflective film 16: Circuit part 17: Optical circulator 19: Cu
Wiring pattern 20: Polyimide 21: IP
F carrier

Claims (2)

[Claims] 1. An electrical wiring comprising an impedance matching type line, a plurality of optical modulators, and an optical semiconductor element in which passive waveguides are integrated on both sides of the optical modulators are electrically connected. In the optical modulator, a passive waveguide is connected to each of the optical input end and the optical output end, and the optical input end and the optical output end of each passive waveguide are installed on the end faces facing each other, and The modulator portion is arranged along the light propagation direction at different distances from the optical input end for each channel, and an electric wiring port for inputting a drive electric signal is provided in the passive conductor. An optical modulator, wherein the optical modulator is formed on an end face different from the light input / output end of the waveguide. 2. The optical modulator according to claim 1, wherein an input port for feeding a high-frequency signal to an electric wiring formed of an impedance matching type line is installed on the opposite end face for each adjacent channel. And a light modulator.