JPH0669586A - Distributed reflector and variable wavelength semiconductor laser using the same - Google Patents

Abstract

PURPOSE:To obtain a variable wavelength semiconductor laser capable of wide band wavelength sweep over a gain bandwidth, by using a distributed reflector wherein one or more phase shifts finely different in one period length of a diffraction grating exist in a specified region, and two or more periods of the diffraction grating containing phase shifts are continuously formed. CONSTITUTION:An active waveguide layer 2 and a non-active waveguide layer 3 are formed on an N-type InP substrate 1. The pattern of a diffraction grating whose pitch is modulated is transferred on resist spread on the surface of the non-active waveguide layer 3. By using the transferred pattern as a mask, etching is performed, and diffraction gratings 10a, 10b are formed. A stripe type waveguide is worked, and the following are laminated in order; a current blocking layer 6, a current blocking layer 7, a clad layer 4 and a cap layer 5. P-type electrodes 9a, 9b, 9c and an N-type electrode 8 are formed. In order to electrically separate the P-type electrode 9a arranged in an active region 101 from a P-type electrodes arranged in distributed reflector regions 102, 103, the P-type electrode and a cap layer 5 are eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable semiconductor laser suitable as a transmission light source, a tunable light source for synchronous detection and a light source for optical measurement in an optical wavelength (frequency) multiplex communication system in the field of optical communications. It is a thing.

[0002]

2. Description of the Related Art In response to an increase in the amount of communication information in the future, research on an optical wavelength (frequency) multiplex communication system has been conducted, but a wide range of wavelength sweeping functions as a transmission light source and a tunable light source for synchronous detection have been proposed. There is a demand, and also from the field of optical measurement, realization of a variable wavelength light source that covers a wide wavelength band is desired. As a variable wavelength light source, a number of distributed reflection type / distributed feedback type semiconductor lasers that can easily sweep the wavelength by current injection have been studied. As an example of the realization of a distributed reflection type semiconductor laser with a wavelength sweeping function, a structural sectional view thereof is shown in FIG. 5 (for example, Electronics Letters Vol. 24, No. 24, 1481 by Tomori et al.
See page 1482, 1988). In FIG. 5, 2 is an active waveguide layer, 3 is an inactive waveguide layer, 10 is a diffraction grating, and 1
Reference numeral 01 indicates an active region, and 102 and 103 indicate front and rear distributed reflection regions, respectively.

[0003]

However, in the above prior art, since the pitch of the diffraction grating in the distributed reflector region is single, λ = 2Λn _eq (Λ: pitch of the diffraction grating, n _eq : equivalent refractive index ), The oscillation wavelength near the Bragg wavelength λ is determined by the electrical equivalent refractive index change Δn _eq of the waveguide equivalent refractive index n _eq . Therefore, since the maximum refractive index change Δn / n of the semiconductor due to the normal current injection is about 1%, the wavelength sweep width of the distributed Bragg reflector semiconductor laser shown in the above-mentioned conventional example is limited to about 100Å, and the wavelength division multiplexing optical communication system. There was a problem that it was insufficient as a light source for use.

The object of the present invention is to solve the above-mentioned problems, and even if the equivalent refractive index change amount Δn _eq in the non-active waveguide region is about the same as the conventional one (about 1%), the gain bandwidth of the active waveguide region (about 10%).
It is to obtain a wavelength tunable semiconductor laser capable of sweeping a broadband wavelength over 00 Å).

[0005]

The above-mentioned object is to provide a substrate,
An optical waveguide including an optical waveguide layer having an optical refractive index larger than that of the substrate and at least one optical confinement layer having a refractive index smaller than that of the optical waveguide layer. By forming periodic unevenness or periodical compositional change, the equivalent refractive index of the optical waveguide is periodically changed to form a diffraction grating, and the diffraction grating period determines the Bragg diffraction condition from the cycle of the diffraction grating. In a distributed reflector that reflects light having a specified wavelength, there is at least one phase shift in which the length of one period of the diffraction grating is slightly different within a certain region. The included diffraction grating is achieved by a wavelength tunable semiconductor laser using a distributed reflector that is periodically formed with a length of the above region as a period and at least two periods or more continuously.

[0006]

In order to achieve the above-mentioned object, the pitch of the diffraction grating is continuously or intermittently changed, and the diffraction grating is repeatedly formed at a period sufficiently longer than the pitch of the diffraction grating. A semiconductor laser having a distributed reflection structure on both sides of the arm has been proposed (Azumamori et al .: Japanese Patent Application No. 4-
49425). An example of the structure of a distributed Bragg reflector laser manufactured by this method is shown in FIG. In the distributed Bragg reflector semiconductor laser of this example, the diffraction gratings 10a and 10b are formed in the front and rear inactive waveguide regions 102 and 103, respectively, and the diffraction grating 10 formed in the front inactive waveguide region is formed.
In a, as shown in FIG. 6B, a region in which the pitch continuously changes from Λ _a to Λ _b has a period M _f (where M _f > Λ _a ,
The diffraction grating 10b, which is repeatedly formed by Λ _b ), and which is similarly formed in the inactive waveguide region on the rear side, has a pitch Λ.
continuously changing region 'from lambda _{b' a} until the period M _r (provided that _{M r> Λ a ', Λ} b') are repeatedly formed in. As shown in FIG. 7A, the reflection characteristic of the front distributed reflector has a wavelength interval Δλ _f = λ ₀ ² / 2n between the wavelength λ _a = 2Λ _a n _eq and the wavelength λ _b = 2Λ _b n _{eq. eq} M _f (λ ₀ = n _eq (Λ _a +
Λ _b )) has a characteristic with periodic reflection peaks. Therefore, for convenience, the wavelengths of the reflection peak points are set to λ ₁ to λ _n . Similarly, the reflection characteristic of the rear distributed reflector is shown in FIG.
From the wavelength λ _a ′ = 2Λ _a ′ n _eq shown in (b), the wavelength λ _b ′ =
Wavelength interval Δλ _r = λ ₀ ² / 2n _eq M up to 2Λ _b ′ n _{eq
At r} , the characteristic becomes periodically having reflection peaks λ ₁ ′ to λ _k ′. Here, the pitch modulation periods M _f and M _r of the diffraction gratings in the front and rear distributed reflection regions are different from each other. Therefore,
When the refractive indices of the front and rear distributed reflection regions are electrically controlled independently, one wavelength λ out of λ _{1 to} λ _n.
One of λ ₁ ′ to λ _k ′ can be tuned to _i (i = 1-n) and laser oscillation can be performed only in the vicinity of λ _i . 7C and 7D show examples of oscillation of λ ₁ and λ ₂ ,
That is, the case where i is 1 and 2 is shown. As described above, in the distributed Bragg reflector semiconductor laser according to the present method, the oscillation wavelength is controlled by independently flowing a current or applying a voltage to the electrodes formed in the front inactive waveguide region having the diffraction grating. Therefore, the large wavelength jump between the reflection peaks of the diffraction grating can be utilized to greatly expand the variable wavelength range.

However, in the above method, it is necessary to make the pitch of the diffraction grating fine in units of Å and to accurately draw over a length of several 100 μm. At present, such a diffraction grating can be formed only by a fine processing method using an electron beam exposure method, but this method also requires an extremely long exposure time, which is a problem in mass production technology.

The present invention realizes the same effect as that of the above-mentioned invention with a diffraction grating having a uniform pitch, and uses a processing technique which is excellent in mass productivity such as a significantly shortened exposure time in electron beam exposure and interference exposure. This makes it possible to fabricate a broadband wavelength tunable semiconductor laser at a significantly lower cost than the above method.

FIG. 8 shows an example of the structure of the diffraction grating according to the present invention.
It shows in (a). The diffraction grating has a periodic repeating structure with a certain length M _f as a unit. FIG. 8B shows a repeating unit area structure. The diffraction grating is formed with _a constant repeating pitch Λ _a , but in some places of the diffraction grating, a grating whose pitch is longer or shorter than that of other portions is engraved. The phase of the diffraction grating is shifted to − or + before and after this portion, which is a phase control region.
Phase shifts of + and-in the portions indicated by p and m in (b), respectively. An enlarged view of the diffraction grating of the portions indicated by A, B, and C is shown in FIG. 8 (c). In part A, the diffraction grating is formed at a constant pitch. In part B, a grating having a small pitch is formed in the central part for only one period, and from this point, the peak position of the diffraction grating is shifted forward as compared with A. Due to this phase shift, the diffraction grating undergoes phase modulation, and equivalently the same effect as when the pitch of the diffraction grating is shortened is obtained. A diffraction grating having a large pitch is synchronously formed in the center of the C portion, and the peak position is shifted backward, contrary to the B portion. Therefore, the diffraction grating provides the effect that the pitch becomes equivalently long. The interval at which the phase shift is inserted is shown in FIG.
As shown in (b), it changes depending on the position, and the + phase shift is on the left side and the − phase shift is on the right side with respect to the center part. Therefore, equivalently, the pitch of the diffraction grating gradually increases. It gives the same effect as the longer one.

FIG. 9 shows the peak position of the n-th diffraction grating in each unit area with respect to n. The solid line shows the diffraction grating in FIG. 9, and the broken line shows the original one. This is the case of the diffraction grating shown in the figure based on. When the pitch of the diffraction grating is constant, the peak position increases linearly with respect to n. In the diffraction grating shown in FIG. 6, since the pitch is continuously reduced, the slope of the curve gradually becomes gentle and the parabola is drawn as a whole. On the other hand, in the diffraction grating shown in FIG. 8, since the pitch is constant, the inclination becomes a straight line, but it changes discontinuously in the phase shift portion, and the curve in the case of the diffraction grating in FIG. 6 is linearly approximated as a whole. It becomes a form to do.
Therefore, it can be seen that if the magnitude of the phase shift and the interval for inserting the phase shift are made sufficiently small, the solid line and the broken line substantially coincide with each other, and the diffraction grating of FIG. 8 exhibits the same characteristics as the diffraction grating of FIG. Since the diffraction grating of FIG. 8 according to the present invention has a constant pitch, it can be formed much more easily than the diffraction grating of FIG. 6 and has the same effect as the diffraction grating of FIG. If it is used as a distributed reflector of a semiconductor laser, the wavelength variable range can be greatly expanded.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. 1A and 1B are diagrams showing a distributed reflector as a first embodiment of the present invention. FIG. 1A is an external view, FIG. 1B is a diagram showing a unit constituting one unit, and FIG. 1C is a diagram showing the configuration of each unit. ,
(D) is a figure which shows a light transmission characteristic. In FIG. 1 (a), 1 is an n-type InP substrate, 3 is an InGaAsP inactive waveguide layer having a bandgap wavelength of 1.3 μm, 4 is a p-type InP cladding layer, and 10 includes a phase shift region periodically. It is a diffraction grating. Reference numeral 5 is a loaded waveguide formed by etching, which has an equivalent refractive index of about 3.2.
Forming an optical waveguide. The diffraction grating is formed at a constant pitch of 2380 Å, and the structure including the phase shift is periodically repeated 20 cycles with a period of 33.36 μm to form a diffraction grating with a total length of about 666 μm. Figure 1
(B) is an enlargement of a repeating unit of 33.36 μm, and one unit is composed of 17 units.
Each unit is formed of three types of units shown in (c). The unit denoted by Nn has a pitch of 2380Å with n cycles. In the portion marked Mn, the pitch of the first diffraction grating is 1904Å, and the phase of the diffraction grating is shifted by this. The second and subsequent diffraction gratings are 2380Å, which includes a total of n periods of diffraction gratings. P
The pitch of the head of the unit marked n is 2856Å. FIG. 1D shows the results of measuring the light transmission characteristics of the distributed reflector shown in FIG. The light transmittance is almost equal to 1 minus the light reflectance, and the reflection characteristics can be estimated from the above measurement. Transmittance is about 100Å
It can be seen that the peaks of reflectance appear at intervals of 100 Å, with a significant decrease at intervals. The above characteristics are shown in FIG.
It can be seen that the reflection characteristic is similar to that of the diffraction grating shown in (3), and that similar characteristics are obtained by the configuration of the distributed reflector of the present invention.

FIG. 2 shows a distributed reflection type semiconductor laser having a wavelength sweeping function as a second embodiment of the present invention. In FIG. 2, (a) is a plan view and (b) is A- shown in the above plan view.
FIG. 6A is a sectional view taken along the line A ′, FIG. 7C is a sectional view taken along the line BB ′ shown in the plan view, and FIG. Figure 2
1, 1 is an n-type InP substrate, 2 is an InGaAsP active waveguide layer having a bandgap wavelength of 1.55 μm, 3 is an InGaAsP inactive waveguide layer having a bandgap wavelength of 1.3 μm, 4 is a p-type InP clad layer, 5 is p (+)
-Type InGaAsP cap layer, 6 is a p-type InP current blocking layer, 7 is an n-type InP current blocking layer, 8 is an n-type electrode, 9a is a p-type electrode provided in the active region 101, and 9b is a front distributed reflector region 102. , A p-type electrode 9c is a p-type electrode provided in the rear distributed reflector region 103, a portion 10a is a portion in which a region of a diffraction grating including a phase shift is repeatedly formed with a period M _f , and a reference numeral 10b is a phase shift. Reference numeral 11 denotes a coupling portion between the active waveguide layer 2 and the non-active waveguide layer 3 in which the region of the diffraction grating including is repeatedly formed with the period M _r . The diffraction grating 10a has the same structure as that of the first embodiment.
A diffraction grating including a phase shift of 3.36 μm forms a diffraction grating of about 670 μm in 20 cycles. Diffraction grating 10
The structure of b is as shown in (d), and a diffraction grating including a phase shift of 35.7 μm forms a diffraction grating of about 710 μm in 20 cycles.

A method of manufacturing the distributed reflection type semiconductor laser having the wavelength sweeping function will be briefly described. First, the active waveguide layer 2 and the inactive waveguide layer 3 are formed on the n-type InP substrate 1 by using the metal organic vapor phase epitaxial growth method. After that, the pattern of the diffraction grating whose pitch is modulated by the electron beam exposure method is transferred to the resist applied on the surface of the inactive waveguide layer 3, and the transfer pattern is used as a mask for etching to perform diffraction gratings 10a and 10b. To form.
Then, the waveguide is processed in a stripe shape to control the transverse mode, and the p-type InP current blocking layer 6, the n-type InP current blocking layer 7, and the p-type InP cladding layer are again formed by using the metalorganic vapor phase epitaxial growth method. 4 and p (+)
Type InGaAsP cap layer 5 is sequentially laminated, and then p
Forming the p-type electrodes 9a, 9b, 9c and the n-type electrode 8, and further providing in the distributed reflector regions 102 and 103 having the p-type electrode 9a provided in the active region 101 and the portions 10a and 10b in which the diffraction grating is formed. In order to electrically separate the p-type electrodes 9b and 9c from each other, the p-type electrode and the p (+)-type InGaAsP above the coupling portion thereof are electrically separated from each other.
The cap layer 5 is removed.

In the diffraction grating of the above semiconductor laser, 10a
The repetition period of the diffraction grating structure including the phase shift is 33.36 μm in the portion (3) and 35.7 μm in the portion 10b.

In the distributed Bragg reflector semiconductor laser having the above-described structure, laser oscillation is generated by passing a current through the active region 101, and the distributed reflector regions 102 and 103 or the phase adjusting region are independently fed with a current or a voltage is applied. By doing so, the oscillation wavelength can be changed. A current is applied to the electrode 9c provided in the distributed reflector region 103 while a constant current is applied to the active region 101 and no current is applied to 9b of the electrodes provided in the front and rear distributed reflector regions 102 and 103. FIG. 8 shows how the oscillation wavelength changes when the oscillation wavelength is changed. In the above semiconductor laser, as shown in FIG. 2, by passing a current through the distributed reflector region 103, the oscillation wavelength can be changed from 1.500 μm to 1.600 μm at intervals of about 100 Å. Further, in the above state, the difference between the currents flowing through the electrodes 9b and 9c is adjusted to select one of the oscillation wavelengths that changes every approximately 100 Å, and the difference between the currents flowing through the electrodes 9b and 9c is made constant. It is possible to finely adjust the oscillation wavelength by simultaneously increasing or decreasing the currents of both electrodes while keeping the same condition. Electrode 9b
The solid line in FIG. 10 shows how the oscillation wavelength changes when the currents flowing in the channels 9 and 9c are simultaneously changed. As shown in the figure, in the present semiconductor laser, current is caused to flow through the electrodes 9b and 9c at the same time so that the oscillation wavelength is 100 Å while causing a wavelength jump.
The degree can be changed. By adjusting the current flowing through the p-type electrodes 9b and 9c according to the above procedure, it is possible to perform rough adjustment and fine adjustment of the oscillation wavelength and select an arbitrary oscillation wavelength over the wavelength range of 1000Å.

In this embodiment, there is no so-called phase adjustment region for adjusting the phase of the reflected light from the diffraction grating by current injection formed by a flat transparent waveguide, but it is distributed with the active region 101 of this embodiment. Return area 102 or 103
If a phase adjustment region is added in between, finer wavelength adjustment becomes possible.

A distributed feedback semiconductor laser with a wavelength sweeping function according to the present invention is shown in FIG. 3 as a third embodiment. 4A is a plan view of the distributed feedback semiconductor laser,
(B) is a sectional view taken along the line AA 'shown in the above plan view, and (c) is a sectional view taken along the line BB' shown in the above plan view. In the figure, 1
Is an n-type InP substrate, 2 has a bandgap wavelength of 1.55
μm InGaAsP active waveguide layer, 3 is an InGaAsP inactive waveguide layer having a bandgap wavelength of 1.3 μm,
4 is a p-type InP clad layer, 5 is a p (+)-type InGaA
sP cap layer, 6 p-type InP current blocking layer, 7 n-type InP current blocking layer, 8 n-type electrode, 9d, 9e
Is a pair of comb-shaped p electrodes provided in the front distributed feedback region 102 ', 9f and 9g is a pair of comb-shaped p electrodes provided in the rear distributed feedback region 103', and 10a is a diffraction grating including a phase shift The region 10b is repeatedly formed with the period M _f , and 10b is the region repeatedly formed with the period M _r of the diffraction grating region including the phase shift.

A method of manufacturing the above semiconductor laser will be briefly described. First, the active layer 2 and the optical confinement layer 3 are formed on the n-type InP substrate 1 by using the metal organic vapor phase epitaxial growth method. After that, the pattern of the diffraction grating whose pitch is modulated by the electron beam exposure method is transferred to the resist applied on the surface of the light confinement layer 3, and the transfer pattern is used as a mask to perform etching to form the diffraction gratings 10a and 10b. . Next, the waveguide is processed into a stripe shape to control the transverse mode, and the p-type InP current blocking layer 6 and the n-type In are again formed by using the metalorganic vapor phase epitaxial growth method.
P current blocking layer 7, p-type InP cladding layer 4 and p
The (+) type InGaAsP cap layer 5 is sequentially manufactured.
After that, the p-type electrodes 9d, 9e, 9f, 9g and the n-type electrode 8 are formed, and further, the portion 10a in which the diffraction grating is formed.
And distributed feedback regions 102 'and 103' with 10b
In order to electrically separate the comb-shaped p-electrodes 9d, 9e, 9f, 9g provided in the respective parts from each other, the p-type electrode and the p (+)-type InGaAsP cap layer 5 above the coupling part are removed. .

In the diffraction grating in the distributed Bragg reflector semiconductor laser with the wavelength sweeping function of this embodiment, the repetition period of the diffraction grating structure including the phase shift in the portion 10a is 33.36.
The portions of 3 μm and 10 b are repeatedly formed with a thickness of 35.7 μm.

In the distributed feedback semiconductor laser having the above structure,
Laser oscillation is generated by passing a current through the distributed feedback regions 102 'and 103', and a pair of comb-shaped p electrodes 9d and 9e,
Alternatively, by adjusting the ratio of currents between 9f and 9g, a spatial distribution of carrier density is created and the refractive index is changed, whereby the oscillation wavelength can be adjusted. The comb-shaped p provided in the distributed feedback region 103 'in a state where a constant current is applied to 9d, 9e, 9f of the comb-shaped electrodes provided in the front and rear distributed feedback regions 102' and 103 'to cause laser oscillation. The change in the oscillation wavelength when the current flowing through the electrode 9g is changed is the same as that in FIG. 2, and the change from 1.500 μm to 1.600 μm
The oscillation wavelength can be changed at intervals of 100Å up to m.

Also, the comb-shaped p electrodes 9d, 9e, 9f, 9g.
It is also possible to finely adjust the wavelength as shown by the solid line and the broken line in FIG.
Thus, in the distributed feedback semiconductor laser of this embodiment, p
By adjusting the current flowing through the mold electrodes 9d to 9g by the above procedure, the oscillation wavelength is roughly adjusted and finely adjusted to 1000
It becomes possible to select any oscillation wavelength over the wavelength range of Å.

As a fourth embodiment of the present invention, FIG. 4 shows another example of the distributed feedback semiconductor laser with wavelength sweeping function. In the figure, (a) is a plan view of the semiconductor laser, (b) is a sectional view taken along the line AA 'in the plan view, and (c) is a sectional view taken along the line BB' in the plan view. In the figure, 1'is a p-type InP substrate, 2 is a bandgap wavelength of 1.55μ.
m InGaAsP active layer, 3 is an InGaAsP optical confinement layer with a bandgap wavelength of 1.3 μm, and 4 is p-type I
nP clad layer, 5 p (+) type InGaAsP cap layer, 6 p type InP current blocking layer, 7 n type InP
A current blocking layer, 8'is a p-type electrode, 9d is a p-type wavelength controlling electrode provided in the front distributed feedback region 102 ', 9f is a p-type wavelength controlling electrode provided in the rear distributed feedback region 103', 9h is a common n electrode formed on the n-type semiconductor, 10
a is a portion in which the region of the diffraction grating including the phase shift is repeatedly formed with the period M _f , 10b is a portion in which the region of the diffraction grating including the phase shift is repeatedly formed with the period M _r , and 12 is an n-type InP conductive layer is there.

A method of manufacturing the above semiconductor laser will be briefly described. First, the active layer 2, the n-type InP conductive layer 12, and the optical confinement layer 3 are formed on the p-type InP substrate 1'by using the metal organic vapor phase epitaxial growth method. After that, the pattern of the diffraction grating having the pitch modulated by the electron beam exposure method is transferred to the resist applied on the surface of the light confinement layer 3, and the transfer pattern is used as a mask for etching.
Form the diffraction gratings a and 10b. Next, the waveguide is processed into a stripe shape in order to control the transverse mode, and n-type InP is again formed by using the metalorganic vapor phase epitaxial growth method.
The current blocking layer 7, the p-type InP current blocking layer 6, the p-type InP cladding layer 4, and the p (+)-type InGaAsP cap layer 5 are sequentially formed. After that, a part of the p-type InP current block layer 6 is removed by etching, and the n-type InP is removed.
The current blocking layer 7 is exposed, and the n-type common electrode 9 is formed thereon.
form h. Next, the p-type electrodes 9d and 9f are formed, and the p-type electrodes 9d and 9f provided in the distributed feedback regions 102 'and 103' having the portions 10a and 10b in which the diffraction grating is formed are electrically isolated from each other. for,
The middle portion thereof is removed up to the p (+) type InGaAsP cap layer 5. In the diffraction grating in the distributed feedback semiconductor laser with the wavelength sweep function of the present embodiment, the repetition period of the diffraction grating structure including the phase shift is 3 in the portion 10a.
The portions of 3.36 μm and 10b are repeatedly formed with a thickness of 35.7 μm.

In the distributed feedback semiconductor laser having the above structure,
Carriers are injected into the active layer 2 by causing a current to flow between the substrate-side p-type electrode 8'and the n-type common electrode 9h, and the distributed feedback region 1 is caused by the optical gain produced thereby.
It oscillates at a wavelength determined by 02 'and 103'. The refractive index of the distributed feedback regions 102 'and 103' is determined by the p-electrode 9
Since it is changed by the carrier injection into the corresponding region by the current between d and 9f and the common electrode 9h, the p electrodes 9d and 9f
The oscillation wavelength can be controlled by injecting a current into f.

A change in the oscillation wavelength when the current flowing through the electrode 9f provided in the distributed feedback region 103 'is changed in the state where a constant current is passed through the n-electrode on the substrate side to cause laser oscillation. Same as the embodiment, but from 1.500 μm to 1.6
It is possible to change the oscillation wavelength at 100Å intervals up to 00 μm.

Further, by simultaneously changing the values of the currents flowing through the electrodes 9d and 9f, the wavelength can be finely adjusted as shown by the solid line and the broken line in FIG. As described above, in the distributed feedback semiconductor laser according to the present embodiment, the oscillation wavelength is roughly adjusted and finely adjusted by adjusting the currents flowing through the p-type electrodes 9d and 9f according to the above-described procedure. It becomes possible to select the oscillation wavelength.

[0027]

As described above, the distributed reflector according to the present invention and the wavelength tunable semiconductor laser using the same are provided on a substrate, an optical waveguide layer having an optical refractive index larger than that of the substrate, and a refractive index greater than that of the optical waveguide layer. In the optical waveguide including one or more optical confinement layers each having a small ratio, the above-mentioned optical waveguide is formed by forming periodic unevenness or periodic composition change in one or more layers forming the optical waveguide. A diffraction grating is formed by periodically changing the equivalent refractive index of the waveguide, and a fixed length is obtained in a distributed reflector having a reflection action for light having a wavelength determined by the Bragg diffraction condition from the diffraction grating cycle. There is at least one phase shift in which the length of one period of the diffraction grating is slightly different, and the diffraction grating including the phase shift is continuous for at least two periods with the length of the region as the period. By configuring the wavelength tunable semiconductor laser using the distributed reflectors formed periodically, it is possible to obtain the wavelength tunable semiconductor laser in which the wavelength sweep over a wide band can be controlled with good control over the gain bandwidth of the active waveguide layer. At the same time, the distributed reflector can be used as a wavelength filter.

[Brief description of drawings]

1A and 1B are diagrams showing a distributed reflector that is a first embodiment of the present invention, in which FIG. 1A is an external view, FIG. 1B is a diagram showing a unit constituting one unit of a diffraction grating, and FIG. The figure which shows the structure of a unit, (d) is a figure which shows a light transmission characteristic.

FIG. 2 is a diagram showing a distributed reflection type semiconductor laser with a wavelength sweeping function, which is a second embodiment of the present invention, in which (a) is a plan view,
(B) is a sectional view taken along the line AA 'shown in the above plan view, (c) is a sectional view taken along the line BB' shown in the above plan view, and (d) is a diagram showing a unit configuration of the diffraction grating.

3A and 3B are diagrams showing a distributed feedback semiconductor laser with a wavelength sweeping function, which is a third embodiment of the present invention, in which FIG. 3A is a plan view of the semiconductor laser, and FIG. ′ Is a sectional view, and (c) is a BB ′ sectional view shown in the above plan view.

FIG. 4 is a diagram showing a distributed feedback semiconductor laser with a wavelength sweeping function according to a fourth embodiment of the present invention, (a) is a plan view of the semiconductor laser, and (b) is AA shown in the plan view. ′ Is a sectional view, and (c) is a BB ′ sectional view shown in the above plan view.

FIG. 5 is a sectional view of a conventional distributed Bragg reflector semiconductor laser.

6A and 6B are diagrams showing a distributed Bragg reflector semiconductor laser described in a reference document, where FIG. 6A is a structural diagram and FIG. 6B is a diagram showing a concept of a diffraction grating.

FIG. 7 is a diagram showing a method of setting an oscillation wavelength by a conventional distributed Bragg reflector semiconductor laser, where (a) is a reflection peak in the front distributed reflector region, (b) is a reflective peak in the rear distributed reflector region,
(C) is a diagram showing an example of oscillation of λ ₁ , and (d) is a diagram showing an example of oscillation of λ ₂ .

8A and 8B are conceptual diagrams of a distributed reflector according to the present invention, FIG. 8A is a diagram showing a structure of a diffraction grating, FIG. 8B is a repeating unit, and FIG. 8C is a diagram showing a diffraction grating in the repeating unit.

FIG. 9 is an explanatory diagram of an operation in the present invention.

10A and 10B are diagrams showing how the oscillation wavelength is adjusted in the present invention, where FIG. 10A is a diagram showing rough adjustment and FIG. 10B is a diagram showing fine adjustment.

[Explanation of symbols]

1, 1'Substrate 2 Active waveguide layer, active layer 3 Inactive waveguide layer, optical confinement layer 10 Diffraction grating 10a Diffraction grating region is formed with period M _f 10b Diffraction grating region is formed with period M _r Part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Ishii 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (5)

[Claims] 1. An optical waveguide is formed on a substrate by an optical waveguide including an optical waveguide layer having an optical refractive index larger than that of the substrate and one or more optical confinement layers having a refractive index smaller than that of the optical waveguide layer. By forming periodical unevenness or periodical compositional change in one or more layers, the equivalent refractive index of the optical waveguide is periodically changed to form a diffraction grating. In a distributed reflector that reflects light having a wavelength determined by Bragg's diffraction condition from the period of, the phase shift in which the length of one period of the diffraction grating is slightly different is within a region of constant length. , There is at least one place, and the diffraction grating including the phase shift is continuous for at least two periods with the length of the region as a period,
A distributed reflector characterized by being formed periodically. 2. The distributed reflector according to claim 1, wherein the substrate is a semiconductor substrate. 3. An active waveguide layer formed in a predetermined region of a semiconductor waveguide, and at least one of before and after the active waveguide layer,
A tunable semiconductor laser having a distributed reflector having a non-active waveguide layer optically coupled to the active waveguide layer and having a diffraction grating in a part or all of the non-active waveguide region, wherein the distributed reflection A tunable semiconductor laser, wherein at least one of the devices is constituted by the distributed reflector according to claim 1 or 2. 4. At least one of the semiconductor layers forming the distributed reflector according to claim 1 or 2 has an optical gain with respect to light in a wavelength band in which the distributed reflector performs a reflecting action. A wavelength tunable semiconductor laser which is formed of an active waveguide layer and which oscillates at one of the reflection wavelengths of the distributed reflector due to the optical amplification action of the active waveguide layer. 5. The wavelength tunable semiconductor laser according to claim 4, further comprising a wavelength control layer which is transparent to oscillated light and whose refractive index can be controlled by changing carrier density due to current injection. Tunable semiconductor laser characterized in that the oscillation wavelength is swept by current injection of