JPH0527146A - Optical functional device - Google Patents

Abstract

PURPOSE:To reduce coupling loss due to the oblique polishing of an optical fiber tip and to easily realize optimum magnification between a semiconductor laser element which has an optional far visual field image full angle at half maximum and a semiconductor optical amplifying element, and an optical fiber as to a coupling optical system between the semiconductor laser element and semiconductor optical amplifying element, and optical fiber. CONSTITUTION:Wedge-like glass 1 is interposed between the semiconductor laser element 4 and optical fiber 2 to control the angle of incidence on the optical fiber 2. A semiconductor optical amplification device is constituted by uniting some optical lenses and the semiconductor optical amplifying elements on an optical amplifying element mounted block and arranging it slantingly to the center axis of an input/output side optical fiber 2. A parallel glass plate for correcting an optical path is installed, specially, for a two-lens coupling optical system. Further, an aspherical lens is used as a 1st lens which converts the projection light from the semiconductor laser element 4 and semiconductor optical amplifying element into parallel light, and a gradient index lens is used as a 2nd lens which converges and couples the parallel light with the optical fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal processing device such as an optical transmitting device and an optical amplifying device, and more particularly to a coupling optical system provided therein.

[0002]

2. Description of the Related Art Conventionally, a coupling optical system provided in an optical transmitter has been described in 1990 Autumn National Convention of the Institute of Electronics, Information and Communication Engineers, 1990, C-192, pp. As discussed in 4-234, semiconductor laser devices and 6 °
A coupling optical system using two aspherical lenses between a single-mode fiber that has been obliquely polished is reported.

[0003]

In the above-mentioned prior art, the reflected light from the tip of the single mode fiber is prevented from returning to the semiconductor laser device by polishing the tip of the single mode fiber at an angle of 6 °. In such a coupling optical system, a coupling loss occurs due to the tip of the single mode fiber being obliquely polished. A first object of the present invention is to reduce the above coupling loss due to the single mode fiber tip being obliquely polished.

Further, in an optical signal processing device having a single-mode fiber whose tip is obliquely polished on the input / output side, coupling due to the single-mode fiber tip being obliquely polished on the input / output side. There is a loss. A second object of the present invention is to reduce the coupling loss due to the single-mode fiber tip being obliquely polished in both the input and output sides in the optical signal processing device.

Further, in a coupling optical system using two aspherical lenses between a waveguide type optical element and a single mode fiber, the numerical aperture is increased and the wavefront aberration is increased by precisely controlling the aspherical shape. Can be lowered. However, when the full-width half-maximum angle of the far-field image of the waveguide type optical element changes, it is necessary to change the shape of at least one aspherical lens in order to obtain the optimum magnification. When the aspherical lens is a glass mold lens, it is necessary to redo the design of the lens shape. A third object of the present invention is to realize a coupling optical system having a high degree of optical coupling, which realizes an optimum magnification between a waveguide type optical element having a full angle at half maximum of an arbitrary far field image and a single mode fiber. Is to be realized.

[0006]

In order to achieve the first object, according to the present invention, the optical axis of the incident light to the optical fiber is set between the waveguide type optical element and the optical fiber so that the center of the optical fiber is the center of the optical fiber. Means for tilting with respect to the axis are provided. As this means,
For example, wedge-shaped glass can be used, and the incident angle to the optical fiber is controlled by adjusting the shape and the refractive index.

In order to achieve the second object, in the optical signal processing device having a coupling optical system using one optical lens between the waveguide type optical element and the input / output side optical fiber, A lens is integrated on a block installed in the optical signal processing device, and the center axis of the block is arranged to be inclined with respect to the center axis of the input / output side optical fiber.

On the input side of the waveguide type optical element, a second lens for converting an optical signal from the input side optical fiber into parallel light and this parallel light are condensed and coupled to the waveguide type optical element. A first lens, a first lens for converting an optical signal from the above-mentioned waveguide type optical element into parallel light on the output side, and a second lens for condensing the parallel light and coupling it to an output side optical fiber whose tip is obliquely polished. In the optical signal processing device provided with a coupling optical system consisting of, the first lenses are integrated on a block installed in the optical signal processing device, and the block center axis is the center of the input / output side optical fiber. Place it at an angle to the axis. Further, a parallel glass plate for correcting the optical path is installed between the first lens and the second lens on the input / output side. In order to achieve the third object, the first lens for converting the light emitted from the waveguide type optical element into parallel light is an aspherical lens, and the parallel light is condensed and coupled to an optical fiber. The lens is a gradient index lens.

[0009]

By the wedge-shaped glass provided between the waveguide type optical element and the optical fiber, the incident light on the optical fiber is incident at an angle with respect to the center axis of the optical fiber, and the tip of the optical fiber is obliquely polished. The coupling loss resulting from this is reduced.

Further, in an optical signal processing device having a coupling optical system using one optical lens between the waveguide type optical element and the input / output side optical fiber, the optical signal processing device is inclined from the input side optical fiber with respect to the central axis thereof. The optical axis of the signal light emitted as a result coincides with the optical axis connecting the optical lens and the waveguide type optical element, and the coupling loss due to the oblique polishing of the input side optical fiber tip is reduced. It At the same time, the signal light focused by the optical lens and incident on the output side optical fiber is incident at an angle with respect to the center axis of the optical fiber, and the coupling loss due to the tip of the output side optical fiber being obliquely polished. Is reduced.

On the input side of the waveguide type optical element, a second lens for converting an optical signal from the input side optical fiber into parallel light and the parallel light are condensed and coupled to the waveguide type optical element. A first lens, a first lens on the output side for converting an optical signal from the above-mentioned waveguide type optical element into a parallel light, and a second lens for condensing the parallel light and coupling it to an output side optical fiber whose tip is obliquely polished. In the optical signal processing device provided with the coupling optical system including the lens, the optical axis of the signal light converted into parallel light by the second lens after being emitted from the input side optical fiber with an inclination with respect to the central axis is , Is moved in parallel by the parallel glass plate,
Coupling loss due to the oblique polishing of the tip of the input side optical fiber, which coincides with the optical axis connecting the first lens and the waveguide type optical element, is reduced. At the same time, the optical axis of the signal light converted into parallel light by the first lens is moved in parallel by the parallel glass plate, is condensed by the second lens, and is incident on the output side optical fiber with an inclination with respect to its central axis. As a result, the coupling loss due to the tip of the output side optical fiber being obliquely polished is reduced.

In a two-lens coupling optical system using an aspherical lens as the first lens and a gradient index lens as the second lens, the second lens cuts a sufficiently long gradient index lens into an appropriate length. By doing so, the focal length can be arbitrarily selected. The first lens can have a large numerical aperture and a small wavefront aberration by precisely controlling the aspherical shape. As described above, it is possible to easily realize a coupling optical system having a high optical coupling degree, which realizes an optimum magnification between a waveguide type optical element having an arbitrary full-width half-maximum angle of a far field image and a single mode fiber.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a principle diagram of this embodiment, and FIG. 2 is a configuration diagram of the device of this embodiment. In FIG. 1, 1 is wedge-shaped glass,
Reference numeral 2 is a single mode fiber, 3 is an aspherical lens, and 4 is a semiconductor laser element. In order to prevent the reflected light from the tip of the single mode fiber 2 from returning to the semiconductor laser element 4, the tip of the single mode fiber 2 is obliquely polished, and the polishing angle is b = 6 °. The refractive index of the core portion of the single mode fiber 2 is n2 to 1.5. In the wedge-shaped glass 1, the angle formed by the vertices is a, and the side facing the single mode fiber 2 is arranged perpendicular to the central axis of the single mode fiber 2. Further, the refractive index of the wedge-shaped glass 1 is n
It is 1. The light emitted from the semiconductor laser device 4 is condensed by the aspherical lens 3 and transmitted through the wedge-shaped glass 1, so that the optical axis is inclined by c and is coupled to the single mode fiber 2. Here, c is given by the equation 1.

[0014]

## EQU1 ## c to (n1-1) a (Equation 1) At this time, the optical axis of the incident light on the single mode fiber 2 and the central axis of the single mode fiber 2 form an angle c, but c is Number 2
When satisfying, the coupling loss due to the tip of the single mode fiber 2 being obliquely polished can be avoided.

[0015]

## EQU2 ## c to (n2-1) b (Equation 2) From the above, the angle a formed by the apexes of the wedge-shaped glass 1 and the refractive index n1 are selected so as to satisfy Equation 3.

[0016]

[Equation 3]           a to (n2-1) b / (n1-1) (Equation 3) In this embodiment, a = 6 ° and n1 = 1.5.

In FIG. 2, 5 is a laser mounting block,
6 is a laser light monitor element, 7 is an airtight package, 8 is a ferrule, 9 is a wedge-shaped glass holder, 10 is a ferrule holder, 11 is a thermistor, and 12 is an electronic cooling element. The procedure for assembling this device will be described. First, after fixing the thermistor 11 on the laser mounting block 5,
The semiconductor laser device 4 with the submount 13 is fixed on the central axis of the laser mounting block 5. The aspherical lens 3 is fixed on the central axis of the laser mounting block 5. The electronic cooling element 12 is fixed to the bottom surface of the airtight package 7 so that it can be maintained at room temperature or a temperature about 10 ° C. lower than room temperature.
The laser mounting block 5 is fixed on the electronic cooling element 12. The single mode fiber 2 with the ferrule 8 and the wedge-shaped glass 1 are integrated in a wedge-shaped glass holder 9. The ferrule holder 10 into which the wedge-shaped glass holder 9 is inserted is fixed to the side wall of the airtight package 7.
At this time, the semiconductor laser element 4 is caused to emit light, and the position of the output light from the single-mode fiber 2 is adjusted to the maximum, the wedge-shaped glass holder 9 is solder-fixed to the ferrule holder 9, and the ferrule holder 9 is hermetically sealed. YAG laser welding is performed on the package 7. Power is supplied to the N electrode of the semiconductor laser device 4 through the lead wire 14, the wire bonding 15, and the submount 13, and to the P electrode through the lead wire 14, the wire bonding 15, and the laser mounting block 5. Further, the resistance value of the thermistor 11 is measured via the lead wires 14 and 26, and a current is passed through the electronic cooling element 12 by the lead wire 14 to cool the entire laser mounting block 5. The cooling capacity was −80 ° C./ampere.

The coupling efficiency of the embodiment apparatus having the above structure was -1.6 dB when the 10 G / s optical transmission semiconductor laser device 4 having a full width at half maximum of the far-field pattern of 35 ° was used. Of these, the coupling loss of -0.9 dB due to the tip of the single mode fiber 2 being obliquely polished is not included. 5.0 dBm at a constant temperature of 20 ° C
The optical output of was obtained. Further, by using the device shown in the above embodiment as the optical transmitter and using the optical receiving device having the minimum receiving sensitivity of -17 dBm, 10 Gb / s, 1
Transmission of 00km is possible.

FIG. 3 is a block diagram showing a second embodiment of the present invention. 2a and 2b are single mode fibers, 3a and 3b
Is an aspherical lens, 8a and 8b are ferrules, 21 is a semiconductor optical amplification element, 23 is an optical amplification element mounting block, 24 is an airtight package, and 25a and 25b are ferrule holders. The tips of the single mode fibers 2a and 2b are obliquely polished, and the polishing angle is b = 6 °. Ferrule 8a
The light input from the attached single-mode fiber 2a is collected by the aspherical lens 3a and coupled to the semiconductor optical amplification element 21. The optical output amplified by the semiconductor optical amplifier element 21 is condensed by the aspherical lens 3b and coupled to the single mode fiber 2b with the ferrule 8b. The numerical aperture of the aspherical lenses 3a and 3b is 0.6 on the semiconductor optical amplification device 21 side.
Is.

The procedure for assembling this apparatus will be described. First, on the optical amplifier mounting block 23, the thermistor 11,
After fixing the studs 22, the semiconductor optical amplification device 21 with the submount 13 is fixed on the central axis of the optical amplification device mounting block 23. The aspherical lenses 3a and 3b are fixed on the central axis of the optical amplification element mounting block 23. The electronic cooling element 12 is fixed to the bottom surface of the airtight package 24 so that it can be maintained at room temperature or a temperature about 10 ° C. lower than room temperature.
An optical amplification element mounting block 23 is provided on the electronic cooling element 12.
To fix. At this time, the central axis of the optical amplification element mounting block 23 is on the central axis of the hermetic package 24 and is inclined by the angle c with respect to the central axis of the hermetic package 24. Here, c is assumed to satisfy the equation 2, and in this embodiment, c
= 3 °. Ferrule holder 25 in which single mode fibers 2a and 2b with ferrules 8a and 8b are inserted
A and 25b are fixed to the side wall of the airtight package 24. At this time, the semiconductor optical amplification element 21 is caused to spontaneously emit light and its position is adjusted so that the output light from the single mode fibers 2a and 2b is maximized. Holders 25a, 25b
Then, the ferrule holders 25a and 25b are YAG laser welded to the hermetic package 24. Power is supplied to the N electrode of the optical amplification element 21 through the lead wire 14, wire bonding 15, stud 22, and submount 13, and to the P electrode through the lead wire 14, wire bonding 15, and optical amplification element mounting block 23. It Further, the resistance value of the thermistor 11 is measured through the lead wire 14, and a current is passed through the electronic cooling element 12 through the lead wire 14 to cool the entire optical amplification element mounting block 23. The cooling capacity was −80 ° C./ampere.

The coupling efficiency of the embodiment apparatus having the above-mentioned configuration has a waveguide structure having a small polarization dependence, and when a semiconductor optical amplification element 21 having a far field pattern full width at half maximum of 50 ° is used, an optical amplification element is obtained. The central axis of the mounting block 23 is the airtight package 24.
When arranged so as to coincide with the central axis of, the coupling efficiency was -3.7 dB on both the input side and the output side. Among them, -0.7 dB is a coupling loss due to the tips of the single mode fibers 2a and 2b being obliquely polished.
On the other hand, the central axis of the optical amplifier mounting block 23 is on the central axis of the hermetic package 24, and the hermetic package 24
By arranging them so that they are inclined by an angle c with respect to the central axis of, the coupling efficiency is -3.0 dB on both the input side and the output side.
Was reduced to. The internal gain of the optical amplification element was 28 dB and the amplification degree of the optical amplification device was 22 dB under the condition where the temperature was constant at 0 ° C. Further, by using the device shown in the above-mentioned embodiment in three stages, transmission of 1.8 Gb / s, 180 km became possible.

FIG. 4 is a block diagram showing the third embodiment of the present invention. 31a and 31b are first lenses, and 32a and 32b
Is the second lens, 33a and 33b are the second lens holders, and 3
4a and 34b are parallel glass plates. First lens 31
a and 31b are aspherical lenses and second lenses 32a and 32a.
A gradient index lens is used for b. Ferrule 8a
The light input from the attached single mode fiber 2a is converted into parallel light by the second lens 32a, and the parallel glass plate 34a
After being transmitted, the light is condensed by the first lens 31a and is coupled to the semiconductor optical amplification device 21. The optical output amplified by the semiconductor optical amplifier device 21 is converted into parallel light by the first lens 31b and transmitted through the parallel glass plate 34b, and then the second light is output.
It is condensed by the lens 32b and is coupled to the single mode fiber 2b with the ferrule 8b. The tips of the single mode fibers 2a and 2b are obliquely polished, and the polishing angle is b =
It is 6 °.

A procedure for assembling this apparatus will be described. First, on the optical amplifier mounting block 23, the thermistor 11,
After fixing the studs 22, the semiconductor optical amplification device 21 with the submount 13 is fixed on the central axis of the optical amplification device mounting block 23. The first lenses 31a and 31b are fixed on the central axis of the optical amplification element mounting block 23. This time,
The semiconductor optical amplification element 21 is caused to emit light naturally, and the first lens 3
The positions are adjusted so that the output lights from 1a and 31b become parallel lights. The electronic cooling element 12 is provided on the bottom surface of the airtight package 24.
And the optical amplification element mounting block 23 is fixed on the electronic cooling element 12. At this time, the central axis of the optical amplification element mounting block 23 is on the central axis of the hermetic package 24 and is inclined by the angle c with respect to the central axis of the hermetic package 24. Here, c satisfies the expression 2, and in this embodiment, c = 3 °. The second lenses 32a and 32b are inserted into the second lens holders 33a and 33b fixed to the side wall of the airtight package 24. The distance from the center of the semiconductor optical amplification device 21 to the second lenses 32a and 32b is x1. The centers of the parallel light beams from the first lenses 31a and 31b deviate from the centers of the second lenses 32a and 32b by y1. Here, y1 satisfies Expression 4.

[0024]

## EQU00004 ## y1 = x1 tanc (Equation 4) The parallel glass plate 34 is provided on the second lens holders 33a and 33b.
The a and 34b are fixed such that their perpendiculars are inclined at an angle e with respect to the central axis of the airtight package 24. The thickness and the refractive index of the parallel glass plates 34a and 34b are d and n3. By passing through the parallel glass plates 34a and 34b, the first
The centers of the parallel light beams from the lenses 31a and 31b move in parallel by y2. Here, y2 satisfies Expression 5.

[0025]

Y2 to d / n3 sin (e + c) (Equation 5) Here, the parallel glass plates 34a, 3 are set so that y1 = y2.
By adjusting the thickness d of 4b, the refractive index n3, etc.,
The center of the parallel light from the first lenses 31a and 31b passes through the centers of the second lenses 32a and 32b. In this embodiment,
x1 = 9 mm, n3 = 1.5, d = 1 mm and e = 42 °. Single mode fiber 2 with ferrules 8a and 8b
The ferrule holders 25a and 25b in which the a and 2b are inserted are fixed to the side wall of the airtight package 24. At this time, the semiconductor optical amplification element 21 is caused to spontaneously emit light and its position is adjusted so that the output light from the single mode fibers 2a and 2b is maximized, and the single mode fiber 2 with the ferrules 8a and 8b is attached.
The a and 2b are fixed to the ferrule holders 25a and 25b by soldering, and the ferrule holders 25a and 25b are welded to the hermetic package 24 by YAG laser welding. Power is supplied to the N electrode of the optical amplification element 21 through the lead wire 14, wire bonding 15, stud 22, and submount 13, and to the P electrode through the lead wire 14, wire bonding 15, and optical amplification element mounting block 23. It Further, the resistance value of the thermistor 11 is measured through the lead wire 14, and a current is passed through the electronic cooling element 12 through the lead wire 14 to cool the entire optical amplification element mounting block 23.

The coupling efficiency of the embodiment apparatus having the above-mentioned structure is
When the same semiconductor optical amplifier element 21 as that of the embodiment is used, and when the central axis of the optical amplifier element mounting block 23 is arranged so as to coincide with the central axis of the airtight package 24, the coupling efficiencies on the input side and the output side are It became -4.0 dB. Of these, -0.7 dB is the single mode fiber 2
This is a coupling loss due to the tips of a and 2b being obliquely polished. On the other hand, the central axis of the optical amplification element mounting block 23 is located on the central axis of the hermetic package 24, and is arranged so as to be inclined by an angle c with respect to the central axis of the hermetic package 24, and the parallel glass plates 34a and 34b are inserted. As a result, the coupling efficiency is -3.3d on both the input and output sides.
B.

Although the second and third embodiments have been described with respect to the semiconductor optical amplifier, it is obvious that they can be applied to the semiconductor optical modulator and the waveguide optical switch.

[0028]

According to the present invention, highly efficient and low reflection optical coupling can be stably obtained between the waveguide type optical element and the single mode fiber. As a result, a high optical output can be obtained in the optical transmission module. In the optical amplifier, 20
Optical amplification of dB or more is possible, and the system can be applied to optical repeater amplifiers, optical preamplifiers, and the like.

Further, in an optical signal processing device having a two-lens coupling optical system using an aspherical lens as the first lens and a gradient index lens as the second lens, a waveguide having full-width half-maximum angles of various far-field images is used. Optimal magnification is realized between the optical device and the single mode fiber, and highly efficient optical coupling can be easily realized.

[Brief description of drawings]

FIG. 1 is a principle diagram of a first embodiment.

FIG. 2 is a configuration diagram of a first embodiment device.

FIG. 3 is a configuration diagram of a second embodiment.

FIG. 4 is a configuration diagram of a third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Wedge glass, 2 ... Single mode fiber, 3 ... Aspherical lens, 4 ... Semiconductor laser element, 5 ... Laser mounting block, 9 ... Wedge glass holder, 11 ... Thermistor, 12 ... Electronic cooling element, 21 ... Semiconductor optical amplifier, 2
3 ... Optical amplification element mounting block, 31 ... First lens, 32
... Second lens, 34 ... Parallel glass plate.

Claims (11)

[Claims] 1. A coupling optical system for optically coupling a waveguide type optical element and an optical fiber, wherein the tip of the optical fiber is obliquely polished, and the optical axis of the incident light to the optical fiber is the above-mentioned. A coupling optical system characterized in that means for tilting with respect to the central axis of the optical fiber is provided between the waveguide type optical element and the optical fiber. 2. The coupling optical system according to claim 1, wherein said means is a wedge-shaped glass. 3. The coupling optical system according to claim 2, wherein the refractive index of the core of the optical fiber is n2, the oblique polishing angle of the tip of the optical fiber is θ, and the refractive index of the wedge-shaped glass is n.
1, the angle a formed by the apexes of the wedge-shaped glass is 0.9 (n2
−1) θ / (n1-1) <a <1.1 (n2-1) θ / (n1
-1) The combined optical system. 4. The coupling optical system according to claim 2, wherein the wedge-shaped glass and the optical fiber are integrated. 5. An optical lens for coupling an optical signal from an input side optical fiber whose tip is obliquely polished to the input side of the waveguide type optical element, and the waveguide side optical element on the output side. In a device having an optical lens for coupling an optical signal from the optical fiber to an output side optical fiber whose tip is obliquely polished, the waveguide type optical element and the optical lens are integrated on a block installed in the device. The refractive index of the core of the optical fiber is n2, the oblique polishing angle of the tip of the optical fiber is θ, and the angle c between the block center axis and the input / output side optical fiber center axis is 0.9 (n2-1). θ <c <1.1 (n
2-1) An optical functional device characterized by θ. 6. A second lens for converting an optical signal from an input side optical fiber whose tip is obliquely polished into parallel light on the input side of a waveguide type optical element and condensing the parallel light to form the waveguide type optical element. A first lens coupled to an optical element, a first lens for converting an optical signal from the above-mentioned waveguide type optical element into a parallel light on the output side, and an output side optical fiber whose parallel light is condensed and its tip is obliquely polished. In a device provided with a two-lens coupling optical system including a second lens to be coupled to, the waveguide type optical element and the input / output side first lens are integrated on a block installed in the device. The refractive index of the core of the optical fiber is n2, the oblique polishing angle of the tip of the optical fiber is θ, and the angle c between the block center axis and the input / output side optical fiber center axis is 0.9 (n2-1). ) .theta. <c <1.1 (n2-1) .theta. Ability apparatus. 7. An optical functional device according to claim 6, wherein a parallel glass plate for correcting an optical path is installed between the first lens and the second lens on the input / output side. 8. The apparatus according to claim 7, wherein the distance from the center of the waveguide type optical element to the second lens is x1, the parallel glass plate has a refractive index n3, and the parallel glass plate has a thickness. d, the angle e formed by the perpendicular line of the parallel glass plate and the center axis of the input / output side optical fiber is 0.9x1tanc <dsin
An optical functional device characterized by satisfying e / n3 <1.1 × 1tanc. 9. A two-lens coupling optical system comprising a first lens for converting light emitted from a waveguide type optical element into parallel light and a second lens for condensing the parallel light and coupling it with an optical fiber. A coupling optical system in which the first lens is an aspherical lens and the second lens is a gradient index lens. 10. A second lens for converting an optical signal from an input-side optical fiber into parallel light on the input side of the waveguide type optical element, and the parallel light is condensed and coupled to the waveguide type optical element. A first lens, which comprises, on the output side, a first lens for converting an optical signal from the above-mentioned waveguide type optical element into parallel light and a second lens for condensing the parallel light and coupling it to an output side optical fiber 2
An optical functional device comprising a single-lens coupling optical system, wherein the first lens is an aspherical lens and the second lens is a gradient index lens. 11. The optical function according to claim 10, wherein the waveguide type optical element and the input / output side first lens are integrated on a block installed in the apparatus. apparatus.