Patent Application
20230223738
The present disclosure relates to a laser light source apparatus including a semiconductor optical modulation device.
SNSs, video-sharing services, and the like have been spreading on a global basis, and an increase in capacity of data transfer has been accelerated. Concomitantly, an increase in speed and a decrease in size of optical transceivers have been progressing to cope with higher speed and larger capacity signal transmission in a limited mounting space.
Disclosed as a conventional laser light source apparatus loaded with a semiconductor optical modulation device is one in which a lead pin penetrating a metal stem and AC-GND are converted into a coplanar line and the coplanar line is connected to a semiconductor optical modulation device mounted on a temperature control module (see, e.g., PTL 1).
[PTL 1] JP 2011-518381 A
In a conventional laser light source apparatus, a semiconductor optical modulation device having a single optical modulator has been used, and a method for inputting an electrical signal to the semiconductor optical modulation device has been a single layer driving method. If the optical modulator is shortened, a band can be widened. However, shortening and an extinction ratio are in a trade-off relationship. Accordingly, there has been a problem that an attempt to shorten the optical modulator to widen a band makes it impossible to ensure a sufficient extinction ratio.
The present disclosure has been made to solve the above-described problem, and is directed to obtaining a laser light source apparatus capable of widening a band while ensuring a sufficient extinction ratio.
A laser light source apparatus according to the present disclosure includes: a metal stem; a lead pin penetrating the metal stem; a support block mounted on the metal stem; a dielectric substrate mounted on a side surface of the support block; a signal line formed on the dielectric substrate and having one end connected to the lead pin; a semiconductor optical modulation device mounted on the dielectric substrate; and a conductive wire connecting the other end of the signal line and the semiconductor optical modulation device, wherein the semiconductor optical modulation device includes a plurality of optical modulators separated from each other.
In the present disclosure, the semiconductor optical modulation device includes the plurality of optical modulators separated from each other. As a result, each of the optical modulators is more shortened than the conventional optical modulator, and thus decreases in electrostatic capacitance. Therefore, a gain corresponding to a frequency band is improved so that a band is widened. An equivalent extinction ratio to that of the conventional one optical modulator can be ensured by the plurality of electro-absorption optical modulators.
A laser light source apparatus according to the embodiments of the present disclosure will be described with reference to the drawings. The same components will be denoted by the same symbols, and the repeated description thereof may be omitted.
Lead pins 2a, 2b, and 2c penetrate the metal stem 1. A support block 3 is mounted on the metal stem 1. The support block 3 is a block composed of a metal material obtained by subjecting a surface of a material having a high thermal conductivity such as Cu to Au plating or the like.
A dielectric substrate 4 is mounted on a side surface of the support block 3. The dielectric substrate 4 is a ceramic plate composed of aluminum nitride (AlN), for example. Differential driving signal lines 5a and 5b and a ground conductor 5c constitute an Au plated and metallized pattern formed on the dielectric substrate 4. Each of the differential driving signal lines 5a and 5b is a coplanar line or a microstrip line, and has an equivalent impedance to an output impedance of a signal generator. The ground conductor 5c is connected to the metal stem 1 with an SnAgCu solder, for example.
A semiconductor optical modulation device 6 is mounted on the dielectric substrate 4. The semiconductor optical modulation device 6 is an optical modulator-integrated laser diode (EAM-LD) obtained by monolithically integrating a distributed feedback laser diode 6a and two electro-absorption optical modulators 6b and 6c. Each of the electro-absorption optical modulators 6b and 6c has an InGaAsP-based quantum well absorption layer, for example.
The differential driving signal lines 5a and 5b have their respective one ends connected to the lead pins 2a and 2b with solders 7a and 7b. Each of the solders 7a and 7b is composed of a material such as SnAgCu. Conductive wires 8a and 8b composed of Au or the like respectively connect the other ends of the differential driving signal lines 5a and 5b and the electro-absorption optical modulators 6b and 6c in the semiconductor optical modulation device 6 to each other. A conductive wire 8c composed of Au or the like connects the lead pin 2c and the distributed feedback laser diode 6a to each other. Ultrasonic vibration crimping, for example, is used for wire bonding.
The metal stem 1 fixes the support block 3, the dielectric substrate 4, and the semiconductor optical modulation device 6. The support block 3 fixes the dielectric substrate 4 and the semiconductor optical modulation device 6. The dielectric substrate 4 fixes the semiconductor optical modulation device 6. Generally, the dielectric substrate 4 is responsible for an electrical insulation function and a heat transfer function. Heat generated in the semiconductor optical modulation device 6 is dissipated to a cooling member (not illustrated) in a negative direction of a Z-axis of the metal stem 1 via the metal stem 1, the support block 3, and the dielectric substrate 4.
The distributed feedback laser diode 6a is supplied with power via the lead pin 2c and the conductive wire 8c, and emits laser light. An electrical signal is applied to the plurality of optical modulators 6b and 6c in the semiconductor optical modulation device 6 via the conductive wires 8a and 8b after being inputted from the lead pins 2a and 2b and transmitted to the differential driving signal lines 5a and 5b, respectively, via the solders 7a and 7b. The metal stem 1, the support block 3, and the ground conductor 5c in the dielectric substrate 4, which are connected to one another, function as AC ground, and an electrical signal inputted to each of the lead pins 2a and 2b is electromagnetically coupled to the metal stem 1.
The laser light emitted by the distributed feedback laser diode 6a is sequentially modulated by the electro-absorption optical modulators 6b and 6c. The modulated laser light is radiated along an optical axis perpendicular to a chip end surface and parallel to a chip main surface from a light emission point of the semiconductor optical modulation device 6.
An n-type electrode pad 6bn of the electro-absorption optical modulator 6b and the p-type electrode pad 6cp of the electro-absorption optical modulator 6c are connected to each other by a conductive wire or the like, whereby the electro-absorption optical modulator 6b and the electro-absorption optical modulator 6c are connected in series. The p-type electrode pad 6bp of the electro-absorption optical modulator 6b and an n-type electrode pad 6cn of the electro-absorption optical modulator 6c are respectively wire-connected to the differential driving signal lines 5a and 5b.
The two electro-absorption optical modulators 6b and 6c in the semiconductor optical modulation device 6 are connected in series. Therefore, letting C1 and C2 be respectively electrostatic capacitances of the electro-absorption optical modulators 6b and 6c, a composite electrostatic capacitance C satisfies C=C1×C2/(C1+C2).
As described above, in the present embodiment, the semiconductor optical modulation device 6 includes the plurality of electro-absorption optical modulators 6b and 6c separated from each other. As a result, each of the optical modulators is more shortened than the conventional optical modulator, and thus decreases in electrostatic capacitance. Therefore, a gain corresponding to a frequency band is improved so that a band is widened. An equivalent extinction ratio to that of the conventional one optical modulator can be ensured by the plurality of electro-absorption optical modulators 6b and 6c.
The plurality of electro-absorption optical modulators 6b and 6c are connected in series between the first and second differential driving signal lines 5a and 5b that each feed a differential signal to the semiconductor optical modulation device 6. A method for inputting an electrical signal to the semiconductor optical modulation device 6 is thus a differential driving method. Accordingly, the plurality of electro-absorption optical modulators 6b and 6c can be driven at an equivalent voltage to the conventional one.
In the present embodiment, a temperature control module that has been provided in a conventional technique is not used, thereby making it possible to reduce cost and reduce assembly takt time by reducing the number of members. A temperature control module may be mounted on the metal stem 1 or the side surface of the support block 3, for example, if necessary, depending on a use environment.
The lower surface of the semiconductor optical modulation device 6 is bonded to a ground conductor 5c provided on the upper surface of the dielectric substrate 4 with a solder 17. The ground conductor 5c is divided into two equal parts, and the matching resistor 15 is arranged in a gap between the two equal parts of the ground conductor 5c. As a result, the ground conductor 5c and the matching resistor 15 can be separated from each other. A plating thickness of the ground conductor 5c is larger than that of the matching resistor 15. Accordingly, the matching resistor 15 does not interfere with the semiconductor optical modulation device 6. Other components and effects are similar to those in the embodiments 1 and 2. When the present embodiment is combined with the embodiment 2, the matching resistor 15 is replaced with matching resistors 15a and 15b.
1 metal stem; 2a,2b lead pin; 3 support block; 4 dielectric substrate; 5a first differential driving signal line; 5b second differential driving signal line; 5c ground conductor; 6 semiconductor optical modulation device; 6b,6c electro-absorption optical modulator; 8a,8b conductive wire; 15 matching resistor; 18 groove; 19 light receiving device; 22 cap; 23 lens
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/045723 | 12/8/2020 | WO |
