JPH01212487A - Wavelength tunable semiconductor laser - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wavelength tunable semiconductor laser, and particularly to a diffraction grating within a laser element.

Coherent optical communication, which aims to increase the capacity of optical communication, uses a laser light source that can change the emission wavelength, so-called a chain.
A laser is required.

As a dual-wavelength semiconductor laser, a so-called DFB laser in which a diffraction grating is incorporated into a crystal has been developed and is already being put into practical use.
- There is also a technology that has been proposed to make the emission wavelength variable by improving the structure of the R laser.

Both DFB lasers and DBR lasers utilize Bragg reflection due to a periodic structure provided in a crystal, but in order to change the emission wavelength of an element whose periodic structure is set as a geometric shape, it is necessary to use some means, e.g. The only method available is to change the refractive index of a guide layer or the like by providing a control electrode and flowing a current, and the wavelength tuning range is limited.

In a DFB type laser, if the period itself of the diffraction grating could be changed to an arbitrary value by external control, it would be extremely beneficial for use in optical communications and the like.

[Prior art and problems to be solved by the invention] Conventionally, in a DFB type laser in which a diffraction grating is provided over the entire length of the resonator, the emission wavelength is determined by the diffraction grating.
It was not possible to make the wavelength variable. DBR type lasers are known to have a structure in which an adjustment region is provided between the optical amplification section and the diffraction grating section, and by passing a current through this region, the refractive index of the guide layer is changed and the emission wavelength is changed. I can do it.

However, the wavelength range that can be changed by such means is extremely narrow, and it is desired to realize a semiconductor laser that can change the wavelength over a wider range.

The purpose of the present invention is to make the period of the diffraction grating itself variable.
It is an object of the present invention to provide an FB type laser, and to provide a DFB type laser in which a standing wave of light introduced from the outside functions as a diffraction grating.

[Means for Solving the Problems]] In order to achieve the above object, in the wavelength tunable semiconductor laser of the present invention, coherent monochromatic light is incident on the active layer for stimulated amplification of light from both ends of the active layer. cause waves,
This causes the active layer to also function as a diffraction grating.

[For production]

Monochromatic light introduced from the outside creates standing waves within the active layer, and the intensity of the light energy applied to the nuclear layer has periodicity in the axial direction. Therefore, the carrier density within the active layer changes periodically and functions as a diffraction grating.

This periodic change in carrier density that occurs in the active layer corresponds to the wavelength of external light, so by changing the wavelength of external light, the emission wavelength of the semiconductor laser can be controlled.

〔Example〕

The drawing is a schematic cross-sectional view showing the structure of a semiconductor laser according to an embodiment of the present invention. The structure and operation of the device will be described below with reference to the drawings.

The device of the present invention is used as a semiconductor laser, and has a p-1nP layer 2 as a cladding layer, an InGaAsP layer 3 as an active layer, and an n-1nP layer 4 as a cladding layer on a p-1nPfI plate 1.
It consists of On both ends of the active layer, an SiN film 5 having a thickness of approximately 1900 mm is deposited as an anti-reflection (AR) coating film, and an n-electrode 6 of AuGe/Au and a p-electrode 7 of AuZn are provided.

The above configuration is applicable to a normal semiconductor laser (II (12),
The device of the present invention is provided with means for generating a standing wave of light incident from the outside within the active layer. This point will be explained below.

First, external light is divided into two by half mirror 1O,
The respective directions are changed by the mirror 9 and the beams enter the prism 11. The prism is made of, for example, GaP crystal and has a high refractive index, and the Si01 layer 8 is a low refractive index layer for improving coupling between incident light and the active layer.

The thickness of the n-type cladding layer 4 through which the incident light passes is 0.5 μm.
is set to . As this value is smaller, the coupling strength of incident light increases, so in this embodiment, the conductivity type on the substrate side is p-type, and the n-type cladding layer, which can be formed thinly, is on the light incident side.

Passes through the n-type cladding layer and enters the high refractive index active layer. - External light incident from both ends travels in opposite directions using the active layer as a waveguide, producing standing waves. The period of this standing wave is λ/2n, where λ is the wavelength of external light in vacuum and n is the refractive index of the active layer.

When the external light becomes a standing wave, the energy applied to the active layer becomes l11w1, and the carrier density in the active layer changes with the same period, so it acts as a diffraction grating for the oscillation light of the semiconductor laser. It turns out.

One of the external light sources that meet this purpose of use is
There is a chainable F center laser.

The wavelength of this laser can be changed, for example, in the range of λ = 1.55 ± 0.2 μm, so if this is used as a wavelength @ control light source, the emission wavelength of the semiconductor laser of the present invention can be tuned within the above wavelength range. You can.

(Effects of the Invention) As described above, in the semiconductor laser of the present invention, since the emission wavelength is determined according to the wavelength of external light, the emission wavelength can be easily and quickly tuned.

Further, if the element of the present invention is used for relaying optical signals, it is possible to emit a transmitted signal having the same wavelength as that of a received signal, thereby realizing long-distance coherent optical communication.

[Brief explanation of the drawing]

The figure is a schematic cross-sectional view showing the structure of the element of the present invention. In the diagram l is a P-1nP substrate, 2 is P 1 n Ps 3 is the active layer, 4 is n-1nP. 5 is AR coat, 6 is an n-electrode, 7 is a p electrode, 8 is SiO snow, 9 is a mirror, 10 is half mirror 1 11 is a prism It is.

Claims (1)

[Scope of Claims] In a semiconductor laser comprising a cladding layer of one conductivity type and a cladding layer of the other conductivity type with an active layer sandwiched therebetween, coherent monochromatic light is transmitted from near both ends of the vertical axis of the active layer. A wavelength tunable semiconductor laser, comprising means for causing light to enter the active layer parallel to the axis and in opposite directions to generate a standing wave of the monochromatic light in the active layer.