光電系畢業(yè)論文中英文翻譯

1、<p>　　畢 業(yè) 設(shè) 計(jì)（論 文）</p><p><b>　　英文翻譯</b></p><p>　　姓 名 </p><p>　　學(xué) 號 </p><p>　　所在學(xué)院 理 學(xué) 院

2、 </p><p>　　專業(yè)班級 </p><p>　　指導(dǎo)教師 </p><p>　　日 期 2012年4月20 日 </p><p><b>　　英文原文</b></p><p>　　1.5

3、Experimental Setup</p><p>　　Due to the many concepts and variations involved in performing the experiments in this project and also because of their introductory nature, Project 1 will very likely be the mos

4、t time consuming project in this kit. This project may require as much as 9 hours to complete. We recommend that you perform the experiments in two or more laboratory sessions. For example, power and astigmatic distance

5、characteristics may be examined in the first session and the last two experiments (frequency and ampl</p><p>　　A Note of Caution</p><p>　　All of the above comments refer to single-mode operation

6、 of the laser which is a very fragile device with respect to reflections and operating point. One must ensure that before performing measurements the laser is indeed operating single-mode. This can be realized if a sing

7、le, broad fringe pattern is obtained or equivalently a good sinusoidal output is obtained from the Michelson interferometer as the path imbalance is scanned. If this is not the case, the laser is probably operating multi

8、mode</p><p><b>　　Warning</b></p><p>　　The lasers provided in this project kit emit invisible radiation that can damage the human eye. It is essential that you avoid direct eye exposu

9、re to the laser beam. We recommend the use of protective eyewear designed for use at the laser wavelength of 780 nm. </p><p>　　Read the Safety sections in the Laser Diode Driver Operating Manual and in the

10、laser diode section of Component Handling and Assembly (Appendix A) before proceeding.</p><p>　　1.5.1 Semiconductor Diode Laser Power Characteristics</p><p>　　1. Assemble the laser mount assembl

11、y (LMA-I) and connect the laser to its power supply. We will first collimate the light beam. Connect the laser beam to a video monitor and image the laser beam on a white sheet of paper held about two to ten centimeters

12、from the laser assembly. Slowly increase the drive current to the laser and observe the spot on the white card. The threshold drive current rating of the laser is supplied with each laser. Increase the current to about 1

13、0-20 mA over the threshol</p><p>　　With the infrared imager or infrared sensor card, observe the spot on the card and adjust the collimator lens position in the laser assembly LMA-I to obtain a bright spot o

14、n the card. Move the card to about 30 to 60 centimeters from the lens and adjust the lens position relative to the laser to obtain a spot where size does not vary strongly with the position of the white card. When the sp

15、ot size remains roughly constant as the card is moved closer or further from the laser, the output can be co</p><p>　　2. Place an 818-SL detector on a post mount (assembly M818) and adjust its position so th

16、at its active area is in the center of the beam. There should be adequate optical power falling on the detector to get a strong signal. Connect the photodetector to the power meter (815). Reduce the background lighting (

17、room lights) so that the signal being detected is only from the laser. Reduce the drive current to a few milliamperes below threshold and, again, check to see that room light is not the domin</p><p>　　3. Inc

18、rease the current and record the output of the detector as a function of laser drive current. You should obtain a curve similar to Figure 1.2. If desired, the diode temperature may also be varied to observe the effects o

19、f temperature on threshold current. When examining laser diode temperature characteristics, the laser diode driver should be operated in the constant current mode as a safeguard against excessive currents that damage the

20、 diode laser. Note that as the diode temperature is re</p><p>　　1.5.2 Astigmatic Distance Characteristics</p><p>　　The laser diode astigmatic distance is determined as follows. A lens is used to

21、 focus the laser beam at a convenient distance. A razor blade is, then, incrementally moved across the beam to obtain data for total optical power passing the razor edge vs. the razor blade position. A plot of this data

22、produces an integrated power profile of the laser beam (Figure 1.9a) which through differentiation exposes the actual power profile (Figure 1.9b) which, in turn, permits determination of the beam diame</p><p&g

23、t;　　1. Assemble the components shown in Figure 1.8 with the collimator lens (LC), in the rotational stage assembly (RSA-I), placed roughly 1 centimeter away from the laser. The beam should travel along the optic axis of

24、 the lens. This is the same lens used in collimating the laser in the previous setup. The approximate placement of all the components are shown in the figure. Make sure that the plane of the diode junction (xz plane in F

25、igure 1.1) is parallel with the table surface.</p><p>　　2. Due to the asymmetric divergence of the light, the cross-section of the beam leaving the laser and, further, past the spherical lens is elliptical.

26、The beam, thus, has two distinct focal points, one in the plane parallel and the other in the plane perpendicular to the laser diode junction. There is a point between the two focal points where the beam cross-section is

27、 circular. With the infrared imager and a white card, roughly determine the position where the beam cross-section is circular.</p><p>　　Figure 1.9 – Procedure for finding astigmatic distance.</p><

28、p>　　3. Adjust the laser diode to lens distance such that the razor blades are located in the xy plane where the beam cross-section is circular.</p><p>　　4. Move the laser diode away from the lens until mi

29、nimum beam waist is reached at the plane of razor blades. Now, move the laser diode about 200 µm further away from the lens.</p><p>　　5. Move razor blade 1 in the x direction across the beam through the

30、 beam spread θx and record the x position and detected intensity at each increment (≤100 µm increments). The expected output is shown in Figure 1.9. The derivative of this curve yields the intensity profile of the b

31、eam in the x direction from which the beam diameter is determined.</p><p>　　6. Repeat with razor blade 2 for θy in the y direction.</p><p>　　7. Move the laser closer to the lens in increments (≤

32、50 µm) through a total of at least than 500µm. Repeat Steps 5 and 6 at each z increment, recording the z position.</p><p>　　8. Using the collected data, determine the beam intensity profiles in the

33、 x and y directions as a function of the lens position z. This is done by differentiating each data set with respect to position. Then, calculate the beam diameter and plot as a function of z. The difference in z for the

34、 minimum in θx and θy is the astigmatic distance of the laser diode. Use of computer software, especially in differentiating the data, is highly recommended.</p><p>　　If the laser junction is not parallel to

35、 the table surface, then for each measurement above, you will obtain an admixture of the two beam divergences and the measurement will become imprecise. If the laser is oriented at 45° to the surface of the table, t

36、he astigmatic distance will be zero.</p><p>　　Different laser structures will have different angular beam divergences and, thus, different astigmatic distances. If you have access to several different laser

37、types (gain guided, index guided), it may be instructive to characterize their astigmatic distances.</p><p>　　1.5.3 Frequency Characteristics of Diode Lasers</p><p>　　In order to study frequency

38、 characteristics of a diode laser, we will employ a Michelson interferometer to convert frequency variations into intensity variations. An experimental setup for examining frequency and, also, amplitude characteristics o

39、f a laser source is illustrated in Figure 1.10.</p><p>　　1. In this experiment, it is very possible that light may be coupled back into the laser, thereby, destabilizing it. An optical isolator, therefore, w

40、ill be required to minimize feedback into the laser. A simple isolator will be constructed using a polarizing beam splitter cube and a quarterwave plate. We orient the quarterwave plate such that the linearly polarized l

41、ight from the polarizer is incident at 45° to the principal axes of the quarterwave plate so that light emerging from the quarterw</p><p>　　In assembling the isolator, make sure that the laser junction

42、(xz plane in Figure 1.1) is parallel to the surface of the table (the notch on the laser diode case points upward) and the beam is collimated by the lens. The laser beam should be parallel to the surface of the optical t

43、able. Set the polarizer and quarterwave (λ/4) plate in place. Place a mirror after the λ/4 plate and rotate the λ/4 plate so that maximum rejected signal is obtained from the rejection port of the polarizing beam split&l

44、t;/p><p>　　2. Construct the Michelson interferometer as shown in Figure 1.12. Place the beam steering assembly (BSA-II) on the optical table and use the reflected beam from the mirror to adjust the quarterwave

45、plate orientation. Set the cube mount (CM) on the optical breadboard, place a double sided piece of adhesive tape on the mount, and put the nonpolarizing beam splitter cube (05BC16NP.6) on the adhesive tape. Next, place

46、the other beam steering assembly (BSA-I) and the detector mount (M818BB) in locat</p><p>　　When long path length measurements are made, the interferometer signal will decrease or disappear if the laser coher

47、ence length is less than the two way interferometer path imbalance. If this is the case, shorten the interferometer until the signal reappears. If this does not work, then check the laser for single-mode operation by loo

48、king for the fringe pattern on a card or by scanning the piezoelectric transducer block (PZB)in BSA-II and monitoring the detector output which should be sinusoidal</p><p>　　3. The Michelson interferometer h

49、as the property that depending on the position of the mirrors, light may strongly couple back toward the laser input port. In order to further reduce the feed-back, slightly tilt the mirrors as illustrated in Figure 1.13

50、. If still unable to obtain single-mode operation, replace the laser diode.</p><p>　　4. Place a white card in front of the detector and observe the fringe pattern with the infrared imager. Slightly adjust th

51、e mirrors to obtain the best fringe pattern. Try to obtain one broad fringe.</p><p>　　5. Position the detector at the center of the fringe pattern so that it intercepts no more than a portion of the centered

52、 peak.</p><p>　　6. By applying a voltage to the piezoelectric transducer block attached to the mirror (part PZB) in one arm of the interferometer (i.e. BSA-II), maximize the output intensity. The output shou

53、ld be stable over a time period of a minute or so. If it is not, verify that all components are rigidly mounted. If they are, then room air currents may be destabilizing the setup. In this case, place a box (cardboard wi

54、ll do) over the setup to prevent air currents from disturbing the interferometer setup.</p><p>　　7. Place the interferometer in quadrature (point of maximum sensitivity between maximum and minimum outputs of

55、 the interferometer) by varying the voltage on the PZB.</p><p>　　8. The output signal of the interferometer due to frequency shifting of the laser is given by ?I∝?φ = 2π/c ?L ?ν where ?L is the difference in

56、 path length between the two arms of the interferometer and ?ν is the frequency sweep of the laser that is induced by applying a current modulation. Remember that in a Michelson interferometer ?L is twice the physical di

57、fference in length between the arms since light traverses this length difference in both directions. ?L values of 3-20 cm represent conven</p><p>　　Before we apply a current modulation to the laser, note tha

58、t the interferometer output signal, ?I, should be made larger than the detector or laser noise levels by proper choice of ?L and current modulation amplitude di. Also recall from Section 1.3 that when the diode current i

59、s modulated so is the laser intensity as well as its frequency. We can measure the laser intensity modulation by blocking one arm of the interferometer. This eliminates interference and enables measurement of the intensi

60、t</p><p><b>　　and</b></p><p>　　for the amplitude change only.Recalling</p><p><b>　　,,</b></p><p><b>　　or</b></p><p>　　w

61、here K is a detector response constant determined by varying ?L.</p><p>　　9. With the interferometer and detection system properly adjusted, vary the drive frequency of the laser and obtain the frequency res

62、ponse of the laser (Figure 1.4 or 1.10a).You will need to record two sets of data: (i) the modulation depth of the interferometer output as a function of frequency, and (ii) the laser intensity modulation depth. The diff

63、erence of the two sets of collected data will provide an estimate of the actual dI/di due to frequency modulation. Also note that if the current mo</p><p>　　Make any necessary function generator amplitude ad

64、justments to keep the current modulation depth of the laser constant as you vary the frequency. This is because the function generator/driver combination may not have a flat frequency response. The effect of this is that

65、 the current modulation depth di is not constant and varies with frequency. So to avoid unnecessary calculations, monitor the current modulation depth by connecting the LASER MONITOR connector on the laser diode driver s

66、ystem to a</p><p>　　10. Keeping the above equations in mind, we will, now, measure the FM chirp characteristics of the laser. At a constant current modulation frequency (choose a modulation frequency where d

67、ν/di varies rapidly, i.e. where the slope of your graph from Step 9, which should be similar to Figure 1.10a, is maximum), vary the current modulation depth di for different laser bias levels and derive a curve such as t

68、he one in Figure1.10b.The output dν should not vary significantly except around threshold and</p><p><b>　　Caution</b></p><p>　　Do not exceed the specified drive currents/output power

69、 ratings of the diode or it may be damaged.</p><p>　　11. The phase noise characteristic behavior (Section1.4) as a function of interferometer path length imbalance ?L may be determined by inducing phase nois

70、e through application of laser current modulation. Make sure that the interferometer is in quadrature. </p><p>　　Set the laser diode current above threshold, apply a small current modulation, and fix the mod

71、ulation frequency at a desired value. Convenient frequencies may include 50 Hz, 2 kHz, and 50 kHz (see Reference 1.5). Monitor the detector output with a spectrum analyzer or an oscilloscope and record the peak-to-peak o

72、utput intensity at interferometer quadrature. You may accomplish this by manually sweeping the PZB voltage to cause a minimum of π/2 phase shift, recording the maximum peak-to-peak inten</p><p>　　1.5.4 Ampli

73、tude Characteristics of Diode Lasers</p><p>　　The measurements of the intensity characteristics are taken by placing the detector before the interferometer as in Figure 1.10 or by blocking one mirror in the

74、interferometer. Again, the laser must be operated single-moded with minimum feedback or the noise level and functionality will drastically change. The relative intensity noise (RIN) is defined as 20log(dI/I) where dI is

75、the RMS intensity fluctuations so that for dI~10-4 , the RIN is -80 dB. Normally, these measurements are made with a sp</p><p>　　When making RIN measurements, electronic and photodetector shot noise must be

76、below the RIN levels. (OPTIONAL) You may determine the shot noise using an incoherent source (e.g. lamp) with an intensity level similar to that of the laser. The resultant frequency spectrum of noise with the light sour

77、ce excited gives a measure of the shot noise level which should be adjusted to be at least 10 dB greater than electronic noise levels. The measured shot noise should be checked with Equation 0.47.</p><p>　　1

78、. Vary the laser drive current from below threshold through and above the threshold and record the laser output power and intensity noise at a desired frequency using a spectrum analyzer. When you calculate the RIN, assu

79、ming that shot and electronic noises are below the RIN level, a plot similar to that presented in Figure 1.10d should be obtained. In most cases, for single-mode operation, the noise peaks at threshold. The shape of the

80、noise curve may vary if the laser is modulated, if it becom</p><p>　　2. It is instructive to operate the laser with modulation signals of varying depth and/or degrading the isolator performance by rotating t

81、he λ/4 plate to increase feedback to the laser. This will illustrate noise properties for various feedback conditions which are important to subsequent sensor and communication experiments. RINs of less than -150dB and -

82、120dB are required for television broadcast signals and sensitive interferometric sensors, respectively.</p><p>　　3. The intensity noise of diode lasers has a 1/f characteristic (performance is degraded as t

83、he frequency is lowered). With the laser above threshold and the photodetector connected to a spectrum analyzer, determine the RIN as a function of modulation frequency. The response shown in Figure 1.10e should be obtai

84、ned where the noise becomes white (flat with frequency) starting somewhere between 100 kHz and 1 MHz for typical lasers.</p><p>　　NOTE: The Michelson interferometer setup used in this project will again be u

85、sed in Project3. It may, therefore, save time to proceed directly to Project3 before completing characterization of diode lasers in Project2.</p><p><b>　　中文翻譯</b></p><p><b>　　1

86、.5 實(shí)驗(yàn)裝置</b></p><p>　　由于在這個項(xiàng)目中執(zhí)行這個實(shí)驗(yàn)時涉及到許多新的概念和變化，也因?yàn)樗鼈兪浅跏夹缘墓ぷ?，?xiàng)目1可能是這個實(shí)驗(yàn)單元中最耗時的項(xiàng)目。 這一項(xiàng)目可能需要9小時才能完成。因此我們建議用兩個或兩個以上的實(shí)驗(yàn)課時來做此實(shí)驗(yàn)。例如，功率和發(fā)散特性可以在第一次實(shí)驗(yàn)中研究，而后兩個特性（頻率和振幅特性）可以在第二次試驗(yàn)中研究。</p><p><b&g

87、t;　　注意事項(xiàng)</b></p><p>　　以上所有的評論說明，就反射和工作點(diǎn)調(diào)節(jié)而言激光器單縱模輸出裝置是十分脆弱的。首先必須保證在測量之前，激光器確實(shí)運(yùn)行于單模態(tài)。如果獲得一個單一的，清晰的干涉圖樣或者進(jìn)行差分掃描時從邁克遜干涉儀獲得一個好的正弦曲線，則可以認(rèn)為其工作于單模態(tài)。如果不是這種情形，激光器可能工作于多模態(tài)，此時應(yīng)調(diào)整它的電流。如果不能通過調(diào)整電流獲得單模輸出，而反射卻可能控制激光模式

88、，在這種情況下，應(yīng)調(diào)整設(shè)備，以盡量減少反射。如果仍然不能獲得單模輸出，激光二極管可能已經(jīng)壞了，需要更換。</p><p><b>　　警告</b></p><p>　　在這個項(xiàng)目裝置中所提供的激光器發(fā)出的不可見光會損害人的眼睛。所以必須注意避免眼睛直接暴露于激光光束中。我們建議使用專門針對780nm的激光護(hù)目鏡。 </p><p>　　在操作前

89、請仔細(xì)閱讀二極管激光器操作手冊中的安全操作章節(jié)和有關(guān)激光二極管組成和處理的章節(jié)（附錄A）。</p><p>　　1.5.1 半導(dǎo)體激光器的功率特性</p><p>　　1. 裝配激光器(LMA-I)并為激光器供電。首先我們將準(zhǔn)直光束。接著將激光光束輸入到一個監(jiān)視器中并使激光光束成像在距激光器約兩到十厘米的白屏上。慢慢的增加激光器驅(qū)動電流并觀察白屏上的光斑。每個激光器都有各自的閾值電流。把

90、電流增加到閾值以上10-20 mA左右。 </p><p>　　通過紅外成像設(shè)備或紅外感應(yīng)卡片，觀察卡片上的光斑并且調(diào)整準(zhǔn)直透鏡在激光裝置LMA-I中的位置以在卡片上獲得一個明亮的光斑。將卡片移至距透鏡30-60cm左右同時調(diào)整激光器與透鏡的相對位置以便獲得一個大小不隨白屏的位置改變而強(qiáng)烈變化的光斑。當(dāng)白屏到激光器的距離被調(diào)近或拉遠(yuǎn)時，而光斑大小依然保持不變，可認(rèn)為此時輸出的光束被準(zhǔn)直了。另外，可通過將激光光束聚

91、焦到無窮遠(yuǎn)來對其進(jìn)行準(zhǔn)直。注意不要使同伴暴露于激光中。</p><p>　　2. 將一個818SL型號的探測器放置在裝置（M818組件)后，并調(diào)整它的位置以使其有效面積處于光束中央。并保證有足夠的光強(qiáng)照在探測器上以產(chǎn)生一個較強(qiáng)的信號。同時將光電探測器連接到功率計(jì)（815）上。實(shí)驗(yàn)時應(yīng)減少背景照明（ 房間的燈光）以使所探測的信號僅來源于激光。將驅(qū)動電流減小到閾值以下數(shù)毫安，并再次檢查確使房間光與激光相比不是探測器

92、中占優(yōu)勢的信號。</p><p>　　3. 增加電流并畫出探測器的輸出與激光器的驅(qū)動電流的關(guān)系曲線。你應(yīng)該得到一個與圖1.2類似的曲線。如果需要，也可以通過改變二極管溫度以觀察溫度對閾值電流的影響。在研究激光二極管溫度特性時，應(yīng)保證激光二極管工作在恒定電流模式以防止過大的電流損害激光二極管。注意，當(dāng)二極管溫度降低時，閾值下降。所有的操作都應(yīng)當(dāng)在二極管斷電的情況下進(jìn)行以防止驅(qū)動電流高于閾值而損壞激光器。為了防止破

93、壞激光器的結(jié)構(gòu)，應(yīng)保證工作電流不超過激光器的最大驅(qū)動電流。</p><p>　　圖1.2 –驅(qū)動電流和輸出功率關(guān)系曲線</p><p>　　1.5.2 散光距離特性</p><p>　　激光二極管散光距離由下列各項(xiàng)決定。先用一個透鏡將激光束聚焦到合適距離。再通過漸次移動光路中的刀片來獲得刀片位于不同位置時通過刀口的總光強(qiáng)數(shù)據(jù)。這樣一些數(shù)據(jù)描繪了激光束的整體光強(qiáng)分布（

94、如圖1.9a），通過差異來顯示實(shí)際的光強(qiáng)分布（如圖1.9b），反過來又可得出光束的直徑。通過測量激光不同位置時的光束大小可以獲得光束直徑與距離的關(guān)系曲線。圖1.9c描繪了兩個有意義的光束直徑：一個為刀口沿垂直激光二極管的結(jié)平面方向另一個沿平行于結(jié)平面方向。激光二極管的散光距離即是這兩個曲線極小值之間的重疊部分。這種方法被稱為刀刃技術(shù)。</p><p>　　1. 用準(zhǔn)直透鏡（LC）按圖1.8所示裝配元件，在合理的

95、裝配步驟中，應(yīng)將準(zhǔn)直透鏡放在距激光器一厘米左右的位置。且光線應(yīng)該沿著透鏡的光軸傳播。這個透鏡與之前準(zhǔn)直激光所用的透鏡相同。所有元件擺放位置如圖所示。應(yīng)確保二極管的結(jié)平面（即圖1.1所示的xz平面) 平行于平臺表面。</p><p>　　2. 由于光的不對稱分布，激光輸出光束的橫截面經(jīng)過球面透鏡后變成橢圓的。因此，光束有兩個明顯的焦點(diǎn)，一個在平行于激光二極管結(jié)平面的平面上另一個在垂直于激光二極管結(jié)平面的平面上。在

96、兩焦點(diǎn)之間存在這樣一點(diǎn)，在此點(diǎn)光束的橫截面是圓形的。用紅外成像儀和白屏，可以粗略地判定橫斷面光束為圓形時的位置。</p><p>　　圖1.8 –測量激光二極管散光距離的實(shí)驗(yàn)裝置</p><p>　　圖1.9 – 確定散光距離的步驟</p><p>　　3. 調(diào)整激光二極管和透鏡間的距離以使刀片位于光束橫斷面為圓形的xy平面上。</p><p&

97、gt;　　4. 把激光二極管移離透鏡直至最小的光腰移動到刀片所處的平面?，F(xiàn)在，再將激光二極管移離透鏡200 µm。</p><p>　　5. 沿x方向移動刀片1同時記錄下x坐標(biāo)的位置和每個單位坐標(biāo)（≤100um遞增）所測的光強(qiáng)。我們將得到如圖1.9所示的輸出曲線。這個光強(qiáng)分布曲線沿x方向的導(dǎo)數(shù)決定了光束的直徑。</p><p>　　6. 在y方向?qū)Φ镀?重復(fù)以上操作。<

98、;/p><p>　　7. 以一定間隔（≤50μ m）移動激光器使其靠近透鏡，使總的移動量不少于500 μm。 在z方向上重復(fù)第5和6步驟，并記錄z的位置。</p><p>　　8. 使用收集的數(shù)據(jù)，可推導(dǎo)出x和y方向光強(qiáng)與于透鏡z坐標(biāo)之間的函數(shù)關(guān)系。這是通過分析每組數(shù)據(jù)與坐標(biāo)間關(guān)系得出的。然后，計(jì)算光束直徑并畫出關(guān)于z的函數(shù)曲線。Z坐標(biāo)方向上對應(yīng)于和最小量的差值為激光二極管的發(fā)散距離。建議

99、使用計(jì)算機(jī)軟件處理數(shù)據(jù)。</p><p>　　如果激光器結(jié)面不平行平臺表面，對上述每一次測量，你將會獲得兩束發(fā)散光的混合，且測量將變得不準(zhǔn)確。如果激光與平臺平面成45°， 發(fā)散距離將變?yōu)榱恪?lt;/p><p>　　不同的激光器結(jié)構(gòu)有不同的角光束發(fā)散角，因此有不同的發(fā)散距離。如果你知道一些不同激光器的型號（附加指導(dǎo)，索引指導(dǎo)），它們的發(fā)散距離可能被標(biāo)出了。</p>&l