JP2018060975A - Direct modulation laser - Google Patents

Abstract

A direct modulation laser capable of simultaneously realizing high-speed operation and high light output is provided. A direct modulation laser includes a DFB (distributed feedback) laser 101, an SOA (semiconductor optical amplifier) 103 formed at the emission end of the DFB laser, and a superposition signal of an AC component signal and a DC component signal on the DFB. And a drive circuit 106 that supplies only the DC component signal to the SOA. [Selection] Figure 1

Description

The present invention relates to a distributed feedback (DFB) directly modulated laser.
To do.

  Directly modulated laser (DML) is an element that directly modulates the light intensity of a laser beam output from the end face of a laser chip by modulating the current value input to the laser chip. Some conventional direct modulation lasers include an active layer having an MQW (Multiple Quantum Well) structure, a ridge waveguide, and a semiconductor layer (Patent Document 1).

Japanese Patent No. 5823999

  In general, when the DML is operated at a high speed, a method of shortening the cavity length of the laser is taken. However, if the resonator length of the DML is short, the resistance of the element increases, and thus there is a problem that the temperature of the element rises when current is injected into the DML, resulting in deterioration of the optical output.

  In other words, since there is a trade-off relationship between high-speed operation of DML and optical output, simply reducing the laser cavity length realizes high-speed operation and high output of DML simultaneously by this trade-off. I couldn't.

  The present invention has been made under the above circumstances, and by providing a semiconductor optical amplifier (SOA) on the laser emission side, high-speed operation and high light output can be realized simultaneously. An object of the present invention is to provide a direct modulation laser capable of satisfying the requirements.

  In order to achieve the above object, the present invention provides a DFB laser, an SOA formed at the emission end of the DFB laser, an AC component signal and a superimposed signal of a DC component signal to the DFB, and the SOA. And a drive circuit that provides only a DC component signal.

  The drive circuit may include a bias tee that outputs the superimposed signal.

  The DC component signal to the SOA may be given according to a ratio of lengths of the DFB laser and the SOA in the optical waveguide direction.

  According to the present invention, high-speed operation and high light output can be realized simultaneously.

It is a figure for demonstrating the structure outline of the direct modulation laser which concerns on 1st Embodiment. It is a figure which shows the lamination example of the direct modulation laser of 1st Embodiment. It is a figure which shows the structure outline of the direct modulation laser which concerns on 2nd Embodiment. It is a figure which shows the structural example of the optical transmission module which mounts the direct modulation laser of FIG. It is a figure which shows the structural example of the optical transmission module which mounts the direct modulation laser of FIG.

  Hereinafter, direct modulation lasers according to embodiments of the present invention will be described. The direct modulation laser of each embodiment is a DFB laser.

<First Embodiment>
[Outline of Overall Configuration of Direct Modulation Laser 100]
FIG. 1 is a diagram for explaining an outline of the overall configuration of a direct modulation laser 100 according to the present embodiment.

  As shown in FIG. 1, the direct modulation laser 100 includes a DFB laser 101 and an SOA 103 in order with respect to the optical waveguide direction, and the separation groove 102 electrically separates the DFB laser 101 and the SOA 103. In this embodiment, the DFB laser 101 and the SOA 103 are monolithically laminated on a single semiconductor substrate.

The drive circuit 106 includes a signal source 10 for an AC component signal I _RF, a signal source 20 for a DC component signal I _d , and a circuit including a capacitor C, a resistor R, and a coil L.

  One end of the DFB laser 101 is connected to a series circuit including a resistor R and a capacitor C of the drive circuit 106, and the other end of the DFB laser 101 is grounded.

One end of the coil L of the drive circuit 106 is connected between one end of the DFB laser 101 and the resistor R, and the other end of the coil L is connected between one end of the SOA 103 and the signal source 20. The other end of the SOA 103 is grounded. In this case, since no AC component flows through the coil L, the AC component signal I _RF from the signal source 10 does not flow to the SOA 103 side. Therefore, a superimposed signal (I _RF + I _DC ) including an AC component and a DC component, which will be described later, is given to the DFB laser 101.

In the present embodiment, the DC component flowing through the DFB laser 101 is given according to the ratio of the lengths of the DFB laser 101 and the SOA 103 in the optical waveguide direction. That is, the DFB laser 101, a DC component signal I _DC is supplied, the SOA103, given a direct current component signal I _SOA. For example, when the SOA length is 50 μm and the DFB laser length is 200 μm, the SOA length is 1/5 with respect to the total length of the SOA 103 and the DFB laser 101, so that I _SOA = (1/5) × I _b . In this case, I _DC = (4/5) × I _b .

In this way, the DC component signal I _SOA injected into the _SOA 103 can be adjusted by adjusting the lengths of the DFB laser 101 and the _SOA 103.

In the present embodiment, the signals I _RF , I _b , I _DC and I _SOA are current signals.

  In FIG. 1, the DFB laser end face 101a is provided with a high reflection (HR) coating, and the SOA emission end face 103a is provided with an anti-reflection (AR) coating.

As described above, by the circuit including the capacitor C, the resistor R, and the coil L, the superimposed signal (I _RF + I _DC ) of the AC component and the DC component is given to the DFB laser 101, and the DC component signal I _SOA is given to the _SOA 103. As a result, it is possible to always ensure the power supply required for the SOA 103.

  In the direct modulation laser 100 of the present embodiment, the optical output from the DFB laser 101 is amplified by the SOA 103. Therefore, even if the resonator length of the DFB laser 101 is shortened, the degradation of the optical output can be amplified by the SOA 103, so that the DFB laser 101 can be operated at high speed and the optical output can be increased.

[Laminated structure of direct modulation laser 100]
Next, the configuration of the direct modulation laser 100 described above will be described with reference to FIGS. 1 and 2.

  FIG. 2 is a diagram illustrating a configuration example of the direct modulation laser 100.

  In FIG. 2, the direct modulation laser 100 includes an n-type InP substrate 1, and includes a DFB laser part layer 3 and an SOA part layer 4 in this order in the optical waveguide direction. An n-type electrode 13 is provided on the back surface of the substrate 1.

  Each of the layers 2 and 4 described above is formed of an InGaAlAs-based material or an InGaAsP-based material and has a quantum well structure.

  The optical waveguide layer 5 formed between the DFB laser part layer 3 and the SOA part layer 4 is made of an InGaAsP-based material. A p-type InP cladding layer 7 is formed on the DFB laser part layer 3, the SOA part layer 4, and the optical waveguide layer 5.

In FIG. 2, a diffraction grating 6 is formed on the DFB laser part layer 3. The insulating film 8 is formed so as to cover the DFB laser part layer 3, the SOA part layer 4, the optical waveguide layer 5, and the cladding layer 7, respectively. A benzocyclobutene (BCB) 9 is formed on the insulating film 8, and a p-type electrode 11 for injecting a signal (I _RF + I _DC ) into the DFB laser part layer 3 and the SOA on the BCB 9 and the SOA. A p-type electrode 12 for injecting the signal I _SOA to the _partial layer 5 is formed.

[Operation of Direct Modulation Laser 100]
Next, the operation of the direct modulation laser 100 described above will be described with reference to FIGS.

  First, when a forward bias is simultaneously applied to the p-type electrodes 11 and 12 of the DFB laser 101 and the SOA 103, the light generated in the DFB laser part layer 3 is periodically fed back by the diffraction grating 6.

  Then, single mode laser light is generated and emitted from the DFB laser part layer 3. The oscillation wavelength of the laser light at this time is 1300 nm, for example.

  The laser light from the DFB laser part layer 3 described above is amplified by the SOA part layer 4 via the optical waveguide layer 5 and emitted to the outside.

  As described above, the direct modulation laser 100 of this embodiment includes the DFB laser 101 and the SOA 103. In this case, even if the resonator length of the DFB laser 101 is shortened, the degradation of the optical output can be amplified by the SOA 103, so that the DFB laser 101 is operated at a high speed and the optical output is increased. Can do.

In addition, since the superimposed signal (I _RF + I _DC ) including an AC component and a DC component is given to the DFB 101 and only the DC component signal I _SOA is given to the _SOA 103 by the drive circuit 106, power supply to the _SOA 103 is ensured. The In this respect, the direct modulation laser 100 can efficiently supply power to the SOA.

Second Embodiment
Hereinafter, the direct modulation laser 100A of the second embodiment will be described. In the following description of the present embodiment, the symbols and the like used in the description of the first embodiment are used as they are unless otherwise specified.

  The direct modulation laser 100A of the present embodiment differs from the first embodiment only in the drive circuit, and therefore the drive circuit will be mainly described.

[Configuration of drive circuit]
First, a configuration example of the drive circuit 106A of the direct modulation laser 100A of the present embodiment will be described with reference to FIG.

  FIG. 3 is a diagram illustrating a configuration example of the driving circuit 106A.

In FIG. 3, the drive circuit 106 </ b> A includes a bias tee 105, and an AC component signal I _RF and a DC component signal Ib are input to the bias tee 105.

  A resistor R of the drive circuit 106A is connected between the bias tee 105 and the DFB laser 101. One end of the coil L is connected between one end of the resistor R and the DFB 101, and the other end of the coil L is connected to the SOA 103.

In this case, since the coil L does not flow an AC component, the AC component of the superimposed signal I from the bias tee 105 does not flow to the SOA 103 side. Therefore, as in the first embodiment, the superimposed signal (I _RF + I _DC ) including an AC component and a DC component is applied to the DFB laser 101, and only the DC component signal I _SOA is applied to the _SOA 103.

Thereby, also in the direct modulation laser 100A, as in the first embodiment, the superimposed signal (I _RF + I _DC ) including the AC component and the DC component is given to the DFB 101, and only the DC component signal I _SOA is given to the _SOA 103. It is supposed to be. Therefore, even in the direct modulation laser 100A, as in the first embodiment, even if the resonator length of the DFB laser 101 is shortened, the degradation of the optical output can be amplified by the SOA 103. In addition to high speed operation, the light output can be increased. In addition, since power supply to the SOA 103 is ensured, power supply to the SOA 103 can be performed efficiently.

  Next, a modification of the direct modulation laser of each of the above embodiments will be described.

(Modification 1)
In the above embodiment, the aspect of mounting the direct modulation lasers 100 and 100A on the optical transmission module is not mentioned, but such an optical transmission module may be configured.

  FIG. 4 shows a configuration similar to FIG. 1 as an example of the optical transmission module 200. In the following description of the present modification, the symbols used in the description of the first embodiment are used as they are unless otherwise specified.

In the example shown in FIG. 4, the optical transmission module 200 has 14 pins. In this case, the DC component signal I _d is supplied to the “3” pin, and the AC component signal I _RF is supplied to the “12” pin.

  The “3” pin is connected to one end of the coil L, and the other end of the coil L is connected to the p-type electrode 11 via the wire 51 and to the p-type electrode 12 via the wire 52.

  On the other hand, the pin “12” is connected to one end of the capacitor C, and the other end of the capacitor C is connected to one end of the resistor R. The other end of the resistor R is connected to the electrode 11. Even in this case, in the optical transmission module 200, the optical output from the DFB laser 101 is amplified by the SOA 103. Therefore, even if the resonator length of the DFB laser 101 is shortened, the degradation of the optical output can be amplified by the SOA 103, so that the DFB laser 101 can be operated at high speed and the optical output can be increased.

  FIG. 5 shows a configuration similar to FIG. 3 as an example of the optical transmission module 200A. In the following description of this modification, the reference numerals and the like used in the description of the second embodiment are used as they are unless otherwise specified.

  In the example shown in FIG. 5, the optical transmission module 200A has 14 pins. In this case, one end of the resistor R is connected to the “12” pin, and the other end of the resistor R is connected to the p-type electrode 11 via the wire 61 and via the coil L and the wire 62. , Connected to the p-type electrode 12.

Also, a bias tee 105 is connected to the “12” pin, and a DC component signal I _d and an AC component signal I _RF are supplied to the bias tee 105. Even in this way, in the optical transmission module 200A, the optical output from the DFB laser 101 is amplified by the SOA 103. Therefore, even if the resonator length of the DFB laser 101 is shortened, the degradation of the optical output can be amplified by the SOA 103, so that the DFB laser 101 can be operated at high speed and the optical output can be increased.

(Modification 2)
In the above description, the case of oscillating at a wavelength of 1300 nm has been described. However, the same effects as in the above embodiment can be obtained even when other wavelengths are applied. For example, also in the case of oscillating in the 1550 nm band, the crystal composition of each component 101, 103 of the direct modulation laser for optical communication can be changed and applied.

(Modification 3)
In the example shown in FIG. 2, a ridge type waveguide is described as an example, but a buried type waveguide may be applied.

DESCRIPTION OF SYMBOLS 1 Substrate 3 DFB laser part layer 4 SOA part layer 5 Optical waveguide layer 6 Diffraction grating 7 Cladding layer 8 Insulating film 9 BCB
10, 20 Signal source 11, 12 P-type electrode 13 N-type electrode 51, 52, 61, 62 Wire 100, 100A Direct modulation laser 101 DFB laser 103 SOA
105 Bias tee 106, 106A Drive circuit 200, 200A Optical transmission module

Claims (3)

A DFB laser,
SOA formed at the output end of the DFB laser;
A direct modulation laser comprising: a driving circuit that provides a superposition signal of an AC component signal and a DC component signal to the DFB, and that supplies only the DC component signal to the SOA.   The direct modulation laser according to claim 1, wherein the drive circuit includes a bias tee that outputs the superimposed signal.   3. The direct modulation laser according to claim 2, wherein the DC component signal to the SOA is given according to a ratio of lengths of the DFB laser and the SOA in the optical waveguide direction.

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