JPS6144483A - Photo pulse generator - Google Patents

Abstract

PURPOSE:To obtain output light of high-speed photo pulse array by a method wherein output light supplied with potential difference to each other are added to those coming from a plurality of laser light souces. CONSTITUTION:An N-InP substrate 51 is provided with semiconductor lasers 11-14 of the same shape and dimensions, having resonance planes 21-24, 31- 34. The output light of each laser 11-14 is led out in one direction by being synthesized in the wave confluence of waveguides 41-44. The lasers 11-14 are subjected to force mode tuning by the drive part and then generate short pulses each shifted in phase by pi/2 with respect to the described frequency (f). The short pulses are modulated in gain by the on-off operations of photo modulators 35-38 with respect to respective frequencies. Each output of the photo modula- tors is synthesized in the waveguides 41-44 and can obtain photo pulse arrays having a repeated frequency 4f that is four times. The photo pulses are turned on and off by impressing voltage on each modulator from other drive parts in forward and reverse directions. For example, a photo pulse aray with a repeated frequency of 8GHz can be obtained with respect to the modulation of 2GHz.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an optical pulse generator that generates a high-speed optical pulse train using short pulse light generated by mode-locking a semiconductor laser.

(Prior art and its problems) Generally, when mode-locking is applied to a semiconductor laser, i p
Although it is possible to generate a short optical pulse train with an extremely narrow width of 100 seconds, it is expected that this mode-locking will be applied to optical communications and optical information processing. Methods for mode-locking this semiconductor laser include self-mode locking and forced mode-locking, and the latter method has greater applicability in that it is possible to control the phase of the pulse train. This forced mode-locking is achieved by externally performing gain modulation at a frequency equal to the longitudinal mode spacing of the semiconductor laser, so that the phase difference between each longitudinal mode becomes constant and a repeating optical pulse train equal to the variable frequency is obtained. .

On the other hand, AlGaAs/GaAs and InGaAsP/In
A normal semiconductor laser made of P with a cavity length of about 300 μm has a vertical wave number interval of 77!6 or about 100 GH.
z, which is a high value and cannot be modulated as it is.

Also, since the refractive index dispersion of this semiconductor laser is large,
Attempts have been made to achieve mode locking using an external mirror to lengthen the resonator length. When the resonator length is lengthened in this way, the longitudinal mode spacing is also narrowed, so that the modulation frequency can be lowered, and it has been reported that an optical pulse train with a repetition rate of several GHz is generated. Regarding this technology,
For example, the magazine “Applied Physics Le
tters', vol. 39.

1981, pp. 525-527.

Although narrow optical pulses are achieved using mode-locking of this semiconductor laser, the repetition frequency is limited by the speed of the external modulator. Therefore, when considering the application as a light source to a high-speed optical transmission system, no advantage such as an increase in transmission speed could be found compared to the existing method using direct modulation of a semiconductor laser.

(Object of the Invention) An object of the present invention is to provide an optical pulse generator capable of generating a high-speed optical pulse train while eliminating such drawbacks.

(Structure of the Invention) The optical pulse generator of the present invention includes a semiconductor laser array consisting of a plurality of semiconductor laser arrays that are driven with forced mode locking at the same frequency with phases shifted from each other, and from each laser of this laser array. The optical modulator includes a plurality of optical modulators that turn on and off the output light of the optical modulator, and a multiplexing section that multiplexes optical pulse trains obtained from the multiple optical modulators through a light guide path.

(Example) The present invention will be explained in detail below using the figures.

FIGS. 1 and 2 are a plan view of an embodiment of the present invention and a sectional view of the portion indicated by the dashed line.

In this embodiment, four semiconductor lasers 11, 12, 13 having the same shape and size are placed on an n-InP substrate 51.

14 is formed. These semiconductor lasers 11°12
．． 13.14 are resonance surfaces 21+22+23.24 respectively
, 31.32, 33.34 are provided, and the length of these resonators is approximately Z5ce. The optical output from each semiconductor laser 11 to 14 is transmitted to an optical modulator '3 knee 5-.

'2NIs' l+ 137' +, a :ll and the optical waveguides 41, 42, 43° 44 combine the signals and take them out in one direction.

In Fig. 2, 52 is n-InP, 53 is InGaAsP (λg = 1.3 μm) which becomes the active layer, 54 is p-InP, and 55 is p-InGaAsP (λg =
1.1/'m), 56 and 57 are electrodes, and 58 is In--GaAsP (λg=1°1 μm) which becomes an optical special wave layer. Such laser sections 11 to 14 and optical waveguide sections 41 to 4
The different layer structures at 4 are made by using two epitaxial growths and the resonant surfaces 21, 22, 23, 24 and 31, 32, 33, 34 are formed by active ion etching.

These four semiconductor lasers 11 to 14 are subjected to forced mode tuning by a driving section (not shown), and each generates a short pulse whose phase is shifted by π/2 with respect to a predetermined frequency f. These short pulses are gain modulated by turning the optical modulators 35 to 38 on and off with respect to their respective frequencies f.

The outputs of these optical modulators 35 to 38 are multiplexed by optical waveguides 41 to 44, respectively, and the repetition frequency is 4f, which is four times
It is possible to obtain an optical pulse train with . In this case, for example, an optical pulse train with a repetition frequency of 8 GHz can be obtained for modulation of 2 GHz. This light pulse turns on,
Turning off is performed by applying voltages to each of the optical modulators 35 to 38 in the forward and reverse directions from another driving section.

In this embodiment, four laser arrays 11 to 14 are used, but it is clear that a light source for faster optical transmission can be realized by further increasing the number of laser arrays.

(Effects of the Invention) As explained above, according to one aspect of the present invention, output light of a high-speed optical pulse train can be obtained by adding output lights from a plurality of laser light sources with mutual phase differences. I can do it.

[Brief explanation of drawings]

FIGS. 1 and 2 are a plan view and a sectional view along a dashed-dotted line of an embodiment of the present invention. In the figure, 11, 12, 13
．． 14... Semiconductor laser, 21.22.23,
24.31, 32.33.34... Resonance surface, 3
5.36.37.38... Light modulator, 41.4
2143.44... Optical waveguide, 51...
・n-InP substrate, 52-- n-InP, 53,
58...InGaAsP, 54...p
-InP, 55...p-InGaAsP156
, 57--electrode. Figure 1 Figure 2

Claims (1)

[Claims] a semiconductor laser array consisting of a plurality of semiconductor laser arrays driven with forced mode locking at the same frequency with phases shifted from each other; a plurality of optical modulators that control on/off the output light of each laser from the laser array; An optical pulse generator including a multiplexing section that multiplexes optical pulse trains obtained from the plurality of optical modulators using a light guide path.