JP2011134962A - Optical transmission module - Google Patents

Abstract

Provided is an optical transmission module in which a cone-shaped coil constituting a bias T circuit is mounted without deteriorating its characteristics.
The optical transmission module houses a laser diode 4 in a casing, and a high frequency signal is supplied to the laser diode 4 via an electrode pin attached to a through hole 2c of a stem 2 constituting the casing. And a bias T circuit. A coil constituting the bias T circuit is formed of a conical coil 7b and mounted in the through hole 2d of the stem 2 by glass sealing.
[Selection] Figure 2

Description

  The present invention relates to an optical transmission module used for optical communication.

  In an optical communication apparatus having an optical transmission function, an optical transmission module having a laser diode (LD) is electrically connected to an external circuit board on which an LD driving driver is mounted via a flexible circuit board. Connected and used. A circuit called a bias T circuit composed of a coil and a capacitor is provided on an external circuit board or a flexible circuit board in order to superimpose a DC component such as a DC current or a DC voltage on a high-frequency signal and supply it to the LD. As a coil used for this bias T circuit, a conical coil having a good frequency characteristic even in high-speed optical communication, in other words, a cone-shaped coil that functions as a desired inductor over a wide range of frequencies is known (for example, Patent Documents 1 to 3). 3).

JP 2004-193886 A JP 2007-109839 A JP 2008-47711 A

  In consideration of the degree of freedom in designing the external circuit board connected to the optical transmission module, the components such as the cone-shaped coil constituting the bias T circuit are not mounted on the external circuit board, but the optical transmission module itself. It is preferable to mount on. However, there is a technical problem that it is difficult to mount the cone-shaped coil on the optical transmission module without deteriorating the characteristics of the coil. However, Patent Documents 1 to 3 do not mention this point.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical transmission module in which a cone-shaped coil constituting a bias T circuit is mounted without deteriorating its characteristics. .

  In order to solve the above problems, the optical transmission module of the present invention has a laser diode housed in a housing, and a high-frequency signal is supplied to the laser diode via an electrode pin attached to a through hole of a stem constituting the housing. In addition, a bias T circuit is provided, and the coil constituting the bias T circuit is formed of a conical coil and is mounted in a through hole of the stem by glass sealing.

  The conical coil is preferably wound on a magnetic material. Moreover, it is preferable that the capacitor which comprises a bias T circuit is mounted in the through-hole of a stem by glass sealing. Furthermore, it is preferable that the capacitor is configured such that the electrode pins are bisected by the glass sealing portion and the bisected ends face each other.

  In the optical transmission module of the present invention, the conical coil is mounted by mounting the conical coil constituting the bias T circuit on the casing by glass sealing. This can be done without deterioration. Furthermore, since the conical coil is provided in the optical transmission module, the degree of freedom in designing the circuit board can be increased.

It is an external view of an example of the optical transmission module of the present invention. It is a figure which shows the mode inside the optical transmission module of FIG. It is a figure which expands and shows the coil member of the optical transmission module of FIG. It is a figure which shows the other example of the signal pin of the optical transmission module of this invention.

  An example of the optical transmission module according to the present invention will be described with reference to FIGS. FIG. 1 is an external view of an example of an optical transmission module, FIG. 2 is a diagram illustrating an internal state of the optical transmission module of FIG. 1, and FIG. 3 is an enlarged view of a coil member and a signal pin of the optical transmission module of FIG. FIG. In FIG. 3, illustration of a stem, a submount, and the like, which will be described later, is omitted.

  As illustrated by reference numeral 1 in FIG. 1, the optical transmission module of the present invention has an LD 4 (see FIG. 2) hermetically sealed in a CAN package including a stem 2 and a cap 3. It is used by being electrically connected to. The optical transmission module 1 converts an electrical signal from an external circuit board into an optical signal by the LD 4 and transmits the optical signal to the outside through a lens 3 a attached to the cap 3. In the following description, the side including the lens 3a is referred to as the front, and the opposite side is referred to as the rear. Moreover, let the Y direction of FIG. 1 be the left-right direction among the directions orthogonal to the front-back direction.

In the optical transmission module 1, the LD 4 is mounted on the mounting portion 2b of the stem 2 in FIG. 2 via the submount 4a.
The stem 2 includes, for example, a stem base 2a formed in a substantially columnar shape from a metal material, and a mounting portion 2b attached to the stem base 2a so as to protrude forward from the stem base 2a. In addition, although illustration is abbreviate | omitted, the optical transmission module 1 has a monitor photodiode (PD: Photo Diode) for feedback control of LD4. The monitor PD is mounted on the stem base 2a, for example.

  The stem base 2a is provided with through holes 2c and 2d which are glass-sealed in a state where various electrode pins (described later) made of a metal material are inserted. Examples of the electrode pins include a signal pin 5 for supplying a high frequency signal from an external circuit board to the LD 4 and a monitor pin 6 for taking out an electrical signal from the monitor PD to the outside. In addition to these pins, a coil member 7 described later is also inserted into the through hole 2d and attached to the stem base 2a by glass sealing. The through hole 2c into which the signal pin 5 is inserted and fixed and the through hole 2d into which the coil member 7 is inserted and fixed are provided adjacent to each other.

  The signal pin 5 has a convex portion 5 a provided so as to protrude in the direction of the coil member 7. The projecting portion 5a is connected to the metal pattern 4b on the submount 4 for mounting the LD by a wire 8, so that the signal pin 5 and the LD 4 are electrically connected.

  The coil member 7 is for superimposing a bias current, which is a direct current component, on the high-frequency signal from the signal pin 5 and supplying it to the LD 4. As shown in FIG. 3, the coil member 7 is formed by winding a conducting wire 7 a in a conical shape. The conical coil 7b is provided. Since the signal pin 5 and the LD 4 are electrically connected as described above, the coil member 7 and the LD 4 are connected to each other by directly electrically connecting the conductive wire 7a led out from the stem 2 to the LD 4 side to the convex portion 5a of the signal pin 5. It is designed to be electrically connected.

  Note that the end 7c of the conductive wire 7a opposite to the connection side with the signal pin 5 is led out from the stem 2, for example, and soldered to an electrode pad or the like of the external circuit board to be electrically connected to the bias current supply source. Is done. Since the conical coil 7b of the coil member 7 has a high impedance over a wide range of frequencies, the coil member 7 can transmit a DC component signal to the LD 4 at a wide range of frequencies without distortion.

  In the present optical module 1, the conical coil 7 b is mounted by sealing the through hole 2 d with glass in a state where the conical coil 7 b of the coil member 7 is disposed in the through hole 2 d of the stem 2. Therefore, the characteristics of the cone-shaped coil 7b do not deteriorate during the mounting. Further, since the conical coil 7b is not physically affected and is physically protected, its characteristics are not deteriorated.

In general, when a cone-shaped coil is mounted on an optical transmission module, since the module itself is small, the conducting wire forming the cone-shaped coil is also very thin, so that the electrical connection between the conducting wire and the LD is very difficult. However, the optical transmission module 1 is easy because the electrical connection is performed as follows.
First, the end portion of the conducting wire 7a of the conical coil 7b and the convex portion 5a of the signal pin 5 are connected in advance. Then, the coil member 7 and the signal pin 5 are inserted into the adjacent through holes 2c of the stem base 2a and attached by glass sealing. Such a mounting method can be performed because the through hole 2d into which the coil member 7 is inserted and fixed is adjacent to the through hole 2c into which the signal pin 5 is inserted and fixed.

  After the coil member 7 and the signal pin 5 are attached to the stem base 2a, the LD 4 is mounted on the submount 4a, and the convex portion 5a of the signal pin 5 and the submount 4a are connected by wire bonding. Thereby, the LD 4 and the signal pin 5 are electrically connected, and the LD 4 and the conductive wire 7a of the cone-shaped coil 7b are electrically connected. As described above, in the present optical transmission module 1, when the conductor 7a of the cone-shaped coil 7 and the LD 4 are electrically connected via the submount 4a, the conductor 7a of the cone-shaped coil 7b and the submount 4a are directly connected. Instead, the electrical connection is very easy because the method described above is used.

  Further, in the present optical transmission module, the cone-shaped coil for constituting the bias T circuit, that is, the cone-shaped coil for superimposing the DC component on the high-frequency signal and supplying it to the LD is provided in the optical transmission module itself. It is not necessary to provide the coil on the board, and the degree of freedom in designing the external circuit board can be increased.

In the optical transmission module 1, since the convex portion 5a of the signal pin 5 is provided, the length of the conducting wire 7a from the cone-shaped coil 7b of the coil member 7 to the signal pin 5 is short, and therefore parasitic caused by the conducting wire 7a. There is little influence of impedance.
Further, since the conical coil 7b is disposed in the through hole of the stem, the conical coil 7b is deformed as an inductor when the LD 4 is mounted or when wire bonding for electrical connection to the LD 4 is performed. The characteristics of the do not change.

The conical coil 7b of the coil member 7 is required to have a high impedance over a wide range of frequencies, and preferably has a high inductance. For this reason, the cone-shaped coil 7b is preferably composed of a wire 7a wound with a narrow pitch (for example, a wire 25a having a diameter of 25 μm wound with 40 turns while being spread at a pitch of 25 μm). Moreover, in order to make it high inductance, you may make it produce the cone-shaped coil 7b by winding conducting wire 7a on a high magnetic body in cone shape. When the high magnetic material is used as described above, the strength of the cone-shaped coil 7b is also improved.
In the example shown in the figure, the distance between the signal pin 5 and the coil pin 7 is different on the left and right sides (the anode side and the cathode side).

Next, another example of signal pins of the optical transmission module of the present invention will be described with reference to FIG.
The signal pin 5 ′ in FIG. 4 has a first pin 5a ′ and a second pin 5b ′ that are continuous in the extending direction. The signal pin 5 ′ has one end portion 5c ′ of the first pin 5a ′ and one end portion 5d ′ of the second pin 5b ′ covered with a glass sealant in the through hole of the stem so as to have a predetermined interval. The capacitor 5e ′ is formed by being fixed so as to face each other. In other words, the signal pin 5 ′ has a shape that is divided into two in the through hole of the stem that is the glass sealing portion, and the two end portions 5c ′ and 5d ′ that are divided are opposed to each other, thereby the capacitor 5e ′. Is configured. By this capacitor 5e ′, the low frequency component of the high frequency signal supplied to the LD can be removed.

  By using the signal pin 5 ′ in which the capacitor 5 e ′ is formed when fixed by glass sealing as described above, that is, by providing a capacitor constituting the bias T circuit in the optical transmission module itself, There is no need to provide the capacitor on the circuit board, and the design freedom of the external circuit board is further increased.

  The one end portion 5c 'of the first pin 5a' and the one end portion 5d 'of the second pin 5b' are larger in diameter than the main body portions 5f 'and 5g', respectively. The reason for this will be described below.

Here, the signal pin includes two pins like the above-described signal pin 5 ′, and it is assumed that both pins have a uniform diameter regardless of the location.
The signal pin preferably has a characteristic impedance of 50Ω as in the transmission line. For this purpose, if the diameter of the glass sealing portion is 0.75 mm and the relative dielectric constant of the sealing glass is 4, the signal pin Needs to be as thin as 0.14 mm.
When the diameter of the two pins constituting the signal pin is thin and uniform regardless of the location as described above, both pins are fixed so that a desired capacitance is formed at the opposite portion of both pins. Is difficult. However, as in the case of the signal pin 5 ′, the diameters of the opposed end portions 5c ′ and 5d ′ are made larger than the diameters of the main body portions 5f ′ and 5g ′, and the facing surface is made larger, so that it is easier and desired Both pins 5a 'and 5b' can be fixed so as to form a capacitance.

  Although the above example is an example of operating the LD in the operation mode, the present invention can be similarly applied to the case of operating in the single mode.

DESCRIPTION OF SYMBOLS 1 ... Optical transmission module, 2 ... Stem, 2a ... Stem base, 2b ... Mounting part, 2c, 2d ... Through-hole, 3 ... Cap, 3a ... Lens, 4 ... Submount, 4a ... Metal pattern, 5, 5 '... Signal pin, 5a ... convex portion, 6 ... monitor pin, 7 ... coil member, 7a ... conducting wire, 7b ... conical coil, 8 ... wire.

Claims (4)

An optical transmission module that houses a laser diode in a housing, supplies a high-frequency signal to the laser diode via an electrode pin attached to a through-hole of a stem constituting the housing, and includes a bias T circuit. There,
The optical transmission module according to claim 1, wherein the coil constituting the bias T circuit is formed of a cone-shaped coil, and is mounted on the through hole of the stem by glass sealing.   The optical transmission module according to claim 1, wherein the conical coil is wound on a magnetic body.   3. The optical transmission module according to claim 1, wherein a capacitor constituting the bias T circuit is mounted on the through hole of the stem by glass sealing. 4.   4. The optical transmission module according to claim 3, wherein the capacitor is configured such that the electrode pin is divided into two portions by the glass sealing portion, and the two end portions are opposed to each other.

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