JPH04340921A - Photosemiconductor device - Google Patents

Abstract

PURPOSE:To provide the photosemiconductor device by realizing high-frequency modulation higher than the modulation frequency of an electric driving system and increasing the transmission capacity. CONSTITUTION:A DFB laser part 4 which oscillates in single longitudinal mode, a Y-shaped branch waveguide 8 which divides the light from the DFB laser part 4 to two waveguides 6a and 6b, and a Y-shaped multiplexing waveguide 10 where the two waveguides 6a and 6b come together are provided on the same semiconductor substrate 2. The two waveguides 6a and 6b are provided with clock signal modulation parts 12a and 12b having electrodes applied with clock signals as electric signals and data signal modulation parts 14a and 14b having electrodes applied with data signals as electric signals.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device, and more particularly to an optical modulator and an integrated optical modulator/semiconductor laser light source used as a light source in a long-distance, large-capacity optical transmission system. Currently, a direct modulation method using a single longitudinal mode semiconductor laser is used as a light source for long-distance, high-capacity optical transmission systems. However, in the direct modulation method, a large wavelength spread occurs due to the chirping (temporal wavelength fluctuation) phenomenon during relaxation oscillation, so it is difficult to dramatically increase the transmission capacity. On the other hand, the external modulation method, which uses a semiconductor laser as a light source and performs modulation using an optical modulator, is capable of ultra-high-speed modulation and has little wavelength chirping that occurs during modulation. It is expected to be used as a light source.

0002

[Prior Art] Conventional optical modulator/semiconductor laser integrated light sources include light sources in which an electro-absorption optical modulator and an asymmetric edge reflectance type DFB (distributed feedback) laser are formed on the same substrate, and electric field Absorption optical modulator and asymmetric λ/4 shift DF
There is a light source in which a B laser is formed on the same substrate.

0003

[Problem to be solved by the invention] The above conventional optical modulator/
In a semiconductor laser integrated light source, the modulation frequency of an optical modulator is caused by the parasitic capacitance of the modulator. That is, the modulation frequency f is f=1/πRC. Here, π is pi, R is matching resistance, and C
indicate the parasitic capacitance, respectively. Therefore, by reducing this capacity, it is possible to increase the modulation frequency to 10 Gb/s. In order to further improve the modulation frequency, it is effective to reduce the capacitance.

[0004] However, at present, there is no electrical drive system such as a pulse pattern generator or microstrip line to achieve a modulation frequency of 10 Gb/s or more.
High frequency modulation of 10 Gb/s or higher cannot be applied. Therefore, there is a certain limit to increasing the transmission capacity by improving the modulation frequency. Therefore, the present invention
Achieves high frequency modulation that exceeds the modulation frequency of electric drive systems,
An object of the present invention is to provide an optical semiconductor device that can increase transmission capacity.

[0005]

[Means for Solving the Problems] The above object is to provide a branching waveguide that branches an optical signal from a light source into N waveguides, and a branching waveguide for branching an optical signal from a light source into N waveguides.
A clock signal modulation section provided in each of the N waveguides and driven by a clock signal whose phase is shifted by 2π/N; and a clock signal modulation section provided in each of the N waveguides and driven by a predetermined data signal. This is achieved by an optical semiconductor device characterized by having a signal modulation section and a multiplexing waveguide that couples the optical signals of the N waveguides.

[0006] The invention also includes a substrate, a laser section provided on the substrate, and a branching waveguide provided on the substrate for branching an optical signal oscillated by the laser section into N waveguides;
Each of the N waveguides is provided with a phase of 2π/N.
a clock signal modulation section that is driven by clock signals that are shifted from each other; a data signal modulation section that is provided on each of the N waveguides and driven by a predetermined data signal;
This is achieved by an optical semiconductor device characterized by having a multiplexing waveguide that combines optical signals of two waveguides.

[0007]

[Operation] That is, in the present invention, an optical signal from a light source is branched into N waveguides by a branching waveguide, and each of these optical signals is set to a predetermined frequency whose phase is shifted by 2π/N in a clock signal modulation section. N data signals are contained with a phase shift by being modulated by a clock signal, each modulated by a predetermined data signal in a data signal modulation section, and then merged into one by a multiplexing waveguide again. It is possible to obtain an optical signal with a frequency N times higher than the predetermined frequency.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on illustrative embodiments. FIG. 1 is a plan view showing an optical semiconductor device according to an embodiment of the present invention. On the same semiconductor substrate 2,
A DFB laser section 4 that oscillates in a single longitudinal mode, and this DFB
A Y-shaped branching waveguide 8 that divides the light from the laser section 4 into two waveguides 6a and 6b, and these two waveguides 6a.
, 6b are provided. The two waveguides 6a and 6b each have a clock signal modulating section 12a, 12b having an electrode to which a clock signal, which is an electric signal, is applied, and a data signal modulating section 12b, which has an electrode to which a data signal, which is an electric signal, is applied. Signal modulation sections 14a and 14b are provided. Further, an AR (anti-reflection) coat 16 is provided on the end face of the Y-shaped multiplexing waveguide 10.

Next, the operation of the optical semiconductor device shown in FIG. 1 will be explained using FIG. 2. FIG. 2 is a diagram showing various signals used in the optical semiconductor device. In the DFB laser section 4, a single longitudinal mode light shown in FIG. 2(a) is continuously oscillated. This optical signal is divided into two by the Y-shaped branch waveguide 8, and each clock signal modulator 12a
, 12b.

One of the clock signal modulators 12a has a frequency of 10 Gb/s, that is, a period of 10 as shown in FIG. 2(b).
It is driven by a 0 ps clock signal. Therefore, the optical signal passing through this clock signal modulation section 12a is as shown in FIG.
As shown in FIG. 2(c), the frequency is 10 Gb/s corresponding to the clock signal in FIG. 2(b). Subsequently, the optical signal shown in FIG. 2(c) passes through the waveguide 6a and enters the data signal modulation section 14a. This data signal modulation section 14a is driven by a predetermined data signal, as shown in FIG. 2(d). In this example, (00101
101...) is the NRZ signal. Therefore, the optical signal that has passed through this data signal modulation section 14a becomes an RZ signal (00101101...) modulated by the data signal of FIG. 2(d), as shown in FIG. 2(e). .

[0011] Also, the other clock signal modulation section 12b
is driven by a clock signal with a frequency of 10 Gb/s shown in FIG. 2(f). The clock signal shown in FIG. 2(f) has a phase shift of π, that is, 50 ps, from the clock signal shown in FIG. 2(b). Therefore, the clock signal is an inversion of the clock signal in FIG. 2(b). Therefore, the optical signal passing through this clock signal modulation section 12b is as shown in FIG. 2(g).
The optical signal has a frequency of 10 Gb/s corresponding to the clock signal of f), and is an inverted optical signal of the optical signal of FIG. 2(c).

Next, the optical signal shown in FIG. 2(g) passes through the waveguide 6b and enters the data signal modulation section 14b. This data signal modulation section 14b is driven by a predetermined data signal, as shown in FIG. 2(h). In this embodiment, it is an NRZ signal of (10101110...). Therefore, the optical signal passing through this data signal modulation section 14b becomes an RZ signal (10101110...) modulated by the data signal of FIG. 2(h), as shown in FIG. 2(i). .

Next, 2 shown in FIGS. 2(e) and 2(i)
The two optical signals are combined by the Y-shaped combining waveguide 10 to form an optical signal as shown in FIG. 2(j). That is, (0100110011110110
) becomes the RZ signal. This optical signal therefore contains two signals with a frequency of 20 Gb/s modulated by the frequency of the electrical drive train of 10 Gb/s. And the frequency containing these two signals is 20Gb/s
The optical signal of A
The light is emitted through the R coat 16.

According to this embodiment, the single longitudinal mode optical signal continuously oscillated from the DFB laser section 4 as a light source is divided into two by the Y-shaped branching waveguide 8, and the light is transmitted to these two. The signals are respectively clock signal modulators 12a,
Frequency 10Gb with phase shifted by π in 12b
/s clock signal, and then modulated with predetermined data signals in the data signal modulation sections 14a and 14b, and then merged by the Y-shaped combining waveguide 10, thereby producing two predetermined data signals. It is possible to obtain an optical signal with a frequency of 20 Gb/s in which the signals are phase-shifted.

For this reason, the modulation frequency of the electric drive system is 10
Achieves high frequency modulation at 20Gb/s, twice the Gb/s,
Transmission capacity can be doubled. Therefore, it is possible to contribute to realizing, for example, the miniaturization of an optical modulator/DFB laser integrated light source. In the above embodiment, the DFB laser unit 4 was used as the light source, but the laser is not limited to this type, and for example, DBR laser, DR laser,
Dynamic single wavelength lasers such as gain-coupled lasers and Fabry lasers
A Perot type laser may also be used.

[0016] Furthermore, using the Y-shaped branch waveguide 8, the DFB
The case where the light from the laser section 4 is divided into two waveguides 6a and 6b has been described, but it can also be divided into N waveguides using a branching waveguide that branches into N (N≧3) waveguides. You can also. In this case, the phase of the clock signal in the clock signal modulation section needs to be shifted by 2π/N. Thereby, the transmission capacity can be improved by up to N times.

[0017] Also, the clock signal modulation units 12a, 12
The arrangement of the data signal modulating sections 14a and 14b may be reversed. That is, the optical signals from the DFB laser unit 4 may first be modulated with predetermined data signals in the data signal modulation units, and then modulated with phase-shifted clock signals in the clock signal modulation units. Furthermore,
In the above embodiment, a case has been described in which the DFB laser section 4 as a light source and the other modulator sections are integrated on the same semiconductor substrate 2, but it goes without saying that the present invention can also be applied to only the modulator section. Nor.

[0018]

As described above, according to the present invention, a branching waveguide is provided for branching an optical signal from a light source into N waveguides, and each of the N waveguides is provided with a phase shift of 2π/N. A clock signal modulation section driven by a predetermined clock signal, a data signal modulation section provided in each of the N waveguides and driven by a predetermined data signal, and optical signals of the N waveguides are coupled. By having a multiplexing waveguide, the optical signal from the light source is split and modulated by the clock signal modulation section with a clock signal whose phase is shifted by 2π/N, and the data signal modulation section modulates the optical signal into a predetermined signal. Since it is modulated with a data signal and then merged into one again by the multiplexing waveguide, it is possible to obtain an optical signal having a frequency N times the predetermined frequency and containing N data signals with shifted phases.

[0019] This makes it possible to realize high-frequency modulation higher than the modulation frequency of the electric drive system and increase the transmission capacity, thereby realizing miniaturization of optical modulators and optical modulator/semiconductor laser integrated light sources. can do.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an optical semiconductor device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the optical semiconductor device shown in FIG. 1;

[Explanation of symbols]

2...Semiconductor substrate 4...DFB laser section 6a, 6b...Waveguide 8...Y-shaped branch waveguide 10...Y-shaped multiplexing waveguide 12a, 12b...Clock signal modulation section 14a, 14b
...Data signal modulation section 16...AR coat

Claims (2)

[Claims] 1. A branching waveguide that branches an optical signal from a light source into N waveguides, and a clock provided in each of the N waveguides and driven by a clock signal whose phase is shifted by 2π/N. It has a signal modulation section, a data signal modulation section that is provided in each of the N waveguides and is driven by a predetermined data signal, and a multiplexing waveguide that couples the optical signals of the N waveguides. An optical semiconductor device characterized by: 2. A substrate, a laser section provided on the substrate, a branching waveguide provided on the substrate for branching an optical signal oscillated by the laser section into N waveguides, and the a clock signal modulation section provided in each of the N waveguides and driven by a clock signal whose phase is shifted by 2π/N; and a clock signal modulation section provided in each of the N waveguides and driven by a predetermined data signal. An optical semiconductor device comprising: a data signal modulation section; and a multiplexing waveguide that couples optical signals from the N waveguides.