JPH1197792A - Light source for variable wavelength semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide precise wavelength accuracy by providing an outer resonance-type semiconductor laser light source part, a driving part, first - third optical couplers, an acoustooptic element, an etalon and a transmissivity measuring part. SOLUTION: The first optical coupler 4 branches outgoing light from the outer resonance-type semiconductor laser light source part (light source) 1, outputs one light, makes the other light incident on the second optical coupler 5 and branches it. One branched light is made incident on the acoustooptic element 7 and the other light is made incident on the third optical coupler 6. In the acoustooptic element 7 and a photodiode array part (PD) 9, signals corresponding to the wavelength of incident light are outputted and they are outputted to a control part 3. The optical coupler 6 branches incident light and makes one light incident on the transmissivity measuring part 11 through the etalon 10. The transmissivity measuring part 11 obtains the transmissivity of the etalon 10 from the transmission light of the etalon 10 and the other incident light branched in the optical coupler 6 and outputs it to the control part 3. The control part 3 controls the driving part 2 so that a wavelength value becomes that which is set to the light source 1 from the signal of PD 9 and the transmissivity of the transmissivity measuring part 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tunable semiconductor laser light source used in all fields of technology using an optical signal source, and more particularly to a tunable semiconductor laser light source used in optical communication and optical coherent measurement technology fields.

[0002]

2. Description of the Related Art Generally, an external resonator type semiconductor laser (hereinafter, referred to as an LD) is used for a light source section used for a variable wavelength light source having a variable wavelength range of about 100 nm.
Then, a single-mode oscillation is performed on one of the mirrors of the external resonator using a diffraction grating that is a wavelength selection element, and the wavelength of reflection of the diffraction grating is mechanically varied, thereby enabling a wide wavelength sweep. I have.

FIG. 5 shows an example of the configuration of a conventional variable wavelength LD light source. In FIG. 5, reference numeral 1 denotes an external resonator type LD light source unit, 2 denotes a drive unit, 3 denotes a control unit, and 12 denotes a control unit.
Is an origin switch. In the variable wavelength LD light source shown in FIG.
The drive unit 2 is operated to the position where operates. The current wavelength value at the operating position of the origin switch 12 is measured by an accurate wavelength meter in advance and stored as the origin wavelength. Then, the drive unit 2 mechanically changes the reflection wavelength of the diffraction grating in the external resonator type LD light source unit 1. Here, the relationship between the state of the drive unit 2 and the oscillation wavelength is known, and the control unit 3
Sets the wavelength according to a known relational expression.

FIG. 6 shows an external resonator type LD light source unit 1.
In FIG. 6, 101 is a diffraction grating, 102, 105, 107 are lenses, 103 is a non-reflection film, 104 is an LD, 106 is an optical isolator,
08 is an optical fiber and 109 is an LD drive circuit. FIG.
In the external resonator type LD light source unit 1 described above, the external resonator is:
It is composed of an LD end face B and a diffraction grating 101, and its resonator length is represented by a line segment AB as a point A on the optical axis X of the diffraction grating 101.
It is. An anti-reflection film 103 is formed on an end surface of the LD 104 on the side of the diffraction grating 101 in order to remove unnecessary reflection. Also, the lenses 102 and 105 are
4 is a collimator for converting each of the outgoing beams into parallel beams.

[0005] In the above, the output light from the external resonator LD 104 is obtained from the LD end face B side, condensed by the lens 107, and extracted by the optical fiber 108.
An optical isolator 106 is inserted on the output side so as not to generate noise due to return light from the subsequent optical system. Note that the LD drive circuit 109 supplies an LD drive current corresponding to a desired light output level.

Next, the optical filter characteristics of the external cavity type LD light source unit 1 will be described with reference to FIGS.
This will be described with reference to (c) and (d). FIG. 7 shows an optical system of the diffraction grating 101. As shown, the angle between the optical axis and the normal Ngr of the diffraction grating 101 is θ, and the grating interval is d.
And incident light and reflected (diffraction) light are set on the same optical axis X. Here, the reflected light spectrum when white light is incident is the filter characteristic of the diffraction grating 101, and the filter characteristic as shown in FIG. 8A is obtained. The reflection peak wavelength λgr is represented by the following Bragg equation: It is determined in (1). λgr = 2d × sin (θ) (1) If the external resonator length is L, the resonance longitudinal mode is mλm = 2L (2), where m is an integer. FIG. 8B shows the spectrum of the longitudinal mode. Therefore, assuming that the gain characteristic of the LD having a gain in the wavelength range of 100 nm or more is as shown in FIG. 8C, the oscillation wavelength of the external resonator type LD light source unit 1 is obtained by the filter characteristic of FIG. A single mode oscillation as shown in (d) is obtained. Thus, in FIG. 8, FIG.
If the characteristics of (b) and (c) are changed,
By appropriately changing L and θ, wavelength sweep can be performed.

[0007]

By the way, the current WD
The M optical communication system is a communication system in which several waves are multiplexed at a wavelength interval of about 1 nm. In order to optimize an amplification band of an optical amplifier and a loss band of an optical fiber, the wavelength interval is set to 0.1 n.
It is necessary to make a fine adjustment in about m. Therefore, the required wavelength accuracy is required to be one digit lower than about 0.01 nm. On the other hand, the setting resolution of the variable wavelength LD light source in the related art is about 0.001 nm, but the setting wavelength accuracy is based on mechanical backlash, hysteresis, and the like.
Due to error factors such as setting reproducibility including temperature fluctuations and temporal changes, the value is at most about ± 0.1 nm. Therefore,
The only way to improve the set wavelength accuracy is to prepare an expensive wavelength meter in addition to the variable wavelength LD light source, measure the output wavelength of the variable wavelength LD light source with the wavelength meter each time the wavelength meter is set, and correct the setting.

Accordingly, an object of the present invention is to provide a variable wavelength LD light source that can guarantee a wavelength accuracy of about ± 0.01 nm.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an external cavity type semiconductor laser light source unit, a driving unit for varying the length of the external cavity, and a driving unit and a semiconductor laser driving current. A first optical coupler for splitting and outputting the output light from the external cavity type semiconductor laser light source as one incident light in the variable wavelength semiconductor laser light source, comprising: a first optical coupler; A second optical coupler that receives one output light from the second optical coupler and outputs two branches, and a third optical coupler that receives one output light from the second optical coupler and further outputs two branches An acousto-optic element that receives the other output light from the second optical coupler and outputs light at an angle corresponding to the wavelength of the incident light, an oscillator that drives the acousto-optic element, and an acousto-optic element. Detecting the incident position of the light of A photodetector array unit that transmits the output light to the control unit, an etalon that receives one output light from the third optical coupler, and the other output light from the third optical coupler and the etalon. An etalon transmittance measuring unit for determining the transmittance of the etalon by comparing the light intensity of the transmitted light and transmitting the transmittance of the etalon to the control unit.

As described above, the output light from the external cavity type semiconductor laser light source section is split into two lights by the first optical coupler as one incident light, and one of the two split output lights from the first optical coupler is output. Is output to the second optical coupler and
One of the output lights from the second optical coupler, which has been branched and output, is incident on the acousto-optic element, and the light is output to the photodetector array at an angle corresponding to the wavelength of the incident light. While detecting the incident position of the light in the light receiver array unit and transmitting the detected position to the control unit, the other output light from the second optical coupler is incident on the third optical coupler and is branched and output. One of the output lights from the third optical coupler is made to enter the etalon transmittance measurement unit via the etalon, and the other is made to directly enter the etalon transmittance measurement unit and output to these etalon transmittance measurement units. Since the light intensity of the transmitted light from the etalon and the light intensity of the output light from the third optical coupler are compared to determine the transmittance of the etalon, the variable wavelength semiconductor laser light source transmits the transmittance of the etalon to the control unit. The following effects are obtained. That is, according to the present invention, the incident position of the light incident from the second optical coupler and output from the acousto-optic element to the PD array unit at an emission angle corresponding to the light wavelength, and
And the etalon transmittance obtained by comparing the intensity of the etalon transmitted light incident on the etalon transmittance measurement unit from the optical coupler via the etalon with the intensity of light directly incident on the etalon transmittance measurement unit from the third optical coupler. Is transmitted to the control unit, the current wavelength value is calculated, and the drive unit is controlled so as to correspond to the wavelength value set in the external cavity type semiconductor laser light source unit, so that the set wavelength accuracy is ± 0. It can be about 01 nm. Therefore, it is not necessary to measure the emitted light wavelength using a wavelength meter other than the variable wavelength LD light source every time the setting is performed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A variable wavelength L according to the present invention will be described below.
An embodiment of the D light source will be described with reference to FIGS. FIG. 1 is a configuration diagram showing a configuration of a variable wavelength LD light source according to an embodiment to which the present invention is applied. However, in FIG. 1, portions common to the respective portions in FIG. 5 described above are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 1, reference numerals 4, 5, and 6 denote optical couplers, reference numeral 7 denotes an acousto-optic element, reference numeral 8 denotes an oscillator, reference numeral 9 denotes a photodetector array unit (hereinafter referred to as a PD array unit), reference numeral 10 denotes an etalon, and reference numeral 11 denotes a transmittance measuring unit (etalon). Transmittance measurement section).

First, an optical coupler 4 exemplified as a first optical coupler takes out the light emitted from the external resonator type LD light source unit 1 as one input and outputs two branches. This optical coupler 4 is 2
One of the branched outgoing lights becomes the output light of the variable wavelength LD light source. The other of the outgoing light branched into two by the optical coupler 4 enters the optical coupler 5 exemplified as a second optical coupler and is further branched into two.

One of the outgoing light beams branched by the optical coupler 5 enters the acousto-optic device 7. Then, the acousto-optic device 7 sets P at an emission angle θ corresponding to the wavelength of the incident light.
Light is output to the D array unit 9. This PD array unit 9
It is arranged at an appropriate distance from the acousto-optic element 7 and outputs a signal corresponding to the position of light emitted from the acousto-optic element 7 at an angle θ to the control unit 3. Here, a method of measuring the current wavelength value by the acousto-optic element 7 and the PD array unit 9 will be described.
This will be described with reference to FIG. FIG. 2 shows an acousto-optic device and a PD.
It is an optical system diagram of an array part. One of the output lights branched into two by the optical coupler 5 is incident on the acousto-optic element 7 and then emitted to the PD array unit 9 at an angle θ. The angle θ of the outgoing light at this time can be obtained from the oscillation frequency F from the oscillator 8, the incident light wavelength λ, and the sound speed V of the ultrasonic wave transmitted through the acousto-optic element 7 by the following equation (3). Can be. θ = sin ⁻¹ (λF / 2V) (3) The light emitted from the acousto-optic element 7 is PD
The light-receiving elements arranged in a line in the array section 9 detect at which position the light is incident. That is, the acousto-optic device 7 converts the wavelength change amount into the angle change amount, and the PD array unit 9 converts the angle change amount into the position change amount, thereby enabling the measurement of the current light wavelength.

The other outgoing light branched into two by the optical coupler 5 is supplied to an optical coupler 6 exemplified as a third optical coupler.
And is further branched into two. One of the two branched output lights passes through the etalon 10 and then passes through the transmittance measuring unit 1.
Incident on 1. The other of the output light branched into two by the optical coupler 6 directly enters the transmittance measuring unit 11. And
The transmittance measuring unit 11 measures the transmitted light of the etalon 10 and the directly incident light from the optical coupler 6, obtains the intensity ratio, that is, the transmittance of the etalon 10, and determines the transmittance of the etalon 10. Send to. And the control part 3
Based on the relationship between the incident position and the wavelength of the PD array and the relationship between the etalon transmittance and the wavelength, which have been measured and stored in advance using a precise wavelength meter, the data of the incident position of the PD array from the PD array unit 9 and the transmission The current wavelength value is calculated from the transmittance data from the rate measuring unit 11, and the driving unit 2 is instructed to set the current wavelength value to a value corresponding to the wavelength value set in the external resonator type LD light source unit 1.

Next, the etalon 10 and the transmittance measuring unit 11
FIGS. 3 and 4 show a method of measuring the current wavelength value according to FIG.
This will be described with reference to FIG. FIG. 3 is an optical system diagram of the etalon, and FIG. 4 is a transmission characteristic diagram of the etalon. In FIG. 3, D is the thickness of the interference etalon, n is the refractive index, and each transmission peak wavelength is represented by k as an integer with respect to the angle φ between the optical axis in the etalon 10 and the normal line N of the etalon 10. , Is obtained by the following equation (4). kλk = 2 nD × cos (φ) (4) Further, each peak interval is generally defined as a free spectral region (hereinafter, referred to as FSR), and the end face reflectance is 2
When set to about 7%, a transmission curve close to a sine wave is shown as shown in FIG. Further, the measurement resolution of the current wavelength is equivalent to the reading resolution of the etalon transmittance. That is,
In order to achieve the set resolution of 0.01 nm, considering the read error in the transmittance curve of FIG. 4 near the transmittance maximum and minimum with a small gradient, it is necessary that the read resolution is not more than transmittance / 50 even at the maximum. . This is practically possible. Therefore, if the rise and fall of the transmission curve can be detected by another method, the error is ±
The FSR for enabling setting at 0.01 nm is 0.2n
m. Therefore, the resolution required for the wavelength measurement by the acousto-optic element 7 and the PD array unit 9 is preferably a resolution capable of detecting the rise and fall of the etalon transmission curve and 0.1 nm or less.

Hereinafter, the wavelength measurement resolution by the acousto-optic device 7 and the PD array unit 9 will be calculated. The sound velocity V in the above formula (3) is determined by the ultrasonic medium in the acousto-optical element 7. For example, when the ultrasonic medium is As ₂ Se ₃ and the oscillation frequency from the oscillator 8 is 200 MHz, When the wavelength of light incident on the element 7 changes by 0.1 nm, the emission angle θ changes by about 5 μradian, and the acousto-optic element 7 and P
If the distance of the D array 9 is about 100 mm, the PD interval of the PD array unit 9 is 5 μm. Setting the element interval of the PD array 9 to 5 μm can be realized by the current PD array manufacturing technology. Therefore, a wavelength measurement resolution of 0.1 nm can be achieved. That is, for example, by designing as described above, the set wavelength accuracy can be set to ± 0.01 nm.

[0017]

As described above, the variable wavelength L according to the present invention is
According to the D light source, the incident position of the light incident from the second optical coupler and output from the acousto-optical element to the PD array unit at an emission angle corresponding to the light wavelength, and the light from the third optical coupler via the etalon The etalon transmittance transmitted to the etalon transmittance measurement unit and the etalon transmittance obtained by comparing the intensity of the light directly incident on the etalon transmittance measurement unit from the third optical coupler to the etalon transmittance are transmitted to the control unit. By calculating the current wavelength value and controlling the driving unit so as to correspond to the wavelength value set in the external cavity type semiconductor laser light source unit, the set wavelength accuracy is ±
It can be about 0.01 nm. Therefore, it is not necessary to measure the emitted light wavelength using a wavelength meter other than the variable wavelength LD light source every time the setting is performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a variable wavelength LD light source according to an embodiment to which the present invention is applied.

FIG. 2 is an optical system diagram of an acousto-optic element and a PD array unit.

FIG. 3 is an optical system diagram of an etalon.

FIG. 4 is a wavelength-transmittance characteristic diagram of an etalon.

FIG. 5 is a configuration diagram showing an example of a variable wavelength LD light source as a conventional technique.

6 is a configuration diagram illustrating a configuration example of an external resonator type LD light source unit of FIG. 5;

FIG. 7 is an optical system diagram of the diffraction grating of FIG.

FIG. 8 is a principle diagram of an oscillation mode selection of a tunable LD light source,
(A) is a wavelength-diffraction grating reflectance characteristic diagram, (b) is a wavelength-
Resonator mode characteristic diagram, (c) wavelength-LD gain characteristic diagram,
(D) is a wavelength-oscillation mode characteristic diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 External resonator type LD light source part 2 Drive part 3 Control part 4, 5, 6 Optical coupler 7 Acousto-optic element 8 Oscillator 9 PD array part 10 Etalon 11 Transmittance measurement part (Etalon transmittance measurement part)

Claims (1)

[Claims] 1. A tunable wavelength semiconductor laser light source comprising: an external cavity type semiconductor laser light source unit; a drive unit for varying the external cavity length; and a control unit for controlling the semiconductor laser drive current. , A first optical coupler for outputting the output light from the external cavity type semiconductor laser light source unit as one incident light into two branches, and inputting one output light from the first optical coupler into two branches. A second optical coupler for outputting, and one of the output lights from the second optical coupler,
A third optical coupler that splits and outputs, an acousto-optic element that receives the other output light from the second optical coupler and outputs light at an angle corresponding to the wavelength of the incident light, and drives the acousto-optic element An oscillator, a light receiving array unit that detects an incident position of light from the acousto-optical element and transmits the incident position to the control unit, and receives one output light from the third optical coupler. An etalon that compares the other output light from the third optical coupler with the light intensity of the transmitted light from the etalon to determine the transmittance of the etalon and transmits the transmittance of the etalon to the control unit A variable wavelength semiconductor laser light source, comprising: a transmittance measuring unit.