JPH0582890A - Semiconductor laser module - Google Patents

Abstract

PURPOSE:To stabilize the lasing light wavelength by providing a first optical filter having a narrow band pass characteristic of one wavelength in the range of lasable wavelength of a semiconductor laser as its central wavelength, and a second optical filter having a given reflectivity in the range of leasable wavelength of the semiconductor laser. CONSTITUTION:A spherical lens 22, optical filters 23 and 24, and a spherical lens 25 are fixed by a low melting point glass in a case 27 in that order. The optical filter 23 has a band pass characteristic of 0.98mum central wavelength, 0.5-nm transmission band width, and 80% maximum transmittance. The surface of the filter is inclined at an angle of approximately ten degrees to the central axis of the case 27 in the normal direction. The optical filter 24 has a 30% reflectivity which is substantially constant having a wavelength width of more than 20nm and a wavelength of 0.98mum as its center, and the surface of the filter is arranged to agree with the central axis of the case 27 in the normal line direction. Then, a semiconductor laser 21 is fixed to the case 27 by resistance heating. On the other hand, a pig tail optical fiber 26 is adhesively bonded to a ferrule 28 and is further adhesively fixed to the case 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser module in which a semiconductor laser and a single mode optical fiber for extracting the emitted light are integrally formed. The semiconductor laser module is used as a light source for pumping light of an erbium-doped optical fiber amplifier used for optical communication, for example.

[0002]

2. Description of the Related Art In a semiconductor laser module with a pigtail optical fiber having a structure in which a single mode optical fiber is coupled to the emitting end of laser light and the laser light is taken out through this optical fiber, conventionally, the light is emitted near the laser chip. An isolator is installed to prevent the reflected light at the optical fiber entrance end or the optical fiber far end from being reinjected into the laser chip to stabilize the oscillation light wavelength.

FIG. 6 is a sectional view showing a structural example of a conventional semiconductor laser module with a pigtail optical fiber.
In the figure, laser light emitted from a semiconductor laser (LD) 61 is made into a parallel beam through a spherical lens 62 provided with an AR coating, and is incident on an optical isolator 63. The laser light that has passed through the optical isolator 63 is condensed via a spherical lens 64 similarly provided with an AR coating, and is coupled to a pigtail optical fiber 65. A ferrule (core) 6 whose end face is AR-coated and obliquely polished is formed at a connection portion between the case (hatched portion in the drawing) 66 of the semiconductor laser module and the pigtail optical fiber 65.
7 is used.

Here, the reflected light at the incident end of the pigtail optical fiber 65 does not return to the semiconductor laser 61 because the end face of the ferrule 67 is obliquely polished.
Further, the reflected return light from the far end of the pigtail optical fiber 65 is also prevented from being reinjected into the semiconductor laser 61 because it is blocked by the optical isolator 63.

As described above, in the conventional semiconductor laser module with a pigtail optical fiber, the optical isolator 63 removes and stabilizes the reflected return light which causes the oscillation wavelength of the semiconductor laser 61 to be unstable. It was

[0006]

By the way, YIG (yttrium-iron-garnet) crystals having a large Verdet constant can be used as a Faraday rotator in an optical isolator operating in a long wavelength band of 1.1 μm or more, which is small and excellent. It realizes the characteristics.

On the other hand, on the wavelength side shorter than 1.1 μm, it cannot be used due to the strong absorption of the YIG crystal itself, and instead, rare earth element-added glass (Faraday glass) with extremely small loss in that wavelength band is used. However, since the rare earth element-added glass has a small Verdet constant, it cannot be downsized, and it is extremely difficult to incorporate an optical isolator in the semiconductor laser module.

It is an object of the present invention to provide a semiconductor laser module which can stabilize the oscillation light wavelength by a method which is completely different from the conventional method and can be miniaturized even in a short wavelength region.

[0009]

According to a first aspect of the present invention, there is provided a semiconductor laser and a single mode optical fiber coupled to the laser light emitting end, and the laser light is transmitted through the optical fiber. In a semiconductor laser module having a configuration to be taken out, the semiconductor laser module has a narrow bandpass characteristic whose center wavelength is one wavelength within a lasing wavelength range of the semiconductor laser, and is on an optical axis connecting the semiconductor laser and the single mode optical fiber A first optical filter whose filter surface is arranged non-orthogonally to its optical axis; and a semiconductor laser and the single-mode optical fiber which have a predetermined reflectance in the oscillating wavelength range of the semiconductor laser. And a second optical filter whose filter surface is arranged orthogonal to the optical axis at a position opposite to the semiconductor laser with respect to the first optical filter on the optical axis connecting the two. When That.

According to a second aspect of the present invention, there is provided a semiconductor laser having a semiconductor laser and a single-mode optical fiber coupled to the laser light emitting end, through which the laser light is taken out. In the module, the semiconductor laser has a narrow bandpass characteristic whose center wavelength is one wavelength within the oscillating wavelength range of the semiconductor laser, and a filter surface is provided at a first cut portion provided in the middle of the single mode optical fiber. A first optical filter arranged non-orthogonally to the optical axis and having a predetermined reflectance in the wavelength range in which the semiconductor laser can oscillate, and with respect to the first cut portion in the middle of the single mode optical fiber; Second provided on the opposite side of the semiconductor laser
And a second optical filter whose filter surface is arranged orthogonal to the optical axis thereof.

[0011]

FIG. 1 is a diagram showing the principle configuration of the present invention. In the figure, a first optical filter 12 and a second optical filter 13 are arranged in series on the AR surface side of a semiconductor laser (LD) 11. Here, the first optical filter 12 has a narrow bandpass characteristic whose center wavelength is one wavelength within the oscillating wavelength range of the semiconductor laser 11, and its filter surface is a laser beam emitted from the semiconductor laser 11. It is installed at an angle to the optical path of. Further, the second optical filter 13 has a predetermined reflectance in the oscillating wavelength range of the semiconductor laser 11,
Further, the filter surface thereof is installed at an angle of 90 degrees with respect to the optical path of the laser light emitted from the semiconductor laser 11.

In the semiconductor laser module according to claim 1, the first optical filter 12 and the second optical filter 13 are installed at the coupling portion between the semiconductor laser 11 and the single mode optical fiber. In the semiconductor laser module described in 1), the single mode optical fiber coupled to the semiconductor laser 11 is installed at two cut portions provided in the middle. It is omitted, and only the semiconductor laser 11, the first optical filter 12, and the second optical filter 13 are shown.

The spectrum of the laser light emitted from the AR surface of the semiconductor laser 11 has a wavelength component of a relatively wide band. When this laser light passes through the first optical filter 12, it is converted into laser light having only a narrow band wavelength component due to its bandpass characteristic, and is incident on the second optical filter 13. At the same time, since the first optical filter 12 is inclined, the laser light reflected there is not incident on the semiconductor laser 11 and is emitted to the outside.

The laser light that has passed through the first optical filter 12 is partially reflected by the second optical filter 13.
Since the second optical filter 13 is installed at an angle of 90 degrees with respect to the optical path, the laser light reflected there passes through the first optical filter 12 again and returns to the semiconductor laser 11 to HR surface and second optical filter 13
A resonator is formed between and. The resonance wavelength of this resonator is matched with the wavelength that passes through the first optical filter 12, and the resonance characteristics of this resonator have wavelength dependence, so that the oscillation light of the semiconductor laser 11 with respect to the reflected return light. The wavelength can be stabilized. The laser light whose oscillation light wavelength is stabilized by this resonator is extracted as the light passing through the second optical filter 13.

[0015]

FIG. 2 is a sectional view showing the configuration of an embodiment of the semiconductor laser module according to claim 1.

In the figure, a semiconductor laser (LD) 21
Is a 0.98 μm oscillation In using a strained quantum well structure for the active layer.
It is a GaAs-SQW-LD. Laser light emitted from this semiconductor laser 21 is converted into a parallel beam through a spherical lens 22 having an AR coating at a wavelength of 0.98 μm,
After passing through the two optical filters 23 and 24,
It is collected through a spherical lens 25 having an R coating and coupled to a pigtail optical fiber 26. A ferrule (core) 28 is used at the connecting portion between the case (hatched portion in the drawing) 27 of the semiconductor laser module and the pigtail optical fiber 26. The semiconductor laser 21, the spherical lenses 22 and 25, the ferrule 28, and the optical filter 2
3, 24 are fixed to the case 27.

Now, the procedure for assembling the semiconductor laser module of this embodiment will be described. A notch is formed inside the case 27 at a position where each component is fixed in advance. First, the ball lens 22, the optical filters 23 and 24, and the ball lens 25 are fixed to the case 27 in this order by low melting glass. The optical filter 23 has a center wavelength of 0.98 μm and a transmission bandwidth of 0.5 n, as indicated by a in FIG. 3 (1).
m, the maximum transmittance is 80%, and the normal direction of the filter surface is about 10 degrees with respect to the central axis of the case 27 (the optical axis connecting the semiconductor laser 21 and the pigtail optical fiber 26). It is installed at an angle. Further, the optical filter 24 is
As shown by b in Fig. 3 (1), 20n centered on a wavelength of 0.98μm
It has a substantially constant reflectance of 30% in a wavelength width of m or more, and is installed such that the normal direction of its filter surface coincides with the central axis of the case 27.

Next, the semiconductor laser 21 is fused and fixed to the case 27 by a resistance heating method. On the other hand, the pigtail optical fiber 26 is adhesively fixed to the ferrule 28 whose end face is obliquely polished to about 8 degrees and AR coating is applied at a wavelength of 0.98 μm, and the position is adjusted so that the coupling with the semiconductor laser 21 is maximized. After that, it is adhesively fixed to the case 27.

The semiconductor laser module thus constructed operates as a resonator based on the operating principle described with reference to FIG. 1, and has a wavelength of 0.98 μm as shown in FIG. 3 (2).
The oscillation light wavelength characteristic of m can be obtained.

FIG. 4 is a diagram showing changes in the oscillation light wavelength with respect to changes in the reflectance of the laser light emitting end face of the pigtail optical fiber 26 in the semiconductor laser module of this embodiment.

In the figure, the horizontal axis represents time, and the reference numeral 41
Indicates the time change of the reflected return light intensity at the laser light emitting end face, reference numeral 42 indicates the time change of the oscillation light wavelength in the semiconductor laser module of this embodiment, and reference numeral 43 indicates the optical filter from the semiconductor laser module of this embodiment. The time change of the oscillation light wavelength when 23 and 24 are removed is shown. As shown in the figure, in the semiconductor laser module of the present embodiment, the change of the oscillation light wavelength is 1 due to the action of the optical filters 23 and 24.
It can be seen that the wavelength is suppressed to nm or less, and the oscillation light wavelength is sufficiently stabilized without using an optical isolator.

In the present embodiment, the semiconductor laser 2
The present invention can be similarly implemented even when 1 has a Fabry-Perot structure. Also, to change the oscillation light wavelength,
A at the end faces of the spherical lenses 22 and 25 and the ferrule 28
This can be dealt with by changing the wavelength of the R coating and the center wavelength of the optical filter 23.

FIG. 5 is a sectional view showing the structure of an embodiment of the semiconductor laser module according to the present invention. In the figure, the wavelength of 0.98 emitted from the semiconductor laser (LD) 51
The laser light of μm is condensed through a spherical lens 52 having an AR coating at a wavelength of 0.98 μm and coupled to a pigtail optical fiber 53. At the connection portion between the case (hatched portion in the figure) 54 of the semiconductor laser module and the pigtail optical fiber 53, the end face is diagonally polished to 0.98 μm.
A ferrule (core) 55 having an AR coating at the wavelength of is used. The semiconductor laser 51,
The ball lens 52 and the ferrule 55 are fixed to the case 54.

On the other hand, the pigtail optical fiber 53 is inserted into the groove 56.
The quartz glass substrate 56 for holding _one, a groove 56 _second width 100μm formed by non-perpendicular to the grooves 56 _1, and the groove 56 _third width 100μm formed by a right angle in the groove 56 ₁ is provided, pigtail optical fiber 53 is cut at the position of the groove 56 _2, 56 _3. The groove 56 ₂ is inserted an optical filter 57 having a characteristic indicated by a in FIG. 3 (1), the groove 56 ₃ 3
The optical filter 58 having the characteristic indicated by b in (1) is inserted. The core portion of the groove 56 _2, 56 pigtail optical fiber 53 that is cut at a position of ₃ is locally heat treated at 1000 ° temperatures above the refractive index for forming the dopant is diffused, is effectively a core diameter It will be doubled. This facilitates the alignment of the optical filter 57, 58 to be inserted into the pigtail optical fiber 53 and the groove 56 _2, 56 _3, has the ability to reduce the connection loss.

Therefore, the normal line direction of the filter surface of the optical filter 57 and the optical axis of the pigtail optical fiber 53 do not coincide with each other, and the component reflected by the optical filter 57 becomes a radiation component of the pigtail optical fiber 53 and becomes the semiconductor laser 51. Does not return. Further, since the normal direction of the filter surface of the optical filter 58 and the optical axis of the pigtail optical fiber 53 coincide with each other, the laser light reflected by the optical filter 58 becomes the propagation mode of the pigtail optical fiber 53 and returns to the semiconductor laser 51.
A resonator is formed between the semiconductor laser 51 and the semiconductor laser 51. That is, even the semiconductor laser module configured as described above operates based on the operation principle described with reference to FIG. 1 and obtains the oscillation light wavelength characteristic of wavelength 0.98 μm as shown in FIG. 3 (2). ..

Also in this embodiment, the change of the oscillation light wavelength with respect to the change of the reflectance of the laser light emitting end face of the pigtail optical fiber 53 was measured.
Even if it was changed from dB to -45 dB, the change of the oscillation light wavelength could be suppressed to 2 nm or less.

[0027]

As described above, according to the present invention, instead of using the conventional optical isolator, a resonator is formed by the semiconductor laser and an external optical filter, and the wavelength dependence of the resonator causes the reflected return light of the semiconductor laser. Since this method suppresses changes in the wavelength of the oscillated light, it is suitable for downsizing and can flexibly support semiconductor laser modules from the short wavelength band to the long wavelength band with the same structure.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention.

FIG. 2 is a cross-sectional view showing the configuration of an embodiment of the semiconductor laser module according to claim 1.

FIG. 3 is a diagram showing characteristics of an optical filter used in the present invention.

FIG. 4 is a diagram showing a change in oscillation light wavelength with respect to a change in reflectance of a laser light emitting end surface of a pigtail optical fiber in an example.

FIG. 5 is a sectional view showing a configuration of an embodiment of the semiconductor laser module according to claim 2;

FIG. 6 is a cross-sectional view showing a configuration example of a conventional semiconductor laser module with a pigtail optical fiber.

[Explanation of symbols]

 11 Semiconductor Laser (LD) 12 First Optical Filter 13 Second Optical Filter 21 Semiconductor Laser (LD) 22,25 Ball Lens 23,24 Optical Filter 26 Pigtail Optical Fiber 27 Case 28 Ferrule 51 Semiconductor Laser (LD) 52 Ball Lens 53 Pigtail optical fiber 54 Case 55 Ferrule 56 Quartz glass substrate 57,58 Optical filter 61 Semiconductor laser (LD) 62,64 Ball lens 63 Optical isolator 65 Pigtail optical fiber 66 Case 67 Ferrule

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yuro Yamada 1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Taisuke Oguchi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A semiconductor laser module having a semiconductor laser and a single-mode optical fiber coupled to the laser light emitting end, wherein laser light is extracted through the optical fiber. It has a narrow bandpass characteristic having one wavelength in the oscillating wavelength range as a central wavelength, and a filter surface is arranged non-orthogonally to the optical axis connecting the semiconductor laser and the single mode optical fiber. And a first optical filter having a predetermined reflectance in the wavelength range in which the semiconductor laser can oscillate and on the optical axis connecting the semiconductor laser and the single-mode optical fiber. And a second optical filter whose filter surface is arranged orthogonal to the optical axis at a position opposite to the semiconductor laser. 2. A semiconductor laser module having a semiconductor laser and a single-mode optical fiber coupled to the laser light emitting end, wherein laser light is taken out through the optical fiber. Having a narrow bandpass characteristic with one wavelength in the oscillating wavelength range as the central wavelength, the filter surface is arranged non-orthogonally to the optical axis of the first cut portion provided in the middle of the single mode optical fiber. A first optical filter, which has a predetermined reflectance in the wavelength range in which the semiconductor laser can oscillate, and which is on the opposite side of the semiconductor laser with respect to the first cut portion in the middle of the single mode optical fiber. And a second optical filter having a filter surface arranged orthogonal to the optical axis of the second cut portion provided in the semiconductor laser module.