JP2000187136A - Aligning method for fiber grating optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved aligning method for optically coupling an optical fiber with a fiber grating to a semiconductor optical amplifier and forming an optical resonator. SOLUTION: This method is an aligning method for a fiber grating optical module positioning the optical fiber 14 having a fiber grating 14a for the semiconductor optical amplifier 16 and forming the optical resonator. In such a case, this method is provided with a coupling step optically coupling a light reflector 54 having prescribed reflectance for the optical fiber so as to form the optical resonator with the light reflection surface 16b of the semiconductor optical amplifier 16, an oscillation step adding current from a power source 48 to the semiconductor optical amplifier 16 and generating laser oscillation in the optical resonator constituted of the light reflection surface 16b of the semiconductor optical amplifier 16 and the light reflector 54 and an aligning step aligning the optical fiber 14 for the semiconductor optical amplifier 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for aligning a fiber grating optical module.

[0002]

2. Description of the Related Art As a prior art relating to an optical module having an optical resonator comprising a light emitting element and an optical fiber having a fiber grating formed thereon, US Pat.
There is a light emitting module described in Japanese Patent Application Publication No. 410-410.

Referring to the publication, this light emitting module has an optical resonator composed of a semiconductor optical amplifier that generates light when a current is applied thereto, and an optical fiber having a fiber grating. To form the optical resonator, a semiconductor optical amplifier is fixed on a pedestal provided in a housing, and then a ferrule provided at a tip portion of an optical fiber is inserted into a washer and fixed, and then the washer is fixed. Is fixed to the housing, thereby positioning the optical fiber with respect to the semiconductor optical amplifier. This positioning is performed under the condition that a current capable of laser oscillation in the above-described optical resonator is applied to the semiconductor optical amplifier in order to reliably perform optical coupling between the semiconductor optical amplifier and the tip of the optical fiber. ing.

[0004]

However, in order to cause laser oscillation in an optical resonator composed of a semiconductor optical amplifier and a fiber grating, at least one longitudinal mode must exist in the reflection band of the fiber grating. is necessary. However, a fiber grating semiconductor laser (hereinafter, referred to as FGL)
When the longitudinal mode interval becomes substantially equal to the reflection bandwidth of the fiber grating, the oscillation state of the FGL becomes unstable. Therefore, when aligning the optical fiber having the fiber grating with respect to the semiconductor optical amplifier, another adjustment has been performed to stabilize laser oscillation. For example, for this adjustment, it is necessary to perform the alignment while adjusting the items such as changing the temperature of the semiconductor optical amplifier and changing the value of the current to be applied. For this reason, a temperature adjusting device for assembly is required, and a time for stabilizing the temperature of the semiconductor optical amplifier is required.

It is an object of the present invention to provide an improved alignment method for optically coupling an optical fiber having a fiber grating to a semiconductor optical amplifier and aligning the optical fiber to form an optical resonator in a fiber grating optical module. To provide.

[0006]

According to the present invention, there is provided a method for aligning a fiber grating optical module, comprising: a light emitting surface having a light emitting surface and a light reflecting surface, wherein light is emitted from the light emitting surface when a current is applied. An amplifier and an optical fiber having a first end optically coupleable to a light emitting surface, a second end, and a fiber grating provided at a predetermined distance from the first end are relatively positioned. A method of aligning a fiber grating optical module, which optically aligns a light emitting surface of a semiconductor optical amplifier and a first end of an optical fiber, comprising: A coupling step of providing light reflecting means for reflecting received light so as to form an optical resonator; and applying a current to the semiconductor optical amplifier, and comprising a light reflecting surface and a light reflecting means of the semiconductor optical amplifier. An oscillation step of causing laser oscillation at a predetermined oscillation wavelength in the resonator; an alignment step of adjusting a relative position of the optical fiber with respect to the semiconductor optical amplifier based on an intensity of light extracted from the second end of the optical fiber; Is provided.

As described above, the light reflecting means having a predetermined light reflectance is provided on the optical fiber so as to form an optical resonator with the light reflecting surface of the semiconductor optical amplifier. A separate optical resonator having a cavity length longer than the cavity length of the optical resonator formed by the reflection surface and the fiber grating is formed. Further, the resonator lengths of the separate optical resonators can be set independently. Therefore, the interval between the longitudinal modes of the laser formed by the separate optical resonators becomes narrow. Thus, some of the longitudinal modes can be in the reflection band of the fiber grating. On the other hand, when a current having a predetermined value is applied to the semiconductor optical amplifier, the laser having the optical resonator formed by the light reflecting surface and the light reflecting means of the semiconductor optical amplifier oscillates. The laser light generated by this laser is extracted through an optical fiber, and the relative position between the semiconductor optical amplifier and the optical fiber is adjusted based on the intensity, so that the semiconductor optical amplifier can emit light in a stable light emitting state. An optical fiber having a fiber grating can be aligned with respect to the optical fiber.

In the method for aligning a fiber grating optical module according to the present invention, the aligning step includes a moving step of relatively moving a position of the optical fiber and a position of the semiconductor optical amplifier, and a second end of the optical fiber. And measuring a light intensity extracted from the light source.

As described above, the position of the optical fiber and the position of the semiconductor optical amplifier are relatively changed, and the intensity of the light extracted from the second end of the optical fiber is measured. Alignment with the semiconductor optical amplifier can be ensured.

In the method of aligning a fiber grating optical module according to the present invention, the light reflecting means may be provided at an end of the optical fiber branched from the optical fiber by the light branching means.

As described above, since a plurality of ends of the optical fiber different from the end facing the semiconductor optical amplifier are provided, the intensity of light from the semiconductor optical amplifier can be measured at one of the ends. At the other end, light from the semiconductor optical amplifier can be reflected.

[0012]

Embodiments of the present invention will be described with reference to the drawings. When possible, the same parts are denoted by the same reference numerals, and description thereof will be omitted.

The configuration of the fiber grating optical module according to the embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view of a fiber grating optical module, which is partially cut away so as to clarify the inside thereof. FIG. 2 is a sectional view showing a main part 10 of the fiber grating laser, taken along a line II in FIG.

Referring to FIGS. 1 and 2, the fiber grating optical module 1 includes a housing 12 and a main part 10 of the fiber grating optical module.

The housing 12 is, in the embodiment shown in FIG. 1, a butterfly type package. Package 12
The main part 10 of the fiber grating optical module is arranged on the bottom surface inside. The main part 10 of the fiber grating optical module is sealed in a package 12 in a state in which an inert gas, for example, nitrogen gas is sealed. The material of the package 12 is a metal, for example, Kovar, and includes a main body 12 a that houses the main part 10 of the fiber grating laser module, a cylindrical part 12 b that guides the optical fiber 14 to the main part 10, and a main part 1.
A plurality of lead pins 12c are provided to enable the zero electrode to be electrically extracted outside the package 12. Tubular part 1
An optical fiber 14 is introduced from the tip of 2b, and this optical fiber 14 passes through the inside of the cylindrical part 12b and reaches the main part 10 of the fiber grating laser module. The plurality of lead pins 12c are provided on both side surfaces of the package 12, and are electrically connected to the semiconductor optical amplifier 16 and the like by using a conductive wire (not shown). Each lead pin 12c is used for supplying a drive current to the semiconductor optical amplifier 16, extracting a current from the light receiving element 18, and supplying a current to the cooling element 28.

The main part 10 of the fiber grating optical module includes mounting members 22, 24, 26 for mounting the semiconductor optical elements 16, 18, and a positioning mechanism for optically coupling the optical fiber 14 to the semiconductor optical amplifier 16. And a unit 30. The alignment mechanism 30 includes a ferrule 32, a first support member 34, and a second support member 36.
And a third support member 38.

The first support member 34 has a contact plane 34a that contacts the receiving surface 24e of the mounting member 24,
a washer having an opposing surface 34b opposing a.
The first support member 34 moves from the contact plane 34 a to the opposing surface 34.
The ferrule 32 into which the optical fiber 14 has been inserted passes through a hole 34c penetrating toward b. First support member 34 used in the present embodiment
Has a shape in which a disk-shaped flat plate having a larger diameter and a disk-shaped flat plate having a smaller diameter are coaxially stacked. The first support member 34 supports the ferrule 32 inserted into the hole 34c provided at the center. First support member 34
Is fixed to the ferrule 32 at the opening of the hole 34c in the facing surface 34b, and is fixed to the mounting member 24 on the outer periphery of the first support member 34.

The second support member 36 includes the first support member 3
4 and is fixed to the ferrule 32 at a position separated by a predetermined length. To ensure a predetermined length, a third support member 38 is sandwiched between the first support member 34 and the second support member 36. The second support member 36 has a contact surface 36a in contact with the third support member 38 and an opposing surface 36b opposed to the contact surface 36a. The second support member 36 is
Hole 3 penetrating from contact plane 36a toward facing surface 36b
6c, and the ferrule 32 passes through the hole 36c. The second support member 34 used in the present embodiment is a flat plate having a disk shape.

The third support member 38 has a tubular portion 38a extending a predetermined length in the direction in which the ferrule 32 is provided, and one end of the tubular portion 38a is placed on the facing surface 34b of the first support member 34. Is in contact with The other end of the tubular portion 38a
Flat plate 38b having hole 38c through which ferrule 32 passes
Is closed by. The flat plate 38b has, on its outer surface, a contact surface 38d with which the second support member 36 contacts. The third support member used in the present embodiment has a bottom surface 38b.
Is a cup shape having a cylindrical portion 38a having a through hole 38c in the central portion thereof.

The second support member 36 is connected to the third support member 3.
The contact surface 38d of No. 8 is brought into contact with the plane 36a, and is fixed to the third support member 38 on the outer periphery of the second support member 36. Further, the second support member 36 is provided with a facing surface 36b.
Is fixed to the ferrule 32 around the opening of the through hole 36c.

Ferrule 32, first to third support members 3
4, 36, 38 can be formed, for example, of stainless steel. Also, ferrule 32, first to third
The fixing of the supporting members 34, 46, 48 is preferably performed at a plurality of positions using, for example, spot welding.

The first pointing member 34 and the second pointing member 36 preferably have a ring shape. As described above, when the outer shape is circular, symmetry is increased in a planar shape viewed from the center axis direction of the circle. For this reason, if fixing is performed by spot welding at a plurality of symmetrical positions, for example, at two opposing points where the axis of symmetry and the outer periphery of the circle intersect, distortion generated during fixing is reduced. Also,
It is preferable that the fixing by spot welding be performed simultaneously with respect to the above-mentioned facing position. By doing so, distortion generated at the time of fixing can be reduced.

The semiconductor optical amplifier 16 includes the chip carrier 2
2 mounted. The chip carrier 16 is formed using, for example, aluminum nitride (AlN) and alumina (Al ₂ O ₃ ). Therefore, the semiconductor optical amplifier 22
The heat generated during the operation of (1) conducts through the chip carrier 22 and reaches the Peltier element 28. The Peltier device 28
When a current flows, it operates as a cooling element. The semiconductor optical amplifier 16 is arranged with its first end face 16a facing the optical fiber insertion surface of the package 12. Although not particularly shown in the drawings, the electrodes formed on the semiconductor optical amplifier 16 are connected to the wiring layer on the chip carrier 22 via conductive wires. This wiring layer is connected to the internal lead of the package 12 by a conductive wire.

The semiconductor optical amplifier 16 has an active layer made of InGaAsP and two clad layers made of InP sandwiching the active layer on two opposing surfaces of the layer on a semiconductor substrate. A semiconductor layer, and the other of the cladding layers is an N-type semiconductor layer. The semiconductor optical amplifier 16 is a light emitting element that generates stimulated emission light by injecting carriers from the cladding layers on both sides into the active layer to form a population inversion. The active layer has a first end face 16.
a and a second end face 16b. First end face 16a
Is smaller than the light reflectance of the second end face. In order to realize this, a low reflection film is formed on the first end face 16a to achieve a reflectance of about 1 to 0.1%. On the other hand, a highly reflective film is formed on the second end face 16b,
A reflectance of 5% or more is achieved. Therefore, the first end surface 16a becomes a light emitting surface, and the second end surface 16b becomes a light reflecting surface. Although not particularly shown in the drawings, the electrodes formed on the semiconductor optical amplifier 16 are connected to the wiring layer on the chip carrier 22 by conductive wires. This wiring layer is connected to the internal lead of the package 12.

The light receiving element 18, for example, a photodiode is mounted on a chip carrier 26. The chip carrier 26 has a photodiode 18 at a position facing an end face 16b facing the end face 16a of the semiconductor optical amplifier 16.
Are provided on the mounting member 24 so that the. This photodiode 18 is a semiconductor optical amplifier 16
It operates as a monitoring photodiode for monitoring the light emitting state of the LED. Although not particularly shown in the drawings, the electrodes formed on the light receiving element 18 are connected to a wiring layer on the chip carrier via conductive wires. This wiring layer is connected to the internal lead of the package 12.

The mounting member 24 is an L-shaped member having a base portion 24a and a wall portion 24b, and the wall portion 24b is provided on a mounting surface 24c of the base portion 24a. The chip carriers 22 and 26 are mounted on the mounting surface 24c of the base portion 24b.
Mounted on top. The mounting member 24 is installed on the Peltier element 28 with the installation surface 24d facing the Peltier element 28. The wall portion 24b is provided with an optical fiber receiving surface 24.
e, a facing surface 24f facing the receiving surface 24e, and a through hole 24g penetrating from the receiving surface 24e to the facing surface 24f. The lens end 14b of the optical fiber 14 is inserted into the through hole 24g.
6 to provide space for optical coupling with the first end face 16a. In the mounting member 24, the mounting surface 24c, the installation surface 24d, the receiving surface 24e, and the facing surface 24f are flat surfaces. The mounting surface 24c and the setting surface 24d are substantially parallel, the receiving surface 24e and the facing surface 24f are substantially parallel, and the mounting surface 24c is substantially perpendicular to the facing surface 24f.

The optical fiber 14 has a fiber grating 14a and two ends 14b and 14c.
One of these ends faces the first end face 16a of the semiconductor optical amplifier 16, and the optical fiber 14 is disposed at a position where the end 14b and the first end face 16a can be optically coupled. I have. The end 14 b optically coupled to the first end face 16 a is connected to the first end face 16 of the semiconductor optical amplifier 16.
It has a lens shape that is processed to be spherical so that light emitted from a can be collected. Therefore, the semiconductor optical amplifier 1
Since there is no need to provide a separate lens between the optical fiber 6 and the optical fiber 14, the optical coupling can be performed directly. As a result, the resonator length can be shortened, and the high-frequency characteristics of the fiber grating laser are improved.

The optical fiber 14 is provided with a diffraction grating (fiber grating) 14a at a position within a core portion separated from the one end 14b having a lens shape by a predetermined distance. An optical fiber suitable for forming such a diffraction grating 14a includes a core portion containing germanium oxide and having a predetermined refractive index, and has a smaller refractive index than the core portion provided around the core portion. It has a clad part. By irradiating the optical fiber with ultraviolet light, regions having different refractive indices are provided at a plurality of locations in the core portion. Such regions are preferably provided periodically. Such a diffraction grating 14a is
It is characterized by characteristic values such as reflectivity, period, diffraction grating length, and the like. Fiber gratings can be designed to combine these property values to have a reflection spectrum in the wavelength region used for alignment in the present application.

The optical fiber 14 is inserted from one end into a through hole extending from one end of the ferrule 32 to the other end thereof.
The tip 14b of the optical fiber projects from the other end of the ferrule 32 by a predetermined length. The ferrule 32 is fixed to the first support member 34 at a position separated by a predetermined distance from the end from which the tip end 14b of the optical fiber projects. The ferrule 32 is fixed to the second support member 36 at a position separated by a predetermined distance from one end into which the optical fiber 14 is inserted. The first support member 34 and the second support member 36 are arranged at positions spatially separated by the third support member 38. Third support member 38
Is a member that enables the second support member 36 to be arranged at a position separated from the first support member 34.

With reference to FIG. 3, a description will be given of the positioning mechanism 30 for optically coupling the optical fiber 14 to the semiconductor optical amplifier 16. FIG. FIG. 3 shows the positioning mechanism 3
FIG. 9 is a schematic diagram showing a state in which a mounting member is fixed to a jig used when assembling while aligning 0.

Referring to FIG. 3, the mounting member 24 is fixed to an assembly jig 40. The mounting member 24 is mounted on the chip carrier 22 on which the semiconductor optical amplifier 12 is mounted.
c and has already been assembled to the state where the electrical connection is completed. In addition, the light receiving element 28 and the chip carrier 26 are omitted below, unless otherwise specified, in order to make the drawing easy to see. The assembling jig 40 includes a moving mechanism 42 necessary for relatively positioning the mounting member 24 with the positioning mechanism 30 in a three-dimensional space. The translation mechanism 42 includes a translation mechanism 42a in the X-axis direction of the coordinate axes shown in FIG. 3, a translation mechanism 42b in the Y-direction toward the paper surface, a translation mechanism 42c in the Z-axis direction, and a Z-axis. And a rotation mechanism 42d for performing φ rotation around. In particular, although not shown, the ferrule 32, first to first
Third indicating member 34, 36, 38 and mounting member 24
A welding device is also provided as a fixing means for fixing each. This welding device is preferably, for example, a laser welding device using a YAG laser.

The positioning mechanism 30 is positioned on the receiving surface 24 e of the mounting member 24 fixed to the jig 40 while being roughly aligned with the optical axis 44 of the semiconductor optical amplifier 12.
The ferrule 32, the first support member 34, the third support member 38, and the second support member 36 are arranged in this order from below in FIG. The first support member 34, the second support member 36, and the third support member 38 are arranged in a state where the optical fiber 14 inserted into the ferrule 32 has passed through a hole provided at the center thereof. I have.

Next, referring to FIG. 3, an optical coupling relationship used for adjusting the relative position of the optical fiber with respect to the semiconductor optical amplifier 16 will be described.
The first end portion 14b of the optical fiber 14 is formed into a spherical tip,
Further, it is arranged so as to face the light emitting surface 16a of the semiconductor optical amplifier 16. Second end surface 14 of optical fiber 14
c is optically coupled to a measuring device 46, for example, a power meter, as light monitoring means capable of measuring light intensity (light power). By using this measuring device 46, the intensity of the light transmitted through the optical fiber 14 and reaching the end 14c can be measured. A power supply 48 is connected to the semiconductor optical amplifier 16 via a conductive line 50 for applying a current.

The optical fiber 14 has an optical branching means 52, for example, an optical coupler (fused silica coupler) between the fiber grating 14a and the second end 14c. The optical branching means 52 achieves an optical coupling with the optical fiber 14, preferably a relatively loose coupling, so that the optical fiber shunt 52
a and branching (coupling) of propagating light between the optical fiber main path 14 and the optical fiber main path 14.

A light reflecting means 54 is provided at the end 52b of the shunt 52a. The light reflecting means 54 has a predetermined light reflectance at the emission wavelength of the semiconductor optical amplifier 16 and reflects light incident on the light reflecting means 54. Light reflecting means 54
Is to form a reflection coating film on the optical fiber end face 54b, arrange a mirror facing the optical fiber end face 54b, and form a fiber grating (diffraction grating) on the core of the optical fiber constituting the shunt 52a. , Etc. The fiber grating used as the light reflecting means 54 can reflect light having a wavelength used for alignment, or has a light reflection spectrum in a light wavelength band generated by the semiconductor optical amplifier 16. The light reflectivity of the light reflecting means 54 should be such that a longitudinal mode caused by the optical resonator constituted by the light reflecting means 54 and the light reflecting surface 16b of the semiconductor optical amplifier 16 can be observed. Should be fine.

The optical fiber 14 is provided with a semi-reflective coating film directly on the second end 14c without providing an optical coupler, so that the light branching means 52 and the light reflecting means 54 are provided.
At the end 14 c of the optical fiber 14.
At this time, the second end 14c has a semi-reflective coating film and is connected to the power meter 46. Therefore, light transmitted through the semi-reflective coating film is applied to the power meter 46. Further, the light branching unit 52 and the light reflecting unit 54 can be a half mirror separate from the optical fiber. The half mirror is provided so as to face the end 14c of the optical fiber 14, and has an angle of 4 with respect to the traveling direction of the light emitted from the end 14c of the optical fiber 14.
Angled 5 degrees. One of the lights split by the half mirror is input to the light monitoring means 46, and the other light is reflected by the light reflection means 54 and returned to the optical fiber 14 via the end 14c of the optical fiber 14. That is,
The optical fiber 14 is capable of transmitting a part of the received light,
It is preferable that a part of the received light is optically coupled to a light transmitting / reflecting means capable of reflecting the light.

When a current is supplied from the power supply 46 to the semiconductor optical amplifier 16 after assembling such an optical coupling, light is generated in the active layer of the semiconductor optical amplifier 16. The generated light is reflected on the light reflecting surface 16b and is emitted from the light emitting surface 16a. Here, the current applied to the semiconductor optical amplifier 16 is temporarily
If optical coupling between the optical fiber 14 and the optical fiber 14 is achieved, the optical coupler 5 optically coupled to the optical fiber 14
A current value at which laser oscillation occurs in an optical resonator including a reflecting mirror 54 provided on one end surface 52b of the shunt 52a drawn from the optical path 2 and the light reflecting surface 16b of the semiconductor optical amplifier 16, that is, this optical resonance The current is above the threshold of the vessel. Such a current value depends on the light reflectance of the reflection mirror 54, but is a value that always exists when the optical resonator is formed.

In such an optical connection, if the optical coupling between the semiconductor optical amplifier 16 and the optical fiber 14 becomes sufficiently close, laser oscillation occurs. Therefore, at the other end 14c of the optical fiber, High light intensity can be observed.
Therefore, the degree of the achievement of the alignment can be determined based on the observed value.

When a separate optical resonator is provided by providing a reflection mirror on the outside, an optical resonator length longer than the resonator length of the optical resonator built in the fiber grating optical module is realized. That is, the longitudinal mode interval based on the external resonator is a value that can be determined independently of the components of the fiber grating optical module.

When an external optical resonator is provided, a suitable optical resonator length is estimated. Oscillation wavelength λ ₀ , effective resonator length L
Assuming × n, the vertical mode interval is represented by the following equation.
Here, n is the effective refractive index of the optical path of the optical resonator. △ λ = λ ₀ when ^2/2 / n / L fiber grating optical fiber being drawn from the module to 10 cm, external resonator length L =
Since it is 10 cm, the longitudinal mode interval Δλ is about 8 pm. Therefore, even if the half width of the reflection characteristic of the grating 14a provided in the optical fiber is 0.1 nm,
A sufficient number of vertical modes are inserted between the half widths. The number of longitudinal modes can be increased by further increasing the length of the external resonator. If the optical resonator length is set to 50 cm, the longitudinal mode interval becomes 1/5 of the above value, and a state that can be regarded as pseudo continuous can be created. Therefore, a method for performing the centering extremely efficiently as compared with the related art is provided.

Since this alignment method is applicable even if the half-width of the grating formed in the optical fiber 14 is 0.1 nm or less, a fiber grating optical module suitable for WDM (wavelength division multiplexing system) is manufactured. It is also applicable to More specifically, in the WDM system, 0.6 nm is determined as a standard value of the adjacent wavelength interval. The half width of the light spectrum of the light source satisfying this standard must be 0.1 nm or less, that is, a grating having this half width is required. Even with a fiber grating having such a narrow reflection spectrum characteristic, if L = 10 cm, about 10 longitudinal modes can be made to exist in the reflection spectrum band of the grating. Therefore, even if the laser oscillation is used, the oscillation can be stably maintained, so that the optical fiber 14 and the semiconductor optical amplifier 16 can be quickly aligned.

Subsequently, referring to FIGS. 4A, 4B, 5A and 5B, the positioning mechanism 30 is formed on the mounting member 24. The procedure will be described. FIGS. 4A to 5B are assembly cross-sectional views each taken along a line II in FIG. 1.

4A to 5B, similarly to FIG. 3, the light receiving element 18 and the chip carrier 2 are provided.
6 is omitted. Although the assembly jig 40 and the moving mechanism 42 are not shown in FIGS. 4A to 5B, they are used to relatively position the mounting member 24 with the positioning mechanism 30 in the three-dimensional space. Used as needed. 4A to 5B, the semiconductor optical amplifier 16 is assembled to a state where it can operate when a voltage is applied to a predetermined electrode on the mounting member 24.

FIG. 4A shows a step of fixing the ferrule 32 into which the optical fiber 14 has been inserted and fixed to the first support member 34. When the ferrule 32 is inserted into the hole 34c, the first support member 34 contacts the contact surface 34a of the first support member 34 with the receiving surface 24 of the mounting member 24.
e. The tip 14b of the optical fiber is inserted into the through hole 24g of the mounting member 24 so as to come to a predetermined position from the first end face 16a of the semiconductor optical amplifier 16, and the Z-axis direction of the optical fiber 14 with respect to the mounting member 24. The position is adjusted. This alignment is performed based on the light intensity at the end of the optical fiber with the semiconductor optical amplifier 16 in a light emitting state. After the Z alignment is completed, the ferrule 32 is fixed to the first support member 34 at a plurality of locations S1 around the hole 34c by using spot welding using a YAG laser.

FIG. 4B shows a centering step of aligning the optical fiber 14 with the semiconductor optical amplifier 16. Alignment means that the light emitted from the light emitting surface 16a of the semiconductor optical amplifier 16 is converted into a spherically shaped end 14 of the optical fiber 14.
b from the light emitting surface 16a
And the end 14b achieve an optically coupled alignment. This state corresponds to, for example, the semiconductor optical amplifier 1
This is realized by arranging the distal end portion 14b of the optical fiber 14 in the main traveling direction of the light emitted from the sixth light emitting surface 16a and optically matching the optical fiber within a predetermined error range.

More specifically, the first support member 34 to which the ferrule 32 is fixed is brought into contact with the receiving surface 24e of the mounting member 24 while the first support member 34 is moved. The light intensity obtained from the other end 14c of the optical fiber 14 is measured. The movement and the measurement can be repeated until the measured value of the light intensity becomes equal to or more than a predetermined value, or until the measured value of the light intensity reaches the maximum value. As described above, since the optical fiber 14 is relatively moved with respect to the semiconductor optical amplifier 16 and the light intensity extracted from the optical fiber 14 is measured, the optical fiber 14 is moved relative to the semiconductor optical amplifier 16. Alignment is possible, and by repeating the movement and the measurement as described above, it is possible to reliably reach a desired connection state. When the light intensity is measured while moving the relative position of the optical fiber and the semiconductor optical amplifier 16 in this manner, the alignment can be performed while sequentially monitoring the relative position and the optical coupling state. The position where the desired light intensity is obtained in this manner is the position where the first support member 34 should be fixed to the mounting member 24. After the alignment is completed, a plurality of spots S2 on the outer peripheral portion of the first support member 34 are formed by spot welding using a YAG laser.
, The first support member 34 is fixed to the mounting member 24. When this step is completed, the tip 1 of the optical fiber 14 is
4b was aligned with the light emitting surface 16a of the semiconductor optical amplifier 16.

Referring to FIG. 5A, the ferrule 32
Represents a step of being fixed to the second support member 36.
The first support member 34 already has the receiving surface 2 of the mounting member 24.
4e. Subsequently, the third support member 38
Are disposed on the facing surface 34b of the first support member 34.
The optical fiber 1 is inserted into the through hole 38 c of the third support member 38.
The ferrule 32 to which 4 is fixed is passed. Also,
On the contact surface 38d of the third support member 38, the second mounting member 36 is disposed in a state where the second mounting member 36 contacts the flat surface 36a. Second, the ferrule 32 is inserted into the through hole 36c of the mounting member 36. After the placement is complete,
By the spot welding using the YAG laser, the ferrule 32 moves the second support member 36 at a plurality of locations S3 around the opening of the through hole 36c on the facing surface 36b.
Is fixed.

Referring to FIG. 5B, the second support member 36 is fixed to the third support member 38. As a result, the positioning of the tip 14b of the optical fiber 14 with respect to the semiconductor optical amplifier 16 is completed. The state is shown.

After the assembling step shown in FIG. 5A, the ferrule 32 is connected to the spot welds S1 and S2.
Is fixed to the mounting member 24 by the spot welding portion S3, and the second support member 36 is fixed to the third support member 36 because the through hole 38c is larger than the outer shape of the ferrule 32. It is movable in a limited range while being in contact with the contact surface 38d of the support member 38. Therefore, when the second support member 36 is moved on the contact surface 38d, the spot welded portion S1 becomes a fulcrum, and the distal end portion 14b of the optical fiber 14 moves in response to the movement of the second support member 36. I do. However, the travel distance of the tip 14b is, according to the principle of leverage, a reduced distance determined by the ratio of the distance between the spot weld S1 and the tip 14b to the distance between the spot weld S3 and the spot weld S1. Only moved. Therefore, if the light intensity obtained from the other end 14c of the optical fiber 14 is measured while the semiconductor optical amplifier 16 is in a light emitting state as in the alignment process, the position of the tip 14b can be finely adjusted. This adjustment gives the opportunity to readjust the misalignment resulting from the fixation in spot welding S2. By leveraging the principle of leverage,
The amount of fine-tuning or readjustment possible is
Depends on the length of the tubular portion 38a of the supporting member 38.

In this embodiment, when the positions of the semiconductor optical amplifier 16 and the optical fiber 14 are aligned, the ferrule 32 is fixed at two positions at different distances from the light emitting surface 16a of the semiconductor optical amplifier 16. 32 and 36. At this time, the position closer to the light emitting surface 16a (S1,
After fixing S2), it is fixed at a far position (S3). Thus, the first end 14a of the optical fiber 14 and the light emitting surface 16a of the semiconductor optical amplifier 16 are
After partially fixing the relative position of the optical fiber 14, the optical coupling state between the optical fiber 14 and the semiconductor optical amplifier 16 is adjusted in a state where the semiconductor optical amplifier 16 emits light. Can be finely adjusted optically. Even in such an adjustment, as described above, the desired optical coupling is achieved by repeating the movement and the measurement, or by performing the measurement while moving.

After the positioning is completed, the second support member 36 is fixed to the third support member 38 at a plurality of locations S4 on the outer peripheral portion by spot welding using a YAG laser. When this step was completed, the tip 14b of the optical fiber 14 was finally fixed in a state where it was aligned with the light emitting surface 16a of the semiconductor optical amplifier 16 and optical coupling was achieved.

As a result of these steps, the alignment mechanism 30 has been completed. Light reflecting surface 1 of semiconductor optical amplifier 16
The optical resonator formed from the optical fiber 6b and the fiber grating 14a formed on the optical fiber 14 was assembled until it was able to stably oscillate. However, as is clear from the above description, laser oscillation based on this optical resonator has not been performed yet. Therefore, it is not adjusted so that at least one longitudinal mode of the optical resonator including the semiconductor optical amplifier 16 and the fiber grating is included in the reflection band of the fiber grating.

In the above-described method of aligning the fiber grating optical module, the longitudinal mode is subsequently adjusted. The matching of the longitudinal mode is defined as the light reflection surface 16 b of the semiconductor optical amplifier 16 and the fiber grating 14.
This refers to moving the longitudinal mode of the optical resonator formed from the wavelength a to the wavelength band of light that can be reflected by the fiber grating.

In the above group of steps for alignment, the optical adjustment of the optical resonator composed of the fiber grating 14a and the light reflecting surface 16b of the semiconductor optical amplifier 16, that is, the adjustment of the longitudinal mode is not performed. Simply, the first end 14 b of the optical fiber 14 is connected to the semiconductor optical amplifier 16.
Only a suitable arrangement is realized by two alignments so that the first end face 16a can be optically coupled to the first end face 16a.
Therefore, the longitudinal mode of the above-mentioned optical resonator substantially coincides with the maximum reflection wavelength of the fiber grating 14a, and does not always coincide substantially with the maximum gain wavelength of the semiconductor optical amplifier 16. Therefore, a step of achieving this coincidence state within a practical range is required.

As described above, after the optical coupling is achieved through the steps described with reference to FIGS. 4A to 5B, the light composed of the optical fiber 14 and the semiconductor optical amplifier 16 is obtained. The longitudinal mode of the resonator is adjusted within the wavelength band that can be reflected by the fiber grating, and the laser based on the optical resonator is oscillated. Therefore, the longitudinal mode can be adjusted in a stable state.

This is performed according to the following procedure.

Since the alignment of the optical fiber 14 and the semiconductor optical amplifier 16 has been completed, the fiber grating 14a of the optical fiber 14 and the light reflecting surface 1 of the semiconductor optical amplifier 16
6b can be oscillated. A current sufficient for the laser to oscillate is applied to the semiconductor optical amplifier 16. The adjustment of the longitudinal mode is performed by changing the temperature of the semiconductor optical amplifier 16 by applying a current to a thermoelectric cooler (thermoelectric cooler) 28 on which the semiconductor optical amplifier 16 is mounted, for example, a Peltier element.

The reason why the vertical mode can be adjusted by changing the temperature in this manner will be described below. The active layer and the cladding layer of the semiconductor optical amplifier 16
It is formed using a semiconductor material. When the temperature of such a semiconductor material is changed, the optical refractive index changes. Increasing the temperature increases free carriers,
The refractive index decreases. As the refractive index decreases, the speed of light propagating through the medium increases, so that the effective optical resonator length decreases. For this reason, the longitudinal mode moves to the shorter wavelength side. For example, the effective optical cavity length L × n is to 10 mm, the longitudinal mode interval (△ lambda) is ^{_{△ λ = λ 0 2/2}} / n
/ L, Δλ is several tens of nm at most. With such an interval, the longitudinal mode can be adjusted by changing the temperature.

Generally, the fiber grating optical module having the configuration described in the present application is a semiconductor optical amplifier 1
6 is provided with an optical resonator composed of the light reflecting surface 16b and the fiber grating 14a, and the laser oscillation wavelength of the optical resonator has the maximum product of the reflection characteristic of the fiber grating 14a, the longitudinal mode of the resonator, and the gain characteristic of the semiconductor optical amplifier. Laser oscillation occurs at the wavelength.

As in the prior art, when the alignment is performed using the longitudinal mode generated by applying a current to the semiconductor optical amplifier to form the population inversion in the active layer, this longitudinal mode is There is at most about one in the light reflection band of the fiber grating. The wavelength of this longitudinal mode is
When the wavelength does not substantially match the maximum reflection wavelength of the fiber grating, there is a case where the alignment cannot be performed stably. Generally, this agreement is not achieved in many cases. In particular, when the wavelength dependence of the reflection characteristics of the fiber grating is large, that is, in the wavelength region where the slope of the reflection spectrum is large, even if the change in the optical output is monitored, as a result of the alignment, the optical fiber and the semiconductor optical amplifier become inconsistent. In some cases, it is not possible to distinguish whether the coupling efficiency has been improved or whether the optical output has changed as a result of movement of the longitudinal mode, for example, due to a change in temperature.

However, as already described in detail, in the method for aligning the fiber grating semiconductor laser according to the present invention, the light reflecting surface 16 of the semiconductor optical amplifier 16 is used.
b, a light reflecting means 54 having a predetermined light reflectance is provided so as to be optically coupled to the optical fiber 14 so as to form an optical resonator. A separate optical resonator having an optical resonator length longer than the optical resonator formed from the fiber grating 14a is formed. For this reason, the interval between the longitudinal modes of the laser formed by the separate optical resonators can be set independently, and the interval becomes narrow. Therefore,
Some of these longitudinal modes are
a can be within the reflection band. When a predetermined value of current is applied to the semiconductor optical amplifier 16, the semiconductor optical amplifier 16
A fiber grating laser having an optical resonator formed by the light reflecting surface 16b and the fiber grating 14a can stably oscillate. If the laser light oscillating stably is taken out through the optical fiber 14 and the optical fiber 14 is aligned with the semiconductor optical amplifier 16 based on this intensity, the semiconductor light can be output in a stable light emitting state. The optical fiber 14 having the fiber grating 14a can be aligned with the amplifier 16.

[0062]

As described above in detail, according to the method of aligning a fiber grating optical module according to the present invention, a predetermined light reflection is performed so as to form a light reflection surface and an optical resonator of a semiconductor optical amplifier. A light reflecting means having a ratio is provided. Therefore, a separate optical resonator having an optical resonator length longer than the optical resonator formed by the light reflecting surface of the semiconductor optical resonator and the fiber grating is formed. The interval between longitudinal modes of the laser formed by the separate optical resonators can be shortened. Thus, some of this longitudinal mode can be in the reflection band of the fiber grating. Therefore, when a current of a predetermined value is applied to the semiconductor optical amplifier, a laser having an optical resonator formed by the light reflecting surface and the light reflecting means of the semiconductor optical amplifier can oscillate. As described above, the laser light oscillating based on the separate optical resonator is taken out through the optical fiber, and the optical fiber is aligned with the semiconductor optical amplifier based on the intensity, thereby stabilizing the operation. In the light emitting state, it becomes possible to align the optical fiber having the fiber grating with respect to the semiconductor optical amplifier.

Accordingly, there has been provided an improved method of aligning a fiber grating optical module for optically coupling an optical fiber having a fiber grating to a semiconductor optical amplifier to form an optical resonator.

[Brief description of the drawings]

FIG. 1 is a perspective view of a fiber grating laser module.

FIG. 2 is a sectional view showing a main part 10 of the fiber grating laser taken along a line II in FIG. 1;

FIG. 3 is a schematic diagram showing a state in which a mounting member is fixed to an assembling jig.

FIGS. 4 (a) and 4 (b) are each an assembled cross-sectional view taken along the line II of FIG. 1;

5 (a) and 5 (b) are each an assembled cross-sectional view shown in the II section of FIG. 1. FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fiber grating optical module, 10 ... Main part of fiber grating laser module, 12 ...
Housing, 12a: body part, 12b: tubular part, 12c
... Lead pins, 16 ... Semiconductor optical amplifiers, 18 ... Light receiving elements, 22, 24, 26 ... Mounting members, 28 ... Cooling elements, 3
0: Positioning mechanism, 32: Ferrule, 34: First
, A second support member, 38, a third support member, 42, a moving mechanism, 42a, a translation mechanism in the X-axis direction, 42b, a translation mechanism 42b, 42c in the Y direction.
... Translation mechanism in the Z-axis direction, 42d ... φ around the Z-axis
Rotating mechanism for rotating 46, power meter, 48, power supply 50, conductive wire, 52, light branching means, 52a, shunt, 52
b: one end face of the shunt, 54: light reflecting means

Continued on the front page F term (reference) 2H037 AA01 BA02 CA08 DA03 DA04 DA06 DA18 2H050 AC84 AD16 5F072 AB13 JJ20 KK07 KK30 RR01 TT22

Claims (3)

[Claims] 1. A semiconductor optical amplifier having a light emitting surface and a light reflecting surface, wherein light is emitted from the light emitting surface when a current is applied thereto, and a first optically coupleable optically coupled to the light emitting surface. An optical fiber having an end, a second end, and a fiber grating provided at a predetermined distance from the first end is relatively aligned, and the light emitting surface of the semiconductor optical amplifier and the A method of aligning a fiber grating optical module that optically couples the first end of an optical fiber to a first end of an optical fiber, comprising: receiving a light so as to form an optical resonator with the light reflecting surface of the semiconductor optical amplifier. A coupling step of providing light reflecting means for reflecting the reflected light; applying a current to the semiconductor optical amplifier; and a predetermined oscillation wave in an optical resonator comprising the light reflecting surface and the light reflecting means of the semiconductor optical amplifier. And an alignment step of adjusting a relative position between the semiconductor optical amplifier and the optical fiber based on an intensity of light extracted from the second end of the optical fiber. Alignment method for fiber grating optical module. 2. The step of arranging comprises: a step of relatively moving a position of the optical fiber and a position of the semiconductor optical amplifier; and measuring a light intensity extracted from a second end of the optical fiber. The method for aligning a fiber grating optical module according to claim 1, further comprising a measuring step. 3. The fiber grating optical module according to claim 1, wherein the light reflecting means is provided at an end of the optical fiber branched from the optical fiber by a light branching means. Core method.