JP2000164970A - Optical element module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce parasitic inductance on a signal propagation path which reaches a semiconductor laser by forming coplanar lines at signal inputs of first and second boards, thereby constituting an optical element module. SOLUTION: A first coplanar line 3, metallized so as to provide an input impedance of 50 Ω, is formed on a first aluminum nitride board 2, a thin film resistance 4 for impedance matching with a semiconductor laser 1 is formed along the way of a center conductor for propagating input signals on this coplanar line 3, second coplanar lines 9 are formed on a lead-side second ceramic board 8 which forms outer terminals of a package 6, and the first and second coplanar lines 3, 9 are interconnected through a flexible wiring board 10 having coplanar lines, thus constituting an optical element module.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical device module such as a semiconductor laser module for optical communication and an external modulator module, and more particularly to a broadband optical device module used under high-speed modulation in the gigabit band.

[0002]

2. Description of the Related Art Conventionally, an optical element module for converting an optical signal and an electric signal has been used in the field of optical communication.

An example of a semiconductor laser module in which the optical element is a semiconductor laser will be described with reference to FIG. 6 (see Japanese Patent No. 2661669). Laser light emitted from the semiconductor laser 1 housed in the package 6 is condensed by a lens 13 and coupled to an optical fiber 14 whose axis coincides with its optical axis.

A semiconductor laser 1 is mounted on a first microstrip line 16 made of a metal formed on a first substrate 2 made of a ceramic material or the like so that a signal propagation direction and a light emission direction coincide with each other. The first substrate 2 is mounted on a carrier 5 made of a metal plate or the like, and the carrier 5 is mounted on a thermoelectric cooling element (not shown). By adjusting the length of the first microstrip line 16, the position of the semiconductor laser 1 in the package 6 can be freely set.

Further, a second microstrip line 17 is formed on a second substrate 8 made of a ceramic material for forming external terminals of the package 6, and a first microstrip line 16 and a first bonding wire 18. Second microstrip line 17
A chip resistor 19 for impedance matching with the semiconductor laser 1 is placed on the way. A modulation signal 7 supplied from a modulation circuit (not shown) passes through a second microstrip line 17, a chip resistor 19, a first bonding wire 18, and a first microstrip line 16,
The semiconductor laser 1 is reached. On the upper surface of the semiconductor laser 1,
The other electrode pattern is formed, and is connected to the carrier 5 by a second bonding wire 20 as a relay point for grounding to the case ground.

On the side of the semiconductor laser 1 opposite to the lens 13, a monitoring photodiode 15 for monitoring backward emission light of the semiconductor laser 1 is arranged. In this figure, other external terminals implanted in the package 6 and other circuit portions in the package 6 connected to these external terminals (such as connection from the carrier 5 to the case ground) are to be simplified. , Not shown.

FIG. 7 is an equivalent circuit diagram simply showing the signal propagation path, and a modulated signal light can be obtained by driving the semiconductor laser 1 with a predetermined electric signal.

Here, the first bonding wire 18 and the second bonding wire 20 are about 1 mm long and about 1 mm long.
Expressed as nH inductance. The inductance value is proportional to the length of the bonding wires 18 and 20,
It is inversely proportional to the number of wires. In semiconductor laser modules used under high-speed modulation in the gigabit band, it is necessary to suppress losses and reflections in the electrical connection between the semiconductor laser drive circuit and the semiconductor laser, and the inductance on the signal propagation path must be minimized. Therefore, the bonding wire length is generally minimized, and the inductance is reduced by bonding a plurality of wires.

[0009]

In the prior art, since the bonding wires 18 and 20 are arranged on the signal propagation path, reflection and loss of the modulated signal occur due to the parasitic inductance of the bonding wires 18 and 20.
The modulation frequency of the semiconductor laser module was band-limited.

Also, the first microstrip line 16
Is set between the semiconductor laser 1 and the monitoring photodiode 15, and in order to obtain sufficient receiving sensitivity of the photodiode 15, it is actually necessary to set the distance to 1 mm or less. Therefore, wire bonding to the first microstrip line 17 has been difficult.

In addition, when a matching resistor for impedance matching with the semiconductor laser 1 is housed in the package 6, as described above, the first microstrip line 1
Since the distance 6 is short, it is impossible to place the chip type resistor 19 in the middle of the second microstrip line 17 by means of a thin film. Needed. There is a problem that the soldered portion of the chip resistor tends to cause electrical reflection.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a semiconductor laser module or an optical element module having a wide band by reducing a parasitic inductance on a signal propagation path to a semiconductor laser. is there.

[0013]

SUMMARY OF THE INVENTION The present invention comprises a first substrate for mounting and fixing an optical element such as a semiconductor laser or an external modulator chip disposed in a package, and a second substrate for forming external terminals. An optical element module is formed by forming a coplanar line in the signal input / output portions of the first and second substrates.

Further, the present invention is characterized in that the coplanar lines of the first substrate and the second substrate are connected by a flexible wiring board on which the coplanar lines are formed.

That is, the above object can be achieved by forming a coplanar line in place of the first and second microstrip lines and connecting by a flexible wiring board having a coplanar line formed in place of the bonding wire. The coplanar line has a degree of freedom in forming the center conductor width, which is an input signal line, and is not limited to a straight line. Further, the flexible wiring board on which the coplanar line is formed is not regarded as inductance, and does not receive electric reflection or loss.
Further, by forming the impedance matching resistor as a thin film in the middle of the coplanar line, it is possible to suppress the electrical reflection of the soldered portion of the chip resistor and to improve the frequency bandwidth of the optical element module.

[0016]

A coplanar line is formed on the first and second substrates, and each coplanar line is connected by a flexible wiring board having the same coplanar line formed thereon. By forming a thin film resistor for use, it is possible to reduce the parasitic inductance on the signal propagation path, not receive electrical reflection or loss, improve the small signal frequency response characteristics of the optical element module, and improve the bandwidth be able to.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a plan view showing the structure of a semiconductor laser module according to the present invention in which the optical element is a semiconductor laser. 6 are given the same reference numerals.

[0019] A first layer made of aluminum nitride material
The input impedance is 5
A first coplanar line 3 having 0Ω is formed.
A thin film resistor 4 for impedance matching with the semiconductor laser 1 is formed in the middle of the center conductor through which the input signal of the first coplanar line 3 propagates. The semiconductor laser 1 is mounted and fixed on a portion of the first coplanar line 3 which is the end of the center conductor.

The first substrate 2 is mounted and fixed on a carrier 5 made of a conductive material such as a copper tungsten material by means of soldering or the like, and is mounted on a thermoelectric cooling element for temperature control of the semiconductor laser 1 (not shown). It is mounted and housed and fixed in the package 6.

The package 6 is a 14-pin butterfly type package using a ceramic substrate for forming leads of a semiconductor laser module used at a modulation speed of 10 Gb / s. A second coplanar line 9 is provided on a second substrate 8 which is a lead-side ceramic substrate to which the modulation signal 7 is input.
Is formed, and the first coplanar line 3 and the second coplanar line 9 are connected by a flexible wiring board 10 on which the coplanar line is also formed.

An optical signal emitted from the semiconductor laser 1 is condensed by a lens 13, led out of an optical fiber 14, and a monitoring photodiode 15 for monitoring backward emitted light from the semiconductor laser 1 is provided. I have.

FIG. 2 shows the details of the flexible wiring board 10. The three copper foils 11 having a thickness of 20 μm or less have an impedance of 50 μm between the width of the center copper foil through which the modulation signal 7 passes and the copper foils on both sides provided on the case ground.
It is set to have a size of Ω, and is fixed and formed by an insulator 12 made of a polyimide resin. Copper foil 11
Are slightly exposed so that connection by soldering or the like is possible. Note that, instead of the copper foil 11, a gold foil may be used, and the connection may be made by means such as thermocompression bonding.

Since the flexible wiring board 10 is thin and soft and has good flexibility, workability is not inferior to wire bonding.

The modulation signal 7 has an input impedance of 50
The semiconductor laser 1 passes through the center conductor of the second coplanar line 9 set to Ω, the center conductor of the flexible wiring board 10, the center conductor of the first coplanar line 3 and the thin film resistor 4.
Leads to. The p-side of the semiconductor laser 1 is connected to ground (COM) patterns on both sides of the first coplanar line 3 by bonding wires 20, and is grounded to a case ground.

FIG. 3 is a sectional view of a microstrip line substrate used in a conventional module, and FIG. 4 is a sectional view of a coplanar line substrate used in the present invention. In the case of the microstrip line substrate shown in FIG. 3, its characteristic impedance is determined by the thickness H of the substrate, the relative permittivity εr, and the line width W. Generally, since the substrate thickness H is constant, the line width also needs to be constant.

On the other hand, in the case of the coplanar waveguide substrate shown in FIG. 4, the ratio is determined by the center conductor width W, the ratio of the distance G to the ground conductor (ground pattern), and the relative permittivity εr of the substrate. Therefore, the center conductor width W can be freely set on the same substrate, and as shown in the first coplanar line 3 and the second coplanar line 9 in FIG.
And the connection by the flexible wiring board 10 having the coplanar line is also possible.

FIG. 5 is a simplified equivalent circuit diagram showing a signal propagation path according to this embodiment. As shown in FIG. 5, the signal propagation path is affected by the parasitic inductance of the bonding wires 18 and 20 shown in the conventional example of FIG. It turns out there is no.

Since the bandwidth in the small signal frequency response characteristic of the semiconductor laser module is inversely proportional to the inductance value, the inductance is reduced as in the present embodiment, so that the conventional 3 dB bandwidth is 25 GHz. On the other hand, the bandwidth is improved to 28 GHz, and the band can be widened. Further, since there is no wire bonding near the photodiode, workability can be improved.

In the above example, the semiconductor laser 1 is used as an optical element. However, an optical element module can be formed by using an optical element such as an external modulator chip.

[0031]

According to the present invention, there are provided a first substrate for mounting and fixing an optical element such as a semiconductor laser or an external modulator chip disposed in a package, and a second substrate for forming external terminals. By forming a coplanar line in the signal input / output portions of the first and second substrates to form the optical element module, the parasitic inductance on the input signal propagation path can be reduced, and the bandwidth of the optical element module is improved. Broadband.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of an optical element module according to the present invention.

2A and 2B show a flexible wiring board used for the optical element module of the present invention, wherein FIG. 2A is a plan view and FIG. 2B is an end view.

FIG. 3 is a sectional view of a microstrip line substrate.

FIG. 4 is a sectional view of a coplanar waveguide substrate.

FIG. 5 is an equivalent circuit diagram simply showing a signal propagation path of the optical element module of the present invention.

FIG. 6 is a plan view illustrating a configuration of a conventional optical element module.

FIG. 7 is an equivalent circuit diagram simply showing a signal propagation path of a conventional optical element module.

[Explanation of symbols]

 1: Semiconductor laser 2: First substrate 3: Coplanar line 4: Thin film resistor 5: Carrier 6: Package 7: Modulation signal 8: Second substrate 9: Coplanar line 10: Flexible wiring board 11: Copper foil 12: Insulation Body 13: Lens 14: Optical fiber 15: Photodiode

Claims (4)

[Claims] 1. An optical element module comprising an optical element such as a semiconductor laser or an external modulator chip in a package and an optical fiber for inputting / outputting an optical signal to / from the optical element, wherein the optical element is mounted and fixed. An optical element module, comprising: a first substrate that forms an external terminal; and a second substrate that forms an external terminal, wherein a coplanar line is formed in an electric signal input / output portion of the first and second substrates. 2. The optical element module according to claim 1, wherein the coplanar lines of the first substrate and the second substrate are connected by a flexible wiring board. 3. The optical element module according to claim 2, wherein said flexible wiring board forms a coplanar line. 4. The optical element module according to claim 1, wherein a thin film resistor for impedance matching is formed in the input signal propagation path of the coplanar line on the first substrate.