JPH02271582A - Optosemiconductor device - Google Patents

Abstract

PURPOSE:To monitor the laser beams entering from a laser into a light modulator without losing the high frequency property of a circuit by providing a means for detecting the physical quantity of the specified terminal impedance which changes by the currents flowing in the terminal impedance. CONSTITUTION:The modulated signals from a modulation signal source 1 are applied to a transmission path 2 through an inner resistance Rs, and are supplied to a light modulator 3, and the light modulator 3 modulates the laser beams from a laser 50. The terminal impedance 5 is connected in parallel with the light modulator 3, and it takes the matching with characteristic impedance. And the terminal impedance 5 of the light modulator 3 and the detection means 9 are coupled, and the detection means 9 detects the physical quantity which changes by the currents flowing in the terminal impedance 5. Hereby, the laser beam power that the light modulator absorbed can be monitored without giving the electric influence on the modulation circuit.

Description

[Detailed Description of the Invention] [Summary] This invention relates to an optical semiconductor device that monitors the power of laser light that is a light source in high-speed optical communications, etc., and monitors the laser light that enters the optical modulator from the laser without impairing the high frequency characteristics of the circuit. The present invention aims to provide an optical semiconductor device capable of optical modulation, including a variable absorption layer arranged to receive incident laser light of a predetermined wavelength and absorbing the laser light in accordance with a modulation signal from a modulation signal source; a terminal impedance connected in parallel with the optical modulator with respect to a modulation signal source, and means for detecting a predetermined physical quantity of the terminal impedance that changes depending on a current flowing through the terminal impedance, The laser light power absorbed by the optical modulator is configured to be monitored by detecting a physical quantity.

[Industrial Application Field] The present invention relates to optical communication technology, and particularly to an optical semiconductor device that monitors the power of a laser beam that is a light source in high-speed optical communication.

Optical communication systems are becoming faster, reaching 100 bits/s.
Ultra high-speed systems up to EC are also being considered.

In a direct modulation system in which the laser is driven on and off, a chirping phenomenon in which the wavelength of the laser oscillation light fluctuates occurs to an extent that cannot be ignored. In an external modulation system in which a laser is oscillated with a constant power and a modulator is used to modulate the laser beam with a constant output, chirping is significantly reduced.

[Prior Art] Conventionally, the optical output of a semiconductor laser used for optical communication has been monitored by detecting the optical output from the end face of the laser using a photodetector. The current flowing through the drive circuit was controlled so that the optical output of the laser remained constant, mainly to compensate for the decrease in output due to long-term use.

In order to perform high-speed optical communication, an external modulation system is being considered in which a constant current is passed through a laser to emit the laser, and a separate optical modulator is used to modulate the laser. A high-speed signal from a modulation signal source is applied to an optical modulator via a transmission line, and the incident laser light is turned on and off to form a modulation signal. In order to match the high-speed transmission line, a terminal impedance is connected in parallel near the optical modulator, for example, 50
It is matched with the characteristic impedance of Ω.

FIGS. 2(A) and 2(B) show such a conventional optical modulation circuit. FIG. 2(A) shows an equivalent circuit. A signal from a modulation signal source 51 is transmitted through an internal resistor Rs. The signal is applied to an electro-absorption type optical modulator 53, which is a reverse bias diode, through a line with a characteristic impedance ZC. Laser light from the laser 50 enters the optical modulator 53 and is modulated. A termination impedance 55 is connected in parallel to the optical modulator 53. For example, when the characteristic impedance of the line is 50Ω, the optical modulator 53 and the termination impedance 55 are designed to match the characteristic impedance of 50Ω. In addition, since this is a high frequency circuit, all wiring is L.
If the wiring length is increased, impedance matching cannot be achieved.

FIG. 2(B) shows an example of the structure of such an optical modulation circuit, which includes an optical modulator 53 having a pin diode structure on a metal stem 59, and a terminal impedance 55 realized by a chip resistor. A wire 57 from the modulating signal source connects the optical modulator 53 and the termination impedance 55 in parallel.

Optical modulator 53 has a high resistivity l-type light absorption layer 65 between p region 61 and n region 63.

When no bias is applied to the light absorption layer 65,
It has a bandgap that transmits the incident laser light 67 from the laser 50, but when a reverse bias from the modulation signal source is applied via the wire 57, the bandgap narrows depending on the magnitude of the bias electric field. , incident laser beam 67
Normally, a reverse bias electric field is applied so that the incident laser beam 67 is almost completely absorbed. In this way, the modulated output light 6 which modulates the incident light on and off
Generates 9.

Note that since this is a high frequency circuit, the bonding wire 57 is set as short as possible to suppress the L component.

[Problems to be Solved by the Invention] By the way, when monitoring the light emitted from the laser rear facet, it is assumed that the main laser beam from the laser front facet and the laser light from the laser rear facet are proportional. The light emitted from the end face may not change in the same way as the light emitted from the front end face.

In particular, in the case of a distributed feedback (DFJ) laser, it is difficult to consider the forward light and the backward light to be the same, and the light emitted from the rear end face and the main laser light emitted from the front end face do not change in the same way.

That is, even if the light emitted from the rear end face is monitored, it may not mean that the main laser light actually being used is being monitored.

For this reason, it is preferable to monitor the main laser beam actually emitted from the front end face.

However, when attempting to monitor in a high-frequency circuit, coupling the L and C components breaks the matching and changes the high-frequency characteristics.For this reason, it is difficult to monitor the main laser beam without disturbing the characteristics of the high-frequency circuit. was difficult.

An object of the present invention is to provide an optical semiconductor device that can monitor laser light incident on an optical modulator from a laser without impairing the high frequency characteristics of the circuit.

[Means for Solving the Problems] FIGS. 1(A) to (C) are diagrams illustrating the principle of the present invention, and FIG. 1(A) is a conceptual diagram. In FIG. 1(A), a modulated signal from a modulated signal source 1 is applied to a transmission line 2 via an internal resistor R3, and is supplied to an optical modulator 3. Optical modulator 3 modulates laser light from laser 50. A terminal impedance 5 is connected in parallel with the optical modulator 3 and is matched with the characteristic impedance. The detector 9 is coupled to the terminal impedance 5 and the terminal impedance 5
Detects a predetermined physical quantity that changes depending on the current flowing through the sensor.

FIG. 1(B) is a block diagram showing one coupling form between the terminal impedance 5 and the detection means 9. FIG.

The terminal impedance 5 includes a resistor 5a, and the detection means 9 includes a temperature detector 9a. That is, when the resistor 5a generates heat due to the current flowing through the terminal impedance 5, the temperature detector 9a detects the heat generated.

FIG. 1(C) shows another example of a coupling form between the termination impedance 5 and the detection means 9. The termination impedance 5 includes a light emitting diode 5b, and the detection means 9 includes a photodetector 9b. The light-emitting diode 5b emits light due to the current flowing through the light-emitting diode 5b. The photodiode 9b receives the emitted light and generates a detection signal. A detection signal from the detection means is supplied to a control circuit 10 that controls the power supply of the laser 50, for example.

[Function] By coupling the terminal impedance 5 of the optical modulator 3 and the detection means 9, and by detecting the physical quantity that changes depending on the current flowing through the terminal impedance 5 with the detection means 9, the optical modulator 3 can be operated without electrically affecting the modulation circuit. , the laser light power absorbed by the optical modulator 3 can be monitored.

The terminal impedance 5 includes a resistor 5a, and the detection means 9 includes a temperature detector 9a so as to detect the heat generated by the resistor 5a.
With this, the averaged laser light power can be monitored with a simple configuration.

The terminal impedance 5 is provided with a light emitting diode 5b, and the detection means 9 is arranged to receive the light emitted by the light emitting diode 5b.
With the photodetector 9b, the current flowing through the termination impedance 5 can be easily monitored without electrical coupling. In this case, the terminal impedance 5 and the detection means 9 can be separated in distance.

[Example] An embodiment of the present invention is shown in FIGS. 3(A) and 3(B).

FIG. 3(A) shows a circuit diagram, in which a modulation signal source 11 applies a modulation signal to an electroabsorption optical modulator 13 via an internal resistor R3. A resistor 15 serving as a termination impedance is connected in parallel to the field absorption optical modulator 13. In other words, the optical modulator 13 and the resistor 15 match the characteristic impedance of the line.

A temperature detector 19 is provided near the resistor 15, and an electrical signal from the temperature detector 19 is applied to an amplifier 20. That is, when heat is generated due to the current flowing through the resistor 15, the temperature detector 19 detects the temperature rise, and the amplifier 20 amplifies it to form a detection signal. This detection signal is supplied to the control circuit 10 to control the laser power source 40.

FIG. 3(B) shows an example of a structure for realizing the circuit of FIG. 3(A). A metal stem 17 is provided with a notch 18, and the parts on both sides of the notch are thermally isolated to some extent. are doing. On the stem 17, an electro-absorption optical modulator 13 is mounted on one side, and on the other side with a notch 18 in between.
A resistor 15 in the form of a chip resistor and a thermocouple 19a are mounted.

In order to apply a signal from the modulation signal source 11 to the electro-absorption optical modulator 13, the wire 12 connects to the electro-absorption optical modulator 13.
A wire 14 is bonded to the upper surface of the electro-absorption optical modulator, and a wire 14 is further bonded to the resistor 15 from the upper surface of the electro-absorption optical modulator.
A resistor 15 is connected in parallel to the optical modulator 13.

A notch 18 is provided between the electroabsorption optical modulator 13 and the resistor 15 to provide thermal isolation. Laser light enters from the rear and exits to the front.

In order not to make the length of the wire 14 too long, the cutout 18 is, for example, at a depth of in, @0,2~0.31111
to a certain degree.

The resistor 15 is composed of a chip resistor having a size of, for example, about 0.311×0.31111. Also, thermocouple 1
9a is, for example, 0.4 part mx0.4ux0°2II1
It has a size of about 1.

The electroabsorption optical modulator 13 has a length of, for example, 200 to 300 mm.
It is about μm. The electroabsorption optical modulator 13 has a p-type region 2
1 and the n-type region 23, there is a variable light absorption region 25 that absorbs incident laser light when an electric field is applied. The variable light absorption region 25 is a high resistivity (L-type) region. For example, when the incident laser beam is a 1.55 μm laser beam,
The variable light absorption region 25 has a gap wavelength of 1.45, for example.
Indium, gallium, arsenic, phosphorus (InGa) on the order of μm
AsP) can be composed of mixed crystals.

For example, when incident laser light is input from the rear of the electro-absorption optical modulator 13 and the variable light absorption region 25 absorbs the light and reduces it to almost zero, a photocurrent proportional to the intensity of the incident laser light is generated. A portion flows through wire 14 to resistor 15 . The resistor 15 generates Joule heat due to the flowing current. The generated Joule heat increases the temperature of the contact portion of the resistor 15 and the stem 17. The thermocouple 19a detects this temperature rise. By processing the signal from the thermocouple, it is possible to know the temperature, that is, the amount of photocurrent generated by the optical modulator 13, and therefore the intensity of the incident laser light.

FIG. 4 shows another embodiment partially modified from the embodiments in FIGS. 3A and 3B. In FIG. 4, a chip resistor 15 and a thermocouple are mounted on a stem 17 having a notch 18. 19a is mounted as in FIG. 3(B).

In the embodiment shown in FIG. 3(B), the laser as the light source was provided externally, but in this embodiment, the distributed feedback (DFB) laser 27 as the light source is connected to the electroabsorption optical modulator 13.
It is integrated into one.

A DFB laser has a diffraction grating along an optical waveguide to selectively reflect only a single wavelength of light and emit it in a predetermined direction. As a basic structure, both the DFB laser 27 and the electroabsorption modulator have a pin photodiode structure. for example,
InGaAs with a different composition as an active layer on an InP substrate
P is formed, and the region of the DFB laser 27 constitutes a laser oscillation region, and the region of the electroabsorption optical modulator 13 constitutes a variable light absorption region. Note that a diffraction grating is formed on the substrate in the DFB laser 27 portion, so that monochromatic light is efficiently reflected.

A DFB laser 27 provides a constant laser output to the electroabsorption optical modulator 13. The electro-absorption optical modulator 13 controls the input laser beam on and off using a drive signal from a modulation signal source (not shown).

When the electroabsorption optical modulator 13 absorbs the input laser beam, a photocurrent is generated, and a portion of the current flows through the resistor 15.

The current causes the resistor 15 to generate Joule heat, increasing its temperature. Thermocouple 19a detects the temperature and monitors the current generated in electroabsorption optical modulator 13.

5(A), (B), and (C) show other embodiments of the present invention, and FIG. 5(A) shows a circuit diagram.

In FIG. 5 (A>), the signal from the modulation signal source 11 is applied to the electro-absorption optical modulator 13 via the internal resistor R3. A terminal impedance 26 configured by series connection with the terminating impedance 26 is connected for impedance matching.

A light receiving diode 29 is arranged so as to be coupled with the light emitted from the light emitting diode 24, and an amplifier 20 amplifies the signal from the light receiving diode 29. The light receiving diode 29 may be a photocell type that generates photovoltaic force, or a photodiode type that receives a reverse bias voltage from a bias source vb via a load resistor 28 and changes its resistance depending on incident light.

When the electroabsorption optical modulator 13 absorbs incident light in response to a signal from the modulation signal source 11, a photocurrent is generated, and the photocurrent flows through the light emitting diode 24 via the resistor 22.

This drive current causes the light emitting diode 24 to emit light, which enters the light receiving diode 29 .

The current flowing through the light emitting diode 24, that is, the current generated in the electroabsorption optical modulator 13, can be monitored based on the signal detected by the light receiving diode 29, and the intensity of the incident laser light can be monitored.

As the light emitting diode 24, one that generates light of a wavelength different from the wavelength of the laser light that is the main optical signal can be used.

For example, in a 1.5-μm band optical communication system, a GaAs light-emitting diode may be used as the light-emitting diode 24, and a Si photodiode may be used as the light-receiving diode 29.Since the wavelength of the light from the light-emitting diode varies, it is necessary to avoid optical noise. can be easily processed.

FIG. 5(B) shows one form of realizing the circuit of FIG. 5(A), a termination having an electroabsorption optical modulator 13, a light emitting diode 24, and a resistor 23 built in on a metal stem 17°. An impedance 26 and a light receiving diode 29 are mounted.

The light emitting diode in the termination impedance 26 is arranged adjacent to the light receiving diode 29 and optically coupled thereto. When incident light enters the electroabsorption optical modulator 13 and is absorbed, the generated photocurrent flows through the termination impedance 26. The light emitting diode in the termination impedance 26 emits light due to the current, and the light receiving diode 29 placed nearby receives the light.

FIG. 5(C) shows another form of realizing the circuit of FIG. 5(A).

Similar to FIG. 5(B), a terminal impedance 26 including an electroabsorption optical modulator 13 and a light emitting diode is mounted on the stem 17°.

An optical fiber 30 is placed near the light output surface of the light emitting diode with a terminal impedance 26, and couples the output light from the light emitting diode into the fiber.

A light receiving diode 29 is arranged at the other end of the optical fiber 30 to detect light from the light emitting diode.

Such a light receiving diode 29 can be separated from the light emitting diode by a desired distance.

Although the present invention has been described above with reference to embodiments, it will be obvious to those skilled in the art that the present invention is not limited to these and that, for example, various modifications, changes, improvements, combinations, etc. are possible.

[Effects of the Invention] As described above, according to the present invention, the photocurrent generated by the electroabsorption optical modulator flows through the termination impedance, and the detection means detects a predetermined physical quantity that changes depending on the current flowing through the termination impedance. By detecting this, it is possible to monitor the amount of light absorbed by the electro-absorption optical modulator, that is, the power of the incident laser light, without affecting the high-frequency characteristics of the high-frequency circuit.

When temperature is taken as a physical quantity that changes depending on the current flowing through the terminal impedance, the averaged laser light power can be monitored with a simple configuration by detecting the temperature with a temperature detector.

If a light emitting diode is built into the terminal impedance as a physical quantity that changes depending on the current flowing through the terminal impedance, and the light emitted from the light emitting diode is taken, the electroabsorption type optical modulator absorbs the laser by detecting the light emitted from the light emitting diode. Optical power can be monitored.

In this case, the detection means can be placed at a desired distance from the termination impedance.

[Brief explanation of drawings]

FIGS. 1(A), (B), and (C) are diagrams explaining the principle of the present invention, FIG. 1(A) is a conceptual diagram, and FIG. 1(B) is a schematic block diagram showing one coupling form. FIG. 1(C) is a schematic block diagram showing the combination of songs, FIGS. 2(A) and (B) show the conventional technology, FIG. 2(A) is a circuit diagram, and FIG. 2(B) is a 3(A) and 3(B) show an embodiment of the present invention, FIG. 3(A> is a circuit diagram, and FIG. 3(B) is a perspective view showing a structural example. FIG. 4 is a perspective view of a structural example showing another embodiment of the present invention. FIGS. 5(A), (B), and (C) show other embodiments of the present invention. FIG. The circuit diagram, FIG. 5(B) is a perspective view of a configuration example showing one coupling form, and FIG. 5(C) is a perspective view of a configuration example showing another coupling form. In the figure, a b a b modulation Signal source Optical modulator Terminal impedance Resistor Light emitting diode Detection means Temperature detector Photodetector control circuit Modulation signal source wire 17, 17 9a b Optical modulator wire resistance stem notch Temperature detector Thermocouple amplifier P-type Head area resistance N-type Region ED Variable light absorption region Termination impedance DFB Laser load resistance Light receiving diode Optical fiber bias source Laser modulation signal source Optical modulator Termination resistor Wire stem P-type head area N-type region Variable light absorption region Input light Output Light (A) Conceptual diagram ( B) Connection type 1 (C) Connection type 2 Figure 1 (A) Circuit diagram (B) Structure example Figure 3 (A) Circuit diagram (B) Perspective view Figure 2 (A) Circuit diagram Figure 5 (Part 1)

Claims (4)

[Claims] (1) An electroabsorption optical modulator (3) including a variable absorption layer arranged to receive an incident laser beam of a predetermined wavelength and absorbing the laser beam according to a modulation signal from a modulation signal source.
and a termination impedance (5) connected in parallel with the optical modulator (3) with respect to the modulation signal source, and for detecting a predetermined physical quantity of the termination impedance that changes depending on the current flowing through the termination impedance (5). means (9), and monitors laser light power absorbed by the optical modulator by detecting the physical quantity. (2) The optical semiconductor according to claim 1, further comprising a semiconductor laser device (27) integrated with the optical modulator, and a control circuit that controls a power supply for the semiconductor laser device based on the output signal of the detection means. Device. (3) The optical semiconductor device according to claim 1 or 2, wherein the detection means (9) includes a temperature detector (9a) arranged near the terminal impedance (5). (4) a photodetector (9b), wherein the termination impedance (5) includes a light emitting diode (5b), and the detection means (9) detects a signal from the light emitting diode (5b);
The optical semiconductor device according to claim 1 or 2, comprising: