JP2021114526A - Wavelength variable laser - Google Patents

Abstract

To provide a wavelength variable layer capable of improving luminous efficiency.SOLUTION: A wavelength variable layer includes a waveguide in which gain regions and wavelength adjustment regions are alternately arranged in a propagation direction of light and the wavelength adjustment region is located on one end in the propagation direction of the light.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a tunable laser.

As an optical device, a tunable laser having a gain function for laser oscillation and a wavelength adjustment function is known. For example, a region having a gain and a region for wavelength adjustment are alternately arranged in the laser element (Patent Document 1 and the like).

Japanese Unexamined Patent Publication No. 4-147686

Luminous efficiency may decrease because a part of the plurality of gain regions does not contribute to the output of light. Therefore, it is an object of the present invention to provide a tunable laser capable of improving luminous efficiency.

The wavelength tunable laser according to the present disclosure includes a waveguide in which gain regions and wavelength adjustment regions are alternately arranged and provided in the light propagation direction, and the wavelength adjustment region is provided at one end in the light propagation direction. Is located.

According to the above disclosure, the luminous efficiency can be improved.

FIG. 1A is a plan view illustrating the tunable laser according to the first embodiment. FIG. 1B is a cross-sectional view illustrating a tunable laser. FIG. 2 is an enlarged cross-sectional view of the gain region and the wavelength adjustment region.

[Explanation of Embodiments of the present disclosure]
First, the contents of the embodiments of the present disclosure will be listed and described.
One embodiment of the present disclosure includes (1) a waveguide in which gain regions and wavelength adjustment regions are alternately arranged and provided in the light propagation direction, and the wavelength adjustment is performed at one end in the light propagation direction. A tunable laser in which the region is located. This improves the luminous efficiency.
(2) An attenuator, a modulator and an amplifier provided along the light propagation direction may be provided. The tunable laser functions as an integrated laser element.
(3) The amplifier may be located at the other end in the light propagation direction. Light is emitted from the amplifier.
(4) The period in which the gain region and the wavelength adjustment region are aligned may be 100 μm or less. As a result, a high gain can be obtained and the wavelength can be adjusted.
(5) The gain region includes an active layer, a first contact layer provided on the active layer, and a first electrode in contact with the upper surface of the first contact layer, and the wavelength adjustment region is a wavelength adjustment. It may include a layer, a second contact layer provided on the wavelength adjusting layer, and a second electrode in contact with the upper surface of the second contact layer. Since the wavelength adjusting layer absorbs light less easily than the active layer, the output of light increases.

[Details of Embodiments of the present disclosure]
Specific examples of the tunable laser according to the embodiment of the present disclosure will be described below with reference to the drawings. It should be noted that the present disclosure is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

FIG. 1A is a plan view illustrating the tunable laser 100 according to the first embodiment, and FIG. 1B is a cross-sectional view illustrating the tunable laser 100. FIG. 2 is an enlarged cross-sectional view of the gain region 17 and the wavelength adjustment region 18.

As shown in FIGS. 1A and 1B, the variable wavelength laser 100 includes a variable wavelength light source 10, a variable optical attenuator (VOA) 12, a modulator (MOD) 14, and a semiconductor optical amplifier (SOA). An optical attenuator integrated laser (EML) equipped with an amplifier (16). As shown in FIG. 1A, the tunable light source 10, VOA12, MOD14 and SOA16 include the optical waveguide 11, and are arranged in order along the extending direction of the optical waveguide 11.

The tunable light source 10 includes a plurality of gain regions 17 and a wavelength adjustment region 18. The number of gain regions 17 and the number of wavelength adjustment regions 18 are, for example, seven. The plurality of gain regions 17 and the plurality of wavelength adjustment regions 18 are arranged alternately along the light propagation direction. The active layer in the gain region 17 and the wavelength adjusting layer 27 in the wavelength adjusting region 18 form the optical waveguide 11. The gain region 17 is located at the end of the tunable light source 10 on the VOA 12 side, and the wavelength adjustment region 18 is located at the end on the opposite side. The wavelength adjustment region 18 is located at one end of the tunable laser 100, and the SOA 16 is located at the other end. An antireflection film (not shown) may be provided on the end face of the wavelength adjustment region 18 located at the end of the tunable laser 100.

As shown in FIG. 1B, in the tunable light source 10, VOA12, MOD14 and SOA16, an electrode 31 is provided on the lower surface of the substrate 20, and the lower clad layer 22 is laminated on the upper surface of the substrate 20. The lower clad layer 22 and the upper clad layer 28 extend over the tunable light source 10, VOA 12, MOD 14 and SOA 16. A gallium indium arsenic phosphorus (GaInAsP) layer 24 is embedded in the lower clad layer 22. A GaInAsP layer 24 extending along the stretching direction of the optical waveguide 11 is provided across the VOA 12, MOD 14 and SOA 16. The wavelength tunable light source 10 is provided with, for example, a plurality of GaInAsP layers 24 provided at a predetermined period. The GaInAsP layer 24 has a different refractive index than the lower clad layer 22. The portion where the plurality of GaInAsP layers 24 and the lower clad layer 22 arranged on the tunable light source 10 are lined up along the extending direction of the optical waveguide 11 functions as a diffraction grating 23 (corrugation).

The surface of the tunable laser 100 is covered with an insulating film 38. The contact layer is exposed from the plurality of openings of the insulating film 38, and the electrodes come into contact with the contact layer exposed from the openings as described later.

In the VOA 12, the absorption layer 40, the upper clad layer 28, the contact layer 44, and the electrode 50 are laminated in this order on the lower clad layer 22. The electrode 50 contacts the upper surface of the contact layer 44. In the MOD 14, the absorption layer 40, the upper clad layer 28, the contact layer 46, and the electrode 52 are laminated in this order on the lower clad layer 22. The electrode 52 contacts the upper surface of the contact layer 46. The absorption layer 40 spans VOA12 and MOD14. In the SOA 16, the active layer 42, the upper clad layer 28, the contact layer 48, and the electrode 54 are laminated in this order on the lower clad layer 22. The electrode 54 contacts the upper surface of the contact layer 48. One GaInAsP layer 24 stretches across VOA12, MOD14 and SOA16.

As shown in FIGS. 1B and 2, in the gain region 17, the active layer 26, the upper clad layer 28, (the first contact layer) and the electrode 32 (the first electrode) are laminated in this order on the lower clad layer 22. There is. The electrode 32 comes into contact with the upper surface of the contact layer 30. In the wavelength adjustment region 18, the wavelength adjustment layer 27, the upper clad layer 28, the contact layer 34 (second contact layer), and the electrode 36 (second electrode) are laminated in this order on the lower clad layer 22. The electrode 36 comes into contact with the upper surface of the contact layer 34. In the tunable light source 10, the plurality of GaInAsP layers 24 are separated from each other.

The substrate 20 is, for example, a semiconductor substrate formed of n-type indium phosphide (InP). The lower clad layer 22 is formed of, for example, n-type InP. The upper clad layer 28 is formed of, for example, p-type InP. The active layer 26 is, for example, a multi-strained quantum well having a well layer of GaInAsP and a barrier layer of GaInAsP and having a band gap of a PL (photoluminescence) wavelength of 1.527 μm. The wavelength adjustment layer 27 is formed of GaInAsP which is lattice-matched to InP and has a band gap at a PL wavelength of 1.42 μm. The absorption layer 40 is a multi-strained quantum well having a well layer of GaInAsP and a barrier layer of GaInAsP and having a band gap of 1.476 μm in PL wavelength. The active layer 42 is a multi-strained quantum well having a well layer of GaInAsP and a barrier layer of GaInAsP and having a band gap of a PL wavelength of 1.527 μm. The active layer 26 and the wavelength adjusting layer 27 are adjacent to each other. The absorption layer 40, the wavelength adjustment layer 27, and the active layer 42 are adjacent to each other. The active layer 26, the wavelength adjusting layer 27, the absorption layer 40, and the active layer 42 are located at the same height and form an optical waveguide 11.

The contact layers 30, 34, 44, 46 and 48 are formed, for example, by p-type GaInAs. The insulating film 38 is formed of an insulator such as silicon nitride (SiN) or silicon oxide (SiO _2). The electrode 31 is an n-type electrode made of a metal such as gold (Au). The electrodes 32, 36, 50, 52 and 54 are p-type electrodes made of a metal such as Au.

The length L1 of the gain region 17 and the length L2 of the wavelength adjustment region 18 in the light propagation direction shown in FIG. 2 are, for example, 40 μm, respectively. The period T of the arrangement of the gain region 17 and the wavelength adjustment region 18 is 80 μm. The length L3 of the contact layer 30 in the gain region 17 and the length L4 of the contact layer 34 in the wavelength adjustment region 18 in the light propagation direction are, for example, 30 μm. The lengths of these contact layers 30 and 34 (contact lengths) are equal to the lengths of the electrodes 32 and 36 in the direction of light propagation. The distance D1 between the contact layer 30 and the contact layer 34 in the light propagation direction is, for example, 10 μm. The distance D1 is equal to the distance between the electrode 32 and the electrode 36. The distance D2 from the end of the electrode 32 and the end of the electrode 36 to the boundary between the gain region 17 and the wavelength adjustment region 18 is, for example, 5 μm. The distance between the contact layer 30 and the active layer 26 in the layer stacking direction is equal to the distance between the contact layer 34 and the wavelength adjusting layer 27, and this distance D3 is 2 μm or less, for example, 1.6 μm.

The active layer 26 has a gain and emits light when a current is injected from the electrode 32 through the contact layer 30. Light having a predetermined wavelength is selected by the diffraction grating 23. The wavelength is adjusted by injecting a current from the electrode 36 into the wavelength adjusting layer 27 through the contact layer 34 and changing the refractive index of the wavelength adjusting layer 27. As a result, the tunable light source 10 emits light having a wavelength in the range of, for example, 1532 nm or more and 1536 nm or less. The absorption layer 40 absorbs light by injecting an electric current from the electrodes 50 and 52. The active layer 42 has a gain and amplifies light when a current is injected from the electrode 54. The lower clad layer 22 and the upper clad layer 28 sandwich the optical waveguide 11 from above and below, and confine the light in the optical waveguide 11. The light propagating through the optical waveguide 11 is emitted from the end face of the SOA 16 to the outside of the tunable laser 100.

When the gain region 17 is located at the end of the tunable laser 100 opposite to the SOA 16, the gain region 17 is unlikely to contribute to the output of light to the VOA 12 side. Since the current injected into the gain region 17 does not contribute to light emission, the light emission efficiency is lowered.

According to the first embodiment, as shown in FIG. 1B, the wavelength adjustment region 18 is located at the end of the tunable laser 100. Therefore, all the gain regions 17 of the tunable light source 10 contribute to the output of light. Therefore, it is possible to improve the luminous efficiency.

The tunable laser 100 is an integrated laser element including VOA12, MOD14, and SOA16 arranged along the light propagation direction. The light emitted by the tunable light source 10 can be attenuated, modulated and amplified. The tunable laser 100 can oscillate at a wavelength of, for example, 1532 nm to 1536 nm, and can be applied to a wavelength division multiplexing communication system. The tunable laser 100 may have a tunable light source 10 without having at least one of VOA 12, MOD 14 and SOA 16.

The wavelength adjustment region 18 is located at one end of the tunable laser 100, and the SOA 16 is located at the other end. As a result, the luminous efficiency is improved and light can be emitted from the SOA 16. The VOA 12 or MOD 14 may be arranged at the end opposite to the wavelength adjustment region 18.

The period T is, for example, 100 μm or less, and may be 90 μm or less, 80 μm or less, and the like. As a result, a high gain can be obtained, and the tunable laser 100 can oscillate at a wavelength of, for example, 1532 nm to 1536 nm. As an example, the period T is 80 μm, the contact lengths L3 and L4 are 30 μm, and the ratios L3 / T and L4 / T are 0.375. The number of gain regions 17 and the number of wavelength adjustment regions 18 may be 7 or less, or 7 or more.

The gain region 17 includes an active layer 26, a contact layer 30, and an electrode 32. The wavelength adjustment region 18 includes a wavelength adjustment layer 27, a contact layer 34, and an electrode 36.

Although the examples of the present disclosure have been described in detail above, the present disclosure is not limited to such specific examples, and various modifications and modifications are made within the scope of the gist of the present disclosure described in the claims. It can be changed.

10 Wavelength variable light source 11 Optical waveguide 12 Variable optical attenuator 14 Modulator 16 Semiconductor optical amplifier 17 Gain region 18 Wavelength adjustment region 20 Substrate 22 Lower clad layer 23 Diffraction grating 24 GaInAsP layer 26, 42 Active layer 27 Wavelength adjustment layer 28 Upper clad Layers 30, 34, 44, 46, 48 Contact layers 31, 32, 36, 50, 52, 54 Electrodes 38 Insulation film 40 Absorption layer 100 Tunable laser

Claims (5)

The gain region and the wavelength adjustment region are alternately arranged in the light propagation direction, and the waveguide is provided.
A tunable laser in which the wavelength adjustment region is located at one end in the light propagation direction. The tunable laser according to claim 1, further comprising an attenuator, a modulator or an amplifier provided along the light propagation direction. The tunable laser according to claim 2, wherein the attenuator, the modulator or the amplifier is located at the other end in the light propagation direction. The wavelength tunable laser according to any one of claims 1 to 3, wherein the period in which the gain region and the wavelength adjustment region are aligned is 100 μm or less. The gain region includes an active layer, a first contact layer provided on the active layer, and a first electrode in contact with the upper surface of the first contact layer.
Any of claims 1 to 4, wherein the wavelength adjustment region includes a wavelength adjustment layer, a second contact layer provided on the wavelength adjustment layer, and a second electrode in contact with the upper surface of the second contact layer. The wavelength tunable laser according to one item.

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