JPH02119287A - Semiconductor laser of variable wavelength - Google Patents

Abstract

PURPOSE:To prevent enlarging of spectral line width when the wavelength is varied by inserting a buffer region to reduce a leak current between active and phase control regions of a variable wavelength Bragg reflection type laser and by optically coupling the active region and a distribution Bragg reflection region. CONSTITUTION:After electrodes 400, 410 are formed, a groove 170 is formed which enables electrical separation of a distribution Bragg reflection region 300, a phase control region 200, a buffer region 210, and an active region 100. When a current is injected to the phase control region 200 and a distribution Bragg reflection region 300, the wavelength of transmitted light changes to the short wave side, and increase of spectral line width is small. This means that a leak current is reduced due to the insertion of the buffer region.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wavelength tunable semiconductor laser used for optical transmission, optical measurement, etc.

[Conventional technology]

A wavelength tunable semiconductor laser is one of the key devices for FDM optical communication, coherent optical communication, optical measurement, etc. Tunable semiconductor lasers require a wide tunable tuning width with a wide oscillation wavelength, but especially in coherent optical communications and optical measurements, a narrow spectral linewidth is required even when the wavelength is tunable.

Conventionally, several studies have been made on wavelength tunable semiconductor lasers. Among them, the wavelength tunable Bragg reflection (DBR) laser, which consists of three regions: an active region, a phase control region, and a distributed Bragg reflection region, has a wavelength tunable range of 100 nm.
Wide range of people and promising. An example of this document is Electronics Letters (Elec.
tronics Letters) Magazine Volume 24 No. 8 57
I can list a 7-page paper.

[Problem to be solved by the invention]

However, conventional wavelength tunable DBR lasers have the following problems. In this laser, the carrier density injected into the phase control region and the DBR region is adjusted to control the oscillation wavelength. However, when the carrier is injected (
1) Absorption increases in the phase control region and DBR region, (
2) Some of the carriers injected into the phase control region leak into the active region, which causes the carrier density in the active region to fluctuate, resulting in the oscillation spectrum linewidth expanding to about three times that when no carriers are injected. was.

An object of the present invention is to provide a wavelength tunable laser in which the spectral line width does not widen even when the wavelength is varied.

[Means to solve the problem]

The wavelength tunable semiconductor laser of the present invention is a wavelength tunable semiconductor laser in which an active region, a phase control region, and a distributed Bragg reflection region are arranged in series, and each region is optically coupled. A buffer region for reducing leakage current is inserted between the phase control region and the buffer region is optically coupled to the active region and the distributed Bragg reflection region.

[Effect]

The wavelength tunable semiconductor laser of the present invention is characterized in that the spectral linewidth does not widen when the wavelength is tuned. Explain the principle.

In conventional wavelength tunable semiconductor lasers, when current is injected into the phase control region, the spectral linewidth increases significantly. This is thought to be because part of the injected current leaks into the active region, causing fluctuations in carrier density in the active region. Therefore, if a buffer region is provided between the active region and the phase control region and the leakage current from the phase control region can be limited to the buffer region, the leakage current to the active region can be reduced. In this structure, fluctuations in carrier density in the active region are suppressed, so an increase in spectral line width is suppressed. Furthermore, if an active layer is provided in the DBR region and used with carriers constantly injected into the DBR region, the equivalent refractive index can be controlled and the DB
Rather than reducing the absorption loss in the R region, it can even provide a gain. Therefore, it is possible to prevent an increase in the spectral line width due to absorption loss in the DBR region when tuning the wavelength.
Further reduction in spectral linewidth is expected.

〔Example〕

This embodiment will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing the structure of a wavelength tunable semiconductor laser according to a first embodiment of the present invention. FIG. 2 shows the second embodiment of the present invention.
FIG. 2 is a perspective view showing the structure of a wavelength tunable semiconductor laser according to an embodiment of the present invention. FIG. 3 is a diagram showing the measured spectral linewidth of the experimentally produced element when the wavelength is varied. The structure of this embodiment will be explained below according to the manufacturing procedure.

First, a first example will be described. A diffraction grating with a period of 2380 is formed in the distributed Bragg reflection region 300 of the n-type InP substrate 110 by photolithography. Next, by the first LPE growth, non-doped InGa
A'sP light guide N120 (λ, = 1.3 μm, thickness 0.3 μm>), n-type 1nP buffer layer 130 (thickness 0.1 μm), non-doped InGaAsP active layer 14
0 (λg = 1.53 μm, thickness 0.1 μm), p
An InP type cladding layer 150 (thickness: 0.2 μm) is sequentially grown. After selectively removing the InP cladding layer 150 and active layer 140 in the phase control region 200, buffer region 210, and distributed Bragg reflection region 300, a second LPE is performed.
A p-type 1nP cladding layer 160 is formed in the buffer region, phase control region, and distributed Bragg reflection region by growth.

A buried structure is used for carrier confinement and transverse mode control. After forming a striped mesa sandwiched between two parallel grooves by mesa etching, the third LPE
Embedded growth is performed to embed a mesa through growth. Here, a double channel planar embedding structure was used as the embedding structure. Finally, after forming electrodes 400 and 410 on the substrate side and the growth layer side, the distributed Bragg reflection region 3
00 and phase control region 200, phase control region 200 and buffer region 210, buffer region 210 and active region 100
In order to provide electrical isolation between the two substrates, a groove 170 having a width of 20 μm is formed except for the vicinity of the central mesa. The length of the distributed Bragg reflection region and the phase control region on one side are each 30
0 μm and 100 μm, and the total length of the element is 500 μm.

An example of the characteristics of the device prototyped in this way is shown in FIG.
When a current was injected into the wavelength, the transmission wavelength changed to the shorter wavelength side. At this time, the spectral linewidth increases to 1.5 times that when no control current is injected. Conventional wavelength variable DBR
It can be seen that this is considerably smaller than the increase (3 times) in the spectral line width of the laser. This is because the current leaking from the phase control region to the active layer was several mA in the prior art, but by inserting the buffer region, the leakage current was reduced to about 0.1 mA.

Next, a second embodiment will be described. A non-doped InGaAsP light guide layer 120 (λ
t=IAJ1m, thickness 0.3μm), n-shaped n? Buffer layer 130 (thickness 0.1 μm), non-doped active layer 1n
GaAsP 140 (λ□=1.53.um, thickness 0.1 μm), p-type InP clad J1150
(thickness: 0.2 μm). Phase control area 20
0. After selectively removing the InP cladding layer 150 and the active layer 140 in the buffer region 210, a p-type InP cladding M160 is formed in the buffer region and the phase control region by second LPE growth.

A buried structure is used for carrier confinement and transverse mode control. After forming a striped mesa sandwiched between two parallel grooves by mesa etching, the third LPE
Embedding growth is performed by growth. Here, a double channel planar embedding structure was used as the embedding structure. Finally, electrodes 400 and 410 are placed on the substrate side and the growth layer side.
After forming the distributed Bragg reflection region 300 and the phase control region 200, the phase control region 200 and the buffer region 210
, to provide electrical isolation between the buffer region 210 and the active region 100, the width is 20 μm except near the central mesa.
m grooves 170 are formed.

The length of the distributed Bragg reflection region and the phase control region on one side is
They are 300 μm and 100 μm, respectively, and the total length of the element is 500 μm.

An example of the characteristics of the device prototyped in this way is shown in FIG. 3 by a dashed line. Phase control region 200 and distributed Bragg reflection region 3
When a current was injected into 00, the transmission wavelength changed to 100 shorter wavelengths. At this time, the amount of change in the spectral line width was less than 10% of that when no control current was injected. It can be seen that this is a great improvement compared to the increase in spectral line width (3 times) of the conventional wavelength tunable DBR laser.

Note that the material and composition of the element need not be limited to the above-mentioned embodiments, and may be other semiconductor materials (for example, GaAs-based materials), and the optical waveguide structure may also have the function of guiding light. If it has, it may have any structure other than a planar structure or an embedded structure.

〔Effect of the invention〕

In conventional wavelength tunable semiconductor lasers, the spectral linewidth increases by more than three times when the wavelength is tuned, but with the wavelength tunable semiconductor laser of the present invention, the spectral linewidth hardly changes even when the wavelength is tuned. became.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the structure of a wavelength tunable semiconductor laser according to a first embodiment of the present invention. FIG. 2 shows the second embodiment of the present invention.
FIG. 2 is a perspective view showing the structure of a wavelength tunable semiconductor laser according to an embodiment of the present invention. FIG. 3 is a diagram showing the measured spectral linewidth of the experimentally produced element when the wavelength is varied. 100...active region, 110...substrate, 120...
- Light guide layer, 130...buffer layer, 140...
Active layer, 150, 160...Clad layer, 200...
・Phase control area, 210...Buffer area, 300・
...Distributed Bragg reflection area, 0°0...electrode.

Claims (1)

[Claims] An active region made of a semiconductor multilayer structure containing an active layer that participates in light emission, a phase control region made of a semiconductor multilayer structure having an optical waveguide mechanism, and a distributed Bragg reflection region made of a semiconductor multilayer structure containing a diffraction grating. In the wavelength tunable semiconductor laser in which the regions are arranged in series and the respective regions are optically coupled, a buffer region made of a semiconductor multilayer structure including an optical waveguide mechanism is provided between the active region and the phase control region. A wavelength tunable semiconductor laser, wherein the buffer region is optically coupled to the active region and the distributed Bragg reflection region.